What kind of air flotation machine is dissolved air flotation machine integrated air flotation machine vortex air flotation machine

Types and comparison of air floaters

Types and comparison of air floaters

0 preface

Air flotation equipment is a type of micro-bubble that is introduced into the water or generates a large amount of fine bubbles, so that the air adheres to the suspended particles in the form of highly dispersed micro-bubbles, causing the density to be less than that of water, and floating on the surface by the buoyancy principle. A water treatment device that achieves solid-liquid separation. The air floatation method can be divided into diffuse air floatation, dissolved air flotation (including vacuum air floatation) and electrolytic air floatation. It is currently used in water supply, industrial wastewater and municipal wastewater treatment. Compared with other solid-liquid separation equipment, air flotation equipment has the characteristics of less investment, minimal ground, high degree of automation and convenient operation and management. In practice, targeted selection and use should be carried out according to the characteristics of wastewater treatment process, water quality and quantity of wastewater. The following combines years of practical experience to introduce the application of several air flotation devices for reference by peers and users in design, transformation and selection.

1 electrolytic air flotation equipment

The electrolyzed air flotation device directly electrolyzes the wastewater with an incapable anode and cathode. The tiny bubbles of hydrogen and oxygen generated by electrolysis float the flocculated suspension to the surface of the water. Achieve solid-liquid separation. The size of the bubbles generated by the electrolysis method is much smaller than the size of the bubbles generated by the dissolved air flotation and the diffused air flotation, and no turbulence is generated. The equipment removes a wide range of pollutants, and in addition to reducing BOD, organic matter wastewater also has oxidation, decolorization and bactericidal effects, and has strong adaptability to changes in wastewater load, less sludge generation, less land occupation, and no noise. It has developed rapidly in recent years. Electrolytic air flotation equipment currently has problems such as electrolytic energy consumption and large plate loss, and high operating costs, thus limiting the promotion and use of such equipment.

2 diffuse air flotation equipment

The air-dispersing air-floating device sucks air into a vacuum negative pressure state caused by the centrifugal force of the high-speed rotating impeller, and becomes a fine air bubble and diffuses into the water. The bubbles are brought up to the surface by the bottom of the pool rising to the surface of the water and adhering to the suspended solids in the water. Achieve solid-liquid separation. The resulting scum is continuously scraped out of the pool by a slowly rotating scraper. The mechanical shearing force of the water flow and the bubble generated by the diffusing plate are large (about 1 mm in diameter), and it is not easy to adsorb with fine particles and flocs, but it is easy to break the flocs. Therefore, the air flotation is not suitable for processing. Waste water with fine particles and flocs. The air flotation device has an air float time of about 30nim and a dissolved air volume of 0.51m ³ /m ³ (gas/water). The linear speed around the rotating impeller is approximately 12.5 m/s.
The equipment is used in small-scale sewage treatment projects such as paint, tanning, oil refining, printing and dyeing, chemistry, dairy processing, fiber production, paper making, food and beverage, slaughtering, textile, mechanical processing, municipal sewage. See Table 1 for the operation in some industries.

Table 1 The operation of air flotation equipment in some industries

According to the data of Table 1, the removal rate of COD (BOD) was 43.38%-89.1% after treatment, the de-treatment of SS was 90%-99.8%, and the removal rate of fat was 78%-99.3%. The throughput is between 25 and 163 m ³ /h. It can be seen that the air flotation equipment has a limited amount of wastewater treatment, but the treatment effect on insoluble materials and suspended solids is more obvious. The degreasing effect is generally about 80%. The removal rate of oils, gels and suspended solids in the treated wastewater is above 95%. The addition of suitable chemicals can reduce the COD and BOD in the wastewater by more than 60%.

3 dissolved air vacuum flotation equipment

The supersaturated air in the water can be released as fine bubbles during decompression, so that the impurity particles in the water are adhered and floated. Achieve solid-liquid separation. If the air is first pressurized to dissolve in water to form an air supersaturated solution, and then reduced to atmospheric pressure to precipitate air, it is called pressurized dissolved air flotation; if the wastewater is aerated under normal pressure, it is induced under vacuum conditions. The dissolved gas escapes, which is called vacuum air flotation.
The dissolved air vacuum flotation device is an air flotation device that dissolves air under water under normal pressure or pressure and precipitates under a negative pressure. The advantages of the vacuum type air flotation device are that the formation of bubbles, its adhesion to the particles, and the floating of the bubbles and the floccules are all carried out in a stable environment, the possibility of floc destruction is small, and the energy required for the entire air floatation process. Small amount. The disadvantage is that the amount of dissolved gas in water is limited, and it is not suitable for wastewater containing suspended solids with a concentration greater than 250-300 mg/L; another disadvantage is that a sealed container is required, and a scraping machine is required in the container, and the structure is complicated, so Less practical use in engineering. The amount of air that can be obtained by the equipment is affected by the achievable vacuum (typically operating vacuum of 40 kPa), the amount of fine bubbles precipitated is very limited, and the structure is complicated, and the operation and maintenance are inconvenient, and it has been gradually eliminated.

4 pressurized dissolved air flotation equipment

The pressurized dissolved air flotation device pressurizes the water to (3-4)×10 ⁵ Pa, and simultaneously adds air to dissolve the air in the water, and then suddenly reduces to normal pressure, and the air dissolved in the water is in the form of tiny bubbles ( The bubble diameter is about 20-100 μm), which is precipitated from the water and floats the suspended particles in the water on the surface of the water. Thereby achieving solid-liquid separation. Pressurized dissolved air flotation equipment is a kind of air flotation equipment with a wide range of applications. The equipment can be widely applied to various types of wastewater treatment (especially oily wastewater treatment), sludge concentration and feed water treatment.
Pressurized dissolved air flotation equipment mainly consists of air-saturated equipment, air release and equipment mixed with wastewater, solid-liquid or liquid-liquid separation equipment. According to the type, nature and treatment efficiency of the suspended solids contained in the raw water, it can be divided into three types: pressurized dissolved air flotation, partially pressurized dissolved air flotation and reflux pressurized dissolved air flotation.
At present, the application of pressure dissolved air flotation method is widely used. Compared with other air flotation devices, it has the following characteristics:
(1) Under pressurized conditions, the air solubility is large, and the number of air bubbles used for air supply and floating is large, and the air floating effect can be ensured;
(2) The dissolved gas is released under sudden decompression, and the generated bubbles are not only fine, uniform in particle size, large in density, but also stable in floating and small in disturbance to liquid, so it is especially suitable for solid-liquid separation of loose flocs and fine particles;
(3) The process and equipment are relatively simple, easy to manage and maintain;
(4) Especially for partial reflow type, the treatment effect is remarkable and stable, and energy consumption can be greatly saved.
4.1 Combined air flotation equipment <br> This equipment belongs to pressurized dissolved air flotation. It is widely used in industrial wastewater treatment such as paper making, printing and dyeing, electroplating, chemicals, food, and oil refining. See Table 2 for some enterprise applications.

Table 2 Practical application of pressurized dissolved gas combination air flotation

It can be seen from the data in Table 2 that the COD and SS removal rates of the treated wastewater combined with the air flotation equipment are between 78% and 95%, and the treatment capacity is around 30-150 m ³ /h.
4.2 Efficient shallow pool flotation device <br> appear shallow pools efficient flotation equipment, flotation is a major breakthrough in water purification technology. It changes the static air inflow from the traditional air-floating static water, and uses the “zero speed principle” to apply the “zero speed principle” to make the flotation body float vertically on the water in a relatively static environment to achieve solid-liquid separation. The “zero speed principle” reduces the floating distance to small size, and is not affected by the flow rate of the water. The floating speed reaches or approaches the theoretical value of Zui, and the residence time of the sewage in the purification tank is reduced from 30-40 minutes of conventional air flotation to 30-40 minutes. It only takes 3-5 minutes, which greatly improves the processing efficiency, and the equipment volume is greatly reduced. It can be overhead, stacked, and placed on the building, with less land occupation or no land occupation. With the rotation of the water distribution device, the bubbles uniformly mixed with the sewage in advance can completely fill the entire purification pool, and there is no air floating dead zone and bubble unevenness zone, thereby greatly improving the purification efficiency.
The shallow pool air flotation device is to install the water inlet, the water outlet and the air flotation scraper on the rotary machine that rotates around the center of the air floating pool. Both the rotating frame and the scraper bucket are driven by the motor and can be steplessly regulated. Rotate at the same speed as the influent flow rate. The wastewater enters the water from the rotating water inlet in the center of the pool, and the water is distributed through the inflow water distributor. The moving speed of the influent water distributor can be the same as the inflow water flow rate. The raw water enters the pool to produce zero speed. According to the "zero speed principle", the water will not disturb the water flow in the pool. The ups and downs of the particles in the pool are carried out in an ultra-quiet state, thereby greatly improving the efficiency of the flotation cell. The spiral scraping device has very little disturbance to the water body, and only the scum which has been sufficiently separated is scraped, and the solid content is high. Compared with other air flotation devices, it has the following characteristics:
(1) Designed using “shallow pool theory”, “zero speed principle” and “new dissolved gas mechanism”;
(2) The hydraulic retention time is short, only 3-5 minutes, and the depth of the pool does not exceed 700mm;
(3) The micro-bubbles are extremely small and the density is extremely high. It is not necessary to condense them into a large squid in advance, which can greatly reduce the dosage and greatly reduce the running cost;
(4) The adhesion of fine bubbles and flocs occurs in the entire air flotation separation process including the contact zone;
(5) Forced water distribution, the water in and out is static;
(6) The discharge of clean water is carried out after solid-liquid separation, and the scum is instantaneously isolated and eliminated, and the water body disturbance is small;
(7) The solid content of the slag is as high as 3%-5%, and the suspended matter removal rate is 99.5%. The bottom of the pool is provided with a scraping board to automatically scrape off the settled sludge;
(8) The dissolved gas pipe adopts unique design, small volume, high dissolved gas efficiency, convenient operation and small floor space;
(9) The equipment has high operating efficiency, good stability, large processing capacity and less one-time investment;
(10) Reasonable selection of dissolved gas and chemical addition points to ensure the realization of copolymer flotation;
(11) It has a number of adjustment functions, which can change with the change of water quality and quantity of treated water.
Shallow pool air flotation is a new type of high-efficiency air flotation treatment equipment for industrial wastewater physicochemical treatment. It is widely used in papermaking white water recycling, tanning, textile, soap making, food, carbon black, fiber products, oil extraction, beer, municipal wastewater reuse and other fields. . Reasonable allocation of auxiliary equipment such as dosing equipment, dissolved gas equipment, pumps, etc. can reduce the total amount of suspended solids in wastewater by more than 90%. The air-floating hydraulic retention time is only 3-5nim. The use of this equipment can greatly reduce investment and operating costs, and save a lot of cultivated land, especially when used to treat large-scale sewage. The performance comparison of pressurized dissolved air flotation treatment equipment at home and abroad and the application of shallow pool air flotation equipment in the paper industry are shown in Table 3 and Table 4, respectively.

Table 3 Comparison of performance of pressurized dissolved air flotation equipment at home and abroad

Table 4 Practical application of high-efficiency shallow pool air flotation equipment

It can be seen from Table 3 that the data show that the shallow air flotation treatment is better than the aeration air flotation, and the COD and SS treatment technical indicators and the use effect of the ion flotation in the shallow pool air flotation are better.
From the statistical analysis of Table 4, the removal rate of suspended solids in shallow pool air flotation equipment is over 92.8%, the removal rate of COD is above 65.3%, and the removal effect of SS on treatment facilities is more obvious. In addition, the data indicates that shallow pool air flotation equipment The processing capacity is above 300-850m ³ /h.

4 Conclusion

(1) The amount of treated air in the air flotation equipment is 25-163m ³ /h, the amount of treated wastewater is small, and the treatment effect on insoluble materials and suspended solids is more obvious. The degreasing effect is generally about 80%. The removal rate of oils, gels and suspended solids in the treated wastewater is above 95%. The addition of suitable chemicals can reduce the COD and BOD in the wastewater by more than 60%.
(2) The pressure dissolved gas combination air flotation equipment has limited processing capacity, and the processing capacity is about 30-150 m ³ /h. After adding suitable chemicals, the COD and SS removal rates of the treated wastewater are all about 80%.
(3) The treatment capacity of shallow pool air flotation equipment is above 300-850m ³ /h, the removal rate of suspended solids is over 92.8%, the removal rate of COD is above 65.3%, and the removal effect of SS on equipment is obvious. At the same time, the hydraulic retention time of the equipment is only 3-5 minutes, which occupies less space than other air flotation equipments. It has high technical content and convenient operation and management. The treated water can fully meet the requirements of process water reuse, saving water resources and considerable Economic benefits.
(4) For the application and comparison of several kinds of air flotation equipment, it is recommended that when selecting the air flotation equipment in the wastewater treatment process, it should be comprehensively considered according to the water quality and quantity of wastewater, the recyclable value of wastewater, the land area, equipment investment and other factors. Under the premise of the requirement, when the wastewater treatment capacity is less than 300m ³ /h, the air flotation or pressure dissolved air flotation equipment can be selected. When the wastewater treatment scale exceeds 300m ³ /h, the shallow pool air flotation equipment should be considered.

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