How to calculate the instrument air and nitrogen sealing volume?
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As the title suggests, I would like to ask everyone: there are 20 pneumatic cut-off valves and 55 pneumatic control valves – how should the amount of instrument air be calculated? Should working hours for instrument air be considered? There are also storage tanks inside the device that need to be sealed with nitrogen; how is the amount of nitrogen required for sealing calculated? Is it related to the size of the jar?
1) Regarding the issue of instrument air: The HGT20510-2014 \"Design Code for Instrument Air Supply\" and the SHT-2013 \"Design Code for Instrument Air Supply in Petrochemical Industries\" provide relevant tables specifying the amount of instrument air required. According to section 4.1.2 of the HG standards, each control valve requires 0.7–1.5 Nm3/h of air; the air consumption for shut-off valves should be estimated based on the cylinder capacity and the approximate number of operations per hour； In Table 4.2.2 of the SH standard, each pneumatic control valve consumes 1 Nm3/h of air; switches with a diameter of less than 10” consume 1.7 Nm3/h each, while switches with a diameter greater than 10” consume 3.4 Nm3/h each. 2) Regarding the nitrogen sealing issue: The normal amount of nitrogen sealing gas should be determined based on the volumetric flow rate of the liquid medium entering and leaving the storage tank, with a 1.1-fold margin taken into account. In a closed container, as the liquid level drops, the pressure inside the container decreases; at this point, the volume flow rate of nitrogen supplied must be at least equal to the volume flow rate of the liquid medium leaving the tank.
Thank you for your reply. I would like to ask whether a cut-off valve and a control valve are the same type of valve?
Nitrogen sealing volume = 0.178 * tank volume + tank production volume flow rate
The calculation of the nitrogen sealing gas supply volume can refer to the provisions in HGT 20570.16 \"Installation of Gas Seals\" – 2.0.1: The gas supply volume for the tank’s gas seal should be greater than or equal to the sum of the gas volume required to replenish what is drawn out of the tank by the pump, and the gas volume needed to compensate for the condensation and contraction of gas within the tank due to changes in external temperature. 1) The amount of air required to be pumped out of the storage tank in order to remove the liquid stored there is equal to the pump’s maximum output capacity ； 2) The amount of gas that needs to be added to compensate for the condensation and contraction of the gas inside the storage tank due to changes in temperature is specified in API Standard 2000, \"Venting of Aboveground and Underground Storage Tanks.\" For storage tanks with a volume of ≥3180 m3, this amount of gas is related to the surface area of the tank’s shell and roof; 0.6 m3 of gas per square meter of surface area is required to be added per hour ； For storage tanks with a volume of < 3180 m3, 0.178 m3 of gas seal gas must be added per hour for each cubic meter of volume. The aforementioned gas volume allows the temperature of the gas inside the tank to change by 37.8°C per hour, which is considered safe. Table 2.0.1 lists the gas supply requirements for various types of tanks, except for those commonly used storage tanks that require such supply due to changes in external temperatures. 3) By adding the air volumes required in steps 1) and 2), the air consumption required for the air seal device can be obtained.
Okay, got it, thanks :)
HG20570 Single Envelope Section
A cut-off valve is just another name for a on/off valve; their function is the same – to cut off flow