Thesis on

STUDIES ON PURIFICATION OF NATURAL GAS

USING CRYOGENIC TECHNOLOGY

Submitted by

BISWAJIT DEBNATH

Class Roll no: 001310302012

Examination Roll No: M4CHE1508

Registration No: 124707 of 2013-14

Session: 2013-2015

Master of Chemical Engineering

Project Supervisor

Prof. (Dr.) Kajari Kargupta

This project report is submitted towards the completion of

Master of Engineering degree in Chemical Engineering

DEPARTMENT OF CHEMICAL ENGINEERING

JADAVPUR UNIVERSITY

KOLKATA 700 032

Faculty of Engineering & Technology Department of Chemical Engineering

Jadavpur University Kolkata 700032

DECLARATION OF ORIGINALITY

I, Sri Biswajit Debnath, declare that this thesis is my own work and has not been submitted in any form for another degree at any university or other institute of tertiary education. Information derived from the published and unpublished work of others has been acknowledged in the text and a list of references is given in this thesis. I also declare that I have pursued the Master of Chemical Engineering course in accordance with the requirements of the universitys regulation, Research practice and ethical policies have been complied with appropriately Name: Biswajit Debnath

Exam Roll No: M4CHE1508

Class Roll Number: 00131302012

Thesis Title: Studies on Purification of Natural Gas Using Cryogenic

Technology.

Signed: ___________________ Date: ___________

Faculty of Engineering & Technology Department of Chemical Engineering

Jadavpur University Kolkata 700032

C E R T I F I C A T E

This is to certify that Mr. Biswajit Debnath, a final year student of

Master of Chemical Engineering Examination student of Chemical

Engineering department, Jadavpur University (Class Roll No:

001310302012; Examination Roll No: M4CHE1508; Registration No:

124707 of 2013-14), has completed the thesis work titled Studies on

Purification of Natural Gas Using Cryogenic Technology under the

supervision of Prof. (Dr.) Kajari Kargupta during his Masters

Curriculum. This work has not been reported earlier anywhere and can be

approved for submission in partial fulfillment of the course work.

________________________ Prof. (Dr.) Kajari Kargupta Thesis Supervisor Department of Chemical Engineering Jadavpur University

Prof. (Dr.) Chandan Ghua Head of the department Department of Chemical Engineering Jadavpur University

Dean Faculty of Engineering and Technology Jadavpur University

Faculty of Engineering & Technology Department of Chemical Engineering

Jadavpur University Kolkata 700032

CERTIFICATE OF APPROVAL

The foregoing thesis, entitled as Studies on Purification of Natural Gas

Using Cryogenic Technology is hereby approved by the committee of

final examination for evaluation of thesis as a creditable study of an

engineering subject carried out and presented by Mr. Biswajit Debnath

(Class Roll No: 001310302012; Examination Roll No: M4CHE1508;

Registration No: 124707 of 2013-14) in a manner satisfactory to warrant

its acceptance as a perquisite to the degree of Master of Automobile

Engineering. It is understood that by this approval, the undersigned do not

necessarily endorse or approve any statement made, opinion expressed or

conclusion drawn therein, but approve the thesis only for the purpose for

which it is submitted.

Committee of final examination for evaluation of thesis

To my family, my friends and

my inspirations (Late Suptish C. Nandy,

Late Jim Morrison and Late B.B. King)

i

C O N T E N T S

List of Figures v

List of Tables viii

Nomenclature ix

Acknowledgement 1

ABSTRACT 3

CHAPTER 1: INTRODUCTION 4-23

1.0 Energy Demand

1.1 Natural Gas

1.2 Existing Carbon Capture and Storage Technologies

1.2.1 Chemical Looping

1.2.2 Absorption

1.2.3 Adsorption

1.2.4 Membrane Technology

1.2.4 Cryogenic Technology

1.3 Research Methodology

CHAPTER 2: LITERATURE REVIEW 24-39

2.0 Historical Background

2.1 Detailed Literature Review

2.1.1 Thermodynamics and Solidification

2.1.2 Conventional Cryogenic Technology

2.1.3 Non-conventional Cryogenic Technology

2.1.4 Hybrid Technology

2.2 Research Gap

2.3 Objectives

CHAPTER 3: MODEL DESCRIPTION 40 52

3.0 Problem Statement

3.1 Nucleation Theory

3.2 Description of packed bed setup

3.3 Experimental Procedure

ii

3.4 Transport Phenomena Model for CO2 Separation on Single Packing

3.4.1 Mass-transfer and kinetics of nucleation

3.4.2 Energy-Balance Equation

3.4.3 Thermodynamic, mass and heat transfer correlations used for simulation

3.5 Transport phenomena model for CO2 capture using cryogenically cooled packed

bed with multiple Packing

3.5.1 Modeling of Desublimation of Carbon dioxide inside the

Capture/Deposition Zone of the Packed Column

3.6 Solution Technique

CHAPTER 4: RESULTS & DISCUSSION 53 85

4.0 Desublimation kinetics of Carbon dioxide on a single packing from gas stream

4.1 Results of simulation with pure carbon dioxide feed gas stream

4.1.1 Variation of frost layer thickness () with time at different inlet gas flowrate

4.1.2 Rate of frost layer deposition with time at different inlet gas flowrate

4.1.3 Rate of change of frost layer thickness with time at different inlet gas

flowrate

4.1.4 Variation of Interface Temperature with time at different inlet gas flowrate

4.2 Results of simulation with carbon dioxide and methane mixture as feed gas stream

4.2.1 Variation of frost layer thickness () with time at different bulk pressure

4.2.2 Rate of change of frost layer deposition with time at different inlet gas

flowrate

4.2.3 Variation of Particle Temperature with time at different bulk Pressure

4.2.4 Variation of Interface Temperature with time at different inlet gas flowrate

4.3 Effect variation of CO2 percentage on Frost Layer Thickness

4.4 Effect of CO2 composition on Particle Temperature

4.5 Dynamics of CO2 capture inside a cryogenically cooled packed bed with pure CO2 as feed

4.5.1 Variation of frost layer thickness with time at different position along the

bed for co current flow

4.5.2 Variation of frost layer thickness with time at different position along the

bed for counter current flow

iii

4.5.3 Contour plot of frost layer thickness with time and axial position for co

current flow

4.5.4 Contour plot of frost layer thickness with time and axial position for counter

current flow

4.5.5 Surface plot of frost layer thickness with time and axial position for counter

current flow

4.5.6 Growth of frost layer thickness with time and axial position for counter

current flow

4.5.7 Variation of outlet mass flowrate thickness with time and axial position for

counter current flow

4.5.8 Surface Plot of frost layer thickness with time and axial position for counter

current flow

4.5.9 Percentage separation of carbon dioxide of with axial position at different

time for counter current flow

4.5.10 Contour plot of percentage separation of carbon dioxide with time and

axial position for counter current flow

4.5.11 Contour plot of frost layer deposition on only packing surface

(heterogeneous nucleation) with time and axial position for counter current flow

4.5.11 Surface plot of frost layer deposition on only packing surface

(heterogeneous nucleation) with time and axial position for counter current flow

4.5.12 Contour plot of frost layer deposition on only bed wall (heterogeneous

nucleation) with time and axial position for counter current flow

4.5.13 Surface plot of frost layer deposition on only bed wall (heterogeneous

nucleation) with time and axial position for counter current flow

4.5.14 Effect of homogeneous nucleation on saturation time during the capture

cycle

4.5.15 Effect of inlet gas feed flowrate on bed saturation time during the capture

cycle

4.6 Dynamics of CO2 capture inside a cryogenically cooled packed bed with 80%

CO2 as feed

4.6.1 Variation of frost layer thickness with time at different position along the

bed for counter current flow

iv

4.6.2 Variation of normalized mass flow with axial distance at different time

for 80% CO2 composition in feed gas mixture and countercurrent flow

4.7 Validation of simulation results with experimental results

CHAPTER 5: CONCLUSION 86 87

5.0 Conclusion

5.1 Future Scope

References 98 101

Appendix I 102 104

Appendix II 105 106

v

List of figures

Fig no Description

Fig. 1 Demand of Natural Gas by Region projected to 2035.

Fig. 2 Reserves to Production (R/P) ratios of natural gas by regions

Fig.3 Natural Gas Consumption by sector, 2013

Fig. 4 Natural Gas Consumption by country, 2013

Fig. 5 Distribution of high CO2 gas fields by country.

Fig. 6 General Carbon Capture and Storage process.

Fig. 7 Post, Pre and Oxyfuel combustion processes.

Fig. 8 Process flow diagram of a typical amine-solvent (MDEA)-based chemical

absorptionsystem for the separation of CO2 and other acid gases from natural gas.

Fig. 9 Pressure Temperature Phase Diagram for CO2.

Fig. 10 Gibbs Free energy difference for homogeneous and heterogeneous nucleation

Fig. 11 The Packed Bed Experimental Setup

Fig. 12 Schematic diagram of a packed bed and a single packing with frost layer

Fig. 13 Schematic Diagram explaining the Algorithm

Fig. 14 Effect of inlet gas flow rate on carbon dioxide frost layer thickness ()

Fig. 15 Effect of inlet gas flow rate on rate of deposition of carbon dioxide frost layer

Fig. 16 Effect of inlet gas flow rate on rate of change of carbon dioxide frost layer

Fig. 17 Effect of inlet gas flow rate on Interfacial Temperature (Ti)

Fig. 18 Effect of bulk pressure on frost layer thickness with time

Fig. 19 Effect of inlet gas flow rate on rate of deposition of frost layer thickness

Fig. 20 Effect of bulk pressure on Particle Temperature (Tp)

Fig. 21 Effect of inlet gas flow rate on Interfacial Temperature (Ti)

Fig. 22 Effect of variation of carbon dioxide in feed gas stream on frost layer thickness

Fig. 23 Effect of variation of carbon dioxide in feed gas stream on Particle Temperature

(Tp)

Fig. 24 Growth of CO2 frost with time at different axial position of the bed for

Co current flow at 5 lpm inlet gas flowrate and Temperature Profile 3

Fig. 25 Growth of CO2 frost with time at different axial position of the bed for

Counter current flow at 5 lpm inlet gas flowrate and Temperature Profile

Fig. 26 Contour plot of CO2 frost vs. time vs. Axial position for

vi

Co current flow at 5 lpm inlet gas flowrate and Temperature Profile 3

Fig. 27 Contour plot of CO2 frost vs. time vs. Axial position for Counter current flow at 5

lpm inlet gas flowrate and Temperature Profile 1

Fig. 28 Contour plot of CO2 frost vs. time vs. Axial position for Counter current flow at

10 lpm inlet gas flowrate and Temperature Profile 3

Fig. 29 Surface plot of CO2 frost vs. time vs. Axial position for Counter current flow at

5 lpm inlet gas flowrate and Temperature Profile 3

Fig. 30 Growth of CO2 frost with time at different axial position of the for Counter

current flow at 10 lpm inlet gas flowrate and Temperature Profile 3

Fig. 31 Variation of outlet Mass flowrate with time at different axial position of the for

Counter current flow at 10 lpm inlet gas flowrate and Temperature Profile 3

Fig. 32 Surface plot of outlet mass flowrate vs. time vs. Axial position for Counter

current flow at 10 lpm inlet gas flowrate and Temperature Profile 2

Fig. 33 Percentage separation of CO2 frost vs. Axial position at different time for

Counter current flow at 5 lpm feed flowrate and Temperature Profile 3

Fig. 34 Contour plot of percentage separation of CO2 vs. time vs. Axial position for

Counter current flow at 5 lpm inlet gas flowrate and Temperature Profile 3

Fig. 35 Contour plot of deposition of CO2 frost on packing vs. time vs. Axial position

for Counter current flow at 5 lpm inlet gas flowrate and Temperature Profile 3

Fig. 36 Surface plot of deposition of CO2 frost on packing vs. time vs. Axial position for

Counter current flow at 5 lpm inlet gas flowrate and Temperature Profile 3

Fig. 37 Contour plot of deposition of CO2 frost on bed wall vs. time vs. Axial position

for Counter current flow at 5 lpm inlet gas flowrate and Temperature Profile 3

Fig. 38 Surface plot of deposition of CO2 frost on bed wall vs. time vs. Axial position

for Counter current flow at 5 lpm inlet gas flowrate and Temperature Profile 3

Fig. 39 Effect of Homogeneous Nucleation on the saturation time for the capture cycle

for Counter current flow at 5 lpm inlet gas flowrate and Temperature Profile 3

Fig. 40 Effect of inlet gas feed flowrate on the saturation time for the capture cycle for

Counter current flow at 5 lpm inlet gas flowrate and Temperature Profile 3

Fig. 41 Growth of CO2 frost with time at different axial position of the bed for Counter

current flow at 5 lpm inlet feed gas flowrate and Temperature Profile 3

Fig. 42 Variation of normalized mass flow with axial distance at different time for

Counter current flow at 5 lpm inlet gas flowrate and Temperature Profile 3

vii

Fig. 43 Comparison of simulation and experimental results of variation of percentage

CO2 with time at different bed temperature profiles for Counter current flow at 5

lpm gas flowrate

viii

List of tables

Table no. Description

1 Typical Composition of natural Gas

2 U.S. pipeline composition specifications for natural gas delivery

3 PVTX experimental data for carbon dioxide mixtures

ix

NOMENCLATURE Symbol Property

mass of CO2 frost deposited on the packing

mass transfer co-efficient in the CO2 stream side

bulk pressure in the flue gas

saturation pressure of CO2 at the interface

t time

h convective heat transfer co-efficient

latent heat of desublimation for CO2

T temperature within the frost layer

radial distance from the surface of the packing

density of the glass packing

specific heat of the packing material

thermal conductivity of the CO2 frost

frost layer thickness

Sh Sherwood number

Nu Nusselts number

Re Reynolds number

Pr Prandtls number

Sc Schmidts number

Density of CO2 frost

Total number of packing particle in a single layer

Mass of CO2 flowing into the column

Mass of CO2 flowing out of the column

Q Volumetric flow rate of CO2 in

CO2 Density of CO2 in gas phase

x

Mass of N2 flowing out of the column

Density of nitrogen gas in the column

Mass fraction of CO2 in exit stream of single layer

mg Mass flow rate of the CO2 stream

Cg Specific heat capacity of CO2 gas

Tg Temperature of the flowing CO2 stream

Ap Cross-sectional area of the packed column

n Packing density

1

Acknowledgement

It would be a great pleasure for me to take the opportunity to humbly express my gratitude for

the innumerable gestures of help, cooperation and encouragement which I have received from

my teachers, friends and all of my well wishers during this course. First of all, I would like to

express my immense gratitude to the Chemical Engineering Department of Jadavpur University

for assigning me the project entitled Studies on Purification of Natural Gas using Cryogenic

Technology.

I am deeply indebted to my Project Supervisor Prof. (Dr.) Kajari Kargupta, for

providing me with an opportunity to work on this interesting field which has a great impact on

making a clean environment upon successful exploitation. Her insight and expertise in the field

of modeling and simulation have enriched me more than anything else. Also I would like to take

this opportunity to acknowledge that her guidance not only helped to complete my project but

also showed me new light in my life. She has been always there even when I pretended to

understand everything and anything but I didnt. Her commitment, dedication and undisputed

love towards me have helped me to grow both as a human being as well as in the field of

chemical engineering.

I am very grateful to Prof. (Dr.) Chandan Guha, Head of the Department, Chemical

Engineering Department and all other faculty members for their help and cooperation. I want to

thank all the teachers and staff of the Chemical Engineering Department.

I would like to extend my thanks to our lab mates who have supported me. My sincere

appreciation also extends to all my colleagues and others who have provided assistance at

various occasions. I would also like to thank Ms. Shubhanwita Saha, Mrs. Punam

Mukhopadhyay, Mr. Rahul Baidya, Mr. Rayan Kundu, Ms. Upasana Das and Ms. Aryama

Raychaudhuri for their help in peer reviewing the thesis and help with the English. I would also

like to extend my gratitude towards Ms. Ditipriya Hazra, Ms. Sanghamitra Das, Mr. Riju De and

Mr. Shambojit Roy for their help in downloading research papers which I were unable to access.

2

I would also like to acknowledge Ms. Eapsita Pahari, Ms. Suchismita Paul, Mrs.

Moumita Sardar, Ms. Shimanti Chandra and my specially good friend MON for their help and

mental support when I was struggling to figure out things regarding this project.

And last but not least I would like thank Lokenath Baba, Jim Morrison (JimDa), Lucile

II, Mr. Bapi Debnath my father, Mrs. Rekha Debnath my mother, Mr. Swarup Mondal my meso,

Ms. Sayantani Mondal my sister and my maternal grandparents for their love, blessings, faith in

me and all other kinds of support during the period of my Masters Degree.

Biswajit Debnath

P.G. Student

Department of Chemical Engineering

Jadavpur University

3

ABSTRACT

The growing concern of low carbon foot print and energy demand it is now necessary to invade

the impure gas wells and proper technology for methane enrichment. In this study cryogenic

separation of carbon dioxide has been carried out in the solid vapour zone, from pure carbon

dioxide and carbon dioxide gas mixtures. A two step model has been considered the mass

transfer from bulk gas to the packing and the nucleation of carbon dioxide frost on the packing.

These two resistances are considered to be in parallel. A single packing was considered for

transport phenomena modeling and there after it was embedded into a multiple packing model.

Simulations were carried out to study the spacio- temporal evolution of frost layer thickness both

in single packing and multiple packing. The effects of bulk pressure and composition of carbon

dioxide on frost layer thickness, rate of change of frost layer thickness, rate of frost deposition,

interfacial temperature and partial temperature were simulated. The results showed that higher

carbon dioxide concentration results in higher frost layer thickness. Simulations were also

carried out for the total bed. Contour and 3D surface plots of frost layer thickness and mass flow

rate reveals that effective separation depends on inlet pressure flow rate, temperature profile and

flow configuration. They also affect the frost deposition. It was also found that counter current

flow configuration with respect to liquid nitrogen ensures better separation than co-current flow

configuration. The significance of the study is in design and optimization of cryogenic separation

of carbon dioxide from flue gas and natural gas.

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CHAPTER

1 INTRODUCTION

6

1.0 Energy Demand The appetite for oil, natural gas, and other energy sources is growing dramatically, with

worldwide energy consumption projected to increase by more than 40 percent by 2035. The

growing demand is fueled by a population that is predicted to increase 25 percent in the next 20

years, with most of that growth in countries with emerging economies, such as China and India.

This phase of very high energy consumption growth is driven by the industrialization and

electrification of non-OECD economies, notably China. The 2002-2012 decade recorded the

largest ever growth of energy consumption in volume terms over any ten year period. There is a

clear long-run shift in energy growth from the OECD to the non-OECD. Virtually all (95%) of

the projected growth is in the non-OECD, with energy consumption growing at 2.3% p.a. OECD

energy consumption, by contrast, grows at just 0.2% p.a. over the whole period and is expected

to fall from 2030 onwards. By sector, industry will always remain the dominant source of growth

for primary energy consumption, both directly and indirectly (in the form of electricity). Industry

accounts for more than half of the growth of energy consumption. Although it is forecasted that

the growth in renewable (6.4% p.a.) is going to be the fastest amongst all the fuels but in the final

decade (considering a projection till 2035) gas is the largest single contributor to growth that

being the fastest growing among fossil fuels (1.9% p.a.) and the only one to grow more rapidly

than total energy. Rising energy demand from economic output and improved standards of living

will likely put added pressure on energy supplies. For example, in China alone, demand is

expected to increase by 75 percent by 2035. Simultaneously worldwide consumption of

petroleum and other liquid fuels raised from 87 MMbbl/d in 2010 to 98 MMbbl/d in 2020 and

projected to rise to 119 MMbbl/d in 2040. The growth in other liquid supplies is attributed to by-

products of natural gas production (in the case of NGPL) and government policies aimed at

increasing the use of alternative liquid fuels in the transportation sector. Other liquid supplies

account for between 14% and 17% of total liquid fuel supplies throughout the projection period

of 2040. Energy demand will grow, especially in the non-OECD (Organization for Economic

Co-operation and Development) countries, which accounts for much of the uncertainty about

future demand growth.

Global demand for natural gas is projected to grow by 1.9% p.a., reaching 497 Bcf/d by

2035, with non-OECD growth (2.7% p.a.) outpacing the OECD (1% p.a.). Global gas supply is

expected to grow to 172 Bcf/d by 2035. Shale gas is the fastest growing source of supply (6.5%

7

Fig. 1: Demand of Natural Gas by Region projected to 2035

(B.P. Energy Outlook 2035)

p.a.), providing nearly half of the growth in global gas. On the demand side, shale gas gives US

natural gas a competitive advantage relative to other fuels. This is already visible in the power

sector, where gas is likely to continue to grow (0.5% p.a.) at the expense of coal, despite the

rapid expansion of renewables. Next, gas is expected to gain market share in the industrial sector,

from 39% in 2012 to 42% by 2035. And finally, gas will start to penetrate the transport sector.

Gas is the fastest growing fuel (18% p.a.) in a sector where overall demand is falling (-0.9%

p.a.). By 2035 gas will account for 8% of US transport sector fuels, almost matching biofuels.

1.1 Natural Gas Natural gas is used primarily as a fuel and as a raw material in manufacturing. It is used in

home furnaces, water heaters, and cooking stoves. As an industrial fuel, it is used in brick,

cement, and ceramic-tile kilns; in glass making; for generating steam in water boilers; and as a

clean heat source for sterilizing instruments and processing foods. As a raw material in

petrochemical manufacturing, natural gas is used to produce hydrogen, sulfur, carbon black, and

ammonia. Ethylene, an important petrochemical, is also produced from natural gas.

8

The discovery of natural gas dates from ancient times in the Middle East. Thousands of

years ago, it was noticed that natural gas seeps ignited by lightning created burning springs. In

Persia, Greece, or India, people built temples around these eternal flames for their religious

practices. However, the energy value of natural gas was not recognized until approximately 900

BC in China, and the Chinese drilled the first known natural gas well in 211 BC.

Natural gas exists in nature under pressure in rock reservoirs in the Earths crust, either in

conjunction with and dissolved in heavier hydrocarbons and water or by itself. It is produced

from the reservoir similarly to or in conjunction with crude oil. Natural gas has been formed by

the degradation of organic matter accumulated in the past millions of years. The principal

constituent of natural gas is methane. Other constituents are paraffinic hydrocarbons such as

ethane, propane, and the butanes. Many natural gases contain nitrogen as well as carbon dioxide

and hydrogen sulfide. Trace quantities of argon, hydrogen, and helium may also be present. The

composition of natural gas can vary widely. Table 1-1 outlines the typical makeup of natural gas

before it is refined.

Table 1: Typical Composition of natural Gas (Wikipedia)

Name Formula Volume (%)

Methane CH4 70-90%

Ethane, Propane & Butane C2H6, C3H8, C4H10 0-20%

Carbon Dioxide CO2 0-8%

Oxygen O2 0-0.2%

Nitrogen N2 0-5%

Hydrogen sulphide H2S 0-5%

Rare gases A, He, Ne, Xe trace

Natural gas can also contain a small proportion of C5+ hydrocarbons. When separated, this

fraction is a light gasoline. Some aromatics such as benzene, toluene, and xylenes can also be

present, raising safety issues due to their toxicity. Natural gas can contain other contaminants

too. Acid contaminants, such as mercaptans (R-SH), carbonyl sulfide (COS), Carbon dioxide

(CO2) and carbon disulfide (CS2) might be present in small quantities. Mercury can also be

present either as a metal in vapour phase or as an organo-metallic compound in liquid fractions.

Concentration levels are generally very small, but even at very small concentration levels,

9

mercury can be detrimental due its toxicity and its corrosive properties (reaction with aluminium

alloys).

According to ExxonMobil Energy Outlook Report 2015, global demand for natural gas is

projected to rise by 65 percent from 2010 to 2040, the largest volume growth of any energy

source. The extensive utilization of NG has led to decreased NG reserves to production ratio over

regions of the world, among which Middle East has the highest ratio as shown in Figure 2.

Fig. 2: Reserves to Production (R/P) ratios of natural gas by regions

Natural gas, also called the prince of hydrocarbons as it has many applications. The

proportion of the natural gas consumed for energy production in major fields including

industrial, commercial, residential, transportation and in generating electricity for the year 2009

is shown on Fig. 3.

10

Fig.3: Natural Gas Consumption by sector, 2013

Natural gas consumption is the highest in United States and Russia, followed by North America

and Middle East. Figure 4 shows the natural gas domestic consumption worldwide in 2013.

Fig.4: Natural Gas Consumption by country, 2013 (Enerdata.net)

11

Natural gas consists primarily of methane (70-90% of the total component) and other light and

heavier hydrocarbons. The impurities present in natural gas need to be removed to meet the

pipeline quality standard (NaturalGas.org 2010). The allowable amounts of common impurities

in U.S. for the delivery of the natural gas to the pipe line are given below.

As one of the major contaminates in natural gas feeds, carbon dioxide must optimally be

removed as it reduces the energy content of the gas and affect the selling price of the natural gas.

Moreover, it becomes acidic and corrosive in the presence of water that has a potential to

damage the pipeline and the equipment system. In addition, when the issue of transportation of

the natural gas to a very far distance is a concern, the use of pipelines will be too expensive so

that Liquefied Natural Gas (LNG), Gas to Liquid (GTL) and chemicals are considered to be an

alternative option. In LNG processing plant, while cooling the natural gas to a very low

temperature, the CO2 can be frozen and block pipeline systems and cause transportation

drawback. Hence, the presence of CO2 in natural gas remains one of the challenging gas

separation problems in process engineering for CO2/CH4 systems.

Table 2. U.S. pipeline composition specifications for natural gas delivery

(Al-Juaied 2004; Baker 2004)

Components U.S. Pipeline Specification

Hydrocarbons (C3+) 950 1050 Btu/scf dew point -20OC

CO2 < 2 mol%

H2S < 4 ppm

H2O < 0.1 gm/m3 (

12

Fig. 5: Distribution of high CO2 gas fields by country (Maqsood et al., 2014)

The chaos around the world with crude oil and due to increased demand on natural gas has

stimulated the researchers to develop, design and modify cryogenic technology for Natural Gas

separation. Presence of carbon dioxide (CO2) and other sour gases in varying quantities in

different natural gas resources has endorsed several innovative sequestrating technologies to be

invented to mitigate the anthropogenic CO2 emission as well as maintaining greenhouse gas level

in the atmosphere. And research is still going on.

Despite of the fact that several literatures is available on removal of sulfur containing

gases and higher hydrocarbons, now the focus must be shifted towards the removal of carbon

dioxide efficiently form gas stream. With growing economy and population driving the demand

of energy associated with lean and green slogans have made it imperative for the researchers to

innovate and materialize new technologies to deal with the natural gas reserves containing CO2

up to 80%. Natural gas is mostly considered as a "clean" fuel as compared to other fossil fuels,

the natural gas found in reservoirs deposit is not necessarily "clean" and free of impurities. One

third of the proven natural gas reserves are estimated to be sour. Malaysia alone constitutes more

than 13 Tscf of undeveloped natural gas because of the high CO2 concentration. In some gas

fields, the concentration of CO2 exceeds 70 percent (Darman & Harum, 2006). Therefore

separation of carbon dioxide is necessary to maintain the selling price of the natural gas with

13

quality because CO2 reduces the calorific value of the gas making it economically unfeasible.

The high content of CO2 in natural gas enhances the formation of carbonic acids and dry ice

causing corrosion and clogging of delivery pipelines. Hence, the removal of CO2 from the

natural gas is important for maintaining the quality of the product to satisfy the customer. Also,

purification of raw natural gas is necessary so as to not facilitate pipeline corrosion and to satisfy

the pipeline standards for different NG companies. Therefore, the impurities must be removed to

meet the pipe-line quality standard specifications as a consumer fuel, enhance the calorific value

of the natural gas, avoid pipelines and equipment corrosion and further overcome related process

bottle necks.

1.2 Existing Carbon Capture and Storage Technologies Raw natural gas collected from the wells is often impure. Purification is carried out at different

stages to meet different pipeline specification, as standardized internationally & nationally. CO2

being one of the most notorious acid gases purification is important as to meet standards &

commercialization.

Fig. 6: General Carbon Capture and Storage process

14

Different existing technologies are there which are widely used for CO2 separation from natural

gas stream as well as flue gas streams which evolves in different processes in industries. Existing

technologies includes absorption, adsorption, cryogenic technology, membrane technology,

chemical looping etc. These technologies have been developed over the years in order to meet

environmental regulations, pipeline specifications and optimize the operational costing. Figure 6

represents a general Carbon Capture and Storage process.

Fig. 7: Post, Pre and Oxyfuel combustion processes

Oxyfuel Combustion is the process by which nearly pure oxygen fires power plants instead of

air, producing a flue gas stream comprising water and carbon dioxide. The water is condensed

which leaves the pure CO2 stream. Generally, there exists as Air Separation Unit (ASU) which is

built on the front end of Oxyfuel combustion power plants, which employs cryogenic technology

to distill out Oxygen from air. This process is very difficult & energy intensive. Since, firing is

carried out with pure Oxygen, it causes high flame temperature. As a result the boilers are

required to be rebuilt & circulation of flue gas is required to control heat flux & flame

15

temperature. An ASU and Oxyfuel combustion decrease plant electrical output by approximately

30% (Nielson 2012).

In post combustion carbon capture process, the CO2 is captured from the flue gas after fuel

combustion [Fig. 7]. While this process can be retrofitted to any existing process plant, dilute

CO2 concentration present on the flue gas at low pressure makes it energy intensive to capture as

a large volume of gases are required to be handled.

In the following section, different CCS technologies have been discussed in details.

1.2.1 Chemical Looping Chemical looping is a process in which oxygen, typically from air, oxidizes a metal oxide

particle in an oxidizing reactor, releasing heat and is then transported to a reducing reactor where

it mixes with fuel & converts to a less oxidized state. In this case, generally two fluidized beds

are interconnected that allows the metal oxide particles to circulate between both reactors. Here

the metal oxide acts as an oxygen carrier, no other elements of air comes into contact with fuel

and doesnt mix up with CO2 produced from fuel oxidation. As a result, the flue gas stream

contains only water & CO2. The disadvantage is that metal oxides are expensive & deactivate

with time. Actually, the cycling temperatures of the metal oxides represent a significant amount

of entropy generation with the loss in Gibbs free energy associated with it (Nielson 2012).

1.2.2 Absorption Absorption process is one of the most well known, established, industrially applicable state of

the art technologies in natural gas purification process where a component of a gaseous phase is

contacted with a liquid in which it is preferentially soluble. Most of the conventional CO2

removal processes from natural gas are based on either chemical or physical or simultaneous

physical-chemical absorption process. Absorption is usually carried out in a countercurrent tower

(column), through which liquid descends and gas ascends. The reverse process (which is also

termed as stripping process, desorption) is employed when it is required to remove the absorbed

gases from the solvent for the purpose of recovery of the gas or the solvent or both. The

efficiency of any sorbent to absorb CO2 or H2S is expressed by its loading capacity. The two

major cost intensive factors associated with the absorption process include: i) the solvent

circulation rate and loading capacity required to achieve the degree of sweetening and ii) the

16

high energy consumption regarding the regeneration of the solvent (Biruh Shimekit and Hilmi

Mukhtar 2012, Kidnay and Parrish, 2006, Mullick 2014).

Absorption process can be classified into two categories- a) physical absorption process

and b) chemical absorption process. In physical absorption process implemented for CO2

removal the major controlling parameters are temperature, pressure of the feed gas stream and

partial pressure of the acid gas components present in the feed gas stream. A condition of low

feed temperature and high partial pressure (10 bars or more) is favorable for commercialization

of the process physical solvents have weak affinity towards the acid gas components. Hence, it is

necessary to employ high solvent circulation rate and limited loading capacity. In this case, less

energy is required for the regeneration step compared to traditional amine based processes as it is

carried out in low pressure. However, if the carbon dioxide is to be utilized for Enhanced Oil

Recovery (EOR), the cost of compressing the gas increases energy requirement. This method can

be implemented where the feed stream is rich in carbon dioxide and the product purity doesnt

matter a lot (Yeo et al, 2012). Chemical absorption process, takes place as exothermic reaction

between the chemical sorbent and the target acid gas component (CO2) at low temperature.

During the process, strong chemical bonds are formed between the target component and the

functional group of the chemical sorbent. The percentage separation of acid gas component is

dependent on the loading capacity of the sorbent predetermined by the available active sites (Yeo

et al., 2012, Christopher et. al., 2008). In the chemical process industry two types of chemical

solvents are used 1) Aqueous amine solution and 2) Carbonate solution. Selective absorption of

acid gases by exothermic chemical reaction with amine groups is the key concept of this process

and it is widely applied in the natural gas industries. The common amine based solvents used for

the absorption process are monoethanolamine (MEA), diethanolamine (DEA) triethanolamine

(TEA), diisopropanolamine (DIPA), diglycolamine (DGA) and methyldiethanolamine (MDEA)

that reacts with the acid gas (CO2 and H2S) to form a complex or bond. The basicity is provided

by the amine function, and it provides reactivity to remove the acid gases. The hydroxyl groups

serve to increase the solubility of amine in water. This effect reduces the vapor pressure of the

amines so that less is lost out the top of the absorber or stripper (Glasscock 1990, Biruh

Shimekit and Hilmi Mukhtar 2012). The Sour gases are brought in contact with the amine

solution in a countercurrent flow through an absorption column allowing the sorbent to strip out

CO2 or H2S selectively from the NG. The sweetened gas comes out from the top of the column

17

where as the sorbent loaded with sour gas components exits from the bottom which is further

directed to another column for regeneration. The stripping or desorption is carried out at a higher

temperature (about 373 K 473 K) giving out a high concentrated pure CO2 stream after

dehydration. The regenerated solvent is cooled down and recycled to the top of the column.

Absoprtion is well known for being the easiest and most common method for acid gas removal

from natural gas; but high solvent regeneration cost, equipment corrosion by acid compounds,

low loading capacity, amine degradation by SOx, NOx, HCl, HF, and O2 in flue gas, high solvent

circulation rate etc are some of the barrier towards the wide application in real field. (Liu et. al.,

2009; Olajire, 2010).

Fig. 8: Process flow diagram of a typical amine-solvent (MDEA)-based chemical absorption system

for the separation of CO2 and other acid gases from natural gas (Hubbard, 2010; Kohl and Nielsen,

1997)

CO2 removal from sour gas stream at a high pressure and temperature by using hot alkali

carbonate solutions like potassium carbonate (K2CO3) or sodium carbonate (NaCO3) was first

implemented in 1950s (Kohl and Nielsen, 1997). The process was first commercialized by US

Bureau of Mines as Benfield Process in 1954. Since the rate of absorption of CO2 by carbonate

solution increases with rise in temperature, the process is carried out at a high temperature 383 K

389 K. In cryogenic process units, the stringent allowance for the presence of very low CO2

level endorsed the modification of the process design. The new Hi-Pure design combines the

18

amine solution and carbonate solution process to enhance the rate of CO2 absorption (Rufford et

al., 2012).

Another kind of technology called the hybrid absorption process technology has been

developed where the effects of physical and chemical absorption processes have been combined

in a single unit operation by using mixed solvents. Sulfinol-D licensed by Shell Global Solutions,

Sulfinol-M, Amisol process licensed by Lurgi are some of the well known hybrid absorption

processes. (Rajani, 2004, Kohl and Nielsen, 1997).

1.2.3 Adsorption The process of adsorption can be described as the adhesion or retention of selective components

of feed gas stream brought into contact to the surface of certain solid adsorbent as the result of

the force of field at the surface. The reverse process is known as desorption in which the

adsorbed foreign molecules are released. High pressure and low temperature is favorable for

adsorption whereas low pressure and high temperature is suitable for regeneration or desorption.

In natural gas industries, removal of water, sulphur, mercury and heavy hydrocarbons are carried

out based on adsorption. Although adsorption process is rarely applied for bulk separation of

CO2 from CH4, there are kinetics-based adsorption processes that have been implemented in

USA for the recovery of methane from landfill gas. These gases mainly comprises of methane

(50-65%), carbon dioxide (35-50%), a trace amount of nitrogen and sulfur compounds. In this

process, carbon molecular sieve is used as the adsorbent. In use of this process, it can be possible

to recover more than 90% methane with 87-89% purity (Yang 1997, Tagliabue et al., 2009).

Depending on the nature and strength of the surface forces, adsorptive gas separation process can

be divided into two types a) physical adsorption and b) chemisorption. In physical adsorption

the gas molecules are adsorbed in the surface pores, there is no chemical reaction associated with

it. In chemisorption there is a formation of a chemical bond between the sorbate and the solid

surface (covalent interaction of CO2 and the surface of the adsorbent) which facilitates larger

adsorption capacity. These kinds of interactions are strong, highly specific, and often not easily

reversible. Chemisorption is sometimes employed for removal of trace concentrations of

contaminants. However, the difficulty of regeneration makes such systems unviable for most

process applications. The forces of physical adsorption are weaker (a combination of Van der

Waals forces and electrostatic forces) than the forces of chemisorptions which means the heats of

19

physical adsorption are lower. Since there is no covalent bond formation the adsorbent is more

easily regenerated. Physical adsorption at a surface is so fast, and the kinetics of physical

adsorption is usually controlled by mass or heat transfer rather than by the intrinsic rate of the

surface process (Meyers 2001).Based on regeneration methods, adsorption process is most

commonly divided into temperature swing adsorption (TSA), pressure swing adsorption (PSA)

and displacement desorption. In TSA, desorption is achieved by increasing the temperature of

the adsorption bed, either by applying heat to the bed or by purging with a hot purge gas.

Thermal swing adsorption is very reliable to remove minor component. The main limitation is

the adsorption cycle time that is required to cool down the bed. Moreover, high energy

requirements and large heat loss are on the cards. (Mersmann et al. 2011). PSA is a well known

technology for the removal of CO2 from gaseous streams containing methane. In PSA,

regeneration is carried out by lowering the operating partial pressure to desorb the adsorbate

(Kerry 2007). This can be obtained either by depressurization or by evacuation or by

implementing both. It is more suitable for bulk separation. Another type of desorption is

Displacement desorption. It is similar to purge gas stripping as the temperature and pressure are

maintained constant, but instead of an inert purge, an adsorbable species is used to displace the

adsorbed component from the bed. It is generally used when desorption by pressure swing or

thermal swing fails to be practical. Fluidised and moving bed operations (Seader and Henley,

2006), and fixed- bed electrothermal-swing adsorption (ESA) (An et al., 2011; Grande and

Rodrigues, 2008) are some of the less commonly applied adsorption techniques. The most

important factors for sustainable application of this technology are a) high selectivity and good

adsorption capacity of the target component, b) high surface area available for adsorption, c) fast

adsorption/desorption rate, d) physical and chemical stability, e) high regenerability and f) cost

of the adsorbent. Most commonly used commercially available adsorbents are - Activated

carbon, zeolites, molecular sieves etc. However, some novel adsorbents has been developed for

higher CO2 adsorption capacity Metal-organic frameworks (MOFs), zeolitic imidazolate

frameworks (ZIFs), surface functionalised silicas and porous carbons. Despite of novel

innovations and improved application specific researches this technology possesses some

disadvantages a) Very large, thick walled and heavy weighted adsorption tower which needs

high maintenance cost, b) low CO2 selectivity and adsorptivity of the available adsorbents, c)

high cost and low efficiency of CO2 adsorption in natural gas industries and d) production of

20

large amount of waste water and sludge (Hao et al., 2011, Biruh Shimekit and Hilmi

Mukhtar 2012, Mullick 2014 ).

1.2.4 Membrane Technology A membrane is a thin barrier placed between two phases or mediums, which allow one or more

constituents to selectively pass from one medium to the other in the presence of an appropriate

driving force while retaining the rest (Binay K Dutta, 2009). The separation of gas mixtures

with membranes has emerged from being a laboratory curiosity to becoming a rapidly growing,

commercially viable alternative to traditional methods of gas separation within the last two

decades. Membrane gas separation has become one of the most significant new unit operations to

emerge in the chemical industry in the last 25 years (Prasad et al. 1994). The important criteria

for selecting membrane materials for gas separation are based on the following key factors (a)

intrinsic membrane permselectivity (b) ability of the membrane material to resist swelling

induced plasticization (chemical resistance, which is quite rare but mostly fulfilled by inorganic

membranes) and (c) ability to process the membrane material into a useful asymmetric

morphology with good mechanical strength under adverse thermal and feed mixture conditions.

The polymer membrane material should have good interaction and sorption capacity preferably

with one of the components of the mixture for an effective separation (Biruh Shimekit and

Hilmi Mukhtar 2012).The first large scale industrial application of gas separation membrane

came to the market in the year 1980. It was launched by Permea used for hydrogen separation

and it was called PRISM. Since that inception the business of membranes has grown into a

$150 million/year and it will continue to grow in the coming future. There has been a lot of

research on this topic for last three decades but not even 10 type of polymer is available for

commercial gas separation. Most importantly, these polymers were not specifically designed for

gas separation hence improvement in such area is important that can provide higher selectivity in

gas separation. Apart from this, membranes must be thermally and chemically stable, resistive to

ageing, plasticization (for polymeric membranes), cost effective and must be easy to scale up.

Membrane technologies evolved from the discovery of Acid gas removal technique from natural

gas. The removal of CO2 from natural gas is the only large scale membrane based process in

practice today. There are more than 200 plants have been installed and most of them are installed

by Kvaerner-GMS, Universal Oil Products and Cynara (Baker et al. 2004). Membranes used

21

for gas separation are mainly classified into three categories based on the structure and materials:

polymeric membranes, inorganic membranes and mixed matrix membranes. During the last two

decades dozens of new polymers have been described in the literature, which have been

developed for gas separation. The largest group among these are probably polyimides. Cellulose

acetate Ethyl cellulose, Polycarbonate, brominated, Polydimethylsiloxane, Polymide (Matrimid),

Polymethylpentene, Polyphenyleneoxide, Polysulfone are the other polymers which are of

practical importance for gas separation. Cellulose acetate, polysulfone and polyimides are by far

the most important polymers for gas separation membranes (Nunes and Peinemann 2001).

Based on the operating temperature whether below or above the polymer glass transition

temperature, polymeric membranes can further be classified as rubbery polymers and glassy

polymers. In spite of, simple flow configuration and low cost, these polymeric membranes

cannot compete the conventional amine solvent absorption process due to low permeability, less

selectivity, degradation over time, non resistive against corrosive and high temperature

environment, unable to handle large volume of gas stream, low thermal and chemical stability.

Another major problem with polymeric membranes is the probability of plasticization of the

membrane after a limit of pressure of CO2 (Tin et. al., 2004, Larikov et. al., 2011, Rufford et

al. 2012). The current market for inorganic membranes for gas separation is extremely small. It

is not believed that the market share of inorganic membranes will increase significantly in the

near future. The main obstacle is their high price and some principle difficulties during

reproducible large-scale production. On the other hand fascinating research results have been

published in the recent past such as, unmatched selectivity for carbon dioxide/methane

separation with ceramic membranes (Tsai et al. 2000). There are different types of inorganic

membranes like ceramic membrane, nanoporous carbon membrane, Perovskite-type oxide

membranes etc. Dense inorganic membranes are prepared by spreading a thin metal layer of

palladium, nickel, silver, zirconia etc. and since all of these are expensive metals, sophisticated

handling is required. Also, the high capital cost, unstable mechanical properties, low

permeability reduce the applicability extensively. Ceramic, carbon and zeolite membranes are

commonly used for CO2/CH4 separation. A new development in the field of inorganic

membranes is zeolite based membranes. Silicalite-1 MFI membrane, Y-type zeolite membrane,

SAPO-34 zeolite membrane, KY-type zeolite membrane, DDR type zeolite membrane, A-type

zeolite membrane and T-type zeolite membrane (Yeo et al, 2012) are various types of zeolite

22

membranes which can be applied for CO2 separation from CH4 based on competitive adsorption.

Several obstacles such as expensive material, difficulty in producing the thin porous structure,

insufficient mechanical strength necessitates further research and investigation for successful

deployment in industries. Due to the different drawbacks of the existing membrane processes, it

is highly desirable to provide an alternative cost effective membrane which combines

homogeneously interpenetrating polymeric matrices for ease of processibility and inorganic

particle for high permeability and selectivity well above the upper-bound limit (Shekhawat,

Luebke et al. 2003, Biruh Shimekit and Hilmi Mukhtar 2012).). The combinations of the

superior gas selectivities of molecular sieves with the processibility of polymeric membranes

have attracted many researchers. The hybrid membranes consisting of inorganic molecular sieves

and polymers are often referred to as mixed matrix membranes (Mahajan and Koros, 2000,

Nunes and Peinemann 2001). It is still in developmental stage. The major challenges for

successful exploitation of membrane technology are a) high permeability and b) high selectivity.

Natural gas obtained from geological sources is at a high pressure. Hence high driving force is

there for permeation. But flue gas is generally at a low pressure. Therefore, high compression is

needed for permeation through membrane which makes the process overall process expensive

(Mullick 2014).

1.2.5 Cryogenic Technology Cryogenics is the science that studies the production and behavior of materials at very low

temperatures spanning the range between 100 K (-173oC) and absolute zero (0 K or -273oC). The

word cryogenics has been derived from two Greek words cryos which means icy cold and

genes means born i.e. "the production of freezing cold"; however, the term is used today as

a synonym for the low-temperature state. And with the chaos around the world with crude oil the

demand of natural gas have increased. This has stimulated the researchers and they have shown

the anarchy to develop, design and modify cryogenic technology for Natural Gas separation. Of

course, a novel method which can simultaneously capture, remove and transport carbon dioxide

holds enormous promises for real life industrial applications. Cryogenic technology is

advantageous over other existing amine absorption or PSA/TSA based processes A) No

chemicals and solvents are required by the process, hence no recurring consumable costs; B) No

process makeup water supply and further treatment are required; C) No process heating systems

23

are required; D) No solvent regeneration equipments are required; E) Water is removed

immediately downstream of the inlet separator so corrosion potential is scant; F) carbon dioxide

is available at higher pressure and can be used for Enhanced Oil Recovery or sequestration

purposes; G) Natural Gas Liquids (NGL) obtained as a by-product which has good market

potential; H) There is no chances for foaming and I) No special winterization requirements for

cold climates. Moreover, if process integration is employed and the required cold duty is

obtained at relatively low costs from a liquefied natural gas (LNG) re-gasification terminal,

cryogenic carbon capture becomes extremely attractive and economically feasible. Despite of so

many advantages, this technology still could not replace the conventional processes described

before. The main reason for this is the high cooling cost for the process. At atmospheric pressure,

CO2 directly de-sublimes from gas phase to solid phase below the saturation temperature. But for

operation in the gas-liquid zone, high compression of the feed gas is necessary which increases

the capital cost. Another problem is the solid formation, often columns are plugged by solid CO2

clusters and ice that comes from the water vapor freezing in the CO2 feed mixture. That is why,

the researchers are currently motivated to develop and establish the desublimation process

industrially (Mullick 2014).

The cryogenic technology can be classified into two major sections a) Conventional Cryogenic

Technologies and b) Non-conventional Cryogenic Technologies. In the next chapter, these

technologies have been discussed in details.

24

1.3 Research Methodology

The work was carried out as follows

Firstly, a detailed literature review was carried out. More than 80 sources of literature including

journal papers, conference proceedings, thesis works, books, articles and websites have been

reviewed. The references cited in each relevant literature were examined to find out additional

sources of information.

Secondly, the research gap was identified from the detailed literature review and the research

questions were formulated.

Then, according to our research question, the work was divided into two sections a)

Experimentation and b) Transport phenomena modeling and Simulation. The work being a joint

collaboration between Universiti of Tecknologi PETRONAS and Jadavpur University, the

experimental part was carried out at Universiti of Tecknologi PETRONAS and the transport

phenomena modeling and simulation were carried by us at Jadavpur University.

Experiments were conducted in a setup at different initial bed temperature profiles both in

counter current and co-current configurations. Feed composition, flowrate and initial temperature

were varied and experiments were conducted.

Then, a two step transport phenomena model was developed considering a single packing to

study the spacio temporal evolution and kinetics of the frost layer on a single packing, which

was further used to compute the frost layer of the total packed bed.

Thereafter, the model equations were solved using the GEARs algorithm (ode15s library

function available in MATLAB) in MATLAB considering a pseudo homogeneous state. The

initial bed temperature profiles obtained from the experiments has been used for the simulation.

The results obtained were analyzed to study the spacio temporal evolution of frost layer and to

predict the frost layer kinetics.

25

CHAPTER 2

LITERATURE REVIEW

26

2.0 Historical Background It is believed that the first ever successful liquefaction of any cryogenic gas was carried out not

earlier than 1877, by a French mining engineer Cailletet who produced a mist of liquid oxygen

droplets. He succeeded in pre-cooling a container filled with oxygen at 300 atm and then

expanding the gas by suddenly opening the valve of the container. Around the same time, a

Swiss physicist Pictet was also independently successful in liquefying oxygen by cascade

cooling.

A breakthrough was made in London in 1892 when James Dewar developed the vacuum

jacketed double-walled containers with silvered inner walls. This invention facilitated successful

liquefaction of hydrogen and helium in large quantities by 1898. In the mean time, Linde was

granted a patent on air liquefaction in Germany in 1885 and became the pioneer in industrial

scale production of cryogenic liquids.

In 1902, a French engineer Claude established L Air Liquid to develop and produce his

air liquefaction system in which a large fraction of cooling was obtained by using an expansion

engine. Five years later, in 1907, Linde installed the first air liquefaction plant in the USA.

During the period between the two World Wars, a number of developments took place in the

field of cryogenics. After the World War II, in 1947, Collins, a mechanical engineer, developed

an efficient cryostat for liquefaction of helium at MIT, USA. This could be used for safe and

sustained maintenance of temperature for experimental studies between ambient and 2 K. The

impact of this development was so remarkable in boosting the confidence level of researches

engaged in cryogenic applications that anything earlier than this era was jocularly referred to as

BC or Before Collins. The newer developments are continually taking place even today

(Mukhopadhyay 2010).

2.1 Detailed Literature Review A huge number of literatures are available on carbon dioxide capture and recovery technologies

based on cryogenic separation. Extensive study showed that these technologies can be classified

into three categories - (A) Conventional cryogenic technology, (B) Non-conventional cryogenic

technology and (C) Hybrid technology. Other than the technological aspects, the internal

thermodynamics and the science associated with the governing phenomena have also been

27

considered in this review of reported studies. The following sections have been developed to

give a brief idea on the subject considered in this thesis.

2.1.1 Thermodynamics and Solidification The research on Natural gas purification using cryogenic technology is totally based on

the science of Thermodynamics. The Cryogenic Technology finds its origin in the Second Law

of Thermodynamics. And then there is Equation of State that describes the properties of fluid

mixtures and provides the mathematical relationships between the state functions associated with

the process. Concern toward understanding of the mechanisms of these technologies and the

proper design of the equipment necessitates a deep look into the thermodynamic analysis of CO2

- natural gas phase equilibrium.

Fig.9: Pressure Temperature Phase Diagram for CO2

The above figure shows the Pressure Temperature phase diagram for pure Carbon

Dioxide. It clearly shows that at higher pressure within the cryogenic limits, the CO2 becomes

solid. The general or conventional cryogenic distillation columns operate at a higher pressure and

often the solidification of the CO2 becomes a problem for the Heat Exchangers associated. That

is why the non-conventional ones are operated at normal atmospheric or lower pressure and to

28

eliminate the problem of solid CO2 packed beds are employed. In the latter, the zone of operation

is the Solid vapour region of the phase diagram.

Thermodynamic data for the methane-carbon dioxide binary system is available at three

primary sources in literature. These data sets also include the solid-liquid-vapour region of the

binary mixture. The first set of data was reported by Donnely et. al. (1954). This data includes

three phase data points from -78.6 to 57.78 0C. Critical conditions for CH4-CO2 system were

also presented. Different data points for SLE were also measured. Vapour liquid equilibrium for

different pressure ranges was also determined. Pikaar (1959) provided the second set of data. A

constant volume cell was used to measure the 1, 3, 5, 10 and 20 % CO2 frost lines along with the

dew and bubble point lines of theses mixtures in the region of three phase locus. Davis et. al.

(1962) measured the three phase locus for the binary mixture from the triple point of carbon

dioxide to -175.61oC. In addition to that they also measured the composition of vapour and liquid

phase along the solid-liquid-vapour locus of methane carbon dioxide system. Eggemen et. al.

(2005) found that unreliable CO2 freezing temperature predictions are being made by several of

the commercial process simulators typically used by gas processors. In general, they found the

existing experimental data were adequate and that thermodynamic models, both equation of state

and activity coefficient based, can be used to make accurate predictions of CO2 freezing

temperatures. However, previous works was not adequately addressed how to properly apply

these models within a process simulation. According to them it was the improper formulation of

the CO2 freezing calculations was the cause of the unreliable predictions made by the

commercial process simulators. They showed how to properly formulate the thermodynamic

calculations to be used for prediction of CO2 solids formation. Procedures for heat exchangers,

expanders and columns have been discussed. Common pitfalls (convergence to spurious roots,

convergence to physically meaningful but useless solutions, non-convergence of numerical

algorithms, improper formulation of temperature safety margins, etc.) can be avoided by using

these procedures.

Many other phase equilibrium experimental data for CO2 is available in literature. A summary of

this is given below.

29

Table 3: PVTX experimental data for carbon dioxide mixtures (Maqsood et al. 2014)

Source Year Type Mixture Temperature range

(oC)

Pressure range

(bar)

Donnelly and Katz

(1954)

1954 TPxy CO2-CH4 -106 to 29 20-74

Kaminishi et al.

(1968)

1968 TPxy CO2/CO, CO2/Ar, CO2/CH4,

CO2/CO/H2

- 50 to 10 24-200

Neumann and Walch

(1968)

1968 TPxy CO2-CH4 -65, -228 to -53.15 440-690

Arai et al. (1971) 1971 PVTX CO2-CH4, CO2-N2 -20 to 15 50-150

Sarashina et al. (1971) 1971 PVTX CO2-CH4-N2 -40 to 0 60-100

Davalos et al. (1976) 1976 TPxy CO2-CH4 -43 to -23 9-85

Hwang et al. (1976) 1976 TPxy CO2-CH4 -120 to -54 20-65

Mraw et al. (1978) 1978 TPxy CO2-CH4 -184 ton -65 5-63

Somait and Kidnay

(1978)

1978 TPxy CO2-CH4, CO2-N2 -3 30-120

Al-Sahhaf et al.

(1983)

1983 TPxy CO2-CH4, CO2-N2, CO2-CH4-

N2

-54 to -23 5.8-160.15

Magee and Ely (1988) 1988 TPxy CO2-CH4 -48 to 127 20-350

Ely et al. (1989) 1989 TPxy CO2-CH4, CO2-N2 -23 to 57 23-320

Trappehl and Knapp

(1987)

1989 TPxy CO2-CH4, CO2-N2 -53 20-120

Al-Sahhaf (1990) 1990 TPxy CO2-CH4-N2 -43 to -23 62.1-100.34

Xu et al. (1992) 1992 TPxy CO2-CH4, CO2-N2, CO2-CH4-

N2

15 and 20 51.1-91.1

Seitz et al. (1996) 2002 PVTX CO2-CH4-N2 50-250 199-999

2.1.2 Conventional Cryogenic Technology Conventional Cryogenic Technology is a very old process where the operation is carried out at a

very low temperature. Conventional Cryogenic Technology includes simple Cryogenic

distillation and extractive distillation. Cryogenic distillation is carried out at an extremely low

temperature and high pressure to separate CO2 and other components based on their different

boiling point. This method directly produces liquid CO2 or CO2 vapor at a high pressure which

reduces extra costs of compression for storage purpose. This technology is not economical and

30

energetically viable for dilute gas streams. One of the major operating problems for this method

is solid formation and choking of column in the older top section of the distillation columns in

both low and high pressure ranges. Solid formation during separation of CO2 has been reported

in literature (Katz & Donnely , 1954). Gas Processors Association (RR-10, 1974) published

liquid phase composition of CO2- CO4 binary gas mixture at S-L-V locus. Maqsood et al. (2014)

predicted the solid formation in the distillation column inside the convergence look utilizing

GPA the data they found that increasing the column pressure might be help full to avoid solid

formation. However methane loss will increase and the purity of methane will be questionable.

Henson et al. (2001) derived a low order wave model for cryogenic nitrogen purification

column and compared the MATLAB simulated results with a first principles model developed

within the commercial dynamic simulator HYSYS. Plant (Hyprotech). The authors used the non

linear wave modelling concept to model the cryogenic nitrogen separation column and

performed rigorous modelling of the combined reboiler/condenser assembly and verified the

model using the dynamic simulator. The model is capable of producing acceptable prediction of

composition responses for various types of disturbances. However, the constant wave pattern

assumption used in the wave model development invariably leads to some degree of modelling

error. They proposed on-line model adaptation as a possible approach to overcome the constant

wave shape assumption. Panopoulos et. al. (2013) suggested a cryogenic method for recovery

of H2 and CH4 from a rich-CO2 stream in a pre-combustion carbon capture system. They

modeled their process using Aspen Plus based on differences in thermodynamic properties and

evaluated the effects of it on the efficiency of the system. They also studied the effect of

operating parameters of the (Purification & Compression Unit) PCU integration on the

performance of the system. Maqsood et. al. (2014) synthesized efficient cryogenic distillation

sequence for purification of natural gas having medium and high concentration of carbon dioxide

contained. Calculations for conventional and hybrid distillation column sequences were

performed using the heuristic and evolutionary strategies. Three different sequences direct,

indirect and mixed were chosen for different feed compositions selected from the literature. It

was found that direct sequence is the best options for separation of CO2 from natural gas with

different feed composition in respect of minimum vapour flow, marginal vapour flow and energy

requirements. They also found hybrid cryogenic network requires considerably lower energy

31

and showed significant reduction in capital cost of the columns compared to the conventional

cryogenic network.

Maqsood et. al. (2014) presented a techno- economic evaluation of cryogenics network for

separation of carbon dioxide from natural gas with different feed compositions. Equipment

sizing and cost estimation has been carried out for the cryogenic networks using the co relations

provided in the literature.

Maqsood et. al. (2015) conducted a study with different configurations of cryogenic distillation

networks to remove carbon dioxide from natural gas feed with high heavy hydro carbon

contained they investigated three different case studies along with conventional cryogenic

network. They found that higher operating pressure leads to reduction of energy requirements but

operational problems in distillation columns can arise due to thermodynamic behavior of

methane - carbon dioxide system.

Extractive Distillation

In order to prevent solid formation inside the distillation column extractive distillation is

a suitable option. Holmes et al. (1982) patented and extractive distillation process, introducing

heavier hydro carbon (C2-C5 alkanes) or other non polar liquids which are miscible with methane

at the column conditions in the condenser section of the distillation column. This help to avoid

solidification of carbon-dioxide. Holmes et al. (1983) executed pilot studies on cryogenic acid

gas / hydrocarbon separation process and validated the work. Valencia et al. (1985) patented a

method for separating carbon dioxide from methane using Helium as an additive which

facilitated the separation process and prevented solid carbon dioxide formation. However the

separation of He from CH4 at higher pressure is quite problematic. Atkinson et al. (1988)

introduced a dual pressure distillation process intended for the removal of high concentration

carbon dioxide from methane. It comprises of two distillation columns operating indifferent

pressure to avoid carbon dioxide solidification. ZareNezhad et al.(2009) reported an extractive

distillation technique for producing CO2 enriched injection gas for enhance oil recovery (EOR)

fields. No external solvent is required in this case. In this technique a part of natural gas liquid

stream comprising of iso-butane and heavier components were added to the top of a CO2 stripper

followed by ethane and propane stripping of ethane and heavier components stream. Due to this

the azeotropic mixture of carbon dioxide and ethane breaks down which increases the tray

efficiency. Berstad et al. (2012) reported presented a low-temperature process for CO2 removal

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from natural gas before liquefaction. They simulated a three distillation column network by using

C5 as an additive in ASPEN Hysys with PengRobinson equation of State for the separation of

CO2 from natural gas. Berstad et al. (2013) presented a review on low temperature carbon

dioxide technologies and discussed their potential. This gives us detailed idea about the

applicability, energy efficiency of the technologies discussed with the base line technology.

2.1.3 Non-conventional Cryogenic Technology

There is always an alternative way to everything as they say that the grass is always greener on

the other side. Researchers found a few alternative ways to discover the real potential of the

cryogenic technologies. These alternative things are referred to as the Non-Conventional

Cryogenic Technologies. These non-conventional cryogenic technologies focuses on separation

of carbon dioxide by utilizing one of the major disadvantages of the conventional cryogenic

processes into its working principle. Actually the solidification of CO2 in the solid vapour zone

is utilized to desublimate carbon dioxide from the gas stream.

Schah et al. (2011) conducted a feasibility study of Carbon capture by desublimation. They

modeled the process using ASPEN Plus featuring finned-plate heat exchangers. The process

cooled the incoming flue gas with a condensing heat exchanger and there after another heat

exchanger desublimated the remaining water vapour in the flue gas. Finally a third heat

exchanger desublimated the Carbon dioxide. In this model, both water and carbon dioxide froze

and desublimated directly on the heat exchanger surface there by requiring periodical

regeneration of the heat exchanger. An economic analysis compared to a common MEA

absorption showed that this desublimation process has superior capture performance that requires

comparatively less energy penalty. A continuous process that avoids losses due to regeneration

employee parallel heat exchanger trains makes it really attractive. Clodic et al. (Clodic et al.

2005; Clodic and Younes 2002; Clodic and Younes 2003; Perrotin and Clodic 2005; Clodic

and Younes 2006; Clodic and Younes 2006) have patented a desublimating carbon capture

system quite similar to the one that Schah model. Schahs design employs a series of heat

exchangers that operates at successively decreasing temperatures. The first one condenses water,

the latter remaining water vapour and the last one desublimates carbon dioxide. Clodic uses a

flat-plate heat exchanger for the desublimating stage instated of the finned heat exchanger as

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used by Schah. The cold and clean flue gas exits the last exchanges going through a regenerating

heat exchanger to cool the incoming flue gas. After the CO2 & the H2O loading in the heat

exchanger reaches a maximum, the flue gas is diverted into a parallel system. Then the heat

exchanger enters the regenerations mode. During this period valves isolate the frozen CO2 as

they warm up. This melts the CO2 and pressurizes the system. The water and CO2 flow out of the

heat exchanger as liquids under pressure. The heat exchanger pressure drops back to that of the

flue gas, the heat exchangers cool back to cryogenic temperatures; and there by resuming the

process. Certain challenges exist in the work of Clodic. They are - (1) The sublimating CO2

creates an insulating layer between the heat exchanger and the flue gas decreasing the heat

transfer and increasing the pressure drop; (2) the system is inherently a semi-batch or batch

process; (3), the amount of CO2 that is captured is small compared to the mass of the heat

exchangers on which it collects, and cycling the large mass of heat exchanger material from the

capture temperature of around 140 K to the CO2 melting temperature of about 220 K generates

large amounts of entropy and decreases the process efficiency and (4) pressurizing the heat

exchangers at commercial scale will require a valve that sustains 8-70 bar pressure in a duct that

is nominally 30 feet in diameter, which presents a significant practical (rather than fundamental)

problem.

Cryogenically Cooled Packed Bed

Tuinier et. al., (2010, 2011) has developed a novel process concept for carbon capture and

storage based on dynamic packed beds with a moving interface between water and carbon

dioxide. The process concept is based on the periodic operation of cryogenically cooled packed

beds. The process cycle consists of three consecutive steps cooling, capture and recovery steps

respectively. A front of desublimating- sublimating CO2 is formed and it moves based in the

temperature profile inside the bed. Nitrogen initially cools the packed bed. Once flue gas enters

the packed bed, water condenses and freezes, then CO2 desublimates onto the packing material.

As the bed reaches maximum H2O and CO2 loading, the flue gas is diverted to a parallel system

and pure CO2 flows into the bed above the desublimation temperature but below the freezing

temperature of H2O. The solid CO2 in the bed sublimates and leaves with the CO2 stream. Warm

nitrogen then evaporates the water, followed by a recycle steam of cold clean flue gas to cool the packing material. After the capture cycle, the bed is regenerated for further use. The process was

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reported for atmospheric pressure separation of low CO2 flue gases using dynamic beds. This

process can be made continuous if three columns are built in parallel. The temporal evolution of

axial temperature, concentration, and mass deposition profiles occurring in the beds can be well

described by a validated one-dimensional pseudo-homogeneous axially dispersed plug flow

model. Aliredza (2013) reported the experimental and simulation work on recovery of CO2

using cryogenic packed bed. Figure 9 shows the schematic representation of cryogenic packed

bed. Abul Hassan et al. (2013) developed an experimental setup for cryogenic separation of

CO2 from natural gas with high CO2 content. In this study, the CO2 concentration was used up to

70%. The separation principle of CO2 from natural gas was based on desublimation principle in

countercurrent cryogenic packed bed. They also simulated the cryogenic packed considering a 1

dimensional pseudo homogeneous model (Abul Hassan et al. 2013). Due very steep gradients

of temperature and concentration the solution is tough to get. Finite difference, Forward-Time

Central Space (FTCS) scheme is used for simultaneous numerical solution of the model. The

scheme was found to be efficient as the results compared with the experimental ones showed

promising potential for industrialization. Multiple cryogenic packed beds have been used for

simultaneous dehydration as well as CO2 separation by Karen (Karen Hui, 2013) and Abul

Hassan et al. (Abul hassan et al., 2014). Aditi Mullick (2014) have modeled and simulated the

separation of CO2 onto cryogenically cooled packing using reduced order transport phenomena

models. The transport mechanism and dynamics of cryogenic CO2 capture have been addressed

using a model based on single packing. The nucleation kinetics and growth rate of deposition of

CO2 frost on a single cooled packing is studied using a two-step model, which takes into account

the diffusion from supersaturated gas phase to the gas solid interface and relatively slower

crystallization kinetics and nucleation on a heterogeneous surface (packing) in series. Recently,

Abul Hassan et al. published a paper where they have explored the minimization of energy

consumption for a counter current switched packed bed intended to separate CO2 and other

components of natural gas (Abul hassan et al., 2014). They conducted experiments with a

switched packed bed setup by changing different operating parameters and compared the results

with other co-current or jacket cooled constant temperature configurations. They also

investigated the effects of the important process parameters initial temperature profiles of the

cryogenic bed, feed composition, and feed flow rate on energy requirement, bed saturation, bed

pressure and cycling times. The energy consumption of countercurrent switched packed bed was

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compared with the conventional cryogenic distillation process and it saves 662 kJ energy per kg

CO2; for a constant inlet feed composition. The effect of feed composition on the energy

requirement revealed that countercurrent switched cryogenic packed beds have potential for

substantial energy savings during purification of natural gas with high CO2 content.

Stirling Coolers

Song et al. has developed a cryogenic carbon capture technology similar to Clodic, but has

managed to make it a truly continuous process (Song, Kitamura et al. 2012; Song, Kitamura et

al. 2012; Song, Kitamura et al. 2012; Song, Kitamura et al. 2013). Song uses a similar three

heat exchanger design but uses Stirling coolers (SC) instead of plate heat exchangers. A Stirling

cooler generates an acoustic pulse that creates a refrigeration effect inside a pulse tube cold

finger (Hu, Dai et al. 2010). Stirling coolers have high efficiency, high reliability, and small

footprint and volume. The first SC pre-cools and dehydrates the flue gas. The condensed water

leaves as a separate stream, while the cool flue gas continues to a second SC. The second SC

desublimates the CO2 as a solid on the surface of the cold finger, while the clean flue gas

exhausts. A mechanical scraping rod is used to keep the surface of that heat exchanger clean,

while solid CO2 falls into a storage chamber where at third SC provides cooling to keep the CO2

in a solid state. Song et al., (2013) evaluated the properties of this free piston Stirling cooler

system and briefly compared its performance with other cryogenic methods. They found that this

approach is better than LN and LNG in terms of energy consumption but high pre-chill time,

vibration and less deposition area are disadvantages for this system. They suggested integrating

this method with amine methods is an effective approach. They are looking forward to make this

a vibration proof system. Song et al. (2013) experimentally tested the performance of the Free

Piston Stirling Cooler (FPSC) system for CO2 capture. The effect of flowrate of the gas stream

and temperature of FPSC was investigated in detail. They found that the system can capture 95%

CO2 from simulated flue gas and consume 0.55MJ of electrical energy per kg of carbon dioxide

recovered which is the least compared to other dominant technologies. Song et al., (2014)

presented a process simulation and energy analysis of cryogenic CO2 capture process based on

Stirling coolers. They simulated the overall energy flow Stirling coolers based cryogenic CO2 capture process. Theoretical analysis of the energy consumption for each of the unit in the

capture system was also under taken. They also compared energy consumption of this process

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with other established technologies and claimed there process to be least energy consuming (1.6

MJ/KG CO2). Furthermore; they extended their work and investigated the influence of capture

conditions on the performance on the systems; based on three levels and variables and in central

composite design. They optimized the system with the objective of maximum CO2 recovery,

CO2 productivity and minimum energy consumption. They compared there result with

experimental data. They found that under the optimal condition 95.20% CO2 can be removed.

Song et al., (2015) investigated the Co-efficient Of Performance (COP) of the Fitted Piston

based Stirling coolers (FPSC). The key parameters were also investigated in order to improve the

COP. It was found mat