Throttle

Abstract

A throttle ring (1) for a piston compressor has an axial ring axis (Ar), an axial height (h), a radially inner running surface (2), a radially outer peripheral surface (3), an upper flank (4), and a lower flank (5). When the throttle ring (1) is in use, the upper flank (4) faces the compression space (11) of the piston compressor. The running surface (2) has at least one circumferential groove (6) in the circumferential direction. The circumferential groove is connected to the outer peripheral surface (3) by at least one radial bore (7).

Description

Technical Field

[0001] The present invention relates to the technical field of piston compressors. In particular, it relates to a throttle ring, a piston rod seal structure (arrangement, layout) having such a throttle ring, and a piston compressor having such a piston rod seal structure. The present invention further relates to a method for compressing boil-off gas generated during the storage of liquefied natural gas.

Background Art

[0002] Compressors are generally used to compress fluids such as gases or aerosols. In a piston compressor, the rotational movement of the crankshaft generated by the drive device is converted into the reciprocating movement of one or more pistons by a connecting rod, so as to compress the gas or aerosol sucked into the compressor unit. A seal system of the piston rod, so-called packing, is used for the piston rod that moves to seal the working chamber on the crank side. Since the seal element is in contact with the vibrating piston rod, it is always worn.

[0003] A characteristic of the compression process in a piston compressor is the generation of a dynamic pressure component. The dynamic pressure component refers to the pressure difference generated between the final compression pressure and the suction pressure at each compression stage during one rotation of the crankshaft. When this dynamic pressure component exceeds the limit value, it causes the flow and severe wear of the seal element. In particular, in the case of a segmented seal element, the dynamic pressure component may often lead to the destruction of the related hose spring or clamp ring, or to the early failure of the seal system.

[0004] To protect the actual sealing element from these adverse effects of the dynamic pressure distribution (dynamic pressure profile), so-called pressure breakers or throttle rings are known from prior art. These are intended to keep the dynamic pressure distribution away from the actual sealing element by being used at the packing inlet, i.e., on the compression chamber side. Typically, such throttle rings are designed from the outset as frictionless sealing elements or as frictionless sealing elements with minimal shrinkage wear. However, it has been found that common non-contact throttle rings do not contribute much to sealing the dynamic pressure component. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Swiss Patent No. 439897 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] For example, the throttle ring known from Patent Document 1 has the drawback that the pulsating pressure component is not sufficiently attenuated. As a result, the majority of the dynamic pressure component loads the actual sealing element, especially the first sealing element positioned directly toward the compression chamber. Similar to a chain reaction, the dynamic pressure component moves further within the packing as wear progresses, causing the downstream sealing element to wear out rapidly even under low to medium loads, and resulting in a significantly shortened service life of the piston rod seal system. Foreign matter in the compressed fluid can enter, for example, between the sealing element and the moving piston rod, further increasing friction and worsening the wear of the sealing element. In addition, there is a risk that parts (fragments) resulting from the failure of the sealing element or its clamping element may enter the compression chamber, damaging important internal components such as pressure valves, or at least impairing the function of important components.

[0007] Based on the aforementioned prior art, the object of the present invention was to eliminate such and other drawbacks of the prior art and, in particular, to provide the throttle ring of the type described at the beginning that provides improved dynamic pressure sealing, ensures better protection against any foreign matter that may be present, and can be manufactured economically.

[0008] A further object of the present invention is to provide a piston rod seal structure for a dry-running compressor capable of supplying compressed natural gas to a propulsion system of a ship that uses compressed natural gas as fuel, and / or to a reliquefaction unit. Here, the natural gas is preferably in the form of liquefied natural gas (LNG) or boil-off gas. [Means for solving the problem]

[0009] This problem is solved, in particular, by a throttle ring, piston rod seal structure (arrangement), compressor, and method having the features of the independent claim. Advantageous design and further development are the subject of the dependent claim.

[0010] The problem is solved by a throttle ring, particularly for a piston compressor. The throttle ring according to the present invention comprises an axially running ring axis, an axial height, a radially inward running surface, and an outer circumferential surface as a radially outward circumferential surface. The radially inward running surface is the surface that restricts the central recess of the throttle ring through which the oscillating piston rod can move. The throttle ring according to the present invention further has an upper flank and a lower flank, the upper flank facing the compression chamber of the piston compressor or facing the compression chamber side in the intended use of the throttle ring. The radially inward running surface has at least one circumferential groove in the circulating direction. This circumferential groove is connected to the outer circumferential surface as a radially outward circumferential surface by at least one radial bore or radial channel. Through at least one radial bore, the radially inward running surface of the throttle ring is in fluid communication with the outer circumferential surface, which is a radially outward circumferential surface. The radial bore preferably has a circular cross-section, but may have other shapes, such as a rectangular cross-section.

[0011] Such a throttle ring has the advantage that the dynamic pressure component is sealed so that a nearly constant pressure is applied to the downstream sealing element of the piston rod seal structure, as will be described in more detail below. The throttle ring according to the present invention has the further advantage of preventing the chain reaction wear of the sealing element described at the beginning by keeping foreign matter present in the compression chamber or the fluid being compressed away from the sealing element of the piston rod seal structure. The throttle ring thereby prevents both wear material or even fragments from moving from the sealing system into the compression chamber or the fluid to be compressed, and prevents particles present in the fluid to be compressed from entering the piston rod seal system. In other words, the throttle ring according to the present invention is a bidirectional fouling trap.

[0012] The throttle ring according to the present invention is particularly suitable for compressing low molecular weight gases such as hydrogen and methane to a high final compression pressure in dry running. In particular, by using the throttle ring of the present invention in a dry running compressor, it is possible to achieve a pressure increase of preferably up to 300 bar (30 MPa), and especially preferably up to 1000 bar (100 MPa), without significantly reducing the service life of the compressor.

[0013] Dry-type travel compressors have the advantage that the liquid being compressed is not contaminated with lubricating oil. Therefore, the purity of the liquid being compressed is not negatively affected. This is particularly important in applications where the fluid is returned to the storage tank, such as when boil-off gas generated during the storage or transport of liquefied natural gas (LNG) is reliquefied and supplied to the storage tank as liquefied natural gas.

[0014] Preferably, the throttle ring is designed as an endless ring. An endless ring, also known as an uncut ring, is designed to have no protrusions and to be continuous in the circumferential direction.

[0015] Such endless rings are not only mechanically particularly elastic, but can also be produced economically. During the compression phase, the fluid flowing into the piston rod seal structure is at a pressure higher than the suction pressure of the compression phase being considered. As the pressure in the compression chamber decreases towards the suction pressure, the fluid stored in the piston rod seal structure flows back into the compression chamber.

[0016] Preferably, the throttle ring has at least one radially extending channel, and preferably four to six such circumferentially spaced channels. Particularly preferably, the upper flank of the throttle ring has at least one radially extending channel. Preferably, the radial channel has a rectangular surface.

[0017] These radially extending channels are also called pressure equalization grooves or return flow grooves. By providing such radially extending channels, backflow of fluid into the piston rod seal structure is significantly improved. That is, the throttle ring not only has virtually no sealing effect at this stage (phase), but can also be made free from the effects of wear. Furthermore, by using return flow grooves within the packing, particularly on the throttle ring according to the present invention, the dynamic pressure component can be dissipated during the suction stroke by returning it to the compression chamber through the radial channels, resulting in a much more stable pressure distribution. If return flow grooves are not used, the dynamic pressure component moves towards the packing outlet, which may place an unstable load on the individual packing elements. This unstable pressure distribution can cause rotational and translational motion of the seal elements, resulting in damage to the seal elements and chamber.

[0018] Preferably, the radial bore has a diameter between 0.5 mm and 3 mm, preferably between 0.75 mm and 1.25 mm, and more preferably 1 mm. Here, multiple radial bores may all have the same diameter, or they may have different diameters from one another.

[0019] A predetermined diameter range not only allows for optimal pressure relief or damping of the dynamic pressure component, but also prevents abrasion and / or fragments from the packing from passing through the radial bore. Thus, a preferred diameter range provides the maximum possible protection of the compression chamber from foreign matter from the packing.

[0020] Preferably, the multiple radial bores extending from each circumferential groove toward the circumferential surface are arranged axially symmetrically with respect to the ring axis. This arrangement (structure) of radial bores results in uniform pressure relief on the throttle ring and, in particular, high stability.

[0021] Preferably, the circumferential groove runs substantially parallel to the upper flange and the lower flange of the throttle ring. Such a groove running parallel to the upper flange and the lower flange of the throttle ring can be manufactured particularly easily, for example, by milling.

[0022] According to the present invention, it is preferable that the running surface of the throttle ring is configured with a plurality of circumferential grooves. The running surface having such a plurality of circumferential grooves can be regarded as a labyrinth seal. The functional principle is that when the compressed fluid flows through a plurality of constrictions (constrictions, throttle points) connected in series, the pressure energy is dissipated as heat, and throttling is repeated. In this throttle ring, the constriction is a web disposed between two adjacent circumferential grooves. Due to the pressure gradient, the compressed fluid is first accelerated toward the throttle point, resulting in the conversion of pressure energy into velocity energy. In the subsequent circumferential groove (circular groove), the outflowing volume flow is decomposed into small turbulent vortices and converted into frictional heat. This process is repeated according to the number of circumferential grooves (circular grooves) until the end of the throttle ring.

[0023] Preferably, the plurality of circumferential grooves are arranged in a range of 10% to 90% with respect to the axial height of the throttle ring. Particularly preferably, the circumferential grooves are arranged in a range of 25% to 75% with respect to the axial height of the throttle ring.

[0024] Preferably, the radial bore has a diameter in the range of 50% to 150% of the width of the circumferential groove in the axial direction. The arrangement of the circumferential grooves in the indicated preferred region of the running surface has the advantage that the throttle ring thus obtained is mechanically particularly stable. In particular, the ring edge formed between the outermost groove in the axial direction and each of the upper flange or the lower flange is mechanically sufficiently stable in this way. Therefore, the risk that the throttle ring itself causes fragments can be reduced.

[0025] Unless otherwise indicated, the term "axial height" in this specification means the axial height of the radially inner running surface. When the two flanks of the throttle ring are arranged at a parallel spacing from each other, the axial height of the outer peripheral surface (radially outer circumferential surface) will as a result correspond to the axial height of the radially inner running surface.

[0026] Preferably, each of the circumferential grooves has a groove depth between 0.5 mm and 3 mm. Further or alternatively, the circumferential grooves preferably have a groove width between 0.5 mm and 3 mm.

[0027] These preferred dimensions of the circumferential grooves make it possible to particularly effectively retain wear debris (abrasion) and / or fragments from the packing within the circumferential grooves. Also, according to the present invention, it is also possible to make the groove widths of the circumferential grooves that circumscribe in the circumferential direction different from each other.

[0028] The presence of circumferential grooves with different widths from each other has the advantage that this makes it possible to particularly well retain wear debris and / or fragments of different sizes from each other within the circumferential grooves.

[0029] Preferably, the groove width decreases in the direction of the upper flank. In the direction of the upper flank of the throttle ring, i.e., in the direction of the compression chamber, as each circumferential groove narrows, wear debris and / or fragments from the packing can move between the circumferential grooves until they are finally trapped in a circumferential groove of an appropriate size. This can enhance the protective function of the throttle ring.

[0030] Alternatively, according to the present invention, the groove width may increase from both flanks (upper flank and lower flank) in the direction of half the axial height. This has the advantage that wear and / or debris from both sides, i.e., the compression chamber side and the drive side, are optimally resealed within the throttle ring.

[0031] In particular, a modified high-temperature polymer having properties that satisfy the requirements imposed on such a throttle ring, with respect to mechanical stability and wear resistance, can be used in the manufacture of the throttle ring according to the present invention.

[0032] Preferably, the throttle ring is made of plastic. For example, polytetrafluoroethylene (PTFE), polyetheretherketone (PEEK), polyetherketone (PEK), polyimide (PI), polyphenylene sulfide (PPS), polybenzimidazole (PBI), polyamideimide (PAI), polyamide (PA), polyximethylene (POM), or modified epoxy resin can be used to manufacture the throttle ring according to the present invention.

[0033] Particularly preferred, the throttle ring is made of polytetrafluoroethylene (PTFE). The plastics used may be modified with fillers. Polymers modified with such fillers are also called filler polymers.

[0034] The fillers added are typically carbon, graphite, metal, ceramic, glass beads, solid lubricants, and / or fibrous materials such as carbon fibers, aramid fibers, and glass fibers.

[0035] Such fillers can, for example, not only improve the tribological properties of the plastic used, but also increase thermal resistance and reduce cold flow.

[0036] Particularly preferable, the throttle ring is made of plastic modified with a solid lubricant. The entire throttle ring can also be made from a single material. Such throttle rings have the advantage of being particularly efficient to manufacture, for example, by injection molding.

[0037] According to the present invention, it is also conceivable that the running surface of the throttle ring is provided with a wear protection layer in at least a region of the surface that can come into contact with the piston rod of the piston compressor.

[0038] For example, the wear-resistant layer may be a diamond-like carbon (DLC) layer. Alternatively, the throttle ring could be made of metal, while the running surface could be constructed from a material that allows for dry running, such as plastic or ceramic.

[0039] This problem is further solved by a piston rod seal structure for sealing the piston rod, which is movable and vibrates in the longitudinal direction of the piston compressor. The piston rod seal structure according to the present invention comprises at least one throttle ring as described herein and at least one seal element arranged downstream of the throttle ring.

[0040] The term "sealing element" refers to all elements that seal the passage of the piston rod into the inside of the cylinder, specifically the seal ring and / or throttle ring. Such a piston rod seal structure exhibits high damping capability for dynamic pressure distribution and a long service life.

[0041] In particular, the piston rod seal structure can be used in dry-travel piston compressors. This has the advantage that the compressed fluid is not contaminated by lubricants. Preferably, the piston rod seal structure has at least one channel for supplying and removing coolant.

[0042] Since most of the wear that occurs on sealing elements is caused by frictional heat, wear can be reduced by cooling the sealing elements within the packing. This problem is further solved by a dry-travel piston compressor having a piston rod seal structure as described herein.

[0043] Compressors are typically subjected to prolonged continuous operation or frequent on / off switching, which can lead to high heat generation due to friction. Therefore, conventionally, compressors that could ensure sufficient cooling through oil lubrication were primarily used. However, with oil lubrication, there is a risk of contamination of the compressed fluid (the fluid being compressed) by the lubricating oil inside the compressor unit housing seeping into the compressed fluid through the piston-cylinder pair. This risk does not exist in the dry-travel piston compressor described herein.

[0044] This problem is further solved by a process for compressing boil-off gas generated during the storage of liquefied natural gas (LNG). The process according to the present invention comprises the steps of providing at least one dry-travel piston compressor according to the present invention, compressing the boil-off gas to be compressed in a single-stage or multi-stage compression, and supplying the compressed boil-off gas at least partially as fuel to a multi-fuel engine. The pressure increase obtained by the single-stage or multi-stage compression is at least 200 bar (20 MPa), preferably at least 250 bar (25 MPa). Alternatively to or in addition to supplying the compressed boil-off gas as fuel to a multi-fuel engine, the process according to the present invention may include reliquefaction of the boil-off gas.

[0045] In the process according to the present invention, the use of a throttle ring in a compressor as described herein has the advantage that, due to the contribution of the throttle ring according to the present invention, the compressor can be operated without the use of lubricants even when the pressure rises to 300 bar (30 MPa), and at the same time, a very long service life on the order of 4000 operating hours is achieved. On the other hand, the boil-off gas to be compressed can be compressed to a degree that allows a multi-fuel engine designed for gas operation to be operated with it. Secondly, the boil-off gas is not contaminated with lubricating oil during reliquefaction.

[0046] The process according to the present invention is preferably suitable for a vessel capable of operating on liquefied natural gas, which is equipped with a dual-fuel ship engine. Various embodiments of the present invention are described below with reference to the drawings, where the same or corresponding elements are designated by the same reference numerals. [Brief explanation of the drawing]

[0047] [Figure 1] A throttle ring according to the present invention. [Figure 2a] A top view of the first embodiment of the throttle ring. [Figure 2b] A cross-section of Figure 2a along line AA. [Figure 2c] A cross-section of Figure 2a along line BB. [Figure 3a] Top view of the packing cartridge. [Figure 3b] A cross-section of Figure 3a along line CC. [Figure 3c] A cross-section of Figure 3a along line DD. [Modes for carrying out the invention]

[0048] Figure 1 is a perspective view of a throttle ring 1 for a piston compressor. The throttle ring 1 has a ring axis Ar that runs axially and an axial recess having a radially inward running surface (radial inner running surface) 2 in the axial direction. The piston rod 14 (approximately shown in Figure 3b) can move along this axial recess. The diameter of the axial recess is set such that the throttle ring 1 can completely surround the piston rod 14, while not contacting or hardly contacting the surface of the moving piston rod 14. For example, the axial play of the throttle ring 1 is between 0.1 and 0.25 mm. This ensures that when the throttle ring 1 is used as intended, no or very little frictional heat is generated. In the illustrated example, three circumferential grooves 6 are formed on the radially inward running surface 2, spaced apart from each other in the direction of the ring axis Ar (circulating direction). These circumferential grooves 6 run in the circumferential direction and are of an endless design. In the illustrated example, as shown in more detail in the cross-section in Figure 2c, the middle of the three circumferential grooves 6 is connected to the outer circumferential surface (radially outward circumferential surface) 3 by six radial bores 7. The throttle ring 1 further has an upper flank 4 and a lower flank 5 positioned opposite the throttle ring 1. In the illustrated example, the upper flank 4 has six radial channels 8 that extend radially and have a rectangular cross-section. Of course, it is also possible that the multiple radial channels 8 have different cross-sectional shapes from each other.

[0049] Figure 2a shows a top view of the throttle ring 1 of Figure 1 with the upper flank 4 facing upwards. The radially inward running surface 2 and the outer circumferential surface 3 (radially outward circumferential surface) run concentrically with respect to each other. In this embodiment, the multiple radial bores 7 and further multiple radial channels 8 are arranged axially symmetrically with respect to the ring axis Ar, so that they are equally spaced relative to each other in the circumferential direction. In the circumferential direction, for example, one, two, four, six, or eight radial bores 7 can be arranged equally spaced relative to each other, and therefore preferably they are arranged equally spaced relative to each other.

[0050] Figure 2b is a view of the embodiment shown in Figure 2a, cross-sectioned radially along line AA. The ring body of the throttle ring 1 may be rectangular, as in this embodiment. The three circumferential grooves 6 extend substantially parallel to the two flanks (upper flank 4 and lower flank 5) of the throttle ring 1. In the embodiment described above, the three circumferential grooves 6 have approximately equal groove width and groove depth. Of course, it is also possible for the circumferential grooves 6 to have different groove widths and / or groove depths. Furthermore, for example, two or all of the circumferential grooves 6 may have one or more radial bores 7 through which each circumferential groove 6 is in fluid communication with the outer circumferential surface 3.

[0051] Figure 2c shows a cross-section along line BB in Figure 2a. The ring body of the throttle ring 1 has a height h in the direction of the ring axis Ar. A radial bore 7 is shown, which opens from the outer circumferential surface 3 into the middle of three circumferential grooves 6, thus connecting the radially inward running surface 2 to the outer circumferential surface 3. The middle of the three circumferential grooves 6 is positioned at half the axial height of the throttle ring 1 h / 2. In each case, the web 9 positioned between two circumferential grooves represents a throttle point that is linked to a piston rod (shown in Figure 3b) that reciprocates within the axial recess of the throttle ring 1.

[0052] Figure 3a is a top view of a piston rod seal structure (arrangement, configuration, sequence) 10 having two cooling channels (cooling passages) 16, which are a coolant supply passage and a coolant discharge passage. In this embodiment, the piston rod seal structure 10 is configured to include two seal elements 13 and a throttle ring 1, as will be described in more detail in the following drawings.

[0053] Figure 3b shows an axial cross-section of the piston rod seal structure 10 along line CC in Figure 3a. In the installed state, the piston rod drive unit is located on the second side surface 12, while the compression chamber is located on the first side surface 11. The packing is designed as a dry-running seal structure and in this embodiment comprises two chamberings 17 arranged successively in the direction of the piston rod 14, and a seal element 13 positioned therein. The throttle ring 1 is located adjacent to the seal element 13 on the compression chamber side.

[0054] Figure 3c shows an axial cross-section of the piston rod seal structure 10 following line DD in Figure 3a, which passes through not only the lubrication channel 15 but also one of the multiple cooling channels 16.

[0055] In an advantageous embodiment, the throttle ring 1 described above is configured such that each of the circumferential grooves 6 on the radially inward running surface 2 is connected to the outer circumferential surface (radially outward circumferential surface) 3 by at least one radial bore 7, preferably two, four, six, or eight radial bores 7.

[0056] In an advantageous embodiment, the throttle ring 1 described above is designed such that the radially inward running surface 2 of the throttle ring 1 is formed of a material having a hardness greater than that of the flanks (4,5).

[0057] In an advantageous embodiment, the throttle ring described above is designed such that the multiple circumferential grooves 6 are spaced apart from each other by a distance of 0.5 mm to 5 mm, preferably 1 mm to 3 mm, in the direction of the ring axis Ar.

Claims

1. A throttle ring (1) for a piston compressor, The throttle ring (1) has an axial ring axis (Ar), an axial height (h), a radially inward running surface (2) and an outer circumferential surface (3), and an upper flank (4) and a lower flank (5). The upper flank (4) faces the compression space (11) of the piston compressor when the throttle ring (1) is used as intended. The radially inward running surface (2) has a plurality of circumferential grooves (6) that run in the circumferential direction, and the circumferential grooves (6) are connected to the outer surface (3) by at least one radial bore (7). The multiple circumferential grooves (6) are arranged in a range of 10% to 90% of the axial height (h) of the throttle ring (1). The multiple circumferential grooves (6) have different groove widths (Bn) from each other. The groove width (Bn) decreases in the direction of the upper flank (4), or increases in the direction of half the axial height (h / 2) from both the upper flank (4) and the lower flank (5). Throttle ring (1).

2. The throttle ring (1) is formed as an endless ring. The throttle ring (1) according to claim 1.

3. The throttle ring (1) has at least one channel (8) extending in the radial direction. The throttle ring (1) according to claim 1 or 2.

4. The radial bore (7) has a diameter in the range of 0.5 mm to 3 mm. A throttle ring (1) according to any one of claims 1 to 3.

5. The radial bores (7) extending from each of the circumferential grooves (6) to the outer circumferential surface (3) are arranged axially symmetrically with respect to the ring axis (Ar). A throttle ring (1) according to any one of claims 1 to 4.

6. The circumferential groove (6) extends substantially parallel to the upper flank (4) and the lower flank (5) of the throttle ring (1). A throttle ring (1) according to any one of claims 1 to 5.

7. Each of the circumferential grooves (6) has at least one of a groove depth (Tn) between 0.5 mm and 3 mm and a groove width (Bn) between 0.5 mm and 3 mm. A throttle ring (1) according to any one of claims 1 to 6.

8. The throttle ring (1) is made of plastic. A throttle ring (1) according to any one of claims 1 to 7.

9. The radially inward traveling surface (2) is provided with a wear protection layer in at least the area of ​​the surface (9) that can come into contact with the piston rod (14) of the piston compressor. A throttle ring (1) according to any one of claims 1 to 8.

10. A piston rod seal structure (10) for sealing a vibrating piston rod (14) that is movably mounted in the longitudinal direction of a piston compressor, wherein the piston rod seal structure (10) is A throttle ring (1) according to any one of claims 1 to 9, At least one seal element (13) is attached downstream of the throttle ring (1), A piston rod seal structure (10) is provided.

11. The piston rod seal structure (10) described in claim 10 is provided, Dry-type piston compressor.

12. A method for compressing boil-off gas generated during the storage of liquefied natural gas (LNG), wherein the method is: A step of providing at least one dry-travel piston compressor according to claim 11, The process of compressing the boil-off gas in a single stage or in multiple stages, At least one of the following steps: supplying the compressed boil-off gas to a multi-fuel engine as fuel, and reliquefying the boil-off gas, It is equipped with, The pressure increase achieved by the single-stage compression or the multi-stage compression is at least 200 bar (20 MPa). method.

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