Steam turbine

A steam turbine includes a turbine casing, in which a turbine rotor is accommodated so as to extend along a direction of flow of steam, and a plurality of turbine pressure sections are mounted to the turbine rotor, which includes, in combination, at least two or more of a turbine high pressure portion, a turbine intermediate pressure portion and a turbine low pressure portion. The turbine casing is divided into two casing sections, each of the divided turbine casing sections being further divided into a turbine casing upper half and a turbine casing lower half, and the turbine casing lower halves of the divided turbine casing sections being connected to each other by a fastening member such as stud bolt inserted from a side of the turbine low pressure portion.

BACKGROUND OF THE INVENTION
 The present invention relates to a steam turbine in which two or more
 turbine pressure sections including a high pressure turbine, an
 intermediate pressure turbine and a low pressure turbine are combined and
 accommodated into one turbine casing.
 In a conventional steam turbine, in order to increase an output power
 thereof, a turbine casing is divided into a high pressure turbine casing,
 an intermediate pressure turbine casing and a low pressure turbine casing,
 and a turbine rotor (turbine shaft) provided with a turbine nozzle and a
 turbine movable blade are accommodated in each of the casings to
 constitute a high pressure turbine section, an intermediate pressure
 turbine section and a low pressure turbine section, and the turbine rotors
 of the respective turbine sections are directly connected in their shafts
 in so-called a power train connection for operation.
 If the high, intermediate and low pressure turbines are arranged as the
 power train, although depending on its output power, the steam turbine has
 a long span of at least about 30 m or longer. Therefore, two or more of
 the high, intermediate and low pressure turbines are combined and
 accommodated in one casing to shorten the span, thereby realizing a
 so-called high-low (high-and-low) pressure integrated type turbine or a
 high-intermediate (high-and-intermediate) pressure integrated type
 turbine.
 If the steam turbine is formed into any of the high-low pressure integrated
 type turbine and the high-intermediate pressure integrated type turbine,
 the turbine rotor must inevitably handle steam having different pressures
 and temperatures. However, in recent years, there is realized a high-low
 pressure integrated turbine rotor or a high-intermediate pressure
 integrated turbine rotor, in which a portion of the turbine rotor which is
 exposed to steam having high pressure and temperature is made stronger
 against high-temperature, and a portion of the turbine rotor which is
 exposed to steam having low pressure and temperature is provided with
 tensile strength and toughness against low temperature by changing thermal
 treatment conditions.
 Further, in a recent thermal power plant, there has been widely used a
 combined cycle power plant in which a steam turbine and a heat recovery
 means are combined with a gas turbine instead of a conventional power
 plant.
 As a steam turbine applied to this combined cycle power plant, one having
 output power of 100 MW or more is selected in view of output power of 100
 MW of a current gas turbine, the steam pressure is set to 100 kg/cm.sup.2,
 the steam temperature is set to 500.degree. C., the blade height of the
 turbine movable blade of the final stage of the lower pressure turbine is
 made to 36 inches or higher in a region of 50Hz at the revolution number
 of 3,000 rpm and is made to 33.5 inches or higher in a region of 60Hz at
 the revolution number of 3,600 rpm. In this case, since the steam turbine
 is made into a so-called single-shaft type turbine in which the shaft is
 directly coupled to the gas turbine, the high-low pressure integrated type
 or the high-intermediate pressure integrated type is employed to shorten
 the shaft span and to reduce the site or space required for installation.
 As described above, in the combined cycle power plant, which has widely and
 mainly utilized instead of the conventional power plant, the number of
 shafts directly coupling the steam turbine to the gas turbine is made five
 or more to increase the total output power to 1,000 MW or greater, and the
 steam turbine is made into the high-low pressure integrated type or the
 high-intermediate pressure integrated type, and the area required for
 installing the five shafting, i.e. shaft-alignment, is further reduced so
 as to effectively utilize the site or space.
 In a recent thermal power plant, even if the high-low pressure integrated
 type or the high-intermediate pressure integrated type is employed for a
 steam turbine applied to the combined cycle power plant so as to further
 reduce the area required for installation, there provide several problems
 such as followings in its structure.
 PROBLEM 1
 For example, in the case of a steam turbine employing the high-low pressure
 integrated type, as shown in FIG. 10, turbine nozzles 2 and turbine
 movable blade 3 of the high-low pressure integrated type rotor 1 are
 combined to form a pressure stage 4, and the stage 4 is arranged in a
 multistage manner along a flowing direction of steam, and the stage 4 is
 accommodated in a turbine casing 5.
 The turbine casing 5 is divided into a high pressure turbine casing section
 6 made of cast steel and a low pressure turbine casing section 7 made of
 steel plate. When the low pressure turbine casing section 7 is connected
 to the high pressure turbine casing section 6, a high pressure turbine
 casing flange 9a and a low pressure turbine casing flange 9b provided
 downstream of a low pressure steam inlet 8 are connected with each other
 by means of stud bolt 10 inserted from the side of the high pressure
 turbine casing section 6.
 The turbine casing 5 including both the high and low pressure turbine
 casing sections 6 and 7 is formed into a split type comprising upper half
 portion and a lower half portion.
 In such turbine casing 5, when the high pressure turbine casing flange 9a
 which is the lower half portion and the low pressure turbine casing flange
 9b which is the lower half portion are connected to each other, since the
 stud bolt 10 is inserted from the side of the high pressure turbine casing
 section 6, there is a problem that the low pressure steam inlet 8
 constitutes an obstacle for the connecting operation, and this requires
 much labor for a worker.
 Especially in a recent combined cycle power plant, it is required to
 increase both the output powers of the gas turbine and the steam turbine
 and to reduce the number of shaft connection or alignment to reduce the
 area required for installation. Accordingly, the diameter of the low
 pressure steam inlet 8 tends to be greater and thus, its connecting
 operation takes much labor for the worker, and a new or improved
 countermeasure has been required.
 PROBLEM 2
 In the conventional steam turbine, as shown in FIG. 12, the turbine casing
 5 has a double cylindrical structure comprising an outer (external) casing
 11 and an inner (internal) casing 12, and for example, a high-intermediate
 pressure integrated turbine rotor 15 comprising a turbine high pressure
 portion 13 and a turbine intermediate pressure portion 14 is accommodated
 in the internal casing 12. Similarly, a low turbine casing 16 is formed
 into a double cylindrical structure comprising an outer casing 16a and an
 inner casing 16b, a low pressure turbine rotor 18 including turbine low
 pressure portions 17a and 17b having opposite directions of stream flow is
 accommodated in the inner casing 16b, and the low pressure turbine rotor
 18 and the high-intermediate pressure integrated turbine rotor 15 are
 connected with each other through a coupling 19.
 In the case of another type steam turbine as shown in FIG. 13, for example,
 the high-intermediate pressure integrated turbine rotor 15 is accommodated
 in the inner casing 12 as in the above case, and the low pressure turbine
 rotor 18 including a turbine low pressure portion 20 having a single
 current of steam is accommodated in the inner casing 16b of the low
 pressure turbine casing 16. In each of the low pressure turbines 16 shown
 in FIGS. 12 and 13, a turbine exhaust chamber 21 is formed in a cone-like
 recess 22 and is connected to a steam condenser (not shown).
 In each of the steam turbines shown in FIGS. 12 and 13, the
 high-intermediate pressure integrated turbine 15 and the low pressure
 turbine rotor 18 are pivotally supported by three or four journal bearing
 23 to elongate the spans of the turbine casings 5 and 16, and a difference
 in temperature (expansion work load) per one turbine stage is relatively
 reduced to provide a margin in design.
 However, in a steam turbine of the high-low pressure integrated type
 applied to the combined cycle power plant, for example, the pressure of
 supplied steam is high, its specific volume is small and its volume flow
 rate is small, and therefore, the height of each of the turbine nozzle 2
 and the turbine movable blade 3 is lower than that of conventional
 turbine. For this reason, the secondary flow loss in the steam flowing
 through the turbine nozzle 2 and the turbine movable blade 3 becomes
 greater as compared with the conventional turbine.
 For example, the steam flowing through the movable blade 3a has pressure
 higher in a belly side 24 of the movable blade 3a than that in a back side
 25 of the adjacent one 36 as shown in FIG. 11. Therefore, when the steam
 flow colliding against a front edge 26 of the one movable blade 3a becomes
 a secondary flow vortex SF (channel vortex) and flows to the back side 25
 of the adjacent movable blade 3b, the secondary flow vortex involves a
 turbine driving steam ST (mainstream), disturbs the flow of the turbine
 driving steam ST, which is a cause to lower the blade efficiency.
 Especially, if the blade height of each of the turbine movable blades 3a
 and 3b is lowered, the steam flow receives influence of boundary layers
 formed at the side of tips (blade tops) and root (blade root portions) of
 the movable blades 3a and 3b, and the flow is deteriorated, which is a
 cause to increase the so-called secondary flow loss. Incidentally, the
 blade height and the secondary flow loss have such a relation as shown in
 FIG. 14 that if the blade height is lower than 25 mm, the secondary flow
 loss is increased.
 As described above, the steam turbine employing the high-low pressure
 integrated type has a problem that the secondary flow loss is increased
 and the blade efficiency is lowered as compared with a conventional
 turbine.
 PROBLEM 3
 In the case of a conventional high-intermediate pressure integrated type
 steam turbine, if the pressure and the temperature of the supplied steam
 are increased, thermal stress generated in the turbine casing is
 increased, and a fastening force of bolt which fastens the flanges
 (horizontal couplings) of the turbine casing divided into the upper half
 portion and the lower half portion is weakened, and there is a possibility
 of steam leakage. Therefore, as shown in FIG. 15, the turbine casing 5 is
 divided, as a double structure, into the outer casing 11 and the inner
 casing 12, and the high-intermediate pressure integrated turbine rotor 15
 including the turbine high pressure portion 13 and the turbine
 intermediate pressure portion 14 is accommodated in the inner casing 12 so
 as to moderate the thermal stress generated in each of the casings 11 and
 12.
 However, in the case of the recent steam turbine employing the
 high-intermediate pressure integrated type or high-low pressure integrated
 type aiming to simplify the structure and to lower the manufacturing
 costs, an expensive cost will be required for forming the turbine casing 5
 into the double structure, which retrogresses to the requirement of the
 times. Therefore, it is desired to form a turbine casing of the steam
 turbine into a single body, but if the turbine casing is formed into the
 single body, there is a problem of the above-described thermal stress and
 a possibility of leaking the steam will be caused.
 Therefore, in the steam turbine employing the high-intermediate pressure
 integrated type or high-low pressure integrated type, if the turbine
 casing is formed into the single body, it is necessary to prepare a
 sufficient countermeasure to moderate the above-described thermal stress
 and to prevent the steam leakage.
 PROBLEM 4
 In the case of a conventional steam turbine in which a high pressure
 turbine rotor including a turbine high pressure portion and a low pressure
 turbine rotor including a turbine low pressure portion disposed so as to
 oppose to the high pressure turbine rotor are directly coupled to each
 other through their shafts, for example, as shown in FIG. 16, a crossover
 tube 29 is provided between a split-type high pressure turbine casing
 upper half 27 and a split-type low pressure turbine casing upper half 28,
 and the turbine exhaust gas which has been expanded by the turbine high
 pressure portion 13 is supplied to opposed turbine low pressure portions
 17a and 17b arranged through the crossover tube 29.
 In the steam turbine of this type, a steam lead tube 31 accommodating a
 governing valve (steam control valve) 30 is continuously and integrally
 formed with the high pressure turbine casing upper half 27, and the steam
 supplied from a steam generator such as a boiler is supplied to a turbine
 high pressure portion 13 while controlling the flow rate thereof in
 accordance with the load by the steam control valve 30.
 Further, in the case of the steam turbine of this type, at the time of a
 periodical inspection, the high pressure turbine casing upper half 27 and
 the low pressure turbine casing upper half 28 are opened. However, if the
 crossover tube 29 and the steam lead tube 30 are provided on the high
 pressure turbine casing upper half 27, a tube flange heating member must
 be removed, a bolt of the tube flange portion must be removed, and the
 crossover tube 29 must be removed and repaired at the time of the periodic
 inspection, the inspection takes a long time, and thus, there provides a
 problem that an operation starting driving schedule is hindered.
 Especially, since the steam lead tube 30 is directly exposed to the steam
 of high pressure and high temperature, seizing is frequently caused on the
 bolt and the nut of the tube flange, and when it is required to remove
 them, such operation takes much labor for a worker for a long time.
 Therefore, in the case of the recent steam turbine employing the high-low
 pressure integrated type or high-intermediate pressure integrated type, it
 is required to improve the structure such that at the time of the periodic
 inspection, the inspection can be carried out within a short time and the
 operation starting driving can be done more rapidly after the inspection.
 PROBLEM 5
 In the case of a conventional steam turbine in which the high-intermediate
 pressure integral type and the low pressure turbine are combined for
 example, as shown in FIGS. 12 and 13, the shafts of the high-intermediate
 pressure integrated turbine rotor 15 and the low pressure turbine rotor 18
 are directly coupled to each other through the coupling 19, each of the
 turbine rotors 15 and 18 is pivotally supported by four or three journal
 bearings 23 so as to enhance the rigidity of the shaft alignment.
 Furthermore, in the case of a steam turbine employing the high-low pressure
 integrated type, for example, as shown in FIG. 17, a high-intermediate-low
 pressure integrated turbine rotor 32 including the turbine high pressure
 portion 13 and the turbine intermediate pressure portion 14 and the
 turbine low pressure portion 20 is pivotally supported by the journal
 bearings 34a and 34b placed on bases 33a and 33b so as to provide the
 margin in design for rigidity of the shaft arrangement. In the steam
 turbine of this type, a turbine exhaust chamber 21 of the turbine low
 pressure portion 20 is formed in the cone-shaped recess 22 so as to secure
 a place for installing the journal bearing 34.
 In generally, in the case of the steam turbine, if the pressure and the
 temperature of the supplied steam are increased and its output power is
 increased, since the number of stages each comprising a combination of the
 turbine nozzle and the movable blade is increased to cope with such
 increased output power, the span of the bearing of the turbine rotor tends
 to be longer. Therefore, in the case of the high-intermediate-low pressure
 integrated turbine rotor 32 provided at its single shaft with the turbine
 high pressure portion 13 and the turbine intermediate pressure portion 14
 and the turbine low pressure portion 20, the bearing span is elongated,
 and if the bearing span is represented by S and the shaft diameter of the
 high-intermediate pressure integrated turbine rotor 32 is represented by
 D.sub.o, as the ratio S/D.sub.o of the shaft diameter to the bearing span
 is increased, the rigidity of the shaft is lowered, the characteristic
 value of the shafting of this kind, e.g., the critical speed is lowered,
 and the probability of generation of the shaft vibration is increased.
 Especially, in the case of a steam turbine applied to the combined power
 plant under the condition that the steam pressure is 100 kg/cm.sup.2, the
 steam temperature is 500.degree. C. and the output power is 100 MW or
 greater, and the height of a turbine movable blade of the final stage of
 the turbine low pressure portion 20 in the region of 50 Hz at the
 revolution number of 3,000 rpm is designed to be 36 inches or more, and
 the height in the region of 60 Hz at the revolution number of 3,600 rpm is
 designed to be 33.5 inches or more, there are problems that the additional
 weight due to employment of long blade as the high-intermediate-low
 pressure integrated turbine rotor 32 having the elongated bearing span is
 added, the critical speed is further lowered, and the secondary critical
 speed approaches the rated revolution speed, and the detuning becomes
 difficult.
 PROBLEM 6
 The conventional turbine low pressure portions 17a, 17b and 20 shown in
 FIGS. 12, 13 and 17 are formed in the cone-shaped recess 22 for securing
 the installation place for the journal bearings 23 and 34b. However, if
 they are formed in the cone-shaped recess 22, the expanded turbine exhaust
 gas from the turbine low pressure portions 17a, 17b and 20 collides
 against the casing wall surface 35, providing a problem that the turbine
 exhaust gas loss is increased. In this case, in order to suppress the
 turbine exhaust gas loss of the turbine exhaust chamber 21 to a low level
 while keeping the shape of the cone-shaped recess 22, it is necessary to
 secure the axial length of the turbine exhaust chamber 21 so that the flow
 rate is sufficiently lowered until the turbine exhaust gas collides
 against the casing wall surface 35.
 However, if the axial length of the turbine exhaust chamber 21 is
 sufficiently secured, the bearing span of the high-intermediate-low
 pressure integrated turbine rotor 15 or the high-intermediate-low pressure
 integrated turbine rotor 32 is further elongated, the rigidity of the
 shaft alignment is lowered and, accordingly, the characteristic value of
 the shaft arrangement, e.g., the critical speed is lowered, which is a
 cause of generation of the shaft vibration. If the shaft diameter is
 increased to prevent the shaft from vibrating, there is a problem of
 rubbing due to steam leakage or contact with labyrinth.
 As described above, if the shape of the conventional turbine exhaust
 chamber 21 is formed into the cone-like recess 22 shape, there are
 provided several problems mentioned above, and it is necessary to improve
 the shape of the turbine elements while securing the installation place
 for the journal bearings 23 and 34b.
 SUMMARY OF THE INVENTION
 The present invention has been accomplished in view of the above
 circumstances, and it is a primary object of the invention to provide a
 steam turbine capable of improving the connection working of a
 high-intermediate pressure integrated turbine casing and a low pressure
 turbine casing accommodating a high-intermediate-low pressure integrated
 turbine rotor.
 It is another object of the present invention to provide a steam turbine
 capable of suppressing, to a low level, the increase in the secondary flow
 loss which is caused by the fact that the pressure and the temperature of
 a turbine driving steam are increased and the blade height of a turbine
 movable blade is lowered as compared with a conventional turbine.
 It is a further object of the present invention to provide a steam turbine
 capable of making strong the fastening force of a bolt when a turbine
 casing is divided into an upper half and a lower half and the divided
 upper and lower halves are connected to each other by the bolt for forming
 the turbine casing in which a high-intermediate-low pressure integrated
 turbine rotor or a high-intermediate pressure integrated turbine rotor
 into a single body.
 It is a still further object of the present invention to provide a steam
 turbine capable of easily removing a turbine casing at the time of a
 periodic inspection.
 It is a still further object of the present invention to provide a steam
 turbine capable of suppressing a shaft from vibrating to a low level and
 suppressing a turbine exhaust gas loss of a turbine exhaust chamber to a
 low level.
 These and other objects can be achieved according to the present invention
 by providing, in one aspect, a steam turbine comprising:
 a turbine casing;
 a turbine rotor accommodated in the turbine casing so as to extend along a
 direction of flow of steam; and
 a plurality of turbine pressure sections to be mounted to the turbine rotor
 including, in combination, at least two or more of a turbine high pressure
 portion, a turbine intermediate pressure portion and a turbine low
 pressure portion,
 wherein the turbine casing is divided into two casing sections, each of the
 divided turbine casing sections being further divided into a turbine
 casing upper half and a turbine casing lower half, the turbine casing
 lower halves of the divided turbine casing sections being connected to
 each other by a fastening member such as stud bolt inserted from a side of
 the turbine low pressure portion.
 In another aspect, there is provided a steam turbine comprising:
 a turbine casing;
 a turbine rotor accommodated in the turbine casing so as to extend along a
 direction of flow of steam; and
 a plurality of turbine pressure sections to be mounted to the turbine rotor
 including, in combination, at least two or more of a turbine high pressure
 portion, a turbine intermediate pressure portion and a turbine low
 pressure portion,
 wherein the turbine casing is divided into two casing sections, each of the
 divided turbine casing sections being further divided into a turbine
 casing upper half and a turbine casing lower half, the turbine casing
 upper halves of the divided turbine casing sections are connected to each
 other by a fastening member such as stud bolt inserted from either one of
 sides of the turbine high pressure portion and the turbine low pressure
 portion.
 In a further aspect, there is provided a steam turbine comprising:
 a turbine casing;
 a turbine rotor accommodated in the turbine casing so as to extend along a
 direction of flow of steam; and
 a plurality of turbine pressure sections to be mounted to the turbine rotor
 including, in combination, at least two or more of a turbine high pressure
 portion, a turbine intermediate pressure portion and a turbine low
 pressure portion, the two or more turbine pressure portions being provided
 with pressure stages each including a turbine nozzle and a movable blade
 in combination,
 wherein a partial arc admission is formed to each of the pressure stages on
 an upstream side of a steam flow in the turbine casing.
 In this aspect, coordinate axes are placed on a center of the turbine rotor
 and the turbine rotor is divided into first, second, third and fourth
 quadrants in the counterclockwise direction, the partial arc admission is
 formed in an angular region connecting the first and fourth quadrants. A
 height of each of the turbine nozzle and the movable blade in the pressure
 stage in which the partial arc admission is formed is set to 25 mm or
 more.
 In a still further aspect, there is provided a steam turbine comprising:
 a turbine casing;
 a turbine rotor accommodated in the turbine casing so as to extend along a
 direction of flow of steam; and
 a plurality of turbine pressure sections to be mounted to the turbine rotor
 including, in combination, at least two or more of a turbine high pressure
 portion, a turbine intermediate pressure portion and a turbine low
 pressure portion,
 wherein the turbine casing is divided into two casing sections, each of the
 divided turbine casing sections being further divided into a turbine
 casing upper half and a turbine casing lower half, the turbine casing
 upper and lower halves of the divided turbine casing sections being formed
 with flanged portions respectively, and at least one of the flanged
 portions of the turbine casing upper and lower halves being formed with a
 steam passage.
 In a still further aspect, there is provided a steam turbine comprising:
 a turbine casing;
 a turbine rotor accommodated in the turbine casing so as to extend along a
 direction of flow of steam; and
 a plurality of turbine pressure sections to be mounted to the turbine rotor
 including, in combination, at least two or more of a turbine high pressure
 portion, a turbine intermediate pressure portion and a turbine low
 pressure portion,
 wherein the turbine casing is divided into two casing sections, each of the
 divided turbine casing sections being further divided into a turbine
 casing upper half and a turbine casing lower half, the turbine casing
 lower halves of the divided turbine casing sections being formed with
 steam inlets.
 In this aspect, the steam inlets includes a high pressure steam inlet
 portion and a low pressure steam inlet portion.
 In a still further aspect, there is provided a steam turbine comprising:
 a turbine casing;
 a turbine rotor accommodated in the turbine casing so as to extend along a
 direction of flow of steam; and
 a plurality of turbine pressure sections to be mounted to the turbine rotor
 including, in combination, at least two or more of a turbine high pressure
 portion, a turbine intermediate pressure portion and a turbine low
 pressure portion,
 wherein the turbine rotor is supported at both longitudinal ends thereof by
 a high pressure side journal bearing and a low pressure side journal
 bearing accommodated in a bearing box in a manner that either one of the
 high pressure side journal bearing and the low pressure side journal
 bearing is overhung apart from a base to shorten a bearing span.
 In this aspect, the journal bearing overhung apart from the base is the low
 pressure side journal bearing.
 The turbine casing is provided with a steam outlet portion on a side of
 which a turbine exhaust chamber is formed, the turbine exhaust chamber is
 formed with a recess opposed to the low pressure side journal bearing, and
 the recess is formed in one of a convex curved surface and a pseudo curved
 surface toward the low pressure side journal bearing. An angle between a
 curved surface and a straight surface or between straight surfaces of the
 pseudo curved surface is set to 140.degree. C. or greater.
 In a still further aspect, there is provided a steam turbine comprising:
 a turbine casing;
 a turbine rotor accommodated in the turbine casing so as to extend along a
 direction of flow of steam; and
 a plurality of turbine pressure sections to be mounted to the turbine rotor
 including, in combination, at least two or more of a turbine high pressure
 portion, a turbine intermediate pressure portion and a turbine low
 pressure portion, the two or more turbine pressure portions being provided
 with pressure stages each including a turbine nozzle and a movable blade
 in combination,
 wherein a steam having pressure of 100 kg/cm.sup.2 or higher and
 temperature of 500.degree. C. or higher is supplied to at least one or
 more of the turbine high pressure portion, the turbine intermediate
 pressure portion and the turbine low pressure portion so that an output
 power of the steam becomes 100 MW or greater, and a height of a turbine
 movable blade of a final stage of the turbine lower pressure portion is
 made to 36 inches or more in a region at a revolution number of 3,000 rpm
 and is made to 33.5 inches or more in a region at a revolution number of
 3,600 rpm.
 According to the steam turbine of the present invention of the characters
 mentioned above, the turbine casing for accommodating the
 high-intermediate-low pressure integrated turbine rotor is divided into
 the high-moderate pressure integrated turbine casing and the low pressure
 integrated turbine casing, and these turbine casing are further divided
 into the turbine casing upper halves and the turbine casing lower halves,
 and when these turbine casings are connected, they are connected by the
 stud bolt to be inserted through the turbine casing lower halves from the
 side of the turbine low pressure portion. Therefore, there is no obstacle
 as compared with the conventional turbine, and it is possible to reduce
 the labor of the worker at the time of the connecting operation.
 Furthermore, according to the steam turbine of the present invention, the
 pressure state having a low blade height is formed with the partial arc
 admission (air passage), and the height of the turbine nozzle and the
 turbine movable blade is set to 25 mm or higher. Therefore, it is possible
 to secure the volume flow rate of the turbine driving steam required for
 the design, it is possible to secure the stable steam flow rate and to
 suppress the secondary flow loss of steam to the low level.
 Still furthermore, at least one of flanges of the turbine casing upper half
 and the turbine casing lower half of the high-intermediate pressure
 integrated turbine casing is formed with the steam passage, and the
 flanges and the connection bolt are cooled. Therefore, it is possible to
 moderate the thermal stress of the turbine casing upper half and the
 turbine casing lower half, and the turbine casings can be formed into a
 single body, and it is possible to reduce its weight and its size.
 Still furthermore, the turbine casing for accommodating the high-low
 pressure integrated turbine rotor is divided into the high pressure
 turbine casing section and the low pressure turbine casing section, and
 these turbine casing sections are further divided into the turbine casing
 upper halves and the turbine casing lower halves, and each of the turbine
 casing sections is provided with the high pressure steam inlet and the low
 pressure steam inlet. Therefore, there is no obstacle as compared with the
 conventional turbine, and hence, at the time of the periodic inspection,
 it is possible to easily open the turbine casing upper halves of the
 turbine casing sections.
 Still furthermore, according to the steam turbine of the present invention,
 at least one of the high pressure side journal bearing and the low
 pressure side journal bearing pivotally supporting the opposite ends of
 the high-intermediate-low pressure integrated turbine rotor is separated
 from the base and overhung so as to shorten the bearing span. Therefore,
 it is possible to maintain the rigidity of the shafting, i.e. shaft
 alignment, at the high level and to suppress the shaft vibration to the
 low level.
 Still furthermore, the recess of the turbine exhaust chamber in the
 high-intermediate-low pressure integrated turbine casing is formed into
 the curved surface or the pseudo curved surface, it is possible to
 suppress the turbine exhaust gas loss to the low level to improve the
 rigidity of the shafting due to the shortening of the bearing span and to
 stably operate the steam turbine.
 The nature and further characteristic features of the present invention
 will be made more clear from the following descriptions made with
 reference to the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
 A steam turbine according to preferred embodiments of the present invention
 will be described hereunder with reference to the accompanying drawings.
 FIG. 1 is a schematic sectional view showing a first embodiment of a steam
 turbine of the present invention, and this first embodiment is applicable
 to solve the "Problem 1" mentioned hereinbefore encountered in the prior
 art.
 The steam turbine according to this first embodiment is applied to a
 combined cycle power plant which is designed such that the height of a
 turbine movable blade of the final pressure state of a turbine low
 pressure portion (section) under the conditions that the steam pressure is
 100 kg/cm.sup.2 or more, the steam temperature is 500.degree. C. or more,
 and the blade height is 36 inches or more in a region of 50 Hz at the
 revolution number of 3,000 rpm and is 33.5 inches in a region of 60 Hz at
 the revolution number of 3,600 rpm.
 This steam turbine employs a high-intermediate-low pressure type, for
 example, and a turbine high pressure portion 36, a turbine intermediate
 pressure portion 37 and a turbine low pressure portion 38 are combined
 into one high-intermediate-low pressure integrated turbine rotor (turbine
 shaft) 39 and accommodated in a turbine casing 40. The
 high-intermediate-low pressure integrated turbine rotor 39 constitutes
 pressure stages 43 each comprising a combination of a turbine nozzle 41
 and a turbine movable blade 42, and the stages 43 are arranged in a row
 along the direction of flow of steam, and these stages 43 are accommodated
 in the turbine casing 40.
 The high-intermediate-low pressure integrated turbine rotor 39 is supported
 at its opposite ends by journal bearings 45a and 45b provided on bases
 (base portions) 44a and 44b.
 On the other hand, the turbine casing 40 is divided into a
 high-intermediate pressure integrated turbine casing section 46 and a low
 pressure integrated turbine casing section 47 and is provided, at the side
 of the high-intermediate pressure integrated turbine casing section 46,
 with a low pressure steam inlet 48 for supplying low pressure steam to the
 turbine low pressure portion 38.
 The high-intermediate pressure integrated turbine casing section 46 and the
 low pressure integrated turbine casing section 47 are further divided into
 split turbine casing upper halves 46a, 47a and split turbine casing lower
 halves 46b, 47b, respectively, and each of the upper and lower halves 46a,
 47a . . . is provided with a high-moderate pressure integrated turbine
 casing flange 49 and a low pressure turbine casing flange 50.
 When the high-intermediate pressure integrated turbine casing flange 49 and
 the low pressure turbine casing flange 50 of the lower halves 46b, 47b are
 connected to each other, they are connected by means of stud bolt 51
 inserted from the turbine low pressure portion 38 in this first
 embodiment. The high-intermediate pressure integrated turbine casing
 flange 49 and the low pressure turbine casing flange 50 of the higher
 halves 46a, 47a are connected to each other by inserting the stud bolt 51
 from the turbine low pressure portion 38 or the turbine intermediate
 pressure portion 37.
 As described above, in this first embodiment, since the stud bolt 51 for
 connecting the high-intermediate pressure integrated turbine casing flange
 49 and the low pressure turbine casing flange 50 of the lower halves 46b,
 47b is inserted from the side of the turbine low pressure portion 38, the
 output power of the steam turbine is increased and in this case, even if
 the diameter of the low pressure steam inlet 48 is increased, there
 constitutes no obstacle and, thus, when the flanges are connected to each
 other, it is possible to reduce the labor of a worker, the fastening
 operation of the stud bolt 51 can reliably be carried out, and the steam
 leakage can surely be prevented.
 FIG. 2 is a schematic sectional view showing a second embodiment of a steam
 turbine of the present invention, in which constituent elements similar to
 those in the first embodiment and portions corresponding thereto are
 represented by the same reference numerals. This second embodiment is
 particularly applicable to solve the "Problem 2" encountered in the prior
 art mentioned hereinbefore.
 In the steam turbine according to this second embodiment, among the stages
 43 each comprising the combination of the turbine nozzle 41 and the
 turbine movable blade 42, a stage having the low blade height H is formed
 with a partial arc admission (air passage) 52 which is partially opened
 along its annular direction and the rest is closed.
 In this second embodiment, if the pressure and the temperature of the steam
 supplied to the steam turbine are increased, its volume flow rate is
 reduced, and at the time of designing, the height H of each of the turbine
 nozzle 41 and the turbine movable blade 42 is lowered, and in this case,
 the secondary flow loss in the steam flow passing through the turbine
 nozzle 41 and the turbine movable blade 42 is increased. The second
 embodiment has been accomplished in view of this fact, and among the
 stages 43, the one stage located upstream of the steam flow is formed with
 the partial arc admission 52 so as to increase the height of the turbine
 nozzle 41 and the movable blade 42 to 25 mm or higher. In the stage
 located downstream of the steam flow, the height of the turbine nozzle 41
 and the movable blade 42 is 25 mm or more, and therefore, the stage is
 formed with a full arc admission.
 As shown in FIG. 3, when coordinate axes are placed on the center 0 of the
 high-intermediate-low pressure integrated turbine rotor 39 and the turbine
 rotor is divided into the first, second third and fourth quadrants in the
 counterclockwise direction, the partial arc admission 52 is set such that
 the partial arc admission angle .alpha. is in a region from the first to
 fourth quadrants in the clockwise direction. The stages 43 in the rest of
 the annularly formed stages are occluded with blind plates 53.
 As described above, in this embodiment, since the stage located upstream of
 the steam flow is formed with the partial arc admission 52 such that the
 height H of the turbine nozzle 41 and the turbine movable blade 42 becomes
 25 mm or higher so as to secure the volume flow rate required for the
 design thereof, it is possible to secure the stable steam flow rate and to
 suppress the secondary flow loss of steam to the low level.
 Further, in this embodiment, the partial arc admission angle .alpha. of the
 partial arc admission is set in the range from the first to fourth
 quadrants in the clockwise direction so that the pushing force Fs of steam
 is applied toward the turbine casing lower half of the
 high-intermediate-low pressure integrated turbine rotor 39 and therefore,
 it is possible to maintain the high-intermediate-low pressure integrated
 turbine rotor 39 in a relatively stable state.
 FIG. 4 is a partial sectional view showing a third embodiment of a steam
 turbine of the present invention, in which constituent elements similar to
 those in the first embodiment and portions corresponding thereto are
 represented by the same reference numerals. This third embodiment
 represents one suitable for solving the "Problem 3" encountered in the
 prior art mentioned hereinbefore.
 The steam turbine according to this third embodiment employs a
 high-intermediate-low pressure integrated type for example. A steam
 passage 55 is formed in at least one of flanges (horizontal couplings)
 54a, 54b of the turbine casing upper halve 46a and the turbine casing
 lower halve 46b of the high-intermediate integrated turbine casing 46 in
 the high-intermediate pressure integrated turbine casing 46 and the low
 pressure turbine casing 47 accommodating the high-intermediate-low
 pressure integrated turbine rotor 39 including the stage 43 comprising the
 combination of the turbine nozzle 41 and the movable blade 42. The flange
 54a of the turbine casing upper half 46a and the flange 54b of the turbine
 casing lower half 46b are cooled by flowing steam supplied from the
 turbine high pressure portion 36 so as to maintain the strength thereof as
 well as the strength of the bolt which connects the turbine casing upper
 half 46a and the turbine casing lower half 46b.
 As described above, in this embodiment, the steam passage 55 is formed in
 at least one of flanges 54a, 54b of the turbine casing upper halve 46a and
 the turbine casing lower halve 46b, and the flanges 54a, 54b and the bolt
 56 are cooled to maintain their strength at the high level. Therefore,
 even if the turbine casing upper half 46a and the turbine casing lower
 half 46b are formed into a single casing, such a single casing will
 provide a sufficient strength and it becomes possible to prevent the steam
 from leaking from the gap between the flanges 54a and 54b.
 Therefore, according to this embodiment, since the high-intermediate
 pressure integrated turbine casing 46 can be formed into the single body,
 the weight and size thereof can be reduced compactly, and the
 manufacturing cost can also be reduced.
 FIG. 5 is a schematic sectional view showing a fourth embodiment of a steam
 turbine of the present invention, in which constituent elements similar to
 those in the first embodiment and portions corresponding thereto are
 represented by the same reference numerals. This embodiment is
 particularly applicable to solve the "Problem 4" encountered in the prior
 art mentioned hereinbefore.
 The steam turbine according to this embodiment employs a high-low pressure
 integrated type. In the low pressure turbine 47 and the high pressure
 turbine casing 58 for accommodating, therein, a high-low pressure
 integrated turbine rotor 57 having the pressure stage 43 comprising the
 combination of the turbine nozzle 41 and the turbine movable blade 42, the
 turbine casing lower halves 46b, 47b are with provided a high pressure
 steam inlet 59 and a low pressure steam inlet 48, respectively.
 As described above, according to this embodiment, since the turbine casing
 lower halves 46b, 47b are provided the high pressure steam inlet 59 and
 the low pressure steam inlet 48, respectively. Therefore, at the time of
 periodic inspection, it is possible to easily remove the turbine casing
 upper halves 46a, 47a, and the time of the periodic inspection can be
 shortened.
 FIG. 6 is a schematic sectional view showing a fifth embodiment of a steam
 turbine of the present invention, in which constituent elements similar to
 those in the first embodiment and portions corresponding thereto are
 represented by the same reference numerals. This fifth embodiment is
 particularly suitable for solving the "Problem 5" in the prior art.
 The steam turbine of this fifth embodiment employs a high-intermediate-low
 pressure integrated type. The high-intermediate-low pressure integrated
 turbine rotor 39 including the turbine high pressure portion 36, the
 turbine intermediate pressure portion 37 and the turbine low pressure
 portion 38 is accommodated in the high-intermediate-low pressure
 integrated turbine casing 60. Between the opposite ends of the
 high-intermediate-low pressure integrated turbine rotor 80, one end of the
 high-intermediate-low pressure integrated turbine rotor 39 closer to the
 turbine high pressure portion 36 is pivotally supported by a high pressure
 side journal bearing 63 accommodated in a high pressure bearing box 62
 placed on the base 61a, another end of the high-intermediate-low pressure
 integrated turbine rotor 39 closer to the turbine low pressure portion 38
 is pivotally supported by a low pressure side journal bearing 65
 accommodated in a low pressure bearing box 64 placed on the base 61b. The
 low pressure bearing box 64 is abutted against a cone-shaped recess 67 of
 an exhaust chamber 66, the low pressure side journal bearing 65 is
 separated and overhung from the base 61b, and the bearing span is made
 shorter than that of the conventional bearing shown in FIG. 17.
 As described above, according to this embodiment, the low pressure side
 journal bearing 65 pivotally supporting the one end of the
 high-intermediate-low pressure integrated turbine rotor 39 is separated
 and overhung from the base 61b, and the bearing span of each of the high
 pressure side journal bearing 63 and the low pressure side journal bearing
 65 is shortened. Accordingly, it is possible to improve the rigidity of
 the shafting to suppress the shaft vibration and to stably operate the
 steam turbine.
 FIG. 7 is a schematic sectional view showing a sixth embodiment of a steam
 turbine of the present invention, in which constituent elements similar to
 those in the first and fifth embodiments and portions corresponding
 thereto are represented by the same reference numerals. This sixth
 embodiment is particularly suitable for solving the "Problem 6" in the
 prior art.
 The steam turbine of this sixth embodiment employs a high-intermediate-low
 pressure integrated type. In this embodiment, the recess 67 of the turbine
 exhaust chamber 66 is formed into a curved surface 67a having curvature R
 which is convex toward the low pressure bearing 64. The angles .phi.1,
 .phi.2 connecting the curved surface 67a of the curvature R (corresponding
 to the length d of a projection surface) and the straight surface 67b
 (corresponding to the length c of the projection surface) may be made to
 140.degree. or greater as shown in FIG. 8, or the adjacent straight
 surfaces 67b and 67c may be connected to each other through continuous
 straight lines each having angle .theta.i (i=1, 2, 3, . . . ) of
 140.degree. or greater. In this case, if the angle .phi.1, .phi.2 or
 .theta.i formed between the adjacent surfaces of the recess 67 of the
 turbine exhaust chamber 66 is less than 140.degree. C., a break-away is
 generated in the flow of the turbine exhaust gas at such angle to increase
 the exhaust gas loss and, therefore, it may be better to set this angle to
 140.degree. or greater.
 As described above, according to the present embodiment, since the recess
 67 of the turbine exhaust chamber 66 is formed into the curved surface 67a
 or the pseudo curved surface toward the low pressure bearing box 64, it is
 possible to suppress the exhaust gas loss and to shorten the bearing span
 as compared with that of the conventional cone-shaped recess 67, and it is
 possible to improve the rigidity of the shafting, i.e. shaft alignment,
 and to stably operate the steam turbine.
 It is to be noted that the present invention is not limited to the
 described embodiments and many other changes and modifications may be made
 without departing from the scopes of the appended claims.