Distributed Reforming of Diesel, JP-8, and Other Heavy Hydrocarbon Fuels for Fuel Cell Applications: Challenges and Issues

Reforming diesel, JP-8 (Jet Propellant 8 – standard U.S. military kerosene-based jet fuel), and other heavy hydrocarbon fuels is one option being investigated for providing H₂ for distributed mobile and stationary fuel cell systems for military and civilian applications. Unlike natural gas, which is another hydrocarbon fuel being investigated, these fuels are high-boiling-point, multi-component liquids that contain high concentrations of refractory sulfur and aromatic compounds that can negatively impact the efficiency and operating lifetime of the fuel processor. Fuel injection, desulfurization, and carbon deposition are major issues that fuel processor developers must address when designing fuel processors for these fuels. The fuel injection system must prevent direct injection of liquid onto the catalyst surface and poor mixing of the fuel and oxidants (i.e., air and/or steam), both of which can result in excessively high temperatures that can damage or destroy the reforming catalyst. A highly efficient desulfurization process is required that can reduce the sulfur concentration to acceptable levels for both fuel processor and fuel cell catalysts without requiring large amounts of materials or complicated processes, and without generating excessive amounts of disposable waste. Highly active reforming catalysts and the proper choice of operating conditions (i.e., ratio of fuel to oxidant[s], temperature, residence time) are required for effective reforming of aromatic compounds to prevent carbon deposition on the reforming catalyst as well as in the fuel processor downstream of the reformer. In this paper, we will discuss how the chemical and physical properties of these fuels influence the design of the fuel processor focusing on the fuel injection system, the choice of desulfurization process, and the design and operation of the reformer. We will also discuss various approaches and design options for developing highly efficient fuel processors for reforming these fuels for both polymer electrolyte and solid oxide fuel cells.