Craig Hawthorne

Analysis and Comparison of Reactivity and CO2 Capture Capacity of Fresh Calcium-Based Sorbents and Samples From a Lab-Scale Dual Fluidized Bed Calcium Looping Facility

Naturally occurring limestone and samples from a lab-scale dual fluidized bed (DFB)calcium looping test facility were analyzed in a thermogravimetric analyzer. The reactivityof the samples evaluated at typical carbonation conditions prevailed in the carbonatorwas compared with raw samples. The rate of carbonation and carbonation capacity ofthe samples were compared with respect to the following three categories: number ofcalcination-carbonation cycles, carbonation temperature, and CO2 concentration. It issuspected that the much lower activity of the DFB sample is attributed to the differencesin experimental conditions, i.e., partial carbonation of the DFB particles, fast heatingrate in the calciner and thus a rapid calcination reaction, and particle attrition in thecirculating fluidized bed calciner riser. These harsh conditions lead to sintering and thusa loss of surface area and reactivity. Sintered DFB samples showed low (nearly one-thirdof the raw samples) but stable conversions with increasing number of cycles. Hydrationwas used as an attempt to regenerate the lost capture capacity of partially carbonatedand sintered DFB sample. Hydration of the DFB sample was successful in increasing themaximum capture capacity in the fast reaction regime to values almost as high as that ofa fresh sample in its first carbonation cycle. Although more investigation is required toinvestigate the effect of hydration on the CaO particle morphology, a process modificationto enhance the CO2 capture efficiency of the carbonator via particle hydration wasproposed.