Abstract:

Gas-phase zero-valent mercury adsorption experiments were carried out on two 300MW class coal-fired generating units circulating fluidized bed boilers and pulverized coal boiler fly ash samples in a fixed bed adsorption reactor. The effects of temperature, inlet mercury concentration and inlet gas flow on mercury adsorption efficiency of fly ash samples were explored. Weber and Morris diffusion model, pseudo-first and pseudo-second order kinetic models, and Elovich kinetic model were adopted to explore the mechanism of mercury adsorption on fly ash samples and the difference of adsorption kinetic between the circulating fluidized bed boiler fly ash and pulverized coal boiler fly ash. The results show that the penetration time and adsorption capacity of the circulating fluidized bed boiler fly ash are much higher than that of the pulverized coal boiler fly ash under the same condition. Adsorption capacity of fly ash samples is the highest at 150℃. Mercury adsorption on fly ash samples increases with an increase of initial mercury concentration due to the enhancement of mercury diffusion force onto the fly ash surface and reduce the external diffusion resistance. The pseudo-second order kinetic model and Elovich kinetic model are more applicable to reflect Hg adsorption on fly ash. The mercury adsorption on the fly ash was affected by external diffusion, internal diffusion and surface adsorption, in which surface chemical adsorption plays a key role. Under the same work condition, the particle internal diffusion coefficient, order kinetic constant and initial adsorption rate of the circulating fluidized bed boiler fly ash are all higher than those of the pulverized coal boiler fly ash.

Key words: fly ash, mercury, adsorption, kinetic theory, kinetic model, adsorption mechanism

摘要：

在固定床吸附反应器内对两台300MW等级燃煤发电机组循环流化床锅炉和煤粉锅炉飞灰样品进行气相零价汞吸附实验，通过改变实验工况研究温度、入口汞浓度和入口气体流量对飞灰汞吸附能力的影响。采用颗粒内扩散模型、准一阶和准二阶动力学模型、耶洛维奇（Elovich）模型对实验数据分别进行拟合，从动力学的角度探讨两种锅炉飞灰对气相零价汞吸附的影响机制以及两种锅炉飞灰与气相零价汞之间吸附动力学行为差异。结果表明：相同工况下循环流化床锅炉飞灰汞吸附过程的穿透时间和平衡吸附量远大于煤粉锅炉飞灰。吸附温度为150℃时，两种锅炉飞灰对气相零价汞的平衡吸附量最大。由于外扩散阻力随气体入口流量的增加而减小，入口汞浓度的增加可提高传质推动力，飞灰对汞的吸附得以增强。动力学分析表明飞灰的零价汞吸附由外扩散、内扩散和表面化学吸附共同控制，其中表面化学吸附是该吸附过程中的控制步骤；准二阶动力学模型和Elovich动力学模型更适合于描述该吸附过程。相同实验条件下，循环流化床锅炉飞灰吸附过程拟合所得的颗粒内扩散系数、准一阶动力学常数和初始吸附速率均大于煤粉锅炉飞灰。

关键词: 飞灰, 汞, 吸附, 动力学理论, 动力学模型, 吸附机制