Potential and limitations of power generation via chemical looping combustion of gaseous fuels

Abstract

Pressurized chemical looping combustion (CLC) was studied with regard to its potential for power generation from gaseous fuels, such as natural gas. A process simulation model was set up for a simplified gas turbine combined cycle (GTCC) around a pressurized CLC reactor system and studied with respect to process parameters influencing electric efficiency. The process model is based on typical large scale GTCC arrangements with a gas turbine topping cycle and a heat recovery steam generator unit (HRSG). The results are compared to conventional GTCC process with similar arrangement and process parameters. It was found that the CLC process comes along with considerable technological limitations for the efficiency of the combined cycle: (i) turbine inlet temperature is limited by the oxygen carrier material, (ii) pressure drop of CLC AR path increases the required air compression work, and (iii) the requirement for low pressure steam for gas-sealing between air reactor and fuel reactor reduces the efficiency of the steam cycle. These effects limit the achievable net electric efficiency to values below 45%, which is similar to what could be reached with atmospheric pressure CLC in a conventional steam cycle power plant arrangement (e.g. Benson-type steam generator). The gas turbine inlet temperature (TIT) was identified as the greatest limitation to the process, the pressure ratio has to be reduced accordingly to maintain sufficient exhaust gas temperatures for the HRSG, which limits the efficiency potential of the gas turbine. As a conclusion, when it comes to power generation from gaseous fuels, these limitations will need to be resolved to make CLC technology competitive to conventional GTCC power plants combined with post combustion CO2 capture technologies.