Exergetic Assessment of a Syngas-Redox (SGR)-Based IGCC Plant for Generating Electricity

Abstract

Carbon capture from advanced Integrated Gasification Combined-Cycle (IGCC) processes should outperform conventional coal combustion with subsequent CO2 separation in terms of efficiency and CO2 capture rates. This paper provides a thermodynamic assessment, using exergy analysis, of a novel Syngas Redox (SGR) process for generating electricity. The power island of the proposed process uses syngas produced by coal gasification and then cleaned through high-temperature gas desulfurization (HGD). Hematite (Fe2O3) is used as an oxygen carrier to oxidize the syngas. To achieve a closed-cycle operation, the reduced iron particles are first partially re-oxidized with steam and then fully re-oxidized with pressurized air. One advantage of this design is that the resulting hydrogen (using steam in the re-oxidation section) can be utilized within the same plant or be on sold as a secondary product. In the proposed process, diluted hydrogen is combusted in a gas turbine. Heat integration is central to the design. The different requirements of syngas cooling, particle-regeneration, and coal drying necessitated the use of a heat-recovery steam generator (HRSG) supplying steam at three pressure levels. To establish a benchmark, the rate of exergy destruction within the SGR process was compared to a coal-fed Shell gasification IGCC design with Selexol-based pre-combustion capture. Process simulation was undertaken using Aspen Plus and EES (Engineering Equation Solver).

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Identifiers

DOI

10.1115/imece2012-87288

Journal

Volume 6: Energy, Parts A and B

Year

2012