Suppression of Natural Limestones Deactivation During Cyclic Carbonation
Abstract - The paper summarizes the sorption characteristics of limestones with various levels of calcium carbonate. The sorption capacities change during cyclic calcinations and carbonations were investigated using laboratory apparatus using a vertical quartz reactor. Utilization of the right limestones and conditions of processing provided long-term sustainability of as high as 11 kg of CO2 / 100 kg limestone. Method of reactivation of the spent limestone using a gas saturated by water vapor was proposed to eliminate decreasing of the capacity of the carbonate looping process. I. INTRODUCTION This study focuses on the application of limestones to high-temperature CO2 separation from flue gas using carbonate looping. Post-combustion capture of CO2 emissions from coal-fired power plants as well as district heat-plants was identified as the most appropriate application for carbonate looping. The simplified diagram of the process, based on documents [1] is presented in Fig. 1. Although the carbonate looping is still not a technology expanded into industrial practice but there are a few pilot units operating around the world. Alonso et al. presented the main findings of their experience with the operating of the pilot plant utilizing CaO looping, incorporated within a facility for combusting biomass inside an in-flux reactor [2]. For more detail please visit>>> Utilization of CaO based sorbents to aid in high temperature CO2 separation out of industrial process has been subject to relatively numerous studies. A high degree of economic viability of these materials makes them attractive candidates for the solution of problems related to the reduction of CO2 emissions to the atmospheric air. The main obstacle for the use of CaO-based sorbents in the industrial process is the gradual decline in sorption capacity, manifested in the repeated cycles of carbonation (i.e. thermochemical decarbonation) or carbonation. Based on data from experiments Abanades suggested an empirical formula (1) that describes the relationship of the conversion from CaO and CaCO3 on the number of cycles [3]. In (1) the meaning of the symbols is as follows the meaning of xN is: xN represents conversion during N-th cycle. fm and fw are constants. The formula was in good agreement with the data from experiments in many conditions, however its validity has been limited to just 20 cycles. In their study, Wang and Anthony so came up with a different formula that was valid for a wide range of cycles. These authors considered a combination of thermal sintering along with other irreversible processes such as growth of crystals and the reaction in CaO with impurities present in the gas, to be important factors that reduce the efficiency of CaO-based absorbents. They also expressed the assumption that the rate of degradation isn't significantly dependent on the experiment conditions [4].

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