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CARBON CREDIT- A New Measure to Shed off GHG Emission
Subhasish Mitra
M.Tech
Department of Chemical Engg, IIT Kanpur
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Combined power cycle: Brief Recap
Brayton cycle
Rankine cycle
Fuel used : Natural Gas
Plant capacity : 400 MW
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Power Plant Process Flow Diagram-Base case CCS facility excluded:
Steam boiler
Gas Turbine Block
HP Steam turbine LP Steam turbin
Steam condenser
Flue gas disposed tostack GHGs emission.
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CO2
Emission A Known Nuisance
1. CO2 is the ubiquitous Green House Gas and liable for globalwarming.
2. Fossil fuel powered power plants are the epicenters for CO2
emission due to voluminous flue gas disposal beside other
industries, automobiles and residential release.
3. Major concern is observed in the recent past to reduce CO2
emission through various measures and policy formulation (e.
Kyoto protocol).
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Brief Case Study:
Govt decided to put mandate on implementing CO2
capture facility at the power plant site.
Normal emission limit from power plant : 1.65 to 1.95
million ton CO2/yr.
Emission limit posed by EPA is 7% reduction on 1990
emission figure of 0.479 tons of CO2/MWh generated
which translates to 1.425 million ton CO2/yr for our plant.
Plant capacity : 400 X8000 Mwh/yr
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Where does our plant stand?
CO2 Emission : 4079 kmol/hr which translates to 1.44million ton CO2/yr.
The plant exceeds EPA recommended limit by 0.012
million ton CO2 p.a.
Since CO2 emission by the plant is more than EPA
recommendation, so plant decides to invest upon CCS to
earn CARBON CREDIT.
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What is Carbon Credit?
An instrument created to represent one metric ton of CO2 avoided
or removed by a carbon reducing project.
Some definitions:
Key component of national and international attempts to mitigate t
growth in concentrations of (GHGs). One Carbon Credit is equal to
one ton of Carbon.
A "credit" to emit a ton of carbon dioxide (CO2) issued as part of anemissions trading scheme such as the European Emissions
Trading Scheme.
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Company adopts this CCS scheme
NG toPower Plant
To Oil/Gasreservoir for EOR
Oil out
Void oil/gaswell for
storage
Amineabsorptionplant
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Amine absorption plant simplified PFD:
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CCS Project Feasibility Analysis:
A Hysys simulation is made to study the feasibility of
integrating proposed CCS process with the existing plant.
Major challenge is to provide huge thermal energy to the
stripper reboiler. Even auxiliary boiler is also reported.
But simulation shows reboiler demand can be internallymet.
Around 85% CO2 scrubbing efficiency is obtained from
simulation.
With all economic analysis, it turns out that project is
feasible.
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Power Plant Process Flow Diagram-Modified case CCS facility included:
Stripper reboilersteam is supplied
from the partiallyderated LP steamturbine.
CCS unit: Fluegas compression,absorption &transportation
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CO2 absorption unit:
Steam to stripperreboiler suppliedfrom LP steam
turbine O/L.
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CO2 Transportation Unit:
Transport pump
Transportcompressor
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0.55Combined cycle efficiency
0.284Rankine cycle efficiency
0.37Gas turbine cycle efficiency
0.45Overall efficiency
MW1072.65Heat input by NG@LHV
MW1.585Condensate pump
MW283Boiler heat input
MW136.2Compressor
MW16.63ST-2 output
MW65.31ST-1 output
MW400GT output
Energy efficiency before CCS
Energy Efficiency Before Implementing CCS:
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Energy Efficiency After Implementing CCS:
%15.56Efficiency reduction
0.38efficiency
MW1072.65Heat input by NG@LHV
MW1.432Transport pump
MW18.42Transport compressorMW0.102Lean amine pump
MW0.067Rich amine pump
MW47.94Flue gas blower
MW283Boiler heat input
MW1.585Condensate pump
MW136.2Compressor
MW9.869ST-2 output
MW65.31ST-1 output
MW400GT output
Energy efficiency after CCS
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Important Facts Behind Economic Analysis:
Price hike in electricity follows yearly compounding,
i.e. P1 = P(1+i)n and stops at break even point. n = no of years.
Straight line depreciation model is followed.
Payback period is calculated as
Capital Investment/(Carbon Credit Earned + Depreciation/yr)
ROI = (Net Profit/Capital Investment) x 100
Credit from injecting CO2
for EOR not considered.
Decline in Carbon credit due to escape from sequestration not
considered.
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Cooling Utility Cost for CCS:
4.02 million $Total
175243.3941043.120.02110Compressor stage-4cooler
102166.898608.140.0215.83
Compressor stage-3
cooler
102236.996608.550.0215.834
Compressor stage-2
cooler
115275.104686.180.0216.578
Compressor stage-1
cooler
330684.2841968.360.02118.87Precooler
314737.1351873.440.02117.96
Stripper column
condenser
2884506.25917169.680.021164.6
Flue gas blower
aftercooler
Total coolingcost ($/yr)
CW flow
rate (t/hr)
Cost $/ton of
CW
Equipmentcooling duty
(MW)Cooling cost
Cooling water Delta T = 80C, Sp. Heat capacity = 4.314 KJ/Kg/K
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60.34 million $Total
1266666.6670.091.76Transport pump
16323555.560.0922.67Total compressor power
2.68Transport compressor ST-4
3.97Transport compressor ST-3
5.83Transport compressor ST-2
5.88Transport compressor ST-1
90666.670.090.13Lean amine pump
59511.110.090.08Rich amine pump
42604444.440.0959.17Flue gas blower
Total cost ($)/yrElectricity cost
($) / kwhCapacity (MW)Equipment
Electricity consumption cost for CCS:
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Raw Material Cost:
529.5 ton1.72.42688350MEA make up
10 min
(assumed)
Absorption
loop inventory
Total cost
(million $/yr)
Unit cost
($/kg)Qty (kg/hr)
Raw material cost
Basis:
Make up is replacement of degraded MEA
MEA degradation rate : 2.5 wt% / week
Absorption loop inventory : 10 min
*Total Carbon Reduction Cost :
$ 56.8 million/Ton of CO2
*5% contingency cost is included.
Reported CO2 reductio
cost in literature:$37-74/ton of CO2
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Expenditure Summary for CCS:
yrs6.14Payback period
million $18.62Carbon credit earned/yr
million $13.44Revenue after Tax deduction
%10Tax deduction
million $9.61Taxable revenue
million $14.4Revenue/yr through electricty
% pa5Hike in electricity price
million $4.87Revenue lost/yr
Mwhr6.76Electricity generation reduced
million $4.79Depreciation/yr
million $0Salvage value
years30Plant life
million $69.54Annual Carbon reduction cost
million $14.36Annual loan installment
%15Bank loan interest rate
10Loan repayment duration (Year)
million $143.6
Investment cost
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CCS P j b k l i
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CCS Project break even analysis
-60
-40-20
0
20
40
6080
100
120
Y1 Y2 Y3 Y4 Y5 Y6 Y7 Y8 Y9 Y10
Production cost
Revenue after ta
ROI
Hike in electricityprice stopped.
Break even
point at ~ 6 yrs
Costfigures
inmillion$/%
ROI
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