Pressure setting behind the nitrogen seal valve
Thread Content
A nitrogen seal valve is installed on the roof of the atmospheric pressure storage tank (with a design pressure of 2 KPa). The nitrogen seal valve is a self-acting on-off type control valve; nitrogen injection begins when the pressure in the storage tank falls below 0.2 kPa, and the valve closes when the pressure exceeds 0.5 kPa. The nitrogen pressure in front of the nitrogen seal valve is 0.6 Mpa. What should be the pressure behind the valve? Are there any relevant regulatory requirements?
A self-acting control valve will suffice; combined with a pressure-regulating safety valve as a safeguard, it can maintain a constant pressure of 0.5 kPa.
It is now recommended to use pilot-operated or self-acting on-off control valves.
Enter “self-acting control valve” in Baidu’s entry page or search for it on Taobao; understanding its principle first will make things easier. There are principle animation videos in Baidu’s image section that make it easy to understand.
The nitrogen seal pressure is generally set based on the saturated vapor pressure of the medium; lower the pressure setting of the nitrogen seal valve, and less nitrogen will be consumed, but it cannot be set too low. When the pressure of the nitrogen seal valve is low, higher requirements are placed on the selection of such valves; it is necessary to take one’s own actual conditions into consideration
The flow rate behind the valve is calculated based on the discharge volume of the storage tank. The so-called discharge volume refers to the maximum discharge capacity set by the pump, which determines how much nitrogen needs to be supplied
The set pressure behind the valve is generally determined based on the operating range of the product’s secondary pressure
Can I choose 1.2 kPa?
It depends on the medium in question; as long as the nitrogen pressure is higher than the vapor pressure of the medium, nitrogen sealing works by using nitrogen to suppress the volatile gases emitted by that medium. In large storage tank areas, the pressure is generally kept below 1 KPa, while chemical plants usually set a higher value, with some systems operating at 2 KPa
That is, a nitrogen-sealed valve (a self-acting control valve with a special structure) should be used, with the required adjustment range downstream of the control valve being 0.2–0.5 KPa
Is there any standard for this? Is the pressure after nitrogen sealing determined based on experience?