Effect of cooling charge air on the gas turbine performance and feasibility of using absorption refrigeration in the “Kelanitissa” power station, SriLanka.
One of the drawbacks of the gas turbine is that performance drops rapidly when ambient air temperature increases. This is a major drawback for gas turbines operated in a tropical country like Sri Lanka. In Colombo, commercial capital of Sri Lanka where this study was carried out, the ambient temperature typically varies between 250C and 320C.
The Kelanithissa gas turbine plant has single shaft gas turbine (GE MS5001 R) operated in open cycle which uses diesel as fuel (Designed for dual fuel) and Designed heat rate of the gas turbine is 13,980kJ/kWh at an efficiency of 25.8%. The designed exhaust temperature is 5130C.
In this study Kelanitissa gas turbine unit was used for assessment of the performance with the changes in ambient air temperature. Two approaches were used to study this phenomenon. Firstly, the performance parameters were calculated by using actual data acquired by the operation history of the power plant. Secondly, the performance was analyzed using thermodynamic principles. Then results of the two approaches were compared.
The gas turbine studied has a designed heat rate of 13,980kJ/kWh. The present performance values, when compared to designed values, showeda very poor performance. Originally designed efficiency of 25.8%, Maximum efficiency achieved at 330C was 21.2%. When the turbine was operated in 330C, a 4.6% reduction in efficiency was observed.
Estimated cooling load for the inlet air cooling is 679.87 RT. Cost per unit cooling load of the 2 stage direct fired absorption system is $751-721 (according to 600RT-700RT). For the worst case scenario we can take the value $751 per RT value and exhaust system is 98% of the cost from direct fired system(Broad USA inc., 2008). Then we can take $736/RT as the cost for an exhaust driven absorption chiller system. Total cost for the 679.87 RT systems is $ 500,370.72(Rs. 65Mn).
Payback period of the project is 11 years but the present value after 19 years is exceeding the project cost. Present value for 19 years is Rs. 65.86Mn. Bringing down the temperature from 27oC to ISO value of 15 0C would give Rs.6 Mn of annual saving.
 D.R.Kodituwakku, Dr.N.S.Senanayake, Ruchira Abeyweera, “Effect of cooling charge air on the gas turbine performance and feasibility of using absorption refrigeration in gas power station, Sri Lanka”, SLEMA Journal 2014