Thermodynamic Analysis of Direct Steam Reforming of Ethanol in Molten Carbonate Fuel CellSource: Journal of Fuel Cell Science and Technology:;2008:;volume( 005 ):;issue: 002::page 21012DOI: 10.1115/1.2759509Publisher: The American Society of Mechanical Engineers (ASME)
Abstract: 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 1986, 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 280mA∕cm2. 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 190mA∕cm2 are 99.8, 109.8, and 113.7mW∕cm2 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.
keyword(s): Pressure , Temperature , Fuels , Equilibrium (Physics) , Ethanol , Hydrogen , Molten carbonate fuel cells , Steam reforming , Density , Fuel cells AND Current density ,
|
Collections
Show full item record
contributor author | José Luz Silveira | |
contributor author | Antonio Carlos de Souza | |
contributor author | Márcio Evaristo da Silva | |
date accessioned | 2017-05-09T00:28:44Z | |
date available | 2017-05-09T00:28:44Z | |
date copyright | May, 2008 | |
date issued | 2008 | |
identifier issn | 2381-6872 | |
identifier other | JFCSAU-28933#021012_1.pdf | |
identifier uri | http://yetl.yabesh.ir/yetl/handle/yetl/138364 | |
description abstract | 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 1986, 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 280mA∕cm2. 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 190mA∕cm2 are 99.8, 109.8, and 113.7mW∕cm2 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. | |
publisher | The American Society of Mechanical Engineers (ASME) | |
title | Thermodynamic Analysis of Direct Steam Reforming of Ethanol in Molten Carbonate Fuel Cell | |
type | Journal Paper | |
journal volume | 5 | |
journal issue | 2 | |
journal title | Journal of Fuel Cell Science and Technology | |
identifier doi | 10.1115/1.2759509 | |
journal fristpage | 21012 | |
identifier eissn | 2381-6910 | |
keywords | Pressure | |
keywords | Temperature | |
keywords | Fuels | |
keywords | Equilibrium (Physics) | |
keywords | Ethanol | |
keywords | Hydrogen | |
keywords | Molten carbonate fuel cells | |
keywords | Steam reforming | |
keywords | Density | |
keywords | Fuel cells AND Current density | |
tree | Journal of Fuel Cell Science and Technology:;2008:;volume( 005 ):;issue: 002 | |
contenttype | Fulltext |