RU2469766C1 - Settling tank for purification of oil-containing wastewater - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: settling tank contains reservoir 1 with input branch pipe 3 and branch pipes of water 4 and oil 5 output. Filtering-coalescing packets 2 are made in form of plates of porous-cellular polymer material and are installed with clearance. Plates are made of similar material, 0.1-0.5 m thick, with clearance between them being made 0.05-0.2 m wide, and packet being made with total thickness 0.5-2 m. Volume of precipitation zone is made 3 and more times larger than volume of packet. Precipitation zone 7 is located between filtering-coalescing packets 3.

EFFECT: invention makes it possible to ensure high degree of industrial oil wastewater purification.

2 dwg

Description

The invention relates to the field of preparation of oil field wastewater used in the reservoir pressure maintenance system for waterflooding of oil fields, including fields with productive formations with low permeability, and is used to purify oil-containing wastewater from oil and solids.

Known sump for the purification of oily wastewater from oil and mechanical impurities (ed. St. USSR No. 617377, IPC C02C 1/26, B01D 17/02, publ. 30.07.1978, bull. No. 28), including a tank, filters with coalescing loading, forming among themselves the preliminary sludge chambers with a down pipe for supplying waste water, overflow partitions, inclined shelves, a horizontally located perforated distributor.

The disadvantages of such a sump should include:

- the difficulty in installing overflow partitions, inclined shelves and a perforated distributor inside the tank and eliminating gaps between them and the wall of the apparatus body;

- the inability to control the equal and uniform flow of purified water into both filters with a coalescing load;

- the complexity of the control of the interfacial level in the apparatus.

Closest to the claimed invention is a device for separating emulsions (RF patent 2105584, IPC B01D 17/04, publ. 02.27.1998), made in the form of a filter-coalescing package, represented by a block of sections from plates of porous-cellular materials, laid in layers in the order an increase in the density of cells and pores from section to section and at an angle not lower than the angle of fluid ejection in the direction of the moving flow, the material of the first sections being a porous-cellular metal or alloy, and the last section being a porous-cellular material.

The disadvantages of such a sump are:

- colmatization of the hydrophobic surface of the porous-cellular polymer material of the last section with highly viscous or solid oil components (asphaltenes, paraffins, mechanical impurities), which will lead to a decrease in the efficiency of this section and frequent replacement of the material;

- the penetration of a layer of oil (or oil droplets coarsened on the surface of the material) into the water discharged through drainage pipes, which will lead to a deterioration in its quality;

- low efficiency of this device with a variable initial water cut of the oil emulsion (which is a frequent occurrence in oilfield practice), since the design of the apparatus, namely the installation angle of the filter-coalescing packet, is determined by the water cut value of the incoming raw materials;

- the difficulty in mounting the coalescing package at an angle, fixing it inside the tank and eliminating gaps between the material and the wall of the apparatus body;

- the proposed method for the regeneration of porous-cellular materials by blowing or washing is ineffective, because with a sufficiently high porosity of the material of the coalescing packet, the actual speed of its flow around the washing water and, therefore, the friction force of the water on the surface is low;

- the use of foamed metals and polycellular polymeric materials significantly increases the cost of the proposed device.

An object of the invention is to increase the efficiency of wastewater treatment due to the uniform distribution of the stream of purified water throughout the entire volume of the coalescing filter, since spaces are provided between the foamed porous-cellular material plates, due to the fact that after filtering the water there is a settling zone with a volume that provides the greatest the effectiveness of the sump, as well as through the regeneration of the filter-coalescing package without stopping the sump.

This technical problem is solved with the help of a sump containing a container with an inlet pipe and water and oil outlet pipes, a filter-coalescing packet that overlaps the tank space between the inlet pipe and the outlet pipes with the formation of a settling zone and made in the form of plates of porous-cellular polymer material installed with a gap.

New is that the plates are made of the same material with a thickness of 0.1-0.5 m, and the gap between them is made with a width of 0.05-0.2 m, and the package is made with a total thickness of 0.5-2 m, while the volume the sedimentation zone is made more than the package volume by 3 or more times, and the tank is horizontal and cylindrical, equipped with an additional inlet pipe installed on the opposite side from the inlet pipe, and an additional filter-coalescing package made and installed similarly to the main one, while the zone is defended Niya is located between the main and additional packages.

Figure 1 shows the proposed sump, a longitudinal section. Figure 2 shows the proposed sump with two filter-coalescing packages, a longitudinal section.

The sump for water purification contains a container 1 (see figures 1, 2), a filter-coalescing packet 2, a pipe for introducing water with a distributor 3; the outlet pipe for treated water with a switchgear 4, the pipe outlet for trapping oil 5; manhole 6 for mounting a filter-coalescing package 2; zone for water sedimentation 7. Moreover, the filter-coalescing package 2 consists of plates of porous-cellular polymer material 8 with a thickness of 0.1-0.5 m, installed with a gap 9 of a width of 0.05-0.2 m

The sump works as follows.

Purified water containing oil and a solid impurity (see FIGS. 1, 2), through a nozzle with a distributor 3 located in the upper part of the tank 1, is directed to a filter-coalescing packet 2. When a liquid passes through a porous-cellular polymer material, a drop of oil coarsened, forming a film of oil. The latter, having reached a critical thickness, breaks away from the material under the influence of a fluid flow, floats in the gaps 9 and the zone for settling water 7 in the upper part of the tank and is discharged from the apparatus through the nozzle 5. The purified wastewater is discharged through the distributor and nozzle 4.

The real wastewater of oil fields is a polydisperse emulsion containing drops of oil from units to hundreds of microns. Studies in laboratory and field conditions showed that after the passage of water through the plate 8 of the porous-cellular polymer material, the dispersion of oil particles was in three ranges with relatively clear boundaries.

The first range was characterized by particles with a diameter of 3 to 5 mm, representing oil droplets formed as a result of contact coalescence of smaller droplets on the surface of the material and subsequent separation from it under the influence of hydrodynamic flow forces. The gap 9 between the plates 8 with a width in the range from 0.05 to 0.2 m provides a time sufficient for the emergence of these drops of oil to the upper part of the tank 1, which ensures the purity of the subsequent plates. Also, the preservation of the gaps 9 between the plates 8 contributes to an even distribution of the flow of purified water throughout the depth and area of the filter-coalescing package 2.

In the second range, the particle diameter of the oil ranged from 30 to 100 microns. In this range there were droplets, coalesced in the volume of pores and cells of the material due to the hydrodynamic factor. To remove droplets with the indicated size (using sedimentation) it takes a little longer time than in the first case, therefore, after the filter-coalescing packet 2 it is necessary to provide a zone for settling water 7. As studies show, the volume of the sedimentation zone should be 3 or more times more package volume.

The third range is represented by particles with a diameter of up to 10 μm. These are oil particles that have passed through a filter-coalescing packet 2, without being coalesced. The amount of these particles mainly determines the residual concentration of oil in purified water at the outlet of the sump.

Studies have shown that there is a direct correlation between the efficiency of water purification and the thickness of the filter-coalescing packet 2, since with an increase in the thickness of packet 2, the residence time of water in it increases, and, accordingly, the probability of oil droplets contacting on the surface of a hydrophobic material increases. It was found that the optimal thickness of the package 2 is a range from 0.5 to 2.0 m. A further increase in the thickness of the package 2 does not significantly improve the cleaning efficiency, but significantly increases its cost and the cost of its installation.

In the study of the influence of the thickness of the plate 8 of the coalescing material on the efficiency of the coalescence process in laboratory conditions, it was found that with an increase in the thickness of the plate 8 to 0.5 m, a significant increase in the effect of oil coalescence occurs. A further increase in the thickness of the plate 8 leads to a slight change in the effect of enlargement, which is explained by a decrease in the proportion of coarse oil droplets as it moves through the plate 8.

The effective operation of the sump directly depends on the quality of installation of the filter-coalescing bag 2 inside the tank 1. It is installed by gradually installing the plates 8, fastening them to the wall of the tank 1 with spacers, tightening the plates 8 together while maintaining the gaps 9 between them and sealing the gaps between the plates 8 and the walls of the housing of the tank 1.

To increase the capacity of the sump, it is proposed to install two filter-coalescing bags 2 (see FIG. 2) located at opposite ends of the sump inside, and cleaned water should be discharged through a pipe with a distributor 4 located in the center of the sump.

To obtain actual data on the concentration of oil in wastewater after filter-coalescing packet 2, to obtain reliable data on the hydraulic resistance of packet 2, to determine the optimal technological parameters and effective methods of material recovery, a sump (volume 200 m ³ ) was made for testing in field conditions.

As a filter-coalescing package 2 in the sump, a set of plates 8 (see figure 2) made of foamed polyurethane was used. Wastewater flowed through an inlet pipe with a distributor 3 onto a polymer material on which coarsening of oil droplets took place. Under the influence of gravity, coarse oil droplets were torn off from the surface of the material and flowed out to the zone for settling 7. Oil was collected in the upper part of the tank 1 in the form of a film and was discharged through the outlet pipe of the oil line 5, and purified water was discharged from the tank 1 through the outlet pipe lines 4.

The tests were carried out on the installation of oil treatment on the line after the existing treatment facilities as a stage of post-treatment of wastewater.

The table shows the results of field tests of the sump. Comparing the results obtained, the table shows the results of the equipment used for the treatment of oilfield wastewater at OAO TATNEFT.

Parameter Sump (e.g. vertical steel tank) Hydrocyclone Flotator Proposed Sump The concentration of oil in purified water at the exit, mg / DM ³ 40 to 60 25 to 40 From 15 to 30 10 to 20 The cost of water treatment, rubles / m ³ 0.5 -1.0 4.0-5.0 4.0-5.0 2.0-3.0

As can be seen from the table, the proposed technical solution allows to achieve a high degree of oilfield wastewater treatment, which is not achieved using traditional methods for the oilfield, at lower capital and operating costs.

The design features of the proposed sump allow the regeneration of the filter-coalescing packet 2 by removing suspended solids and highly viscous oil components from the surface of the material with a petroleum paraffin solvent (for example, a gasoline fraction recovered by rectification or oil separation, which is used as a paraffin solvent for washing oil wells) . Regeneration is carried out without stopping the sump by periodic dosing through a dispersing device of the solvent into the stream of water entering the treatment. The frequency of regeneration depends on the quality of the treated wastewater supplied to the entrance of the sump, and is specified during operation.

Field trials have shown that washing the filter-coalescing packet 2 with a hydrocarbon solvent is the most effective, technologically acceptable and inexpensive method of regeneration. It was found that the optimal regeneration mode is achieved when the ratio of solvent and water supply is 1:20 for 30 minutes, which is at least 2 times less than the cleaning time of the closest analogue.

This technical solution allows for a high degree of oilfield wastewater treatment. The concentration of oil in purified water is less than 20 mg / dm ³ , mechanical impurities - less than 10 mg / dm ³ , which meets the requirements for injection into productive formations even with low permeability. Using the proposed sedimentation tank eliminates the volley discharge of contaminants into the reservoir pressure maintenance system and ultimately reduces the loss of injectivity of injection wells and improves oil recovery, and the regeneration of the filter-coalescing packet by dosing the hydrocarbon solvent directly into the flow without stopping the operation of the settler allows achieving stable quality of purified water for a long period.

Claims (1)

A sump for the purification of oily wastewater containing a container with an inlet pipe and water and oil outlet pipes, a filter-coalescing packet that overlaps the tank space between the inlet pipe and the outlet pipes with the formation of a settling zone and made in the form of porous-cellular polymer material plates installed with a gap, characterized in that the plates are made of the same material with a thickness of 0.1-0.5 m, and the gap between them is made with a width of 0.05-0.2 m, and the package is made with a total thickness of 0.5-2 m, with the volume of the zone of sedimentation is made more than the volume of the package by 3 or more times, and the tank is horizontal and cylindrical, equipped with an additional inlet pipe installed on the opposite side from the inlet pipe, and an additional filter-coalescing package made and installed similarly to the main one, while sedimentation is located between the main and additional packages.

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