(554d) Process Design of a Coal-Based Hydrogen Plant with CO2 Capture and Its Improvement
AIChE Annual Meeting
Wednesday, November 19, 2014 - 4:30pm to 4:55pm
In this study it was aimed to design and evaluate a Coal-to-H2 process for producing an ultrapure hydrogen (99.99+ vol.%) from a synthesis gas originating from a dry coal-fed gasification where a dual-stage Selexol unit was included for recovering CO2 as well as H2S.
Since the operation of a carbon capture unit gives rise to a significant energy penalty, it is essential to estimate the thermal and electrical energy consumption involved in capturing CO2 accurately. A flow sheeting simulation of the dual-stage Selexol process was constructed using Honeywell UniSim and its operating conditions were found given the two carbon capture targets of 90% and 95%. In addition it was elucidated why the two solvent cycles for capturing CO2 and H2S should be integrated in designing the dual-stage Selexol unit by showing how much energy the integrated dual-stage Selexol unit could save in comparison to the unintegrated equivalent.
An in-house dynamic multi-column (up to 12 beds) Pressure Swing Adsorption (PSA) simulator was utilised in simulating the H2 PSA unit for producing ultrapure hydrogen from the shifted syngas. The number of the adsorption columns required to maximise the H2 recovery was found under the condition to meet the H2 product purity target. The H2 recovery of the H2 PSA in the Coal-to-H2 process with carbon capture can be substantially higher than what would be expected of the H2 PSA in conventional natural gas-fed H2 plants without carbon capture.
Finally, the Coal-to-H2 process with carbon capture has been improved by more efficient use of the H2 PSA tail gas. The process improvements can increase the yield of the ultrapure hydrogen product and reduce the energy penalty involved in carbon capture at the same time.