287993 Chemical Looping Combustion (CLC) for CO2 Capture in Coal-Based Integrated Gasification Combined Cycle (IGCC) Power Plants – Performance and Cost Analysis
Chemical looping combustion (CLC) is an indirect combustion process in which fuel is combusted without direct contact with air. Transfer of oxygen between air and fuel takes place with the aid of an oxygen-carrier (OC), usually oxides of transient metals. The reduced form of metal oxide extracts O2 from air in one reactor and then transfers it to fuel in a subsequent reactor. Since the fuel does not come in direct contact with air, the products of combustion contain only carbon dioxide (CO2) and water (H2O). CO2 stream of very high purity can be obtained by condensing the water vapor. Gaseous fuels such as natural gas or syngas (CO and H2) can be used as fuels in CLC, for inherent CO2 capture. The focus of this paper is the use of CLC for CO2 capture in a coal-based integrated combined cycle power plant (IGCC) using two different configurations (high pressure and atmospheric pressure), in terms of the overall thermodynamics and cost.
CO2 capture in conventional IGCC designs involves a water gas shift reaction to convert CO in the syngas from gasifier to CO2 and subsequent capture of CO2 using a physical absorption solvent (Selexol or Rectisol). Alternatively, CLC can be used for CO2 capture in a coal-based IGCC. The products from the CLC reactor system are two separate streams of oxygen-depleted air and combustion products (CO2 and H2O), both at high temperature. Two configurations of IGCC power plants using CLC can be formulated – high pressure CLC and atmospheric pressure CLC. In the high pressure configuration, CLC process takes place at a high pressure and the exhaust streams from both reactors can be expanded in separate gas turbines to generate electricity. The hot exhaust from these turbines can be used to generate steam in a heat recovery steam generator (HRSG) for further electricity production. Water can be condensed from the CO2-stream in order to obtain high purity CO2 for further compression and storage. On the other hand, in the atmospheric pressure CLC configuration, CLC process occurs at atmospheric pressure and the hot exhaust streams from the reactors are cooled down to generate steam in HRSG, which is used to generate electricity in steam turbines. The advantage of atmospheric pressure CLC is the absence of air compressor which is required in the high-pressure CLC configuration. However, the reactor size increases with decreasing pressure which will affect the capital cost of the system. The relative advantages and disadvantages of both these configurations will be studied in terms of their thermodynamic performance as well as capital and operating costs.
Performance and cost models are developed to perform a detailed thermodynamic and economic analysis of an IGCC plant using CLC for CO2 capture. Chemical equilibrium models will be used to simulate the CLC reactions, using NiO/Ni CuO/Cu and Fe2O3/Fe3O4 as the oxygen carriers. The effect of varying syngas compositions and operating conditions such as temperature will also be studied. A comparison will be made with a conventional IGCC power plant with CO2 capture in order to understand the relative feasibility of CLC when applied to IGCC.
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