| Nano CaO/mayenite micro-sphere CO2 sorbent can be widely used in industrial processes, such as the CO2 separation from flue gas and the hydrogen production from CO2 reactive sorption enhanced methane reforming (ReSER). Since both the processes require the fluidized bed reactor system to realize effective energy conservation and emission reduction, it is necessary to study the fluidizing attrition performance of sorbent for the future commercial uses.First, the nano CaO/mayenite micro-sphere sorbent was prepared by a spray-drying technique from the slurry containing nano CaCO3 precursor of the nano CaO. The nano CaO/mayenite micro-sphere sorbent contain nano CaO as CO2 reactive adsorprion component and a framework of mayenite, which was formed under certain conditions with the variation of the Ca/Al molar ratio and the calcination temperature. The formation machnism of the nano CaO/mayenite micro-sphere sorbent was proposed by BET, XRD, SEM and TEM characteristics, respectively.Second, the attrition behavior of the sorbent had been investigated by a method of air jet for the measurement of the attrition lost (ASTM D5757). Sorbent with an optimization of attrition resistance was formed under a calcination temperature of 900-1000℃and a Ca/Al mole ratio of 2.3 to 3.5. The fine lost under attrition condition of the space velocity of 165.9m/s (air flow rate:0.3m3/hr) was below 2.1% The sorbent with a high attrition resistance was introduced to the further experiments.The sorbent attrition behavior, being subject to the varied fluidizing conditions, such as the space velocity, the initial loading mass of sorbent, attrition time and the attrition temperature has been analyzed. We concluded that the space velocity would be the main influence factor of the sorbent attrition loss. The attrition loss is increasing with the increasing of the space velocity. The initial loading mass of sorbent and the attrition temperature play no significant role on the sorbent attrition loss. And with the attrition time stream on, the sorbent attrition process has been divided into two phase:the high attrition loss phase and the no attrition loss phase.By comparison of the CaO based sorbent prepared by adding some strength material, and nano CaO/mayenite micro-sphere sorbent, The attrition studies showed that nano CaO/mayenite micro-sphere sorbent has an advantage of the attrition resistance, due to a complete formation of nano Ca12Al14O33 framework. By analysis of experimental results, we concluded that the mechanism of attrition was mainly the abrasion of the particle surface, with little particle fragmentation.The durability of sorption capacities evaluated by a TGA method showed the decreasing of the capacity during multiple cycling runs of carbonations and calcinations. The sorbent with the optimum attrition resistance showed its sorption capacity, which was still above 12mol/Kg after 40 carbonation/regeneration cycles. A fixed fluidized bed (FFB) reactor was used to evaluate the target sorbent fluidizing sorption performance:(1) The carbonation temperature in the FFB was 590℃. And the sorbents started to decompose, when the fluidized bed temperature reaches 720℃. These conditions are nearly the same as in the TGA system, which means the sorbent particle in the FFB showed a highly favorable performance of mass and heat transferring. (2) With the variation of space velocity, an optimum W/F has been found, under which a more effective process, a faster reaction rate and a shortened period of CO2 sorption can be archived. (3) After 20 carbonation/regeneration cycles in the FFB, the sorbent sorption capacity has decreased sharply. Its conversion is 20% lower than that in the TGA after 20 cycles. It indicated that the sorbent fluidizing attrition behavior in FFB has negative effect on the CO2 sorption capacity, comparing to that in TGA. |
PDF Full Text Request