Study On Chemical Looping Combustion Of Iron Ore Oxygen Carriers Modified By Biomass Ash

Chemical looping combustion（CLC）is a new,efficient,and green combustion technology and carbon capture pathway.The combustion products are CO₂ and H₂O,which can be separated by simple condensation without additional energy consumption.Exploring a suitable oxygen carrier is the key to further progress in CLC technology.Natural iron ore has the advantages of economic and environmental protection,anti–sintering,easy to obtain,stable reaction and so on.However,the low reactivity of natural iron ore oxygen carriers limits the large-scale application of chemical looping combustion based on natural iron ore oxygen carriers,so it is necessary to modify natural iron ore oxygen carriers to improve the reactivity.In this paper,two kinds of herbaceous biomass ash（rape stalk ash and rice stalk ash）,one kind of woody biomass ash（platane wood ash）,and one kind of aquatic biomass ash（Ulva Lactuca ash）with different contents of K,Na,Ca,and Si were used to modify natural iron ore by dry calcination method.A batch fluidized bed reactor was set up to carry out CLC experiment,and the oxygen carriers before and after the reaction were characterized and analyzed.The physical and chemical properties of iron ore modified by biomass ashes and the effects of different reaction conditions on the chemical looping combustion process were investigated experimentally.In this paper,chemical looping combustion experiments were carried out with CO as fuel to screen oxygen carriers preliminarily.The effects of reaction temperature,biomass ash type,biomass ash loading and cycle numbers on CO concentration and CO conversion were studied to evaluate the reactivity and stability of oxygen carriers.The results showed that the reactivity of iron ore can be promoted by increasing temperature.The reactivity and stability of the iron ore were promoted by rape stalk ash,platane wood ash and Ulva Lactuca ash,while rice stalk ash showed inhibition effect.Based on the above,Datong bituminous coal was used as fuel to further explore the mechanism of biomass ash affecting the reactivity of iron ore.The results showed that the content of（K+Na+Ca）on iron ore modified by rape stalk ash,platane wood ash and Ulva lactuca ash was higher,and the Si content was lower.Which can improve the reactivity and cycle stability of iron ore obviously,and the promotion effect of K on the reactivity of iron ore was better than that of Na and Ca.The iron ore modified by 20%rice stalk ash with high Si content and low K/Si content can inhibit the reactivity and stability of iron ore.Besides,increasing the steam flow rate in a certain range can promote the chemical looping combustion.The experiments of pyrolysis,gasification and chemical looping combustion were carried out with Datong anthracite coal as fuel.Compared with bituminous coal,anthracite coal has lower volatile content,longer gasification time and lower peak value of gasification products.In the process of chemical looping combustion reduction reaction,the gasification rate and carbon conversion of anthracite coal were obviously lower than that of bituminous coal,and coke can not react completely.In the range of 800–950°C,increasing temperature will promote the chemical looping combustion process of anthracite coal,and the effect of temperature was more obvious than bituminous coal.On the whole,the reactivity of oxygen carrier could be improved by increasing the temperature in the range of 800–950°C.The biomass ash with high content of K,Na,and Ca can promote the reactivity and stability of iron ore.when the loading amount of biomass ash was 20%,the modification effect on iron ore was better,in which the improvement effect of K is the most obvious,while the biomass ash with high content of Si can inhibit the reactivity and stability of iron ore.In a certain range,increasing the flow rate of steam properly can promote the chemical looping combustion.