Abstract:

The emission characteristics of volatile organic compounds(VOCs) in the cold coke water discharge, tower top venting and storage of materials(coking feedstock, sewage and waste oil) in the delayed coking unit of a petrochemical enterprise are analyzed. The environmental implications are calculated and compared based on the ·OH loss rate and the maximum increment reactivity method. Corresponding control strategy are proposed in this study. The results show that annual VOCs amounts is 50.3 t and emission intensity per ton of processing capacity is 41.9 g in this delayed coking unit. The VOCs emission of large breathing loss of storage tanks accounts for more than 90%(mass ratio) of the total emission. The VOCs emission of coking feedstock tank is higher than that of other storage tanks. The VOCs emission of tower top venting process is higher than that of cold coke water discharge process. Alkanes account for 68.1%～82.3% of the VOCs in coking pollution sources, and C⁺₅ are dominant species. The delayed coking related VOCs has profound and distinct influences on ambient ozone, the large breathing loss of waste oil tank and vapor venting of tower top are recommended as prime sources. As top reactivity contributor, the C⁺₆ alkane such as methylpentane, methylcyclopentane and methylcyclohexane, propylene, butene and xylene are the active components that need to be controlled preferentially.

Key words: delayed coking unit, volatile organic compounds, emission characteristics, environmental implications, reactivity, ozone

摘要：

对某石化企业延迟焦化单元冷焦水外排、塔顶放空和物料(焦化原料、污水及污油)存储等环节的挥发性有机物(VOCs)排放特征进行了分析。基于·OH自由基损失速率和最大增量反应活性法，量化了焦化装置对环境的影响情况，并提出了管控建议。结果表明：该延迟焦化装置VOCs年度排放量达50.3 t,吨加工量排放强度为41.9 g;储罐大呼吸损耗VOCs排放量在排放总量中占比超过90%(质量比),原料罐VOCs排放量高于其他储罐，塔顶放空过程VOCs排放量高于冷焦水外排过程。烷烃在焦化污染源VOCs组成中占比为68.1%～82.3%,C₅以上组分为优势物种。焦化装置不同环节对环境臭氧产生差异化的重要影响，污油罐大呼吸过程和塔顶放空过程为需要重点管控的排放环节；甲基戊烷、甲基环戊烷、甲基环己烷等C₆及以上直链烷烃和环烷烃，丙烯，丁烯，二甲苯等是需要优先控制的活性组分。

关键词: 延迟焦化装置, 挥发性有机物, 排放特征, 环境影响, 反应活性, 臭氧