EBOOK - Handbook of Industrial Drying (Advances in Drying Science and Technology) - Full Edition (Arun S. Mujumdar)

Cẩm nang Sấy công nghiệp (Những tiến bộ trong khoa học và công nghệ sấy) (Arun S. Mujumdar).

This Fourth Edition book includes 12 new chapters covering computational fluid dynamic simulation; solar, impingement, and pulse combustion drying; drying of fruits, vegetables, sugar, biomass, and coal; physicochemical aspects of sludge drying; and life-cycle assessment of drying systems. Addressing commonly encountered dryers as well as innovative dryers with future potential, the fully revised text not only delivers a comprehensive treatment of the current state of the art, but also serves as a consultative reference for streamlining industrial drying operations to increase energy efficiency and cost-effectiveness.

TABLE OF CONTENTS

Section I Fundamental Aspects

chapter 1|28 pages

Principles, Classication, and Selection of Dryers

Title

Abstract 

Drying commonly describes the process of thermally removing volatile substances (moisture) to yield a solid product. Moisture held in loose chemical combination, present as a liquid solution within the solid or even trapped in the microstructure of the solid, which exerts a vapor pressure less than that of pure liquid, is called bound moisture. Moisture in excess of bound moisture is called unbound moisture.

chapter 2|20 pages

Experimental Techniques in Drying

Title

Abstract 

The calculation of drying processes requires a knowledge of a number of characteristics of drying techniques, such as the characteristics of the material, the coefcients of conductivity and transfer, and the characteristics of shrinkage. In most cases these characteristics cannot be calculated by analysis, and it is emphasized in the description of mathematical models of the physical process that the so-called global conductivity and transfer coefcients, which re¤ect the total effect on the partial processes, must frequently be interpreted as experimental characteristics. Consequently, these characteristics can be determined only by adequate experiments. With experimental data it is possible to apply analytical or numerical solutions of simultaneous heat and mass transfer to practical calculations.

chapter 3|26 pages

Basic Process Calculations and Simulations in Drying

Title

Abstract 

Since the publication of the rst and second editions of this handbook, we have been witnessing a revolution in methods of engineering calculations. Computer tools have become easily available and have replaced the old graphical methods. An entirely new discipline of computer-aided process design (CAPD) has emerged. Today even simple problems are solved using dedicated computer software. The same is not necessarily true for drying calculations; dedicated software for this process is still scarce. However, general computing tools including Excel, Mathcad, MATLAB®, and Mathematica are easily available in any engineering company. Bearing this in mind, we have decided to present here a more computer-oriented calculation methodology and simulation methods than to rely on old graphical and shortcut methods. This does not mean that the computer will relieve one from thinking. In this respect, the old simple methods and rules of thumb are still valid and provide a simple commonsense tool for verifying computer-generated results.

chapter 4|34 pages

Transport Properties in the Drying of Solids

Title

Abstract 

Drying is a complicated process involving simultaneous heat, mass, and momentum transfer phenomena, and effective models are necessary for process design, optimization, energy integration, and control. The development of mathematical models to describe drying processes has been a topic of many research studies for several decades. Undoubtedly, the observed progress has limited empiricism to a large extent. However, the design of dryers is still a mixture of science and practical experience. Thus the prediction of Luikov that by 1985 “would obviate the need for empiricism in selecting optimum drying conditions,” represented an optimistic perspective, which, however, shows that the efforts must be increased [1]. Presently, more and more sophisticated drying models are becoming available, but a major question that still remains is the measurement or determination of the parameters used in the models. The measurement or estimation of the necessary parameters should be feasible and practical for general applicability of a drying model.

chapter 5|14 pages

Spreadsheet-Aided Dryer Design

Title

Abstract 

Computer-aided design is based on computer simulators, whereas computer simulators are based on process modeling. The basic terms, such as modeling, simulation, and design, are dened in Table 5.1. Modeling is the procedure of translating the physical laws of a process to mathematical equations to analyze or design the process. Simulation is the appropriate software, which predicts the real performance of a process. It is based on mathematical modeling plus the appropriate graphics interface in a computer environment. Design is a procedure of sizing and rating a process in order to achieve specic goals, such as economic production, product quality, and protection of the environment.

Section II Description of Various Dryer Types

chapter 6|12 pages

Indirect Dryers

Title

Abstract 

Generally, indirect dryers have higher energy efciency than the direct dryers, because the energy lost through the exhaust gas stream is greatly reduced; the heat load of the dryers is only from the material as it dries. Waste heat source can also be used to cut drying energy costs. The vapor produced from the drying material can also be used as a heating medium in a subsequent stage of drying, hence reducing the consumption of the primary heat transfer medium. If the vaporization rate is high, e.g., when drying pulp, a two-or three-stage dryer may be economic.

chapter 7|22 pages

Rotary Drying

Title

Abstract 

Rotary drying is one of the many drying methods existing in unit operations of chemical engineering. The drying takes place in rotary dryers, which consist of a cylindrical shell rotated upon bearings and usually slightly inclined to the horizontal. Wet feed is introduced into the upper end of the dryer and the feed progresses through it by virtue of rotation, head effect, and slope of the shell and dried product withdrawn at the lower end. A simplied diagram of a direct-heat rotary dryer is presented in Figure 7.1. The direction of gas ¤ow through the cylinder relative to the solids is dictated mainly by the properties of the processed material. Cocurrent ¤ow is used for heat-sensitive materials even for high inlet gas temperature due to the rapid cooling of the gas during initial evaporation of surface moisture, whereas for other materials countercurrent ¤ow is desirable in order to take advantage of the higher thermal efciency that can be achieved in this way. In the rst case, gas ¤ow increases the rate of solids ¤ow, whereas it retards it in the second case [3,19,20,35].

chapter 8|30 pages

Fluidized Bed Dryers

Title

Abstract 

Fluidized bed dryers (FBDs) are used extensively for the drying of wet particulate and granular materials, and even slurries, pastes, and suspensions, that can be ¤uidized in beds of inert solids. They are commonly used in processing many products such as chemicals, carbohydrates, foodstuff, biomaterials, beverage products, ceramics, pharmaceuticals in powder or agglomerated form, health-care products, pesticides and agrochemicals, dyestuffs and pigments, detergents and surface-active agents, fertilizers, polymer and resins, and tannins. They are also useful in manufacturing products for calcination, combustion, incineration, waste management processes, and environmental protection processes. Important advantages of ¤uidized bed operation include good solids mixing, high rates of heat and mass transfer, and easy material transport.

chapter 9|36 pages

Industrial Spray Drying Systems

Title

Abstract 

Spray drying is a suspended particle processing (SPP) technique that utilizes liquid atomization to create droplets that are dried to individual particles when moved in a hot gaseous drying medium, usually air. It is a one-step continuous unit processing operation. It has become one of the most important methods for drying the ¤uid foods in the Western world. The development of the process has been intimately

associated with the dairy industry and the demand for drying of milk powders. Spray drying used in dairy industry dates back to around 1800, but it was not until 1850 that it became possible in industrial scale to dry the milk. However, this technology has been developed and expanded to cover a large food group that is now successfully spray-dried. Over 25,000 spray dryers are now estimated to be commercially in use to dry products from agrochemical, biotechnology products, ne and heavy chemicals, dairy products, dyestuffs, mineral

9.1 Introduction ......................................................................................................................................................................191 9.2 Principles of Spray Drying Processes ............................................................................................................................. 192

9.2.1 General................................................................................................................................................................. 192 9.2.2 Atomization ......................................................................................................................................................... 193

9.2.2.1 Drop Size and Size Distribution ........................................................................................................... 194 9.2.2.2 Wheel Atomizers .................................................................................................................................. 195 9.2.2.3 Pressure Nozzles ................................................................................................................................... 197 9.2.2.4 Pneumatic Nozzles ................................................................................................................................ 198 9.2.2.5 Novel Types of Atomizers..................................................................................................................... 199 9.2.2.6 Selection of Atomizers .......................................................................................................................... 199

9.2.3 Chamber Design .................................................................................................................................................. 200 9.2.3.1 Chamber Shape ..................................................................................................................................... 200 9.2.3.2 Air-Droplet Contact Systems ................................................................................................................ 201 9.2.3.3 Powder and Air Discharge Systems ...................................................................................................... 203

9.2.4 Ancillary Equipment ........................................................................................................................................... 203 9.2.4.1 Fans ....................................................................................................................................................... 204 9.2.4.2 Powder Separators ................................................................................................................................. 205

9.2.5 Thermal Efciency .............................................................................................................................................. 206 9.3 Spray Drying Systems ..................................................................................................................................................... 208

9.3.1 Process Layouts and Applications ....................................................................................................................... 208 9.3.2 Energy Savings .....................................................................................................................................................214 9.3.3 Safety Aspects ..................................................................................................................................................... 215 9.3.4 Control Systems ....................................................................................................................................................216 9.3.5 Selection of Spray Dryers

chapter 10|22 pages

Theoretical Modeling and Numerical Simulation of Spray Drying Processes

Title

Abstract 

Particle formation technologies are utilized today in many areas, including pharmaceutical, medical and biomedical, biotechnology, chemical, optical and optoelectronic, cosmetic, printing, painting, ceramics, materials design, nutrition, and for other applications. Spray drying is one of the widely used processes for producing small particles by rapid moisture evaporation from a spray of droplets. Spray drying involves multiphase transport phenomena between drying agent, droplets and particles, and chamber boundaries. These transport phenomena occur on multiple scales because of simultaneous external and internal heat and mass transfer in each phase. Therefore, purely experimental studies would be insufcient and would not encompass all the basic physical processes, predict parametric behavior, and optimize the power consumption of spray drying. On the other hand, realistic modeling and numerical simulation of spray drying are highly demanding tasks for engineers in designing spray dryer systems and in choosing suitable operating conditions.'

chapter 11|10 pages

Drum Dryers

Title

Abstract 

The drum dryer is commonly used to dry viscous, concentrated solutions, slurries or pastes on rotating steam-heated drums.1,2 It can also be used to dry concentrated solutions or slurries that become more viscous or pasty because of ¤ashing or boiling off of moisture or of irreversible thermochemical transformations of their content that occur on their rst contact with the hot drum surface.3−5

The viscous slurry or paste is mechanically spread by the spreading action of two counter-rotating drums into a thin sheet that adheres on the hotter drum in single drum dryers or split sheets on both hot cylinders in double drum dryers. The adhering thin sheet of paste is then rapidly dried conductively by the high heat ¤ux of the condensing steam inside the drum. For very wet slurries that produce wet sheets, the drying of the wet thin sheet can be further enhanced by blowing hot dry air on the sheet surface. The thin sheet containing heat-sensitive materials, such as vitamins, can also be dried at a lower temperature in a vacuum.

chapter 12|24 pages

Freeze Drying

Title

Abstract 

Certain biological materials, pharmaceuticals, and foodstuffs, which may not be heated even to moderate temperatures in ordinary drying, may be freeze-dried. The substance to be dried is usually frozen. In freeze drying, the water or another solvent is removed as a vapor by sublimation from the frozen material in a vacuum chamber. After the solvent sublimes to a vapor, it is removed from the drying chamber where the drying process occurs.

chapter 13|20 pages

Microwave and Dielectric Drying

Title

Abstract 

It is sometimes surprising to realize that dielectric and microwave heating have been in use for quite some time. It appears to many engineers that these are new forms of heating when in fact practical applications began during World War II and the home microwave oven was invented shortly afterward. Yet these remain small industries, and for the most part, the equipment manufacturers are likewise small companies. The older of the two, dielectric heating, is a workhorse heating method used in many industries, including plastics, wood, ceramics, furniture, textiles, and paper. It is also by far the larger of the two industries; however, it is not very well known to many industrialists, whereas the microwave heating is well known, but its industrial applications are far fewer. To try to quantify the relationship, probably only 200-300 MW of microwave power is in use globally for industrial heating purposes, whereas a single large dielectric heating system may employ as much as 2-3 MW of power. The annual worldwide sales of industrial microwave heating systems probably amounts to only less than 20 0 million dollars, but the sales of the home microwave ovens in the United States is of the order of 1.5-2.0 billion dollars. The reasons for the relatively small size of these markets are several, but two stand out: First, the heating mechanisms are not familiar to most engineers, and second, they often represent a radical departure from conventional systems and there is generally a tendency to resist real innovation in most industries.

chapter 14|48 pages

Solar Drying

Title

Abstract 

Open-air sun drying has been used since time immemorial to dry plants, seeds, fruits, meat, sh, wood, and other agricultural or forest products as a means of preservation. However, for large-scale production the limitations of openair drying are well known. Among these are high labor costs, large area requirement, lack of ability to control the drying process, possible degradation due to biochemical or microbiological reactions, insect infestation, and so on. In order to benet from the free and renewable energy source provided by the sun several attempts have been made in recent years to develop solar drying mainly for preserving agricultural and forest products.

chapter 15|20 pages

Spouted Bed Drying

Title

Abstract 

The applicability of the spouted bed technique [1-5] to drying of granular products that are too coarse to be readily ¤uidized (e.g., grains) was recognized in the early 1950s. Interest in this area received appreciable impetus two decades later as the energy-intensive drying processes were reexamined with renewed vigor. Spouted bed dryers (SBDs) display numerous advantages and some limitations over competing conventional dryers. Because of the short dwell time in the spout, SBDs can be used to dry heat-sensitive solids, such as foods, pharmaceuticals, and plastics. With simple modication the so-called modied spouted beds can be designed to ensure good mixing, controlled residence time, minimum attrition, and other desirable features. Also, the operations of coating, granulation agglomeration, and cooling, among others, can be carried out by the same apparatus by varying the operating parameters. SBDs can be used for solids with constant

as well as falling rate drying periods. Using inert solids as the bed material, SBDs have been used successfully to dry pastes, slurries, and heat-sensitive materials.

chapter 16|10 pages

Impingement Drying

Title

Abstract 

Impinging jets of various congurations are commonly used in numerous industrial drying operations involving rapid drying of materials in the form of continuous sheets (e.g., tissue paper, photographic lm, coated paper, nonwovens, and textiles) or relatively large, thin sheets (e.g., veneer, lumber, and carpets), or even beds of coarse granules (e.g., cat or dog food). In this chapter, we will not examine the last-mentioned application, which is a novel operation in which hot jets are directed normally onto thin beds of pellets transported on a slow-moving conveyor. The jets pseudo¶uidize the bed to ensure good gas-solid contact needed for effective drying.

chapter 17|12 pages

Pneumatic and Flash Drying

Title

Abstract 

Drying is a separation process that converts a wet solid, semisolid, or liquid feedstock into a solid product by evaporation of the liquid into a vapor phase via heating. Essential features of the drying process are phase change and production of a solid, dried product.

chapter 18|12 pages

Conveyor Dryers

Title

Abstract 

The conveyor dryer is conceptually very simple. Product is carried through the dryer on conveyors and hot air is forced through the bed of product. It is often described as simply a conveyor in a box with hot air. The reality, however, is that the conveyor dryer is one of the most versatile dryers available. Few drying technologies can match the conveyor dryer’s ability to handle such a wide range of products. Products as varied in composition, shape, and size as coated breakfast cereals, nuts, animal feed, charcoal briquettes, and rubber can be dried in a conveyor dryer. Although it is simple in concept, an improper understanding of the heat and mass transfer processes in the conveyor dryer will surely lead to poor product handling, wasted energy, and nonuniform product quality. This chapter describes the various conveyor dryer congurations that are available, typical products that can be dried in the conveyor dryer, and how to properly size and operate a conveyor dryer. This information will help anyone involved in conveyor dryer design, operation, or evaluation.

chapter 19|16 pages

Infrared Drying

Title

Abstract 

Drying is the most common and most energy-consuming industrial operation. With literally hundreds of variants used in drying of particulate solids, pastes, continuous sheets, slurries, or solutions, it provides the most diversity among chemical engineering unit operations.

chapter 20|12 pages

Superheated Steam Drying

Title

Abstract 

Although the concept was originally proposed over 100 years ago and the rst industrial applications were reported some 60 years ago in Germany, superheated steam drying has emerged only in the past decade or so as a viable new technology with immense potential. Essentially, superheated steam drying (SSD) involves the use of superheated steam in a direct (convective) dryer in place of hot air, combustion, or ¤ue gases as the drying medium to supply heat for drying and to carry off the evaporated moisture. Any direct or direct and indirect (e.g., combined convection and conduction) dryer can be operated as an SSD, in principle. The technology involved is more complex and hence this conversion is not simple. Additional criteria must be considered when selecting a dryer for SSD operation.

chapter 21|58 pages

Special Drying Techniques and Novel Dryers

Title

Abstract 

Increasing demands for new and high-quality products, energy-efcient processes, environment protection, and the like have stimulated progress in drying science and technology. Mujumdar has presented a summary of the motivation for development of new drying technologies and identied a number of trends, which include the following [1]:

• Use of superheated steam in direct dryers • Increased use of indirect (conduction) heating • Use of combined (or integrated) heat transfer modes • Use of volumetric heating (microwave [MW]/radio-

frequency [RF] elds) in specialized situations • Use of two-stage (or multistage) dryers • Use of intermittent heat transfer • Use of novel combustion technologies (e.g., pulse

combustion for ¤ash drying) • Use of novel gas-solid contactors (e.g., 2D spouted

beds, intermittent or rotating spouted beds) • Design of ¤exible, multiprocessing dryers • Combination of different dryer types

Many of these topics are covered in detail elsewhere in this handbook. There are numerous other technologies that have reached various stages of maturity-ranging from concepts and pilot-scale demonstrations to large-scale industrial applications. Several of these have been reviewed in the recent literature [2].

chapter 22|12 pages

Intermittent Drying

Title

Abstract 

Various intermittent drying operations have recently increasingly been used at laboratory, pilot, and industrial scales. They all aim to improve product quality and/or process performance by reducing energy consumption. Intermittent drying is a drying operation with several periods of varying external dehydration conditions with different drying rates. In intermittent drying, air¤ow temperature, velocity and/or humidity, heat input, pressure, and/or other external drying parameters (such as microwave (MW) or RF) are applied in a discontinuous manner to suit the drying kinetics and quality requirements of the material. The idea is often to introduce tempering periods to even out the internal moisture content and temperature elds. The quality of the nal dried product can also be enhanced along with process performance. In each tempering period, moisture gets redistributed inside the material. This produces several desired effects. Quality is enhanced by avoiding or reducing overheating or overdrying of the surface layer. Quality degradation can be due to surface cracking, breakage, or crusting, and under certain conditions even scorching of the material. The drying rate can also increase as the material surface gets rewetted to that higher heat/mass transfer can occur at the exposed surface of the material.

chapter 23|16 pages

Pulse Combustion Drying

Title

Abstract 

Pulse combustion is a specic form of combustion-driven oscillation. Combustion oscillations can be an inherent problem or a potential benet in enclosed combustion systems, such as gas turbine combustors, afterburners, furnaces, and rocket engines. Oscillations can produce benecial increases in heat transfer rates and reduce pollutant formation. In other situations, these instabilities are undesirable because they may reduce the thermodynamic efciency of a combustor or become a source of system failure if their amplitude is not kept within an acceptable range. Oscillations in the pulse combustion drying systems are desired and useful. Combustion with oscillations may be treated as some regular form of unstable combustion.

Section III Drying in Various Industrial Sectors

Title

chapter 24|24 pages

Drying of Foodstuffs

Title

Abstract 

The removal of moisture from solids is an integral part of food processing. Almost every food product is dried at least once at one point of its preparation. The main objectives of dehydration are summarized as follows [32].

chapter 25|12 pages

Drying of Fish and Seafood

Title

Abstract 

Drying in earlier times was done in the sun, now many types of sophisticated equipment and methods are used to dehydrate foods. During the past few decades, considerable efforts have been made to understand some of the chemical and biochemical changes that occur during dehydration and to develop methods for preventing undesirable quality losses [57]. Foods can be divided into three broad groups based on the value added through processing by drying. In the case of

cereals, legumes, and root crops, very little value is added per ton processed. More value per unit mass is added to foods such as vegetables, fruits, and sh, and considerably more to high-value crops such as spices, herbs, medicinal plants, nuts, bioactive materials, and enzymes [3].

chapter 26|10 pages

Grain Drying

Title

Abstract 

Grain has been an important agricultural commodity and primary food source for centuries. The present distribution of the world’s population has made strong demands on grainhandling technology. Irrespective of whether it is international trade or demands within a country, grain needs low moisture levels for safe storage. Drying has always been the most common method of preserving grain. In the days of premechanization of agriculture, enough grain was usually stored by hanging ears of corn in barn lofts and attics to meet the needs of a community. As mechanization of agriculture spreads to meet the needs of a population that was rapidly growing and urbanizing, mechanical methods for drying large quantities of grain were needed. Grain now travels thousands of miles either in large grain-carrying ships or in different types of carriers on wheels, and must reach its destination in a highquality state. Proper drying of these huge quantities of grain is a prerequisite to safe storage and delivery.

chapter 27|28 pages

Grain Property Values and Their Measurement

Title

Abstract 

The world produces annually about 2 billion tonnes (Gt) of grains and oilseeds [1] that are handled and stored on-and off-farm for periods of up to 3 years. Often the storage period may be longer than 3 years, for example, when the grain is stored for potential famine relief. To design handling, inspection, and storage systems for grains and oilseeds, data on many properties of individual seeds and seeds in bulk are needed. The properties of interest are: bulk and particle densities, porosity, roundness, sphericity, friction coefcients of grains against commonly used bin wall materials, emptying and lling angles of repose, equilibrium moisture content (EMC), specic heat, thermal conductivity, dielectric

constant, electrical conductivity, re¤ectance, terminal velocity, and drag coefcient. There are many methods of measuring these properties. In this chapter, only the methods that are currently in use or widely accepted methods are described. Representative property values for common grains and oilseeds are summarized from the published literature.

chapter 28|16 pages

Drying of Rice

Title

Abstract 

Rice is one of the world’s primary food crops and is a major source of dietary energy for more than half of the people on this planet. Paddy is usually milled or polished into white rice for cooking even though unpolished rice contains much more nutritional bioactive components and dietary energy. A major component of rice grain is starch, which in turn is composed of polysaccharides; two types of polysaccharides found in rice starch are amylose and amylopectin. The amounts of amylose and amylopectin determine the quality of rice, both in terms of physical and chemical characteristics.

chapter 29|26 pages

Drying of Fruits and Vegetables

Title

Abstract 

From the point of view of consumption, fruits are plant products with aromatic ¤avor that are naturally sweet or normally sweetened before usage [1]. Apart from providing ¤avor and variety to human diet, they serve as important and indispensable sources of vitamins and minerals although they are not good or economic sources of protein, fat, and energy. The same is true in the case of vegetables, which also play an important role in human nutrition in supplying certain constituents in which other food materials are decient and in adding ¤avor, color, and variety to the diet [2].

chapter 30|10 pages

Drying of Herbal Medicines and Tea

Title

Abstract 

Herbal medicine is part of human civilization. It has been used in China for nearly 5000 years. One of the oldest and most important documents is the Egyptian Ebers papyrus (ca. 1550 bc), which includes more than 700 prescriptions using natural products such as caraway, coriander, garlic, linseed, peppermint, gs, fennel, anise, poppy, and castor oil [1]. Shen Nong’s Materia Medica was compiled by ancient Chinese in about 200 bc, which described the properties and usages of 365 types of Chinese medicines in three categories. In ancient Greece there was a guild of rhizomatists or root collectors, who gathered, prepared, and sold medicinal plants. The Greek botanist and physician, Dioscorides (ad 40-90), compiled the rst systematic description of 579 plants and their 4700 medicinal uses and modes of action. His work titled De Materia Medica was of central importance to European medicine until the seventeenth century [1]. Ayurveda is the principal traditional medical system of India, Pakistan, Nepal, and Sri Lanka, which has also in¤uenced medicine in Tibet, Burma, and Malaysia.

chapter 31|14 pages

Drying of Potato, Sweet Potato, and Other Roots

Title

Abstract 

For many centuries potato, Solanum tubersum, has served as the primary food source for people in many parts of the world. The potato, with a total production in excess of 300 million tons, is one of the major food crops grown in a wide variety of soils and climatic conditions. Many cultivars of potatoes are grown, however, a few cultivars account for most of the potatoes produced. These differ in time of maturity, yield, appearance, disease resistance, marketing, and processing quality. The majority of potatoes are used as table food these days, frequently consumed in different forms of processed potato products. In developed countries, more than

50% of potatoes produced are consumed as processed products. The processed products may be in the form of chips, granules, ¤akes, power, dice, strips, powder, etc. [1].

chapter 32|20 pages

Osmotic Dehydration of Fruits and Vegetables

Title

Abstract 

Water as a main constituent of most foods affects food stability, microbial as well as chemical, and is responsible for the consumer perception of many organoleptic attributes, i.e., juiciness, elasticity, tenderness, and texture. It is generally accepted that it is not the quantity of water in food but its thermodynamic state that is responsible for its in¤uence on food stability and texture. The thermodynamic state of water in food is expressed by its activity, which is 0 for absolutely dry material and 1 for pure water. The lower the water activity the more stable is the food, and the texture changes from juicy and elastic to brittle and crunchy.

chapter 33|22 pages

Drying of Pharmaceutical Products

Title

Abstract 

The pharmaceutical industry is one in which quality of the nal product cannot be compromised. Any deterioration of the product (e.g., by microbial infection, oxidation, thermal decomposition, contamination by metallic particles or by unremoved organic solvent) must be avoided at any cost. In light of that the Good Manufacturing Practices (GMP) for drug manufacture (see, e.g., Ref. [1]) put numerous demands on the drying stage of the drug manufacturing process. Noncontaminating dryer construction materials are used, like polished stainless steel or enameled iron. Closed-cycle dryers are often required

as moisture removed is often an organic solvent or their mixture. Drying must be often performed in inert gas to avoid oxidation or explosion if solvent is ¤ammable. To avoid thermal decomposition in many instances vacuum and freeze drying must be employed.

chapter 34|14 pages

Drying of Nanosize Products

Title

Abstract 

Nanomaterials represent today’s cutting edge in the development of novel advanced materials, which promise tailor-made functionality for unique applications in all important industrial sectors. Nanomaterials can be clusters of atoms, grains 100 nm in size, bers that are less than 100 nm in diameter, lms that are less than 100 nm in thickness, nanoholes, and composites that are a combination of these. In other words, it implies that the microstructures (crystallites, crystal boundaries) are nanoscale [1]. Nanomaterials include atom clusters, nanoparticles, nanotubes, nanorods, nanowires, nanobelts, nanolms, compact nanostructured bulk materials, and nanoporous materials [2]. Materials in nanosize range exhibit

fundamentally new properties and functionalities such as surface effects, dimensionality effects, quanta effects, and quanta tunnel effects, etc.

chapter 35|12 pages

Drying of Ceramics

Title

Abstract 

The demand for high-quality ceramics is increasing in many elds. The applications are spreading to highly functional materials known as the “ne ceramics” as well as materials for house-ware and buildings. Although material science for ceramics has advanced signicantly during the last few decades, the production processes still rely on old methods. Particularly, R&D has not addressed the drying process, and drying is usually carried out slowly in order to avoid undesirable cracks and deformations. The reason is often attributed to the fact that ceramic drying involves maintaining a molded conguration. Although ceramics are sensitive to the surrounding atmosphere during drying, it is very difcult to predict the heat-and mass-transfer rates and the air ¤ow pattern in dryers with sufcient accuracy and generalize the results to the wide variety of ceramics. Many ceramic manufacturers are small companies, and they may not wish to invest much effort in ceramic drying R&D as drying occurs only at the pretreatment stage in ceramic production. However, drying is important for precisely designing the molding, determining the high-efcient heating rate in a dryer, and completing the drying so as to reduce the ratio of failure during sintering and yielding the qualied productions.

chapter 36|10 pages

Drying of Peat and Biofuels

Title

Abstract 

The use of biomass and peat, for both the industrial sector and the district heating, has greatly increased since the rst oil crisis in 1973. The biomass utilized so far is wood and agricultural wastes, including bark, straw, and bagasse. Biomass grown especially for fuel purposes is still a technique in the experimental state. The use of peat as a fuel is limited to countries with domestic resources, such as the former Soviet Union, Canada, the United Kingdom, Ireland, Finland, and Sweden.

chapter 37|24 pages

Drying of Fibrous Materials

Title

Abstract 

Fibers are regarded as very elongated particles. Staple bers that are spun into yarns have length/diameter ratios greater than 10,000. The ber lengths of cotton are of the order 25-75 mm; wool bers may exceed 100 mm and are variable in length even when shorn from the same sheep; ¤ax bers may be available in lengths up to 1 m [1]. The corresponding diameters of textile bers range between 3 and 500 μm.

chapter 38|10 pages

Drying of Textile Products

Title

Abstract 

The word “textiles” comes from the Latin textilis, meaning “woven”; but in textile science, textile is dened as any product made from bers. Thus textiles refers not only to woven fabrics but also to nonwoven fabrics, knitted fabrics, tufted fabrics such as carpets and bedspreads, and specially constructed fabrics [1]. Figure 38.1 depicts the major segments and linkages of the textile industry, from bers to products. The textile mill portion of the textile complex includes many chemical wet processes such as slashing, dyeing, printing, latex bonding, and nishing. In many of these processes, drying is required to remove the excess moisture in the porous materials to produce the desired product. For example, the typical steps used to produce latex-backed tufted carpet are shown schematically in Figure 38.2.

chapter 39|24 pages

Drying of Pulp and Paper

Title

Abstract 

Ts’ai-Lun apparently produced a sheet of paper in about a.d. 100 in China and became the rst recorded papermaker in the world. However, it took about 1000 years for this new art to reach Europe. In the medieval era, the progress of papermaking was very slow and the major ingredient of paper was old rags. By the beginning of the nineteenth century, the progress of this industry was enormously accelerated. The rst practical paper machine was produced in the early 1800s; then continuous drying techniques were introduced to the industry by means of cylinder drying in 1817 by John Dickinson; later, in the mid-1840s, the extensive use of wood as a cellulose-ber source began by the advent of the rst wood grinder. Today, papermaking has become one of the major industries in the world. The production of paper increased enormously, over 60 million tons per year in the United States alone. The machine speeds also increased up to 10-15 m/s and even higher for tissue products, to keep pace with the increased production rates.

chapter 40|50 pages

Drying of Wood: Principles and Practices

Title

Abstract 

A cross section of a tree (Figure 40.2), from the core to the outer region, shows the following features:

• Pith, a small core of tissue located near the middle of a tree’s stem or branches, which originates from the primary growth of the plant

• Woody material, the most important part of mature trees, which is differentiated into sapwood (outer region), where the sap migrates from roots to leaves and heartwood (inner region) that is no longer used for sap transport, which exists only when the stem, at that height, is old enough

• Bark, differentiated into an outer corky dead part (external part of the stem), whose thickness varies greatly with species and age of trees, and an inner thin living part (just near the cambium zone), which carries food from the leaves to the growing elements

40.1.1.1 Knots As the tree grows in height (primary growth), branching is initiated by lateral bud development. Knots are the

835 40.3.4 Practical Considerations ...................................................................................................................................... 836

40.3.4.1 Schedule Development .......................................................................................................................... 836 40.3.4.2 Kiln Control .......................................................................................................................................... 838 40.3.4.3 Volatile Emissions................................................................................................................................. 838 40.3.4.4 Equalization and Stress Relief .............................................................................................................. 839

40.3.5 Less-Common Drying Methods .......................................................................................................................... 839 40.3.5.1 Vacuum Drying ..................................................................................................................................... 839 40.3.5.2 Dehumidier Kilns ............................................................................................................................... 840 40.3.5.3 High-Frequency Electrical Heating ...................................................................................................... 841 40.3.5.4 Solar Drying.......................................................................................................................................... 841

References ................................................................................................................................................................................. 842

bases of branches, which have been covered as the tree grows laterally. After a branch dies, the trunk continues to increase in diameter and surrounds that portion of the branch while the dead branch is still present. This branch has to drop from the tree before clearwood can form. If the knot was alive when the trunk grew around it, the xylem

of the trunk and the branch are continuous and the knot ts tightly into the wood. If the branch was dead when the trunk grew around it, no anatomical connection exists between the xylem of the knot and the trunk. The knot is nonadhesive; it may fall out of the wood, leaving a knothole (Figure 40.3).

chapter 41|14 pages

Biomass Drying for an Integrated Bioenergy Plant

Title

Abstract 

Energy supply and demand data show that the world annual consumption of energy was 510.6 quadrillion Btu in 2010 (1.50  × 1014 kWh or 12.87 billiontonnes of oil equivalent): 84% of this came from fossil fuels including oil, gas, and coal, which released 31.6 billion metric tonnes of carbon dioxide into the atmosphere (EIA, 2012). The heavy reliance of human beings on fossil fuels has already caused serious consequences such as climate change and a looming energy crisis. Therefore, nding alternative and sustainable energy resources has been an urgent issue to ensure future energy supply and to reduce greenhouse gas emissions.

chapter 42|6 pages

Drying in Mineral Processing

Title

Abstract 

Thermal removal of water from solids or slurries is an important operation carried out in numerous mineralprocessing and metallurgical-processing applications. Although drying is a highly energy-intensive operation that is also increasingly difcult at lower moisture contents, no special attention is generally given to the technical and economical aspects of the drying process employed in the mineral-or metallurgical-processing industry. It is therefore not surprising that most dryers found in these industries are of the conventional type, as discussed later in this chapter. Detailed descriptions and design considerations of specic dryer types (e.g., rotary, ¤uid bed, and spray) are presented elsewhere in this handbook. The interested reader is referred to relevant sections for further information. The objective of this chapter is to summarize the types of dryers currently used in practice, to discuss any special aspects with illustrations, and to identify possible new concepts that may be applicable in the mineral industry.

chapter 43|16 pages

Dewatering and Drying of Wastewater Treatment Sludge

Title

Abstract 

Sludge is the name that describes a muddy or slushy mass, deposit, or sediment as (1) the precipitated solid matter produced by water and sewage treatment processes; (2) mud from a drill hole in boring; (3) the muddy sediment in a steam boiler; (4) waste from a coal washery; or (5) the precipitated or settled matter from industrial processes. Water treatment sludge consists of suspended solids, coagulation chemicals, usually an alum or polymers with a limited amount of biological materials. A comprehensive review of industrial sludge can be found elsewhere [1]. In that review, sludge from petroleum, metal-nishing, ¤ue gas cleaning, water treatment, pulp and paper processing, polymer plants, chemical plants, as well as mineral and metallurgical industries are discussed. The sludge addressed in this chapter is the by-product of a wastewater treatment plant. Brief reviews on the treatment, usage, and disposal of this type of sludge are available [2,3]. In this chapter, we take a comprehensive approach to examine the literature on sludge dewatering and drying in order to give readers a relatively detailed and complete picture of this area that is growing with the expenditures on environmental cleanup and control, amounting to about US $150 billion in the United States and about US $400 billion globally in 1997 [4].

chapter 44|12 pages

Physicochemical Aspects of Sludge Drying

Title

Abstract 

Untreated municipal sludge could be regarded as hazardous waste material due to its high organic and metallic content. Decreasing sludge moisture content is the primary objective for all sustainable sludge management strategies. Although a signicant amount of free water in sludge is removed by mechanical dewatering processes, the moisture content of sludge is still higher than 70% (dry basis). According to the current regulations, the percent solids of sewage sludge shall be equal to or greater than 90%, based on the moisture content and total solids prior to storage for all kinds of land applications. In addition, high moisture content would make sludge conveying, pumping, and transportation extremely difcult. Composition of the sludge depends on wastewater characteristics and the treatment technology employed [1].

chapter 45|22 pages

Drying of Biotechnological Products

Title

Abstract 

Biotechnology is the action aiming at producing useful products for various branches of the economy by means of biological components and microorganisms, viruses, animal and vegetable cells, as well as extracellular substances found within tissues. The growing scope of these activities includes production of a biological system, a producer strain, using the recombination technique and cell engineering. As a result of processes taking place in the presence of microorganisms, materials of various forms are produced, such as microorganisms similar to the inlet materials, e.g., yeast and bacteria. The product may be a substance with a complex chemical structure in the form of a high-molecular polymer or organic compound (e.g., antibiotics, vitamins, and organic acids).

chapter 46|20 pages

Drying of Coated Webs

Title

Abstract 

The objective of this chapter is to review brie¤y the drying process, drying equipment, drying strategies, and web handling available for coated webs. Based on the substrate materials, coated webs can be divided into three types: (1)  coated paper and paperboard; (2) coated plastic lms (e.g., photographic lms) and tapes (e.g., adhesive tapes, magnetic tapes, pressure-sensitive tapes, and photosensitive tapes); and (3) coated metallic sheets. Paper and paperboard are coated on machine or off machine, while plastic lms, tapes, or metallic sheets are generally coated off machine. (On machine indicates the coating operation that is done on the web before it is removed from the original manufacturing machine, whereas off machine implies the coating operations done on a free-standing machine remote from the original machine.)

During the coating process, some coated webs require a single coating; other webs require more than one coating layer either by passing a web of material through a single coating station more than one time or by coating a web with a multiple-station coating machine. In the converting industry, paper, lms, and foils can be combined together to form multiple-layer structures in a process called laminating. In the graphic arts industry, the coated papers are further coated

with ink to generate the desired images through a single printing station or multiple-color-printing units. Figure 46.1 shows a nished Polaroid instant color picture containing polyester supports on the top and bottom with active layers sensitized to the three primary colors (blue, green, and red), timing layers, and spacing layers to display the image between the supports.

chapter 47|24 pages

Drying of Polymers

Title

Abstract 

Spurred by continually escalating energy costs, along with the advent of new competitive polymers accompanied by new and extended applications of polymers and plastics, interest in the energy-intensive operation of drying of polymers has been on the rise in recent years.

chapter 48|10 pages

Drying of Enzymes

Title

Abstract 

Enzymes are protein catalysts of high molecular weight, which are produced not only by plants and animals but also mainly by microorganisms as a result of fermentation processes. Enzymes fall into two categories: (1) bulk industrial enzymes, which mainly include proteases for detergents, amylases for textile desizing and starch hydrolysis, pectinases for fruit-juice clarication, and proteases for the leather industry (Table 48.1); and (2) analytical enzymes.

chapter 49|14 pages

Drying and Denaturation of Proteins in Spray Drying Process

Title

Abstract 

Proteins derived from various natural sources such as plant, animal, and milk are converted into dry powder form to enhance their stability and for long-term storage. Even therapeutic proteins such as antibodies, which are usually delivered after reconstitution, are also rst converted into powder (Sane et al., 2004). Dry therapeutic proteins are being increasingly used in their native form for inhalation and pulmonary and transdermal delivery (Johnson, 1997). Nontherapeutic proteins such as milk proteins are important ingredients in manufactured functional and health foods. They are also converted into dry powder form.

chapter 50|14 pages

Product Functionality-Oriented Drying Process Related to Pharmaceutical Particles Engineering

Title

Abstract 

Drying of drug products serves many different purposes to the pharmaceutical and health industry. One main purpose is the removal of moisture that minimizes unwanted reactions to the drug, extending the shelf life of the drug product. The spray drying and freeze drying processes are typically used to achieve this as the drug is produced by wet processes. Physical properties of the drug products need to be engineered to aid in the delivery to the human body. Such application can be found in drug encapsulation via spray

and freeze drying. The ability of the spray dryer to generate ne powder for inhaler application and for tabletting is also another advantage for the pharmaceutical industry. Particles for tabletting are normally further processed by a ¤uidized bed dryer/granulator to make them easy ¤owing and in certain products coated to improve the performance of the drug particles. Therefore, this chapter presents a discussion of how the three key drying processes, viz., spray drying, freeze drying and ¤uidized bed drying, are used in industry to make functional pharmaceutical products.

chapter 51|24 pages

Drying of Coal

Title

Abstract 

Drying of low-rank coal (LRC) is carried out to increase its caloric value and facilitate its transport. Wet coal is difcult to load or unload from railway cars owing to freezing, which is a problem in colder climates. The presence of moisture causes a reduction in friability of coal, makes it difcult to control blending operations, worsens the quality of grinding (if coal is ground), and impedes separation and classication as well as the pneumatic transport of pulverized coal. Friable coal suitable for combustion in modern steam boilers is obtained only when the moist coal is dried. Coal must also be dried for the following processes: (1) briquetting, (2) coking, (3) gasication, (4) low-temperature carbonization, (5) liquid

fuel synthesis, and others. The nal moisture content requirement for coal is different depending on the process in which it is used. The following is a summary of approximate ranges of moisture content of coal required for various processes.

Section IV Miscellaneous Topics in Industrial Drying

chapter 52|20 pages

Dryer Feeding Systems

Title

Abstract 

Feeders are devices that introduce a variety of materials into dryers at a controlled, specied rate. Usually, the feeder is located at the interface stage between material-handling equipment or upstream process and the dryer. The materialhandling equipment may be a hopper or a bin whereas the upstream process may be a reactor, crystallizer, lter, hydrocyclone, centrifuge, etc.

chapter 53|32 pages

Dryer Emission Control Systems

Title

Abstract 

Dryers are one of the major sources of atmospheric emissions in industrial operations as the majority of industrial dryers operate in an open-cycle system. A drying installation may cause air pollution by the emission of dust, gases, and odors. Even plumes of clean water vapor are unacceptable in some areas. The nature of the emissions is determined by the material being dried and the operating conditions. As no such

attention is paid to environmental protection, these emissions are no longer permissible in many countries and it is logical that effective means of controlling pollution must be developed. New drying plants must be designed with emission control systems capable of meeting the most severe local requirements so that they can provide the necessary performance; existing plants can be modied and tted with control systems in order to meet new regulations.

chapter 54|24 pages

Energy Aspects in Drying

Title

Abstract 

It has become apparent in recent years that energy resources, especially natural gas and oil, are limited. Consequently, all industrial sectors in all parts of the world need to identify more efcient methods of energy utilization. Despite periodic ¤uctuations, there is a tendency for energy costs to increase and, consequently, in many cases, energy should become an important element of innovations to drying practice and changes in equipment technology. Many studies, publications, and monographs are concerned with optimized energy utilization; most of these refer to a specic industry (e.g., chemical, ceramic, and metallurgical). However, a process-oriented approach would be more justied, as it would be based on a particular equipment or operation regardless of the branch of industry. Factors that lead to inefcient energy usage in industrial environment include emphasis on rst cost when implementing capital improvements, deferred or

reduced maintenance due to decreased operating budgets, and retooling production operations to meet changing business conditions without considering impact to the efciency of existing facility operations [1].

chapter 55|26 pages

Heat Pump Drying Systems

Title

Abstract 

Heat pump dryers have been known to be energy efcient when used in conjunction with drying operations. The principal advantages of heat pump dryers emerge from the ability of the heat pumps to recover energy from the exhaust gas as well as their ability to control the drying gas temperature and humidity. Many researchers have demonstrated the importance of producing a range of precise drying conditions to dry a wide range of products and improve their quality. At the same time, MacArthur (1984) has mentioned the need to optimize component and system design to increase energy efciency in heat pump systems.

chapter 56|26 pages

Safety Aspects of Industrial Dryers

Title

Abstract 

The statistics of industrial accidents show that drying should be regarded as a potentially hazardous operation that has brought a number of reported incidents with serious results for personnel and equipment [1,2]. The data indicate that the accident rate per 105 workers at risk is considerably greater in the food industry than, e.g., in the chemical industry. Approximately 8%–9% of all dust explosions in the food industry is related to the drying operation (Figure 56.1). The other data for the period 1967-1983 in the German sugar

industry indicate that drying contributes to 37% of all accidents [3], whereas in the French milk industry an average of four major accidents in spray dryers were reported annually [4]. Based on 89 accidents that happened in 1965-2000, 415 people were injured and 16 fatalities were reported in The Accident Database [5]. It is worth to note that in most cases of spray dryer accident in the food industry re was observed whereas an explosion experienced in <10% [6]. The above reports underline the importance of safety from re and explosion hazards in dryers and in the ancillary equipment.

chapter 57|18 pages

Control of Industrial Dryers

Title

Abstract 

Today, most industrial dryers are equipped with varying levels of automatic controllers. Often they use simple control strategies based, for example, simply on the exhaustgas temperature for a direct dryer. Small-scale and slow drying operations are often controlled (or adjusted for process upsets) manually. Very high production units, those involving very rapid drying or units that produce products within stringent quality specications, must be equipped with some degree of automatic control. Although commercial dryers currently use conventional control strategies, it is expected that within the next decade more and more industrial dryers will utilize model-based control (MBC), fuzzy logic control (FLC), or neural nets control when the dryer performance is highly nonlinear and difcult to predict with simple mathematical models. Some improvements in dryer controls became available because of the development of better sensors and analyzers, whereas others are by-products of new, more sophisticated, computer-based control techniques [1]. This chapter provides an introductory overview of both the conventional and the emerging control schemes

for industrial drying. Examples are cited with reference to the more common dryers (e.g., spray, ¤ash, ¤uid-bed dryers). Relevant information is also provided to the readers interested in intelligent control systems based on expert systems, fuzzy logic, or neural nets. It is inconceivable that within this decade equipment suppliers will market “smart” dryers that can adjust their operating parameters consistent with the needs of product quality during drying. However, such a possibility exists for some dryer types in a longer term.

chapter 58|18 pages

Solid–Liquid Separation for Pretreatment of Drying Operation

Title

Abstract 

The diversity of substances and the competitive efforts have evolved into many variants for solid-liquid separation equipment. Before categorizing the equipment for pretreatment of the feed material to the drying operation, it is useful to look at the entire eld of solid-liquid separation. It can be divided as shown in Table 58.1 [1,2].

chapter 59|20 pages

Frying of Foods

Title

Abstract 

Frying is dened as a process of cooking and drying through contact with hot oil. It is intended to make food more palatable and tasteful, but at the same time makes food safer and provides a preservative effect that results from thermal destruction of microorganisms and enzymes, and a reduction in water activity at the surface or throughout the food. The shelf life of fried products is mostly determined by the moisture content after frying. Products that retain a moist interior should be consumed shortly after preparation, or can be stored for a relatively short time under chilling conditions or for a longer time under freezing conditions. Most of these foods-with the exception of par-fried goods-are not produced on a commercial scale for distribution to retail stores, but are important in catering applications. Foods that are dried throughout during frying have a shelf life up to several

months, which is mostly limited by quality deterioration of the absorbed oil and development of a rancid odor and ¤avor. Storage stability of these products may be increased by using packaging materials with adequate barrier properties.

chapter 60|20 pages

Simprosys: Software for Dryer Calculations

Title

Abstract 

Over the past 25 years, considerable effort has been devoted to the development of various software programs applicable to the design, operation, and optimization of drying systems (Marinos-Kouris et al., 1996; Menshutina and Kudra, 2001; Kemp et al., 2004; Kemp, 2007). However, few commercial drying software products have been available on the market and well accepted by the industry. In fact, the most prominent one is proprietary and available only to the sponsors.

chapter 61|10 pages

Life Cycle Assessment of Drying Systems

Title

Abstract 

Drying is one of the most energy-intensive unit operations in industrial processing. In case of evaporative drying, a large part of the required energy is used in the form of thermal heat (i.e., heat generated directly by combustion of fuel or indirectly from steam or using hot oil through a heat exchanger) in the drying process. The drying system would include infeed material handling and loading components, dryer unit, out-feed handling and unloading components, and heat plant and accessories. Drying is a very diverse unit operation in chemical engineering. Some distinguishing features of the drying unit operation are the variation in the material size and shape, variety of drying media used, and the wide range of drying times. This is why there are over 400 different types of dryers reported in the literature and over 100 distinct types of dryers commonly available (Mujumdar, 2006).

chapter 62|22 pages

Thermo-Hydro-Mechanical Aspects of Drying

Title

Abstract 

Although the progress in the development of knowledge on drying has been marked by an impressive array of papers and a number of books, including three editions of Handbook of Industrial Drying (Ed. A.S. Mujumdar),1 very little research has been devoted to the thermo-hydro-mechanical aspects of drying of capillary porous materials (wood, sol-gel coatings, ceramics, alumina gel, etc.). The deformations of these materials (e.g., shrinkage strains and warping) and the drying-induced stresses, which are responsible for crack formation, have been still marginally examined. Only relatively recently, one can observe a stronger research effort focused on the coupling of the heat and mass transfers with

the mechanical behavior of these materials during drying.2-9 This new look at the drying processes comes from the necessity for the improvement of the quality and the strength of dried products, as drying is the process that may violate both these properties, mainly because of crack formation at high drying rates, particularly when drying thick bodies.

chapter 63|10 pages

Supercritical Fluid-Assisted Drying

Title

Abstract 

The science and practices of industrial drying have been evolving mostly due to emerging areas related to the development of advanced materials, novel bioproducts and microelectronic chips, as well as formulation of powdery blends with requirement of narrow and uniform particle size distribution. The production of microelectronic chips faces the same challenges in drying and opportunities as for products of biological origin: high quality, high purity, suitable crystallinity, nonmodi-ed physical functionalities, oxygen sensitivity, solubility of dried product, stickiness, and thermosensitivity. Thus, development of advanced products and/or materials requires novel drying procedures and more effective alternative techniques. Such needs for improved and energy-efcient dryers have also been pointed out in a paper entitled “Global R&D needs in drying” by Mujumdar and Huang in 2007 [1]. Supercritical ¤uid-assisted drying is one of these alternatives that uses supercritical ¤uid as the drying medium instead of heated air. Such a technique has been developed in recent years [2-5]. Supercritical ¤uids have unique properties in that their densities and solubilities are similar to those of the liquids and their compressibility is akin to that of the gases. More importantly, there are no surface tension effects that can cause problems in drying highly porous materials since the solid structures can collapse as the water in liquid phase is removed due to conventional drying. Thus, one of the key features of supercritical ¤uid drying is that no liquid-gas phase change occurs during drying mechanism. Among supercritical ¤uids, carbon dioxide (CO2 ) is being used increasingly and promoted at small, pilot, or large scales to dehydrate high-value natural bioactive ingredients [6-10], aerogels [11-23], or nanomaterials [24].

chapter 64|20 pages

Industrial Crystallization

Title

Abstract 

Crystallization from solution is known to produce particles of high purity and of an approximately uniform size. The major elds of application are in the chemical, pharmaceutical, and food industries. However, in some cases, difculties in separation and drying of the crystals turn into the obstacles of an otherwise ideal method.

chapter 65|12 pages

Cost-Estimation Methods for Dryers and Drying Processes

Title

Abstract 

When capital cost estimates of a denitive investment are required to obtain budget authorization, competitive quotes from vendors have to be requested, as these quotes are the most reliable estimates.

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This Fourth Edition book includes 12 new chapters covering computational fluid dynamic simulation; solar, impingement, and pulse combustion drying; drying of fruits, vegetables, sugar, biomass, and coal; physicochemical aspects of sludge drying; and life-cycle assessment of drying systems. Addressing commonly encountered dryers as well as innovative dryers with future potential, the fully revised text not only delivers a comprehensive treatment of the current state of the art, but also serves as a consultative reference for streamlining industrial drying operations to increase energy efficiency and cost-effectiveness.

TABLE OF CONTENTS

Section I Fundamental Aspects

chapter 1|28 pages

Principles, Classication, and Selection of Dryers

Title

Abstract 

Drying commonly describes the process of thermally removing volatile substances (moisture) to yield a solid product. Moisture held in loose chemical combination, present as a liquid solution within the solid or even trapped in the microstructure of the solid, which exerts a vapor pressure less than that of pure liquid, is called bound moisture. Moisture in excess of bound moisture is called unbound moisture.

chapter 2|20 pages

Experimental Techniques in Drying

Title

Abstract 

The calculation of drying processes requires a knowledge of a number of characteristics of drying techniques, such as the characteristics of the material, the coefcients of conductivity and transfer, and the characteristics of shrinkage. In most cases these characteristics cannot be calculated by analysis, and it is emphasized in the description of mathematical models of the physical process that the so-called global conductivity and transfer coefcients, which re¤ect the total effect on the partial processes, must frequently be interpreted as experimental characteristics. Consequently, these characteristics can be determined only by adequate experiments. With experimental data it is possible to apply analytical or numerical solutions of simultaneous heat and mass transfer to practical calculations.

chapter 3|26 pages

Basic Process Calculations and Simulations in Drying

Title

Abstract 

Since the publication of the rst and second editions of this handbook, we have been witnessing a revolution in methods of engineering calculations. Computer tools have become easily available and have replaced the old graphical methods. An entirely new discipline of computer-aided process design (CAPD) has emerged. Today even simple problems are solved using dedicated computer software. The same is not necessarily true for drying calculations; dedicated software for this process is still scarce. However, general computing tools including Excel, Mathcad, MATLAB®, and Mathematica are easily available in any engineering company. Bearing this in mind, we have decided to present here a more computer-oriented calculation methodology and simulation methods than to rely on old graphical and shortcut methods. This does not mean that the computer will relieve one from thinking. In this respect, the old simple methods and rules of thumb are still valid and provide a simple commonsense tool for verifying computer-generated results.

chapter 4|34 pages

Transport Properties in the Drying of Solids

Title

Abstract 

Drying is a complicated process involving simultaneous heat, mass, and momentum transfer phenomena, and effective models are necessary for process design, optimization, energy integration, and control. The development of mathematical models to describe drying processes has been a topic of many research studies for several decades. Undoubtedly, the observed progress has limited empiricism to a large extent. However, the design of dryers is still a mixture of science and practical experience. Thus the prediction of Luikov that by 1985 “would obviate the need for empiricism in selecting optimum drying conditions,” represented an optimistic perspective, which, however, shows that the efforts must be increased [1]. Presently, more and more sophisticated drying models are becoming available, but a major question that still remains is the measurement or determination of the parameters used in the models. The measurement or estimation of the necessary parameters should be feasible and practical for general applicability of a drying model.

chapter 5|14 pages

Spreadsheet-Aided Dryer Design

Title

Abstract 

Computer-aided design is based on computer simulators, whereas computer simulators are based on process modeling. The basic terms, such as modeling, simulation, and design, are dened in Table 5.1. Modeling is the procedure of translating the physical laws of a process to mathematical equations to analyze or design the process. Simulation is the appropriate software, which predicts the real performance of a process. It is based on mathematical modeling plus the appropriate graphics interface in a computer environment. Design is a procedure of sizing and rating a process in order to achieve specic goals, such as economic production, product quality, and protection of the environment.

Section II Description of Various Dryer Types

chapter 6|12 pages

Indirect Dryers

Title

Abstract 

Generally, indirect dryers have higher energy efciency than the direct dryers, because the energy lost through the exhaust gas stream is greatly reduced; the heat load of the dryers is only from the material as it dries. Waste heat source can also be used to cut drying energy costs. The vapor produced from the drying material can also be used as a heating medium in a subsequent stage of drying, hence reducing the consumption of the primary heat transfer medium. If the vaporization rate is high, e.g., when drying pulp, a two-or three-stage dryer may be economic.

chapter 7|22 pages

Rotary Drying

Title

Abstract 

Rotary drying is one of the many drying methods existing in unit operations of chemical engineering. The drying takes place in rotary dryers, which consist of a cylindrical shell rotated upon bearings and usually slightly inclined to the horizontal. Wet feed is introduced into the upper end of the dryer and the feed progresses through it by virtue of rotation, head effect, and slope of the shell and dried product withdrawn at the lower end. A simplied diagram of a direct-heat rotary dryer is presented in Figure 7.1. The direction of gas ¤ow through the cylinder relative to the solids is dictated mainly by the properties of the processed material. Cocurrent ¤ow is used for heat-sensitive materials even for high inlet gas temperature due to the rapid cooling of the gas during initial evaporation of surface moisture, whereas for other materials countercurrent ¤ow is desirable in order to take advantage of the higher thermal efciency that can be achieved in this way. In the rst case, gas ¤ow increases the rate of solids ¤ow, whereas it retards it in the second case [3,19,20,35].

chapter 8|30 pages

Fluidized Bed Dryers

Title

Abstract 

Fluidized bed dryers (FBDs) are used extensively for the drying of wet particulate and granular materials, and even slurries, pastes, and suspensions, that can be ¤uidized in beds of inert solids. They are commonly used in processing many products such as chemicals, carbohydrates, foodstuff, biomaterials, beverage products, ceramics, pharmaceuticals in powder or agglomerated form, health-care products, pesticides and agrochemicals, dyestuffs and pigments, detergents and surface-active agents, fertilizers, polymer and resins, and tannins. They are also useful in manufacturing products for calcination, combustion, incineration, waste management processes, and environmental protection processes. Important advantages of ¤uidized bed operation include good solids mixing, high rates of heat and mass transfer, and easy material transport.

chapter 9|36 pages

Industrial Spray Drying Systems

Title

Abstract 

Spray drying is a suspended particle processing (SPP) technique that utilizes liquid atomization to create droplets that are dried to individual particles when moved in a hot gaseous drying medium, usually air. It is a one-step continuous unit processing operation. It has become one of the most important methods for drying the ¤uid foods in the Western world. The development of the process has been intimately

associated with the dairy industry and the demand for drying of milk powders. Spray drying used in dairy industry dates back to around 1800, but it was not until 1850 that it became possible in industrial scale to dry the milk. However, this technology has been developed and expanded to cover a large food group that is now successfully spray-dried. Over 25,000 spray dryers are now estimated to be commercially in use to dry products from agrochemical, biotechnology products, ne and heavy chemicals, dairy products, dyestuffs, mineral

9.1 Introduction ......................................................................................................................................................................191 9.2 Principles of Spray Drying Processes ............................................................................................................................. 192

9.2.1 General................................................................................................................................................................. 192 9.2.2 Atomization ......................................................................................................................................................... 193

9.2.2.1 Drop Size and Size Distribution ........................................................................................................... 194 9.2.2.2 Wheel Atomizers .................................................................................................................................. 195 9.2.2.3 Pressure Nozzles ................................................................................................................................... 197 9.2.2.4 Pneumatic Nozzles ................................................................................................................................ 198 9.2.2.5 Novel Types of Atomizers..................................................................................................................... 199 9.2.2.6 Selection of Atomizers .......................................................................................................................... 199

9.2.3 Chamber Design .................................................................................................................................................. 200 9.2.3.1 Chamber Shape ..................................................................................................................................... 200 9.2.3.2 Air-Droplet Contact Systems ................................................................................................................ 201 9.2.3.3 Powder and Air Discharge Systems ...................................................................................................... 203

9.2.4 Ancillary Equipment ........................................................................................................................................... 203 9.2.4.1 Fans ....................................................................................................................................................... 204 9.2.4.2 Powder Separators ................................................................................................................................. 205

9.2.5 Thermal Efciency .............................................................................................................................................. 206 9.3 Spray Drying Systems ..................................................................................................................................................... 208

9.3.1 Process Layouts and Applications ....................................................................................................................... 208 9.3.2 Energy Savings .....................................................................................................................................................214 9.3.3 Safety Aspects ..................................................................................................................................................... 215 9.3.4 Control Systems ....................................................................................................................................................216 9.3.5 Selection of Spray Dryers

chapter 10|22 pages

Theoretical Modeling and Numerical Simulation of Spray Drying Processes

Title

Abstract 

Particle formation technologies are utilized today in many areas, including pharmaceutical, medical and biomedical, biotechnology, chemical, optical and optoelectronic, cosmetic, printing, painting, ceramics, materials design, nutrition, and for other applications. Spray drying is one of the widely used processes for producing small particles by rapid moisture evaporation from a spray of droplets. Spray drying involves multiphase transport phenomena between drying agent, droplets and particles, and chamber boundaries. These transport phenomena occur on multiple scales because of simultaneous external and internal heat and mass transfer in each phase. Therefore, purely experimental studies would be insufcient and would not encompass all the basic physical processes, predict parametric behavior, and optimize the power consumption of spray drying. On the other hand, realistic modeling and numerical simulation of spray drying are highly demanding tasks for engineers in designing spray dryer systems and in choosing suitable operating conditions.'

chapter 11|10 pages

Drum Dryers

Title

Abstract 

The drum dryer is commonly used to dry viscous, concentrated solutions, slurries or pastes on rotating steam-heated drums.1,2 It can also be used to dry concentrated solutions or slurries that become more viscous or pasty because of ¤ashing or boiling off of moisture or of irreversible thermochemical transformations of their content that occur on their rst contact with the hot drum surface.3−5

The viscous slurry or paste is mechanically spread by the spreading action of two counter-rotating drums into a thin sheet that adheres on the hotter drum in single drum dryers or split sheets on both hot cylinders in double drum dryers. The adhering thin sheet of paste is then rapidly dried conductively by the high heat ¤ux of the condensing steam inside the drum. For very wet slurries that produce wet sheets, the drying of the wet thin sheet can be further enhanced by blowing hot dry air on the sheet surface. The thin sheet containing heat-sensitive materials, such as vitamins, can also be dried at a lower temperature in a vacuum.

chapter 12|24 pages

Freeze Drying

Title

Abstract 

Certain biological materials, pharmaceuticals, and foodstuffs, which may not be heated even to moderate temperatures in ordinary drying, may be freeze-dried. The substance to be dried is usually frozen. In freeze drying, the water or another solvent is removed as a vapor by sublimation from the frozen material in a vacuum chamber. After the solvent sublimes to a vapor, it is removed from the drying chamber where the drying process occurs.

chapter 13|20 pages

Microwave and Dielectric Drying

Title

Abstract 

It is sometimes surprising to realize that dielectric and microwave heating have been in use for quite some time. It appears to many engineers that these are new forms of heating when in fact practical applications began during World War II and the home microwave oven was invented shortly afterward. Yet these remain small industries, and for the most part, the equipment manufacturers are likewise small companies. The older of the two, dielectric heating, is a workhorse heating method used in many industries, including plastics, wood, ceramics, furniture, textiles, and paper. It is also by far the larger of the two industries; however, it is not very well known to many industrialists, whereas the microwave heating is well known, but its industrial applications are far fewer. To try to quantify the relationship, probably only 200-300 MW of microwave power is in use globally for industrial heating purposes, whereas a single large dielectric heating system may employ as much as 2-3 MW of power. The annual worldwide sales of industrial microwave heating systems probably amounts to only less than 20 0 million dollars, but the sales of the home microwave ovens in the United States is of the order of 1.5-2.0 billion dollars. The reasons for the relatively small size of these markets are several, but two stand out: First, the heating mechanisms are not familiar to most engineers, and second, they often represent a radical departure from conventional systems and there is generally a tendency to resist real innovation in most industries.

chapter 14|48 pages

Solar Drying

Title

Abstract 

Open-air sun drying has been used since time immemorial to dry plants, seeds, fruits, meat, sh, wood, and other agricultural or forest products as a means of preservation. However, for large-scale production the limitations of openair drying are well known. Among these are high labor costs, large area requirement, lack of ability to control the drying process, possible degradation due to biochemical or microbiological reactions, insect infestation, and so on. In order to benet from the free and renewable energy source provided by the sun several attempts have been made in recent years to develop solar drying mainly for preserving agricultural and forest products.

chapter 15|20 pages

Spouted Bed Drying

Title

Abstract 

The applicability of the spouted bed technique [1-5] to drying of granular products that are too coarse to be readily ¤uidized (e.g., grains) was recognized in the early 1950s. Interest in this area received appreciable impetus two decades later as the energy-intensive drying processes were reexamined with renewed vigor. Spouted bed dryers (SBDs) display numerous advantages and some limitations over competing conventional dryers. Because of the short dwell time in the spout, SBDs can be used to dry heat-sensitive solids, such as foods, pharmaceuticals, and plastics. With simple modication the so-called modied spouted beds can be designed to ensure good mixing, controlled residence time, minimum attrition, and other desirable features. Also, the operations of coating, granulation agglomeration, and cooling, among others, can be carried out by the same apparatus by varying the operating parameters. SBDs can be used for solids with constant

as well as falling rate drying periods. Using inert solids as the bed material, SBDs have been used successfully to dry pastes, slurries, and heat-sensitive materials.

chapter 16|10 pages

Impingement Drying

Title

Abstract 

Impinging jets of various congurations are commonly used in numerous industrial drying operations involving rapid drying of materials in the form of continuous sheets (e.g., tissue paper, photographic lm, coated paper, nonwovens, and textiles) or relatively large, thin sheets (e.g., veneer, lumber, and carpets), or even beds of coarse granules (e.g., cat or dog food). In this chapter, we will not examine the last-mentioned application, which is a novel operation in which hot jets are directed normally onto thin beds of pellets transported on a slow-moving conveyor. The jets pseudo¶uidize the bed to ensure good gas-solid contact needed for effective drying.

chapter 17|12 pages

Pneumatic and Flash Drying

Title

Abstract 

Drying is a separation process that converts a wet solid, semisolid, or liquid feedstock into a solid product by evaporation of the liquid into a vapor phase via heating. Essential features of the drying process are phase change and production of a solid, dried product.

chapter 18|12 pages

Conveyor Dryers

Title

Abstract 

The conveyor dryer is conceptually very simple. Product is carried through the dryer on conveyors and hot air is forced through the bed of product. It is often described as simply a conveyor in a box with hot air. The reality, however, is that the conveyor dryer is one of the most versatile dryers available. Few drying technologies can match the conveyor dryer’s ability to handle such a wide range of products. Products as varied in composition, shape, and size as coated breakfast cereals, nuts, animal feed, charcoal briquettes, and rubber can be dried in a conveyor dryer. Although it is simple in concept, an improper understanding of the heat and mass transfer processes in the conveyor dryer will surely lead to poor product handling, wasted energy, and nonuniform product quality. This chapter describes the various conveyor dryer congurations that are available, typical products that can be dried in the conveyor dryer, and how to properly size and operate a conveyor dryer. This information will help anyone involved in conveyor dryer design, operation, or evaluation.

chapter 19|16 pages

Infrared Drying

Title

Abstract 

Drying is the most common and most energy-consuming industrial operation. With literally hundreds of variants used in drying of particulate solids, pastes, continuous sheets, slurries, or solutions, it provides the most diversity among chemical engineering unit operations.

chapter 20|12 pages

Superheated Steam Drying

Title

Abstract 

Although the concept was originally proposed over 100 years ago and the rst industrial applications were reported some 60 years ago in Germany, superheated steam drying has emerged only in the past decade or so as a viable new technology with immense potential. Essentially, superheated steam drying (SSD) involves the use of superheated steam in a direct (convective) dryer in place of hot air, combustion, or ¤ue gases as the drying medium to supply heat for drying and to carry off the evaporated moisture. Any direct or direct and indirect (e.g., combined convection and conduction) dryer can be operated as an SSD, in principle. The technology involved is more complex and hence this conversion is not simple. Additional criteria must be considered when selecting a dryer for SSD operation.

chapter 21|58 pages

Special Drying Techniques and Novel Dryers

Title

Abstract 

Increasing demands for new and high-quality products, energy-efcient processes, environment protection, and the like have stimulated progress in drying science and technology. Mujumdar has presented a summary of the motivation for development of new drying technologies and identied a number of trends, which include the following [1]:

• Use of superheated steam in direct dryers • Increased use of indirect (conduction) heating • Use of combined (or integrated) heat transfer modes • Use of volumetric heating (microwave [MW]/radio-

frequency [RF] elds) in specialized situations • Use of two-stage (or multistage) dryers • Use of intermittent heat transfer • Use of novel combustion technologies (e.g., pulse

combustion for ¤ash drying) • Use of novel gas-solid contactors (e.g., 2D spouted

beds, intermittent or rotating spouted beds) • Design of ¤exible, multiprocessing dryers • Combination of different dryer types

Many of these topics are covered in detail elsewhere in this handbook. There are numerous other technologies that have reached various stages of maturity-ranging from concepts and pilot-scale demonstrations to large-scale industrial applications. Several of these have been reviewed in the recent literature [2].

chapter 22|12 pages

Intermittent Drying

Title

Abstract 

Various intermittent drying operations have recently increasingly been used at laboratory, pilot, and industrial scales. They all aim to improve product quality and/or process performance by reducing energy consumption. Intermittent drying is a drying operation with several periods of varying external dehydration conditions with different drying rates. In intermittent drying, air¤ow temperature, velocity and/or humidity, heat input, pressure, and/or other external drying parameters (such as microwave (MW) or RF) are applied in a discontinuous manner to suit the drying kinetics and quality requirements of the material. The idea is often to introduce tempering periods to even out the internal moisture content and temperature elds. The quality of the nal dried product can also be enhanced along with process performance. In each tempering period, moisture gets redistributed inside the material. This produces several desired effects. Quality is enhanced by avoiding or reducing overheating or overdrying of the surface layer. Quality degradation can be due to surface cracking, breakage, or crusting, and under certain conditions even scorching of the material. The drying rate can also increase as the material surface gets rewetted to that higher heat/mass transfer can occur at the exposed surface of the material.

chapter 23|16 pages

Pulse Combustion Drying

Title

Abstract 

Pulse combustion is a specic form of combustion-driven oscillation. Combustion oscillations can be an inherent problem or a potential benet in enclosed combustion systems, such as gas turbine combustors, afterburners, furnaces, and rocket engines. Oscillations can produce benecial increases in heat transfer rates and reduce pollutant formation. In other situations, these instabilities are undesirable because they may reduce the thermodynamic efciency of a combustor or become a source of system failure if their amplitude is not kept within an acceptable range. Oscillations in the pulse combustion drying systems are desired and useful. Combustion with oscillations may be treated as some regular form of unstable combustion.

Section III Drying in Various Industrial Sectors

Title

chapter 24|24 pages

Drying of Foodstuffs

Title

Abstract 

The removal of moisture from solids is an integral part of food processing. Almost every food product is dried at least once at one point of its preparation. The main objectives of dehydration are summarized as follows [32].

chapter 25|12 pages

Drying of Fish and Seafood

Title

Abstract 

Drying in earlier times was done in the sun, now many types of sophisticated equipment and methods are used to dehydrate foods. During the past few decades, considerable efforts have been made to understand some of the chemical and biochemical changes that occur during dehydration and to develop methods for preventing undesirable quality losses [57]. Foods can be divided into three broad groups based on the value added through processing by drying. In the case of

cereals, legumes, and root crops, very little value is added per ton processed. More value per unit mass is added to foods such as vegetables, fruits, and sh, and considerably more to high-value crops such as spices, herbs, medicinal plants, nuts, bioactive materials, and enzymes [3].

chapter 26|10 pages

Grain Drying

Title

Abstract 

Grain has been an important agricultural commodity and primary food source for centuries. The present distribution of the world’s population has made strong demands on grainhandling technology. Irrespective of whether it is international trade or demands within a country, grain needs low moisture levels for safe storage. Drying has always been the most common method of preserving grain. In the days of premechanization of agriculture, enough grain was usually stored by hanging ears of corn in barn lofts and attics to meet the needs of a community. As mechanization of agriculture spreads to meet the needs of a population that was rapidly growing and urbanizing, mechanical methods for drying large quantities of grain were needed. Grain now travels thousands of miles either in large grain-carrying ships or in different types of carriers on wheels, and must reach its destination in a highquality state. Proper drying of these huge quantities of grain is a prerequisite to safe storage and delivery.

chapter 27|28 pages

Grain Property Values and Their Measurement

Title

Abstract 

The world produces annually about 2 billion tonnes (Gt) of grains and oilseeds [1] that are handled and stored on-and off-farm for periods of up to 3 years. Often the storage period may be longer than 3 years, for example, when the grain is stored for potential famine relief. To design handling, inspection, and storage systems for grains and oilseeds, data on many properties of individual seeds and seeds in bulk are needed. The properties of interest are: bulk and particle densities, porosity, roundness, sphericity, friction coefcients of grains against commonly used bin wall materials, emptying and lling angles of repose, equilibrium moisture content (EMC), specic heat, thermal conductivity, dielectric

constant, electrical conductivity, re¤ectance, terminal velocity, and drag coefcient. There are many methods of measuring these properties. In this chapter, only the methods that are currently in use or widely accepted methods are described. Representative property values for common grains and oilseeds are summarized from the published literature.

chapter 28|16 pages

Drying of Rice

Title

Abstract 

Rice is one of the world’s primary food crops and is a major source of dietary energy for more than half of the people on this planet. Paddy is usually milled or polished into white rice for cooking even though unpolished rice contains much more nutritional bioactive components and dietary energy. A major component of rice grain is starch, which in turn is composed of polysaccharides; two types of polysaccharides found in rice starch are amylose and amylopectin. The amounts of amylose and amylopectin determine the quality of rice, both in terms of physical and chemical characteristics.

chapter 29|26 pages

Drying of Fruits and Vegetables

Title

Abstract 

From the point of view of consumption, fruits are plant products with aromatic ¤avor that are naturally sweet or normally sweetened before usage [1]. Apart from providing ¤avor and variety to human diet, they serve as important and indispensable sources of vitamins and minerals although they are not good or economic sources of protein, fat, and energy. The same is true in the case of vegetables, which also play an important role in human nutrition in supplying certain constituents in which other food materials are decient and in adding ¤avor, color, and variety to the diet [2].

chapter 30|10 pages

Drying of Herbal Medicines and Tea

Title

Abstract 

Herbal medicine is part of human civilization. It has been used in China for nearly 5000 years. One of the oldest and most important documents is the Egyptian Ebers papyrus (ca. 1550 bc), which includes more than 700 prescriptions using natural products such as caraway, coriander, garlic, linseed, peppermint, gs, fennel, anise, poppy, and castor oil [1]. Shen Nong’s Materia Medica was compiled by ancient Chinese in about 200 bc, which described the properties and usages of 365 types of Chinese medicines in three categories. In ancient Greece there was a guild of rhizomatists or root collectors, who gathered, prepared, and sold medicinal plants. The Greek botanist and physician, Dioscorides (ad 40-90), compiled the rst systematic description of 579 plants and their 4700 medicinal uses and modes of action. His work titled De Materia Medica was of central importance to European medicine until the seventeenth century [1]. Ayurveda is the principal traditional medical system of India, Pakistan, Nepal, and Sri Lanka, which has also in¤uenced medicine in Tibet, Burma, and Malaysia.

chapter 31|14 pages

Drying of Potato, Sweet Potato, and Other Roots

Title

Abstract 

For many centuries potato, Solanum tubersum, has served as the primary food source for people in many parts of the world. The potato, with a total production in excess of 300 million tons, is one of the major food crops grown in a wide variety of soils and climatic conditions. Many cultivars of potatoes are grown, however, a few cultivars account for most of the potatoes produced. These differ in time of maturity, yield, appearance, disease resistance, marketing, and processing quality. The majority of potatoes are used as table food these days, frequently consumed in different forms of processed potato products. In developed countries, more than

50% of potatoes produced are consumed as processed products. The processed products may be in the form of chips, granules, ¤akes, power, dice, strips, powder, etc. [1].

chapter 32|20 pages

Osmotic Dehydration of Fruits and Vegetables

Title

Abstract 

Water as a main constituent of most foods affects food stability, microbial as well as chemical, and is responsible for the consumer perception of many organoleptic attributes, i.e., juiciness, elasticity, tenderness, and texture. It is generally accepted that it is not the quantity of water in food but its thermodynamic state that is responsible for its in¤uence on food stability and texture. The thermodynamic state of water in food is expressed by its activity, which is 0 for absolutely dry material and 1 for pure water. The lower the water activity the more stable is the food, and the texture changes from juicy and elastic to brittle and crunchy.

chapter 33|22 pages

Drying of Pharmaceutical Products

Title

Abstract 

The pharmaceutical industry is one in which quality of the nal product cannot be compromised. Any deterioration of the product (e.g., by microbial infection, oxidation, thermal decomposition, contamination by metallic particles or by unremoved organic solvent) must be avoided at any cost. In light of that the Good Manufacturing Practices (GMP) for drug manufacture (see, e.g., Ref. [1]) put numerous demands on the drying stage of the drug manufacturing process. Noncontaminating dryer construction materials are used, like polished stainless steel or enameled iron. Closed-cycle dryers are often required

as moisture removed is often an organic solvent or their mixture. Drying must be often performed in inert gas to avoid oxidation or explosion if solvent is ¤ammable. To avoid thermal decomposition in many instances vacuum and freeze drying must be employed.

chapter 34|14 pages

Drying of Nanosize Products

Title

Abstract 

Nanomaterials represent today’s cutting edge in the development of novel advanced materials, which promise tailor-made functionality for unique applications in all important industrial sectors. Nanomaterials can be clusters of atoms, grains 100 nm in size, bers that are less than 100 nm in diameter, lms that are less than 100 nm in thickness, nanoholes, and composites that are a combination of these. In other words, it implies that the microstructures (crystallites, crystal boundaries) are nanoscale [1]. Nanomaterials include atom clusters, nanoparticles, nanotubes, nanorods, nanowires, nanobelts, nanolms, compact nanostructured bulk materials, and nanoporous materials [2]. Materials in nanosize range exhibit

fundamentally new properties and functionalities such as surface effects, dimensionality effects, quanta effects, and quanta tunnel effects, etc.

chapter 35|12 pages

Drying of Ceramics

Title

Abstract 

The demand for high-quality ceramics is increasing in many elds. The applications are spreading to highly functional materials known as the “ne ceramics” as well as materials for house-ware and buildings. Although material science for ceramics has advanced signicantly during the last few decades, the production processes still rely on old methods. Particularly, R&D has not addressed the drying process, and drying is usually carried out slowly in order to avoid undesirable cracks and deformations. The reason is often attributed to the fact that ceramic drying involves maintaining a molded conguration. Although ceramics are sensitive to the surrounding atmosphere during drying, it is very difcult to predict the heat-and mass-transfer rates and the air ¤ow pattern in dryers with sufcient accuracy and generalize the results to the wide variety of ceramics. Many ceramic manufacturers are small companies, and they may not wish to invest much effort in ceramic drying R&D as drying occurs only at the pretreatment stage in ceramic production. However, drying is important for precisely designing the molding, determining the high-efcient heating rate in a dryer, and completing the drying so as to reduce the ratio of failure during sintering and yielding the qualied productions.

chapter 36|10 pages

Drying of Peat and Biofuels

Title

Abstract 

The use of biomass and peat, for both the industrial sector and the district heating, has greatly increased since the rst oil crisis in 1973. The biomass utilized so far is wood and agricultural wastes, including bark, straw, and bagasse. Biomass grown especially for fuel purposes is still a technique in the experimental state. The use of peat as a fuel is limited to countries with domestic resources, such as the former Soviet Union, Canada, the United Kingdom, Ireland, Finland, and Sweden.

chapter 37|24 pages

Drying of Fibrous Materials

Title

Abstract 

Fibers are regarded as very elongated particles. Staple bers that are spun into yarns have length/diameter ratios greater than 10,000. The ber lengths of cotton are of the order 25-75 mm; wool bers may exceed 100 mm and are variable in length even when shorn from the same sheep; ¤ax bers may be available in lengths up to 1 m [1]. The corresponding diameters of textile bers range between 3 and 500 μm.

chapter 38|10 pages

Drying of Textile Products

Title

Abstract 

The word “textiles” comes from the Latin textilis, meaning “woven”; but in textile science, textile is dened as any product made from bers. Thus textiles refers not only to woven fabrics but also to nonwoven fabrics, knitted fabrics, tufted fabrics such as carpets and bedspreads, and specially constructed fabrics [1]. Figure 38.1 depicts the major segments and linkages of the textile industry, from bers to products. The textile mill portion of the textile complex includes many chemical wet processes such as slashing, dyeing, printing, latex bonding, and nishing. In many of these processes, drying is required to remove the excess moisture in the porous materials to produce the desired product. For example, the typical steps used to produce latex-backed tufted carpet are shown schematically in Figure 38.2.

chapter 39|24 pages

Drying of Pulp and Paper

Title

Abstract 

Ts’ai-Lun apparently produced a sheet of paper in about a.d. 100 in China and became the rst recorded papermaker in the world. However, it took about 1000 years for this new art to reach Europe. In the medieval era, the progress of papermaking was very slow and the major ingredient of paper was old rags. By the beginning of the nineteenth century, the progress of this industry was enormously accelerated. The rst practical paper machine was produced in the early 1800s; then continuous drying techniques were introduced to the industry by means of cylinder drying in 1817 by John Dickinson; later, in the mid-1840s, the extensive use of wood as a cellulose-ber source began by the advent of the rst wood grinder. Today, papermaking has become one of the major industries in the world. The production of paper increased enormously, over 60 million tons per year in the United States alone. The machine speeds also increased up to 10-15 m/s and even higher for tissue products, to keep pace with the increased production rates.

chapter 40|50 pages

Drying of Wood: Principles and Practices

Title

Abstract 

A cross section of a tree (Figure 40.2), from the core to the outer region, shows the following features:

• Pith, a small core of tissue located near the middle of a tree’s stem or branches, which originates from the primary growth of the plant

• Woody material, the most important part of mature trees, which is differentiated into sapwood (outer region), where the sap migrates from roots to leaves and heartwood (inner region) that is no longer used for sap transport, which exists only when the stem, at that height, is old enough

• Bark, differentiated into an outer corky dead part (external part of the stem), whose thickness varies greatly with species and age of trees, and an inner thin living part (just near the cambium zone), which carries food from the leaves to the growing elements

40.1.1.1 Knots As the tree grows in height (primary growth), branching is initiated by lateral bud development. Knots are the

835 40.3.4 Practical Considerations ...................................................................................................................................... 836

40.3.4.1 Schedule Development .......................................................................................................................... 836 40.3.4.2 Kiln Control .......................................................................................................................................... 838 40.3.4.3 Volatile Emissions................................................................................................................................. 838 40.3.4.4 Equalization and Stress Relief .............................................................................................................. 839

40.3.5 Less-Common Drying Methods .......................................................................................................................... 839 40.3.5.1 Vacuum Drying ..................................................................................................................................... 839 40.3.5.2 Dehumidier Kilns ............................................................................................................................... 840 40.3.5.3 High-Frequency Electrical Heating ...................................................................................................... 841 40.3.5.4 Solar Drying.......................................................................................................................................... 841

References ................................................................................................................................................................................. 842

bases of branches, which have been covered as the tree grows laterally. After a branch dies, the trunk continues to increase in diameter and surrounds that portion of the branch while the dead branch is still present. This branch has to drop from the tree before clearwood can form. If the knot was alive when the trunk grew around it, the xylem

of the trunk and the branch are continuous and the knot ts tightly into the wood. If the branch was dead when the trunk grew around it, no anatomical connection exists between the xylem of the knot and the trunk. The knot is nonadhesive; it may fall out of the wood, leaving a knothole (Figure 40.3).

chapter 41|14 pages

Biomass Drying for an Integrated Bioenergy Plant

Title

Abstract 

Energy supply and demand data show that the world annual consumption of energy was 510.6 quadrillion Btu in 2010 (1.50  × 1014 kWh or 12.87 billiontonnes of oil equivalent): 84% of this came from fossil fuels including oil, gas, and coal, which released 31.6 billion metric tonnes of carbon dioxide into the atmosphere (EIA, 2012). The heavy reliance of human beings on fossil fuels has already caused serious consequences such as climate change and a looming energy crisis. Therefore, nding alternative and sustainable energy resources has been an urgent issue to ensure future energy supply and to reduce greenhouse gas emissions.

chapter 42|6 pages

Drying in Mineral Processing

Title

Abstract 

Thermal removal of water from solids or slurries is an important operation carried out in numerous mineralprocessing and metallurgical-processing applications. Although drying is a highly energy-intensive operation that is also increasingly difcult at lower moisture contents, no special attention is generally given to the technical and economical aspects of the drying process employed in the mineral-or metallurgical-processing industry. It is therefore not surprising that most dryers found in these industries are of the conventional type, as discussed later in this chapter. Detailed descriptions and design considerations of specic dryer types (e.g., rotary, ¤uid bed, and spray) are presented elsewhere in this handbook. The interested reader is referred to relevant sections for further information. The objective of this chapter is to summarize the types of dryers currently used in practice, to discuss any special aspects with illustrations, and to identify possible new concepts that may be applicable in the mineral industry.

chapter 43|16 pages

Dewatering and Drying of Wastewater Treatment Sludge

Title

Abstract 

Sludge is the name that describes a muddy or slushy mass, deposit, or sediment as (1) the precipitated solid matter produced by water and sewage treatment processes; (2) mud from a drill hole in boring; (3) the muddy sediment in a steam boiler; (4) waste from a coal washery; or (5) the precipitated or settled matter from industrial processes. Water treatment sludge consists of suspended solids, coagulation chemicals, usually an alum or polymers with a limited amount of biological materials. A comprehensive review of industrial sludge can be found elsewhere [1]. In that review, sludge from petroleum, metal-nishing, ¤ue gas cleaning, water treatment, pulp and paper processing, polymer plants, chemical plants, as well as mineral and metallurgical industries are discussed. The sludge addressed in this chapter is the by-product of a wastewater treatment plant. Brief reviews on the treatment, usage, and disposal of this type of sludge are available [2,3]. In this chapter, we take a comprehensive approach to examine the literature on sludge dewatering and drying in order to give readers a relatively detailed and complete picture of this area that is growing with the expenditures on environmental cleanup and control, amounting to about US $150 billion in the United States and about US $400 billion globally in 1997 [4].

chapter 44|12 pages

Physicochemical Aspects of Sludge Drying

Title

Abstract 

Untreated municipal sludge could be regarded as hazardous waste material due to its high organic and metallic content. Decreasing sludge moisture content is the primary objective for all sustainable sludge management strategies. Although a signicant amount of free water in sludge is removed by mechanical dewatering processes, the moisture content of sludge is still higher than 70% (dry basis). According to the current regulations, the percent solids of sewage sludge shall be equal to or greater than 90%, based on the moisture content and total solids prior to storage for all kinds of land applications. In addition, high moisture content would make sludge conveying, pumping, and transportation extremely difcult. Composition of the sludge depends on wastewater characteristics and the treatment technology employed [1].

chapter 45|22 pages

Drying of Biotechnological Products

Title

Abstract 

Biotechnology is the action aiming at producing useful products for various branches of the economy by means of biological components and microorganisms, viruses, animal and vegetable cells, as well as extracellular substances found within tissues. The growing scope of these activities includes production of a biological system, a producer strain, using the recombination technique and cell engineering. As a result of processes taking place in the presence of microorganisms, materials of various forms are produced, such as microorganisms similar to the inlet materials, e.g., yeast and bacteria. The product may be a substance with a complex chemical structure in the form of a high-molecular polymer or organic compound (e.g., antibiotics, vitamins, and organic acids).

chapter 46|20 pages

Drying of Coated Webs

Title

Abstract 

The objective of this chapter is to review brie¤y the drying process, drying equipment, drying strategies, and web handling available for coated webs. Based on the substrate materials, coated webs can be divided into three types: (1)  coated paper and paperboard; (2) coated plastic lms (e.g., photographic lms) and tapes (e.g., adhesive tapes, magnetic tapes, pressure-sensitive tapes, and photosensitive tapes); and (3) coated metallic sheets. Paper and paperboard are coated on machine or off machine, while plastic lms, tapes, or metallic sheets are generally coated off machine. (On machine indicates the coating operation that is done on the web before it is removed from the original manufacturing machine, whereas off machine implies the coating operations done on a free-standing machine remote from the original machine.)

During the coating process, some coated webs require a single coating; other webs require more than one coating layer either by passing a web of material through a single coating station more than one time or by coating a web with a multiple-station coating machine. In the converting industry, paper, lms, and foils can be combined together to form multiple-layer structures in a process called laminating. In the graphic arts industry, the coated papers are further coated

with ink to generate the desired images through a single printing station or multiple-color-printing units. Figure 46.1 shows a nished Polaroid instant color picture containing polyester supports on the top and bottom with active layers sensitized to the three primary colors (blue, green, and red), timing layers, and spacing layers to display the image between the supports.

chapter 47|24 pages

Drying of Polymers

Title

Abstract 

Spurred by continually escalating energy costs, along with the advent of new competitive polymers accompanied by new and extended applications of polymers and plastics, interest in the energy-intensive operation of drying of polymers has been on the rise in recent years.

chapter 48|10 pages

Drying of Enzymes

Title

Abstract 

Enzymes are protein catalysts of high molecular weight, which are produced not only by plants and animals but also mainly by microorganisms as a result of fermentation processes. Enzymes fall into two categories: (1) bulk industrial enzymes, which mainly include proteases for detergents, amylases for textile desizing and starch hydrolysis, pectinases for fruit-juice clarication, and proteases for the leather industry (Table 48.1); and (2) analytical enzymes.

chapter 49|14 pages

Drying and Denaturation of Proteins in Spray Drying Process

Title

Abstract 

Proteins derived from various natural sources such as plant, animal, and milk are converted into dry powder form to enhance their stability and for long-term storage. Even therapeutic proteins such as antibodies, which are usually delivered after reconstitution, are also rst converted into powder (Sane et al., 2004). Dry therapeutic proteins are being increasingly used in their native form for inhalation and pulmonary and transdermal delivery (Johnson, 1997). Nontherapeutic proteins such as milk proteins are important ingredients in manufactured functional and health foods. They are also converted into dry powder form.

chapter 50|14 pages

Product Functionality-Oriented Drying Process Related to Pharmaceutical Particles Engineering

Title

Abstract 

Drying of drug products serves many different purposes to the pharmaceutical and health industry. One main purpose is the removal of moisture that minimizes unwanted reactions to the drug, extending the shelf life of the drug product. The spray drying and freeze drying processes are typically used to achieve this as the drug is produced by wet processes. Physical properties of the drug products need to be engineered to aid in the delivery to the human body. Such application can be found in drug encapsulation via spray

and freeze drying. The ability of the spray dryer to generate ne powder for inhaler application and for tabletting is also another advantage for the pharmaceutical industry. Particles for tabletting are normally further processed by a ¤uidized bed dryer/granulator to make them easy ¤owing and in certain products coated to improve the performance of the drug particles. Therefore, this chapter presents a discussion of how the three key drying processes, viz., spray drying, freeze drying and ¤uidized bed drying, are used in industry to make functional pharmaceutical products.

chapter 51|24 pages

Drying of Coal

Title

Abstract 

Drying of low-rank coal (LRC) is carried out to increase its caloric value and facilitate its transport. Wet coal is difcult to load or unload from railway cars owing to freezing, which is a problem in colder climates. The presence of moisture causes a reduction in friability of coal, makes it difcult to control blending operations, worsens the quality of grinding (if coal is ground), and impedes separation and classication as well as the pneumatic transport of pulverized coal. Friable coal suitable for combustion in modern steam boilers is obtained only when the moist coal is dried. Coal must also be dried for the following processes: (1) briquetting, (2) coking, (3) gasication, (4) low-temperature carbonization, (5) liquid

fuel synthesis, and others. The nal moisture content requirement for coal is different depending on the process in which it is used. The following is a summary of approximate ranges of moisture content of coal required for various processes.

Section IV Miscellaneous Topics in Industrial Drying

chapter 52|20 pages

Dryer Feeding Systems

Title

Abstract 

Feeders are devices that introduce a variety of materials into dryers at a controlled, specied rate. Usually, the feeder is located at the interface stage between material-handling equipment or upstream process and the dryer. The materialhandling equipment may be a hopper or a bin whereas the upstream process may be a reactor, crystallizer, lter, hydrocyclone, centrifuge, etc.

chapter 53|32 pages

Dryer Emission Control Systems

Title

Abstract 

Dryers are one of the major sources of atmospheric emissions in industrial operations as the majority of industrial dryers operate in an open-cycle system. A drying installation may cause air pollution by the emission of dust, gases, and odors. Even plumes of clean water vapor are unacceptable in some areas. The nature of the emissions is determined by the material being dried and the operating conditions. As no such

attention is paid to environmental protection, these emissions are no longer permissible in many countries and it is logical that effective means of controlling pollution must be developed. New drying plants must be designed with emission control systems capable of meeting the most severe local requirements so that they can provide the necessary performance; existing plants can be modied and tted with control systems in order to meet new regulations.

chapter 54|24 pages

Energy Aspects in Drying

Title

Abstract 

It has become apparent in recent years that energy resources, especially natural gas and oil, are limited. Consequently, all industrial sectors in all parts of the world need to identify more efcient methods of energy utilization. Despite periodic ¤uctuations, there is a tendency for energy costs to increase and, consequently, in many cases, energy should become an important element of innovations to drying practice and changes in equipment technology. Many studies, publications, and monographs are concerned with optimized energy utilization; most of these refer to a specic industry (e.g., chemical, ceramic, and metallurgical). However, a process-oriented approach would be more justied, as it would be based on a particular equipment or operation regardless of the branch of industry. Factors that lead to inefcient energy usage in industrial environment include emphasis on rst cost when implementing capital improvements, deferred or

reduced maintenance due to decreased operating budgets, and retooling production operations to meet changing business conditions without considering impact to the efciency of existing facility operations [1].

chapter 55|26 pages

Heat Pump Drying Systems

Title

Abstract 

Heat pump dryers have been known to be energy efcient when used in conjunction with drying operations. The principal advantages of heat pump dryers emerge from the ability of the heat pumps to recover energy from the exhaust gas as well as their ability to control the drying gas temperature and humidity. Many researchers have demonstrated the importance of producing a range of precise drying conditions to dry a wide range of products and improve their quality. At the same time, MacArthur (1984) has mentioned the need to optimize component and system design to increase energy efciency in heat pump systems.

chapter 56|26 pages

Safety Aspects of Industrial Dryers

Title

Abstract 

The statistics of industrial accidents show that drying should be regarded as a potentially hazardous operation that has brought a number of reported incidents with serious results for personnel and equipment [1,2]. The data indicate that the accident rate per 105 workers at risk is considerably greater in the food industry than, e.g., in the chemical industry. Approximately 8%–9% of all dust explosions in the food industry is related to the drying operation (Figure 56.1). The other data for the period 1967-1983 in the German sugar

industry indicate that drying contributes to 37% of all accidents [3], whereas in the French milk industry an average of four major accidents in spray dryers were reported annually [4]. Based on 89 accidents that happened in 1965-2000, 415 people were injured and 16 fatalities were reported in The Accident Database [5]. It is worth to note that in most cases of spray dryer accident in the food industry re was observed whereas an explosion experienced in <10% [6]. The above reports underline the importance of safety from re and explosion hazards in dryers and in the ancillary equipment.

chapter 57|18 pages

Control of Industrial Dryers

Title

Abstract 

Today, most industrial dryers are equipped with varying levels of automatic controllers. Often they use simple control strategies based, for example, simply on the exhaustgas temperature for a direct dryer. Small-scale and slow drying operations are often controlled (or adjusted for process upsets) manually. Very high production units, those involving very rapid drying or units that produce products within stringent quality specications, must be equipped with some degree of automatic control. Although commercial dryers currently use conventional control strategies, it is expected that within the next decade more and more industrial dryers will utilize model-based control (MBC), fuzzy logic control (FLC), or neural nets control when the dryer performance is highly nonlinear and difcult to predict with simple mathematical models. Some improvements in dryer controls became available because of the development of better sensors and analyzers, whereas others are by-products of new, more sophisticated, computer-based control techniques [1]. This chapter provides an introductory overview of both the conventional and the emerging control schemes

for industrial drying. Examples are cited with reference to the more common dryers (e.g., spray, ¤ash, ¤uid-bed dryers). Relevant information is also provided to the readers interested in intelligent control systems based on expert systems, fuzzy logic, or neural nets. It is inconceivable that within this decade equipment suppliers will market “smart” dryers that can adjust their operating parameters consistent with the needs of product quality during drying. However, such a possibility exists for some dryer types in a longer term.

chapter 58|18 pages

Solid–Liquid Separation for Pretreatment of Drying Operation

Title

Abstract 

The diversity of substances and the competitive efforts have evolved into many variants for solid-liquid separation equipment. Before categorizing the equipment for pretreatment of the feed material to the drying operation, it is useful to look at the entire eld of solid-liquid separation. It can be divided as shown in Table 58.1 [1,2].

chapter 59|20 pages

Frying of Foods

Title

Abstract 

Frying is dened as a process of cooking and drying through contact with hot oil. It is intended to make food more palatable and tasteful, but at the same time makes food safer and provides a preservative effect that results from thermal destruction of microorganisms and enzymes, and a reduction in water activity at the surface or throughout the food. The shelf life of fried products is mostly determined by the moisture content after frying. Products that retain a moist interior should be consumed shortly after preparation, or can be stored for a relatively short time under chilling conditions or for a longer time under freezing conditions. Most of these foods-with the exception of par-fried goods-are not produced on a commercial scale for distribution to retail stores, but are important in catering applications. Foods that are dried throughout during frying have a shelf life up to several

months, which is mostly limited by quality deterioration of the absorbed oil and development of a rancid odor and ¤avor. Storage stability of these products may be increased by using packaging materials with adequate barrier properties.

chapter 60|20 pages

Simprosys: Software for Dryer Calculations

Title

Abstract 

Over the past 25 years, considerable effort has been devoted to the development of various software programs applicable to the design, operation, and optimization of drying systems (Marinos-Kouris et al., 1996; Menshutina and Kudra, 2001; Kemp et al., 2004; Kemp, 2007). However, few commercial drying software products have been available on the market and well accepted by the industry. In fact, the most prominent one is proprietary and available only to the sponsors.

chapter 61|10 pages

Life Cycle Assessment of Drying Systems

Title

Abstract 

Drying is one of the most energy-intensive unit operations in industrial processing. In case of evaporative drying, a large part of the required energy is used in the form of thermal heat (i.e., heat generated directly by combustion of fuel or indirectly from steam or using hot oil through a heat exchanger) in the drying process. The drying system would include infeed material handling and loading components, dryer unit, out-feed handling and unloading components, and heat plant and accessories. Drying is a very diverse unit operation in chemical engineering. Some distinguishing features of the drying unit operation are the variation in the material size and shape, variety of drying media used, and the wide range of drying times. This is why there are over 400 different types of dryers reported in the literature and over 100 distinct types of dryers commonly available (Mujumdar, 2006).

chapter 62|22 pages

Thermo-Hydro-Mechanical Aspects of Drying

Title

Abstract 

Although the progress in the development of knowledge on drying has been marked by an impressive array of papers and a number of books, including three editions of Handbook of Industrial Drying (Ed. A.S. Mujumdar),1 very little research has been devoted to the thermo-hydro-mechanical aspects of drying of capillary porous materials (wood, sol-gel coatings, ceramics, alumina gel, etc.). The deformations of these materials (e.g., shrinkage strains and warping) and the drying-induced stresses, which are responsible for crack formation, have been still marginally examined. Only relatively recently, one can observe a stronger research effort focused on the coupling of the heat and mass transfers with

the mechanical behavior of these materials during drying.2-9 This new look at the drying processes comes from the necessity for the improvement of the quality and the strength of dried products, as drying is the process that may violate both these properties, mainly because of crack formation at high drying rates, particularly when drying thick bodies.

chapter 63|10 pages

Supercritical Fluid-Assisted Drying

Title

Abstract 

The science and practices of industrial drying have been evolving mostly due to emerging areas related to the development of advanced materials, novel bioproducts and microelectronic chips, as well as formulation of powdery blends with requirement of narrow and uniform particle size distribution. The production of microelectronic chips faces the same challenges in drying and opportunities as for products of biological origin: high quality, high purity, suitable crystallinity, nonmodi-ed physical functionalities, oxygen sensitivity, solubility of dried product, stickiness, and thermosensitivity. Thus, development of advanced products and/or materials requires novel drying procedures and more effective alternative techniques. Such needs for improved and energy-efcient dryers have also been pointed out in a paper entitled “Global R&D needs in drying” by Mujumdar and Huang in 2007 [1]. Supercritical ¤uid-assisted drying is one of these alternatives that uses supercritical ¤uid as the drying medium instead of heated air. Such a technique has been developed in recent years [2-5]. Supercritical ¤uids have unique properties in that their densities and solubilities are similar to those of the liquids and their compressibility is akin to that of the gases. More importantly, there are no surface tension effects that can cause problems in drying highly porous materials since the solid structures can collapse as the water in liquid phase is removed due to conventional drying. Thus, one of the key features of supercritical ¤uid drying is that no liquid-gas phase change occurs during drying mechanism. Among supercritical ¤uids, carbon dioxide (CO2 ) is being used increasingly and promoted at small, pilot, or large scales to dehydrate high-value natural bioactive ingredients [6-10], aerogels [11-23], or nanomaterials [24].

chapter 64|20 pages

Industrial Crystallization

Title

Abstract 

Crystallization from solution is known to produce particles of high purity and of an approximately uniform size. The major elds of application are in the chemical, pharmaceutical, and food industries. However, in some cases, difculties in separation and drying of the crystals turn into the obstacles of an otherwise ideal method.

chapter 65|12 pages

Cost-Estimation Methods for Dryers and Drying Processes

Title

Abstract 

When capital cost estimates of a denitive investment are required to obtain budget authorization, competitive quotes from vendors have to be requested, as these quotes are the most reliable estimates.

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