Piston compressor and method of operating same

Abstract

A piston compressor 1 for compressing gas comprises a cylinder 2, and also comprises a piston 3, a piston rod 16, a packing seal 12, a crosshead 17, and a drive shaft 21. The piston 3 is arranged in the cylinder 2 so as to be movable in a longitudinal direction L. The piston 3 is connected to the crosshead 17 via the piston rod 16. The packing seal 12 is arranged between the piston 3 and the crosshead 17. The piston rod 16 extends through the packing seal 12. The crosshead 17 is driven by the drive shaft 21. A controllable magnetic bearing 13 is arranged between the piston 3 and the crosshead 17. The magnetic bearing 13 applies a magnetic force F to the piston rod 16 at least perpendicular to the longitudinal direction L. m The control device 22 can detect the magnetic force F exerted on the piston rod 16 by the magnetic bearing 13. m Control.

Description

[Technical field]

[0001] The present invention relates to a piston compressor and a method for operating the same. [Background technology]

[0002] Patent document 1 discloses a piston compressor having a horizontally extending cylinder in which a piston that is horizontally reciprocable is arranged. This piston compressor has the disadvantage that guide rings and / or sealing rings arranged on the piston are subject to relatively high wear and that the piston compressor can only be operated at relatively low rotational speeds. Patent document 2 discloses a piston compressor with a vertically extending cylinder. The piston can be designed as a labyrinth piston or as a piston with captured piston rings. This piston compressor also has the disadvantage that wear can occur. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2014 / 139565 [Patent Document 2] German Patent Application Publication No. 3805670 Summary of the Invention [Problem to be solved by the invention]

[0004] SUMMARY OF THE DISCLOSURE The object of the present invention is to provide a piston compressor which is more advantageous. Preferably, the piston compressor comprises a piston which is arranged so as to be movable in a horizontal or vertical direction. [Means for solving the problem]

[0005] This problem is solved by a piston compressor having the features of claim 1. The dependent device claims relate to further advantageous embodiments. 8 The solution is furthermore solved by a method having the features of: The dependent method claims relate to further advantageous method steps.

[0006] This problem is solved in particular by a piston compressor for compressing gases. The piston compressor comprises a cylinder, a piston, a piston rod, a packing seal, a crosshead, a magnetic bearing and a drive shaft. The piston is arranged in a longitudinally movable manner in the cylinder. The piston is connected to the crosshead via the piston rod. A packing seal is arranged between the piston and the crosshead, through which the piston rod passes. The crosshead is driven by the drive shaft. A magnetic bearing is arranged between the piston and the crosshead. The magnetic bearing is capable of exerting a magnetic force on the piston rod at least perpendicular to the longitudinal direction. A sensor is arranged to detect a state variable of the piston compressor. The magnetic bearing is designed as a controllable magnetic bearing. A control device controls the magnetic force exerted by the magnetic bearing on the piston rod in dependence on the state variable. It is particularly preferred that the cylinder extends substantially horizontally.

[0007] The problem is further solved by a piston compressor, in particular for compressing gases. The piston compressor comprises a substantially horizontally extending cylinder and comprises a piston, a piston rod, a packing seal, a crosshead and a drive shaft. The piston is arranged to be longitudinally movable within the cylinder. The piston is connected to the crosshead via a piston rod. A packing seal is arranged between the piston and the crosshead, through which the piston rod extends. The crosshead is driven by the drive shaft. A controllable magnetic bearing is also arranged between the piston and the crosshead. The magnetic bearing is capable of exerting a magnetic force on the piston rod at least perpendicular to the longitudinal direction. A control device controls the magnetic force exerted by the magnetic bearing on the piston rod.

[0008] The problem is further solved in particular by a method for operating a piston compressor, which comprises a piston reciprocating longitudinally in a cylinder. The piston is driven via a piston rod. A magnetic force acts on the piston rod, which acts at least perpendicularly to the longitudinal direction. State variables of the piston compressor are detected. The magnetic force is controlled depending on the state variables. As a result, a magnetic force, preferably a relief force, acts on the piston via the piston rod. Particularly preferably, the longitudinal direction extends substantially horizontally.

[0009] The problem is further solved in particular by a method for operating a piston compressor, which comprises a piston reciprocating longitudinally in a cylinder, the longitudinal direction extending substantially horizontally. The piston is driven via a piston rod. A controllable magnetic force acting at least perpendicularly to the longitudinal direction is exerted on the piston rod. As a result, a relief force is exerted on the piston via the piston rod. The magnetic force is characterised in that it is controlled in dependence on a state variable.

[0010] The piston compressor according to the invention for compressing a gas comprises a controllable magnetic bearing arranged between a piston and a crosshead of the piston compressor. A piston rod connects the piston to the crosshead. The piston rod extends through the magnetic bearing. The magnetic bearing exerts a controllable magnetic attraction on the piston rod at least perpendicular to the extension direction of the piston rod. The piston compressor according to the invention also comprises a control device and at least one sensor. The control device is adapted to supply a current or power to an electromagnet arranged in the controllable magnetic bearing. The control device is adapted to adjust or change the supplied current or power depending on values ​​measured by the sensor in order to influence the position of the piston relative to the cylinder so that the piston at least temporarily has a favorable position in the cylinder. The controllable magnetic bearing is preferably designed as a radial bearing with a plurality of electromagnets, the electromagnets of which are arranged distributed in the circumferential direction and are controllable by the control device. However, it is also possible to design the magnetic bearing so that the magnetic force acts in only one direction or in only one dimension, for example by arranging two controllable electromagnets opposite each other (opposite each other) or symmetrically relative to the piston rod, so that the magnetic force exerted by these electromagnets on the piston rod acts in only one direction.

[0011] A piston compressor comprises at least one cylinder and a piston arranged to be movable back and forth in the cylinder. In a preferred embodiment, the interior of the cylinder, and therefore also the movement of the piston, extends horizontally or substantially horizontally. Such a piston compressor is also called a horizontal piston compressor. The magnetic bearing exerts a controllable magnetic attraction on the piston rod at least in a direction perpendicular to the extension direction of the piston rod, and thus exerts a vertical upward force on the piston rod, preferably in a direction opposite to gravity.

[0012] In a preferred embodiment, the piston, which is made movable in the horizontal direction, is provided with a so-called guide ring, which rests on the inner surface of the cylinder. The attractive and / or repulsive forces that the magnetic bearing exerts on the piston rod at least in the vertical direction have the effect that the contact force of the piston supported by the inner surface of the cylinder is reduced or that the piston or the guide ring no longer contacts the inner surface of the cylinder. The piston or the guide ring of the piston thus only rests on the inner surface of the cylinder with a reduced contact force and therefore reciprocates in the cylinder, particularly preferably without contacting the inner surface of the cylinder. In the case of a piston having a guide ring, the use of a magnetic bearing brings the advantage that the contact force of the guide ring on the inner surface of the cylinder and thus the wear of the guide ring is reduced, so that the service life or life cycle before the guide ring has to be replaced is longer. Furthermore, the piston compressor can be operated (operated) at a higher rotational speed if desired, so that preferably no increased wear or heating occurs.

[0013] Particularly preferably, the piston of the piston compressor according to the invention is designed as a labyrinth piston. Such a labyrinth piston, as known per se, has a labyrinth structure on the piston surface which serves to seal between the piston and the cylinder inner surface. The attractive force exerted by the magnetic bearing on the piston rod is preferably controlled so that the piston moving back and forth does not come into contact with the cylinder inner surface along the entire stroke path. However, the piston compressor according to the invention is also suitable for pistons, which have piston rings and, if necessary, are further provided with guide rings.

[0014] In a further preferred embodiment, the cylinder interior and therefore also the movement of the piston extend vertically or substantially vertically. The magnetic bearing exerts a controllable magnetic attractive force on the piston rod at least in a direction perpendicular to the extension direction of the piston rod and therefore exerts a force on the piston and the piston rod that extends radially or substantially radially with respect to the piston rod. The attractive force and / or repulsive force exerted by the magnetic bearing on the piston rod at least in the radial direction has the effect of reducing the contact force of the piston ring bearing on the cylinder inner surface, in particular the one-sided contact force. Since the piston or its piston rings, in particular pistons designed as labyrinth pistons, no longer contact the cylinder inner surface, the piston or the piston rings of the piston rest (rest) only with a reduced contact force on the cylinder inner surface, so that particularly preferably the labyrinth piston reciprocates in the cylinder without contacting the cylinder inner surface. The use of magnetic bearings reduces the wear of the piston rings, which has the advantage of increasing the service life of the piston compressor or the life cycle of the piston compressor before maintenance is required. There is also the option of operating the piston compressor at higher rotational speeds (rpm). If the piston compressor is equipped with a labyrinth piston, the use of magnetic bearings has the advantage that contact between the labyrinth piston and the cylinder inner surface can be even better avoided, since any eccentric arrangement of the labyrinth piston with respect to the cylinder interior can be at least partially compensated with the aid of the magnetic bearings, so that no mutual contact occurs. The use of magnetic bearings brings the additional advantage that the piston compressor can be safely operated without mutual contact occurring, even with a reduced gap width between the labyrinth piston outer surface and the cylinder inner surface. This reduction in the gap width increases the efficiency of the piston compressor and reduces losses during compression.

[0015] In a further preferred embodiment, the piston compressor comprises at least one piston and one cylinder, preferably a plurality of pistons and cylinders, which are preferably arranged on a common frame and are preferably driven by a common crankshaft. In a preferred embodiment, such a piston compressor is arranged on a ship. In calm sea conditions, the cylinders, and therefore also the movement of the pistons, are vertical or substantially vertical. In rough or stormy seas, as the wave height increases, the ship undergoes an increasing rolling or pitching movement, so that the entire piston compressor, and therefore also in particular the longitudinal direction of the piston rod, has an extension direction which is variable as a function of time depending on the wave movement (wave action) and deviates from the vertical by an angle β. In a preferred embodiment, the angle β, and preferably the angle β as a function of time, is measured as an additional state variable.

[0016] In ships, multi-stage piston compressors are used, for example, to compress exhaust gases accumulated in liquefied gas containers to a pressure of 200 bar to 500 bar (20 MPa to 50 MPa) and to use the compressed gas to fuel the ship's gas or diesel engines. Piston compressors arranged on ships are preferably controlled as a function of state variables and additional state variables such that the force exerted by the magnetic bearing at least in the radial direction on the piston rod is reduced, in particular the one-sided contact force, or the piston or the piston ring of the piston, and in particular the piston designed as a labyrinth piston, no longer contacts the cylinder inner surface. It is thus ensured on board ships that, even under waves, the piston or the piston ring of the piston compressor rests (rests) only with reduced contact force against the cylinder inner surface or, in particular, the labyrinth piston or the piston reciprocates in the cylinder without contacting the cylinder inner surface. The use of magnetic bearings provides the advantage that the wear of piston rings is reduced even under wave motion or the contact of the labyrinth structure of the labyrinth piston with the cylinder inner surface is avoided. Piston compressors arranged on ships have a longer service life or a longer life cycle before piston compressor maintenance is required, especially when the gap width between the piston outer diameter and the cylinder inner surface is small. The magnetic bearings are preferably controlled to have a damping effect on the piston rod radially relative to the piston rod longitudinal axis in order to damp the movement of the piston rod and the piston radially relative to the longitudinal axis, for example to reduce the maximum amplitude of the occurrence of resonant vibrations or other transverse vibrations of the piston caused by wave motion.

[0017] The wave motion, or the additional state variable that is measured and derived as a result, is a relatively slow process compared to the rotational speed of the piston compressor. The period of the water wave motion is 10 to 1000 times slower than the rotational period of the piston compressor, making it possible to pre-calculate the short-term changes of the additional state variable. Then, in order to feed this value into the control of the magnetic bearing, the predicted movement of the piston compressor based on the wave motion is predicted for a certain time point, for example in the range of 1 to 50 seconds, and the magnetic bearing is controlled by a predictive control that controls the magnetic bearing depending on the predicted movement. In this way, the magnetic bearing is controlled in such a way that the predicted movement of the piston compressor due to the wave motion is taken into account when influencing or controlling the position of the piston rod or piston.

[0018] The piston compressor according to the invention also has the advantage that it can be operated at higher rotational speeds or higher average piston speeds, since the piston or the guide ring no longer contacts the cylinder inner wall at all or only rests on the cylinder inner wall with a reduced contact force. Operation at such high rotational speeds (rpm) is particularly advantageous in piston compressors with so-called dry running pistons, i.e. labyrinth pistons, or in piston compressors with pistons with self-lubricating sealing rings, i.e. pistons with piston rings or sealing rings that are not oil-lubricated, i.e. also called unlubricated pistons. The controllable magnetic bearings can be used either as support bearings that hold the piston without contacting the cylinder inner wall, or as relief bearings by reducing the force that the piston exerts on the cylinder inner wall in case of contact with the inner wall. The controllable magnetic bearings can also perform a centering function for pistons that extend substantially vertically. As a result, the piston is centered and is preferably held without contacting the cylinder inner wall.

[0019] In one embodiment, the magnetic bearing is arranged at a predetermined position of the horizontal piston compressor. However, since the position of the center of gravity of the piston changes constantly during operation due to the reciprocating motion, the length of the lever arm formed by the piston rod between the magnetic bearing and the piston center of gravity changes constantly during operation. Therefore, a control device provided for supplying power to the magnetic bearing is preferably designed in such a way that the magnetic force exerted by the magnetic bearing on the piston rod is controllably changed depending on the position of the piston or depending on the length of said lever arm. Preferably, at least one force acting in the vertical direction is exerted on the piston rod. Particularly preferably, the magnetic bearing is designed as a radial bearing capable of exerting two-dimensionally controllable forces perpendicular to the longitudinal direction of the piston rod, preferably vertical and horizontal forces, on the piston rod. Advantageously, such a radial bearing is controlled so that the piston does not come into contact with the cylinder inner surface during operation in any of its possible positions, neither the lower cylinder inner surface nor the upper cylinder inner surface nor the side cylinder inner surface.

[0020] The magnetic bearing is preferably controlled depending on measured state variables, in particular if the piston is to be prevented from contacting the cylinder inner surface during operation, which state variables comprise at least one of the following variables: the displacement path of the piston in the cylinder, the displacement path of the piston rod in the extension direction of the piston rod, the displacement path of the piston rod perpendicular to the extension direction of the piston rod, or the rotation angle of the drive shaft. In further preferred embodiments, the state variables are at least the vertical distance of the piston rod to the magnetic bearing, in particular the gap width of the magnetic bearing between the piston rod and the magnetic bearing.

[0021] The sensors for detecting the state variables are preferably designed to detect at least one of the following: the longitudinal inclination angle β relative to the vertical, the inclination angle β as a function of time, the gap width between the inner surface of the cylinder and the side of the piston, and the position of the mutual contact point of the piston and the cylinder.

[0022] Piston compressors are typically equipped with a packing seal with a sealing ring. The piston rod extends through this packing seal or through the sealing ring of the piston rod in order to seal the cylinder interior from the outside. In a particularly preferred embodiment, a magnetic bearing is also arranged in the packing seal in addition to the sealing ring. It is particularly preferred that such a modified packing seal with a magnetic bearing is designed as a replacement part. It is particularly preferred that such a modified packing seal has the same dimensions as a previously known packing seal without a magnetic bearing, so that the packing seal with a magnetic bearing can be used for retrofitting and upgrading existing piston compressors.

[0023] In a further, preferred embodiment, the modified packing seal also includes cooling channels that, in a modified packing seal mounted in a piston compressor, are connected to a cooling circuit for cooling the magnetic bearings and / or the packing seal.

[0024] The drawings used to explain the embodiments show the following: [Brief description of the drawings]

[0025] [Figure 1] 1 is a schematic simplified longitudinal section through a piston compressor; [Diagram 2] Schematic diagram of a control device. [Diagram 3] 4 shows an exemplary course of the magnetic force as a function of a state variable, i.e. as a function of the rotation angle of the drive shaft; [Figure 4] Longitudinal section through a known packing seal. [Diagram 5] 1 is a longitudinal section through a packing seal according to the invention. [Figure 6] Diagram of a radial magnetic bearing. [Figure 7]FIG. 1 is a diagram of a tilted piston compressor, for example installed on a ship with wave motion. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] In the drawings, the same parts are generally designated by the same reference symbols. FIG. 1 shows a piston compressor 1 for compressing a gas. The piston compressor 1 comprises horizontally extending cylinders 2, each with a longitudinal direction L, and pistons 3 movable in the cylinders 2 in the direction of extension of the cylinders 2. The piston compressor 1 also comprises a piston rod 16, a packing seal 12, a magnetic bearing 13, a crosshead 17, a pushrod 19 and a drive. The crosshead 17 comprises a linear guide 18. The drive comprises, for example, a crank 20 with a drive shaft 21. In the illustrated exemplary embodiment, the piston 3 is double-acting and comprises a sealing or piston ring 4 and a guide ring 5. The piston 3 divides the interior of the cylinder 2 into a first internal space 6 and a second internal space 7. The two internal spaces 6, 7 are provided with inlet valves 8, 9 and outlet valves 10, 11, respectively. The cylinder 2 is connected to a housing 15 via an intermediate piece 14. The intermediate piece 14 also comprises a packing seal 12 and a magnetic bearing 13. The magnetic bearing 13 applies a magnetic force F to the piston rod 16 at least in the vertical direction (up and down direction). m The control device 22 detects a state variable Z of the piston compressor 1 via a signal line 24 and a sensor (not shown). The state variable Z of the piston compressor 1 is, for example, a displacement path s(t) of the piston in the cylinder 7 as a function of time, a displacement path s(t) of the piston rod 16 as a function of time, and / or a rotation angle α(t) of the drive shaft 21. The control device 22 controls the magnetic force exerted by the magnet on the piston rod 16 by controlling the current of the electromagnet of the magnetic bearing 13 via a signal line 25.

[0027] In a simple embodiment, the control device (driver) 22 measures the state variable Z and the magnetic force F m The motor can be operated in a control mode (drive mode) in which the state variable Z is changed as a function of the state variable Z. In this case, the feedback can be omitted. FIG. 3 shows an example of such a control mode, in which the progression of the curve K1 is defined. The curve K1 represents the state variable Z, here the rotation angle α of the drive shaft 21, and the magnetic force F to be generated as a function of the rotation angle α. m In the illustrated exemplary embodiment, the angle α=0° corresponds to the bottom dead center of the piston 3 relative to the second internal space 7, and α=180° corresponds to the top dead center. m is smallest at the bottom dead center. This is because the lever arm formed by the piston rod 16 between the center of gravity S of the piston 3 and the magnetic bearing 13 is the shortest at the bottom dead center. On the other hand, the lever arm formed by the piston rod 16 between the center of gravity S of the piston 3 and the magnetic bearing 13 is the longest at the top dead center, so the magnetic force F m is largest. The rotation angle α is measured by a sensor (not shown) and is supplied to the control device 22 via a signal line 24. The curve progression degree K1 can be preset, for example, based on empirical values. In this embodiment, it is particularly preferable to use a piston 3 having a guide ring 5 as shown in FIG. 1. The guide ring 5 bears against the inner surface of the cylinder 2, so that the magnetic force F m This helps to reduce the bearing force of the guide ring 5 against the inner surface of the cylinder 2. As a result, the wear of the guide ring 5 is reduced in particular. The curve K1 shown in FIG. 3 is a graph showing the magnetic force F as a function of the crankshaft rotation angle α (crankshaft angle) from 0° to 180°. m In the subsequent section from 180° to 360° (not shown), the magnetic force F m starts from the value at 180° and the magnetic force F at 0° m The magnetic field at an angle of 0° moves in the opposite direction to the value of F m The value is the same as for an angle of 360°.

[0028] In a further preferred embodiment, a measuring device, for example a sensor 26, is provided to measure the position of the piston rod 16 and / or the piston 3 at least in the vertical direction. FIG. 2 shows an embodiment for measuring the position of the piston rod 16 in the vertical direction. In a preferred embodiment, the sensor 26 is arranged close to the magnetic bearing 13 or even inside the magnetic bearing 13. The sensor 26 preferably measures the distance D between the upper coil core 13a of the magnetic bearing 13 and the surface of the piston rod 16. The magnetic bearing 13 preferably comprises at least an upper coil core 13a with a coil 13b and a lower coil core 13c with a coil 13d. As shown in FIG. 6, the magnetic bearing 13 can also be designed as a radial magnetic bearing with several electromagnets distributed in the circumferential direction. In that case, the magnetic force F exerted on the piston rod 16 is preferably measured. m The coils 13b, 13d are made individually controllable so that the direction of the beam can be determined by corresponding control of the coils 13b, 13d.

[0029] In a preferred operating method, the set point of the distance D is preset to the controller 22 via a set point specification 28. The controller 22 drives the coils 13b, 13d with current via a signal line 25 such that the piston rod 16 has a substantially constant distance D relative to the upper coil core 13a, regardless of the stroke s(t) or the crankshaft angle α(t). As a result, the piston rod 16 acts as a magnetic armature for the two coil cores 13a, 13c. Preferably, the magnetic bearing 13 can exert both an upward force and a downward magnetic attraction on the piston rod 16, making it possible to control the position of the piston rod 16 relative to the magnetic bearing 13 with particular precision.

[0030] Therefore, the controllable magnetic force F m A force (F) acting at least in the vertical direction acts on the piston rod 16. m ), that is, relief force (rescue force, rescue force) F hThe piston compressor 1 is preferably operated such that a magnetic force F acts on the piston 3 via the piston rod 16 and opposes the force of gravity F. m is controlled or varied as a function of a state variable Z, such as the distance D, the stroke s(t), or the angle of rotation α(t). The arrangements described in Figures 1 to 3 and the methods described are also suitable for operating or controlling a piston compressor having a vertically extending cylinder and a vertically moving piston.

[0031] FIG. 7 shows the piston compressor 1 according to FIG. 1 with a cylinder 2 or the interior of the cylinder extending substantially vertically, a piston rod 16 extending substantially vertically and a piston 3 movable in said direction. In FIG. 7, the piston compressor 1 is arranged in a ship heeled at a heel angle. The cylinder 2 and the piston rod 16 therefore have an inclination angle β with respect to the vertical direction V. The piston compressor 1 is preferably arranged in the ship such that the cylinder 2 and the piston rod 16 are exactly vertical or at least approximately vertical when the sea is quite calm. It is of course also possible to arrange the piston compressor 1 on land, with the cylinder 2 and the piston rod 16 preferably extending exactly vertically or at least approximately vertically. Preferably, the inclination angle β with respect to the vertical direction V is measured by a sensor 26, not shown. The inclination angle β is preferably measured as a function of time t. The magnetic force F m acts on the piston rod 16, and the piston rod 16 exerts a relief force F h to the piston 3, so that the position of the piston 3 in the cylinder 2 is adjusted to the acting relief force F h The magnetic bearings 13 are controlled via a controller 22 so as to be influenced by

[0032] As the state variable Z for controlling the magnetic bearing 13, in addition to or instead of the state variable Z already described, at least one of the following variables is suitable: the inclination angle β of the cylinder with respect to the vertical direction V, the gap width (gap width) between the inner surface of the cylinder and the side surface of the piston, and the position of the contact point between the piston and the cylinder.

[0033] Preferably, the magnetic bearings 13 are controlled such that the mutual distance between the piston rod 16 and the magnetic bearings 13, perpendicular to the longitudinal direction L, and / or the distance between the cylinder inner surface and the piston side surface, is kept constant or substantially constant. Preferably, the piston 3 is held without wall contact in the cylinder 7. Preferably, the tilt angle β(t) assumed between the vertical direction V and the longitudinal direction L is also measured as a state variable Z as a function of time t. Particularly preferably, in the case of a piston compressor arranged on a ship, the magnetic force F m is controlled by predictive control. Preferably, the state variable Z comprises the tilt angle β(t) as a function of time t, such that the state variable Z depends on time t. Particularly preferably, the state variable Z comprises, in addition to the tilt angle β(t) as a function of time t, at least one additional state variable as described herein. As a result, the state variable comprises a combination of at least two state variables as described herein. For example, the resulting state variable comprises a state variable Z of the movement of the piston rod perpendicular to the longitudinal direction L. Since the state variable Z of the movement of the piston rod perpendicular to the longitudinal direction L is combined with the state variable Z of the tilt angle β(t) as a function of time t, with the aid of predictive control and with knowledge of the state variable Z of the tilt angle β(t) as a function of time t, it is possible to: predict the expected movement of the piston rod perpendicular to the longitudinal direction L due to the tilt angle β(t) at time t+Δt. This predicted state variable Z V Using (t+Δt), the magnetic bearing 13 can be controlled.

[0034] Preferably, the predicted state variable Z V(t+Δt) is calculated from the state variable Z(t) depending on the tilt angle β(t) at the future time t+Δt. m is the predicted state variable Z V It is controlled at the current time t depending on (t+Δt).

[0035] Particularly preferably, a piston compressor according to the invention with a controllable magnetic bearing is used in combination with a transport vessel used in sea transport. The longitudinal section shown in FIG. 4 shows a packing seal 12 known per se, which comprises a number of chamber rings 12a. Inside the chamber rings 12a, a sealing ring 12b is arranged. Furthermore, the packing seal 12 comprises a fastening part 12c, to which all the chamber rings 12a are fastened in a manner not shown in detail. The packing seal 12 is connected via the fastening part 12c to a cylinder housing 2a of the cylinder 2. A piston rod 16 extends through the packing seal 12. The cylinder housing 2a has a recess which corresponds to the outer contour 12d of the packing seal 12, so that the entire packing seal 12 can be inserted into this recess. If necessary, the entire packing seal 12 can be replaced.

[0036] FIG. 5 shows a longitudinal section through a packing seal 12 according to the invention, which is equipped with a magnetic bearing 13. FIG. 6 shows a partial section through the magnetic bearing 13. The magnetic bearing 13 is designed as a radial bearing and comprises eight coil cores 13a, 13c. Two opposing coil cores 13a, 13c are given reference numbers. The coil cores 13a, 13c are wound with coils 13b, 13d. Furthermore, the end face 13e of the coil core 13a facing the piston rod 16 is shown. The packing seal 12 according to FIG. 5 comprises two chamber rings 12a, in which a seal ring 12b is arranged inside the chamber ring 12a. The packing seal 12 also comprises two emergency bearings 12f, 12g, each with a bearing surface 12h, 12i. In case of power failure of the magnetic bearing 13 or for example when the piston compressor is switched off, the piston rod 16 can rest on the emergency bearings 12f, 12g. The packing seal 12 further comprises a holder 12k for a sensor 26. At least one sensor 26 is arranged at the top. Preferably, a number of sensors 26 are arranged at a distance from one another in the circumferential direction. Furthermore, the packing seal 12 comprises a fastening part 12c. To this fastening part 12c, preferably all components shown in FIG. 5 are connected. The packing seal 12 has an outer contour 12d. In a preferred embodiment, the outer contour 12d of the packing seal 12 according to the invention is of similar or identical dimensions to the known packing seal 12 shown in FIG. 4, so that the packing seal 12 according to the invention can be used in existing piston compressors 1 with known packing seals 12. Preferably, the piston compressor 1 upgraded with the packing seal 12 according to the present invention also comprises a control device 22, so that existing piston compressors 1 can also be equipped with the device according to the present invention or can also be operated with the process according to the present invention.

[0037] In a further, preferred embodiment, as shown in FIG. 5, the packing seal 12 according to the invention also comprises cooling channels 12l, for example passing through the inside of the outer casing 12e and / or through the inside of the coil cores 13a, 13c. The cooling channels 12l form part of a cooling circuit for cooling the magnetic bearing 13 and / or the packing seal 12. The cooling circuit is only shown diagrammatically. The fastening part (mounting part) 12c has a connection 12m for the cooling circuit, which is accessible from the outside, preferably at an end face of the fastening part 12c, with the supply and discharge lines of the cooling circuit preferably passing through the fastening part 12c. Since the cooling circuit inside the packing seal 12 is predefined and completely constructed, in order to supply the cooling medium (coolant) from the outside to the cooling circuit inside the packing seal 12 after installation of the packing seal 12, the supply and discharge lines of the cooling circuit only need to be connected to the fastening part 12c. In FIG. 5, in particular, the connection channels (communicating flow paths) arranged inside the emergency bearing 12g, which connect the cooling channels 12l to each other in fluid communication, are not shown.

[0038] In the embodiment shown in Fig. 1, a piston compressor 1 is shown with a piston 3, which has a piston or sealing ring 4 as well as a guide ring 5. It is also possible to omit the guide ring 5. In another embodiment, not shown, the piston 3 can also be designed as a labyrinth piston, which preferably does not contact the inner wall of the cylinder 2.

Claims

1. A piston compressor (1) for compressing a gas, the piston compressor (1) comprising a cylinder (2), a piston (3), a piston rod (16), a packing seal (12), a crosshead (17), a magnetic bearing (13), and a drive shaft (21); The piston (3) is disposed within the cylinder (2) so as to be movable in a longitudinal direction (L); The piston (3) is connected to the crosshead (17) via the piston rod (16), The packing seal (12) is disposed between the piston (3) and the crosshead (17) such that the piston rod (16) extends through the packing seal (12); The crosshead (17) is driven by the drive shaft (21), The magnetic bearing (13) is disposed between the piston (3) and the crosshead (17); The magnetic bearing (13) is configured to receive at least a magnetic force (F ｍ ) can be acted on the piston rod (16), The piston (3) is provided with a plurality of seal rings (4), A sensor (26) is arranged to detect a state variable (Z) of the piston compressor (1); The magnetic bearing (13) is designed as a controllable magnetic bearing (13), A control device (22) controls the magnetic force (F) exerted by the magnetic bearing (13) on the piston rod (16) as a function of the state variable (Z). ｍ ) is controlled, the sensor (26) is designed to detect as the state variable (Z) at least one of the following variables: a displacement path of the piston in the cylinder, a displacement path of the piston rod in an extension direction of the piston rod, a displacement path of the piston rod in a direction perpendicular to the extension direction of the piston rod, a movement of the piston in a direction perpendicular to the extension direction of the piston rod, and a rotation angle of the drive shaft; The packing seal (12) comprises at least one fastening portion (12c), the magnetic bearing (13), and at least one chamber ring (12a), which are arranged consecutively in the longitudinal direction (L); The chamber ring (12a) has a seal ring (12b) disposed therein, The packing seal (12) comprises at least two emergency bearings (12f, 12g) spaced apart from one another in the longitudinal direction (L). Piston compressor.

2. The piston (3) is provided with a guide ring (5).

2. A piston compressor according to claim 1.

3. The cylinder (2) extends substantially horizontally. A piston compressor according to claim 1 or 2.

4. The cylinder (2) extends substantially vertically. A piston compressor according to claim 1 or 2.

5. The sensor (26) is further configured to detect at least one of the following variables: an inclination angle (β) of the longitudinal direction (L) with respect to a vertical direction (V) when the cylinder (2) extends substantially in the vertical direction (V); a gap width between an inner surface of the cylinder and a piston side surface; and a position of a mutual contact point between the piston and the cylinder. A piston compressor according to any one of claims 1 to 4.

6. The packing seal (12) is configured as a replacement part, The packing seal (12) includes both at least one seal ring (12b) and the magnetic bearing (13). A piston compressor according to any one of claims 1 to 5.

7. The packing seal (12) and the magnetic bearing (13) are provided with cooling channels (12l) for a cooling medium. A piston compressor according to any one of claims 1 to 6.

8. A method of operating a piston compressor (1), comprising a cylinder (2), a piston (3), a piston rod (16), a packing seal (12), a crosshead (17), a magnetic bearing (13), and a drive shaft (21), the piston (3) comprising a plurality of seal rings (4), the piston (3) reciprocating in a longitudinal direction (L) within the cylinder (7), the packing seal (12) comprising at least one fastening portion (12c) arranged successively in the longitudinal direction (L), and the magnetic bearing (13) and a drive shaft (21), (13) and at least one chamber ring (12a), the chamber ring (12a) having a seal ring (12b) arranged therein, the packing seal (12) having at least two emergency bearings (12f, 12g) arranged at a distance from each other in the longitudinal direction (L), the piston (3) is driven via the crosshead (17) and the piston rod (16), and a magnetic force (F) acting at least perpendicular to the longitudinal direction (L) is applied to the piston (3). ｍ ) acts on the piston rod (16) by means of the magnetic bearing (13), As a state variable (Z) of the piston compressor (1), at least one variable among a displacement path of the piston in the cylinder, a displacement path of the piston rod in an extension direction of the piston rod, a displacement path of the piston rod in a direction perpendicular to the extension direction of the piston rod, a movement of the piston in a direction perpendicular to the extension direction of the piston rod, and a rotation angle of the drive shaft is detected; The magnetic force (F ｍ ) is under control, As a result, the relief force (F ｈ ) is exerted on the piston (3) via the piston rod (16), A method for operating a piston compressor (1).

9. The longitudinal direction (L) is substantially horizontal. The method according to claim 8.

10. The longitudinal direction (L) is substantially vertical. The method according to claim 8.

11. The longitudinal direction (L) has an inclination angle (β) in the range of ±10° with respect to the vertical direction (V); The method of claim 10.

12. The state variables (Z) further comprise at least one of the following variables: a movement of the piston rod (16) perpendicular to the longitudinal direction (L); a gap width in the magnetic bearing (13) between the piston rod (16) and a magnet of the magnetic bearing (13); The method according to any one of claims 8 to 11.

13. the relative position of the piston rod (16) and the magnetic bearing (13) perpendicular to the longitudinal direction (L) of the piston rod (16) is measured as the state variable (Z); The method of claim 12.

14. As the state variable (Z), at least one variable is used among an inclination angle (β) of the cylinder with respect to a vertical direction (V) when the cylinder (2) extends substantially in the vertical direction (V), a gap width between an inner surface of the cylinder and a side surface of the piston, and a position of a mutual contact point between the piston and the cylinder. The method according to any one of claims 8 to 13.

15. At least one of the mutual distance between the piston rod (16) and the magnetic bearing (13) perpendicular to the longitudinal direction (L) and the distance between the cylinder inner surface and the piston side surface is kept constant. The method according to any one of claims 8 to 14.

16. The piston (3) is held within the cylinder (7) without contacting the walls. The method according to any one of claims 8 to 15.

17. As said state variable Z, the tilt angle (β(t)) assumed between the vertical direction (V) and the longitudinal direction (L) when the cylinder (2) extends substantially in said vertical direction (V) is additionally measured as a function of time (t); The method according to any one of claims 8 to 16.

18. The magnetic force (F ｍ ) is controlled by a predictive control system, The method according to any one of claims 8 to 17. Claim 19: The state variable (Z) comprises an inclination angle (β(t)) as a function of time (t) such that the state variable (Z) is time-dependent when the cylinder (2) extends substantially vertically (V).

20. The method of claim 18.

20. Predicted state variable Z Ｖ (t+Δt) is calculated from the state variable Z(t) depending on the tilt angle (β(t)) for a future time point (t+Δt), The magnetic force (F ｍ ) is the predicted state variable Z Ｖ (t+Δt) at the current time (t), 20. The method of claim 19.

21. The magnetic force (F ｍ ) is fixedly predetermined as a function of the state variable (Z); The method according to any one of claims 8 to 20.

22. Use of a piston compressor according to any one of claims 1 to 7 in a transport vessel.

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