(157a) Fuel Processing of Logistic Fuels for SOFC-Based APU Systems

This work describes the processing of logistic fuels (e.g.. JP-8/kerosene, DF-2/Diesel), for 1-10 kWe solid oxide fuel cell (SOFC) based auxiliary power units (APU). The fuel processing system consists of a desulfurizer, a catalytic reformer and a burner.

      The sulfur content in JP-8, for instance, can be as high as 3000 ppm by weight (ppmw). In SOFC systems, effective desulfurization is essential for the performance of downstream catalytic reformer and stack(s). The system described herein uses a dual bed regenerable desulfurizer, developed by Aspen Products Group, Inc., to reduce the sulfur level in the inflowing liquid fuel from levels as high as 3000 ppmw to a level of less than 15 ppmw. The absorbents utilized in the desulfurization process are fully regenerable in situ during system operation. The desulfurizer consists of two absorbent beds, with one working in desulfurization mode while the other one working in regeneration mode. The system operates fully automated as it cycles between regeneration and desulfurization modes in order to maintain a constant flow of desulfurized fuel to the reformer. In this presentation, the effect of operating conditions on sulfur removal efficiency and fuel loss of the desulfurizer will be discussed. The general control strategy of the desulfurizer, especially during bed switching, and some testing results will be presented. 

      The desulfurized fuel is fed to an autothermal reformer (ATR) where it reacts with air and steam to generate CO and H₂ for the SOFC stack.  A portion of the anode exhaust stream is recycled to the reformer to provide the steam required for the reformer. The reformer performance was evaluated using desulfurized fuel, air and a simulated anode recycle stream. The reforming efficiency decreases with increasing oxygen to carbon (O₂/C) ratio. The effect of steam to carbon (S/C) ratio is more complicated as the reformer efficiency initially increases with increasing S/C ratio and then decreases after S/C reaches 2.0. The optimum operating condition of the reformer is also determined by the formation of the olefins. The olefin products in reformate are detrimental to stack performance due to coke formation, whose formation under different operating conditions will be discussed. The reforming efficiency and pressure drop tradeoffs with different pore size ceramic foam catalysts will also be presented.

      This work was supported by the U.S. Army’s Tank Automotive Research Development and Engineering Center (TARDEC) with Program Managers Jeff Ratowski and Kevin Centeck.  This support is gratefully acknowledged.