Does a catalytic cracking stabilization loop reflux tank need a safety valve?
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1. The pressure in the catalytic cracking stabilizer is controlled using a thermal bypass; the reflux tank is installed at a higher level than the condenser. To prevent the liquid level in the reflux tank from being affected by external conditions, it must be insulated with a thermal insulation layer. As the tower pressure increases, the opening of the bypass control valve decreases, which reduces the pressure in the reflux tank. The liquid phase from the condenser flows into the reflux tank, increasing the condensation area for the gas phase in the condenser and thus accelerating the condensation of the gas phase at the top of the tower; as a result, the tower pressure decreases ； Conversely, as the tower pressure decreases, the opening of the bypass control valve increases, which leads to an increase in the pressure in the reflux tank. The liquid phase in the reflux tank then flows toward the condenser, reducing the condensation area of the gas phase in the condenser and slowing down the flow of gas at the top of the condenser tower; as a result, the pressure at the top of the tower rises. It can be considered as the same pressure system; the stabilizer already has a safety valve at the pressure source, so a safety valve is not necessary in the reflux tank. 2. If the reflux tank is more than 7.5 meters above the ground, fire conditions need not be considered. 3. The inlet and outlet valves of the reflux tank are closed to create a sealed space. Taking thermal expansion into account, the nozzle area is calculated to be 100 mm2 when insulation is present and 5000 mm2 when there is no insulation. After comprehensive consideration, a larger value is chosen when insulation is available; thus, a J-type valve is selected, with the actual area of its nozzle being 934.8 square millimeters. The safety valve has an inlet of DN50/CL300 and an outlet of DN80/CL150; one is in use and the other is as a backup. Guys, is this the right way to conduct such an analysis? ? ? 4. Additionally, in the event that the pressure control valve of the stabilizer fails and the reflux pump keeps pumping, won’t it deflate the reflux tank? It doesn’t have a nitrogen sealing system. But it seems that the nitrogen sealing system also has a pressure control valve; however, no one considered the possibility that this valve might fail and cause the tank to deflate. I’d like to ask the experts.
The last edit to this post was made by The Man in Black with a Knife on 2024-5-13 at 17:07. 5. Additionally, for this stabilizer system, the safety valve of the stabilizer should be of the gas-phase type and installed in the gas phase area; it must be located above the reflux tank. Therefore, the safety valve of the reflux tank should also be of the gas phase type, and its installation location should be above the liquid level of the reflux tank.
The design analysis is generally reasonable, but the following points still need attention: 1. Even though the stabilizer column in the same pressure system already has safety valves, considering that the reflux tank is a separate container, there may be specific risks under certain conditions; therefore, it is advisable to equip the reflux tank with safety valves as well to enhance the safety of the system. 2. The fact that fire conditions are not considered at heights exceeding 7.5 meters above the ground is determined based on specific standards and regulations; it is necessary to consult the relevant provisions. 3. The selection of a safety valve must be determined based on the actual operating conditions and calculation results, to ensure that pressure can be effectively released in case of abnormalities and to prevent damage to the equipment. 4. To address the risk of failure in the stabilizer tower pressure control valve, appropriate preventive and corrective measures should be designed, such as installing a dual-control system and conducting regular maintenance inspections, in order to reduce this risk. Since the reflux tank does not have a nitrogen sealing system, it is necessary to consider whether such a system should be installed based on the actual process requirements and safety standards. If there is a possibility of failure in the pressure control valve of the nitrogen sealing system, appropriate safety measures should also be in place to prevent deformation or damage to the tank. .
It doesn’t have to be at ground level; 7.5 units from the platform it’s on is also acceptable