Highly efficient and compact natural gas fuel processor for 5-50 kW class PEMFCs

U. Jung, K.Y. Koo
Korea Institute of Energy Research,
Korea

Keywords: fuel processor, reforming efficiency, hydrogen production, PEMFC

Summary:

Fuel processor for supplying the hydrogen rich gas to fuel cell stack is looked on as a miniaturized chemical plant whose unit processes consist of desulfurization, steam methane reforming (SMR), water gas shift (WGS), and preferential oxidation (PrOX). A highly efficient fuel processor, along with fuel cell stack, is a key component of the PEMFC system. Especially, PEMFC system requires a highly efficient and compact fuel processor due to space restriction for installation and to achieve high electrical efficiency. KIER fuel processor satisfies these prerequisites to achieve high thermal efficiency and compact fuel processor volume through optimized thermal network and compact structural engineering design. 5kW class fuel processor is successfully scaled up to 10, 20 and 50kW class fuel processors. Heat transfer area, linear gas velocity, degree of mixing and distribution of reactants, etc are considered for main design parameters for the scale-up design of 10-50kW class fuel processors. In particular, more stable catalytic layer temperature control was possible by separating and modularizing high temperature (SMR) and low temperature (WGS, PrOX) reaction parts of the fuel processor. The modular fuel processor consists of three catalytic reaction parts including SR, WGS, and PrOx, and the optimal operating temperature control of each catalytic layer is possible by optimizing the heat exchange network using the reactant water as a refrigerant. Furthermore, maintenance is advantageous by replacing the module in case of catalyst damage. From the experimental results of designed KIER 5kW class fuel processor, very high thermal efficiency of 81% on a LHV basis was achieved through the effective heat exchange network between heat source (combustion heat from flue gas, exothermic reaction heat of WGS and preferential oxidation) and sink (endothermic heat of SMR, visible and latent heat of water, visible heat of natural gas). Such thermal network configuration reveals the temperature of both the reformed gas and the flue gas at the exit of the fuel processor lower than 100oC. In case of compactness, integration of unit processes composing fuel processor and arrangement of catalyst layers are very important factors. Through the optimized structural design, the volume of fuel processor can be reduced to 10L/kW with insulation. It is also confirmed that water and natural gas as feed are well mixed and feed mixture is uniformly distributed to the catalyst layer. Moreover, a quick start-up time of less than 45 min was achieved with the use of an auxiliary electric heater. The application of highly efficient KIER fuel processor promises to improve the FC efficiency and secure maneuverability. In addition, KIER continuous to develop low-cost and durable fuel processor by simplifying and modularizing its structure based on accumulated fuel reformer design know-how.