Effect of phosphorous transformation on the reduction of PM10 formation during co-combustion of coal and sewage sludge

摘要

Co-combustion of Municipal Sewage Sludge with coal will become increasingly widely used,regarded as an important incineration method with the high thermal efficiency,low emissions,low investment and operating costs.However, the presence of phosphorus in fine particle has gained increased attention due to its environmental adverse affection and deactivation of SCR DeNOx catalysts. Therefore, the behavior of phosphorus in fine particles during co-combustion of coal and sewage sludge was investigated in a 25 kW quasi one-dimensional down-fired pulverized coal combustor,where PM10 was collected from the furnace centerline in the outlet of flue gas cooler by using a two-stage nitrogen-aspirated,water-cooling isokinetic sampling probe followed a 13-stage electric low pressure impactor. Then the formation mechanism of PM10 was investigated by observing the different fractions of sewage sludge in the coal. Similar to the coal combustion, the particle-sizedistributions (PSD) of PM10 mass concentration by cocombustion of sewage sludge with coal exhibit two distinct modes separated by a fraction of 0.1570.263um,ultrafine mode and intermediate mode.With the sewage sludge blended sludge up to 15% (thermal ratio), the mass concentration of the total fly ash and PM10+ (Dp＞10μm) vastly increased from 1088 and 547 mg/Nm3 (during coal combustion) to 5059 and 4403 mg/Nm3.However, the mass concentration of fine particulates,such as PM1,PM2.5 and PM10 was maintained at the emission level of coal combustion.When the fraction of sewage sludge less than 15%, the mass concentration of fine particle is higher than the emission during coal combustion,while the growth rate is only by the 3.6%,7.9% and 4.8% of the total concentration of fly ash (5% thermal). The change of the PSD of mass concentration during cocombustion of sewage sludge and coal,mainly was caused by the interaction between Si、 Al and Ca、Fe、 K、 Na、 Mg,which lowed the fusing temperature of the aluminosilicate and silicate, then readily aggregated to form larger particles.Sulphate and phosphate process during the cooling of flue gas will reduced the mass concentration of fine particle,when the fraction of sewage sludge was 15% (thermal), the phosphate and P2O5 will dominantly increased in the ultrafine mode.