PISTON COMPRESSOR AND METHOD FOR OPERATING SAME

Abstract

The piston compressor for compressing a gas having a cylinder and also including a piston, a piston rod, packing, a crosshead and a drive, wherein: the piston is disposed for movement in a longitudinal direction L inside the cylinder; the piston is connected to the crosshead by means of a piston rod; packing is disposed between the piston and the crosshead, through which packing the piston rod runs; the crosshead is driven by the drive; in addition an activatable magnetic bearing is disposed between the piston and the crosshead; the magnetic bearing can generate a magnetic force F.sub.m on the piston rod, at least perpendicularly to the longitudinal direction L; and an activation device activates the magnetic force F.sub.m generated by the magnetic bearing on the piston rod.

Claims

1-26. (canceled)

27. A piston compressor for compressing a gas, comprising a cylinder, a piston, a piston rod, a packing seal, a crosshead, a magnetic bearing, and a drive, wherein the piston is arranged movably in a longitudinal direction L within the cylinder, wherein the piston is connected to the crosshead via the piston rod, wherein there is arranged, between the piston and the crosshead, the packing seal through which the piston rod extends, wherein the crosshead is driven by the drive, the magnetic bearing being arranged between the piston and the crosshead, the magnetic bearing being capable of exerting a magnetic force F.sub.m on the piston rod at least perpendicularly to the longitudinal direction L, and wherein the piston comprises a plurality of sealing rings, wherein a sensor is arranged for detecting a state variable Z of the piston compressor, the magnetic bearing is designed as a controllable magnetic bearing, and a control device controls the magnetic force F.sub.m exerted by the magnetic bearing on the piston rod as a function of the state variable Z, and wherein the sensor is designed to detect a state variable Z a variable selected from the group consisting of a displacement path of the piston in the cylinder, a displacement path of the piston rod in the direction of extension of the piston rod, a displacement path of the piston rod perpendicular to the direction of extension of the piston rod, a movement of the piston perpendicular to the direction of extension of the piston rod, and an angle of rotation of the drive shaft.

28. The piston compressor according to claim 27, wherein the piston comprises a guide ring.

29. The piston compressor according to claim 27, wherein the cylinder extends in a substantially horizontal direction.

30. The piston compressor according to claim 27, wherein the cylinder extends in a substantially vertical direction.

31. The piston compressor according to claim 27, wherein the sensor is furthermore configured to detect a parameter selected from the group consisting of an angle of inclination (β) of the longitudinal direction L with respect to the vertical (V), a gap width between the inner surface of the cylinder and the side surface of the piston, and a location of a mutual contact point of the piston and the cylinder.

32. The piston compressor according to claim 27, wherein the packing seal is configured as a replacement part, and the packing seal comprises both a sealing ring and the magnetic bearing.

33. The piston compressor according to claim 27 wherein the packing seal and the magnetic bearing comprise cooling channels for a cooling medium.

34. The piston compressor according to claim 27, wherein the packing seal comprises, arranged successively in the longitudinal direction L, a fastening part, the magnetic bearing, and a chamber ring with a sealing ring arranged therein.

35. The piston compressor according to claim 34, wherein the packing seal comprises at least two emergency bearings which are arranged mutually spaced in the longitudinal direction L.

36. A method for operating a piston compressor comprising a cylinder, a piston, a piston rod, a packing seal, a crosshead, a magnetic bearing, and a drive, wherein the piston comprises a plurality of sealing rings, comprising the steps of: moving back and forth the piston in a longitudinal direction L within the cylinder, the piston being driven via the crosshead and the piston rod, and exerting a magnetic force F.sub.m acting at least perpendicularly to the longitudinal direction L by the magnetic bearing on the piston rod, wherein as a state variable Z of the piston compressor a variable is detected selected from the group consisting of: a displacement path of the piston in the cylinder, a displacement path of the piston rod in the direction of extension of the piston rod, a movement of the piston perpendicular to the direction of extension of the piston rod, and an angle of rotation of the drive shaft, and the magnetic force F.sub.m is controlled depending on the state variable Z, and a relief force F.sub.h is thereby exerted on the piston via the piston rod.

37. The method according to claim 36, wherein the longitudinal direction L is substantially in horizontal direction.

38. The method according to claim 36, wherein the longitudinal direction L is substantially in vertical direction.

39. The method according to claim 36, wherein the longitudinal direction L has an angle of inclination β in the range of +/−10° with respect to the vertical V.

40. The method according to claim 36, wherein the state variable Z furthermore comprises a variable selected from the group consisting of: a movement of the piston rod perpendicular to the longitudinal direction L, and a gap width within the magnetic bearing between the piston rod and a magnet of the magnetic bearing.

41. The method according to claim 40, wherein a mutual position of the piston rod and the magnetic bearing, perpendicular to the longitudinal direction L of the piston rod, is measured as a state variable Z.

42. The method according to claim 36, wherein as a state variable Z furthermore a variable is detected which is selected from the group consisting of: an angle of inclination β of the cylinder with respect to the vertical V, a gap width between the inner surface of the cylinder and the side surface of the piston, and a location of a mutual point of contact between the piston and the cylinder.

43. The method according to claim 36, wherein a mutual distance between piston rod and magnetic bearing and/or a distance between cylinder inner surface and piston side surface, perpendicular to the longitudinal direction L, is kept constant.

44. The method according to claim 36, wherein the piston is held in the cylinder without contacting the wall.

45. The method according to claim 36, wherein, as a state variable Z, the angle of inclination β(t) assumed between the vertical V and the longitudinal direction L is additionally measured as a function of time t.

46. The method according to claim 36, wherein the magnetic force F.sub.m is controlled by means of a predictive control system.

47. The method according to claim 46, wherein the state variable Z comprises the angle of inclination β(t) as a function of time t, so that the state variable Z is dependent on time t.

48. The method according to claim 47, wherein a predictive state variable ZV(t+Δt) is calculated from the state variable Z(t) depending on the inclination angle β(t) for a future point in time t+Δt, and the magnetic force F.sub.m is controlled at the current point in time t depending on the predictive state variable ZV(t+Δt).

49. The method according to claim 36, wherein the magnetic force F.sub.m is fixedly predetermined as a function of the state variable Z.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The drawings used to explain the embodiments show:

[0025] FIG. 1 a schematically simplified longitudinal section through a piston compressor;

[0026] FIG. 2 a schematic illustration of a control device;

[0027] FIG. 3 an exemplary progression of the magnetic force as a function of a state variable, namely the angle of rotation of a drive shaft;

[0028] FIG. 4 a longitudinal section through a known packing seal;

[0029] FIG. 5 a longitudinal section through a packing seal according to the invention;

[0030] FIG. 6 a radial magnetic bearing;

[0031] FIG. 7 an inclined piston compressor, for example on a ship with wave motion.

[0032] In principle, the same parts are given the same reference signs in the drawings.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

[0033] FIG. 1 shows a piston compressor 1 for compressing a gas, comprising a cylinder 2 extending in the horizontal direction and comprising a piston 3 movable within the cylinder 2 in the direction of extension of the cylinder 2 respectively in the longitudinal direction L. The piston compressor 1 also comprises a piston rod 16, a packing seal 12, a magnetic bearing 13, a crosshead 17 with a linear guide 18, a push rod 19 and a drive, for example a crank 20 with a drive shaft 21. In the exemplary embodiment shown, the piston 3 is of double-acting design and comprises sealing or piston rings 4 as well as a guide ring 5, the piston 3 dividing the interior of the cylinder 2 into a first interior space 6 and a second interior space 7, these two interior spaces each having an inlet valve 8, 9 and an outlet valve 10, 11. The cylinder 2 is connected to a housing 15 via an intermediate piece 14, with the packing seal 12 and the magnetic bearing 13 also being arranged in the intermediate piece. The magnetic bearing 13 exerts a magnetic force F.sub.m on the piston rod 16 at least in the vertical direction. A control device 22 detects a state variable Z of the piston compressor 1 via a signal line 24 and a sensor not shown, for example the displacement path s(t) of the piston in the cylinder 7 as a function of time, the displacement path s(t) of the piston rod 16 and/or an angle of rotation α(t) of the drive shaft 21 as a function of time. The control device 22 controls, via a signal line 25, the current in the electromagnets of the magnetic bearing 13 and thereby the magnetic force exerted by the magnets on the piston rod 16.

[0034] In a simple embodiment, the drive device 22 can be operated in a drive mode in which a state variable Z is measured, and the magnetic force F.sub.m is modified as a function of the state variable Z. In this case, feedback can be dispensed with. FIG. 3 shows an example of such a control mode in which the progression of a curve K1 is specified, the curve K1 specifying the relationship between the state variable Z, in the present case the angle of rotation α of the drive shaft 21, and the magnetic force F.sub.m to be generated as a function of the angle of rotation α. In the illustrated exemplary embodiment, the angle α=0° corresponds to the bottom dead center and α=180° to the top dead center of the piston 3 with respect to the second interior space 7, the magnetic force F.sub.m being smallest at the bottom dead center, 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 shortest, and wherein the magnetic force F.sub.m is largest at the top dead center 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 longest. The angle of rotation α is measured by a sensor not shown and fed to the control device 22 via the signal line 24. The curve progression K1 can be predetermined, for example, on the basis of empirical values. This embodiment is particularly preferred if, as shown in FIG. 1, a piston 3 having a guide ring 5 is used, wherein the guide ring 5 bears against the inner surface of the cylinder 2, and wherein the magnetic force F m serves to reduce the bearing force of the guide ring 5 against the inner surface of the cylinder 2, thereby in particular reducing wear of the guide ring 5. The curve K1 shown in FIG. 3 only shows the progression of the magnetic force F.sub.m as a function of the crankshaft angle α between 0° and 180°. In the subsequent section between 180° and 360°, which is not shown, the force F.sub.m, starting from the value at 180°, runs in the reverse direction to the value of F.sub.m at the angle of 0°, this value being identical to the value at the angle of 360°.

[0035] 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 which measures 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, wherein the sensor 26 preferably measures the distance D between an upper coil core 13a of the magnetic bearing 13 and the surface of the piston rod 16. Preferably, the magnetic bearing 13 comprises at least an upper coil core 13a with coil 13b and a lower coil core 13c with coil 13d. As shown in FIG. 6, the magnetic bearing 13 can also be designed as a radial magnetic bearing with a plurality of electromagnets distributed in the circumferential direction, wherein their coils 13b, 13d can preferably be controlled individually so that the direction of the magnetic force F.sub.m exerted on the piston rod 16 can be determined by a corresponding control of the coils 13b, 13d.

[0036] In a preferred operating method, a setpoint for the distance D is predetermined for the control device 22 via the setpoint specification 28, with the control device 22 driving the coils 13b, 13d with current via the signal line 25 in such a way that the piston rod 16 has an essentially unaltered, constant distance D with respect to the upper coil core 13a, irrespective of the stroke s(t) or the crankshaft angle α(t). The piston rod 16 thereby acts as a magnetic armature of the two coil cores 13a, 13b. Preferably, the magnetic bearing 13 can exert both an upward force and a downward magnetic attraction force on the piston rod 16, so that the position of the piston rod 16 relative to the magnetic bearing 13 can be controlled particularly precisely.

[0037] The piston compressor 1 is thus preferably operated in such a way that a controllable magnetic force F.sub.m is exerted on the piston rod 16, so that a force F.sub.m acting at least in the vertical direction, or a relief force F.sub.h, is exerted on the piston 3 via the piston rod 16, which counteracts the force of gravity F, the magnetic force F.sub.m being controlled or varied as a function of a state variable Z such as, for example, the distance D, the stroke s(t) or the angle of rotation α(t). The arrangement described in FIGS. 1 to 3 and the method described are also suitable for operating or controlling a piston compressor with a cylinder extending in the vertical direction and a piston moving in the vertical direction.

[0038] FIG. 7 shows the piston compressor 1 shown in FIG. 1 with a cylinder 2 or an interior of a cylinder extending essentially in the vertical direction, with a piston rod 16 extending essentially in the vertical direction, and with a piston 3 movable in this direction. In FIG. 7, the piston compressor 1 is arranged on a ship heeled with a heel angle, which is why the cylinder 2 and the piston rod 16 have an angle of inclination β with respect to the vertical V. The piston compressor 1 is preferably arranged in the ship in such a way that the cylinder 2 and the piston rod 16 are exactly in the vertical direction or at least approximately in the vertical direction when the sea is absolutely calm. The piston compressor 1 could of course also be arranged on land, and the cylinder 2 and the piston rod 16 preferably extend exactly in vertical direction or at least approximately in vertical direction. Preferably, the angle of inclination β with respect to the vertical V is measured by a sensor 26 not shown, the angle of inclination β preferably being measured as a function of time t. The magnetic bearing 13 is controlled via the control device 22 in such a way that a magnetic force F.sub.m is exerted on the piston rod 16, and that the piston rod 16 transmits a relief force F.sub.h to the piston 3, so that, due to the acting relief force Fri, the position of the piston 3 within the cylinder 2 is influenced, if possible.

[0039] As a state variable Z for controlling the magnetic bearing 13, at least one of the following variables is suitable, in addition to or instead of the state variables Z already mentioned: Angle of inclination β of the cylinder relative to the vertical V, gap width between the inner surface of the cylinder and the side surface of the piston, location of a mutual point of contact between the piston and the cylinder.

[0040] Preferably, the magnetic bearing 13 is controlled in such a way that the mutual distance between the piston rod 16 and the magnetic bearing 13 and/or the distance between the cylinder inner surface and the piston side surface, perpendicular to the longitudinal direction L, is kept constant or substantially constant. Preferably, the piston 3 is held without wall contact in the cylinder 7. Preferably, the angle of inclination β(t) assumed between the vertical V and the longitudinal direction L is also measured as a function of time t as the state variable Z. Particularly preferred, in the case of a piston compressor arranged on a ship, the magnetic force F.sub.m is controlled by means of a predictive control. Preferably, the state variable Z comprises the inclination angle β(t) as a function of time t, such that the state variable Z is dependent on time t. In a preferred embodiment, the state variable Z comprises, in addition to the inclination angle β(t) as a function of time t, at least one further state variable mentioned herein, so that such a resulting state variable consists of a combination of at least two state variables mentioned herein. For example, a resulting state variable could comprise the state variable Z of the movement of the piston rod perpendicular to the longitudinal direction L, and be combined with the state variable Z of the inclination angle β(t) as a function of time t, so that with the aid of the predictive control and the knowledge of the state variable Z of the angle of inclination β(t) as a function of the time t, the expected movement of the piston rod perpendicular to the longitudinal direction L caused by the angle of inclination β(t) at the time t+Δt can be predicted, and the magnetic bearing 12 can be controlled with this predictive state variable Zv (t+Δt).

[0041] Preferably, a predictive state variable Zv (t+Δt) is calculated from the state variable Z(t) depending on the angle of inclination β(t) for a future point in time t+Δt, and the magnetic force F.sub.m is controlled at the current point in time t depending on the predictive state variable Zv (t+Δt).

[0042] Particularly preferred, the piston compressor according to the invention comprising the controllable magnetic bearing is used in combination with a transport ship used for transports over the sea.

[0043] The longitudinal section shown in FIG. 4 shows a packing seal 12 known per se, comprising a plurality of chamber rings 12a in which sealing rings 12b are arranged. In addition, the packing seal 12 comprises a fastening part 12c, to which all chamber rings 12a are fastened in a manner not shown in detail. The packing seal 12 is connected to a cylinder housing 2a of a cylinder 2 via the fastening part 12c, wherein a piston rod 16 extends through the packing seal 12. The cylinder housing 2a has a recess which corresponds to an outer contour 12d of the packing seal 12, so that the entire packing seal 12 can be inserted into this recess and, if necessary, the entire packing seal 12 can be replaced.

[0044] FIG. 5 shows a longitudinal section through a packing seal 12 according to the invention comprising a magnetic bearing 13. FIG. 6 shows a partial section of the magnetic bearing 13, which is designed as a radial bearing and comprises eight coil cores 13a, 13c, the two opposing coil cores 13a, 13c being provided with reference signs. The coil cores 13a, 13c are wound with coils 13b, 13d. In addition, 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 sealing rings 12b are arranged. The packing seal 12 also includes two emergency bearings 12f, 12g each having a bearing surface 12h, 12i. In the event of a 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, wherein at least one sensor 26 is arranged at the top, and wherein preferably a plurality of sensors 26 are arranged mutually spaced in the circumferential direction. In addition, the packing seal 12 comprises a fastening part 12c, to which 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 similarly or identically dimensioned 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 having the known packing seal 12. Preferably, a piston compressor 1 upgraded with the packing seal 12 according to the invention is also provided with a control device 22, so that existing piston compressors 1 can also be provided with the device according to the invention or existing piston compressors 1 can be operated with the process according to the invention.

[0045] In a further, preferred embodiment, the packing seal 12 according to the invention, as shown in FIG. 5, also comprises cooling channels 121, which run, for example, inside the outer casing 12e and/or inside the coil cores 13a, 13c, the cooling channels forming part of a cooling circuit in order to cool the magnetic bearing 13 and/or the packing seal 12. The cooling circuit is shown only schematically, the supply lines and the discharge lines of the cooling circuit preferably running through the mounting part 12c in such a way that the mounting part 12c has connections 12m for the cooling circuit which are accessible from the outside, preferably on its end face, and in that the cooling circuit inside the packing seal 12 is predefined and fully configured, so that after installation of the packing seal 12 only the external coolant supply from the outside needs to be connected to the fastening part 12c in order to supply the cooling circuit inside the packing seal 12 with coolant. In FIG. 5, in particular, the connecting channels arranged inside the emergency bearing 12g and mutually connecting the cooling channels 121 in a fluid-conducting manner are not shown.

[0046] In the embodiment shown in FIG. 1, a piston compressor 1 comprising a piston 3 with piston rings or sealing rings 4 and a guide ring 5 is shown. The guide ring 5 could be dispensed with. In another embodiment, not shown, the piston 3 could also be designed as a labyrinth piston, wherein this labyrinth piston preferably does not touch the inner wall of the cylinder 2.