The form of air flotation process

The air flotation water purification process has been developed in various forms. According to the way of generating bubbles, it can be divided into: air flotation by air distribution method (including rotor crushing air method, microporous air distribution method, impeller scattered air flotation method, etc.) electrolytic air flotation method; biochemical air flotation method (including biological air flotation method) method, chemical gas flotation); dissolved air flotation (including vacuum flotation, full dissolved air, partial dissolved air and partial reflux dissolved air of pressure air flotation).

1. Cloth air flotation

Cloth air flotation is a method of using mechanical shearing force to break the air mixed in water into fine air bubbles for air flotation. According to the different methods of crushing bubbles, air flotation is divided into four types: suction flotation of water pump suction pipe, jet air flotation, diffuser plate aeration flotation and impeller air flotation.

(1) The water pump suction pipe sucks air flotation

This is a very simple air flotation method. Due to the limitation of the working characteristics of the water pump, the air intake should not be too much, generally not more than 10% of the water intake (by volume), otherwise it will destroy the negative pressure work of the water pump suction pipe. In addition, the bubbles are not completely broken in the pump, the particle size is large, and the air flotation effect is not good. This method is used to treat the oily wastewater after passing through the oil removal tank, and the oil removal efficiency is generally 50%~65%.

(2) Jet air flotation

The method of air flotation is carried out by mixing air into the wastewater with a water-carrying air jet. The high-speed water flow from the nozzle makes the suction chamber form a negative pressure, and sucks air from the suction pipe. After the water-air mixture enters the throat section, intense energy exchange is performed, and the air is crushed into tiny bubbles, which are then diffused straight. The kinetic energy is converted into potential energy, which further compresses the air bubbles, increases the solubility of air in water, and finally enters the air flotation tank for gas-water separation. The size and related parameters of each part of the ejector are generally determined by experiments to determine the optimal size.

(3) Diffuser plate aeration and flotation

This kind of cloth air flotation is relatively traditional. The compressed air passes through the diffuser plate or diffuser tube with fine pores, so that the air enters the water in the form of fine air bubbles, but the pores of the diffuser device are too small and easy to block. If the pore size of the microplate is too large, a surfactant must be added to form usable micro-bubbles, which limits the use of this method. However, the elastic membrane microporous aerator developed and developed in recent years overcomes the shortcomings of easy blockage or large pore size of the diffusion device, and the microporous disc made of microporous elastic material plays the role of expansion and closing.

(4) Impeller air flotation

The impeller rotates at a high speed under the drive of the motor, forming a negative pressure under the cover to inhale the air, and the waste water enters through the small holes on the cover. After the gas mixture flows steadily through the rectifier plate, it rises smoothly and vertically in the tank body for air flotation. The formed foam is continuously scraped out of the groove by the slowly rotating scraper.

The diameter of the impeller is generally 200~400mm, and it is not more than 600~700mm. The rotational speed of the impeller is mostly 900~1500r/min, and the circumferential speed is 10~15m/s. The water filling depth of the air flotation tank is generally 1.5~2.0m but not more than 3m, which is related to the suction volume. The distance between the impeller and the guide vanes can also affect the size of the air intake. Practice has proved that the air intake will be greatly reduced if the distance exceeds 8mm.

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