Issue of sharing one nitrogen tank for instrument air and process air
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Dear experts, background: The instrument gas and process gas in the tank farm share the same nitrogen tank. There is a situation now: automatic air replenishment occurs when the nitrogen seal pressure in the storage tank is low. The air supply pneumatic valve opens. However, once the nitrogen sealing pressure is restored, it no longer meets the pressure requirement for closing the pneumatic valve (the storage tank is equipped with devices such as breather valves, fans, and pressure relief vents, which prevent the pressure from rising too high). Is there any way to solve this problem? The issue of sharing nitrogen cannot be resolved in the short term.
The pressure requirements for the control valves associated with the instruments are much higher than those required for the protective gas in the storage tank. Nitrogen storage tanks need to take both of these factors into account; it is necessary to ensure that the flow of nitrogen into the tank is significantly greater than the flow out, or else high and low pressure protection mechanisms should be installed.
It’s best to draw a simple flowchart; otherwise, it’s hard to give suggestions
It’s best to draw a simple flowchart; otherwise, it’s hard to give suggestions
Make the change by adding another storage tank, so as to avoid difficulties in inspections in the future. In fact, the material storage tanks can be sealed more tightly to prevent nitrogen leakage, ensuring that nitrogen remains effective and that the pressure inside the tanks doesn’t drop after a short time; there must be a leak somewhere； After sealing it, have someone check whether it’s possible to replace the breathing valve with one that can handle a higher pressure; this will allow for pressure balance between the material storage tank and the nitrogen storage tank, and it should then be possible to turn off your automatic air supply valve
It seems that you are using a large amount of nitrogen for sealing; when the valve was opened to supply more nitrogen, the pressure dropped, resulting in insufficient pressure for the instruments to use. According to the specifications, this is not allowed; the gas used for instruments should be stored in a separate tank, and the accountant must ensure that there is enough gas for the instruments to function for at least 30 minutes after the supply is cut off. If you want to use it this way, then replace the nitrogen supply valve with a control valve to supply nitrogen in small amounts evenly, provided that there is sufficient gas flow.
By differential pressure protection, do you mean the interlock that controls the air inlet valve of the nitrogen tank based on the pressure difference before and after the tank, or do you mean the control of the air inlet valve via high/low pressure sensors built into the nitrogen tank itself?