Life Cycle Assessment of Chemical Processes and Products

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ABSTRACT

LI, YONG. Life Cycle Assessment of Chemical Processes and Products. (Under the direction of Dr. Michael R. Overcash).

Growing concerns about national energy security, global climate change, and depletion of natural resources have made the development of sustainable technology and products a priority worldwide. Our society has realized that environment-related

problems should be viewed on a more global and systematic scale. In order to combat further environmental damage, a preventive approach, life cycle assessment (LCA) becomes necessary as a step towards the development of sustainable practices.

In this study, environmental assessment of carbon dioxide application in soybean oil and bitumen production has been investigated using life cycle approach.

Environmental performance of carbon dioxide application is compared with current industrial processes in soybean and bitumen production. In soybean oil production, three stages of soybean oil processing are studied in detail: pre-processing, extraction and separation, and post-processing. For extraction, hexane (current industrial process) and supercritical CO2 (R&D lab scale process) methods are compared in detail. The initial life

cycle comparison finds that the lab scale CO2 system is not as good in life cycle impacts

as the hexane system. However, reasonable engineering improvements of typical scale-up practices will make the CO2 technology better than hexane and eliminate the hexane

emissions. Utilization of membrane techniques to separate the small molecular CO2 from

the soybean oil hydrocarbon appears to be a much better R&D direction for development. In bitumen production, Carbon dioxide-bitumen extraction process and hot

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production. Hot water extraction requires more energy than carbon dioxide extraction because of the heating demand of large water flow in the process. Our results show that the energy burden of carbon dioxide process is mainly because of the low solubility of bitumen in isopropyl benzoate solvent and low solubility of isopropyl benzoate in carbon dioxide.

Furthermore, Three carpet products: polyvinyl chloride (PVC) backed tile, styrene butadiene latex (SBL) backed broadloom, and polyurethane (PU) backed broadloom, are studied and compared using a life cycle approach. Based on the structure and

composition of carpet tile product, carpet tile supply chain is grouped into four

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LIFE CYCLE ASSESSMENT OF CHEMICAL PROCESSES AND

PRODUCTS

By

Yong Li

A Dissertation submitted to the Graduate Faculty of North Carolina State University

In partial fulfillment of the requirement for the Degree of

Doctor of Philosophy

Chemical Engineering

Raleigh, NC 2007

APPROVED BY

Ruben G. Carbonell Perry L. Grady

Christine S. Grant David F. Ollis Co-chair of Advisory Committee

Michael R. Overcash

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DEDICATION

I dedicate this to my parents, Jishan Li and Li’ai Cai, for their unconditional love

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BIOGRAPHY

EDUCATION

PhD in Chemical Engineering. Department of Chemical & Biomolecular Engineering of North Carolina State University, Raleigh, NC, 2002- Aug. 2007

MS in Chemical Engineering. Department of Chemical Engineering of University of Maryland, College Park, MD. 1999-2001

MS in Biochemical Engineering. Tianjin University, Tianjin, China. 1996-1999 BS in Chemical Engineering. Tianjin University of Science & Technology, Tianjin, China. 1992-1996

HONORS

2005 Mentored Teaching Assistantship (MTA), NCSU 1998 Honor student of Tianjin University

1996 Honor student of Light Industry Union of China

1995 Top Prize of Tianjin Wang Kechang Scholarship, Tianjin, China

ACTIVITIES

2004-2006 Treasure, International Society for Pharmaceutical Engineering (ISPE), NCSU chapter

2004 Group leader, NCSU international students orientation team

2003 NCSU Department of Chemical Engineering Graduate Recruiting Captain 2004-2005 VP, NCSU Dancesport Club

PRESENTATION & CONFERENCE

• Li Y, Griffing E, and Overcash MR, Life Cycle Inventories of Carpet Products.

InLCA/LCM conference, Washington D.C. Oct. 2006.

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• Realff MJ, Overcash MR, and Li Y. Life Cycle Assessment of Carpet Products. CARE 3rd annual conference, May 2005.

PUBLICATIONS

• Li Y, Griffing E, Overcash MR, and Rice G, Life cycle analysis of carbon dioxide, J Chem Technol Biotechnol, accepted, 2007

• Li Y, Higgins M, Griffing E, and Overcash MR. Life cycle assessment of soybean oil production. J Food Process Eng, Vol.29, 429-445, 2006.

• Li Y, Han ZW, He ZM, Wan J. Separation and purification of proteins by

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ACKNOWLEDGEMENTS

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LIST OF TABLES

Table 2.1. US commercial carbon dioxide production of 2003………..……….7

Table 2.2. Mass balance table of ammonia/CO2 process………….……….……….12

Table 2.3. Composition of the waste stream from H2 plant…..……….17

Table 2.4. Mass balance table of CO2 production process from H2 plant……….18

Table 2.5. Composition of the feed stream from natural deposit……… ……..19

Table 2.6. Mass balance of CO2 production from natural deposit……….21

Table 2.7. Mass balance of CO2 production from fossil fuel combustion……….27

Table 2.8. LCI input-output mass data of CO2 production processes without allocation .……….………28

Table 2.9. LCI potential energy recovery data of CO2 production processes without allocation. ………....30

Table 2.10. LCI energy input data of CO2 production processes without allocation ...31

Table 2.11. Quasi-microscopic allocation details of CO2 production processes …..……32

Table 2.12. LCI energy input data of CO2 production processes with allocation ………33

Table 3.1. Characterization of bitumen and tar sand……….45

Table 3.2. Composition of bitumen in Athabasca……….58

Table 3.3. LCI data summaries (on a 1000 kg/hr raw bitumen production base) of extraction processes .………..…… 59

Table 3.4. Comparison of properties of supercritical carbon dioxide with liquid solvents ……….……….60

Table 3.5. Energy consumption of hot water and IPB-CO2 extraction processes…….…63

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Table 3.7. Comparison of total energy-associated emissions between hot water and CO2

methods ……….66

Table 5.1. Summary of process inputs of carpet manufacturing processes………….…119

Table 5.2. Summary of process waste of carpet manufacturing processes…………..…120

Table 5.3. Summary of energy consumption of carpet manufacturing processes….…..121

Table 5.4. Physical properties of carpet coating compounds (nylon face fiber is excluded) ….………..……….124

Table 6.1. GTG LCI summary of nylon 6 and nylon 66 fibers…..…..………….……..136

Table 6.2. Average transportation distance and mode contribution………....139

Table 6.3. Energy conversion factors between process energy and natural resource energy ………...140

Table 6.4. CTG energy data of nylon 6 with allocation……….…..141

Table 6.5. CTG energy data of nylon 66 with allocation……..……….… 142

Table 6.6. CTG natural resource consumption of nylon 6 and nylon 66 with allocation ..………...………...143

Table 6.7. Energy module………143

Table 6.8. Energy comparison of polyamides ………...….146

Table 7.1. Compositions of carpet products………....155

Table 7.2. CTG energy consumption of PET………..158

Table 7.3. CTG energy consumption of polypropylene………..158

Table 7.4. CTG energy consumption of PVC……….163

Table 7.5. CTG energy consumption of SBL……….…….163

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LIST OF FIGURES

Figure 2.1. Process flow diagram of carbon dioxide production from ammonia/CO2

process……….9

Figure 2.2. Process flow diagram of CO2 production from H2 process……….14

Figure 2.3. Process flow diagram of CO2 production from natural deposit………..20

Figure 2.4. Process flow diagram of CO2 production from fossil fuel combustion……...24

Figure 2.5. Energy comparison of CO2 production processes based on quasi-microscopic allocation among byproducts………...…………..…………...35

Figure 3.1. Simplified overview of bitumen oil production system………..44

Figure 3.2. Flow sheet of hot water bitumen extraction process………..….47

Figure 3.3. Flow sheet of bitumen extraction using IPB and liquid CO2………..49

Figure 3.4. Flow sheet of bitumen upgrading process………...55

Figure 3.5. Athabasca bitumen viscosity.………..64

Figure 3.6. Comparison of total energy associated emissions between hot water and CO2 method……..……….………67

Figure 4.1. Overview of soybean oil production process. Dotted line indicates the system boundary of soybean oil life cycle studies……..……….…….77

Figure 4.2. Process flow diagram of pre-processing of soybean oil production…………78

Figure 4.3. Flow diagram of degumming process………...………..79

Figure 4.4. Flow diagram of caustic refining, bleaching, hydrogenation, and deodorization operation in post-processing………...……...79

Figure 4.5. Simplified conventional extraction operations.……….……..80

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Figure 4.7. Soybean CO2 extraction process energy variation in response to percent

change in specific process variables found in just the extraction method

……….………...84

Figure 4.8. Cradle to gate energy consumption comparison..………...88

Figure 4.9. Life cycle assessment for extraction/separation phase of soybean oil production using Eco-indicator 95 (Goedkoop 1995)……….….92

Figure 5.1. Typical tufted carpet structure………...100

Figure 5.2. Process flow diagram of the PVC tile carpet manufacturing process……...105

Figure 5.3. Process flow diagram of polyolefin tile carpet manufacturing process……109

Figure 5.4. Process flow diagram of SBL broadloom manufacturing process…………113

Figure 5.5. Process flow diagram of polyurethane broadloom carpet……….116

Figure 5.6. Energy consumption of carpet manufacturing processes………..122

Figure 6.1. Molecular structure of nylon: (a) nylon 6; (b) nylon 66……….……...129

Figure 6.2. Process flow diagram of nylon 6 fiber production………132

Figure 6.3. Process flow diagram of nylon 66 fiber production………..135

Figure 6.4. CTG chemistry tree of nylon 6 and nylon 66: (a) nylon 6; (b) nylon 66…..138

Figure 6.5. CTG energy details of nylon fiber with allocation………145

Figure 7.1. Schematic of carpet life cycle (Steps inside the dotted line are included in this study)………..……….………155

Figure 7.2. Chemical trees of PET and polypropylene: (a) PET; (b) polypropylene.….157 Figure 7.3. Chemical trees of PVC, SBL, and polyurethane………...160

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Figure 7.5. Environmental assessment comparison of nylon 6 and nylon 66 (impact

values of nylon 6 are set to be 100%)………..….…..167

Figure 7.6. Global warming impact comparison……….168

Figure 7.7. Acidification impact comparison………..169

Figure 7.8. HH noncancer impact comparison………170

Figure 7.9. HH cancer impact………..171

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1. Review of Life Cycle Assessment

Environmental problems in the chemical industry have been increasing in

magnitude and complexity even though highly efficient end-of-pipe technologies have

been developed to reduce emissions in the 1980s. In order to combat further

environmental damage, an integrated and preventive approaches, life cycle assessment

(LCA), seems necessary as a step towards the development of sustainable practices.

The concept of environmental life cycle assessment (LCA) was developed from

the idea of comprehensive environmental assessments of products, which was conceived

in Europe and in the USA in the late 1960s and early 1970s. It is an environmental

management tool that enables quantification of environmental burdens and the potential

impacts over the whole life cycle of a product, process or activity (Azapagic 1999). It

started as a tool for calculating energy requirements and solid wastes back to the late

1960s (Miettinen and Hamalainen 1997). Initial studies were simple with little attention

given to evaluating potential environmental effects. In the early 1970s, extensive energy

studies were conducted, based on the life cycle approaches, for a range of industrial

systems due to the oil crisis (FAVA and Page 1992). By the end of 1980s, numerous

studies using LCA had been performed (Udo de Haes 1993). However, many of these

studies were performed using different methods and without a common theoretical

framework. Consequently, the results between studies with the same goals often differed

considerably, which prevented LCA from becoming a more accepted analytical

technique. LCA has received wider attention and methodological development after it is

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Chemistry (SETAC) and International Standardization Organization (ISO) at the

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References:

Azapagic, A. (1999). "Life cycle assessment and its application to process selection,

design and optimisation." Chemical Engineering Journal, 73(1), 1-21.

FAVA, J. A., and Page, A. (1992). "Application of product life cycle assessment to

product stewardship and pollution prevention programs." Water Science and

Technology, V26(1-2), P275-287.

Miettinen, P., and Hamalainen, R. P. (1997). "How to benefit from decision analysis in

environmental life cycle assessment (LCA)." European Journal Of Operational

Research, 102(2), 279-294.

Udo de Haes, H. A. (1993). "Applications of life cycle assessment: Expectations,

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2. A Life Cycle Inventory of Carbon Dioxide as a Solvent and

Additive for Industry and in Products

Abstract

Life cycle inventories of four industrial carbon dioxide production processes were reported. The inventory data were calculated using design-based methodology. Energy consumptions and critical emissions of four carbon dioxide processes were compared. Quasi-microscopic allocation was applied to processes with multiple products. The inventory data of this study are transparent and can be used in other life cycle studies.

Keywords

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2.1 Introduction

Life cycle assessment (LCA) is an environmental management tool that enables quantification of environmental burdens and potential impacts over the whole life cycle of a product, process or activity (Azapagic 1999). It started as a tool for calculating energy requirements and solid wastes in the late 1960s (Miettinen and Hamalainen 1997). Initial studies were simple with little attention given to evaluating potential

environmental effects. In the early 1970s, extensive energy studies were conducted based on the life cycle approach for a range of industrial systems due to the oil crisis (FAVA and Page 1992). Since 1980s, numerous studies using LCA have been performed (Udo de Haes 1993). However, many of the results in these studies have not been transparent. Therefore, the use of those results, especially the life cycle inventory data, is limited. In this study, we will investigate the environmental footprint of carbon dioxide

manufacturing. The goal of this study is to present the life cycle inventory of commercial carbon dioxide in a transparent way that the results can be used for other life cycle studies.

In nature, carbon dioxide is a product of human and animal metabolism and a reactant in plant photosynthesis. Carbon dioxide is also produced by combustion of carbonaceous materials. Natural deposits of carbon dioxide have also been found

underground in a gaseous state. Deposits can be highly concentrated or mixed with other gases.

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processes such as the hydrogen process, using steam reforming of natural gas. Because gaseous carbon dioxide cannot be transported economically over long distances, the gaseous carbon dioxide is usually liquefied for sale. Since carbon dioxide is increasingly being used as a solvent and in other processes (Cheng et al. 2001; Subramaniam 2001; Tamer S. Ahmed et al. 2006; Wood and Cooper 2001), the life cycle inventory (LCI) of this chemical can be used in a number of new life cycle studies.

2.2 Methodology

In spite of more and more interest in LCA, the available life cycle inventory information is still far less than desired. In the chemical industry, companies have considered some information needed in life cycle studies as competitive intelligence. In this study, we use design-based approach methodology (Jimenez-Gonzalez and Overcash 2000; Overcash 1994) to obtain most of the life cycle inventory data, in which the life cycle information of each gate-to-gate subsystem is obtained using chemical engineering design techniques. The gate-to-gate subsystems are linked through a production chain (referred to as the chemical tree), which includes extraction of raw materials and

manufacturing processes. Whenever the site-specific information is available, it is applied to the process design in each study. The functional unit is defined as 1000 kg of liquid carbon dioxide product. In all these commercial processes, the input of reactants is mostly fuel and fuel production processes are not included in this analysis, the goal is a gate-to-gate of the actual CO2 production. In an effort to be more transparent and reflect

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2.3 Life cycle inventory of CO2 production

The carbon dioxide industry is concentrated among a few global companies (e.g. Air Liquide, BOC, and Praxair). Commercial carbon dioxide can be generated as a by-product of several industrial processes. Large amounts of carbon dioxide can also be recovered from natural underground deposits. The US commercial carbon dioxide

production distribution of 2003 is shown in Table 2.1. In this study, we will include three major carbon dioxide production processes: ammonia process, refinery hydrogen process, and natural deposit carbon dioxide production. We will also discuss the carbon dioxide production from fossil fuel combustion used to make steam for industrial utilization. The processes and LCI presented here are representative of the company-specific processes found to produce CO2 by the routes shown (Kirk et al. 1992; Ullmann c1985-c1996.).

The CO2 production from ethyl alcohol is not included because CO2 from ethyl alcohol

fermentation is often used directly inside the alcohol industry, such as in beer production but not for ethanol fuel production.

Table 2.1. US commercial carbon dioxide production of 2003(Ishikawa 2003)

Sources

Production, Metric tons

per day Percentage

Ammonia by-product 7.13E+03 24%

Ethyl alcohol by-product 5.82E+03 20%

Natural deposit 6.50E+03 22%

Refinery hydrogen by-product 5.77E+03 20%

Others 4.19E+03 14%

Total 2.94E+04 100%

2.3.1 Carbon dioxide as a by-product of ammonia process

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secondary reformers to oxidize methane to hydrogen and carbon monoxide. The gas mixture is then fed through two shift converters to oxidize carbon monoxide to carbon dioxide. Carbon dioxide is then separated and purified. The remaining nitrogen and hydrogen are reacted to produce ammonia. The flow diagram of CO2 production from

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Secondary reformer Shift converter High temp. Shift converter Low temp. Primary reformer 1 (g) Natural gas 378.9kg/hr 25 oC

4(g) Air 940 kg/hr 25 oC

Heat recovery A

Heat recovery B

Heat recovery C Cooler 1 3 (l)

25oC 5 (g) 497.8 oC 27.2 atm

6 (g) 760oC 27.2 atm

7 (g) 788oC 31 atm

8 (g) 974oC 31 atm

9 (g) 360oC 31 atm

10 (g) 427oC 31 atm

11 (g) 243oC 31 atm

12 (g) 266oC

31 atm 13 (g)

90oC 31 atm

14 (g/l) 40oC 31 atm Cmp 1 C2 C1 C4 (g) P 1 2 (l)

Water 1018 kg/hr 25oC

C

C17 C18 47 (g)

Water 89.9 kg/hr CO239.5 kg/hr NO 3.0 kg/hr NO24.6 kg/hr N2475.1 kg/hr Ar 8.7 kg/hr O222.7 kg/hr 788oC

48 (g) Air 584.1 kg/hr 25 oC

Heating fuel

Burner

C3

C4

C3

All cooling water has20 o_{C and 50}o_C_{as input and}

output temperature respectively.

All steam streams have temperature of207 o_C_but

input stream is gas phase and output stream is liquid phase.

15 (l) Water 435.0 kg/hr 25 oC Gas/liquid Separator A

A 16 (g) 40oC 31 atm

(a)

Carbon dioxide

absorber Carbon dioxide

stripper

B

Heat exchanger A

Co o le r 2 Cooler 3 P 3 19 (g/l) 80 oC 25 (l)

41oC

22 (l) 82oC

20 (g)

82oC 21 (g)

25oC 17 (g)

76oC 20 atm

Boiler

S1 24 (l)

78oC C7 S2 C8 C9 C10 18 (g/l) 76oC

18a (g/l) 76oC 16 (g)

40oC 31 atm

23 (l) 82oC Heater 1

S3

S4

26 (g) 288oC 20 atm

input stream is gas phase and output stream is liquid phase. P 2 A Cmp2 Cooler 7 C19 C20 Refrigeration 3 21a (g) 280 o_C

18 atm

21b (g) 25 o_C

18 atm 21c (l)

Liquid CO2product

1000 kg/hr -22 o_C

18 atm

Carbon dioxide

absorber Carbon dioxide

stripper

B

Heat exchanger A

Co o le r 2 Cooler 3 P 3 19 (g/l) 80 oC 25 (l)

41oC

22 (l) 82oC

20 (g)

82oC 21 (g)

25oC 17 (g)

76oC 20 atm

Boiler

S1 24 (l)

78oC C7 S2 C8 C9 C10 18 (g/l) 76oC

18a (g/l) 76oC 16 (g)

40oC 31 atm

23 (l) 82oC Heater 1

S3

S4

26 (g) 288oC 20 atm

input stream is gas phase and output stream is liquid phase. P 2 A Cmp2 Cooler 7 C19 C20 Refrigeration 3 21a (g) 280 o_C

18 atm

21b (g) 25 o_C

18 atm 21c (l)

Liquid CO2product

1000 kg/hr -22 o_C

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(c ) B Methanator Ammonia Converter Ammonia Storage Heat recovery D

Cooler 4

26 (g) 288oC 20 atm 27 (g) 313oC 20 atm

28 (g) 121oC 20 atm

43oC 20 atm

Steam-turbine centrifugal compressor A

177oC 170 atm

Cooler 5

Steam-turbine centrifugal compressor B

32 (g) 93oC 204 atm

Cooler 6

Refrigerator 1

34 (l/g) -23oC 204 atm Gas/Liquid

Separator C Heat exchanger B

36 (g) 158oC 177 atm

Heat recovery E

37 (g) 37oC 177 atm

38 (g) 254oC 177 atm

41 (g) 38oC 177 atm

Refrigerator 2 43 (l/g)

-23oC 177 atm

Gas/Liquid Separator D NH3840.4 kg/hr

Water 8.0 kg/hr S7 316 oC (g)

29 (g) C11

C12

S8 149 oC (l) 30 (g) C13 S6 S5 C14 S8 S9 C16 (l/g) 39 (g)

38oC 177 atm

46 (l) -23oC

44 (g) -23oC 177 atm S11

S12

C

45 (l) -23oC 177 atm 42 (l)

-23oC 204 atm 31 (g) 177oC 170 atm 177oC 170 atm

40 (g) 38oC

177 atm C15

35 (g) -23 oC 204 atm

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Table 2.2. Mass balance table of ammonia/CO2 process

Stream Total flow, kg/1000 kg CO

2

methane nitrogen hydrogen ammonia carbon dioxide carbon monoxide Argon oxygen Monoethanolami ne NO NO

2

Water

Gas Liquid Solid

1 378.9 378.9

2 1017.8 1017.8

4 940.0 721.0 219.0

7 1396.9 87.2 124.0 300.2 318.4 567.1

8 2337.0 7.3 721.0 124.0 245.5 492.7 746.5

11 2336.8 7.3 721.0 153.4 885.5 85.3 484.3

12 2336.7 7.3 721.0 158.9 1005.9 8.5 435.0

16 1901.7 7.3 721.0 158.9 1005.9 8.5 17 901.8 7.3 721.0 158.9 6.0 8.5

18 13914.2 999.9 2583.5 10330.8

20 999.9 999.9

21c -999.9 -999.9

22 12914.3 2583.5 10330.8

26 901.8 7.3 721.0 158.9 6.0 8.5

27 899.4 14.4 721.0 156.0 8.0

32 4750.6 317.9 2313.0 520.1 1073.8 517.9 8.0

40 3841.8 303.5 1592.0 364.1 1072.9 509.2

41 71.3 14.4 27.1 5.9 15.3 8.7

42 836.9 829.0 8.0

43 71.3 14.4 27.1 5.9 15.3 8.7

44 59.9 14.4 27.1 5.9 3.8 8.7

45 11.5 11.5

46 -848.4 -840.4 -8.0

48 584.1 448.0 136.1

15 -435.0 -435.0

47 -643.5 -475.1 -39.5 -8.7 -22.7 -3.0 -4.6 -89.9

Fugitive

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2.3.2 Carbon dioxide as a by-product of refinery H2 process

Fig. 2.2 (a), (b), and (c) are the hydrogen process in the refinery that produces the process stream ©, as the source of the CO2. This stream is used to provide heat for the

first reactor and then to preheat reactor input streams. The waste stream from a refinery H2 process has about 82.4% of carbon dioxide, as shown in Table 2.3, thus making this

stream a prime candidate for commercial carbon dioxide. Liquid water is removed from the CO2 waste stream through a gas-liquid separator. Then, the gas stream passes though

an activated alumina dryer to remove the remaining water. The dried gas stream is then compressed and cooled to 260 oC and enters a catalytic reactor. In the catalytic reactor, the CO2 waste is mixed with excess volumes of O2 for combustion of the hydrocarbons

and hydrogen. The combustion catalytic reactor is operated at 20.4 atm and 260 oC(CJ Heim 2003). The product stream is dried with an activated alumina dryer and sent to a light knock-out column, where the excess oxygen is vented to atmosphere and the CO2 is

liquefied at –22 oC and 18 atm. The process flow diagram of the CO2 purification process

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R 1: Partial Oxidation

Reactor Unit 1,300o_{C, 20 atm}

HeatX 2 Heater 1

A

6 (g) 7b (l)

20 atm Compressor 1

Compressor 2

Pump 1 650o_C

20 atm

Quencher: Mx 1 1 (g)

305.5 kg Methane 32.4 kg Ethane 23.7 kg Propane 16 kg Water 25.0 oC

2 (g) 289 o_C

20 atm

3 (g) 650 o_C 20 atm

7 (g) 1300 oC 20 atm

4 (g) 362.6 kg Oxygen 25.0 o_C

5 (g) 416.4 oC

20 atm 7a (l)

746.3 kg Water 25.0 o_C

8 (g) 222.1 o_C

20 atm Fugitive Replacement of Reactants(g)

1.5 kg Methane 0.2 kg Ethane 0.1 kg Propane 25 o_C

C D

E

15 (g) 1771 o_C

16 (g) 1310 o_C 17 (g)

1310 o_C 18 (g)

841 o_C

19 (g) 1310 o_C

20 (g) 1115.0 o_C

(a)

A _{Gas Mixture}

370o_{C 20 atm}

Pressure Swing Absorption Unit (PSA) 19 atm – 1 atm Condenser

8 (g)

10 (g)

362.2 o_C

19 atm GTrb 1 Pump 4 HX 3 HX 4 11a 70oC 1 atm 10a (g)

70o_C

B

9 (g)

C1 C3 C2 C5 C6 14 (g)

70 o_C

13 (g)

103.5 kg Hydrogen

0.1 kg Methane 70.0 o_C

19 atm

11b (l)

400.2 kg Water 25.0 o_C

LTrb 1 11 (l) 19 atm 70o_C

12 (g) 70oC 19 atm R2: Shift converter

C4

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B

Furnace

14 (g) 70 o_C

Fugitive Losses (Total) (g)

5.0 kg Carbon dioxide

3.2 kg Carbon monoxide

1.5 kg Methane

0.6 kg Hydrogen

0.2 kg Ethane

0.1 kg Propane

15 (g) 1771 o_C

14a (g)

237.2 kg Oxygen

25.0 o_C

C (R3) HX 4a C7 C8 F D E 18 (g)

841 o_C 20 (g)

1115 o_C 21 (g) 913 o_C

22 (g) 25.0 o_C

Mx 2

(c) 26 (g) 25 o_C

23 (l) 25 o_C

Activated Alumina Dryer 1 T: 25 o_C

29 (g) 25 o_C

31 (g) 260o_C 20.4 atm Oxygen

5 kg Waste water

3.14 kg

HX6

Catalytic reactor P: 30 atm

T: 25 o_C 27 (g)

295 o_C 20.4 atm

32 (g) 260 o_C 20.4 atm

30 (g) 420 o_C 20.4 atm C14 HX7 Wastewater 2.06 kg 33 (g) 25 o_C 20.4 atm

34(l) 25 o_C 20.4 atm

Activated alumina Dryer 2 T: 25 o_C P: 20.4 atm 35 (g)

25 o_C 20.4 atm G C13 C11 C12 Cmp 3 Cmp 2 g/l separator 1

24 (g) 25 o_C

Waste water 212 kg

22(g) 25 o_C

25 (l) 25 o_C

HX5 C9

C10

28 (g) 260 o_C 20.4 atm F

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Lights knock out (g/l separation 2)

T: -22 o_C P: 18 atm

37 (g) 17.1 o_C 18 atm

1000 kg Liquid CO2 G

36 (g) 25 o_C 20.4 atm

6.9 kg Waste gas

38 (g/l) -22 o_C 18 atm

39 (g) -22 o_C 18 atm

40 (g) -148o_C

42 (l) -22o_C 18 atm

GTrb 2

41 (g) 25o_C

Refrigeration 1

Ambient heating

GTrb3

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Table 2.3. Composition of the waste stream from H2 plant

Feed Stream Component Weight Percentage

Carbon dioxide, CO2 82.4

Water. H2O 17.5

Oxygen 0.1

Methane, CH4, 0.01

Ethane, C2H6 0.01

Propane, C3H8 0.01

Hydrogen 0.01

Carbon monoxide 0.001

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Table 2.4. Mass balance table of CO2 production process from H2 plant.

Gas Liquid Solid

Streams Total Flow Methane Ethane Propane Oxygen Carbon monoxide Carbon dioxide Water Hydrogen

1 377.6 305.5 32.4 23.7 16.0

4 362.6 362.6

7 740.3 4.2 0.1 0.1 1.2 632.6 0.0 16.0 86.1

7a 746.3 746.3

8 1486.6 4.2 0.1 0.1 1.2 632.6 0.0 762.3 86.1

9 1486.6 4.2 0.1 0.1 1.2 69.2 885.3 400.2 126.3

11 400.2 400.2

11b -400.2 0.0 0.0 0.0 0.0 0.0 0.0 -400.2 0.0

12 1086.4 4.2 0.1 0.1 1.2 69.2 885.3 0.0 126.3

13 -103.6 -0.1 0.0 0.0 0.0 0.0 0.0 0.0 -103.5

14 982.8 4.1 0.1 0.1 1.2 69.2 885.3 0.0 22.8

14a 237.2 237.2

15 1220.0 0.1 0.1 0.1 1.2 0.0 1005.2 213.2 0.1

17 854.0 0.1 0.1 0.1 0.8 0.0 703.6 149.3 0.1

19 366.0 0.0 0.0 0.0 0.4 0.0 301.5 64.0 0.0

21 1220.0 0.1 0.1 0.1 1.2 0.0 1005.2 213.2 0.1

23 -212.0 0.0 0.0 0.0 0.0 0.0 -1.0 -211.0 0.0

24 1007.7 0.1 0.1 0.1 1.2 0.0 1004.0 2.1 0.1

25 -3.1 0.0 0.0 0.0 0.0 0.0 -1.0 -2.1 0.0

26 1004.6 0.1 0.1 0.1 1.2 0.0 1003.0 0.0 0.1

29 5.0 5.0

32 1009.3 0.0 0.0 0.0 4.2 0.0 1004.0 1.1 0.0

34 -2.1 0.0 0.0 0.0 0.0 0.0 -1.0 -1.1 0.0

35 1007.2 0.0 0.0 0.0 4.2 0.0 1003.0 0.0 0.0

39 6.9 4.2 2.7

41 -6.9 0.0 0.0 0.0 -4.2 0.0 -2.7 0.0 0.0

42 -1000.0 0.0 0.0 0.0 0.0 0.0 -1000.0 0.0 0.0

Fugitive loss

(35)

2.3.3 Carbon dioxide from natural deposit

A number of CO2 natural reservoirs have been discovered at various locations in

the central United States. The gaseous underground CO2 is at high pressure and can be

highly concentrated. Three reservoirs in southern Colorado and northern New Mexico are currently supplying CO2 to the oil industry in the Permian Basin of west Texas and

eastern New Mexico(Heller 1994). This CO2 serves as a solventfor underground injection

thus enhancing oil recovery in wells. The feed stream has about 92% mole fraction of CO2. The detailed composition of the feed stream is shown in Table 2.5(Rice March

1996).

Table 2.5. Composition of the feed stream from natural deposit Feed Stream Component Weight Percentage

Carbon dioxide, CO2 96.4

Methane, CH4 2.52

Nitrogen, N2 0.74

Ethane, C2H6 0.12

Water. H2O 0.069

Propane, C3H8 0.042

Helium, He 0.0038

Iso-Butane 0.014

Others (heavies) 0.056

(36)

Crude CO2gas 1114.74 kg/hr

1(g/l) 25 oC 49 atm

3(g) 25 oC 49 atm 2(l) 25 oC Waste gas

-26.7 kg/hr

Activated alumina dryer 1

T: 25 oC P: 49 atm

4(l) 49 atm

25 oC

5(g) 25 oC 49 atm Heavies knock out

(g/l separator 1) T: 25 oC P: 49 atm

6(g) 24 atm -100 oC

8(g) -100oC 24 atm

9(l) -100 oC 24 atm

Demethaniser (R1) T: -100 oC P: 24 atm

10 (g) 25 oC Oxygen

16 kg/hr Waste Gas

combustion Waste water

0.736 kg/hr

6a (g) 25 oC

6b (g) 25 oC Air

6 kg/hr

Catalytic reactor (R4) P: 20.4 atm

T: 468 oC 5a (g)

-17.3 oC 24 atm

Refrigeration 1

A 5 b (l)

-100oC 24 atm

HX2 9a (l)

-100 oC 20.4 atm

12 (g) 468 oC 20.4 atm

11 (g) 420 oC 20.4 atm C2

50 oC HX4 P2 S4 Wastewater 18.8 kg/hr 13(l) 25 oC

12a (g) 25 oC 20.4 atm Activated

alumina dryer 2 T: 25 oC P: 20.4 atm 14(g)

25 oC 20.4 atm B

C1 20 oC

C 7(g)

-100 oC 24 atm

9b (g) 200 oC 20.4 atm Gtrb 1 Ltrb 1 Cmp 1 S3 (a) Waste gas 55.5 kg/hr 8e(g) 25 oC 8d (g) 25 oC

Wastewater 11.3 kg/hr

Air 55.6 kg/hr

8c (g) 25 oC Electric power

generation

A _-1008 (g)oC 24 atm

Lights knock out (g/l separation 2) T: -22 oC P: 18 atm 15(g)

17.1 oC 18 atm

Liquid CO2gas

1000 kg/hr

B

14(g) 25 oC 20.4 atm

Waste gas 31.1 kg/hr

16(g/l) -22 oC 18 atm

17(g) -22 oC 18 atm

18(g) -148oC

19(l) -22oC 18 atm C5

20 oC

Refrigerant compression

7c (g) 25 oC Waste gas 99.5 kg/hr

7b(l) 25 oC

Waste water 48.6 kg/hr

7a (g) 25 oC

Air 100 kg/hr

7(g) -100 oC 24 atm HX1

S2 S1

8b (g) 25oC 8a (g)

-195 oC Gtrb 4

Gtrb 3

GTrb 2

18a (g) 25oC

C Refrigeration 2 Ambient heating (R2) (R3) (b)

(37)

As shown in Fig. 2.3, the natural CO2 deposit is taken as 49 atm and first enters a

high-pressure activated alumina dryer, which removes water from the feed stream. In the heavies knock-out column, the more dense components, such as hexane and benzene are removed from the feed stream. A small amount CO2 is also lost in this unit. Methane and

other impurities lighter than CO2 are removed in the demethaniser column, which is

operated at –100 oC and 20.4 atm(Steve Robertson 1998). In the catalytic reactor, the CO₂

is mixed with an excess of stoichiometric O2 necessary for combustion of the remaining

hydrocarbons. The combustion catalytic reactor is operated at 20.4 atm and 468 oC (CJ Heim 2003). The product stream is dried with a medium pressure activated alumina dryer and sent to a light knock-out column, where the excess oxygen and inerts are vented to the atmosphere and the CO2 is liquefied. The mass flows of this process are shown in

Table 2.6.

Table 2.6. Mass balance of CO2 production from natural deposit

Streams To

tal Flo w , kg/ hr C arbon di oxi de

Methane Ni

trogen

Et

hane

Propane Heliu

m

Isobut

ane

n-Pent

ane

Oxygen Air Water

1 1115 1075 28.1 8.27 1.36 0.469 0.0425 0.155 0.623 0.766

3 1114 1075 28.1 8.27 1.36 0.469 0.0425 0.155 0.623 0 0 0

4 17.6 16.8 0.100 0

1.30E-04

0.0469 0

9.32E-03

0.623 0

5 1096 1058 28.0 8.27 1.36 0.422 0.0425 0.145

6.23E-04

0 0 0

6b 6.00 6.00

7 48.1 20.4 21.6 6.05 0.0497

9.75E-03

0.0328 2.24E-03

4.80E-06

0 0 0

7a 100 100

8 11.2 4.76 5.04 1.41 0.0116

2.28E-03 7.66E-03 5.22E-04 1.12E-06

0 0 0

8c 55.6

9 1034 1032 2.80E-03

0.414 1.29 0.409 0 0.142

6.17E-04

0 0 0

(38)

Table 2.6. (continued)

10 16.0 16.0

12 1050 1037 0 0.414 0 0 0 0 0 9.17 0 3.22

14 1031 1022 0 0.414 0 0 0 0 0 9.17 0 0

19 -1000 -1000 0 0 0 0 0 0 0 0 0 0

2 -0.766 0 0 0 0 0 0 0 0 0 0 -0.766

6a -26.7 -24.3 0 -0.393 0 0

-2.13E-03

0 0 0 2.42 -4.40

7b -48.6 0 0 0 0 0 0 0 0 0 0 -48.6

7c -99.5 -79.7 0 -6.05 0 0 -0.0328

-2.24E-03

-4.80E-06

0 -13.7 0

8d -11.3 0 0 0 0 0 0 0 0 0 0 -11.3

8e -55.5 -18.6 0 -1.41 0 0

-7.66E-03

0 0 0 -35.5 0

13 -18.8 -15.6 0 0 0 0 0 0 0 0 0 -3.22

18a -31.1 -21.6 0 -0.414 0 0 0 0 0 -9.17 0 0

Fugitive Losses

-5.54 -5.37 -0.141 0

-6.79E-03

-2.34E-03

-2.13E-04

-7.73E-04

-0.0125 0 0 0

2.3.4 Carbon dioxide from fossil fuel combustion

Fossil fuel combustion is one of the greatest contributions to CO2 emissions in the

world. Combustion in industry is after a part of the utilities plant to generate steam, and hence a CO2 stream is produced. Carbon dioxide can be recovered as a pure product from

this source as shown in Fig. 2.4. The fuel oil is pumped into a combustor and oxygen is provided from air. The combustion temperature is generally about 550 oC(Juan P. Mercader 1989). The gas stream from the combustor with 17.4% CO2, 74.3% nitrogen,

and 7.9% water, passes through a scrubber. Sulfur dioxide is removed in a scrubber and 10% of CO2 is lost into the wastewater stream. The exit gas stream passes through the

absorber, CO2 is absorbed, and then released in the regenerator by heating the CO2-rich

(39)

(40)

(41)

P1 1 (l) 428 kg Kerosene 0.873 kg Sulfur 25.0 o_C

2 (l) 25 o_C

3 (g) 5616 kg Nitrogen

1512 kg Oxygen 25.0 oC

2c (g) 5621 kg Steam

100o_C

Combustor ( R1 )

3a (g) 25 o_C

2a (l) 5621 kg Water

20 o_C P1a

Blower 1 2b (l)

20 o_C

C

Fugitive Losses (Total) (g) 6.57 kg Carbon dioxide 8.72E-03 kg Sulfur dioxide 25 o_C

3b(g) 550o_C

(a) Water 32258.8 kg/hr Liquid CO2 1000 kg/hr P2 4 (l) 3.23E+04 kg Water 25.0 oC 5 (l) 25 oC

6 (l) 56.6 oC

7(g) 57 oC

10c (g) 25oC

11 (l) 17.0 kg Water 5.07 kg Carbon dioxide

6.28E-04 kg Sulfur dioxide 25.0 oC

12 (g) 25oC

13 (g) 279.4 oC

18 atm 15 (l)

10.2 kg Water 5.04 kg Carbon dioxide

25.0 oC

18 (l) 1000 kg Carbon dioxide

-22.0 oC 18 atm Activated carbon purification Cmp1 10a (l)

25 oC Scrubber

(Mixer 1)

10 (g) 25oC

C9 20 oC

C10 50 oC

HX6 14 (g/l)

25oC 18 atm Refrigeration 1

16 (g) 25oC 18 atm

Activated alumina dryer 1

C3 20 oC

C4 50 oC

P3

HX1 6b (l)

3.22E+04 kg Water 131 kg Carbon dioxide

56.2 kg Nitrogen 4.00 kg Oxygen 2.14 kg Kerosene 1.73 kg Sulfur dioxide

25.0 oC

10b (l) 539 kg Water 15.4 kg Carbon dioxide 0.229 kg Monoethanol

Amine 6.97E-05 kg Sulfur

dioxide 25.0 oC

P7

P6

g/l separator 1

A B

g/l separator 2 17 (l)

25 oC 18 atm

6a (l) 56.6 oC P3a

17a (l) 3.31 kg Carbon

dioxide 1.13 kg Water

25.0 oC C

3b(g) 550oC

(42)

HX2

A

8 (g) 5560 kg Nitrogen

654 kg Water 154 kg Carbon dioxide

21.0 kg Oxygen 2.29 kg Monoethanol Amine

0.0166 kg Sulfur dioxide 25.0 oC

Reboiler

( HX4 ) 7 (g)

56.6 oC

P4

HX 3

C6

Absorber

Regenerator

C7

C8

HX5

B

8g (l) 60oC

8b (l) 60oC 8a (l)

60oC

8c (l) 90oC

9 (g) 125oC

10 (g) 25oC

8d (l) 125oC 8e (l) 125oC 8f (l) 90oC

P5 S1 _S2

C5 P5a

7a (g) 534 kg Water 2.50 kg Monoethanol Amine

25.0 oC All cooling water has20 o_{C and 50}o_C_{as input and}

(43)

Table 2.7. Mass balance of CO2 production from fossil fuel combustion

Streams To

tal Flo

w

,

kg/

hr

C

arbon di

oxi

de

Oxygen Ni

trogen

Kerosene Sul

fur di

oxi

de

Sulfur Water Monoet

h

anol

Amine

1 428 428 0.873

3 7128 1512 5616

2a 5621 5621

2c -5621 -5621

3b 7557 1314 25.0 5616 2.14 1.74 0 598 0

4 3.23E+04 3.23E+04

6 3.24E+04 131 4.00 56.2 2.14 1.73 0 3.22E+04 0

7 7450 1183 21.0 5560 0 0.0174 0 687 0

7a 537 534 2.50

8a 1.30E+04 1029 0 0 0 8.72E-04 0 9710 2286

9 1596 1029 0 0 0 6.97E-04 0 567 0.229

10a 554 15.4 0 0 0 6.97E-05 0 539 0.229

10c 1042 1013 0 0 0 6.28E-04 0 28.4 0

12 1020 1008 0 0 0 0 0 11.3 0

16 1004 1003 0 0 0 0 0 1.13 0

17 1000 1000 0 0 0 0 0 0 0

18 -1000 -1000 0 0 0 0 0 0 0

6b -3.24E+04 -131 -4.00 -56.2 -2.14 -1.73 0 -3.22E+04 0

8 -6391 -154 -21.0 -5560 0 -0.0166 0 -654 -2.29

10b -554 -15.4 0 0 0 -6.97E-05 0 -539 -0.229

11 -22.1 -5.07 0 0 0 -6.28E-04 0 -17.0 0

15 -15.2 -5.04 0 0 0 0 0 -10.2 0

17a -4.44 -3.31 0 0 0 0 0 -1.13 0

Fugitive Losses -6.58 -6.57 0 0 0 -8.72E-03 0 0 0

(44)

2.4 Results and discussion

As a chemical product, carbon dioxide product has a very short supply chain. As a result, the environmental footprint of carbon dioxide production process is often more important than that of the CO2 supply chain from a life cycle point of view. The LCI

input-output data of CO2 production processes (gate-to-gate or GTG) are shown in Table

2.8, and the LCI process potential energy recovery data and process energy input data are presented in Table 2.9 and 10. The quality of the energy used is designated as electricity (E), 207oC steam (S), and high temperature heat from burners and hot air (G-natural gas, HF-heating fuel).

Table 2.8. LCI input-output mass data of CO2 production processes without allocation.

From NH3 plant From H2 plant From natural deposit From fossil fuel

Input materials

Chemical

Amount, [kg/1000kg CO2]

Natural gas 379 365 - -

Oxygen from air 355 237 162 1512

Carbon dioxide

deposit - - 1115 -

Oxygen (Pure) - 367 16 -

Kerosene (0.2%

sulfur) - - - 429

Nitrogen from air 1169 - - -

Water 1018 158 - 5972

Total 2921 1127 1293 7913

Nonreacting inputs

Chemical

Process water - 604 - 32793

Total 0 604 0 32793

Ancillary inputs

Chemical

Monoethanol amine - - - 2.5

Oxygen (Pure) - - 16 -

Total 0 0 16 2.5

Product

Chemical Amount, [kg] Amount, [kg] Amount, [kg] Amount, [kg]

Carbon dioxide 1000 1000 1000 1000

(45)

Hydrogen - 104 - -

Steam - - - 5621

Total 1848.2 1103.5 1000 6621

Process Emissions Air emission

Chemical

Ar 11.27 - - -

CH4 - 1.42 0.14 -

CO 1.89 3.16 - -

CO2 44.56 8.09 149.63 160.00

Ethane - 0.16 0.01 -

Hydrogen - 0.74 - -

Helium - - 0.04 -

Monoethanol Amine - - - 2.30

SO2 - - - 0.03

Isobutane - - 0.00 -

n-Pentane - - 0.01 -

NH3 5.45 - - -

NO 2.99 - - -

NO2 4.57 - - -

Propane - 0.22 - -

Total 70.73 13.79 149.84 162.32

Water emission

CO2 - 3.01 15.6 160

Monoethanol Amine - - - 0.23

SO2 - - - 1.70

Kerosene - - - 2.14

Total 0.00 3.01 15.6 164.069

-

Benign output flows

Chemical

Nitrogen from air 475 - - -

Oxygen from air 23 4 - 25

Water 525 615 - 33391

Total 1023 619 0 33411

Table 2.8 shows that CO2 production from fossil fuel has the largest amount of

water usage, where this is water for reaction or as solvent and not water utilities for cooling or steam (largely uncontaminated and reused). This can be tracked to the

(46)

differences of emitted chemicals, such as ammonia process with noticeable ammonia emission, and hydrogen process with hydrogen emission.

Table 2.9. LCI potential energy recovery data of CO2 production processes without allocation.

From Ammonia From hydrogen From natural deposit From Fossil fuel

PFD label Process Unit Energy Recovered, MJ/1000 kg CO2 Energy Recovered, MJ/1000 kg CO2 Energy Recovered, MJ/1000 kg CO2 Energy Recovered, MJ/1000 kg CO2

GTrb1 Gas turbine 1 - -2.21E+01 -3.22E+01

-GTrb2 Gas turbine 2 - -5.26E+00 -5.40E+00

-GTrb3 Gas turbine 3 - -6.14E-01 -2.58E+00

-R2 Reactor 2 - -1.62E+02 -

-Hx3 Heat exchanger 3 - -1.19E+03 - -3.41E+02

Hx4 Heat exchanger 4 - -1.88E+01 -3.09E+02

Hx4a Heat exchanger 4a -1.01E+03

Hx5 Heat exchanger 5 - -1.62E+01 - -2.86E+01

Hx6 Heat exchanger 6. - -4.91E-01 - -1.20E+02

Hx7 Heat exchanger 7 - -1.08E+02 -

-LTrb1 Liquid turbine 1 - -4.40E-01 -3.17E-01

-Second reformer -8.06E+02 - -

-Heat Recover A -2.99E+03 -

-Heat Recover B -1.17E+03 -

-Heat Recover C -8.65E+02 -

-Heat Recover D -3.48E+02 -

-Heat Recover E -7.17E+02 -

-Cooler 1 -7.13E+01 -

-Cooler 2 -4.60E+02 -

-Cooler 3 -1.20E+01 -

-Cooler 4 -6.40E+01 -

-Cooler 5 -4.08E+01 -

-Cooler 6 -2.22E+02 -

-Cooler 7 -1.17E+02 - -

-Total -7.88E+03 -2.53E+03 -3.49E+02 -4.90E+02

(47)

-Table 2.10. LCI energy input data of CO2 production processes without allocation.

From ammonia From hydrogen

From natural deposit

From fossil fuel

PFD label Unit Energy input [MJ / 1000 kg CO2] Energy Type Energy input [MJ / 1000 kg CO2] Energy Type Energy input [MJ / 1000 kg CO2] Energy Type Energy input [MJ / 1000 kg CO2] Energy Type

Blw1 Blower 1 9.10E-01 E

Cmp1 Compressor 1 5.94E+02 E 2.98E+02 E 7.83E+00 E 3.11E+02 E

Cmp2 Compressor 2 3.00E+02 E 1.76E+02 E -

-Cmp3 Compressor 3 - 3.20E+02 E -

-Cmp4 Compressor 4 - 2.45E+00 E -

-Dryer1 Dryer 1 - 1.13E+01 S 3.96E+00 S

-Dryer2 Dryer 2 - 4.90E+00 S 1.46E+01 S

-HX1 Heat exchanger 1 - 4.42E+00 S 0.00E+00

HX2 Heat exchanger 2 - 7.29E+02 S

-HX4 Heat exchanger 4 - - - 1.71E+03 S

Refrigerator elect. 1 2.82E+02 E 3.41E+01 E 5.35E+01 E 1.14E+02 E

Refrigerator elect. 2 4.11E+00 E - 3.48E+01 E

-Refrigerator elect. 3 1.98E+02 E - -

-P1 Pump 1 2.93E-03 E 2.46E+00 E 2.15E-01 E 4.39E-05 E

P2 Pump 2 4.96E-02 E - - 6.68E-01 E

P3 Pump 3 3.72E-02 E - - 2.46E-01 E

P4 Pump 4 - - - 1.31E+00 E

P5 Pump 5 - - - 1.17E+00 E

P6 Pump 6 - - - 6.20E-05 E

P1a Pump 1a - - - 3.60E-01 E

P3a Pump 2a - - - 2.88E+00 E

P5a Pump 3a - - - 7.47E-01 E

Primary reformer 7.11E+03 HF - -

-CO2 stripper 2.02E+03 S - -

-Heater 1 6.45E+02 S - -

-Methanator 2.43E+01 S - -

-Steam turbine C.

Compressor A 2.86E+03 S - -

-Steam turbine C.

Compressor B 1.17E+03 S - -

-NH3 converter 1.30E+02 S - -

-Refrigerator

regression - - -4.26E+01 E

-Elec. Generation - - -6.00E+02 E

-Total 1.53E+04 8.49E+02 2.05E+02 2.14E+03

(48)

three allocation approaches to an ammonia plant: macroscopic approach, microscopic approach, and microscopic approach(Seungdo Kim 2000). In the quasi-microscopic approach, the unit process can be divided into joint sub-process and separated sub-process, which is useful in identifying key issues of the targeted

product/function. In our study, we applied the quasi-microscopic allocation approach to carbon dioxide production processes. Based on Fig. 2.1 to Fig. 2.4, the allocation details of four carbon dioxide production processes are listed in Table 2.11.

Table 2.11. Quasi-microscopic allocation details of CO2 production processes

Ammonia

plant H2 plant

Natural deposit process

Fossil fuel combustion plant

Jointed sub-processes (a) (a)+(b)+(c) (a)

Separated sub-process for CO2 (b) (d)+(e) (a)+(b) (b)+(c)

Separated sub-process for Ammonia (c)

In the jointed sub-process, mass allocation is used to assign energy consumption and emission data to the related products. Mass allocation can be calculated by the following equation.

Allocation factor = (1000 kg CO2 product)/(1000 kg CO2 +Mass of other products) (1)

(49)

ammonia process has 8.5%. In addition, the fossil fuel process requires 1.71e+3 MJ steam to release CO2 from the absorbent, and the ammonia process consumes 3.85e+3

MJ fuel energy in the primary reformer. As a result, the GTG energy consumption of natural deposit process is the lowest among all four processes. However with the data in Table 2.8 and 9, the reader can use any allocation procedure to meet the needs of their study.

Table 2.12. LCI energy input data of CO2 production processes with allocation.

ammonia From

From hydrogen From natural deposit From fossil fuel PFD lab el Un it Energy i nput [MJ /

1000 kg _CO2

]

Energy Type Energy i

nput

[MJ /

1000 kg _CO2

]

nput

[MJ /

1000 kg _CO2

]

nput

[MJ /

1000 kg _CO2

]

Energy Type

Blw1 Blower 1 1.37E-01 E

Cmp1 Compressor 1 3.21E+02 E 2.70E+02 E 7.83E+00 E 3.11E+02 E

Cmp2 Compressor 2 3.00E+02 E 1.59E+02 E - -

Cmp3 Compressor 3 - 3.20E+02 E - -

Cmp4 Compressor 4 - 2.45E+00 E - -

Dryer1 Dryer 1 - 1.13E+01 S 3.96E+00 S -

Dryer2 Dryer 2 - 4.90E+00 S 1.46E+01 S -

HX1 Heat exchanger 1 - - 4.42E+00 S -

HX2 Heat exchanger 2 - - 7.29E+02 S -

HX4 Heat exchanger 4 - - - 1.71E+03 S

Refrigerator elect. 1 - E 3.41E+01 E 5.35E+01 E 1.14E+02 E

Refrigerator elect. 2 - - 3.48E+01 E -

Refrigerator elect. 3 1.98E+02 E - - -

P1 Pump 1 1.59E-03 E 2.23E+00 E 2.15E-01 E 6.63E-06 E

P2 Pump 2 4.96E-02 E - - 6.68E-01 E

P3 Pump 3 3.72E-02 E - - 2.46E-01 E

P4 Pump 4 - - - 1.31E+00 E

P5 Pump 5 - - - 1.17E+00 E

P6 Pump 6 - - - 6.20E-05 E

P1a Pump 1a - - - 5.85E-02 E

P3a Pump 2a - - - 2.88E+00 E

P5a Pump 3a - - - 7.47E-01 E

Primary reformer 3.85E+03 HF - - -

CO2 stripper 2.02E+03 S - - -

Heater 1 6.45E+02 S - - -

Methanator - S - - -

Steam turbine C.

(50)

Steam turbine C.

Compressor B - S - - -

NH3 converter - S - - -

Refrigerator regression - - -4.26E+01 E -

Elec. Generation - - -6.00E+02 E -

Total 7.33E+03 8.05E+02 2.05E+02 2.14E+03

Carbon dioxide production from fossil fuel combustion is not a major source of carbon dioxide supply in the US market. This method, however, is attractive because the process can produce significant amount of steam as shown in Table 2.8. The carbon dioxide production from the ammonia process and the hydrogen process are more complicated than the other two processes because carbon dioxide is produced as a by-product.

Fig. 2.5 shows the net energy and energy input requirement of all four processes with the quasi-microscopicallocation. Net energy is the energy input requirement of a process minus the process potential recoverable energy. Potential recoverable energy includes recoverable energy from heating and cooling units when process heat integration is applied. Although the ammonia process produces more CO2 product in the US than any

other process, it requires the most energy among the four processes. Natural deposits consume much less energy than the other three processes, because the process does not require much compression energy and the process is operated at low temperature. After considering the potential recoverable energy, natural deposit process and hydrogen

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Energy comparison of CO2 production processes

-1.60E+03 -6.00E+02 4.00E+02 1.40E+03 2.40E+03 3.40E+03 4.40E+03 5.40E+03 6.40E+03 7.40E+03 8.40E+03

CO2 from H2 plant

CO2 from ammonia

CO2 from natural deposit

CO2 from fossil fuel

CO2 production processes

Energy, MJ/1000 kg product

Energy input requirement Net energy

Figure 2.5. Energy comparison of CO2 production processes based on quasi-microscopic allocation among byproducts

2.5 Conclusion

The life cycle inventories of carbon dioxide are produced in this study. A transparent LCI result is presented and the result can be easily used in other studies. Despite being the main commercial CO2 production processes, the ammonia and hydrogen processes

require more energy than the other two processes. Ammonia and hydrogen processes have other significant emissions besides CO2 because of the characteristics of both

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The three CO2 production processes in this study have multiple products; therefore,

allocation is necessary for these three in order to compare the LCI data with each other. When allocation is unavoidable, we suggest presenting the LCI data both with allocation and without allocation, to allow user to easily change the allocation procedure for their study. In addition, since there are multiple life cycle impact assessment (LCIA)

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Macromolecules, 39(1), 15-18.

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3. Life Cycle Analysis of Bitumen Production from Tar Sand

Using Supercritical CO

2

Abstract

Life cycle of bitumen product is investigated in this paper. Carbon dioxide-bitumen extraction process and hot water-dioxide-bitumen extraction process are compared from the life cycle point of view. The life cycle inventory data are calculated using design-based methodology. We find extraction step consumes more energy than other steps in the life cycle of bitumen production. Hot water extraction requires more energy than carbon dioxide extraction because of the heating demand of large water flow in the process. Our results show that the energy burden of carbon dioxide process is mainly because of the low solubility of bitumen in isopropyl benzoate solvent and low solubility of isopropyl benzoate in carbon dioxide. We believe that the most effective way to improve the environmental performance of carbon dioxide extraction process is to find a better solvent.

Keywords

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3.1 Introduction

As the world oil resources decrease and world oil prices rise, interest has increased in the extraction of bitumen from tar sands as alternative oil resources. Although bitumen is a form of petroleum, it has not been treated as a petroleum supplement for many years since tar sand oil is not producible by the methods commonly used in ordinary oilfields.

Researchers have investigated and applied different methods to bitumen extraction from tar sand. These studies have documented that the bitumen production system has a significant impact on the local environment, such as water quality, air quality, and ecological effects. For example, water consumption by steam injection operations in Alberta ranges from 3.9 to 9.3 tons of water consumed per ton of bitumen produced (United States Congress Senate Committee on Energy and Natural Resources and Production. 1980). However, no systematic study of the life cycle of bitumen has so far been done. We thus lack quantitative data to evaluate the environmental impact of bitumen production system.

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publish) proposed a CO2 precipitation method that eliminates the distillation unit in the

organic extraction method. It significantly reduces the steam energy consumption and leaves less solvent residue in the waste sand stream than most organic solvent extraction methods. However, this method has high-pressure equipment, which has a large capital investment, and compression of CO2 consumes electricity. Which extraction method is

environmentally, and economically more acceptable than the others? How much does the extraction contribute to the life cycle of the bitumen production system? To answer these questions, we conducted a life cycle inventory of bitumen production systems.

In this study, we generate environmental information on the expected life cycle of bitumen products. It includes a detailed illumination of the environmental relationships for the bitumen product. By studying the life cycle of bitumen, we are able to recognize the improvement potentials and make valuable suggestions for future bitumen production. Life cycle inventory data are collected and simulated on each stage of the bitumen production system. Different methods, especially bitumen extraction methods are compared.

3.2 Methodology

“Life Cycle Assessment is now the most sophisticated tool with which to consider and quantify the consumption of resources and the environmental impacts associated with a product or process. By considering the entire life cycle and the associated

environmental burdens, LCA identifies opportunities to improve environmental

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chemical industry, companies have considered some information needed in life cycle studies as competitive intelligence. In this study, we use design-based approach

methodology (Jimenez-Gonzalez and Overcash 2000; Overcash 1994) to obtain most of the life cycle inventory data, in which the life cycle information of each gate-to-gate subsystem is obtained using chemical engineering design techniques. The gate-to-gate subsystems are linked through a production chain, which includes extraction of raw materials, manufacturing process, transportation, reuse and disposal, etc. Whenever the site-specific information is available, it is applied to the process design in each study. In an effort to be more transparent and reflect the main process variables, the energy values and chemical losses are for the actual manufacturing processes. Energy to generate the utilities and emissions after waste management is not included.

3.3 Goal and scope

The goal of this LCA study is to establish knowledge of bitumen production and application of supercritical CO2 extraction processes. Environmentally, the most

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Tar sand mining

Tar sand crushing Tar sand

Extraction

Solvent: hot water or organic solvents

Separation

Solvent production

CO2 compression

Bitumen upgrade

Recycle Decompression

Deasphalt oil product

Figure 3.1. Simplified overview of bitumen oil production system

3.4 Bitumen production system

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Table 3.1. Characterization of bitumen and tar sand (Hepler and His)

Properties Values Units Typical density of Athabasca

bitumen at 15 oC 1.01 g/cm3

Heat combustion of Athabasca

bitumen 41.2 kJ/g

Heat capacity of Athabasca

bitumen at 25 oC 1.7 J/K/g

Viscosity of Athabasca bitumen

at 25 oC 2.84e+3 g/cm/s

Average bitumen composition

C: 83.2% ; H: 10.4% ; O:

0.94%; N: 0.36%; S: 4.8% Weight percent

Average tar sands composition

Bitumen: 11%; water: 4%;

sands: 85% Weight percent

Average tar sands density 1.96 g/cm3

There are two main approaches for producing bitumen from tar sand reservoirs: (1), mining tar sand as an ore for subsequent extraction and upgrading of the bitumen, and (2), in-situ methods to reduce the viscosity of the tar sand bitumen so that it will flow to a producing well. The advantages of the in-situ approach over surface mining methods are that the former would eliminate the need for handling and processing vast tonnages of bitumen-bearing materials and for disposing of resultant spent sand waste. However, the recovery efficiency of the in-situ approach is no greater than 50 percent compared to a 90 percent, or greater, recovery efficiency from processing mined tar sand (Frazier 1976). Also, the water consumption of the steam in-situ method is much more than that of ex-situ methods (United States Congress Senate Committee on Energy and Natural Resources and Production. 1980). Technically and economically, in-situ bitumen production is not likely to be practical in the near future.

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crude oil product suitable for shipment to a petroleum refinery. There are two well-studied methods for bitumen extraction: hot water extraction and organic solvent extraction. However, Zaki et al. developed a third method, CO2 precipitation to cut the

distillation requirement of the organic extraction method (Nael N. Zaki et al. In publish). There is also an alternative method for separating and upgrading bitumen from tar sands: the retorting approach, which is similar to that used for oil shale (Ramler 1970). This method is associated with high temperature, which increases degradation and contamination of the oil. It also has lower oil recovery efficiency than extraction. In this research, one hot water extraction process and one CO2 precipitation process are used in