Views: 398 Author: Site Editor Publish Time: 2024-07-01 Origin: Site
The size of microbubbles is one of the most important factors affecting flotation efficiency. Microphotography allows people to monitor the size of generated bubbles through computers intuitively.
Cassel used this method to study the relationship between humic acid removal rate and bubble size. After experimental analysis, he believed that in the dissolved air flotation process, when the bubble diameter is less than 50μm, the removal rate is relatively high; when bubbles above 80μm are generated, there is almost no water purification effect.
If the generated bubbles are less than 10μm, then the water purification efficiency will no longer increase with the decrease in diameter, and the bubble concentration is the main factor affecting the water purification efficiency;
In the process of taking pictures of air floccules using microphotography technology, it was found that no bubbles with a diameter greater than 100μm were detected on the surface of the air floccules, so when the bubble diameter is more significant than 100μm, the floccules cannot adhere to it.
Through the analysis of bubble size, it can be seen that the bubble size dramatically influences the flotation water purification effect, and the component that affects the bubble size is the pressure-dissolved air releaser.
After the saturated dissolved air water with pressurized dissolved air passes through the releaser and decompresses, many microbubbles will be precipitated from the water. Then, the structure of the releaser will have a significant influence on the bubble size.
The diameter of the small hole of the releaser and the number of deflections of the dissolved air water were experimentally studied. The study found that when the small hole diameter is 2~2.5mm, and the number of deflections of the dissolved air water is less than two, the bubble size that can be generated is negligible. A good water purification effect can be achieved.
The simplest and most common releaser in life is the ordinary gate valve, which achieves the purpose of energy dissipation by reducing the cross-sectional area of the water flow. However, the gate valve cannot evenly distribute the released air water, which will release large bubbles, smash the flocs, and make it challenging to adhere to the flocs, so the gate valve is not used as a releaser.
There are various forms of dissolved air releasers. The most widely used in my country are TS-type releasers and TJ-type releasers. Figure 1-1 is the TS-type releaser's gas release working principle diagram.
Figure 1-1 Gas release flow chart of TS type releaser
When the dissolved air water released from the pressure-dissolved air tank passes through the releaser, it will first enter the orifice 1. Orifice 1 is smaller than the diameter of the dissolved air-water inlet at the lower end. The water flow section suddenly shrinks. At this time, the pressure energy of the dissolved air water is reduced and converted into the kinetic energy of air molecules;
The dissolved air water passing through orifice 1 enters hole chamber 2. It collides, causing the dissolved air water to continue to reduce pressure and convert into the kinetic energy of air molecules. At this time, most of the air molecules have obtained substantial kinetic energy and begin to form microbubbles;
The water flow enters gap 3, the section shrinks, the turbulence is more intense a local vacuum occurs, and almost all the air molecules are released;
When the water flow passes through 4 and 5, 95% of the pressure energy of the dissolved air water has been converted into the kinetic energy of gas molecules, forming micron-sized bubbles, which are finally released from outlet 6 of the releaser.
The different internal structures of the releaser will significantly impact the size and density of the generated bubbles. Still, various types of releasers have a standard feature: to make the dissolved air water have a higher pressure change in the releaser.
The dissolved gas pressure affects the air that can be dissolved in a specific volume of water. At the same temperature, the higher the pressure, the greater the amount of gas dissolved in water. This will affect the size and number of bubbles generated and directly impact the flotation effect.
The releaser is arranged in the contact area of the flotation tank. Its arrangement can be divided into ① reverse contact type ② co-directional push flow type ③ vertical radiation type according to the installation direction of the releaser (as shown in Figure 1-2).
Each placement method of the releaser affects the release angle of dissolved air water. It can be seen that the release angle of dissolved air water is also an essential factor influencing the flotation water purification effect.
Reverse contact
Co-directional push flow
Vertical Radiation
Figure 1-2 Arrangement of the releaser nozzle orientation
