P1: OTA/XYZ JWBS080-fm P2: ABC JWBS080-Vant October 28, 2011 7:16 Printer Name: Yet to Come P1: OTA/XYZ JWBS080-fm P2: ABC JWBS080-Vant October 28, 2011 7:16 Printer Name: Yet to Come DRYING IN THE PROCESS INDUSTRY P1: OTA/XYZ JWBS080-fm P2: ABC JWBS080-Vant October 28, 2011 7:16 Printer Name: Yet to Come P1: OTA/XYZ JWBS080-fm P2: ABC JWBS080-Vant October 28, 2011 7:16 Printer Name: Yet to Come DRYING IN THE PROCESS INDUSTRY C.M van ’t Land A JOHN WILEY & SONS, INC., PUBLICATION P1: OTA/XYZ JWBS080-fm P2: ABC JWBS080-Vant October 28, 2011 7:16 Printer Name: Yet to Come Copyright © 2012 by John Wiley & Sons All rights reserved Published by John Wiley & Sons, Inc., Hoboken, New Jersey Published simultaneously in Canada No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning, or otherwise, except as permitted under Section 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400, fax 978-750-4470, or on the web at www.copyright.com Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, 201-748-6011, fax 201-748-6008, or online at http://www.wiley.com/go/permission Limit of Liability/Disclaimer of Warranty: While the publisher and author have used their best efforts in preparing this book, they make no representations or warranties with respect to the accuracy or completeness of the contents of this book and specifically disclaim any implied warranties of merchantability or fitness for a particular purpose No warranty may be created or extended by sales representatives or written sales materials The advice and strategies contained herein may not be suitable for your situation You should consult with a professional where appropriate Neither the publisher nor author shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages For general information on our other products and services or for technical support, please contact our Customer Care Department within the United States at 877-762-2974, outside the United States at 317-572-3993 or fax 317-572-4002 Wiley also publishes its books in a variety of electronic formats Some content that appears in print may not be available in electronic formats For more information about Wiley products, visit our web site at www.wiley.com Library of Congress Cataloging-in-Publication Data Land, C.M van ’t, 1937– Drying in the process industry / C.M van ’t Land p cm Includes bibliographical references and index ISBN 978-0-470-13117-6 (hardback) Drying Drying apparatus Chemical processes I Title TP363.L229 2011 660 28426–dc22 2011012195 Printed in the United States of America 10 P1: OTA/XYZ JWBS080-fm P2: ABC JWBS080-Vant October 28, 2011 7:16 Printer Name: Yet to Come CONTENTS Preface ix Introduction Drying as Part of the Overall Process 2.1 2.2 2.3 2.4 Residual Moisture / Optimization of the Dewatering Step / 10 Process Changes to Simplify Drying / 10 Combination of Drying and Other Process Steps / 12 2.5 Nonthermal Drying / 15 2.6 Process Changes to Avoid Drying / 17 2.7 No Drying / 19 Procedures for Choosing a Dryer 3.1 3.2 3.3 3.4 3.5 3.6 Selection Schemes / 21 Processing Liquids, Slurries, and Pastes / 31 Special Drying Techniques / 33 Some Additional Comments / 34 Testing on Small-Scale Dryers / 37 Examples of Dryer Selection / 38 Convective Drying 4.1 4.2 4.3 4.4 21 41 Common Aspects of Continuous Convective Dryers / 42 Saturated Water Vapor Pressure / 43 Wet-Bulb Temperature / 44 Adiabatic Saturation Temperature / 46 v P1: OTA/XYZ JWBS080-fm P2: ABC JWBS080-Vant vi October 28, 2011 7:16 Printer Name: Yet to Come CONTENTS 4.5 4.6 4.7 4.8 4.9 4.10 4.11 4.12 4.13 4.14 4.15 4.16 Humidity Chart / 47 Water–Material Interactions / 49 Drying with an Auxiliary Material / 52 Gas Velocities / 54 Heat Losses / 55 Electrical Energy Consumption / 57 Miscellaneous Aspects / 59 Material Balance (kg·h−1 ) / 61 Heat Balance (kJ·h−1 ) / 61 Specific Heat of Solids / 63 Gas Flows and Fan Power / 64 Direct Heating of Drying Air / 65 Continuous Fluid-Bed Drying 5.1 5.2 5.3 5.4 5.5 General Description / 67 Fluidization Theory / 70 Drying Theory for Rectangular Dryers / 76 Removal of Bound Moisture from a Product in a Rectangular Dryer / 88 Circular Fluid-Bed Dryers / 90 Continuous Direct-Heat Rotary Drying 6.1 6.2 117 General Description / 117 Design Methods / 120 Drying in Seconds / 122 Application of the Design Methods / 126 Spray Drying 8.1 8.2 8.3 8.4 8.5 8.6 8.7 8.8 8.9 99 General Description / 99 Design Methods / 103 Flash Drying 7.1 7.2 7.3 7.4 67 General Description / 133 Single-Fluid Nozzle / 138 Rotary Atomizer / 143 Pneumatic Nozzle / 145 Product Quality / 149 Heat of Crystallization / 153 Product Recovery / 154 Product Transportation / 154 Design Methods / 155 133 P1: OTA/XYZ JWBS080-fm P2: ABC JWBS080-Vant October 28, 2011 7:16 Printer Name: Yet to Come CONTENTS Miscellaneous Continuous Convective Dryers and Convective Batch Dryers 9.1 9.2 9.3 9.4 9.5 9.6 9.7 9.8 9.9 10 11 163 Conveyor Dryers / 164 Wyssmont Turbo-Dryer / 169 Nara Media Slurry Dryer / 170 Anhydro Spin Flash Dryer / 172 Hazemag Rapid Dryer / 174 Combined Milling and Drying System / 176 Batch Fluid-Bed Dryer / 178 Atmospheric Tray Dryer / 182 Centrifuge–Dryer / 184 Atmospheric Contact Dryers 10.1 10.2 10.3 10.4 10.5 10.6 10.7 10.8 vii 189 Plate Dryers / 189 Mildly Agitated Contact Dryers (Paddle Dryers) / 193 Vigorously Agitated Contact Dryers / 198 Vertical Thin-Film Dryers / 202 Drum Dryers / 204 Steam-Tube Dryers / 208 Spiral Conveyor Dryers / 212 Agitated Atmospheric Batch Dryers / 213 Vacuum Drying 217 11.1 Vacuum Drying / 219 11.2 Freeze-Drying / 232 11.3 Vacuum Pumps / 242 12 Steam Drying 251 12.1 Sugar Beet Pulp Dryer / 252 12.2 GEA Exergy Barr–Rosin Dryer / 255 12.3 Advantages of Continuous Steam Drying / 257 12.4 Disadvantages of Continuous Steam Drying / 257 12.5 Additional Remarks Concerning Continuous Steam Drying / 258 12.6 Eirich Evactherm Dryer / 258 13 Radiation Drying 13.1 13.2 Dielectric Drying / 264 Infrared Drying / 278 263 P1: OTA/XYZ JWBS080-fm P2: ABC JWBS080-Vant viii 14 15.3 15.4 339 Cyclones / 340 Fabric Filters / 343 Scrubbers / 346 Electrostatic Precipitators / 349 Dryer Feeding Equipment 17.1 17.2 17.3 17.4 17.5 17.6 17.7 17.8 17.9 17.10 313 Continuous Moisture-Measurement Methods for Solids / 313 Continuous Moisture-Measurement Methods for Gases / 321 Dryer Process Control / 327 Energy Recovery / 335 Gas–Solid Separation Methods 16.1 16.2 16.3 16.4 289 Product Quality / 289 Safeguarding Drying / 291 Continuous Moisture-Measurement Methods, Dryer Process Control, and Energy Recovery 15.2 17 Printer Name: Yet to Come Product Quality and Safeguarding Drying 15.1 16 7:16 CONTENTS 14.1 14.2 15 October 28, 2011 357 Fluid-Bed Dryers / 358 Direct-Heat Rotary Dryers / 360 Flash Dryers / 360 Spray Dryers / 361 Conveyor Dryers / 361 Hazemag Rapid Dryer / 363 Anhydro Spin Flash Dryer / 365 Plate Dryers / 365 Vigorously Agitated Contact Dryers / 365 Vertical Thin-Film and Drum Dryers / 365 Notation 369 Index 377 P1: OTA/XYZ JWBS080-c17 P2: ABC JWBS080-Vant October 28, 2011 11:57 Printer Name: Yet to Come REFERENCES 367 top part of the dryer and is distributed by means of the agitator The solution or slurry flows downward The feed to a drum dryer can be pumped into the space between the two rolls, or by means of a top- or bottom-application roll The feed can also be pumped into a trough and applied by dipping, splashing, or spraying REFERENCES [1] Vreeland, R., Baccheti, J.H (1982) Equipment plugging eliminated with fluid bed dryer Chemical Processing, 45(12), 24–25 [2] Perry, R.H., Green, D.W (2008) Perry’s Chemical Engineers’ Handbook, McGraw-Hill, New York, p 12–64 [3] Motek, H (1983) Possibilities for using pivoted flap gates in bulk material preparation Journal for Preparation and Processing, 24, 439–443 P1: OTA/XYZ JWBS080-c17 P2: ABC JWBS080-Vant October 28, 2011 11:57 Printer Name: Yet to Come P1: OTA/XYZ JWBS080-bm P2: ABC JWBS080-Vant October 28, 2011 12:0 Printer Name: Yet to Come NOTATION A A1 A2 AC Acrit Airflow1 Airflow2 Ar a B Bi b Constant in equation (4.1) Constant in equation (4.6) Heat transfer area Moisture content Product area Sample area Area of body Feed moisture content Nozzle area Area of body Product moisture content Corrected nozzle area Critical moisture content Airflow taken in by the dryer (10◦ C) Airflow leaving the dryer (TAout ) Archimedes number Constant in TAout = a·TAin + b Cyclone inlet height Exponent in equation (8.3) Heat diffusion number Proportionality constant in equation (13.3) Product area per m3 dryer volume Gas area per m3 of liquid — kg·kg−1 m2 kg·kg−1 m2 m2 m2 % by weight m2 m2 % by weight m2 kg·kg−1 m3 ·h−1 m3 ·h−1 — ◦ C m — — m−1 m2 ·m−3 m2 ·m−3 Bed width Constant in equation (4.1) Constant in equation (4.6) Rotary dryer parameter Biot number Constant in TAout = a·TAin + b Cyclone inlet width Exponent in equation (8.3) m — K−1 μm−0.5 — ◦ C m — Drying in the Process Industry, First Edition C.M van ’t Land © 2012 John Wiley & Sons, Inc Published 2012 by John Wiley & Sons, Inc 369 P1: OTA/XYZ JWBS080-bm P2: ABC JWBS080-Vant 370 October 28, 2011 12:0 Printer Name: Yet to Come NOTATION C CC CK Cap c cg ∗ cg cp cs cv cw D Constant in equation (4.1) Constant in equation (8.1) Constant in a Nusselt equation and in a Sherwood equation Nozzle area correction factor Constant in equation (8.5) Product mass flow Constant in expressions for Q2 and Q3 Exponent in Equation (8.3) Water vapor concentration Water vapor concentration at saturation Air specific heat at constant pressure Solid specific heat Air specific heat at constant volume Wien’s constant (2897) — — — — — kg·h−1 K — kmol·m−3 kmol·m−3 J·kg−1 ·K−1 J·kg−1 ·K−1 J·kg−1 ·K−1 μm·K Dryer diameter Line diameter Nozzle diameter Cyclone diameter Cyclone gas outlet diameter Agitator diameter Constant in expression for Q tot2 Exponent in equation (8.3) Nozzle diameter Atomizer wheel diameter Weight-average droplet size Weight-average particle size Droplet size below which 95% by weight of a sample can be found Distance between the feeding point and the axis of an atomizing wheel Particle size Sauter diameter (Chapters and 8) Average particle size (Chapter 6) m m m m m mm — — m m μm μm μm E E(x) Evap Electric field strength Electric field strength at depth x Dryer water evaporation load V·m−1 V·m−1 kg·h−1 kg·s−1 F Fanpower Fr Specific product mass flow Fan power Froude number kg·m−2 ·h−1 kW — Dc De d d1 d50 d95 dd dp ¯ dp m μm μm μm P1: OTA/XYZ JWBS080-bm P2: ABC JWBS080-Vant October 28, 2011 12:0 Printer Name: Yet to Come NOTATION 371 f Constant in expression for Airflow2 Electromagnetic field frequency — s−1 G Gair G H2 O Gmf Gs Gasflow2 g Specific dry airmass flow Dry airmass Evaporated water mass Minimum fluidization mass velocity Solid mass Gas flow leaving the dryer Acceleration due to gravity kg·m−2 ·h−1 kg kg kg·m−2 ·s−1 kg m3 ·h−1 m·s−2 H Enthalpy per kilogram of dry air hexp Atomizer wheel vane height Height Planck’s constant (6.6·10−34 ) Settled bed height Expanded bed height J·kg−1 kJ·kg−1 m m J·kmol−1 J·kg−1 kJ·kg−1 m m J·s m m I I0 Microwave detector signal Microwave reference detector signal — — K Coefficient in equation (6.4) Constant in equation (8.3) Cyclone pressure-loss constant Deflagration index Mass transfer coefficient Partial mass transfer coefficient (liquid-side) — — — bar·m·s−1 m·s−1 m·s−1 Dryer length Line length Lewis number Fluid-bed dryer length for free-water evaporation Fluid-bed dryer length for cross-flow heating Fluid-bed dryer length for cross-flow cooling Height of a transfer unit m m — m m m m Atomizer wheel feed Mass Molecular weight kg·h−1 kg kg·kmol−1 H h K st k kl L Le L1 L2 L3 Le M Flash dryer height Spray dryer chamber cylindrical height Heat of evaporation P1: OTA/XYZ JWBS080-bm P2: ABC JWBS080-Vant 372 October 28, 2011 12:0 Printer Name: Yet to Come NOTATION m Exponent of the Reynolds number Mass — kg N Agitator rotational speed Atomizer wheel rotational speed Rotary dryer rotational speed Theoretical energy for the adiabatic compression of kg of air Nusselt number Nusselt number for laminar flow Nusselt number for turbulent flow Number of velocity heads Number of transfer units Exponent in equation (6.4) Number Number of vanes in an atomizer wheel min−1 min−1 min−1 J·kg−1 P Power consumption Pair Pmax Pred Psat Pstat Ptot PowerG1 PowerG2 Powerrot Pr p Pressure Specific power generation Air partial pressure Maximum explosion pressure Maximum pressure on venting Saturated water vapor pressure Pressure at which a relief vent opens System pressure Fan power required for Airflow1 Fan power required for Gasflow2 Rotary dryer motive power Prandtl number pressure Pressure loss kW W bar absolute W·m−3 N·m−2 bar absolute bar gauge N·m−2 bar absolute N·m−2 kW kW kW — bar mbar N·m−2 N·m−2 N·m−2 N·m−2 N·m−2 N·m−2 bar absolute N·m−2 N·m−2 Radiation energy density Enthalpy flow for the evaporated water Enthalpy flow for the dry solids W·m−2 kJ·h−1 kJ·h−1 Nu Nulam Nuturb NH Nt n p1 p2 pc pg ∗ pg p Q Q1 Q2 Air pressure before compression Fluid pressure upstream of a nozzle Air pressure after compression Fluid pressure downstream of a nozzle Capillary water vapor pressure Water vapor partial pressure Saturated water vapor pressure — — — — — — — — P1: OTA/XYZ JWBS080-bm P2: ABC JWBS080-Vant October 28, 2011 12:0 Printer Name: Yet to Come NOTATION 373 Q3 Qtot1 Qtot2 Enthalpy flow for the residual water Net heat Steady-state dryer-heat requirement kJ·h−1 kJ·h−1 kJ·h−1 R Contact dryer radius Universal gas constant (8314) Air specific mass Universal gas constant for water Water vapor specific mass Reynolds number Caplillary radius m J·kmol·K−1 kg·m−3 J·kg−1 ·K−1 kg·m−3 — m Sc Sh Sol Dryer area Product area per meter of dryer length Rotary dryer slope Schmidt number Sherwood number Dry solids flow m2 m2 ·m−1 — — — kg·h−1 T Temperature T1 Tf Tg Ti Tp (t) Tp (x) Ts TW TAin TAout TPin TPout T ( T)m t t1 t2 t3 Initial air temperature Feed temperature Gas temperature Heating medium inlet temperature Product temperature at time t Product temperature at position x Adiabatic saturation temperature Wet-bulb temperature Drying air temperature Spent drying-gas temperature Feed temperature Product exit temperature Temperature difference Logarithmic mean temperature difference Time Duration of the first drying period Duration of the second drying period Duration of the cooling period K C K ◦ C K ◦ C ◦ C ◦ C K K ◦ C ◦ C ◦ C ◦ C K K s s s s U Heat transfer coefficient kJ·m−2 ·h−1 ·K−1 W·m−2 ·K−1 V Air volume for batch fluid-bed drying Dryer volume m3 m3 RA RD RW Re rc S ◦ P1: OTA/XYZ JWBS080-bm P2: ABC JWBS080-Vant 374 October 28, 2011 12:0 Printer Name: Yet to Come NOTATION v v1 v2 vF vi v mf v rel Sample volume Volume Atomizer wheel circumferential velocity Circumferential velocity Contact dryer agitator circumferential velocity Electromagnetic field propagation velocity Particle terminal velocity Velocity Water specific volume Fluid velocity upstream of a nozzle Fluid velocity downstream of a nozzle Fluidization velocity Cyclone inlet velocity Minimum fluidization velocity Gas–liquid relative velocity m3 m3 m·s−1 m·s−1 m·s−1 m·s−1 m·s−1 m·s−1 m3 ·kg−1 m·s−1 m·s−1 m·s−1 m·s−1 m·s−1 m·s−1 W W in W out WAflow w Rotary dryer mass including product Water flow to the dryer Water flow leaving the dryer Evaporated water flow Rotary dryer holdup kg kg·h−1 kg·h−1 m3 ·h−1 kg X X3 Xe Mass fraction Size range mass fraction Equilibrium solid moisture content per kg of dry matter Gas water content in kg per kg of dry air Kilogram of water vapor raised per kg of steam fed Length or depth Entering air water content Leaving air water content — — kg·kg−1 kg·kg−1 kg·kg−1 m kg·kg−1 kg·kg−1 αo Heat transfer coefficient Radiation absorption coefficient Heat transfer coefficient for fluidized particle W·m−2 ·K−1 — W·m−2 ·K−1 γ γ = c p /cv — δ Penetration depth of electromagnetic waves m ε ε0 ε1 ε2 Radiation emission coefficient Dielectric permittivity of free space (8.854·10−12 ) Radiation emission coefficient of body Radiation emission coefficient of body — F·m−1 — — v x xi xo α P1: OTA/XYZ JWBS080-bm P2: ABC JWBS080-Vant October 28, 2011 12:0 Printer Name: Yet to Come NOTATION 375 εr εr Relative dielectric constant Loss factor — — η ηad Efficiency Gas–liquid ratio Adiabatic compression efficiency — — — λ λG λmax λS Electromagnetic field wavelength Gas thermal conductivity Wavelength of maximum radiation energy density Solid thermal conductivity m W·m−1 ·K−1 μm W·m−1 ·K−1 μ μl Fluid dynamic viscosity Fluidization gas dynamic viscosity Microwave radiation absorption coefficient Liquid dynamic viscosity N·s·m−2 N·s·m−2 m2 ·kg N·s·m−2 v Fluidization gas kinematic viscosity m2 ·s−1 ρ ρb ρF ρg ρl ρp ρS ρ Specific mass Bulk density particulate material Fluidization gas specific mass Gas specific mass Liquid specific mass Particle specific mass Solid specific mass Specific mass difference kg·m−3 kg·m−3 kg·m−3 kg·m−3 kg·m−3 kg·m−3 kg·m−3 kg·m−3 σ Air–water surface tension Stefan–Boltzmann’s constant (5.675·10−8 ) N·m−1 W·m−2 ·K−4 τ Drying time Residence time in dryer h φh φ H2 O φl φm φmol φp φv φ Heat flow Water-vapor flow rate Water flow rate through a nozzle Airmass flow Mass flow Product flow rate Gas flow Loss angle W·m−2 kg·s−1 L·min−1 kg·s−1 kmol·m−2 ·s−1 kg·s−1 m3 ·h−1 — Air relative humidity — P1: OTA/XYZ JWBS080-bm P2: ABC JWBS080-Vant October 28, 2011 12:0 Printer Name: Yet to Come P1: OTA/XYZ JWBS080-IND P2: ABC JWBS080-Vant October 28, 2011 12:2 Printer Name: Yet to Come INDEX Absorption wheels, 49 Adiabatic saturation temperature, 46–47 Agitated pan dryer, 23–24, 213–215 Anhydro Spin Flash Dryer, 172–174 feeding equipment for, 365 pressure-shock resistant type, 173 self-inertization of, 173 See also Safeguarding drying Antoine equation, 43 Archimedes number, 96 Backmixing of product, 119, 361 Baghouse, 343–346 Band dryer, 25–27 See also Conveyor dryer Belt dryer, 27 See also Conveyor dryer Bernoulli’s law, 138–139 Biot number, 80, 95–96, 126 Caking, 289–290 Centrifuge-dryer, 13, 15, 184–187 Cone dryer with screw, 221–226 Contact dryers, batchwise, 23–24, 213–215 Contact dryers, continuous drum dryers, 204–208 feeding equipment for, 365–367 horizontal, mild agitation, 193–197 horizontal, vigorous agitation, 198–202 plate dryer, 24–26, 189–193 spiral conveyor dryer, 212–213 steam-tube dryer, 28, 208–212 vertical thin-film dryer, 202–204 Convective dryers classification, 41 Convective drying airflows, calculation of, 64–65 air-inlet and air-outlet temperatures, 42–43, 53, 56–57 compared to contact drying, 126 direct heating of drying air, 59, 65 efficiency of, 52–54 electric energy consumption, 57–59 fan power, calculation of, 57–58, 64–65 gas velocities at, 54–55 heat balance of, 61–63 heat losses of, 55–57 heating, method for, 59 investment for, 60–61 material balance for, 61 materials of construction at, 60 modes of flow at, 42 motive power at, 58–59 net heat for, 63 residence times at, 60 Conveyor dryers, 164–168 design method for, 167 drying curve for, 167–168 example, 167–168 feeding equipment for, 361–363 tray test for, 167–168 Cooperation with dryer manufacturers, 1, 37 Cyclones, see Gas-solid separation Dalton’s law, 43 Desorption isotherms, 49–50 Dewatering step, 10 Dew point, 60 Drying in the Process Industry, First Edition C.M van ’t Land © 2012 John Wiley & Sons, Inc Published 2012 by John Wiley & Sons, Inc 377 P1: OTA/XYZ JWBS080-IND P2: ABC JWBS080-Vant 378 October 28, 2011 12:2 Printer Name: Yet to Come INDEX Dielectric constant, 314 Dielectric drying, 33, 264–278 breakdown at, 269–270 comparing RF and MW, 268–269 heat generation formula, 266–267 Lambert-Beer’s law, 269 loss factor at, 267–268 microwave drying, 272–278 of grind stones, 290–291 of pasta, 275 of a pharmaceutical product, 276–277 process control of, 278 process safety at, 278 of sugar lumps, 275–276 radio frequency drying, 270–272 of food, 271–272 of textile, 271, 272 Disk dryer, see Contact dryers, continuous Drum dryers, 12, 15, 204–208 feeding equipment for, 367 Dryers combining types, 36 comparison of types, 34–36 data collection for, initial, 21–22, 37 feed types, selection schemes for, 21–31 testing on small-scale dryers, 37–38 types, 4–5 Drying of aspirin, 186 avoiding, 17–18 of baby food, 208 combination with other process steps, 12–15 of DDGS, 252, 255 definition of, development of, 6–7 of dibenzoyl peroxide, 19 energy consumption of, of fluorspar, 175 of high-density polyethylene, 26 mechanisms of, of municipal sludge, 255 no drying, 19 nonthermal, 15–16 of nylon, 230–231 of onions, 164 of an organic peroxide, 38–39, 180–182 of organotin compounds, 39 of pasta, 275 of peat, 256 of a pharmaceutical product, 276–277 of polycarbonate granules, 49 of polyester chips, 166, 230 of polyolefins, 199 reasons for, of salt, 38, 82–88 of sand, 90–95 of silica, 210 simplification of, 10–12 of sludge, 199 of sugar beet pulp, 252–255 of wood chips, 252 systems, 5–7 Drying curve, 86–88, 167–168 Drying and milling combined of coal, 176 of wheat, 176 Dust explosions, see Safeguarding drying Electrical energy consumption of rotary atomization, 59, 145 of a rotary dryer, 58–59, 110 Electrofilters, see Electrostatic precipitators Electrostatic precipitators, see Gas-solid separation Energy recovery, 335–337 by exhaust gas recycle, 335 by heat exchange, 335–337 by a heat pump, 337 by scrubbing, 337 Evaporator/Crystallizer/Dryer, 32 See also Contact dryers, continuous Feeding equipment for Anhydro Spin Flash Dryer, 365 for conveyor dryers, 361–363 for direct-heat rotary dryers, 360 for flash dryers, 360–361 for fluid-bed dryers, 358–359 for Hazemag Rapid Dryer, 363–364 for plate dryers, 365 for spray dryers, 361 for vertical thin-film dryers, 365–367 for vigorously agitated continuous horizontal contact dryers, 365 Film drum dryers, 32 See also Drum dryers Filter-dryer, 13, 226–230 P1: OTA/XYZ JWBS080-IND P2: ABC JWBS080-Vant October 28, 2011 12:2 Printer Name: Yet to Come INDEX Filters, fabric, see Gas-solid separation Fires, see Safeguarding drying Flame arrestor, 304 Flash dryers, 25, 28, 117–130 backmixing feed with product, 119 design methods for, 120–122 application of, 126–130 drying in seconds in, 122–126 dust formation in, 119 feeding equipment for, 360–361 process control of, 119–120, 331 Fluid-bed conditioner-cooler, 290 Fluid-bed cooler, 70 Fluid-bed dryer, batch, 22–24, 178–182 Fluid-bed dryers, continuous air velocities in, superficial, 76 circular type, 67–68, 90–95 example, 90–95 feeding equipment for, 358–359 elutriation from, 73 fluidization point, 70 minimum fluidization velocity, 70, 73–76 rectangular type, 25–26, 29–31, 68–69, 76–86 bound moisture removal in, 88–90 design methods for, 76–81 drying curve for, 86–88 example, 82–86 feeding equipment for, 358–359 heat-exchanging surfaces in, 69–70 process control of, 332 temperature and moisture profile in, 77 Fluid-bed dryers/granulators, 32 Fluid-bed granulation, 70 Freeze drying, 34, 232–242 of food, 237–242 freezing rate for, 238, 240 of pharmaceutical materials, 233–237 collapse of, 237 freezing rate for, 233–235 polymorphology of, 234 pressure rise method for, 236 Froessling equation, 125 Froude number, 198 Gas-solid separation by cyclones, 340–342 by electrostatic precipitation, 349–355 379 by fabric filters, 343–346 by scrubbers, 346–349 Grashof number, 96 Grosvenor chart, 43, 48 See also Humidity chart Hazemag Rapid Dryer, 174–176 feeding equipment for, 363–364 Heat of crystallization, 153–154 Heat of evaporation, 2–3 Humidity chart, 47–49 Hydrates, 52 Hygroscopicity, 51 Inerting, 301–302 Infrared drying body types at, 280–281 by electricity, 282–284 by gas combustion, 284–286 Kirchhoff’s law, 282 process control of, 285–286 process safety of, 286 Stefan-Boltzmann’s law, 280 wavelengths of infrared radiation, 279 Wien’s law, 280 IR drying, see Infrared drying Kopp’s law, 63–64 Light ash, 12 Loss-in-weight feeder, 358 Lyophilization, see Freeze drying Melt granulation, 12 Milling-drying system, 25–27, 176–178 Moisture bound, 4–5 critical content, equilibrium content, 49–51 free, 4–5 residual, Moisture measurement absolute methods, 313–314 continuous, of gases by chilled-mirror hygrometer, 323–325 by electrical capacitance, 327 by psychrometry, 322–323 by zirconium oxide potentiometry, 325–327 P1: OTA/XYZ JWBS080-IND P2: ABC JWBS080-Vant 380 October 28, 2011 12:2 Printer Name: Yet to Come INDEX Moisture measurement (Continued ) continuous, of solids by electrical capacitance, 314–315 by infrared reflection, 316–318 by microwaves, 318–321 by temperature, 321 inferential methods, 313–314 Mollier H/x diagram, 43, 48 See also Humidity chart Molten salt, as heating medium, 199 MW drying, see Dielectric drying Nara Media Slurry Dryer, 170–172 comparison with a spray dryer, 172 Newton’s law of cooling, 79 NOx , 59 Paddle dryers, 193–197 Pan dryer, 33, 214 See also Contact drying, batchwise Partial pressure, 46, 48 Particle velocity, terminal, 54 Plate dryer, 24–26, 189–193 feeding equipment for, 365 Pneumatic dryer, see Flash dryer Process control of batch dryers, 334 of continuous contact dryers, 334 control loop, 328–329 of conveyor dryers, 333 derivative action of, 330 feedback type, 329–330 feedforward type, 329 of flash dryers, 331 of fluid-bed dryers, 332 integral action of, 330 proportional action of, 330 of rotary dryers, 333 of spray dryers, 331–332 Product quality, 289–291 Radiation drying, see Dielectric drying, Infrared drying Relative humidity, 48 RF drying, see Dielectric drying Ring dryer, 120 See also Flash dryers Rotary coolers, 99 Rotary dryers, contact, see Contact dryers, continuous Rotary dryers, direct design methods for, 103–110 example, 111–116 feeding equipment for, 360 process safety of, 101 residence time in, 101, 109–110 Rotary dryer, indirect-direct, 99 Rotary dryer, Roto-Louvre type, 100 Safeguarding drying classification of powders, 291 of contact dryers, 310–311 by containment, 303 in convective dryers, 308–310 deflagration, 292 detonation, 292 dust explosions, 291, 294–306 cube-root law for, 300 deflagration index of, 300 Hartmann apparatus, modified, 295–297 maximum pressure of, 299–300 maximum rate of pressure rise of, 299–300 minimum explosible concentration for, 296–297 minimum ignition energy for, 297–299 minimum ignition temperature of, 297–298 minimum oxygen concentration for, 297 fires, 293–294 Grewer oven, 293–294 hot storage test, 294 self-ignition temperature of, 293–294 smolder temperature of, 293, 298 by inertization, 301–302 by pressure resistance, 303 by pressure-shock resistance, 173, 303 by relief venting, 303–304 by self-inertization, 301–302 by suppression, 304–306 Saturated water vapor pressure, 43 Sauter diameter, 73–75 Scrubbers, see Gas-solid separation Seeding of crystallizers, 11 Soda manufacture, 12 Solvent evaporation, 24–26, 39–40 P1: OTA/XYZ JWBS080-IND P2: ABC JWBS080-Vant October 28, 2011 12:2 Printer Name: Yet to Come INDEX Sorption isotherms, 49–51 of milk powder, 51 Specific heat of solids, 63–64 Spiral conveyor dryer, 212–213 Spray dryers, 12, 31–32, 133–161 air-inlet temperatures, 138 bulk density of product, 151–152 combination with fluid-bed dryer, 138, 156 comparison with Nara Media Slurry Dryer, 172 design methods for, 155–157 example, 157–161 feeding equipment for, 361 flow modes in, 135–136 particle size increase in, 31, 153 pneumatic nozzle for, 137–138, 145–149 process control of, 331–332 product recovery from, 154 quality of product, 149–153 reasons for employing them, 134 rotary atomizer for, 136–137, 143–145 single-fluid nozzle for, 136, 138–143 transportation of product, 154–155 Steam drying, batchwise, 258–262 solvent removal at, 252, 258–262 viscosity increase at, 259 Steam drying, continuous, 251–258 advantages of, 257 disadvantages of, 257–258 flash dryer type, 255–257 fluid-bed dryer type, 252–255 odor emission, avoiding of, 257 pressure at, 252–253 sugar beet pulp drying, 252–255 Steam-tube dryer, 28, 208–212 Surface-to-volume diameter, 73–76 Thin-film dryer, 15, 202–204 See also Contact dryers, continuous Thomson’s formula, 50 Tray dryer, atmospheric, 182–184 Tumbler, see Vacuum dryers, batchwise Vacuum dryers batchwise, 22, 221–232 agitated, 22, 221–231 tray dryers, 22, 231–232 tumble dryers, 39, 230–231 continuous, 219–221 Vacuum pumps dry vacuum pumps, 245–249 gas ballast for, 245, 246, 249 liquid ring pump, 242–243 with gas-driven ejector, 243 oil-sealed pumps, 243–245 Water vapor capillary depression, 50 Water vapor pressure, saturated, 43 Wet-bulb temperature, 44–46 Wyssmont Turbo-Dryer, 169–170 381 ... dielectric drying Dielectric drying (radio-frequency drying and microwave drying) is the only process in which heat is developed in the material being dried rather than having heat diffused into the. .. mechanism at contact drying Radiation This type of drying can, in principle, be nonpenetrating, such as the drying of paint by infrared radiation, or penetrating, such as the drying of food or pharmaceuticals... this book is to assist the process development engineer, the process engineer, and the plant engineer in their selection of drying equipment The theoretical background of drying and criteria to