REMOVAL EFFICIENCY OF POLYCHLORINATED DIBENZO-P-DIOXINS AND DIBENZOFURANS IN FLUE-GAS GENERATED FROM MUNICIPAL SOLID-WASTE INCINERATORS BY WATER SPRAY INTO THE GAS-FLOW

In a municipal solid waste incinerator (MSWI), the flue gas at the temperature of about 900-degrees-C was cooled to 3 stages in 300-400-degrees-C at the outlet of furnace by regulated water spray (Exp.I). In another MSWI, the flue gas at the temperature of about 280-degrees-C was cooled to about 160-degrees-C by water spray, and filtered by a fabric filter (FF) after dry lime powder spray into the cooled gas flow (Exp.II). Gas samples were collected before and after water spray (Exp.I and II) and at outlet of FF (Exp.II). Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in the gas samples were investigated for the variation of their amounts, constitutions of the homologous compounds and distributions to the gaseous and solid phases. Further, the removal efficiency of PCDDs and PCDFs in the cooled flue gas by FF was also determined in Exp.II. When water was sprayed into the high temperature gas flow in Exp.I. the amounts of PCDDs and PCDFs in gaseous phase decreased accompanied with increasing amount of sprayed water, but those in solid phase showed similar levels with any amount of sprayed water. In the case of Exp.II, amounts of PCDDs and PCDFs in gaseous phase decreased similarly to those in Exp.I, but those in solid phase remarkably increased after water spray. The removal efficiency of total PCDDs and PCDFs by FF was 95.7-97.5% in cooled gas, and 84.0-92.9% of those in the gaseous phase, after cooling with water spray. At the outlet of a furnace and inlet of a dust removing equipment in the flue gas flow of MSWI, the water spray affected on decrease of amounts of PCDDs and PCDFs in the gaseous phase. Furthermore, the gas treatment by the combination of water spray, lime powder spray and filtration by FF showed high efficiency for decrease of PCDDs and PCDFs in the gas to be discharged to atmosphere.