orc working fluids comparison ecos presentation
DESCRIPTION
ORC working media selectionTRANSCRIPT
ECOS 2010ECOS 2010June
Gary Zyhowski, Andrew Brown, Abdennacer Achaichia
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Topics Line-upTopics Line up• Introduction• Power Plant ExamplePower Plant Example
– Thermodynamics– Economics
• Comparison of Water and HFC-245fa– Pinch point– Sensible heating
• HFC-245fa properties– Exit Superheat and Recuperation
• Comparison of HFC-245fa and Isopentane– Turbine sizing
O t t– Output– “Drop-in” comparison
• Benefits to the Environment• Conclusions
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• Conclusions
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IntroductionIntroduction
• Drivers for Development of Medium- and Low-Grade Heat Utili ti T h l iUtilization Technologies
– growth in energy consumption and emissions li h– climate change
– environmental legislation– binding targets for renewable energy– increased focus across the manufacturing sector on the economic
benefits of energy and fuel conservation
• Need to reduce current fossil fuel combustion emissions• Need to reduce current fossil fuel combustion emissions– mix of renewable and cleaner energy technologies will be
necessary to meet future demand. – geothermal power is a prime example
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geothermal power is a prime example
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IntroductionIntroduction• Geothermal Power
– EU 2030 target of 5% of total electric power production– US has ~350GW potential
• Accessible Industrial Waste Heat Energy– Estimated at 1.06 x 1013 megajoules in the US
• Organic Rankine Cycle Systems are a robust means of thermal energy conversionenergy conversion– industrial waste heat– efficiency improvement in power stations– geothermal and solar heatgeothermal and solar heat– efficiency typically between 10 and 20%, depending on temperature
levels and availability of a suitably matched fluid. – attractive option for heat recovery in the range of 90 ºC to 200ºC,
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ORC System – Basic LayoutORC System Basic Layout
Vapor3 Work
OutputVapor3 Work
Output
Vapor Generator
TurbineHeat Input
Vapor Generator
TurbineHeat Input
44
Liquid
12
Liquid
12
Pump
Condenser1
Pump
Condenser1
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Heat OutputHeat Output
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Power Plant Example – Thermodynamic Analysis
Table 1. Steam Conditions for Simple Turbine Arrangement.
Power Plant Example Thermodynamic Analysis
Steam Conditions for Simple Turbine Arrangement
Outlet Location Temperature Pressure Enthalpy liq Enthalpy vap Entropy vapOutlet Location TemperatureºC
PressurekPa
Enthalpy, liq.kJ/kg
Enthalpy,vapkJ/kg
Entropy,vapkJ/kg K
From Boiler 537.8 8274 3486.7 6.8229
From 1st turbine 152.0 500.0 640.0 2748.8 6.8299
From Reheater 482.2 413.7 3446.3 8.1256
From 2nd turbine 135.0 29.2 552.0 2676.3 8.1274
From condenser 55.0 19.3 223.9
From Pump 58.0 8619 243.1
Enthalpy and entropy values use ASHRAE thermodynamic reference stateEnthalpy and entropy values use ASHRAE thermodynamic reference state
Net Heat Output 1389.2 kJ/kg steam
Heat Input 3822.1 kJ/kg steam
Theoretical cycle 0.363
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efficiency
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Power Plant Example – HFC-245fa BottomingPower Plant Example HFC 245fa Bottoming
HFC-245fa Rankine cycle
Outlet Location TemperatureºC
PressurekPa
Enthalpy, liq.kJ/kg
Enthalpy,vaporkJ/kg
Entropy,vaporkJ/kg KC kPa kJ/kg kJ/kg kJ/kg K
From Boiler 125.0 2113 490.1 1.811
From turbine 51.9 213 447.5 1.811
From condenser 95 7213 246.5
From pump 97.7 2113 249.1
Enthalpy and entropy values use ASHRAE thermodynamic reference state
Work done on 245fa - pump 2.53 kJ/kg
Net mech energy/unit mass 245fa 39.75kJ/kg
Thermal input to 245fa/cycle 241.0kJ/kg
Mass Ratio 9.07 kg 245fa per kg steam condensedg p g
Net ORC Work Out/unit mass steam
362.7 kJ/kg
Combined cycle work output 1792.5kJ/kg steam
Combined cycle efficiency 0.456
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Combined cycle efficiency 0.456
% Increase in efficiency 25.6
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Power Plant Example – Simple Payback AnalysisPower Plant Example Simple Payback Analysis
M h i l P (W) P i l d i it 1 39 109 W 5 0 kJ/hMechanical Power (W) = Power in load circuit (We)/commercial efficiency
1.39 x 109 W or 5.0 kJ/hr
Steam mass flow (kg/hr) = mechanical power (kJ/hr)/heat input with reheat (kJ/kg)
1.27 x 106 kg/hr steam
ORC work = Mass Flow Steam (kg/hr) x Net Work Out/Unit mass steam (kJ/kg)
4.6x108 kJ/hr or 128MW
Plant electric output increase, % 25
ORC System Cost ($1500 to $2000/KW) $192M to $256M
Value of Power produced in ORC ($0.085/kWhr) $95MV p O C ($ / W ) $
Payback (assumes operating cost is small) 2 to 3 years
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Comparison of Water to HFC-245fa - Pinch PointComparison of Water to HFC 245fa Pinch Point
H2O: High latent heat of vaporization yields low mass flow. Results in decreased energy capture
from source via sensible heating. Evidenced as a smaller reduction in source temperature
170
200
170
200
150
170
43.3 kJ/s137.8
147 ºC
110 ºC
Overall Efficiency = cycle efficiency x total thermal power extractedtotal thermal power available
HFC-245fa 8.1%Water 3.5%
Ab'
b150
170
43.3 kJ/s137.8
147 ºC
110 ºC
Overall Efficiency = cycle efficiency x total thermal power extractedtotal thermal power available
HFC-245fa 8.1%Water 3.5%
Ab'
b
erat
ure,
°C
100
50
0.02 kg/sWater 0.51 kg/s
HFC-245fa1.02kg/sFlowing Source Fluid
110 C
B B'
100
50
0.02 kg/sWater 0.51 kg/s
HFC-245fa1.02kg/sFlowing Source Fluid
110 C
B B'
Tem
pe
100 200 300 400
5040 51.6 kJ/s 142.1 kJ/s
B B'
100 200 300 400
5040 51.6 kJ/s 142.1 kJ/s
B B'
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100 200 300 400100 200 300 400
Thermal Power, kW (kJ/s)
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HFC-245fa Enthalpy Drops and SuperheatsHFC 245fa Enthalpy Drops and Superheats
Enthalpy drop and superheat enthalpy of HFC-245fa (isentropic expansion).•HFC-245fa expander exit gas has more superheat than entering gas.
TemperatureExpander Inlet
TemperatureCondensing
Enthalpy DropExpansion
Superheat Enthalpy kJ/kg
•A recuperator puts this energy into condensed HFC-245fa rather than rejecting it.
Expander InletºC
CondensingºC
ExpansionkJ/kg
kJ/kg
148.9 21.1 56.0 29.3
162.8 21.1 61.1 48.1
176.7 21.1 64.9 65.1
148.9 15.4 60.1 29.8
162.8 15.4 65.5 48.4
176.7 15.4 69.9 64.7
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Comparison of HFC-245fa and IsopentaneComparison of HFC 245fa and Isopentane
Turbine Sizing
Turbine diameter D= ds Q0.5 / H0.25 Assume a specific diameter of 4 (Balje Diagram)
Q is the volumetric flow rate (m3/s)
H is head (m2/s2)
ds is specific diameter (dimensionless)
H d i d t i d f th ti PR [1 ( 1) H/ 2 ] / 1Head is determined from the equation PR=[1+(γ–1) H/ a2 ]γ/γ-1
PR is the turbine pressure ratio (dimensionless),
i th i t i t (*di i l )γ is the isentropic exponent (*dimensionless)
*for an ideal gas this is the heat capacity at constant pressure /heat capacity at constant volume, Cp/Cv)
a is the speed of sound in the particular working fluid (m/s).
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p p g ( )
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Comparison of HFC-245fa and IsopentaneComparison of HFC 245fa and Isopentane
Geothermal hot water source: HFC-245fa and isopentane working fluid comparison.Basis: 5000kj/second delivered for working fluid vapor generation j f g f p g
90ºC source*
Mass flow,kg/sec
Turbine Exit flow,m3/sec
Turbine Diameter,m
Theoretical electrical output, kWe
% difference relative to HFC-245faDi t O t tsource kg/sec m3/sec m kWe
HFC-245fa 22.4 2.34 0.474 473.5
Isopentane 11.9 3.94 0.526 476
Diameter Output
+ 11 + 0.5p
120C source*
HFC-245fa 20.6 2.30 0.418 646.5
Isopentane 10.6 4.06 0.470 531
*30ºC condensing (working fluid temperature)
+ 12 +4
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** exit condition limited by 9:1 pressure ratio.
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Comparison of HFC-245fa and IsopentaneComparison of HFC 245fa and Isopentane
“Drop-in” of isopentane in a turbine initially sized for HFC-245fa.
90°C Source Turbine Diameter, m
Volumetric flow rate (turbine exit), m3/sec
Mass flow, kg/sec
Electrical Output, kWe
% Change kWe vs. HFC-245fa
Isopentane 0.474 3.20 9.6 383 (19.0)
HFC-245fa 0.474 2.34 22.4 473.5
120°C Source
Isopentane 0 418 3 22 8 4 531 (17 9)Isopentane 0.418 3.22 8.4 531 (17.9)
HFC-245fa 0.418 2.30 20.6 646.5
Thermal efficiency Isopentane HFC-245fa
90°C source 0.0952 0.0947°
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120°C source 0.1344 0.1293
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Comparison of HFC-245fa and IsopentaneComparison of HFC 245fa and Isopentane
Temperature Reduction of a Flowing Fluid Source
S t d li 5000kJ/ (f 90°C ) t b il•System delivers 5000kJ/s (from a 90°C source) to boiler•Assume source flow rate of 100kg/second•Latent heat of HFC-245fa at 80°C and sensible heating from 30°C to 80°C = 224 kJ/kg •Mass flow x heat delivered to working fluid = heat from source Water, or 5000kJ/s g ,
q=mCpΔT q is the heat removed (kJ/s)
m is mass flow (kg/s)
Cp is heat capacity at constant pressure (kJ/kg K)
ΔT is the temperature difference (°C) p ( )
The source temperature drop with HFC-245fa is ~12°C
Since the HFC-245fa and Isopentane sizing is based on the same heat input to
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the boiler, it serves as a check that the source temperature drop with Isopentane is ~12°C
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Benefits to the EnvironmentBenefits to the Environment
•Can address needs for additional capacity and/or increased efficiency•Avoided CO2 emissions when ORC system electric power displaces grid powerAvoided CO2 emissions when ORC system electric power displaces grid power•When appended to NG or diesel gensets
–Additional power with no additional CO2 emissions–10-15% additional power output (more or less depending on design and conditions) p p ( p g g )–No additional fuel consumption
•Renewable sources such as geothermal and solar can be utilized•Accessing manufacturing sector waste heat sources improves energy efficiency
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ConclusionsConclusions
•HFC-245fa is a suitable working fluid for ORC applications
Hi h h t it t ib t t hi h l ffi i i•High heat capacity contributes to high cycle efficiencies
•Desirable latent heat to heat capacity ratio for ORC
•Particularly well suited for source temperatures of 90°C to 150°Cy p
•HFC-245fa provides a non-flammable fluid option
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