PROCESS ECONOMICS

PROGRAM SRI INTERNATIONAL

Menlo Park, California

Abstract

Process Economics Program Report No. 63B

SULFUR DIOXIDE REMOVAL FROM FLUE GASES

(March 1980)

94025

Flue Gas Desulfurization (FGD) systems will be increasingly applied

to industrial boilers because of the increasing use of sulfur-bearing

coals and the adoption of stricter SO2 emission regulations by federal

and state agencies.

An evaluation is made of the technology, economics, and commercial

status of FGD systems for industrial boilers at a capacity of 100 mega-

watts cogenerating electricity and steam for an industrial complex.

Four commercially applied FGD processes are evaluated, namely, two

"throwaway" procedures producing a disposable gypsum waste and two re-

generable procedures reducing SO2 to salable elemental sulfur. The

processes are respectively:

l Limestone/Lime

l Double Alkali

l Citrate

l Wellman-Lord.

Other promising developmental processes with potential commercial

application are also described.

A summary of existing governmental regulations on SO2 emission

control and proposed modifications is presented.

A general review of boiler NOx control processes is presented re-

flecting the intense interest in Japan and the United States in abating

NOx pollution.

PEP '78 LAW

-

0

Report No. 63B

SO2 REMOVAL FROM FLUE GASES

PART I

SUPPLEMENT B

LEONARD A. WASSELLE

March 1980

A private report by the

PROCESS ECONOMICS PROGRAM

Menlo Park, California 94025

For detailed marketing data and information, the reader is

referred to one of the SRI programs specializing in marketing

research. The CHEMICAL ECONOMICS HANDBOOK Program covers

most major chemicals and chemical products produced in the

United States and the WORLD PETROCHEMICALS Program covers

major hydrocarbons and their derivatives on a worldwide basis.

In addition, the SRI DIRECTORY OF CHEMICAL PRODUCERS services

provide detailed lists of chemical producers by company, prod-

uct, and plant for the United States and Western Europe.

ii

CONTENTS

VOLUME I -

l

a -

a -

l

1 INTRODUCTION. . . . . . . . . . . . . . . . . . . . . . . 1

2 SUMMARY.........; ...............

General ......................... Current Status. ..................... Selection of FGD Processes for Industrial Boilers .... Economics ........................ Bases of Design .................... Capital and Operational Costs .............

Technical Aspects .................... Limestone/Lime Processes. ............... Double Alkali Process ................. Citrate Process .................... Wellman-Lord Process. ................. Other SO, Removal Processes .............. Nitrogen Oxides Removal ................

3 STATUS OF INDUSTRIAL AND UTILITY FLUE GAS DESULFURIZATION.....................

Status of Regulations . . . . . . . . . . . . . . . . Status of Industrial Flue Gas Desulfurization (FGD) . Status of Utility FGD . . . . . . . . . . . . . . . . Status of FGD Plants in Japan . . . . . . . . . . . . Status of Research, Development, and Demonstration Programs. . . . . . . . . . . . . . . . . . . . . . . The Shawnee Advanced Program for Utility Prototype Testing of Limestone/Lime Scrubbing of SO2. . . . . The EPA Pilot FGD Scrubber Program. . . . . . . . . Louisville Gas and Electric . . . . . . . . . . . . Industrial Boiler FGD-Rickenbacker Air Force Base . Wellman-Lord/Allied Chemical Demonstration Program. Aqueous Carbonate Demonstration Program . . . . . . Citrate Scrubbing Demonstration Program . . . . . .

. .

. .

. .

. .

. .

. . 72

. . 73

. . 73

. . 74

. . 74

. . 75

. . 75

4 LIMESTONE/LIME PROCESS. .................

Introduction. ..... ., ................ Chemistry ........................ Magnesium-Promoted Scrubbing. .............. Review of Process and Design Conditions ......... Magnesium Addition. .................. Limestone Stoichiometry and Particle Size .......

ix

3

3 4 8 10 11 12 21 21 23 25 26 28 29

31

31 33 47 66

71

79

79 80 90 92 93 98

CONTENTS

4 (Continued)

Scrubbers ........................ 99

Forced Oxidation of Sludge. ............... 109 Particulate Control ................... 120

Scaling and Subsaturated Operation. ........... 122

Sludge Disposal ..................... 129 IUCS Process. ..................... 136

Dravo Process ..................... 140

Chemfix Process .................... 141

Bases of Design. .................... 149 Process Description ................... 151

Process Discussion. ................... 156 Cost Estimates. ..................... 167

Capital Costs ..................... 167 Operating Costs .................... 168

5 DOUBLE ALKALI PROCESS. .................

Introduction. ...................... Chemistry ........................ Absorption. ...................... Regeneration. .....................

Review of Process Design Considerations ......... Sulfate Removal .................... Dilute and Concentrated Double Alkali Processes .... SO2 Control ...................... Scaling ........................ Chlorides Control ................... Sodium and Calcium Consumption. ............ Waste Solids. ..................... Water Balance and Filter Cake Washing .........

Summary of EPA Double Alkali Development and Commercial Applications. ...................... Double Alkali Process References. ............ Bases of PEP Design--Double Alkali Process. ....... Process Description ................... Process Discussion, ................... Cost Estimates. ..................... Capital Costs ..................... Operating Costs ....................

179

179 181 181 183 184 184 189 191 191 193 193 194 195

196 197 201 203 210 213 213 214

X

CONTENTS

VOLUME II

6 CITRATE PROCESS .....................

Introduction. ...................... Chemistry ........................ Absorption. ...................... Regeneration. ..................... Oxidation .......................

Sulfur Melting. ..................... Hydrogen Sulfide Generation .............. Sulfate Removal ....................

Process Development Review. ............... Bases of Design. .................... Process Description ................... Process Discussion, ................... Cost Estimates. ..................... Capital Costs ..................... Operating Costs ....................

7 WELLMAN-LORD PROCESS. ..................

Introduction. ...................... Chemistry ........................ Commercial Applications ................. Bases of Design. .................... Process Description ................... Process Discussion. ................... Cost Estimates ...................... Capital Costs ..................... Operating Costs ....................

8 MATERIALS OF CONSTRUCTION IN WET FLUE GAS DESULFURIZATION. . . . . . . . . . . . . . . . . . . . .

9 OTHER SO, REMOVAL PROCESSES . . . . . . . . . . . . . . .

Magnesium Oxide Slurry Scrubbing Process (Mag-Ox) . . . . Atomics International Aqueous Carbonate Process (ACP) . . Shell Flue Gas Desulfurization (SFGD) Process

297

297 304

Shell/UOP-Copper Oxide Process. . . . . . . . . . . . . . 310

Monsanto Cat-Ox Process . . . . . . . . . . . . . . . . . 314

Catalytic/IFP Ammonia Process . . . . . . . . . . . . . . 318

TVA-EPA Ammonia-Ammonium Bisulfate Regeneration Process . 322

Ionics Electrolytic Regeneration Process. . . . . . . . . 326

xi

221

221 223 223 226 230 230 231 234 234 237 239 245 249 249 253

259

259 262 266 271 273 280 282 282 283

289

CONTENTS

9 (Continued)

Westvaco Activated Carbon Process ............ Bergbau-Forschung/Foster Wheeler (BF/FW) Dry Adsorption. ....................... Other Carbon Sorption Processes ............. Reinluft. ....................... sumitomo. ....................... Lurgi Sulfacid Process. ................

Spray Dryer SO2 Absorption. ............... Chiyoda T-121--Jet Bubbling Scrubbing Systems ......

10 NITROGEN OXIDES REMOVAL.................

FGT Processes . . . . . . . . . . . . . . . . . . . . . . Dry Processes . . . . . . . . . . . . . . . . . . . . . . Selective Catalytic Reduction (SCR), Dry, NO, (only). . Selective Noncatalytic Reduction, Dry, NO, (only) . . .

Wet Processes . . . . . . . . . . . . . . . . . . . . . . Oxidation/Absorption/Reduction, Wet, Simultaneous. SO2-NOx........................ Absorption/Reduction, Wet, Simultaneous NO,-SO2 . . . . Absorption/Oxidation, Wet Consecutive SO2-NO, . . . . .

CITED REFERENCES....................... 393

PATENT REFERENCES BY COMPANY. . . . . . . . . . . . . . . . . 405

332

336 342 342 342 344 345 349

357

361 367 367 376 378

380 384 387

Xii

ILLUSTRATIONS

VOLUME I

2.1

2.2

3.1

4.1

4.2

4.3

4.4

4.5

4.6

4.7

4.8

4.9

4.10

4.11

4.12

4.13

4.14

4.15

Capital Costs vs FGD Size. . . . . . . . . . . . . .

Flue Gas Desulfurization Total Operating Costs vs Plant Capacity. . . . . . .

Utility FGD, Present Application, Projected Growth and Need. . . . . . . . . . . . . . . . . . .

Limestone/Lime Wet Scrubbing Process . . . . . . . .

Limestone Scrubbing Effect of Liquor Magnesium-Ion Concentration and Scrubber Inlet Liquor pH on SO2 Removal. . . . . . .

Limestone Scrubbing Effect of Scrubber Inlet Liquor pH and Liquor Magnesium-Ion Concentration on SO2 Removal . . . . .

Limestone Scrubbing Effect of Effective Magnesium-Ion Concentration and Slurry Flow Rate on SO2 Removal. . . . . . . . . . .

Early Designs of Packed Bed and Venturi Scrubbers for Limestone/Lime FGD . . . . . . . . . . . . . . .

Spray Tower Designs for Limestone/Lime FGD . . . . .

Two Stage Forced Oxidation Tests in the Venturi/Spray Tower System . . . . . . . . . . . . .

Single-Stage Forced Oxidation Tests in the TCA System with One Tank . . . . . . . . . . . . . .

Filter Leaf Tests of Absorber Slurry at Different Degrees of Oxidation . . . . . . . . . . .

Effect of pH on Oxidation Absorber Slurry. . . . . .

Bisulfite Ratio vs pH. . . . . . . . . . . . . . . .

Relative Saturation of Gypsum as an Indication of Scaling Potential . . . . . . . . . . . . . . . .

Magnesium Concentration and Saturation vs. Oxidation. . . . . . . . . . . . . . . . . . . .

IUCS Fixation Process for Limestone FGD Sludge . . .

Physical Properties of Stabilized Sludge and Fly Ash.....................

14

17

54

82

94

95

96

101

105

110

111

118

119

124

126

128

137

138

xiii

4.16

4.17

4.18

4.19

4.20

4.21

4.22

4.23

4.24

4.25 Limestone FGD

4.26 Lime FGD

5.1

5.2

5.3

5.4

5.5

ILLUSTRATIONS

Dravo Process for Sludge Fixation. . . . . . . . . .

Chemfix Process for Sludge Fixation. . . . . . . . .

Combustion Engineering Fixation Process. . . . . . .

Research-Cottrell Fixation Process . . . . . . . . .

Flue Gas Desulfurization Magnesium-Promoted Limestone Scrubbing with Sludge Oxidation. . . . . . . . . . .

SO Removal vs. Number of Stages 176 BW Horizontal Scrubber . . . . . . . . . . . . .

SO Removal vs. L/G Ratio 178 IW Horizontal Module . . . . . . . . . . . . . .

Inlet vs. Outlet Grain Loading 170 MW Horizontal Module . . . . . . . . . . . . . .

Limestone/Lime Flue Gas Desulfurization Effect of Plant Capacity on Unit Capital Investment.....................

Effect of Operating Level and Plant Capacity on Total Operating Costs . . . . . . . . . . . . . .

Effect of Operating Level and Plant Capacity on Total Operating Costs . . . . . . . . . . . . . .

Double Alkali SO2 Scrubbing and Sodium Regeneration--Concentrated Mode Schematic Diagram. . . . . . . . . . . . . . . . . .

CaS04/CaS03 Ratio in Reactor Solids as a Function of Reactor Liquor Composition . . . . . . .

Double Alkali Flue Gas Desulfurization . . . . . . . . . . . . . .

Double Alkali Flue Gas Desulfurization Effect of Plant Capacity on Unit Capital Investment.....................

Double Alkali Flue Gas Desulfurization Effect of Operating Level and Plant Capacity on Total Operating Costs . . . . . . . . . . . . . .

xiv

142

144

145

146

407

164

165

166

172

176

177

180

188

409

217

219

ILLUSTRATIONS

6.1

6.2

Typical Citrate Process. . . . . . . . . . . . . . .

Effect of pH on SO2 Absorption in Citrate Solution . . . . . . . . . . . . . . . . . .

6.3 Regeneration Step

6.4

6.5

Reaction Time with H2S . . . . . . . . . . . . . . .

Regeneration Step pH and Thiosulfate Concentration . . . . . . . . . .

Effect of Temperature on Hydrolysis of CS2 with Steam........................

6.6

6.7

Effect of Temperature on Reaction of Sulfur, Methane, and Steam. . . . . . . . . . . . . . . . .

Citrate Process Flue Gas Desulfurization . . . . . . . . . . . . . . 411

6.8

6.9

Effect of Gas Concentration and Solution Temperature on SO2 Absorption. . . . . . . . . . . .

Effect of H2S04 Concentration (pH) on SO2 Absorption. . . . . . . . . . . . . . . . . . . . .

6.10 Effect of Citrate Concentration on SO2 Absorption at 35°C . . . . . . . . . . . . . . . . .

6.11 Citrate Process Flue Gas Desulfurization Sulfur Recovery Effect of Plant Capacity on Unit Capital Investment.,...................

6.12

7.1

7.2

7.3

7.4

VOLUME II

Citrate Process Flue Gas Desulfurization with Sulfur Recovery Effect of Operating Level and Plant Capacity on Total Operating Costs . . . . . . . . . . . . . .

Wellman-Lord SO2 Recovery Process. . . . . . . . . .

Allied Chemical SO2 Reduction Process. . . . . . . .

Wellman-Lord/Allied Chemical Nipseo Plant Unit No.l.....................

FGD Sodium Sulfite--SO2 Reduction Process (Wellman-Lord/Davy Powergas) . . . . . . . . . . . .

222

225

228

229

232

233

250

251

252

256

258

260

261

270

413

xv

-.

ILLUSTRATIONS

7.5

7.6

8.1

8.2

9.1

9.2

9.3

9.4

9.5

9.6

9.7

9.8

9.9

9.10

9.11

9.12

9.13

9.14 Regeneration System

Wellman-Lord Process Flue Gas Desulfurization Sulfur Recovery Effect of Plant Capacity on Unit Capital Investment...... . . . . . . . . . . . . . . .

Wellman-Lord Flue Gas Desulfurization with Sulfur Recovery Effect of Operating Level and Plant Capacity on Total Operating Costs . . . . . . . . . . . . . .

Effect of pH and Chloride Ions on the Localized Attack of Types 316L and 317L Stainless Steels in SO2 Scrubber Environments . . . . . . . . . . . .

Effect of Molybdenum Content in Alloys Subject to SO2 Scrubber Environments . . . . . . . .

The Absorption of Sulfur Dioxide from Boiler Flue Gas. . . . . . . . . . . . . . . . . . .

The Regeneration of Magnesium Oxide. . . . . . . . .

ACP Block Flow Diagram . . . . . . . . . . . . . . .

Gas Cleaning Subsystem Process Flow Diagram. . . . .

Parallel Passage Reactor . . . . . . . . . . . . . .

SFGD Flow Scheme at SYS. . . . . . . . , . . . . . .

Monsanto Cat-&t System for SO2 Removal from Stack Gas . . . . . . . . . . . . . . . . . . ,

The Reheat Cat-Ox System at Wood River #4. . . . . .

Catalytic/IFP Regenerative FCD Process Schematic . . . . . . . . .

Absorption Section of Catalytic/IFP Process. . . . .

Catalytic/IFP Ammonia Scrubbing Process Process Flow Diagram . . . . . . . . . . . . . . . .

TVA-EPA Amnonia-Amnonium Bisulfate (ABS) Regeneration Process . . . . . . . . . . . . . . . .

SO2 Removal Section Stone and Webster/Ionics SO2 Removal and Recovery Process . . . . . . . . . . . . . . . . . .

Stone and Webster/Ionics SO2 Removal and Recovery Process . . . . . . . . . . . . . . , . . .

286

288

291

293

299

300

305

307

312

313

315

317

319

320

323

325

329 0

330

a xvi

ILLUSTRATIONS

9.15

9.16

9.17

9.18

9.19

9.20

9.21

9.22

9.23

9.24

9.25

10.1

10.2

10.3

10.4

10.5

10.6

10.7

10.8

10.9

10.10

10.11

Schematic Diagram of "A" and "B" Electrolytic Cells........................

Catalytic/Westvaco FGD Process Schematic . . . . . .

Westvaco/Catalytic Activated Carbon FGD Process. . .

BF/FW Activated Char Dry Adsorption FGD System. . . . . . . . . . . . . .

Adsorption Solids and Gas Flow Arrangements. . . . .

BF/FW Dry Adsorption Regeneration and Resox systems....................

SO2 Removal: Wet Sorbent In/Dry Out with Baghouse . . . . . . . . . . . . . . . . . . .

Spray Absorber and Flue Gas Distribution system....................

Pilot Plant Process Flow Diagram Chiyoda T-121. . . . . . . . . . . . . . . . .

Jet Bubbling Reactor . . . . . . . . . . . . .

Effect of pH on Limestone Utilization Jet Bubble Reactor System. . . . . . . . . . .

Sumitomo Chemical Flue Gas NOx Removal Process

Temperatures Below Which NH4HS04 Forms . . . .

Flow Diagram of Hitachi, Ltd., Process . . . .

. . .

. . . 346

. . . 348

. . .

. . .

. . .

. . .

. . .

. . .

Flow Diagram of Hitachi Zosen Process. . . . . . . .

Flow Diagram of Mitsui Engineering and Shipbuilding Process . . . . . . . . . . . . . . . .

Flow Diagram of Exxon Thermal Denox Process. . . . .

Flow Diagram of Ishikawajima-Harima Heavy Industries Process . - . . . . . . . . . . . . . . .

Flow Diagram of Moretana Calcium Process . . . . . .

Flow Diagram of Asahi Chemical Process . . . . . . .

Flow Diagram of Mon Alkali Permanganate Process. . .

Gas Composition and Suitable Processes . . . . . . .

331

334

335

337

339

341

350

351

355

369

370

371

373

374

379

382

383

386

391

392

xvii

TABLES

VOLUME I

2.1

2.2

2.3

2.4

2.5

2.6

3.1

3.2

3.3

3.4

3.5

3.6

3.7

3.8

3.9

3.10

3.11

3.12

Q 3.13 \..

3.14

3.15

3.16

Operating FGD Systems. . . . . . . . . . . . . . . .

Summary of FGD Systems . . . . . . . . . . . . . . .

Summary of Capital and Operational Costs for Limestone, Lime, and Double Alkali FGD Systems . . .

Summary of Direct vs. Indirect Operational Costs Limestone, Lime, and Double Alkali Processes . . . .

Summary of Capital and Operational Costs for Citrate and Wellman-Lord FGD Systems . . . . . . . .

Summary of Direct vs. Indirect Operational Costs Citrate and Wellman-Lord Processes . . . . . . .

Number and SCFM of Industrial Boiler FGD Systems

Start-Up Year and SCFM of Industrial Boiler FGD systems.....................

Operational FGD Systems on Industrial Boilers. .

Under Construction FGD Systems on Industrial Boilers. . . . . . . . . . . . . . . . . . . . .

Planned FGD Systems on Industrial Boilers. . . .

U.S. Industrial Boiler SO2 Control Processes . .

Summary of Disposal Practices for FGD Systems on Industrial Boilers. . . . . . . . . . . . . .

Summary by Vendor of FGD Systems on Industrial Boilers.....................

Number of Total Coal Fired MW of FGD Systems . .

Total FGD Megawatt Capacity by Year. . . . . . .

Summary of FGD Systems by Company. . . . . . . .

. .

. .

. . 36

. . 37

. . 40

. . 41

. . 42

. .

. .

. .

. .

. .

Summary of Operating FGD Systems by Process and Generating Units . . . . . . . . . . . . . . . . . .

Summary of FGD Systems Under Construction. . . . . .

Summary of Planned FGD Systems . . . . . . . . . . .

Summary of FGD Systems by Vendor . . . . . . . . . .

Summary of Sludge Disposal Practices for Operational FGD Systems. . . . . . . . . . . . . . .

xix

6

9

13

16

19

20

34

43

48

51

52

55

56

58

60

63

67

TABLES

3.17

3.18

3.19

4.1

4.2

4.3

4.4

4.5

4.6

4.7

4.8

4.9

4.10

4.11

4.12

Capacities of Utility Steam Power Plants and FGD Systems in Japan . . . . . . . . . . . . . . . . . .

FGD Systems Applied to Utility Power Plants in Japan........................

Commercial Organizations Active in Research on Sulfur Oxide Removal from Stack Gases. . . . . . . .

69

70

77

Limestone/Lime Process Individual Species . . . . . . . . . . . . . . . . .

Limestone/Lime Process

86

Reactions Considered . . . . . . . . . . . . . . . . 87

Results of Two-Stage Forced Oxidation Tests on the Venturi/Spray Tower System Limestone Slurry with High Fly Ash Loadings. . . . .

Results of One-Stage Forced Oxidation Tests on the TCA System Limestone Slurry with High Fly Ash Loadings. . . . .

Summary of the Dewatering Characteristics of Shawnee Scrubber Solids. . . . . . . . . . . . . . .

112

114

EPA-Sponsored FGD Waste and Water Projects . . . . .

Companies Providing Commercial Fixation Processes. .

FGD by Magnesium-Promoted Limestone Slurry with Sludge Oxidation Stream Flows....................

117

131

134

154

Limestone for FGD by Magnesium-Promoted Limestone Scrubbing with Forced Oxidation Estimated Capital Investment . . . . . . . . . . . .

Lime for FGD by Magnesium-Promoted Lime Scrubbing with Forced Oxidation Estimated Capital Investment . . . . . . . . . . . .

Limestone for FGD by Magnesium-Promoted Limestone, Scrubbing with Sludge Oxidation Estimated Operating Costs. . . . . . . . . . . . . .

Lime for FGD by Magnesium-Promoted Lime, Scrubbing with Forced Oxidation Estimated Operating Costs. . . . . . . . . . . . . .

171

173

174

Q

175

TABLES

5.1

5.2

5.3

5.4

5.5

5.6

Double Alkali Process in the United States Summary of Significant Operating and Planned Full-Scale Systems . . . . . . . . . . . . . . . . .

Double Alkali Process in Japan Summary of Significant Operating and Planned Full-Scale Systems . . . . . . . . . . . . . . . . .

FGD--Double Alkali Process Bases for Material and Energy Balances . . . . . . .

FGD by Double Alkali Process Stream Flows. . . . . . . . . . . . . . . . . . . .

FGD--By Double Alkali Process Estimated Capital Investment . . . . . . . . . . . .

FGD by Double Alkali Process Estimated Operating Costs. . . . . . . . . . . . . .

199

200

202

209

216

218

6.1 FGD by Citrate Process Stream Flows. . . . . . . . . . . . . . . . . . . . 244

6.2 FGD by Citrate Process and Sulfur Recovery Estimated Capital Investment . . . . . . . . . , . .

6.3 FGD by Citrate Process

7.1

7.2

Estimated Operating Costs. . . . . . . . . . . . . . 257

Wellman-Lord Installations in the United States. . . 267

Wellman-Lord Installations in Japan and West Germany....................

7.3 FGD by Sodium Sulfite-SO2 Reduction Process (Wellman-Lord/Davy Powergas) Stream Flows . . . . . . . . . . . . . . . . . . . .

7.4

7.5

VOLUME II

255

268

279

FGD by Wellman-Lord/Davy Powergas/Allied Chemical Process Estimated Capital Investment . . . . . . . . . . . .

FGD by Wellman-Lord/Davy Powergas/Allied Chemical Process

285

Estimated Operating Costs. . . . . . . . . . . . . . 287

xxi

TABLES

9.1

9.2

9.3

10.1

10.2

10.3

10.4

10.5

10.6

10.7

10.8

10.9

Operating and Planned Magnesia Scrubbing Units on U.S. Power Plants . . . . . . . . . . . . . . . .

Operating Magnesia Scrubbing Units on Japan Power Plants . . . . . . . . . . . . . . . . . . . .

Status of Development--BF/FW Flue Gas Desulfurization Process. . . . . . . . . . . . . . .

NO, Emissions from Utility and Industrial Operations in 1975 . . . . . . . . . . . . . . . . .

NO, Emission Standards for New Boiler Sources. . . .

EPA Goals for Low NO, Rmission Levels. . . . . . . .

Current Flue Gas Denitrification Processes . . . . .

Major NO, Removal Plants of Power Companies. . . . .

Status of Development of the Flue Gas Denitrification Processes. . . . . . . . . . . . . .

Process Conditions for Dry SCR NO, Removal Processes. . . . . . . . . . . . . . . . . . . . . .

Comparison of Oxidation-Absorption-Reduction Processes. . . . . . . . . . . . . . . . . . . . . .

Comparison of Absorption-Reduction Processes . . . .

302

303

343

358

360

360

363

364

365

377

385

388

xxii