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Reduction of Emissions from Combined Cycle Plants by CO2
Capture and Storage
John Davison Project Manager
IEA Greenhouse Gas R&D Programme (IEAGHG)
The Future Combined Cycle Plant
Berlin, 28th-30th March 2012
Overview
• CO2 capture and storage (CCS) technologies • Impacts of CCS on efficiencies and costs • Combined cycle plants with CCS in systems
with high amounts of renewables
IEA Greenhouse Gas R&D Programme (IEAGHG) • An collaborative research ‘Implementing Agreement’
established in 1991 by the International Energy Agency • Based at Cheltenham, UK • Aim: Provide members with definitive information on the role that technology can play in reducing greenhouse gas emissions.
Scope: All greenhouse gases, all fossil fuels and comparative assessments of technology options Focus: On CCS in recent years
• About 20 country members and 20 industrial sponsors
Membership
CO2 Emission Projections
Chart from UK Committee on Climate Change, 2009
• <100g/kWh by 2030 • More difficult to achieve
without CCS
Sleipner capturing and
injecting 1 Mt/y CO2 since 1996
Weyburn capturing and
injecting 2.5 Mt/y CO2 since 2000 In-Salah capturing and injecting
1.2 Mt/y CO2 since 2004
Snøhvit capturing and injecting 0.7 Mt/y
CO2 since 2006
CO2 Storage
CO2 Capture • Post combustion capture
• Separation of CO2 from flue gas
• Pre-combustion capture • Reaction of fuel to produce H2 and CO2 • Separation of CO2 • Combustion of H2 in a gas turbine
• Oxy-combustion • Combustion of fuel using purified O2 rather than air
Post Combustion Capture Liquid solvent scrubbing
Reduced-CO2 flue gas
Absorber (40-60°C)
CO2
CO2-rich solvent
Low pressure steam
CO2-lean solvent
Condenser
Flue gas
Stripper (90-120°C)
Reboiler
Cooling water
Direct contact cooler
Excess water
Water wash
Water
Post-Combustion Capture
• Urea plant, Kakinada, India
• 450 t/d of CO2 captured from natural gas steam reformer flue gas
• KS-1 solvent
Courtesy of MHI
• CCGT, Bellingham, USA
• Operated 1991-2005 • 330 t/d of CO2 captured
• MEA solvent
• Food grade CO2 product
Courtesy of Fluor
Plant Layout
Absorber Direct contact cooler
CO2 compressor
HRSG Gas turbine
Stripper
CCGT (2x450MW) CO2 capture plant
Flue Gas Recycle
• CO2 concentration in absorber feed is increased • Smaller absorber tower • Extra cost for recycle gas cooling and duct • Overall cost is lower and efficiency is marginally higher • Impacts on combustor operation and emissions
CO2 capture
Direct contact cooler and fan
Air
Recycled flue gas
Gas turbine
CO2
HRSG
Natural gas
Reduced-CO2 flue gas
Thermal Efficiency
Source: Study for IEAGHG by Parsons Brinckerhoff, 2012
Efficiency Reduction
Capital Cost
2011 EPC costs, excluding owner’s costs and interest during construction Source: Report for IEAGHG by Parsons Brinckerhoff, 2012
Cost of Electricity Low CO2 emission cost
2011 costs 8% discount rate 25 year plant life Base load operation
€6/GJ (LHV) gas price €5/t CO2 stored €10/t CO2 emission cost
Cost of Electricity Breakeven CO2 emission cost
€65/t CO2 emission cost required for ‘no capture’ to match the proprietary solvent CCS cost of electricity
Pre-Combustion Capture
Power
Hydrogen-rich gas
CO2 capture Compression, transport and
storage
Gas, coal or
biomass
Combined cycle power plant
Flue gas
Reforming or gasification
CO2 Shift conversion
Air or O2 and steam
Steam
CO+H2O = H2+CO2
Pre-Combustion Capture • Natural gas fuel
• Pre-combustion capture is less attractive in general than post combustion capture
o Lower efficiency o Higher capital cost
• Scope for technological improvement
• Coal and biomass gasification • Economics depend on relative prices of natural gas and solid fuels
• Issues to be considered • Combustion of hydrogen-rich gas in gas turbines is being addressed by
turbine manufacturers
The Role of CCS Plants in Electricity Systems • How will CCS plants have to operate?
• Variability of electricity demand • Impacts of high amounts of other low-CO2 generation technologies
• Operating flexibility of CCS plants • Impacts of load factor on economics
Electricity Demand
UK data, 2011
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Elec
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Hours
Wintermaximum
Summerminimum
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Ele
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W
Hours
Electricity Demand
Base load (60% of total generation)
Need to decarbonise this electricity to achieve low emissions targets
Intermediate/ peak load (40% of total generation)
UK data, 2011
The Role of CCGTs with CCS in Electricity Systems Marginal operating cost merit order
• Wind / solar / marine energy • Nuclear • Coal with CCS • Natural gas with CCS • Fossil fuels without CCS
• Combined cycle plants with CCS will have to be able operate flexibly and at intermediate load
• CCS flexibility requirements depend on how much renewables and nuclear are used
Lower marginal cost - operate whenever available
Higher marginal cost - operate at lower load factor
Impact of Renewables/Nuclear on Fossil Fuel Plant Operation
IEAGHG modelling of UK electricity system, Based on half-hourly power demand and wind data, 2011 Wind generation scaled to 35% of total demand
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0 2000 4000 6000 8000 10000
Elec
tric
ity g
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Hours
Total demand
Residualdemand with35% wind
Residualdemand with35% wind,25% nuclear
Plant Load Factors
UK system assuming 35% wind, 25% nuclear
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20
40
60
80
100
0 10 20 30 40 50 60 70 80 90 100
Plan
t loa
d fa
ctor
%
% of annual residual generation(fossil fuels etc)
Flexibility of CCS Plants • CO2 capture imposes some additional constraints on
operating flexibility • Constraints can in general be overcome by design • Possibility of better flexibility than non-CCS plants • Interaction between the electricity system requirements and
plant capabilities
Flexibility of CCS Plants • CO2 compressors
• Turndown limited to c70% • Can be overcome by use of multiple compressors or CO2 recycle
• Post combustion capture • Ability to vent flue gas
o A low-cost technique for peak generation but high CO2 emissions
• Ability to operate the absorber and stripper independently by including buffer storage solvent
o Enables faster start-up and possibility of higher peak generation
• Pre-combustion capture • Integrated plants have relatively poor flexibility
o Long start up and shut down times o Gasification/ reforming, shift conversion and pre-combustion capture is ‘a chemical
plant’
• Non-integrated plants can overcome these constraints
Pre-combustion Capture - Non-integrated Plant
Fuel conversion and CO2 capture - full load operation
Hydrogen-rich gas
CO2 capture Compression, transport and
storage
Fuel
Power plant - flexible operation
Underground hydrogen storage
(salt cavern) Power
Power plant (combined or simple cycle)
Flue gas
Methane reforming or coal
gasification
CO2 Shift conversion
• Only the power plant has to operate flexibly • CCS can operate continuously, no need for flexibility • High utilisation of CCS equipment • Capture cost is almost independent of power plant load factor • Can build-up H2 infrastructure for later use by renewables
Hydrogen Storage • Salt caverns are widely used for natural gas storage
• Solution mined caverns
• Commercial experience of hydrogen storage in salt caverns • UK
o Chemical complex at Teesside o 3 caverns, 200-300 tonnes H2 each o Operated for many years, no discernible leakage
• USA o E.g. Air Liquide, Texas o Cavern 75m diameter, 450m long o Enough hydrogen for 1000MWe plant for a week o No scale-up needed for CCS plants
Costs of Electricity Effects of CCS, load factor and fuel
2011 costs 8% discount rate 25 year plant life
Natural gas €6/GJ (LHV) Coal €2/GJ (LHV) €5/tonne CO2 stored No CO2 emission cost
Lower load factors do not necessarily mean lower profitability
Costs of Electricity with CCS Post combustion capture
2011 costs 8% discount rate 25 year plant life
€5/tonne CO2 stored No CO2 emission cost
2011 costs 8% discount rate 25 year plant life
Natural gas €6/GJ Coal €2/GJ €5/tonne CO2 stored No CO2 emission cost
Costs of Electricity with CCS Pre and post combustion capture
2011 costs 8% discount rate 25 year plant life
Natural gas €8/GJ Coal €2/GJ €5/tonne CO2 stored No CO2 emission cost
Costs of Electricity with CCS Pre and post combustion capture
Barriers to CCS • Technical issues
• Scale-up to large plant sizes • Demonstration of operation of CCS in power plants • More demonstration of long term CO2 storage in various geologies
• Economics • Obtaining funding for demonstration plants has been difficult • Uncertainty about economic incentive for large scale CO2 abatement in
the longer term
• Regulatory and public acceptance • Many regulatory hurdles have been overcome but some remain • Level of public awareness of CCS is low
Summary • Increasing interest in CCS for combined cycle plants • Gas turbine power plants with CCS can complement other low-
CO2 generation technologies • Flexible • Relatively low fixed costs • Able to achieve very low overall electricity system emissions
• The optimum CCS technology depends on various factors: • Fuel prices • Emission requirements • Other generation technologies on the grid
• CCS has been demonstrated at industrial plants and small power plants but full-size power plant demonstrations are needed
