Hot nitrogen pumping and conveying device of nitrogen compressor

Abstract

The invention discloses a nitrogen compressor hot nitrogen pumping and conveying device, which relates to the field of industrial gas conveying, and comprises a hot nitrogen conveying pipe, an output end butt flange arranged at the right end of the hot nitrogen conveying pipe, a reinforcing sleeve arranged at the left end of the hot nitrogen conveying pipe, an input control valve and an input end butt flange, the cleaning device comprises two vertical fixed stop levers, a linear rail rod, an in-pipe cleaning mechanism and an external force driving mechanism, the two vertical fixed stop levers are symmetrically fixed to the two ends of the interior of the hot nitrogen conveying pipe, the moving type in-pipe cleaning device can complete real-time cleaning while conveying hot nitrogen, shutdown for pipe disassembly is not needed, and the cleaning efficiency is improved. And the device can flexibly select an automatic airflow cleaning mode or an external force active cleaning mode according to the flow of the hot nitrogen by virtue of magnetic linkage between the external force driving mechanism and the in-pipe cleaning mechanism, so that the gas transmission stability is not influenced, and the controllable and reliable cleaning action is ensured.

Description

Technical Field

[0001] This invention belongs to the technical field of industrial gas transportation, specifically relating to a nitrogen compressor extraction and transportation device for nitrogen. Background Technology

[0002] Nitrogen compressors are widely used in industrial production to provide stable high-pressure hot nitrogen to meet the needs of equipment cleaning, pressure maintenance, or process manufacturing. At the output end of the nitrogen compressor, a hot nitrogen delivery pipe is usually required to reliably deliver high-temperature, high-pressure nitrogen to the designated device or workstation. As production equipment has increasingly higher requirements for continuous operation, safety, and internal cleanliness, the structure of the delivery pipe often not only undertakes the delivery function, but also needs to have functions such as easy maintenance, pipe wall cleaning, and pressure monitoring to ensure the stability of hot nitrogen delivery. In particular, when hot nitrogen flows at high temperatures for a long time, dust particles or oxide deposits are easy to accumulate on the pipe wall. If they cannot be cleaned in time, it will affect the delivery efficiency and system safety. However, most existing hot nitrogen conveying structures adopt fixed or disassembled cleaning methods, which cannot continuously and effectively clean the inside of the pipeline under closed conditions. As a result, the machine must be shut down after the deposits accumulate, which not only increases maintenance costs but also affects the stability of the conveying. In addition, due to the lack of a cleaning mechanism that can be controlled to move inside the pipe, the cleaning range is usually limited, and the cleaning action cannot be coordinated with the airflow direction, resulting in limited cleaning effect. Summary of the Invention

[0003] The purpose of this invention is to provide a nitrogen compressor hot nitrogen conveying device to solve the problem mentioned in the background art that most existing hot nitrogen conveying structures adopt fixed or disassembly cleaning methods, and the inside of the pipeline cannot be effectively cleaned continuously under closed conditions, resulting in the need to stop the machine after the accumulation of deposits, which not only increases maintenance costs, but also affects the stability of the conveying.

[0004] To achieve the above objectives, the present invention provides the following technical solution: a hot nitrogen delivery device for a nitrogen compressor, comprising a hot nitrogen delivery pipe, an output end flange disposed at its right end, a reinforcing sleeve disposed at its left end, an input control valve, and an input end flange. The hot nitrogen delivery pipe has a set of moving pipe cleaning devices, which include vertical fixed stops, linear track rods, a pipe cleaning mechanism, and an external force driving mechanism. Two vertical fixed stops are provided and symmetrically fixed at both ends inside the hot nitrogen delivery pipe. The linear track rod is welded between the two vertical fixed stops. The pipe cleaning mechanism is sleeved on the linear track rod. The external force driving mechanism is used to drive the pipe cleaning mechanism from outside the pipe.

[0005] Preferably, the external force driving mechanism and the pipe cleaning mechanism are linked by magnetic force, and the vertical fixed stop bar is used to limit the movement range of the pipe cleaning mechanism along the track.

[0006] Preferably, the pipe cleaning mechanism includes a magnetic cleaning ring, cleaning brushes, strip-shaped airflow rotating fan blades, and a metal movable inner sleeve. The metal movable inner sleeve is fitted outside the linear track rod, the magnetic cleaning ring is fitted outside the metal movable inner sleeve, multiple strip-shaped airflow rotating fan blades are provided and are fixed at equal intervals between the magnetic cleaning ring and the metal movable inner sleeve, and the cleaning brushes are located outside the magnetic cleaning ring.

[0007] Preferably, the movable metal inner sleeve can move along a straight track rod, and the magnetic cleaning movable ring moves synchronously through the rotating fan blades of the strip-shaped airflow, so that the cleaning bristles adhere to the inner wall of the hot nitrogen gas delivery pipe and move synchronously.

[0008] Preferably, the external force driving mechanism includes a linear sliding bracket, a bracket fixing block, and a U-shaped adjusting block. There are two bracket fixing blocks, which are respectively welded to the input end flange and the front end of the reinforcing sleeve. The left end of the linear sliding bracket is fixedly connected to the two bracket fixing blocks, which is used to provide a sliding adjusting path for the U-shaped adjusting block in the front-back and left-right directions.

[0009] Preferably, the external force driving mechanism further includes a push-pull handle and a driving neodymium magnet. The driving neodymium magnet is connected to the U-shaped adjusting block to achieve magnetic driving. The push-pull handle is fixed to the front end of the opening of the U-shaped adjusting block by a metal sealing plate for operating the U-shaped adjusting block.

[0010] Preferably, the cleaning brush bristles are made of Inconel nickel alloy, and the magnetic cleaning ring is made of iron-chromium-cobalt permanent magnet alloy, which can be driven by a neodymium magnet to magnetically attract and move within the hot nitrogen delivery pipe.

[0011] Preferably, the driving rubidium magnet moves the magnetic cleaning ring to the vertical fixed stop located on the left side of the pipe, and then it can continue to slide to achieve magnetic disengagement. Subsequently, the hot nitrogen gas flow acts on the strip-shaped airflow to rotate the fan blades, pushing the cleaning mechanism in the pipe to move in the conveying direction.

[0012] Preferably, the plurality of strip-shaped airflow rotating fan blades have an inclined blade structure, which can generate rotation under the action of airflow and drive the cleaning bristles to scrape the pipe wall. When the airflow is insufficient, the pipe cleaning mechanism can be moved by an external force driving mechanism.

[0013] Preferably, the middle section of the hot nitrogen delivery pipe is provided with a pressure monitoring mechanism. The pressure monitoring mechanism includes a sealing welded sleeve, a pressure monitoring tube head, a sealing fixing sleeve, and a pressure monitoring gauge. The sealing welded sleeve is welded to the outside of the hot nitrogen delivery pipe. The pressure monitoring tube head is vertically welded to the center of the top of the sealing welded sleeve and is connected to the inside of the hot nitrogen delivery pipe. The top of the tube head is provided with a threaded joint. The sealing fixing sleeve is threaded on the outside of the threaded joint. The pressure monitoring gauge is located at the top of the sealing fixing sleeve. The U-shaped adjusting block can avoid the sealing welded sleeve by its own groove structure.

[0014] Compared with the prior art, the present invention provides a nitrogen compressor heat extraction nitrogen conveying device, which has the following beneficial effects: This invention constructs a moving pipe cleaning device inside and outside the hot nitrogen delivery pipe that can be switched according to the working conditions. This allows the pipe to be cleaned in real time while delivering hot nitrogen, without the need to stop the machine and disassemble the pipe, which significantly reduces the frequency of maintenance and cleaning costs. The moving pipe cleaning device relies on the magnetic linkage between the external force driving mechanism and the pipe cleaning mechanism. It can flexibly select the automatic airflow cleaning mode or the external force active cleaning mode according to the size of the hot nitrogen flow rate. This does not affect the stability of gas delivery, and ensures that the cleaning action is controllable and reliable, adapting to various pressure and flow rate conditions. This device utilizes the coordinated movement of the metal movable inner sleeve of the pipe cleaning mechanism, the strip-shaped airflow rotating fan blades, and the magnetic cleaning moving ring. This allows the pipe cleaning mechanism to move and rotate from left to right inside the pipe for combined cleaning. When the airflow acts on the inclined strip-shaped airflow rotating fan blades, it not only provides a driving force to the cleaning mechanism towards the nitrogen output end, but also generates a cutting disturbance to drive the entire cleaning mechanism to rotate. This allows the Inconel alloy cleaning bristles densely distributed on the outer wall of the magnetic cleaning moving ring to simultaneously complete the three actions of scraping, rotating, and displacing. This effectively removes stubborn dirt such as carbon deposits and oxide layers attached to the pipe wall. The cleaning range is continuous and uniform, far superior to the traditional cleaning method that relies solely on unidirectional dragging. To enable the cleaning mechanism to reciprocate back and forth within the pipe and to address the issue of insufficient movement when the airflow is low, an external force drive mechanism is added to the outer wall of the hot nitrogen delivery pipe. This mechanism uses a neodymium magnet to magnetically attract and magnetize the cleaning ring at intervals along the pipe wall. Users only need to push or pull the handle to move the cleaning mechanism back and forth along the linear track, achieving controllable cleaning under low airflow conditions. This eliminates the need to disassemble the delivery pipe or additional cleaning components, significantly improving maintenance efficiency. The U-shaped adjustment block's forward and backward adjustment capability also allows for fine-tuning of the magnetic attraction position, ensuring a stable and reliable magnetic coupling process that prevents detachment or displacement during operation. The two vertical fixed stops and the linear track rod used in this invention form a stable limiting and guiding relationship, which not only ensures that the cleaning mechanism operates in the central axial position of the pipeline for a long time and avoids cleaning blind spots, but also effectively prevents the cleaning mechanism from slipping off the track, ensuring that its movement range is controlled and safe and reliable. The magnetic cleaning moving ring is made of iron-chromium-cobalt permanent magnet alloy, which can maintain long-term magnetic stability in high temperature and high pressure transportation environment. The cleaning bristles are made of Inconel nickel alloy, which has the characteristics of heat resistance, corrosion resistance and wear resistance, which can provide sufficient cleaning force without damaging the pipe wall structure, meeting the working conditions of long-term hot nitrogen transportation. Attached Figure Description

[0015] Figure 1 This is a front view of the external three-dimensional structure of a nitrogen compressor heat extraction nitrogen conveying device according to the present invention.

[0016] Figure 2 This is a front view of the external planar structure of a nitrogen compressor heat extraction nitrogen conveying device according to the present invention.

[0017] Figure 3 This is a schematic diagram of the external three-dimensional structure of the pressure monitoring mechanism of the present invention.

[0018] Figure 4 This is a front sectional three-dimensional structural schematic diagram of a nitrogen compressor heat extraction nitrogen conveying device according to the present invention.

[0019] Figure 5 This is a front-view three-dimensional structural diagram of the motion-type pipe cleaning device of the present invention.

[0020] Figure 6 This is a right-side perspective three-dimensional structural diagram of the in-pipe cleaning mechanism of the present invention.

[0021] Figure 7 This is a partial right-side three-dimensional structural diagram of the external force driving mechanism of the present invention.

[0022] Figure 8 This is a right-side perspective three-dimensional structural diagram of the motion-type pipe cleaning device of the present invention.

[0023] In the diagram: 1. Output flange; 2. Hot nitrogen delivery pipe; 3. Motion-type pipe cleaning device; 4. Pressure monitoring mechanism; 5. Input control valve; 6. Input flange; 7. Reinforcing sleeve; 8. Sealing welded sleeve; 9. Pressure monitoring pipe head; 10. Sealing fixing sleeve; 11. Pressure monitoring gauge; 12. Vertical fixed stop bar; 13. Linear track rod; 14. Pipe cleaning mechanism; 15. External force drive mechanism; 16. Magnetic cleaning movable ring; 17. Cleaning brush; 18. Strip-shaped airflow rotating fan blade; 19. Metal movable inner sleeve; 20. Linear sliding bracket; 21. Push-pull handle; 22. Bracket fixing block; 23. U-shaped adjusting block; 24. Driving neodymium magnet. Detailed Implementation

[0024] 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. Example 1

[0025] This invention provides, for example Figure 1-8The device shown is a nitrogen compressor hot nitrogen delivery device, comprising a hot nitrogen delivery pipe 2, an input end flange 6 and an output end flange 1 located at both ends of the pipe, a reinforcing sleeve 7 installed outside the delivery pipe, a moving pipe cleaning device 3 for internal cleaning, a pressure monitoring mechanism 4 for real-time monitoring of internal pressure, and a manually driven external force drive mechanism 15. The entire delivery device uses the hot nitrogen delivery pipe 2 as the main passage, and its interior continuously receives high-temperature nitrogen flow from the nitrogen compressor. Therefore, the hot nitrogen delivery pipe 2 is made entirely of stainless steel to ensure high requirements for pipe wall strength, heat resistance, and internal cleanliness. On the side of the hot nitrogen delivery pipe 2 near the input end, a reinforcing sleeve 7 is welded to its outer wall. An input control valve 5 is installed on the left end of the reinforcing sleeve 7, and the left end of the input control valve 5 is connected to the input end flange 6 for quick connection with the upstream pipeline.

[0026] like Figure 1 , Figure 2 , Figure 3 and Figure 4 As shown, the other end of the hot nitrogen gas delivery pipe 2 is welded to the output flange 1 to achieve a stable connection with the downstream collection system or processing equipment. In order to ensure the real-time reliability of the delivery process, a pressure monitoring mechanism 4 is set in the middle of the hot nitrogen gas delivery pipe 2. The pressure monitoring mechanism 4 extends upward from the sealing welding sleeve 8 to the pressure monitoring pipe head 9. The top of the pressure monitoring pipe head 9 is connected to the sealing fixing sleeve 10 by a thread, and a pressure monitoring gauge 11 is set on its top to display the pressure value inside the pipe, providing a monitoring basis for the hot nitrogen gas delivery and cleaning process. Example 2

[0027] like Figure 1 , Figure 4 , Figure 5 , Figure 6 , Figure 7 and Figure 8 As shown, in order to achieve continuous cleaning inside the pipeline, the present invention arranges the pipe cleaning mechanism 14 of the moving pipe cleaning device 3 inside the hot nitrogen conveying pipe 2. The mechanism consists of two vertical fixed baffles 12 facing each other, a linear track rod 13 welded between the two baffles, and the pipe cleaning mechanism 14 sleeved on the outside of the linear track rod 13. The two vertical fixed baffles 12 are respectively welded to the inner wall of the pipe near the input end and the output end. The maximum range of movement of the pipe cleaning mechanism 14 is limited by closing both ends to prevent it from falling off. The linear track rod 13 passes horizontally between the two vertical fixed baffles 12 and serves as the internal guide core of the pipe cleaning mechanism 14.

[0028] Furthermore, the pipe cleaning mechanism 14 is installed around the linear track rod 13. Its core is a metal movable inner sleeve 19, which can slide left and right along the linear track rod 13. Multiple strip-shaped airflow rotating fan blades 18 are welded to its outer periphery. The strip-shaped airflow rotating fan blades 18 are set with an inclined structure so that the high-speed hot nitrogen airflow can generate a driving force on the fan blades when it passes by. A magnetic cleaning movable ring 16 is fitted around the outer periphery of the metal movable inner sleeve 19. The magnetic cleaning movable ring 16 is made of iron-chromium-cobalt permanent magnet alloy and forms a magnetic response with the external driving neodymium magnet 24. Several cleaning bristles 17 are evenly arranged on the outer wall of the magnetic cleaning movable ring 16. The cleaning bristles 17 are made of Inconel alloy, which makes them still have good elasticity and grinding performance in the high temperature atmosphere and can always stick to the inner wall of the hot nitrogen gas delivery pipe 2.

[0029] Furthermore, an external force drive mechanism 15 is arranged on the outside of the front side of the hot nitrogen delivery pipe 2 to assist in driving the left and right movement of the magnetic cleaning movable ring 16. The external force drive mechanism 15 supports the linear sliding bracket 20 through two bracket fixing blocks 22 welded to the reinforcing sleeve 7 and the input end flange 6, so that the linear sliding bracket 20 is arranged parallel to the hot nitrogen delivery pipe 2. A U-shaped adjusting block 23 is sleeved on the outside of the linear sliding bracket 20. The U-shaped groove of the U-shaped adjusting block 23 allows it to be finely adjusted back and forth, and can also slide left and right along the linear sliding bracket 20 to accurately correspond to the position. The internal cleaning mechanism 14 inside the hot nitrogen delivery pipe 2 has a U-shaped adjusting block 23 with a driving neodymium magnet 24 fixed to its rear side. The driving neodymium magnet 24 faces the hot nitrogen delivery pipe 2 and uses magnetic force to act on the magnetic cleaning movable ring 16 through the pipe wall, thereby realizing the magnetic drag of the internal cleaning mechanism 14. The front end of the U-shaped adjusting block 23 is fixed with a push-pull handle 21 by a metal plate and screws. The operator can realize the adjustment and driving action by pushing and pulling the handle 21. At the same time, the metal plate closes the front opening, so that the U-shaped adjusting block 23 can only move in two directions along the linear sliding bracket 20.

[0030] Furthermore, when the external force driving mechanism 15 pushes the driving rubidium magnet 24 in a certain direction, the driving rubidium magnet 24 and the magnetic cleaning ring 16 generate a magnetic interaction, causing the pipe cleaning mechanism 14 to move synchronously along the inside of the hot nitrogen gas delivery pipe 2. During the movement, the cleaning bristles 17 on the outer periphery of the magnetic cleaning ring 16 maintain close contact with the pipe wall, achieving the effect of continuously brushing away the attached substances. When the driving rubidium magnet 24 moves to the position corresponding to the vertical fixed stop 12, the magnetic cleaning ring 16 will be blocked at the stop. If the driving rubidium magnet 24 continues to move in that direction, due to the increased distance, the magnetic cleaning ring 16 will eventually disengage from the driving rubidium magnet 24. Then, under the thrust of the subsequent hot nitrogen gas flow, the strip-shaped airflow rotates the fan blade 1. 8. Under the action of fluid, it begins to rotate or is pushed as a whole, causing the pipe cleaning mechanism 14 to move in the opposite direction and continuously rotate and scrape. In this way, the pipe cleaning mechanism 14 can achieve reciprocating motion under the dual action of airflow and external force drive mechanism 15. Even when the airflow is small, it can be manually driven by push and pull handle 21 to ensure that the cleaning work can be performed at any time. During the entire cleaning process, the cleaning bristles 17 are in continuous contact with the pipe wall and the rotation ability of the strip airflow rotating fan blade 18 makes the inner wall deposits fully stripped, ensuring that the hot nitrogen gas delivery pipe 2 maintains a high level of cleanliness and delivery efficiency during long-term operation. The internal pressure changes can be monitored in real time by the pressure monitoring mechanism 4 to further verify the effectiveness of the cleaning mechanism's operation.

[0031] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A hot nitrogen delivery device for a nitrogen compressor, comprising a hot nitrogen delivery pipe (2), an output end flange (1) disposed at its right end, a reinforcing sleeve (7) disposed at its left end, an input control valve (5), and an input end flange (6), characterized in that: The hot nitrogen gas delivery pipe (2) has a set of moving pipe cleaning device (3). The cleaning device includes a vertical fixed stop bar (12), a linear track bar (13), a pipe cleaning mechanism (14), and an external force driving mechanism (15). There are two vertical fixed stops bar (12), which are symmetrically fixed at both ends inside the hot nitrogen gas delivery pipe (2). The linear track bar (13) is welded between the two vertical fixed stops bar (12). The pipe cleaning mechanism (14) is sleeved on the linear track bar (13). The external force driving mechanism (15) is used to drive the pipe cleaning mechanism (14) from outside the pipe.

2. The nitrogen compressor heat extraction and nitrogen conveying device according to claim 1, characterized in that: The external force driving mechanism (15) and the pipe cleaning mechanism (14) are linked by magnetic action, and the vertical fixed stop bar (12) is used to limit the movement range of the pipe cleaning mechanism (14) along the track.

3. The nitrogen compressor heat extraction and nitrogen conveying device according to claim 2, characterized in that: The tube cleaning mechanism (14) includes a magnetic cleaning ring (16), cleaning brushes (17), strip-shaped airflow rotating fan blades (18), and a metal movable inner sleeve (19). The metal movable inner sleeve (19) is fitted outside the linear track rod (13), the magnetic cleaning ring (16) is fitted outside the metal movable inner sleeve (19), multiple strip-shaped airflow rotating fan blades (18) are provided and are fixed at equal intervals between the magnetic cleaning ring (16) and the metal movable inner sleeve (19), and the cleaning brushes (17) are set outside the magnetic cleaning ring (16).

4. The nitrogen compressor heat extraction and nitrogen conveying device according to claim 3, characterized in that: The metal movable inner sleeve (19) can move along the straight track rod (13) and drive the magnetic cleaning movable ring (16) to move synchronously through the strip airflow rotating fan blade (18), so that the cleaning bristles (17) fit against the inner wall of the hot nitrogen gas delivery pipe (2) and move synchronously.

5. A nitrogen compressor heat extraction nitrogen conveying device according to claim 4, characterized in that: The external force driving mechanism (15) includes a linear sliding bracket (20), a bracket fixing block (22) and a U-shaped adjusting block (23). There are two bracket fixing blocks (22), which are welded to the front end of the input end flange (6) and the front end of the reinforcing sleeve (7) respectively. The left end of the linear sliding bracket (20) is fixedly connected to the two bracket fixing blocks (22), which is used to provide the U-shaped adjusting block (23) with a sliding adjustment path in the front-back and left-right directions.

6. The nitrogen compressor heat extraction and nitrogen conveying device according to claim 5, characterized in that: The external force driving mechanism (15) also includes a push-pull handle (21) and a driving neodymium magnet (24). The driving neodymium magnet (24) is connected to the U-shaped adjusting block (23) to achieve magnetic driving. The push-pull handle (21) is fixed to the front end of the opening of the U-shaped adjusting block (23) by a metal sealing plate for operating the U-shaped adjusting block (23).

7. A nitrogen compressor hot nitrogen conveying device according to claim 6, characterized in that: The cleaning brush bristles (17) are made of Inconel alloy, and the magnetic cleaning ring (16) is made of iron-chromium-cobalt permanent magnet alloy and can be driven by a neodymium magnet (24) to magnetically attract it to move it in the hot nitrogen delivery pipe (2).

8. A nitrogen compressor heat extraction nitrogen conveying device according to claim 7, characterized in that: The driving rubidium magnet (24) moves the magnetic cleaning ring (16) to the vertical fixed stop (12) located on the left side of the tube, and then it can continue to slide to achieve magnetic disengagement. Subsequently, the hot nitrogen gas flow acts on the strip-shaped airflow to rotate the fan blade (18), pushing the tube cleaning mechanism (14) to move in the conveying direction.

9. A nitrogen compressor heat extraction nitrogen conveying device according to claim 8, characterized in that: The multiple strip-shaped airflow rotating fan blades (18) have an inclined blade structure, which can generate rotation under the action of airflow and drive the cleaning bristles (17) to scrape the pipe wall. When the airflow is insufficient, the pipe cleaning mechanism (14) can be moved by the external force driving mechanism (15).

10. A nitrogen compressor heat extraction nitrogen conveying device according to claim 9, characterized in that: The middle section of the hot nitrogen gas delivery pipe (2) is provided with a pressure monitoring mechanism (4). The pressure monitoring mechanism (4) includes a sealing welding sleeve (8), a pressure monitoring tube head (9), a sealing fixing sleeve (10), and a pressure monitoring gauge (11). The sealing welding sleeve (8) is welded to the outside of the hot nitrogen gas delivery pipe (2). The pressure monitoring tube head (9) is vertically welded to the center of the top of the sealing welding sleeve (8), which is connected to the inside of the hot nitrogen gas delivery pipe (2). The top of the sleeve is provided with a threaded joint. The threaded joint is threaded with a sealing fixing sleeve (10). The top of the sealing fixing sleeve (10) is provided with a pressure monitoring gauge (11). When the U-shaped adjusting block (23) passes through the sealing welding sleeve (8), it can avoid it through its own groove structure.

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