Integration Options for Post-Combustion CO Capture using Molten ... · Molten Carbonate Fuel Cell...
Transcript of Integration Options for Post-Combustion CO Capture using Molten ... · Molten Carbonate Fuel Cell...
Integration Options for Post-Combustion CO2 Capture using Molten Carbonate Fuel Cells TCCS-9, Trondheim, Norway 12 – 14th June 2017 Presented by: Stuart Lodge (BP): CCP4 Capture Team
This presentation has been prepared for information purposes only. All statements
of opinion and/or belief contained in this document and all views expressed and all
projections, forecasts or statements relating to expectations regarding future events
represent the CCP’s own assessment and interpretation of information available to it
as at the date of this document.
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Contents
Section One | Molten Carbonate Fuel Cells for CO2 Capture background Section Two | Starting schemes for consideration Section Three | Key performance factors Section Four | Improved process schemes Section Five | Cost and efficiency impacts and conclusions
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Objective
The work reported in this presentation was to understand
the value of process integration that may be applied in
new-build versus retrofit applications of molten carbonate
fuel cells for high efficiency post-combustion CO2 capture.
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Background: Technology Comparison
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60%Why study MCFC? Power plant net efficiency (LHV)
• In a previous CCP evaluation
the MCFC case is the only
capture technology which
shows an improved efficiency
compared to the base case
(NGCC + amine capture)
• This result stimulates the need
for further investigation into
application options of the
MCFC technology for high
efficiency CO2 capture
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Background: What are MCFCs?
Cathode (+)
2O2 + 4CO2 + 8e- 4CO32-
Anode (-)
CH4 + 4CO3
2- 2H2O + 5CO2 + 8e-
MCFC
Electrolyte 4CO32-
Flue Gas
(~ 4% CO2)
Gas to Stack
(low CO2)
CO2 rich gas &
exhaust syngas
Fuel feed
to MCFC
↑ Simultaneously separates CO2 and produces power @ high efficiency (~50% LHV)
↑ High operating temperature (650°C) needed to achieve conductivity of carbonate electrolyte and to provide internal natural gas reforming by an affordable catalyst
↑ Low NOX (direct destruction in MCFC) and SO2/H2S (previous capture)
Based on carbonate ions (CO32-) passing through a solid Li-K matrix electrolyte
↓ Low materials durability (corrosion) and low contaminants tolerance
↓ High CAPEX and OPEX
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Background: Using MCFC for capture Two different schemes studied
Integrated MCFC for CO2 Capture case Utilising high temperature of the gas turbine
Non-integrated MCFC for CO2 Capture case Suitable for retrofit applications
Cathode
Anode
MCFC
CO2 Separation
and Compression
HRSG Air Gas
Turbine
Natural Gas CO2 for Storage
Gas to Stack NGCC
Cathode
Anode
MCFC
CO2 Separation
and Compression
Air
Gas
Turbine
Heat
Recovery
Steam Cycle
NGCC
Natural Gas
Gas to Stack
CO2 for Storage
Preheaters
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Molten Carbonate Fuel Cell – Integrated Case In detail
Starting Design
Natural Gas
Air Gas
Turbine Cathode
Anode
MCFC
Steam Cycle
CO2 Separation
and Compression
HRSG
CO2 for Storage
Gas to Stack
Unconverted fuel / syngas
recycled to MCFC Anode
Steam for heat exchange
Steam for MCFC
Flue Gas
Preheater
to GT
Preheater
to MCFC
Key Features:
• MCFC directly downstream of the GT to use high grade heat
• Fuel for MCFC preheated by cathode exhaust directly
• Fuel cell exhausts feed the HRSG
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Molten Carbonate Fuel Cell – Non-integrated Case In detail
Key Features:
• MCFC downstream of
full Power cycle
• Heat recovery from
MCFC critical to
performance
• MCFC preheating
provided by burning fuel
Air
Gas
Turbine
Natural
Gas
Heat
Recovery
Steam Cycle
Cathode
Anode
MCFC
CO2 Separation
and Compression
NGCC
CO2 for Storage
Gas to Stack
Water
Unconverted fuel / syngas
recycled to MCFC Anode
Flue Gas
Pre-Heater
Heat
Recovery
Pre-Heater
Combustor
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Heat Integration – Key to Performance but challenges exist…
Recovery of heat from MCFC exhausts key to reaching higher
efficiency performance for both process cases
• Challenge = High operating temperature of MCFC ~ 650°C
Recuperative gas-to-gas heat exchanger design for main heat
transfer area, the MCFC pre-heater
• Challenge = Few recuperative designs at large scale
Presence of “syngas” type composition at these high temperature
presents challenges
• Challenge = “metal dusting” at the temperatures required
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Heat Integration Study
Existing industrially relevant recuperative heat
exchange designs:
• Ljungstrom type rotating wheel
• Pressed plate compact heat exchanger
Limited application at NGCC scale:
• Require significant heat exchange area
• Costs will therefore be significant
How can we optimise the necessary heat
exchange area?
Ljungstrom wheel
Pressed plate exchanger
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Non-integrated case pre-heating optimisation Recuperative heat exchange vs. burning fuel for preheat
Partial burning of Syngas identified as best balance between equipment
areas and potential cost vs. overall efficiency
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Full preheat with heatexchanger
30% of syngas burntfor preheating
100% syngas topreheating
Full preheat withburning syngas &
natgas
Surf
ace a
rea –
m²
Overa
ll Effic
iency - %
LH
V
Pre-heater
exchanger area
MCFC area
Efficiency
Syngas to pre-heating combustor increases
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Heat Integration Study – Metal Dusting
What is it? a chemical damage mechanism to metal
caused by carbon ingress and over-saturation
How does it happen? High thermodynamic activity
of carbon in the gas (aC > 1), calculated from the
reaction:
CO + H2 C + H2O
High temperature syngas has high carbon activity
What are the choices? Higher chromium steels can be employed in
the heat exchanger at higher cost
Or
The heat exchange network can be re-arranged taking into
consideration CO concentrations and gas stream temperatures, in
order to avoid metal dusting conditions
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Dealing with the Challenges…
Recovery of heat from MCFC exhausts key to reaching higher
efficiency performance for both process cases
• Challenge = High operating temperature of MCFC ~ 650°C Balanced heat recovery and recycle stream combustion for preheat
Recuperative gas-to-gas heat exchanger design for main heat
transfer area, the MCFC pre-heater
• Challenge = Few recuperative designs at large scale Identified industrially relevant examples of heat exchangers
Presence of “syngas” type composition at these high temperature
presents challenges
• Challenge = “metal dusting” at the temperatures required Reconfigured process flow scheme to reduce heat exchange surface
temperatures whilst still maximising heat integration
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Molten Carbonate Fuel Cell – Integrated Case Updated process flow scheme
Starting Design
Natural Gas
Air Gas
Turbine Cathode
Anode
MCFC
Steam Cycle
CO2 Separation
and Compression
HRSG
CO2 for Storage
Gas to Stack
Unconverted fuel / syngas
recycled to MCFC Anode
Steam for heat exchange
Steam for MCFC
Flue Gas
Preheater
to GT
Preheater
to MCFC
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Molten Carbonate Fuel Cell – Integrated Case Updated process flow scheme
Natural Gas
Air Gas
Turbine Cathode
Anode
MCFC
Steam Cycle
CO2 Separation
and Compression
HRSG
Sulphur
Removal
CO2 for Storage
Gas to Stack
Unconverted fuel / syngas
recycled to MCFC Anode
Hot water for heat exchange
Steam for MCFC
Flue Gas
Preheater
to GT
Preheater
to MCFC
Key Changes:
• Sulphur removal included
• Preheating uses hot water to reduce heat exchanger surface
temperatures – limit metal dusting
• No significant change to overall efficiency (~57% LHV)
Revised Design
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Molten Carbonate Fuel Cell – Non-integrated Case Updated process flow scheme
Air
Gas
Turbine
Natural
Gas
Heat
Recovery
Steam Cycle
Cathode
Anode
MCFC
CO2 Separation
and Compression
NGCC
CO2 for Storage
Gas to Stack
Water
Unconverted fuel / syngas
recycled to MCFC Anode
Flue Gas
Pre-Heater
Heat
Recovery
Pre-Heater
Combustor
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Molten Carbonate Fuel Cell – Non-integrated Case Updated process flow scheme
Air
Gas
Turbine
Natural
Gas
Heat
Recovery
Steam Cycle
Cathode
Anode
MCFC
CO2 Separation
and Compression
NGCC
CO2 for Storage
Gas to Stack
Water Sulphur
Removal
Unconverted fuel / syngas
recycled to MCFC Anode
Flue Gas
Ljungstrom
Pre-Heater
Heat
Recovery
Key Changes:
• Pre-heater combustor
limited to 30% of
recycled syngas
• Heat recovery afforded
by a ljungstrom type heat
exchanger
Pre-Heater
Combustor
(~30% of
recycled
syngas)
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Capital cost estimates
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NGCC + amine MCFC Integrated MCFC Non-Integrated
Results/discussion
• Both MCFC cases have higher
overall capital costs than the base
amine case.
• The non-integrated case shows the
largest capital costs due to poorer
heat recovery resulting in larger
primary heat exchangers and
MCFC unit
• Both MCFC cases offer lower
specific capital costs due to the
additional electricity generated by
the MCFC.
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Conclusions from our evaluation
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NGCC + amine MCFC Integrated case MCFC non-integratedcase
Specific cost of CO2 avoided
$ 2
01
4 / t
CO
2 a
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ide
d
• The integrated MCFC is a high performing CO2 capture technology in terms of energy penalty and cost of CO2 avoided
• Utilising the high temperature heat from the gas turbine is clearly beneficial to efficiency & equipment count for the integrated case
• The non-integrated case is clearly advantaged for retrofit applications, but this comes at higher capital cost
• The higher capital cost negates the improved overall efficiency when compared to the baseline technology impacting CO2 avoided costs
• The cost of the novel MCFC equipment and their reliability continue to be a key uncertainty in the technology in both configurations
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NGCC + amine MCFC Integrated case MCFC non-integratedcase
Eff
icie
ncy -
% L
HV
Efficiency - % LHV
Further information…
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End