Behavior of Dolomites under Fluidized Bed Sorption-Enhanced Gasification Conditions

This work investigates the behavior of dolomites during sorption-enhanced gasification in dual interconnected fluidized bed systems for the production of H2-rich syngas. Two sorbents, one of Italian origin, the other of Polish origin, with CaO content ranging from 60 to 63 wt %, and MgO content around 32-33 wt %, were subjected to calcination/carbonation cycles (10 cycles for each test) in a lab-scale apparatus. In particular, the temperature of the fluidized bed carbonation stage was varied between 600 and 700 degrees C, both in the absence and in the presence of water vapor. With an eye to the role of the operating conditions, for each material, the following aspects were investigated: CO2 capture capacity, fragmentation tendency, and elutriation phenomena upon surface wear. The discussion was then extended by recalling previous results obtained on a set of 6 limestones (rich in Ca) under the same operating conditions through a comparison analysis between the behavior of dolomites versus limestones. In particular, it was observed that steam is capable of positively influencing the dolomite behavior in terms of CO2 capture; the elutriation rate is markedly more relevant upon calcination than carbonation, negatively affected by the presence of steam, and less extensive for sorbents showing higher CO2 capture. Normalizing the CO2 capture on the CaO content, the performance of dolomites is comparable to that of limestones, although dolomites have a more fragile structure that increases their tendency to undergo fluidized bed fragmentation.