EXECUTIVE SUMMARY... I ACRONYMS AND ABBREVIATIONS ... III LIST OF SYMBOLS ... V L ATIN SYMBOLS ... V G REEK SYMBOLS ... VCONTENTS ... VII

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CONTENTS

EXECUTIVE SUMMARY... I ACRONYMS AND ABBREVIATIONS ... III LIST OF SYMBOLS ... V L ATIN SYMBOLS ... V G REEK SYMBOLS ... ^V CONTENTS ... VII

INTRODUCTION ... 11

B ^ACKGROUND ... 11

G OALS ... 12

M ^ETHODOLOGY ... 12

1 CO-FIRING ... 15

1.1 D EFINITIONS AND REASONS ... 15

1.2 S TATE OF THE ART ... 17

1.2.1 Biomass co-firing routes ... 17

1.2.1.1 Direct co-firing ... 17

1.2.1.2 Indirect co-firing... 19

1.2.1.3 Parallel co-firing... 21

1.2.1.4 Retrofitting boilers for 100% biomass combustion... 22

1.2.2 Worldwide distribution... 23

1.2.3 Logistic chains ... 25

1.2.3.1 Resource and harvest ... 27

1.2.3.2 Storage... 27

1.2.3.3 Transport... 28

1.3 F UTURE PERSPECTIVES ... 29

1.3.1 Potential overview... 29

1.3.2 Novel pre-treatment technologies... 30

1.3.2.1 Pelletisation ... 31

1.3.2.2 Pyrolysis ... 31

1.3.2.3 Torrefaction ... 32

2 ISSUES RELATED TO CO-FIRING... 35

2.1 H ANDLING AND PREPARATION ... 35

2.1.1 Straw... 35

2.1.2 Wood... 37

2.1.3 RDF... 38

2.1.4 Sewage sludge ... 39

2.2 F OULING , SLAGGING AND CORROSION ... 41

2.2.1 Straw... 44

2.2.2 Wood... 45

2.2.3 RDF... 46

2.2.4 Sewage sludge ... 46

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2.3 P OLLUTANTS ... 47

2.3.1 Particulates ... 47

2.3.1.1 Straw ... 47

2.3.1.2 Wood... 48

2.3.1.3 Sewage sludge... 48

2.3.1.4 RDF... 48

2.3.2 Sulphur Dioxide ... 48

2.3.2.1 Straw ... 48

2.3.2.2 Wood... 50

2.3.2.3 Sewage sludge... 50

2.3.2.4 RDF... 50

2.3.3 Nitrogen Oxides ... 51

2.3.3.1 Straw ... 52

2.3.3.2 Wood... 55

2.3.3.3 Sewage sludge... 56

2.3.3.4 RDF... 57

2.4 A SH UTILIZATION ... 58

2.5 S IGNIFICATIVE EXPERIENCES ON CO - FIRING RETROFIT AND REPOWERING ... 58

2.5.1 10 % biomass co-firing at Naantali-3... 58

2.5.2 100 % biomass repowering at Les Awirs-4 ... 60

2.5.3 Refurbishment of Amager-1... 61

3 EXISTING KEMA TOOLS FOR BOILER MODELING ... 65

3.1 P REDICTION OF BOILER PERFORMANCES ... 65

3.2 I NTRODUCTION TO SPENCE

^AND GRASP

... 65

3.3 S TANDARD SPENCE

' S HEAT EXCHANGER CALCULATION ... 68

3.4 D ETAILED BOILER MODEL ... 70

3.4.1 Furnace... 70

3.4.2 Convective Part ... 73

3.4.3 Performances ... 78

4 NEW SIMPLIFIED BOILER MODEL: 1

APPROACH AND RESULTS EVALUATION .... 79

4.1 D ESIGN OF HEAT EXCHANGERS : ^{THE LOG} - MEAN TEMPERATURE DIFFERENCE METHOD ... 79

4.2 P REDICTION OF OFF - DESIGN BEHAVIOR : THE EFFECTIVENESS -NTU METHOD ... 81

4.3 T HEORETICAL APPROACH TO HEAT TRANSFER MODELING ... 82

4.3.1 Design-mode procedure ... 84

4.3.2 Partload procedure ... 85

4.4 P ROCEDURE CALLS FOR DIFFERENT TYPES OF HEAT EXCHANGERS ... 88

4.4.1 Radiant superheaters ... 88

4.4.2 Screens... 89

4.4.3 Convective superheaters ... 90

4.4.4 Economizers ... 91

4.5 H EAT TRANSFER TO BOILER WALLS AROUND HEAT EXCHANGERS ... 92

4.6 V ^ALIDATION ... 97

4.6.1 Temperature test ... 98

4.6.1.1 Platen superheater ... 99

4.6.1.2 Primary superheater... 102

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4.6.2 Carbon dioxide and water test... 105

4.6.2.1 Platen superheater ... 105

4.6.2.2 Primary superheater... 106

4.7 E VALUATION OF THE ACCURACY OF THE 1

SIMPLIFIED MODEL VERSION ... 110

5 NEW SIMPLIFIED BOILER MODEL: 2

APPROACH AND VALIDATION ... 113

5.1 I DEAS FOR THE CALCULATION OF THE HEAT TRANSFER COEFFICIENT ... 113

5.1.1 Splitting the overall transfer coefficient into radiative and convective ... 113

5.1.2 Radiative heat transfer coefficient from flue gas ... 114

5.1.3 Convective heat transfer coefficient from flue gas ... 116

5.2 M ODIFICATIONS TO THE HEAT EXCHANGER PROCEDURES ... 118

5.2.1 New design procedures steps ... 118

5.2.2 New partload procedures steps... 120

5.2.3 The role of the correction factor F in the design procedure... 123

5.3 V ALIDATION OF THE NEW VERSION ... 123

5.4 E VALUATION OF THE ACCURACY OF THE 2

SIMPLIFIED MODEL VERSION ... 126

6 OVERALL BOILER SIMULATION AND COMPARISON... 127

6.1 T HE REFERENCE CASE ... 127

6.2 C OMPLETE BOILER MODEL ... 129

6.2.1 Schematization ... 129

6.2.1.1 Combustion air and flue gas path... 131

6.2.1.2 Working fluid path... 131

6.2.2 Calculations order and iterations ... 132

6.2.3 Differences between the detailed and the simplified model schematization ... 134

6.2.3.1 Initial values requirement... 134

6.2.3.2 Wall flows distribution... 135

6.3 C OMPARISON OF THE RESULTS ... 141

6.3.1 Furnace... 141

6.3.2 Steam production and temperatures ... 144

6.4 D ISCUSSION ... 148

6.4.1 Computational time... 149

CONCLUSIONS ... 151

REFERENCES ... 155

APPENDIX A... 161