Research Papers: Gas Turbines: Cycle Innovations

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

[+] Author and Article Information
M. Sorgenfrei

e-mail: sorgenfrei@iet.tu-berlin.de

G. Tsatsaronis

e-mail: tsatsaronis@iet.tu-berlin.de
Institute for Energy Engineering,
Technische Universität Berlin,
Marchstrasse 18,
Berlin 10587, Germany

Contributed by the Cycle Innovations Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received May 8, 2013; final manuscript received October 15, 2013; published online November 22, 2013. Assoc. Editor: Paolo Chiesa.

J. Eng. Gas Turbines Power 136(3), 031702 (Nov 22, 2013) (9 pages) Paper No: GTP-13-1122; doi: 10.1115/1.4025885 History: Received May 08, 2013; Revised October 15, 2013

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 an exergy analysis of a syngas redox (SGR) process for generating electricity. The power island of the proposed process uses syngas produced by coal gasification and is then cleaned through a high-temperature gas desulfurization (HGD) process. 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 sold as a secondary product. In the proposed process, diluted hydrogen is combusted in a gas turbine. Heat integration is central to the design. Thus far, the SGR process and the HGD unit are not commercially availiable. 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 precombustion carbon capture. Some thermodynamic inefficiencies were found to shift from the gas turbine to the steam cycle and redox system, while the net efficiency remained almost the same. A process simulation was undertaken, using Aspen Plus and the engineering equation solver (EES).

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Fig. 1

Flow diagram of the conventional IGCC plant with CO2 capture

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Fig. 2

Temperature profiles of the BASE case

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Fig. 3

Flow diagram of the SGR-based IGCC plant with inherent CO2 capture (SGR case)

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Fig. 4

Temperature profiles of the SGR case

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Fig. 5

Exergy destruction ratios at the subsystem level for both cases

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Fig. 6

Exergy destruction ratios of the redox cycle within the SGR process

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Fig. 7

Exergy destruction ratios of the steam cycle for both cases




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