Experimental investigations on combustion and emission behaviour during oxy-coal combustion [Elektronische Ressource] / vorgelegt von Bhupesh Dhungel
200 Pages
English
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Experimental investigations on combustion and emission behaviour during oxy-coal combustion [Elektronische Ressource] / vorgelegt von Bhupesh Dhungel

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200 Pages
English

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Published 01 January 2010
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EXPERIMENTAL INVESTIGATIONS ON COMBUSTION
AND EMISSION BEHAVIOUR DURING OXY-COAL
COMBUSTION

Von der Fakultät Energie-, Verfahrens- und Biotechnik der Universität Stuttgart
zur Erlangung der Würde eines Doktors der Ingenieurwissenschaften (Dr.-Ing.) genehmigte
Abhandlung


vorgelegt von
M.Sc. Bhupesh Dhungel
aus Kathmandu, Nepal

Tag der mündlichen Prüfung: 20.01.2010
Hauptberichter: Prof. Dr. techn. G. Scheffknecht
Mitberichter: Prof. Filip Johnsson, Göteborg


Institut für Feuerungs- und Kraftwerkstechnik (IFK)
Universität Stuttgart
2010























ACKNOWLEDGEMENTS

My sincere acknowledgement goes to my supervisor, Professor G. Scheffknecht for
his invaluable advice and support throughout this work. Professor Filip Johnsson from
Chalmers University of Technology is greatly acknowledged for reviewing this work.
My department head, Jörg Maier is greatly acknowledged for his guidance,
availability, support, critical review, and encouragement throughout this work. The technical
assistance of Maik Schneider during tests was invaluable and deserves special recognition.
Assistance by Leema Al-Makhadmeh for the preparation of this work is highly
acknowledged. All my colleagues at the Institute of Process Engineering and Power Plant
Technology are greatly acknowledged for creating a beautiful and relaxed working
atmosphere.
The financial support by the European Commission through the ASSOCOGS,
OXYMOD and ENCAP project is highly acknowledged. University and industrial partners in
the ASSOCOGS, OXYMOD and ENCAP projects are greatly acknowledged for their support
and guidance.
My sincere thanks to Dr. Surjit Singh and Dr. Jim Rogerson for proof reading this
work.
Finally, my greatest appreciation goes to my parents, my wife Sambhavi and my son
Sarvesh. Thank you very much for all your support.

















CONTENTS

LIST OF FIGURES ................................................................................................................ V
LIST OF TABLES ................. IX
NOMENCLATURE ............................................................................................................... IX
SUMMARY .......................................................................................................................... XIII
KURZFASSUNG ................ XXI

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

2. OVERVIEW OF OXY-COAL COMBUSTION TECHNOLOGY ................................ 5
2.1. OPTIONS FOR CO REDUCTION ........................................... 5 2
2.1.1. Post-Combustion Capture ..................................................... 7
2.1.2. Pre-Combustion Capture ...................................................... 8
2.1.3. Oxy-Coal Combustion .......................................................... 9
2.2. THE OXY-COAL COMBUSTION PROCESS ....................... 12
2.2.1. History and Status ............................................................................................... 12
2.2.2. Techno-Economic Review .................. 14
2.2.3. Possible Configurations of an Oxy-Coal Combustion Plant ............................... 18

3 COMBUSTION AND EMISSION BEHAVIOUR DURING OXY-COAL
COMBUSTION ................................................................................................................. 23
3.1. COMBUSTION BEHAVIOUR DURING OXY-COAL COMBUSTION ............... 23
3.2. EMISSION BEHAVIOUR DURING OXY-COAL COMBUSTION ...................... 26
3.2.1. CO Concentration .............................................................................................. 26 2
3.2.2. Nitrogen Oxide Emission .................... 26
I 3.2.3. Reduction of Nitrogen Oxide during Oxidant Staging ....................................... 31
3.2.4. SO Emission ...................................................................... 37 2
3.2.5. CO Emission ....................................... 41

4. EXPERIMENTAL SET-UP AND PARAMETERS ....................................................... 43
4.1. EXPERIMENTAL SET-UP ...................................................... 43
4.1.1. Description of the 20 kW Once Through Furnace .............................................. 43
4.1.2. Burner Configuration .......................................................... 45
4.1.3. Fuel-Feeding System ........................................................... 46
4.1.4. Oil Cooled Sampling Probe and Suction Pyrometer for Gas Temperature
Measurement ....................................................................................................... 47
4.1.5. Burnout Oxidant Probe ....................................................................................... 48
4.1.6. Air Supply System .............................. 49
4.1.7. O /CO Supply and Mixing System .................................................................... 49 2 2
4.1.8. Standard Flue Gas Analysis ................ 50
4.1.9. FTIR for HCN and NH Measurement ............................................................... 51 3
4.1.10. H S Analyser ....................................................................... 52 2
4.2. FUEL AND ASH CHARACTERISATION .............................................................. 52
4.2.1. Analysis Methods ................................................................ 52
4.2.2. Analysis of the Coals and Char used .................................. 53
4.3. EXPERIMENTAL PARAMETERS .......................................... 54

5. COMBUSTION AND EMISSION BEHAVIOUR DURING UN-STAGED
COMBUSTION ................................................................................................................. 57
5.1. RESULTS .................. 57
5.1.1. Combustion Behaviour during O /CO Combustion .......................................... 58 2 2
II 5.1.2. Combustion Behaviour in the Gas Phase ............................................................ 66
5.1.3. Emission Behaviour during O /CO Combustion ............... 69 2 2
5.2. SUMMARY OF RESULTS ....................................................................................... 74

6. REDUCTION OF NITRIC OXIDE BY OXIDANT STAGING DURING OXY-COAL
COMBUSTION ................................................................................................................. 77
6.1. RESULTS .................. 77
6.1.1. NO Formation Mechanism in a Fuel Rich Environment ................................... 78 x
6.1.2. NO Emission Rate at the Furnace End .............................................................. 87 x
6.2. SUMMARY OF RESULTS ....................................................... 92

7. FATE OF RECYCLED NITROGEN OXIDE DURING OXY-COAL
COMBUSTION ................................................................................................................ 95
7.1. RESULTS .................. 95
7.1.1. Fate of NO Injected via the Burner ..................................................................... 96
7.1.2. Fate of NO Injected via the Over-Fire Port ....................... 105
7.1.3. Overall Reduction of Recycled NO and its Implication during O -RFG 2
Combustion ....................................................................................................... 107
7.2. SUMMARY OF RESULTS ..................................................................................... 110

8. FATE OF SULPHUR DURING OXY-COAL COMBUSTION ................................. 113
8.1. RESULTS ................................................................................................................ 113
8.1.1. Behaviour of Injected SO in the Radiative Section of the Furnace ................. 114 2
8.1.2. Behaviour of Injected SO in the Convective Section/Flue Gas Path of the 2
Furnace .......................................................................................................................... 116
8.1.3. SO and H S Formation Mechanism in O /CO Environment ......................... 122 2 2 2 2
III 8.1.4. SO and H S Formation Mechanism in O /RFG Environment ......................... 126 2 2 2
8.2. SUMMARY OF RESULTS ..................................................................................... 129

9. SUMMARY, CONCLUSIONS AND RECOMMENDATIONS ................................. 131
9.1. SUMMARY OF ACCOMPLISHED TASKS ......................................................... 131
9.2. CONCLUSIONS ...................................................................... 134
9.3. LIMITATIONS AND RECOMMENDATIONS ..................................................... 139

REFERENCES ..................................................................................................................... 143
APPENDIX A: DEFINATION OF UNIQUE TERMS 159
APPENDIX B: CROSS SENSITIVITY OF THE ANALYSERS USED ........................ 169
IV LIST OF FIGURES

Figure 2.1 Options for CO capture ..................................................................................... 7 2
Figure 2.2 Schematic of oxy-coal combustion technology ................ 10
Figure 2.3 Configuration of an advanced supercritical pulverised fuel oxy-combustion
plant with CO capture ..................................................................................... 19 2
Figure 3.1 Summary of NO emissions reported in open literatures ................................... 28
Figure 3.2 Simplified path of homogeneous NO formation .............. 32
Figure 3.3 Schematic of oxidant staging ............................................................................ 34
Figure 4.1 Schematic of the 20 kW once through furnace ................. 44
Figure 4.2 Dimensions of the burner openings (A) for coal combustion, (B) for natural gas
combustion and (C) burner quarl ...................................................................... 45
Figure 4.3 Typical calibration curve of the fuel feeding unit ............ 46
Figure 4.4 Dimensions and position of oil-cooled probe and suction pyrometer illustrating
(A) gas and solid sampling by oil-cooled probe (B) gas temperature
measurement by suction pyrometer .................................................................. 48
Figure 5.1 Axial (A) O , (B) NO (C) SO and (D) CO concentration profiles during air-2 , 2
blown, OF21 and OF27 combustion for a medium volatile bituminous coal,
Klein Kopje ....................................................................................................... 59
Figure 5.2 Axial CO concentration profiles during air-blown, OF21 and OF27 combustion
for Lausitz brown coal ...................................................................................... 61
Figure 5.3 Axial (A) C, (B) H, (C) N and (D) S fractions in the ash/char collected during
air-blown and OF27 combustion, for a medium volatile bituminous coal, Klein
Kopje and the Lausitz brown coal .................................................................... 62
Figure 5.4 Axial flame/gas temperature profiles during air-blown and OF27 combustion
for a medium volatile bituminous coal, Klein Kopje ....................................... 63
V Figure 5.5 Comparison of axial (A) O , (B) NO, (C) SO and (D) CO concentration 2 2
profiles during OF27 combustion, for all 4 coals ............................................ 65
Figure 5.6 Axial (A) O , (B) NO, (C) CO and (D) CO concentration profiles during air-2 2
blown and OF27 combustion with natural gas ................................................ 67
Figure 5.7 Emission rate at the furnace end during combustion with (A) medium volatile
bituminous coal, Klein Kopje and (B) Lausitz brown coal ............................. 70
Figure 5.8 Comparison of (A) NO emission rate, (B) SO emission rate, (C) conversion x 2
of fuel-N to NO and (D) conversion of fuel-S to SO during air-blown and 2
OF27 combustion for all four coals investigated ............................................. 72
Figure 5.9 Comparison of un-burned carbon in the ash [%] and NCV loss [%] during air-
blown and OF27 combustion ............................................................................ 74
Figure 6.1 Axial concentration profile for a medium volatile bituminous coal, Klein Kopje
and Lausitz brown coal during air-blown and OF27 combustion for a burner
oxygen ratio of 0.75 and a residence time in reduction zone of 3 seconds ...... 79
Figure 6.2 Overall fuel-NO reduction route during fuel-rich condition ............................ 81
Figure 6.3 Comparison of (A) NO, (B) HCN and (C) CO concentration profiles during
combustion with a medium volatile bituminous coal Klein Kopje for different
burner oxygen ratios and a residence time in reduction zone of 3 seconds ...... 82
Figure 6.4 Comparison of (A) NO, (B) HCN, (C) NH and (D) CO concentration profiles 3
during combustion with Lausitz brown coal for different burner oxygen ratios
and a residence time in reduction zone of 3 seconds ........................................ 84
Figure 6.5 Comparison of NO and CO concentration profiles of all four coals during
combustion with a burner oxygen ratio of 0.75 and a residence time in the
reduction zone of 3 seconds .............................................................................. 86
VI