DEVELOPMENT OF CHEMICAL ABSORPTION SYSTEM FOR BIOGAS UPGRADING

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DEVELOPMENT OF CHEMICAL ABSORPTION SYSTEM FOR BIOGAS UPGRADING

BY

FOUAD R. H. ABDEEN

A thesis submitted in fulfilment of the requirement for the degree of Doctor of Philosophy (Engineering)

Kulliyyah of Engineering

International Islamic University Malaysia

JUNE 2018

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ii

ABSTRACT

Biogas has been given a great attention recently as a fossil fuel supplement. Produced via anaerobic digestion, biogas is usually composed of 40 – 60 % methane, 40 – 60 % carbon dioxide (CO2), and 100 – 3,000 ppm of hydrogen sulfide (H2S). The presence of CO2 and H2S decreases the quality of biogas as an efficient and safe fuel. Several methods have been employed for the purpose of upgrading and purifying biogas.

Chemical absorption is believed to be among the most potential for the removal of the two main impurities present in biogas H2S and CO2. The presence of large fraction of CO2 in biogas limits its utilization to power generation at low energy-conversion efficiency. This thesis aims at investigating and extending the knowledge required for the implementation of chemical absorption of CO2 for biogas upgrading. A laboratory- scale packed-column apparatus containing efficient and cheap packing material (plastic bioball) was designed and fabricated to perform the experimental work in this thesis. Initial absorption runs were performed to select the best solvent type and concentration between 10 – 50 % monoethanolamine (MEA), 4 – 12 % aqueous sodium hydroxide, and 5 – 25 % aqueous ammonia. 20 – 30 % MEA has shown the highest ability for producing methane-rich biogas using the absorber-column apparatus. The fabricated absorber apparatus was used to optimize the biogas upgrading process using MEA as a scrubbing solvent. The statistical analysis and optimization process were carried out varying MEA concentration in the range 20 – 30 % and at ranges of gas flow rate 4 – 8 kg/h, solvent flow rate 40 – 010 kg/h and column active height 100 – 200 cm. Box-Behnken design of experiment was selected, and the statistical analysis and the optimization of the chemical absorption process were performed using Design Expert (v10) software. Statistical solutions of optimum sets of conditions were obtained and verified experimentally. The optimization process have resulted in producing upgraded biogas with up to 95.7 % (98.7 % after drying) methane content and with enhanced CO2 loading capacity up to 4.8 mole- CO2/kg-MEA. Calculations were performed to scale up the laboratory scale absorber apparatus to an industrial scale apparatus. The Acid Gas property package of Aspen Hysys (v8.8) simulation software was verified using experimental data and used to analyze the performance of the industrial scale version of the absorber apparatus.

Integrated designs were built for three biogas upgrading systems using MEA and aqueous ammonia as scrubbing solvents. The simulation results have demonstrated the ability of producing upgraded biogas containing less than 0.5 % CO2 and more than 99.5 % methane after drying. Among the three suggested designs, MEA-based system with complete solvent regeneration and recycle has shown highest energy demand with 3.8 MW. However, the specific energy demand of the reboiler of the system was calculated to be 4.93 MJ per kg-CO2 removed which is lower than the value of 5.57 recently reported in literature. Aqueous ammonia-based system and hybrid ammonia- amine system have shown to require less energy, estimated with 240 and 302 kW, respectively. However, the production of a considerable amount of ammonia-rich solvent through these systems is considered a major drawback. The future studies performed in the field should verify the possible strategies for converting theses ammonia-rich liquids to valuable products such as ammonia-based fertilizers.

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iii

ثحبلا ةصلاخ

ABSTRACT IN ARABIC

ةقيرطب ةداع يويلحا زاغلا جاتنا متي .يروفحلأا دوقولل ليدبك ةيرخلأا ةنولآا في ايربك امامتها يويلحا زاغلا ىقلا دقل و ةيئاوهلالا يرمختلا ي

نم نوكت – 01

% 01 و ،ناثيلما نم – 01

% 01 ديسكأ نيثا نوبركلا

) (CO

2

، 011

– ينجورديلها ديتيبرك نم نويللما في ءزج 0111

S) (H

2

دوجو برتعي.

CO

2

و S H

2

علا نم ت تيلا لماو نم للق

قرط ةدع مادختسا تم دقل .نمآو لاعف دوقوك يويلحا زاغلا ةدوج لجا نم

.يويلحا زاغلا ةيقنتو ينستح دعي

لاا ااتم

رثكأ ينب نم يئايميكلا في ةيلاعف قرطلا

ةلازإ S , H

2

CO

2

قاطن ىلع ااتما زاهج ميمات تم ،ةساردلا هذه في .

زاغلا ةيقنت ةيلمع ىلع نوبركلا ديسكا نياثل يئايميكلا ااتملاا ةيلمع فورظو لماوع يريغت رثا ةسارد ضرغل برتخلما ينملاوناثياونوم ينب بيذم لضفأ رايتخلا ااتما تايلمع ةدع ءارجا تم دقل .يويلحا (MEA)

، لولمحو

مويدوالا ديسكورديه و ،

اينوملأا لولمح ترهظأ دقو .

ةدام ىلع ةردق ىلعأ ينملاوناثياونوم يويلحا زاغلا جاتنإ

نيغلا

ناثيلما زاغب .

زاغلا ةيقنت ةلمع ينستح لجا نم ةساردلا هذه في هعينات تم يذلا ااتملاا واهج مادختسا تم دقو

ينملاوناثياونوم ةدام مادختسبا يويلحا .

امك لك يريغتب كلذو ةيقنتلا ةيلمعل ينستحو يئااحا ليلبتح ةيلمع ءارجا تم

ينب ينملاوناثياونولما ةدام زيكرت :نم – 01

% 01 ينب زاغلا قفدت لدعم و ، - 0

8 قفدت لدعمو ،ةعاس / مجك

لما ينب بيذ – 01

011 ةعاس / مجك و،

عافترا ينب ااتملاا دومع – 011

.مس 011 تم دقو دامتعا ات ميم

Box-Behnken

و يئااحلاا ليلحتلا تييلمع في يئايميكلا ااتملاا ةيلمع ينستح

جمنارب مادختسبا

Design

Expert (version 10)

. .ةيبرخلما ةبرجتلبا اهنم دكأتلا تم امك ااتملاا ةيلمعل ىلثلما فورظلا ىلع لوالحا تمو

يويلحا زاغلا جاتنإ في ينسحتلا ةيلمع ترفسأ دقو ن ةجردب

لات ءاق لىإ

٪ 7.59 عمو ناثيلما ىوتمح ااتما ةعس

لىإ لات . 8

لوم 0 CO

2

/ مغك .ينملاوناثياونوم كلذ لىا ةفاضلإبا

ميمات لجا نم ةمزلالا تبااسلحا ءارجا تم

ذ يئايميك ااتما زاهج و

ىمست جذانم ةمزح نم ققحتلا تم دقو .بركا ةعس Acid Gas

جمنارب في ةنمضتلما

Aspen Hysys (v8.8)

مادختسا تم ثم ةاكالمحا جمنارب نم اتهلايثبم ةيبرخلما براجتلا جئاتن ةنراقبم ةاكحملل

قاطن ىلع يئايميكلا ااتملاا ماظن ءادأ ليلحتل ةاداك ةمزلحا هذهو جمنابرلا اذه يعانص

. دقو ميماات تينب

ت ةيلمعل ةلماكتم لأاو ينملاوناثياونولما تيدام مادختسبا يويلحا زاغلا ةيقن

تابيذمك ءالمبا ةلوللمحا اينوم .

جئاتنل اقفو

،ةاكالمحا براقي ام ىلع يوتيح ىقنم زاغ جاتنا تم دقف

٪ 775.

و ناثيلما نم

٪ 15.

CO

2

. ةقاطلا ةميق تردق دقو

ةيقنتلا ةيلمع في ةكلهتسلما ةيلاجملاا ينملاوناثياونوم ةدام ادختسبا

براقي ابم اجيم 058

طاو ةقاطلا تردق دقو .

هتسلما براقي ابم كلهتسلما بيذلما ديدتج ةيلمع في ةكل لوج اجيم 0570

نم مارغوليك لكل نوبركلا ديسكأ نيثا

وهو

نع لقي ام لا

ةميق ــــــــب ةردقلماو ةقباسلا تاساردلا نم اهيلا لصولا تم تيلا . .5.9

كلذبو زاغلا ةيقنت ةيلمع نا تابثا تم

لا ةيمك ثيح نم ةيدمج ةقيرطلا هذبه يويلحا .ةكلهتسلما ةقاط

ءالمبا ةلوللمحا اينوملاا نم ةيربك ةيمك جاتنا ناف ،كلذ عمو

ةيقنتلا ةيلمعل ابحاام بيذمك اينوملاا ىلع ةدمتعلما

ناف ،كلذ ىلع ءانب .ةيلمعلا هذه في يسيئر بيع برتعي

زكرت نا بيج لالمجا اذه في ةيلبقتسلما تاساردلا يلع

حتب ةلكشلما هذله ةيجيتاترسا لولح لثم ةدئاف تاذ داوم لىا اهليو

.اينوملاا نم ةعنالما تادامسلا

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APPROVAL PAGE

The thesis of Fouad R H Abdeen has been approved by the following:

_____________________________

Maizirwan Mel Supervisor

_____________________________

Mohammed Saedi Jami Co-Supervisor

_____________________________

Sany Izan Ihsan Co-Supervisor

_____________________________

Ahmad Faris Ismail Co-Supervisor

_____________________________

Maan Al Khatib Internal Examiner

_____________________________

Mohamed Kheireddine Bin Taieb Aroua External Examiner

_____________________________

Rosli Mohd Yunus External Examiner

_____________________________

Radwan Jamal Yousef Elatrash Chairman

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v

DECLARATION

I hereby declare that this thesis is the result of my own investigations, except

where otherwise stated. I also declare that it has not been previously or concurrently submitted as a whole for any other degrees at IIUM or other institutions.

Fouad R H Abdeen

Signature ... Date ...

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vi

COPYRIGHT

INTERNATIONAL ISLAMIC UNIVERSITY MALAYSIA

DECLARATION OF COPYRIGHT AND AFFIRMATION OF FAIR USE OF UNPUBLISHED RESEARCH

THE IMPACT OF MOBILE INTERFACE DESIGN ON INFORMATION QUALITY OF M-GOVERNMENT SITES

I declare that the copyright holders of this thesis are jointly owned by the student and IIUM.

No part of this unpublished research may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise without prior written permission of the copyright holder except as provided below

1. Any material contained in or derived from this unpublished research may be used by others in their writing with due acknowledgement.

2. IIUM or its library will have the right to make and transmit copies (print or electronic) for institutional and academic purposes.

3. The IIUM library will have the right to make, store in a retrieved system and supply copies of this unpublished research if requested by other universities and research libraries.

By signing this form, I acknowledged that I have read and understand the IIUM Intellectual Property Right and Commercialization policy.

Affirmed by Fouad R H Abdeen

……..……….. ………..

Signature Date

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vii

ACKNOWLEDGEMENTS

In the Name of Allah, the Beneficent, the Merciful. Praise is to Allah, the Almighty, on whom ultimately we depend for sustenance and guidance. My utmost gratitude goes to Him, for He only made this study possible, and gave me the knowledge and strength to carry it out to the best of my knowledge and ability. I would like to express my sincere gratefulness to my supervisors Assoc. Prof. Dr. Maizirwan Mel, Assoc.

Prof. Dr. Mohammed Saedi Jami, Assoc. Prof. Dr. Sany Izan Ihsan and Prof. Dr.

Ahmad Faris Ismail for guiding me to successfully accomplish this study, and for sharing their extensive knowledge on the subject matter.

I am exceptionally thankful to my wife, parents, brothers, and sisters for their continuous encouragement and support during the course of this study. Their motivation was the fuel that kept me going, and got me through the difficulties and hard times.

Last but not least, I would like to thank everyone who in one way or another contributed to my study.

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CHAPTER TWO: LITERATURE REVIEW ... 10

2.1 Introduction... 10

2.2 Overview on Biogas ... 11

2.2.1 Biogas Demand ... 11

2.2.2 Biogas Production Process ... 12

2.2.3 Biogas Utilization ... 14

2.3 Biogas Upgrading and Purification Techniques ... 15

2.3.1 Water Scrubbing ... 16

2.3.2 Pressure Swing Adsorption ... 17

2.3.3 Biological Treatment... 18

2.3.4 Membrane Separation ... 18

2.3.5 Cryogenic Separation ... 19

2.3.6 Chemical Absorption ... 21

2.4 Absorption Systems Design Considerations ... 22

2.4.1 Mass Transfer Considerations ... 23

2.4.2 Absorption Column Design Considerations ... 25

2.4.2.1 Packing Type and Column Dimensions Considerations .. 28

2.4.2.2 Flooding Velocity and Pressure Drop Considerations ... 30

2.5 Chemical Absorption of Carbon Dioxide for Biogas Upgrading ... 32

2.5.1 Amine Scrubbing ... 33

2.5.1.1 Theory and Background ... 33

2.5.1.2 Amines Regeneration ... 35

2.5.1.3 Amines Degradation ... 36

2.5.1.4 Corrosion ... 37

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2.5.1.5 Improved Processes ... 38

2.5.1.6 Cases of Amine Scrubbing for Biogas Upgrading ... 38

2.5.2 Caustic Solvents Scrubbing ... 42

2.5.2.2 Solvent Regeneration ... 44

2.5.2.3 Mineral Carbonation ... 45

2.5.2.4 CO2 Absorption Using Carbonate Solutions ... 47

2.5.2.5 Cases of Caustic Scrubbing and Mineral Carbonation for Biogas Upgrading ... 48

2.5.3 Aqueous Ammonia ... 53

2.5.3.2 Aqueous Ammonia for CO2 Absorption ... 53

2.5.3.3 Aqueous Ammonia for Biogas Upgrading ... 54

2.6 Statistical Analysis and Optimization ... 56

2.7 Chemical Absorption Process Scale Up and Simulation ... 59

2.7.1 Packed Column Absorption Process Scale up ... 59

2.7.2 Simulation of CO2 Absorption and Biogas Upgrading Processes ... 60

2.8 Chapter Summary ... 65

CHAPTER THREE: MATERIALS AND METHODS ... 68

3.2 Materials and Chemicals Preparation ... 68

3.2.1 Packing Material ... 68

3.2.2 Biogas and Absorbing Solvents Preparation ... 70

3.2.3 Gas Analyzer ... 71

3.3 Equations and Apparatus Design Considerations ... 72

3.3.1 Packed Column Dimensions ... 72

3.3.2 Mass Balance and Flow Rates Determination ... 73

3.3.3 Summary of Apparatus Design Considerations ... 76

3.4 Experimental Procedure... 78

3.5 Solvent Type and Concentration Selection Method ... 79

3.6 Data Analysis ... 80

3.7 Statistical Analysis and Optimization Method ... 81

3.8 Scale Up Method and Simulation Basis ... 84

3.8.1 Scale Up Method ... 84

3.8.2 Simulation Software and Basis ... 85

CHAPTER FOUR: RESULTS AND DISCUSSION ... 89

4.2 Absorption System Design and Fabrication ... 89

4.2.1 Fabrication of Absorber Column Apparatus ... 90

4.2.2 Flow Rates Range Calculations Results ... 92

4.3 Solvent Type and Concentration Determination Results... 97

4.4 Biogas Upgrading Using MEA Experimental, Statistical Analysis and Optimization Results ... 103

4.4.1 Biogas Upgrading Using MEA Experimental Results ... 104

4.4.2 Statistical Analysis Results ... 107

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x

4.4.2.1 Model Selection and Evaluation ... 108

4.4.2.2 Factors Effects and Interactions ... 119

4.4.3 Optimization Results ... 126

4.4.3.1 Optimization Criteria ... 127

4.4.3.2 Optimum Solutions ... 128

4.4.3.3 Experimental Verification of Optimum Solutions... 131

4.4.4 Important Findings Drawn from Biogas Upgrading Using MEA in Laboratory-Scale ... 132

4.5 Simulation of Industrial Scale Biogas Upgrading Process ... 133

4.5.1 Verification of Acid Gas Property Package ... 134

4.5.2 Scale Up of Packed Column ... 139

4.5.3 Simulation of Integrated Biogas Upgrading Processes ... 140

4.5.3.1 Biogas Upgrading Using MEA Simulation Results ... 141

4.5.3.2 Biogas Upgrading Using Aqueous Ammonia Simulation Results ... 156

4.5.3.3 Biogas Upgrading Using Hybrid Ammonia and Amine System Simulation Results ... 164

CHAPTER FIVE: CONCLUSIONS AND RECOMMENDATIONS ... 175

5.1 Conclusions ... 175

5.2 Recommendations... 179

REFERENCES ... 181

APPENDIX A: APPARATUS DETAILS AND CALCULATIONS ... 198

APPENDIX B: SCALE UP CRITERIA AND CALULATIONS ... 201

APPENDIX C: SIMULATION SOFTWARE SET UP DETAILS ... 202

APPENDIX D: ACHIEVEMENTS ... 205

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LIST OF TABLES

Table 2.1 Methane yield for a list of feedstock types 13 Table 2.2 Composition in v/v % and low heat value (LHV) of the gases

used as fuel

15

Table 2.3 Overview on energy demand and methane losses of different upgrading technologies

22

Table 2.4 HOG based on packing size and type 29

Table 2.5 Published cases implementing amine scrubbing for biogas upgrading

41

Table 2.6 Published cases implementing caustic scrubbing for biogas upgrading

49

Table 2.7 Published cases implementing BABIU and AwR. 51 Table 2.8 Published cases implementing aqueous ammonia scrubbing

for biogas upgrading

55

Table 3.1 Characteristics of the packing material 69

Table 3.2 Solvents prepared in five different concentrations 71 Table 3.3 Summary of equations and apparatus design consideration 76

Table 3.4 Set of solvent type selection experiments 80

Table 3.5 Box-Behnken design of experiment for the four process parameters with their coded levels

83

Table 4.1 Packing height calculated based on the aimed CO2

concentration in upgraded biogas (y2)

91

Table 4.2 Characteristics of the packed column 91

Table 4.3 CO2 mole fraction and mole ratio in entering and exiting streams

93

Table 4.4 Properties of the different solutions estimated using Aspen Hysys software

95

Table 4.5 Flooding values for different values of liquid and gas flow rates

96

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Table 4.6 Upgraded biogas composition for various types of solvents and concentrations

98

Table 4.7 Actual values of four process factors 104

Table 4.8 Set of experiments including verification runs and their actual values

106

Table 4.9 Sample calculation of using Equations 3.6 – 3.8 106 Table 4.10 A comparison of the actual versus predicted values for the

verification runs using three different models

113

Table 4.11 Analysis of variance of the modified quadratic model for the methane % response

114

Table 4.12 Final equation in terms of actual factors for predicting methane %

114

Table 4.13 Analysis of variance of the modified quadratic model for the CO2 % response

116

Table 4.14 Final equation in terms of actual factors for predicting CO2 % 116 Table 4.15 Analysis of variance of the modified quadratic model for the

CO2 loading capacity response

118

Table 4.16 Final equation in terms of actual factors for predicting CO2

loading capacity

118

Table 4.17 Optimization criteria 127

Table 4.18 Optimum solutions and their predicted values 131 Table 4.19 The actual results for the optimum solutions 132

Table 4.20 A summary of scale up calculation results 139

Table 4.21 Specifications of the absorber and regenerator columns used for simulating biogas upgrading using MEA

142

Table 4.22 Properties of material streams involved in MEA-based system simulation

153

Table 4.23 Composition of main material streams involved in MEA- based system simulation

154

Table 4.24 Properties of material streams involved in the ammonia-based system simulation

162

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Table 4.25 The composition of the streams involved in the ammonia- based system simulation

163

Table 4.26 Properties of material streams involved in the hybrid system simulation

169

Table 4.27 The composition of the streams involved in the hybrid system simulation

170

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LIST OF FIGURES

Figure 1.1 A flow chart of main steps in the research activities 7 Figure 2.1 Gas absorber using a solvent regenerated by stripping 27 Figure 2.2 Generalized pressure drop correlation published in 31

Figure 3.1 Plastic bioball packing material 69

Figure 3.2 Portable infrared gas analyzer COMBIMASS GA-m manufactured by Binder Group (Germany)

71

Figure 3.3 Material balance diagram for a countercurrent absorption column

74

Figure 3.4 Equilibrium curve and operating line for absorption column 75 Figure 3.5 Flow sheet of the absorber column apparatus 77 Figure 4.1 CH4 and CO2 v/v % in biogas upgraded using MEA 98 Figure 4.2 CH4 and CO2 v/v % in biogas upgraded using aqueous NaOH 100 Figure 4.3 CH4 v/v % in biogas upgraded using aqueous ammonia 101 Figure 4.4 CO2 and NH3 v/v % in biogas upgraded using aqueous

ammonia

102

Figure 4.5 The normal probability plot of residuals for methane % response using model 1

109

Figure 4.6 A plot of residuals versus experimental runs using model 1 110 Figure 4.7 The normal probability plot of residuals for methane %

response using model 2

111

Figure 4.8 A graph of the actual methane % values versus the values predicted by model 2

112

Figure 4.9 A graph of the actual CO2 % values versus the values predicted by the selected model

115

Figure 4.10 A graph of the actual CO2 loading capacity values versus the values predicted by the model

117

Figure 4.11 The effect of process factors on the methane % response 120

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Figure 4.12 (a) Interaction between gas flow and liquid concentration factors on methane % response. (b) Response surface plot showing contour lines on the “gas flow”-“liquid concentration” plane

121

Figure 4.13 Interaction effects on methane % response. (a) Interaction between liquid flow and liquid concentration. (b) Interaction between gas flow and column height

122

Figure 4.14 The effect of process factors on the CO2 loading capacity response

124

Figure 4.15 Interaction effects on CO2 loading capacity between (a) gas flow and column height, (b) liquid flow and column height, (c) liquid concentration and column height and (d) gas flow and liquid flow

125

Figure 4.16 Response surface plot for methane % as a function of gas flow and liquid flow

128

Figure 4.17 Response surface plot for CO2 loading capacity as a function of gas flow and liquid flow

129

Figure 4.18 Overlay plot for the methane % above 95 and CO2 loading capacity above 4.5

130

Figure 4.19 Process flow diagram for a simple absorber column using Aspen Hysys simulation software

135

Figure 4.20 Simulation versus experimental composition of biogas upgraded using different concentrations of MEA

136

Figure 4.21 Simulation versus experimental CH4 percentages in biogas upgraded using different concentrations of aqueous ammonia

137

Figure 4.22 Simulation versus experimental CO2 and NH3 percentages in biogas upgraded using different concentrations of aqueous ammonia

138

Figure 4.23 PFD of integrated design for biogas upgrading using Aspen Hysys

141

Figure 4.24 Methane mole % as a function of reboiler duty at different MEA mass flow rate

145

Figure 4.25 CO2 mole % as a function of reboiler duty at different sets of MEA mass flow rate

146

Figure 4.26 Effect of reboiler duty and MEA solvent flow on water loss 148

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Figure 4.27 Effect of reboiler duty and MEA solvent flow on MEA loss 148 Figure 4.28 Effect of reboiler duty and solvent circulation rate on cooler

duty

149

Figure 4.29 CH4 and CO2 mole % as a function of number of stages 151 Figure 4.30 Energy consumed in MEA-based biogas upgrading process 155 Figure 4.31 A process flow diagram of aqueous ammonia dual absorption

column system

157

Figure 4.32 Methane and CO2 mole percentage in scrubbed gas at different solvent flow rates

158

Figure 4.33 Effect of water temperature on upgraded gas composition 160 Figure 4.34 Effect of number of stages on upgraded gas composition 161 Figure 4.35 PFD of hybrid ammonia and MEA absorption system 166 Figure 4.36 Methane and water mole percentage at different solvent flow

rate

167

Figure 4.37 Water loss and total energy as a function of MEA flow 168

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LIST OF ABBREVIATIONS

MEA monoethanolamine

ppm parts per million

LHV low heating value

HPWS highly pressurized water scrubbing PSA pressure swing adsorption

DEA diethanolamine

DGA diglycolamine

TEA triethanolamine

MDEA methyldiethanolamine

PZ piperazine

DMcT 2,5-dimercapto-1,3,4-thiadiazole DTPA diethylenetriamine pentaacetic acid HEDP hydroxyethylidenediphosphonic acid BABIU bottom ash for biogas upgrading AwR alkaline with regeneration

BA bottom ash

MSWI BA municipal solid waste incinerator bottom ash APC air pollution control

SSS stainless steel slag

AOD argon oxygen decarburization M molar concentration, mole per liter DOE design of experiment

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xviii OFAT one factor at a time method ANOVA analysis of variance

NRTL non-random-two-liquid thermodynamic model

e-NRTL electrolyte non-random-two-liquid thermodynamic model UNIQUAC universal quasi chemical model

PR Peng-Robinson equation of state

PFD process flow diagram

mbar-g millibar gauge pressure bar-g bar gauge pressure

kW kilo watt

MW mega watt

kJ kilo Joule

MJ mega Joule

GJ giga Joule

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xix

LIST OF SYMBOLS

P partial pressure above solution Caq concentration in liquid

KH Henry’s constant

ΔH enthalpy change

Gm gas molar flow

Lm liquid molar flow

xi mole fraction of solute in liquid yi mole fraction of solute in gas Gmˈ solute-free gas flow rate Lmˈ solute-free liquid flow rate Xi mole ratio of solute i in liquid Yi mole ratio of solute i in gas Z packing height of the column NOG number of theoretical plates HOG height of transfer unit

SF safety factor

FLV x-axis term in the pressure drop correlation K4 y-axis term in the pressure drop correlation

Lw liquid mass flow rate per cross sectional area (kg/m²s) Vw gas mass flow rate per cross sectional area (kg/m2s) ρV gas density (kg/m³)

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xx ρL liquid density (kg/m³) Fp packing factor (m^-1)

μL liquid viscosity (Pa.s or Ns/m²)

𝑥_{𝑚𝑎𝑠𝑠} mass fraction of pure solvent in the scrubbing liquid 𝐿_{𝑚𝑎𝑠𝑠} mass flow of scrubbing liquid (kg/h)

L/G Liquid to gas flow ratio

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1

CHAPTER ONE INTRODUCTION

1.1 BACKGROUND OF THE STUDY

Fossil fuel supplements have been of great interest to researchers recently due to the depletion and increasing price of the conventional energy sources. In particular, attention has been given to biogas production from anaerobic digestion (Qian, Sun, Ju, Shan, & Lu, 2017). Biogas is being produced worldwide via anaerobic digestion of various types of biological wastes including vegetables and fruits wastes, animal dung and droppings, industrial wastewater, municipal waste, land fill and many others (Dieter & Angelika, 2008; Vindiš, Stajnko, Berk, & Lakota, 2012).

The product of the anaerobic digestion of biomass is a gas mixture composed mainly of methane (CH4), carbon dioxide (CO2), water vapor (H2O), hydrogen sulfide (H2S) and trace amounts of other gases such as nitrogen (N2) and hydrogen (H2) (Gueguim Kana, Oloke, Lateef, & Adesiyan, 2012). Being environmentally friendly and cheap, biogas has been raised as one of the most important supplements of conventional energy sources for electricity generation (Kapdi, Vijay, Rajesh, &

Prasad, 2005). However, biogas quality should be improved prior to its utilization in fields such as grid injection and vehicle fuel.

Biogas purification and upgrading processes are usually performed for the removal of contaminants such as H2S and CO2 to increase the quality of the biogas.

Most of the researches performed for biogas cleaning were focused on H2S removal for its safe utilization in power generation. However, biogas upgrading processes by the removal of CO2 is greatly important if the biogas is to be utilized as a valuable vehicle fuel or injected to gas grid (Awe, Zhao, Nzihou, Minh, & Lyczko, 2017). In

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addition, biogas upgrading processes still require intensive research to improve their techno-economic performance. For most of the common biogas upgrading techniques, the upgrading process is usually operated at energy extensive non-ambient conditions such as elevated pressures and decreased temperatures (Ward, Hobbs, Holliman, &

Jones, 2008).

Development of energy-efficient biogas upgrading process is considered an important step towards increasing the quality of biogas as an alternative valuable fuel.

This research aims at investigating existing techniques used in the upgrading and purification of biogas and suggesting improvements for the purpose of performing biogas upgrading in the optimum conditions. More focus in this research is given to upgrading biogas using chemical absorption methods at ambient temperature and low pressure.

1.2 PROBLEM STATEMENT

Biogas production by anaerobic digestion of organic matter has attracted the attention of governments as well as individuals in numerous countries around the world. For instance, it is estimated that more than 50 % of palm oil mills in Malaysia have established biogas plants (Chin, Poh, Tey, Chan, & Chin, 2013). The biogas plants established in the aforementioned field perform biogas cleaning for the purpose of producing H2S-free gas. However, various developed countries have imposed new rules demanding and encouraging biogas upgrading processes by the removal of CO2

for the purpose of facilitating its utilization as a valuable fuel source in vehicles or gas girds (Awe et al., 2017). In addition, most of the published work on biogas treatment investigated H2S removal process without targeting CO2 removal. Whereas, the presence of CO2 in biogas decreases the quality of biogas as an efficient fuel and

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limits its utilization to power generation at low energy-conversion efficiency. This is due to the fact that the combustion quality of the fuel biogas decreases with the presence of CO2 since it is inert in terms of combustion. Thus, biogas upgrading by CO2 removal is an important step in improving biogas quality and converting it to methane-rich fuel prior to its utilization as a valuable source of energy.

Several methods have been employed for the purpose of upgrading biogas.

Due to the high fraction of CO2 in biogas, chemical absorption technique is believed to possess distinctive importance over other techniques since it is performed using solvents with relatively high CO2 loading capacity. In fact, most of previously published works have discussed the development of chemical absorption systems using columns packed with expensive material and fixed packing height and operated at non-ambient costly pressures and temperatures. For this, most of the published work on laboratory-scale instruments was not suitable for implementation in the industrial scale. Therefore, there is a lack of finding practical applicability of the use of chemical absorption for the biogas upgrading process at ambient temperature and pressure. Hence, designing and fabricating a laboratory-scale absorber apparatus using cheap and available packing material for implementing biogas upgrading using chemical absorption is greatly important. The fabrication of a laboratory scale apparatus for the manipulation of different process parameters, including the usually hard-to-change factor (column height), is believed to pave the way for industrializing the biogas upgrading process.

Solvent type and concentration are considered to be among the most important factors influencing techniques of chemical absorption of gasses. Most of the published cases on the absorption of CO2 using a chemical solvent are applied to post- combustion carbon capture and natural gas sweetening processes. The CO2-containing

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gas in these applications has different fraction of CO2 when compared to biogas. Thus, due to the lack of experimental data comparing between solvent type and concentration for biogas upgrading, using a laboratory scale apparatus to select between solvent type and concentration is highly essential.

In addition, most of the published cases on optimizing the biogas upgrading and purification by chemical absorption were focused on H2S removal rather than CO2

removal (White, 2012). Therefore, selecting a suitable absorption solvent and performing experimental absorption runs to comprehensively analyze the effects of process factors with the aid of a proper statistical design of experiment is certainly required. Moreover, analyzing the effects of absorption process factors such as column height, solvent concentration and flow rates for the purpose of producing methane-rich biogas with optimum solvent capacity is extremely advantageous for the industrialization of the biogas upgrading process.

Furthermore, currently, numerous software programs have customized packages for simulating the chemical absorption of CO2. However, little work is published on verifying and implementing the recent simulation tools for biogas upgrading. Therefore, it is uniquely valuable to demonstrate the feasibility of biogas upgrading by chemical absorption in industrial scale using a verified and reliable simulation tool.

1.3 RESEARCH OBJECTIVES

The main objective of this study is to upgrade biogas at ambient conditions. However, the specific objectives of the present study are summarized as follows:

1- To design and fabricate a laboratory-scale packed column apparatus for the upgrading of biogas using chemical absorption.

Kulliyyah of

DEVELOPMENT OF CHEMICAL ABSORPTION SYSTEM FOR BIOGAS UPGRADING