Technical field of the invention

The present invention refers to a method of processing of oil sludge and oil sediments and finds application in dewatering of waste oil sludge, waste oil lubricants and heavy oil, deposited in ponds and lagoons, as well as of waste products from the oil refining industry.

The suggested method can be applied also in the processing of oil sediments from tanks designed for storage of oil products, as well as in other industrial and domestic sources of water, containing oil products, such as parking lots, vehicle servicing stations, handling and storage areas for oil products, petrol stations and distribution stations, industrial sites and machine servicing facilities, etc., which are close to residential areas and where the avoidance of residual pollution of soils and water basins with oil products as well as the suggestion of reliable and environmentally f iendly solutions are critical.

The method can find application also in the sphere of processing of ship wastewaters polluted with oil products, fuel, lubricants and greases. In the areas of the large ports, the ship waste waters can be collected and treated, and the resulting oil products can be reused, while the quality of the treated waste waters can be guaranteed.

State of the art

During the treatment of crude petroleum in the oil refining industry significant quantities of waste are produced and large quantities of oil sludge and oil sediments are deposited, which are hazardous to environment and people. There are technologies for processing of deposited oil sludge based on the present state of the art but the proposed methods are, on the one hand, extremely energy-consuming, because the treatment is carried out at high temperatures, and, on the other hand, they cause production of harmful emissions in the air and pollution of the underground waters.

In patent RU 2193578 C2 [1], published on 27.11.2002„A method for processing of oil-containing sludge" is described, according to which the oil sludge is treated at high thermal gradient. The heating is performed within one or several stages, each of them characterized by heating speed within the interval of 1,25 - 20,0 degrees/min. and temperature regimen - from ambient temperature up to 700°C for separation of the respective oil fraction. The process takes place in an inert gas or nitrogen-gas environment, and limited access of air. As a result of the treatment light and heavy oil fractions are obtained, the, residual component being tar oil. This method, known from RU 2193578 C2, requires extremely high power input, due to the high working temperature at which it takes place -from 90 to 700°C and the necessity of provision of inert gas medium.

According to Patent RU 2078740 CI [2], published on 10.05.1997, there is another method known for processing of oil sludge, produced in the oil-refining plants and at the locations for oil extraction. According to this method the raw oil sludge and the oil sediments are extracted by the sludge settler, then treated with demulsification agent, filtered for separation of particles with sizes greater than 10 mm., afterwards, processed and heated with water steam up to 40-50°C, and finally, settled for 15-20 min. Within this period, the oil sludge is separated into 4 (four) phases - oil-product phase, water phase, suspension (slurry) of water and oil sediments, and sediment. The oil-product phase is to be treated again in several stages whereby at every stage a new potion of demulsification agent is added. In the first stage, the oil product phase is heated by water steam up to temperature of 70- 75°C, centrifuged, treated with the demulsification agent, and after that, in the second stage it is further heated up to temperature of 90- 98°C, then separated and, as a result, oil and water are separated. The water phase is removed and directed for utilization by the auxiliary facilities. The sediment is removed and washed away by hydrocarbon solvents and water steam. In the suspension of water and oil sediments a medium of microorganisms is introduced, which are cultivated in aerobic conditions, utilizing the hydrocarbon compounds of the oil sediments as nutrient medium. During the process of their multiplication the microorganisms purge the suspension from the hydrocarbons and from the other harmful compounds. According to the known method, the processing of the oil- product phase is carried out at relatively high temperatures - up to 98° C and it requires a precise dosing of the demulsification agent at each of the stages, which necessitates extended storage of the sludge in the holding tanks before filtering due to the kinetic control of the process of de-emulsification, which makes the process a complex and expensive one.

The closest in suitability solution based on the present state of the art is the «Method and facility for processing of petroleum and oil sediments polluted water» by international request PCT/SE9902046, published - WO 00/29334 on 25.05.2000. [3]

According this method the petroleum and oil sediments polluted water is treated through addition of chemicals - demulsification agent and flocculant. The water processed is to be pre-heated up to 50°C for reduction of their viscosity and filtered, and after that the demulsification agent is fed. The treated mixture is further heated up to 90°C and subjected to centriiugation until obtaining of three phases: oil, water and solid phase. The oil and the solid phases are removed. The water phase, containing emulsified petroleum is submitted to additional separation, by heating-up to 50 to 90°C in a buffer tank and the flocculant is added, whereby the mixture is to be re-circulated several times. After the processing, the solution is to be settled for certain period and the clean water is taken away. This method is illustrated by the .facility for processing of petroleum and oil sediments polluted water consisting of connected in series tank-gravity settler, extraction assembly, tank for water heating - up to 50°C and filtering assembly, and after that, a heating device for heating up to 90°C is provided and connected with the centrifuge. Before the heating device, there is an input line provided from the device for preparation and dosing of the demulsification agent. At the exit of the centrifuge there are outlets for the water, oil and solid phase provided, whereby the oil and solid phase are taken away into the respective tanks. The water phase is fed into a buffer tank, where it is heated to 50 - 90°C and part of this tank there is a device for preparation, dosing and feeding of the flocculant.

The methods used hitherto, described above, are based on pre-heating of the oil sediments and sludge up to 95-98°C and then treated, due to which they have: low efficiency of the process, due to the intensive energy consumption for heating up of the oil sludge and oil sediments; high degree of fire hazard, due to the discharge of light oil fractions during the processing, caused by the high working temperature of the processed sludge and oil sediments; considerable discharge of harmful emissions, polluting the environment and posing threats for life and health of the workers in the area of the facility; quick wearing out of certain elements of the machines and facilities, due to the high temperature of the processed oil sludge and oil sediments; low output, since the technological idle time for the natural separation of the phases takes a period of 5-6 hours and the follow-up draining; waste product of significant content of mechanical impurities and oil-products, which must be further treated.

Disclosure of the invention

The present invention intends to propose a method for processing of sludge and sediments of oil products, deposited in ponds and lagoons, along with sediments from tanks for storage of oil-products and waste waters from ship facilities, whereby the processing is to be performed at low energy cost, high output capacity, reduced gas emissions in the atmosphere and high degree of separation of components from the sludge and oil sediments-oil, water and solid phase.

The method for processing of oil sludge and oil sediments utilizes a process of treatment with demulsification agent and adding of flocculant. The processed sludge and oil sediments are pre-heated for reduction of their viscosity and filtered, and after that the demulsification agent is fed. The treated mixture is further heated and submitted to centrifugation until obtaining of three phases: oil, water and solid phases. The water phase is submitted to additional separation, while the solid phase is removed.

According to the invention, during the processing of the oil sludge and oil sediments during the treatment with the demulsification agent through direct feeding of steam the mixture is heated up to 50-55°C, and then the mixture is homogenized. After the homogenization, the treated oil sludge and oil sediments are sent for centrifugation. The flocculant is added immediately before the centrifugation. After the centrifugation, the resulting oil and water phases are submitted to fine separation through further centrifugal separation.

The homogenization of the oil sludge and oil sediments according to one of the preferred variants, is carried out by stirring for 45 to 60 min., and at the same time they are heated with steam up to 50 - 55 C, and the demulsification agent used for the treatment is between 1 to 5 g/1 depending on the amount of the incoming sludge and oil sediments.

The flocculant used should preferably be high molecular weight cation-active poly- electrolyte.

According to one preferred embodiment, the demulsification agent is based on glycerol-ethylene oxide-propylene oxideadduct, with an additive of fatty acid. Possible variant is to use fatty acid and thin spindle oil as an additive.

According to another preferred embodiment, the demulsification agent is based on fatty alcohol-ethylene oxide-propylene oxide adduct. Another possible embodiment is where the demulsification agent is with additive of fatty acid or fatty acid and thin spindle oil.

According to the third preferred embodiment, the demulsification agent is based on sodium bis(2-ethylhexyl) sulfosuccinate. In this case, it is possible that the demulsification agent tis with an additive of fatty acid or fatty acid and thin spindle oil.

The feeding of steam for heating up of the mixture to 50 -55 ⁰ C causes input of additional quantity of water and the simultaneous heating-up, which contributes to the reduction of friction forces during agitation, reducing thus the wall (low velocity) effect. This way, the energy consumption for processing the waste sludge and oil sediments is reduced along with the harmful emissions in the atmosphere. The homogenization, which is performed for 45 to 60 min. simultaneously with the steam and required quantity of demulsification agent feeding aims at breaking down of the water-oil bonds. The previously input water, which was fed during the steam condensation, improves the diffusion of the demulsification agent within the dispersed system.

The dosing and feeding of flocculant before the centrifugation process increases the degree of separation of the solid from the liquid phases and prevents blockages and occurrence of unnecessary dead (lost-circulation) zones. This results in higher speed of separation and increased efficiency of the method.

After the centrifugation process, the three phases obtained - oil, water and solid, will have the following parameters: water - content of mechanical impurities up to 1000 mg/1 and content of oil- products up to 1000 mg/1 ; oil phase - content of water up to 2% and content of mechanical impurities up to 1% ; solid phase - content of water - less than 70%.

One of the preferred ways of centrifugation is the fine centrifugal (swirling) separation of the organic and the water phases. In this case, the resulting oil and water phases will have the following parameters: water - content of mechanical impurities less than 30 mg/1 and content of oil- products less than 10 mg/1 ; oil phase - content of waterless than 1% and content of mechanical impurities up to 0,2 % ; solid phase - content of waterless than 70% The separated solid phase after the fine separation of the oil is in small quantities 2 - 3% and is re-directed for liquidation towards the solid phase, separated during the processing of the oil sludge.

The proposed method for processing of oil sludge and oil sediments has the following advantages: high energy and financial efficiency of the process, due to the relatively low energy input for heating up the oil sludge and oil sediments to a maximum of 50 - 55° C, considerably lower than in the methods used hitherto; increased efficiency of separation within the individual phases - water, oil and solid, due to the input of flocculant before the centrifugation process and the pre- treatment with suitable demulsification agent, whereby steam for heating-up is added and the sludge and oil sediments are homogenized; reduced fire hazard, since the lower working temperature of the sludge and oil sediments minimizes the risk of discharging of light oil-products and hence, the hazard of off-gassing and fires; reduced discharge of harmful emissions polluting the environment and waters and posing threats for life and health of the workers in the area of the facility; improved reliability and safety of machines and facilities, due to the lower working temperature of the processed sludge; low content of mechanical impurities and oil-products in the resulting water phase, which allows discharging into water basins without secondary pollution; high output capacity of the proposed method, because of the technological idle time for separation of the phases takes 20 to 30 minutes, which provides opportunity for a continuous processing, without the necessity of storage in buffer tanks.

Brief description of the drawings

One embodiment of the method according to the invention is illustrated in the enclosed Figure 1, which represents summarized technological diagram of the sequence of operations for processing of oil sludge and oil sediments.

Examples for implementation of the invention

The method according to the invention and the information specified above is designed for processing of wide range of waste oil-products -„light" and„heavy" sludge and oil sediments with the following initial parameters:

The method is implemented through the following sequence of groups of operations (item 1, 2, 3 and 4) in figure 1 :

1. Scooping, pre-heating to 40-45 °C and filtering: The initial raw oil sludge and oil sediments are scooped out of the storage facilities, lagoons or tanks for storage of waste oil-products and are subjected to filtering, intended to remove any coarse mechanical impurities - polymer granules of previous technological stages, grass and other contaminants, that have fallen in during the prolonged outdoor storage or inside the tanks. For reduction of its viscosity the sludge is pre-heated up to 40-45 °G within a device for pre-heating - tank or heat- exchanger.

The heated-up sludge and oil sediments are then fed for two-staged filtering into a two-stage pressurized mechanical filter, which reduces the harmful emissions. During the first stage of filtering the coarse mechanical impurities with size exceeding 5 mm. are removed, while in the second stage of filtering the mechanical impuritiesexceedingl,2 mm of size are removed.

2. Processing - treatment with demulsification agent, further heating-up to 50- 55°C and homogenization:

The prepared, pre-heated mixture of filtered sludge and oil sediments is processed through treatment with demulsification agent then, further heated-up and homogenized. To this end, the mixture is fed into a device for additional heating-up (tanks), where steam is fed for heating up to temperature of 50-55°C. Thus, the additional amount of water is also supplied and in the same time the mixture is continuously homogenized. Introduction of the steam contributes to the reduction of the friction forces during the agitation and reduced the wall (low-velocity) effect. Furthermore, the water input by the steam and obtained through the steam condensation, improves the diffusion of the demulsification agent within the dispersed system. In the device for further heating-up together with the steam to the treated mixture is added the demulsification agent, which selection and composition aims at separation of the water from the processed sludge within the low-temperature interval of 50- 55°C.

According to one of the preferred embodiments, to the treated sludge and oil sediments with content of 7% to 25% of oil-products the input demulsification agent is based on glycerol-ethylene oxide-propylene oxide adduct with an additive of fatty acid. Implementation with an additive of fatty acid and thin spindle oil is also possible. The amount of demulsification agent is 1 - 5 g/1, depending on the amount of the input sludge. Depending on the contents of the processed sludge and oil sediments this mixture can be diluted with water, whereby up to 30% of added water ensures stability of the mixture.

The demulsification agent for the implementation of the present method may be based on fatty alcohol-ethylene oxide-propylene oxide adducts. Depending on the contents of the output sludge and oil sediments an additive of fatty acid- up to 20% may be added.

During the operation of oil boreholes sludge with content of oil-products exceeding 25 - up to 45 % are produced, where the suitable demulsification agent is to be based on sodium bis(2-ethylhexyl) sulfosuccinate. If necessary, for some types of sludge it will be possible to add up to 20% of fatty acid for better separation of the individual components.

The proposed technology allows processing of sludge with greater content of oil- products, ensuring their extraction and utilization. All of the above specified types of demulsification agents can be combined with thin spindle oil as an additive, which will lead to reduction of the viscosity of the oil phase and accelerate flowing out of the films between the water droplets.

After the introduction of the necessary quantity of demulsification agent in the device for additional heating-up - the tanks, which are equipped with agitators, an additional homogenization is implemented through the agitation for 45 to 60 min.

The processing, including the treatment with demulsification agent, the process of steam feeding and homogenization aims at breaking-down of the emulsion bonds of the water-oil emulsions and provides the opportunity for separation of the phases during the next three-phase centrifugation.

3. Centrifugation and feeding of flocculant:

The de-emulsified dispersed system is centrifuged in order to separate the water from the organic and solid phases, which may be implemented in the three-phase centrifuge. Using the device for preparation and dosing (including the dosing pump integrated in it) the flocculant is to be prepared and dosed, to be supplied just before the centrifugation process, i.e. before the input to the centrifuge, and into the output pipework from the device for additional heating-up. The addition of the flocculant - high molecular weight poly-electrolyte, causes the removal of the mechanical impurities contained in the sludge, by forming floccules. Depending on the nature of the processed sludge and oil sediments, different types of poly-electrolytes are used - anionic, cationic, neutral and other. According to one of the preferred embodiments, in the particular case of oil sludge and oil sediments with the cited above parameters, the flocculant is high molecular weight cation-active poly-electrolyte.

The preparation and dosing of the flocculant before the centrifugation process, i.e.at the input of the centrifuge, increases the degree of separation of the solid from the liquid phases and prevents the centrifuge from blockages and occurrence of unnecessary dead (lost-circulation) zones. This way, a higher speed of separation and increased efficiency of the method is achieved. After the three stage centrifugation process three phases are produced - oil, water and solid phase, with the following parameters:

The solid phase is directed for burning out in incinerators or for another type of treatment. The water and the oil phases are subjected to further centrifugal separation.

4. Additional centrifugal (swirling) separation:

The final stage provides for fine purification of the organic and water phases through additional centrifugal separation. One possible variant is the utilization of centrifugal (swirling) separators, intended for products with low content of mechanical impurities - 4- 5 %. The centrifugal separators operate at speed of 7000 to 8000 rpm and feature utilization of double-acting separation (centripetal) pump.

After the fine purification of the oil phase the resulting„commodity" product is stored and may be used for secondary processing in the refineries or be input as component of boiler fuels. Depending on the composition, the resulting product may be re-directed and used as additive in the road construction industry. After the fine purification of the water phase the resulting waste waters will have parameters, which meet the requirements for discharging of the waste waters into water recipients. One of the preferred solutions at the centrifugal separators for the water phase is integration of a device for continuous monitoring of the oil contents in the water. It may be of the peripheral filter type, which will perform constant monitoring and tracking of the admissible content of oil in the waste water, for example, 10 ppm, by automatically changing the capacity of the separator and adjusting the quantities of water supplied for processing.

After the additional centrifugal separation, the resulting oil and water phases will have the following parameters:

Application of the invention

The invention is intended mainly for processing of sludge, obtained after processing of oil and sediments from tanks for storage of oil-products, tanks of the petrol storage bases and petrol stations, of oil terminals, petroleum tanker ships, ship fuel tanks and other waste oil products. What characterizes these types of sludge and oil sediments is that they represent stable water and oil emulsions, whose processing is extremely hard. The method according to the invention is based on the phase separation of waste oil sludge, as a result from which individual components are obtained as final products, which then can be individually treated without any hazard of secondary pollutions of the environment.

The implementation of the method according to the present invention is illustrated through the described herein below sample series of operations (fig. 1) and suitably selected facilities and devices, and demulsification agents and flocculants, providing the complete coverage of the of oil sludge and oil sediments processing process.

The oil sludge and oil sediments are stored in lagoons, holding tanks or tanks. Scooping out of sludge with relatively low viscosity from the holding tanks is performed by facilities for extraction, for example, submersible pump-for the liquid phase, which is pumped out directly from the holding tank or the lagoon. In this case, the pump is installed onto a floating hull, which may be situated at various locations within the holding tank. The submersible pump may be positioned at various depths, and the sludge will be supplied to the location for follow-up treatment over a hose- line.

For sludge of high viscosity, the extraction may be performed, for example, through auger facility for extraction and transportation. The denser phase is scooped out by means of "hollow" auger, which is positioned directly into the holding tank. The auger must preferably be equipped with top drive, providing the option for taking out of oil sediments without their direct contact with motor and reduction gear, which are mounted at the top part of the auger.

An essential stage before processing of the oil sludge is its filtering, which targets separation of the coarse mechanical impurities already available in the material - polymer granules, grass, incidental coarse contaminants /polyethylene bags, bottles, rags and other/. The filtering is obligatory, and before it the sludge is to be heated to a temperature of 40 - 45°C aiming at reduction of viscosity. The heating-up is to be done in a pre-heating tank, which may be equipped with a heat-exchanging coil or another type of heating-up method available. A heat-exchanger may be used, preferably of the„pipe-in-pipe" type, where the treated sludge and the heating-up agent are to be supplied in counter-flow directions. The heating-up agent -the steam will have pressure of 6 to 10 bars and temperature of 230 - 250°C. In this way the heat losses are minimized and the heating-up is implemented quickly and efficiently. Heat exchangers, equipped with pipe bundle are not suitable for heating up of oil sludge, due to the tendency of forming up of scaling on the pipes, obstructing the heat exchange process and resulting in low efficiency.

The sludge heated-up in this way is then supplied to the filtering assembly, for example, a pressurized filter, consisting of two stages: stage for coarse filtering and stage for fine filtering. The coarse filtering degree is preferably a self-cleaning filter with coarseness of the filtering element up to 5 mm, while the fine filtering degree should be self-cleaning filter with coarseness of the filtering element of up to 1 ,2 mm. The capacity of the filtering system must be in compliance with the total capacity and mainly with the follow-up three-phase centrifugation of the oil sludge.

The processing of the oil sludge continues by an additional heating-up to 50 - 55 °C, addition of the demulsification agent and homogenization.

The filtered oil sludge from the holding buffer tank will be fed into the device for additional heating-up, which preferably and depending on the capacity are two tanks with capacity of 100 m ³ , for example. These tanks are equipped with an agitator - propeller moving at a speed of 36 rpm, providing good homogenization. The sludge is further heated up to temperature of 50 - 55°C by means of direct input of steam into the tanks. Simultaneously with the steam feeding, the demulsification agent is prepared and dosed.

For processed sludge and oil sediments with content of 7% to 25% of oil-products, the demulsification agent is to be input together with main component- Glycerol- ethylene oxide-propylene oxide adduct- 90% and an additive of fatty acid- 10%. The amount of demulsification agent is within the limits of 1 to 5 g/1, calculated in relation to the amount of the sludge being input. Depending on the composition of the processed sludge and oil sediments, this mixture may be diluted with water, whereby the mixture remains stable at up to 30% of added water.

The main component- Glycerol-ethylene oxide-propylene oxide adduct is a star polymer with glycerine core, to which are attached chains, containing hydrophobic polypropylene section and hydrophilous polyethylene section. During the adsorption of the phase boundary, the oil/water adduct position sits hydrophobic parts to the oil phase, while the hydrophilous ones - to the water phase. This causes displacement of the natural stabilizers from the surfaces of the fatty (oil) film. The additive of fatty acids acts in identical manner, and they also are adsorbed in a competitive manner onto the film surfaces and displace the natural stabilizers. An additional intensification of the de-emulsifying effect occurs due to the opportunity for de- stabilization of the oil film and by means of forming of a "bridge" between the water droplets through penetration of the individual hydrophilous chains of the adduct to the different water phases.

When choosing another preferred embodiment of the present method the demulsification agent is based on a fatty alcohol-ethylene oxide-propylene oxide adduct. Depending on the composition of the raw sludge and oil sediments an additive of fatty acid up to 20% can be added. The main component - fatty alcohol-ethylene oxide-propylene oxide adduct is a linear three-block co-polymer. The break-down mechanism of the sludge emulsion when using this type of demulsification agent is analogous to the one described in the first case - substitution of the natural sludge stabilizers of the phase boundary oil/water due to the competitive adsorption of the molecules of the adduct, causing de- stabilization and breaking down of the oil film. The main difference between the two types of demulsification agents specified is the way of transfer of the respective molecules to the surfaces of the emulsion droplets. The second demulsification agent is poorly soluble in water (long-chain fatty alcohols are part of its composition) and manifests better solubility in its oily phase. Upon its introduction in the sludge emulsion it diffuses in the oil fraction (continuous dispersed medium), distributes itself within, it and is adsorbed onto the surfaces of the water droplets, substituting certain amount of the natural sludge stabilizers.

The transfer of the first type of demulsification agent to the surfaces of the water droplets is implemented in another way due to the fact, that it is poorly soluble in the oil fraction. Its introduction in the emulsion system is done via dispersion of saturated water solution within the sludge. The molecules of the demulsification agent diffuse in the volume of the droplets from the solution to their surfaces, where the competitive adsorption is taking place. The oil film formed between the droplet of the solution and sludge droplet is unstable and it breaks down. Fusion of the two droplets results in the transfer of the demulsification agent and thus, a step-like rearrangement of its molecules into the water fraction occurs, which speeds up the process of coalescence.

Due to this difference in the transfer of the molecules, the first type of demulsification agent turns inefficient for sludge of higher percentage content of water fraction (higher concentration of emulsion droplets), while the second type of demulsification agent is inefficient in cases of sludge of higher percentage content of oil fraction.

For sludge with content of 25% to 45% of oil-products, the demulsification agent used is based on sodium bis(2-ethylhexyl) sulfosuccinate. Up to 20% fatty acid is also possible to be added.

The main component - sodium bis(2-ethylhexyl) sulfosuccinate consists of two short hydrophobic chains and a hydrophilous part. For this reason, in case of competitive adsorption along the inter-phase boundary, this demulsification agent above all, destroys the network formation of the coating on the surface of the water droplets. It is also possible that its action is also connected with formation of micro-emulsion droplets as an intermediate phase and hence, it is inefficient in case of considerably higher content of the oil fraction.

The fatty acids additive acts in a way identical to the first type of demulsification agents (they are competitively adsorbed on the film surfaces displacing the natural stabilizers).

To all of the above specified types of demulsification agents an additive of thin spindle oil may be added, which will cause reduction of the viscosity of the oil phase and speeding up of the flowing out of the films between the water droplets.

The competitive type of demulsification agent, selected depending on composition of the oil sludge and oil sediments, respectively, is dosed by a device for preparation and dosing of demulsification agent with the dosing pump installed on it, equipped with flow meter. The preferred variant is using dosing auger pump, consisting of metal rotor, rubber stator and drive train. Using of centrifugal dosing pump is inefficient, due to the specific nature and viscosity of the demulsification agent used. After the dosing of demulsification agent into the device for additional heating-up is performed homogenization of the mixture through stirring for 45 to 60 minutes, which aims at breaking down of the water-oil /emulsion/ bonds. The relatively low temperature of 50 to 55°C, compared with the one of many other facilities - up to 95 - 98°C, results in reduction of the harmful emissions, polluting the environment and posing to a great extent an explosion and fire hazard.

The oil sludge prepared in this way by the auger pump with preferred flow rate of 7 to 15m /h is fed for processing in the three-phase centrifuge of„decanter" type, for example. The centrifuge then separates the three phases - water, oil and mechanical impurities. The light phase separated thus from the oil-products and the water phase are drained by gravity, while the heavy phase is taken away under pressure. The actuation of the centrifuge is performed by means of electric motor and belt transmissions. The speed of the centrifuge is adjusted by frequency converter. The auger of the centrifuge is the mechanism, through which the extraction of the solid phase is performed. The drum and the auger of the centrifuge rotate in one direction, and the revolutions of the auger, depending on the type of the centrifuge exceed the ones of the drum by 13 - 15 rpm. This difference in the speed - the differential speed causes the normal extraction of the solid phase. The maximum speed of rotation of the centrifuge 10 is 3 000 rpm

Aiming at better phase separation, before the centrifugation process, at the input of the centrifuge, onto the output pipe work from the device for additional heating-up, flocculant - poly-electrolyte is fed. Initially, in the device for preparation and dosing of flocculant is prepared a 0,5% solution of the cation-active poly-electrolyte, which is further diluted by water to a concentration of 0,1 - 0,2%. This flocculant is supplied by a dosing pump, which may be auger one, and equipped with metal rotor and rubber stator and provided with variable ratio mechanism to change the flow rate. The amount of the dosed flocculant - poly-electrolyte is measured by flow meter.

Separation into three phases takes place in the centrifuge as a result from the centrifugal forces: water phase, oil phase and solid phase. The resulting oil and water phases after the three-phase centrifugation are submitted to additional centrifugal separation aiming at achieving of parameters, meeting the requirements for these products. The system for additional fine separation of the oil and the water phases includes centrifugal (swirling) separators.

The oil phase is supplied to the centrifugal separator, which has an integrated double centripetal pump and is equipped with self-cleaning disc vessel. The solid phase is pressure discharged by means of the above-specified pump and is re-directed to the incineration devices, for example. The same pump removes also the oil phase, which is stored in commodity tanks.

The resulting oil-products will have water content of less than 1% and content of mechanical impurities of less than 0,2%.

The water phase is also preferably supplied to a centrifugal self-cleaning separator, intended for separation of the water - oil emulsions and for simultaneous removal of the solid phase. The separator comprises an integrated double centripetal pump and is equipped with self-cleaning disc vessel. The solid phase is pressure discharged by means of the above-specified pump and is re-directed to the device for burning out. The oil-products are discharged by means of the same pump with pressure up to2,5 bars and are stored in commodity tanks.

In case of measuring of higher oil content, the capacity of the processing system for wastewater is automatically reduced through the provided metal peripheral filter- part of the centrifugal separator for processing of the water phase. The peripheral filter is used for continuous monitoring of the contents of oil in the water and continuous measurement of the maximum admissible content of oil in the treated water - 10 ppm.

The treated water will have oil content of less than 10 mg/1 and content of mechanical impurities of less than 30 mg/1 and may be discharged into the respective receiving waters.

The above data have been obtained through the following methods for measurement of water in oil- analytical methods of DIN 38 409 - HI 8 or ASTM 4298.

Cited references:

1. Patent RU 2193578 C2

2. Patent RU 2078740 CI

3. WO 00/29334, international application PCT/SE9902046