Concept study on ATR and SR fuel processors for liquid hydrocarbons

Models for auxiliary power units (APU) based on-board hydrocarbon fuel processors (FP) for hydrogen production for polymer-electrolyte-membrane (PEM) fuel cells were coded in Matlab/Simulink software considering the following: (i) either an autothermal (ATR) or a steam reforming (SR) unit fed with several fuels (road distribution net fuels: gasoline, light diesel, heavy diesel, and biodiesel; reference fuels in internal combustion enginer (ICE) applications: isooctane for gasoline and cetane for diesel oils); (ii) the secondary units for the CO cleanup process (water gas shift and CO preferential oxidation reactors: WGS and COPROX); (iii) the auxiliary units for the balance of plant of the whole system (afterburner, heat exchangers, water recovery radiators, air compressor, and water and fuel pumps), necessary to properly operate the FP; and (iv) the PEM fuel cell. First, a study on the feasibility of the substitution during the simulations of the real liquid fuels available for automotive traction (mixtures of various organic compounds) with their reference fuel counterparts (pure substances normally used as references for ICE applications) enlightened that isooctane and cetane are not satisfactory substitutes of gasoline and diesel oils, respectively. Then, beyond the prevalent goal of comparing the ATR and the SR options, particular attention was paid to the models as design tools for the optimization of the FP scheme to obtain the highest possible energy conversion efficiency within the constraints imposed by, e.g., catalyst and materials durability and self-sustainability of the system as concerns energy and water balances. From the simulation results, gasoline emerges as the most effective fuel, whereas the highest performance, in terms of efficiency, seems to belong to the SR APU system (efficiency up to 39%), which is, though, characterized by a plant complexity higher than that of its ATR counterpart (efficiency slightly exceeding 36%).