Application of the calcium looping cycle to CO2 mitigation in the cement process

Abstract

The Ca-looping cycle is a novel means of capturing CO2 from an industrial or power flue gas. It has an inherent synergy with cement production in that a by-product is predominantly CaO, which forms nearly 70 % of the material feed to a cement works. However, integration of the two processes will inevitably lead to a decrease in the thermal efficiency of producing 1 kg of clinker due to the energy penalty of the Ca-loop calciner. Furthermore, experimental studies are required to determine whether any change in the trace element inventory of the sorbent takes place due to cycling between calcination and carbonation conditions, and whether such changes impact on the phase composition or mechanical properties of the subsequent cement produced. For the flow-sheeting part of this investigation, the thermal efficiency of producing 1 kg clinker when integrated with Ca-looping was found to increase by between 0.15 and 1.49 MJ depending on the configuration. For the experimental part of this investigation, it was found that cycling in the absence of fuel did not lead to a change in trace element content of the sorbent. However, in the presence of fuel combustion, the trace element inventory of the sorbent was seen to increase. Al increased for all three fuels indicating that ash from the fuel was mixing with the sorbent during the calcination step. Cycling in the presence of Lea Hall coal led to an increase in B and Na, whilst cycling in the presence of refuse-derived-fuel led to an increase in Cu, Na and Ti. The production of cement from cycled sorbent indicated that cycling in the absence of fuel did not lead to a change in phase composition. This was also the case for cements produced from sorbent cycled in the presence of continuously fed La Jagua and Lea Hall coals. However, a slight increase in the % wt. alite was observed for cements produced from sorbent exposed to batch-fed La Jagua. Lastly, after undergoing performance tests it was found that there was a general downward trend in the strength of the cement mortars produced with increasing cycle number. Setting times were within the range set out in the British and American Standards.