Research Papers

Thermodynamic Analysis of Direct Steam Reforming of Ethanol in Molten Carbonate Fuel Cell

[+] Author and Article Information
José Luz Silveira

Energy Department, College of Engineering of Guaratinguetá, Sao Paulo State University (UNESP), 333 Guaratinguetá, Sao Paulo 12500-000, Braziljoseluz@feg.unesp.br

Antonio Carlos de Souza

Energy Department, College of Engineering of Guaratinguetá, Sao Paulo State University (UNESP), 333 Guaratinguetá, Sao Paulo 12500-000, Brazilcaetanodesouza@yahoo.com.br

Márcio Evaristo da Silva

Energy Department, College of Engineering of Guaratinguetá, Sao Paulo State University (UNESP), 333 Guaratinguetá, Sao Paulo 12500-000, Brazilevaristosm@yahoo.com.br

J. Fuel Cell Sci. Technol 5(2), 021012 (Apr 18, 2008) (6 pages) doi:10.1115/1.2759509 History: Received October 25, 2005; Revised June 07, 2006; Published April 18, 2008

Fuel cell as molten carbonate fuel cell (MCFC) operates at high temperatures. Thus, cogeneration processes may be performed, generating heat for its own process or for other purposes of steam generation in the industry. The use of ethanol is one of the best options because this is a renewable and less environmentally offensive fuel, and is cheaper than oil-derived hydrocarbons, as in the case of Brazil. In that country, because of technical, environmental, and economic advantages, the use of ethanol by steam reforming process has been the most investigated process. The objective of this study is to show a thermodynamic analysis of steam reforming of ethanol, to determine the best thermodynamic conditions where the highest volumes of products are produced, making possible a higher production of energy, that is, a more efficient use of resources. To attain this objective, mass and energy balances were performed. Equilibrium constants and advance degrees were calculated to get the best thermodynamic conditions to attain higher reforming efficiency and, hence, higher electric efficiency, using the Nernst equation. The advance degree (according to Castellan1986, Fundamentos da Fisica/Quimica, Editora LTC, Rio de Janeiro, p. 529, in Portuguese) is a coefficient that indicates the evolution of a reaction, achieving a maximum value when all the reactants’ content is used of reforming increases when the operation temperature also increases and when the operation pressure decreases. However, at atmospheric pressure (1atm), the advance degree tends to stabilize in temperatures above 700°C; that is, the volume of supplemental production of reforming products is very small with respect to high use of energy resources necessary. The use of unused ethanol is also suggested for heating of reactants before reforming. The results show the behavior of MCFC. The current density, at the same tension, is higher at 700°C than other studied temperatures such as 600 and 650°C. This fact occurs due to smaller use of hydrogen at lower temperatures that varies between 46.8% and 58.9% in temperatures between 600 and 700°C. The higher calculated current density is 280mAcm2. The power density increases when the volume of ethanol to be used also increases due to higher production of hydrogen. The highest produced powers at 190mAcm2 are 99.8, 109.8, and 113.7mWcm2 for 873, 923, and 973K, respectively. The thermodynamic efficiency has the objective to show the connection among operational conditions and energetic factors, which are some parameters that describe a process of internal steam reforming of ethanol.

Copyright © 2008 by American Society of Mechanical Engineers
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Figure 1

Some internal steam reforming process configurations (Silveira , (2))

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Figure 2

Gibbs energy as function of temperature Souza (11)

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Figure 3

Advance degree of global reaction of steam reforming of ethanol as function of temperature

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Figure 4

Rates of hydrogen and carbon dioxide produced as function of temperature

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Figure 5

Rates of hydrogen produced and volume of ethanol unused as function of temperature

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Figure 6

Advance degree as function of pressure in five temperatures

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Figure 7

Tension as function of current density (Freni (9))

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Figure 8

Power density as function of fuel input (T=923K; P=1atm; Ri=0.75Ωcm2)

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Figure 9

Input flow of fuel (l/h) and product flow of reforming (l/h)

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Figure 10

Power density as function of current density of cell (Silveira , (2))

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Figure 11

Comparison with methane and ethanol as fuels for DIR-MCFC (Silveira , (2))



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