Dioxins/Furans Distribution in the Unit Processes of Heat Exchangers and Bag Filters of Waste Incinerator System

摘要

Despite various studies, PCDDs/DFs behavior in MSWIs has been not well estimated because of complicated factors (operating conditions of incinerator, waste composition and flue gas treatment facilities). In this research, characteristic of dioxins behavior was investigated at unit processes after the boiler of MSWIs incinerator. In order to know PCDDs/DFs behavior, it is necessary to analyze experimental conditions of treatment facilities (temperature, flue gas flow rate, etc.) and incinerator operating conditions(furnace temperature, waste feeding rate, combustion gas flow rate, etc.) as well as the concentration of other air pollutants(SOx, NOx, CO, etc.) during PCDDs/DFs sampling period. The facilities were composed of Boiler for recovering heat, Cooling tower for decreasing temperature and Bag Filter for filtering Fly Ash, removing PCDDs/DFs and Acid Gas by injecting Activated Carbon + Ca(OH)_2. Flue gas was sampled at Boiler outlet, Bag Filter inlet and outlet coincidently. Ash samples were collected at Boiler, Cooling Tower, Bag Filter Hopper, respectively. The facilities were divided into two sections (Boiler + Cooling Tower, Bag Filter). Boiler and Cooling tower section showed a very similar behavior regardless of temperature variations. In contrast, PCDDs/DFs level through Bag Filter relatively increased specially in high-Chlorinated PCDDs/DFs. The result indicated that Low Chlorinated dioxins were removed in greater amount than High-Chlorinated dioxins at Bag filter section. Through Mass Balance Calculations extended over the Unit Processes, the release of PCDDs/DFs fro the incinerator had been also evaluated in terms of the total emission rate. Dioxins mass flux was calculated from concentrations measured in three solid residues of processes as well as in flue gases. In conclusion, the PCDDs/DFs concentration decreased consistently through Boiler + Cooling Tower +B/F in flue gases and increased in ashes, respectively. It would be considered that there exist some kinds of mechanism to increase PCDDs/DFs concentrations when flue gas passes both Cooling Tower and Bag Filter because of condensation and adsorption on the Fly Ash surface and memory effect.