Abstract:

Small coal-fired boilers (≤35t∙h⁻¹) are a significant source of air pollution in the Beijing-Tianjin-Hebei region, serving as one of the main equipment for dispersed coal consumption. While the small coal-fired boilers upgrading has seen some success, the assessment of their environmental benefits at the city level remains insufficient, which limits the formulation and implementation of precise emission reduction strategies to a certain extent. Based on the small coal-fired boilers upgrading inventory collected by the Ministry of Ecology and Environment of the People’s Republic of China, this study established a city-level air pollutant emission inventory for small coal-fired boilers in the Beijing-Tianjin-Hebei region using the emission factor method. Additionally, we employed the WRF-CAMx air quality model to simulate the environmental effect of small coal-fired boilers upgrading from 2013 to 2017 in cities within this region. The results indicate that from 2013 to 2017, the Beijing-Tianjin-Hebei region upgraded approximately 8×10⁴ small coal-fired boilers, totaling 16.5×10⁴ t of capacity, with a high cumulative coal reduction of 3.18×10⁷ t. The small coal-fired boilers upgrading has played an important role in air pollution control. Specifically, the emissions of NO_x, SO₂, PM_2.5, PM₁₀, and VOCs decreased to 4.77×10⁴, 19.3×10⁴, 2.85×10⁴, 3.02×10⁴, and 1.54×10⁴ t, respectively. However, the scale is disproportionate to the emission reduction of pollutants. Notably, coal-fired small boilers ≤1 t∙h⁻¹ constitute only 15.9% of the total upgrading scale but contribute 74.6% and 89.2% to the emission reduction of PM_2.5 and PM₁₀, respectively. Air quality modeling results show that the small coal-fired boilers upgrading has improved air quality in the Beijing-Tianjin-Hebei region, with the annual average PM_2.5 concentrations in Beijing, Tianjin and Hebei provinces decreasing by 1.96%, 3.54% and 2.95%, respectively. The improvements were particularly significant in industrial-intensive areas, with maximum reductions reaching 2.72 μg∙m⁻³. Among the various upgrading methods, coal-to-gas and elimination contributed the most to air quality improvement, aligning with the distribution of their scale. The results of this study will help the relevant authorities better understand the necessity and potential environmental improvement effects of small coal-fired boiler upgrading. Furthermore, this research may serve as a model for advancing similar upgrades in the Northeast region, the North Slope of Tianshan Mountain, and other urban agglomerations, as well as for promoting ultra-low emission upgrading of larger coal-fired boilers exceeding 65 t∙h⁻¹.

Key words: the small coal-fired boilers upgrading, Beijing-Tianjin-Hebei region, boiler scale, upgrading methods, coal reduction, emission reduction of air pollutants, air quality improvement

摘要：

燃煤小锅炉（≤35 t∙h⁻¹）作为散煤消耗的主要设备之一，其排放也是京津冀等区域大气污染的重要来源。尽管燃煤小锅炉清洁改造工作已经取得了一定成效，但关于其城市尺度的环境效益评估尚不充分，这在一定程度上限制了精准减排策略的制定与实施。基于生态环境部收集的燃煤小锅炉清洁改造清单数据，采用排放因子法建立京津冀地区城市级燃煤小锅炉大气污染物排放清单，并利用WRF-CAMx空气质量模型模拟评估2013－2017年京津冀地区各城市燃煤小锅炉清洁改造的环境效益。结果显示，2013－2017年期间，京津冀地区完成约8万台、16.5万蒸吨燃煤小锅炉清洁改造，累积减煤量高达3.18×10⁷ t。燃煤小锅炉清洁改造对大气污染控制具有重要作用，2013－2017年京津冀地区常规大气污染物NO_x、SO₂、PM_2.5、PM₁₀和VOC_S的减排量分别为4.77×10⁴、19.3×10⁴、2.85×10⁴、3.02×10⁴、1.54×10⁴ t。但其规模与污染物减排量不成比例，≤1 t∙h⁻¹的燃煤小锅炉虽然仅占京津冀地区总清洁改造规模的15.9%，但其对PM_2.5和PM₁₀的减排贡献高达74.6%和89.2%。空气质量模拟结果也表明燃煤小锅炉清洁改造在一定程度上改善了京津冀地区的空气质量，北京市、天津市和河北省的PM_2.5年平均浓度分别下降了1.96%、3.54%和2.95%。工业密集区的改善效果尤为显著，最高降幅可达2.72 μg∙m⁻³。不同改造方式中，煤改气及淘汰对空气质量改善贡献最大，这主要与其改造规模大小分布相一致。研究结果有利于相关部门更好地了解燃煤小锅炉清洁改造的必要性和潜在环境改善效果，亦可为东北地区、天山北坡城市群等城市群深化燃煤小锅炉清洁改造以及推进65 t∙h⁻¹以上燃煤锅炉超低排放改造工作树立典范。

关键词: 燃煤小锅炉清洁改造, 京津冀地区, 锅炉规模, 改造方式, 减煤量, 大气污染物减排, 空气质量改善