Studies On A Plate-fin Reformer For Methanol Steam Reforming In Fuel Cell Systems

This paper is to develop the fuel processing system with high energy density. Thefocus is on small on-site hydrogen generation system and on-board hydrogengeneration system for the proton exchange membrane fuel cell (PEMFC).The methanol steam reforming system, which is adopted in the reformer, has beenthermodynamically analyzed and calculated. A compact plate-fin reactor (PFR)consisting of closely spaced plate-fins, in which endothermic and exothermicreactions take place in alternate chambers, has been studied. In the PFR, which wasbased on a plate-fin heat exchanger, catalytic combustion of the reforming gas, as asimulation of the fuel cell anode off gas (AOG), supplied the necessary heat for thereforming reaction. One reforming chamber, which was for hydrogen production,was integrated with two vaporization chambers and two combustion chambers toconstitute a single unit of PFR. The PFR is very compact, easy to be placed on boardand to scale up. The effect of the ratio of water/methanol on the performance of thePFR has been investigated, and temperature distributions in different chambers werestudied. Besides, the stationary behavior of the plate-fin reactor was also investigated.Heat transfer of the reactor was enhanced by internal plate-fins as well as by externalcatalytic combustion, which offer both high methanol conversion ratio and low COconcentration.A model describing the reaction process in the PFR was derived using athree-dimensional numerical model for crossflow arrangement. Temperaturedistributions in different chambers and composition distributions in reformingchamber have been caculated, and the effect of the ratio of water/methanol on theperformance of the PFR has also been calculated. Theoretical predictions of thetemperature distributions in the PFR were in good agreement with experimentalvalues. In addition, the numerical model was able to accurately predict the methanolconversion and the reformate composition in reforming chamber. The numericalmodel was also used to describe the effect of configuration parameter on methanolreforming in PFR. The computational results indicate that the combined flowarrangement, which include crossflow, coflow and counterflow, should be adopted inpractical reactor design. The material with higher thermal conductivity should beselected preferentially. In order to minimize the heat transport resistance, small finspace and height should be applied in the reactor design. Based on the PFR, a scale-up reactor was designed and operated continuously for1000 hours, with high methanol conversion ratio and low CO concentration. Acompact integrated fuel processing system consisting of a 5kW PFR and multi-stagepreferential oxidation reactor is designed in this paper. Both internal plate-fins andexternal catalytic combustion were used to enhance heat transfer of the reformer,which offer both high methanol conversion ratio and low CO concentration. So thatthe water–gas shift reactor, which provides primary CO cleanup, is not necessary inthis fuel processing system. It will result in simplification of the fuel processingsystem design and capital cost reduction. The performance of the main componentsin the fuel processing system has been investigated. The axial temperatures of thedifferent chamber in 5kW PFR were uniform, and the temperatures at the inlet andoutlet of the PROX reactors were controlled strictly by plate-fin exchangers so that itcan minimize parasitic hydrogen oxidation. In addition, the results indicated that thisfuel processing system can provide a high concentration of hydrogen and the systemefficiency is always kept above 75%. It is further demonstrated that the fuelprocessing system could be operated autothermally and exhibited good test stability.