Preparation And Characteristics Of CA-Based Compound Oxygen Carrier Used In Chemical-Looping Gasification

Compared to various kinds of present existing technologies to control CO2emission from fossil combustion, chemical-looping combustion (CLC) receives great attention for its three distinguished advantages, such as high combustion efficiency by decreasing the combustion irreversibility, eradication of NOx formation as well as CO2inherent separation without energy consumption. Coal based chemical-looping gasification (CCLG) has the similar principle with chemical-looping flameless combustion, is a promising industrial application technology. CCLG process used stream/CO2as gasifying agent is based on the transfer of oxygen and heat from the air to the coal by means of a solid oxygen-carrier avoiding direct contact between coal and air in gasifier. The main conclusions are summarized as follows:Firstly, one kind of Ca-based compound oxygen carrier was prepared by chemical impregnation and further processed by extruding granulation plant, which is characterized by simple operation and high yield. An investigation into the reduction reactivity between compound oxygen carriers and the coal was carried out in TGA and a fluidized bed, respectively. Gasification performance into several different kinds of coal was investigated in fluidized bed. Considering gasification reaction rate, carbon conversion and syngas in the product, shenmu coal was selected to be fuel for chemical-looping gasification.Ca-based compound oxygen carriers used γ-Al2O3and cement as inert carrier respectively were prepared by chemical impregnation. A series of experiments on the reduction reactivity between compound oxygen carriers and the coal were carried out in TGA. Experiment of CaAlNi10oxygen carrier and coal was carried out in fluidized bed by ten redox cycles. The reaction rate was in order from fast to slow:CaAlNi10> CaAlFe10> CaFeCement> CaAl. Reduction degree from high to low was in order: CaAlFe10> CaAlNilO> CaFeCement> CaAl. Therefore, y-Al2O3is better than cement as an inert carrier.It showed that the CaAlFe oxygen carrier presented the high reactivity and excellent cycling stability in the fluidized bed during ten redox cycles.The reaction rate for the compound oxygen carrier impregnated with nickel nitrate, reacting with coal was much faster than that for fresh CaSO4oxygen carrier. The reaction between CaAlNi oxygen carrier and coal took place at a lower temperature than that between fresh CaSO4oxygen carrier and coal. The initial reaction temperature of chemical looping process ranged from850℃to800℃. Increasing impregnation amount of Ni ions has a slight effect on the reaction rate, which hardly shortens the reaction time. CaAlNilO oxygen carrier and coal were examined in a fluidized bed by ten redox cycles. Further, NiO was able to capture S which released by CaSO4. The CaAlNilO oxygen carrier particles were featured by the high reactivity and regeneration rate and excellent cycling stability in the fluidized bed during ten redox cycles.Finally, the attrition of compound oxygen carriers was carried out in a fluidized bed at ambient conditions. Both reducing particle sizes and increasing gas velocity are beneficial to establish equilibrium and reduce the attrition rate. The attrition resistance of CaFeCement was better than CaAlNi10and CaAlFe10. Combined gasification reaction rate, cycling stability, and attrition rate in the product, the CaAlNilO oxygen carrier is appropriate for industrial production.