(562h) Techno-Economic Assessment of Membrane Reactor Technologies for Pure Hydrogen Production for Fuel Cell Vehicle Fleets

In the context of a desirable ‘carbon neutral’ energy economy, among the most promising solutions for replacing today’s GHG emitting vehicles is the use of hydrogen as an energy carrier. In the pathway towards a future infrastructure based on renewable energy sources, a medium term step would rely on the use of fossil fuels for on-site production of hydrogen, feeding small fleets of fuel cell vehicles. Great interest is on natural gas as a primary source due to its high hydrogen to carbon ratio. State of the art technology for the production of hydrogen from natural gas include a series of reacting steps typically involving steam reforming (above 800°C), a water gas shift reactor and final purification of hydrogen through pressure swing adsorption (PSA). An alternative that has been subject of growing interest is the use of thin (2-50 micron thick) Pd-alloy materials as hydrogen perm-selective membranes for the embedded extraction of pure hydrogen from the chemical reactor; this system is usually known as ‘membrane reactor’.
Within a membrane reactor, the continuous extraction of hydrogen from the reacting mixture shifts the equilibrium conversion of reactants towards higher values, hence production of hydrogen can go beyond the equilibrium limit of traditional reactors. The process intensification obtained with the use of membrane reactors reduces the number of components and eliminates the need for batch operating PSA filters, besides allowing a more compact system.
This paper studies the adoption of palladium based membrane reactor technologies for pure hydrogen production from natural gas. In particular, three system layouts are analysed and compared to the traditional option: (i) autothermal reforming membrane reactor, (ii) steam reforming membrane reactor (externally heated) and (iii) water gas shift membrane reactor downstream of a steam reformer. The comparison is made in terms of performances and techno-economic considerations for the design of compact systems for on-site production of hydrogen at filling stations. The systems are designed for 50 Nm3/h of hydrogen, which corresponds to refilling 25 vehicles a day with 4 kg of hydrogen (approximately 420 km driving range on fuel cell vehicles with 70 MPa storage tank).