DROSSELRING

Description

[0001] The present invention relates to the technical field of piston compressors, in particular to a throttle ring, a piston rod seal assembly with such a throttle ring, and a piston compressor with such a piston rod seal assembly. The invention further relates to a method for compressing boil-off gas arising during the storage of liquefied natural gas.

[0002] Compressors are typically used to compress fluids such as gases or aerosols. In a reciprocating piston compressor, the rotary motion of a crankshaft, generated by a drive unit, is converted by connecting rods into a reciprocating motion of one or more pistons, which is used to compress the drawn-in gas or aerosol in a compressor unit. To seal the crank-side working chamber, piston rod sealing systems, known as packings, are used on the moving piston rod. Due to the contact of the sealing elements with the oscillating piston rod, they are subject to constant wear.

[0003] A characteristic feature of the compression process in a reciprocating piston compressor is the occurrence of a dynamic pressure component. This dynamic pressure component is the pressure difference that occurs between the final compression pressure and the suction pressure of the respective compression stage during one crankshaft revolution. Above a critical value, this dynamic pressure component leads to flow of the sealing elements and / or to excessive wear. In particular, in segmented sealing elements, this dynamic pressure component often leads to fractures of the associated hose springs or clamping rings, which can result in premature failure of the sealing system.

[0004] See for example EP2056003 A1, which discloses a packing ring consisting of several parts.

[0005] To protect the actual sealing elements from these negative effects of the dynamic pressure curve, so-called pressure breaker or throttle rings are known from the state of the art. These are installed at the packing inlet, i.e., on the compression chamber side, and are intended to keep the dynamic pressure curve away from the actual sealing elements. Such throttle rings are typically designed either as frictionless sealing elements from the start or as frictionless sealing elements with low run-in wear. However, it has been shown that the conventional, non-contact throttle rings do not make a significant contribution to sealing the dynamic pressure component.

[0006] For example, the throttle ring known from CH 439 897 has the disadvantage that pulsating pressure components are only insufficiently dampened. As a result, the majority of the dynamic pressure component loads the actual sealing elements, in particular the first sealing element arranged directly towards the compression chamber. Similar to a chain reaction, the dynamic pressure component migrates further into the packing as wear progresses, causing the subsequently arranged sealing elements to wear out quickly even at low to medium loads and significantly reducing the service life of the piston rod sealing system. The wear of the sealing elements is further increased by foreign matter in the fluid to be compressed, as these can, for example, get between the sealing element and the moving piston rod and thus increase friction even further.There is also a risk that parts resulting from the fracture failure of the sealing elements or their clamping elements will enter the compression chamber and damage critical components, such as the pressure valve, or at least impair their function.

[0007] Based on the cited prior art, the present invention is based on the object of eliminating these and other disadvantages of the prior art and, in particular, of providing a throttle ring of the type mentioned at the outset which provides improved sealing of the dynamic pressure, ensures better protection against any foreign bodies present, and is economically producible.

[0008] The invention is further based on the object of providing a piston rod sealing arrangement for a dry-running compressor which is capable of supplying propulsion systems of ships and / or reliquefaction units powered by compressed natural gas, wherein the natural gas is preferably in the form of liquefied natural gas or boil-off gas.

[0009] The object is achieved in particular by a throttle ring, a piston rod sealing arrangement, a compressor, and a method having the features of the independent claims. Advantageous embodiments and further developments are the subject of the dependent claims.

[0010] This object is achieved in particular with a throttle ring for a piston compressor. The throttle ring according to the invention comprises an axially extending ring axis, an axial height, a radially inner running surface, and a radially outer circumferential surface. The running surface is the surface that defines the central recess of the throttle ring, within which an oscillating piston rod is movable. The throttle ring according to the invention further has an upper flank and a lower flank, wherein the upper flank, when the throttle ring is used as intended, faces the compression chamber of the piston compressor or the compression chamber side. The running surface has at least one groove extending in the circumferential direction, which is connected to the radially outer circumferential surface by at least one radial bore or radial channel.The at least one radial bore provides fluid communication between the radially inner running surface and the radially outer circumferential surface of the throttle ring. The radial bore preferably has a circular cross-section, but can also have other shapes, such as a rectangular cross-section.

[0011] Such a throttle ring has the advantage that the dynamic pressure component is sealed in such a way that an approximately constant pressure is applied to the downstream sealing elements of a piston rod sealing arrangement, as will be described in more detail below. The throttle ring according to the invention has the further advantage that it keeps foreign bodies present in the compression chamber or in the fluid to be compressed away from the sealing elements of a piston rod sealing arrangement and thus prevents the chain reaction-like wear of the sealing elements described above. The throttle ring prevents both the transfer of abrasion or even fragments from the sealing system into the compression chamber or into the fluid to be compressed, as well as the entry of particles present in the fluid to be compressed into the piston rod sealing system. In other words, the throttle ring according to the invention is a dirt trap in both directions.

[0012] The throttle ring according to the invention is particularly suitable for the dry-running compression of low-molecular-weight gases, such as hydrogen or methane, to a high final compression pressure. In particular, the use of the throttle ring according to the invention in dry-running compressors enables pressure increases of preferably up to 300 bar, and particularly preferably up to 1000 bar, to be achieved without significantly impairing the service life of the compressors.

[0013] Dry-running compression has the advantage that the fluid being compressed is not contaminated with lubricants. The purity of the compressed fluid is therefore not negatively affected. This is particularly important for applications where a fluid is fed back into a storage facility, such as boil-off gas generated during the storage or transport of liquefied natural gas (LNG), which can be reliquefied and subsequently fed into the storage facility as liquefied natural gas.

[0014] The throttle ring is designed as an endless ring.

[0015] An endless ring, also known as an uncut ring, has no joint, but is designed without interruption in the circumferential direction.

[0016] Such an endless ring is particularly mechanically resilient and can be produced economically.

[0017] The fluid flowing into the piston rod seal assembly during the compression phase is at a higher pressure than the suction pressure of the compression stage in question. If the pressure in the compression chamber drops back toward the suction pressure, the fluid stored in the piston rod seal assembly flows back into the compression chamber.

[0018] The throttle ring preferably has at least one channel extending in the radial direction, and preferably four to six such channels spaced apart in the circumferential direction. Particularly preferably, the upper flank of the throttle ring has at least one channel extending in the radial direction. The radial channels preferably have a rectangular cross-section.

[0019] Such radially running channels are also called pressure equalization grooves or return flow grooves.

[0020] By providing such radially extending channels, the backflow of fluid flowing into the piston rod sealing arrangement can be significantly improved, i.e. the throttle ring has almost no sealing effect during this phase and is therefore not subject to wear. In addition, the use of backflow grooves in the packing, and in particular on the throttle ring according to the invention, achieves a much more stable pressure distribution, since the dynamic pressure component can be dissipated back into the compression chamber via the radial channels during the suction stroke. Without the use of backflow grooves, the dynamic pressure component can migrate towards the packing outlet and cause unstable loading of the individual packing elements. This unstable pressure distribution leads to rotational and translational movements of the sealing elements and subsequently to damage to the sealing elements and the chambers.

[0021] The radial bores preferably have a diameter between 0.5 mm and 3 mm µm, preferably 0.75 mm to 1.25 mm, and particularly preferably 1 mm. The bores can all have the same diameter or different diameters.

[0022] The specified diameter range allows for optimal pressure relief or damping of the dynamic pressure component while simultaneously preventing abrasion and / or fragments from the packing from penetrating the radial bores. The preferred diameter range thus provides the greatest possible protection of the compression chamber from foreign matter from the packing.

[0023] Preferably, the radial bores extending from the respective circumferential groove to the circumferential surface are arranged axially symmetrically to one another with respect to the ring axis.

[0024] Such an arrangement of the radial bores ensures uniform pressure relief and particularly high stability of the throttle ring.

[0025] Preferably, the circumferential grooves run substantially parallel to the upper and lower flanks of the throttle ring.

[0026] Such grooves running parallel to the upper and lower flanks of the throttle ring can be produced particularly easily, for example by milling.

[0027] According to the invention, it is preferred that the running surface of the throttle ring comprises a plurality of circumferential grooves. Such a running surface with a plurality of circumferential grooves can be regarded as a labyrinth seal, the operating principle of which is that the fluid to be compressed repeatedly dissipates pressure energy into heat as it flows through a plurality of constrictions (throttle points) arranged in series, and is thus throttled. In the present throttle ring, the constrictions are the webs arranged between two adjacent circumferential grooves. The fluid to be compressed is initially accelerated towards the throttle point due to the pressure gradient, whereby pressure energy is converted into velocity energy. In the subsequent circumferential groove, the escaping volume flow breaks up into small, random vortices, converted into frictional heat.This process is repeated according to the number of circumferential grooves until the end of the throttle ring.

[0028] Preferably, the circumferential grooves are arranged in a range of 10% to 90% of the axial height of the throttle ring. Particularly preferably, the circumferential grooves are arranged in a range of 25% to 75% of the axial height of the throttle ring.

[0029] 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.

[0030] The arrangement of the circumferential grooves in the specified, preferred area of ​​the running surface has the advantage that the resulting throttle ring is particularly mechanically stable. In particular, the ring edges formed between the axially outermost grooves and the respective flanks are sufficiently mechanically stable. This reduces the risk of the throttle ring itself becoming a source of fragments.

[0031] Unless otherwise indicated, the term "axial height" in the context of this description refers to the axial height of the radially inner running surface. If the two flanks of the throttle ring are spaced parallel to each other, the axial height of the radially outer circumferential surface therefore corresponds to the axial height of the radially inner running surface.

[0032] Preferably, the circumferential grooves each have a groove depth between 0.5 mm and 3 mm. Additionally or alternatively, the circumferential grooves preferably have a groove width between 0.5 mm and 3 mm.

[0033] These preferred dimensions of the circumferential grooves enable abrasion and / or fragments from the packing to be retained particularly effectively in the circumferential grooves.

[0034] It is also conceivable according to the invention that the grooves running in the circumferential direction have different groove widths.

[0035] The presence of circumferential grooves of different widths has the advantage that different sizes of abrasion and / or different sizes of fragments can be retained particularly well inside the grooves.

[0036] Preferably, the groove width decreases toward the upper flank. By narrowing the respective circumferential grooves toward the upper flank of the throttle ring, i.e., toward the compression chamber, it is possible for debris and / or fragments from the packing to migrate between the circumferential grooves until they are finally trapped in a circumferential groove of a suitable size. This increases the protective function of the throttle ring.

[0037] Alternatively, it is also conceivable according to the invention for the groove width to increase from both flanks toward half the axial height. This provides the advantage that wear debris and / or fragments from both sides, i.e., the compression chamber side and the drive side, are optimally retained inside the throttle ring.

[0038] Modified high-temperature polymers can be used to manufacture the throttle rings according to the invention, the properties of which meet the requirements placed on such throttle rings, in particular with regard to mechanical stability and wear resistance.

[0039] The throttle ring is preferably made of plastic. For example, polytetrafluoroethylene (PTFE), polyetheretherketone (PEEK), polyetherketone (PEK), polyimide (PI), polyphenylene sulfide (PPS), polybenzimidazole (PBI), polyamideimide (PAI), polyamide (PA), polyoxymethylene (POM), or even modified epoxy resin can be used to manufacture the throttle rings according to the invention.

[0040] The throttle ring is particularly preferably made of polytetrafluoroethylene (PTFE).

[0041] The plastics used can be modified with fillers. Such polymers modified with fillers are also referred to as filled polymers.

[0042] The added fillers are usually carbon, graphite, metals, ceramics, glass beads, solid lubricants and / or fibrous materials such as carbon fibers, aramid fibers, glass fibers.

[0043] Such fillers can, for example, improve the tribological properties of the plastic used, increase its temperature resistance and reduce cold flow.

[0044] Particularly preferably, the throttle ring consists of a plastic modified with solid lubricants.

[0045] The entire throttle ring can be made of one and the same material. Such a throttle ring has the advantage of being particularly efficient to manufacture, for example, through an injection molding process.

[0046] According to the invention, it is also conceivable that the running surface of the throttle ring is provided with a wear protection layer at least in the area of ​​the surface that can be brought into contact with a piston rod of the piston compressor.

[0047] For example, the wear protection layer can be a diamond-like carbon layer (DLC).

[0048] It is also conceivable that the throttle ring is made of metal and the running surface is made of a dry-running material such as plastic or ceramic.

[0049] The object is further achieved by a piston rod sealing arrangement for sealing a longitudinally movably mounted, oscillating piston rod of a piston compressor. A piston rod sealing arrangement according to the invention comprises at least one throttle ring as described herein and at least one sealing element arranged downstream of the throttle ring.

[0050] The term "sealing element" refers to all elements that seal the passage of a piston rod into the interior of a cylinder, in particular sealing and / or throttle rings.

[0051] Such a piston rod sealing arrangement has a high damping capacity of the dynamic pressure curve as well as a long service life.

[0052] In particular, the piston rod seal arrangement can be used in a dry-running piston compressor. This offers the advantage that the fluid to be compressed is not contaminated by lubricants.

[0053] Preferably, the piston rod sealing arrangement has at least one channel for the supply and removal of coolant.

[0054] Since a large part of the wear occurring on the sealing elements is due to frictional heat, the wear can be reduced by cooling the sealing elements in the packing.

[0055] The object is further achieved with a dry-running piston compressor with a piston rod seal arrangement as described herein.

[0056] Compressors are typically subjected to long periods of continuous operation or frequent switching on and off, which leads to high heat generation due to friction. In the past, compressors primarily used oil lubrication to ensure sufficient cooling were used. However, with oil lubrication, there is a risk that the lubricating oil in the compressor unit housing could penetrate the piston-cylinder pairing into the fluid being compressed, which could ultimately lead to contamination of the compressed fluid. This risk does not exist with the dry-running piston compressor described here.

[0057] The object is further achieved by a method for compressing boil-off gas that arises during the storage of liquefied natural gas (LNG). The method according to the invention comprises providing at least one dry-running piston compressor according to the invention, single- or multi-stage compression of the boil-off gas to be compressed, and at least partially supplying a multi-fuel engine with the compressed boil-off gas as fuel, wherein the pressure increase achieved by the single- or multi-stage compression is at least 200 bar, preferably at least 250 bar. Alternatively or in addition to supplying a multi-fuel engine with the compressed boil-off gas as fuel, the method according to the invention can include the reliquefaction of boil-off gas.

[0058] The use of a throttle ring in a compressor as described herein in the inventive method offers the advantage that, thanks to the throttle ring according to the invention, the compressor can be operated without the use of lubricants even at a pressure increase of 300 bar, while simultaneously achieving very long service lives on the order of 4,000 operating hours. Firstly, the boil-off gas to be compressed can be compressed to such an extent that a multi-fuel engine designed for gas operation can be powered by it. Secondly, the boil-off gas is not contaminated by lubricants during reliquefaction.

[0059] The method according to the invention is preferably suitable for a ship that can be operated with liquefied natural gas and that comprises a dual-fuel marine engine.

[0060] Various embodiments of the invention are described below with reference to drawings, wherein identical or corresponding elements are provided with identical reference numerals.

[0061] They show: Fig. 1A throttle ring according to the invention; Fig. 2aa plan view of a first embodiment of a throttle ring; Fig. 2ba section through Figur 2a along the line AA; Fig. 2c a section through Figur 2a along the line BB; Fig. 3a a plan view of a packing cartridge; Fig. 3b a section through Figur 3a along the line CC; Fig. 3c a section through Figur 3a along line DD.

[0062] Fig. 1 shows a perspective view of a throttle ring 1 for a piston compressor. The throttle ring 1 has an axially extending ring axis Ar and has a recess in the axial direction with a radially inner running surface 2, along which a piston rod 14 (in Fig. 3b (shown only in outline). The diameter of the axial recess is dimensioned such that the throttle ring 1 can completely enclose the piston rod, whereby the surface of the moving piston rod is not or hardly touched. For example, the axial play of the throttle ring 1 is between 0.1 and 0.25 mm. This ensures that no or only minimal frictional heat is generated when the throttle ring 1 is used as intended. In the example shown, the running surface 2 has three grooves 6 spaced apart from one another in the direction of the ring axis Ar, which run in the circumferential direction and are of endless design. In the example shown, the middle of the three grooves 6 is connected to the radially outer circumferential surface 3 by six radial bores 7, as in Fig. 2c The cross-section shown is shown in even more detail. The throttle ring 1 further has an upper flank 4 and a lower flank 5 arranged opposite it. In the example shown, the upper flank 4 has six radially extending channels 8 with a rectangular cross-section. Of course, it is also conceivable for the radial channels 8 to have a different cross-sectional shape.

[0063] Fig. 2a shows the throttle ring 1 from Fig. 1 in a plan view of the upper flank 4. The radially inner running surface 2 and the radially outer circumferential surface 3 extend concentrically to one another. In the present exemplary embodiment, the radial bores 7 and also the radial channels 8 are arranged axially symmetrically to one another with respect to the ring axis Ar and are evenly spaced from one another in the circumferential direction. For example, one, two, four, six, or eight radial bores 7 could be spaced from one another in the circumferential direction, preferably evenly spaced from one another.

[0064] Fig. 2b shows a radial section through the Fig. 2a shown embodiment along the line AA. The annular body of the throttle ring 1 can, as in the present embodiment, be rectangular. The three circumferential grooves 6 run essentially parallel to the two flanks 4 and 5 of the throttle ring 1. In the previous embodiment, the three circumferential grooves 6 have essentially the same groove widths and groove depths. Of course, it would also be possible for the circumferential grooves 6 to have different groove widths and / or groove depths from one another. It would also be possible, for example, for two or all circumferential grooves 6 to have one or more radial bores 7, via which the respective grooves 6 are in fluid communication with the radially outer circumferential surface 3.

[0065] Fig. 2c shows a section along the line BB according to Fig. 2a . The annular body of the throttle ring 1 has a height h in the axial direction Ar. Shown is a radial bore 7, which opens from the radially outer circumferential surface 3 into the middle of the three circumferential grooves 6 and connects the radially inner running surface 2 with the radially outer circumferential surface 3. The middle of the three circumferential grooves 6 is arranged at half the axial height h / 2 of the throttle ring 1. The webs 9, each arranged between two circumferential grooves, in conjunction with a piston rod (in Fig. 3b shown) represent throttling points.

[0066] Fig. 3a shows a plan view of a piston rod seal assembly 10 with two cooling channels 16, a supply channel, and a discharge channel for the coolant. In the present embodiment, the piston rod seal assembly 10 comprises two sealing elements 13 and a throttle ring 1, as will be explained in more detail in the following drawings.

[0067] Fig. 3b shows an axial section through the piston rod seal arrangement 10 along the line CC in Fig. 3a , wherein, in the installed state, the piston rod drive is located on side 12 and the compression chamber is located on side 11. The packing is designed as a dry-running seal arrangement and, in the present exemplary embodiment, comprises two chamber rings 17 arranged one behind the other in the direction of the piston rod 14, with sealing elements 13 arranged therein. The throttle ring 1 is arranged adjacent to the sealing elements 13 on the compression chamber side.

[0068] Fig. 3c shows an axial section through the piston rod seal arrangement 10 according to the line DD in Fig. 3a , which runs through the lubrication channel 15 and one of the cooling channels 16.

[0069] In an advantageous embodiment, the throttle ring 1 described above is designed such that each of the circumferential grooves 6 on the radially inner running surface 2 is connected to the radially outer circumferential surface 3 by at least one radial bore 7, and preferably two, four, six or eight bores 7.

[0070] In an advantageous embodiment, the throttle ring described above is designed such that the radially inner running surface 2 of the throttle ring consists of a material with greater hardness than that of the flanks.

[0071] In an advantageous embodiment, the throttle ring described above is designed such that the circumferential grooves 6 are spaced apart from one another in the direction of the ring axis Ar at a distance of 0.5 mm to 5 mm, preferably 1 mm to 3 mm.

Claims

1. Throttle ring (1) for a piston compressor, having an axially extending ring axis (Ar), an axial height (h), a radially inner running surface (2) and a radially outer circumferential surface (3), as well as an upper flank (4) and a lower flank (5), wherein the upper flank (4) faces the compression chamber (11) of the piston compressor when the throttle ring (1) is used as intended, wherein the running surface (2) has at least one circumferential groove (6) in the circumferential direction, which is connected to the radially outer circumferential surface (3) by at least one radial bore (7), and wherein the throttle ring (1) is designed as an endless ring.

2. Throttle ring (1) according to claim 1, wherein the upper flank (4) of the throttle ring (1) has at least one channel (8) extending in the radial direction.

3. Throttle ring (1) according to one of the preceding claims, wherein the radial bores (7) have a diameter in the range between 0.5 mm and 3 mm, preferably 0.75 mm to 1.25 mm, and particularly preferably 1 mm.

4. Throttle ring (1) according to one of the preceding claims, wherein the radial bores (7) extending from the respective circumferential groove (6) to the circumferential surface (3) are arranged axially symmetrically to one another with respect to the ring axis (Ar).

5. Throttle ring (1) according to one of the preceding claims, wherein the circumferential grooves (6) run essentially parallel to the upper flank (4) and lower flank (5) of the throttle ring (1).

6. Throttle ring (1) according to one of the preceding claims, wherein the circumferential grooves (6) are arranged in a range of 10% to 90%, preferably 25% to 75%, relative to the axial height (h) of the throttle ring (1).

7. Throttle ring (1) according to one of the preceding claims, wherein the circumferential grooves (6) each have a groove depth (Tn) between 0.5 mm and 3 mm and / or a groove width (Bn) between 0.5 mm and 3 mm.

8. Throttle ring (1) according to one of claims 1 to 6, wherein the circumferential grooves (6) have different groove widths (Bn).

9. Throttle ring (1) according to claim 8, wherein the groove width (Bn) preferably decreases in the direction to the upper flank (4) or increases from both flanks (4, 5) in the direction to half the axial height (h / 2).

10. Throttle ring (1) according to one of the preceding claims, wherein the throttle ring (1) is made of plastic, in particular polytetrafluoroethylene.

11. Throttle ring (1) according to claim 10, wherein the throttle ring (1) consists of a plastic modified with solid lubricants.

12. Throttle ring (1) according to one of the preceding claims, wherein the running surface (2) is provided with a wear protection layer, in particular with a diamond-like carbon layer, at least in the region of the surface (9) which can be brought into contact with a piston rod (14) of the piston compressor.

13. Piston rod seal arrangement (10) for sealing a longitudinally movably mounted oscillating piston rod (14) of a piston compressor, in particular a dry-running piston compressor, wherein the piston rod seal arrangement (10) comprises at least one throttle ring (1) according to one of claims 1 to 12 and at least one sealing element (13) arranged downstream of the throttle ring.

14. A dry-running reciprocating compressor comprising a piston rod seal arrangement (10) according to claim 13.

15. Method for compressing boil-off gas generated during the storage of liquefied natural gas (LNG), in particular on a ship which can be propelled with LNG, the method comprising the steps of: - Providing at least one dry-running piston compressor according to claim 14; - Single or multi-stage compression of the boil-off gas; - at least partial supply of a multi-fuel engine, in particular a dual-fuel marine engine, with the compressed boil-off gas as fuel and / or at least partial reliquefaction of the boil-off gas; wherein the pressure increase achieved by the single-stage or multi-stage compression is at least 200 bar, preferably at least 250 bar.