Efficiency enhancement of a combined cycle power plant by thermal integration of multiple waste heat streams with organic Rankine cycle

Abstract

The study investigated the efficiency improvement of a 9.5 MW gas engine-based combined cycle power plant utilizing multiple waste heat streams in an organic Rankine cycle. Four different waste heat sources were considered: I) boiler stack gas, II) engine jacket water, III) boiler steam, and IV) engines' exhaust gas. Besides, three different organic fluids; R245fa, R134a, and R1234ze(Z) were employed to find the best working fluid in the given operating conditions. The performance analysis of the ORC revealed that R245fa is a suitable potential fluid for cases I and II, whereas R134a performs better for cases III and IV. Integrating the ORC with the boiler stack using R245fa at 8 bar_g provided an additional 16.5% waste gas heat recovery. It increased the net electric efficiency of the existing plant by 0.7%. The jacket water heat recovery further improved the net electric efficiency by 2.1%. By integrating both streams with the ORC in the existing system, the net electrical efficiency was increased from 42.6% to 45.3%. The estimated payback period for the jacket water heat recovery scenario utilizing Chinese ORC equipment was 9.3 years. However, this period was significantly reduced to 4.6 years for general industry applications, rendering it economically viable.