Internal Reforming for Molten Carbonate Fuel Cells

Abstract

Molten carbonate fuel cell systems can be operated with pure hydrogen or carbonaceous fuel gases, like natural gas. The use of natural gas is of advantage because of the present, widespread distribution network installed by the gas industry. The MCFC is not able to consume the methane directly, because the electrochemical reaction taking place at the anode needs hydrogen. There are various concepts for reforming in work and they can be devided into external, integrated and internal. The most promising are integrated and internal reformers, because they use the waste heat of the fuel cells for the endothermic reforming reaction. Thus, the efficiency of the system can be increased from about 50% to about 65%. Besides of the reforming concepts the paper will handle the thermodynamic background and experimental results achieved in our laboratory.

Nickel catalysts for internal reforming in molten carbonate fuel cells

“…,ot r= k[CH4] where k= In (1,2) m where k is the reaction rate constant (m 3 g~al S-I), [CH4] is the methane concentration (mol m-3), oL is the methane conversion, ~bto t is the total gas flow rate at reactor conditions (m 3 s-~), and m is the weight of catalyst (g). Values of the rate coefficients above about 200.10 .6 m 3 g~l s-I could not be measured accurately because they were calculated from methane conversions greater than 93% under which conditions there was significant limitation for diffusion and heat transport.…”

“…1. Internal reforming has attracted considerable attention because it offers several extra advantages in comparison with external reforming: (i) the all-over efficiency of the fuel cell increases due to the consumption of the heat evolved in the cell reaction by the endothermic reforming reaction; this heat consumption is about half of the heat production caused by the current flowing through the internal resistances and by the reversible energy losses in the MCFC [2]; (ii) the water required for the steam-reforming reaction is partially provided by the fuel cell reaction; (iii) there is a more evenly distributed supply of hydrogen over the anode compartment; and (iv) the equilibrium conversion in the steam-reforming reaction (Eq. (1)) is further to the right due to the in situ consumption of hydrogen.…”