Research Papers: Gas Turbines: Cycle Innovations

Analysis of Direct Carbon Fuel Cell Based Coal Fired Power Cycles With CO2 Capture

[+] Author and Article Information
Stefano Campanari

e-mail: stefano.campanari@polimi.it

Matteo C. Romano

Politecnico di Milano—Energy Department,
Via Lambruschini 4,
20156 Milano, Italy

Other DCFC types belonging to the second category are developed for instance by Contained Energy LLC, with a MCFC-based technology using molten carbonates at the electrolyte and as a molten anode medium.

The maximum work which can be extracted from carbon oxidation, defined by the Gibbs free energy variation ΔG as Wmax = ΔH − T0ΔS, is slightly higher than the enthalpy variation ΔH (395.4 kJ/mol at 600 °C versus 394 kJ/mol) since the reaction occurs with a negative entropy variation ΔS. By comparison, the oxidation of hydrogen has a Wmax equal to ≅ 83% of ΔH.

Other kind of fuel cells, operating with gaseous reactants, typically work with 80–85% maximum fuel utilization.

This could significantly influence the plant O&M costs, depending on the make-up flow rate. However, no information are presently available on the expected tin consumption in the regeneration process.

1Corresponding author.

Contributed by the International Gas Turbine Institute of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received June 30, 2012; final manuscript received July 14, 2012; published online November 30, 2012. Editor: Dilip R. Ballal.

J. Eng. Gas Turbines Power 135(1), 011701 (Nov 30, 2012) (9 pages) Paper No: GTP-12-1243; doi: 10.1115/1.4007354 History: Received June 30, 2012; Revised July 14, 2012

This work presents an analysis of the application of direct carbon fuel cells (DCFC) to large scale, coal fueled power cycles. DCFCs are a type of high temperature fuel cell featuring the possibility of being fed directly with coal or other heavy fuels, with high tolerance to impurities and contaminants (e.g., sulfur) contained in the fuel. Different DCFC technologies of this type are developed in laboratories, research centers or new startup companies, although at kW-scale, showing promising results for their possible future application to stationary power generation. This work investigates the potential application of two DCFC categories, both using a “molten anode medium” which can be (i) a mixture of molten carbonates or (ii) a molten metal (liquid tin) flowing at the anode of a fuel cell belonging to the solid oxide electrolyte family. Both technologies can be considered particularly interesting for the possible future application to large scale, coal fueled power cycles with CO2 capture, since they both have the advantage of oxidizing coal without mixing the oxidized products with nitrogen; thus releasing a high CO2 concentration exhaust gas. After a description of the operating principles of the two DCFCs, it is presented a lumped-volume thermodynamic model which reproduces the DCFC behavior in terms of energy and material balances, calibrated over available literature data. We consider then two plant layouts, using a hundred-MW scale coal feeding, where the DCFC generates electricity and heat recovered by a bottoming steam cycle, while the exhaust gases are sent to a CO2 compression train, after purification in appropriate cleaning processes. Detailed results are presented in terms of energy and material balances of the proposed cycles, showing how the complete system may surpass 65% lower heating value electrical efficiency with nearly complete (95%+) CO2 capture, making the system very attractive, although evidencing a number of technologically critical issues.

Copyright © 2013 by ASME
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Grahic Jump Location
Fig. 1

Operating principle of a DCFC [10]

Grahic Jump Location
Fig. 2

Schematic of the first proposed DCFC plant (LTA case)

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Fig. 3

Schematic of the second proposed DCFC plant (MCA case)

Grahic Jump Location
Fig. 4

Effect of cell voltage on plant energy balances




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