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臭氧已成为影响我国夏季空气质量的首要污染物[1]。挥发性有机物 (volatile organic compounds, VOCs) 是生成臭氧和细颗粒物的主要前体物[2-3]。人为源VOCs持续高强度排放是大气污染重要根源[4-5]。开展重点行业VOCs治理是改善城市空气质量的有效途径,并已成为研究热点[6-7]。石化企业是VOCs重点排放源,对区域大气影响显著[8-15]。设备组件与管线泄露、工艺废气、污水集输与处理、储罐和成品油装卸等是石化企业主要VOCs排放源,而不同污染源的VOCs排放特征及环境影响差异性较大[16-23]。现有研究多以石化行业整体为研究对象,而对具体污染源VOCs排放特征及影响尚不多[11-12,16-19,22]。
WEI 等[17]对北京地区炼化企业排放的VOCs进行了采样分析发现,催化裂化装置对周边环境影响最大。MO等[18]研究了我国长三角地区炼化装置的VOCs排放特征。CHEN等[19]指出,成品油装卸单元是重要的VOCs排放源。LV等[23]对我国地方炼化储罐、设备泄露和污水系统VOCs排放现状进行了研究。FENG等[24]通过厂区内强化采样方法,研究了华北地区炼化企业的VOCs组成特征,发现催化重整及污水处理过程中排放的烷烃占比最高,可达到48.0%和59.2%,而丙烯回收及催化裂化单元VOCs则以烯烃为主,另外,长链烷烃是延迟焦化重要组分。ZHANG等[25]在研究了我国珠三角地区炼化企业工艺装置及污水处理环节VOCs组成特征后发现,除化工装置外,其余装置及污水系统VOCs以烷烃为主,而C5~C6是首要组分。比较而言,成品油装卸过程,尤其是成品油装载过程中VOCs排放组分特征及对环境影响的研究相对较少[18]。
基于此,本研究以我国某石化企业的成品油公路罐车装载过程为对象,对汽油、航空煤油和柴油等成品油装载过程外排的VOCs和甲烷进行采样和全组分分析,以明确成品油装载过程中VOCs和甲烷等有机污染物的排放特征,并基于·OH反应速率和最大增量反应活性方法,开展光化学反应活性和臭氧生成潜势研究,进而定量评估成品油装载外排VOCs对周边环境的影响,以期为从源头开展成品油装载过程有机污染物的精准管控提供参考。
某石化企业三类成品油装载环节的有机污染物排放特征、环境影响及控制措施
Emission characteristics, environmental implications and its control measures of organic pollutants from three typical petrochemical oil product loading process
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摘要: 石化行业的成品油装载环节是有机污染物的重点排放源,包括挥发性有机物(VOCs)和甲烷等。对我国某石化企业的汽油、航煤和柴油三类成品油在装载过程中外排的尾气进行了监测,并采用·OH损失速率和最大增量反应活性法,重点分析了装载过程中VOCs和甲烷的排放特征、大气反应活性及环境影响,并提出相关控制措施。结果表明,成品油装载环节外排的VOCs以烷烃为主。每吨成品油在装载过程中排放的VOCs强度达到2.2~36.4 g,其中汽油排放强度最高。丁烷、戊烷和己烷等C4~C6烃是主要烷烃组分;丙酮是含量最高含氧物质;丁烯、异戊二烯和戊烯是最主要的烯烃组分。这类VOCs具有较高大气光化学反应活性和臭氧生成潜势(OFP),大气活性与二甲苯活性相当。VOCs的OFP(即每克VOCs可产生的O3质量)达到1.4~2.7 g·g−1。航煤装载环节外排VOCs的反应活性与臭氧潜势高于汽油和柴油。装载环节外排VOCs的反应活性及臭氧生成潜势主要源于烷烃和烯烃组分,异戊烷、C4~C5烯烃和甲苯等是需优先控制的高活性物质。本研究可为石化企业从源头开展VOCs等有机污染物的精准管控提供参考。Abstract: Petrochemical oil product loading process was key volatile organic compounds (VOCs) and methane emission source which vent valuable oil product into atmosphere and play vital roles in regional air pollution. The vents from loading process of petrol, jet-fuel, and diesel in a petrochemical facility were sampled and measured in this study. The ambient photochemical reactivity was developed based on the value of OH loss rate (LOH). By virtue of the maximum increment reactivity method, source influences in terms of ozone formation potential (OFP) were determined. The emission characteristics of VOCs were analyzed and control measures were developed. The results suggest that alkane was the largest fraction in VOCs of the oil product loading process. The VOCs emission strength of loading process ranges from 2.2 to 36.4 g per ton oil product loaded. The C4~C6 alkane including butane, pentane and hexane were founded to be primary species. Acetone was the main oxygen-containing compound while butene, isoprene and pentene dominate in alkene compounds. The oil product loading process vented VOCs features in relative high photochemical reactivity and OFP, with atmospheric reactivity equivalent to that of xylene and OFP ranging from 1.4~2.7 g·g−1. The atmospheric reactivity and OFP of jet-fuel related VOCs was higher than that of petrol and diesel. The alkane and alkene were found to contribute mostly to VOCs related photochemical reactivity and OFP during the loading process. The isopentane, C4~C5 alkene, and methyl-benzene were recommended to give preferred control priority.
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Key words:
- oil product /
- loading process /
- volatile organic compounds /
- emission source /
- atmospheric reactivity
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表 1 成品油装载过程中有机污染物的质量浓度与排放强度
Table 1. Concentration and emission strength of organic pollutants during oil product loading process
成品油种类 CH4质量浓度/(mg·m−3) VOCs质量浓度/(mg·m−3) CH4排放强度/(g·t−1) VOCs排放强度/(g·t−1) 汽油 104.0 27 096.0 0.14 36.37 航煤 3.2 1 716.8 0.004 2.21 柴油 10.6 4 969.6 0.012 5.95 表 2 成品油装载过程中排放前5位的VOCs组分
Table 2. Top five VOCs species for oil product loading process
汽油 航煤 柴油 物质 占比/% 物质 占比/% 物质 占比% 异戊烷 27.8 异戊烷 31.1 异戊烷 21.9 丙酮 21.2 丙酮 23.5 丙酮 9.0 反-2-丁烯 8.6 正丁烷 7.4 乙酸乙烯酯 6.7 正丁烷 7.5 反-2-丁烯 7.3 正己烷 6.3 正戊烷 7.2 正戊烷 4.4 3-甲基戊烷 5.2 表 3 检测出的VOCs组分·OH反应速率常数
Table 3. Reaction rate with ·OH radical for identified VOCs species (s-1)
烷烃种类 常数 烷烃种类 常数 烯烃种类 常数 芳香烃种类 常数 乙烷 0.248 2,3-二甲基丁烷 5.53 乙烯 8.52 苯 1.22 丙烷 1.09 2-甲基戊烷 5.2 丙烯 26.3 甲苯 5.63 异丁烷 2.36 3-甲基戊烷 5.2 反-2-丁烯 56.4 乙苯 7.0 正丁烷 2.36 2,4-二甲基戊烷 4.77 1-丁烯 31.4 间/对-二甲苯 13.6 异戊烷 3.6 甲基环戊烷 顺-2-丁烯 64 邻-二甲苯 23.1 正戊烷 3.8 2-甲基己烷 1,3-丁二烯 苯乙烯 58 正己烷 5.2 2,3-二甲基戊烷 4.77 1-戊烯 31.4 异丙苯 6.3 正庚烷 6.76 3-甲基己烷 反-2-戊烯 65 正丙苯 5.8 正辛烷 8.11 2,2,4-三甲基戊烷 3.34 异戊二烯 66.6 1,3,5-三甲基苯 56.7 正壬烷 9.7 甲基环己烷 9.64 顺-2-戊烯 66 1,2,4-三甲基苯 32.5 正葵烷 11 2,3,4-三甲基戊烷 6.6 1-己烯 37 1,2,3-三甲基苯 32.5 十一烷 12.3 2-甲基庚烷 1,4-二乙基苯 14.5 环戊烷 4.97 3-甲基庚烷 2-乙基甲苯 11.9 环己烷 6.97 十二烷, 13.2 3-乙基甲苯 18.6 2,2-二甲基丁烷 2.23 4-乙基甲苯 11.8 -
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