On the toxicity of benzene-containing exhaust gases and venting issues
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The exhaust gas contains 0.02% benzene, with the remainder being nitrogen; the operating temperature is 100°C and the pressure is 50 kpag. A buffer tank is installed, and a relief valve is provided at the top to allow evacuation. Discussion on issues: ① The classification of the toxicity level of exhaust gases – as moderate or high hazard. Through calculations and experience, this exhaust gas is considered to pose a poisoning risk; but is it reasonable for the designers of the buffer tank to insist on designing it as a high-hazard substance? ②A pressure relief and venting pipeline is installed at the top of the exhaust gas buffer tank. What are the requirements for the layout of such venting pipelines, based on the classification of poisoning hazards? Is it sufficient to be 3m higher than the highest operating platform within a radius of 8m centered on the pressure relief outlet?
Moderate should be sufficient; leaving it at zero would likely not pass the approval process, as safety and environmental regulations are now so strict
① Regarding the toxicity level of exhaust gases, considering a benzene content of 0.02%, it would likely be classified as moderately hazardous according to general standards. However, designers’ insistence on designing for high hazard levels may be based on the principle of safety precaution, which involves leaving a larger safety margin during the design and operation processes. Given the potential health risks of benzene (such as its effects on the central nervous system and its carcinogenicity), it is reasonable to adopt higher standards in its design. ② If, based on the treatment of exhaust gas buffer tanks for moderate hazards, the layout of the vent pipes is such that the outlet of these pipes is at least 8 meters away from the nearest point in the working area or public area, and 3 meters above the highest operating platform, it can be considered that the basic safety requirements are met. However, if designed for high hazard levels, more stringent measures may be required, such as increasing the venting height, using a secondary gas collection system, or adding air dilution/treatment equipment to reduce potential impacts on the surrounding environment. .
Judgment can be made with reference to GB/T 34710.1—2017 Classification of Mixed Gases – Part 1: Toxicity Classification, and GB 31571–2015 Emission Standards for Pollutants in the Petrochemical Industry.
Originally, this gas was released directly; now it is burned after being buffered. Due to the low operating pressure, the buffer tank was not designed as a pressure vessel, but an overpressure relief device has been installed. The venting mentioned here refers to the pressure relief pipeline. It is basically pure nitrogen; sending it to a flare is certainly not appropriate, and sealed reception is also not feasible.
Thank you! The equipment industry believes that pressure equipment should follow GBT 42594-2023 \"Guidelines for the Classification of Media Hazards in Pressure Equipment\"; according to this standard, a moderate level is sufficient.
Benzene-containing exhaust gases are not allowed to be released directly; they must be recovered and treated before being discharged in compliance with standards.
It was originally a direct discharge system; it is now being modified, and after treatment in a TO furnace, the emissions meet the required standards
This post was last edited by Long_YL08V on 2024-8-30 at 11:14. ① The original flare system did not take this exhaust stream into account and lacked the capacity to handle it； ②The exhaust gas is mainly nitrogen, and sending it to the flare system could lead to instability in the flare.