Reuse Of Deactivated Ca-based Sorbents In Cyclic Calcination/Carbonation For CO₂ Capture

With the increasing worldwide attention to global warming caused mainly by CO₂ emission, the cyclic calcination/carbonation reaction?CCCR? with Ca-based sorbents to capture CO₂ from flue gases has been rapidly developed as an effective technology of the post combustion CO₂ capture. However, mostly because of sintering and sulfuration, the CO₂ carrying capacity decreases with increasing cycles, which produce a lot of spent sorbents. Treatment of spent sorbents, mining and grinding the fresh sorbents reduce the economy to a discount. How to deal with the massive spent sorbents directly determine the total economy and environmental protection of this technology. In order to explore most reasonable ways to reuse deactivated sorbents accord with practice, by means of a customized thermogravimetricanalysis system that can measure weightchange of samplesat constant temperature, the effect oftrace SO₂ on Ca-based sorbents cyclic CO₂ capture and the sulfation behavior of deactivated sorbents after different cycles were studied. The deactivated sorbentswere collected and the concept of metallurgical lime reactivity was used for redetermination in order to explore its possibility of reuse in metallurgy industries.The results show that CO₂ capture ability of deactivated sorbents decreases rapidly as the SO₂ concentration increases, and the phenomenon of small particle size limestone is more obvious than that of big one with the number of cycles. During the followed SO₂ retention, sulfation conversion decreases with the concentration of SO₂ in the carbonation atmosphere increasing. The sulfation conversion of sorbents with particle size in the range of 0.075-0.097 mm decreases with the number of cycles, however, sorbents with particle size in the range of 0.15-0.25 mm and 0.355-0.45 mm reach a relatively higher conversion?close to fresh sorbents? with 5 cycles, properties of BD and SD limestone are similar. Reasons are comprehensive effect of pore size distribution changes with the number of cycles and effect of sulfation behavior during carbonation on followed SO₂ retention. The crushed deactivated sorbents have higher conversion than that of direct sulfation because the unreacted CaO core is liberated from CaSO4 film.The effect of calcination temperature, particle size, calcination atmosphere and cyclic number on lime reactivity was investigated, and the pore structure was analyzed. The results show that average reactivity of lime at different cyclic number decreases relatively with increasing calcination temperature. Within the range of 0.15-1mm, the average reactivity increases with particle size increases. Reactivity of sample calcined in pure N2 is significantly higher than in oxygen enriched atmosphere. With cyclic number increasing, the calcined product reactivity decreases first and then increases and finally falls gradually. The decarburization efficiency of sorbent after about 8 cycles is low, however, it has a relatively high reactivity which promises a great reuse potential. From pore structure analysis, product reactivity is not only determined by the size of reaction area and space, but also determined by the size of resistence from material transport path.