1. Natural Gas System Carbon Capture and
Storage
CHEE 462 – Technical Paper 2
Submitted by: Michael Garibaldi [260353823]
Submitted to: Pierre Bisaillon
February 14, 2014

2. 1
Abstract
An efficient and cost-effective system for capturing carbon dioxide is to treat the exhaust of a new
natural gas-fueled power plant rated for 300 MW and 1000 tonnes of CO2 production per day. A carbon tax
has been put into effect which charges power plants a fee for every tonne of CO2 that leaves in the stack
gas. It is therefore beneficial to the environment and to the plant to include a carbon capturing technology.
There are three known and tested methods that will be evaluated, each of which acts at a different point in
the combustion cycle. Post-combustion carbon capture treats the exhaust from generation directly. Pre-
combustion carbon capture decreases the carbon levels entering the combustion reaction and indirectly
lowers CO2 output. Chemical-looping combustion capture, or oxy-fuel combustion capture, performs
combustion with only oxygen and natural gas, leading to higher thermal efficiencies and a decreased fuel
consumption. This, in effect, also lowers CO2 output in the exhaust gas.
Each technology is compared with a set of selection criteria. The first five criteria are essentialand
will determine if a technology is suited for the plant’s needs. These criteria are CO2 recovery percent,
thermal efficiency, cost of capital, cost per tonne of CO2 over life and cost of solvent. The next four criteria
determine which technology is most appropriate. These include a more stringent range of CO2 recoveries
(90% or above), a more narrow range for thermal efficiency, a minimum cost of CO2 recovery over lifetime
of the plant and secondary CO2 emissions from auxiliary duties.
It is determined conclusively and supported by evidence from numerous reports that post-
combustion carbon capture is the more appropriate carbon sequestration method for this plant. Recovery is
found to be 90% but can be tuned for higher levels. Costs are also moderate and the solvent involved in
CO2 absorption can be regenerated and reused. Fuel efficiency is not enhanced however and long-term
research on alternative energy sources is supported by the findings in this paper.

3. 2
Table of Contents
Abstract..............................................................................................................1
Table of Contents................................................................................................2
Table of Figures and Tables .................................................................................................... 3
Introduction.................................................................................................................................. 4
Background.................................................................................................................................. 5
Selection Criteria........................................................................................................................ 6
Alternatives.................................................................................................................................. 7
Analysis ........................................................................................................................................ 8
Comparison Tables .................................................................................................................... 9
Conclusion and Recommendation .......................................................................................10
Potential Problem Analysis....................................................................................................11
References..................................................................................................................................12

4. 3
Table of Figure and Tables
Table 1: Plant Performance Data......................................................................................................4
Figure 1: The Carbon Energy, Capture and Storage Cycle .................................................................5
Table 2: Essential Criteria for Carbon Dioxide Capture System..........................................................8
Table 3: Desirbale Criteria for the Carbon Dioxide Capture System...................................................8
Table 4: Specifications for Plant without Carbon Capture ..................................................................9
Figure 2: Post-combustion Carbon Capture Block Flow Diagram.......................................................9
Table 5: Specifications for Post-combustion Carbon Capture with Amine Solvent...............................9
Figure 3: Pre-combustion Carbon Capture Block Flow Diagram ........................................................9
Table 6: Specifications for Pre-combustion Carbon Capture with Amine Solvent ..............................10
Figure 4: Chemical-looping Combustion Carbon Capture Block Flow Diagram ..................................9
Table 7: Specifications for Chemical-looping Combustion Carbon Capture ......................................11
Table 8: Comparative Analysis Table for Essential Critera ..............................................................13
Table 9: Comparative Analysis Table for Desirable Criteria.............................................................13
Table 10: Comparison Table for Essential Criteria ..........................................................................14
Table 11: Comparison Table for Desirable Criteria..........................................................................14

5. 4
Introduction
A power plant is to be constructed in the southern regions of the Quebec province. The plant
contains a natural gas-fueled turbine that supports up to 300 megawatts of electrical output to supply a new
industrial complex nearby. Due to increasing concernover rising global carbondioxide levels and the threat
of a probable Greenhouse Effect, regulation dictates that all novel petroleum-fueled power plants recover
substantial amounts of carbon from stackgasesto preventtheir release into the atmosphere. Carbon dioxide,
suspected to be the leading cause of the Greenhouse Effect,is the primary target of the new carbon capture
mandate. Environmental studies show that this recovered carbon can be transformed into solid or liquid
form and stored underground for long periods of time (up to 500,000 years) where it cannot harm natural
ecosystems.
Due to the volume of carbon dioxide released in combustion reactions like those of a natural gas-
fueled power plant, complex capture systems are being designed to ensure that the vast majority of it does
not make it into the atmosphere.Three mechanisms have been proposed for the new plant: post-combustion
capture,pre-combustion capture,and oxy-fuel combustion capture. All three techniques are proven to have
better results for carbon capture than conventional plants with no capture system. These systems can also
be produced on a large scale in order to handle large volumes of exhaust year-round. Each method is
optimal for different applications, however; one of these methods is more beneficial for this specific
application than the rest. The table below is a summary of the plant performance parameters and their
values. From these specifications, an analysis will be drafted to compare each of the capture systems and
to choose which is the most suitable for this operation.

6. 5
Table 1: Plant Performance Data
Parameter Units
Type - Once-Through Steam Generator
Exhaust Gas Flow Rate kg/hr 114000
Power Output MW 300
CO2 Production tonnes/day 1000
CO2 Recovery % 90.00
Inlet Temperature °C 182
Inlet Pressure kPa(g) 0.0 ± 0.04
Inlet Composition
N2 mole % 71.613
Ar mole % 0.871
O2 mole % 2.595
CO2 mole % 8.616
H2O mole % 16.298
SO2 ppmv 24
SO3 ppmv < 2
NO ppmv 57
NO2 ppmv 3
Particulates mg/nm3 < 10
Product Stream Temperature °C 40
Product Stream Pressure kPa(g) 45
Life expectancy years 20
Plant availability % 95
Long-term operation
% of design
capacity 85

7. 6
Background
The carbon cycle begins with mining, or the extraction of fossil fuels from below the Earth’s
surface. These fossil fuels are the product of millions of years of sedimentation and other geological
processes and are rich in energy. The energy contained in these fuels can be recovered by their combustion,
or their burning – most effectively when in a controlled environment such as a combustion engine. To burn
these fuels, however, oxygen is required. This leads to the formation of carbon-oxides, or most
predominantly, carbon dioxide (CO2). Carbon dioxide is released in the form of a gas and typically rises
into the atmosphere, where it blends into the other atmospheric gases. This is a natural process which has
always occurred. Figure 1 below gives an illustrative example of this process.

8. 7
The difference today however, is the volume at which carbon dioxide is produced. In 1992, total
world oil production equaled 60 million barrels per day. This number has grown by millions of barrels each
year since 1992 due to increasing demand. As consumption increases, the burning of fossil fuels such as
oil, natural gas and coalleads to an equivalent number in thousands of megatons of carbon dioxide released
per day. The planet is equipped with several mechanisms to mitigate carbon dioxide build-up in the
atmosphere. These are ocean sequestration and carbon capture by plants, bacteria and fungus. There are
also several man-made sequestration techniques in place such as direct-air capture for industrial carbon
dioxide use. But even when all of these processes are combined, they do not absorb carbon quickly enough,
leading to rising levels of carbon dioxide in the atmosphere. Over time, the rising levels will theoretically
Figure 1: The Carbon Energy, Capture and Storage Cycle

9. 8
result in the entrapment of solar energy in the form of heat, gradually increasing the mean temperature of
the Earth. Furthermore, the world’s oceans, which typically account for the largest amount of carbon
sequestration, are nearing a saturation level. After this saturation is reached, the rate at which CO2 builds
up in the atmosphere will increase exponentially. This is known asthe Greenhouse Effect,the consequences
of which are dire for life everywhere.
Leading environmental agencies across the world have set CO2 reduction quotas to combat the
Greenhouse Effect.Rewardsare given to companies which can boastsignificant amounts of CO2 production
and release into the atmosphere. The energy industry faces the greatest challenge in checking its carbon
emissions. Oil-, natural gas- or coal-powered electrical plants currently face a carbon tax for all exhaust
that is released into the atmosphere. This has led to widespread technological improvement across the
petroleum and energy industry. The new technologies sequester carbon dioxide from the source, from the
exhaust streams of combustion plants. The carbon is trapped in a saturated liquid solution and is converted
into solid calcium carbonate, which is then stored underground. The carbon may also be recovered in
gaseous form and pumped deep into the Earth, or put into use such as in enhanced oil recovery. This allows
for carbon sequestration organizations to sell carbon dioxide back to the oil industry, making additional
incentive for cleaning flue gas.
In a power generation plant, fuel is burned at a high flow rate to create steam in a separate stream.
This steam drives a turbine by a pressure differential which in turn generates electrical energy from
mechanical energy. Three major methods forindustrial carboncapture are known: post-combustion capture,
pre-combustion capture and oxy-fuel combustion capture. Post-combustion capture involves feeding all
exhaust gases generated by a combustion reaction to a treatment unit. The unit typically is composed of an
absorber and a stripper. This process requires a solvent, usually an amine solution, that efficiently absorbs
CO2 from exhaust and which in most cases can be regenerated and reused. Pre-combustion capture, on the
contrary, utilizes the same units as post-combustion capture except in this case,the unit is placed before the
combustion reaction. In this way, the feed fuel is reformed so that carbon is separated and only hydrogen

10. 9
is combusted. On average,however, pre-combustion capture necessitates more fuel to achieve generation
efficiencies equivalent to non-capture processes. The last process, oxy-fuel burning incorporates an oxygen
carrier which selectively binds oxygen from air. The air is released to the atmosphere and the oxygen is
then dissociated from the carrier in another reactorwhere it is used in the combustion reaction with the fuel.
This results in an oxygen-rich combustion reaction and higher efficiency. This type of process often
includes a CO2 recycle to maintain high temperatures for steam generation which in turn also decreases
emissions.

11. 10
SelectionCriteria
The tables below indicate the criteria by which each alternative will be compared so a selection of
the appropriate technology can be made. The criteria are divided into essentialcriteria, or those which must
be met for an alternative to be considered as suitable, and desirable criteria, which define ranges of
specifications that are optimal for the plant design.
Essential Criteria
Carbon dioxide recovery percentage is most relevant to the design of the new plant. It is therefore
necessary that the carbon capture system effectively reduces carbon output. A capture system’s
effectiveness is measured by the volume of carbon found in the product stream of the treatment unit. Also
of importance is that thermal efficiency is not reduced substantially by the addition of a carbon capture
system. A large reduction in thermal efficiency can render the capture system more detrimental than
beneficial for the plant. Typical thermal efficiencies for gas-powered plants are in the range of 55-60%.
Studies on various carbon capture systems set the minimum bound for thermal efficiency at 42.4%, after
which point capture becomes inefficient and fuel is wasted.
Capital expenditure is also considered as a necessary limit to a carbon capture system implemented
in a power plant. For the purposes of this plant, a limit of $100,000,000 CADis the maximum cost of capital
allowable. This number is derived from a cross-study of carbon capture installations which gives the typical
expenses of such a project including costs for equipment, shop fabrication, site installation, engineering,
project management and fees for technology licenses. With a planned life expectancy of 20 years and
assuming 95% plant availability and operation at 85% of design capacity, the cost per tonne of CO2
recovered can also be measured. This calculation is also of importance in determining the desired system.
The value of $300.00 per tonne of CO2 is the high-end estimate put forward by environmental and carbon
recovery papers for the cost of industrial carbon removal. Lastly, the cost of solvent is associated with

12. 11
selection. It is not uncommon that a solvent can be recycled and reused after undergoing regeneration. In
the case of oxygen carriers as well, replacement is needed only on a monthly or discontinuous basis. It is
in fact, always more cost effective to purchase pure O2 than purchasing a complex capture system if the
cost of solvent is greater per tonne than the cost of oxygen. A caveat to this, however, is that pure O2 is fed
on a continuous basis, asit cannot be reused or regenerated;therefore the use of a solvent which regenerates
is almost always preferred to pure O2, as purchase frequency for such a solvent is drastically decreased.
Table 2: Essential Criteria for Carbon Dioxide Capture System
Parameter Units
CO2 Recovery % > 0.00
Cost of Capital $CAD < 100,000,000.00
Cost Over Life
$CAD/tonne CO2
product < 300.00
Thermal Efficiency % ≥ 42.40
Cost of Solvent Less Than
Cost of Pure Oxygen $CAD/tonne solvent < 65.00
Desirable Criteria
Of the alternatives available for carbon capture, that which has the highest carbon dioxide
recovery is desired. A higher thermal efficiency is also preferred,as it indicates less consumption of fuel,
which in turn reduces emissions. Similar to the essential criteria, a lower cost per tonne of CO2 is favored.
The value of $175.00 per tonne of CO2 recovered is the low-end estimate provided in cost analysis reports
by environmental regulatory affairs. Of final importance is the ratio of CO2 emissions from secondary
generation sources to the amount of CO2 recovered. The heating and cooling systems required for solvent
and oxygen carrier regeneration produce carbon emissions which are typically not recovered. It is
practical to assume that any capture system which produces more than a quarter of the carbon that is
recovered loses value as an alternative.

13. 12
Table 3: Desirable Criteria for Carbon Capture System
Parameter Units
Cost Over Life
$CAD/tonne CO2
product < 175.00
Thermal Efficiency % ≥ 60.00
CO2 Recovery % ≥ 90.00
Auxiliary Generation CO2
Emission Low tonnes CO2/day < 250
Alternatives
No Carbon Capture System
The conventional power plant does not feature a carbon capture system. Exhaust gas created by
combustion is released directly to the atmosphere. This alternative therefore features the least carbon
recovery and is not being considered as a viable alternative, but remains as an important reference point
for comparison. Table 4 below gives the exhaust gas composition and CO2 discharge from the
combustion reaction. For all other alternatives, the gas composition described below serves as the inlet
conditions to each of the carbon capture systems. Note that a configuration such as this one would require
a high carbon tax, typically above the $300 CAD per tonne of CO2 range. Such charges would render this
plant configuration extremely fiscally inefficient.
Table 4: Specifications for Plant without Carbon Capture
Parameter Units
Reboiler Duty GJ/hr 0
Fuel Gas Consumption for Reboiler Duty m3
/hr 0
Cooling Duty GJ/hr 0
Total Power Consumption kW 0
CO2 Recovery % 0.00
Outlet Composition
N2 mole % 71.613
Ar mole % 0.871

14. 13
O2 mole % 2.595
CO2 mole % 8.616
H2O mole % 16.298
SO2 ppmv 24
SO3 ppmv < 2
NO ppmv 57
NO2 ppmv 3
Particulates mg/nm3
< 10
Cost of Capital $CAD 0.00
Cost Over Life $CAD/tonne CO2 0.00
Thermal Efficiency % 60
Cost of Solvent
$CAD/tonne
solvent 0.00
CO2 Capture tonnes/day 0
CO2 Emission (Solvent Regeneration
Duty) tonnes/day 0
CO2 Emission (Electrical Load) tonnes/day 0
Net CO2 Emission tonnes/day 1000
Net CO2 Capture tonnes/day 0
CO2 Emission per Tonne Captured 1
Post-combustion Carbon Capture with Amine Solvent
Post-combustion capture features an absorber column that brings the carbon dioxide in the exhaust
gas into contact with a solvent, and a stripper which recovers the solvent for reuse. Figure 2 illustrates the
basic block flow diagram for a post-combustion carbon capture system. The solvent typically used in this
process is an amine solvent, as carbon dioxide is highly miscible while the other components of the gas are
not. The schematic requires a reboiler for the regeneration of solvent, and a condenser for the recovery of
CO2 product. Both the condenser and the reboiler have duties that necessitate additional electrical energy
to be added to the system. The addition of this electricity creates CO2 emission from secondary power
generation.
While the drawing in Figure 2 does not indicate an exhaust recycle stream, it is possible to
incorporate a recycle to enhance CO2 recovery. The system described has a 90% CO2 recovery however

15. 14
and achieving higher levels would require additional reboiler and condenser duties, which may create
difficulty in justifying a recycle stream.
Because the amine solvent can be regenerated, costs for materials are low following the initial
capital cost for fabrication, engineering and installation. This makes post-combustion capture a fiscally
conservative option over the 20-year lifetime of the project. It is also worth noting that the cost per tonne
of CO2 is the sum of two values: one being the cost derived from the capital cost of the capture process and
the other from the cost of CO2 handling operations (approximately equal to $30.00 per tonne of CO2 for
this alternative and all that follow). Table 5 lists all relevant specifications for this CO2 capture plant
configuration.
CO2 Capture Plant
Flue Gas
Blower
Flue Gas
Cooler
Absorber with
Wash Section
L/R Heat
Exchanger
Stripper and
Condenser
CO2 Compression
and Dehydration
CO2 Send Out
Pipeline
Reclaimer Reboiler
Solvent Surge
Tank
Solvent Storage
Tank
Electricity Solvent Instrument Air
Fuel Gas
Exhaust Gas to Atmosphere
Figure 2: Post-combustion Carbon Capture Block FlowDiagram
Table 5: Specifications for Post-combustion Carbon Capture with Amine Solvent
Parameter Units
Reboiler Duty GJ/hr 130
Fuel Gas Consumption for
Reboiler Duty m3
/hr 4080
Cooling Duty GJ/hr 230
Total Power Consumption kW 2575

16. 15
CO2 Recovery % 90.00
Outlet Composition (Treated
Gas)
N2 mole % 87.7
Ar mole % 1.05
O2 mole % 3.18
CO2 mole % 1.05
H2O mole % 6.99
Cost of Capital $CAD 83,100,000.00
Cost Over Life $CAD/tonne CO2 67.00
Thermal Efficiency % 60
Cost of Solvent $CAD/tonne solvent < 50.00
CO2 Capture tonnes/day 1000
CO2 Emission (Solvent
Regeneration Duty) tonnes/day 207
CO2 Emission (Electrical Load) tonnes/day 40
Total CO2 Emission due to
Auxiliary Systems tonnes/day 247
Net CO2 Capture tonnes/day 753
CO2 Emission per Tonne
Captured 0.247
Pre-combustion Carbon Capture
A pre-combustion carbon capture such as the one described in Figure 3 reformsthe natural gas feed
so that all carbon is removed prior to burning. This makes the addition of more fuel a necessity,but ensures
very high carbon capture results. The required electrical duty for secondary systems such as the reboiler
and condenser is also about 50% higher for pre-combustion capture. Like in post-combustion capture
however, the amine solvent is reusable. The system is slightly more complicated than the post-combustion
system on the other hand and therefore requires a slightly higher cost of capital before start-up. Table 6 lists
details pertaining to the pre-combustion carbon capture system’s performance.

17. 16
Sulfur Guard Gas-Gas Heat
Exchanger
Pre-reformer
Auto-Thermal
Reformer
Syngas Cooling
Shift Reactors
Gas Cooling and
Knockout
Turbine
Combustor
Reheat
Fuel Gas
Compressor
AGR
CO2 Compression
Steam Turbine
Condenser
HRSG
Ambient Air
Natural Gas
Stack Gas
H2O
CO2 Product
CO2 Capture Plant
Electricity Solvent
Figure 3: Pre-combustion Carbon Capture Block FlowDiagram
Table 6: Specifications for Pre-combustion Carbon Capture with Amine Solvent
Parameter Units
Reboiler Duty GJ/hr 195
Fuel Gas Consumption for
Reboiler Duty m3
/hr 4610.4
Cooling Duty GJ/hr 345
Total Power Consumption kW 3862.5
CO2 Recovery % 90.50
Outlet Composition
N2 mole % 87.71
Ar mole % 1.06
O2 mole % 3.19
CO2 mole % 1.00
H2O mole % 7.00
Cost of Capital $CAD 88,000,000.00
Cost Over Life $CAD/tonne CO2 65.00
Thermal Efficiency % 47
Cost of Solvent
$CAD/tonne
solvent < 50.00
CO2 Capture tonnes/day 1000

18. 17
CO2 Emission (Solvent
Regeneration Duty) tonnes/day 310.5
CO2 Emission (Electrical
Load) tonnes/day 60
Net CO2 Emission tonnes/day 370.5
Net CO2 Capture tonnes/day 629.5
CO2 Emission per Tonne
Captured 0.3705
Chemical-Looping Combustion Carbon Capture
This system is a type of oxy-fuel combustion capture process. The key elements are an air reactor,
a fuel reactor and an oxygen carrier. The air reactor is fed ambient air which is stripped of its oxygen by
an oxygen carrier, or a solvent with a very high affinity for oxygen molecules. The air is released with the
exhaust gas as its composition is the same as atmospheric air except it is depleted of oxygen. The oxygen
carrier is pumped into the fuel reactor where high temperatures lead to the dissociation of the oxygen
molecules from the carrier. The oxygen molecules are then used in the combustion reaction, creating CO2
and H2O. The pure oxygen input leads to much higher thermal efficiencies for combustion reactors,
resulting in more steam generation with less fuel. Also of major significance is the CO2 recycle stream,
which uses carbon exhaust gases to help satisfy thermal energy requirements, thereby reducing the need
for fuel and drastically reducing carbon in exhaust gases. Figure 4 depicts a block flow diagram for the
typical chemical-looping combustion capture system. Table 7 contains performance and specification data
pertinent to the system that would support the power plant discussed in the introduction.
While some estimates put the cost of capital for a chemical-looping combustion capture system as
high as $90,000,000 CAD,the novel technology described by this paper is estimated to have only a
$31,000,000 CAD capital expenditure. This is a newer, more efficient and simpler system than previously

19. 18
described by many papers in the early 2000s. The combination of novel oxygen carriers and a newly
designed CO2 recycle have the potential to cut costs drastically. Note that electrical costs are higher than
in post-combustion capture by more than 5% due to an increased energy requirement for condensing. This
is reflected in the $70.00 per tonne CO2 cost over lifetime.
Turbine HRSG Cooler
Air
Reactor
Fuel
Reactor
Condenser
CO2
Compression
Feed Prep
&
Combustor
Oxygen Carrier
CO2 Product
Natural Gas
Ambient Air
CO2 Recycle
Oxygen
Carrier
Condenser
Electricity
Oxygen-depleted Air
Figure 4: Chemical-looping Combustion Carbon Capture Block FlowDiagram

20. 19
Table 7: Specifications for Chemical-looping Combustion Carbon Capture
Parameter Units
Reboiler Duty GJ/hr 136.5
Fuel Gas Consumption for
Reboiler Duty m3
/hr 4284
Cooling Duty GJ/hr 241.5
Total Power Consumption kW 2703.75
CO2 Recovery % 99.00
Outlet Composition
N2 mole % 87.72
Ar mole % 1.07
O2 mole % 3.20
CO2 mole % 0.96
H2O mole % 7.01
Cost of Capital $CAD 31,000,000.00
Cost Over Life $CAD/tonne CO2 70.00
Thermal Efficiency % 90
Cost of Solvent
$CAD/tonne
solvent 100.00
CO2 Capture tonnes/day 1000
CO2 Emission (Solvent
Regeneration Duty) tonnes/day 217.35
CO2 Emission (Electrical
Load) tonnes/day 42
Net CO2 Emission tonnes/day 259.35
Net CO2 Capture tonnes/day 740.65
CO2 Emission per Tonne
Captured 0.259
Analysis
Table 8: Comparative Analysis Table for Essential Criteria
Criteria Units Value
No CO2
Capture
Post-
combustion
Pre-
combustion
Oxy-fuel
Combustion
CO2 Recovery % > 0.00 0.00 90.00 90.50 99.00

21. 20
Cost of Capital $CAD
<
100,000,000.00 0.00 83,100,000.00 88,000,000.00 31,000,000.00
Cost Over Life
$CAD/tonne
CO2 < 300.00 0.00 67.00 65.00 70.00
Thermal
Efficiency % ≥ 42.4 60 60 47 90
Cost of Solvent
Less Than Cost of
Pure Oxygen
$CAD/tonne
solvent < 65.00 0.00 < 50.00 < 50.00 100.00
Data for cost of capital, cost over life, cost of solvent, thermal efficiency and CO2 recovery is
compiled and compared with essential criteria in Table 8. An additional column has been added for a plant
without CO2 capture as a reference. Each of the proposed alternatives fit within the criteria given in the
Selection Criteria section. The chemical-looping combustion capture, or oxy-fuel combustion alternative
promises highest CO2 recovery (99%) and lowest capital expenditure ($31,000,000 CAD) when compared
to all options. Additionally, thermal efficiency is maximized under this alternative technology. It also has
an acceptable cost over life ($70 per tonne of CO2). The cost of solvent per tonne as compared to the cost
of pure oxygen per tonne appears to indicate that the chemical-looping technology does not pass in this
particular regard, however. An exception is made for this category, as the cumulative expense for oxygen
over the lifetime of the plant far outweighs the cumulative expense for solvent, or oxygen carrier. While
the cost of the oxygen carrier is $100.00 per tonne, this material is replenished only on a monthly basis,
whereas the pure oxygen is part of a continuous flow. Therefore, assuming that the plant will require one
tonne of pure oxygen per day to produce one equivalent tonne of CO2,the pure oxygen stock will require
replacement on a daily basis. With pure oxygen amounting to $65.00 per tonne, this accumulates a much
larger cost than that of the oxygen carrier in just a single month.
Post- and pre-combustion carbon capture technologies both pass in all essential selection criteria
as well. The notable difference between these two alternatives and the oxy-fuel combustion alternative is
capital cost, which is almost three times larger for pre-combustion carbon capture.Another key observation
is that the thermal efficiency of a pre-combustion capture system is 47% as compared to 60% for post-

22. 21
combustion capture. The CO2 recoveries for post- and pre-combustion capture are 90% and 90.5%,
respectively; however, the large increase in fuel demand does not justify the only slight advantage in
recovery that pre-combustion capture offers. Additionally, recovery for the post-combustion capture can be
enhanced by several percent only by adding a recycle stream for the treated off-gas, while expending less
auxiliary electrical energy on reboiler and condenser duties.
Table 9: Comparative Analysis Table for Desirable Criteria
Criteria Units Value
Post-
combustion
Pre-
combustion
Oxy-fuel
Combustion
Cost Over Life
$CAD/tonne
CO2 product < 175.00 67.00 65.00 70.00
Thermal
Efficiency % ≥ 60.00 60 47 90
CO2 Recovery % ≥ 90.00 90.00 90.50 99.00
Auxiliary
Generation CO2
Emission Low tonnes CO2/day < 250 247 370.5 259.35
Having passed each of the essential criteria however,the three alternatives are then compared with
the desirable criteria also discussed in the Selection Criteria section. The pre-combustion capture alternative
falls short of desired criteria; the CO2 emissions generated by auxiliary power sources is much too large as
compared to the recommended level of no more than 250 tonnes of CO2. Thermal efficiency is also below
levels that would be considered most cost effective and fuel efficient for pre-combustion carbon capture.
This eliminates pre-combustion capture as a viable alternative for the new natural gas plant. The emissions
for the chemical-looping combustion technology are also slightly higher than the recommended level.
Additionally, the secondary CO2 emissions for post-combustion capture are lower than the 250 tonnes of
CO2 limit. This gives the post-combustion option a slight advantage over the oxy-fuel option, as it meets
both essential and desirable criteria. The tables of comparison in the next section provide a visual

23. 22
representation of how the alternatives rank according to essential (Table 10) and desirable (Table 11)
characteristics.
ComparisonTables
Table 10: Comparison Table for Essential Criteria
Criteria Value
No CO2
Capture
Post-
combustion
Pre-
combustion
Oxy-fuel
Combustion
CO2 Recovery > 0.00 FAIL PASS PASS BEST
Cost of Capital
<
100,000,000.00 PASS PASS PASS BEST
Cost Over Life < 300.00 BEST PASS PASS PASS
Thermal
Efficiency ≥ 42.4 PASS PASS PASS BEST
Cost of Solvent
Less Than Cost
of Pure Oxygen < 65.00 BEST PASS PASS
PASS (with
exceptions)
Table 11: Comparison Table for Desirable Criteria
Criteria Units Value
Post-
combustion
Pre-
combustion
Oxy-fuel
Combustion
Cost Over
Life
$CAD/tonne
CO2 product < 175.00 PASS BEST WORST
Thermal
Efficiency % ≥ 60.00 PASS WORST BEST
CO2
Recovery % ≥ 90.00 WORST PASS BEST
Auxiliary
Generation
CO2
Emission
Low
tonnes
CO2/day < 250 BEST FAIL FAIL

24. 23
Conclusionand Recommendations
Post-combustion carbon capture effects only the exhaust gas that leaves the combustion reaction.
Unlike oxy-fuel combustion capture and pre-combustion capture,post-combustion capture with an amine
solvent has the most negligible impact on standard power production with a once-through steam generator
with natural gas as a fuel. The ability to extend CO2 recovery through the addition of an exhaust recycle
also gives the post-combustion alternative flexibility to increase recovery that the other two options
simply do not offer. The capital cost for such a system falls between the two other alternatives, at about
$83,100,000 CAD,accounting for all possible expenses. The recommended configuration for CO2
sequestering in this case is post-combustion carbon capture with an amine solvent. Also of relative
importance is the determination that cost estimates per tonne of recovered CO2 are drastically
overestimated by previous studies ($175-$300 per tonne given when actual cost is $67.00 per tonne). The
time to construct this system from the approval stage to the final plant initiation stage is estimated to be
twenty months.

25. 24
PotentialProblem Analysis
The secondary CO2 emissions generated by reboiler and condenser duties can also be recovered if
the exhaust from these units is treated. Instead of capturing 1000 tonnes of CO2 per day from the plant, the
absorber and stripper would need to have capacity increases of about 1180 tonnes of CO2 per day. This
challenges the current view that 1000 tonnes of CO2 per day is the maximum practical size for a plant of
this specification.
Thermal efficiency of steam generation is neither enhanced nor decreased when post-combustion
carbon capture is implemented. This meansthat fuelwill be consumed at the same rate asit had been before
the new emission regulatory measures and carbon tax were put into effect. Carbon dioxide emissions will
be drastically decreased and all sequestered carbon will be stored so it has the least effect on the global
climate. However, natural gas consumption will not decrease following implementation of the capture
system, raising the issue of how to deal with a depleting natural resource that cannot be regenerated.
Carbon sequestration is not a long-term fix for the global energy crisis. It will certainly allow
industries to continue powering their electrical grids for up to another two-hundred years,but it will become
increasing difficult as reserves decline. Therefore, the energy industry must rely on research towards new
alternative energy sources in order to meet energy demands in the future. With technologies such as post-
combustion carbon capture however, the Greenhouse Effect can be avoided with the aid of new pollution
control measures including a high carbon tax.

26. 25
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