A tank A fluid should be gravity fed to another tankB. Based on the tank volume and hydraulics, flow rate is 180 gpm. Initial padding pressure is 10psig. Above calculations are based on constant 10 psig pressure in tank A.

Please help me how to calculate how much amount of nitrogen flow at 15 psig is required to maintain tank pressure during transfer.

Hi,
Sorry for that I can't understand your problem. The fluid is liquid nitrogen? I guess it is because using "gravity fed". But I can't understand whether 10 psig and 15 psig are the initial pressure in tank A and whether you want to maintain the pressure in tank A and whether the "flow rate 180" is based on maintaining tank A pressure.

Fluid is toluene that is being transfered from one tank to other. Nitrogen at 15 psig will be used as padding to maintain tank pressure at 10psig.

how to find how much amount of nitrogen is required to maintain 10psig pressure during transfer. Initial transfer rate of toluene is 180 gpm.

I think, you need Max. 180 gpm Gaseous Nitrogen at pressure of (24.7 psia-vapor pressure of Toluene at operating temperature) that with having operating temperature could be converted to SCFM unit.

When x amount of volume of toluene is transfered to tank B, x amount of nitrogen is padded into tank A. In other words, the volume flow rates of nitrogen (maintaining in 10 psig) and toluene are the same. And you maintain the pressure in tank A a constant 10 psig, so the pressure drop from tank A to tank B is also a constant. It means that the flow rate of toluene is still a constant and so do the flow rate of nitrogen. Consequently, the nitrogen flow rate is 180 gpm in 10 psig, and I think you can easily calculate the flow rate required in 15 psig by Boyle's law.