Patent Publication Number: US-11022126-B2

Title: Rotary machine

Description:
TECHNICAL FIELD 
     The present invention relates to a rotary machine. 
     BACKGROUND ART 
     A centrifugal compressor as a rotary machine generally includes a rotor that includes a rotary shaft, and a stationary body that includes a casing body provided around the rotor, and compresses, by impellers provided on the rotor, gas sucked in from a suction port and discharges the compressed gas from a discharge port. 
     As a type of the casing body, in addition to a vertical divisional barrel type, there is a horizontal divisional type in which an upper half casing and a lower half casing dividable in a vertical direction are provided and flanges of the two casings are fastened by bolts. 
     A centrifugal compressor for a nitric acid plant sucks in process gas at about 50° C.; however, the temperature of the process gas is raised to about 200° C. along with the pressure rise. 
     At this time, in the horizontal divisional centrifugal compressor, thermal deformation occurs due to temperature difference from an outlet of the process gas to a bearing, in addition to temperature difference from an inlet to the outlet of the process gas. As a result, division surfaces of the two divided casings may be separated. 
     Patent Literature 1 discloses, as a technique to prevent leakage of high-pressure gas from the division surfaces of the upper half casing and the lower half casing, a flange structure of the casing body including the upper half casing and the lower half casing. In the structure, a groove is provided on an upper flange portion of the upper half casing, and a protrusion to be assembled into the groove of the upper flange portion by spigot joint is provided on a lower flange portion of the lower half casing. 
     In Patent Literature 1, if separation occurs on the division surfaces of the casing, the gas is easily collected at an irregular part of the spigot structure, and corrosion may occur on the upper flange portion and the lower flange portion due to the collected gas. Accordingly, it is desirable to eliminate irregularity from the contact surface of each of the upper flange portion and the lower flange portion. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: JP 52-119704 A 
     SUMMARY OF INVENTION 
     Technical Problem 
     Accordingly, an object of the present invention is to provide a rotary machine that makes it possible to prevent leakage of the high-pressure gas from the division surfaces without providing irregularity on the contact surface of each of the upper flange portion and the lower flange portion. 
     Solution to Problem 
     A rotary machine according to the present invention includes: a casing; a rotor that includes a rotatable rotary shaft located inside the casing, and a plurality of stages of impellers fixed to an outer periphery of the rotary shaft; a diaphragm group including diaphragms that are respectively provided in the plurality of stages of the impellers; gas flow paths provided respectively corresponding to the impellers and through which process gas to be compressed flows; and a discharge volute connected to the gas flow paths. The discharge volute is provided to expand inward in an axis line direction of the casing. 
     In the rotary machine according to the present invention, the discharge volute preferably expands inward in the axis line direction, relative to a position on an extension line of a flow of the process gas flowing out from the impeller in a last stage. 
     In the rotary machine according to the present invention, the casing preferably includes an upper half casing and a lower half casing, the upper half casing preferably includes an upper half flange portion, an upper outer peripheral portion of an upper half wall portion connected to the upper half flange portion, and a pedestal that is adjacent to the upper half wall portion in the axis line direction and is higher in height than the upper half flange portion, the lower half casing preferably includes a lower half flange portion and a lower outer peripheral portion of a lower half wall portion connected to the lower half flange portion, and the upper half flange portion and the lower half flange portion are preferably fixed by a first fixing portion. 
     In the rotary machine according to the present invention, a second fixing portion preferably fixes the pedestal and the lower outer peripheral portion by a through bolt. 
     In the rotary machine according to the present invention, the first fixing portion preferably fixes the upper half flange portion and the lower half flange portion by a stud bolt. 
     In the rotary machine according to the present invention, a position of a seat surface of the through bolt that fixes the pedestal and the lower outer peripheral portion is preferably higher than a position of a seat surface of the stud bolt. 
     Advantageous Effects of Invention 
     According to the present invention, it is possible to prevent leakage of the high-pressure gas from the division surfaces without providing irregularity on the contact surface of each of the upper flange portion and the lower flange portion. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  illustrates a schematic configuration of a centrifugal compressor according to an embodiment of the present invention, and is a vertical cross-sectional view taken along a line A-A of  FIG. 2 . 
         FIG. 2  is a diagram illustrating an upper half casing broken at a position near a shaft, according to the embodiment of the present invention. 
         FIG. 3  illustrates a schematic configuration of a centrifugal compressor according to a comparative example, and is a vertical cross-sectional view taken along a line A-A of  FIG. 4 . 
         FIG. 4  is a diagram illustrating an upper half casing of the centrifugal compressor broken at a position near a shaft, according to the comparative example of  FIG. 3 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     An embodiment of the present invention is described below with reference to  FIG. 1  and  FIG. 2 . 
     As illustrated in  FIG. 1 , a rotary machine according to the present embodiment is a uniaxial multistage centrifugal compressor  1  including a plurality of impellers  4 . The centrifugal compressor  1  includes a rotor  2 , a diaphragm group  5 , a sealing device  6 , and a casing assembly  100 . 
     The centrifugal compressor  1  is characterized in that types and positions of bolts fixing a lower half casing  200  and an upper half casing  300  are diversified to secure surface pressure up to end parts of flanges. 
     The rotor  2  rotates around an axis line O. The rotor  2  includes a rotary shaft  3  that extends along the axis line O and serves as a rotor main body, and the plurality of impellers  4  that rotate together with the rotary shaft  3 . 
     The rotary shaft  3  is coupled to a driving source such as a motor. The rotary shaft  3  is rotationally driven by the driving source. The rotary shaft  3  includes a columnar shape around the axis line O, and extends in an axis line direction Da in which the axis line O extends. Both ends of the rotary shaft  3  in the axis line direction Da are rotatably supported by unillustrated bearings. 
     The impellers  4  are fixed to an outer peripheral part of the rotary shaft  3 . The impellers  4  rotate together with the rotary shaft  3  to compress process gas (working fluid) as a compression target, with use of centrifugal force. The impellers  4  are provided in a plurality of stages in the axis line direction Da with respect to the rotary shaft  3 . The impellers  4  according to the present embodiment are disposed between the bearings disposed on both sides in the axis line direction Da with respect to the rotary shaft  3 . Each of the impellers  4  is a so-called closed impeller that includes a disk  4   a , a blade  4   b , and a cover  4   c . A flow path through which the process gas flows is defined by the disk  4   a , the blade  4   b , and the cover  4   c  inside each of the impellers  4 . The plurality of impellers  4  arranged to face the same direction along the axis line direction Da configure an impeller group. The centrifugal compressor  1  according to the present embodiment includes one impeller group. 
     The diaphragm group  5  covers the rotor  2  from outside. The diaphragm group  5  includes a plurality of diaphragms  51  (internal casings) that are arranged in the axis line direction Da, respectively corresponding to the impellers  4  in the plurality of stages. The diaphragms  51  each have a diameter larger than a diameter of each of the impellers  4 , and are arranged so as to be stacked in the axis line direction Da. The diaphragms  51  each include members  51 A and  51 B that are coupled to each other through a return vane  561 . The impellers  4  are respectively accommodated on inner peripheral sides of the diaphragms  51 . The diaphragms  51  and an inner wall  101 W of a casing  101  define flow paths through which the process gas flows, together with the flow paths of the impellers  4 . 
     Here, the flow paths configured by the diaphragms  51  and the inner wall  101 W are specifically described in order from upstream side U that is one side in the axis line direction Da. In the present embodiment, a suction port  52 , a suction flow path  53 , a plurality of diffuser flow paths  54 , a plurality of curved flow paths  55 , a plurality of return flow paths  56 , a discharge volute  57 , and a discharge port  58  are provided in order from the upstream side U through which the process gas flows. 
     Note that the upstream side U and downstream side L of the flow of the process gas used in the present embodiment indicate relative positional relationship. 
     The suction port  52  causes the process gas to flow into the suction flow path  53  from the outside. The suction flow path  53  causes the process gas that has flowed from the outside of the casing  101  described later, to flow into the casing  101 . 
     The suction flow path  53  causes the process gas to flow into the impeller  4  disposed on most upstream side U out of the plurality of impellers  4  arranged in the axis line direction Da. The suction flow path  53  is an annular space that extends inward in a radial direction Dr from the suction port  52 . The suction flow path  53  is connected to an inlet that faces the upstream side U of the impeller  4  while a direction of the suction flow path  53  is gradually changed from the radial direction Dr to the downstream side L that is the other side of the axis line direction Da. The radial direction Dr is a direction orthogonal to the axis line O. 
     The process gas that has flowed out from the impellers  4  to the outside in the radial direction Dr flows into the diffuser flow paths  54 . The diffuser flow paths  54  are respectively connected to outlets of the impellers  4  each facing the outside in the radial direction Dr. The diffuser flow paths  54  extend outward in the radial direction Dr respectively from the outlets of the impellers  4 , and are respectively connected to the curved flow paths  55 . 
     The curved flow paths  55  change a flowing direction of the process gas from a direction toward the outside in the radial direction Dr to a direction toward the inside in the radial direction Dr. In other words, as illustrated in  FIG. 1 , the curved flow paths  55  are flow paths each including a U-shaped vertical cross-section. The curved flow paths  55  are configured by outer peripheral surfaces of the diaphragms  51  outside in the radial direction and an inner peripheral surface of an upper outer peripheral portion  371  of the casing  101  described later. 
     The return flow paths  56  cause the process gas that has flowed through the curved flow paths  55 , to flow into the impellers  4  in next stages, respectively. The return flow paths  56  are each gradually increased in width while extending inward in the radial direction Dr. The return flow paths  56  change the flowing direction of the process gas toward the downstream side in the axis line direction Da, inside the diaphragm group  5  in the radial direction Dr. In the return flow paths  56 , a plurality of return vanes  561  are provided with intervals in a circumferential direction. 
     As illustrated in  FIG. 1 , the discharge volute  57  is formed in an annular shape over the upper half casing  300  and the lower half casing  200  described later. In a comparative example illustrated in  FIG. 3  and  FIG. 4 , the discharge volute  57  is formed so as to expand outward in the axis line direction Da on both of the upper side and the lower side. In contrast, in the present embodiment, the discharge volute  57  is formed so as to expand inward in the axis line direction Da. 
     As compared with the comparative example illustrated in  FIG. 3  and  FIG. 4 , it is possible to avoid the structure in which the casing  101  expands outward in the axis line direction Da because of the expanding (swelling) direction of the discharge volute  57  in the present embodiment. Unlike the comparative example illustrated in  FIG. 3  and  FIG. 4 , an upper half wall portion  370  includes a structure including a pedestal  372  in addition to the upper outer peripheral portion  371  and an upper bearing accommodating portion  373 . The pedestal  372  is lower in height than the upper outer peripheral portion  371 , and is higher in height than an upper half flange portion  310 . An inclined surface  374  connecting the upper outer peripheral portion  371  and the pedestal  372  is provided on the inside in the axis line direction Da, as compared with a wall surface  375  connecting the upper outer peripheral portion  371  and the upper bearing accommodating portion  373  according to the comparative example illustrated in  FIG. 3  and  FIG. 4 . The inclined surface  374  in  FIG. 1  configures an end surface of the upper outer peripheral portion  371  on the downstream side L. 
     The sealing device  6  suppresses leakage of the process gas from the inside to the outside of the casing  101 . The sealing device  6  seals an outer peripheral surface of the rotary shaft  3  over the entire circumference. As the sealing device  6  of the present embodiment, for example, a labyrinth seal is used. 
     The casing assembly  100  accommodates the rotor  2 , the diaphragm group  5 , and the sealing device  6 . The casing assembly  100  includes the lower half casing  200 , the upper half casing  300 , a fixing portion  400 , a seal housing holder  500 , and a sealing member  600 . 
     The lower half casing  200  is fixed to a bottom floor. The lower half casing  200  includes the suction port  52  that opens downward in a vertical direction Dv, and the suction flow path  53  connected to the suction port  52 . A part (lower half) of the discharge volute  57  provided in the lower half casing  200  is connected to the discharge port  58  that opens downward in the vertical direction Dv. 
     The lower half casing  200  is combined with the upper half casing  300  to configure the casing  101 . 
     The casing  101  forms an exterior of the centrifugal compressor  1 . The casing  101  includes a cylindrical shape. The casing  101  is formed such that a center axis thereof is coincident with the axis line O of the rotary shaft  3 . The casing  101  accommodates the impellers  4  in the plurality of stages and the diaphragm group  5 . 
     In the following, more specific configuration of the casing  101  is described with the upper half casing  300  as an example because the lower half casing  200  and the upper half casing  300  include substantially similar configuration except for installation positions. 
     The upper half casing  300  includes a half-split shape, and is disposed on the lower half casing  200  as illustrated in  FIG. 1 . The upper half casing  300  opens downward in the vertical direction Dv. 
     In this example, the suction port  52  and the discharge port  58  described above are provided in the lower half casing  200  and are not provided in the upper half casing  300 . Therefore, a part of the suction flow path  53  provided in the upper half casing  300  and a part of the discharge volute  57  provided in the upper half casing  300  do not communicate with the outside. 
     The shape of the upper half casing  300  as viewed from below in the vertical direction Dv is substantially the same as the shape of the lower half casing  200  as viewed from above in the vertical direction Dv. As illustrated in  FIG. 2 , the upper half casing  300  includes the upper half flange portion  310 , an upper half accommodating recess  350 , and the upper half wall portion  370 . 
     The upper half flange portion  310  is a horizontal surface facing downward in the vertical direction Dv. The upper half flange portion  310  corresponds to a division surface when the casing  101  is divided in a vertical direction. 
     The upper half flange portion  310  includes paired first upper half flange parts  311  and paired second upper half flange parts  312 . 
     The paired first upper half flange parts  311  are separately provided in a width direction Dw with the axis line O in between as viewed from above in the vertical direction Dv. The first upper half flange parts  311  are flat surfaces extending long in the axis line direction Da. Flange surfaces similar to the first upper half flange parts  311  are provided in the lower half casing  200 . 
     The second upper half flange parts  312  are provided on both sides of the first upper half flange parts  311  in the axis line direction Da. The second upper half flange parts  312  are flat surfaces continuous to the first upper half flange parts  311 . The second upper half flange parts  312  are disposed inward of the first upper half flange parts  311  in the width direction Dw as viewed from above in the vertical direction Dv. Flange surfaces similar to the second upper half flange parts  312  are provided in the lower half casing  200 . 
     A plurality of insertion holes  420  into which fixing bolts are respectively inserted are provided in the first upper half flange parts  311  and the second upper half flange parts  312 . The insertion holes  420  penetrate through the upper half flange portion  310  in a thickness direction. The insertion holes  420  are provided at positions matched with positions of fixing holes of the lower half casing  200  when the upper half casing  300  is combined with the lower half casing  200 . 
     The upper half wall portion  370  of the upper half casing  300  is recessed upward in the vertical direction Dv from the upper half flange portion  310 . The upper half accommodating recess  350  is a space covered with an inner peripheral surface of the upper half wall portion  370  as viewed from below in the vertical direction Dv. When the upper half casing  300  and the lower half casing  200  are combined, an accommodating space that is formed by the upper half accommodating recess  350  and a similar recess provided in the lower half casing  200  and extends around the axis line O is formed inside the casing  101 . The members such as the diaphragm group  5  provided in the impellers  4  in the plurality of stages and the sealing device  6  are disposed in the accommodating space. The upper half accommodating recess  350  includes an upper half large-diameter recess  351 , an upper half small-diameter recess  352 , and an upper half step surface  353 . 
     The upper half large-diameter recess  351  is a space in which the diaphragm group  5  and the like are accommodated, together with a similar space of the lower half casing  200 . The upper half large-diameter recess  351  is a space provided around the axis line O. The upper half large-diameter recess  351  is provided on the inside in the width direction Dw so as to be sandwiched between the two first upper half flange parts  311  as viewed from below in the vertical direction Dv. The upper half large-diameter recess  351  includes an upper half corner region  351   a  that is located at a position adjacent to the upper half small-diameter recess  352  in the axis line direction Da, outside the upper half small-diameter recess  352  in the width direction Dw, as viewed from below in the vertical direction Dv. 
     The upper half small-diameter recess  352  is a space in which the sealing device  6  is accommodated, together with a similar recess of the lower half casing  200 . The upper half small-diameter recess  352  is adjacent to the upper half large-diameter recess  351  in the axis line direction Da, and extends in the axis line direction Da. The upper half small-diameter recess  352  is provided on each of both sides of the upper half large-diameter recess  351  in the axis line direction Da. The upper half small-diameter recess  352  is a space formed around the axis line O. The upper half small-diameter recess  352  is provided between the two second upper half flange parts  312  as viewed from below in the vertical direction Dv. The upper half small-diameter recess  352  is smaller in size in the radial direction Dr than the upper half large-diameter recess  351 . 
     The upper half step surface  353  is a surface extending in the radial direction Dr between the upper half large-diameter recess  351  and the upper half small-diameter recess  352  on the downstream side L. The upper half step surface  353  is a part of an inner surface defining the upper half large-diameter recess  351 . More specifically, the upper half step surface  353  is a part of the inner surface of the upper half casing  300  facing inward in the axis line direction Da, and a predetermined region on the axis line O side is recessed toward the downstream side L ( FIG. 1  and  FIG. 2 ). The upper half step surface  353  is a surface that reaches the upper half flange portion  310  and is continuous to a similar step surface of the lower half casing  200  when the upper half casing  300  and the lower half casing  200  are combined. 
     The upper half wall portion  370  ( FIG. 1  and  FIG. 2 ) includes the upper half accommodating recess  350  and is connected to the upper half flange portion  310  at a peripheral edge. The upper half wall portion  370  includes the upper outer peripheral portion  371  and the upper bearing accommodating portion  373  that has a dimension in the vertical direction Dv smaller than that of the upper outer peripheral portion  371  in side view. The pedestal  372  that is higher in height than the upper half flange portion  310  is provided adjacently to the upper outer peripheral portion  371  in the axis line direction Da. The pedestal  372  is lower in height than the upper outer peripheral portion  371 , that is, has a dimension in the vertical direction Dv smaller than that of the upper outer peripheral portion  371  in side view. The upper outer peripheral portion  371  and the pedestal  372  are connected to each other through the inclined surface  374 , and the pedestal  372  and the upper bearing accommodating portion  373  are connected to each other through a wall surface  376 . 
     The inclined surface  374  ( FIG. 1 ) gradually inclines more towards the axis line O from the upstream side U toward the downstream side L in the axis line direction Da as the upper half step surface  353  is recessed toward the downstream side L in the axis line direction Da as described above, in order to secure a thickness necessary to withstand pressure during operation of the centrifugal compressor  1 . 
     The upper outer peripheral portion  371  is formed in a semi-cylindrical shape, and the pedestal  372  is formed such that a top surface thereof is substantially parallel to the upper half flange portion  310 . As illustrated in  FIG. 2 , the pedestal  372  is provided on each of both sides of the axis line O in the width direction Dw. 
     In the pedestal  372 , a through hole  440  into which a through bolt  430  is inserted is provided so as to penetrate the pedestal  372  in a vertical direction. The through hole  440  is provided on the inside in the axis line direction Da and on the inside in the width direction Dw, relative to a through hole  420 L of  FIG. 4  that is located near the seal housing holder  500  on the downstream side L in the comparative example ( FIG. 4 ) similar to the through hole  440 . In other words, the through hole  440  is provided near the inclined surface  374  that connects the upper outer peripheral portion  371  and the pedestal  372 . The through hole  440  is provided at a position matched with a position of a through hole similarly provided in the lower half casing  200  when the upper half casing  300  is combined with the lower half casing  200 . 
     As illustrated in  FIG. 1 , the lower half casing  200  includes a lower half wall portion  270  connected to the lower half flange portion  210 , as with the upper half wall portion  370  of the upper half casing  300 . The lower half wall portion  270  includes a lower outer peripheral portion  271  and a lower bearing accommodating portion  273  that includes a diameter smaller than that of the lower outer peripheral portion  271 . The lower outer peripheral portion  271  and the lower bearing accommodating portion  273  are connected, through a step surface, in this order from the upstream side U to the downstream side L. 
     Further, the lower half casing  200  includes, on the upstream side U, the suction port  52  that opens downward in the vertical direction Dv, and includes, on the downstream side L, the discharge port  58  that opens downward in the vertical direction Dv. 
     As illustrated in  FIG. 1 , the discharge volute  57  of the present embodiment is provided such that a part of the discharge volute  57  provided in the upper half wall portion  370  of the upper half casing  300  expands inward in the axis line direction Da relative to a position on an extension line of the diffuser flow path  54  that causes the high-pressure gas to flow into the discharge volute  57 . The position on the extension line of the diffuser flow path  54  corresponds to a position on an extension line of the flow of the process gas flowing out from the flow path of the impeller  4  in a last stage. 
     Further, a part of the discharge volute  57  provided in the lower half wall portion  270  is also provided so as to expand inward in the axis line direction Da relative to a position on an extension line of the preceding diffuser flow path  54 . 
     As with the comparative example of  FIG. 3  and  FIG. 4 , when the discharge volute  57  is provided so as to expand outward in the axis line direction Da relative to the position of the extension line of the diffuser flow path  54 , a side wall  101 L (including inclined surface  374 ) of the casing  101  on the downstream side L is located on the downstream side L as compared with the side wall  101 L in the present embodiment ( FIG. 1 ), because of outward expansion of the discharge volute  57 . Accordingly, if the through bolt  430  is provided at an insertion position B near the wall surface  375  of the upper half casing  300  illustrated in  FIG. 3 , the through bolt  430  interferes a peripheral edge part of the discharge port  58  provided in the lower half casing  200 . Accordingly, it is necessary to use other fastening member (such as embedded bolt) in place of the through bolt  430 , or it is necessary to set the insertion position at a position separated on the downstream side L from the insertion position B in  FIG. 3 . In the latter case, the side wall  101 L is located on the downstream side L of the casing  101  as compared with the configuration illustrated in  FIG. 3 , and the length of the rotary shaft  3  is accordingly increased. 
     In contrast, in the present embodiment in which the discharge volute  57  is provided so as to expand inward in the axis line direction Da, even in a case where the insertion position B is set to a position near the inclined surface  374  connecting the upper outer peripheral portion  371  and the pedestal  372 , the through bolt  430  does not interfere the peripheral edge part of the discharge port  58  provided in the lower half casing  200  when the through bolt  430  is inserted into the through hole  440  as illustrated in  FIG. 1 . Therefore, it is possible to adopt the through bolt  430  as a bolt to be inserted into the through hole  440 , which avoids increase of the length of the rotary shaft  3 . Since the rotary shaft  3  is made shorter than that in the comparative example, it is possible to sufficiently secure rigidity of the rotary shaft  3 , and to downsize the casing  101  by reducing the diameter of the rotary shaft  3  while securing rigidity. 
     The fixing portion  400  fixes the lower half casing  200  and the upper half casing  300  so as to form the accommodating space while the upper half flange portion  310  and a flange surface similarly provided in the lower half casing  200  are in contact with each other. 
     The fixing portion  400  according to the present embodiment includes a first fixing portion. The first fixing portion includes insertion holes  420  provided in the upper half flange portion  310 , fixing holes provided in the lower half flange portion  210  similar to the insertion holes  420 , and stud bolts  410  that are screwed into the fixing holes while being inserted into the insertion holes  420 . The stud bolt  410  indicates a bolt threaded at both ends. 
     Further, the fixing portion  400  according to the present embodiment includes a second fixing portion. The second fixing portion includes the through hole  440  provided in the pedestal  372 , a through hole provided in the lower outer peripheral portion  271  of the lower half casing  200 , the through bolt  430 , and a nut  450 . The through hole provided in the lower outer peripheral portion  271  is provided at a position matched with the position of the through hole  440  when the upper half casing  300  is combined with the lower half casing  200 . The through bolt  430  is inserted into these through holes. 
     As illustrated in  FIG. 1 , a position of a seat surface  431  of the pedestal  372  at which the fixed through bolt  430  is located, is higher than a position of a seat surface  411  of each of the stud bolts  410 . The thickness of the upper half casing  300  is secured by the height of the seat surface  431 . 
     More specifically, as described above, the inclined surface  374  gradually inclines more towards the axis line O from the upstream side U toward the downstream side L. Accordingly, when the stud bolts  410  are disposed near the inclined surface  374  such that the height position of the seat surface  431  of the through bolt  430  is substantially equal to the position of the seat surface  411  of each of the stud bolts  410 , it is necessary to form a part of the inclined surface  374  in a recessed shape in order to secure a place where a head of the through bolt  430  is positioned. As a result, the thickness of the upper half casing  300  is reduced. 
     In contrast, as the position of the seat surface  431  of the through bolt  430  is higher than the position of the seat surface  411  of each of the stud bolts  410 , it is possible to position the head of the through bolt  430  at a desired position without shaping a part of the inclined surface  374  in a recessed shape. 
     In a case where a stud bolt is used as the bolt to be inserted into the through hole  440  of the second fixing portion, the fastening force is difficult to be distributed, the surface pressure becomes high around the bolt, and the surface pressure may not be secured up to end parts of a mating surface of the upper half flange portion  310  and the end parts of a mating surface of the lower half flange portion  210  corresponding to the upper half flange portion  310 . As the through bolt  430  is adopted, however, the fastening force of the through bolt  430  is widely distributed, and the surface pressure is secured up to the end parts of the mating surfaces of the upper half flange portion  310  and the lower half flange portion  210 . 
     The seal housing holder  500  is provided on each of one side and the other side of the accommodating space in the axis line direction Da. The sealing device  6  ( FIG. 1 ) is fixed inside the seal housing holder  500 . The seal housing holder  500  includes a cylindrical shape around the axis line O. The rotary shaft  3  is inserted into the seal housing holder  500  in a state where the sealing device  6  is held inside the seal housing holder  500 . The seal housing holder  500  is fixed to the lower half casing  200  and the upper half casing  300  through the sealing member  600 . 
     The sealing member  600  seals a space between the lower half casing  200  and the seal housing holder  500  and a space between the upper half casing  300  and the seal housing holder  500 . The sealing member  600  is provided on an outer peripheral surface of the seal housing holder  500  on the outside in the radial direction, and is in contact with the inner peripheral surface of the upper half small-diameter recess  352  and an inner peripheral surface of a similar recess provided in the lower half casing  200 . The sealing member  600  of the present embodiment is an O-shaped ring. 
     In the present embodiment, the upper half casing  300  is placed, from above in the vertical direction Dv, on the lower half casing  200  on which the rotor  2  and the diaphragm group  5  have been placed. In this state, the stud bolts  410  are respectively inserted into the insertion holes  420  of the upper half casing  300 , and front end (lower end) parts of the stud bolts  410  are respectively screwed into the fixing holes of the lower half casing  200 . Further, the through bolt  430  is inserted into the through hole  440  of the pedestal  372 , and the nut  450  is screwed to a thread part of the penetrating through bolt  430 . As a result, the centrifugal compressor  1  that includes the casing assembly  100  and the rotor  2  disposed inside the casing assembly  100  is assembled. 
     [Effects] 
     Effects achieved by the centrifugal compressor  1  according to the present embodiment are described below. 
     When the centrifugal compressor  1  is operated, the high-pressure process gas flows to cause large pressure in the space in which the diaphragm group  5  and the like are disposed. According to the centrifugal compressor  1 , it is possible to prevent leakage of the process gas from a space between the lower half casing  200  and the upper half casing  300  even if such large pressure occurs. 
     Further, in addition to the pressure problem, the division surfaces may be separated due to temperature rise that accompanies pressure rise of the process gas. For example, when the centrifugal compressor  1  is used for a nitric acid plant, the process gas at about 50° C. is raised to about 200° C. along with the pressure rise. Therefore, in the casing  101 , temperature difference occurs between the upstream side U and the downstream side L of the process gas. According to the centrifugal compressor  1 , however, it is possible to avoid thermal deformation due to such temperature difference and to prevent occurrence of separation of the division surfaces of the upper half casing  300  and the lower half casing  200 . 
     The centrifugal compressor  1  according to the present embodiment includes the following characteristic configuration in order to prevent leakage of the high-pressure gas from the inside of the casing. 
     First, the part of the discharge volute  57  provided in the upper half casing  300  and the part of the discharge volute  57  provided in the lower half casing  200  are both provided so as to expand inward in the axis line direction Da. This makes it possible to provide the side wall  101 L (side wall of each of upper half wall portion  370  and lower half wall portion  270 ) of the casing  101  having the thickness corresponding to necessary rigidity, to be receded on the inside in the axis line direction Da as much as possible on the downstream side L. 
     Since the side wall  101 L defining the discharge volute  57  is provided to be receded on the inside in the axis line direction Da, it is possible to set the position of the bolt that is used to assemble the lower half casing  200  and the upper half casing  300  near the sealing device  6  on the downstream side L, to a position on the inside in the axis line direction Da, relative to the position of the insertion hole  420 L in the comparative example ( FIG. 4 ) in which the discharge volute  57  is provided so as to expand outward in the axis line direction Da. In addition, since the side wall  101 L is not present at the position of the insertion hole  420 L, it is possible to bring the position of the bolt close to the axis line O, that is, it is possible to set the position of the bolt to a position on the inside in the width direction Dw relative to the position of the insertion hole  420 L in the comparative example ( FIG. 4 ). 
     In order to secure necessary thickness of the side wall  101 L even though the bolt is provided, the pedestal  372  that is higher in height than the upper half flange portion  310  is provided, and the pedestal  372  and the lower half wall portion  270  are fastened by the through bolt  430 . 
     Using the through bolt  430  makes it possible to widely distribute fastening force and to secure surface pressure up to the end parts of the mating surfaces of the upper half flange portion  310  and the lower half flange portion  210 . This allows for securement of high sealing property. In addition, the through bolt  430  causes the fastening force to act near inner ends of the division surfaces (flanges), as compared with the fastening position ( 420 L) in the comparative example ( FIG. 4 ). This sufficiently contributes to prevention of separation of the division surfaces. 
     Accordingly, the centrifugal compressor  1  makes it possible to more reliably suppress leakage of the high-pressure fluid such as working fluid flowing inside. 
     Hereinbefore, the embodiment of the present invention has been described in detail with reference to drawings; however, the configurations and the combinations thereof in the above-described embodiment are illustrative, and addition, omission, substitution, and other modification of the configurations may be made without departing from the scope of the present invention. Further, the present invention is not limited by the embodiment and is limited only by Claims. 
     In the above-described embodiment, the through bolt  430  is provided on each of the paired pedestals  372  and  372  located on both sides in the width direction Dw, that is, is provided at each of two positions in total. The number of through bolts  430 , however, is not limited thereto, and a plurality of through bolts  430  may be provided on one pedestal  372  in order to sufficiently suppress leakage of the process gas. 
     Further, the centrifugal compressor  1  has been described as an example of the rotary machine in the above-described embodiment; however, the rotary machine is not limited thereto. For example, the rotary machine may be a supercharger or a pump. 
     REFERENCE SIGNS LIST 
     
         
           1  Centrifugal compressor (rotary machine) 
           2  Rotor 
           3  Rotary shaft 
           4  Impeller 
           5  Diaphragm group 
           51  Diaphragm 
           51 A,  51 B Member 
           52  Suction port 
           53  Suction flow path 
           54  Diffuser flow path 
           55  Curved flow path 
           56  Return flow path 
           57  Discharge volute 
           58  Discharge port 
           6  Sealing device 
           100  Casing assembly 
           101  Casing 
           101 L Side wall 
           101 W Inner wall 
           200  Lower half casing 
           210  Lower half flange portion 
           253  Lower half step surface 
           270  Lower half wall portion 
           271  Lower outer peripheral portion 
           273  Lower bearing accommodating portion 
           300  Upper half casing 
           310  Upper half flange portion 
           311  First upper half flange part 
           312  Second upper half flange part 
           350  Upper half accommodating recess 
           351  Upper half large-diameter recess 
           352  Upper half small-diameter recess 
           353  Upper half step surface 
           370  Upper half wall portion 
           371  Upper outer peripheral portion 
           372  Pedestal 
           373  Upper bearing accommodating portion 
           374  Inclined surface 
           375  Wall surface 
           376  Wall surface 
           400  Fixing portion 
           410  Stud bolt (first fixing portion) 
           411  Seat surface 
           420 ,  420 L Insertion hole (first fixing portion) 
           430  Through bolt (second fixing portion) 
           431  Seat surface 
           440  Through hole (second fixing portion) 
           450  Nut (second fixing portion) 
           500  Seal housing holder 
           600  Sealing member 
         O Axis line 
         Da Axis line direction 
         Dr Radial direction 
         Dv Vertical direction 
         Dw Width direction