Development of the self-sustaining integrated diesel fuel processor for hydrogen production and solid oxide fuel cell operation

Abstract

This thesis discusses about hydrogen production using diesel fuel for solid oxide fuel cell (SOFC) operation. Among the several fuel cell types, SOFCs have several merits due to the high operating temperatures, such as high system efficiency and fuel flexibility. Fuel flexibility, which is one in strong points of SOFCs, is essential in the application of the fuel cell system. The operation of the SOFCs does not rely on pure hydrogen as a fuel, but may also use carbon monoxide and light hydrocarbons. The attraction of diesel fuels is due to the fuel flexibility of SOFCs. Among the hydrocarbon fuels, diesel has the highest hydrogen density, so the use of diesel reformate has advantages for SOFC applications. Although these advantages of diesel fueled SOFC system, diesel reforming has several issues. Aromatics and olefins in diesel easily induce the carbon deposition on the reforming catalyst, and aromatics and sulfur compounds hinder the activity of catalyst. Hence long-term operation of diesel reformer is not easy. Moreover, diesel reformate still contains light hydrocarbons (over C1-hydrocarbons) and sulfur compounds (almost $H_2S$). Light hydrocarbons (over C1-hydrocarbons), especially ethylene, induce the carbon deposition on the SOFC anode, and cause catastrophic degradation of SOFC. $H_2S$ in reformate also causes the performance degradation of SOFC. In this thesis, it is found that ethylene is clearly associated with carbon deposition. Not only $O_2/C$, $H_2O/C$ of diesel autothermal reforming (ATR) reaction conditions but also fuel delivery methodology is closely related to the ethylene-induced carbon deposition in diesel reforming. Hence, reaction conditions of ATR are revealed for suppression of both ethylene formation and carbon deposition with fuel atomization using injector. The condition of $O_2$/C = 0.8, $H_2O/C$ = 3 is established for stable operation of diesel ATR, and long-term operation of ATR is successfully tested for 2,500 hours with fuel in...