Sewage treatment how to remove oily residue

Air flotation oily wastewater treatment technology 1 Introduction Air flotation is in the oily wastewater into the air (or natural gas) or try to make the water to produce gas, and sometimes need to add flotation agent or coagulant, so that the sewage particle size of 0.25-25um emulsified oil and dispersed oil or suspended particles in the water adhering to the gas gown, along with the bubbles together with the surface of the water and to be recycled, so as to achieve the removal of oil from oily wastewater The purpose of removing oil and suspended matter from oily wastewater. Air flotation technology is with the development of the oil industry and the gradual development of the Daqing Oilfield Design Institute in the 20th century in the 1960s in the East Oil Reservoir sewage station with a homemade impeller flotation machine flotation experiments were carried out, and satisfactory results were obtained. Adding 100 mg / l of ferrous sulfate, water in the flotation cell residence time of 30 min, can make the import oil content of 20 315 mg / 1 of the electric dehydrator discharge water (water temperature 5O ℃ or so) after flotation oil content down to 60.3 mg / l, in addition to the oil removal efficiency of 99.7. 1991, Dagang oilfield south one-stop wastewater treatment design used in the production of Shenyang Special Equipment Factory imitation of the United States four-stage Impeller flotation machine, put into operation by the test run in addition to the oil efficiency of up to 85, the effluent oil for 18.8 mg / 1, in addition to the oil effect is good Zhongyuan Oilfield, Wen Erlian, Shengli Oilfield 102 station, an oil field in Qinghai and other oily wastewater treatment stations are a full set of treatment facilities from the United States are introduced, are also using the impeller flotation machine, and then one after another in the Shengli Oilfield, Caoqiao, Bin a note, the Jidong Oilfield, Liuji oil station and other wastewater treatment station Flotation machine is used as the treatment equipment for oily wastewater. 2 air flotation method is categorized according to the different methods of generating air bubbles, air flotation technology is divided into the following three kinds. 2.1 dissolved air flotation dissolved air flotation is a pump to lift the wastewater to the dissolved air tank, pressurized 0.3 ~ O.35 MPa (gauge pressure), while injecting compressed air, so that it is supersaturated, and then instantly depressurized, and then suddenly released a large number of dense micro-fine bubbles, so that the bubbles and phi to remove the substance of the combination of the rapid separation from the water, floating to the water surface. 2.2 Impeller type air flotation (mechanical air flotation) Impeller type air flotation using high-speed rotation of the impeller, the inhalation of air into the water shear into fine bubbles, so that the combination of air bubbles and substances to be removed from the water quickly rise and water separation. 2.3 Jet air flotation Jet air flotation is used to high pressure water (O.3 ~ 0.7 MPa) through the injector, the nozzle at the negative pressure, the inhalation of gas medium, after mixing tube of strong shear, so that the gas medium to form fine bubbles, small bubbles captured oil droplets, rise to the liquid surface to form slag. In recent years, a variety of air flotation technology in the field of oilfield oily wastewater treatment is more and more widely used, because for some of the density close to water oil, using natural gravity settling method is difficult to remove from the water, the use of air flotation law is more effective, especially the offshore platform extracted water treatment in the use of induced air flotation device, instead of using the natural sedimentation barriers in addition to the oil is because of the effect of air flotation treatment is good, the equipment is small in size, suitable for the platform Area limited conditions. 3 factors affecting the effect of air flotation 3 1 air-water ratio air-water ratio is an important technical parameter of the air flotation (flotation) machine. The larger the air-water ratio, the better the treatment effect. The greater the number of bubbles, the greater the chance of contact with oil beads. The oil beads attached to the bubbles on the opportunity to increase, the treatment effect will be improved. But it is not the greater the ratio of gas to water, the better, in terms of dissolved air flotation, the amount of gas dissolved in water by the temperature, pressure and other conditions, in general. Water temperature is higher than 40 ℃ when the solubility of gas in the water to reduce more. In addition, the amount of dissolved gas is directly proportional to the gas pressure, increase the gas pressure, can improve the gas-water ratio, but too high a pressure will greatly increase the operating costs, the economy is not calculated. Of course, increase the residence time can also improve the gas-water ratio, but this method reduces the efficiency of the equipment. 3.2 The size of the bubble Due to the different sizes of bubbles by the buoyancy of different, they adhere to the ability of oil droplets are not the same, small bubbles rise slowly, easy to capture oil droplets (especially small oil droplets), and large bubbles rise quickly, large oil droplets are easy to be captured by it. But the bubble is too big, too fast floating speed so that it is not easy to adhere to the oil droplets, and easy to rupture, in addition to the oil effect is not good. When the inlet medium oil content in 1.0 ~ 200 mg / l, dissolved air flotation oil removal rate is the largest. But the gas-water ratio generated by the dissolved air flotation is unfavorable to oil removal. Because the solubility of gas in water is very limited, and impeller air flotation machine and jet flotation machine bubble size is not very ideal, but the gas-water ratio is much superior than the first two, so when the sewage oil content & gt; 200 mg / I, the use of impeller air flotation and jet air flotation is more appropriate. 3 3 Salt content Oilfield produced water generally contains salt, from dozens to hundreds of thousands of mg / 1, the experimental results show that: oil-containing wastewater in the salt content increases in favor of improving the efficiency of oil removal. 3, 4 air flotation chemicals The effect of air flotation treatment of oily wastewater, to a large extent, by the impact of the addition of chemicals, and sometimes play a decisive role. The use of air flotation additives, coagulants and foam wattle can greatly improve the efficiency of air flotation treatment of oilfield extracted water. Foreign agents, especially air flotation additives are mostly compounded polymers, with coagulation, emulsion breaking, foaming and floating a variety of roles. 4 three kinds of flotation machine on the adaptability of fluctuations in process conditions 4.1 Changes in the oil content of the beam water Impeller flotation machine has a greater potential for oil removal, and pressurized dissolved air flotation oil removal capacity and the oil content of the feed water has a greater relationship. 4.2 Changes in water temperature Impeller flotation machine inflation is not affected by the water temperature, the water temperature reaches 90 ℃ can still work normally, while pressurized dissolved air flotation and jet flotation inflation in the water temperature will be significantly reduced, so that the flotation effect is reduced. 4.3 Changes in the flotation process Impeller flotation machine itself stirring role is stronger, and thus the mixing of chemicals before it can be less demanding, and can be added in the middle of the flotation process, to facilitate the adjustment of chemicals. The jet air flotation and pressurized dissolved air flotation is not, before it added to the pharmaceutical mixing requirements are higher, the raw water needs to be pre-added chemicals, adjust the PH value, while adding flocculants pre-coagulation sufficient to improve its treatment effect. 5 The development of domestic and foreign air flotation equipment In recent years, with the wide application of air flotation equipment in sewage treatment works, the structure and types of flotation equipment are also changing and increasing. Dissolved air flotation: shallow pool flotation, high-efficiency flotation, etc.; mechanical flotation mainly vortex-concave air flotation, induced air flotation, as well as spiral propulsion and so on. The following is a description of these types of air flotation equipment as follows. 5.1 Shallow pool air flotation Shallow pool air flotation is based on the traditional air flotation, the use of shallow theory and the principle of "zero speed, cohesion, air flotation, skimming, sedimentation, scraping mud as a whole. The whole equipment is cylindrical, compact structure, shallow pool. The main body of the device consists of five main parts; pool body, rotating water distribution mechanism, dissolved air release mechanism, frame mechanism, water collection mechanism and so on. The water inlet 13, water outlet 13 and scum discharge 13 are all concentrated in the central body of the pool body, the water distribution mechanism, the water collection mechanism, the dissolved gas release mechanism are all tightly connected with the frame and rotate around the center of the pool body. The effective water in the pool; Jenn} for 400 ~ 500 mm, the pool hydraulic residence time of 3 ~ 5 min. The advantages are: shallow pool, suspended solids floating time is shortened to a certain extent to overcome the shortcomings of the poor stability of the scum after floating The disadvantage is the pressure is high (0.4 ~ 1.0 MPa), the bubble is large (30 ~ 100 um), and the pool is shallow also caused by the pool of clear water area is not obvious or no clear water area. 5.2 High-efficiency air flotation technology and its complete sets of equipment is the Ministry of Metallurgical Industry, General Research Institute of Architecture in 1981 to create a leading international level of high-tech water treatment projects. The project inventor Xu Zhi established the adsorption value theory as the basis for design. Compared with the traditional air flotation, the main differences are as follows: a. High-efficiency air flotation improves the oil removal efficiency by expanding the gas-liquid contact area, instead of prolonging the residence time to improve the oil removal efficiency. b. The solubility of the air flotation is not as high as that of the conventional air flotation. b. High sister-in-law air flotation dissolved gas utilization rate of up to 100%, according to the theory of adsorption value, only smaller than the suspended particles than the particle size of the micro-bubbles, with the suspended particles can be effective adsorption. High drum air flotation can produce lum bubbles, while the conventional air flotation bubble diameter is generally more than 50um. 5.3 induced air flotation induced air flotation is a typical mechanical air flotation equipment, began to be used in flotation processing industry. Installed in the machine through the high-speed rotation of the impeller to form a negative pressure will be sucked into the wastewater air, and at the same time the use of its high-speed rotation of the shear effect, the air crushed into small bubbles, rather than dissolved gas and then release the process, the diameter of bubbles is generally & gt; 50um, the inflatable volume can reach 3.2 m ／ min, much larger than the pressurized dissolved air flotation machine. Compared with the dissolved air flotation, induced air flotation has a small footprint, low operating costs. The disadvantage is that the high-speed stirring of the particle size & lt; 30 um oil droplet removal is unfavorable 5.4 vortex concave air flotation vortex concave air flotation is also developed on the basis of impeller air flotation and induced air flotation is different from the impeller is not mounted in the middle of the air flotation tank, but is installed in the flotation tank of the inlet end, relying on the rotating impeller and shear air into the air flotation with the inlet water into the air flotation area and the separation of the area, to achieve the solid-liquid (liquid-liquid) separation purpose. Compared with dissolved air flotation and induced air flotation, vortex air flotation has a small footprint and low energy consumption 5. Spiral propelled air flotation Spiral propelled air flotation originated in the United States, mainly by the propulsion of the spiral device to introduce air and cut and disperse bubbles to achieve the purpose of removing suspended solids. 5.6 Jet air flotation machine Jet air flotation is a new type of wastewater treatment technology that appeared recently. It uses sewage or purified water as the jet fluid, the fluid in the inhalation chamber of the jet to form a negative pressure, inhalation of gas, carrying the gas in the mixing section through the jet is sheared into tiny gas gowns, bubbles in the air flotation chamber in the process of adhering to the rise of the oil beads and solid-phase particles, rising to the surface of the liquid, to achieve the purpose of removing the oil residue. It can deal with all kinds of oilfield extracted water with oil content not higher than 2 ooo mg/l. Compared with the impeller type air flotation method, its advantages are: a. less electrical energy consumption, only equivalent to 33% of the impeller type air flotation method; b. no rotating parts in the liquid flow, shear force is very small; c. the resulting bubble diameter is small, so in the requirements of the operating conditions of the oil removal efficiency is higher than that of the impeller type. However, due to the high requirements of jet air flotation device on the pressure of the jet fluid, water quality and power and other operating conditions, therefore, the application of oilfield extractive water treatment is not as extensive as the impeller air flotation device. According to the characteristics of the jet air flotation method, the process is more suitable for the treatment of extracted water from remote oilfields with small amount of extracted water and low water quality requirements. 6 Conclusion There are many types of air flotation equipment, the choice of what kind of air flotation equipment to specific water quality. Currently used in oilfield oil recovery wastewater treatment, induced float selected more, the process is also more mature; vortex concave air flotation in the petrochemical wastewater has been applied, the effect is also good, but in the oilfield extracted water treatment has not been applied to dissolved air flotation is also applied in the treatment of petrochemical wastewater treatment, because of the release of its dissolved gas is not complete, the general exceeding of the standard of dissolved oxygen in the treatment of extracted water in the oilfield is a very step in the application of jet air flotation. At present, there are applications in the oilfield, such as Xinjiang Tuha oilfield, Wenmi joint station sewage treatment station, the effect is very good.