Thermodynamic Analysis of a biomass-fired micro-CHP with Organic Rankine Cycle

In this project the thermodynamic modelling of a Rankine Cycle with Organic Fluids (so-called ORC) in a Biomass-fired Micro-CHP has been carried out; the system produces electricity and rejects useful heat to a heating loop. The ORC fluids used in the analysis were HFE7000, HFE7100 and n-pentane. Different routines were created to model different cycle types. A simple Pinch-Point analysis based on temperature profiles in the condenser was carried out to calculate the temperature at which the water in the heating loop was leaving the condenser. Modelling results show that increasing the evaporator temperature and decreasing the condenser temperature increase the CHP electrical efficiency. Using an IHE (internal heat exchanger) to recuperate waste heat from the exit of the micro-turbine increases the CHP electrical efficiency approximately by 0.4-0.5% for every 10 K temperature drop on the IHE warm side. Superheating decreases the CHP electrical efficiency approximately by 0.4-0.5% for every 10 K of superheating. Subcooling also decreases the CHP electrical efficiency by 0.5-0.6% for every 10 K of subcooling. Amongst the fluids tested, n-pentane shows the best electrical efficiency, although its flammability can be an issue.