金属氧化物对生物质半焦气化特性和反应动力学影响

Effects of metal oxides on biomass char gasification characteristics and reaction kinetics

为测试生物质半焦中金属氧化物的催化作用,本研究利用热重分析仪比较脱灰半焦(ALC)及负载金属氧化物半焦(ALC-K_(2)O,ALC-Na_(2)O,ALC-CaO,ALC-Fe_(2)O_(3),ALC-MgO)的气化特性,并进行动力学计算。为提高结果准确性,采用等温和非等温实验方法,并利用分布活化能模型(DAEM)和Flynn-Wall-Ozawa(FWO)等转化率法求算动力学。结果表明,金属氧化物对半焦催化效果有明显差异。等温条件下,其气化活性依次为ALC-K_(2)O>ALC-Na_(2)O>ALC-CaO>ALC-Fe_(2)O_(3)>ALC-MgO>ALC。非等温条件下,相同升温速率下,各半焦的特征汽化温度(初始温度、最大速率下温度、结束温度)由小到大依次为ALC-K_(2)O,ALC-Na_(2)O,ALC-CaO,ALC-Fe_(2)O_(3),ALC-MgO,ALC,低特征反应温度表明其高反应活性。动力学分析发现,无论是等温还是非等温气化,活化能数据依次为ALC-K_(2)O<ALC-Na_(2)O<ALC-CaO<ALC-Fe_(2)O_(3)<ALC-MgO<ALC,这与气化活性趋势相吻合。对比等温气化,非等温气化的活化能偏大,但随转化率增加变化平稳。

To probe the catalytic effect of metal oxides in biomass on char gasification,a thermogravimetric analyzer(TGA)was used to systematically compare the gasification characteristics of deashed char(ALC)and the char loaded metal oxides(ALC-K_(2)O,ALC-Na_(2)O,ALC-CaO,ALC-Fe_(2)O_(3),ALC-MgO).To improve result accuracy,both of the isothermal and non-isothermal gasification experiments were conducted.And the distributed activation energy model(DAEM)and Flynn-Wall-Ozawa(FWO)method were used to calculate the reaction kinetics.The results showed that the catalytic effects of metal oxides on char gasification were significantly different.Under the isothermal conditions,the gasification activity followed the order of ALC-K_(2)O>ALC-Na_(2)O>ALC-CaO>ALC-Fe_(2)O_(3)>ALC-MgO>ALC.Under the non-isothermal conditions,for the same heating rate,the characteristic reaction temperature of each char gasification(initial temperature,temperature at the maximum rate,finishing temperature)ranged the order of ALC-K_(2)O<ALC-Na_(2)O<ALC-CaO<ALC-Fe_(2)O_(3)<ALC-MgO<ALC.Lower reaction temperature indicated higher reaction activity.Kinetic analysis found that regardless of isothermal and non-isothermal operation,the calculated activation energy followed the order of ALC-K_(2)O<ALC-Na_(2)O<ALC-CaO<ALC-Fe_(2)O_(3)<ALC-MgO<ALC.This was consistent with the tested gasification behavior.Compared to the isothermal gasification,the activation energy from the non-isothermal gasification was a little large,but more stable for the different conversion rates.