Title page

ABSTRACT

Contents

1. INTRODUCTION 28

PROCESS DESCRIPTION 30

PROBLEM STATEMENT 32

OBJECTIVES 35

CONSTITUTION OF THE DISSERTATION 37

REFERENCES 38

2. CLARIFIER 40

INTRODUCTION 40

LITERATURE REVIEWS 45

Functions of Clarifier 46

Settling Phenomena 50

Design of Clarifier 52

Surface and solids loading rates 53

Types of settling tanks 56

Solid removal mechanisms 58

Inlet structures 59

Weir placement and loading rates 60

Density Current in Clarifier 62

MODEL DEVELOPMENT 65

Turbulence Model 65

Local Density 66

Settling Model 68

Heat Flux Model 72

Boundary Condition 73

EXPERIMENTS 76

TEST CASE 1 78

TEST CASE 2 81

TEST CASE 3 85

CALCULATION RESULTS AND DISCUSSIONS 90

DENSITY EFFECT 90

Suspended Solids 90

Temperature 92

Turbulence Model 93

Settling Models 95

RTD ANAYLSIS AND MODEL VALIDATION 97

DISTRIBUTION OF RADIOTRACER 102

PRACTICAL APPROACHES 104

Hydraulic Loading Condition 104

Geometric Configurations 109

3-D APPROACHES 118

CONCLUSIONS 131

REFERENCES 134

3. SCREW-TYPE DRYER 145

INTRODUCTION 145

LITERATURE REVIEWS 149

Characteristics and Composition of Sludge 149

Sludge Disposal Methods 154

General Drying Process 156

Classification of Drying Systems 158

Transition through the plastic phase 158

Heat transfer 159

Drying/palletizing in one step or separate granulator 160

Partial or complete drying 160

NUMERICAL CALCULATIONS 161

EXPERIMENTS 165

EXPERIMENTAL EQUIPMENT 165

Transfer Rate 166

Gas Partition 166

Heat Transfer 167

EXPERIMENTAL METHODS 168

PROPERTIES OF SEWAGE SLUDGE 169

EXPERIMENTAL RESULTS 171

Drying Process 171

Drying Efficiency 171

Thermal Efficiency 173

CONCLUSIONS 175

REFERENCES 176

4. COMBUSTION FACILITIES 178

INTRODUCTION 179

LITERATURE REVIEW 183

NOx CONTROL TECHNOLOGIES 183

Low NOx Burners 184

Reburning 184

Selective Catalytic Reduction (SCR) 185

Selective Non Catalytic Reduction (SNCR) 186

ALTERNATIVE FUEL, ORIMULSION 197

Fuel Properties 198

Fuel Handling 200

Combustion Characteristics of Orimulsion 201

Solid Residues 212

MODEL DEVELOPMENT 214

GOVERNING EQUATION 214

TURBULENCE MODEL 217

COMBUSTION REACTION MODEL 217

Eddy Breakup Model 217

Two Step Combustion Model 219

Non-Equilibrium CO Oxidation Model 219

NO Formation and Reduction Model 221

SO2 Formation Model 225

DROPLET EQUATION 226

Dispersion Model in Turbulence Flow 227

Devolatilization Rate of Orimulsion Droplet 228

RADIATIVE HEAT TRANSFER MODEL 229

Simple Radiation Model 230

Four-Flux Model 231

EXPERIMENTS 235

FULL-SCALE EXPERIMENT ON SNCR SYSTEM 235

Test Equipment 235

Waste Properties 238

Flue Gas Temperature 241

PRELIMINARY COMBUSTION TESTS FOR ORIMULSION 242

SMALL-SCALE ORIMULSION BOILER (100L/hr) 244

Test Equipment 244

Data Acquisition System 245

Burner Design 247

Combustion Test 248

CALCULATION RESULTS AND DISCUSSION 252

FULL-SCALE MSW INCINERATOR WITH SNCR SYSTEM 252

Standard Operation and Boundary Condition 252

Model Validation 254

Castable Height 257

Mixing Effects 259

Heating Values 263

NSR (Normal Stoichiometric Ratio) 264

Injection Height 267

Wastewater Spraying System 269

ORIMULSION BOILER 271

Preliminary Study 271

Small-Scale Orimulsion Boiler 279

CONCLUSIONS 285

REFERENCES 288

5. CONCLUSIONS AND FUTURE WORKS 295

Clarifier 296

Thermal Dryer 296

SNCR System 297

Combustion of Orimulsion Fuel 297

APPENDIX 299

ACKNOWLEDGMENTS 316

Table 2.1 Analysis of clarification failure by DSS/FSS testing at high ESS 49

Table 2.2 General design considerations for a secondary clarifier 61

Table 2.3 Relationship between temperature and density for water 67

Table 2.4 Relationship between concentration and density for activated sludge 67

Table 2.5 The break-through and the maximum concentration time measured from RTD curves 80

Table 2.6 Influent flow rate during experiment (TEST CASE 2) 84

Table 2.7 Influent flow rate during experiment (TEST CASE 3) 88

Table 2.8 Meteorological data and calculated parameters 89

Table 2.9 Relative SS concentration in the effluent 114

Table 3.1 Low heating value of different combustibles 152

Table 3.2 Regulations for agricultural use of dried sludge 153

Table 3.3 Treatment cost depending on the sludge disposal methods 156

Table 3.4 Classification of the drying systems 160

Table 3.5 Partition ratio and temperature of hot gas at each exit position 164

Table 3.6 Chemical properties of dehydrated sewage sludge 170

Table 3.7 Heavy metal contents of dehydrated sewage sludge before and after drying 170

Table 3.8 Performance of gas-agitated screw type dryer 172

Table 4.1 Domestic applications of SNCR system by industry 188

Table 4.2 NOx control options for various combustion units 189

Table 4.3 Typical properties of Cerro Negro bitumen(Bitor America, 1997) 199

Table 4.4 Fuel composition of Orimulsion 100 and 400 199

Table 4.5 Typical values of several trace elements 200

Table 4.6 Plants that have operated or area were operating commercially as of December 2000 using Orimulsion (Olen 1998b, Quig and Woodworth 1997, Quig 1999, Garcia 1999, 207

Table 4.7 Summary of air pollutant concentrations reported in the literature for Orimulsion and heavy fuel oil(EPA, 2001) 212

Table 4.8 TCLP results for Orimulsion 100 and coal fly ashes(Bitor America, 1997) 213

Table 4.9 Γφ and Sφ expression for 2-D cylindrical coordinate 216

Table 4.10 CO oxidation kinetics parameters 220

Table 4.11 Rate parameters for the SNCR model 225

Table 4.12 Operational conditions of waste incinerator in Daejon 235

Table 4.13 Optimum injection location for SNCR reaction as waste heating values 264

Table 4.14 Standard condition employed in the preliminary study 272

Table 4.15 Standard condition employed in a small-scale boiler 279

Fig. 1.1 Overall schematic for a sludge and waste-related combined treatment system 31

Fig. 2.1 Typical schematic diagram of the activated sludge process 41

Fig. 2.2 Four distinct settling zones 51

Fig. 2.3 Hydraulic and mass flow over a settling tank 53

Fig. 2.4 Circular settling tank with scrapper mechanism and flocculator(Washington State Department of Ecology, 1998) 57

Fig. 2.5 Rectangular settling tank with chain-and-flight type collectors(Washington State Department of Ecology, 1998) 57

Fig. 2.6 Empirical settling velocity models (rh=0.00565, rp=0.02, Cmin=0.002Co) 71

Fig. 2.7 Definition of a rectangular clarifier 74

Fig. 2.8 Definition of a circular clarifier 74

Fig. 2.9 Dimensionless RTD curve in secondary clarifier 77

Fig. 2.10 Dimensionless RTD curve in ideal plug flow condition 77

Fig. 2.11 The locations of detector for RTD study in a final clarifier 79

Fig. 2.12 The response curves at each detector installed in the clarifier 80

Fig. 2.13 The locations of detector for RTD study in a final clarifier 82

Fig. 2.14 The response curves at each detectors installed in the clarifier 83

Fig. 2.15 Observed water qualities 84

Fig. 2.16 Observed temperature data for summer season 84

Fig. 2.17 Radiotracer detection locations near the longitudinal central plane 86

Fig. 2.18 The response curves at each detector installed in the clarifier 87

Fig. 2.19 Observed water qualities 88

Fig. 2.20 Observed SVI value and MLSS concentration 88

Fig. 2.21 Observed temperature data for winter season 89

Fig. 2.22 Flow characteristics in the final rectangular clarifier 91

Fig. 2.23 Density currents induced by temperature difference 93

Fig. 2.24 Comparison of predicted radial velocity profiles (Fr=0.346) with data of scale model at various radial locations(Standard k-ε model) 94

Fig. 2.25 Comparison of predicted radial velocity profiles (Fr=0.346) with data of scale model at various radial locations(RNG k-ε model) 94

Fig. 2.26 Calculation results with discrete settling model(Vs=5.0×10-⁴m/s) 96

Fig. 2.27 Calculation results with monodisperse settling model(V0=1.1×10-³ m/s, Vmax=5.0×10-⁴m/s) 96

Fig. 2.28 Comparison of dimensionless RTDs in the inlet zone 99

Fig. 2.29 Comparison of dimensionless RTDs in the settling zone 100

Fig. 2.30 Comparison of dimensionless RTDs in the withdrawal zone 101

Fig. 2.31 Radiotracer distribution with the elapsed time 103

Fig. 2.32 Streamlines in a secondary circular clarifier under different densimetric Fr 105

Fig. 2.33 Strength of bottom density current for the different Fr 106

Fig. 2.34 Strength of local upward flow in withdrawal zone for the different Fr 106

Fig. 2.35 Flow characteristic of a secondary rectangular clarifier in winter 108

Fig. 2.36 Strength of density current with the inlet position 110

Fig. 2.37 Distributions of SS concentration in a secondary clarifier 111

Fig. 2.38 Comparison of streamlines with the existence of baffle 112

Fig. 2.39 Velocity vector field with inlet baffle at the various inlet positions 113

Fig. 2.40 Flow characteristics as a function of intermediate baffle configuration 115

Fig. 2.41 Flow characteristics with the configuration of outlets 117

Fig. 2.42 3-Dimensional grid generation of a final rectangular clarifier 121

Fig. 2.43 Flow characteristics in the XY plane along the horizontal direction 121

Fig. 2.44 Velocity vector fields in the YZ plane for a 3-D coordinate 122

Fig. 2.45 Velocity vector fields in the XZ plane for a 3-D coordinate 123

Fig. 2.46 Suspended solids concentrations in the YZ plane for a 3-D coordinate 124

Fig. 2.47 Suspended solids concentrations in the XZ plane for a 3-D coordinate 125

Fig. 2.48 Comparison of RTDs calculated from 3-D model in the inlet zone 126

Fig. 2.49 Comparison of RTDs calculated from 3-D model in the settling zone 127

Fig. 2.50 Comparison of RTDs calculated from 3-D model in the withdrawal zone 128

Fig. 2.51 Radiotracer distribution with the elapsed time in a 3-D coordinate 129

Fig. 3.1 Sludge generation and treatment trend in Korea 147

Fig. 3.2 Sludge treatment process in WWTP 150

Fig. 3.3 Water distribution in a sludge particle 151

Fig. 3.4 The different disposal routes for sewage sludge. 155

Fig. 3.5 General drying process 156

Fig. 3.6 Structural changes of sludge during drying 158

Fig. 3.7 Direct and indirect heat transfer 159

Fig. 3.8 Schematic of a combustor in a screw conveyor 163

Fig. 3.9 Hot gas distribution for the fully open side exit 164

Fig. 3.10 Hot gas distribution for the half closed side exit 164

Fig. 3.11 Hot gas distribution for the closed side exit 164

Fig. 3.12 Configuration of gas-agitated screw-type dryer 165

Fig. 3.13 Partition of combustion gas in the screw-type dryer 167

Fig. 3.14 Schematic of drying process for sewage sludge 168

Fig. 3.15 Structural changes of sewage sludge during drying process 171

Fig. 3.16 Water content and drying efficiency with treatment capacity 172

Fig. 3.17 Dehydrated sewage sludge before and after drying 173

Fig. 3.18 Thermal efficiency with fuel consumption rate 174

Fig. 4.1 Orinoco region of Venezuela(Bitor, 1997) 197

Fig. 4.2 Types of instabilities occurring in bitumen-in-water emulsions(Bitor Europe, 1994) 201

Fig. 4.3 Comparison of predicted CO oxidation between global mechanism of Dryer and Glassman(equilibrium model), and the optimized global rate parameters(nonequilibrium 221

Fig. 4.4 Schematic NO reaction sequence and its kinetic rates 224

Fig. 4.5 Planck mean absorption coefficient 231

Fig. 4.6 Constitution of incineration facility 236

Fig. 4.7 Flow chart for SNCR process in Daejon waste incinerator 237

Fig. 4.8 Injection locations in each level of post-combustion chamber 238

Fig. 4.9 Annual waste heating value generated in Daejon City 239

Fig. 4.10 Proximate analysis of the wastes generated in Daejon City 240

Fig. 4.11 Physical composition of the waste generated in Daejon City 240

Fig. 4.12 Flue gas temperature measured on each floor level 241

Fig. 4.13 Preliminary experimental rig for the combustion of Orimulsion fuel 243

Fig. 4.14 Experimental rig for the small-scale combustor of Orimulsion fuel 245

Fig. 4.15 Temperature logs in an Orimulsion boiler 246

Fig. 4.16 Orimulsion and steam flow rates and temperature of Orimulsion 246

Fig. 4.17 Configuration of standard F-jet atomizer 247

Fig. 4.18 Detection locations for combustion gas 248

Fig. 4.19 Observed flame structure with various combustion conditions 250

Fig. 4.20 CO concentration at a different sampling port as Stack O₂ 251

Fig. 4.21 NO concentration at a different sampling port as Stack O₂ 251

Fig. 4.22 SO₂concentration at a different sampling port as Stack O₂ 251

Fig. 4.23 Schematic diagram of a full-scale stoker incinerator 253

Fig. 4.24 Combustion characteristics in post combustion chamber 255

Fig. 4.25 Horizontal temperature profiles at two vertical heights of incinerator 256

Fig. 4.26 Average exit NO and temperature data as the castable height 258

Fig. 4.27 Behavior of reagent for the reference condition 260

Fig. 4.28 NO reduction efficiency as the increase of droplet size 261

Fig. 4.29 NO reduction efficiency as the injection angle of reagent 261

Fig. 4.30 NO reduction efficiency as the increase of droplet injection velocity 262

Fig. 4.31 NO reduction efficiency with the use of tertiary air 262

Fig. 4.32 Temperature distribution with the increase of waste heating value (℃) 263

Fig. 4.33 NO reduction efficiency with NSR in the practical condition 265

Fig. 4.34 NO reduction efficiency with the increase of NSR 266

Fig. 4.35 Reduced NO concentration with the injection height of reagent 268

Fig. 4.36 Temperature and NO reduction with water spraying rate 270

Fig. 4.37 Schematic of a 3-D axi-symmetric Orimulsion combustor 271

Fig. 4.38 Comparison of flame temperature profiles between calculation and measurement 273

Fig. 4.39 Comparison of flame temperature profile between HFO and Orimulsion 274

Fig. 4.40 Isothermal contour plot with the variation of droplet injection velocity (℃) 275

Fig. 4.41 Temperature profile along the centerline with the change of the swirl number in air stream. 276

Fig. 4.42 Comparison of pollutant species concentration between calculation and measurement 278

Fig. 4.43 Schematic of a small-scale Orimulsion boiler (100L/hr) 279

Fig. 4.44 Comparison of temperature with fuel injection rate 282

Fig. 4.45 Comparison of CO concentration for 5% excess O₂ 282

Fig. 4.46 Comparison of SO₂concentration for 5% excess O₂ 283

Fig. 4.47 Comparison of NO concentration for 5% excess O₂ 283

Fig. 4.48 Temperature profiles along the axial distance from burner 284

Fig. 4.49 Flame characteristics by atomizing fluid type in the low NO burner 284

Fig. A1 Major components of ClaSS 1.0 program. 300

Fig. A2 Main window of ClaSS 1.0. 302

Fig. A3 Pull down menu in the File. 302

Fig. A4 Input menu with basic editing skills. 303

Fig. A5 Determination of clarifier geometry. 304

Fig. A6 Grid generation for a 2-D rectangular clarifier. 304

Fig. A7 Selection of clarifier model. 305

Fig. A8 Detection points of radiotracer in a clarifier. 306

Fig. A9 Configuration of a clarifier with distribution port. 306

Fig. A10 Configuration of a clarifier without distribution port. 307

Fig. A11 Inflow condition of a clarifier and selection of turbulent model. 307

Fig. A12 Arranged input data for the execution of Steady state mode. 308

Fig. A13 Arranged input data for the execution of Unsteady state mode. 308

Fig. A14 Input values for Steady state and Unsteady state mode. 309

Fig. A15 Run menu for Steady and Unsteady state modes. 310

Fig. A16 Executing window of steady state mode. 311

Fig. A17 Running window of unsteady state mode. 311

Fig. A18 Calculation result of steady state mode. 312

Fig. A19 Graphic tools to visualize the flow patterns. 313

Fig. A20 Computational domain of Clarifier in Tecplot 7 window. 314

Fig. A21 Normalized concentration profile of tracer along time. 315