Selection issues for safety valves
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This post was last edited by laoda1996 on 2019-8-2 08:32. There is currently a tank containing a 50% ethylene glycol aqueous solution, with an operating temperature of -15°C and an operating pressure of -0.005~0.01 MPag； It features a nitrogen seal system equipped with a control valve, with a maximum nitrogen inlet flow rate of 110 KG/h. To prevent overpressure, foreigners also designed safety valves. The design of these safety valves takes fire conditions into account; the maximum discharge rate is 700 KG/h, and the nozzle of the safety valves is larger than DN100. I believe a 50% ethylene glycol aqueous solution is a non-flammable liquid, so there is no need to consider fire conditions when designing safety valves. Is this correct? Are there any relevant standards? If correct, is the DN50 nozzle of the safety valve sufficient? If fire conditions must be taken into account, is it possible to install a low-pressure non-fire safety valve (with a valve nozzle of DN50 and a pressure setting of 0.01 MPag), along with a high-pressure fire safety valve? How are the setting pressure and maximum discharge rate of this high-pressure fire safety valve calculated?
In the case of a fire, it is not self-ignition but combustion in the surrounding area; it involves calculations conducted while in a fire-prone environment. It has nothing to do with whether you are flammable or not. You can understand it by looking at the calculation formula for the safety valve in a fire situation.
This is a storage tank; in case of a fire, what’s needed is a venting manhole, not a safety valve
The foreigners did not design any discharge manholes; instead, they opted for pressure vents for discharge. I wonder whether it is necessary to take fire situations into account – in the projects carried out by our company, atmospheric storage tanks are not equipped with safety valves or discharge manholes to prevent fires.
Fire safety is definitely something that needs to be taken into account; how could you conduct a review without doing that?
Ethanol definitely raises fire concerns; no matter what is placed inside it, the surrounding area will still catch fire if conditions permit
Safety valves are required only for pressure vessels; at normal pressure, breather valves or burst discs can be used
A breathing valve with a flame arrester is sufficient; a safety valve is not really necessary!
A safety vent with DN50 is definitely not sufficient
Taking into account various conditions such as external fire-induced thermal expansion, failure of the nitrogen seal control valve, and the maximum pumping capacity of the feed pump