Efficiency analysis of a novel electricity and heat co-generation system in the basis of aluminum–water reaction

Abstract

With high calorific value and the environmental friendly features, hydrogen has been attached much importance. Aluminum–water reactions at medium–high temperature perform well in hydrogen generation as well as heat utilization. Active researches of the aluminum–water reactions in recent years can be attributed to the increasing interest of hydrogen generation and energy conversion.In the basis of aluminum–water reactions, the concept of a novel electricity and heat co-generation system was proposed here and it was primarily composed of a reactor, one or two turbines and generators, heat exchanger for heat user, a fuel cell and a pump. Two layouts were designed and analyzed: the one turbine layout (OTL) and the two turbine layout (TTL).The effects of key parameters, such as the steam temperature and pressure at turbine inlet, the heat user temperature and fuel cell conversion efficiency were investigated. The co-generation system could generate heat and electricity of about 22.2 MJ/kg (Al) in the OTL design. The system utilization efficiency, the ratio of the output was approximate 70% and the electricity generation efficiency could reach up to 41.52% (OTL) and 49.25% (TTL) in the two cases respectively. The OTL presented a higher heat user utilization efficiency than TTL, because of the higher turbine outlet parameters. The TTL layout with the integration of fuel cell and heat user enhanced electricity output by 45.06% in comparison with the OTL layout. The steam temperature at turbine inlet showed considerable impacts on the system utilization efficiency at the TTL case. Enhancing fuel cell conversion efficiency benefited the system and fuel cell utilization efficiencies, especially at the TTL case.