Abstract
Hydrogen, as an energy carrier, can take the main role in the transition to a new energy model based on renewable sources. However, its application in the transport sector is limited by its difficult storage and the lack of infrastructure for its distribution. On-board H2 production is proposed as a possible solution to these problems, especially in the case of considering renewable feedstocks such as bio-ethanol or bio-methane. This work addresses a first approach for analyzing the viability of these alternatives by using Pd-membrane reactors in polymer electrolyte membrane fuel cell (PEM-FC) vehicles. It has been demonstrated that the use of Pd-based membrane reactors enhances hydrogen productivity and provides enough pure hydrogen to feed the PEM-FC requirements in one single step. Both alternatives seem to be feasible, although the methane-based on-board hydrogen production offers some additional advantages. For this case, it is possible to generate 1.82 kmol h−1 of pure H2 to feed the PEM-FC while minimizing the CO2 emissions to 71 g CO2/100 km. This value would be under the future emissions limits proposed by the European Union (EU) for year 2020. In this case, the operating conditions of the on-board reformer are T = 650 °C, Pret = 10 bar and H2O/CH4 = 2.25, requiring 1 kg of catalyst load and a membrane area of 1.76 m2.
Highlights
The current energy model, mainly based on fossil fuels, presents two main drawbacks (i) limitation of reservoirs, which are getting scarcer and, increasing the price; and (ii) generation of CO2 emissions during their combustion, definitively contributing to global warming [1]
In the case of ethanol steam reforming, previous studies found a decrease of H2 yield in a traditional fixed-bed reactor due to the production of methane, which cannot be converted into hydrogen at high pressures as the reaction is shifted towards the reactants, to Le Châtelier’s principle [39]
This work addressed a first approach for analyzing the viability of H2 on-board production by membrane reactors in polymer electrolyte membrane fuel cells (PEM-FC) vehicles via mathematical modelling with Aspen-Plus® v
Summary
The current energy model, mainly based on fossil fuels, presents two main drawbacks (i) limitation of reservoirs, which are getting scarcer and, increasing the price; and (ii) generation of CO2 emissions during their combustion, definitively contributing to global warming [1]. Development of on-board hydrogen production systems would be a great solution to overcome these limitations, generating the H2 just inside the vehicle from other compounds and, minimizing its difficult storage and transport [7] This application needs to be carefully addressed, especially in terms of dimensions and weight of the on-board H2 production unit due to the space restrictions in an average vehicle and optimization of power requirements. Requirements of H2 purity are especially important as the PEM-FC (widely proposed for H2-vehicles) can be poisoned with trace amounts of CO [16], and available space inside a typical vehicle for a purification unit is very limited In this context, the use of membrane reactors, which combine both chemical reaction and separation steps in a single device, appears as a very attractive alternative for efficient process intensification [17,18]. Some considerations about energy integration, economy, and environmental impact were addressed
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