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Guangzhou Longkon Eco-Tech Limited

The application of flotation technology in oily wastewater treatment

Update Time:2014-11-17 11:31:36 Writer: Source:
  The application of flotation technology in oily wastewater treatment
Flotation water purification technology at home and abroad is was deep research and promotion of a new water treatment technology.Flotation water purification device has been widely used in petroleum, the papermaking, the printing and dyeing, electricity, electroplating, chemical industry, chemical fiber, wool, leather, electrophoresis paint, food, urban sewage, bath, water and other industries, and achieved good efficiency.

1 the classification of the flotation process and flotation oily sewage purification, the commonly used method

In wastewater purification, and the bubble size according to the formation of air bubbles in water.Flotation process can be divided into four types, namely, gas dissolved air flotation, Japanese float induced air flotation, electricity and chemical air flotation.One of the commonly used method has the following several kinds: gas pressurized dissolved air flotation, the impeller type air flotation and jet air flotation.

1.1 dissolved air flotation process

Dissolved air flotation process can be divided into full flow pressure type, return flow, part of raw water and compressed air, four kinds of full flow pressure dissolved air flotation method of dissolved gas is large, the flotation cell volume small, widely used in oilfield sewage treatment;Return flow dissolved air flotation method is a part of the purification of water back into the dissolving tank pressurization dissolved air, then with to liquid into the flotation cell, therefore, can be in raw water need to advance the coagulation and raw water oil content is higher under the condition of use;Part of raw water dissolved air floatation method and the whole flow pressurized dissolved air flotation method of similar type, is suitable for oilfield sewage processing oil content is low;Pneumatic dissolved air flotation method is through the porous plate, perforated plate, or a special kind of nozzle, the gas pressure in the liquid, than other kinds of dissolved air flotation technology of short residence time.

1.2 impeller flotation process

Air flotation depend on high-speed rotating impeller impeller to produce tiny bubbles.Bubble formed by mechanical mixing in the oily sewage, residence time is short, high oil removal rate, low cost, to adapt to the changes in water oil content.WEMCO company produces the impeller flotation machine is widely used, running effect is good.Some of the big domestic oilfield, liaohe oilfield, shengli oilfield and xinjiang oilfield successively introduced the flotation machine [2].Impeller flotation machine, however, there is the manufacture, maintenance trouble, high energy consumption.In order to overcome the shortcoming of the flotation machine, a jet flotation device.

1.3 jet flotation process

Jet flotation method is to use the principle of jet pump, the use of sewage or purified water for injection fluid, when the water through high-speed nozzle, the nozzle form negative pressure suction chamber, gas is sucked suction chamber, the high speed water by mixing section, carrying gas is cut into tiny air bubbles;In flotation cell, the bubble buoyancy and adhesion on the oil and solid particles, it brought to the surface.Liquid-gas jet pump instead of rotating impeller, it can be used to power a water pump, greatly save the energy consumption, only about half of the impeller flotation bubble diameter is small, and manufacturing installation, convenient maintenance, safe in operation and has a great deal of research and application prospect.But so far, domestic also in jet flotation device have no systematic study.
Developed by Beijing university of science and technology of flotation column team for efficient processing microgranular pulp of LHJ flotation column used in produced liquid of shengli oilfield wastewater treatment, the results show that the oil removal, removing impurity efficiency up to 97%.The characteristics of the new type of short cylinder LHJ flotation column are: (1) the particle and bubble collision was conducted in the catheter, separation process in the cylinder, implements the turbulent collision mineralization, the separation of static good conditions;(2) the water jet technology, the pulp is mixed with gas more fully, dynamic loss reduction, intraductal inspiratory capacity increase;(3) using the balance pipe, that catheter under completely filled fully takes advantage of the effective height of the overflow pipe;(4) the intraductal smooth surface, stable inspiratory capacity, simple and reliable control of the production operation, is a promising high oil removal device.Have oily water to deal with the unit, also can seek advice to sewage treasure project service platform has the similar experience in sewage treatment enterprises.

3.2 flotation in the research on supporting agent

Agents used for the flotation process including coagulant and flotation agent, which directly affects the flotation process of water quality.Richard. J G, Luthry and others in the dissolved air flotation method and treatment of emulsified oil refinery trials found that in all of the anionic, cationic and nonionic flocculant, cationic flocculant WT2640 processing effect is best.The copolymer flocculant is a kind of liquid, has high positive charge, which contains 75% of PDADMA (b M M methyl amine), in the form of two kinds of the coagulation flotation experiment found that before flotation and organic flocculant, can greatly improve the flotation effect.Yang xu on impeller flotation machine with flotation agent was studied, by cationic polymer and surfactant (reverse wetting agent, bubble agent) distribution, after its flocculating ability is strong, strong adhesion flocculated particles and bubbles, oil-water separation speed.To muddy rate around 90%.
  We design a new type of flotation column, multistage circulation to reduce the entrainment in the flotation entrainment and backmixing problem, compared with the conventional flotation column, separation efficiency improved significantly.

Used for treatment of oily wastewater and the flocculant and the development trend of flotation agent supporting agents are: by single inorganic flocculant, organic flocculant development preparation for compound or complex matches, a complete demulsification and coagulation.Flocculation and flotation.
3.3 flotation mechanism of the flotation machine is reviewed

In the researches on the mechanism of the flotation, flotation process was discussed, the effect of various factors on treatment effect for reasonably to improve the flotation process.Determine the correct design method provides a theoretical basis.C.W.B urkhardt "' found in research on the reaction mechanism of impeller flotation, when other things being equal, the concentration of the oil changes with time, the first order reaction kinetics equation to express. For single stage impeller flotation, its expression is:

Dc/dt = - kc lnc0 / ct = kt

Type: C - the concentration of the pollutants, mg/L;

C0 - t = 0 when the concentration of the pollutants, mg/L;

Ct - t = 0 when the concentration of the pollutants, mg/L;

K - rate constant, h - 1;

T a system overall effective retention time, h.

Is actually used multistage impeller flotation, generally for level 4 impeller flotation, its expression is:

C4 / c0 = (1 kt / 4) - 1

Type: C4 - level 4 impeller flotation water contaminants, eventually mg/L

Niel. J.M.V an. Ham and others in the use of perforated plate distributor and puckering plate induced flotation process of dealing with the oil emulsion tests found that the removal rate of oil can be successfully used to represent the first order reaction kinetics model, the rate constant of 2 ~ 60 h - 1, et toshio palace, the former research results that can be used to represent the first order kinetics model.

However, for induction of impeller flotation machine, the use of type fitting on the oil concentration and measured concentration of the oil obtained vary widely, many points more than engineering permissible error range, model is not good, so, should consider when establishing dynamics model not the part of the oil removal effect.Petroleum university Zheng Yuanyang on induction of impeller flotation mechanism research, on the basis of a correction model is put forward, namely:

Dc/dt = -k (c - cl)

Type: CL a deoiling limiting concentration, namely the flotation separation cannot removal oil droplets dispersed oil concentration, and the dissolution of mg/L;

K - flotation rate constant, h - 1

For intermittent induced impeller flotation machine

C = (C0 - Cl) exp (kt) + Cl

3.4 flotation technology application in oilfield oily sewage treatment

Due to different oil field oil content of oily wastewater, appearance is not the same, the more oil, the deeper the color.Crude oil in the unstable state of particles in the sewage, form oil-in-water status, the total oil content in 2000-5000 mg/L.To exist five oily sewage in the oil, the oil slick (> = 100 microns in diameter) accounts for some 30% of the total oil content, it is easily separated from the wastewater;Dispersed oil (10-100 microns in diameter) accounted for about 63% of the oil content, it can also rely on gravity separated from the wastewater, but separation slower;Emulsified oil, 0.1 to 10 microns in diameter () accounted for about 4%, its dispersion is higher, it is difficult to rely on gravity oil/water separation;Dissolve oil, oil wet little solid content.At present, the oily sewage has become the major source of oilfield water injection, for the water quality and through the analysis of the theory of the flotation technology, certainly flotation technology in oilfield oily wastewater treatment has broad application prospects. 
  1) applied in the wastewater treatment process of flotation technology, can improve the treatment effect of wastewater, the treated water quality to achieve the oil layer water injection water quality standard.

(2) with some or all of the flotation technology instead of natural oil removal, coagulation inclined plate oil removal and oil removal technology, can simplify the sewage treatment process, reduce the cost of sewage treatment.Flotation technology is used to deal with smaller particle size of the dispersed droplets, crude oil than serious, serious emulsion of oily sewage, has obvious advantages.

(3) it should be stressed that the stand or fall of flotation technology, depends on the flotation equipment and the supporting agent.Therefore should strengthen the research and development of low cost, simple structure, cover an area of an area small, easy operation and maintenance of efficient flotation degreasing equipment and supporting pharmaceutical development.Because of the characteristic of the new type of flotation column, it is expected to play a bigger role in oily wastewater treatment.Based on the differences of oily sewage water quality, targeted the development of strong adaptability, high efficiency, good, multi-function, low price of pharmaceutical researchers will continue to be a major goal.

(4) to improve the water quality of treated water, oil field sewage floatation process to combine with other wastewater treatment methods adopted.