Screw suppressor, each comprising a screw compressor and a screw expander, with force compensation

Abstract

The invention relates to a screw extruder (1) comprising a screw compressor (8) and a screw expander (9), wherein both the screw compressor (8) and the screw expander (9) each have a main rotor (18, 20) and a secondary rotor (19, 21) each with a helical toothing (4, 5, 6, 7) cooperating with the respective other rotor, and wherein the main rotors (18, 20) and the secondary rotors (19, 21) of the screw compressor (8) and screw expander (9) are each arranged on a common shaft (2, 3), wherein the screw compressor (8) is designed as a screw spindle compressor (8) and the screw expander (9) as a screw spindle expander (9), the main rotors (18, 20) and secondary rotors (19, 21) of which are designed for both the screw compressor (8) and the screw expander (9). for the screw expander (9) each have the same profile cross-section, but are twisted in opposite directions to each other,the twisting creates a chamber closure between the high-pressure side (12, 13) and the low-pressure side (11, 14) of the screw spindle compressor (8) and screw spindle expander (9), respectively.

Description

[0001] The invention relates to a screw expressor comprising a screw compressor and a screw expander, according to the preamble of claim 1.

[0002] A classic screw compressor comprises two helically wound rotors, either connected by a synchronous gearbox or with the contact between the rotors lubricated by an auxiliary fluid. These rotors are driven by an electric motor and compress a fluid from a low pressure level to a high pressure level. The internal volume ratio is achieved through the difference in surface area between the inlet and outlet, where the inlet area is significantly larger than the outlet area. The fluid thus passes through the machine diagonally in both the axial and vertical directions.The efficiency of conventional screw machines with an asymmetrical profile of a convex ("male") main rotor and a concave ("female") secondary rotor depends, among other things, on the high-pressure-side end gap, which must be adjusted to be as small as possible, since this gap connects the high-pressure side of the machine to the low-pressure side. In an expander, this process is reversed, so that a fluid is expanded from a high-pressure level to a low-pressure level, and the resulting torque can be converted into electrical power, for example, via a generator.

[0003] The pressure difference of such machines is limited to approximately 20 bar by the axial and radial pressure forces that occur.

[0004] In heating or cooling cycles, a fluid is first compressed using a compressor to achieve high pressures and temperatures. Heat is then transferred to a process or the environment via a heat exchanger. The fluid is then expanded. Heat can then be added back in via another heat exchanger, either through waste heat recovery, from the environment, or from the cooling process itself.

[0005] In such circuits, the fluid is typically expanded via a throttle, thereby dissipating exergy. By using an expander instead of a throttle, the pressure differential can be used for energy conversion. It is advantageous to position the expander and compressor on a common pair of shafts. This arrangement is called a combined expander / compressor or expressor. This reduces the number of components, requiring fewer bearings and seals. At most, a synchronizing gearbox is needed for the expressor. A generator can be omitted. Depending on the circuit, a motor may also be unnecessary, thus eliminating the need for a shaft bore to the atmosphere and its associated seal.

[0006] Depending on the circuit in which such a machine is used, it may still be necessary to handle very large pressure differentials (>20 bar), which is problematic with conventional screw compressors due to the high forces involved. Large pressure differentials can be required, for example, by the choice of refrigerant in conjunction with the desired pressure or temperature level at the compressor outlet. In this context, the use of supercritical carbon dioxide (sCO2) as a non-toxic refrigerant has become increasingly interesting in recent years. It transitions to a supercritical state at moderate temperatures and high pressures, thus offering applications for heat recovery systems.

[0007] In US patent 6,644,045 B1, the arrangement is used as an expressor with an asymmetric screw expander and compressor to balance some of the gas forces. However, in this system, it is necessary that the fluid within the expander is in the multiphase region, so that the expander is liquid-lubricated and thus synchronizes the compressor. Therefore, the gaps of the compressor must be larger than those of the expander to prevent the rotors of the compressor from contacting each other.

[0008] US patent 4,291,547 B describes a refrigeration cycle that also uses a screw expander instead of an expansion valve to increase overall cycle efficiency. It refers to screw compressors of the Lysholm type (asymmetrical). Furthermore, the expander and compressor are of different sizes and not mounted on common shafts, so the compensation of pressure forces is not addressed.

[0009] WO 1990004107 A1 proposes a combined expander and compressor mounted on a single shaft, with a common outlet port for both. Accordingly, the pressure level at the expander inlet is significantly higher than at the common outlet, and the pressure level at the compressor inlet is significantly lower than at the common outlet. In this way, the expander's power output can be sufficient to drive the compressor without an additional motor, even at the same mass flow rate. This machine is not suitable for balancing pressure forces.

[0010] In his article "Test results of a screw type expander / compressor and the implication of phase separators on the refrigeration process" from the International Refrigeration and Air Conditioning Conference 2004, Paper 720, Ohman uses a screw expander to drive a screw compressor on a common shaft. Both have an asymmetric rotor profile. The underlying idea in this article is to increase the overall efficiency of a refrigeration cycle. In this case, expansion occurs from the expander into the wet vapor region. The liquid phase is separated, and the gas phase is compressed to an intermediate pressure lower than the expander inlet pressure. Pressure equalization is not the primary objective here.

[0011] US Patent 6,185,956 B1 describes a pair of screw engines with an inlet on the high-pressure side where a fluid is drawn in in liquid phase and then expanded into the wet steam region. A radial outlet, located approximately in the center of the engine, then expels a portion of the multiphase fluid. The remaining fluid is intended to be compressed as steam along the remaining rotor length during further rotation until it is finally expelled. The patent does not address the balancing of pressure forces, and a phase transition is required.

[0012] Both US patent 2005 / 0223734 A1 and the article by Stosic, Smith, and Kovacevic, "A twin screw combined compressor and expander for CO2 refrigeration systems," International Compressor Engineering Conference 2002, Paper 1591, present a screw compressor in which an expander and a compressor share a single shaft. The expander is significantly shorter than the compressor and is intended to reduce the compressor's power consumption in a CO2 refrigeration cycle at large pressure differentials. A motor is required to drive the compressor. Furthermore, an arrangement is described in which equal inlet and outlet pressures for the expander and compressor can balance the axial forces at large pressure differentials (approx. 60 bar). However, the radial forces can only be reduced by approximately 20%, which still results in radial forces of approximately 220 kN per rotor.In particular, screw machines with an asymmetrical profile are described and the special feature highlighted is that such machines can be switched between expander and compressor operation when the direction of rotation changes, but also, when the direction of rotation remains the same, the radial position of the high-pressure and low-pressure nozzles can be reversed.

[0013] DE 603 ​​18 522 T2 describes a refrigeration system with a main compressor and an expansion screw compressor. In this system, a conventional screw compressor is used to expand a partially condensing gas. The rotational energy of the screw compressor, generated by the expanding gas, is used to drive a screw compressor. The partially expanded gas is then recompressed in the screw compressor and returned to the cycle. The gas expansion screw compressor and the screw compressor are mounted on continuous drive shafts, allowing the kinetic energy recovered during expansion in the screw compressor to be transferred directly to the screw compressor via these shafts and used to compress the partially expanded gas.This improves the energy balance of the cycle while simultaneously reducing the reaction forces and mechanical bearing loads of the screw expander and screw compressor, since the forces generated in the screw expander and screw compressor are partially opposed and at least partially compensate for each other. The expander functions like a gearbox lubricated by the fluid in the working chamber, with no gap between the male and female rotors of the expander, ideally resulting in only a thin film of fluid. However, this requires a high fluid content (at least 70%) for lubrication. In contrast, a gap is specified for the compressor.The type of gearing between the screw machine and screw compressor stage only allows for an insufficient compensation of acting forces; moreover, the inlet area is limited by the design of the inflow into the expanding screw machine, which also makes it difficult to axially compensate for forces occurring between the screw expander and screw compressor.

[0014] The aforementioned prior art demonstrates that combining an expander with a compressor can be advantageous in heating and cooling circuits. Since, for example, supercritical carbon dioxide is becoming increasingly attractive as a refrigerant due to its properties, machines suitable for very large pressure differentials (>20 bar) are necessary. However, only the use of expanders with asymmetrical profile shapes and geometrically different cross-sections on the main and secondary rotors is described.

[0015] However, operating such machines with an expanded motor combined with a compressor, especially for higher pressure differences of more than 20 bar, is problematic to impossible, since the mechanical load on the rotating components of the expanded motor and compressor is particularly high, requiring complex designs and supports for the forces occurring in the machine and potentially causing significant wear.

[0016] The object of the present invention is therefore to provide a combination of an expander with a compressor that avoids these disadvantages or at least significantly minimizes them.

[0017] The solution to the problem according to the invention, with respect to the screw extruder, results from the characterizing features of claim 1 in conjunction with the features of the preamble. Further advantageous embodiments of the invention are set forth in the dependent claims.

[0018] The invention relates to a generic screw expressor comprising a screw compressor and a screw expander, in which both the screw compressor and the screw expander each have a main rotor and a secondary rotor with each having a twisted toothing that interacts with the other rotor, and the main rotors and the secondary rotors of the screw compressor and screw expander are each arranged on a common shaft.Such a generic screw expressor is further developed in a manner according to the invention by designing the screw compressor as a screw spindle compressor and the screw expander as a screw spindle expander, which have the same profile cross-section but are twisted in opposite directions to each other, wherein the twisting provides a chamber closure between the high-pressure side and the low-pressure side of both the screw spindle compressor and the screw spindle expander.

[0019] The present invention proposes using a screw machine instead of a conventional screw machine with a typically asymmetrical profile and different cross-sectional areas on the main and secondary rotors. In this machine, both rotors have the same cross-sectional area but are twisted in opposite directions. Designing the screw expander and screw compressor as screw spindles with identical cross-sectional areas on the main and secondary rotors, but with opposing twists, offers significant advantages in the arrangement according to the invention. Firstly, the high-pressure-side end gap does not need to be small for the efficiency of the screw compressor; on the contrary, it should even be somewhat larger to allow axial filling of the screw compressor and screw expander.Thus, there is no problem with the precise adjustment of this gap, which is problematic for screw compressors and screw expanders on continuous shafts when considering manufacturing tolerances and thermal expansion. Furthermore, the inlet and outlet areas are significantly larger due to the axial filling and unloading compared to conventional screw machines, thereby reducing inlet and outlet throttling losses and enabling significantly higher rotational speeds than with conventional screw machines. According to the invention, the arrangement of a screw spindle compressor and a screw spindle expander on common shafts results in a screw expressor that, moreover, allows for a comparatively simple design due to internal force balancing of axial and vertical forces with only minor horizontal forces.The respective main and auxiliary rotors are twisted in such a way that the twisting of the rotor profiles alone is sufficient to separate the high- and low-pressure sides, eliminating the need for axial control edges. This is precisely why the term "spindle" is used, distinguishing it from the gearing of a conventional screw machine. Radial control edges can still be present in the housing of a screw spindle compressor and a screw spindle expander; however, the end faces of the rotors then experience the same pressure across their entire surface. Screw expanders and screw compressors can be designed with matching cross-sectional profiles for the main and auxiliary rotors. Therefore, it is conceivable that the main and auxiliary rotors of the screw expander have the same cross-sectional profile, while the main and auxiliary rotors of the screw compressor have different, compatible cross-sectional profiles.However, it is also conceivable that the main rotor and secondary rotor of both screw compressors and screw expanders have the same profile cross-section.

[0020] In a further embodiment, the spindle-shaped rotors of the screw compressor and screw expander should exhibit such a large degree of twist that no connection is formed between the respective high-pressure and low-pressure chambers at the end faces of the screw compressor and screw expander. This allows for more efficient expansion and compression of the fluid conveyed in these chambers. The chamber is sealed off from the high-pressure and low-pressure chambers by the axial overlap of the trailing rotor tooth before the encapsulated working chamber opens towards the high-pressure side. Therefore, changes to the chamber volume do not need to be achieved through the shape of the inlet and outlet surfaces, but can be accomplished, for example, by changing the rotor pitch in the axial direction.

[0021] In one particular design, it is advantageous if both rotors of the screw compressor and screw expander have a symmetrical cross-sectional profile, for example, a symmetrical cycloidal profile. Such profile designs are known and well-established. However, it is also conceivable to use asymmetrical cross-sectional profiles for the rotors of the screw compressor and screw expander, provided that the cross-sectional profiles of the main and secondary rotors remain identical.

[0022] In a first advantageous embodiment, it is conceivable that the screw spindle compressor and the screw spindle expander each have spatially separate high-pressure ports, preferably arranged on opposite sides, in the area of ​​the connecting shafts between the screw spindle compressor and the screw spindle expander, and that the respective low-pressure ports, preferably also arranged on opposite sides, are located at opposite ends of the connecting shaft. The high-pressure section of both the screw spindle compressor and the screw spindle expander is then located separately from each other approximately midway between the screw spindle compressor and the screw spindle expander and can therefore be easily connected to the corresponding feed lines.In this configuration, the low-pressure section of both the screw compressor and the screw expander is located at opposite ends of the connecting shafts and is also easily accessible. Due to the high-pressure and low-pressure ports being positioned on opposite sides of the rotors, the pressure of the fluid being processed has a beneficial effect on the mechanical structure of the screw expander, allowing the forces acting on it to compensate for each other.

[0023] In an alternative embodiment, it is also conceivable that the screw spindle compressor and screw spindle expander each have spatially separated, preferably on opposite sides, low-pressure ports in the area of ​​the connecting shaft between the screw spindle compressor and the screw spindle expander, and that the respective, preferably on opposite sides, high-pressure ports are arranged at the opposite ends of the connecting shaft.

[0024] It is also advantageous to have a separation between the screw spindle compressor and the screw spindle expander, with a shaft passage for each of the connecting shafts. This allows the adjacent fluid-carrying areas, depending on the arrangement of the low-pressure and high-pressure areas, to be reliably separated from one another, and also provides additional support for the through shafts.

[0025] It is particularly advantageous if the rotors of the screw spindle compressor and screw spindle expander rotate in a meshing motion without mechanical contact. This prevents the typical problems that arise from the meshing of rotors due to internal synchronization of their rotational movement when the rotors roll against each other in contact. To achieve smooth rotor operation in this case, adequate lubrication between the contacting areas of the rotors must be ensured. A sufficiently large gap between the rotors, in conjunction with a separate synchronization gear in the screw spindle expander according to the invention, avoids these problems.

[0026] In a further embodiment, a common gearbox can be arranged between the connecting shafts of the screw spindle compressor and the screw spindle expander such that the rotational movements of the rotors of the screw spindle compressor and the screw spindle expander are synchronized with each other. By using a synchronizing gearbox, the screw spindle compressor according to the invention is particularly suitable for processes with pure gas phases or fluids in supercritical conditions. A transition to the wet steam region for the lubrication of the screw spindle expander is then unnecessary.

[0027] Furthermore, it is conceivable that, as with classic screw machines with an asymmetrical profile, the direction of rotation of the screw extruder could be reversed to switch between compressor and expander operation. However, unlike screw machines with an asymmetrical profile (where the main and auxiliary rotors have different cross-sectional areas), an exchange of the high-pressure and low-pressure nozzles is not possible, as the axial position of the high-pressure and low-pressure nozzles is fixed depending on the pitch profile – and thus the internal volume ratio.

[0028] A particular advantage is that the inventive arrangement of the high-pressure and low-pressure ports of the rotors of the screw spindle compressor and screw spindle expander, preferably on opposite sides of the rotors, causes the axial and vertical forces of the screw spindle compressor and screw spindle expander to act in opposite directions and largely cancel each other out. For this purpose, forces in three spatial directions are defined: axial forces point along the rotor axis, horizontal forces point in the direction of the shortest connecting line between the rotor axes, and vertical forces are perpendicular to the other two forces. Due to the large engagement of the rotor teeth and the fact that the two rotors of a screw spindle compressor are identical with respect to their profile shapes, the horizontal forces are small in contrast to screw machines with an asymmetrical profile.Vertical forces are present, but also significantly smaller than in conventional screw compressors. In contrast, axial forces are somewhat larger in individual screw compressors, since the entire pressure difference between high and low pressure acts on the axial projection area. By arranging a screw compressor and a screw expander on a common rotor pair in the inventive arrangement as a screw compressor, the axial and vertical forces of the screw expander and screw compressor act in opposite directions, while the horizontal forces act in the same direction.If, for example, both machines (screw spindle expander and screw spindle compressor) are the same size and operate at the same pressures on the high-pressure and low-pressure sides of each machine, the axial and vertical forces can be balanced, and the horizontal forces are inherently small. In a study using chamber model simulation, a screw expressor for supercritical carbon dioxide was designed in which the resulting horizontal and vertical forces per rotor at a pressure differential of 70 bar are less than 2 kN, representing only about 1% of the resulting forces achieved in US 20050223734 A1 with an expressor using asymmetric screw machines. The axial forces are completely balanced in this configuration.

[0029] In a further embodiment, it is also conceivable that the screw spindle compressor and screw spindle expander have essentially the same diameter. In particular, if the same pressures are present on the high-pressure and low-pressure sides of both the screw spindle compressor and the screw spindle expander, a largely complete balancing of axial and vertical forces is possible.

[0030] Furthermore, it is conceivable that, in the case of pressure differences between the screw spindle compressor and the screw spindle expander, the axial and vertical forces could be balanced by changing the rotor size while maintaining the same center distance. If the pressure difference at the screw spindle compressor differs from that at the screw spindle expander, this could be adjusted by changing the rotor size while maintaining the same center distance. Since the center distance corresponds to the average of the outer and inner diameters of the respective machines, a larger pressure difference at one machine could be addressed by reducing the outer diameter and increasing the inner diameter, thus reducing the corresponding projection area. The required chamber volume for a given mass flow rate could then be corrected by adjusting the rotor pitch.

[0031] A particular advantage is that the screw compressor can be used for media circuits where large pressure differences occur, whereby in the simplest case the screw spindle expander and screw spindle compressor are approximately the same size and should have almost the same pressures on the high and low pressure sides.

[0032] In a further embodiment, the screw expressor can be used for media circuits with a closed loop, in which the mass flow through the screw spindle expander corresponds to the mass flow through the screw spindle compressor when additional power is added to the screw expressor or the screw spindle compressor by a motor.

[0033] Alternatively, it is also conceivable that the screw expressor is used for two separate circuits or a split circuit, in which the mass flow through the screw spindle compressor is smaller than through the screw spindle expander, so that the screw spindle expander alone drives the screw spindle compressor and the screw expressor can be operated with a hermetically sealed outer casing. This eliminates the need for an externally driven rotating shaft that requires sealing against the atmosphere.

[0034] Alternatively, it is also conceivable that a generator can be connected to the screw expressor if the power of the screw spindle expander is greater than that of the screw spindle compressor and the speed of the screw expressor is to be limited.

[0035] It is also conceivable to use the screw expressor for processes with pure gas phases or fluids in supercritical states through the existing synchronization gear.

[0036] The screw expander is preferably used for processes involving pressure and / or temperature increases of a fluid at high pressures using a screw spindle compressor. In a further embodiment, waste heat from processes can be utilized to evaporate or heat the cooler fluid at the screw spindle expander outlet and then reheat it to a pressure and / or temperature level by the screw spindle compressor for reintroduction into a primary process. Since the working fluid is heated by compression, temperature increases of >50°C are possible in heat recovery systems.

[0037] A particularly preferred embodiment of the screw expressor according to the invention is shown in the drawing.

[0038] They show: Figure 1 - a schematic three-dimensional representation of the screw expressor with a screw spindle compressor and a screw spindle expander and the rotors each arranged on continuous shafts, Figure 2 - the main rotors of the screw expressor according to Figure 1 on a continuous shaft and indicated volume flows of fluids passing through the screw spindle compressor and the screw spindle expander of the screw expressor, Figure 3 - a schematic top view of the screw expressor with screw spindle compressor and screw spindle expander in a housing that is only indicated according to Figure 1 as well as the bearings and synchronization gears arranged thereon, Figure 4 - an enlarged view of the rotors of the screw expressor and their engagement with each other according to Figure 1Figure 5 - a section through an exemplary design of the profile cross-section of the rotors of screw spindle compressor and screw spindle expander according to Figure 1 Figure 6 - a graphical representation of the combined forces of the screw expressor according to the invention for equal inlet and outlet pressures at screw spindle compressor and screw spindle expander.

[0039] In the Figure 1The figure shows a schematic three-dimensional representation of the screw expressor 1 with a screw spindle compressor 8 and a screw spindle expander 9, and the rotors 18, 19 and 20, 21 respectively, arranged on continuous shafts 2, 3. All ancillary components of the screw expressor 1, such as the housing 10, bearings 15, etc., have been omitted. The two continuous shafts 2, 3 are visible, on which the two rotors 18, 19 of the screw spindle compressor 8 are arranged on the left side, and, spaced apart from them, the two rotors 20, 21 of the screw spindle expander 9 are arranged on the right side. The two corresponding rotors 18, 19 of the screw spindle compressor 8 mesh with each other in a manner known per se, as do the two corresponding rotors 20, 21 of the screw spindle expander 9.

[0040] In this embodiment, the profile cross-sectional shape of the rotors 18, 19 and 20, 21 are symmetrically designed profiles, which can be described as a symmetrical cycloidal profile shape according to Figure 5The profiles can be designed in a conventional manner and are known in themselves. However, asymmetrical profile cross-sections are also conceivable. The two rotors 18, 19 of the screw spindle compressor 8 are identical in design but have opposing pitches, so that they can, in principle, mesh with each other. However, the two rotors 18, 19 of the screw spindle compressor 8 are arranged axially spaced apart from each other such that the profiles of the rotors 18, 19 do not touch each other and can therefore mesh without contact. Unlike asymmetrical profile shapes, which are widespread in screw machines, the interacting rotors 18, 19 do not have a "male" and "female" profile design, which has particularly positive effects on the forces from the operation of the screw compressor 1. The same applies to the rotors 20, 21 of the screw spindle expander 9.

[0041] The synchronization of the rotation of the two shafts 2, 3 of the screw extruder 1 is therefore not achieved by the contact of the rotors 18, 19 and 20, 21 and a lubricating auxiliary fluid as in many conventional screw machines, but by means of a Figure 3 The gear unit 16, shown only as an indication, is connected to the two shafts 2, 3 and rotates synchronously with each other.

[0042] In the arrangement and design of the screw spindle expander 9 and screw spindle compressor 8 described above, it is important that both rotate synchronously via the shaft 2 connecting the main rotors 18, 20 and the shaft 3 connecting the auxiliary rotors 19, 21, and that the two shafts 2, 3 transmit the forces and loads acting on the rotors 18, 19 and 20, 21 between the screw spindle expander 9 and the screw spindle compressor 8. The screw spindle expander 9 and the screw spindle compressor 8 therefore form a compact unit, which can be referred to as the screw compressor 1.

[0043] In the Figure 2 are only the main rotors 18, 20 of the screw expressor 1 according to Figure 1The diagram shows a continuous shaft 2 and the indicated fluid flow rates as they pass through the screw expressor 1. The high-pressure section 12 of screw spindle expander 9 and the high-pressure section 13 of screw spindle compressor 8 are arranged approximately centrally within the space between screw spindle expander 9 and screw spindle compressor 8, while the two low-pressure sections 11 and 14 are located at opposite ends of shaft 2. This arrangement also determines the flow direction of the two fluid flows through the screw expressor 1. This arrangement also results in the largely complete compensation of forces within the screw expressor 1. The axial forces can be balanced by positioning the high-pressure and low-pressure ports 11, 12, 13, and 14 either both centrally or both at the ends of the rotors 4, 6 and 5, 7.The vertical forces can be largely compensated by applying force to the rotors 4, 6 and 5, 7 of the screw spindle compressor 8 and the screw spindle expander 9 from opposite sides (once from above and once from below). Due to the spindle design of the rotors 18, 19 and 20, 21, the horizontal forces are inherently low because of the large degree of twisting and can be absorbed using conventional bearing techniques.

[0044] In the Figure 3 is a purely schematic top view of the screw expressor 1 with screw spindle compressor 8 and screw spindle expander 9 in a housing 10 that is only indicated according to Figure 1as well as the bearings 15 and synchronization gear 16 arranged thereon, wherein the bearings 15 of the shafts 2, 3 and the synchronization gear 16 can be designed in a manner known per se and are either largely accessible outside the housing 10 or, as not shown here, also arranged inside the housing. The screw spindle expander 9 and the screw spindle compressor 8 of the screw expressor 1 are concealed and sealed inside the housing 10.

[0045] In the Figure 4 The two pairs of rotors 18, 19 and 20, 21 of the screw expressor 1 and their engagement with each other are shown again in an enlarged view according to Figure 1 The volume flow through the rotors of screw spindle compressor 8 and screw spindle expander 9 is also indicated.

[0046] Due to the view of Figure 4 noticeable twisting of the in Figure 5Working spaces are formed between the two rotors 18, 19 and 20, 21 in a manner known per se, with the length of the rotors 18, 19 and 20, 21 being designed such that the working spaces formed are at least temporarily closed to inlet 11, 12 and outlet 13, 14.

[0047] Figure 5 shows a cross-section through an exemplary design of the rotors 18, 19 and 20, 21 of screw spindle compressor 8 and screw spindle expander 9 according to Figure 1 The cross-sections of rotors 18 and 19 are identical, as are those of rotors 20 and 21. The two rotors 20 and 21 shown here are arranged offset from each other by an angle of 90° and rotate synchronously. The same applies to rotors 18 and 19 of the screw compressor 8.

[0048] Figure 6Figure 1 shows a graphical representation of the combined forces of the screw compressor 1 according to the invention for equal inlet and outlet pressures at screw spindle compressor 8 and screw spindle expander 9. It is immediately apparent that the dotted line, representing the simulated combined axial forces, largely balances the opposing axial loads of screw spindle compressor 8 and screw spindle expander 9, whereas the dashed line for the vertical forces initially drops with increasing pressure difference between the high- and low-pressure ports (abscissa) and then slowly rises again. The horizontal forces, which cannot be balanced according to the invention, increase approximately linearly and are also small. Item number list

[0049] 1- Screw compressor or screw spindle compressor 2- Through shaft main rotors 3- Through shaft auxiliary rotors 4- Serration main rotor screw spindle compressor 5- Serration main rotor screw spindle expander 6- Serration auxiliary rotor screw spindle compressor 7- Serration auxiliary rotor screw spindle expander 8- Screw spindle compressor 9- Screw spindle expander 10- Housing 11- Low-pressure inlet screw spindle compressor 12- High-pressure inlet screw spindle expander 13- High-pressure outlet screw spindle compressor 14- Low-pressure outlet screw spindle expander 15- Shaft bearing 16- Synchronizing gear 17- Separation screw spindle compressor / screw spindle expander 18- Main rotor screw spindle compressor 19- Auxiliary rotor screw spindle compressor 20- Main rotor Screw spindle expander 21 - Auxiliary rotor screw spindle expander

Claims

1. Screw expressor (1), comprising a screw compressor (8) and a screw expander (9), wherein both the screw compressor (8) and the screw expander (9) each have a main rotor (18, 20) and a secondary rotor (19, 21) each with a twisted toothing (4, 5, 6, 7) cooperating with the other rotor, and the main rotors (18, 20) and the secondary rotors (19, 21) of the screw compressor (8) and screw expander (9) are each arranged on a common shaft (2, 3), characterized by the fact thatThe screw compressor (8) is designed as a screw spindle compressor (8) and the screw expander (9) as a screw spindle expander (9), whose main rotors (18, 20) and secondary rotors (19, 21) have the same profile cross-section, but are twisted in opposite directions to each other, whereby the twisting provides a chamber closure between the high-pressure side (12, 13) and the low-pressure side (11, 14) of each screw spindle compressor (8) and screw spindle expander (9).

2. Screw expressor (1) according to claim 1, characterized by the fact that The rotors (18, 19, 20, 21) of screw spindle compressor (8) and screw spindle expander (9) have such a large twist in spindle form that no connection is formed between the respective end-face machine gaps of screw spindle compressor (8) and screw spindle expander (9) between the associated high-pressure chamber (12, 13) and low-pressure chamber (11, 14).

3. Screw extruder (1) according to any one of the preceding claims, characterized by the fact that the rotors (18, 19, 20, 21) of screw spindle compressor (8) and screw spindle expander (9) rotate meshing with each other without mechanical contact.

4. Screw extruder (1) according to one of the preceding claims, characterized by the fact that Both rotors (18, 19, 20, 21) of screw spindle compressor (8) and screw spindle expander (9) respectively have a symmetrical profile cross-section, preferably a symmetrical cycloidal profile as a cross-section.

5. Screw expressor (1) according to any one of the preceding claims, characterized by the fact thatThe screw spindle compressor (8) and screw spindle expander (9) each have spatially separated, preferably arranged on opposite sides, high-pressure ports in the area of ​​the connecting shaft (2, 3) between the screw spindle compressor (8) and the screw spindle expander (9), and the respective, preferably arranged on opposite sides, low-pressure ports are arranged at the opposite ends of the connecting shaft (2, 3).

6. Screw extruder (1) according to any one of the preceding claims, characterized by the fact thatThe screw spindle compressor (8) and screw spindle expander (9) each have spatially separated, preferably on opposite sides, low-pressure ports in the area of ​​the connecting shaft (2, 3) between the screw spindle compressor (8) and the screw spindle expander (3), and the respective, preferably on opposite sides, high-pressure ports are arranged at the opposite ends of the connecting shaft (2, 3).

7. Screw extruder (1) according to any one of the preceding claims, characterized by the fact that A separation (17) with a shaft passage for the connecting shafts (2, 3) of screw spindle compressor (8) and screw spindle expander (9) is arranged between screw spindle compressor (8) and screw spindle expander (9).

8. Screw expresser (1) according to any one of the preceding claims, characterized by the fact thata common gearbox (16) between the connecting shafts (2, 3) of screw spindle compressor (8) and screw spindle expander (9) is arranged such that the rotational movement of the rotors (18, 19, 20, 21) of screw spindle compressor (8) and screw spindle expander (9) is synchronized with each other.

9. Screw expresser (1) according to one of the preceding claims, characterized by the fact that For switching between compressor and expander operation, as with classic screw machines with an asymmetrical profile, the direction of rotation of the screw expresser (1) can be reversed.

10. Screw expresser (1) according to any one of the preceding claims, characterized by the fact thatThe arrangement of the rotors (18, 19, 20, 21) of screw spindle compressor (8) and screw spindle expander (9) on common shafts (2, 3), preferably on opposite sides of the rotors, causes the axial and vertical forces of screw spindle compressor (8) and screw spindle expander (9) to act in opposite directions and largely cancel each other out.

11. Screw expresser (1) according to any one of the preceding claims, characterized by the fact that The screw spindle compressor (8) and screw spindle expander (9) have essentially the same diameters.

12. Screw expresser (1) according to one of the preceding claims, characterized by the fact that The equal pressures on the high-pressure side (12, 13) and the low-pressure side (11, 14) of the screw spindle compressor (8) and screw spindle expander (9) allow for a large degree of compensation of the axial forces and the vertical forces.

13. Screw expressor (1) according to claim 12, characterized by the fact that In the case of pressure differences between screw spindle compressor (8) and screw spindle expander (9), a balance of the axial forces and the vertical forces can be achieved by changing the rotor size with the same center distance.

14. Screw expressor (1) according to any one of the preceding claims, characterized by the fact that The screw expressor can be used for media circuits where large pressure differences occur.

15. Screw expresser (1) according to any one of the preceding claims, characterized by the fact that the screw expressor (1) can be used for media circuits with a closed circuit in which the mass flow through the screw spindle expander (9) corresponds to the mass flow through the screw spindle compressor (8) when additional power is added to the screw expressor (1) by a motor.

16. Screw expressor (1) according to any one of claims 1 to 14, characterized by the fact thatthe screw expressor (1) can be used for two separate circuits or a split circuit, in which the mass flow through the screw spindle compressor (8) is smaller than through the screw spindle expander (9), so that the screw spindle expander (9) drives the screw spindle compressor (8) and the screw expressor (1) can be operated hermetically sealed to the outside.

17. Screw expresser (1) according to one of the preceding claims, characterized by the fact that a generator can be connected to the screw expressor (1) if the power of the screw spindle expander (9) is greater than that of the screw spindle compressor (8) and the speed of the screw expressor (1) is to be limited.

18. Screw expresser (1) according to any one of the preceding claims, characterized by the fact that the screw expressor (1) can be used for processes with pure gas phases or fluids in supercritical states through the existing synchronization gear (16).

19. Screw expresser (1) according to one of the preceding claims, characterized by the fact that The screw expressor (1) can be used for processes involving an increase in the pressure and / or temperature of a fluid by means of the screw spindle compressor (8) at high pressures.

20. Screw expressor (1) according to claim 19, characterized by the fact that Waste heat from processes can be used to evaporate or heat the colder fluid at the outlet of the screw spindle expander (9) and to bring it back to a pressure and / or temperature level through the screw spindle compressor (8) in order to add it back to a primary process.

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