This thesis comprises 30 ECTS credits and is a compulsory part in the Master of Science with a Major in Chemical Engineering – Waste Management and Resource Recovery, 120 ECTS credits
No. 2/2009
A LCA Study of Activated Carbon Adsorption and Incineration in Air Pollution Control
Saman Saffarian
ii
A LCA Study of Activated Carbon Adsorption and Incineration in Air Pollution Control
Saman Saffarian, saman.safarian@gmail.com
Master thesis
Subject Category: Technology
University of Borås School of Engineering SE-501 90 BORÅS
Telephone +46 033 435 4640
Examiner: Dr. Peter Therning Supervisor: Dr. Peter Therning
Supervisor, address: University of Borås, School of Engineering SE- 501 90 BORÅS
Client: University of Borås
Date: December 2009
Keywords: Life Cycle Assessment (LCA), Granular Activated Carbon, VOCs incineration, Thermal oxidation, Off- gas treatment, Toluene removal
iii Dedicated to
My parents for their love and endless support
And
My lovely wife, Assal
iv
Acknowledgment
First, I would like to express my warmest gratitude to my supervisor Dr. Peter Therning for his supports and advices. I never would have been able to finish this thesis without his guidance. I would also like to thank Mr. Paul Conlon from Chemviron Carbon/ Calgon Carbon Company for his patience to ask my endless questions and send required information related to process part. Finally, I am indebted to Dr. Peter Bayer from University of Tuebingen, Germany, for his great help on sending the detailed information of his LCA researches.
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Abstract
The main purpose of this thesis was to compare GAC adsorption method, VOCs incineration method and Non-treatment alternative by using LCA to find which method or alternative is environmentally preferable. The LCA framework proposed by ISO 14040 (1997) has been considered in this research. The comparison was made by considering a flue gas contaminated by toluene (with three different concentration 100, 1000, 2000 mg/m3). The plant location where the polluted flue gas is emitted has been assumed to be located in Borås, Sweden. The flow rate of emitted flue gas was 10000m3/hr. The present thesis report contains two main parts.
The results of LCA showed that when the toluene concentration is low (< 100 mg/m3), GAC adsorption method, Non-treatment alternative and VOCs incineration method are respectively preferable from environmental point of view. On the other side, when the toluene concentration of inlet stream is high (>1000 mg/m3), the order of GAC adsorption method, incineration and Non-treatment alternative is more desirable. Furthermore, the results illustrated that as toluene plays the role of fuel as a hydrocarbon, VOCs incineration method is much more suitable when toluene concentration is high due to lower demand on additional fuel. In the other words, high toluene concentration of influent leads to less environmental impact when VOCs incineration method is exploited. Conversely, the environmental impact of GAC adsorption method is increased when the inlet concentration of toluene is escalated.
In overall, the weighted result showed that GAC adsorption method is the most preferable method while Non-treatment alternative is the worst.
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List of Abbreviations
AC Activated Carbon
AP Acidification Potential
BFD Block Flow Diagram
Cis- DCE cis- dichloroethylene
CML Center of Environmental Science, Leiden University, the Netherlands DAR Depletion of Abiotic Resources
DCM Di Chloro Methane
EC European Commission
EDIP Environmental Design of Industrial Products EEA European Environmental Agency
EIA Environmental Impact Assessment EP Eutrophication Potential
EPA Environmental Protection Agency (United States) EPS Environmental Priority Strategies in Product Design
ET Eco Toxicity
FAETP Freshwater Aquatic Eco Toxicity Potential GAC Granular Activated Carbon
GWP Global Warming Potential GWP Global Warming Potential
HT Human Toxicity
IEA Environmental Energy Agency
LCA Life Cycle Assessment
LCI Life Cycle Inventory
LCIA Life Cycle Impact Assessment
LEL Lower Explosive Limit
LP Linear Programming
LU Land Use
MAETP Marine Aquatic Eco Toxicity Potential
MEK Methyl Ethyl Ketone
NMVOC Non-Methane Volatile Organic Compound
NTM Nätverket för Transporter och Milijö (the Swedish Network for Transportation and the Environment)
ODP Ozone Depletion Potential
PAC Powder Activated Carbon
PAH Polycyclic Aromatic Hydrocarbon
PCE Perchloroethylene
POC Photochemical Ozone Creation
POCP Photochemical Ozone Creation Potential
RPM Round Per Minute
RTO Regenerative Thermal Oxidation
SETAC Society of Environmental Toxicology and Chemistry
TCE Trichloroethylene
TETP Terrestrial Eco Toxicity Potential
VC Vinyl chloride
VOC Volatile Organic Compound
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Contents
LIST OF FIGURES ... IX LIST OF TABLES ... X LIST OF TABLE APPENDICES ... XI LIST OF DIAGRAM APPENDICES ... XIV
1. INTRODUCTION ...1
1.1 PURPOSE ...1
2. REVIEW OF LITERATURE ...1
3. BACKGROUND ...3
3.1 VOCS ADSORPTION PROCESS DESCRIPTION ON GAC ...3
3.2 VOCS INCINERATION PROCESS DESCRIPTION ...4
3.2.1 Simple thermal incinerator ...5
3.2.2 Thermal incinerator with regenerative heat recovery ...5
3.2.3 Catalytic incinerator ...6
3.3 LCA METHODOLOGY ...6
4. METHODS ...7
4.1 PROCESS DESIGN ...7
4.1.1 Properties of VOCs adsorption process on GAC ...7
4.1.1.1 Suitable GAC selection ...7
4.1.1.2 Required amount of adsorbent for one week operation ...8
4.1.1.3 Determination of Carbon Adsorption Vessel size ...8
4.1.1.4 Total pressure drop calculation ...9
4.1.1.5 Required steam properties ... 10
4.1.1.6 Equipments’ design (air fan, heater, cooler and decanter) ... 10
4.1.2 Properties of RTO process ... 13
4.1.2.1 Process streams ... 13
4.1.2.2 Input data ... 14
4.1.2.3 RTO process simulation ... 14
4.1.2.4 Required amount of natural gas ... 14
4.1.2.5 RTO equipments ... 15
4.1.3 Non-treatment alternative... 15
4.2 LCA STUDY ... 15
4.2.1 Goal and scope definition ... 15
4.2.1.1 Purpose of study ... 15
4.2.1.2 Stakeholders ... 15
4.2.1.3 Options to model ... 16
4.2.1.4 Functional unit ... 16
4.2.1.5 Environmental impact category ... 16
4.2.1.6 LCA type ... 17
4.2.1.7 System boundaries ... 17
4.2.2 Inventory analysis ... 20
4.2.2.1 Inventory analysis of GAC adsorption method ... 20
4.2.2.1.1 General LCI description for GAC adsorption method ... 20
4.2.2.1.2 Normalized data for Case 1- GAC adsorption method ... 24
4.2.2.1.3 Normalized data for Case 2- GAC adsorption method ... 24
4.2.2.1.4 Normalized data for Case 3- GAC adsorption method ... 25
4.2.2.2 Inventory analysis for VOCs incineration method ... 26
4.2.2.2.1 General LCI description for VOCs incineration method ... 27
4.2.2.2.2 Normalized data for Case 1- VOCs incineration method ... 28
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4.2.2.3 Inventory analysis for Non-treatment alternative ... 31
4.2.3 Life Cycle Impact Assessment ... 31
4.2.3.1 Impact category definition ... 31
4.2.3.2 Classification ... 32
4.2.3.3 Characterization ... 32
4.2.3.4 Weighting ... 33
5. RESULT ( INTERPRETATION OF LCA RESULT) ... 33
6. DISCUSSION ... 35
7. CONCLUSION ... 37
REFERENCES ... 38
APPENDIX 1, MATERIALS AND EQUIPMENTS CATALOGS ... 42
APPENDIX 2, PROCESS CALCULATIONS ... 55
APPENDIX 3, ASPEN PLUS 2006 RESULTS ... 58
APPENDIX 4, LCI CALCULATIONS ... 63
APPENDIX 5, GENERAL DATA FOR LIFE CYCLE INVENTORY ANALYSIS ... 75
APPENDIX 6, LCI NORMALIZED DATA – GAC ADSORPTION METHOD ... 78
APPENDIX 7, LCI NORMALIZED DATA – VOCS INCINERATION METHOD ... 99
APPENDIX 8, LIFE CYCLE IMPACT ASSESSMENT ... 108
APPENDIX 9, WEIGHTING RESULTS ... 117
APPENDIX 10, INTERPRETATION OF RESULT ... 119
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List of Figures
Figure 1. The environmental burdens of collection and recycling in reality ...3
Figure 2. The environmental burdens of collection and recycling- linear function ...3
Figure 3. Adsorption/ desorption process ...4
Figure 4. Simple thermal incineration method ...5
Figure 5. Thermal incinerator with regenerative heat recovery ...5
Figure 6. Catalytic incinerator ...6
Figure 7. LCA framework in ISO 14040 (1997) ...6
Figure 8. Toluene loading on AP4-60 (Chemviron) ...8
Figure 9. Pressure drop for VAPOR-PAC® 10 (Calgon Corporation) ... 10
Figure 10. BFD of process (Aspen Plus 2006) ... 11
Figure 11. RTO simulation by Aspen Plus 2006 ... 14
Figure 12. Baltic natural gas network ... 18
Figure 13. Pipeline direction between natural gas basin and GAC manufacture ... 18
Figure 14. LCI flow chart for GAC adsorption process ... 20
Figure 15. LCI flow chart (GAC adsorption method) - Case 1 ... 25
Figure 16. LCI flow chart (GAC adsorption method) - Case 2 ... 26
Figure 17. LCI flow chart (GAC adsorption method) - Case 3 ... 26
Figure 18. LCI flow chart for VOCs incineration process ... 27
Figure 19. LCI flow chart (VOCs incineration method) - Case 1 ... 30
Figure 20. LCI flow chart (VOCs incineration method) - Case 2 ... 30
Figure 21. LCI flow chart (VOCs incineration method) - Case 3 ... 31
Figure 22. Weighted result ... 35
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List of Tables
Table 1. Specification of VAPOR-PAC® 10 (Calgon Corporation) ...9
Table 2. Results of GAC adsorption process design ... 13
Table 3. The average composition of natural gas in the world ... 14
Table 4. Required amount of natural gas ... 15
Table 5. Energy requirement for transportation of produced GAC ... 21
Table 6. Selected vehicles to transport equipment for GAC adsorption method ... 22
Table 7. Total electrical energy required for running equipment- GAC adsorption method ... 22
Table 8. Energy requirement for natural gas and RTO equipment transportation ... 28
Table 9.Classification of environmental impact potentials ... 32
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List of Table Appendices
Table App 5. 1. Equipments transportation details ... 75
Table App 5. 2. Emission for 1 ton GAC production ... 75
Table App 5. 3. Emission for 2831m 3 natural gas ... 76
Table App 5. 4. Emissions for road and sea transportation (NTM 2002- Euro 3) ... 76
Table App 5. 5. Electricity production based on different energy source in Sweden for 1 TJ net electricity (IEA 2000) and Frischknecht et al. (1996) ... 77
Table App 6. 1. Emissions of natural gas extraction, treatment, transportation by pipeline (GAC adsorption method) - Case 1………..……….……78
Table App 6. 2. Emission of equipment transportation (GAC adsorption method) - Case 1 ... 79
Table App 6. 3. Emission of GAC transportation (GAC adsorption method) - Case1 ... 79
Table App 6. 4. Electricity production emissions in Sweden (GAC adsorp. method)- Case 1 80 Table App 6. 5. Emission of GAC production (GAC adsorption method) - Case 1 ... 82
Table App 6. 6. Total emission of GAC adsorption method (kg/f.u.) - Case 1 ... 83
Table App 6. 7. Natural resource for electricity production in Sweden (GAC adsorption method) – Case 1 ... 84
Table App 6. 8. Total fossil energy for transportation of GAC and equipments (GAC adsorption method) - Case 1 ... 84
Table App 6. 9. Emissions of natural gas extraction, treatment, transportation by pipeline (GAC adsorption method) - Case 2 ... 85
Table App 6. 10. Emission of equipment transportation (GAC adsorption method) - Case 2 . 86 Table App 6. 11. Emission of GAC transportation (GAC adsorption method) - Case 2 ... 86
Table App 6. 12. Electricity production emissions in Sweden (GAC adsor. method)- Case 2 87 Table App 6. 13. Emission of GAC production (GAC adsorption method) - Case 2 ... 89
Table App 6. 14. Total emission of GAC adsorption method (kg/f.u.) - Case 2 ... 90
Table App 6. 15. Natural resource for electricity production in Sweden (GAC adsorption method) – Case 2 ... 91
Table App 6. 16. Total fossil energy for transportation of GAC and equipments (GAC adsorption method) - Case 2 ... 91
Table App 6. 17. Emissions of natural gas extraction, treatment, transportation by pipeline (GAC adsorption method) - Case 3 ... 92
Table App 6. 18. Emission of equipment transportation (GAC adsorption method) - Case 3 . 93 Table App 6. 19. Emission of GAC transportation (GAC adsorption method) - Case 3 ... 93
Table App 6. 20. Electricity production emissions in Sweden (GAC adsor. method)- Case 3 94 Table App 6. 21. Emission of GAC production (GAC adsorption method) - Case 3 ... 96
Table App 6. 22. Total emission of GAC adsorption method (kg/f.u.) - Case 3 ... 97
Table App 6. 23. Natural resource for electricity production in Sweden (GAC adsorption method) – Case 3 ... 98
Table App 6. 24. Total fossil energy for transportation of GAC and equipments (GAC adsorption method) - Case 3 ... 98
Table App 7. 1. Electricity production emissions in Sweden (VOCs incineration method)- Case 1, 2 and 3 ……… ………. .99
Table App 7. 2. Emission of RTO equipment transportation (VOCs incineration method) – Case 1, 2 and 3 ... 101
Table App 7. 3. Natural resource for electricity production in Sweden (VOCs incineration method) – Case 1, 2 and 3... 101
Table App 7. 4. Emissions of natural gas extraction, treatment, combustion and transportation by pipeline (VOCs incineration method) - Case 1 ... 102
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Table App 7. 5. Emission of natural gas transportation by road (VOCs incineration method) -
Case 1 ... 102
Table App 7. 6. Total emission of VOCs incineration method (kg/f.u.) - Case 1 ... 103
Table App 7. 7. Total fossil energy for transportation of natural gas and RTO equipment (VOCs incineration method) - Case 1 ... 103
Table App 7. 8. Emissions of natural gas extraction, treatment, combustion and transportation by pipeline (VOCs incineration method) – Case 2 ... 104
Table App 7. 9. Emission of natural gas transportation by road (VOCs incineration method) - Case 2 ... 104
Table App 7. 10. Total emission of VOCs incineration method (kg/f.u.) - Case 2 ... 105
Table App 7. 11. Total fossil energy for transportation of natural gas and RTO equipment (VOCs incineration method) - Case 2 ... 105
Table App 7. 12. Emissions of natural gas extraction, treatment, combustion and transportation by pipeline (VOCs incineration method) – Case 3 ... 106
Table App 7. 13. Emission of natural gas transportation by road (VOCs incineration method) - Case 3 ... 106
Table App 7. 14. Total emission of VOCs incineration method (kg/f.u.) - Case 3 ... 107
Table App 7. 15. Total fossil energy for transportation of natural gas and RTO equipment (VOCs incineration method) - Case 3 ... 107
Table App 8. 1. Depletion of Abiotic Resources (GAC adsorption method) - Case 1…….. 108
Table App 8. 2. Depletion of Abiotic Resources (GAC adsorption method) - Case 2 ... 108
Table App 8. 3. Depletion of Abiotic Resources (GAC adsorption method) - Case 3 ... 108
Table App 8. 4. Water consumption (GAC adsorption method) ... 108
Table App 8. 5. Global Warming Potential (GAC adsorption method) ... 109
Table App 8. 6. Photochemical Ozone Creation Potential (GAC adsorption method) ... 109
Table App 8. 7. Acidification Potential (GAC adsorption method)... 109
Table App 8. 8. Eutrophication Potential (GAC adsorption method) ... 109
Table App 8. 9. Human Toxicity Potential (GAC adsorption method)... 110
Table App 8. 10. Ecotoxicity Potential- Freshwater Aquatic Eco Toxicity Potential (GAC adsorption method) ... 110
Table App 8. 11. Ecotoxicity Potential- Marine Aquatic Eco Toxicity Potential (GAC adsorption method) ... 111
Table App 8. 12. Ecotoxicity Potential- Terrestrial Eco Toxicity Potential (GAC adsorption method) ... 111
Table App 8. 13. Depletion of Abiotic Resources (VOCs incineration method) - Case 1 ... 112
Table App 8. 14. Depletion of Abiotic Resources (VOCs incineration method) - Case 2 ... 112
Table App 8. 15. Depletion of Abiotic Resources (VOCs incineration method) - Case 3 ... 112
Table App 8. 16. Water consumption (VOC incineration method) ... 112
Table App 8. 17. Global Warming Potential (VOCs incineration method) ... 113
Table App 8. 18. Photochemical Ozone Creation Potential (VOCs incineration method) .... 113
Table App 8. 19. Acidification Potential (VOCs incineration method) ... 113
Table App 8. 20. Eutrophication Potential (VOCs incineration method) ... 113
Table App 8. 21. Human Toxicity Potential (VOCs incineration method) ... 114
Table App 8. 22. Ecotoxicity Potential- Freshwater Aquatic Eco Toxicity Potential (VOCs incineration method) ... 114
Table App 8. 23. Ecotoxicity Potential- Marine Aquatic Eco Toxicity Potential (VOCs incineration method) ... 115
Table App 8. 24. Ecotoxicity Potential- Terrestrial Eco Toxicity Potential (VOCs incineration method) ... 115
Table App 8. 25. Human Toxicity Potential (Non-treatment alternative) ... 116
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Table App 8. 26. Ecotoxicity Potential- Freshwater Aquatic Eco Toxicity Potential (Non-
treatment alternative) ... 116
Table App 8. 27. Ecotoxicity Potential- Marine Aquatic Eco Toxicity Potential (Non- treatment alternative) ... 116
Table App 8. 28. Ecotoxicity Potential- Terrestrial Eco Toxicity Potential (Non-treatment alternative) ... 116
Table App 8. 29. Photochemical Ozone Creation Potential (Non-treatment alternative) ... 116
Table App 9. 1. Weighting result of GAC adsorption method……….. 117
Table App 9. 2. Weighting result of VOCs incineration method ... 118
Table App 9. 3. Weighting result of Non-treatment alternative ... 118
xiv
List of Diagram Appendices
Diagram App 10. 1. Natural resource consumption- GAC adsorption method ... 119
Diagram App 10. 2. Energy consumption- GAC adsorption method ... 119
Diagram App 10. 3. Depletion of Abiotic Resources- GAC adsorption method ... 119
Diagram App 10. 4. Global Warming Potential- GAC adsorption method... 119
Diagram App 10. 5. Photochemical Ozone Creation Potential- GAC adsorption method .... 119
Diagram App 10. 6. Acidification Potential- GAC adsorption method ... 119
Diagram App 10. 7. Eutrophication Potential- GAC adsorption method ... 120
Diagram App 10. 8. Human Toxicity Potential- GAC adsorption method ... 120
Diagram App 10. 9. Ecotoxicity Potential (FAETP)- GAC adsorption method ... 120
Diagram App 10. 10. Ecotoxicity Potential (MAETP) - GAC adsorption method ... 120
Diagram App 10. 11. Ecotoxicity Potential (TETP) - GAC adsorption method ... 120
Diagram App 10. 12. Environmental impact comparison- GAC adsorption method ... 120
Diagram App 10. 13. Weighted result- GAC adsorption method ... 120
Diagram App 10. 14. Natural resource consumption- VOCs incineration method ... 121
Diagram App 10. 15. Energy consumption- VOCs incineration method ... 121
Diagram App 10. 16. Depletion of Abiotic Resources- VOCs incineration method ... 121
Diagram App 10. 17. Global Warming Potential- VOCs incineration method ... 121
Diagram App 10. 18. Photochemical Ozone Creation Potential- VOCs incineration metho . 121 Diagram App 10. 19. Acidification Potential- VOCs incineration method ... 121
Diagram App 10. 20. Eutrophication Potential- VOCs incineration method ... 122
Diagram App 10. 21. Human Toxicity Potential- VOCs incineration method ... 122
Diagram App 10. 22. Ecotoxicity Potential (FAETP) - VOCs incineration method ... 122
Diagram App 10. 23. Ecotoxicity Potential (MAETP) - VOCs incineration method ... 122
Diagram App 10. 24. Ecotoxicity Potential (TETP) - VOCs incineration method ... 122
Diagram App 10. 25. Environmental impact comparison- VOCs incineration method ... 122
Diagram App 10. 26. Weighted result- VOCs incineration method ... 122
Diagram App 10. 27. Photochemical Ozone Creation Potential- Non-treatment alternative . 123 Diagram App 10. 28. Human Toxicity Potential- Non-treatment alternative ... 123
Diagram App 10. 29. Ecotoxicity Potential (FAETP) - Non-treatment alternative ... 123
Diagram App 10. 30. Ecotoxicity Potential (MAETP) - Non-treatment alternative ... 123
Diagram App 10. 31. Ecotoxicity Potential (TETP) - Non-treatment alternative ... 123
Diagram App 10. 32. Environmental impact comparison- Non-treatment alternative ... 123
Diagram App 10. 33. Weighted result- Non-treatment alternative ... 123
Diagram App 10. 34. Natural resource consumption- Case 1 ... 124
Diagram App 10. 35. Natural resource consumption- Case 2 ... 124
Diagram App 10. 36. Natural resource consumption- Case 3 ... 124
Diagram App 10. 37. Natural gas consumption ... 124
Diagram App 10. 38. Energy consumption ... 124
Diagram App 10. 39. Depletion of Abiotic Resources ... 124
Diagram App 10. 40. Global Warming Potential ... 125
Diagram App 10. 41. Photochemical Ozone Creation Potential ... 125
Diagram App 10. 42. Acidification Potential ... 125
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Diagram App 10. 43. Eutrophication Potential ... 125
Diagram App 10. 44. Human Toxicity Potential ... 125
Diagram App 10. 45. Eco Toxicity Potential- (FAETP) ... 125
Diagram App 10. 46. Eco Toxicity Potential- (MAETP) ... 126
Diagram App 10. 47. Eco Toxicity Potential- (TETP) ... 126
1
1. Introduction
Nowadays, it is necessary to reduce the emissions of volatile organic compounds to the atmosphere when several VOCs may affect on human health such as negative impact on reproductive system and birth defect even in very low concentration. They can also be precursors of ozone formation at ground level [1]. Furthermore, some VOCs contribute to global warming indirectly and some of them are toxic and carcinogenic. Eye and throat irritation, damage to liver and central nervous system occur due to prolonged exposure to VOCs [2].
The industries such as chemical plants, refineries, ink manufacturing, paint and color production plants, plastic production, pharmaceutical and food industries emit pollutions like methanol, toluene, acetone, MEK, ethyl benzene, p- xylene, DCM and 1, 2-dicholoroethane [3]. There are many air pollution control methods to remove volatile organic compounds such as incineration, biofiltration, adsorption on activated carbon, etc [3-5].
The sustainability assessment is the traditional approach to evaluate treatment technology methods. It can investigate three main categories from economical, environmental and social point of view [6]. Nowadays, the LCA is used to evaluate and compare products and services from environmental point of view. On the other word, “LCA is an important and comprehensive method for analyzing the environmental impacts of products and services” [7].
1.1 Purpose
The purpose of this study is to compare different strategies and air pollution control methods for VOCs reduction in order to choose the most environmental preferable technique or strategy. A literature study of this field revealed surprisingly a lack of data. As known, no LCA approach has been used to compare non-treatment of polluted flue gas stream with techniques like incineration and gas adsorption. In this work, the flow rate of polluted flue gas is 10000m3/hr. The pollutant is toluene with three different concentrations (case 1=100 mg/m3, case 2=1000 mg/m3 and case 3= 2000 mg/m3). On the other side, the temperature of inlet flue gas and its pressure are 20oC and 101.3 kPa, respectively. The plant where the polluted air is emitted was assumed to be located in Borås, Sweden.
2 Review of literature
As mentioned in the previous chapter, no study has been done to compare air pollution control methods from environmental point of view. However, a few studies have been done so far to compare preferable industrial liquid waste solvents’ treatment.
In a work by Romero-Hernandez, they compared carbon adsorption with a non-treatment alternative to find the best way from environmental point of view. LCA was used to measure photochemical ozone creation potential and global warming potential for both ways. The wastewater stream contaminated by benzene and 1, 2- dichloroethane was used for impact assessment. The assessment considered the emissions of raw material extraction, production, use and regeneration of granular activated carbon. The results illustrated that GWP for adsorption treatment was higher compared to non treatment option. Therefore, the polluted stream should not be treated from environmental point of view. On the other side, the social impact assessment has been conducted. This assessment proved that the polluted stream should be treated morally and legally due to negative impacts on human health [6].
2
In another work Peter Bayer et al compared the influence of recycling GAC to using virgin GAC in the wastewater treatment. They used LCA tools to evaluate environmental and ecological impacts, human health effects and energy consumption. Several contaminants were found in considered wastewater sample such as PCE, TCE, cis- DCE and VC. The concentration of contaminants was 1000 mg/m3. The authors showed that recycling of GAC is more favorable from environmental point of view rather than using virgin GAC [8].
LCA used as a tool for comparing two air pollution control methods has some limitations [9].
In fact, the traditional LCA has some inherent restrictions that could not answer many significant questions. Choosing the functional unit such as kg or tone of waste generated can be useful just for environmental comparison of two or more options. This is not suitable for analyzing of any change in waste generation quantity. On the other hand, LCA mainly discusses on the current society. When LCA will be able to represent future waste management strategy with variable society, it should have a long-term sustainability approach. Therefore, since LCA presents current situation in waste management strategy, it cannot be used for future strategy very well. Another LCA problem is inability to give accurate information if the geographical information is not included. This problem is due to strong dependency of LCA on geographical location. Therefore, it is difficult to find where and when waste management facilities should be installed [9].
Another problem of LCA is the linear relationship. As the recycling is probably non-linear function, LCA cannot be used for identification of recycling rate [9]. If very high recycling rate is considered, the transportation and material processing can increase the fuel consumption, so the emission will be raised. Figure 1 and 2 shows the LCA model introduce by Ekvall et al. This model describes burdens of material production and burdens of collection and recycling in reality from environmental point of view [9]. There are some solutions to overcome mentioned problems. The annual functional unit can be selected to meet any change in waste generated quantity. To avoid the geographical dependency of LCA, site-dependent and site-specific modeling can be useful solutions. Site-dependant modeling would count the environmental conditions and sensitivity of region or country where the polluted gases are emitted. This was integrated in EDIP 2003. EIA or risk assessment is an alternative to get site-specific information. LP would be useful solution to overcome the non- linear problem of LCA. LP model can describe the system partially linear. Totally, LCA can be complete by adding other methodological aspects such as economic analysis, site- dependant modeling, dynamic linear and non-linear modeling [9].
3 Figure 1.The environmental burdens of collection
and recycling in reality [9] Figure 2.The environmental burdens of collection and recycling- linear function [9]
3 Background
3.1 VOCs adsorption process description on GAC
The porous solid medium such as GAC is the main characteristic in adsorption process due to capability of VOCs adsorption. The large volume of VOCs can be adsorbed on GAC due to the porous structure of adsorbent. The adsorption function depends on adsorption medium performance in both equilibrium and kinetics. To adsorb VOCs as much as possible, the adsorbent must have large surface area and higher porosity [2]. AC can be manufactured from coal, wood and nut sells. Most of activated carbons have approximately 1200 m2 area per gram, which is very large area for adsorption [10]. GAC has some advantages compare to another type of adsorbent such as PAC. GAC main advantages are listed below.
1. In the case of using GAC, the operator does not need to determine dosage every day, if the influent conditions are changed [11].
2. If PAC wants to be used in a year round, the advantage of GAC is increased [11].
3. By using GAC instead of PAC, less waste is achieved for disposal [11].
4. The effectiveness is increased by using GAC for VOCs removal compared to PAC[11].
The granular activated carbon can be desorbed after saturation in order to recover solvent such as toluene and also to minimize GAC utilization. As shown in Figure 3, the adsorption/
desorption process consists four main steps; adsorption, desorption, drying and cooling [10].
4
Figure 3.Adsorption/ desorption process [10]
At the first step, the polluted air contains VOCs passes through a GAC column called vessel.
VOCs such as toluene can be absorbed by granular activated carbon surface and the clean air leaves the vessel to atmosphere. A gas analyzer is installed on the top of vessel. As soon as the gas analyzer detects VOCs, it means adsorbent has been saturated and the second step, desorption or regeneration, is started. The regeneration can be done by two methods; steam regeneration or nitrogen regeneration [10]. Each method has some advantages and limitations.
Steam is available in many industries, which can be collected to use in regeneration process.
Furthermore, steam has high-energy content and it can be condensed easily by cooling tower.
The nitrogen regeneration method as a hot gas solution has low energy content and it can be hotter than steam from industrial boiler. Both nitrogen and steam are inert. Nitrogen regeneration method provides no wastewater while steam is converted to wastewater after condensation [12]. The liquid that consist VOCs should be cooled before separating toluene to reuse or disposal. The steamed GAC should be dried and cooled before returning to vessel [10].
3.2 VOCs incineration process description
The thermal treatment of flue gas is one of the most frequently and efficient process for VOCs removal [5]. The principal of this method is based on oxidizing of VOCs at high temperature to produce H2O and CO2. Combustion chamber (as an incinerator) combined with a heat exchanger (as a flue gas pre-heater) is the main equipment in thermal treatment method.
Moreover, air fan is needed to provide equipments’ pressure drop [5]. Almost all VOCs can be incinerated by thermal treatment method [13]. Like all treatment methods, incineration also has some disadvantages. The main incineration problem is incomplete combustion. In some case, incomplete combustion can produce an exhaust gas more harmful than the influent flue gas. Therefore, the combustion process and equipments should be design to prevent incomplete combustion [13].
This is a fact that most combustion occurs in the gas phase, because liquids and solids are also converted to gas phase before burning [13]. As a result reaction rate expressed for any phase is:
Decrease the concentration of A per unit time = r = k CAn [13]
Where; r= Reaction rate, k= Kinetic constant, CA= Concentration of A and n= reaction order
5
Three techniques are available for VOCs thermal treatment; simple thermal incinerator, thermal incinerator with regenerative heat recovery and catalytic incinerator [13]. The properties, benefits and disadvantages of each method are explained as follows.
3.2.1 Simple thermal incinerator
In this method, the contaminated gas stream is mixed with fuel and excess air, if needed.
Burning process occurs in combustion chamber. If inlet stream contains enough VOCs, the addition of fuel can be negligible. In this case, VOCs play the role of fuel, so the cost of operation is decreased due to reduction in fuel consumption. If VOCs concentration in gas stream is more than LEL, no additional fuel would be required. This amount is 43% for toluene. Therefore, almost all air pollution treatments need additional fuel [13]. Figure 4 shows the simple thermal incineration method.
Figure 4.Simple thermal incineration method [13]
3.2.2 Thermal incinerator with regenerative heat recovery
If a heat exchanger is installed into the system, the leaving heat can be transferred to influent gas stream in order to increase temperature. In this case, the outlet temperature and fuel consumption are decreased due to increase influent temperature. In order to existence of gas stream in the process, hot-gas-to-cold-gas heat exchangers should be installed, which are very expensive. They have often severe corrosion problems as well. Figure 5 shows this kind of thermal treatment [13].
Figure 5.Thermal incinerator with regenerative heat recovery [13]
6 3.2.3 Catalytic incinerator
Platinum metal is a common catalyst used in this method. Two porous ceramic materials, ceramic pellets or ceramic honeycomb, are used as a substrate for catalyst. Decreasing the required temperature from 1000-1200oF to 600oF is one of the advantages of using catalyst incinerator. The catalyst is usually expensive, but the reduction in the fuel consumption is significant [13]. The catalytic incinerator is shown in Figure 6.
Figure 6.Catalytic incinerator [13]
3.3 LCA methodology
By quick glance on LCA framework proposed by SETAC 1990-1993, four main methodological approaches have been introduced; goal and scope definition, life cycle inventory analysis, impact assessment and life cycle improvement assessment [7, 14].
Although the life cycle improvement assessment has been proposed as a separate phase in SETAC framework, it is not considered as such in LCA framework in ISO 14040 (1997). In fact, the life cycle improvement assessment just influences on LCA framework in ISO 14040 [14]. LCA framework proposed in ISO 14040 (1997) was used in this study. This framework is shown in Figure 7 [14].
Life Cycle Assessent Framework
Goal and Scope Definition
Inventory Analysis
Impact Assessment
Interpretation
Direct Applications:
• Product Development and Improvment
• Strategic Planning
• Public Policy Makeing
• Marketing
• Other
Figure 7.LCA framework in ISO 14040 (1997)
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4. Methods
This part contains two main sections, process design and LCA study. As the main purpose of this study is comparison of flue gas treatments method by using LCA tool, required energy, raw materials, equipment types, equipments and raw materials producers, etc should be identified to get necessary data required for LCA part. In fact, process design is the pre-step of LCA study in this research. Furthermore, LCA study part contains three first steps of LCA methodology; goal and scope definition, inventory analysis and impact assessment.
4.1 Process design
According to GAC advantage, adsorption on GAC was considered in this study. In addition, steam supposed to be collected from other part of plant and applied for regeneration of GAC.
The adsorption process design includes six main steps; selection of suitable type of GAC, determination of required amount of carbon, vessel size determination, total pressure drop calculation, type and size of other equipments such as air fan, heater, etc and energy consumption [15].
Thermal treatment is an efficient method to destroy almost all VOCs up to 2000 ppm as inlet concentration. The concentrations in this study are 31.25, 312.5 and 625 ppm. Furthermore, incinerator can be designed to handle different flow rates, 1000- 500000 cfm (5886 cfm in this study). The residence time can be also in the range of 0.5-1 second. RTO is available with energy recovery system to decrease the operating costs due to reduce required fuel. Thermal oxidation can be operated with the temperature range of 700- 1000oC, depends on furnace type and inlet VOCs concentration [16].
The ceramic bed is used in RTO to take heat from gases in the combustion zone. If multiple beds are used in RTO process, the heat capturing up to 95% is possible. This heat contains the thermal energy of fuel and also the heat produced by VOCs combustion [16]. As a result, according to available conditions in this study, the selection of RTO method not only fulfills all requirements, but also reduces the operating cost. On the other hand, the operation cost is not as much as catalytic incineration method [13].
Non-treatment alternative has been also investigated in this study. The flue gas was assumed to be emitted without any treatment. These three methods have been compared from environmental point of view by using LCA to find the best one (Result part).
4.1.1 Properties of VOCs adsorption process on GAC
4.1.1.1 Suitable GAC selection
Chemviron Carbon and Calgon Carbon Corporation were selected as supplier and manufacturer of GAC, respectively. According to GAC properties produced by Calgon, among different ranges of GAC, AP4-60 was selected as an adsorbent. This type of GAC has several applications, which were completely relevant to studied cases. It is suitable for VOCs removal and it is also steam re-generable. On the other hand, AP4-60 has low pressure drop, so less energy is consumed [17]. AP4-60 properties are available in Appendix1.1.
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4.1.1.2 Required amount of adsorbent for one week operation
To determine the required amount of adsorbent, toluene Freundlich isotherm at 20oC was used. This isotherm was published as a technical data by Chemviron Carbon for toluene adsorption on AP4-60, Figure 8.
Figure 8.Toluene loading on AP4-60 (Chemviron) [17]
Eight hours per day has been considered as operation time, so the operation time for one week is 40 hour (5 days/ week and 49 weeks/ year have been assumed). Therefore, the flow rate of polluted air is 4×105 m3/week.
Toluene weight entered to vessel is different in three cases. The volumetric toluene concentration in ppmv has been calculated for three cases by considering 3.2 kg/m3 (if Air=1) as toluene vapor density. Toluene vapor density is variable and its range is 3.14 to 3.3 [18, 19]. Toluene weight that should be adsorbed per week has been summarized in Table 2. The calculation details are available in Appendix 2.1.
The required amount of GAC, AP4-60, for three cases was calculated and the result has been shown in Table 2. The calculation details are available in Appendix 2.2. To calculate the amount of required carbon, the adsorption uptake percentage is needed for all cases with different concentrations. This data was gained by using Figure 8 published by Chemviron Carbon Corporation.
4.1.1.3 Determination of Carbon Adsorption Vessel size
The first step of vessel size determination is diameter estimation. At the first step, diameter should be estimated based on reasonable superficial velocity. If the superficial velocity is increased, the pressure drop will be increased [15]. The superficial velocity range for AP4-60 introduced by Chemviron is 0.05-5 m/s [17]. Low superficial velocity has been assumed in this study, 20 cm/s, to avoid high pressure drop creation. By using proposed equation in Appendix 2.3, vessel diameter was calculated (4.2 m).
Due to Chemviron Carbon’s design information, the vessel depth range should be 0.2- 2 m [17]. Therefore, there is a size limitation in this case because required diameter is more than vessel depth. According to achieved data from Chemviron Carbon Corporation, GAC desorption process takes place within maximum 4-5 hours [20]. Therefore, only one vessel assumed to be installed by considering operation time (8 hr/day). In fact, GAC regeneration is
9
done when the system is shut down. The volume of vessel was determined by using GAC bulk density. The bulk density of AP4-60 is 450 kg/m3 given by Chemviron Carbon [17]. Ten percent excess volume was considered for each case. The required volume of vessels was calculated and the results are 0.55, 3.7 and 6.8 m3/week for Case 1, 2 and 3, respectively (see Appendix 2.4).
According to required vessel volume for all three cases and bed depth limitation (~2 m), one vessel can fulfill all requirements for each case. By considering carbon weight, pressure and maximum flow rate, the desirable vessel type manufactured by Calgon Corporation (VAPOR- PAC® 10) was selected. The vessel properties are available in Appendix 1.2. According to different amount of required GAC for each case shown in Table 2, wide range of vessels manufactured by Calgon Corporation could be used. However, due to high flow rate that is constant for each case, only one vessel type was selected. The specification of VAPOR- PAC® 10 is shown in Table 1.
Table 1.Specification of VAPOR-PAC® 10 (Calgon Corporation) [21]
4.1.1.4 Total pressure drop calculation
The atmospheric pressure was considered as treated flue gas effluent pressure to air. Due to atmospheric pressure of effluent treated air and also pressure drop in equipments, higher influent pressure is needed to compress polluted air through vessel. This goal was achieved by installing an air fan. Total pressure drop was used to design suitable air fan [15].
While the purpose is comparison, the length of pipes, number of valves has been assumed to be the same in all three cases. Therefore, pressure drop of pipes and valves were neglected and just one pressure drop was considered (vessel pressure drop). On the other side, the pressure drop for carbon vessels was estimated by using Calgon Corporation diagram, Figure 9.
10
Figure 9.Pressure drop for VAPOR-PAC® 10 (Calgon Corporation) [21]
By using Figure 9, the pressure drop for considered air flow rate (5886 cfm) is approximately 5.9 inch of H2O (∼ 15 cm of H2O) for long-term usage. The total pressure drop for each case is summarized in Table 2.
4.1.1.5 Required steam properties
Steam is used for on-site regeneration of adsorbent [22]. As the steam is usually available in many industries, it was assumed to be collected from other parts. The saturated steam at 140oC was used to desorb adsorbent [22]. Steam consumption was 2.58 kg per 1 kg toluene recovered [23]. According to steam thermodynamic tables, the specific volume of saturated steam at 140oC is approximately 0.5085m3/kg [24]. As activated carbon regeneration was assumed to be operated every day after shutting down, the required amount of steam was calculated per day (Table 2). The calculation details are available in Appendix 2.5. By considering 20oC as water temperature to produce steam, the energy consumption for steam generating was calculated and summarized in Table 2 [25]. The calculation details are available in Appendix 2.6.
4.1.1.6 Equipments’ design (air fan, heater, cooler and decanter) Air fan
If the pressure of effluent treated air supposed to be 101.3 kPa, the required pressure of influent polluted air was calculated as following and summarized for each case in Table 2 [15].
Required influent pressure (kPa) = Total pressure drop (kPa) + Effluent pressure (101.3 kPa) To provide the required influent pressure, air fan was used as pressure changer. Air fans for all three cases were assumed to be supplied by SMJ. Inc. The catalog and technical data of selected air fan is available in Appendix 1.3. Only one air fan was designed for each case. The process BFD was simulated by Aspen Plus 2006 and illustrated in Figure 10. Air fan was assumed to be blower and installed before the adsorption vessel.
11
Figure 10.BFD of process (Aspen Plus 2006)
Two stage contra rotating fan (CR #56- ARRANGE. #4) manufactured by SMJ Inc was selected as pressure changer. The RPM of selected fan is 3500 and engine power range is 2×10-2×20 HP. The power of air fan is 2×15 HP (∼22.37 kW).
Combined drying and cooling
Drying and cooling (D/C) are the next steps after steaming. During steaming, the adsorbent becomes wet and it is not suitable for continuing adsorption process. Therefore, it should be dried and then cooled to prepare for next adsorption cycle. Due to similarity of conditions (steam temperature, air flow rate and amount of used GAC) in this study and research done by Gu et al, the results were used for estimating drying/cooling time [22]. The combined drying/
cooling process were considered by purging of air with 24oC temperature and 200 m3/hr flow rate. The average temperature of ambient air in the plant location is 6.5oC with more than 75% relative humidity [22, 26, 27]. As combined drying/cooling process is inefficient in a very moist environment (more than 50% relative humidity), the air heater was considered in this study to raise the air temperature up to 24oC [22].
Drying is done fast at the beginning and it becomes gradually slow. If air with 24oC temperature passes through the vessel, 30 minute is required to decrease the bed temperature from 115oC down to 25oC [22]. The vessel temperature is decreased very fast due to energy consumed during water and toluene desorption [22]. Due to the same properties of selected GAC in this study (AP4-60) and Sorbonorit 4 (tested by Junjie Gu et al), some available data of Sorbonorit 4 were considered for AP4-60. Therefore, it would be mentioned that cooling/drying time is about 30 min for 96.5 kg saturated Sorbonorit [22]. On the other hand, it was assumed that the required amount of adsorbent for one day operation is saturated and regeneration is done every day after shutting down of system. Therefore, cooling/drying time was calculated based on related data for Sorbonorit by following equation and the results are summarized in Table 2.
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Cooling/drying time (min) =
( ) ( )
( )
kg kg Adsorbent5 . 96
min 30
×
As described, due to high moist environment and low air temperature in Borås, purged ambient air needs to be heated before passing through vessel. The best air heater (MA0-10F) produced by HOTWATT Co. was selected (see Appendix 1.4) [28]. Due to the same conditions for all three cases, just one model of air heater was used, but cooling/ drying time is varied for each case, Table 2. The required electricity power to run the selected air heater was calculated with proposed equation by manufacturer (HOTWATT) with consideration of required flow rate (200m3/hr), ambient air temperature (6.5oC) and purged air temperature (24oC) at atmospheric pressure. Therefore, required energy consumption for each air heater is 2.5 kW (see Appendix 2.7).
Cooler
After desorption, effluent stream contains toluene and water. This stream has relatively high temperature that should be cooled before separating in decanter [10]. Due to cold weather condition in Borås, cooling process was supposed to be done by air cooled heat exchanger to cool down the toluene/ water mixture to 20oC. Effluent temperature of this stream and the cooling capacity achieved from Aspen Plus 2006 are shown in Table 2 [29]. Aspen Plus results are available in Appendix 3.1 and 3.2.
Based on cooling capacity, suitable air cooled heat exchanger were chosen for each case. As shown in Table 2, wide range of cooling capacity is available. There was no air cooled heat exchanger manufacturer with such a wide range production. Therefore, the adequate air cooled heat exchanger for Case 1 and 2 was supposed to be supplied by Advantage Engineering, Inc. Carrier Corporation was also assumed to provide suitable air cooled heat exchanger for Case 3. The selected models of these equipments and their total electrical power are summarized in Table 2. The specifications of air cooled heat exchanger are available in Appendix 1.5 and 1.6.
As the cooling capacity of each air cooled heat exchanger and the volume of toluene water mixture that should be cooled are different in each case, the operation time of every heat exchanger is distinctive. By considering inlet and outlet temperature of mixture, mixture mass, cooling capacity and operation time for each heat exchanger were calculated (53, 60, 60 second per operation day for case 1, case 2 and case3, respectively). Due to small weight of toluene in the mixture, it was neglected in calculations. The calculation details are available in Appendix 2.8.
Decanter
After cooling toluene/water mixture, the solvent should be separated and recovered. As the toluene/water mixture at 20oC is in aqueous phase, decanter was assumed to be used for toluene separation [30]. Based on flow rate of toluene/water mixture, a pressure vessel produced by Franken Filtertechnik KG was used. The flow rate was achieved from Aspen Plus 2006 that are available in Appendix 3.1. The decanter models selected for each case are summarized in Table 2 and their specifications are available in Appendix 1.7.
13 Table 2.Results of GAC adsorption process design
Unit Case1 Case2 Case3
Flow rate of polluted flue gas cfm 5886 5886 5886
Inlet toluene concentration mg/m3 100 1000 2000
ppmv 31.25 312.5 625
Inlet toluene weight kg/ week 40 400 800
Adsorption uptake on GAC, AP4-60 (Fig 8.) % w/w 19 27 29
Required amount of GAC, AP4-60 kg/ week 211 1482 2760
Required amount of steam for regeneration kg/day 21 207 413
Pressure drop through vessel cm of H2O 15 15 15
Total pressure drop∗a kPa 1.47 1.47 1.47
Atmospheric pressure∗b kPa 101.3 101.3 101.3
Required influent pressure of compressor ∗c=a+b kPa 102.77 102.77 102.77
Toluene/water mixture temperature oC 30.2 63.1 73
Toluene/water mixture flow rate kg/hr 1330.359 11571.922 23152.59 Total electrical power of air- cooled heat exchanger kW 3.73 134.22 544.8
Energy consumption for steam generating kWh/day 15.46 152.4 304
Cooling/drying time per day min ∼13 ∼92 ∼172
Cooling capacity of air cooled heat exchanger kW 16.73 623 1540.96
ton 4.76 177.2 438.3
Number of vessel - 1 1 1
Air fan power kW 22.37 22.37 22.37
Air heater power kW 2.5 2.5 2.5
Total volume of vessel m3 0.55 3.7 6.8
Vessel model manufactured by Calgon - VAPOR-
PAC® 10
VAPOR- PAC® 10
VAPOR- PAC® 10
Air fan model manufactured by SMJ Inc. - CR #56-
ARRANG E. #4
CR #56- ARRANG E. #4
CR #56- ARRANG E. #4 Air heater model manufactured by HOTWATT Co. - MA0-
10F1 MA0-
10F1 MA0-
10F1 Air- cooled heat exchanger model (Case 1 and 2
manufactured by Advantage Engineering, Inc and
Case 3 manufactured by Carrier Corporation) - C-5APT- RC
CCC- 180APT-
RC
30XA080- 500 Decanter model manufactured by Franken
Filtertechnik KG [31] - MPT 042 MPT 074 MPT 104
4.1.2 Properties of RTO process
4.1.2.1 Process streams
According to toluene concentration, which is lower than LEL in all cases, fuel should be added for combustion (toluene LEL= 43%) [13]. As a result, natural gas is another inlet stream used as a fuel. The flue gas treated is just one outlet stream in RTO process. As a result, two inlet streams (polluted air, natural gas) and one outlet stream (treated flue gas) were considered as process streams [5].
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The composition of natural gas is varied everywhere. The average composition of natural gas in the world was considered in this study. This composition is shown in Table 3.
Table 3.The average composition of natural gas in the world [32]
CH4 C2H6 C3H8 C4H10 C5H12+ N2 CO2 H2S
89.6% 4.3% 0.8% 0.3% 0.1% 3% 0.8% 1.1%
4.1.2.2 Input data
Polluted air enters to heat exchanger with 20oC at 101.3 kPa should be preheated up to 790oC.
Natural gas was used with 20oC at 101.3 kPa. Natural gas and polluted air are oxidized in the incinerator and the product that is hot gas stream leaves incinerator. The incinerator operates with 900oC at 101.3 kPa. The treated air that has no toluene concentration passes through air fan after leaving heat exchanger. Air fan should provide the pressure drop in the process. The maximum allowable pressure drop in the equipment was assumed to be 3 kPa [5] . According to H2O produced by hydrocarbons’ combustion, the temperature of treated air left from chimney should be high enough to avoid liquid formation. This temperature was assumed to be 155oC.
4.1.2.3 RTO process simulation
The process was simulated by Aspen Plus 2006. All three cases have the same simulations.
Shell and tube heat exchanger was used to simulate RTO process. An air fan was required to provide the equipments’ pressure drops. Due to high percentage of methane in considered natural gas shown in Table 3, just methane was considered as inlet fuel in Aspen Plus simulation. The process simulation is shown in Figure 11.
Figure 11.RTO simulation by Aspen Plus 2006 4.1.2.4 Required amount of natural gas
Required amount of natural gas was the main purpose of RTO simulation. Due to different toluene concentrations, the amount of natural gas needed for each case is different. In the other word, the higher toluene concentration in inlet stream, the lower required natural gas.
15
Aspen Plus results indicated the required amount of inlet natural gas (see Table 4 and Appendix 3.3).
Table 4.Required amount of natural gas
Case 1 Case 2 Case 3
Required amount of natural gas (m3/hr) 53.4 37.6 20.15
4.1.2.5 RTO equipments
RTO equipment used in this study is MODEL 75, AES- 86231 manufactured by Anguil Environmental Systems Inc [33]. This type of RTO equipment contains system fan and combined fan with 50 and 3 HP size, respectively (totally 39.54 kW). By considering flow rate, destruction efficiency, oxidation temperature, etc, this type of RTO is the same for all three cases. The specification of selected RTO equipment is available in Appendix 1.8.
4.1.3 Non-treatment alternative
As no treatment is done in this alternative, no equipment was considered. On the other hand, just toluene emission makes difference between three cases.
4.2 LCA study
By using process design data, GAC adsorption, VOCs incineration and Non-treatment alternative were compared by LCA. This part contains three main methodological approaches in LCA; goal and scope definition, life cycle inventory analysis and impact assessment.
4.2.1 Goal and scope definition 4.2.1.1 Purpose of study
The overall purpose of this study is comparison of two industrial flue gas treatment methods (VOCs incineration and GAC adsorption) and non-treatment alternative to find which one is preferable from environmental point of view.
4.2.1.2 Stakeholders
The relevant stakeholders and audiences of this study were classified under four main categories as following.
• Industries; where their flue gas contains VOCs especially toluene such as refineries, chemical plants, paint and color production plants, plastic manufacturers, ink manufacturers, pharmaceutical plants, food manufacturers, etc.
• Equipment producers; who produce equipments both for production line in mentioned industries and air treatment equipments such as SMJ Inc, HOTWATT, Carrier, Anguil Environmental System Inc, etc.
16
• Material manufacturers; who are producers of raw materials for mentioned industries and also materials for industrial flue gas treatment such as Chemviron Carbon, Calgon Carbon Corporation, etc.
• Authorities; who are decision makers of environmental policies such as EEA, EPA, EC, Swedish Environmental Protection Agency (Naturvårdsverket), etc.
4.2.1.3 Options to model
The flue gas considered in this study was assumed to contain just toluene in three different concentrations 100, 1000, 2000 mg/m3. The flow rate of contaminated flue gas was assumed to be equal for all three cases (10000m3/hr). Among different types of adsorption process, GAC adsorption was considered in this study. On the other hand, required steam for GAC regeneration was collected from other parts of plant, so no equipment was considered for steam generating. RTO was also considered as VOCs incineration method. In non-treatment alternative, flue gas was assumed to be emitted without any treatment.
4.2.1.4 Functional unit
The definition of functional unit should respect function, mass, quality and time unit [34]. In this study, the function is cleaning up the polluted flue gas. The functional flow of the flue gas was divided into two main parts: treated flue gas and toluene captured by the treatment methods. As specific industry has not considered in this study and flue gas treatment was generally investigated, the threshold of emitted toluene concentration was neglected. In the other word, according to Directive 1999/13/EC, limit value of emission in flue gas depends on industry type. Therefore, treated flue gas was assumed to be toluene free [34, 35]. To meet all functional unit factors, the functional unit in this study was defined as treatment of 10000 m3/hr polluted flue gas for a period of one year with no toluene concentration in treated flue gas.
4.2.1.5 Environmental impact category
According to toluene characteristics, it has no significant global environmental effects. In fact, toluene effects are locally [36]. When toluene is released to local environment, it will not present for a long time. It is rapidly evaporated from soil and surface water. The remaining toluene in the soil is broken down by micro-organisms. The toluene existing in the water can be taken by aquatic animals and plants. Toluene also as a VOC can contribute to formation of ground level ozone. It has also negative impacts on human health [36]. Therefore, impact categories of toluene if it is released to environment without any treatment consist of human toxicity, ecotoxicity (emission to water, air, and soil), and photochemical ozone creation potential [7]. On the other hand, GAC production can affect on depletion of energy resource, global warming, photochemical ozone creation, acidification, eutrophication and human health [8].
As natural gas is the main energy source for operating RTO in VOCs incineration method and it is needed for GAC production, environmental impacts of natural gas extraction, purification and transportation were considered in this study. The impact categories considered for natural gas consist of depletion of resources, global warming, human toxicity, photo-oxidant formation, eutrophication, acidification and ecotoxicity [32].
17 4.2.1.6 LCA type
LCA type in this study is a combination of accounting and change-oriented. Because of environmental impact investigation of VOCs incineration and GAC adsorption process, accounting LCA is preferable. On the other hand, due to another purpose of this study, which is comparison of two flue gas treatment methods from environmental point of view, change- oriented LCA could be also applicable. Therefore, the combination of accounting and change- oriented can fulfill the study purposes [7].
4.2.1.7 System boundaries
As system boundary is the baseline for drawing required LCI flowchart, five different boundaries were considered in this study as follows.
System boundary in relation to natural system
The system boundary in relation to natural system is cradle- to- cradle for GAC adsorption method. The system boundary for GAC adsorption was assumed to be started from coal extraction and continue into GAC production. After using produced GAC, it was assumed to be reactivated after one year operation. On the other hand, for GAC production process, natural gas should be extracted and transported to GAC manufacture plant.
This kind of system boundary is completely different for VOCs incineration method. The natural gas should be extracted and transported to plant where the polluted air is emitted.
Natural gas is consumed for operating of RTO and burning toluene in polluted air. Therefore, system boundary in VOCs incineration is cradle- to- grave because there is no recycling process.
Geographical boundaries
The plant where the polluted flue gas is emitted was assumed to be in Borås, Sweden. The selected GAC, AP4-60, is produced by Calgon Carbon Corporation in Datong (Shanxi, province, China) [37]. The produced GAC is transported from Datong to Tianjin port in China (323 km by road vehicles). Due to long distance between China and Sweden, produced GAC is transported from Tianjin to Gothenburg by ship (11496 Nautical miles1). GAC is also transported between Gothenburg to Borås by truck (60 km).
According to European natural gas network published by Inogate, natural gas imported to Sweden is extracted in Yamal field (north of Russia) and transported by pipeline to Gothenburg [38]. The required natural gas for Sweden is fed by Baltic pipeline. In fact, extracted natural gas from north of Russia is exported to Belarus, Poland, Germany, Denmark and Sweden, respectively [39]. The length of Baltic pipeline, from Yamal field to Gothenburg, is approximately 4960 km 2(Red line in Figure 12). Required natural gas for VOCs incineration was assumed to be transported from Gothenburg to Borås (60 km) by road vehicles. Baltic natural gas pipeline is shown in Figure 12.
1 1 Nautical mile= 1.852 km, (http://e-ships.net/dist.htm)
2http://maps.google.com/
18
Figure 12.Baltic natural gas network [38, 39]
On the other hand, required natural gas for GAC production is extracted from Ordos basin in Yinchuan (northeast of China) and transported to GAC manufacturing location in Datong by 885 km pipeline. The pipeline direction from Yinchuan to Datong is shown in Figure 13 with red line [40, 41].
Figure 13.Pipeline direction between natural gas basin and GAC manufacture [41]
The main equipments for GAC adsorption and VOCs incineration methods are provided from USA and Germany. Although the equipments are produced in different cities of USA, they were assumed to be transported to New York port by road vehicles and then transported to Sweden by ship. The transportation way and distance are available in Table App 5.1.
Time horizon
According to LCA type assumed in this study (combination of accounting and change- oriented) both prospective and retrospective time horizon must be considered [7]. If polluted flue gas is emitted without any treatment, the toluene can create ground level ozone. The creation of O3 at ground level has both short-term impacts on human respiratory system and long-term effects on lung system based on exposure duration [42]. According to change- oriented approach of LCA and by considering of 9.5 years for depreciation life of chemical
