RU2773219C1 - Residual oil wastewater treatment plant - Google Patents

Abstract

FIELD: oil industry.

SUBSTANCE: invention relates to the oil industry in the field of additional treatment of wastewater from oil fields to the required quality for the use of water in the reservoir pressure maintenance system (RPMS) of a productive oil reservoir. The invention relates to a wastewater treatment plant for residual oil having a container with the function of a water sump and a device for mixing the treated water with an organic solvent. As a tank with the function of a sump, the installation contains a vertical steel tank (VST), which has two nozzles at different heights of the tank for supplying wastewater to the tank: upper and lower, the upper nozzle is located in the upper part of the tank for supplying water through the manifold to separate the liquid and gas medium, the lower nozzle is located at half the height the upper branch pipe and serves to supply waste water through a dispersant and a manifold to the water body of the tank, the dispersant as a mixing device is connected to a pipeline to supply organic solvent to it for mixing wastewater with solvent in turbulent mode. Wastewater is supplied to the VST through one of two nozzles based on the quality of wastewater controlled at the entrance to the installation by a sampler.

EFFECT: purification of wastewater from residual oil by increasing the density difference between water and oil while ensuring moderate consumption of organic solvent, the possibility of selective use of one of the technological processes of water purification from residual oil, depending on the initial concentration of oil in the wastewater.

1 cl, 1 dwg

Description

The invention relates to the oil industry in the field of post-treatment of waste water from oil fields to the required quality for the use of water in the reservoir pressure maintenance system (RPM) of a productive oil reservoir.

The quality of waste water is largely dependent on the permeability of the reservoir, for example, it is recommended to pump water into low-permeability reservoirs with a residual oil content of no more than 3-5 mg/l. Therefore, in all schematic diagrams of installations for the preliminary discharge of formation and waste water and commercial oil treatment plants, additional treatment of water after its separation from oil in settling tanks with a phase separation function is reflected. The process of post-treatment of waste water from oil particles can take place in horizontal tanks of the OG-200 type with a volume of 200 m ³ and in vertical steel tanks of various sizes: RVS-2000, 3000 and 5000.

A device for treating oily wastewater (AS USSR for the invention No. 1527177) is known, wastewater with oil droplets flows down obliquely mounted triangular plates, oil spreads in the form of a film and is collected above the water in the form of a layer of oil. The accumulation of oil and its removal from the water is achieved due to the mechanical effect on the waste water in the form of a direct type oil-water emulsion. If there is residual oil in the water with a high content of asphaltenes, resins and paraffins, the device will reduce its effectiveness due to the small density difference between water and oil particles and the floating of such oil in the aquatic environment.

It is known to use a hydrophobic filter in the form of a layer of oil above water (RF patent for the invention No. 2341317 "Installation for water treatment", published 20.12.2008). The supply of waste water directly to the liquid-gas phase separation zone of the tank, regardless of the shape and volume of the tank, has a drawback - if the densities of residual oil and water are close, only a part of the oil contained in the waste water will remain on the water surface. The water quality for the RPM system into tight reservoirs will not meet the required level of residual oil content.

A well-known installation for the purification of water from particles of heavy oil, in which toluene is used to remove heavy asphaltene particles from waste water (“Features of the liquid-phase extraction process and their use for the development of wastewater treatment technology”, Azerbaijan Chemical Journal, 2017, No. 3, p. 56-57). This installation for the post-treatment of water from particles of heavy oil is selected in the application as a prototype for the invention. The installation contains mechanical agitators, toluene is introduced into the bottom of the tanks, and waste water is fed into the top of the tanks with the function of extractors.

The installation has the following disadvantages:

- the presence of mechanical agitators requires increased attention and costs for their maintenance;

- significant volumetric costs of expensive toluene relative to the volume of treated waste water, the proportion of water volumes to toluene is 30-36 to 1;

- consistent water purification is technologically and structurally ensured by the presence in the installation of many separate tanks, mixers and pumps for supplying reagents for various purposes; in the event of a breakdown of these devices, the technological cycle is disrupted and the entire installation is disabled;

- the unit is not intended for the preparation of significant volumes of waste water within the range of 4-7 thousand m ³ /day, which are necessary for organizing a reservoir pressure maintenance system in a standard section of an oil field or oil deposit.

The technical task of the invention is to create a plant for post-treatment of waste water from oil products (residual oil) by increasing the density difference between water and oil while ensuring a moderate consumption of organic solvent with the achievement of the following technical result - the design of the plant should allow the use of selectively one of the technological processes of water purification from residual oil depending on the initial concentration of oil in the wastewater.

The technical problem posed is solved in a plant for the treatment of waste water from residual oil, containing a container with the function of a water sump and a device for mixing the treated water with an organic solvent, while according to the invention, the plant consists of a vertical steel tank (RVS) and has two pipe connections at different heights of the tank for supplying wastewater to the sump: upper and lower. The upper branch pipe is located in the upper part of the tank for supplying water through the distribution mother liquor under the section of liquid and gaseous medium, the lower branch pipe is located at half the height of the upper branch pipe and serves to supply waste water through the disperser and mother liquor to the reservoir water volume, the disperser is connected to a pipeline for supplying to it with an organic solvent for mixing waste water with a solvent in a turbulent mode. Waste water is supplied to the RVS through one of the two nozzles, based on the quality of the waste water, controlled at the inlet to the installation.

Schematically, the arrangement of the claimed installation is shown in the figure, where the positions indicate the following components: 1 - the body of the RVS type tank, 2 - the upper pipe for supplying waste water (SW) under the liquid level in the tank, 3 - the lower pipe for supplying water to the middle part of the volume water in the tank, 4 - mother liquors for uniform supply of waste water to the tank, 5 - dispersant for mixing the organic solvent with water and oil globules, 6 - valve on the upper pipe, 7 - valve on the lower pipe, 8 - wastewater sampler, 9 - sump for water and oil, 10 - valve on the organic solvent supply pipeline, 11 - solvent supply pump, 12 - underground container with solvent, 13 - hydrophobic layer of liquid in the VST, 14 - waste water discharge pipe without oil products, 15 - oil drain pipe into the container 16, 17 - a level gauge connected by a cable 18 through a control controller with an electric valve 19.

The wastewater treatment plant based on RVS with a volume of 3000 m ³ or 5000 m ³ is operated in two modes depending on the quality of the treated water. According to the guidelines of the oil companies, the fields organize not only the quality control of waste water for residual oil products at the inlet to the pumping station of the RPM system, but also at intermediate points of the water and oil treatment system to optimize technological processes, for example, saving reagents. Such an intermediate sampler is shown by position 8. The selected water sample after the sump 9 of oil and water can be of two types in terms of quality:

1. The oil content does not exceed the permissible value. For many companies, for fields with high reservoir permeability, this value is 50 mg/l.

2. Waste water is not suitable for injection into the reservoir, since oil products in water exceed the limited value.

Based on the results of the analysis, the installation is operated in one of two modes of water supply to the RVS.

Mode 1 - waste water does not require additional treatment, but the water is sent to the VST-based plant with a dual purpose:

- create a buffer water supply for the uninterrupted operation of the centrifugal pumps of the station of the RPM system;

- clean water from mechanical impurities and oil products, because high-quality water is better than good water.

According to mode 1, water is supplied to the upper pipe 2, valve 7 is closed, valve 6 is open. Water passes through the upper mother liquor 4, is evenly distributed over the interfacial surface, in which oil particles accumulate over time, forming a hydrophobic layer. Passing through this layer, the water is partially freed from residual oil. This is a well-known phenomenon in oil production and wastewater treatment. Gradually, waste water descends down the RVS and enters the branch pipe 14, is discharged from the tank. When moving down, the Archimedes force acts on the oil particles, and some of them float up, forming a hydrophobic layer of oil. The level of this layer of oil in the tank is maintained constant due to the joint programmed operation of the level gauge 17, the oil drain pipe 15 and the electric valve 19 on the pipe 14 of the waste water.

Mode 2 - waste water requires additional purification from oil particles. Water from the separator 9 is supplied to the lower branch pipe 3 through the valve 7, the valve 6 is closed. In the disperser 5, the waste water is mixed with an organic solvent, which is supplied from the underground tank 12 through the valve 10 by the pump 11. ), which serves the fleet of commercial oil tanks.

Due to the chaotic collision in the turbulent mode of oil particles and solvent globules, they merge, the density of the oil solution in the organic solvent decreases, and the Archimedes force acting on the formed hydrocarbon droplets increases. The ascent rate of particles of hydrocarbon composition in water is determined by the formula D.G. Stokes, therefore, a decrease in the density of newly appeared globules of solvent and oil particles that have merged after dispersion leads to a proportional increase in the rate of ascent of hydrocarbon droplets in wastewater. Water for the RPM system is getting better quality.

The transition of the operating mode from the second to the first also has a useful consequence, expressed in that the hydrophobic layer of the liquid 13 above the water is saturated with a solution of oil in an organic solvent. When passing through this layer, oil particles in water come into contact with a hydrocarbon solvent, have time to partially dissolve in it, reduce their density and, as a result, remain in the hydrophobic layer above the water.

Unlike the known wastewater treatment devices and the prototype considered in the application, the proposed installation has the following technical innovations with a positive result:

1. Depending on the quality of the waste water (presence of residual oil), water is directed to the upper branch pipe (relatively clean water) and to the lower pipe (poor water condition). In mode 2, to remove oil particles of significant density, an organic solvent is fed into the waste water through a dispersant. This reduces the density of oil particles and the rate at which oil floats in water.

2. To select the operating mode of the installation, wastewater samples are taken at a specified frequency, and based on the results of the analysis, the operating mode of the installation is selected. This is how the installation differs from known designs - the installation produces wastewater of the required quality at the lowest cost.

3. In contrast to the prototype, the dispersion of the solvent in the water flow occurs without rotating elements, provided by stationary devices of various designs.

4. As an organic solvent, it is proposed to use unstable gasoline with UULF, which, in fact, is one of the elements of the waste-free and efficient operation of an enterprise for the extraction and treatment of oil, gas and associated waste water.

The technological effect of using the plant is to ensure the constant compliance of the wastewater quality in terms of the “residual oil content” parameter without the financial costs of purchasing expensive organic solvents.

Claims (1)

Wastewater treatment plant from residual oil, containing a tank with the function of a water sump and a device for mixing the treated water with an organic solvent, characterized in that the plant contains a vertical steel tank (RVS) as a tank with a sump function, which has two branch pipes at different heights of the tank for supplying waste water to the tank: upper and lower, the upper branch pipe is located in the upper part of the tank for supplying water through the distribution mother liquor under the section of liquid and gas medium, the lower pipe is located at half the height of the upper pipe and serves to supply waste water through the disperser and mother liquor into the water volume of the tank, the dispersant as a mixing device is connected to a pipeline for supplying an organic solvent to it for mixing wastewater with a solvent in a turbulent mode, wastewater is supplied to the RVS through one of two nozzles based on the quality of wastewater controlled at at the entrance to the installation with a sampler.

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