EVALUATION OF AN ORC-BASED MICRO-CHP SYSTEM INVOLVING A HERMETIC SCROLL EXPANDER JF. Oudkerk, S. Quoilin and V. Lemort Thermodynamics laboratory Université de Liège
Micro Combined heat and power CHP: Produced electricity and useful heat Electricity 30 kwh Electricity Power plant: 40% 75 kwh 100 kwh CHP: 30% El 60% Heat 142 kwh Heat 60 kwh Heat Boiler: 90% 67 kwh Micro CHP: <50kW Electric
Electrical power Electrical efficency Global efficiency Fuel ICE 5kWe- 20MWe Technologies Micro- Turbine 15kWe- 300kWe Stirling ORC Fuel cell 1kWe-1.5MWe 1kWe-10MWe 1kWe-1MWe 25-45% 15-30% 10-20% ~10% 30-70% 65-92% 65-90% 65-95% ~90% 90% Gasoline, Diesel, Gas, Gas, Biogas, State Widespread Uncommon Flexible Development, early market Flexible Development, early market Hydrogen or Hydrogenrich gas Proven technology Manufacturer exemple Senertec Capstone Sunmachine Otag Hexis
Scroll expander Volumetric engine: Not avalable yet: Conversion of a compressor Advantages : No check valve Reduced number of moving part Low rotational speed Handle high pressure ratio
Modification of the compressor Discharge and reed valve Floating seal
Gas cycle test rig
Results analysis Maximum electrical isentropic efficiency: 71%
Expander model Supply pressure drop Supply cooling down Isentropic expansion Isochoric expansion Internal leakage Exhaust heat exchange Mechanical losses Electromechanical losses Ambient losses Isothermal fictitious wall
Error max: Flow rate: 2% Power: 6% Exhaust T : 2K Validation of the model
Simulation of losses
Simulation of losses
Simulation of losses
Simulation of losses
Simulation of losses
Simulation of losses
Simulation of losses
Simulation of losses Most significant: Intern volume ratio and electromechanical
Dimensionless expander model Previous model: Dimensional parameters Dimensionless model: Polynomial law for isentropic efficiency and for filling factor Assumption: independent of the size
ORC-based mchp Flue gas Ec Boiler Ev Exp Electrical power Fuel Air Reg Heat consumption Pump Cd
T g,ex,og,computed [ C] T w,ex,computed [ C] Boiler Model Adiabatic combustion chamber Heat exchanger gas/htf Heat exchanger HTF/ambience 200 195 190 185 180 175 170 165 160 155 150 145 140 150 155 160 165 170 175 180 185 190 T g,ex,og,meas [ C] Error bar: 5K 85 80 75 70 65 60 55 50 45 45 50 55 60 65 70 75 80 85 T w,ex,meas [ C]
Components ORC model Heat exchangers: ε-ntu method Pump: Isentropic efficiency Expander: Dimensionless model ORC model: Interconnection of the different components
Fluid selection Maximum inlet temperature of the expander: 135 C Best fluid: R245fa net [-] 0.18 0.16 0.14 0.12 0.1 0.08 0.06 0.04 0.02 0 100 150 200 250 300 T ev [ C] R236fa Isobutane n-butane R245fa HFE7000 Isopentane n-pentane n-hexane n-heptane OMTS Toluene
n H Q load [W] 2500 2000 1500 Average climate EN14825 Seasonal simulation 30000 25000 20000 Heat demand 65 60 55 50 Temperature setting law EN14825 Very High High Medium Low 1000 500 0-15 -10-5 0 5 10 15 T out [ C] 20 25 30 35 15000 10000 5000-10 -5 0 5 10 15 20 25 30 35 40 T out [ C] Tw,tank [ C] 45 40 35 30 25 20-15 -10-5 0 5 10 15 20 T out [ C] ORC based m-chp Model
η electric [%] Results: Electrical efficiency 10 9 8 7 6 5 4 3 2 1 0-10 -5 0 5 10 15 Tout [ C] Very High High Medium Low
Results: Annual efficiencies Annual electrical efficiencies: On/Off coefficient: Low Medium High Very high Electric 7.5 % 7.2% 7% 6.7% Thermal 80 % 80 % 80 % 80 %
Possible improvement 2 expander in series: increase global volume ratio Ok only with Tmax>135 C 0.18 0.16 net [-] 0.14 0.12 0.1 0.08 0.06 0.04 0.02 0 100 150 200 250 300 T ev [ C] R245fa HFE7000 Isopentane n-pentane n-hexane n-heptane Toluene
Possible improvement 14 12 Result with n-pentane, Tev=190 C, High temperature application 10 8 6 4 2 2 expander/n- Pentanne 1 expander/ R245fa 1 Ex 2 Ex Electric 7 % 11 % Thermal 80 % 72 % 0-10 -5 0 5 10 15
Conclusion Investigation of an expander: Good achieved performance (71% efficiency) Well suited for low grade heat source ORC Validated semi empirical model ORC based mchp Annual electrical efficiency of 7% Need a more suitable expander: higher maximum inlet temperature, higher built in volume ratio Can be competitive with other technologies
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