Patent Application
20180023584
The present invention generally relates to a centrifugal compressor used in a chiller system. More specifically, the present invention relates to a centrifugal compressor with a magnetic bearing backup system.
A chiller system is a refrigerating machine or apparatus that removes heat from a medium. Commonly a liquid such as water is used as the medium and the chiller system operates in a vapor-compression refrigeration cycle. This liquid can then be circulated through a heat exchanger to cool air or equipment as required. As a necessary byproduct, refrigeration creates waste heat that must be exhausted to ambient or, for greater efficiency, recovered for heating purposes. A conventional chiller system often utilizes a centrifugal compressor, which is often referred to as a turbo compressor. Thus, such chiller systems can be referred to as turbo chillers. Alternatively, other types of compressors, e.g. a screw compressor, can be utilized.
In a conventional (turbo) chiller, refrigerant is compressed in the centrifugal compressor and sent to a heat exchanger in which heat exchange occurs between the refrigerant and a heat exchange medium (liquid). This heat exchanger is referred to as a condenser because the refrigerant condenses in this heat exchanger. As a result, heat is transferred to the medium (liquid) so that the medium is heated. Refrigerant exiting the condenser is expanded by an expansion valve and sent to another heat exchanger in which heat exchange occurs between the refrigerant and a heat exchange medium (liquid). This heat exchanger is referred to as an evaporator because refrigerant is heated (evaporated) in this heat exchanger. As a result, heat is transferred from the medium (liquid) to the refrigerant, and the liquid is chilled. The refrigerant from the evaporator is then returned to the centrifugal compressor and the cycle is repeated. The liquid utilized is often water.
A conventional centrifugal compressor basically includes a casing, an inlet guide vane, an impeller, a diffuser, a motor, various sensors and a controller. Refrigerant flows in order through the inlet guide vane, the impeller and the diffuser. Thus, the inlet guide vane is coupled to a gas intake port of the centrifugal compressor while the diffuser is coupled to a gas outlet port of the impeller. The inlet guide vane controls the flow rate of refrigerant gas into the impeller. The impeller increases the velocity of refrigerant gas. The diffuser works to transform the velocity of refrigerant gas (dynamic pressure), given by the impeller, into (static) pressure. The motor rotates the impeller. The controller controls the motor, the inlet guide vane and the expansion valve. In this manner, the refrigerant is compressed in a conventional centrifugal compressor. A conventional centrifugal compressor may have one or two stages. A motor rotates one or more impellers via a shaft. A bearing system supports the shaft of the motor.
The bearing system in the conventional centrifugal compressor may include a gas bearing. The gas bearing uses refrigerant gas to support the shaft of the motor. See for example U.S. Pat. No. 5,857,348.
In a centrifugal compressor, magnetic bearings may also be used as a bearing system. Magnetic bearings support a rotating shaft of a motor using magnetic force. While magnetic bearings have advantage in that they support a rotating shaft without physical contact and thus they do not need lubricant oil, magnetic bearings require a backup bearing system in the case of power or control system failure.
As the backup bearing system for the magnetic bearings, rolling-element bearings including ball bearings or ceramic bearings can be used. However, it has been discovered that ball bearings need lubricant oil and such oil-lubricated bearings may not be sufficient in terms of reliability. It has also been discovered that ceramic bearings are relatively high in cost although they do not need lubricant oil.
Therefore an object of the present invention is to provide a centrifugal compressor with a magnetic bearing backup system which does not need lubricant oil, and achieves relatively low cost and relatively high reliability.
One or more of the foregoing objects can basically be achieved by providing a centrifugal compressor adapted to be used in a chiller system, the centrifugal compressor including a casing, an impeller, a motor, a diffuser, a magnetic bearing, and a magnetic bearing backup system including at least one dynamic gas bearing and at least one hydrostatic gas bearing. The casing has an inlet portion and an outlet portion. The impeller is attached to a shaft rotatable about a rotation axis. The motor is configured and arranged to rotate the shaft in order to rotate the impeller. The diffuser is disposed in the outlet portion downstream of the impeller. The magnetic bearing rotatably supports the shaft. The magnetic bearing backup system is configured and arranged to support the shaft when the magnetic bearing stops operating. The at least one dynamic gas bearing and the at least one hydrostatic gas bearing of the magnetic bearing backup system are disposed radially inwardly relative to the magnetic bearing.
One or more of the foregoing objects can also be achieved by providing a magnetic bearing backup system for a centrifugal compressor adapted to be used in a chiller system, the magnetic bearing backup system including at least one gas bearing selected from a dynamic gas bearing and a hydrostatic gas bearing. The at least one gas bearing is configured and arranged to support a shaft of the centrifugal compressor when the magnetic bearing stops operating. The at least one gas bearing is disposed radially inwardly relative to a magnetic bearing of the centrifugal compressor.
These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses preferred embodiments.
Referring now to the attached drawings which form a part of this original disclosure:
Selected embodiments will now be explained with reference to the drawings. It will be apparent to those skilled in the art from this disclosure that the following descriptions of the embodiments are provided for illustration only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.
Referring initially to
The chiller systems 10 and 10′ are conventional, except for the centrifugal compressors 22 and 22′ which include a magnetic bearing backup system in accordance with the present invention. Therefore the chiller systems 10 and 10′ will not be discussed and/or illustrated in detail herein except as related to the centrifugal compressors 22 and 22′ which includes a magnetic bearing backup system in accordance with the present invention. However, it will be apparent to those skilled in the art that the conventional parts of the chiller systems 10 and 10′ can be constructed in variety of ways without departing the scope of the present invention. In the illustrated embodiments, the chiller systems 10 and 10′ are preferably water chillers that utilize cooling water and chiller water in a conventional manner.
The centrifugal compressors 22 and 22′ are identical to each other, except the centrifugal compressor 22′ is a two stage compressor. Thus, it will be apparent to those skilled in the art from this disclosure that the single stage compressor 22 is identical to the centrifugal compressor 22′, except for the removal of parts. Therefore, the two stage compressor 22′ includes all the parts of the single stage compressor 22, but also includes additional parts. Accordingly, it will be apparent to those skilled in the art from this disclosure that the descriptions and illustrations of the two stage compressor 22′ also apply to the single stage compressor 22, except for parts relating to the second stage of compression and modifications related to the second stage of compression (e.g., the housing shape, shaft end shape, etc.). In view of these points, and for the sake of brevity, only the two stage compressor 22′ will be explained and/or illustrated in detail herein. The compressor 22′ will be explained in more detail below.
Referring again to
The chiller systems 10 and 10′ further includes an expansion valve (expansion mechanism) 29 to supply refrigerant gas to a magnetic bearing backup system 50 in accordance with the present invention. The expansion valve 29 is disposed in a refrigerant supply line, which connects an area between the compressor 22 or 22′ and the condenser 24, to supply refrigerant gas to the magnetic bearing backup system 50, as explained in more detail below.
Referring now to
The centrifugal compressor 22′ includes a first stage impeller 34a and a second stage impeller 34b. The centrifugal compressor 22′ further includes a first stage inlet guide vane 32a, a first diffuser/volute 36a, a second stage inlet guide vane 32b, a second diffuser/volute 36b, a compressor motor 38, and a magnetic bearing assembly 40 as well as various conventional sensors (only some shown). A casing 30 covers the centrifugal compressor 22′. The casing 30 includes an inlet portion 31a and an outlet portion 33a for the first stage of the compressor 22′. The casing 30 also includes an inlet portion 31b and an outlet portion 33b for the second stage of the compressor 22′.
The chiller controller 20 receives signals from the various sensors and controls the inlet guide vanes 32a and 32b, the compressor motor 38, and the magnetic bearing assembly 40 in a conventional manner, as explained in more detail below. Refrigerant flows in order through the first stage inlet guide vane 32a, the first stage impeller 34a, the second stage inlet guide vane 32b, and the second stage impeller 34b. The inlet guide vanes 32a and 32b control the flow rate of refrigerant gas into the impellers 34a and 34b, respectively, in a conventional manner. The impellers 34a and 34b increase the velocity of refrigerant gas, generally without changing pressure. The motor speed determines the amount of increase of the velocity of refrigerant gas. The diffusers/volutes 36a and 36b increase the refrigerant pressure. The diffusers/volutes 36a and 36b are non-movably fixed relative to the casing 30. The compressor motor 38 rotates the impellers 34a and 34b via a shaft 42. The magnetic bearing assembly 40 magnetically supports the shaft 42. In this manner, the refrigerant is compressed in the centrifugal compressor 22′.
In operation of the chiller system 10, the first stage impeller 34a and the second stage impeller 34b of the compressor 22′ are rotated, and the refrigerant of low pressure in the chiller system 10 is sucked by the first stage impeller 34a. The flow rate of the refrigerant is adjusted by the inlet guide vane 32a. The refrigerant sucked by the first stage impeller 34a is compressed to intermediate pressure, the refrigerant pressure is increased by the first diffuser/volute 36a, and the refrigerant is then introduced to the second stage impeller 34b. The flow rate of the refrigerant is adjusted by the inlet guide vane 32b. The second stage impeller 34b compresses the refrigerant of intermediate pressure to high pressure, and the refrigerant pressure is increased by the second diffuser/volute 36b. The high pressure gas refrigerant is then discharged to the chiller system 10.
Referring to
The thrust disk 45 extends radially from the shaft 42 in a direction perpendicular to the rotational axis X, and is fixed relative to the shaft 42. A position of the shaft 42 along rotational axis X (an axial position) is controlled by an axial position of the thrust disk 45. The first and second radial magnetic bearings 44 and 46 are disposed on opposite axial ends of the compressor motor 38. Various sensors detect radial and axial positions of the shaft 42 relative to the magnetic bearings 44, 46 and 48, and send signals to the chiller controller 20 in a conventional manner. The chiller controller 20 then controls the electrical current sent to the magnetic bearings 44, 46 and 48 in a conventional manner to maintain the shaft 42 in the correct position. The magnetic bearing assembly 40 is preferably a combination of active magnetic bearings 44, 46, and 48, which utilizes gap sensors 54, 56 and 58 to monitor shaft position and send signals indicative of shaft position to the chiller controller 20. Thus, each of the magnetic bearings 44, 46 and 48 are preferably active magnetic bearings.
Referring now to
The shaft 42 includes a first radial magnetic bearing portion 64, a second radial magnetic bearing portion 66, an axial magnetic bearing support portion (not shown), and an enlarged portion 70. In addition, backup bearing portions 72a and 72b are disposed at opposite ends of the shaft 42. The magnetic bearing backup systems 50a and 50b are disposed to respectively surround the backup bearing portions 72a and 72b of the shaft 42, and radially support the shaft 42 in a case such as power failure or system failure, as explained in more detail below.
The first radial magnetic bearing portion 64 is magnetically radially supported by the first radial magnetic bearing 44 in a conventional manner. The axial magnetic bearing support portion has the thrust disk 45 fixedly mounted thereon in a conventional manner. The thrust disk 45 is axially magnetically supported by the axial magnetic bearing 48 in a conventional manner. The second radial magnetic bearing portion 66 is magnetically radially supported by the second radial magnetic bearing 46 in a conventional manner.
The backup bearing portions 72a and 72b have smaller diameters than the first radial magnetic bearing portion 64 and the second radial magnetic bearing portion 66. Also, a gap N between the magnetic bearing backup systems 50a, 50b and the backup bearing portions 72a, 72b is smaller than a gap M between the radial magnetic bearings 44, 46 and the radial magnetic bearing portions 64, 66 as shown in
Referring to
As shown in
In the case of power or control system failure, refrigerant gas is supplied from an area between the compressor 22 or 22′ and the condenser 24 in the chiller system 10 or 10′ to the inlet conduit 84 through the refrigerant supply line SL, as explained in more detail below. The refrigerant gas supplied from the inlet conduit 84 is introduced to the gap G1 between the bearing casing 88 and the bearing stator 92, and then flows to the orifices 86 through the gap G1. The refrigerant gas flowing into the orifices 86 reaches a gap G2 between the bearing stator 92 and the shaft 42, and then creates a flow of the refrigerant gas as shown in
As shown in
The gas bearing configurations of the illustrated embodiment are merely examples. However, it will be apparent to those skilled in the art from this disclosure that various changes and modifications can be made in the dynamic gas bearing 80 and the hydrostatic gas bearing 82 used for the magnetic bearing backup system 50. For example, the precise number, location and/or structure of the orifices 86 and the inlet conduit 84 in the hydrostatic gas bearing 82 can be changed. Also, the exact groove configuration may be calculated based on refrigerant flow simulation and/or the characteristics of the grooves 74 of the shaft 42 to make the dynamic gas bearing 80 more efficient.
In a normal operation, the magnetic bearing assembly 40 magnetically supports the shaft 42. However, when the magnetic bearing assembly 40 stops operating in the case of power or control system failure, the magnetic bearing backup system 50 supports the shaft 42 as a backup of the magnetic bearing assembly 40. As discussed above, the chiller systems 10 and 10′ has the expansion valve 29. The expansion valve 29 is disposed in the refrigerant supply line SL which connects an area between the compressor 22 or 22′ and the condenser 24 to supply refrigerant gas from the area between the compressor 22 or 22′ and the condenser 24 to the magnetic bearing backup system 50 in the case of power or control system failure. The expansion valve 29 is a solenoid valve or a motor-operated valve which is closed by power supplied thereto in a normal state, and the expansion valve 29 shares a power supply with the magnetic bearing assembly 40. Thus, when the power supply system shuts down, the magnetic bearing assembly 40 stops operating, and the expansion valve 29 is opened at the same time. This allows the refrigerant gas to flow into the magnetic bearing backup system 50 from the area between the compressor 22 or 22′ and the condenser 24 through the expansion valve 29.
In a case where the pressure difference between the suction side and the discharge side of the compressor 20 or 22′ is large, the pressure of the refrigerant gas introduced into the hydrostatic gas bearing 82 through the inlet conduit 84 is high, and thus a flow of the refrigerant gas is created in the gap G2 between the bearing stator 92 of the hydrostatic gas bearing 82 and the shaft 42 as shown in
In the illustrated embodiment, the refrigerant gas introduced from the area between the compressor 22 or 22′ and the condenser 24 is returned to the area between the compressor 22 or 22′ and the evaporator 28 in the chiller systems 10 and 10′ as shown in
Referring to
In step S106, the chiller controller 20 calculates the rotation speed of the shaft 42 of the compressor 20 or 22′. The chiller controller 20 then calculates the shaft supporting force by the dynamic gas bearing 80 in the current rotation speed of the shaft 42 of the compressor 20 or 22′ in step S107. Next, it is determined whether or not the dynamic gas bearing 80 can support the shaft 42 depending on the shaft supporting force of the dynamic gas bearing 80 (step S108). In a case where the shaft supporting force is sufficient (Yes in step S108), the shaft 42 is supported by the dynamic gas bearing 80 using the flow of the refrigerant gas created by the grooves 74 (step S109). In a case where the shaft supporting force is not sufficient (No in step S108), the process will return to step S102. See *B in
When the shaft 42 is supported by the hydrostatic gas bearing 82 using the flow of the refrigerant gas supplied thereto in step S105, the process may also proceed to step S106. See *A in
As shown in
In the magnetic bearing backup system 50 in accordance with the present invention, the dynamic gas bearing 80 and the hydrostatic gas bearing 82 support the shaft 42 as a backup of the magnetic bearing assembly 40 in the case of power or control system failure as discussed above. In summary, in a case where the rotation speed of the shaft 42 is high and the pressure difference in the compressor 20 or 22′ is large, both of the dynamic gas bearing 80 and the hydrostatic gas bearing 82 support the shaft 42. In a case where the rotation speed of the shaft 42 is high and the pressure difference in the compressor 20 or 22′ is small, mainly the dynamic gas bearing 80 supports the shaft 42. In a case where the rotation speed of the shaft 42 is low and the pressure difference in the compressor 20 or 22′ is large, mainly the hydrostatic gas bearing 82 supports the shaft 42. See Table 1 below. Incidentally, the case of power or control system failure includes any event that causes the shaft 42 not to be supported by the magnetic bearing assembly 40.
Referring to
In the illustrated embodiment, the control sections are sections of the chiller controller 20 programmed to execute the control of the parts described herein. However, it will be apparent to those skilled in the art from this disclosure that the precise number, location and/or structure of the control sections, portions and/or chiller controller 20 can be changed without departing from the present invention so long as the one or more controllers are programmed to execute control of the parts of the chiller system 10 or 10′ as explained herein.
The chiller controller 20 is conventional, and thus, includes at least one microprocessor or CPU, an Input/output (I/O) interface, Random Access Memory (RAM), Read Only Memory (ROM), a storage device (either temporary or permanent) forming a computer readable medium programmed to execute one or more control programs to control the chiller system 10 or 10′. The chiller controller 20 may optionally include an input interface such as a keypad to receive inputs from a user and a display device used to display various parameters to a user. The parts and programming are conventional, and thus, will not be discussed in detail herein, except as needed to understand the embodiment(s).
In terms of global environment protection, use of new low GWP (Global Warming Potential) refrigerants such like R1233zd, R1234ze are considered for chiller systems. The global warming potential (GWP) of low global warming potential refrigerants is approximately 300 or less. One example of the low global warming potential refrigerant is low pressure refrigerant in which the evaporation pressure is equal to or less than the atmospheric pressure. For example, low pressure refrigerant R1233zd is a candidate for centrifugal chiller applications because it is non-flammable, non-toxic, low cost, and has a high COP compared to other candidates such like R1234ze, which are current major refrigerant R134a alternatives. In the illustrated embodiment, the cooling medium is refrigerant used in the chiller system 10 or 10′. Preferably the refrigerant is at least one of a low pressure refrigerant (LPR) and a low global warming potential (GWP) refrigerant. More specifically, the low pressure refrigerant (LPR) may be R1233zd and/or the low global warming potential (GWP) refrigerant may be R1234ze or R1234yf. The refrigerant may be a mixed refrigerant which includes at least one of the above-mentioned low global warming potential (GWP) refrigerants. However, the magnetic bearing backup system in accordance with the present invention can apply to a chiller system which uses any of the above-mentioned refrigerants.
In understanding the scope of the present invention, the term “comprising” and its derivatives, as used herein, are intended to be open ended terms that specify the presence of the stated features, elements, components, groups, integers, and/or steps, but do not exclude the presence of other unstated features, elements, components, groups, integers and/or steps. The foregoing also applies to words having similar meanings such as the terms, “including”, “having” and their derivatives. Also, the terms “part,” “section,” “portion,” “member” or “element” when used in the singular can have the dual meaning of a single part or a plurality of parts.
The term “detect” as used herein to describe an operation or function carried out by a component, a section, a device or the like includes a component, a section, a device or the like that does not require physical detection, but rather includes determining, measuring, modeling, predicting or computing or the like to carry out the operation or function.
The term “configured” as used herein to describe a component, section or part of a device includes hardware and/or software that is constructed and/or programmed to carry out the desired function.
The terms of degree such as “substantially”, “about” and “approximately” as used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed.
While only selected embodiments have been chosen to illustrate the present invention, it will be apparent to those skilled in the art from this disclosure that various changes and modifications can be made herein without departing from the scope of the invention as defined in the appended claims. For example, the size, shape, location or orientation of the various components can be changed as needed and/or desired. Components that are shown directly connected or contacting each other can have intermediate structures disposed between them. The functions of one element can be performed by two, and vice versa. The structures and functions of one embodiment can be adopted in another embodiment. It is not necessary for all advantages to be present in a particular embodiment at the same time. Every feature which is unique from the prior art, alone or in combination with other features, also should be considered a separate description of further inventions by the applicant, including the structural and/or functional concepts embodied by such feature(s). Thus, the foregoing descriptions of the embodiments according to the present invention are provided for illustration only, and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.
