Mechanism Study On Dioxins Removal From MSWI Flue Gas By Activated Carbon Injection Coupled With Baghouse Filtration

Activated carbon injection (ACI) coupled with baghouse filtration (BF) is a widely used end-of-pipe treatment method to control dioxin emission from municipal solid waste incinerators. This paper focuses on optimizing dioxin removal efficiency, improving capability of industrial application and cost reduction, etc., for this entrained-flow adsorption method. The model of dioxin removal efficiency by ACI+BF system is established. The model describes the potentially substantial contribution of fly ash to dioxin removal, as a function of its residual carbon content. Moreover, the model monitors partitioning of dioxins between vapor and particulate phase and predicts dioxin removal efficiency for each congener separately. Thus, the model allows to predict dioxin removal efficiency in actual industrial process and to select ACI operating parameters rationally based on the required removal efficiency. The required ACI-dosage is estimated for typical fluidized bed and mechanical grate incinerators to meet the emission regulation of0.1ng TEQ/Nm3(11%O2). The practical effects of the principal parameters affecting adsorption removal of dioxins by ACI+BF system are analyzed. These parameters include temperature, activated carbon (AC) dosage, adsorbent characteristics (grain-size, pore structure, specific surface area of AC, lignite cokes (HOK) or mineral adsorbent), contact time during entrained-flow, fly ash concentration and characteristics, and type of incinerator. In order to improve adsorption capacity of activated carbon for dioxin removal, modifying activated carbon by KOH and ZnCl2to achieve the regulation of its pore size distribution (so called internal diffusion) is carried out. Results show that KOH method has significant effect on2～5nm pore diameter range, which is critical for the adsorption of dioxins. Particularly the condition of KOH/AC=6,800℃has the most significant effects. This condition provides an idea for activated carbon modification method for dioxin adsorption: excessively increasing the number of micropores leads to micropores collapse and merge into mesopores.