| OCR Text |
Show Table 7 PCDDs/PCDFs in Flue Gas and ESP Ash ~ Normal Operation Reburning Operation (ESP Inlet) (ESP Inlet) 0 .., .:.. 10.8% 7.1% Hcf 378 ppm 218 ppm CO 26 ppm 12 ppm PCDDs+ Flue Gas 2.8 ng/Nm3 0.4 ng/Nm3 PCDFs Fly Ash( ESP) 3.1 ngl g(TEQ) 2.5 ngl g(TEQ) Note: HCl, COand Dioxin densities are corrected to 12% Oz. In this furnace, excess air was supplied from under the stoker, and the ignition loss of bottom ash is kept under 1 %. The average CO density at time of dioxins analysis was 26ppm, and dioxins density (TEQ) at EP inlet was kept at 2.8ng/Nm\ both respectable levels. With the reburning test, combustion air volume was reduced to approximately 60% of normal operation. This did not increase the ignition loss of the ash, and the average CO density remained at 1 2ppm, and dioxins were further reduced to the level of 0.4nglNm3 . It was remarkable that the test showed dioxin reduction ratio of 1/7, attaining the guideline value of 0.5ng/Nm::, even though the residence time after secondary air injection was only 0.8 second. When reburning technology is incorporated into a new plant, it is possible to double the residence time after secondary air injection. This certainly will enable further reduction of the dioxins generation, and it is reasonable to anticipate attaining the target of 0.1 ng/Nm=' in the future. 6. Summary of Operational Test The followings are the findings from the latest test. (1 ) Recirculating gas injected into the furnace swirls the combustion gas inside the furnace, reducing NOx by about 30% without increasing CO. (2) Adding reburning reduces NOx and CO simultaneously by more than 500/0. (3) By lengthening the reburning time to 0.7 sec., NOx can be reduced to less than SOppm (4) By lengthening the burn-out time to 0.8 sec., CO can be lowered under 10ppm. (5) NOx reduction effect varies according to the locations of natural gas injection nozzles. (6) Dioxins can be reduced below 0.5ng/Nm: TEQ. (7) For achieving best reburning results, the O~ density of whirling gas mixture should be kept at minimum. Since the furnace used for this test was 1 5 years old, concerns had been expressed not to have enough residence time for reburning. However, the test has 9 |
