The subject-matter disclosed herein relates to a expander-compressor system comprising a cooling fluid circuit for cooling one or more magnetic bearings of the system.
Magnetic bearings are largely used for controlling the position of a rotor of a machine on which the magnetic bearing is installed due to several advantages including very low and predictable friction and the ability to run without lubrication and in vacuum. Typically, magnetic bearings are used in industrial machines such as compressors, turbines, pumps, motors and generators.
In particular, magnetic bearings can be Active Magnetic Bearing (=AMB) or Passive Magnetic Bearing (=PMB). A passive magnetic bearing uses permanent magnets to generate magnetic levitation; however, passive magnetic bearings are difficult to design. As a result, most magnetic bearings are active magnetic bearings.
In general, an active magnetic bearing is an electro-magnetic system which has a stator with several electro-magnets positioned around a rotor, which is typically coupled to a shaft; the electro-magnets of the stator generate attracting forces on the rotor in order to maintain the position of the rotor relative to the stator.
Rotating machines, such as compressors or expanders, which use active magnetic bearing are well known; for example, international patent application WO2017050445A1 discloses a turbomachine system, in particular a turbine stage, provided with an active magnetic bearing and a cooling system (in an open-loop configuration) in order to dissipate heat in the magnetic bearing. The so-called “instrument air”, which is an extremely clean supply of compressed air free from contaminates (such as moisture and particulates) and is typically easily procurable and available in industrial plants (for example for pneumatic equipment or valve actuation), may be used as cooling fluid in the cooling system; instrument air enters the cooling system at low temperature, cools the magnetic bearings and then is discharged at higher temperature.
However, it is desirable to consume as less cooling fluid as possible. From European patent application EP3450701A1 is known a cooling system in a closed-loop configuration to cool down active magnetic bearings of a turbomachine system, in particular a compressor or pump or turbine or turbo-expander.
It is to be noted that known cooling systems include an external blower or an additional impeller installed on the shaft of the rotating machine (outside of the casing of the machine) to circulate the cooling fluid.
It would be desirable to have an expander-compressor system with at least one magnetic bearing and a cooling fluid circuit to cool the at least one magnetic bearing having small consumption of cooling fluid.
According to an aspect, the subject-matter disclosed herein relates to an expander-compressor system having an expander and a compressor working with a process gas (which may be the same process gas or different process gas) and a shaft that mechanically couples the expander and the compressor and that is positioned inside a casing. The expander-compressor system has further a magnetic bearing arranged to act on the shaft, and a cooling fluid circuit arranged in a closed-loop configuration and configured to cool the magnetic bearing through circulation of a cooling fluid. The cooling fluid circuit comprises a heat exchanger configured to remove heat from the cooling fluid. The magnetic bearing is positioned inside the casing while the heat exchanger is positioned outside the casing. The expander-compressor system has further at least one dry gas seal (=DGS), preferably two dry gas seals, configured to avoid leakage of process gas to the cooling fluid circuit.
A more complete appreciation of the disclosed embodiments of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
The subject-matter disclosed herein relates to an innovative expander-compressor system, i.e. typically a compressor and an expander connected by a common shaft and configured to process at least a process fluid, having at least one magnetic bearing, i.e. a device that allows unimpeded rotation thanks to opposed magnets that keep rotating parts slightly spaced from fixed parts. The innovative expander-compressor system is provided with a cooling fluid circuit, in which flows a cooling fluid in order to cool the magnetic bearing, which tends to heat up during work. The cooling fluid circuit is arranged in a closed-loop configuration in order to recirculate the fluid and avoid the release thereof to the environment, reducing therefore the amount of cooling fluid required for cooling the magnetic bearing. The expander-compressor system comprises further at least one dry gas seal (=DGS), preferably two dry gas seals, configured to avoid leakage of process gas to the cooling fluid circuit. The cooling fluid circuit comprises a pump or a blower to circulate the cooling fluid in the cooling fluid circuit and a heat exchanger to remove heat from the cooling fluid, such that the cooling fluid enters into a casing of the expander-compressor system, cools the magnetic bearing, exits from the casing, is cooled by the heat exchanger and then returns to the casing. The cooling fluid circuit comprises further a valve, for selectively feed the cooling fluid to the cooling fluid circuit, and a vent, to remove gases leaked in the cooling fluid circuit.
Reference now will be made in detail to embodiments of the disclosure, an example of which is illustrated in the drawings. Each example is provided by way of explanation of the disclosure, not limitation of the disclosure. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the scope or spirit of the disclosure. In the following description, similar reference numerals are used for the illustration of figures of the embodiments to indicate elements performing the same or similar functions. Moreover, for clarity of illustration, some references may be not repeated in all the figures.
In
Typically, with non-limiting reference to
The expander-compressor system 1000, 2000 has further a casing 600 which houses at least the shaft 800. It is to be noted that the expander 700 and the compressor 900 are not housed in the casing 600; in particular, the casing 600 is configured to isolate mechanical components and fluids that are inside the casing 600 from the surrounding environment, for example from the expander 700 and the compressor 900. In other words, the compressor 900 and the expander 700 are positioned outside the casing 600.
Considering
Advantageously, the magnetic bearings 500, 510, 520 have a stator mechanically coupled or integral with the casing 600 and/or a rotor mechanically coupled or integral with the shaft 800. For example, as shown in
According to preferred embodiments (see e.g.
Advantageously, the expander-compressor system 1000, 2000 further comprises a rotating bodies bearing; preferably, the expander-compressor system 1000, 2000 comprises two rotating bodies bearings 410 and 420, a first rotating bodies bearing 410 positioned between the expander 700 and the first radial magnetic bearing 510 and a second rotating bodies bearing 420 positioned between the compressor 900 and the second radial magnetic bearing 520. Preferably, the rotating bodies are made of ceramic material. It is to be noted that rotating bodies bearing typically comes into use in the case that the load on the magnetic bearings exceeds their capacity or in the case of failure of the magnetic bearing system while it is not used during normal operation of the expander-compressor system 1000, 2000. In fact, the life these rotating bodies bearings is very limited in time as the ceramic rotating bodies may quickly wear out and reduce in size. In other words, rotating bodies bearings typically acts as safety bearings of the system.
As it will be apparent from the following, the expander-compressor system 1000, 2000 further comprises at least one dry gas seal 310, 320 arranged at the casing around the first end of the shaft and/or the second end of the shaft; preferably, the expander-compressor system 1000, 2000 has two dry gas seals 310 and 320: the first dry gas seal 310 arranged at the casing 600 around the first end of the shaft 800, in particular between the expander 700 and the radial magnetic bearing 510, more preferably between the expander 700 and the first rotating bodies bearing 410, and the second dry gas seal 320 arranged at the casing 600 around the second end of the shaft 800, in particular between the compressor 900 and the radial magnetic bearing 520, more preferably between the compressor 900 and the second rotating bodies bearing 420. Advantageously, the dry gas seals 310 and 320 are configured to provide sealing within the casing 600 on a first side of the dry gas seal, in particular a first side towards the expander 700 or compressor 900, through a flow of a process gas, in particular an expander process gas or a compressor process gas, and on a second side of the dry gas seal, in particular a second side towards the inside of the casing 600, through a flow of a seal gas, in particular nitrogen gas.
With non-limiting reference to
According to the first embodiment shown in
According to the second embodiment shown in
According to other embodiments not shown in the figures, there may be both an internal pump or blower and an external pump or blower.
In
According to the first embodiment, at least the first side 5001 of the thrust disk 5100 comprises a plurality of grooves 5151-1 configured to pump the fluid as a result of the rotation of the thrust disk 5100 of the axial thrust magnetic bearing 500. In a preferred embodiment (see
Advantageously, as shown in
Advantageously, the grooves 5151 are curved-shaped; more advantageously, the grooves 5151 are configured to define a preferential direction which may be followed by the cooling fluid. It is to be noted that the width and/or the depth of the grooves 5151 may not be constant: for example, the width at the area around the inner periphery 5112 may be greater than the width at the area around the outer periphery 5114. Advantageously, if the thrust disk 5100 has grooves 5151 both on the first side 5001 and second side 5002, the geometry of the grooves 5151 is preferably the same both on the first side 5001 and on the second side 5002 of the thrust disk 5100.
Advantageously, the cooling fluid enters the axial thrust magnetic bearing 500 in order to cool it down; in particular, the cooling fluid flows on the thrust disk 5100 from the area around the inner periphery 5112 to the area around the outer periphery 5114. More advantageously, most part of the fluid that flows on the thrust disk 5100 is configured to flow in the preferential direction defined by the grooves 5151; in other words, the fluid is guided to flow along the grooves 5151 so that, with the rotation of the thrust disk 5100 due to the rotation of the shaft 800, the grooves 5151 are configured to pump the cooling fluid. It is to be noted that only the cooling fluid that flows along the grooves 5151 is subjected to the pumping effect of the thrust disk 5100, while the cooling fluid that flows outside the grooves 5151 is not subjected to any pumping effect.
According to the second embodiment shown in
Advantageously, the blades 6252 are smaller than the thrust disk 6100; in particular, a height of the blades 6252 might be in the range 5-15% of the diameter of the thrust disk 6100 (measured at the outer periphery 6214). Advantageously, a width of the blades 6252 is less than or equal to the thickness of the thrust disk 6100; preferably, the width of the blades 6252 is 70-100% of the thickness of the thrust disk 6100.
It is to be noted that the blades 6252 may have a blade profile with two concavities, for example to make the pumping effect on the fluid more effective and/or to help collect fluid at the thrust disk outlet; in particular, the blades 6252 may have a first concavity oriented toward the first side 6001 and a second concavity oriented towards the second side 6002; preferably, the first and the second concavities of the blades 6252 form a central ridge of the blade profile.
As explained above, with non-limiting reference to
According to the preferred embodiments shown for example in
In particular, a first part of the cooling fluid enters in the side inner chamber 621 and a second part of the cooling fluid enters in the second side inner chamber 622; advantageously, the first part and the second part of the cooling fluid have substantially the same flow rate; more advantageously, the flow rates of the first part and the second part of the cooling fluid are substantially equal to the half of the total flow rate circulating in the cooling fluid.
Once that the cooling fluid has passed through the gap and has cooled the radial magnetic bearings 510, 520, it reaches the axial thrust magnetic bearing 500. In particular, the axial thrust magnetic bearing 500 receives the first part of the cooling fluid from a first inlet 101-1 at a first side 1001, 2001 of the thrust disk 1100, 2100 and the second part of the cooling fluid from a second inlet 101-2 at a second side 1002, 2002 of the thrust disk 1100, 2100, so that the first part of the cooling fluid is configured to cool down the first side 1001, 2001 of the thrust disk 1100, 2100, in particular a first half of the thrust disk 1100, 2100, and the second part of the cooling fluid is arranged to cool down the second side 1002, 2002 of the thrust disk 1100, 2100, in particular a second half of the thrust disk 1100, 2100. Advantageously, the axial thrust magnetic bearing 500 is arranged so that the cooling fluid enters the axial thrust magnetic bearing 500 through the first and the second inlets 101-1 and 101-2, passes through the gap between the section 610 of the casing 600 (including the stator 512) and the thrust disk 1100, 2100 and exits the axial thrust magnetic bearing 500 through the outlet 102.
According to the preferred embodiments shown for example in
Considering
With non-limiting reference to
Advantageously, the cooling fluid is instrument air or nitrogen or other inert gas. It is also to be noted that the temperature of the cooling fluid entering the casing 600 and of the cooling fluid exiting from the casing 600 is different; in particular, the temperature of the cooling fluid entering the casing 600 is lower than the temperature of the cooling fluid exiting from the casing 600; for example, the difference between the temperature of the cooling fluid entering the casing 600 and exiting from the casing 600 may be in the range of 20° C.-50° C.
As already explained, the expander-compressor system 1000, 2000 may comprise at least one dry gas seal (=DGS), preferably two dry gas seals 310 and 320 (see e.g.
Considering
In other words, the dry gas seals 310 and 320 prevent leakage of process gas inside the casing 600, in particular into the cooling fluid circuit 1110, 2110. However, a small part of the seal gas may leakage into the cooling fluid circuit 1110, 2110, for example 1 Nl/min.
In order to avoid pressurization of the cooling fluid circuit 1110, 2110, the expander-compressor system 1000, 2000 advantageously comprises further a vent 113, in particular a calibrated orifice, which is configured to discharge fluid from the cooling fluid circuit 1110, 2110, in particular to discharge fluid partially coming from the dry gas seal 310 and 320. In other words, in the cooling fluid circuit 1110 and 2110 may circulate cooling fluid and a small portion of extra fluid which is a leakage of seal gas from the dry gas seal 310 and 320 to the cooling fluid circuit 1110, 2110. Advantageously, the orifice is calibrated so that the amount of fluid discharged by the vent 113 is equal to the amount of extra fluid that is leaked in the cooling fluid circuit 1110, 2110.
Number | Date | Country | Kind |
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102021000026741 | Oct 2021 | IT | national |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2022/025471 | 10/12/2022 | WO |