UTILIZATION OF WASTE HEAT FROM INTERCOOLED, REHEAT AND RECUPERATED GAS TURBINES FOR POWER GENERATION IN ORGANIC RANKINE CYCLES

asme-orc2015 Tracking Number 28

Organic Rankine cycle (ORC) is a very attractive technology for the conversion of low-grade thermal energy into electrical and/or mechanical energy. As the ORC has a wide range of power, it can recover the waste heat from power cycles such as turbines and/or microturbines of gas. The ORC bottoming cycle is currently incorporated into the exhaust of recuperative gas turbines to further lower the temperature of the exhaust gas, yielding similar overall efficiency to that of conventional gas turbine and steam combined cycles. However, a certain amount of thermal energy in the intercooler is not effectively utilized in the intercooled gas turbine cogeneration cycles. The temperature of the compressed air at the intercooler inlet could be found about 120 ℃-250 ℃. This is an ideal energy source to be used in an ORC for power generation. In this investigation, a thermodynamic analysis was carried out on combined cycles comprising recuperated, intercooled and reheat gas turbines and two ORCs (recuperated ICRHGT-ORCs) to recover waste heat from the intercooler and the exhaust of recuperated gas turbine. Three existing gas turbines were performed as the topping cycles with appropriate modifications. The following organic fluids were considered as the working fluids in ORCs: R123, R245fa, toluene and cyclohexane. A computer program was then designed for computations of system performance. Thermodynamic analyses were performed to study the effects of parameters including evaporator temperatures and degrees of superheat at the ORC turbine inlet on the combined cycle performance. These parameters were then optimized with thermal efficiency as the objective function by means of a genetic algorithm. It was found that all the three modified gas turbines with bottoming ORCs had higher performance, with thermal efficiency increase of 7.8% to 15.2%, in comparison to their original values.