Investigation On The Utilization Of Alkaline Industrial Residues In CCUS Processes

The application of alkaline industrial residues to carbon capture, utilization andstorage (CCUS) is not only a novel method for the utilization of alkaline industrial residuesas resources, but also can help reduce the cost of CCUS technologies. Therefore, it isconsidered to be quite promising. However, little related work has been done. In this thesis,two typical alkaline residues, i.e. papermaking lime mud and coal fly ash, were investigatedunder typical CCUS conditions, i.e., Ca-looping for CO2capture and CO2mineralsequestration, respectively.The calcination and carbonation properties of a papermaking lime mud wereinvestigated in a TG reactor and compared with those of a natural limestone. Lime mudshows a faster decomposition rate than limestone, indicating a shorter calcination time anda more compact calciner are expected if lime mud is used instead of limestone. However,CaO derived from lime mud has a lower carbonation conversion ratio than that derivedfrom limestone. The poorer carbonation performance of CaO derived from lime mud maybe ascribed to the lower surface area caused by the enhanced sintering resulting from highNa, K impurities in lime mud. It’s suggested to remove the Na, K impurities of lime mudprior to carbonation to mitigate sintering.In the study of the utilization of coal fly ash in CO2mineral sequestration, an indirectcarbonation route is adopted where calcium is extracted selectively from coal fly ash priorto carbonation. In the calcium extraction process, recyclable ammonium salt (i.e.,NH4Cl/NH4NO3/CH3COONH4) solution was used as the calcium extraction agent.NH4Cl/NH4NO3/CH3COONH4were confirmed to be effective calcium extraction agents forthe high-calcium coal fly ash investigated. In the Ca-rich leachate carbonation step,traditional carbonation method by bubbling CO2yields low carbonation efficiency. A newmethod by adding NH4HCO3is proposed and testified to be more effective in improving thecarbonation efficiency, with carbonation efficiency nearly doubling that by CO2. PCC witha purity up to9798%is obtained, which meets the purity requirement (≥97%) ofindustrially used PCC. It is estimated based on the experimental results that0.17tons ofPCC could be produced from1ton of coal fly ash by this method, reducing0.111tons CO2 at the same time if the obtained PCC substitutes for the PCC manufactured by theconventional energy-intensive method.