西安市燃煤锅炉颗粒物中有机碳和元素碳的排放特征研究

Emission Characteristics of Organic Carbon and Elemental Carbon in Particulate Matters from Coal-Fired Boilers in Xi’an City

燃煤锅炉是城市地区含碳气溶胶的重要来源之一,本研究采集分析了西安市9个燃煤锅炉的PM_(10)和PM_(2.5)样品中的有机碳(OC)和元素碳(EC)。结果表明:燃煤锅炉颗粒物中OC在PM_(2.5)中的质量占比高于在PM_(10)中质量占比,而EC在PM_(10)中的质量占比高于在PM_(2.5)中质量占比。OC、EC和总碳气溶胶(TC)在PM_(10)中的质量占比分别为4.35%±1.09%、4.25%±1.02%和8.60%±1.87%,在PM_(2.5)中的质量占比分别为6.91%±1.09%、2.62%±0.41%和9.53%±1.40%。不同锅炉类型的OC/EC(二者浓度比)差异较大。链条炉、循环流化床和煤粉炉的OC/EC在PM_(10)中分别为1.50±0.96、0.89±1.06和12.03±8.48,在PM_(2.5)中分别为6.72±5.70、1.19±0.65和11.62±5.83。不同锅炉排放的PM_(10)和PM_(2.5)中含碳气溶胶的主导成分不同,通过含碳气溶胶的成分组成可以准确区分锅炉排放来源。PM_(10)中TC和EC的质量占比均呈链条炉(10.64%±5.13%和5.79%±4.78%)>循环流化床(7.25%±2.23%和4.15%±1.14%)>煤粉炉(4.85%±1.84%和0.50%±0.25%),OC的质量占比呈链条炉(4.85%±2.33%)>煤粉炉(4.35%±2.09%)>循环流化床(3.10%±3.37%)。PM_(2.5)中TC和OC的质量占比均呈链条炉(12.97%±5.57%和9.25%±5.63%)>煤粉炉(5.57%±1.86%和5.02%±1.79%)>循环流化床(4.92%±5.41%和2.94%±3.53%),EC的质量占比呈链条炉(3.71%±3.84%)>循环流化床(1.97%±1.88%)>煤粉炉(0.55%±0.07%)。不同锅炉类型对PM_(10)中的EC影响较大,对PM_(2.5)中的OC影响较大,主要是由于不同类型锅炉燃煤燃烧方式和燃烧效率差异所致。

Coal-fired boilers are one of the important emission sources of carbonaceous aerosols in urban areas.In this study,a multifunctional portable dilution channel sampler and a Model 5L-NDIR OC/EC analyzer were used to collect the mass concentration of organic carbon(OC)and elemental carbon(EC)in PM_(10) and PM_(2.5),which were from nine coal-fired boilers in Xi’an city.Among the particulate matters emitted from coal-fired boilers,we find that the mass fraction of OC in PM_(2.5) was higher than that in PM_(10),while the counterpart of EC was higher in PM_(10).The mass fractions of OC,EC,and total carbon(TC)in PM_(10) were 4.35%±1.09%,4.25%±1.02% and 8.60%±1.87% accordingly,and were 6.91%±1.09%,2.62%±0.41% and 9.53%±1.40%,respectively,in PM_(2.5).The OC/EC ratios(refer to their concentration ratios)varied greatly for particulate matters from different boiler types,which were 1.50±0.96,0.89±1.06 and 12.03±8.48 in PM_(10),and 6.72±5.70,1.19±0.65 and 11.62±5.83 in PM_(2.5),respectively,from the chain-grate boiler,fluidized bed boiler and pulverized coal-fired boiler.In additional,the dominant components of carbonaceous aerosols in PM_(10) and PM_(2.5) changed significantly with different boilers,which can be used to accurately distinguish their major sources as a result.The mass proportions of TC and EC in PM_(10) ranked in the order of chain-grate boiler(10.64%±5.13%and 5.79%±4.78%)>fluidized bed boiler(7.25%±2.23% and 4.15%±1.14%)>pulverized coal-fired boiler(4.85%±1.84% and 0.50%±0.25%),and were chain-grate boiler(4.85%±2.33%)>pulverized coal-fired boiler(4.35%±2.09%)>fluidized bed boiler(3.10%±3.37%)for those of OC.However,the fractions of TC and OC in PM_(2.5) were in the order of chain-grate boiler(12.97%±5.57%and 9.25%±5.63%)>pulverized coal-fired boiler(5.57%±1.86% and 5.02%±1.79%)>fluidized bed boiler(4.92%±5.41% and 2.94%±3.53%),and were chain-grate boiler(3.71%±3.84%)>fluidized bed boiler(1.97%±1.88%)>pulverized coal-fired boiler(0.55%±0.07%)for the counterparts of EC.Different types of boilers have greater impacts on EC in PM_(10) and OC in PM_(2.5).This is mainly due to the discrepancy in coal combustion methods and combustion efficiencies of different boiler types.