Ali Bolatturk

Thermodynamic analysis and optimization of various power cycles for a geothermal resource

ABSTRACT In this study, geothermal resources in Kutahya-Simav region having geothermal water at a temperature suitable for power generation is considered. The study is aimed to yield the method of the most effective use of the geothermal resource and a rational thermodynamic comparison of various cycles for a given resource. Maximum first law efficiencies vary between 6.9 to 10.6% while the second law efficiencies vary between 38.5 to 59.3% depending on the cycle considered. The maximum power output, the first law, and the second law efficiencies are obtained for Kalina cycle followed by combined cycle and binary cycle.

An Investigation of Energy Versus Exergy Based Optimization for Power Cycles

A comparison of optimization studies based on energy and exergy methods and for the ideal and actual working models of common power cycles are performed. The cycles considered include the simple gas-turbine cycle, the regenerative gas-turbine cycle, the regenerative gas turbine cycle with reheating and intercooling, the simple steam cycle, the reheat steam cycle, and the combined gas-vapor cycle. The optimization is performed to determine the optimum pressure ratios in gas-turbine cycles and the optimum boiler pressures in steam cycles that maximize the thermal efficiency of the cycle in energy method and the exergy efficiency in exergy method. The optimum points are also searched for maximizing the net work of the cycle in both energy and exergy methods. The results show that the optimum boiler pressures that maximize the network are identical based on both energy and exergy approaches and for both ideal and actual operating models in simple steam and reheat steam cycles. The optimum boiler pressures that maximize the cycle efficiency are about the same based on both energy and exergy approaches when ideal operations are considered in simple and reheat steam cycles. The optimum points differ when actual operations are considered for these cycles. The optimum pressure ratios that maximize the network are identical based on both energy and exergy approaches but different depending on the selection of an ideal or actual model in simple and regenerative gas-turbine cycles, and in combined cycle. No agreement with respect to the optimum pressure ratios that maximize the cycle efficiency is observed for all types of gas-turbine cycles including the combined cycle.

Thermodynamic Evaluation of First and Second Law Performance of Evaporative Cooling Schemes for Regenerative Gas Turbines

In this study, effect of evaporative cooling on performance of regenerative gas turbine cycle is investigated considering simple regenerative cycle and regenerative cycle with intercooling and reheating. Evaporative cooling is applied to inlet air in simple regenerative cycle while it is applied to compressor inlet air and air between the compressor stages in reheat regenerative cycle. The first and second law performances of the cycles incorporating evaporative cooling are compared to the corresponding conventional cycles. Effects of the temperature and relative humidity of the ambient air, the turbine inlet temperature, and the pressure ratio on the net work, the thermal efficiency, and the second-law efficiency of the cycles are investigated. It appears that evaporative cooling increases thermal efficiency, net work, and optimum pressure ratio. With respect to simple regenerative cycle at a turbine inlet temperature of 1400 K and at a pressure ratio of 20, the thermal efficiency and the net work increase by 1.5 percent and 4 percent, respectively by inlet cooling in simple regenerative cycle while they increase by 18.3 percent and 12.2 percent, respectively by inlet cooling and intercooling in reheat regenerative cycle. With respect to conventional regenerative cycle with intercooling and reheating, evaporative cooling applied to inlet air and for intercooling provides essentially no increase in thermal and second-law efficiencies while it increases the net work 8.2 percent to 17.8 percent depending on the ambient conditions. Increasing turbine inlet temperature gives a linear increase in the optimum pressure ratio. As the ambient temperature increases and the relative humidity decreases, evaporative cooling becomes more effective in improving cycle performance.