Co-production of hydrogen, electricity and CO2 from coal with commercially ready technology.: PartA:: Performance and emissions

This two-part paper investigates performances, costs and prospects of using commercially ready technology to convert coal to H-2 and electricity, with CO2 capture and storage. Part A focuses on plant configuration and the evaluation of performances and CO2 emissions. Part B focuses on economics, establishing benchmarks for the assessment of novel technologies and guidelines for technological development. In the co-production plants considered in the paper, coal is gasified to synthesis gas in an entrained flow gasifier. The syngas is cooled, cleaned of particulate matter, and shifted (to primarily H-2 and CO2) in sour water-gas shift reactors. After further cooling, H2S is removed from the syngas using a physical solvent (Selexol); CO2 is then removed from the syngas, again using Selexol; after being stripped from the solvent, the CO2 is dried and compressed to 150 bar for pipeline transport and underground storage. High purity H-2 (99-999%) is extracted from the H-2-rich syngas via a pressure swing adsorption (PSA) unit and delivered at 60 bar. The PSA purge gas is compressed and burned in a conventional gas turbine combined cycle, generating co-product electricity. The H-2/electricity ratio can be varied by lowering the steam-to-carbon ratio in the syngas or by letting part of the de-carbonized syngas by-pass the PSA unit. Performances and emissions of H-2/electricity co-production with CO2 capture are compared with those of a system that vents the CO2. We examine different methods of syngas heat recovery (quench versus radiant cooling) and explore the effects of changing the electricity/H-2 ratio, gasifier pressure and hydrogen purity. Results show that state-of-the-art commercial technology allows transferring to de-carbonized hydrogen 57-58% of coal LHV, while exporting to the grid decarbonized electricity amounting to 2-6% of coal LHV. In contrast to decarbonizing coal IGCC electricity, which entails a loss of 6-8 percentage points of electricity conversion when capturing CO2 as an alternative to venting it, CO2 capture for H-2 production gives a minor energy penalty (similar to 2 percentage points of export electricity). For H2 production, the efficiency gain achievable by hot syngas cooling vs. quench is a modest 2 percentage point increase in electricity for export, compared to 2-4 percentage points in the electricity case. Reducing H-2 purity or increasing gasification pressure has minor effects on performance. (c) 2004 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.