Abstract:
In a centrifugal compressor, for the purpose of preventing the positions of a diaphragm and a head flange in a radial direction from moving with respect to a casing, preventing the unstable vibration of the rotor and enabling an efficient and stable operation even on high-pressure conditions, there is provided a barrel-shaped centrifugal compressor including a casing, a diaphragm located in the casing to define a flow channel, and a head flange attached to the end of the casing by a shear key, wherein in the inner peripheral surface of the casing and the outer peripheral surface of abutment portions of the diaphragm and the head flange in which they are abutted on the inner peripheral surface of the casing, sliding key grooves which are vertical to the surfaces are provided at least two portions in a peripheral direction, and sliding keys are provided in the key grooves.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a barrel-shaped centrifugal compressor, and more particularly, it relates to an assembly structure of a diaphragm and a head flange of a centrifugal compressor. 
     DESCRIPTION OF RELATED ART 
     A centrifugal compressor includes a casing in which a flow channel is formed by a diaphragm, and compresses a gas sucked through a suction port by the rotation of impellers to discharge the gas through a discharge port. A pressure of the gas is held by a casing, a head flange provided at the end of the casing and a shear key which presses the head flange. A rotor having the impellers is rotatably supported by bearings attached to the head flange. 
     In the casing, the gas compressed by the impellers are sealed by an eye labyrinth seal of impellers eye portion, an interstage labyrinth seal between impeller stages, and a balance piston labyrinth seal provided in the final stage. As shown in, for example, FIG. 1 of JP-A-6-249186, the labyrinth seal has a structure including a plurality of ring-like teeth in a gap between a rotor and a stator, and owing to a pressure loss of a fluid flowing through tip gaps of the teeth, the leakage of the fluid is decreased. In this labyrinth seal, when a shaft is displaced in a radial direction with respect to the seal in a state where a leakage flow in the seal has a circumferential velocity, unbalance occurs in a circumferential pressure distribution in the seal, to generate a fluid force which causes the unstable vibration of the rotor (hereinafter referred to as the unstable fluid force). In particular, when the rotor rotates at a high speed or when a differential pressure between an inlet and an outlet of the seal is large, the unstable fluid force becomes larger, which might cause the unstable vibration of the rotor. 
     When the pressure in the casing becomes high, the casing expands owing to an internal pressure, whereby a gap is made among the inner peripheral surface of the casing, a diaphragm and a head flange, and the positions of the diaphragm and head flange in the radial direction might move with respect to the casing. When the positions of the diaphragm and head flange in the radial direction move with respect to the casing, the rotor supported by the bearings and the labyrinth seal attached to the diaphragm also relatively move, and the tip gap of the labyrinth seal might partially decrease. When the tip gap decreases, the increase of the unstable fluid force or contact of the teeth with the rotor might be caused. On the other hand, when the tip gap is enlarged to avoid this problem, the leakage increases to lower an efficiency. 
     BRIEF SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a centrifugal compressor which enables a stable operation even on high pressure conditions while suppressing leakage from a seal. 
     To achieve the above object, according to the present invention, there is provided a barrel-shaped centrifugal compressor comprising a casing, a diaphragm located in the casing to form a flow channel, and a head flange attached to the end of the casing by a shear key, wherein in an inner peripheral surface of the casing and outer peripheral surfaces of contact portions of the diaphragm and the head flange in which they contact with the inner peripheral surface of the casing, at least two sliding key grooves which are vertical to the surfaces are provided in a peripheral direction, and sliding keys are provided in the key grooves. 
     According to the present invention, it is possible to prevent the movement of the diaphragm and the head flange in the radial direction with respect to the casing, and hence the decrease of tip gaps of labyrinth seal teeth is suppressed, whereby the increase of an unstable fluid force and the contact of the teeth with a rotor are avoided, and the rotor can be stabilized. 
     Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1A  and  FIG. 1B  are sectional views which are vertical to a rotating shaft and which show a portion of the sliding key of a centrifugal compressor of an embodiment according to the invention; 
         FIG. 2  is a sectional view which is parallel to a rotating shaft and which shows a whole structure of the centrifugal compressor of the embodiment; 
         FIG. 3A  and  FIG. 3B  are sectional views which are vertical to the rotating shaft and which show the enlarged sliding key locating portion of the centrifugal compressor of the embodiment; 
         FIG. 4  is a sectional view which is parallel to the rotating shaft and which shows the enlarged sliding key locating portion of the centrifugal compressor of the embodiment; and 
         FIG. 5A  and  FIG. 5B  are sectional views which are vertical to a rotating shaft and which show a sliding key locating portion of a centrifugal compressor of another embodiment according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, embodiments of the present invention will be described with reference to the drawings. 
       FIG. 2  is a sectional view which is parallel to a rotating shaft  3  and which shows a whole structure of a centrifugal compressor  1  of an embodiment according to the invention, and  FIG. 1A  and  FIG. 1B  are diagrams showing sections of a locating portion for a sliding key  2  of the centrifugal compressor  1 , which is vertical to the rotating shaft  3 . 
     In  FIG. 2 , a pressure in the centrifugal compressor  1  is kept by a barrel-shaped casing  4  and a head flange  5  located at the end of the casing  4 . The head flange  5  is held by several shear keys  6  divided in a peripheral direction. In the casing  4 , a flow channel  8  is defined by a diaphragm  7  having a vertically dividable structure in the drawing. In the center of the diaphragm  7 , there is disposed a rotor  10  including the rotating shaft  3  and a plurality of stages (e.g., five stages in  FIG. 2 ) of impellers  9  mounted on the rotating shaft  3 . In the diaphragm  7 , there are formed a suction flow channel  11  through which a gas is introduced into the first-stage impellers  9 , a diffuser  12  which converts kinetic energy of the gas discharged from each-stage impellers  9  to pressure energy, a return channel  13  through which the compressed gas from the diffuser  12  is introduced into the next-stage impellers  9 , and a discharge flow channel  14  through which the gas is discharged from the final-stage impellers  9 . The casing  4  is provided with a suction port  15  and a discharge port  16 , and the ports are connected to the suction flow channel  11  and the discharge flow channel  14  of the diaphragm, respectively. 
     The rotor  10  is rotatably supported via radial bearings  17  provided at the end of the rotor on a suction side (the left side of  FIG. 2 ) and the end thereof on a discharge side (the right side of  FIG. 2 ). Moreover, at the suction-side end of the rotor  10  is provided a thrust bearing  18  which is subjected to a thrust load, and at the discharge-side end thereof is provided a balance piston  19  which offsets the thrust load. Moreover, at the discharge-side end, the rotor  10  is connected to a driving unit (not shown) such as a motor, and by the driving of the driving unit, the rotor  10  is rotated. Moreover, by the rotation of the rotor  10 , the gas is sucked through the suction port  15 , successively compressed by the plurality of stages of impellers  9 , and finally discharged through the discharge port  16 . 
     During assembling, after locating the rotor  10  in the diaphragm  7 , the diaphragm  7  and the head flange  5  are inserted into the casing  4  in this order from the left side of  FIG. 2 , and the head flange  5  is held by the shear keys  6 . Afterward, the radial bearings  17  and the like are located. Disassembling is performed in a reverse procedure. 
     In a gap between each-stage impellers  9  and the diaphragm  7  is provided a labyrinth seal, whereby the gas discharged form the impellers  9  is prevented from returning to the inlet side of the impellers  9  or the previous-stage impellers  9  through the gap. Moreover, in a gap between the balance piston  19  and the diaphragm  7  is also provided a labyrinth seal, whereby the high-pressure gas discharged from the final-stage impellers  9  is prevented from leaking to a low pressure portion (a gap between the casing  4  and the diaphragm  7  or the suction flow channel  11 ) in the casing  4 . A partial section A which is an abutment portion of the diaphragm  7  and the head flange  5  with respect to the casing  4  will be described later in detail with reference to  FIG. 3A ,  FIG. 3B , and  FIG. 4 . 
     In  FIG. 1A  as a sectional view which is vertical to the rotating shaft  3 , in a casing inner peripheral surface  21  and a diaphragm outer peripheral surface  22 , sliding key grooves  20   a  and  20   b  which are vertical to the surfaces, respectively, are provided at two portions, and sliding keys  2  are inserted into the grooves. At this time, the sliding key grooves  20   a  and  20   b  are provided below a horizontal plane passing the center of the casing inner peripheral surface  21 , thereby enhancing ease of assembling/disassembly work. It is to be noted that the locating portions for the sliding key  2  in the casing inner peripheral surface  21  and the diaphragm outer peripheral surface  22  have been described above with respect to  FIG. 1A , and a structure in the casing inner peripheral surface  21  and a head flange outer peripheral surface  23  is similar to the above structure, and is shown in  FIG. 1B  including the head flange  5 . 
       FIG. 3A  is a sectional view showing the enlarged partial section A shown in  FIG. 1A .  FIG. 3B  is a sectional view showing the enlarged partial section A shown in  FIG. 1B . The sliding key grooves  20   a  and  20   b  and a sliding key groove  20   c  have the same width (b), and the sliding key groove  20   a  is provided vertically in the casing inner peripheral surface  21  so that a side surface  24  (a sliding surface) of the sliding key groove  20   a  becomes parallel to a straight line passing through the center of the key groove width and the center of the casing inner peripheral surface  21 . The sliding key groove  20   b  is provided vertically in the diaphragm outer peripheral surface  22  so that a side surface  25  (a sliding surface) becomes parallel to a straight line passing through the center of the key groove width and the center of the diaphragm outer peripheral surface  22 . It is to be noted that the locating portions for the sliding key  2  in the casing inner peripheral surface  21  and the diaphragm outer peripheral surface  22  have been described above with respect to  FIG. 3A , and a structure of the locating portions for the sliding key in the casing inner peripheral surface  21  and the head flange outer peripheral surface  23  is similar to the above structure, and is shown in  FIG. 3B  in the case of the head flange  5 . Side surfaces  27  (sliding surfaces) of the sliding key  2  are parallel to each other. In this manner, when the sliding key grooves  20   a ,  20   b  and  20   c  and the sliding keys  2  are provided, the diaphragm  7  and the head flange  5  can move only in a radial direction with respect to the casing  4 . Furthermore, as shown in  FIG. 1A  and  FIG. 1B , sliding keys  2  are provided at two portions in the peripheral direction so that moving directions of the two sliding keys  2  intersect with each other at the center of the rotating shaft  3 , whereby the only relative movement held around the same center is allowed. In consequence, even when the casing  4  expands owing to an internal pressure and gaps between the casing inner peripheral surface  21  and the diaphragm outer peripheral surface  22  and between the casing inner peripheral surface  21  and the head flange outer peripheral surface  23  enlarge, the casing  4 , the diaphragm  7  and the head flange  5  can constantly hold the same center. 
       FIG. 4  is a sectional view which is parallel to the rotating shaft and which shows the enlarged partial section A of  FIG. 2 . As shown in  FIG. 4 , when the abutment portions of the diaphragm  7  and the head flange  5  with respect to the casing  4  are provided with the sliding key  2 , these three components can be held around the same center at the same time. Moreover, an axial length La of the sliding key groove  20   a  in the casing inner peripheral surface  21  is set to be larger than a sum of an axial length L of the sliding key  2  and an axial length Lb of the key groove  20   b  in the diaphragm. Moreover, the axial length Lb of the key groove  20   b  in the diaphragm and an axial length Lc of the key groove  20   c  in the head flange are set to be smaller than the axial length L of the sliding key  2 , respectively, with the proviso that the sum of Lb and Lc is set to be larger than L so that sliding is not constrained. In consequence, while the sliding keys  2  are securely operated, during the assembling and disassembling, an attaching operation of the sliding keys  2  can easily be performed. In the present embodiment, each of Lb and Lc is set to be larger than the half of L. After locating the diaphragm  7  in the casing  4 , the sliding keys  2  are inserted into the sliding key grooves  20   a , and the inserted sliding keys are slid toward the diaphragm  7  and inserted into the sliding key grooves  20   b . Afterward, when the head flange  5  is located, the sliding keys  2  are also inserted into the sliding key grooves  20   c , whereby the assembling can be performed as shown in  FIG. 4 . 
     A dimension of the sliding key  2  is determined so that the key bears the own weights of the diaphragm  7  and the head flange  5  and a variable load due to vibration during the operation of the centrifugal compressor  1 . In the centrifugal compressor in which the casing  4  has an outer diameter of about 1300 mm, the length L, the width b and a height h of the sliding key  2  may be about 100 mm, 60 mm, and 60 mm, respectively. 
     As described above, according to the centrifugal compressor of the embodiment described with reference to  FIG. 1A  to  FIG. 4 , it is possible to prevent the unstable vibration of the rotor during a high-pressure operation. Specifically, in the casing inner peripheral surface and the outer peripheral surfaces of the abutment portion of the diaphragm and the head flange, sliding key grooves which are vertical to the surfaces are provided at least two portions in the peripheral direction, and the sliding keys are provided in the key grooves, whereby the movement of the diaphragm and the head flange in the radial direction with respect to the casing can be prevented. In consequence, the decrease of the tip gaps of the labyrinth seal teeth is suppressed, and the increase of an unstable fluid force and the contact of the teeth with the rotor are avoided, whereby the rotor can be stabilized. Moreover, when the key grooves are located at the positions below the horizontal plane passing the center of the casing, during the assembling and disassembling, the casing inner peripheral surface can be prevented from being damaged by wrongly dropped keys. Furthermore, the key grooves are provided at two positions which do not face each other in the peripheral direction, and hence the increase of a processing amount and the increase of an operation amount during the assembling and disassembling are suppressed, whereby the above effect can be obtained at the lowest cost. 
     It is to be noted that in the above embodiment, the two sliding keys  2  are symmetrically arranged, but do not have to be symmetrically arranged. Moreover, in the embodiment, two sliding keys  2  are arranged so that the keys do not face each other. However, as shown in  FIG. 5A  and  FIG. 5B , also when a pair of sliding keys  2  facing each other and at least one sliding key  2  are provided, a casing  4 , a diaphragm  7  and a head flange  5  can be held around the same center. 
     It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.