燃煤固硫及催化燃烧一体化添加剂的催化作用机理研究

燃煤固硫及催化燃烧一体化添加剂的催化作用机理研究

  • 摘要: 用热重法研究了燃煤固硫及催化燃烧一体化添加剂对峰峰烟煤的催化燃烧和催化固硫作用,采用非等温燃烧反应模型和粒子模型,计算了加入一体化添加剂前后煤的燃烧反应动力学和固硫反应动力学参数,对一体化添加剂的催化作用机理进行了分析。结果表明,一体化添加剂中金属催化组分Fe2O3对煤的燃烧和固硫组分CaO的固硫均起到了较好的催化促进作用。一体化添加剂的加入可提高煤的燃烧反应速率,外加金属离子通过电荷迁移使碳表面的棱、角、缺陷等活性部位增加,加快了氧气的吸附速度,使反应活化能和频率因子降低。在燃烧固硫反应,一体化添加剂中金属助剂Fe2O3催化了SO2转变为SO3的过程,使固硫组分CaO的硫酸盐化反应表面化学反应速度常数k和有效扩散系数D增大,在固硫反应的产物层扩散控制阶段,Fe2O3的存在使得CaO晶粒团之间相互接触黏连的几率减小,减轻了固硫产物CaSO4的团聚,弱化了扩散作用的影响,减轻了CaO固硫反应的孔窒息效应。

     

    Abstract: An integrated additive that has catalysis and sulfur retention functions was investigated by thermogravimetry analysis. In the TG experiments of catalytic sulfation reaction, 4.1‰ of SO2 was introduced into the system at the appointed temperature. Results show that in the presence of Fe2O3, the sulfation efficiency of CaO is 12%~58% higher than that of pure CaO at the temperature range of 650 ℃~1 000 ℃. TG curves can be divided into two ranges according to the slope, which indicates there are two different mechanisms for the sulfation reaction of CaO. In the TG study of catalytic coal combustion reaction in the airflow, results show that the mass-loss rate of coal sample doped with integrated additive increases in the main combustion interval. The ignition temperature t1 and burnout temperature t2 shift to low temperature region. The shape of DTG curve of sample doped with additive becomes sharp. Furthermore, the kinetic parameters of coal combustion reaction and CaO sulfation reaction with and without additives were calculated according to the nonisothermal combustion model and grain model respectively. Results show that catalytic promoter Fe2O3 in additive exhibits high catalytic performances both for sulfur retention of CaO and coal combustion. The promotion of coal combustion rate attributes to the increasing of active site of carbon surface by ion exchange between carbon and adding metal, thus the adsorption rate of oxygen is accelerated while the active energy and pro-exponent coefficient are decreased. The catalytic promoter Fe2O3 in the additive catalyzes the reaction of SO2 to SO3 in the chemical reaction control region and accelerates the sulfation reaction rate of CaO in the diffusion control region. Fe2O3 alleviates the aggregation of CaSO4 and weakens the pore closure in the CaO sulfation reaction.

     

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