Gas Turbine Evaporative Cooling, A Novel Method for Combined Cycle Plant Part Load Optimization

In power plant engineering, gas turbine (GT) evaporative cooling is traditionally thought as one of the few power augmentation alternatives for existing plants. For most combined cycle plants operating at part load, the GT Inlet Guide Vanes (IGV) will throttle the air flow to the combustor to maintain the turbine exhaust temperature (TET) as high as possible, thus maximizing the overall combined cycle efficiency. The IGV air throttling results in a reduction of the turbine inlet air temperature (TIT) due to a reduction on the mass of fuel burned in the combustors as the available combustion air decreases due to IGV throttling to maintain an optimum air to fuel ratio, resulting on a lower TET compared with the same GT at base load. The compounded result of these effects limits the maximum steam production capacity on the heat recovery steam generator, particularly for the high-pressure section, hampering the efficiency of the steam turbine. The methodology developed in the subject study aims at counteracting the afore-mentioned effects by optimizing the evaporative cooler air/water ratio which results in the lower possible heat rate for full load and part load operation. By dynamically controlling the air/water ratio, a preheating effect can be achieved in the compressor inlet air, which results on higher exhaust gas temperature, thus augmenting the high-pressure steam production on the heat recovery steam generator and accordingly the steam turbine efficiency. For a newly built 907 MWe Combined Cycle Gas Turbine (CCGT) plant, application of the evaporative cooling part load optimization methodology presented in this study could lead to a potential reduction of up to 158kJ/kWh on heat rate and 9.318 g/kWh of CO2 emissions if compared with the same plant without dynamic control of the evaporative cooler air/water ratio.

Energy-Exergy Analysis of Solarized Triple Combined Cycle Having Intercooling, Reheating and Waste Heat Utilization

Heliostat-based solar thermal power system consisting of a combination of the Brayton cycle, Rankine cycle, and organic Rankine cycle is a potential option for harnessing solar energy for power generation. Among different options for improving the performance of solarized triple combined cycle the option of introducing intercooling and reheating in the gas turbine cycle and utilizing the waste heat for augmenting the power output needs investigation. Present study considers a solarized triple combined cycle with intercooling and reheating in gas turbines while using the heat rejected in intercooling in heat recovery vapour generator and heat recovery steam generator separately in two different arrangements. A comparison of two distinct cycle arrangements has been carried out based on Ist law and IInd law of thermodynamics with the help of thermodynamic parameters. Results show that triple combined cycle having intercooling heat used in heat recovery vapour generator offers maximum energy efficiency of 63.54% at 8 CPR & 300K ambient temperature and maximum exergetic efficiency of 38.37% at 14 CPR & 300 K. While the use of intercooling heat in heat recovery steam generator offers maximum energy and exergetic efficiency of 64.15% and 39.72% respectively at 16 CPR & 300 K ambient temperature.