Single screw machine for compressing and / or expanding a gas

Abstract

The present invention relates to a single-screw machine for the compression and / or expansion of a gas, comprising a housing in which a central screw (2) and at least one star rotor (3) are rotatably mounted. The central screw (2) has spiral grooves (21) on its circumference (22), which have an open end (212) and a closed end (211). The star rotor (3) has teeth (31) that engage with the spiral grooves (21) and move along the spiral grooves (21) when the central screw rotates. A recess (23) is provided in the central screw (2) at the closed end of each spiral groove (21), into which the teeth (31) of the star rotor (3) do not project when moving along the spiral groove (21).

Description

[0001] The present invention relates to a single-screw machine for the compression and / or expansion of a gas according to the preamble of claim 1.

[0002] Single-screw compression machines are state-of-the-art in industrial sectors where gaseous media need to be compressed and / or expanded. These machines consist of a central screw and one or two star rotors housed within a casing. They are arranged in such a way that a volume varies with each change in the angle of rotation, thus generating a continuous compression or expansion cycle. The central screw, for example, has an approximately cylindrical or conical shape and features several helical grooves around its circumference. The star rotors are positioned so that their axis of rotation is perpendicular to the axis of rotation of the central screw and have several plate-like teeth around their circumference that engage with the helical grooves of the screw rotor. The geometries of the helical grooves and the teeth are precisely matched to ensure a good seal between the teeth and the inner surfaces of the helical grooves.Each spiral groove has an open end through which gas to be compressed enters the groove or expanded gas exits, and a closed end where the groove's depth decreases until it terminates at the cylindrical circumference of the central screw. A tooth of a star rotor engages in a spiral groove, thus enclosing the gas within. The spiral groove, the engaging tooth, and an inner wall surface of the housing define a completely enclosed compression and expansion chamber. During compression, the central screw is driven to rotate, and the star rotors, which engage with the spiral grooves, also rotate. The central screw rotates in such a way that the star rotor teeth move along the spiral grooves toward their closed end, reducing the internal volume of the compression and expansion chambers. This compresses the gas within.Such a single-screw compressor is described, for example, in US2011070117A1. During expansion, pressurized gas is introduced into the compression and expansion chambers and, as it expands, presses against the teeth of the star rotors. Since the star rotors engage with the spiral grooves of the central screw, the central screw is also driven in rotation.

[0003] The compression process in a compression and expansion chamber ends when the tooth of the star rotor approaches the closed end of the spiral groove. Conversely, the expansion process in a compression and expansion chamber begins when the tooth of the star rotor engages the closed end of the spiral groove and moves toward the open end. At this point, the compression and expansion chamber, which is moved across the inner wall surface of the housing by the rotation of the central screw, reaches a gas port located on the inner wall surface of the housing. Through this port, the compressed gas escapes from the compression and expansion chamber during compression and enters the compression and expansion chamber during expansion.To achieve the maximum pressure ratio during compression, the internal volume of the compression and expansion chamber must be as small as possible (or only as small as necessary if the target pressure ratio is lower than the maximum pressure ratio) when the gas port is reached. For this purpose, the gas port is positioned in the last area of ​​the housing's inner wall surface over which the compression and expansion chamber moves during compression, just before the star rotor tooth reaches the closed end of the spiral groove. The gas port is thus located in close proximity to the star rotor opening through which the star rotor protrudes into the housing. However, the gas port and the star rotor opening must be spaced apart and separated by a partition, otherwise high-pressure gas would escape from the gas port to the star rotor opening on the low-pressure side.

[0004] During compression, the tooth of the star rotor is moved further along the spiral groove due to the continued rotation of the central screw. The compression and expansion chamber becomes so small that only the partition wall remains between the tooth of the star rotor and the end of the spiral groove, and the compression chamber no longer has contact with the gas port. From this point on, the compression and expansion chamber is completely closed again, and the remaining gas within it represents a dead volume. This gas can be compressed but cannot be expelled through the gas port and expands when the low-pressure side of the compression and expansion chamber is opened. The energy used to compress this dead volume is therefore lost, negatively impacting the compressor's efficiency. To minimize this energy loss, the dead volume, i.e., the volume of gas that can be compressed, must be reduced.The internal volume of the spiral groove between its closed end and the tooth of the star rotor should be as small as possible. Another problem with this dead space volume is that the gas contained within it becomes overcompressed to extreme pressures when the tooth of the star rotor reaches the end of the spiral groove and the internal volume of the compression and expansion chamber is reduced to virtually zero. This overcompression not only causes significant unnecessary energy consumption, which in turn negatively impacts the compressor's efficiency, but can also damage the compressor and accelerate its normal wear and tear due to the extreme pressures.

[0005] At the beginning of the expansion cycle, the opposite problem arises: Before the spiral groove reaches the gas opening, the compression and expansion chamber is completely closed. The internal volume of the compression and expansion chamber is increased by the movement of the star rotor tooth away from the closed end of the spiral groove, but no gas can enter. A vacuum is thus created in the compression and expansion chamber, and the energy expended to achieve this is lost, negatively impacting the efficiency of the expander.

[0006] In the prior art, the dead space volume and the overcompression of the gas contained within it are minimized in the compression process by enlarging the gas opening in the partition towards the star rotor opening. To allow the compressed gas to escape as completely as possible through this enlargement into the gas opening, the partition is very thin in this area. This ensures that the volume of the compression and expansion chamber is as small as possible at the last moment before the star rotor tooth reaches the end of the spiral groove and is completely closed off by the partition. The internal volume of the compression and expansion chamber, which is maximally compressed at the end, is therefore significantly smaller, but not completely eliminated, so that overcompression still occurs at the end of each compression cycle.Single-screw compressors with such an enlargement of the gas opening in the partition wall to the star rotor opening are disclosed, for example, in EP2359006B1 and in EP2246572B1, the enlargement being clearly visible in Figure 7 of EP2246572B1 with reference numeral 18a and in Figures 12 and 13 of EP2359006B1 with reference numeral 715.

[0007] Tests revealed that, due to the very thin partition wall, the gas port expansion area does not provide a good seal against the star rotor opening. The inventors identified a leakage of high-pressure gas from the gas port expansion, across the thinned partition wall, to the star rotor opening during both compression and expansion. This is where the shortest leakage path with the maximum pressure differential is found. This leakage represents a significant loss of efficiency for the single-screw engine. Furthermore, while the thinning of the partition wall between the gas port and the star rotor opening in the notch area minimizes over-compression of the gas in the dead space volume (during compression) and the vacuum (during expansion), it does not completely eliminate them.

[0008] The present invention therefore aims to provide a single-screw machine for the compression and / or expansion of a gas, in which overcompression of the gas in the compression and expansion chamber at the end of the compression process and / or the generation of a vacuum in the compression and expansion chamber at the beginning of the expansion process is reduced, while at the same time ensuring better sealing against leaks to the star rotor opening.

[0009] This problem is solved by the single-screw machine according to claim 1. Further features and embodiments are set forth in the dependent claims, and their advantages are explained in the following description.

[0010] The core of the invention is the design of a recess in the central screw at the closed end of the spiral groove, into which the tooth of the star rotor cannot engage. This recess provides the compression and expansion chamber with additional volume, which at the end of compression and at the beginning of expansion, when the tooth of the star rotor reaches or moves away from the end of the spiral groove, also represents the minimum volume of the compression and expansion chamber. At the end of the compression process, the recess collects the gas that remains trapped between the tooth of the star rotor, the end of the spiral groove, and the partition between the gas opening and the star rotor opening when the tooth moves to the end of the spiral groove. This completely prevents overcompression of the gas in the compression and expansion chamber at the end of the compression process.The previously known enlargement of the gas opening in the partition towards the star rotor opening is therefore only partially or not at all necessary, and the partition need not have any dilution or only a slight dilution. This ensures a better seal against leaks to the star rotor opening. Since the tooth of the star rotor cannot engage in the recess, the recess creates a dead volume of gas which can be compressed but cannot be expelled through the gas opening and expands again when the compression chamber opens on the low-pressure side. Therefore, the design of a recess in the central screw is a priori disadvantageous, as the energy expended to compress this dead volume is lost.However, tests have shown that the inventive recess can be dimensioned and positioned on the central screw in such a way that the energy loss caused by the dead space volume is more than compensated by the combination of efficiency gains achieved by completely avoiding overcompression and by better sealing against leakage to the star rotor opening, thus improving the overall efficiency of the single-screw machine.

[0011] During expansion, the vacuum generated in the compression and expansion chamber is significantly reduced by the recess according to the invention, because the compression and expansion chamber already has the minimum volume created by the recess from the outset, and the recess also allows for earlier connection to the inlet opening. The ratio between the increased volume at the time the access to the gas port opens and the initial volume of the compression and expansion chamber is therefore significantly smaller than in the prior art, where the initial volume of the compression and expansion chamber was virtually zero.

[0012] The single-screw machine according to the invention can be unidirectionally suitable for the compression or expansion of a gas, or bidirectionally suitable for both compression and expansion of a gas. In the present patent specification, the statements relating to the compression of a gas also apply analogously to the expansion of a gas, even if expansion is not explicitly mentioned, and vice versa.

[0013] The figures show: Figure 1a Inner wall surface of the housing without enlargement of the gas opening in the partition wall to the star rotor opening. Figure 1b Inner wall surface of the housing with enlargement of the gas opening in the partition wall to the star rotor opening. Figures 2-3 Design variants of the recess in the central screw.

[0014] The single-screw machine according to the invention comprises a housing in which a central screw 2 with spiral grooves 21 on its circumference 22 and at least one star rotor 3 with teeth 31, preferably two star rotors 3, are housed, as is known from the prior art described above (see above). Figure 2 and 3 , left). The central screw 2 is surrounded by an inner wall surface 11 of the housing, on which a gas opening 12 for the inlet and / or outlet of pressurized gas (outlet of compressed gas - inlet of gas to be expanded) is located (see. Figure 1a-bEach spiral groove 21 has a closed end 211 at one end of the central screw, located near the gas opening 12, and an open end 212 at the opposite end of the central screw. The teeth 31 of the star rotor 3 project through a star rotor opening 13 of the housing into the spiral grooves 21 of the central screw 2. The central screw 2 and the star rotor 3 are rotatably connected to the housing. When the central screw 2 rotates, at least one tooth 31 of each star rotor 3 engages in a spiral groove 21 of the central screw 2, thereby enclosing at least one compression and expansion chamber, which is bounded by the tooth 31, the spiral groove 21, and the inner wall surface 11 of the housing.During compression, the rotation of the central screw 2 moves the teeth 31 of the star rotor 3 along the spiral groove 21, thereby reducing the volume of each compression chamber until the spiral groove 21 passes over the gas opening 12. This connects the compression chamber to the gas opening 12, allowing the compressed gas to escape from the compression chamber through the gas opening 12. During expansion, compressed gas enters the compression and expansion chambers through the gas opening 12 and expands within them. This pushes the tooth 31 of the star rotor 3 along the spiral groove 21 towards the open end, rotating the central screw. According to the invention, a recess 23 is provided in the central screw 2 at the closed end 211 of at least one spiral groove 21, preferably each spiral groove 21, into which the teeth 31 of the star rotor 3 do not protrude as they move along the spiral groove 21.This recess 23 provides the compression and expansion chamber with additional volume, which, at the end of compression when the tooth 31 of the star rotor 3 reaches the end of the spiral groove 21, also represents the minimum volume of the compression and expansion chamber and cannot be reduced further. The recess 23 collects the gas that remains trapped between the tooth 31 of the star rotor 3 and the end of the spiral groove 21 when the tooth 31 is moved to the end of the spiral groove 21. This completely prevents overcompression of the gas in the compression chamber at the end of the compression process. During expansion, the additional volume of the recess 23 provides the compression and expansion chamber with a minimum output volume greater than zero, thus preventing excessive vacuum in the compression and expansion chamber.The spiral groove 21 has, in the area of ​​its closed end 211, a substantially V-shaped profile with a first side surface 213 and a second side surface 214 on both sides of an inner edge 215.

[0015] The closed end 211 of the spiral groove 21 is the point where the inner edge 215 of the spiral groove 21 meets the circumference 22 of the central screw and the depth of the spiral groove 21 becomes zero. The recess 23 according to the invention is produced by material removal starting from a conventional central screw 2 with conventional spiral grooves 21 and extends to or encompasses the point where the inner edge 215 of the spiral groove 21 meets the circumference 22 of the central screw and the depth of the spiral groove 21 becomes zero.

[0016] The recess 23 can, in principle, have any geometry and extend in any direction around the closed end 211 of the spiral groove 21. The recess 23 can: exclusively in the first side surface 213, exclusively in the second side surface 214, in the first and in the second side surface 213, 214, in the first side surface 213 and in the circumference 22 of the central screw, in the second side surface 214 and in the circumference 22 of the central screw, or in the first and in the second side surface 213, 214 and designed to fit the circumference of the central screw.

[0017] In the version according to Figure 2 The recess 23 is primarily formed in the first side surface 213. It also extends slightly around the circumference 22 of the central screw, thereby widening the spiral groove 21 (in a direction parallel to the axis of rotation A of the central screw and towards the closed end of the spiral groove 21).

[0018] In the version according to Figure 3The recess 23 is formed in the second side surface 214 and also extends around the circumference 22 of the central screw. The recess 23 thus makes the spiral groove 21 longer (tangentially to the axis of rotation A of the central screw in one direction).

[0019] The aforementioned geometries of recess 23 all essentially fulfill the same function. However, depending on the available tools, certain geometries may be easier to manufacture.

[0020] It is particularly advantageous if the recess 23 is as in the version shown in the Figure 3The spiral groove 21 is extended at its closed end 211, meaning that the recess 23 extends in a direction tangential to the axis of rotation A of the central screw and against the direction of rotation of the central screw 2 over the point where, without the recess 23, the inner edge 215 of the spiral groove 21 would meet the circumference 22 of the central screw. In this case, the recess 23 forms a passage through which gas can escape from the compression and expansion chamber to the gas opening 12 for a longer period at the end of the compression cycle, since, due to the rotation of the central screw, the spiral groove 21 no longer directly overlaps the gas opening 12. Thus, some of the gas that remains trapped at the end of compression between the spiral groove 21, the tooth 31 of the star rotor 3, and the partition 14 can continue to escape to the gas opening 12, thereby minimizing the dead space volume.At the beginning of the expansion cycle, gas from the gas opening 12 can enter the compression and expansion chamber earlier through the recess 23, thus compensating for the vacuum created therein.

[0021] The length by which the spiral groove 21 is extended by the recess 23 in a direction tangential to the axis of rotation A of the central screw can be less than, equal to or greater than the thickness of the partition 14 in the housing between the gas opening 12 and the star rotor opening 13: If this length is less than the thickness of the partition 14 in the housing between the gas port 12 and the star rotor port 13, it is ensured that the recess 23 does not bridge the partition 14 and does not establish a direct connection between the gas port 12 and the star rotor port 13 when it is moved across the partition 14 by turning the central screw. Thus, no pressurized gas can escape from the gas port 12 to the star rotor port 13, but a certain dead volume of gas always remains trapped in the compression and expansion chamber. If this length is equal to the thickness of the partition 14 in the housing between the gas port 12 and the star rotor port 13, a direct connection between the gas port 12 and the star rotor port 13 is avoided, and the dead volume of gas in the compression and expansion chamber is simultaneously minimized.If this length is greater than the thickness of the partition 14 in the housing between the gas port 12 and the star rotor port 13, a direct connection is temporarily established between the gas port 12 and the star rotor port 13, through which pressurized gas escapes from the gas port 12 to the star rotor port 13. However, there is no dead space volume of gas in the compression and expansion chamber.

[0022] The three lengths mentioned above, by which the spiral groove 21 is extended by the recess 23 in a direction tangential to the axis of rotation A of the central screw, each have their advantages and disadvantages and can be useful depending on the desired effect. A leakage of pressurized gas from the gas port 12 to the star rotor port 13 due to a temporary direct connection between the gas port 12 and the star rotor port 13 represents a certain loss of efficiency in the single-screw engine. A dead volume in the compression and expansion chamber causes over-compression of the gas in the compression and expansion chamber at the end of the compression process and excessive vacuum in the compression and expansion chamber at the beginning of the expansion process, thus also representing a certain loss of efficiency in the single-screw engine.Depending on the specific design of the single-screw machine, the efficiency loss due to leakage or the efficiency loss due to dead space volume may be greater. The optimal length by which the spiral groove 21 is extended by the recess 23 in a direction tangential to the axis of rotation A of the central screw can be determined for a specific single-screw machine through simple tests and by measuring the efficiency of the machine in each test. For example, one can start with a central screw 2 without a recess 23, which is then provided with an increasingly longer recess 23. The same central screw 2 can always be used, with the recess 23 simply being incrementally enlarged.Starting from a central screw 2 without a recess, the efficiency should increase with the increasing length of the recess 23, due to the gradual reduction of the dead space volume, until maximum efficiency is reached and then decreases again due to the increasing losses from the increasing leakage.

[0023] Similar to the thinning of the partition wall 14 known from the prior art, the design variant of the recess 23, which projects over part of the partition wall 14 and provides an extended access to the gas opening 12, presents the problem that the function of the partition wall 14 as a seal between the gas opening 12 and the star rotor opening is impaired because the effective separation thickness between the star rotor opening 13 and the access to the gas opening 12 is reduced. Even with the present recess 23, there is a leakage of pressurized gas from the gas opening 12 through the recess 23, across the partition 14, and to the star rotor opening 13. However, with the present recess 23 in the central screw 2, the effective separation thickness between the star rotor opening 13 and the gas opening 12 is reduced only exactly once per compression or expansion cycle, and this occurs very temporarily at the end of the compression or expansion cycle.At the beginning of the expansion, when the recess 23 is rotated over the partition 14, this represents a significant improvement over the prior art thinning of the partition 14. This is because the leakage from the compression and expansion chamber to the star rotor opening occurs continuously throughout the entire compression and expansion process via the thinned partition 14, and not only temporarily at the end of compression or the beginning of expansion. The present recess 23 therefore ensures a better seal against leakage across the partition 14 to the star rotor opening.

[0024] The recess 23 according to the invention in the central screw at the closed end of the spiral groove prevents overcompression of the gas in the compression and expansion chamber at the end of the compression process and excessive vacuum in the compression and expansion chamber at the beginning of the expansion process. The enlargement 15 of the gas opening in the partition 14 towards the star rotor opening, known from the prior art, is therefore only partially present (see figure 23). Figure 1b ) or not at all (see above). Figure 1a) is necessary, and the partition 14 needs to have no dilution at all or only a slight dilution. This ensures a better seal against leaks to the star rotor opening. Another advantage of the invention is the strengthening of the partition 14, which has a positive effect on the service life of the compressor. There is a considerable pressure difference between the compression and expansion chamber, in which gas is compressed to high pressure, and the star rotor opening, in which the pressure of the low-pressure side prevails. A strengthened partition 14 without dilution or with a slight dilution can better withstand this pressure difference and is less susceptible to unwanted deformation.

Claims

1. A single-screw machine for the compression and / or expansion of a gas comprising a housing in which a central screw (2) and at least one star rotor (3) are rotatably mounted, wherein the central screw (2) has spiral grooves (21) on its circumference (22) which have an open end (212) and a closed end (211), wherein the star rotor (3) has teeth (31) which engage with the spiral grooves (21) and move along the spiral grooves (21) when the central screw is rotated. characterized by the fact that in the central screw (2) at the closed end (211) of each spiral groove (21) a recess (23) is formed into which the teeth (31) of the star rotor (3) do not protrude when moving along the spiral groove (21).

2. Single-screw machine according to claim 1 characterized by the fact thata spiral groove (21) in the region of its closed end (211) has a first side surface (213) and a second side surface (214) on both sides of an inner edge (215), and the recess (23) is optionally designed: • exclusively in the first side surface (213), • exclusively in the second side surface (214), • in the first and in the second side surface (213, 214), • in the first side surface (213) and in the perimeter (22) of the central screw (2), • in the second side surface (214) and in the perimeter (22) of the central screw (2), or • in the first and in the second side surface (213, 214) and in the perimeter (22) of the central screw (2).

3. Single-screw machine according to claim 1 or claim 2 characterized by the fact that the recess (23) extends the spiral groove (21) at its closed end in a direction tangential to the axis of rotation (A) of the central screw (2) and against the direction of rotation of the central screw (2).

4. Single-screw machine according to one or more of claims 1 to 3 characterized by the fact that the central screw (2) is surrounded by an inner wall surface (11) of the housing, on which a gas opening (12) for the inlet and / or outlet of pressurized gas and a star rotor opening (13) through which the teeth (31) of the star rotor (3) protrude are located, a partition (14) is present between the gas opening (12) and the star rotor opening (13), and the length by which the spiral groove (21) is extended by the recess (23) in a direction tangential to the axis of rotation (A) of the central screw (2) is less than the thickness of the partition (14) between the gas opening (12) and the star rotor opening (13).

5. Single-screw machine according to one or more of claims 1 to 3 characterized by the fact thatthe central screw (2) is surrounded by an inner wall surface (11) of the housing, on which a gas opening (12) for the inlet and / or outlet of pressurized gas and a star rotor opening (13) through which the teeth (31) of the star rotor (3) protrude are located, a partition (14) is present between the gas opening (12) and the star rotor opening (13), and the length by which the spiral groove (21) is extended by the recess (23) in a direction tangential to the axis of rotation (A) of the central screw (2) is equal to the thickness of the partition (14) between the gas opening (12) and the star rotor opening (13).

6. Single-screw machine according to one or more of claims 1 to 3 characterized by the fact thatthe central screw (2) is surrounded by an inner wall surface (11) of the housing, on which a gas opening (12) for the inlet and / or outlet of pressurized gas and a star rotor opening (13) through which the teeth (31) of the star rotor (3) protrude are located, a partition (14) is present between the gas opening (12) and the star rotor opening (13), and the length by which the spiral groove (21) is extended by the recess (23) in a direction tangential to the axis of rotation (A) of the central screw (2) is greater than the thickness of the partition (14) between the gas opening (12) and the star rotor opening (13).

7. Single-screw machine according to one or more of claims 1 to 6 characterized by the fact thatthe central screw (2) is surrounded by an inner wall surface (11) of the housing, on which there is a gas opening (12) for the inlet and / or outlet of pressurized gas and a star rotor opening (13) through which the teeth (31) of the star rotor (3) protrude, wherein the partition (14) between the gas opening (12) and the star rotor opening (13) has a thinning (15) on the side of the gas opening (12).

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