Analysis of a reheat gas turbine cycle with chemical recuperation using ASPEN

Gains in the power output and thermal efficiency of industrial gas turbines have occurred in the past, primarily from increased firing temperatures and operating pressures. More recently, there is growing interest in investigating advanced cycle concepts that make use of one or more of the following performance enhancement modifications: compression intercooling, reheat expansion and exhaust heat recovery. Recent attention has focused, in particular, on the chemical heat recovery concept. The ''waste'' heat in the turbine exhaust is used to convert a methane-steam mixture into a hydrogen-rich fuel in a methane-steam reformer. The potential benefits of such cycles include high conversion efficiency, ultra-low NOx emission levels (less than 1 ppm) and high power density per unit of land. However, such cycles require high turbine exhaust temperatures, which may be achieved effectively by staging the turbine expansion and including a reheat combustor. ABB recently unveiled its new GT26 series stationary gas turbines using staged expansion with reheat combustion, allowing high thermal efficiencies with relatively low turbine inlet temperatures. This type of turbine appears particularly well-suited for chemical heat recovery. In this paper, we present a CRGT cycle based on a reheat gas turbine with key design features similar to those of ABB's GT26 machine. The cycle analysis is performed using Aspen Technology's ASPEN + process simulation software. The paper includes a detailed first and second law analysis of the cycle. (C) 1997 Elsevier Science Ltd.