| Chemical looping combustion technology has the property of inherent carbon dioxide capture,and its large-scale industrial application is not only conducive to alleviating the problem of energy shortage,but also to achieve near zero CO2 emissions in the process of traditional energy utilization.The key to chemical looping combustion technology lies in the development of high-performance oxygen carrier which should have high reactivity,stability and economic.Oxygen carriers based on natural copper and iron ore has the property of low cost and environmental benigin.Copper ore is highly reactive,but its melting point is low,whereas iron ore has the opposite properties,i.e.lower reactivity but high temperature resistant.Combining these two ores is promising for developing new and result in synergy effect of having advantages of both ores.Based on this,this thesis uses abundant raw materials and pollution-free of copper ore,iron ore as the active ingredient and low cost cement as binder to bind copper ore and iron ore fines for the development of a new oxygen carrier.More than 1400 types of cement-bonded ore oxygen carrier samples were prepared by bonding copper ore and iron ore fine powder with nine typical cements in the market.Weight ratio,cement type and oxygen carrier preparation procedure,raw precursor strength,particle strength,particle yield and reactivity of oxygen carrier were studied and compared.CA70 cement was selected as the best binder according comprehensive evaluations of crushing/shear strength,particle yield and particle strength.Through this binder,the hydration reaction time of cement in the preparation process of oxygen carrying system is reduced to less than 2 days,which greatly reduces the time required for oxygen carrier synthesis using cement as binder.The oxygen carrier synthesized based on CA70 binding has an oxygen transport capacity of about 23%.In a fluidized bed reactor,CA70 bonded oxygen carrier has good cyclic reaction performance.At 850℃,900℃and 950℃,the increase of temperature enhances the oxygen carrier’s reactivity against CH4 and CO,and the gas conversion was increased significantly at the same time.There is no bed agglomeration after 10 cycles at the three temperatures.During CH4 experiments,the increase of gas concentration resulted in longer reduction time and promote the carbon deposition.The conversion rate can reach 80%at 950℃and 5 vol.%concentration.At 900℃and 950℃,CO can achieve nearly 100%conversion in the early reduction stage,and at950℃,CO conversion can reach more than 99%in the entire reduction stage.There is no sintering phenomenon after 30 cycles at the three temperatures and the oxygen transport capacity of oxygen carrier is relatively stable at around 23%-21%.The average particle size increased slightly,due to the swelling of particles.But its phase composition and surface structure are still stable.Crystal phase composition and microstructure remain relatively stable.Therefore,through the research in this thesis,CA70 cement was successfully selected as a binder for copper and iron ore binding which is promising for large-scale oxygen carrier preparation in chemical looping process. |
