SRF 연소에 따른 PCDD/DFs 발생특성 및 배출계수 비교

Abstract

A comparison analysis of emission characteristic in the flue gases including polychlorinated dibenzo-p-dioxins and furans (PCDD/DFs) was performed about combustion process by the SRF facility. The annual emission amount of PCDD/DFs was also calculated in this study. The lab scale combustion experiment with combustible wastes was carried out and the components analysis of municipal solid wastes bringing into the SRF production facility was also performed. Furthermore, the concentration of PCDD/DFs was measured at the after combustion stage and the stack. The result of component analysis showed that the average content of combustible waste was 87.8% and the paper was a dominant content with 24.6% on average. The content of vinyl and plastics containing a large quantity of precursors of PCDD/DFs was measured as 26.2%. However, the seasonal variation of these contents was large and showed 32.8% in winter. The total average moisture content of combustible wastes was 22.3% of and the calorific value was measured as 3,873.1 kcal/kg with a weighted average. Seasonal samples for laboratory scale experiments were prepared by mixing combustible materials among the samples for the component analysis except organic matter, incombustibles and other combustible materials. The mean concentration of PCDD/DFs was 1.593 ng I-TEQ/Nm3 (ranging 0.302~3.558 ng I-TEQ/Nm3) in the theoretical air injection experiments and the analytical concentration of the experiment with excess air was 0.987 ng I-TEQ/N㎥ (ranging 0.075~2.401 ng I-TEQ/N㎥). Concentration levels of PCDD/DFs of samples in winter with high vinyl and plastic contents were high. Furthermore, its analysis of contribution patterns showed a similar pattern, except that some substances were not detected. The contribution rate of PCDFs was measured as 98.06% and 94.34%, respectively. Emission factors of experiments using theoretical air and excess air condition were 12.981 ng I-TEQ/kg (2.277-28.529 ng I-TEQ/kg) and 14.667 ng I-TEQ/kg (1.325-36.113 ng I-TEQ/kg) on average, respectively. The result of experiment using theoretical air condition showed higher concentration. On the other hand, the emission factor showed a higher trend in experiments with excess air conditions. These results were attributed to the fact that the concentration per unit amount of combustion products was low and the emission factor per unit weight was high because of the increase in the amount of combustion gas, which is the main factor of the emission factor calculation. The experimental results were compared with previous studies about open burning representing uncontrolled combustion. The emission concentration of this study were lower than study of municipal waste incineration showing 12.53～14.09 ng I-TEQ/N㎥ by (Nammari et. al., 2004). However, it was much higher concentration than a previous result about domestic waste having 0.070～0.126 ng WHO-TEQ/㎥ and construction wood showing 0.224～0.274 ng WHO-TEQ/㎥ (Moon, 2007). As a result of comparing the emission factors with the previous studies, the emission factors of this study were largely higher than Kim’s study indicating paper (0.046 ng I-TEQ/kg), vinyl & plastics (5.368 ng I-TEQ/kg) and waste vinyl for agriculture (0.472 ng I-TEQ/kg) (Kim, 2008). Comparing the emission factors with Moon's study presenting domestic waste (7.325 ng I-TEQ/kg), Agriculture (8.940 ng I-TEQ/kg) and Construction Wood (10.875 ng I-TEQ/kg), spring and autumn samples showed similar or low, while summer and winter samples were high (Moon, 2007). Concentration of PCDD/DFs sampled at the after combustion stage of the SRF boiler facility was 1.027～0.858 ng I-TEQ/N㎥. The final emission concentration identified in five on site measurements ranged 0.012 through 0.073 ng I-TEQ/N㎥ and its average concentration was 0.046 ng I-TEQ/N㎥. This study was compared with the result of emission concentration and emission factor of existing municipal solid waste incineration facilities. Emission concentrations and emission factors of existing large incineration facilities with similar capacities were similar or lower than those of this study (Hwang et. al., 2008, Sung, 2012). Emission factor comparison results were about 3 times higher than previous studies having 0.09 ng I-TEQ/kg (ranges 0.00-0.49 ng I-TEQ/kg). The PCDD/DFs emissions estimates for the SRF facility were 239.5 ng I-TEQ/MWh, which was much higher than the solid fuels (15～164 ng I-TEQ/MW) and liquid/gaseous fuels (98～77 ng I-TEQ/MWh) of existing thermoelectric power plants. Based on the above results, the annual emissions of PCDD/DFs generated from the SRF facility were 0.047 g I-TEQ/yr. This estimation was exceedingly high, corresponding to 2.47% of total annual emissions from the MSWI facilities. Assuming that annual 870,346.61 tones of SRF are burned, excluding Bio-SRF, the annual emissions of PCDD/DFs are 0.252 g I-TEQ/yr. This result corresponds to 13.3% of the annual amount of the MSWI facilities. The results showed that the variation of emission concentration and emission factor of PCDD/DFs during incineration is large, according to the physical composition of SRF. SRF is produced by recovering combustible materials of 50 through 60% of municipal waste. Thus the physical composition of the SRF is determined by the composition of the bringing waste. Moreover, the amount variation of PCDD/DFs is largely influenced by the content of vinyl and plastics depending on the content of chlorine compounds. PCDD/DFs is emitted an average of 0.943 ng I-TEQ/N㎥ in the incineration process and an average final emission concentration of 0.046 ng ng I-TEQ/N㎥. Therefore, it is considered that the generated PCDD/DFs are reduced by 95.12% through the air pollution control devices. In the SRF production facility, combustion experiments using SRF products according with fuel quality standards were conducted. Notwithstanding incineration in a high efficiency combustion facility with ignition loss of less than 1%, the facility produced higher PCDD/DFs than the pyrolysis process. The final emission concentrations of PCDD/DFs were also higher than those of general large incineration plants. In the case of a general incineration facility, which is a stoker type, it is considered to have a combustion efficiency indicating a ignition loss of 5%. Compared to incineration of raw municipal waste, the production and combustion of SRF increases the content of vinyl and plastics per unit weight and increases the PCDD/DFs precursors. Therefore, it shows higher emissions of PCDD/DFs than incineration facilities of the same combustion capacity. The SRF boiler facility exhibited high PCDD/DFs emission characteristics compared to thermoelectric power plants, Therefore, although SRF has some effects as an alternative energy source for fossil fuels, it does not seem to be effective in terms of air pollution management. Researches have been carried out on the domestic PCDD/DFs emission inventory. Thermoelectric power plants use homogeneous composition fuels, and the variation of emission inventory caused by fuels is not large. By contrast, combustion of SRF showed a large variation of PCDD/DFs emission from the large facilities, and this variation became bigger in small facilities. Considering these results, the PCDD/DFs emissions deviations according to the facility size should be considered when creating an emission inventory for SRF-use facilities. In terms of air pollution management, the measurement cycle for PCDD/DFs should be converted to a period based on the emission factor instead of the classification by facility size. Moreover, it is necessary to examine the transition to the measurement system as once per quarter rather than the current half-yearly measurement to sources with large emission variations such as SRF facilities. In the future study, it will be additionally necessary to accumulate more systematic and diverse data for the emission inventory for SRF combustion facilities.