The Zero Emission Carbon Concept (ZECA): Extents of Reaction with Different Coals in Steam/Hydrogen, Tar Formation and Residual Char Reactivity

Abstract

A high pressure wire mesh reactor has been modified to investigate the reactions underlying the zero emission carbon concept (ZECA) process. This is a novel power generation concept that involves producing hydrogen from coal. An earlier paper has described the concept, the wire mesh reactor used for laboratory scale tests, and results of tests with H2 and He. In this paper, results of tests with a range of coals are described, together with tar emission and char reactivity measurements. The tests with a range of coals (from lignite through to bituminous have shown that the performances of the different fuels do vary widely, but not as a direct function of their rank. With lignites, high conversions were achieved in a H2/steam mixture. Lower conversions were apparent with the other coals. However, reaction conditions were not optimized to achieve the highest conversion level. Pittsburgh No. 8 coal (high volatile bituminous) was also found to be reactive, whereas Wyodak (sub-bituminous) and Daw Mill (bituminous) coals had a similar reactivity to each other, but lower than the other fuels tested. The amount of primary tar was measured, by collection in a cooled trap, immediately above the wire mesh. This is material formed during the release of the volatiles with only a limited time for further reaction. Slightly higher quantities of tar were measured during tests with H2 than with He. Residual char reactivities declined with increasing temperature and hold time at peak temperature, although steam did appear to have an activation effect at low formation hold times.