supercritical co2 power cycle development & commercialization

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

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

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

High density fluid = compact equipment:

Turbomachinery

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10MW sCO2 turbine

10MW steam turbine

Non-condensing expansion

Condensing expansion

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

CO2 cycles – Simple cycle limitations

Highly recuperated cycle limits performance

at higher heat source temperature12

Heat addition

CO2 cycles – Cascading can increase

available ∆T

Heat extraction limitations of simple

recuperated cycle mitigated

13

Heat addition

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)

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)

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

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

First “commercial-scale” system at

~7.5MW, utilizes commercial technology

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From Sandia National Laboratory report

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

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

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)

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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