Liquid filter and method for removing mechanical impurities and soluble salts from wellhead gas

Abstract

The present invention discloses a liquid filter and method for removing mechanical impurities and soluble salts from wellhead gas. The liquid filter includes a buffer tank, a vertical cylinder and a filtrate circulation system; the lower end of the vertical cylinder is connected to the upper end of the buffer tank, and includes a tray filter device, a defoamer and a treatment gas pipe; the filtrate circulation system includes a filtrate circulation pump, a filtrate replenishment pump, a circulating liquid inlet pipe and a circulating liquid outlet pipe. The filtrate circulation system is used to maintain the circulation of the filtrate in the buffer tank and the three-dimensional cylinder, so that the wellhead gas entering the liquid filter is continuously in contact with the filtrate during the rising process, thereby removing mechanical impurities such as dust and soluble salts therein, reducing the harm caused by mechanical impurities such as dust and soluble salts in the wellhead gas to downstream transmission pipelines and devices, extending the maintenance period of the device, and realizing the long-term stable operation of the device, so as to achieve the purpose of reducing the maintenance cost and operation cost of the production device.

Description

Technical Field

[0001] The present disclosure relates to the technical field of gas purification containing mechanical impurities such as salt and dust, and in particular to a liquid filter and a method thereof for removing mechanical impurities and soluble salts from wellhead gas. Background Art

[0002] The statements in this section only provide background information related to the present disclosure, and these statements may constitute prior art. In the process of implementing the present invention, the inventors found that there are at least the following problems in the prior art.

[0003] During the gas field exploitation process, the natural gas coming out of the wellhead contains mechanical impurities such as dust and free water, and the free water contains soluble salts. If the wellhead natural gas (hereinafter referred to as wellhead gas) is not free of dust and salt in free water, the mechanical impurities such as dust and salt in free water carried by the wellhead gas will enter the amine solution system and other solution systems during the downstream desulfurization process, and will continue to accumulate, causing damage such as blockage and corrosion of equipment and pipelines; at the same time, it will have an adverse effect on the process technology of the treatment station. Therefore, wellhead gas usually needs to be purified by removing mechanical impurities such as dust and free water.

[0004] At present, the purification technology for removing mechanical impurities such as dust and free water in wellhead gas usually adopts sedimentation method and mechanical filtration method.

[0005] Sedimentation is a unit operation that uses mechanical methods to separate heterogeneous mixtures. It is an operation process that uses the density difference between natural gas and mechanical impurities such as dust and free water to make natural gas and mechanical impurities such as dust and free water move relative to each other to achieve separation. In this way, the natural gas in the wellhead gas is separated from mechanical impurities such as dust and free water, and the purpose of removing mechanical impurities such as dust and free water in the wellhead gas is achieved. According to the different external forces used to achieve the sedimentation operation, the sedimentation process is divided into gravity sedimentation and centrifugal sedimentation. Among them: (i) Gravity sedimentation is a sedimentation process that occurs under the action of gravity. It is achieved through a gravity separator. It uses the density difference between natural gas and mechanical impurities such as dust and free water. The density of mechanical impurities such as dust and free water is greater than that of natural gas. In the gravity separator, natural gas and mechanical impurities such as dust and free water move relative to each other. The flow velocity in the gravity separator is lower than the flow velocity in the pipeline before entering the gravity separator, and there is a certain residence time. Relative movement occurs between natural gas and mechanical impurities such as dust and free water. Gravity separators are divided into two types: vertical gravity separators and horizontal gravity separators. Vertical gravity separators are often used to remove mechanical impurities such as dust and free water from wellhead gas. Wellhead gas enters from the middle of the gravity separator, and natural gas flows to the upper section of the gravity separator. Natural gas is discharged from the upper port of the gravity separator, and mechanical impurities such as dust and free water settle to the lower section of the gravity separator. Mechanical impurities such as dust and free water are discharged from the lower port of the gravity separator, thereby achieving the separation of natural gas from mechanical impurities such as dust and free water in the wellhead gas, and achieving the purpose of removing mechanical impurities such as dust and soluble salts in free water from the wellhead gas. (ii) Centrifugal sedimentation is a sedimentation process that occurs under the action of inertial centrifugal force. It is achieved through a cyclone separator and utilizes the density difference between natural gas and mechanical impurities such as dust and free water. The density of mechanical impurities such as dust and free water is greater than that of natural gas. In the cyclone separator, natural gas and mechanical impurities such as dust and free water move relative to each other. The wellhead gas enters tangentially from the air inlet pipe on the upper part of the cylinder of the cyclone separator, and moves in a spiral motion from top to bottom under the constraint of the cyclone separator wall. Under the action of inertial centrifugal force, mechanical impurities such as dust and free water are thrown to the wall of the cyclone separator, and then fall along the wall of the cyclone separator to the bottom of the cone and are separated from the natural gas. The mechanical impurities such as dust and free water are discharged from the bottom of the cone of the cyclone separator, and the natural gas moves in a spiral motion from bottom to top near the central axis and is discharged from the top of the cyclone separator. In this way, the natural gas in the wellhead gas is separated from mechanical impurities such as dust and free water, and the purpose of removing mechanical impurities such as dust and soluble salts in free water in the wellhead gas is achieved.

[0006] The mechanical filtration method is to allow natural gas to pass through the pores of the filter element under the action of pressure difference, while large particles of dust and other mechanical impurities and some free water are retained on the filter element, thereby realizing the separation of natural gas from mechanical impurities such as dust and free water in the wellhead gas, and achieving the purpose of removing mechanical impurities such as dust in the wellhead gas and soluble salts in free water.

[0007] The gravity sedimentation method is limited by the size of the gravity separator, the sedimentation separation time is limited, and the removal rate of small particles of dust and other mechanical impurities and free water is low. In the purification process of removing dust and other mechanical impurities and free water from wellhead gas, the size of the gravity separator is usually designed to separate mechanical impurities such as dust and free water with a particle size greater than 10um at an efficiency of 95%. Therefore, a large amount of mechanical impurities such as dust and soluble salts still enter the downstream transportation pipelines and devices, causing damage to the downstream transportation pipelines and devices.

[0008] The centrifugal sedimentation method has a large pressure drop in the cyclone separator, which is limited by the pressure drop allowed in the process of removing mechanical impurities such as dust and free water from the wellhead gas and the structure of the cyclone separator itself. In the process of removing mechanical impurities such as dust and free water from the wellhead gas, the cyclone separator is usually designed to separate mechanical impurities such as dust and free water with a particle size greater than 5um at an efficiency of 95%. Therefore, a large amount of mechanical impurities such as dust and soluble salts still enter the downstream transportation pipelines and devices, causing damage to the downstream transportation pipelines and devices; at the same time, the wellhead gas has a fast flow rate in the cyclone separator, and the mechanical impurities such as dust entrained in the wellhead gas seriously erode the cyclone separator wall, resulting in a short service life of the cyclone separator and high operating costs.

[0009] The removal efficiency of mechanical filtration depends on the size of the filter pores. Sand with a diameter smaller than the filter pores will pass through the pores. The smaller the filter pores, the greater the pressure drop of the wellhead gas passing through the filter. The pressure drop is limited by the allowable pressure drop in the wellhead gas removal process of mechanical impurities such as dust and free water. In the wellhead gas removal process of mechanical impurities such as dust and free water, the cyclone separator is usually designed to separate mechanical impurities such as dust and free water with a particle size greater than 0.5um with an efficiency of 98%. Therefore, a large amount of mechanical impurities such as dust and soluble salts still enter the downstream transportation pipelines and devices, causing harm to the downstream transportation pipelines and devices; at the same time, with the increase of mechanical impurities such as dust and free water attached to the filter element, the pressure drop of the wellhead gas passing through the filter element will also increase. When the pressure drop reaches the limit, the filter element must be replaced, and the operating cost is high. Summary of the invention

[0010] In view of the above problems, the object of the present invention is to solve part of the problems in the prior art, or at least alleviate these problems.

[0011] Liquid filter used to remove mechanical impurities and soluble salts from wellhead gas, including

[0012] A buffer tank, comprising a wellhead gas connection pipe and a sewage discharge valve; the wellhead gas connection pipe is located at the top of the buffer tank and is used to connect the wellhead gas;

[0013] A vertical cylinder, the lower end of which is connected to the buffer tank; the vertical cylinder comprises a tray filter device, a filtrate removal device and a process gas connection pipe; the tray filter device is fixedly arranged at the lower part of the vertical cylinder, and the filtrate removal device is fixedly arranged at the upper part of the vertical cylinder; the process gas connection pipe is located at the top of the vertical cylinder and is used to release the wellhead gas;

[0014] The filtrate circulation system comprises a filtrate circulation pump, a circulating liquid inlet pipe and a circulating liquid outlet pipe; the circulating liquid inlet pipe is connected to the vertical cylinder and has a higher level than the tower plate filtering device; the circulating liquid outlet pipe is located at the bottom of the buffer tank and is connected to the buffer tank.

[0015] Furthermore, the buffer tank also includes a waste oil discharge system.

[0016] Furthermore, the dirty oil discharge system includes an oil separator and a dirty oil discharge pipe; the oil separator is arranged inside the buffer tank and fixedly connected to the bottom of the buffer tank; the dirty oil discharge pipe is fixedly arranged at the bottom of the buffer tank.

[0017] Furthermore, the buffer tank is provided with a dirty oil level meter.

[0018] Optionally, the filtrate removal device is a demister.

[0019] The tray filtration device comprises a first tray and a second tray, which are connected via a first downcomer; the circulating liquid inlet pipe is located between the first tray and the demister.

[0020] The filtrate circulation system also includes a filtrate replenishment pump.

[0021] The buffer tank is provided with a filtrate level meter.

[0022] The method for removing mechanical impurities and soluble salts from wellhead gas comprises the following steps:

[0023] Establishing buffer tank levels;

[0024] Open the inlet valve of the filtrate circulation pump and start the filtrate circulation pump;

[0025] Open the wellhead gas cut-off valve and let the wellhead gas enter the buffer tank through the wellhead gas pipe;

[0026] Wellhead gas passes through a buffer tank for initial impurity removal;

[0027] The wellhead gas rises through the vertical cylindrical tray filter device and contacts the filtrate flowing down the downcomer in countercurrent flow to perform secondary impurity removal;

[0028] The wellhead gas after secondary impurity removal rises and passes through the demister to intercept the filtrate entrained in the treated wellhead; the filtrate returns to the tower plate filter device, and the treated wellhead gas is sent out through the treated gas outlet valve.

[0029] Further, the following steps are used to establish the buffer tank level:

[0030] Step 1: Open the replenishing liquid shut-off valve and send the filtrate to the liquid filter through the filtrate replenishing pump to establish the buffer tank liquid level;

[0031] Step 2: Start the filtrate replenishing pump, and send the filtrate to the liquid filter through the filtrate replenishing pump to establish the liquid level of the buffer tank;

[0032] Step 3, stop the filtrate replenishing pump;

[0033] Step 4: Close the replenishing liquid shut-off valve.

[0034] The method for removing mechanical impurities and soluble salts from wellhead gas also includes filtrate treatment, including the following steps:

[0035] The filtrate flowing down from the downcomer is deposited at the bottom of the buffer tank. In the buffer tank, oil and water are separated because they are immiscible and have a density difference. Water is at the bottom and oil is at the top. The oil layer enters the oil storage tank through the oil separator and is discharged from the liquid filter through the dirty oil discharge valve.

[0036] 50% to 98% of the filtrate at the bottom of the buffer tank is circulated through the filtrate circulation pump, and the remaining 50% to 2% of the filtrate at the bottom of the buffer tank is discharged from the liquid filter through the sewage discharge valve.

[0037] The present invention has the following beneficial effects:

[0038] 1. Compared with the gravity sedimentation method, the present invention has a higher efficiency in removing mechanical impurities such as dust and soluble salts entrained in the wellhead gas, eliminating the harm of mechanical impurities such as dust and soluble salts entrained in the wellhead gas to downstream processing equipment and process systems, reducing the maintenance of downstream equipment, greatly reducing the pollution to downstream process media, and low operating costs;

[0039] Compared with the centrifugal sedimentation method, the present invention has a higher efficiency in removing mechanical impurities such as dust and soluble salts entrained in the wellhead gas, eliminating the harm of mechanical impurities such as dust and soluble salts entrained in the wellhead gas to downstream processing equipment and process systems, requiring less maintenance for downstream equipment, greatly reducing the pollution to downstream process media, and having low operating costs. At the same time, the wellhead gas has a low flow rate in this system, and mechanical impurities such as dust have little damage to the equipment in the present invention, resulting in low maintenance costs and low operating costs;

[0040] Compared with the mechanical filtration method, the present invention has a higher efficiency in removing free water and sand entrained in the wellhead gas, eliminates the harm of mechanical impurities such as dust and free water entrained in the wellhead gas to downstream processing equipment and process systems, reduces the maintenance of downstream equipment, greatly reduces the pollution to downstream process media, and has low operating costs. At the same time, the present invention does not require replacement of equipment and equipment-related components, and has low operating costs.

[0041] 2. The waste oil discharge system can separate the waste oil from the sewage, thus achieving safe discharge and avoiding environmental pollution.

[0042] 3. The filtrate circulation system can keep the liquid filter in the filtering state all the time. In combination with the tray filter device, the impurity removal medium is evenly distributed, ensuring a more uniform and sufficient contact between the wellhead gas and the filtrate, greatly improving the impurity removal efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a schematic diagram of the present invention;

[0044] Figure 2 It is a schematic diagram of the tower plate structure of the present invention;

[0045] Figure 3 The figure is a step diagram of the method for removing impurities according to the present invention.

[0046] Among them, 1-buffer tank; 2-circulating liquid outlet pipe; 3-wastewater discharge pipe; 4-filtrate level meter; 5-oil separator; 6-dirty oil discharge pipe; 7-dirty oil level meter; 8-wellhead gas pipe; 9-first tower plate support ring; 10-circulating liquid inlet pipe; 11-demister support ring; 12-demister; 13-process gas pipe; 14-first tower plate; 15-first downcomer; 16-vertical cylinder; 17-second tower plate; 18-second tower plate support ring; 19-second downcomer; 20-wellhead gas shut-off valve; 21-supplementary liquid shut-off valve; 22-filtrate replenishment pump; 23-filtrate circulation pump; 24-filtrate circulation pump inlet valve; 25-wastewater discharge valve; 26-dirty oil discharge valve; 27-process gas outlet valve; 28-overflow weir. DETAILED DESCRIPTION

[0047] The present invention is further described below in conjunction with the accompanying drawings. The embodiments of the present invention are only used to illustrate the present invention rather than to limit the present invention. Without departing from the technical idea of ​​the present invention, various substitutions and changes can be made according to common technical knowledge and customary means in the field, which should all be included in the scope of the present invention.

[0048] like Figure 1 As shown, the liquid filter used to remove mechanical impurities and soluble salts from wellhead gas includes

[0049] The buffer tank 1 includes a wellhead gas pipe 8 and a sewage discharge valve 25; the wellhead gas pipe 8 is located at the top of the buffer tank 1 and is used to connect the wellhead gas;

[0050] A vertical cylinder 16, the lower end of which is connected to the buffer tank 1; the vertical cylinder 16 includes a tray filter device, a filtrate removal device and a process gas pipe 13; the tray filter device is fixedly arranged at the lower part of the vertical cylinder 16, and the filtrate removal device is fixedly arranged at the upper part of the vertical cylinder 16; the process gas pipe 13 is located at the top of the vertical cylinder 16, and is used to release the wellhead gas;

[0051] The filtrate circulation system includes a filtrate circulation pump 23, a circulating liquid inlet pipe 10 and a circulating liquid outlet pipe 2; the circulating liquid inlet pipe 10 is connected to the vertical cylinder 16 and has a horizontal height higher than the tower plate filtering device; the circulating liquid outlet pipe 2 is located at the bottom of the buffer tank 1 and is connected to the buffer tank 1.

[0052] like Figure 1 As shown, the wellhead gas pipe 8 is located at the top of the buffer tank 1, the circulating liquid outlet pipe 2 is located at the bottom of the buffer tank 1, and the vertical cylinder 16 is located at the upper part of the buffer tank 1, and can be fixedly connected to the buffer tank 1 by welding or other means. The filtrate removal device is a demister 12, which is connected through a demister support ring 11 fixedly arranged on the upper part of the vertical cylinder 16, and is used to intercept the filtrate entrained in the treated gas, and the filtrate is returned to the first tower plate 14, and the treated gas is sent out of the liquid filter through the treated gas pipe 13 and the treated gas outlet valve 27.

[0053] like Figure 1 As shown, the tray filtration device comprises at least two trays and a downcomer. Figure 2 As shown, the tray filtration device includes a first tray 14 and a second tray 17, which are connected through a first downcomer 15; the circulating liquid inlet pipe 10 is located between the first tray 14 and the demister 12. The first tray 14 is fixedly connected to the vertical barrel 16 through a first tray support ring 9 fixedly connected to the vertical barrel 16, and the second tray 17 is fixedly connected to the vertical barrel 16 through a second tray support ring 18 fixedly connected to the vertical barrel 16. The first downcomer 15 and the second downcomer 19 are both located inside the vertical barrel 16 and fixedly connected to the vertical barrel 16 by welding or the like. Figure 1 shown.

[0054] There are two other functions of setting up a tray filter:

[0055] 1. Make the medium evenly distributed. Figure 2 As shown, since the wellhead gas rises from the bottom to the top and the filtrate flows from the top to the bottom, they both need to pass through several layers of tower plates. The tower plates are flat and have densely packed holes on them, which allows the gas and liquid to contact each other very evenly and fully.

[0056] 2. It has a certain supporting function. Some towers are packed towers, and some packing can be loaded on the tray. The purpose of the packing is also to make the medium evenly distributed.

[0057] The filtrate circulation system can continuously feed filtrate into the vertical cylinder 16, and then flow downward through the tray filter device into the buffer tank 1, and repeat the circulation through the filtrate circulation pump 23. It is mainly used to keep the filtrate circulating in the tray filter device of the vertical cylinder 16 and the buffer tank 1, so that the entire liquid filter always maintains the filtrate filtering state. Mechanical impurities such as dust and soluble salts entrained in the wellhead gas are blocked by the filtrate and enter the buffer tank 1 through the downcomer 19 with the filtrate.

[0058] In order to ensure the circulation of the filtrate, a certain amount of filtrate needs to be added to the buffer tank 1 in advance. Figure 1 As shown, the filtrate circulation system further includes a filtrate replenishing pump 22, which is connected to the pipeline between the filtrate circulation pump 23 and the circulating liquid inlet pipe 10, so that the filtrate can be replenished into the filtrate circulation system through the replenishing liquid cut-off valve 21 and the filtrate replenishing pump 22. The filtrate replenishing pump 22 can replenish the filtrate for the first time. The buffer tank 1 is provided with a filtrate level meter 4, as shown in FIG. Figure 1 As shown, the filtrate can be added to the liquid filter at normal times according to the filtrate level. The filtrate can also be discharged through the sewage discharge connection pipe 3 and the sewage discharge valve 25 according to the filtrate level. Generally speaking, 50% to 98% of the filtrate at the bottom of the buffer tank 1 is circulated through the filtrate circulation pump 23, and the remaining 50% to 2% of the filtrate at the bottom of the buffer tank 1 is discharged from the liquid filter through the sewage discharge valve 25.

[0059] The circulating liquid inlet pipe 10 is located on the side of the vertical cylinder 16 and is fixedly connected to the vertical cylinder 16 by welding or other methods.

[0060] The buffer tank 1 also includes a waste oil discharge system, such as Figure 1 As shown, it is mainly used to separate the filtrate from the oil, and realize the separate discharge of the filtrate and the oil to avoid environmental pollution. The dirty oil discharge system includes an oil separator 5 and a dirty oil discharge pipe 6; the oil separator 5 is arranged inside the buffer tank 1 and is fixedly connected to the bottom of the buffer tank 1; the dirty oil discharge pipe 6 is fixedly arranged at the bottom of the buffer tank 1.

[0061] Since the wellhead gas is filtered multiple times in the buffer tank 1 and the vertical cylinder, the filtrate flowing down through the second downcomer 19 is deposited at the lower part of the buffer tank 1, and oil-water separation is achieved in the buffer tank 1, with water at the lower part and oil at the upper layer. The oil layer passes over the oil separator 5 and enters the oil storage tank, and is then discharged from the liquid filter through the dirty oil discharge valve 26.

[0062] The buffer tank 1 is provided with a dirty oil level meter 7. Figure 1The dirty oil level gauge 7 is located on the side of the buffer tank 1 and is fixedly connected to the buffer tank 1 by welding or other methods. The dirty oil level gauge 7 can be used to observe the liquid level of the dirty oil, so that the dirty oil can be discharged regularly to achieve safe discharge.

[0063] The process steps are described as follows:

[0064] The wellhead gas enters the liquid filter from the upper part of the buffer tank 1 through the wellhead gas cut-off valve 20; after the wellhead gas enters the liquid filter, some mechanical impurities such as dust and free water are separated in the upper part of the buffer tank 1, and some mechanical impurities such as dust and free water separated in the upper part of the buffer tank 1 are deposited at the bottom of the buffer tank 1, and the wellhead gas carries the remaining mechanical impurities such as dust and free water into the tower plate filtration device, and contacts the filtrate sent by the filtrate circulation pump 23 in countercurrent; the wellhead gas passes through the filtrate layer on the tower plate, and in this process, the free water entrained in the wellhead gas merges with the filtrate on the tower plate, and the mechanical impurities such as dust entrained in the wellhead gas In the filtrate layer blocked on the tray, the wellhead gas carries a small amount of filtrate with low soluble salt content and leaves the tray filter device, entering the upper half of the liquid filter; the wellhead gas further separates the entrained filtrate in the upper half of the liquid filter, and the filtrate falls onto the tray filter device. After the wellhead gas enters the demister 12 at the top of the vertical container, it is sent out of the system through the treated gas outlet valve 27; the filtrate on the tray flows into the buffer tank 1 through the downcomer; 50% to 98% of the filtrate is sent to the tray filter device through the filtrate circulation pump; 50% to 2% of the filtrate is discharged from the equipment through the sewage discharge valve; the filtrate is replenished by the filtrate replenishing pump.

[0065] Working principle:

[0066] When the wellhead gas passes through the tray filter device, the physical properties of the free water carried by the wellhead gas are exactly the same as those of the filtrate in the filtrate layer on the tray, and the free water carried by the wellhead gas quickly dissolves with the filtrate in the filtrate layer on the tray; when the wellhead gas passes through the tray filter device, the mechanical impurities such as dust carried by the wellhead gas are blocked in the filtrate layer on the tray under the resistance of the filtrate layer on the tray; when the wellhead gas passes through the tray filter device, the natural gas is insoluble in the filtrate, and the density of the natural gas is smaller than that of the filtrate, and the natural gas passes through the filtrate layer on the tray. The flow rate of the natural gas is low after passing through the filtrate layer on the tray, and the amount of filtrate carried by the natural gas after passing through the filtrate layer on the tray is small. At the same time, after the gravity sedimentation separation in the upper half of the liquid filter, the free water carried by the natural gas is basically completely separated. The purpose of removing mechanical impurities such as dust and soluble salts in the wellhead gas is achieved.

[0067] like Figure 3 As shown, the method for removing mechanical impurities and soluble salts from wellhead gas is characterized by comprising the following steps:

[0068] Establish the buffer tank 1 level;

[0069] Open the filtrate circulation pump inlet valve 24 and start the filtrate circulation pump 23;

[0070] Open the wellhead gas cut-off valve 20, and let the wellhead gas enter the buffer tank 1 through the wellhead gas connecting pipe 8;

[0071] The wellhead gas passes through the buffer tank 1 for initial impurity removal;

[0072] The wellhead gas rises through the tray filter device of the vertical cylinder 16 and contacts the filtrate flowing down the downcomer in countercurrent flow to perform secondary impurity removal;

[0073] The wellhead gas after secondary impurity removal rises and passes through the demister 12, intercepting the filtrate entrained in the treated wellhead; the filtrate returns to the tray filter device, and the treated wellhead gas is sent out through the treated gas outlet valve 27.

[0074] After the wellhead gas enters the buffer tank 1, the volume flow rate decreases. The density of natural gas is smaller than that of mechanical impurities such as dust and free water. Under the action of gravity, natural gas, mechanical impurities such as dust and free water move relative to each other in the buffer tank 1, and some mechanical impurities such as dust and free water are separated. The mechanical impurities such as dust and free water separated by the buffer tank 1 are deposited at the bottom of the buffer tank 1, realizing the initial impurity removal.

[0075] The wellhead gas from the buffer tank 1 enters the lower part of the vertical cylinder 16, and contacts the filtrate flowing down from the first downcomer 16 in countercurrent at the upper part of the second tray 17. Mechanical impurities such as dust and soluble salts entrained in the inlet gas are blocked by the filtrate and enter the buffer tank 1 through the second downcomer 19 with the filtrate. The thickness of the filtrate layer is achieved by adjusting the height of the overflow weir 28 of the second downcomer 19.

[0076] The wellhead gas passes through the second tower tray 17 and then enters the first tower tray 14, and is countercurrently contacted with the filtrate sent by the filtrate circulation pump 23 and the filtrate replenishment pump 22 at the upper part of the first tower tray 14. Mechanical impurities such as dust and soluble salts entrained in the inlet gas are further blocked by the filtrate, and enter the second tower tray 17 along with the filtrate through the first downcomer 15. The thickness of the filtrate layer is achieved by adjusting the height of the overflow weir 28 of the first downcomer 15.

[0077] As a result, the wellhead gas is purified for the second time.

[0078] The following steps can be used to establish the buffer tank 1 level:

[0079] Step 1: Open the replenishing liquid shut-off valve 21, and send the filtrate to the liquid filter through the filtrate replenishing pump 22 to establish the liquid level of the buffer tank 1;

[0080] Step 2: Start the filtrate replenishing pump 22, and send the filtrate to the liquid filter through the filtrate replenishing pump 22 to establish the liquid level of the buffer tank 1;

[0081] Step 3, stop the filtrate replenishing pump 22;

[0082] Step 4: close the replenishing liquid cut-off valve 21.

[0083] The method for removing mechanical impurities and soluble salts from wellhead gas also includes filtrate treatment, including the following steps:

[0084] The filtrate flowing down from the second downcomer 19 is deposited at the lower part of the buffer tank 1. In the buffer tank 1, oil and water are separated because oil and water are immiscible and have a density difference. Water is at the lower part and oil is at the upper layer. The oil layer enters the oil storage tank through the oil separator 5 and is discharged from the liquid filter through the dirty oil discharge valve 26.

[0085] 50% to 98% of the filtrate in the lower part of the buffer tank 1 is circulated through the filtrate circulation pump 23 , and the remaining 50% to 2% of the filtrate in the lower part of the buffer tank 1 is discharged from the liquid filter through the sewage discharge valve 25 .

[0086] The present invention provides a liquid filter and a method for removing mechanical impurities such as dust and soluble salts from wellhead gas. The liquid filter and a method are used in a purification process for removing mechanical impurities such as dust and soluble salts from wellhead gas, thereby improving the removal rate of mechanical impurities such as dust and soluble salts from wellhead gas, reducing the entry of mechanical impurities such as dust and soluble salts from wellhead gas into downstream transportation pipelines and devices, reducing the harm caused by mechanical impurities such as dust and soluble salts in wellhead gas to downstream transportation pipelines and devices, reducing the pressure drop of the process, reducing the corrosion of soluble salts entrained in the wellhead gas to equipment and pipelines, reducing the pollution of soluble salts entrained in the wellhead gas to process media, extending the maintenance period of the device, and realizing long-term stable operation of the device, so as to achieve the purpose of reducing the maintenance cost and operation cost of the production device.

[0087] The fixed connection not specifically mentioned above may be a connection method such as riveting, welding, bolt connection, etc., and the movable connection may be a connection method such as hinged connection.

Claims

1. A method for removing mechanical impurities and soluble salts from wellhead gas by using a liquid filter, characterized in that: The liquid filter comprises: The buffer tank (1) comprises a wellhead gas pipe (8) and a sewage discharge valve (25); the wellhead gas pipe (8) is located at the top of the buffer tank (1) and is used to receive wellhead gas; the wellhead gas pipe (8) is opened and closed by the wellhead gas cut-off valve (20); A vertical cylinder (16), the lower end of which is in communication with the buffer tank (1); the vertical cylinder (16) comprises a tray filter device, a filtrate removal device and a process gas pipe (13); the tray filter device is fixedly arranged at the lower part of the vertical cylinder (16), and the filtrate removal device is fixedly arranged at the upper part of the vertical cylinder (16); the tray filter device comprises a first tray (14) and a second tray (17); the first tray (14) and the second tray (17) are in communication with each other through a first downcomer (15), and a second downcomer (19) is arranged below the second tray (17); the filtrate removal device is a demister (12); the circulating liquid inlet pipe (10) is located between the first tray (14) and the demister (12); the process gas pipe (13) is located at the top of the vertical cylinder (16), and is connected to a process gas outlet valve (27) for releasing wellhead gas; A filtrate circulation system, comprising a filtrate circulation pump (23), a circulating liquid inlet pipe (10) and a circulating liquid outlet pipe (2); the circulating liquid inlet pipe (10) is in communication with the vertical cylinder (16) and has a higher level than the tray filter device; the circulating liquid outlet pipe (2) is located at the bottom of the buffer tank (1) and is in communication with the buffer tank (1); a filtrate circulation pump inlet valve (24) is provided between the circulating liquid outlet pipe (2) and the filtrate circulation pump (23); The method for removing mechanical impurities and soluble salts from wellhead gas comprises the following steps: Establish the liquid level of the buffer tank (1); Open the filtrate circulation pump inlet valve (24) and start the filtrate circulation pump (23); Open the wellhead gas cut-off valve (20) to allow the wellhead gas to enter the buffer tank (1) through the wellhead gas connecting pipe (8); The wellhead gas passes through a buffer tank (1) for initial impurity removal; The wellhead gas rises and passes through the tray filter device of the vertical cylinder (16), and contacts the filtrate flowing down from the first downcomer (15) and the second downcomer (19) in countercurrent flow, thereby performing secondary impurity removal; The wellhead gas after secondary impurity removal rises and passes through the demister (12), intercepting the filtrate entrained in the treated wellhead gas; the filtrate returns to the tray filter device, and the treated wellhead gas is sent out through the treated gas outlet valve (27).

2. The method for removing mechanical impurities and soluble salts from wellhead gas by using a liquid filter according to claim 1, characterized in that: The filtrate circulation system further comprises a filtrate replenishing pump (22) which is in communication with a pipeline between the filtrate circulation pump (23) and the circulating liquid inlet pipe (10); the filtrate replenishing pump (22) is connected to a replenishing liquid shut-off valve (21); The following steps are used to establish the liquid level in the buffer tank (1): Step 1: Open the replenishing liquid shut-off valve (21) and send the filtrate to the filtrate device through the filtrate replenishing pump (22) to establish the liquid level of the buffer tank (1); Step 2: starting the filtrate replenishing pump (22), delivering the filtrate to the liquid filter through the filtrate replenishing pump (22), and establishing the liquid level of the buffer tank (1); Step 3, stop the filtrate replenishing pump (22); Step 4: Close the replenishing liquid shut-off valve (21).

3. The method for removing mechanical impurities and soluble salts from wellhead gas by using a liquid filter according to claim 1, characterized in that: The buffer tank (1) further comprises a dirty oil discharge system; the dirty oil discharge system comprises an oil separator (5) and a dirty oil discharge pipe (6); the oil separator (5) is arranged inside the buffer tank (1) and is fixedly connected to the bottom of the buffer tank (1); the dirty oil discharge pipe (6) is fixedly arranged at the bottom of the buffer tank (1) and is connected to the dirty oil discharge valve (26); The method for removing mechanical impurities and soluble salts from wellhead gas also includes filtrate treatment, including the following steps: The filtrate flowing down from the second downcomer (19) is deposited at the lower part of the buffer tank (1). In the buffer tank (1), oil and water are separated due to the immiscibility of oil and water and the difference in density between oil and water. The water is at the lower part and the oil is at the upper layer. The oil layer enters the oil storage tank through the oil separator (5) and is discharged from the liquid filter through the dirty oil discharge valve (26). 50% to 98% of the filtrate in the lower part of the buffer tank (1) is circulated for use via a filtrate circulation pump (23), and the remaining 50% to 2% of the filtrate in the lower part of the buffer tank (1) is discharged from the liquid filter via a sewage discharge valve (25).

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