Mass transfer resistance in membrane separators
Topic: MSc project
Mentor: Boon, J. (Jurriaan)
Education: Chemical Engineering, Applied Physics
Email/tel.: boon@ecn.nl / +31 224 56 4576
Unit/Group: Bee / SPT
Text:
Fossil fuels will continue to play a major role in the supply of energy for decades to come, and consequently CO2 capture and storage (CCS) will be necessary to reach greenhouse gas emission targets. Of all process steps involved in CCS, capture is by far the most expensive and the Energy research Centre of the Netherlands (ECN) has a strong R&D programme on pre-combustion CO2 capture. In pre-combustion capture, fossil fuels are converted to synthesis gas: mainly CO and H2. Water-gas shift (WGS) is then applied to increase both the CO2 and H2 contents of the syngas. H2 and CO2 are separated; the H2 is to be used for power production and the CO2 is available for underground storage. The high CO2/H2 partial pressures in precombustion processes create a strong driving force for carbon capture, allowing for relatively low associated energy consumption. Moreover, conventional processes for reaction and separation can be improved by application of H2 selective Pd-alloy membranes that are able to separate H2 from synthesis gas at elevated temperature (250-600°C) and pressure (30-40 bar). However, in a combined effort of bench-scale tests and modelling, it has been shown that mass transfer resistances significantly lower the overall transmembrane flux that can be achieved - particularly for state-of-the-art high-flux membranes.
Reliable scale-up of pilot scale membrane modules to industrial scale requires a thorough understanding of the mass transfer resistances involved. A 2D model of module hydrodynamics is being prepared, and will be validated with experimental data from ECN's bench-scale Process Development Unit (PDU). Reduction to a 1D model would allow for faster calculations, easy evaluation of the impact of module layout, and potentially incorporation in flowsheeting software. However, in order for a 1D model to give a proper description of the mass transfer resistances in the membrane module, there is a need for an improved Sh correlation for mass transfer, specifically accounting for the drift flux.
In the project, the student will develop, based on existing models, both 2D and 1D membrane module models. These are to be validated with membrane separation experiments performed on ECN's PDU. The models will allow for an evaluation of the dimensionless mass transfer coefficient Sh in relevant conditions. The goal is to develop a new Sh-correlation that is valid for membrane separators and allows construction of accurate 1D module models. Depending on the preference of the candidate and the nature of the work, part of the project may be done at ECN's research facility in Petten.
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