STEP Pilot Plant Advances Supercritical CO2 Power Cycles ...
Supercritical CO2 Power Cycle Development & Commercialization
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Transcript of Supercritical CO2 Power Cycle Development & Commercialization
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Power cycle development
• Steam cycles dominant for
>300 yrs, mostly Rankine
• Gas Brayton cycles –
catching up last 50 years
• Organic Rankine Cycles
(ORC) relatively recent
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Why a new power cycle?
• Steam
– Good efficiency at lower turbine inlet
temperature
• Low compression work (pumping incompressible liquid)
• High expansion ratio (large work extraction / unit mass
of fluid)
– 2-phase heat addition limits turbine inlet
temperature
– Expansion into 2-phase region = blade erosion
– Corrosion, water treatment issues3
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Why a new power cycle?
• Gas Brayton cycles
– Good fuel-power conversion efficiency
– Require high (combustion) turbine inlet temperatures for efficient operation
– Compression work large fraction of developed power
• ORC
– Best solution at low temperatures, dry expansion
– Working fluids are more difficult to handle – generally require secondary transfer loop, limits turbine inlet temperature
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Characteristics of an ideal power cycle
• Good utilization of available heat
– High expansion, low compression work
– Direct coupling to heat source
• Benign working fluid
– Non-corrosive, non-toxic, thermally stable
– Dry expansion to avoid erosion
• Low capital cost
• Low operation & maintenance (O&M) costs
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Supercritical CO2 meets these characteristics
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sCO2 cycle history
• 1960’s – Feher proposes use of a recuperated closed-loop sCO2 based power cycle– Recognized that CO2 properties allow for Brayton-style cycle,
but with Rankine-like compression work
• 2000’s – MIT, Sandia, others consider sCO2 nuclear power cycle– Three “Supercritical CO2 Power Cycle” Symposia
– 2008, Sandia builds small sCO2 test loop for turbomachinery (simple and recompression cycles)
• 2007 – Echogen founded with vision of commercializing a sCO2 waste heat recovery heat engine– 2009, builds ~ 250kWe demonstration simple cycle system
– 2011, begins construction of 7.5MWe commercial system
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sCO2 cycles – Simple recuperated cycle
Good heat utilization at low heat source
temperature
Compact equipment set
2-phase
Supercritical fluid
Superheated
vapor
Subcooled
liquid
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High density fluid = compact equipment:
Heat exchangers
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>15MW
>300m² heat transfer area
~13000kg
Core ~ 1.5 x 1.5 x 0.5 m
Comparable S&T:
>850m²
~50000kg
Shell ~ 1.2m diameter x 12m length
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High density fluid = compact equipment:
Turbomachinery
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10MW sCO2 turbine
10MW steam turbine
Non-condensing expansion
Condensing expansion
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Simple single-phase exhaust heat exchangers
• Boiling process in steam systems limits maximum fluid temperature, requires
multiple pressures to achieve close approach to exhaust temperature
• ORC systems require intermediate heat transfer loop, plus boiling heat transfer
Constant temperature
boiling process
Continuous
temperature increase
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CO2 cycles – The challenge with a simple
recuperated architecture
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Heat addition
Expansion workCompression work
Low pressure ratio cycle => recuperation => can limit ∆T of heat addition
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CO2 cycles – Simple cycle limitations
Highly recuperated cycle limits performance
at higher heat source temperature12
Heat addition
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CO2 cycles – Cascading can increase
available ∆T
Heat extraction limitations of simple
recuperated cycle mitigated
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Heat addition
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CO2 cycles – recompression yields high heat
to power efficiency, but very low ∆T
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Heat addition
Recompression cycle specifically designed
for low ∆T applications (nuclear, CSP)
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Applications of the sCO2 cycle
Geothermal (Low T, thermosiphon)
Concentrated Solar Thermal (CSP)
(High T, low DT)
Exhaust & waste heat recovery (Moderate T, high DT)
Topping cycle (High T, low DT)
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250 kW demonstration system: initial field tests
completed at American Electric Power (AEP)
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Designed for full access
and ease of maintenance
Shop packaged / modular design
for ease of installation
Commercial size demonstration
unit at AEP’s test facility
Measured performance in line with cycle model
predictions – 140 hours, 93 turbine starts
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250 kW demonstration system: long-term tests
at Akron Energy Systems (AES) during 2012
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Hardware transferred and delivered by truck Cooling tower installation
Heat engine delivery and placement System installation now underway
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First “commercial-scale” system at
~7.5MW, utilizes commercial technology
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From Sandia National Laboratory report
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First 7.5MW system is currently in fabrication
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Subsystem and component testing planned for 3Q through 4Q 2012
Full system installation and testing in early 2013
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System installation comparison:
7.5MW steam vs. sCO2
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Smaller installation footprint compared to a HRSG/steam system for
gas turbine bottom cycling
Gas turbine Steam sCO2
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sCO2 = Higher power at lower CAPEX for
CCGT applications
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• High output power + low cost + low O&M = low LCOE
• sCO2 the clear solution for gas turbine heat recovery
DP HRSG sCO2
sCO2 + LM2500
DP-HRSG + LM2500
LM2500 Simple Cycle
SP-HRSG + LM2500
Inst
all
ed
co
st
Ne
t p
ow
er
(kW
e)
Ambient temperature (°C)
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Levelized Cost of Electricity (LCOE) ─
The Key Performance Metric
• Lower capex of sCO2 system provides major advantage
• Faster startup times (~20min vs 45-90 min for steam) = higher average output in peaking applications
• Lower footprint, zero water usage in dry-cooled applications
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Summary
• sCO2 cycles have significant advantages in several
applications over steam
– Good thermodynamic performance
– Low installed capex
– Favorable LCOE
• Broad range of applications under consideration
• Waste heat recovery first commercial application
– Demonstration system proved feasibility
– First full-scale application in 2013
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