Combined power and hydrogen from a LPG reforming system based on membrane reactors technology

The environmental issues, due to the global warming caused by the rising concentration of greenhouse gases in the atmosphere, require new strategies aimed to increase power plants efficiencies and to reduce CO2 emissions. Therefore, the introduction of hydrogen as an energy carrier complementary to electricity can play an important and increasing role in the energy systems. Hydrogen can be produced from different feedstocks, such as natural gas, coal or oil derived products. Liquid Petroleum Gas (LPG) is a fuel which has a high potential as hydrogen carrier due to its easy storage and existing infrastructure, its safety and non-toxicity, and its easy decomposition with water, producing a syngas rich in hydrogen. Recent studies have demonstrated the energy suitability of novel systems for co-generation of hydrogen and electricity, the so-called CPH (combined power and hydrogen) systems. These systems are designed to co-generate electrical power already within the fuel processing island by a steam power section in which the losses due to the steam condensation are reduced because the steam needed for the fuel processing island is bled, at the operating pressure, from the expansion line. This paper focuses on the performance analysis of a CPH system based on authothermal reforming of LPG obtained by using membrane reactors technology. With respect to a conventional configuration consisting of a reactor unit in series with a separation unit, the membrane reactor represents a modern configuration in which an integrated reaction/separation unit has many potential advantages, such as the capital costs reduction, the system simplification and the improvement of hydrogen yield. In order to evaluate the CPH system performance, a sensitivity analysis is carried out by varying the critical operating parameters such as the steam to carbon ratio at the reforming reactor and the reforming pressure. Therefore, the performance of the CPH plants have been evaluated and the plant configurations have been compared by using new parameters, the marginal and apparent efficiencies. Results show that in comparison with the ATRHP reference plant (the system designed to maximize the hydrogen production with the minimum power consumption), the CPH systems present, obviously, lower hydrogen efficiencies (about 80.3 vs. 81.8%), but electrical power is generated with efficiencies higher than both the conversion efficiency of hydrogen in a fuel cell system (for CPH,30 the apparent efficiency, referred to the HHV of hydrogen, is greater than 71%) and the conversion efficiency of a gas turbine combined cycle (for CPH,30 the marginal efficiency, referred to the HHV of LPG, is greater than 58%).