Regarding the issue of nitrogen seal gas velocity
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I would like to ask everyone: How is the pressure difference and flow rate for nitrogen supply calculated? For example, if the pressure difference is 2 KPa and the pipe diameter is 20 mm, how can the gas flow rate be determined? I mainly want to figure out whether the diameter of the nitrogen supply pipe is sufficient; if it does not match the discharge volume from the storage tank, it could cause negative pressure in the tank.
The calculation of the nitrogen supply pressure difference and flow rate can be performed using the discharge formula. First, it is necessary to know the pipe length L (assumed to be 10 m) and the aerodynamic viscosity μ (assumed to be 1.85 x 10^-5 kg/(m·s)). Then, the gas flow velocity V can be calculated using the formula for flow in a vibrating tube: V = K * √(2ΔP / ρ), where K is a correction factor that can be taken as 1 during calculation ； ΔP is the pressure difference, which is 2 KPa ； ρ is the gas density; under normal circumstances, the density of air at room temperature, 1.225 kg/m^3, can be used. The gas flow velocity can be obtained by substituting the values and performing the calculation. Additionally, the issue of whether the diameter of the nitrogen supply pipe is sufficient can also be determined using the flow discharge formula. Based on the flow rate requirements and gas velocity of the gas supply pipeline, the minimum required pipe diameter can be calculated. If the diameter of the gas supply pipeline is smaller than the required diameter, it will result in an increased gas flow rate and a greater pressure difference, which may in turn cause negative pressure in the storage tank. .
The maximum exhaust volume is calculated based on the maximum inflow and outflow rates of the storage tank as well as the maximum gas volume resulting from temperature differences. Based on a pipe diameter of 25 mm, it is determined whether the gas velocity exceeds the maximum flow rate allowed for that diameter. A differential pressure of 2 kPa has an negligible effect on volume changes. Mainly, the pressure of the nitrogen main pipe is calculated using PV=nRT.
You are right; for now, we should not consider the main pipeline. Assuming there is an adequate supply of gas, with zero pressure inside the tank and a pressure of 2 KPA in the main pipeline, meaning a pressure difference of 2 KPA, and the diameter of the nitrogen supply valve being 25, how can we calculate the gas velocity or flow rate? This value needs to match the amount of material being discharged; otherwise, an accident could occur :)
Simply put, under a pressure difference of 2 KPA, how much air can pass through vents with a diameter of 25 or 20 mm?
Why is the differential pressure 2 kPa? What is it for?
Supply pressure: 2 KPA, assuming the condition when the pressure inside the tank drops to zero
I’m sorry, I don’t know why I can only see your answer now. What is the unit at the end of this formula? KPa/(kg/m3)？ I didn’t understand. Could you also explain the calculation process? :)
Nitrogen sealing for the storage tank; the pressure in the nitrogen supply pipeline is 2 KPa. When the pressure inside the tank drops to zero, the pressure difference is 2 KPa. What needs to be calculated is the rate or flow rate at which air can be supplied at this point, in order to determine whether it is sufficient to fill the volume of the tank that has been emptied due to discharge, and thus prevent accidents caused by negative pressure in the tank
The nitrogen sealing gas volume can be calculated using the same method as that for control valves, namely pipe resistance plus the pressure drop across the control valve (actual Kv).