High-purity H₂ production with CO₂ capture based on coal gasification

A novel hybrid concept is proposed, combining Pd-alloy membrane and low temperature separation technology, to produce pure H₂ from gasified coal and capture the main part of the generated CO₂. 75% of the H₂ produced from gasification and water-gas shift is separated from the shifted syngas through H₂-selective Pd-alloy membranes. After water removal, the H₂-depleted, CO₂-rich retentate stream is compressed and cooled, after which CO₂ is condensed out at a purity level of ∼99%. The “waste” volatiles from the low-temperature CO₂ separation constitute a low heating value syngas that is burnt in a gas turbine. The gas turbine with a steam bottoming cycle generates a surplus of electricity that could be employed for H₂ liquefaction. Altogether, the concept has the potential to be developed into a stand-alone high-purity H₂ production unit with CO₂ capture, suitable e.g. for remote areas from where H₂ and possibly also CO₂ must be transported by ship. However, the investigations of three different process alternatives, as well as three membrane separator parameters, illustrate that there are many degrees of freedom in the proposed concept that require further analysis, both individually and how they interact, in order to establish an optimized and purposeful stand-alone H₂ production concept.