In our work, we usually choose storage tanks to store part of the gas in case of emergency. Generally speaking, the gas volume refers to the volume under standard atmospheric pressure (≈ 0.1MPa). For a 100m3 tank, it can store 100m3 gas under 0.1MPa (atmospheric pressure).

Because the volume of gas decreases with the increase of pressure, that is, with the increase of absolute pressure, more gas can be contained in the same tank. When the pressure is not too high and the temperature is not too low, there is a simple relationship between the pressure, temperature, volume and mass of the gas, which is called the equation of state of ideal gas and can be expressed as

PV=MRT P1V1/(M1T1)=P2V2/（M2T2）

When the volume and temperature of the tank remain unchanged, the

M2/M1=P2/P1

When the pressure of the tank rises to 3.0MPa gauge pressure, the pressure in the tank is 31 times of the original (3.0 + 0.1) MPA / 0.1MPa, that is, the mass of the gas in the tank is 31 times of the original, that is, the volume under normal pressure is 3100m3.

Because the gas users have certain requirements on the gas supply pressure, when using the storage tank to supply gas, the maximum pressure is reduced to the minimum pressure required by the users. If the minimum pressure of the user's gas is 1 MPa gauge pressure, there is still 100m3 × (1 + 0.1) MPA / 0.1MPa = 1100m3 gas left in the tank, and the actual gas supply is (3100-1100) m3 = 2000m3. The higher the inflation pressure is, the lower the user's demand pressure is, the more gas the tank with a certain volume can supply. However, the inflation pressure is limited by the strength of the tank and can not exceed the design allowable pressure. Therefore, the amount of gas that each tank can store and supply is limited.

The selection of tank is a comprehensive factor of pressure and volume. The reserve gas required by the user is taken as the actual gas supply of the tank. Considering the influence of pressure and volume on the equipment cost, the most economical tank is selected.