Abstract:
The invention relates to a reverse rotation preventing structure of a centrifugal compressor. The reverse rotation preventing structure of the centrifugal compressor comprises: a discharge pipeline of the centrifugal compressor; a suction pipeline of the centrifugal compressor; a bypass pipeline for connecting the discharge pipeline and the suction pipeline, wherein a predetermined valve is formed thereon; a control means for controlling an operation of the centrifugal compressor; and a detecting means for generating a predetermined signal to the control means if the operation of the centrifugal compressor is suddenly stopped, thereby opening the bypass pipeline.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a centrifugal compressor, and more particularly, to a reverse rotation preventing structure of a centrifugal compressor, which is capable of preventing a reverse rotation in the compressor caused by a backward flow of a fluid due to a pressure difference between a suction side and a discharge side, when an operation of the compressor is suddenly stopped due to a power failure or a power shutdown caused by an abnormal operation of the compressor. 
   2. Description of the Related Art 
   Generally, a compressor is a machine that converts the mechanical energy into the compression energy of a compressive fluid, and is classified into a reciprocating type, a scroll type, a centrifugal (turbo) type and a vane (rotary) type. 
   Among them, the centrifugal compressor (so-called turbo compressor) sucks a fluid in an axial direction using a rotation force of an impeller and then discharges the fluid in a centrifugal direction, to thereby perform a compression operation. The centrifugal compressor is classified into two types, i.e., one-stage centrifugal compressor and two-stage centrifugal compressor, according to the number of the impellers and the compression chambers. Also, the centrifugal compressor is classified into two types, i.e., a back-to-back type and a face-to-face type, according to the type of the arrangement of the impellers. 
   Hereinafter, two-stage centrifugal compressor of the face-to-face type will be described with reference to  FIG. 1 . 
   Referring to  FIG. 1 , the centrifugal compressor of the face-to-face type includes a motor housing  1 , a first bearing plate  2 A and a second bearing plate  2 B disposed at both ends of the motor housing  1 , a shroud plate  3  mounted on an external face of the first bearing plate  2 A, a first compression casing  4 A mounted on an external face of the shroud plate  3 , a bearing cover  5  mounted on an external face of the second bearing plate  2 B, a volute casing  6  covering the bearing cover  5 , a second compression casing  4 B mounted on an external face of the volute casing  6 , and a motor M mounted on the interior of the motor housing  1 . 
   Here, a suction port SP is formed on one side of the motor housing  1  and a discharging port DP is formed on one side of the volute casing  6 . 
   A first compression chamber SC 1  is constituted with the shroud plate  3  and the first compression casing  4 A, and a second compression chamber SC 2  is constituted with the volute casing  6  and the second compression casing  4 B. 
   The motor M providing the rotation force includes a stator MS, a rotor MR mounted on the interior of the stator MS, and a rotating shaft  7  rigidly fixed into the rotor MR. Also, both ends of the rotating shaft  7  of the motor M are passed through the first bearing plate  2 A and the second bearing plate  2 B, respectively. In particular, the rotating shaft  7  is supported in a radial direction by radial bearings  9 A and  9 B disposed inside the plates  2 A and  2 B and is supported in an axial direction by a thrust bearing  10 . 
   A first impeller  8 A and a second impeller  8 B respectively disposed at the first compression chamber SC 1  and the second compression chamber SC 2  are attached to both ends of the rotating shaft  7  of the motor M. Further, the impellers  8 A and  8 B are arranged in the face-to-face type. In other words, the impellers  8 A and  8 B are arranged to face to each other in a direction of sucking the fluid. A reference number  13  that is not described represents a power supplying line. 
   According to the conventional two-stage centrifugal, or turbo, compressor of the face-to-face type, a low-temperature and low-pressure refrigerant is sucked into the suction port SP by the rotation of the rotating shaft  7  and the two impellers  8 A and  8 B. Here, the rotating shaft  7  is rotated by the driving of the motor M, and the two impellers  8 A and  8 B are connected to both ends of the rotary shaft  7 . The sucked refrigerant flows into the first compression chamber SC 1  through the first gas passage  11  and is primarily compressed by the first impeller  8 A. The primarily compressed refrigerant, so-called provisionally compressed refrigerant, is sucked into the second compression chamber SC 2  through the second gas passage  12  and is secondarily compressed by the second impeller  8 B, thereby achieving an effective compression operation. The secondarily compressed refrigerant is gathered in the volute casing  6  and is discharged through the discharge port DP. 
   Therefore, in case where the centrifugal compressor is normally operated, the pressure difference between the suction port SP and the discharge port DP becomes high. 
   However, there is an occasion that an operation of the compressor is suddenly stopped due to a power failure during the normal compression operation or a power shutdown caused by an abnormal operation of the centrifugal compressor. At this time, to achieve the pressure equilibrium between the high-pressure discharge port DP and the low-pressure suction port SP, the refrigerant abruptly flows backward from the discharge port DP to the suction port SP through the refrigerant passage  12 . 
   By the way, due to the abruptly backward flow of the refrigerant from the discharge port DP to the suction port SP, a reverse torque is instantaneously applied to the impellers  8 A and  8 B fixed on both ends of the rotating shaft  7 . Further, the rotating shaft  7  is also rotated in a reverse direction. 
   At this time, in case where the impellers  8 A and  8 B and the rotating shaft  7  are rotated in the reverse direction, there is a problem that a performance of two dynamic-pressure air radial bearings  9 A and  9 B for supporting a radial load of the rotating shaft is degraded. Also, there is a problem that parts constituting the bearings  9 A and  9 B may be damaged. 
   Further, there is a disadvantage that a severe noise occurs due to the abruptly backward flow of the refrigerant from the high-pressure discharge port DP to the low-pressure suction port SP when the operation of the centrifugal compressor is suddenly stopped. 
   Furthermore, an impulse occurring during the backward flow of the refrigerant as well as the damages to the parts result in a shortening of a durability of the centrifugal compressor. 
   SUMMARY OF THE INVENTION 
   Accordingly the present invention has been devised to solve the foregoing problems of the prior art, and it is an object of the invention to provide a reverse rotation preventing structure of a centrifugal compressor, in which a stress that may cause an abnormal noise and a damage to parts of the centrifugal compressor at an emergency stop of the centrifugal compressor can be prevented by forming an additional path that can allow a fluid to be bypassed from a high-pressure side to a low-pressure side when an operation of the centrifugal compressor is suddenly stopped. 
   Further, it is another object of the present invention to improve a durability of the centrifugal compressor and an operational reliability thereof in the long run. 
   According to an aspect of the present invention, a reverse rotation preventing structure of a centrifugal compressor comprises: a suction pipe through which a low-pressure fluid sucked into the centrifugal compressor flows; a discharge pipe extended from a discharge port, through which a high-pressure fluid flows; a fluid passage pipe connected between the suction pipe and the discharge pipe, wherein an opening and closing of the fluid passage pipe is controlled by a predetermined bypass valve mounted thereon; and a power-down detecting means for detecting a power-down of the centrifugal compressor and generating a power-down detecting signal for opening the bypass valve, so that the high-temperature refrigerant is allowed to flow to the suction pipe through the fluid passage pipe. 
   A reverse rotation preventing structure of a centrifugal compressor can prevent an abnormal noise and a damage to parts of the centrifugal compressor by reducing a reverse rotation of a rotating shaft and an abnormal flow of a refrigerant in the centrifugal compressor, which are caused by a backward flow of the refrigerant when an operation of the centrifugal compressor is suddenly stopped. Particularly, the present invention can prevent a dynamic-pressure air bearing for supporting a load of a rotating shaft from being damaged. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above object, other features and advantages of the present invention will become more apparent by describing the preferred embodiment thereof with reference to the accompanying drawings, in which: 
       FIG. 1  is a sectional view of a conventional two-stage centrifugal compressor; 
       FIG. 2  is a sectional view showing a reverse rotation preventing structure of a centrifugal compressor in accordance with an embodiment of the present invention; 
       FIG. 3  is a sectional view showing a reverse rotation preventing structure of a centrifugal compressor in accordance with another embodiment of the present invention; 
       FIG. 4  is a sectional view showing a normal operation state of a centrifugal compressor in accordance with the present invention; and 
       FIG. 5  is a sectional view showing a sudden stop state of a centrifugal compressor in accordance with the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Hereinafter, preferred embodiments relating with a reverse rotation preventing structure of a centrifugal compressor in accordance with the present invention are described in detail with reference to the accompanying drawings. The same reference numbers as the prior art will represent the same elements as the prior art. 
     FIG. 2  is a sectional view showing a reverse rotation preventing structure of a centrifugal compressor in accordance with the present invention. 
   Referring to  FIG. 2 , the reverse rotation preventing structure of the centrifugal compressor includes a structure for preventing a backward flow of a refrigerant from a discharge port DP to a suction port SP in case where an operation of the compressor is suddenly stopped due to a power failure or a power shutdown caused by an abnormal operation of the centrifugal compressor. 
   The reverse rotation preventing structure of the centrifugal compressor in accordance with the present invention includes a suction pipe  51  connected to the suction port SP, a discharge pipe  52  connected to the discharge port DP, a fluid passage pipe  53  formed as a connection pipeline between the suction pipe  51  and the discharge pipe  52 , and a bypass valve  54  formed on the fluid passage pipe  53 . 
   Also, a power-down detecting unit  50  for detecting a continuously supplied power and a power shutdown is mounted on a power supplying line  13 . If the power-down detecting unit  50  detects the power shutdown, the power-down detecting unit  50  transmits a predetermined signal to a control unit and the control unit opens or closes the bypass valve  54  in response to the predetermined signal. 
   An operation of the centrifugal compressor in accordance with the present invention will be described below. 
   In case where an external power fails or is shut down due to an abnormal operation of the centrifugal compressor, the power-down detecting unit  50  mounted on the power supplying line  13  detects the power failure or the power shutdown. If the power-down detecting unit  50  detects the power failure or the power shutdown, the control unit allows the bypass valve  54  to be open. 
   If the bypass valve  54  is open, the high-pressure refrigerant gas of both the discharge pipe  52  and the discharge port DP is bypassed to the suction pipe  51  through the fluid passage pipe  53 . If the pressure equilibrium between the suction pipe  51  and the discharge pipe  52  is achieved, the fluid does not flow through the fluid passage pipe  53  any more. In other words, the pressure equilibrium between the suction port SP and the discharge port DP is achieved by the flow of the fluid through the fluid passage pipe  53 . 
   Meanwhile, it is desired that the fluid passage pipe  53  is disposed at the nearest position of the suction port SP and the discharge port DP so that the high-pressure fluid can rapidly flow to the low-pressure side of the centrifugal compressor. 
   Meanwhile, a check valve that allows the fluid to flow only in one direction can be used as the bypass valve  54  mounted within the fluid passage pipe  53 . The check valve is used to prevent the fluid from flowing from the low-pressure side to the high-pressure side in case where an amount of the fluid exceeding the equilibrium state flows from the high-pressure side to the low-pressure side, thereby preventing an occurrence of a vibration within the centrifugal compressor. 
     FIG. 3  is a sectional view showing a reverse rotation preventing structure of a centrifugal compressor in accordance with another embodiment of the present invention. 
   Referring to  FIG. 3 , if an operation of the compressor is suddenly stopped, the bypass valve  54  is open in response to a signal generated by the power-down detecting unit  50 , so that the fluid primarily flows to the suction pipe  51  through the fluid passage pipe  53 . Then, to prevent a remaining refrigerant gas of the discharge pipe  52  from flowing backward to the suction port SP through the discharge port DP, the centrifugal compressor of the present invention further includes a check valve  55  formed on a predetermined position between the discharge pipe  52  and the fluid passage pipe  53 . At this time, the remaining refrigerant gas of the discharge pipe  52  is the fluid that does not primarily flow to the suction pipe  51  through the fluid passage pipe  53  and remains in the discharge pipe  52 . 
   Hereinafter, an operation of the reverse rotation preventing structure of the centrifugal compressor in accordance with the present invention will be described in detail. 
     FIGS. 4 and 5  are views showing an operation of the centrifugal compressor in accordance with the present invention. 
     FIG. 4  is a view showing a normal operation state of the centrifugal compressor. Referring to  FIG. 4 , the suction pipe  51  and the discharge pipe  52  are connected to the suction port SP and the discharge port DP, respectively. The fluid passage pipe  53  that connects the suction pipe  51  and the discharge pipe  52  is closed by the bypass valve  54 . 
   In a state that the fluid passage pipe  53  is closed, the low-temperature and low-pressure refrigerant that is sucked through the suction port SP is compressed at two stages and is normally discharged through the discharge port DP in a state of high-temperature and high-pressure. 
   In case where an operation of the centrifugal compressor is suddenly stopped due to the power failure or the power shutdown caused by the abnormal operation of the centrifugal compressor, the flow of the fluid is instantaneously stopped and flows backward. 
     FIG. 5  is a view showing a sudden stop state of the centrifugal compressor in accordance with the present invention. Referring to  FIG. 5 , the power-down detecting unit  50  mounted on the power supplying line  13  detects whether or not the power supplied to the centrifugal compressor is down. 
   Further, the power-down detecting unit  50  transmits a predetermined signal to the control unit and the control unit transmits a signal to the bypass valve  54  thereby opening the closed bypass valve  54 . If the bypass valve  54  is open, the abruptly backward flow of the refrigerant from the discharge port DP to the suction port SP through the refrigerant passage  12  (referring to  FIG. 2 ) is stopped. 
   After the suction pipe  51  is communicated with the discharge pipe  52  by the open bypass valve  54 , the fluid continuously flows through the fluid passage pipe  53  until the pressure equilibrium between the suction port SP and the discharge port DP is achieved. 
   The reverse rotation preventing structure of the centrifugal compressor in accordance with the present invention reduces the reverse rotation of the rotating shaft and the abnormal flow of the refrigerant in case where the operation of the centrifugal compressor is suddenly stopped, thereby preventing the abnormal noise and the damage to the parts of the centrifugal compressor. Particularly, the centrifugal compressor of the present invention can prevent the degradation of the dynamic-pressure air bearings for supporting a load of the rotating shaft. 
   Further, the reverse rotation preventing structure of the centrifugal compressor in accordance with the present invention can reduce a long-term stress burdened to the parts of the centrifugal compressor. 
   Furthermore, the present invention can improve an entire durability and a reliability of the centrifugal compressor. 
   Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions can be made without departing from the scope and spirit of the invention as defined in the accompanying claims.