Study On Effect Of Ash And Active Element Modification On Performance Of Ca-based Oxygen Carrier In Chemical Looping Combustion

The chemical looping combustion technology(CLC)can realize non-mixed contact combustion of fuel and air with the use of oxygen carriers(OCs),which has efficient and economical CO2 capture ability and avoids the generation of pollutant NOx.It has become an important breakthrough to solve the problem of global warming caused by greenhouse gases.Coal ash will inevitably accumulate in the system during CLC using coal as fuel and therefore it is necessary to explore the interaction between coal ash and OCs.In this research,CaSO4/Ben OC was taken as the research object,and the self-built intermittent fluidized bed was used as the main experimental device.The study was carried out from the aspects of reaction temperature,modification component types,addition amount,and action mechanism,etc.The influence of Fe,K and Na in ash and coal ash on the reaction activity,thermal stability,carbon deposition and SO2 release of Ca-based OCs.The main contents are as follows:(1)After mixing CaSO4/Ben OC and coal ash mechanically,the CLC cycle experiment was carried out in a batch fluidized bed reactor to study the effect of the reaction temperature,the type of coal ash and the amount of addition on the reaction activity of the OC,thermal stability and pore development.The experimental results show that the SHT ash with highest Fe content had the most significant promoting effect on the CaSO4/Ben reduction reaction,but also led to the most serious carbon deposition phenomenon.The high content of Ca in ZM ash can inhibit the release of SO2 in the reaction and enhance the stability of OC.The relatively high content of K and Na in SY ash was easy to form low melting point solid solution,which led to the agglomeration of OC and changed its porous surface structure and hindered fuel conversion.(2)Based on a batch fluidized bed experimental device and a thermogravimetric analyzer,the Fe2O3 modified CaSO4/Ben was subjected to multiple cycle experiments and reaction performance tests.The shrinking nucleus model was used to obtain the activation energy of the reaction between the oxygen carriers with different Fe2O3 content and CO.The research results showed that the added Fe2O3 preparation process increased the specific surface area and pore volume of CaSO4/Ben OC,increased OC reduction reaction rate,and maintained a higher CO2 concentration in the system.15 wt%was the optimal loading of Fe2O3,which reduced the activation energy of the OC and CO reaction from 88.72 kJ/mol to 43.08 kJ/mol,the reaction activity was significantly improved,and the cycle stability was good.(3)The impregnation method was used to prepare CaS04/Ben OCs modified with different alkali metals(K,Na),and it was found that the addition of alkali metals had a greater impact on the crystal structure of the OCs and the fuel conversion rate.The effect of Na improving the reaction performance of the OC and inhibiting the release of SO2 was more prominent,but the phenomenon of slagging and carbon deposition was aggravated;the high temperature volatilization of K caused the structural strength of the OC to decrease,and the cycle of the OC was shortened.K and Na had a synergistic effect when modified together,and the problem of slagging and agglomeration on the surface of the OC was alleviated.Ca60Ben-10K&Na had the best overall performance.While significantly improving the fuel conversion rate in the reaction,it inhibited the deactivation of the OC and maintained a high cycle stability.