Cryogenic CO2/H2S capture
technologies for
remote natural gas processing
Mehdi Panahi
Trial Lecture
December 1st, 2011
Trondheim
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Outline
1. Introduction
2. Cryogenic technologies
-
Ryan Holmes method
-
Controlled freeze zone (CFZ) method
-
Cryocell method
-
Sprex method
-
Twister technology
3. Conclusions
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Outline
1. Introduction
2. Cryogenic technologies
-
Ryan Holmes method
-
Controlled freeze zone (CFZ) method
-
Cryocell method
-
Sprex method
-
Twister technology
3. Conclusions
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CO2 effect on Global warming
Green house gases cause global warming: CO2, the major one
World energy demand is increasing
• more fossil fuels
• 130% rise in CO2 emissions by 2050
• rise in global average temperature by 6°C
Intergovernmental Panel on Climate Change (IPCC):
“Emissions must be reduced by 50% to 85% by 2050 if global
warming is to be confined to between 2°C to 2.4°C”
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CO2 emission from gas processing plants
Associated CO2 with natural gas is one of the sources of
global CO2 emissions
CO2 content in natural gas varies between 2-65% and in
some reserves is even more!
Increasing demand for natural gas has made reserves with
high CO2 content economically
H2S is often present with CO2 in natural gas reserves
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Definitions and Spec in gas processing plants
Natural gas containing H2S > 4 ppm is called “sour gas”
Natural gas containing acidic gases like CO2/H2S is called
“acid gas”
To produce “sweet gas”, CO2 and H2S (for technical and
environmental reasons) must be removed and stored
Specs. for natural gas pipelines:
CO2: ≤ 2-4 mol% (varies by the country)
H2S: ≤ 4 ppm
Specs. of natural gas for LNG plants:
CO2: < 50 ppm
H2S: < 4 ppm
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High acid gas content natural gas reserves
Most high CO2 natural gas resources are located in SE Asia,
NW Australia, Central USA, North Africa and Middle East
It is estimated 1/5-1/3 of global natural gas resources have
significant amounts of CO2 and H2S
Natuna gas field in Indonesia, the largest high CO2 reserve:
(>70%v)
LaBarge gas field (65% CO2) in SW Wyoming (USA),
discovered in 1963, production delayed until1986 because of
high CO2 concentration
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Different (old/new) Technologies for
CO2/H2S removal
Adsorption (chemical,C / physical,P)
Activated carbon (C), Chemsweet (C), Molecular sieves (P), Zinc oxide (C)
Absorption (mostly chemical)
ADIP, Alkazid, Amisol, Benfield, Catacarb, CNG (P), Estasolvan, Flexsorb SE,
Flour Econamine, Flour solvent, Giammarco-Vetrocoke, MEA, MDEA, Purisol
(P), Rectisol (P), Seaboard, Selexol (P), Sepasolv MPE (P), SNPA-DEA,
Stretford, Sulfiban, Sulfinol, Tripotassium Phosphate, Vaccum Carbonate,
Zinc oxide
Cryogenic distillation
Controlled Freeze Zone (CFZ), Ryan Holmes, Cryocell, Sprex, Twister
Membrane
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Applications of different technologies in gas
processing plants for removing of acid gases
Adsorption
Suitable for reducing CO2 content from 3% to 0.5%
Not applicable for high CO2 concentration streams since it needs
frequent regeneration of solid bed
Absorption
Suitable for low pressure streams with CO2 content of 3-25%
This method is the conventional method, which is widely used in
natural gas processing industries
Not suitable for very high CO2 concentration streams due to large
solvent recirculation and consequently large heat duty in the stripper
for solvent regeneration
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Applications of different technologies in gas
processing plants for removing of acid gases
Membrane
Flexible for different CO2 concentrations, but maintaining
high performance of membrane in presence of varying
contaminants of natural gas stream is a challenge
Traditional technologies:
- remove acid gases at near atmospheric pressures,
- required significant amount of energy to compress acid gases for
re-injection for Enhanced Oil Recovery (EOR)
Cryogenic distillation
Suitable for removing high CO2/H2S contents from natural gas streams
especially for offshore applications
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Outline
1. Introduction
2. Cryogenic technologies
-
Ryan Holmes method
-
Controlled freeze zone (CFZ) method
-
Cryocell method
-
Sprex method
-
Twister technology
3. Conclusions
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Phase diagram for
CO2/CH4 in 650 Psia
(44 bar)
Point 1:
Feed
Target:
Feed:
Chilling the feed
50% CH4/50% CO2
-8 (-22°C)
Liquid: 18% CH4
Solidification
point of CO2
Point 2: reaching the
VL zone
Point 3:
Point 4:
(-62°C)
natural gas product
with 1% CO2
Vapor: 72% CH4
Vapor: 85%
CH4
Achieving natural gas
with CH4 purity of >85%
is not possible in one
conventional distillation
column
Figure from: H.G. Donnelly and D.L. Katz, Phase equilibria in the
carbon dioxide-methane system, I&EC, 46 (1954), 3, 511-517
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Outline
1. Introduction
2. Cryogenic technologies
-
Ryan Holmes method
-
Controlled freeze zone (CFZ) method
-
Cryocell method
-
Sprex method
-
Twister technology
3. Conclusions
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Ryan Holmes method
Invented by Arthur S. Holmes and James S. Ryan at Koch
Process Systems, US in 1982
Agent should have a
freezing temp. below
condenser Temp.
Idea: Adding a solids-preventing
agent e.g. NGL, to the solids
potential zone of cryogenic
distillation column
Pre-cooler
By adding sufficiently agent, the
liquid composition is moved
away from the freezing point
Cooling to
cryogenic
temperatures
This method is commonly used in gas processing plants
Suitable for offshore applications?
The Figure from: A. S. Holmes, J. M. Ryan, Cryogenic distillation separation of
acid gases from methane, US patent, 1982
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Outline
1. Introduction
2. Cryogenic technologies
-
Ryan Holmes method
-
Controlled freeze zone (CFZ) method
-
Cryocell method
-
Sprex method
-
Twister technology
3. Conclusions
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Controlled Freeze Zone method (CFZTM)
CFZTM method:
invented at Exxon production research in 1983
patented in 1985
First pilot plant (the picture in the right) at
Exxon’s Clear Lake Gas plant in Pasedena (1987):
0.6 MMSCFD, CO2 (from 15% to 65%),
pressure (38-42 bar)
Quality of products:
while the design of top product (natural gas) specification
was pipeline specs, it met LNG feed required specs!
The design of methane loss at the bottom product
(liquid CO2) was 1%, but it reached 0.5%
Further studies were stopped due to collapse in oil prices
Figure from: J. A. Valencia, P. S. Northorp, C. J. Mart, Controlled Freeze Zone™
Technology for enabling processing of high CO2 and H2S gas reserves, ExxonMobil
Upstream Research Company IPTC 12708 (2008)
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Exxon’s first CFZ commercial demonstration
plant at Shute Creek gas processing plant
Scale up: 23
Integrated with a gas field injection
Initial tests prove removal of CO2
content from 65% down to <1000ppm
(July 2011)
The tests are still being done in 20112012
Figure from: C. Condon, M. Parker, Shute Creek Gas Treating Facility Project
Updates, The Wyoming Enhanced Oil Recovery Institute 5th Annual Wyoming
CO2 Capture Conference, 13 July 2011
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CFZ method: thermodynamic concept
82 bar
critical point of
methane
42 bar
critical point of
CO2
14 bar
-101°C
-57°C
-1°C
32°C
Rather than avoiding solidification, CFZ allows acid gases to freeze
Operating at higher pressure than CO2 solidification pressure (?)
Limitation of locus of the critical points
Still far from the required purity for methane product
Figure from the references below:
H.G. Donnelly and D.L. Katz, Phase equilibria in the carbon dioxide-methane system,
I&EC, 46 (1954), 3, 511-517 and J. A. Valencia, P. S. Northorp, C. J. Mart, Controlled
Freeze Zone™ Technology for enabling processing of high CO2 and H2S gas reserves,
ExxonMobil Upstream Research Company IPTC 12708 (2008)
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CFZ distillation operation
Operating the column in lower pressure than solidification pressure
Operation crosses the solidification region
3 operational zones are present:
1. Stripping section (conventional distillation)
2. Solidification (controlled freeze zone, CFZ) section
3. Rectifying section (conventional distillation)
Feed (mixture of CH4 and CO2) enters somewhere near the middle of column
Reboiler duty; allowable loss of methane in CO2 liquid bottom product
Condenser temperature; required specs for purified methane
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Liquid from the top distillation section is sprayd into the CFZ section
Warmer temperature vaporize the lighter components
methane product (high quality)
available in high pressure
Solid (pure CO2) is formed in CFZ
section and fall on the liquid layer
Bottom part of CFZ is kept above
solidification temperature

CO2 product (liquid)/or any other acid gas, easily to be
pumped for geo-sequestration or for EOR purposes
Vapor rises from the bottom distillation section to the CFZ section
Colder temperature in CFZ section condenses CO2
Figure from: B.T.Kelly, J. A. Valencia, P. S. Northorp, C. J. Mart, Controlled Freeze
Zone™ for developing sour gas reserves, Energy Procedia 4 (2011), 824-829
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Optimal operation of CFZ distillation
Operational temperature will depend on feed composition and
product specification
CFZ distillation operates at constant pressure
Optimized pressure of CFZ column depends on
• pressure of the gas reserve,
• required pressure for purified natural gas (sales spec),
• geometry of the column
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Advantages of CFZ method
Suitable for high CO2/H2S content natural gas reserves
Separation is done in a single column, low investment
cost, less challenges for offshore applications
Purified natural gas product in high pressure (reduce the
compressor work to export by the pipeline)
Availability of CO2/H2S product in liquid form, readily to be
pumped for EOR, geo-sequestration purposes
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Outline
1. Introduction
2. Cryogenic technologies
-
Ryan Holmes method
-
Controlled freeze zone (CFZ) method
-
Cryocell method
-
Sprex method
-
Twister technology
3. Conclusions
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Cryocell method
This method was developed by Cool Energy Ltd and
tested in collaboration with Shell in Australia (Perth)
Idea:
CO2 sublimation point: -78.5°C (at 1 bar)
CH4 (major component of Natural gas) sublimation
point: -182°C (at 1 bar)
Mixture of light hydrocarbons + CO2 at certain T,P:
Vapor-Liquid-Solid phases
Solid phase: pure CO2, Vapor/Liquid phase: CO2 +
hydrocarbons
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Thermodynamic behavior of mixture of
hydrocarbons + CO2
1- Mixture (feed) at pressure > 50 bar and ambient temperature
2- Feed is cooled down to above solidification
temperature of CO2(liquid phase)
before JT
valve
3- Liquid is isenthalpic flashed through a
Joule-Thomson valve into a separator; solidvapor-liquid
Selection of appropriate:
after JT
valve
- pre-cooling temperature
- flash pressure
to minimize CO2 content in vapor phase
and methane content in liquid phase
VLSE diagram for a high CO2 content
natural gas: 50% CO2, 40% CH4, 10%
other light hydrocarbons
Figure from: A. Hart and N. Gnanendran, Cryogenic CO2 Capture in Natural Gas,
Energy Procedia 1 (2009), 697-706
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Different Cryocell configurations
Based on natural gas composition:
- high (>20%) or low (<20%) CO2 composition
- lean (recovery uneconomical) or rich of NGLs
4 process flow configurations
low CO2/lean Natural gas
low CO2/Rich Natural gas
high CO2/lean Natural gas
high CO2/Rich Natural gas
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Cryocell process diagram for low CO2/lean Natural gas
Base case Cryocell flow diagram
Figure from: A. Hart and N. Gnanendran, Cryogenic CO2 Capture in Natural Gas,
Energy Procedia 1 (2009), 697-706
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Cryocell process diagram for high CO2/Rich Natural gas
Additional bulk CO2 removal column and NGL recovery
Figure from: A. Hart and N. Gnanendran, Cryogenic CO2 Capture in Natural Gas,
Energy Procedia 1 (2009), 697-706
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Cryocell field results
Design of demonstration plant based on scheme for low
CO2-lean gas (2008, 2009)
Removing down CO2 content from 60% to 26%, 40% to
14%, 21% to 4% and from 13% to 3%
Excellent match between tests and simulation results
(Aspen Hysys + CryoFlash)
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Comparison between Cryocell and Amine Absorption
Amine
Sale gas rate, MMSCFD
Investment cost
(1000 AUD), accuracy 30%
37.7
CryoCell
27.8
38.2
29.6
CO2 20%
CO2 35%
CO2 20%
CO2 35%
64,359
108,777
48,877
67,464
Compression Power (MW)
1.9
3.8
4.3
7
Electrical load (MW)
1.3
2.2
0.2
0.3
Process Heating (MW)
19
35
< 0.1
< 0.1
Other advantages of Cryocell: No need for chemical solvent,
no make up water, no heating system, no potential foaming
Cryocell has higher maintenance costs for rotating equipment
Suitable for offshore applications
The data from: A. Hart and N. Gnanendran, Cryogenic CO2 Capture in Natural Gas,
Energy Procedia 1 (2009), 697-706
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Outline
1. Introduction
2. Cryogenic technologies
-
Ryan Holmes method
-
Controlled freeze zone (CFZ) method
-
Cryocell method
-
Sprex method
-
Twister technology
3. Conclusions
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Sprex (Special pre-extraction) method
Patented by IFP in 1994 and further developed in joint
with TOTAL
Idea:
Improving the economics of amine absorption processes for
removal of high H2S content (as high as 40%) in natural gas,
where acid gases are re-injected to the reservoir
Temperature of cryogenic section is -65°C
High pressure liquid H2S ready to be pumped into the reservoir
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Sprex (Special pre-extraction) method
A temperature of
-60°C to -70°C
must be attained
Much smaller
amine absorption
Figure from: ToTAL website
http://www.total.com/MEDIAS/MEDIAS_INFOS/239/EN/sour-gas2007.pdf?PHPSESSID=cec2fdfc960710c595870d3827bb4269
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Comparison of Sprex method with Amine
absorption
Raw gas flowrate (MMSM3/day)
4.6 (165 MMSCFD)
Treatment Pressure
70 bar
Acid gas injection pressure
150 bar
Feed gas composition
H2S:35%, CO2:7.5%, C1:65.2%, C2+:1%
Treated gas specs
H2S: 4ppm, CO2: 2%
Amine
Amine+Sprex 30
Capex (MM USD)
153
128
Power consumption (MW)
52
30
Steam consumption (MW)
46
34
Sprex decreses the amine absorption size significantly
The data from: F. Lallemand, F. Lecomte and C. Striecher, “Highly Sour Gas
Processing, H2S bulk removal with the Sprex Process”, IPTC 10581, 2005
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Outline
1. Introduction
2. Cryogenic technologies
-
Ryan Holmes method
-
Controlled freeze zone (CFZ) method
-
Cryocell method
-
Sprex method
-
Twister technology
3. Conclusions
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Twister method
Idea: condensation and separation in supersonic velocity
(extremely short residence time), thermodynamically similar
to a turbo-expander
Pressure
Expansion
Distillation Recovery
Temperature drop by transforming
pressure to kinetic energy (i.e.
supersonic velocity)
Figure from: P. Schinkelshoek, H. D. Epsom, Supersonic gas conditioning
commercialization of Twister technology, 87th annual convention, Grapevine, Texas,
USA
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Twister method
Twister method has been successfully applied for water dehydration
and NGL/LPG extraction
First commercial offshore application in 2004 for dehydration of 600
MMSCFD sour gas at Bintulu in Malaysia (6 Twister tubes in two
parallel dehydration units)
A Twister process scheme has been developed for H2S/CO2 bulk
removal from sour gas
An amine absorption process is needed to purify the outlet of Twister
to the required specs; methane recovery of 95% is expected
Compact lightweight Twister can significantly decrease the size of
conventional absorption processes, suitable for offshore applications
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Outline
1. Introduction
2. Cryogenic technologies
-
Ryan Holmes method
-
Controlled freeze zone (CFZ) method
-
Cryocell method
-
Sprex method
-
Twister technology
3. Conclusions
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Conclusions
Increasing demand for natural gas has made high acid gas reserves
economically
Cryogenic technologies are suitable for offshore applications
processes, and operation in high pressure;
- small sizes compared to conventional amine absorption
- less energy requirement
- separation of acid gases in liquid form and high pressure; readily
to be pumped to the reservoir
CFZ, Cryocell, Sprex and Twister seem to be very promising and
advanced options
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References
[1] Sources of CO2 IPCC Special Report on Carbon dioxide Capture and Storage
http://www.ipcc.ch/pdf/special-reports/srccs/srccs_chapter2.pdf
[2] J. Hao, P.A. Rice, S.A. Stern, Upgrading low-quality natural gas with H2S and CO2 selective polymer
membranes: Part I. Process design and economics of membrane stages without recycle streams, Journal
of Membrane Science, 209, 1, 177-206
[3] D. A. Coyle, V. Patel, Process and Pump services in the LNG industry, Proceedings of 22nd
international pump user symposium 2005,
[4] http://en.wikipedia.org/wiki/Sour_gas
[5] WFJ Burgers, PS Northrop, HS Kheshgi, JA Valencia, Worldwide development potential for sour gas,
Energy Procedia, 4 (2011), 2178–2184
[6] H. J. Herzog and E. M. Drake, Carbon dioxide recovery and disposal from large energy systems, Energy
and the Environment, 12 (1996), 145-166
[7] J. A. Valencia, B. K. Mentzer, Processing of High CO2and H2S Gas with Controlled Freeze Zone™
Technology, ExxonMobil Upstream Research Company GASEX 2008 Conference
[8] http://www.fischer-tropsch.org/DOE/DOE_reports/GRI/gri-86_0009-1/86_00091,%20Part%204,%20Pages%20298%20-%20409.pdf
[9] E. Keskes, C.S. Adjiman, A. Galindo, and G. Jackson, a physical absorption process for the capture of
CO2 from CO2-rich natural gas streams, Chemical Engineering Department, Imperial College London,
http://www.geos.ed.ac.uk/ccs/Publications/Keskes.pdf
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References
[10] H.G. Donnelly and D.L. Katz, Phase equilibria in the carbon dioxide-methane system, I&EC, 46 (1954),
3, 511-517
[11] J. A. Valencia, P. S. Northorp, C. J. Mart, Controlled Freeze Zone™ Technology for enabling processing
of high CO2 and H2S gas reserves, ExxonMobil Upstream Research Company IPTC 12708 (2008)
[12] B.T.Kelly, J. A. Valencia, P. S. Northorp, C. J. Mart, Controlled Freeze Zone™ for developing sour gas
reserves, Energy Procedia 4 (2011), 824-829
[13] C. Condon, M. Parker, Shute Creek Gas Treating Facility Project Updates, The Wyoming Enhanced Oil
Recovery Institute 5th Annual Wyoming CO2 Capture Conference, 13 July 2011
[14] A. Hart and N. Gnanendran, Cryogenic CO2 Capture in Natural Gas, Energy Procedia 1 (2009), 697706
[15] P. Schinkelshoek, H. D. Epsom, Supersonic gas conditioning commercialization of Twister technology,
87th annual convention, Grapevine, Texas, 2008
[16] P. Schinkelshoek, H. D. Epsom, Supersonic gas conditioning for NGL recovery, offshore technology
conference, Houston, 2008
[17] A. S. Holmes, J. M. Ryan, Cryogenic distillation separation of acid gases from methane, US patent,
1982
[18] http://www.total.com/MEDIAS/MEDIAS_INFOS/239/EN/sour-gas2007.pdf?PHPSESSID=cec2fdfc960710c595870d3827bb4269
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Thank you for your
attention!
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