The invention relates to a reciprocating compressor with a piston which can be moved back and forth in a cylinder in order to form a compression chamber in the cylinder, wherein at least one suction valve and at least one pressure valve are provided on the compression chamber, wherein at least one connection chamber with a fixed connection chamber volume is provided, which is connected to the compression chamber via an overflow opening, wherein a sequence valve is provided for opening and closing the overflow opening and a sequence valve control unit is provided for activating the sequence valve. Furthermore, the invention relates to a method for operating such a reciprocating compressor and to a valve assembly for a reciprocating compressor.
The regulation of the capacity or the delivery rate of a reciprocating compressor by means of a connection chamber is a well-established principle that is mainly used in reciprocating compressors with a constant speed. The dead space can be increased by the connection chamber, so that the pressure increase and decrease rate of the compressor is flattened and the quantity of the conveyed medium can be reduced. This form of regulation is hardly lossy and is often used, especially in medium-sized and large compressors, to adjust the operating point of the compressor to its drive. The type of change in the volume of the dead space by means of the connection chamber can in principle take place in two ways. On the one hand, one or more connection chambers with an unchangeable volume can be provided and can be connected in series or in parallel via one or more valves. On the other hand, a connection chamber with a variable volume can be provided, wherein the volume is variable by movement of a piston.
A gradual connection of several connection chambers with different volumes is known, for example, from CN 111188759 A or U.S. Pat. No. 5,735,675 A. In this case, individual partial volumes of the connection chamber are connected to the compression chamber via hydraulic or pneumatic actuators by opening of a valve. Depending on the design, connection is relatively slow compared to the compressor speed. The sequence valve remains open over a longer period of time, so that the associated connection chamber remains connected to the compression volume. This type of regulation makes it possible to change the quantity of the conveyed medium only in discrete steps; stepless and precise quantity regulation is not possible.
Designs are also known from GB 487916 A, in which the sequence valve can be kept closed via a mechanical spring or a pneumatically or hydraulically adjustable closing pressure. These valves open automatically as soon as the pressure in the compression chamber exceeds the closing pressure on the sequence valve. When the sequence valve opens, the connection chamber volume is connected during the compression process and from this time the pressure increase curve is flattened. By adaptation of the closing pressure and thus the time of connection of the connection chamber, it is possible to achieve a simple stepless control of the gas quantity delivered. However, this design also allows only a slow adjustment of the connection time compared to the compressor speed. Due to compressibility effects in the region of the pneumatic or hydraulic closing pressure application as well as friction effects on the valve sealing elements, the opening time of the valve and thus the quantity of gas delivered is greatly dependent on these effects. Precise control of the quantity of gas delivered is only possible to a limited extent with this design.
It is therefore an object of the present invention to provide an improved stepless capacity regulation by means of a connection chamber for a reciprocating compressor, by which a more precise and faster adaptation of the delivery rate is made possible even in the case of large reciprocating compressors.
This object is achieved according to the invention in that the sequence valve is designed as an automatic ring valve which automatically opens and closes the overflow opening depending on a pressure ratio between a pressure in the connection chamber and a pressure in the compression chamber, wherein the sequence valve opens automatically when the pressure in the connection chamber is greater than the pressure in the compression chamber, in that an unloader is provided, which can be actuated by an electrically controllable actuator in order to keep the sequence valve in an open state independently of the pressure ratio, and in that the electromagnetic actuator can be controlled by the sequence valve control unit for actuation. This makes it possible to react very precisely to load changes of the compressor within a very short time, in particular within one compression cycle or one revolution of the crankshaft, which was previously not possible due to the seat valves used and in particular due to the relatively slow pneumatic or exclusively hydraulic actuation.
A flow cross-sectional area of the overflow opening in the open state of the sequence valve is preferably at least 5%, preferably at least 10%, particularly preferably at least 15%, of a bore cross-sectional area of a bore of the cylinder. The bore diameter of the bore of the cylinder is preferably at least 100 mm, preferably at least 500 mm, particularly preferably at least 800 mm. The throttling losses can be reduced by large flow cross sections and the force required to keep the valve open can be reduced. The advantage of the ring valve increases in particular with the size of the compressor, in particular the bore diameter.
The actuator preferably has a switching frequency of at least 5 Hz, preferably at least 10 Hz, particularly preferably at least 20 Hz. An electromagnetic actuator or an electrohydraulic actuator is advantageously provided as the actuator. As a result, very precise closing times of the valve can be achieved. Electromagnetic actuators and electrohydraulic actuators are particularly well suited for this.
It is advantageous if the suction valve and/or the pressure valve is also designed as an automatic valve, preferably as an automatic ring valve, because this means that no actuators are required for actuation. The suction valve and/or the pressure valve are preferably arranged on a peripheral surface of the cylinder in the compression chamber and/or the sequence valve is arranged on an end face of the cylinder of the reciprocating compressor opposite a piston head of the piston. This is advantageous because there is a lot of space for the sequence valve on the end face. In addition, simple installation and retrofitting of the sequence valve can thereby be made possible.
The sequence valve preferably has a plurality of concentrically arranged, at least partially annular overflow openings, wherein each overflow opening is assigned a sealing element and the unloader acts on the sealing elements through the annular overflow openings. As a result, the flow cross section can be increased and the throttling forces reduced. It can be advantageous here if a plurality of annular sealing elements are connected via radial webs to form a sealing plate, as a result of which fewer individual components are required, which makes assembly easier, for example.
Furthermore, it can be advantageous for the sequence valve to have a valve housing in which the connection chamber is provided, wherein the electromagnetic actuator is arranged outside the valve housing and is connected to the unloader via a transmission rod which protrudes through a wall of the valve housing into the connection chamber. As a result, the actuator can be protected from the high temperatures and pressures in the connection chamber and a simple connection to the control unit is possible.
The sequence valve control unit is preferably designed to control the sequence valve depending on a load signal and/or depending on a crank angle signal of the reciprocating compressor. As a result, the connection chamber can advantageously be connected and disconnected depending on the operating state of the reciprocating compressor.
The object is also achieved with a valve assembly in that the sequence valve is designed as an automatic ring valve which automatically opens and closes the overflow opening depending on a pressure ratio between a pressure in the connection chamber and an ambient pressure, wherein the sequence valve opens automatically when the pressure in the connection chamber is greater than the ambient pressure, and in that an unloader is provided which can be actuated by an electrically controllable actuator in order to keep the sequence valve in an open state independently of the pressure ratio, wherein the actuator can be controlled by the sequence valve control unit for actuation.
In addition, the object is achieved with a method in that the sequence valve opens automatically at an opening point in the expansion stroke before the suction valve opens when a pressure in the connection chamber is greater than a pressure in the compression chamber, wherein the unloader is activated in order to keep the sequence valve in the open state independently of the pressure in the connection chamber and the pressure in the compression chamber, and the unloader is deactivated after the closing of the suction valve at a certain time in the compression stroke, so that the sequence valve closes automatically at a fixed closing point in the compression stroke due to the pressure in the compression chamber, which is higher relative to the pressure in the connection chamber, wherein the unloader is actuated by the actuator and the actuator is controlled by the sequence valve control unit.
The present invention is explained in greater detail below with reference to
A section through a compressor housing 10 of a reciprocating compressor 1 in the region of a cylinder 2 is shown schematically in each of
In this case, the lateral forces are absorbed by a separate joint, the so-called crosshead, which is mounted on plain bearings in the cylinder 2 or the crankcase. As a result, the piston rod 4 performs a purely axial movement. Of course, direct driving of the piston by means of a push rod would also be possible. The lateral forces are absorbed by the piston 3 and supported on the cylinder 2. However, the type of drive is secondary for the invention and essentially depends on the design, the size and the application of the reciprocating compressor 1. The crosshead design is used, for example, in double-acting reciprocating compressors. The embodiment in
In a known manner, a compression chamber 5 is formed in the cylinder 2 above a piston head 3a of the piston 3, and in this compression chamber a compression medium such as air or a certain gas is compressed by the movement of the piston 3. The compression medium can be drawn in from one or more suction lines 7 via one or more suction valves 6 and can be fed to one or more pressure lines 9 via one or more pressure valves 8. Depending on the structural design of the reciprocating compressor 1, one or more suction valves 6 and/or one or more pressure valves 8 can be arranged on the circumference of the cylinder 2, for example as shown. If a separate cylinder head (not shown) is provided on the reciprocating compressor 1, then an arrangement of the suction valve 6 and/or pressure valve 8 on the cylinder head of the reciprocating compressor 1 would also be possible. In this case, the compression chamber 5 would be formed between the piston head 3a of the piston 3 and the cylinder head.
In
In an analogous manner, the pressure valve 8, designed as a ring valve, opens automatically during a compression stroke of the piston 3 depending on the pressure ratio between a pressure in the pressure line 9 and the relatively higher pressure in the compression chamber 5 in the direction of the pressure line 9. If necessary, a preloading device, for example in the form of spring elements, can also be provided on the pressure valve 8 in order to generate a preloading force, by which the pressure valve 8 is preloaded in the direction of the closed state. Depending on the specific structural design of the reciprocating compressor 1, a certain constant delivery rate thus results for each speed of the reciprocating compressor 1. In the case of large compressors, which are usually operated at a constant speed, the delivery rate is therefore essentially constant.
However, it is often desirable to change the delivery rate despite the constant speed. As mentioned at the outset, one or more connection chambers with a constant or variable connection chamber volume can be provided for this purpose, and can be selectively connected to the compression chamber 5. As a result, the dead space in the cylinder 2 is increased, whereby the pressure increase or decrease in the compression chamber 5 can be flattened, as will be explained in more detail below with reference to
For example, a separate unit in the form of suitable hardware and/or software can be provided as the sequence valve control unit 14. The sequence valve control unit 14 can be controlled, for example, by a higher-level compressor control unit 16 of the reciprocating compressor 1, but could of course also be integrated into this unit. The compressor control unit 16 can, for example, transmit a load signal L about the current load state of the reciprocating compressor 1 to the sequence valve control unit 14. Depending on this, the sequence valve control unit 14 can set a specific operating mode for the capacity regulation and can set and change the closing point SP and the opening point OP of the sequence valve 13 accordingly depending on the load signal L.
A supply quantity (=delivered quantity of the compressed compression medium), a power consumption of an electric drive machine of the reciprocating compressor (=drive machine load) or a pressure of the compressed compression medium can be used, for example, as a load signal L, wherein in the case of multi-stage compressors, for example, an intermediate pressure between two compression stages can be used. In order to be able to assign the closing point SP and the opening point OP of the sequence valve 13 to the compression cycle, the compressor control unit 16 can, for example, also transmit a crank angle signal φ to the sequence valve control unit 14. The crank angle signal φ can be detected by a crank angle sensor of the reciprocating compressor 1, for example. As a result, a closed control loop can be implemented in an advantageous manner, so that precise control of the closing point SP is made possible.
According to the invention, the sequence valve 13 is designed as an automatic ring valve which automatically opens and closes the overflow opening(s) 12 depending on a pressure ratio between a pressure in the connection chamber 11 and a pressure in the compression chamber 5, wherein the sequence valve opens in the direction of the compression chamber 5 when the pressure in the connection chamber is greater than the pressure in the compression chamber 5. In addition, an unloader 15 is provided, which can be actuated by a suitable actuator 17. The unloader 15 is provided in order to keep the sequence valve 13 in an open state after it has opened automatically, as will be explained in detail below with reference to
As shown in
The actuator 17 is preferably arranged outside the valve housing 18 and is connected to the unloader 15 via a transmission rod 20 which protrudes through a wall of the valve housing 18 into the connection chamber 11. On the one hand, this is advantageous for thermal reasons because the actuator 17 is not exposed to the temperatures and pressures in the connection chamber 11. On the other hand, a simpler electrical connection to the sequence valve control unit 14 is thus possible. In addition, the connection chamber 11 can be made smaller with the same connection chamber volume, because the volume of the actuator 17 does not reduce the connection chamber volume of the connection chamber 11. The valve housing 18 is advantageously constructed in several parts. In the example shown in
The use according to the invention of an automatic ring valve with unloader 15 and a suitable, in particular electromagnetic, actuator 17 now makes it possible to react very precisely to load changes of the compressor 1 within a very short time, in particular within one compression cycle or one revolution of the crankshaft. For example, it is possible to close the sequence valve 13 in the compression stroke within a maximum of 5°, preferably a maximum of 3° crank angle after the unloader 15 has been actuated. In the prior art, such rapid control of the sequence valves was previously not possible due to the valve geometries used and in particular due to the relatively slow pneumatic or exclusively hydraulic actuation.
By the use of a ring valve in particular, the capacity regulation can be used particularly advantageously with larger reciprocating compressors 1 that have a bore diameter B of the cylinder 2 of at least 100 mm, preferably at least 500 mm, particularly preferably at least 800 mm. The bore diameter B is formed in
Although a greater valve lift would partially reduce this disadvantage, it would lead to longer closing times, which is also disadvantageous because, under certain circumstances, a sufficiently rapid reaction to load changes would not be possible. On the other hand, it is often not possible to increase the valve lift because the axial space in the compression chamber is limited. In addition, with seat valves, due to the comparatively large valve area, relatively large forces would be required to keep the valve open in the compression stroke, which under certain circumstances could not be applied by an actuator, or could only be applied insufficiently. Due to their design, ring valves therefore have great advantages over seat valves, in particular the greater the bore diameter B of the cylinder 2 is. The ring valve is preferably dimensioned such that a flow cross-sectional area of the overflow opening(s) 12 when the sequence valve 13 is open is at least 5% of a bore cross-sectional area of the bore of the cylinder 2 or a cross-sectional area of the cylindrical valve housing section 26 with the housing diameter Dv, preferably at least 10%, more preferably at least 15%. As a result, a sufficiently large area can be made available so that the compression medium does not heat up to an unacceptably high level as a result of throttling in the region of the overflow opening(s) 12.
Furthermore, it is advantageous that the actuator 17 has a switching frequency of at least 5 Hz, preferably at least 10 Hz, particularly preferably at least 20 Hz. As a result, the unloader 15 can be actuated very quickly, so that closing times of the sequence valve 13 of less than 5° CA, preferably less than 3° CA, can be implemented. In the example shown, the suction valve 6 and the pressure valve 8 are arranged on a peripheral surface of the cylinder 2 in the compression chamber 5 and the sequence valve 13 is arranged on an end face of the cylinder 2 in the compression chamber 5 opposite the piston head 3a of the piston 3. This arrangement is advantageous because it means that a relatively large area is available for the sequence valve 13. Of course, a different arrangement would also be conceivable in principle. In the example shown, a bevel 26a is provided at the free end of the cylindrical housing portion 26 of the first housing part 18a, which faces the compression chamber 5 in the assembled state, at least in the region of the pressure and suction valves 6, 8. In order to simplify manufacture, the bevel 26a is preferably in the form of a chamfer running around the entire circumference of the housing portion 26. As a result, in the installed state of the valve assembly VG on the reciprocating compressor 1 in the region of the suction and pressure valves 6, 8, an annular gap is formed with a substantially triangular cross section. This allows the compression medium to flow over the valves 6, 8 even when the piston 3 is at top dead center.
In order to achieve as large an available overflow cross section as possible, the sequence valve 13 preferably has a plurality of concentrically arranged overflow openings 12, which are at least partially annular, as is shown, for example, in
As shown by way of example in
The sequence valve 13 preferably also has a so-called valve catcher 24, which, for example in the example according to
In the closed state of the sequence valve 13, the sealing element or elements 21 is/are in contact with the valve seat plate 23 and close the overflow openings 12 of the valve seat plate 23. If the pressure in the connection chamber 11 exceeds the pressure in the compression chamber and, if applicable, any preloading force of the preloading device during the expansion stroke of the piston 3, the sealing element or elements 21 is/are automatically displaced in the direction of the valve catcher 24. When the sequence valve 13 is in its maximum open state, the sealing element or elements 21 can also bear against the valve catcher 24. The valve lift can thus be limited by the valve catcher 24. Suitable openings 24a are advantageously also provided in the valve catcher 24 in order to keep the throttling effect of the open sequence valve 13 as low as possible.
The unloader 15 is arranged here inside the connection chamber 11 and the unloader fingers 15a of the unloader 15 protrude through the overflow openings 12 in order to act on the sealing element(s) 21. The unloader 15 is connected to the actuator 17 by means of the transmission rod 20. The actuator 17 can be controlled by the sequence valve control unit 14 in order to actuate the unloader 15. The working stroke of the unloader 15 can be fixed, but could also be adjustable, for example by means of a suitable adjusting device that can be provided in the valve assembly VG. The adjusting device could, for example, be designed in such a way that the length of the transmission rod 20 can be changed or that a common position of the actuator 17 including the transmission rod 20 and the unloader 15 can be adjusted.
In
In
In contrast to
As a result, in the embodiment according to
The use of the valve assembly VG in a method for regulating the capacity of the reciprocating compressor 1 is explained in more detail below with reference to
At point A, the piston 3 is at bottom dead center UT at the beginning of the compression stroke, with the suction valve 6 and the pressure valve 8 closed. The movement of the piston 3 compresses the compression medium in the compression chamber 5 until the opening pressure pD of the pressure valve is reached and the pressure valve 8 opens at point B. The compressed compression medium is displaced from the compression chamber 5 into the pressure line 9 through the open pressure valve 8. At point C, the piston 3 reaches top dead center OT and the pressure valve 8 closes. The expansion stroke of the piston 3 now begins, with the piston 3 being moved again in the opposite direction towards bottom dead center UT. The volume in the compression chamber 5 increases again and the pressure p decreases.
When the opening pressure pS of the suction valve 6 is reached, the suction valve 6 opens and fresh compression medium is drawn in through the suction valve 6 from the suction line 7 at an essentially constant pressure until the piston 3 again reaches the bottom dead center UT and the work cycle is completed. The area F0 enclosed by the solid line between the points A-B-C-D-A corresponds to the maximum work of the compressor 1 with the connection chamber 11 deactivated or of a reciprocating compressor 1 without the connection chamber 11, as shown in
By selection of the closing point SP and opening point OP of the sequence valve 13, the delivery rate can be set essentially steplessly between the maximum delivery rate (area FO) and a minimum delivery rate (area F3-
By appropriate control of the sequence valve 13, the delivery rate of the compressor 1 can now be steplessly adjusted between the maximum delivery rate (area F0-
Since the sequence valve 13 is designed according to the invention as an automatic ring valve, during the expansion stroke of the piston 3, purely due to the pressure ratio between the pressure in the connection chamber 11 and the relatively lower pressure in the compression chamber (5), the sealing element(s) 21 are lifted off from the valve seat plate 23 in the direction of the compression chamber 5, whereby the overflow opening(s) 12 are exposed. As a result, no additional opening force is required, which would have to be applied by the actuator 17 via the unloader 15. In the first operating mode (
In the second operating mode (
As can be seen in
The sealing element(s) 21 of the sequence valve 13 are held in the open position by the unloader fingers 15a of the unloader 15 until the following compression stroke, after the suction valve 6 has already been closed again at point A. For this purpose, the actuator 17 generates a holding force that counteracts a closing force that is exerted on the sealing element or elements 21 by the pressure ratio between the pressure in the compression chamber 5 and the (relatively lower) pressure in the connection chamber 11 and the resulting flow of the compression medium into the connection chamber 11. By the use of a ring valve as the sequence valve 13 according to the invention, the required holding force that has to be applied by the actuator 17 can be kept relatively low, which means that the mechanical loads on the valve assembly VG can consequently also be kept low.
To close the sequence valve 13, the unloader 15 is deactivated, that is to say moved away from the sealing elements 21 in the opposite direction, in that the actuator 17 is controlled by the sequence valve control unit 14 at a specified point in time. This results in a reduction or removal of the holding force, so that in the first operating mode the sequence valve 13 closes automatically at the first closing point SP1 by the flow forces acting on the sealing element(s) 21. The sequence valve 13 is preferably designed in such a way that the flow forces acting during the closing process result in a deformation, in particular a deflection, of the sealing element(s) 21. This temporarily leads to a further narrowing of the flow cross-section, which generates an increased pressure drop during the closing process. As a result, a sufficiently high restoring force can be generated so that the closing process is made possible in a crank angle range of at most 5°, preferably at most 3° crank angle after deactivation of the unloader 15.
After closing of the sequence valve 13 at the first closing point SP1 at a first sequence valve closing pressure pSP1 in the compression chamber 5 and a first sequence valve closing volume VSP1(φ) in the compression chamber 5, the pressure prevailing at this point in time in the connection chamber 11 is enclosed and essentially corresponds to the first sequence valve closing pressure pSP1. By selection of the first closing point SP1, the first opening point OP1 of the sequence valve 13 can consequently also be defined in the subsequent expansion stroke. The sequence valve closing pressure pSP1 and the sequence valve opening pressure pOP1 are (ignoring pressure losses) essentially at the same pressure level pSP1˜pOP1, as can be seen in
In
As already mentioned, it is advantageous if the sequence valve control unit 14 receives a load signal L of the reciprocating compressor 1, for example from the compressor control unit 16 (
Number | Date | Country | Kind |
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50359/2021 | May 2021 | AT | national |