Power cycle development Steam cycles dominant for >300 yrs, - - PowerPoint PPT Presentation

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
• f fluid)

– 2-phase heat addition limits turbine inlet temperature – Expansion into 2-phase region = blade erosion – Corrosion, water treatment issues

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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

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

8 >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 work Compression 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 temperature

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Heat addition

CO2 cycles – Cascading can increase available T

Heat extraction limitations of simple recuperated cycle mitigated

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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

18 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 Installed cost Net power (kWe) 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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