Views: 889 Author: Site Editor Publish Time: 2024-10-30 Origin: Site
Operation suggestions for dissolved air flotation equipment in Waterworks
By investigating the operation of air flotation processes in different Waterworks, we summarize the problems that may be encountered during the operation of the Waterworks and conduct empirical analysis and solutions.
Table of contents(Click to go to where you want to see)
1.1 The setting of dissolved gas pressure
1.2 Effective control of gas-water ratio
1.3 Selection of dissolved air flotation reflux ratio
1.4 Dosage design
2. Dissolved Air Flotation Design Optimization Suggestions
2.1 Scraper settings
2.2 Selection of dissolved air water pipeline
2.3 Selection of dissolved air tank
2.4 Perforated water distribution board
3. Dissolved Air Flotation Operation and Maintenance Recommendations
Through the test and evaluation of the performance indicators of different types of flotation equipment, it is concluded that the change of dissolved air pressure directly affects the size of microbubble particles in the water, and the size of microbubble particles has a significant influence on the pollution removal efficiency of flotation equipment.
The experiments in various parts conclude that the dissolved air pressure of the flotation equipment can be set at 0.40MPa, and the bubble particle size is maintained at about 20μm~25μm. In actual production, according to the conditions of each Waterworks, it is generally set at 0.30MPa~0.36MPa, and the bubble particle size is maintained below 30μm.
According to the relevant specifications, the recommended value of dissolved air pressure is 0.2MPa~0.5MPa, and the recommended value of bubble particle size is 20μm~60μm. During the experimental test, the bubble particle size under each dissolved air pressure meets the specification requirements so that it can be initially set according to the above pressure conditions for actual use.
After analyzing and studying several flotation equipment's performance indicators and operating effects, the experiment shows that the gas-water ratio during equipment operation will affect the dissolved gas efficiency and the bubble particle size. A gas-water ratio that is too large or too small is not conducive to the stable operation of the process. Due to different types of equipment, the corresponding gas-water ratio values will vary. Specific problems should be analyzed in practical applications, but the gas-water ratio cannot be ignored.
The water level in the dissolved gas tank directly impacts the flotation efficiency of the dissolved gas flotation device. When the water level in the dissolved gas tank is too low, the gas is greater than the water, and giant bubbles are easily generated; when the water level is too high, the water is greater than the gas, which will reduce the contact volume between water and gas, resulting in a decrease in the concentration of bubbles in the water outlet.
Therefore, it is necessary to optimize the dissolved gas tank, and a porous partition can be set inside it to increase the contact area between gas and water through the role of the partition, thereby improving the gas dissolution efficiency.
As an essential parameter of the flotation system, the appropriateness of the reflow ratio in the actual application directly affects the flotation effect, equipment investment, and operating costs. The general guidance value in the design specification is 5%~10%, and 11%~15% is used when the algae content is high.
Through extensive research, the reflow ratio of most Waterworks is 10%. Increasing the reflow ratio can improve turbidity and algae removal efficiency when the water quality fluctuates wildly. Therefore, the selection of the reflow ratio should be comprehensively considered from the aspects of treatment effect, investment, energy consumption, etc., and is generally selected at 8%~10%.
When designing the dosage, the Waterworks should make reasonable settings based on the operating conditions of the Waterworks with the same raw water in the area. Generally, during the high algae and high turbidity period in summer, the coagulant dosage needs to be appropriately increased, and the dosage concentration should be between 3% and 10%.
Through the automatic dosing device for sewage treatment, more accurate, stable, and efficient addition of chemicals can be achieved, improving the efficiency of the sewage treatment system and the quality of treated water. This device helps reduce manual intervention and management costs while improving the stability and reliability of wastewater treatment.
During air flotation, if the scraping is not timely, the broken sludge in the sludge layer will sink, affecting the water quality.
Commonly used sludge removal methods include mechanical and hydraulic sludge removal. When using a scraper to remove sludge, the driving speed should be no more than 5m/min. According to actual operating experience, it should be kept at 2~3m/min. The downstream scraping effect is relatively good;
In addition, downstream scraping can avoid the increase of the moving shear force on the interface between the sludge and the water body during reverse operation without affecting the water quality; the scraper blade should be designed in an L shape. This type of scraper blade can reduce the phenomenon of the scraper blade sinking or extending downward due to the squeezing of the sludge;
However, mechanical scraping is prone to problems such as jamming and chain breakage. Using scrapers will also increase energy consumption, and the sludge on the liquid surface will be disturbed during operation.
The hydraulic slag removal method is to set an adjustable water outlet weir at the end slag tank of the flotation separation zone and use the rising liquid level in the separation zone to remove the slag, which will not cause slag disturbance on the fluid surface. Still, there are problems such as significant water demand, high water content of slag, and incomplete slag removal.
Therefore, most water plants use mechanical scraping slag removal, which can automatically scrape slag and improve work efficiency.
In the flotation process, the return water is pressurized and passed into the dissolved air tank from the top of the dissolved air tank, and then flows from the bottom of the dissolved air tank into the releaser at the bottom of the flotation tank to be released under reduced pressure. Therefore, when designing the pipeline direction of dissolved air water, to prevent the dissolved air water from generating a significant pressure loss in the water delivery pipeline, the dissolved air tank and the releaser in the flotation tank are generally discharged in parallel. After the dissolved air water is transported out from the bottom of the dissolved air tank, it directly enters the bottom of the flotation tank. The branches of the dissolved air-water delivery pipeline are connected to their respective releases, respectively, which can reduce the pressure loss caused by the series connection of the releasers.
The unreasonable design of dissolved air water pipelines in many Waterworks has caused a waste of dissolved air pressure. Therefore, this experience and lesson should be learned in future engineering design to optimize the delivery pipeline, reduce losses along the way, and improve release efficiency.
The air dissolving tank, indispensable in the flotation system, generally adopts the filled air dissolving tank. Filling fillers increases the turbulence in the tank, improves the dispersion of the liquid phase, and improves the efficiency of air dissolving. However, the fillers in the air-dissolving tank are easily polluted and blocked and need to be cleaned regularly;
Some Waterworks also choose to install water ejectors in the tank and use jet-pressurized air-dissolving tanks instead of traditional filled ones. Common ones are horizontal air dissolving tanks, which have automatic safety pre-pressure relief systems and sensors for automatic control of gas-liquid balance, can realize automatic air filling of air compressors, do not contain fillers, and therefore will not be blocked.
To ensure uniform water discharge from the separation zone, avoid short-circuiting, and improve the water quality of the discharge, a perforated water distribution plate should be installed in the separation zone. However, the flotation separation effect will be affected since the holes cause significant head losses to the bubbles. Therefore, it should be carefully checked during the design calculation.
Due to reasons such as rusting of pipes, erosion, and shedding of attachments in the tank, sludge attachment in the tank, and high turbidity of dissolved air water, the releaser will be blocked. Uneven scum and large bubbles will be found on the liquid surface. The uneven release of bubbles will increase the turbidity of the outlet water.
There are anti-blocking releasers that can automatically use hydraulic cleaning, which reduces the maintenance and cleaning cycle and increases the service life of the flotation process; conventional releasers still need regular maintenance and cleaning.
A filter can be installed at the connection pipe between the releaser and the dissolved air tank to prevent the releaser from being blocked. It is recommended that better-quality water, such as filtered water, be used for return water, which can reduce cleaning times and save workforce and material resources.