LNG (Liquefied Natural Gas) deep purification device and process thereof

Abstract

The invention discloses an LNG deep purification device and technology, and relates to the technical field of natural gas purification, the LNG deep purification device comprises a cold box, a low-temperature separator and a low-temperature washing tower, one side of the low-temperature separator is provided with an intermediate tank, and a vacuum pump is arranged between the intermediate tank and the low-temperature separator; the input end and the output end of the vacuum pump are respectively provided with a first connecting pipe and a second connecting pipe and are communicated with the intermediate tank and the low-temperature separator; and the device further comprises a filtrate assembly, a driving assembly and a breathing type cleaning assembly. Through arrangement of the turbine shell, the turbine blades, the differential mechanism and the like, the multiple driven defoaming discs are driven by the differential mechanism to rotate at different speeds, in the rotating process, ice blocks condensed on the driven defoaming discs can be mutually cleaned away, the problems that part of the ice blocks are continuously bonded, and cleaning is not thorough are solved, and the service life of the driven defoaming discs is prolonged. And the separation effect of the defoaming disc is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of natural gas purification, and in particular to an LNG deep purification device and a process thereof. Background Art

[0002] LNG is the abbreviation of liquefied natural gas. It refers to a form of energy that converts natural gas into a liquid state after a series of treatments by cooling it to about -162°C. In the processing of heavy hydrocarbon natural gas, cryogenic separation technology is often used to remove the heavy hydrocarbon components. This process uses the fine-pore defoaming screen equipped in the cryogenic separator to achieve effective separation. However, since the defoaming screen has an extremely small pore size and the entire process is carried out under low temperature conditions, the moisture carried in the natural gas is easily solidified and frozen on the screen in this environment, thereby increasing the risk of freezing of the defoaming screen.

[0003] The Chinese patent application number CN202311207302.1 discloses an anti-freezing LNG skid-mounted device for low-temperature washing and removal of heavy hydrocarbons. It includes a cold box, a low-temperature separator and a low-temperature washing tower. The lower part of the low-temperature washing tower is provided with a purified natural gas inlet, and the upper part of the low-temperature washing tower is provided with a low-temperature heavy hydrocarbon inlet. The low-temperature heavy hydrocarbon inlet is connected to the bottom of the low-temperature separator through a heavy hydrocarbon pipeline. The top of the low-temperature washing tower is provided with a gas phase outlet, and the gas phase outlet is connected to the A channel inlet of the cold box. The A channel outlet of the cold box is connected to the middle part of the low-temperature separator. The top of the low-temperature separator is provided with a gas phase natural gas outlet, and the gas phase natural gas outlet is connected to the B channel inlet of the cold box; thus, before entering the cold box, the heavy hydrocarbons are first removed by the low-temperature washing tower to reduce the heavy hydrocarbon content, thereby reducing the risk of freezing of the cold box. Although the invention has optimized the structure of the problem of freezing and blocking when removing heavy hydrocarbons by low-temperature washing, the following problems still exist: 1. When the condensed ice is crushed by separating the two defoaming trays up and down, the problem of one-side separation and one-side condensation may easily occur, that is, when the two defoaming trays are separated up and down, the condensed ice is only separated from one of them and remains on the surface of the other one, resulting in incomplete cleaning of the ice. Since the low-temperature separation box maintains a continuous low temperature, the remaining ice will be more strongly bonded to the defoaming tray over time.

[0004] 2. Even if the ice cubes are crushed during the separation of the two defoaming plates, the top ice cubes need to pass through multiple layers of defoaming nets during the downward falling process. During this process, it is easy to stick to the defoaming plates again, especially the several defoaming plates at the bottom, which have the highest probability of re-condensation with the ice cubes, and may even cause large-scale freezing blockage in the holes of the defoaming nets, affecting the separation effect and efficiency of natural gas.

[0005] To this end, the present invention proposes an LNG deep purification device and process to solve the above problems. Summary of the invention

[0006] The object of the present invention is to provide an LNG deep purification device and process thereof, so as to solve the technical problem proposed in the above background technology that the defoaming plate fails to thoroughly clean the condensed ice cubes, resulting in freezing and blockage.

[0007] To achieve the above object, the present invention provides the following technical solution: an LNG deep purification device, comprising a low-temperature separator, a cold box and a low-temperature scrubber, an intermediate tank is provided on one side of the low-temperature separator, a vacuum pump is provided between the intermediate tank and the low-temperature separator, the input end and the output end of the vacuum pump are respectively provided with a first connecting pipe and a second connecting pipe and are connected to the intermediate tank and the low-temperature separator, and further comprising: The filtrate assembly is coaxially arranged inside the low-temperature separator, and includes a plurality of defoaming discs arranged in an overlapping manner up and down. The defoaming discs are in an inverted cone structure, and the outermost defoaming discs are fixedly connected to the inner wall of the low-temperature separator, and a defoaming net is fixedly connected to the defoaming discs. When the purified natural gas enters the low-temperature separator, the filtrate assembly removes the mist heavy hydrocarbons in the purified natural gas; A driving assembly is coaxially arranged inside the low temperature separator and below the filtrate assembly, and is used to drive a part of the defoaming disk in the filtrate assembly to rotate; The breathing cleaning component includes an outer cleaning unit and an inner cleaning unit, which cleans the outermost and innermost surfaces of the defoaming disks and cleans other defoaming disks by inhaling and exhaling.

[0008] Preferably, the defoaming net is provided with defoaming holes, the shape of the defoaming holes is an inclined rectangle or waist shape, and the inclination directions of the defoaming holes on every two adjacent defoaming plates are opposite.

[0009] Preferably, the driving assembly comprises a turbine shell, the interior of the turbine shell is coaxially connected with turbine blades, an air inlet pipe is arranged on the circumferential side of the turbine shell, the air inlet pipe is connected to the second connecting pipe by a flange, and an air outlet is arranged on the top side of the turbine shell away from the air inlet pipe, a rotating shaft is coaxially fixed on the top of the turbine blades, the outermost defoaming disc is a fixed defoaming disc, all the defoaming discs located inside the fixed defoaming disc are driven defoaming discs, and a differential mechanism is arranged on the driven defoaming disc; When the rotating shaft rotates, the rotation speed of each driven defoaming disk decreases step by step.

[0010] Preferably, the differential mechanism includes a support column eccentrically arranged on the fixed defoaming plate, and a through hole is penetrated through the bottom of each driven defoaming plate, and an annular rack is coaxially fixed on the inner wall of the through hole. The number of teeth of each annular rack is different and changes in a gradient manner. A plurality of transmission gears arranged vertically are coaxially fixed on the support column, and each of the transmission gears is respectively meshed with the corresponding annular rack, and a plurality of driving gears meshing with the transmission gears are coaxially fixed on the rotating shaft.

[0011] Preferably, a first scraper member located outside the fixed defoaming plate is coaxially fixed on the rotating shaft, and a second scraper member is fixedly connected to one end of the rotating shaft that passes through the innermost driven defoaming plate.

[0012] Preferably, the first scraper comprises a connection plate coaxially fixed with the rotating shaft, a plurality of connection rods are evenly distributed on the circumference of the connection plate, one end of each connection rod away from the connection plate is fixedly connected to a first scraper, a first conical strip is provided on one side of the first scraper, and the first scraper matches the conical surface of the fixed defoaming plate; When the rotating shaft drives the connecting plate, the connecting rod and the first scraper to rotate, the first scraper can clean the outer wall of the fixed defoaming plate.

[0013] Preferably, the second scraper comprises a connection box coaxially fixed to the rotating shaft, a plurality of second scrapers evenly distributed on the circumference of the connection box are arranged on the circumferential side, a second conical strip is arranged on one side of each of the second scrapers, and the second scrapers match the inner wall of the innermost driven defoaming disc; When the rotating shaft drives the connecting box and the second scraper to rotate, the second scraper can clean the inner wall of the driven defoaming plate.

[0014] Preferably, the breathing cleaning assembly comprises a connecting tube coaxially fixed to the bottom of the fixed defoaming plate, the rotating shaft is sealingly and rotatably connected to the connecting tube, a reciprocating thread located in the connecting tube is provided on the rotating shaft, a piston plate moving up and down is provided in the connecting tube, and the piston plate matches the reciprocating thread, and a plurality of connecting holes evenly distributed around the circumference are provided on the top of the connecting tube; The external cleaning unit includes an annular box that rotates coaxially and sealed with the top of the connecting tube. The annular box is connected to the connecting tube through a connecting hole. A first flow channel is opened inside the first scraper. A plurality of first air holes distributed equidistantly are opened on the contact surface between the first scraper and the fixed defoaming plate.

[0015] Preferably, the internal cleaning unit includes an air groove coaxially opened on the rotating shaft, a cavity is formed in the connecting box, and the connecting box is connected to the air groove, a plurality of circulation holes located at the bottom of the air groove are opened on the rotating shaft, a second flow channel is opened inside the second scraper, and a plurality of second air holes equidistantly distributed are opened on the contact surface between the second scraper and the driven defoaming plate.

[0016] An LNG deep purification process comprises the following steps: Step 1: The natural gas enters the low-temperature scrubber for the first heavy hydrocarbon removal and then enters the cold box; Step 2: The natural gas entering the cold box undergoes a second heavy hydrocarbon removal and then enters the intermediate tank; Step 3: The vacuum pump pumps the natural gas in the intermediate tank to the low-temperature separator for the third heavy hydrocarbon removal; Step 4: The heavy hydrocarbons removed by the low-temperature separator enter the low-temperature scrubber and come into contact with the natural gas for reverse flushing; Step 5: After three dehydrogenation steps, the natural gas re-enters the cold box for cryogenic throttling to generate liquefied natural gas.

[0017] The beneficial effects of the present invention are: 1. The present invention optimizes the shape and angle of the defoaming plate and the defoaming hole through the arrangement of the defoaming plate, the defoaming net and the defoaming hole, increases the aperture of a single defoaming hole, and reduces the probability of condensation of mist-like heavy hydrocarbons inside the defoaming hole. At the same time, the defoaming plates that cooperate with each other and the staggered defoaming holes can achieve close cooperation to ensure the separation effect of natural gas and heavy hydrocarbons.

[0018] 2. The present invention is configured by a turbine shell, turbine blades and a differential mechanism. When the purified natural gas enters the turbine shell, the gas drives the turbine blades to rotate and drives the rotating shaft to rotate. At this time, multiple driven defoaming discs rotate at unequal speeds under the drive of the differential mechanism. During the rotation, each driven defoaming disc can clean each other of the ice cubes condensed thereon, and the outermost driven defoaming disc can clean the inner wall of the fixed defoaming disc to prevent the problem of continuous adhesion of some ice cubes and incomplete cleaning, thereby improving the separation effect of the defoaming disc.

[0019] 3. The present invention is provided with a connecting cylinder, a piston plate, an external cleaning unit and an internal cleaning unit. The piston plate moves up and down in the connecting cylinder, and the upper and lower sides of the connecting cylinder respectively "inhale" and "exhale", so that the gas can not only clean the condensed ice cubes, but also deeply clean the inside of multiple driven defoaming disks to prevent fine ice particles from being retained on the surface and in the holes of the defoaming disks. Firstly, it avoids large-scale condensation of fine ice particles in the tiny gap between each two defoaming disks, and secondly, it can clean the inside of the defoaming holes to prevent large-scale condensation inside and inconvenience in cleaning, thereby improving the separation effect of the defoaming disks. Moreover, when the internal cleaning unit is in the "exhalation" state, the gas ejected downwards and the rising natural gas collide with each other. Since the ejected gas has a fast flow rate, it can further cool the natural gas, further liquefy the heavy hydrocarbons, and further improve the separation effect of the natural gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the process of deep purification of LNG of the present invention.

[0021] Figure 2 It is a schematic diagram of the overall structure of the LNG deep purification device of the present invention.

[0022] Figure 3 It is a plan cross-sectional view of the present invention.

[0023] Figure 4 It is a three-dimensional cross-sectional view of the present invention.

[0024] Figure 5 It is a schematic diagram of the three-dimensional structure of the filtrate component in the present invention.

[0025] Figure 6 It is a schematic diagram of the separation of the fixed defoaming disc and the driven defoaming disc in the present invention.

[0026] Figure 7 It is a half-section schematic diagram of the driving assembly in the present invention.

[0027] Figure 8 It is a three-dimensional schematic diagram of the first scraping member in the present invention.

[0028] Fig. 9 It is a three-dimensional cross-sectional schematic diagram of the filtrate assembly in the present invention.

[0029] Fig.10 for Fig. 9 A magnified schematic diagram of center A.

[0030] Fig.11 It is a schematic structural diagram of the second scraping member in the present invention.

[0031] Fig.12 It is a planar cross-sectional view of the breathing cleaning component in the present invention.

[0032] Fig.13 It is a schematic diagram of the three-dimensional structure of the connecting tube in the present invention.

[0033] The accompanying drawings are marked as follows: 1. Low temperature separator; 11. Cold box; 12. Low temperature washing tower; 2. Intermediate tank; 3. Vacuum pump; 31. First connecting pipe; 32. Second connecting pipe; 4. filtrate assembly; 41. defoaming plate; 411. fixed defoaming plate; 412. driven defoaming plate; 42. defoaming net; 421. defoaming hole; 5. driving assembly; 51. turbine housing; 52. turbine blades; 53. air inlet pipe; 54. air outlet; 55. rotating shaft; 6. Breathing cleaning assembly; 61. External cleaning unit; 611. Ring box; 612. First flow channel; 613. First air hole; 62. Internal cleaning unit; 621. Air groove; 622. Second air hole; 63. First scraper; 631. Connecting plate; 632. Connecting rod; 633. First scraper; 64. Second scraper; 641. Connecting box; 642. Second scraper; 65. Connecting cylinder; 66. Reciprocating thread; 67. Piston plate; 68. Connecting hole; 7. Differential mechanism; 71. Support column; 72. Ring rack; 73. Transmission gear; 74. Driving gear. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention. Example 1

[0035] In the actual production process, since the defoaming screen has an extremely small pore size and the entire process is carried out under low temperature conditions, the moisture carried in the natural gas is easily solidified and frozen on the screen in this environment, thereby increasing the risk of freezing of the defoaming screen. This embodiment is specially invented to solve the above problem.

[0036] See also Figures 1 to 4 As shown, an LNG deep purification device according to an embodiment of the present invention comprises a low-temperature separator 1, a cold box 11 and a low-temperature scrubber 12. An intermediate tank 2 is provided on one side of the low-temperature separator 1, a natural gas inlet is provided at the bottom of the intermediate tank 2, a natural gas inlet is provided at the bottom of the low-temperature scrubber 12, and a heavy hydrocarbon reflux port is provided at the top. The natural gas enters the low-temperature scrubber 12 through the inlet. During this process, the heavy hydrocarbons above spray downward and collide with the natural gas, thereby enhancing the dehydrogenation effect of the natural gas. At the same time, a natural gas outlet is provided on the other side of the top of the low-temperature scrubber 12, and this outlet It is connected to one of the air inlets of the cold box 11. After secondary dehydrogenation in the cold box 11, one of the air outlets of the cold box 11 is connected to the air inlet at the bottom of the intermediate tank 2. A vacuum pump 3 is arranged between the intermediate tank 2 and the low-temperature separator 1. The input end and the output end of the vacuum pump 3 are respectively provided with a first connecting pipe 31 and a second connecting pipe 32 and are connected with the intermediate tank 2 and the low-temperature separator 1. The heavy hydrocarbons recovered by the low-temperature separator 1 enter the low-temperature washing tower 12 again through the heavy hydrocarbon reflux port provided on the low-temperature washing tower 12, forming three complete dehydrogenations. It also includes a filtrate component 4, a drive component 5 and a breathing cleaning component 6.

[0037] See also Figures 4 to 6 As shown, the filtrate assembly 4 is coaxially arranged inside the low-temperature separator 1, and includes a plurality of defoaming plates 41 which are overlapped with each other. The defoaming plates 41 are inverted cone structures. It should be noted that there are tiny gaps between the conical surfaces of each defoaming plate 41, and they are not in direct contact. The outermost defoaming plate 41 is fixedly connected to the inner wall of the low-temperature separator 1, and a defoaming net 42 is fixedly connected to the defoaming plate 41. When the purified natural gas enters the low-temperature separator 1, the filtrate assembly 4 removes the mist heavy hydrocarbons in the purified natural gas.

[0038] See also Figure 3 and Figure 4 As shown, the driving assembly 5 is coaxially arranged inside the low-temperature separator 1 and below the filtrate assembly 4, so as to drive a part of the defoaming disc 41 in the filtrate assembly 4 to rotate.

[0039] The breathing cleaning component 6 includes an outer cleaning unit 61 and an inner cleaning unit 62, which cleans the surfaces of the outermost and innermost defoaming discs 41, and cleans other defoaming discs 41 by inhaling and exhaling.

[0040] The defoaming net 42 is provided with defoaming holes 421, which are in the shape of an inclined rectangle or waist. The inclination directions of the defoaming holes 421 on every two adjacent defoaming plates 41 are opposite, and the staggered angle between every two adjacent defoaming holes 421 is an acute angle.

[0041] During use, the diameter of the defoaming holes 421 on a single defoaming plate 41 is relatively large, but the defoaming holes 421 arranged in pairs can achieve a tight aperture effect. When the natural gas passes through multiple defoaming plates 41 in sequence, due to the large aperture, the misted heavy hydrocarbons are difficult to condense in the holes.

[0042] By configuring the defoaming plate 41, the defoaming net 42 and the defoaming holes 421, the shapes and angles of the defoaming plate 41 and the defoaming holes 421 are optimized, the aperture of a single defoaming hole 421 is increased, and the probability of condensation of mist-like heavy hydrocarbons inside the defoaming holes 421 is reduced. At the same time, by cooperating with the defoaming plates 41 in pairs, the staggered defoaming holes 421 can achieve close cooperation, thereby ensuring the separation effect of natural gas and heavy hydrocarbons. Example 2

[0043] When the condensed ice cubes are crushed by separating the two defoaming trays 41 up and down, the problem of one-side separation and one-side condensation is easy to occur, that is, when the two defoaming trays 41 are separated up and down, the condensed ice cubes are separated from only one of them and remain on the surface of the other, resulting in incomplete cleaning of the ice cubes. Since the low-temperature separation box is at a continuous low temperature, the remaining ice cubes are more strongly bonded to the defoaming tray 41 as time goes by. In view of the above problems, further improvements are made on the basis of the above embodiments.

[0044] See also Figure 7 and Fig. 9 As shown, the driving assembly 5 includes a turbine shell 51, and the interior of the turbine shell 51 is coaxially connected to the turbine blades 52, an air intake pipe 53 is arranged on the circumferential side of the turbine shell 51, the air intake pipe 53 is connected to the second connecting pipe 32 by a flange, and an air outlet 54 is opened on the top side of the turbine shell 51 away from the air intake pipe 53, a rotating shaft 55 is coaxially fixed on the top of the turbine blades 52, the outermost defoaming plate 41 is a fixed defoaming plate 411, and all the defoaming plates 41 located inside the fixed defoaming plate 411 are driven defoaming plates 412, and a differential mechanism 7 is arranged on the driven defoaming plate 412, and when the rotating shaft 55 rotates, the rotation speed of each driven defoaming plate 412 decreases step by step.

[0045] See also Fig.10 As shown, the differential mechanism 7 includes a support column 71 eccentrically arranged on the fixed defoaming plate 411, and a through hole is opened through the bottom of each driven defoaming plate 412. An annular rack 72 is coaxially fixed on the inner wall of the through hole. The number of teeth of each annular rack 72 is different and changes in a gradient manner. A plurality of transmission gears 73 arranged vertically are coaxially fixed on the support column 71, and each transmission gear 73 is respectively meshed with the corresponding annular rack 72. A plurality of driving gears 74 meshing with the transmission gears 73 are coaxially fixed on the rotating shaft 55. In this embodiment, the rotation speed of the innermost driven defoaming plate 412 is the smallest.

[0046] It should be noted that an annular groove is provided at the bottom of each driven defoaming plate 412, and a plurality of circumferentially evenly distributed balls are arranged in the annular groove to reduce the friction of each driven defoaming plate 412, so that the driving component 5 can better drive the driven defoaming plate 412.

[0047] During use, the vacuum pump 3 is started to pump the natural gas in the intermediate tank 2 into the interior of the low-temperature separator 1. After the natural gas enters the turbine shell 51, the turbine blades 52 rotate under the drive of the gas, and the multiple driving gears 74 rotate under the drive of the rotating shaft 55. After being driven by the multiple transmission gears 73 and the annular rack 72, each driven defoaming plate 412 rotates at a different speed. During the rotation process, since the gap between each defoaming plate 41 is very small, the condensed ice can be cleaned in each rotation.

[0048] Through the arrangement of the turbine shell 51, the turbine blades 52 and the differential mechanism 7, when the purified natural gas enters the turbine shell 51, the gas drives the turbine blades 52 to rotate and drives the rotating shaft 55 to rotate. At this time, the multiple driven defoaming plates 412 rotate at unequal speeds under the drive of the differential mechanism 7. During the rotation, each driven defoaming plate 412 can clean each other of the ice cubes condensed thereon, and the outermost driven defoaming plate 412 can clean the inner wall of the fixed defoaming plate 411 to prevent the problem of continuous adhesion of some ice cubes and incomplete cleaning, thereby improving the separation effect of the defoaming plate 41. Example 3

[0049] Considering that the outer wall of the fixed defoaming plate 411 and the inner wall of the innermost driven defoaming plate 412 cannot be cleaned during the rotation of the driven defoaming plate 412, in order to prevent condensation and affect the separation effect of natural gas, further improvements are made on the basis of the above embodiment.

[0050] See also Figure 8 and Fig.11 As shown, a first scraper 63 located outside the fixed defoaming plate 411 is coaxially fixed on the rotating shaft 55, and a second scraper 64 is fixedly connected to one end of the rotating shaft 55 that passes through the innermost driven defoaming plate 412.

[0051] See also Fig.11 As shown, the first scraper 63 includes a connecting disk 631 coaxially fixed with the rotating shaft 55, and a plurality of connecting rods 632 are evenly distributed on the circumference of the connecting disk 631. The end of each connecting rod 632 away from the connecting disk 631 is fixedly connected to a first scraper 633, and a first conical strip is provided on one side of the first scraper 633. The first scraper 633 matches the conical surface of the fixed defoaming plate 411. When the rotating shaft 55 drives the connecting disk 631, the connecting rod 632 and the first scraper 633 to rotate, the first scraper 633 can clean the outer wall of the fixed defoaming plate 411.

[0052] See also Fig.11 As shown, the second scraper 64 includes a connecting box 641 coaxially fixed with the rotating shaft 55, and a plurality of second scrapers 642 evenly distributed on the circumference are arranged on the circumferential side of the connecting box 641, and a second conical strip is arranged on one side of each second scraper 642, and the second scraper 642 matches the inner wall of the innermost driven defoaming plate 412, and when the rotating shaft 55 drives the connecting box 641 and the second scraper 642 to rotate, the second scraper 642 can clean the inner wall of the driven defoaming plate 412.

[0053] It should be supplemented that the first scraper 633 and the second scraper 642 are not in direct contact with the wall of the defoaming plate 41 , and a small gap is maintained between them, not only to reduce friction, but also to prevent frictional heat generation that causes the temperature in the low-temperature separator 1 to rise.

[0054] During use, when the rotating shaft 55 rotates, the multiple first scrapers 633 make circular motions around the outer wall of the fixed defoaming plate 411, and during the motion, the first conical bars strike and scrape off the ice cubes condensed thereon. At the same time, the multiple second scrapers 642 make circular motions around the inner wall of the innermost driven defoaming plate 412, and the second conical bars strike and scrape off the ice cubes condensed thereon.

[0055] Through the arrangement of the first scraper 633, the second scraper 642 and the rotating shaft 55, as the continuous input of natural gas drives the rotating shaft 55 to rotate, the first scraper 633 and the second scraper 642 can clean the outer wall of the fixed defoaming plate 411 and the inner wall of the innermost driven defoaming plate 412 to prevent a large area of ​​condensation between the two and affect the separation of natural gas and heavy hydrocarbons. Example 4

[0056] As the broken ice cubes fall downward, the top ice cubes need to pass through multiple layers of defoaming nets 42, and in this process, they are easily adhered to the defoaming trays 41 again, especially the lower defoaming trays 41, which have the highest probability of re-condensing with the ice cubes, and may even cause large-area freezing in the holes of the defoaming nets 42. In view of the above problems, further improvements are made on the basis of the above embodiments.

[0057] See also Fig.12 and Fig.13 As shown, the breathing cleaning assembly 6 includes a connecting tube 65 coaxially fixed to the bottom of the fixed defoaming plate 411, the rotating shaft 55 is sealed and rotatably connected to the connecting tube 65, the rotating shaft 55 is provided with a reciprocating thread 66 located in the connecting tube 65, a piston plate 67 that moves up and down is provided in the connecting tube 65, and the piston plate 67 is matched with the reciprocating thread 66, and a plurality of connecting holes 68 evenly distributed around the circumference are provided on the top of the connecting tube 65.

[0058] See also Fig.11 and Fig.12 As shown, the external cleaning unit 61 includes an annular box 611 which rotates coaxially and sealedly with the top of the connecting tube 65. The annular box 611 is connected to the connecting tube 65 through a connecting hole 68. A first flow channel 612 is provided inside the first scraper 633. The contact surface between the first scraper 633 and the fixed defoaming plate 411 is provided with a plurality of first air holes 613 distributed equidistantly.

[0059] See also Fig.11 and Fig.12As shown, the internal cleaning unit 62 includes an air groove 621 coaxially opened on the rotating shaft 55, a cavity is formed in the connecting box 641, and the connecting box 641 is connected to the air groove 621, a plurality of circulation holes located at the bottom of the air groove 621 are opened on the rotating shaft 55, a second flow channel is opened inside the second scraper 642, and a plurality of equally spaced second air holes 622 are opened on the contact surface between the second scraper 642 and the driven defoaming plate 412.

[0060] During use, when the rotating shaft 55 rotates, the piston plate 67 moves up and down in the connecting tube 65, and the upper and lower sides in the connecting tube 65 respectively perform "inhalation" and "exhalation". When the piston plate 67 moves up, the gas above the piston plate 67 enters the multiple first flow channels 612 through the connecting hole 68 and the annular box 611 respectively, and is ejected from the multiple first air holes 613. The ejected gas performs deep cleaning of the interior of the multiple driven defoaming plates 412. At the same time, the upward movement of the piston plate 67 causes a relative negative pressure to be generated in the second flow channel. At this time, a large amount of gas enters the second flow channel through the second air hole 622 and enters the connecting tube 65 through the air groove 621.

[0061] When the piston plate 67 moves downward, the first air hole 613 changes to the "inhalation" state, and the second air hole 622 is in the "exhalation" state. The gas ejected from the second air hole 622 can also deeply clean the defoaming plate 41. On this basis, the gas ejected downwards collides with the rising natural gas. Since the ejected gas moves at a very high speed, the natural gas can be further cooled.

[0062] Through the connection tube 65, the piston plate 67, the external cleaning unit 61 and the internal cleaning unit 62, the piston plate 67 moves up and down in the connection tube 65, and the upper and lower sides of the connection tube 65 perform "inhalation" and "exhalation" respectively, so that the gas can not only clean the condensed ice cubes, but also deeply clean the interior of multiple driven defoaming disks 412 to prevent small ice particles from being retained on the surface and in the holes of the defoaming disks 41. First, it is to avoid large-scale condensation of small ice particles in the tiny gap between each two defoaming disks 41, and second, it can clean the interior of the defoaming hole 421 to prevent large-scale condensation inside and inconvenience in cleaning, thereby improving the separation effect of the defoaming disk 41. Moreover, when the internal cleaning unit 62 is in the "exhalation" state, the gas ejected downwards and the rising natural gas collide with each other. Since the ejected gas has a fast flow rate, it can further cool the natural gas, further liquefy the heavy hydrocarbons, and further improve the separation effect of the natural gas. Example 5

[0063] An LNG deep purification process comprises the following steps: Step 1: The natural gas enters the low-temperature scrubber 12 for the first heavy hydrocarbon removal and then enters the cold box 11.

[0064] Step 2: The natural gas entering the cold box 11 enters the intermediate tank 2 after the second heavy hydrocarbon removal.

[0065] Step 3: The vacuum pump 3 pumps the natural gas in the intermediate tank 2 into the low-temperature separator 1 to remove the heavy hydrocarbons for the third time.

[0066] Step 4: The heavy hydrocarbons removed by the low-temperature separator 1 enter the low-temperature washing tower 12 and come into contact with the natural gas for reverse washing.

[0067] Step 5: After three dehydrogenation steps, the natural gas re-enters the cold box 11 and is cryogenically throttled to generate liquefied natural gas.

[0068] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. An LNG deep purification device, comprising a low-temperature separator (1), a cold box (11) and a low-temperature scrubber (12), characterized in that: An intermediate tank (2) is provided on one side of the low-temperature separator (1), a vacuum pump (3) is provided between the intermediate tank (2) and the low-temperature separator (1), the input end and the output end of the vacuum pump (3) are respectively provided with a first connecting pipe (31) and a second connecting pipe (32) and are connected to the intermediate tank (2) and the low-temperature separator (1), and further comprising: The filtrate assembly (4) is coaxially arranged inside the low-temperature separator (1), and comprises a plurality of defoaming discs (41) arranged in an overlapping manner up and down, wherein the defoaming discs (41) are of an inverted cone structure, the outermost defoaming disc (41) is fixedly connected to the inner wall of the low-temperature separator (1), and a defoaming net (42) is fixedly connected to the defoaming disc (41). When the purified natural gas enters the low-temperature separator (1), the filtrate assembly (4) removes the mist heavy hydrocarbons in the purified natural gas; A driving assembly (5) is coaxially arranged inside the low-temperature separator (1) and below the filtrate assembly (4), and is used to drive a portion of the defoaming disc (41) inside the filtrate assembly (4) to rotate; The breathing cleaning component (6) comprises an outer cleaning unit (61) and an inner cleaning unit (62), which cleans the surfaces of the outermost and innermost defoaming discs (41) and cleans the other defoaming discs (41) by inhaling and exhaling.

2. The LNG deep purification device according to claim 1, characterized in that: The defoaming net (42) is provided with defoaming holes (421), the defoaming holes (421) are in the shape of an inclined rectangle or waist, and the defoaming holes (421) on every two adjacent defoaming plates (41) are inclined in opposite directions.

3. The LNG deep purification device according to claim 2, characterized in that: The driving assembly (5) comprises a turbine shell (51), the interior of which is coaxially rotatably connected to turbine blades (52), an air intake pipe (53) is provided on the circumferential side of the turbine shell (51), the air intake pipe (53) is connected to the second connecting pipe (32) via a flange, and an air outlet hole (54) is provided on the top side of the turbine shell (51) away from the air intake pipe (53), a rotating shaft (55) is coaxially fixed to the top of the turbine blades (52), the outermost defoaming disc (41) is a fixed defoaming disc (411), and all defoaming discs (411) located inside the fixed defoaming disc (411) are driven defoaming discs (412), and a differential mechanism (7) is provided on the driven defoaming disc (412); When the rotating shaft (55) rotates, the rotation speed of each driven defoaming disc (412) decreases step by step.

4. The LNG deep purification device according to claim 1, characterized in that: The differential mechanism (7) comprises a support column (71) eccentrically arranged on a fixed defoaming plate (411); a through hole is formed through the bottom of each driven defoaming plate (412); an annular rack (72) is coaxially fixed on the inner wall of the through hole; the number of teeth of each annular rack (72) is different and changes in a gradient manner; a plurality of transmission gears (73) arranged vertically are coaxially fixed on the support column (71); each transmission gear (73) is respectively meshed with a corresponding annular rack (72); and a plurality of driving gears (74) meshed with the transmission gears (73) are coaxially fixed on the rotating shaft (55).

5. The LNG deep purification device according to claim 4, characterized in that: A first scraper (63) located outside the fixed defoaming plate (411) is coaxially fixed on the rotating shaft (55), and a second scraper (64) is fixedly connected to one end of the rotating shaft (55) that passes through the innermost driven defoaming plate (412).

6. The LNG deep purification device according to claim 1, characterized in that: The first scraping member (63) comprises a connecting plate (631) fixed coaxially with the rotating shaft (55); a plurality of connecting rods (632) are evenly distributed on the circumference of the connecting plate (631); one end of each connecting rod (632) away from the connecting plate (631) is fixedly connected to a first scraper (633); a first conical strip is provided on one side of the first scraper (633); the first scraper (633) matches the conical surface of the fixed defoaming plate (411); When the rotating shaft (55) drives the connecting plate (631), the connecting rod (632) and the first scraper (633) to rotate, the first scraper (633) can clean the outer wall of the fixed defoaming plate (411).

7. The LNG deep purification device according to claim 6, characterized in that: The second scraper (64) comprises a connection box (641) fixed coaxially with the rotating shaft (55); a plurality of second scrapers (642) evenly distributed around the circumference of the connection box (641) are provided on a circumferential side; a second conical strip is provided on one side of each of the second scrapers (642); the second scrapers (642) match the inner wall of the innermost driven defoaming disc (412); When the rotating shaft (55) drives the connecting box (641) and the second scraper (642) to rotate, the second scraper (642) can clean the inner wall of the driven defoaming plate (412).

8. The LNG deep purification device according to claim 6, characterized in that: The breathing cleaning assembly (6) comprises a connecting tube (65) coaxially fixed to the bottom of the fixed defoaming disc (411); the rotating shaft (55) is sealingly rotatably connected to the connecting tube (65); a reciprocating thread (66) located in the connecting tube (65) is provided on the rotating shaft (55); a piston plate (67) that moves up and down is provided in the connecting tube (65); the piston plate (67) matches the reciprocating thread (66); and a plurality of connecting holes (68) evenly distributed around the circumference are provided on the top of the connecting tube (65); The external cleaning unit (61) comprises an annular box (611) which rotates coaxially and in a sealed manner with the top of the connecting tube (65); the annular box (611) is connected to the connecting tube (65) via a connecting hole (68); a first flow channel (612) is provided inside the first scraper (633); and a plurality of first air holes (613) which are equidistantly distributed are provided on the contact surface between the first scraper (633) and the fixed defoaming plate (411).

9. The LNG deep purification device according to claim 8, characterized in that: The internal cleaning unit (62) comprises an air groove (621) coaxially provided on the rotating shaft (55); a cavity is formed in the connecting box (641), and the connecting box (641) is in communication with the air groove (621); a plurality of circulation holes located at the bottom of the air groove (621) are provided on the rotating shaft (55); a second flow channel is provided inside the second scraper (642); and a plurality of second air holes (622) distributed at equal intervals are provided on the contact surface between the second scraper (642) and the driven defoaming plate (412).

10. An LNG deep purification process, used in the LNG deep purification device according to claim 9, characterized in that: The following steps are involved: Step 1: The natural gas enters the low-temperature scrubber (12) to remove the heavy hydrocarbons for the first time and then enters the cold box (11); Step 2: The natural gas entering the cold box (11) undergoes a second heavy hydrocarbon removal and then enters the intermediate tank (2); Step 3: The vacuum pump (3) pumps the natural gas in the intermediate tank (2) into the low-temperature separator (1) to remove heavy hydrocarbons for the third time; Step 4: The heavy hydrocarbons removed by the low-temperature separator (1) enter the low-temperature washing tower (12) and come into contact with the natural gas for reverse washing; Step 5: After three dehydrogenation steps, the natural gas re-enters the cold box (11) for cryogenic throttling to generate liquefied natural gas.

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