Tài liệu Sulfuric acid manufacture analysis, control and optimization

Sulfuric Acid Manufacture Intentionally left as blank Sulfuric Acid Manufacture Analysis, Control, and Optimization By Matthew J. King Perth, Western Australia William G. Davenport Tucson, Arizona Michael S. Moats Rolla, Missouri AMSTERDAM • BOSTON • HEIDELBERG • LONDON • NEW YORK • OXFORD PARIS • SAN DIEGO • SAN FRANCISCO • SINGAPORE • SYDNEY • TOKYO Elsevier 30 Corporate Drive, Suite 400, Burlington, MA 01803, USA 525 B Street, Suite 1800, San Diego, CA 92101-4495, USA Second edition © 2013, 2006 Elsevier Ltd. All rights reserved. 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 or otherwise without the prior written permission of the publisher. Permissions may be sought directly from Elsevier’s Science & Technology Rights Department in Oxford, UK: phone (þ44) (0) 1865 843830; fax (þ44) (0) 1865 853333; email: [email protected]. Alternatively you can submit your request online by visiting the Elsevier web site at http://elsevier.com/locate/permissions, and selecting Obtaining permission to use Elsevier material Notice No responsibility is assumed by the publisher for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions or ideas contained in the material herein. Because of rapid advances in the medical sciences, in particular, independent verification of diagnoses and drug dosages should be made. British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress For information on all Elsevier publications visit our web site at store.elsevier.com Printed and bound in Poland 13 14 15 16 17 10 9 8 ISBN: 978-0-08-098220-5 7 6 5 4 3 2 1 Contents Preface xv 1 Overview 1.1 Catalytic oxidation of SO2 to SO3 1.2 H2SO4 production 1.3 Industrial flowsheet 1.4 Sulfur burning 1.5 Metallurgical offgas 1.6 Spent acid regeneration 1.7 Sulfuric acid product 1.8 Recent developments 1.9 Alternative processes 1.10 Summary 2 Production and consumption 2.1 Uses 2.2 Acid plant locations 2.3 Price 2.4 Summary 11 13 14 14 16 3 Sulfur 3.1 3.2 3.3 3.4 3.5 3.6 3.7 19 20 20 21 22 23 28 29 4 Metallurgical offgas cooling and cleaning 4.1 Initial and final SO2 concentrations 4.2 Initial and final dust concentrations 4.3 Offgas cooling and heat recovery 4.4 Electrostatic collection of dust 4.5 Water scrubbing 4.6 H2O(g) removal from scrubber exit gas 4.7 Summary burning Objectives Sulfur Molten sulfur delivery Sulfur atomizers and sulfur burning furnaces Product gas Heat recovery boiler Summary 1 1 3 4 4 6 6 7 7 7 8 31 31 33 34 35 37 43 44 vi Contents 5 Regeneration of spent sulfuric acid 5.1 Spent acid compositions 5.2 Spent acid handling 5.3 Decomposition 5.4 Decomposition furnace product 5.5 Optimum decomposition furnace operating conditions 5.6 Preparation of offgas for SO2 oxidation and H2SO4 making 5.7 Summary 47 47 51 51 52 53 54 56 6 Dehydrating air and gases with strong sulfuric acid 6.1 Chapter objectives 6.2 Dehydration with strong sulfuric acid 6.3 Dehydration reaction mechanism 6.4 Residence times 6.5 Recent advances 6.6 Summary 59 59 61 64 65 70 70 7 Catalytic oxidation of SO2 to SO3 7.1 Objectives 7.2 Industrial SO2 oxidation 7.3 Catalyst necessity 7.4 SO2 oxidation “heatup” path 7.5 Industrial multicatalyst bed SO2 oxidation 7.6 Industrial operation 7.7 Recent advances 7.8 Summary 73 73 73 75 84 84 87 89 89 8 SO2 oxidation catalyst and catalyst beds 8.1 Catalytic reactions 8.2 Maximum and minimum catalyst operating temperatures 8.3 Composition and manufacture 8.4 Choice of size and shape 8.5 Catalyst bed thickness and diameter 8.6 Gas residence times 8.7 Catalyst bed temperatures 8.8 Catalyst bed maintenance 8.9 Summary 91 91 95 95 96 97 98 99 100 100 9 Production of H2SO4(ℓ) from SO3(g) 9.1 Objectives 9.2 Sulfuric acid rather than water 9.3 Absorption reaction mechanism 9.4 Industrial H2SO4 making 9.5 Choice of input and output acid compositions 9.6 Acid temperature 103 103 104 105 107 115 116 Contents 9.7 9.8 9.9 9.10 9.11 vii Gas temperatures Operation and control Double contact H2SO4 making Intermediate versus final H2SO4 making Summary 116 116 118 120 120 Break 123 10 Oxidation of SO2 to SO3—Equilibrium curves 10.1 Catalytic oxidation 10.2 Equilibrium equation 10.3 KE as a function of temperature 10.4 KE in terms of % SO2 oxidized 10.5 Equilibrium % SO2 oxidized as a function of temperature 10.6 Discussion 10.7 Summary 10.8 Problems 125 125 127 128 129 129 132 132 132 11 SO2 oxidation heatup paths 11.1 Heatup paths 11.2 Objectives 11.3 Preparing a heatup path—The first point 11.4 Assumptions 11.5 A specific example 11.6 Calculation strategy 11.7 Input SO2, O2, and N2 quantities 11.8 Sulfur, oxygen, and nitrogen molar balances 11.9 Enthalpy balance 11.10 Calculating level L quantities 11.11 Matrix calculation 11.12 Preparing a heatup path 11.13 Feed gas SO2 strength effect 11.14 Feed gas temperature effect 11.15 Significance of heatup path position and slope 11.16 Summary 11.17 Problems 135 135 135 136 136 136 137 138 139 140 142 143 143 145 147 148 149 150 12 Maximum SO2 oxidation: Heatup path-equilibrium curve intercepts 12.1 Initial specifications 12.2 % SO2 oxidized-temperature points near an intercept 12.3 Discussion 12.4 Effect of feed gas temperature on intercept 12.5 Inadequate % SO2 oxidized in first catalyst bed 12.6 Effect of feed gas SO2 strength on intercept 12.7 Minor influence—Equilibrium gas pressure 151 151 151 153 153 154 154 154 viii Contents 12.8 12.9 12.10 12.11 12.12 12.13 12.14 Minor influence—O2 strength in feed gas Minor influence—CO2 in feed gas Catalyst degradation, SO2 strength, and feed gas temperature Maximum feed gas SO2 strength Exit gas composition
intercept gas composition Summary Problems 155 155 157 158 159 160 160 13 Cooling first catalyst bed exit gas 13.1 First catalyst bed summary 13.2 Cooldown path 13.3 Gas composition below equilibrium curve 13.4 Summary 13.5 Problem 161 161 161 164 164 164 14 Second 14.1 14.2 14.3 14.4 14.5 14.6 14.7 14.8 14.9 14.10 14.11 14.12 14.13 catalyst bed heatup path Objectives % SO2 oxidized redefined Second catalyst bed heatup path A specific heatup path question Second catalyst bed input gas quantities S, O, and N molar balances Enthalpy balance Calculating 760 K (level L) quantities Matrix calculation and result Preparing a heatup path Discussion Summary Problem 167 167 167 168 170 170 171 171 172 173 173 173 175 176 15 Maximum SO2 oxidation in a second catalyst bed 15.1 Second catalyst bed equilibrium curve equation 15.2 Second catalyst bed intercept calculation 15.3 Two bed SO2 oxidation efficiency 15.4 Summary 15.5 Problems 177 177 178 180 181 181 16 Third catalyst bed SO2 oxidation 16.1 2-3 Cooldown path 16.2 Heatup path 16.3 Heatup path-equilibrium curve intercept 16.4 Graphical representation 16.5 Summary 16.6 Problems 183 183 184 187 187 187 187 Contents ix 17 SO3 and CO2 in feed gas 17.1 SO3 17.2 SO3 effects 17.3 CO2 17.4 CO2 effects 17.5 Summary 17.6 Problems 189 189 193 193 197 197 198 18 Three 18.1 18.2 18.3 18.4 18.5 18.6 18.7 18.8 18.9 18.10 18.11 18.12 18.13 199 199 199 199 201 202 202 204 204 206 206 207 208 209 19 After-H2SO4-making SO2 oxidation 19.1 Double contact advantage 19.2 Objectives 19.3 After-H2SO4-making calculations 19.4 Equilibrium curve calculation 19.5 Heatup path calculation 19.6 Heatup path-equilibrium curve intercept calculation 19.7 Overall SO2 oxidation efficiency 19.8 Double/single contact comparison 19.9 Summary 19.10 Problems 211 211 213 213 215 216 216 217 221 222 227 20 Optimum double contact acidmaking 20.1 Total % SO2 oxidized after all catalyst beds 20.2 Four catalyst beds 20.3 Improved efficiency with five catalyst beds 20.4 Input gas temperature effect 20.5 Best bed for Cs catalyst 20.6 Triple contact acid plant 20.7 Summary 229 230 230 231 231 232 233 234 21 Enthalpies and enthalpy transfers 21.1 Input and output gas enthalpies 21.2 H2SO4 making input gas enthalpy 235 235 238 catalyst bed acid plant Calculation specifications Example calculation Calculation results Three catalyst bed graphs Minor effect—SO3 in feed gas Minor effect—CO2 in feed gas Minor effect—Bed pressure Minor effect—SO2 strength in feed gas Minor effect—O2 strength in feed gas Summary of minor effects Major effect—Catalyst bed input gas temperatures Discussion of book’s assumptions Summary x Contents 21.3 21.4 21.5 21.6 22 Heat transfers Heat transfer rate Summary Problems 239 240 241 241 Control of gas temperature by bypassing 22.1 Bypassing principle 22.2 Objective 22.3 Gas to economizer heat transfer 22.4 Heat transfer requirement for 480 K economizer output gas 22.5 Changing heat transfer by bypassing 22.6 460 K Economizer output gas 22.7 Bypassing for 460, 470, and 480 K economizer output gas 22.8 Bypassing for 470 K economizer output gas while input gas temperature is varying 22.9 Industrial bypassing 22.10 Summary 22.11 Problems 243 243 243 245 245 246 247 247 23 H2SO4 making 23.1 Objectives 23.2 Mass balances 23.3 SO3 input mass 23.4 H2O(g) input from moist acid plant input gas 23.5 Water for product acid 23.6 Calculation of mass water in and mass acid out 23.7 Interpretations 23.8 Summary 23.9 Problem 251 252 252 253 253 255 255 258 261 262 24 Acid temperature control and heat recovery 267 24.1 Objectives 267 24.2 Calculation of output acid temperature 267 24.3 Effect of input acid temperature 272 24.4 Effect of input gas temperature 273 24.5 Effect of input gas SO3 concentration on output acid temperature 273 24.6 Adjusting output acid temperature 274 24.7 Acid cooling 275 24.8 Target acid temperatures 276 24.9 Recovery of acid heat as steam 276 24.10 Steam production principles 278 24.11 Double-packed bed absorption tower 278 24.12 Steam injection 279 24.13 Sensible heat recovery efficiency 279 24.14 Materials of construction 280 248 249 249 250 Contents 24.15 24.16 xi Summary Problems 280 280 25 Making sulfuric acid from wet feed gas 25.1 Chapter objectives 25.2 WSA feed Gas 25.3 WSA flowsheet 25.4 Catalyst bed reactions 25.5 Preparing the oxidized gas for H2SO4(ℓ) condensation 25.6 H2SO4(ℓ) condenser 25.7 Product acid composition 25.8 Comparison with conventional acidmaking 25.9 Appraisal 25.10 Alternatives 25.11 Summary 283 283 284 285 287 288 289 291 291 292 292 293 26 Wet sulfuric acid process fundamentals 26.1 Wet gas sulfuric acid process SO2 oxidation 26.2 Injection of nanoparticles into cooled process gas 26.3 Sulfuric acid condensation 26.4 Condenser temperature choices 26.5 Condenser acid composition up the glass tube 26.6 Condenser re-evaporation of H2O(ℓ) 26.7 Condenser acid production rate 26.8 Condenser appraisal 26.9 Summary 295 295 299 302 305 307 307 308 309 310 27 SO3 gas recycle for high SO2 concentration gas treatment 27.1 Objectives 27.2 Calculations 27.3 Effect of recycle extent 27.4 Effect of recycle gas temperature on recycle requirement 27.5 Effect of gas recycle on first catalyst SO2 oxidation efficiency 27.6 Effect of first catalyst exit gas recycle on overall acid plant performance 27.7 Recycle equipment requirements 27.8 Appraisal 27.9 Industrial SO3 gas recycle 27.10 Alternatives to gas recycle 27.11 Summary 313 313 313 314 315 317 Sulfur 28.1 28.2 28.3 28.4 325 325 325 326 328 28 from tail gas removal processes Objectives Environmental standards Acid plant tail gas characteristics Industrial acid plant tail gas treatment methods 318 319 319 319 321 323 xii Contents 28.5 28.6 28.7 Technology selection Capital and operating costs Summary 337 338 338 29 Minimizing sulfur emissions 29.1 Industrial catalytic SO2 þ 0.5O2 ! SO3 oxidation 29.2 Methods to lower sulfur emissions 29.3 Summary 341 341 343 347 30 Materials of construction 30.1 Chapter objectives 30.2 Corrosion rate factors for sulfuric acid plant equipment 30.3 Sulfuric acid plant materials of construction 30.4 Summary 349 349 349 351 356 31 Costs of sulfuric acid production 31.1 Investment costs 31.2 Production costs 31.3 Summary 357 357 360 362 Appendix A Appendix B Appendix C 363 369 Sulfuric acid properties Derivation of equilibrium equation (10.12) Free energy equations for equilibrium curve calculations Appendix D Preparation of Fig. 10.2’s equilibrium curve Appendix E Proof that volume% = mol% (for ideal gases) Appendix F Effect of CO2 and Ar on equilibrium equations (none) Appendix G Enthalpy equations for heatup path calculations Appendix H Matrix solving using Tables 11.2 and 14.2 as examples Appendix I Enthalpy equations in heatup path matrix cells Appendix J Heatup path-equilibrium curve: Intercept calculations Appendix K Second catalyst bed heatup path calculations Appendix L Equilibrium equation for multicatalyst bed SO2 oxidation Appendix M Second catalyst bed intercept calculations Appendix N Third catalyst bed heatup path worksheet Appendix O Third catalyst bed intercept worksheet Appendix P Effect of SO3 in Fig. 10.1’s feed gas on equilibrium equations Appendix Q SO3-in-feed-gas intercept worksheet Appendix R CO2- and SO3-in-feed-gas intercept worksheet Appendix S Three-catalyst-bed “converter” calculations Appendix T Worksheet for calculating after-intermediate-H2SO4making heatup path-equilibrium curve intercepts 379 383 387 389 393 399 401 405 413 417 421 427 429 431 439 441 443 451 Contents After-H2SO4-making SO2 oxidation with SO3 and CO2 in input gas Appendix V Moist air in H2SO4 making calculations Appendix W Calculation of H2SO4 making tower mass flows Appendix X Equilibrium equations for SO2, O2, H2O(g), N2 feed gas Appendix Y Cooled first catalyst bed exit gas recycle calculations Answers to numerical problems Index xiii Appendix U 453 459 461 465 475 481 493 Intentionally left as blank Preface We have made several additions and changes to this second edition of Sulfuric Acid Manufacture. The first change is the addition of a third author, Dr. Michael S. Moats, Associate Professor of Metallurgical Engineering at the Missouri University of Science and Technology. We welcome Michael to our team. The second is the addition of seven new chapters: Chapter Chapter Chapter Chapter Chapter Chapter Chapter 25 26 27 28 29 30 31 Making Sulfuric Acid from Wet Feed Gas Wet Sulfuric Acid Process Fundamentals SO3 Gas Recycle for High SO2 Concentration Gas Treatment Sulfur from Tail Gas Removal Processes Minimizing Sulfur Emissions Materials of Construction Costs of Sulfuric Acid Production We add one new unit to this edition—parts per million SO2 by volume, where SO2 can be any gas. It is defined as
ppmv ¼ Nm3 of SO2 per total Nm3 of gas  1  106 where Nm3 may be (i) measured or (ii) calculated from measured gas masses by the relationship: 22:4 Nm3 contains 1 kg mol of ideal gas: Once again we have received exceptional help from our industrial colleagues, who so kindly showed us around their plants and answered all our questions. We have continued to visit acid plants during preparation of this edition—we thank our hosts most profusely. One of the authors would specifically like to thank his son George Davenport and his nephew Andrew Davenport for their help with (i) wet sulfuric acid and (ii) cooled catalyst bed exit gas recycle calculations. xvi Preface In our first edition preface, we expressed the hope that our book would bring us as much joy as Professor Dr. von Igelfeld’s masterpiece Portuguese Irregular Verbs had brought him. Indeed it has! We hope now that this second edition will continue to bring us this same good fortune. Matthew J. King Perth, Western Australia William G. Davenport Tucson, Arizona Michael S. Moats Rolla, Missouri 1 Overview Sulfuric acid is a dense clear liquid. It is used for making fertilizers, leaching metallic ores, refining petroleum, and manufacturing a myriad of chemicals and materials. Worldwide, about 200 million tonnes of sulfuric acid is consumed per year (Apodaca, 2012). The raw material for sulfuric acid is SO2 gas. It is obtained by: (a) burning elemental sulfur with air (b) smelting and roasting metal sulfide minerals (c) decomposing contaminated (spent) sulfuric acid catalyst. Elemental sulfur is far and away the largest source. Table 1.1 describes three typical sulfuric acid plant feed gases. It shows that acid plant SO2 feed is always mixed with other gases. Sulfuric acid is almost always made from these gases by: (a) catalytically reacting their SO2 and O2 to form SO3(g) (b) reacting (a)’s product SO3 with the H2O(ℓ) in 98.5 mass% H2SO4(ℓ), 1.5 mass% H2O(ℓ) sulfuric acid. Industrially, both processes are carried out rapidly and continuously (Fig. 1.1). The standard state for SO2, SO3, O2, N2, and CO2 is gas in the acid plant. Each is referenced in this book, for example, as O2 not O2(g). The standard state for H2O, S, and H2SO4 is gas or liquid in the acid plant. Each is referenced accordingly. 1.1 Catalytic oxidation of SO2 to SO3 O2 does not oxidize SO2 to SO3 without a catalyst. All industrial SO2 oxidation is done by sending SO2 bearing gas down through “beds” of catalyst (Fig. 1.2). The reaction is: 400-630  C þ 0:5O2 ƒƒƒƒƒ! SO3 SO2 in dry SO2 , O2 , N2 gas in feed gas catalyst in SO3 , SO2 , O2 , N2 exit gas (1.1) It is strongly exothermic (DH 25 C ¼  100 MJ/kg mol of SO3). Its heat of reaction provides considerable energy for operating the acid plant. 1.1.1 Catalyst At normal operating temperature, 400-630  C, SO2 oxidation catalyst consists of a molten film of V, K, Na, Cs pyrosulfate salt on a solid porous SiO2 substrate. The molten film rapidly absorbs SO2 and O2 and rapidly produces and desorbs SO3 (Chapters 7 and 8). Sulfuric Acid Manufacture. http://dx.doi.org/10.1016/B978-0-08-098220-5.00001-0 © 2013 Elsevier Ltd. All rights reserved. 2 Sulfuric Acid Manufacture Table 1.1 Typical compositions (volume%) of acid plant feed gases entering SO2 oxidation “converters,” 2013. The gases may also contain small amounts of CO2 and SO3. Gas Sulfur burning furnace Sulfide mineral smelters and roasters Spent acid decomposition furnace SO2 12 10 9 O2 9 11 11 N2 79 79 76 Absorption Converter Drying Furnace Figure 1.1 Modern 4100 tonnes/day sulfur burning sulfuric acid plant, courtesy PCS Phosphate Company, Inc. (2012). The main components are the catalytic SO2 oxidation “converter” (tall, right), twin H2SO4(ℓ) making (“absorption”) towers (middle, right of stack) and a sulfur burning furnace (middle, bottom). The air dehydration (“drying”) tower is left of the stack. The catalytic converter is 16.5 m diameter. 1.1.2 Feed gas drying Equation (1.1) indicates that catalytic oxidation feed gas is almost always dry.1 This dryness avoids: (a) accidental formation of H2SO4 by the reaction of H2O(g) with the SO3 product of catalytic SO2 oxidation 1 A small amount of sulfuric acid is made by wet catalysis. This is discussed in Section 1.9 and Chapters 25 and 26. Overview 3 Catalyst Catalyst ~20 m Catalyst Catalyst ~0.5-1 m ~12 m Figure 1.2 Catalyst pieces in a catalytic SO2 oxidation “converter.” Converters are typically 20 m high and 12 m diameter. They typically contain four, 0.5- to 1-m-thick catalyst beds. SO2-bearing gas descends the bed at 3000 Nm3/min. Catalyst pieces are 10 mm in diameter and length. Copyright 2013 MECS, Inc. All rights reserved. Used by permission of MECS, Inc. (b) condensation of the H2SO4(ℓ) in cool flues and heat exchangers (c) corrosion. The H2O(g) is removed by cooling/condensation (Chapter 4) and by dehydration with H2SO4(ℓ) (Chapter 6). 1.2 H2SO4 production Catalytic oxidation’s SO3 product is made into H2SO4(ℓ) by contacting catalytic oxidation’s exit gas with strong sulfuric acid (Fig. 1.3). The reaction is: 80-110  C þ H 2 O ðl Þ H2 SO4 ðlÞ , SO3 ƒƒƒƒƒƒƒ! in SO3 SO2 , O2 , N2 gas in strengthened sulfuric acid in 98:5% H2 SO4 ðlÞ, 1:5% H2 OðlÞ sulfuric acid DH  25  C  130 MJ=kg mol of SO3 (1.2) Reaction (1.2) produces strengthened sulfuric acid because it consumes H2O(ℓ) and makes H2SO4(ℓ). H2SO4(ℓ) is not made by reacting SO3(g) with pure H2O(ℓ). This is because Reaction (1.2) is so exothermic that the product of the SO3 þ H2O(ℓ) ! H2SO4 reaction would be hot H2SO4 vapor—which is difficult and expensive to condense.