Thermodynamic analysis on the part-load performance of a microturbine system for micro/mini-CHP applications

A gas turbine system is extensively investigated for micro/mini-Combine Heat and Power (CHP) applications. The prime mover in the system, i.e., the microturbine, has a nameplate electrical capacity of 65 kW while the coupled Waste Heat Recovery System (WHRS) produces 112 kW. Experiments were conducted for assorted power demands spanning from part-load to full-load operations. A simple thermodynamic model together with a nonlinear optimization scheme is applied to determine the properties at various state points that are not provided by the manufacturer. The second law analysis and the Energy Utilization Factor (EUF) technique are employed to assess the efficacy of the system. The actual chemical compositions of the CNG, the exhaust gas, the moist air and subsequently the amount of water condensation at the dead state are accounted for in the analysis. Here, the excess air usage in the combustion process at various loads is quantitatively reported for the first time. The results show that the combustor is responsible for almost 70% of the total exergy destruction followed by the recuperator, the compressor, and the turbine in the descending order. The first law efficiency of the system varies from 15.7% at 25% load to 28.95% for full load operation. The itemized exergetic efficiency for all the processes is evaluated while the second law efficiency of the overall system is found to be around 30.4% at full load condition. The presented results pinpoint the bottleneck of the microturbine operation, particularly at part-load conditions and are crucial in designing and performance mapping of an optimized cogeneration system.