Lab-scale tests of different materials for the selection of suitable sorbents for CO_2 capture with H_2 production in IGCC processes

摘要

In this work two different types of materials, potassium carbonate promoted hydrotalcites and natural dolomites, have been investigated at laboratory scale to select the most promising sorbent to be used in a water gas shift membrane reactor (WGSMR). Sorbents were prepared by calcination in the temperature range of 500-800 ℃. Two experimental campaigns were carried out, the first one in a thermobal-ance under dynamic conditions (cooling down in a CO_2/N_2 stream) and the second one in a fixed bed reactor under isothermal conditions at 300 ℃. The influence of the preparation method, system pressure and water content in the feed gas on the performance of the sorbents has been investigated and the results obtained are described in this paper. As expected, K-doped hydrotalcite-based sorbents provided higher CO_2 capture capacities than natural dolomites, which were found to require a deeper study to optimise their performance. For hydrotalcites, steam partial pressures, Mg/Al ratio and calcination temperature were found to play a crucial role in their CO_2 capture capacities. Material Mg61-K_2CO_3 calcined at 600 ℃ provided an initial CO_2 capture capacity of 9 mol/kg at P_(CO2) = 0.34 bar and P_(H2O) = 4.55 bar so this material was pre-selected to be used in the WGSMR system. Under those operating conditions formation of MgCO_3 is suspected to occur so detailed studies are being carried out to confirm this hypothesis. The efficiency of thermal regeneration and depressurisation as regeneration method was explored at 1 bar and 5 bar in four sorption-desorption cycles and the combination of both approaches was found to provide the best results. Cycling behaviour and optimisation of the regeneration conditions are being carried out before going to the membrane reactor.