The exhaust port of the crude benzene condenser being connected to VOCs causes instability in the pressure of the benzene removal tower (pressure buildup)
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The actual operating temperature at the top of the debenzene tower in our company’s crude benzene unit is 91°C, while the pressure at the top of the tower is 1.8 KPa. The benzene and benzene vapor exiting the debenzene tower proceed to a condensation cooler for cooling. Parameters of the crude benzene condenser: the operating pressure in the shell side is 0.05 MPa (50 KPa), the inlet temperature is 95°C, and the outlet temperature is 25°C. The pipeline for venting non-condensable gases in the shell side has a diameter of DN50, whereas the pipes in the VOCs system here are designed with a diameter of only DN80. The benzene vapor emitted from the exhaust port of the condensing cooler contains a high amount of water; when it enters the VOCs system pipes, it condenses together with water vapor within those pipes and cannot be removed in a timely manner. As a result of this, the following situation occurs: 1) If the VOCs system pipes are not isolated, the condensate will accumulate in the water seal, and the condensed benzene vapor will flow into the sewer ； 2) If the VOCs pipeline is disconnected, the DN50 valve for venting non-condensable gases must be opened; otherwise, pressure will build up at the top of the benzene removal tower. For case 1), we plan to collect the condensate discharged from the water seal in a sealed manner and then send it to the residue tank for unified treatment. Regarding situation 2), there is no better solution for now; please give me some advice!
For scenario 2), if opening the DN50 valve for venting non-condensable gases would cause pressure buildup at the top of the benzene removal tower, the following solutions can be considered: 1. Adjust the process parameters of the crude benzene condenser, such as increasing the exit temperature of the shell side or the operating pressure on the shell side, in order to reduce the moisture content of the benzene vapor discharged from the condenser’s exhaust port. 2. Check the VOCs system pipes for any blockages or leaks to ensure they are unobstructed. 3. Consider increasing or adjusting the pipe size so that the VOCs system pipes can handle condensate and water vapor more effectively, preventing accumulation within the pipes. 4. Consider separating the benzene vapor from the water vapor at the condenser exhaust outlet for better treatment. Separation equipment such as separation tanks can be used to separate the condensate from water vapor, allowing for the selection of an appropriate treatment method. 5. If possible, consult professional technicians or equipment suppliers to obtain more specialized advice and solutions. Please note that for this issue, it is best to consult professionals in the relevant field to ensure the effectiveness and safety of the solution. .
Based on our preliminary on-site analysis, we immediately took the following actions: 1. Strengthened the proper operation of the condensing coolers, carried out backflushing on schedule to ensure that the outlet temperature of these coolers remained below 30°C, and regularly cleaned the heat exchangers. After backwashing, the outlet temperature dropped below 30°C, the pressure at the top of the tower fell to 1.6 KPa, and the condition at the non-condensable gas outlet improved significantly. The following tasks are also to be carried out: 1) Remove the water seal at that location, but install a collection pipe at the lowest point of the pipeline and lead it to an adjacent underground condensate tank for centralized treatment. 2) An opening is made above the crude benzene outlet pipe at the bottom of the condensation cooler to allow non-condensable gases to escape (currently an opening is made on the side, which may cause the benzene liquid to be ejected under high pressure); these gases are then discharged in real time through the original pipeline and a vent pipe (to the VOCs pipeline). The crude benzene and condensed water continue to flow through the original pipeline to the oil-water separator (the slope and flow direction of the pipelines are adjusted to reduce flow resistance).
Based on the information you provided, you have already taken some measures to address the issue of unstable pressure in the benzene removal tower, and have achieved certain results. Here are some suggestions for the new job you mentioned: 1) Remove the water seal in that area, and arrange for a collection pipe at the lowest point to lead the condensate to an underground collection tank nearby for centralized treatment; this approach can prevent the accumulation of condensate in the water seal and its flow into the gutters. Ensure that the condensate can be discharged in a timely manner and properly treated to avoid environmental impact. 2) An opening is made above the crude benzene outlet pipe at the bottom of the condensation cooler to allow non-condensable gases to be drawn out, which are then discharged in real time through the original pipeline and a vent pipe (to the VOCs pipeline). The crude benzene and condensed water continue to flow through the original pipeline to the oil-water separator: this approach allows for an increase in the number of exhaust outlets, thereby improving the flow of exhaust gases. Non-condensable gas is vented through openings to reduce the likelihood of benzene liquid spraying out. At the same time, adjust the pipeline slope and flow direction to reduce flow resistance, ensuring that crude benzene and condensate can flow smoothly to the oil-water separator. I hope the above suggestions are helpful to you. If you have any other questions, feel free to ask. .
A water seal is installed at the lowest point of the collection pipeline; the pipeline is regulated using control valves and pressure regulators to stabilize the pressure, which has a much smaller impact on the top of the crude benzene tower. Several such cases have been implemented already
This post was last edited by dmz329227 on 2023-7-20 07:13. Yes, I agree with your view. The purpose of removing the water seal is to prevent condensate in the VOC pipes from causing blockages, and also to avoid the water seal water from overflowing into the gutter due to unstable pressure; it has little impact on pressure buildup. The factor affecting the pressure holding capacity is still the poor backwashing efficiency of the condensing cooler.