Study On The Reaction Performance Of Iron- And Nickel-based Oxygen Carrier For Chemical Looping Combustion

A series of negative impact brought by global warming has caused people to pay more attention to the main greenhouse gas CO₂. Chemical looping combustion as a novel combustion technology can not only achieve low energy consuming for CO₂ recovery and ultilization, graded use of chemical energy, but also effectively increase the combustion efficiency, inhibit and eradicate the formation of NOX. So it attracts widely attention. In this paper oxygen carriers of chemical looping combustion fueled by coal char and CH₄ is researched in a thermo-gravimetric analysis (TGA),fixed-bed reactor (FxB) and fluidized-bed reactor (FzB).After analyzing and summarizing the research work on oxygen carriers in and abroad, based on the demands of oxygen carriers in chemical looping combustion by gaseous fuel, Fe(NO₃)₃·9H₂O and Al(OC₃H₇)₃ are selected as the main raw materials to prepare 12 different kinds of iron-based oxygen carriers according to the process of sol-gel-derived NiO/NiAl₂O₄ oxygen carriers. X-ray diffraction (XRD), scanning electron microscope (ESEM), and N2 adsorption-desorption (BET) methods are utilized to characterize the physicochemical properties of oxygen carriers. And then the desirable oxygen carriers are selected to be researched in TGA, FxB and FzB.The reduction reactivity between 6 kinds of iron-based oxygen carriers and coal char are researched in TGA. The results show that iron-based oxygen carriers react rapidly with coal char at the temperature 880℃. Considering several factors synthetically, Oxygen carriers with contents of 60% Fe₂O₃, sintering temperature of 1100℃and sintering time of 6 hours is selected to circularly react with char/air in TGA. The result shows that iron-based oxygen carriers have extremely good circular reactivity.In the fixed-fluidized-bed multifunction reactor, the reactivity of iron- and nikel-based oxygen carriers separate with CH₄/air is researched at 900℃and the physicochemical properties of the samples is characterized before and after the reaction. The results are as follows. The maxium concentration of CO₂ from the reaction of iron-based oxygen carriers with CH₄ in fixed-bed reactor is 51.2%,higher than 44% in fluidized-bed reactor and the concentration of unreacted CH₄ in fixed-bed reactor is lower than it in fluidized-bed reactor. The reaction of carbon deposition is avoided. The maxium concentration of CO₂ from the reaction of nikel-based oxygen carriers with CH₄ in fixed-bed and fluidized-bed reactor is 73.5% and 70.8% higher than that of the reaction of iron-based oxygen carriers with CH₄. Carbon deposition happens. The concentration of CO and H₂ from the reaction of both kinds of oxygen carriers with CH₄ is very low. The reactivity of nikel-based oxygen carriers is higher than iron-based oxygen carriers. The sintering behavior is observed on the surface of both types of oxygen carriers, but the porous beehive structure of particle is still maintained after several circle reduction-oxidation reactions.