The influence of applying a solar dish to parallel-flow configurations of a Brayton cycle

Abstract

When adding additional pressure loss components to a Brayton cycle, parallel-flow cycles can be a viable alternative for single-shaft and twin-shaft gas turbines. This study seeks to investigate how a solar heat input, captured via a solar dish and open-cavity tubular receiver, influences various simple and recuperated parallel-flow cycle configurations. Two solar receiver placements are considered: before the combustor, and before the power turbine (which is in parallel with the cycle). Various power turbine split-off points are considered: after the compressor, after the recuperator, after the solar receiver and after the combustor. In this work, various novel solar-dish parallel-flow Brayton cycles that make use of combinations of commercial radial turbochargers to form microturbine configurations are therefore investigated. The best-performing main shaft turbocharger, the G25-550 (AR = 0.92), was selected for analysis together with the GBC14-200 or the GBC17-250 as the power turbine. Variable recuperator dimensions were also introduced to obtain maximum fuel-based thermal efficiencies while remaining within, or as close as possible to, the maximum allowable gasifier turbine inlet temperatures. For unrecuperated cycles, the cycle with the solar receiver placed before the combustor and the power turbine split-off point directly after the combustor provided the best fuel-based thermal efficiency of 7 % at a pressure ratio of 2.75 (with 14.5 kW power output). For recuperated cycles, the cycle with a split-off point directly after the compressor, flowing to both the solar receiver and power turbine, achieved the highest fuel-based thermal efficiency of 22 % at a pressure ratio of 1.5 (with 3 kW power output).