Calculation of the safety valve for propylene oxide storage tanks
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For a 200-cubic-meter propylene oxide storage tank equipped with internal cooling coils, should the safety valve be calculated based on an external fire scenario or on a chilled water failure scenario? If, based on the fire conditions, the calculated area of the safety valve throat is too large, please help explain this. Thank you
Two safety valves can be designed, or an automatic control system combined with safety valves can be used for overpressure protection. Among them, the safety valve serves as a backup. If two safety valves are designed, one is used for cooling scenarios with lower release volumes, and the other is intended for use in case of a fire. If an automatic control system is used, refer to the descriptions in ASME standards and prepare an overpressure analysis report.
It is inappropriate to install a safety valve on such a large tank; instead, a vent valve, rupture disc, and pressure relief manhole should be installed
Propylene oxide is a hazardous material; it cannot be discharged directly into the atmosphere or allowed to enter storage tanks through the air. Therefore, it is inappropriate to install vent valves, manholes, or rupture disks that are connected to the atmosphere. The safety valve or automatic pressure relief system should be directed to a closed downstream system, such as a recovery tank.
For cyclopropane, considerations such as flame arresters and nitrogen protection are also necessary!
I wonder if the LZ’s PO storage tank is a low-pressure tank rather than a pressure vessel? In our installations, the volume of the PO storage tanks ranges from 400 to 1500 m3. All of them are equipped with an internal cooling coil and a nitrogen seal; in addition, each tank has one double-acting breathing valve with a flame arrester, as well as one single-acting breathing valve with a flame arrester. Safety valves or rupture disks are not used. The design and selection of the breather valve take into account the inflow and outflow volume of PO as well as the pressure of the nitrogen seal ； The inhalation gas is nitrogen, and the exhaled gas is nitrogen plus a small amount of PO; it is collected using a breathing valve with an exhalation tube and sent to a condenser for recovery. For reference!
Thanks to the person above; I’ve learned something:victory:
Huh, a propylene oxide storage tank does not necessarily require a safety valve; a vent valve and a rupture disc can be installed instead. When production takes place in seasons with higher temperatures, propylene oxide in the storage tank may evaporate; a small cooler can be installed on top of the tank. If there is a concern that air may enter the storage tank during loading, a nitrogen seal can be used (though it is then ineffective due to the large amount of nitrogen required)
For reference: The PO storage tanks in our company are all buried. Perhaps due to their relatively small size, even in the event of a fire, the environmental factors and the area affected by the fire are minimal; as a result, the flow rate during a fire is not high.