An Integrated Gasification Zero Emission Plant Using Oxygen Produced in a Mixed Conducting Membrane Reactor

Abstract

Integrated gasification combined cycles (IGCCs) exhibit conditions favourable to CO2 sequestration. In this article, simulations of the Integrated Gasification Zero Emission Plant (IGZEP) concept are presented. The idea behind this concept is to use oxygen produced in a Mixed Conducting Membrane (MCM) reactor in an IGCC. Previous studies have shown that it is beneficial to integrate an MCM reactor in a natural gas fired cycle, and the objective of this article is to quantify the advantages of integrating the same type of reactor with an IGCC the way it is suggested in the IGZEP concept. The core of the membrane reactor is a ceramic membrane, which separates oxygen from air exiting the gas turbine compressor. The reactor operates at temperatures around 900 °C and is driven by a difference in oxygen partial pressure. The oxygen permeating the membrane is used in a Texaco gasifier, whereas the oxygen-depleted air is sent to a high temperature combustor. The rest of the cycle is essentially similar to a “standard” IGCC. The simulations performed resulted in a CO2 capture penalty of 6.4% points (Lower Heating Value, LHV) and a net cycle efficiency of 32.5% (LHV). Despite this quite low efficiency, the IGZEP concept is interesting since one of the main reasons for the low net efficiencies is the low efficiency of the Texaco gasifier model used. Other models for Texaco gasifiers with higher efficiency have been found in literature. Nevertheless, it is judged more interesting to compare IGZEP’s penalty for oxygen generation with that of existing competitors. It is shown that the total oxygen production penalty can be decreased from 4.9% points in the reference case to 4.3% points in IGZEP. That is, about 0.6% points in net efficiency may be gained by replacing a standard (non-integrated) cryogenic air distillation unit with an MCM reactor. Other studies have also shown that this strategy may entail lower investment and electricity production costs.