A combined cycle plant with air and fuel recuperator for captive power application, Part 1: Performance analysis and comparison with non-recuperated and gas turbine cycle with only air recuperator

• A combined gas–steam cycle for captive application is proposed and analyzed.
• The cycle uses gas turbine exhaust heat for subsequent air and fuel preheating.
• Further heat recuperation takes place for steam generation in the HRSG.
• Effect of pressure ratio and steam injection to combustor on performance is studied.
• Comparison with non-recuperated and cycle with only air recuperator is provided.

In this paper, a simulation based performance of a recuperated combined gas turbine (GT) and steam turbine (ST) cycle is presented. The proposed combined cycle (CC) utilizes GT exhaust heat for air and fuel preheating sequentially one after the other. Comparison of performance of the recuperated CC is made with a non-recuperated CC and a CC with only the air recuperator (AR). At a compressor pressure ratio (CPR) of 12, the CC with both AR and fuel recuperator (FR) shows 16.8% and 54.44% gain in performance over the cycle with only the AR and no recuperators. A parametric study based on variation of CPR and steam injection rate (STIR) indicate improvement in efficiency and power with increase in CPR and STIR both. With CPR, the net GT power increases, however the net ST power shows a decreasing trend particularly for the cycle without recuperators. With STIR, the net GT power increases and the bottoming ST power although decreases but with less significance. The net ST power of the CC plant without recuperators is significantly less for the bottoming ST cycle to be economically feasible. The CC plant shows an average 53.32% gain in efficiency and power over the plant without the bottoming ST cycle.