Energy Transfer and Conversion in the Allam Cycle with a Multi-Stream Heat Exchanger

Abstract

A multi-stream heat exchanger model in the Allam cycle is proposed to analyze energy transfer and conversion process in this paper. This model was developed in Aspen Plus and utilized three multi-stream heat exchanger modules, considering the effects of turbine exhaust, air separation unit compression reheating and the dew point of water vapor on energy transfer in the system. The constructed multi-stream heat exchanger model is extensively discussed in the Allam system. Simulation results indicate that the cycle efficiency increases with the increase in turbine inlet temperature. However, without considering the penalty effect of the air separation unit, system efficiency reaches a maximum value. Reheating by the air separation unit partially reduces the temperature difference at the hot end of the multi-stream heat exchanger, but it is only when the turbine inlet temperature exceeds 1150°C that the outlet temperature difference of the multi-stream heat exchanger could potentially reach 20°C. The impact of air separation unit reheating on the variation trend of system efficiency is significant, and the optimal operating conditions for the system with or without the penalty effect of the air separation unit are different.

Keywords: Allam cycle, NET power cycle, Supercritical CO2, Thermodynamic analysis.