Factors Affecting The Dissolved Gas Volume of The Pressurized Dissolved Gas Tank

1. Pressure value in dissolved air tank

The pressure in the gas-dissolving tank directly affects the amount of dissolved gas. The greater the pressure value, the greater the theoretical value of the dissolved gas.

Although increasing the pressure in the gas dissolving tank can increase the amount of dissolved gas, it will also increase the manufacturing difficulty and cost of the gas dissolving tank, pipeline, and releaser, increase energy consumption, and reduce economic benefits.

According to Henry's law, the solubility of the absorbent in the liquid phase is proportional to its equilibrium partial pressure in the gas phase.

P^*_A=Ex_{A (1-1)}

_In: P^*A — Equilibrium partial pressure of solute A in the gas phase (Kpa);

    x_A   — The mole fraction of solute A in the solution;

      E  —     Henry coefficient (Kpa).

At present, relevant literature also provides relevant regulations for calculating theoretical dissolved gas content.

V_t = 7500 × K_t ×P

Among them: K_t is the Henry coefficient of air solubility at different temperatures.

Table 1-1 Henry coefficient of air dissolution at different water temperatures

2. Dissolved gas temperature

The temperature in the dissolved gas tank also directly affects the amount of dissolved gas. In formula 1-1 (, the Henry coefficient decreases with increasing temperature, which means that the dissolved gas volume decreases with increasing temperature.

Therefore, the lower the temperature in the dissolved gas tank and the higher the temperature in the flotation tank, the better the amount of dissolved gas released. However, achieving this effect requires a lot of energy consumption, which is not applicable in engineering.

3. Unit contact area and residence time

The air transfer from the gas phase to the water in the liquid phase is a mass transfer process and a diffusion process. The mass transfer dynamics are the concentration differences on both sides of the gas-liquid interface. The molecules of the substance are transferred from one phase with a higher concentration to another with a lower concentration.

Relationship between gas unsaturation and dissolution rate:

The relationship between the surface area per unit volume of water and the dissolution rate:

Combining the above two formulas gives the following:

In :  — The dissolution rate of air in water

      Cs — Solubility of air in water at a specific temperature and gas partial pressure(L/m³)

      C   — Air content in water(L/m³)

        — The surface area of a solution per unit volume（m^-1）

      K_g  —  Gas migration coefficient (cm/min)

The above formula shows that the larger the surface area per unit volume of solution, the higher the gas dissolution rate. This is mainly because the more significant the contact area, the larger the area for mass transfer.

It can also be seen that the gas dissolution rate gradually decreases with the increase of residence time in the gas dissolution tank. This is because the difference between the saturated solubility of air in the solution and the actual solubility at this temperature and pressure is gradually shrinking.

Therefore, it can be considered that the increase in the residence time of the solution in the gas dissolution tank can increase the final gas dissolution volume. Still, the gas dissolution rate per unit time tends to decrease.