Performance and emission characteristics of natural gas combined cycle power generation system with steam injection and oxyfuel combustion.

Abstract

Natural gas combined cycle power generation systems are gaining popularity due to their high power generation efficiency and reduced emission. In the present work, combined cycle power generation configuration systems studied with natural gas as primary fuel oxidizes with air and pure oxygen separately. Steam is injected in main combustion chamber and reheater combustion chamber individually and simultaneously to understand the performance of combined cycle work output and greenhouse gas emission. The effect of pressure ratio, turbine inlet temperature, isentropic efficiency, ambient temperature on combined cycle work output, thermal and exergy efficiency are carried out with and without steam injection. In present range of investigation, it is observed that the steam injection increases gas cycle efficiency and decreases the steam cycle efficiency. Ideal pressure ratio found to be 25 in all different combined cycle power generation system configurations. Maximum CO2 emission reduction (7.2%) occurs when steam is injected in reheater combustion chamber for fuel combustion with air and (3.2%) when steam injection in both combustion chambers for oxy fuel configuration. Thermal efficiency of combined cycle system increased by 8.2% when 10% steam injection in both combustion chambers. In oxyfuel combustion, higher ratio of recycle flue gas brings higher thermal efficiency and highest thermal efficiency achieved when steam is injected in main combustion chamber only. Maximum exergy destruction found in combustion chambers (57%), steam injection lowers exergy destruction by 4%. More than 10% steam in combustion chamber brings combined cycle thermal efficiency down.