Assessment of Aqua-Ammonia Refrigeration for Pre-Cooling Gas Turbine Inlet Air

Power providers in Oman encounter the greatest demand for electricity during the summer months. More than 70% of Oman electric power originate from gas turbines. Unfortunately, the power output of gas turbines decreases with increasing ambient temperature. The growth in electricity generation to the summer peak load has been achieved at a very high cost of installing new generators. This paper presents an assessment of using the exhaust heat to run an aqua-ammonia refrigeration system to cool the inlet air. The performance of two General Electric aeroderivative gas turbines, the LM2500+ and the LM1600, with and without absorption refrigeration was investigated. Climate data series from Fahud, central Oman, was used for modeling the variations in ambient temperature during the year to account for the effects of climate condition in the gas turbine performance simulation. Most of the gas turbines in Oman operate on a simple cycle with exhaust heat discharged to the atmosphere. Vapor absorption refrigeration system uses heat from gas turbine exhaust as its source of energy to cool the inlet ambient air to 7°C. It was observed that the available exhaust heat from the gas turbine exceeded the heat required to run the aqua-ammonia absorption refrigeration system. For meteorological conditions existing in the particular site considered in Oman, pre-cooling gas turbine inlet air to 7°C augments power, on a yearly basis, of LM2500+ and LM1600 by 20% and 14% respectively. During the peak hours in summer months, when power is mostly needed, the percentage of power augmented climbed to 39% and 33% for the two gas turbines. It has been concluded that chilling the inlet air of the gas turbine with aqua-ammonia absorption refrigeration is technically feasible and economically appealing.