Figure 1 is a simplified block flow diagram for a coal gasification-based hydrogen production plant using current, commercial technologies at tractable scales. It is one of the cases recently defined and analyzed by NETL in order to compare fossil fuel-based hydrogen production options, with particular attention to accurately estimating costs and performance efficiency along with careful quantification of global warming potentials of hydrogen production systems.
The plant in question uses Air Products (formerly Shell)-type dry feed pressurized entrained flow, oxygen-blown slagging gasifiers fed with bituminous coal. Because the coal reacts with oxygen (supplied by a conventional cryogenic air separation plant) and steam at a temperature of 1,427 °C (2,600 °F) in the gasifier to produce principally hydrogen and CO with little CO2 formed, this type of gasifier is a logical choice for a dedicated hydrogen production system/plant. Syngas cooling, water quench, and particulate collection via cyclone and filters ensue with further cooling to generate process steam and to prepare the syngas for scrubbing removal of chloride and ammonia. The scrubbed syngas then goes through a sour water gas shift reactor to maximize hydrogen yield by reacting carbon monoxide in the syngas with steam. The syngas from sour shift is then cooled further before mercury removal, and followed by hydrogen sulfide (H2S) removal in a single-stage acid gas removal (AGR) unit, in this case utilizing MDEA solvent. Desulfurized syngas from the AGR is routed through the pressure swing absorption (PSA) unit to recover a 99.9% pure H2 product. Residual gases from the PSA have significant fuel value and are combusted in a boiler to generate steam for auxiliary power generation in a steam turbine. Acid gas from the AGR unit is sent to the sulfur recovery unit (SRU) to recover sulfur as a byproduct.
Figure 1: Block flow diagram, hydrogen production gasification plant without CO2 capture1