Abstract
ABSTRACTGas-fired boilers are the main stationary sources of NOx in Beijing. However, the understanding of gas-fired boilers is limited. In the present study, the emission characteristics of NOx, SO2, and CO from gas-fired boilers in Beijing were established using category-specific emission factors (EFs) from field measurements. To obtain category-specific EFs, boilers were classified through influence analysis. Factors such as combustion mode, boiler type, and installed capacity were considered critical for establishing EFs because they play significant roles in pollutant formation. The EFs for NOx, CO, and SO2 ranged from 1.42–6.86 g m–3, 0.05–0.67 g m–3 and 0.03–0.48 g m–3. The emissions of NOx, SO2, and CO for gas-fired boilers in Beijing were 11121 t, 468 t, and 222 t in 2014, respectively. The emissions were spatially allocated into grid cells with a resolution of 1 km × 1 km, and the results indicated that top emitters were in central Beijing. The uncertainties were quantified using a Monte Carlo simulation. The results indicated high uncertainties in CO (–157% to 154%) and SO2 (–127% to 182%) emissions, and relatively low uncertainties (–34% to 34%) in NOx emission. Furthermore, approximately 61.2% and 96.8% of the monitored chamber combustion boilers (CCBs) met the standard limits for NOx and SO2, respectively. Concerning NOx, low-NOx burners and NOx emission control measures are urgently needed for implementing of stricter standards. Adopting terminal control measures is unnecessary for SO2, although its concentration occasionally exceeds standard limits, because reduction of its concentration can be achieved thorough control of the sulfur content of natural gas at a stable low level. Furthermore, the atmospheric combustion boilers (ACBs) should be substituted with CCBs, because ACBs have a higher emission despite lower gross installed capacity. The results of this study will enable in understanding and controlling emissions from gas-fired boilers in Beijing.
Highlights
Beijing, the capital city of China, experiences severe air pollution, making it rank among the most polluted megacities globally (Gurjar et al, 2008; Wu et al, 2016; Zhang et al, 2016)
The combustion of natural gas produces NOx, which is the major contributor to PM2.5 pollution due to the increase of [NO3–/SO42–] ratio (1.05) in Beijing according to the source apportionment published by the Beijing Municipal Environmental Protection Bureau (BMEPB) (BMEPB, 2014)
Jklm where Ei is the emissions of the specific pollutant i in 2014 (t); EFi is the emission factors (EFs) measured (g m-3), which is calculated based on Eq (2) as described in section 2.2.1, A represents the natural gas consumption (m3); i represents the type of pollutants, namely NOx, SO2, or CO; j represents the combustion mode; k represents the type of boiler; l represents the installed capacity of boiler; and m represents the specific district
Summary
The capital city of China, experiences severe air pollution, making it rank among the most polluted megacities globally (Gurjar et al, 2008; Wu et al, 2016; Zhang et al, 2016). A series of air pollution control measures have been implemented to improve air quality. The emission characteristics of gas-fired boilers in the Netherlands and Asia were established by Pulles et al (2004) through field measurement and by Kato et al (1992) through theoretical analysis, respectively. Yao et al (2009) established a NOx emission factor based on the field measurements of 64 gas-fired boilers in China. Xue et al (2014) compiled a NOx emission inventory in Beijing through field measurements of five gas-fired boilers. The emission characteristics were obtained by establishing category-specific EFs of NOx, SO2, and CO based on field measurements for gas-fired boilers and the emission inventory, determining spatial characteristics with high resolution, and calculating uncertainty using a Monte Carlo simulation. To obtain the EFs, the gas-fired boilers were classified through influence analysis
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