Abstract
The integration of mixed ionic electronic conducting (MIEC) membranes for air separation in a small-to-medium scale unit for H2 production (in the range of 650–850 Nm3/h) via auto-thermal reforming of methane has been investigated in the present study. Membranes based on mixed ionic electronic conducting oxides such as Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) give sufficiently high oxygen fluxes at temperatures above 800 °C with high purity (higher than 99%). Experimental results of membrane permeation tests are presented and used for the reactor design with a detailed reactor model. The assessment of the H2 plant has been carried out for different operating conditions and reactor geometry and an energy analysis has been carried out with the flowsheeting software Aspen Plus, including also the turbomachines required for a proper thermal integration. A micro-gas turbine is integrated in the system in order to supply part of the electricity required in the system. The analysis of the system shows that the reforming efficiency is in the range of 62%–70% in the case where the temperature at the auto-thermal reforming membrane reactor (ATR-MR) is equal to 900 °C. When the electric consumption and the thermal export are included the efficiency of the plant approaches 74%–78%. The design of the reactor has been carried out using a reactor model linked to the Aspen flowsheet and the results show that with a larger reactor volume the performance of the system can be improved, especially because of the reduced electric consumption. From this analysis it has been found that for a production of about 790 Nm3/h pure H2, a reactor with a diameter of 1 m and length of 1.8 m with about 1500 membranes of 2 cm diameter is required.
Highlights
Approximately 95% of all the hydrogen used is produced from fossil fuels as primary feedstock, where technologies such as natural gas reforming and coal gasification are applied at very large scale [1]
The detailed mass balance of the reference case is reported in Table 5 and it is referring to an auto-thermal reforming membrane reactor (ATR-MR) module operated at 10 bar, fuel fed at 650 °C after pre-reforming using a mixture of methane and H2O (S/C = 2.4) and air fed at 900 °C with an O2 concentration of 17.9% after the pre-burner
The amount of H2-rich syngas used in a pre-combustor to pre-heat air from 600 °C up to 900 °C is 8.9% of the total syngas produced, while the main stream is sent to the pressure swing adsorption (PSA) unit
Summary
Approximately 95% of all the hydrogen used is produced from fossil fuels as primary feedstock, where technologies such as natural gas reforming and coal gasification are applied at very large scale [1]. Auto-thermal reforming (ATR) combines both SMR and POX so that the heat required for the endothermic reaction is supplied by using a proper amount of oxidant and no external furnace and indirect heat exchangers are required, making the system more compact All these systems require water-gas-shift reactor(s) to enhance the H2 yield and some form of gas purification such as a pressure swing adsorption (PSA). H2 production using oxygen perm-selective membranes has been studied, amongst others by Gallucci et al [16,17] They proposed a multi-stage fluidized bed membrane reactor, where oxygen membranes are used to permeate O2 that reacts with methane and steam to form reformed syngas in the bottom part and where H2 selective membranes are used in the top part of the reactor to separate pure. The membrane flux, membrane dimension and scale-up is based on experimental results that have been obtained with permeation tests of a Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) membrane, which is shortly described first
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