K_2CO_3修饰钙基载氧体的煤化学链气化反应特性

Coal Chemical-Looping Gasification of Ca-Based Oxygen Carriers Decorated by K_2CO_3

以膨润土(Bentonite)为载体,采用机械混合-浸渍法制备了Ca SO4-K2CO3/Bentonite(Ca KBen)复合载氧体。在流化床反应器中,以水蒸气作为气化、流化介质,考察复合载氧体Ca KBen与不同煤种的化学链气化反应特性,并对该载氧体的循环特性、作用机理及气化动力学方程进行了研究。结果表明:复合载氧体Ca KBen适用于不同煤种的化学链气化过程。900℃时,与纯煤气化相比,Ca KBen化学链气化的碳转化率提高17.88%,反应时间缩短10 min,复合载氧体Ca KBen表现出良好的反应活性和催化性能。十次循环实验过程中,冷煤气效率稳定在85%以上,表明复合载氧体Ca KBen具有良好的循环特性。XRD、SEM分析表明十次循环实验后,钙基载氧体的晶相结构稳定,主要以CaS O4形式存在,K+主要以K2CO3形式存在,载氧体表面变得疏松多孔,该结构有利于化学链气化反应的进行。活性位扩展模型很好地体现了复合载氧体Ca KBen与煤化学链气化的动力学规律,验证了气化过程中CaS O4与K2CO3具有协同作用。

The Ca-based compound oxygen carriers （CaKBen） were prepared by using mechanical mixing-impregnation methods to load CaSO4 and K2CO3 on bentonite （Ben） particle. In a batch fluidized bed reactor employing steam as gasification-fluidization medium, the coal chemical looping gasification characteristics of different coal species were studied. The results demonstrate that the prepared oxygen carriers are suitable for coal chemical-looping gasification. At 900℃, the carbon conversion of coal gasification with CaKBen increases by 17.88% compared with the general coal gasification, while the reaction time is shortened 10 min. The oxygen carriers are featured by the high reactivity. The cold gas efficiency maintains at about 85% during ten redox reaction cycles, which indicates that the CaKBen oxygen carrier has an excellent recycling ability. The X-ray diffraction （XRD） images show that after ten circle redox reactions, the crystle construction of the oxygen carriers principally are in the form of CaSO4 and K2CO3. Meanwhile, the SEM images indicate that the surface of the oxygen carriers becomes porous after ten circle redox reactions, which favors the chemical looping gasification. The kinetics of coal chemical looping gasification can be well explained by active site extending model, and the synergy of CaSO4 and K2CO3 is verified during the coal chemical looping gasification process.