Elektroflotation for cleaning waste water from oil

Oil production is a new industry in Kazakhstan that promotes the economy and makes noticeable social development. This industry has many environmental impacts such as air pollution, soil pollution and hazards associated with waste production.

On-shore exploration, like the case in Sudan, carries potential risks for local inhabitants and may cause severe damage to the environment upon which their daily life depends. Also off shore oil production represent a great risk to the marine environment.The environmental costs of oil development have been extensive. They included destruction of wildlife and biodiversity, loss of fertile soil and degradation of farmland. Oil & gas reservoirs have a natural water layer (formation water) that being denser liesunder the hydrocarbons. To achieve maximum oil recovery, in certain stages of oil field life, additional water is injected in the reservoirs to help force the oil to the surface. Both formation and injected water are eventually produced along with the hydrocarbons. This produced water is the largest volume waste stream in oil production operations. Other wastes that may be generated during this process include the residual wastes that remain after separation of the oil [1-2].

Almost all oilfields produce large quantities of contaminated water. For every barrel of oil produced around the world approximately 2-10 barrels of water is associated. Water production quantities continue to increase as the oil and gas fields reach maturity. Since great quantities of this water are produced in arid areas, the concept of finding beneficial uses for produced water arises in recent years to convert a high-cost liability into an asset.

At the surface, produced water is separated from the oil, treated to remove as much oil as possible, and either discharged or injected back into the wells. The general approach for produced water treatment is de-oiling and de-mineralizing before disposal or utilization. uality of produced water discharges to surface or reinjected to wells is controlled by rigid environmental regulations in all countries. In Kazakhstan the Ministry of Energy and Mining developed national environmental regulations for petroleum industry [1-2].

The composition of produced water is strongly field- dependent and includes a variety of inorganic and organic compounds. Produced water contains small amounts of emulsified oil, organic compounds including dissolved hydrocarbons, organic acids, phenols and traces of chemicals added during production, inorganic compounds, suspended solids, dissolved solids and natural low-radioactive elements Petroleum products are the most common pollutants. A large number of these impurities contained in the effluent of motor and car companies, railway companies and agricultural equipment, tank farms, pumping stations and loading points. Wastewater treatment,

there are certain difficulties associated with the release of these parts of the emulsified oil and oil products, which form water

At present, the actual problem is the development of effective methods of nonchemical intensification elektroflotatsion cleaning oil and oily water. Positive results were obtained in the purification of water high effect can be achieved by using a combination of titanium and graphite electrodes. Concentration of oil in this case decreases from 350 to 10 mg / l (see Table 1.2) In Table 1 we studied the effect of current density on the degree of purification titanium water from oil..

The current density was varied 25-200 A / m2, and the degree of purification of water has increased from 69.6% Oil - 89.2%, depending on the salinity of the power consumption of 0.2-1.2 kWh / m3. In Table 2 we studied the effect of electrolysis duration of the degree of purification of water from oil. Electrolysis time value varied 1060 minutes while the degree of purification of water from petroleum increased 89.2% - 99.8%. Use of insoluble electrode-cleaning preferred emulsions, despite this increase in energy consumption. Increased electrode life, decrease in foam volume and simplify the technology of its processing compensates for the extra power consumption. Test installation with such elektroreaktor revealed some features of cleaning water from oil products. Thus, the cleaning efficiency in floto depends primarily on the concentration and dispersion of oil particles.

Effect of extraction increases with their size and quantity without changing the cleaning, the residual oil wherein the concentration of 1-5 mg / l.In addition to the electrical parameters, on the degree of extraction of oil and oil products is greatly affected by hardware design and hydraulic parameters of the process electroflotation. For example, proposed by "Ford Motor" elektroflotator countercurrent movement of the water and gas bubbles, as well as a rotating feed and collection device allows more uniform distribution of water in the unit volume and to increase cleaning efficiency.

Electroflotation is one of the most effective ways to purify water from oil and butter, it is carried out in devices with insoluble or soluble electrodes.Experiments were carried out special electrochemical cell (Figure 4). Design of the apparatus for cleaning elektroflotatsion quite simple. The electrodes can be carried out in the form of plates disposed at the bottom of the unit horizontally or vertically, occupies almost the entire area of the bottom to prevent the flow patterns that prevent flotation contaminants Politkovskaya was found that the efficiency of this method is equivalent to the treatment of urban wastewater in the aeration tanks to incomplete cleaning, more efficient and easier to use than biochemical methods of aeration or biofiltration. When using insoluble electrodes flotation efficiency depends on the size of recoverable drops. For example, if the recovery rate of the particle diameter of 18 micrometers is 62.5%, the diameter of 10 micron - 23.3%. Particle diameter of 5 m oil electroflotation almost recovered, and a diameter greater than 22 microns are removed effectively

Table 5- Effect of current density on the degree of purification of titanium water from Oil

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ater purification devices elektroflotatsion include electrolytic generation of gas bubbles, the adhesion of gas bubbles and dirt particles, transportation of aggregates formed "gas bubble - particle pollution" on the surface of the liquid to be treated. An important and often determined by the stage of the process is elektroflotation adhesion of gas bubbles and dirt particles, which occurs at the molecular level. Approximation vesicle particles is effected by external hydrodynamic forces, and the distance between them is reduced to 10 ~ 6 mm, molecular forces start to act. In this case, the act of sticking particles to the bubble is accompanied by a sharp decrease in the surface energy of the boundary layers and the emergence of forces that seek to reduce the wetted surface.

The flotation process flows more successfully than the more general surface of the gas bubbles and the greater area of contact with them floatable particles. In systems with the same degree of liquid gas filling the total surface of the smaller bubbles will be greater and the distance between the particles and smaller bubbles, which enhances the probability of their collision.

A major role in the process of performing electroflotation bubbles of hydrogen evolved at the cathode. When studying the mechanism and kinetics of the hydrogen evolution cathode was shown that the size and rate of formation of hydrogen bubbles depend on the composition and temperature of the electrolyte, the surface tension at the interface "electrode - solution" electrode material, its shape and surface roughness of the current density. By changing these parameters, it is possible to adjust the size and intensity of gas bubbling in the electrolysis, ie. E. Corrected depending on the nature of the contamination of water purification process. The size of gas bubbles produced at the electrodes depends on the balance of forces acting on the bubble at the time of their formation and growth: surface tension. First firmly holds the more bubbles on the electrode, the greater the perimeter through which the bubble is attached to poverhnosti second substantially proportional to the volume of the bubble.

Fundamental studies of BN Kabanov and Frumkin showed that the size and shape of bubbles released on the electrodes, it is possible to uniquely identify a contact angle characterizing the surface tension on the three-phase boundary "electrode - water- gas" and determining the equilibrium condition of the surface forces interacting phases. Bubble detachment from the electrode surface occurs when the hydrostatic uplift force exceeds the holding force of surface tension. Consequently, the balance of the bubble is determined by the action of only capillary forces and gravity.

The surface tension depends on the electrode potential and adjusted to a maximum electrocapillar curve near the point of zero charge of the electrode.

The bubble size at the time of separation from the electrode depends on the magnitude of the contact angle (Fig. 4.34). In addition, growth kinetics, and separation of hydrogen bubbles affects the electric field. Due to excess OH- ions in the cathode layer of hydrogen bubbles acquire a negative charge, which causes their repulsion from the electrode surface. In a significant protrusions on the surface of the electrode is observed uneven electric field intensity and most of it, which ensures rapid growth and detachment of small bubbles. The higher the field strength and the amount of the charge, the greater the ponderomotive forces, comes off the vial from the electrode, and the smaller bubbles. This is also due to the effect of current density on the value of the bubbles.

Effect of the electrode surface and the curvature on the number and size of bubbles produced on the cathodes of electrolytic hydrogen from the BM studied wire mats. Established that the bubble diameter of the pull has a significant impact on the efficiency of the purification process elektroflotatsion liquids. It was also revealed

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that an increase in the degree of dispersion of bubbles, t. E. A decrease, increases the effectiveness of electroflotation suspended particles of organic origin. The dispersion of bubbles depends, in turn, from the wire cathode parameters: the material and surface curvature of the reciprocal of its radius.

Similar results were obtained in a number of other raoot performed under the direction of V. Ivanov LISI. .

Electroflotation is used for sewage treatment, oil fields, oil depots, refineries, tanneries, fur factories, pulp and paper and electrochemical industries, as well as the separation and compaction of activated sludge after aeration on biological wastewater treatment plants. Effects of treatment may be as follows: petroleum derivatives - 90% suspended solids - 70% by Fats - 80%; detergents may be removed at 60-70% •

A promising direction is the ion electroflotation wastewater treatment and recovery of both metals from dilute solutions, and various valuable substances from seawater. Under appropriate conditions it is possible to separate ions of different elements that have the same magnitude and sign of the charges.

Design of devices for elektroflotatsion, clean simple enough. The electrodes can be carried out in the form of plates disposed at the bottom of the unit horizontally or vertically, occupying almost the entire area of the bottom to prevent the flow patterns that prevent flotation contaminants.

To prevent the formation of deposits include various modifications of the placement of the electrodes in the apparatus. 3 Anodes of graphite or other resistant material electrolytically formed as separate triangular prisms arranged in a checkerboard pattern, and the cathode 5 - in the form of individual wire screens, angled and positioned above the anode prisms parallel to their faces. For supplying electrical current to the conductive sleeve molded prism 4. In the upper part of the apparatus located chute 1 for collection and removal of condensate foam, which is placed in the conduit 2 for steam-foaming, and at the bottom - the conical bottom for collecting the precipitate.

Table 6 - Effect of electrolysis on the degree of purification of water from oil

Electroflotation method has some significant advantages over other methods of flotation wastewater: ease of manufacturing devices and the simplicity of their service; possibility of regulating the degree of cleaning fluid depending on a phase state of particulate contamination by changing only one parameter (current density) in the process; high degree of dispersion of the gas bubbles, which provides the efficiency of attachment of insoluble impurities; no moving parts in the work area devices, ensuring their reliability and precluding mixing liquid to be treated and grinding it contains suspended particles; additional mineralization of organic pollutants with

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simultaneous disinfection of wastewater generated due to the anode of the electrolysis products - atomic oxygen and chlorine.

LITERATURE

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