This document summarizes a thermo-economic optimization of subcritical and transcritical organic Rankine cycle (ORC) systems for low-temperature heat sources between 100-150°C. The authors developed models for ORC components like heat exchangers and turbines to evaluate seven working fluids. Genetic algorithms optimized cycle parameters to minimize specific investment costs. Results showed transcritical cycles with R1234ze(e) and R1233zd(e) had the lowest costs, around 2000€/kWe for a 150°C heat source. A breakdown of costs for R1234ze(e) at 150°C showed a total investment of 941k€ and net power of 604kW.
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Thermo-Economic Optimization of Subcritical and Transcritical ORC Systems
1. THERMO-ECONOMIC OPTIMIZATION OF SUBCRITICAL AND
TRANSCRITICAL ORC SYSTEMS
THOMAS TARTIÈRE, BENOIT OBERT, LAURENT SANCHEZ
ASME ORC 2013 – 2ND INTERNATIONAL SEMINAR ON ORC POWER SYSTEMS
3. ASME ORC 2013
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PROBLEM STATEMENT
Application :
Low-temperature heat source (100°C – 150°C ), medium power (200-1000 kWe)
Question :
Do transcritical cycles result in a better profitability?
Based on the SURORC Project (2012), funded by the French Energy Agency (ADEME), realized with partners:
5. ASME ORC 2013
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HEAT EXCHANGERS
Plate heat exchangers
Evaporator
Welded plate heat exchanger (suitable for pressure up to 200 bar)
Condenser
Semi-welded plate heat exchanger (suitable for pressure<40 bars, temperature<150°C)
Cost
Linear with respect to heat transfer area
• High heat transfer efficiency
•Low refrigerant charge
• Small temperature approach
• Lower cost
• Compact size
6. ASME ORC 2013
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HEAT EXCHANGERS
Model (inspired from Quoilin 2011)
Enthalpy discretization of the heat exchanger. Iterate on geometry until total ∆P=30 kPa.
Outputs: total heat transfer area A + refrigerant charge
Condensation heat transfer correlation from Yan (1998)
Evaporation heat transfer correlation from Hsieh (2002)
Supercritical heat transfer correlation from Jackson (1979)
Limits
• Few experimental results on heat transfer and pressure drops with refrigerants at supercritical
pressures
• High uncertainty of subcritical heat transfer and pressure drop correlations at high pressures
8. ASME ORC 2013
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AXIAL TURBINE PRELIMINARY DESIGN
Inputs: ,fluid, ω, Tin, Pin
Nstage = i+1
Compute:
• Velocity triangles
• Thermo properties
• Turbine geometry
• Blade heights bk …
Flow Mach < 1 and
bk’s adequate
END and cost calculation
NO
YES
Outputs
• Number of stages
• Geometry of the turbine wheels
• Height and number of the turbine blades
10. ASME ORC 2013
AXIAL TURBINE COST
Fixed cost (valid only in a limited range of power and rotation speed)
• Bearings
• Mechanical seals
• Lubrication system
• Other…
Variable cost
Manufacturing time for the weel and casing
Stator Rotor
V1 V2
11. ASME ORC 2013
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OTHER COST FUNCTIONS
Refrigerant : from 6.5€/kg to 27€/kg
Generator :
Pump :
Mechanical parts:
• Piping (purchase + welding):
• Other (skid, insulation, installation…) : fixed cost
Electrical equipments, instrumentation and controls : fixed cost
Other fixed cost :
Engineering, transportation, installation, insurance…
12. ASME ORC 2013
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GENETIC ALGORITHM OPTIMIZATION
Heat source : 15 kg/s of water at T=100…150°C
Optimization parameters
• Relative evaporation pressure P_evap/P_crit : 0,1 … 1,3
• Superheating : 3 … 30°C
• Evaporator pinch temperature difference : 3 … 15°C
Objective function
Minimize SIC (Specific Investment Cost) = Total Investment Cost/Net output Power
Other parameters
Condensation temperature : 30°C
Condenser subcooling : 3°C
Water cooling inlet : 15°C
Water cooling outlet : 25°C
Turbine efficiency : 85 %
Generator efficiency : 95%
Pump efficiency : 70%
18. THANK YOU
THOMAS TARTIÈRE, BENOIT OBERT, LAURENT SANCHEZ
ENERTIME
62,64 RUE JEAN JAURÈS, 92800 PUTEAUX, FRANCE
WWW.ENERTIME.COM
thomas.tartiere@enertime.com