jeetu911,
I assume that you have provided N2 blanket over tank material and you want to calculate peak flow rate of inlet N2 when unloading being done. This N2 flow rate can be used for related control valve sizing, line sizing etc.
Basically this N2 inlet flow depends upon unloading rate out of tank.
But considering worst case scenario, assume that tank is empty at atmospheric pressure (A1 condition). Another B1 condition of tank desired pressure of 1.5 kg/cm2g. Find out N2 density at both these A1 & B1 scenario. you know tank volume i.e. 10m3. Based on density difference and tank volume, you can calculate how much kg of N2 is required ( density * volume) for makeup within the tank.
Find out time, depending on your operation scenario, in which pressure make up need to be done in that tank. Thus you can fix N2 flow rate required (i.e. worst case scenario).
Hope my assumption of scenario helps you to arrive at solution.