OPTIMIZATION OF COMBINED CYCLE EFFICIENCY WITH SUPPLEMENTRY HEATING

Abstract

As other commodities energy has become the most important part of human life. At present 80% of energy production in the world is from fossil fuels. Due to increased prices of fuel and their continue depletion and limited resources, it has become necessary to search for new areas and different methods to generate it scientists and engineers are developing new and better technologies. Among various energy converting devices steam and gas turbines are extensively used for converting thermal energy into mechanical work.

In the beginning years of development of turbine technology water was the only working fluid therefore hydraulic power plant were the only means of energy generation, later steam turbine came to existence and is still main prime mover for energy generation. Due to inherent disadvantages use of gas turbine was practiced, it also has poor efficiency because about sixty percent of total heat generated in combustion chamber goes waste with exhausted flue gases. To use wasted thermal energy concept of combined cycle has been introduced. The significance of combined cycle power plant is that it utilizes the waste energy for generation of steam to run steam turbine. This leads to increased power output and efficiency.

Combined cycle power plants are gaining increasing acceptance as alternative to conventional or nuclear steam cycle due to high thermal efficiency as high as 60% utilizing natural gas as fuel.

In this present thesis” Optimization of combined cycle efficiency with supplementary heating” Steam has been generated in two stages , one at 20 bar and 813K in high pressure turbine and in second stage at 10 bar and 623K in a low pressure turbine. The turbine inlet temperature is variable. Specific work output and thermal efficiency of combined cycle with variable supplementary heating has been calculated with different A/F ratios and pressure ratios. The pressure has been varied in the range of 4 to 20. A/F ratio has been varied in the range of 70 to 85. Supplementary heating range is taken from 0.0 to 0.5. The optimum point has been searched and its analysis has been done.