A design method suitable for an oilfield sewage treatment system drying yard

Abstract

This invention provides a design method for a drying field in an oilfield wastewater treatment system. A pretreatment sedimentation tank is installed at the bottom discharge inlet of the large tank in the drying field; a semi-submerged oil-blocking float is designed and installed at the liquid surface in the drying field; a U-shaped tubular oil separator is added near the overflow outlet; uniform perforations are made in the transverse water inflow direction of the water distribution pipe in the drying field to reduce circulating flow in the liquid preparation area and avoid dead zones; a mesh grid with the same particle size as the sand and gravel filter media is laid under each layer of sand and gravel filter media in the drying field to facilitate cleaning and recycling of the filter media. This invention has been applied in five sites, ensuring stable and compliant effluent quality at this node of the drying field, solving the problems of excessive oil content in the wastewater of the drying field's wastewater tank and the high cost and risk of cleaning oily waste; extending the replacement cycle of the sand and gravel filter media at the bottom of the drying field, realizing the recycling of the sand and gravel filter media after cleaning, solving the problem of high replacement costs of sand and gravel filter media in the drying field, and achieving the goal of improving quality and efficiency.

Description

Technical Field

[0001] This invention belongs to the field of surface engineering water treatment in the petroleum industry, and in particular relates to a design method for a drying field suitable for oilfield wastewater treatment systems. Background Technology

[0002] No relevant technology was found in domestic literature. Backwash water from filters, external fluids, and bottom sludge from large tanks enter the drying area of ​​oilfield water treatment stations. The composition of the incoming fluids is unstable. The external fluids and bottom sludge from large tanks contain high levels of oil, mud, and sand. The fluid inflow time is relatively concentrated, and the outflow volume is large. The bottom of the drying area is covered with sand and gravel filter media to filter produced water. When the filtration capacity is insufficient, the incoming fluid overflows directly from the high outlet into the underground pool, causing the oil content in the underground pool to exceed the standard. This leads to abnormal operation of the water system, increases the frequency of cleaning the underground pool and replacing the filter media in the drying area. The cleaning and decontamination operations of the drying area and sewage pool are in confined spaces with significant safety risks. Moreover, the cost of treating the replaced oily sand and gravel as hazardous waste is high, which increases the production and operation costs.

[0003] The mainstream technologies for treating wastewater in drying plants are natural sedimentation and infiltration filtration. However, due to safety and environmental concerns, large-volume drying plants that increase natural sedimentation time are gradually losing their market appeal. The instantaneous large-volume discharge of oily and silty wastewater into the drying plant poses a significant challenge to infiltration filtration technology, often resulting in untimely filtration and infiltration, causing water quality to exceed standards at that point and affecting the normal operation of the system. The pretreatment sedimentation tank, semi-submerged oil-blocking flotation device, "U"-shaped tubular oil separator, and mesh grids with the same particle size laid under each layer of filter media designed in this invention solve the problems of excessive oil content in wastewater in drying plant wastewater ponds, high cost and risk of cleaning up oily wastewater, and high replacement cost of sand and gravel filter media. The advantages are obvious.

[0004] In conclusion, given the drawbacks of natural sedimentation and infiltration filtration methods in drying field water treatment, a redesign of the drying field is necessary. Summary of the Invention

[0005] The purpose of this invention is to solve the problems of excessive oil content in wastewater in drying field sewage ponds and high replacement costs of sand and gravel filter media, reduce the generation of hazardous waste, avoid the high cost and high risk of cleaning up oily waste, and provide a design method for drying fields suitable for oilfield wastewater treatment systems.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] A design method for a drying field in an oilfield wastewater treatment system includes a pretreatment sedimentation tank, sand and gravel filter media, a float track, a float, an oil separator, an overflow outlet, a water distribution pipe, and a drainage pipe.

[0008] The pretreatment sedimentation tank is located at the bottom sewage inlet of the large tank in the drying field, serving as an unloading point for external liquids and for pretreatment of oilfield wastewater.

[0009] The float track consists of two partition nets, baffles are hung on the float track, and the float is set in the float track;

[0010] The oil separator is located at the overflow port to block oil stains;

[0011] The sand and gravel filter media consists of four layers. Each layer of sand and gravel filter media is covered with a mesh grid of the same size as the sand and gravel filter media in that layer, which is used for cleaning and recycling of the sand and gravel filter media.

[0012] The water distribution pipe is located in the center of the drying field and is used for oilfield wastewater to enter the drying field;

[0013] The drainage pipes are located at the bottom of the drying area and are evenly distributed. The lower part is connected to the underground pool. A mesh grid is laid between the drainage pipes and the lowest layer of sand and gravel filter material to prevent the filter material from seeping into and blocking the water pipes.

[0014] Furthermore, the volume ratio of wastewater treated at the water treatment plant to that of the drying field is 30:1 to 25:1, and the volume ratio of the drying field to the underground pool is 1:0.5 to 1:1.

[0015] Furthermore, the volume of the pretreatment sedimentation tank is 5-10 m³. 3 Furthermore, the ratio of the volume of the pretreatment sedimentation tank to the station's water treatment capacity is 1:500.

[0016] Furthermore, the float is a semi-submersible oil-blocking float, used to buffer and stabilize water flow and mud.

[0017] The float utilizes the density difference between oil and water to make the oil slicks on the water surface float up and down together on the same liquid surface. The density of the float is greater than the density of oil and less than the density of water, and the lateral width of the float is the same as the width of the float track.

[0018] Furthermore, the oil separator is a U-shaped tubular oil separator, with an oil separator baffle installed 20cm from the bottom of the overflow pool, and the outer wall of the overflow pool is lowered by 10cm to form a U-shaped tubular oil separator.

[0019] Furthermore, the sand and gravel filter media consists of quartz sand, fine sand, coarse stone, and pebbles from top to bottom. The particle size of the sand and gravel filter media is laid out in a flat manner from small to large, and the thickness of each layer of filter media is less than or equal to 1 / 8 of the depth of the drying field.

[0020] Among them, the cleaning and recycling of sand and gravel filter media only includes sand and gravel, but does not include quartz sand.

[0021] Furthermore, the water distribution pipe has evenly distributed openings on both sides.

[0022] The embodiments of the present invention bring the following beneficial effects:

[0023] This invention addresses the challenges posed by the large and concentrated influent volume at drying plants, particularly the presence of wastewater with high oil, mud, and sand content. This often leads to delayed filtration and infiltration, resulting in substandard water quality and disrupting system operation. The invention addresses this by installing a 10m... 3 The system includes a pretreatment sedimentation tank; a semi-submerged oil-blocking float is designed and installed at the liquid surface in the drying field; a U-shaped oil separator is installed near the overflow outlet using the principle of a U-shaped pipe; uniform openings are made in the transverse water inflow direction of the water distribution pipe in the drying field to reduce the circulating flow in the liquid preparation area and avoid dead zones; a mesh grid with the same particle size as the filter media in each layer of the drying field is laid at the bottom of the filter media, which facilitates the cleaning and recycling of sand and gravel filter media, ensuring that the oil content in the underground pool water is stable and meets the standards and that the sand and gravel filter media in the drying field can be recycled after cleaning, thus achieving the purpose of energy saving and consumption reduction. This invention has been applied in 5 field stations, ensuring that the effluent quality at this node of the drying plant is consistently up to standard (oil content ≤50mg / L, suspended solids content ≤30mg / L). It solves the problems of excessive oil content in the sewage tank of the drying plant and the high cost and risk of cleaning up the oily waste. The cleaning cycle of the drying plant has been extended from once every 7 months to once every 2 years. It also extends the replacement cycle of the bottom filter media of the drying plant, realizing the recycling of sand and gravel filter media after cleaning. The sand and gravel filter media can basically achieve zero replacement and only need to be cleaned once every 4 years, solving the problem of high replacement cost of sand and gravel filter media in the drying plant and achieving the goal of improving quality and efficiency.

[0024] Other features and advantages of the invention will be set forth in the following description. The objects and other advantages of the invention are realized and obtained through the structures particularly pointed out in the description, claims, and drawings.

[0025] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0026] Figure 1 This is a design drawing of a drying field suitable for an oilfield wastewater treatment system, provided as an embodiment of the present invention.

[0027] In the diagram, 1-sand and gravel filter media, from top to bottom: quartz sand, fine sand, coarse gravel, and pebbles; 2-float track; 3-baffle mounted on the float track; 4-float; 5-oil-separating baffle of the "U"-shaped tubular oil separator; 6-overflow outlet; 7-water distribution pipe; 8-filter port. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] like Figure 1 As shown, an embodiment of the present invention provides a design method for a drying field suitable for an oilfield wastewater treatment system, including a pretreatment sedimentation tank, sand and gravel filter media, a float track, a float, an oil separator, an overflow outlet, a water distribution pipe, and a drainage pipe.

[0030] The pretreatment sedimentation tank is located at the bottom sewage inlet of the large tank in the drying field, serving as an unloading point for external liquids and for pretreatment of oilfield wastewater.

[0031] The float track consists of two partition nets, baffles are hung on the float track, and the float is set in the float track;

[0032] The oil separator is located at the overflow outlet to prevent oil from entering the underground pool;

[0033] The sand and gravel filter media consists of four layers. Each layer of sand and gravel filter media is covered with a mesh grid of the same size as the sand and gravel filter media in that layer, which is used for cleaning and recycling of the sand and gravel filter media.

[0034] The water distribution pipe is located in the center of the drying field and is used for oilfield wastewater to enter the drying field;

[0035] The drainage pipes are located at the bottom of the drying area and are evenly distributed. The lower part is connected to the underground pool. A mesh grid is laid between the drainage pipes and the lowest layer of sand and gravel filter material to prevent the filter material from seeping into and blocking the water pipes.

[0036] This invention provides Embodiment 1, which is described in detail below:

[0037] In this embodiment, a 5-10m³ volume outlet is provided at the bottom of the large tank in the drying field for wastewater discharge. 3 The pretreatment sedimentation tank has a volume ratio of 1:500 to the station's water treatment capacity. It is used for bottom discharge of large tanks and as an unloading point for external wastewater containing complex components such as mud and sand, so as to avoid the mud and sand in the external wastewater affecting the treatment effect of the drying field.

[0038] In this embodiment, a semi-submerged oil-blocking float (including a float, a float track, and baffles) is designed and installed at the surface of the drying field. The float utilizes the density difference between oil and water to make the oil sludge on the water surface float up and down together on the same surface. The density of the float is greater than the density of oil and less than the density of water, and the lateral width of the float is equal to the width of the float track. Two meshes are used as the float track, which allows the float to float vertically up and down with the sewage surface. The baffles installed on the float track also play a good role in blocking oil, with an oil blocking effect of 78%, and also have the function of buffering and stabilizing the mud and sand in the water flow.

[0039] In this embodiment, a U-shaped tubular grease trap is installed near the overflow outlet. Utilizing the principle of the U-shaped tube, the grease trap can be blocked 100%. An grease trap baffle is installed 20cm from the bottom of the overflow pool near the overflow outlet, and the outer wall of the overflow pool is lowered by 10cm to form a U-shaped tubular grease trap.

[0040] In this embodiment, the four layers of filter media in the drying field, from top to bottom, are quartz sand, fine gravel, coarse stone, and pebbles. The top layer is quartz sand, and the bottom layers are gravel of different particle sizes. The gravel filter media are laid flat with the particle size increasing from small to large to stabilize the foundation. The thickness of each layer of filter media is less than or equal to 1 / 8 of the depth of the drying field to prevent the filter media from being washed away by the water flow. A mesh grid of the same size as the particle size of the filter media in each layer is laid at the bottom to facilitate the cleaning and recycling of the gravel filter media. Since each cleaning of the drying tank will result in some loss of quartz sand, the cleaning and recycling of the filter media only includes gravel and does not include quartz sand.

[0041] In this embodiment, the backwash water and other water treatment system drainage are evenly discharged into the drying field through the water distribution pipe. In order to make the flow velocity of the oil-water mixture flowing out of the water distribution hole lower than the flow velocity of the liquid in the water distribution pipe, reduce the circulation flow in the liquid distribution area, and avoid dead zones, the water distribution pipe is evenly perforated in the transverse water inflow direction. The total area of ​​the perforations is generally three times the cross-sectional area of ​​the manifold. Taking the inlet main pipeline as Φ114 as an example, Φ32 holes are evenly distributed on both sides with a hole spacing of 100mm.

[0042] In this embodiment, the drainage pipes at the bottom of the drying field are evenly distributed, and the lower part of the drainage pipes is connected to the underground pool. The water filtered by the drying field directly enters the underground pool. A mesh grid is laid between the drainage pipes and the bottom layer of filter material to prevent the filter material from seeping into and blocking the water pipes. The drainage pipes are arranged in sequence at intervals of 1.5 meters to ensure that the filtered water is discharged into the underground pool in a timely manner.

[0043] In this embodiment, when the amount of oily sludge in the drying field reaches 1 / 4 of the drying field volume, it is pumped to the next process for oily sludge treatment by a sludge discharge pump.

[0044] In this embodiment, the volume ratio of wastewater treated by the water treatment plant to that of the drying field is 30:1 to 25:1, and the volume ratio of the drying field to the underground pool is 1:0.5 to 1:1.

[0045] This invention provides a second embodiment, taking the Ningyi Station drying plant as an example, to illustrate the application of this invention in detail:

[0046] The drying pool at Ningyi Station has a sand and gravel filter material at the bottom. There is only one horizontal drainage pipe in the center of the bottom of the drying area, which is used to filter sewage. When the filtration capacity is insufficient, oil often enters the underground pool from the overflow outlet at the top, causing the oil content in the sewage pool to exceed the standard. After exceeding the standard, the cleaning operation is carried out 4-5 times a year, and the cleaning cost is about 80,000 yuan. The sewage pool cleaning operation is in a confined space and has a significant safety risk. The drying tank at Ningyi Station measures 8.0*4.0*1.6m. Following the method described in this invention, the drying area structure was modified. A pretreatment sedimentation tank of approximately 2.5*2.5*1.6m was installed at the bottom sewage inlet of the large tank in the drying area. Two 8.0*0.8m mesh screens were used as float tracks, and hollow stainless steel balls were used as floats, allowing the floats to float vertically up and down with the sewage surface. A 0.4m high sheet metal was suspended above the float tracks, forming a semi-submerged oil-blocking float, which effectively blocks oil and buffers and stabilizes the mud and sand in the water flow. Utilizing the principle of a U-shaped pipe, a U-shaped pipe-type oil separator was installed at the overflow outlet. An overflow tank near the overflow outlet was installed at a distance from the bottom of the tank. An oil-blocking baffle is installed at a depth of 20cm, lowering the outer wall of the overflow tank by 10cm to form a "U"-shaped tubular oil-blocking trough. This achieves a 100% oil blocking rate, increasing wastewater treatment capacity and reducing the workload of wastewater recycling, thus achieving energy conservation and consumption reduction. A mesh grid of the same particle size as the filter media in each layer is laid at the bottom of each layer. The sand and gravel filter media is cleaned on-site with the extracted water from the water injection tank. After cleaning, it is filled into the drying field according to particle size. The water distribution pipe in the drying field is located 2.0m in the center of the drying field, with a length of 6.5m and a diameter of Φ114. Φ32 holes are evenly distributed on both sides with a hole spacing of 100mm. The drainage pipes at the bottom of the drying field are evenly distributed and arranged at 1.5-meter intervals.

[0047] This invention provides Embodiment 3, taking the Wang Silian drying field as an example, to illustrate the application of this invention in detail:

[0048] The Wang Silian drying yard has a pool bottom lined with pebbles, coarse stones, fine sand, and quartz sand. The sand and gravel filter media particles are distributed from the inside out in order of decreasing size. There is only one horizontal drainage pipe in the center of the bottom of the drying yard, which is used to leak and filter sewage. When the filtration capacity is insufficient, oil often enters the underground pool from the overflow outlet at the top, causing the oil content in the sewage pool to exceed the standard. After exceeding the standard, the sewage pool needs to be cleaned 3-4 times a year, with a cleaning cost of about 120,000 yuan. The sewage pool cleaning operation is in a confined space and has a significant safety risk. The Wang Silian drying pond consists of two identical 10.0*5.0*4.8m tanks. Following the method described in this invention, the drying area structure was modified. A pretreatment sedimentation tank of approximately 2.5*2.5*1.6m was installed at the bottom sewage inlet of the large tank in the drying area. Two 10.0*2.4m mesh screens were used as float tracks, and hollow stainless steel balls were used as floats, allowing the floats to float vertically up and down with the sewage surface. A 2.0m high sheet metal was suspended above the float tracks, forming a semi-submerged oil-blocking float, which effectively blocks oil and buffers and stabilizes the mud and sand in the water flow. Utilizing the principle of a "U"-shaped pipe, an instrument was installed 40cm from the bottom of the overflow tank near the overflow outlet. Oil-blocking baffles were installed, lowering the outer wall of the overflow tank by 20cm. A U-shaped tubular oil-blocking trough was added at the overflow outlet, achieving a 100% oil blocking rate. This increased wastewater treatment capacity and reduced the workload of circulating wastewater treatment, achieving energy conservation and consumption reduction. A mesh grid of the same particle size as the filter media in each layer was laid at the bottom. The sand and gravel filter media were cleaned on-site with the extracted water from the water injection tank. After cleaning, the media were filled into the drying field according to particle size. The water distribution pipe in the drying field was located 2.5m in the center of the drying field, with a length of 8.5m and a diameter of Φ114. Φ32 holes were evenly distributed on both sides with a hole spacing of 100mm. The drainage pipes at the bottom of the drying field were evenly distributed, arranged in 6 rows with a 1.5-meter interval.

[0049] It should be noted that, in this document, the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0050] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A design method for a drying field suitable for oilfield wastewater treatment systems, characterized in that, It includes a pretreatment sedimentation tank, sand and gravel filter media, float track, float, oil separator, water distribution pipe and drainage pipe; The pretreatment sedimentation tank is located at the bottom sewage inlet of the large tank in the drying field, serving as an unloading point for external liquids and for pretreatment of oilfield wastewater. The float track consists of two partition nets located above the right end of the sand and gravel filter media in the drying field. Baffles are hung on the float track, and the float is placed inside the float track. The float is a semi-submerged oil-blocking float placed at the liquid surface in the drying field to buffer and stabilize the mud and sand in the water flow. The float utilizes the density difference between oil and water to cause the oil on the water surface to float up and down synchronously with the float on the same liquid surface. The density of the float is greater than the density of oil and less than the density of water, and the lateral width of the float is the same as the width of the float track. An oil separator is installed on the right side of the sand and gravel filter material in the drying field to prevent oil from entering the underground pool. The sand and gravel filter media consists of four layers laid at the bottom of the drying field. Each layer of sand and gravel filter media is covered with a mesh grid, the mesh size of which is the same as the particle size of the sand and gravel filter media in that layer, for the purpose of cleaning and recycling the sand and gravel filter media. The water distribution pipe is horizontally installed in the center of the space above the sand and gravel filter material in the drying field, and is used for oilfield wastewater to enter the drying field. The drainage pipes are located at the bottom of the drying area and are evenly distributed. The lower part of the drainage pipes is connected to the underground pool. A mesh grid is laid between the drainage pipes and the lowest layer of sand and gravel filter material to prevent the filter material from seeping through and blocking the drainage pipes.

2. The design method for drying fields in oilfield wastewater treatment systems according to claim 1, characterized in that, The volume ratio of wastewater treated at the oilfield water treatment station to that of the drying field is 30:1 to 25:1, and the volume ratio of the drying field to the underground pool is 1:0.5 to 1:

1.

3. The design method for drying fields in oilfield wastewater treatment systems according to claim 1, characterized in that, The volume of the pretreatment sedimentation tank is 5-10 m³. 3 Furthermore, the volume ratio of the pretreatment sedimentation tank to the wastewater treatment capacity of the oilfield water treatment station is 1:

500.

4. The design method for drying fields in oilfield wastewater treatment systems according to claim 1, characterized in that, A vertical oil-separating baffle is installed 20cm from the bottom of the oil-separating tank.

5. The design method for a drying field in an oilfield wastewater treatment system according to claim 1, characterized in that, The sand and gravel filter media consists of quartz sand, fine sand, coarse stone, and pebbles from top to bottom. The sand and gravel filter media are laid flat with the particle size increasing from top to bottom, and the thickness of each layer of filter media is less than or equal to 1 / 8 of the depth of the drying field. The cleaning and recycling of sand and gravel filter media does not include quartz sand.

6. The design method for drying fields in oilfield wastewater treatment systems according to claim 1, characterized in that, The water distribution pipe has evenly distributed openings on both sides.

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