New low-pressure exhaust gas treatment processes for chemical tank farms, loading/unloading equipment, and plant vacuum systems

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Currently, chemical plants generally have low-pressure exhaust gases originating from chemical storage areas, loading and unloading processes, and the plant’s vacuum systems. Before 2015, such emissions were treated as unorganized emissions, with no mandatory requirements for their treatment; however, in 2015, the emission standards for petrochemical pollutants specified that these emissions must be treated to meet specified standards, and those standards were further reduced. Such waste gases are mostly organic emissions, namely VOCs. Due to the large fluctuations in volume and concentration, as well as the intermittent nature of their emission, they present significant challenges for treatment. In the past, a treatment process involving condensation followed by adsorption was commonly used; condensation allows for the recovery of some organic compounds, but it requires high energy consumption, and the concentration of organic substances remains high after condensation. Adsorption, on the other hand, is only effective for organic compounds within a certain boiling point range and those with stable chemical properties. The gases emitted from chemical plants often consist of substances that are prone to polymerization or oxidation, making it difficult to remove them through adsorption. Additionally, there is a risk of combustion associated with the use of activated carbon for adsorption. Irregularly replacing the activated carbon outlet will still result in excess levels. Such waste gases have represented a major challenge for petrochemical plants since 2015; currently, the absorption + catalytic incineration process route has proven to be quite effective. High-concentration exhaust gases are first absorbed by absorbents from the main plant under specific operating conditions, thereby removing the useful chemicals from them, which can then be reused in the main plant. It has generated certain economic benefits; the low-concentration exhaust gas exiting the absorber is sent to a catalytic incineration system, where the organic compounds within it are catalytically decomposed at a specific temperature, resulting in emissions that meet regulatory standards. The catalytic incineration system does not involve open flames, does not consume fuel, is explosion-proof and energy-efficient, and can be installed in explosion-proof environments. Taking a butanol plant in Jiangsu as an example, the exhaust gases from its tank areas, loading/unloading facilities, and vacuum packaging systems posed challenges to the company’s operations. Processes such as cryogenic treatment and activated carbon adsorption were employed, but the problem of odorous gases persisted. As part of environmental compliance requirements, modifications were carried out; since the introduction of an absorption plus catalytic combustion system, not only have large amounts of organic products been recovered, but the remaining exhaust gases have also been completely decomposed. The emissions of non-methane hydrocarbons are now around 1 mg/m3, and the odor problem has been completely resolved, making this plant a model project in this sector. The same is true for a chemical company in Yantai. This process flow has strong versatility in the petrochemical industry and has been widely and successfully applied in recent years.