Zero-Emission Carbon Concept (ZECA): Equipment Commissioning and Extents of the Reaction with Hydrogen and Steam

摘要

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. The first step involves reacting coal in a steam-hydrogen mixture to form primarily CH_4. The product gas is then steam-reformed and shifted to maximize the H_2 content. CO_2 is removed by the carbonation of CaO, to give a nearly pure stream of H_2. The CaCO_3 is calcined in a separate reactor to release the CO_2 stream for storage. This paper outlines initial results from experiments simulating the carbon-hydrogen and carbon-steam reactions taking place in the gasifier. Experiments were carried out under inert gas (pyrolysis) and under reactive gas atmospheres. Extents of the reaction were calculated by subtracting the weight loss during pyrolysis from conversions in a reactive atmosphere under otherwise the same experimental conditions. Therefore, data presented in this way show the impact on the level of conversion caused by the presence of H_2. It has not been possible to directly measure the amount of CH4 formed with this type of reactor. Initial results have shown that under 7 MPa of pure hydrogen, at temperatures between 750 and 1050 ℃, and with a 10 s hold time, between 15 and 25% (w/w, daf) of Daw Mill coal (U.K.) reacted with H_2. Rates of the reaction were rapid during the pyrolytic stage, the first few seconds of the test, but then rapidly declined to low values. Preliminary tests have been performed to assess the impact of the reaction with steam under the ZECA conditions. The data indicate extents of the reaction that are greater than those achieved in H_2 alone, so that, when the two reactants are present together, moderate to high overall conversions were achieved with the bituminous coal.