Novel H2 manufacturing routes. Simulation and thermodynamic analysis of membrane based processes

Nowadays hydrogen is gaining more and more attention mainly because it is generally regarded as an important future fuel. Although H2 can be produced from a wide variety of resources using a range of different technologies, natural gas is generally preferred and will remain in the near future the major feedstock for the manufacture of H2. Catalytic partial oxidation (CPO) is seen as a key technology for the conversion of methane in H2. The H2 produced by the conventional CPO process is mixed with other gases. For this fuel gas mixture rich in H2, the fuel cell does not convert at least 15% of the H2 that has been fed into it. Membrane reactors can be used to produce pure H2, and then the utilization of the hydrogen produced can be enhanced, in the mean time, the process can be simplified. The membrane reactors which have been studied, include the O2-membrane CPO reactor, the H2-membrane CPO reactor, the two-membrane CPO reactor (a CPO reactor with O2 and H2 permeable membrane), and the H2-membrane water-gas-shift (WGS) reactor. Three integrated processes around these membrane reactors are proposed and compared with the conventional CPO process based on the results of a thermodynamic analysis. For performing a thermodynamic analysis, a wide range of data is required. To fulfil the data requirement, the simulation has to be accomplished, especially for the CPO and WGS reactors, without and with membranes. The simulation work is based on the kinetics of the reaction and membrane permeation mechanisms. With the simulation models the profiles of temperature and molar fraction of different species along the reactor' s axial coordinate have been simulated. The validity of the simulation work has been confirmed by the comparison of simulation results with the experimental data. Because of the key role played by the CPO reactors in each corresponding integrated processes, the production rates of useful products by different CPO reactors have been simulated and compared. The effect of each adjustable inlet condition on the output of the CPO reactors has been shown and discussed. On the basis of the simulation work and the knowledge of the characteristics of the conventional CPO reactor and the membrane CPO reactors, the thermodynamic analysis of the integrated conventional and membrane CPO methane conversion processes has been carried out. The results have been used to design and optimise the processes around each CPO reactor. The most efficient process has been identified. The resulting exergy balance for each process has been used to determine where and to what extent the exergy, that part of the energy contained that is available for useful work (such as electricity from a fuel cell), is dissipated. Also on the basis of the simulation work, the thermodynamic analysis of an integrated H2 production process with a fixed-geometry H2-membrane reactor has been described. The effect of different inlet conditions on the overall exergy efficiency of the process has been shown and discussed. The simulation and thermodynamic analysis have provided a quantitative tool to get insight into and to understand the various hydrogen production processes.Aerospace Engineerin