STEAM TURBINE DRIVING MACHINE, AND SHIP AND GAS LIQUEFACTION APPARATUS EACH EQUIPPED WITH STEAM TURBINE DRIVING MACHINE

Abstract

 A steam turbine driver which enables using two shafts without increasing an installation space, and can further independently drive the two output shafts with a simple configuration is provided. A steam turbine driver (1A) includes: an ahead high-pressure turbine (7) driven upon supply of steam; a first drive shaft (4) driven by the ahead high-pressure turbine (7); an ahead first low-pressure turbine (11) and an ahead second low-pressure turbine (13) driven upon supply of steam discharged from the ahead high-pressure turbine (7); and a second drive shaft (14) driven by the ahead first low-pressure turbine (11) and the ahead second low-pressure turbine (13), the steam turbine driver further including a steam dump pipe (33) and a pressure reducing valve (35) that control a pressure of the steam discharged from the high-pressure turbine (7) and supplied to the first low-pressure turbine (11) and the second low-pressure turbine (13).

Description

{Technical Field}

[0001] The present invention relates to a steam turbine driver including two drive shafts, and a marine vessel and a gas liquefaction apparatus each equipped with the steam turbine driver.

{Background Art}

[0002] Steam turbines including a high-pressure turbine rotated upon supply of superheated steam guided from a boiler, and a low-pressure turbine rotated upon supply of superheated steam discharged from the high-pressure turbine have been known as steam turbines for rotating propellers of marine vessels (e.g., see PTL 1). In the marine steam turbines, the high-pressure turbine and the low-pressure turbine are arranged side by side in a beam direction. Rotational output powers respectively obtained from the turbines are combined by a speed reducer to rotate one propeller.
Two output shafts for rotating the propeller may be required due to an increase in the size of marine vessels. In this case, if the steam turbine disclosed in PTL 1 is employed, the high-pressure turbine and the low-pressure turbine need to be provided for each of the output shafts. However, it is difficult to install the high-pressure turbine and the low-pressure turbine for each of the output shafts due to restrictions in installation space (especially in the beam direction) within an engine room.
Thus, when two output shafts are required in marine vessels, a low-speed diesel main engine direct connection system or an electric motor propulsion system is mostly employed.

[0003] To solve the problem of the installation space for the steam turbine, a steam turbine as disclosed in PTL 2 described below has been proposed. In the steam turbine, a high-pressure turbine and a low-pressure turbine are arranged side by side in a beam direction. One of output shafts is driven by the high-pressure turbine, and the other of the output shafts is driven by the low-pressure turbine, thereby avoiding an increase in the installation space.
However, since a single superheated-steam flow method in which the low-pressure turbine is driven by superheated steam discharged from the high-pressure turbine is employed, the output power of the high-pressure turbine and the output power of the low-pressure turbine inevitably become uneven. To solve the problem, the unevenness in the output power is eliminated by providing a shaft generator or an electric motor at each of the output shafts and electrically connecting the shaft generators or the electric motors in the steam turbine disclosed in PTL 2.

{Citation List}

{Patent Literature}

[0004] 

{PTL 1}
Japanese Unexamined Patent Application, Publication No. 2006-17007 ({0027}, Fig. 1)

{PTL 2}
Japanese Unexamined Patent Application, Publication No. 2009-56868

{Summary of Invention}

{Technical Problem}

[0005] Although the steam turbine disclosed in PTL 2 can advantageously eliminate the unevenness in the output power between the respective output shafts, it is necessary to provide the shaft generators or the electric motors, resulting in a facility complication and a cost increase.

[0006] The present invention has been made in view of such circumstances, and an object thereof is to provide a steam turbine driver which enables using two shafts without causing an increase in installation space, and can further independently drive the two output shafts with a simple configuration, and a marine vessel and a gas liquefaction apparatus each equipped with the steam turbine driver.

{Solution to Problem}

[0007] To achieve the above object, a steam turbine driver, and a marine vessel and a gas liquefaction apparatus each equipped with the steam turbine driver according to the present invention employ the following solutions.
That is, a steam turbine driver according to a first aspect of the present invention includes: a high pressure-side turbine that is driven upon supply of steam; a first drive shaft that is driven by the high pressure-side turbine; a low pressure-side turbine that is driven upon supply of steam discharged from the high pressure-side turbine; and a second drive shaft that is driven by the low pressure-side turbine, the steam turbine driver further including a pressure control means that controls a pressure of the steam discharged from the high pressure-side turbine and supplied to the low pressure-side turbine.

[0008] A configuration in which two shafts using a single steam flow are provided is enabled by employing the first drive shaft driven by the high pressure-side turbine, and the second drive shaft driven by the low pressure-side turbine that is driven by supply of the steam discharged from the high pressure-side turbine in the steam turbine driver. Accordingly, the configuration with two shafts can be achieved without causing an increase in installation space.
The pressure control means is provided so as to control the pressure of the steam discharged from the high pressure-side turbine and supplied to the low pressure-side turbine. The pressure of the steam flowing into the low pressure-side turbine can be thereby set without being affected by operating conditions of the high pressure-side turbine. Consequently, the output power of the high pressure-side turbine, and the output power of the low pressure-side turbine can be independently controlled. The independent control of the two shafts can be achieved with a simple configuration in which the pressure control means is added as described above.
Examples of the high pressure-side turbine include a configuration in which a single high-pressure turbine driven by high-pressure superheated steam guided from a boiler is provided, and a configuration in which a medium-pressure turbine driven by superheated steam obtained by reheating exhaust steam from the high-pressure turbine by the boiler is provided in addition to the high-pressure turbine.
For example, the output powers of the respective drive shafts of the steam turbine driver may be used for driving a propeller of a marine vessel, may be used as a power source of a compressor for liquefying gas, or may be used for driving a power generator.

[0009] In the steam turbine driver according to the first aspect, the pressure control means may include: a steam dump path that branches a portion of the steam discharged from the high pressure-side turbine and guides the portion to a condenser; a pressure reducing valve that reduces the pressure of the steam flowing through the steam dump path; and a control section that controls the pressure reducing valve such that the steam flowing into the low pressure-side turbine has a predetermined pressure.

[0010] The pressure of the steam guided to the low pressure-side turbine is reduced by guiding a portion of the steam discharged from the high pressure-side turbine to the condenser through the steam dump path. At this point, the pressure reducing valve that reduces the pressure of the steam flowing through the steam dump path is controlled by the control section such that the steam flowing into the low pressure-side turbine has a predetermined pressure value. Accordingly, the steam pressure at an inlet of the low pressure-side turbine can be independently controlled irrespective of the exhaust pressure of the high pressure-side turbine.

[0011] Moreover, in the steam turbine driver according to the first aspect, steam guided from a separate system from an exhaust system of the high pressure-side turbine may be supplied to the low pressure-side turbine.

[0012] The output power of the low pressure-side turbine is increased by supplying superheated steam from the separate system to the low pressure-side turbine. The output power can be thereby adjusted independently from the high pressure-side turbine. Accordingly, the low pressure-side turbine can be stably controlled.
Examples of the steam guided from the separate system include utility steam guided from a boiler desuperheated steam line. In this case, the separate system can be made independent from a main turbine system, so that more stable operation can be expected.

[0013] Moreover, in the above configuration, the low pressure-side turbine may be composed of two low-pressure turbines of a first low-pressure turbine and a second low-pressure turbine provided in parallel with respect to the superheated steam supplied from the high pressure-side turbine, the steam from the separate system being supplied only to the first low-pressure turbine.

[0014] The low pressure-side turbine is divided into the two low-pressure turbines, and the steam from the separate system is supplied only to the first low-pressure turbine. Accordingly, the controllability of the low pressure-side turbine is improved.

[0015] Moreover, in the above configuration, a check valve that prevents the steam from flowing reversely from the first low-pressure turbine toward the high pressure-side turbine may be provided in a steam supply path that connects an inlet side of the first low-pressure turbine and an exhaust side of the high pressure-side turbine.

[0016] Since the steam is supplied to the first low-pressure turbine from the separate system, the pressure of the steam supplied from the separate system may become higher than the pressure of the superheated steam discharged from the high pressure-side turbine depending on pressure conditions of the superheated steam (that is, depending on a set pressure value of the pressure control means), thereby possibly causing the steam to flow reversely from the first low-pressure turbine toward the high pressure-side turbine. Thus, the check valve is provided so as to prevent the reverse flow, so that stable operation is achieved.

[0017] Also, a marine vessel according to a second aspect of the present invention includes: the steam turbine driver described in any of the above configurations; a first propeller that is rotationally driven by the first drive shaft; and a second propeller that is rotationally driven by the second drive shaft.

[0018] Since a twin-screw marine vessel including two propellers can be achieved by using the steam turbine driver capable of independently driving the two shafts by use of the aforementioned steam turbine driver, a marine vessel having excellent installability and cost advantages can be provided.
The high pressure-side turbine and the low pressure-side turbine can be applied not only to an ahead turbine, but also to an astern turbine.

[0019] Also, a gas liquefaction apparatus according to a third aspect of the present invention includes: the steam turbine driver described in any of the above configurations; a first compressor that is rotationally driven by the first drive shaft; a second compressor that is rotationally driven by the second drive shaft; a first cold energy output section that obtains cold energy by expanding a refrigerant compressed by the first compressor; and a second cold energy output section that obtains cold energy by expanding a refrigerant compressed by the second compressor, wherein the first cold energy output section and the second cold energy output section cool and liquefy liquefied gas.

[0020] The liquefied gas is liquefied by independently driving the two compressors by use of the steam turbine driver capable of independently driving the two shafts, and thereby obtaining two expansion cycles. Accordingly, a gas liquefaction apparatus having excellent installability and cost advantages can be provided.

{Advantageous Effects of Invention}

[0021] Since the pressure control means is provided so as to control the pressure of the superheated steam discharged from the high pressure-side turbine and supplied to the low pressure-side turbine, the output power of the high pressure-side turbine and the output power of the low pressure-side turbine can be independently controlled with a simple configuration.

{Brief Description of Drawings}

[0022] 

{Fig. 1}
Fig. 1 is a schematic configuration diagram illustrating a steam turbine driver according to a first embodiment of the present invention.

{Fig. 2}
Fig. 2 is a schematic configuration diagram illustrating a steam turbine driver according to a second embodiment of the present invention.

{Fig. 3}
Fig. 3 is a schematic configuration diagram illustrating an example in which the steam turbine driver according to the present invention is applied to a gas liquefaction apparatus.

{Fig. 4}
Fig. 4 is a schematic configuration diagram illustrating an example in which the steam turbine driver according to the present invention is applied when an existing single-screw marine vessel is converted into an FSRU.

{Description of Embodiments}

[0023] In the following, embodiments according to the present invention will be described by reference to the drawings.

{First Embodiment}

[0024] In the following, a first embodiment of the present invention will be described based on Fig. 1.
Fig. 1 shows a steam turbine driver 1A for use in a twin-screw marine vessel including two propellers. The steam turbine driver 1A includes a starboard engine 3 and a port engine 5.

[0025] The starboard engine 3 includes an ahead high-pressure turbine (high pressure-side turbine) 7 and an astern turbine 9.
Main drive steam as high-pressure superheated steam is guided to the ahead high-pressure turbine 7 from an unillustrated marine boiler through a main steam pipe 8. A main steam valve 10, the opening degree of which is controlled by an unillustrated control section, is provided in the main steam pipe 8 so as to control the output power of the high-pressure turbine 7. The opening degree of the main steam valve 10 is adjusted in ahead motion, and the main steam valve 10 is fully closed in astern motion.
The main drive steam as high-pressure superheated steam is guided to the astern turbine 9 from the unillustrated marine boiler in the astern motion.
The ahead high-pressure turbine 7 and the astern turbine 9 are mounted onto a single first drive shaft 4. A speed reducer 20 reduces the rotational speed of the output power and transmits the output power to a propeller shaft 24 supported by a thrust bearing 22. An unillustrated starboard-side propeller is mounted to a distal end of the propeller shaft 24 so as to apply a propulsive force to the marine vessel.

[0026] The port engine 5 includes an ahead first low-pressure turbine (low pressure-side turbine) 11, an ahead second low-pressure turbine (low pressure-side turbine) 13, and an astern turbine 15. The ahead first low-pressure turbine 11, the ahead second low-pressure turbine 13, and the astern turbine 15 are mounted onto a single second drive shaft 14. A speed reducer 21 reduces the rotational speed of the output power and transmits the output power to a propeller shaft 25 supported by a thrust bearing 23. An unillustrated port-side propeller is mounted to a distal end of the propeller shaft 25 so as to apply a propulsive force to the marine vessel.
The ahead first low-pressure turbine 11 and the astern second low-pressure turbine are coaxially placed face-to-face with each other such that their expansion processes are parallel to each other.

[0027] An exhaust steam pipe 27 is connected to an exhaust side of the ahead high-pressure turbine 7. A first supply pipe 29 connected to a steam inlet of the ahead first low-pressure turbine 11, a second supply pipe 31 connected to an inlet of the ahead second low-pressure turbine 13, and a steam dump pipe (steam dump path) 33 connected to an unillustrated condenser are also connected to the downstream side of the exhaust steam pipe 27. A pressure reducing valve 35, the opening degree of which is adjustable within a range from a fully closed state to a fully open state, is provided in the steam dump pipe 33. The opening degree of the pressure reducing valve 35 is controlled by an unillustrated control section. The steam dump pipe 33, the pressure reducing valve 35, and the control section that controls the pressure reducing valve 35 constitute a pressure control means that controls the pressure of superheated steam supplied to the respective low-pressure turbines 11 and 13.

[0028] A low-pressure drive steam pipe 37 is connected to a steam inlet of the ahead first low-pressure turbine 11. Low-pressure drive steam as utility steam is guided from a boiler desuperheated steam line and supplied to the ahead first low-pressure turbine 11. A low-pressure drive steam valve 38, the opening degree of which is adjusted by an unillustrated control section, is provided in the low-pressure drive steam pipe 37. Accordingly, the low-pressure drive steam from the low-pressure drive steam pipe 37 as well as the steam discharged from the ahead high-pressure turbine 7 is supplied to the ahead first low-pressure turbine 11.

[0029] The steam turbine driver 1A having the above configuration operates as follows.
The main drive steam as high-pressure superheated steam is supplied to the ahead high-pressure turbine 7 from the marine boiler to rotationally drive the ahead high-pressure turbine 7. Thus, the propeller shaft 24 is driven via the first drive shaft 4 and the speed reducer 20, and the starboard-side propeller is rotated. An ahead thrust is thereby generated. The output power of the starboard-side propeller is adjusted by the opening degree of the main steam valve 10.

[0030] The superheated steam discharged from the ahead high-pressure turbine 7 flows through the exhaust steam pipe 27, and flows through the first supply pipe 29 and the second supply pipe 31 provided in parallel with each other. The superheated steam flowing through the first supply pipe 29 is guided to the ahead first low-pressure turbine 11 to rotationally drive the ahead first low-pressure turbine 11. Similarly, the superheated steam flowing through the second supply pipe 31 is guided to the ahead second low-pressure turbine 13 to rotationally drive the ahead second low-pressure turbine 13.
The pressure of the superheated steam supplied to the respective low-pressure turbines 11 and 13 as described above is adjusted by the pressure reducing valve 35 provided in the steam dump pipe 33. That is, the amount of steam guided to the condenser through the steam dump pipe 33 is increased by increasing the opening degree of the pressure reducing valve 35, so that the pressure of the superheated steam guided to the respective low-pressure turbines 11 and 13 is lowered. Conversely, the amount of steam guided to the condenser through the steam dump pipe 33 is reduced by decreasing the opening degree of the pressure reducing valve 35, so that the pressure of the superheated steam guided to the respective low-pressure turbines 11 and 13 is raised. The opening degree control of the pressure reducing valve 35 is performed by the unillustrated control section. The opening degree is adjusted based on a thrust required for the port-side propeller.

[0031] When the ahead first low-pressure turbine 11 and the ahead second low-pressure turbine 13 are rotationally driven, the propeller shaft 25 is driven via the second drive shaft 14 and the speed reducer 21, and the port-side propeller is rotated. An ahead thrust is thereby generated. The output power of the port-side propeller is adjusted by the opening degree of the pressure reducing valve 35 as described above.
When the output power of the port-side propeller is insufficient, the low-pressure drive steam guided from the low-pressure drive steam pipe 37 is supplied to the ahead first low-pressure turbine 11. The pressure of the supplied low-pressure drive steam is controlled by the low-pressure drive steam valve 38.
The steam obtained after rotationally driving the ahead first low-pressure turbine 11 and the ahead second low-pressure turbine 13 is guided to the condenser as exhaust steam.

[0032] In the astern motion, the main drive steam is supplied to the respective astern turbines 9 and 15 to rotationally drive the turbines 9 and 15. Accordingly, the starboard-side propeller and the port-side propeller are rotated in a reverse direction to generate an astern thrust. The steam obtained after rotationally driving the respective astern turbines 9 and 15 is guided to the condenser as exhaust steam.

[0033] Following effects are obtained by the present embodiment described above.
A configuration in which two shafts using a single steam flow are provided is enabled by employing the first drive shaft 4 driven by the ahead high-pressure turbine 7, and the second drive shaft 14 driven by the ahead first low-pressure turbine 11 and the ahead second low-pressure turbine 13 that are driven by supply of the steam discharged from the high-pressure turbine 7. Accordingly, the configuration with two shafts can be achieved without causing an increase in installation space.

[0034]  The steam dump pipe 33 and the pressure reducing valve 35 are provided so as to control the pressure of the steam discharged from the ahead high-pressure turbine 7 and supplied to the ahead first low-pressure turbine 11 and the ahead second low-pressure turbine 13. Accordingly, the pressure of the steam flowing into the ahead first low-pressure turbine 11 and the ahead second low-pressure turbine 13 can be set without being affected by operating conditions of the ahead high-pressure turbine 7. Consequently, the output power of the ahead high-pressure turbine 7, and the output power of the ahead first low-pressure turbine 11 and the ahead second low-pressure turbine 13 can be independently controlled. The independent control of the two shafts can be achieved with a simple configuration in which the steam dump pipe 33, the pressure reducing valve 35, and the control section that controls the pressure reducing valve are added as described above.

[0035] The low-pressure drive steam is supplied from the low-pressure drive steam pipe 37 as a separate superheated steam supply system from the first supply pipe 29 and the second supply pipe 31 in which the exhaust steam from the ahead high-pressure turbine 7 is guided. The output power of the ahead first low-pressure turbine 11 can be thereby increased independently from a main steam system guided to the ahead high-pressure turbine 7. Accordingly, the port engine 5 driven by the ahead first low-pressure turbine 11 and the ahead second low-pressure turbine 13 can be stably controlled.
Also, the low pressure-side turbine is divided into the two low-pressure turbines (the ahead first low-pressure turbine 11 and the ahead second low-pressure turbine 13), and the steam is supplied only to the ahead first low-pressure turbine 11 from the low-pressure drive steam pipe 37. Accordingly, the controllability of the low pressure-side turbine (the ahead first low-pressure turbine 11 and the ahead second low-pressure turbine 13) is improved.

{Second Embodiment}

[0036] Next, a second embodiment of the present invention will be described based on Fig. 2. The present embodiment is achieved by further improving the configuration of the first embodiment. Therefore, the same components as those in the configuration of the first embodiment are assigned the same reference numerals, and the description thereof is omitted.
An ahead medium-pressure turbine 40 mounted onto the same first drive shaft 4 as that of the ahead high-pressure turbine 7 is provided in the starboard engine 3 of a steam turbine driver 1B in the present embodiment. The ahead high-pressure turbine 7 and the ahead medium-pressure turbine 40 constitute the high pressure-side turbine. The ahead medium-pressure turbine 40 is driven by superheated steam obtained by reheating the exhaust steam from the ahead high-pressure turbine 7 by a reheater 42. To be more specific, a bypass pipe 44 is branched from the exhaust steam pipe 27 on the exhaust side of the high-pressure turbine 7. The exhaust steam is partially guided to the reheater 42 through the bypass pipe 44 and reheated therein. The reheated steam is guided to the ahead medium-pressure turbine 40 through a reheated steam supply pipe 46. The flow rate of the steam bypassed to the reheater 42 is determined by adjusting the opening degree of a bypass valve 49 that is provided in the exhaust steam pipe 27 of the ahead high-pressure turbine 7. The opening degree of the bypass valve 49 is controlled based on a predetermined function given to a first control section 52. For example, as shown by a pattern indicated by reference numeral 52, when an ahead rotational speed (RPM (AHEAD)) is low, the opening degree of the bypass valve 49 is increased to reduce the flow rate of the steam bypassed to the reheater 42. When the ahead rotational speed is high, the opening degree of the bypass valve 49 is decreased to increase the flow rate of the steam bypassed to the reheater 42. The reheater 42 is generally configured as a portion of the unillustrated marine boiler.

[0037] The first control section 52 also controls the main steam valve 10. For example, the main steam valve 10 is controlled such that the opening degree is increased along with an increase in the ahead rotational speed (RPM (AHEAD)), that is, a throttle is applied as shown by a pattern indicated by reference numeral 22.

[0038] The superheated steam discharged from the ahead medium-pressure turbine 40 passes through an exhaust steam pipe 48, and joins the exhaust steam guided from the ahead high-pressure turbine 7 at a junction 50. The steam is branched into the steam dump pipe 33 from a junction exhaust steam pipe 54 provided after the junction, and, similarly to the first embodiment, further branched into the first supply pipe 29 and the second supply pipe 31 connected in parallel with each other.
A pressure sensor 56 that measures the pressure of the steam reduced by the pressure reducing valve 35 provided in the steam dump pipe 33 is provided in the junction exhaust steam pipe 54. The pressure sensor 56 also partially constitutes the pressure control means of the present invention. A measurement pressure value PV measured by the pressure sensor 56 is fed to a second control section 58. The second control section 58 compares a set pressure value SV given from outside and the measurement pressure value PV, and outputs an instruction value OP obtained by, for example, PID control to the pressure reducing valve 35 so as to obtain the set pressure value SV. The opening degree of the pressure reducing valve 35 is controlled based on the instruction value OP.
The dump steam, the pressure of which is reduced through the pressure reducing valve 35, is guided to a condenser 60.

[0039] The superheated steam, the pressure of which is control as described above, is guided to the ahead first low-pressure turbine 11 and the ahead second low-pressure turbine 13 through the first supply pipe 29 and the second supply pipe 31, respectively. This point is similar to the first embodiment. In the present embodiment, however, a check valve 62 is provided in the first supply pipe 29. The check valve 62 prevents the steam from flowing reversely from the ahead first low-pressure turbine 11 toward the high pressure-side turbine (the ahead high-pressure turbine 7 and the ahead medium-pressure turbine 40).
The steam obtained after passing through the ahead first low-pressure turbine 11 and the ahead second low-pressure turbine 13 is guided to the condenser 60.

[0040] A pressure reducing valve 64 that controls the pressure of the utility steam to a constant value is provided in the low-pressure drive steam pipe 37. The low-pressure drive steam passing through the pressure reducing valve 64 is branched at a branch point 66, and thereafter guided to the low-pressure drive steam valve 38. The opening degree of the low-pressure drive steam valve 38 is controlled by a third control section 68. To be more specific, the low-pressure drive steam valve 38 is controlled such that the opening degree is increased along with an increase in the ahead rotational speed (RPM (AHEAD)). Accordingly, a deficiency in the output power of the low pressure-side turbine (the ahead first low-pressure turbine 11 and the ahead second low-pressure turbine 13) is compensated for independently from the main steam. While the opening degree of the low-pressure drive steam valve 38 is controlled as described above in the ahead motion, the low-pressure drive steam valve 38 is fully closed in the astern motion.

[0041] Moreover, in the present embodiment, a high-pressure astern turbine 70 on the starboard side, and a low-pressure astern turbine 72 driven by exhaust steam from the high-pressure astern turbine 70 are employed instead of the astern turbines 9 and 15 both driven by the main steam in the first embodiment.
The high-pressure astern turbine 70 is rotationally driven by the main steam guided from an astern main steam pipe 74 that is branched from the main steam pipe 8.
A main steam valve 76 is provided in the astern main steam pipe 74. The opening degree of the main steam valve 76 is controlled by a fourth control section 78. The opening degree of the main steam valve 76 is controlled in the astern motion, and the main steam valve 76 is fully closed in the ahead motion.
The superheated steam discharged from the high-pressure astern turbine 70 passes through an astern exhaust steam pipe 78, and is then branched into a steam dump pipe 80. A pressure reducing valve 82 is provided in the steam dump pipe 80.
A pressure sensor 84 that measures the pressure of the steam reduced by the pressure reducing valve 82 is provided in the astern exhaust steam pipe 78. A measurement pressure value PV measured by the pressure sensor 84 is fed to a fifth control section 86. The fifth control section 86 compares a set pressure value SV given from outside and the measurement pressure value PV, and outputs an instruction value OP obtained by, for example, PID control to the pressure reducing valve 82 so as to obtain the set pressure value SV. The opening degree of the pressure reducing valve 82 is controlled based on the instruction value OP.
As described above, the steam dump pipe 80, the pressure reducing valve 82, the pressure sensor 84, and the fifth control section 86 for the astern motion constitute the pressure control means of the present invention.
The dump steam, the pressure of which is reduced through the pressure reducing valve 82, is guided to the condenser 60.

[0042] The superheated steam flowing through the astern exhaust steam pipe 78 without being branched into the steam dump pipe 80 is guided to the low-pressure astern turbine 72 through a supply pipe 88. A low-pressure steam valve 90 is provided in the exhaust steam pipe 78. The opening degree of the low-pressure steam valve 90 is controlled by a sixth control section 92. For example, the low-pressure steam valve 90 is controlled such that the opening degree is increased along with an increase in an astern rotational speed (RPM (ASTERN)), that is, a throttle is applied as shown by a pattern indicated by reference numeral 92.

[0043] An astern low-pressure drive steam pipe 96 that is branched from the branch point 66 of the low-pressure drive steam pipe 37 and joins the astern supply pipe 88 at a junction 94 is provided. An astern low-pressure drive steam valve 98 is provided in the low-pressure drive steam pipe 96. The opening degree of the low-pressure drive steam valve 98 is controlled by the sixth control section 92. For example, as shown by a pattern indicated by reference numeral 92, when the astern rotational speed (RPM (ASTERN)) is low, the low-pressure drive steam valve 98 is fully closed. When the astern rotational speed (RPM (ASTERN)) exceeds a predetermined value, the opening degree is gradually increased so as to increase the output power.
The low-pressure steam valve 90 and the low-pressure drive steam valve 98 for the astern motion are fully closed in the ahead motion.

[0044] The steam turbine driver 1B having the above configuration operates as described below.
In the ahead motion, the main steam valve 76, the low-pressure steam valve 90, and the low-pressure drive steam valve 98 for the astern motion are fully closed.
The main drive steam as high-pressure superheated steam is supplied to the ahead high-pressure turbine 7 from the marine boiler to rotationally drive the ahead high-pressure turbine 7. Thus, the propeller shaft 24 is driven via the first drive shaft 4 and the speed reducer 20, and the starboard-side propeller is rotated. An ahead thrust is thereby generated. The output power of the starboard-side propeller is adjusted by the opening degree of the main steam valve 10 controlled by the first control section 52.

[0045] The superheated steam discharged from the ahead high-pressure turbine 7 flows through the exhaust steam pipe 27. A portion of the superheated steam is branched into the bypass pipe 44 according to the opening degree of the bypass valve 49 controlled by the first control section 52, and a remaining portion thereof flows to the downstream side of the exhaust steam pipe 27. The superheated steam flowing through the bypass pipe 44 is reheated in the reheater 42 to become the reheated steam, which is guided to the ahead medium-pressure turbine 40 through the reheated steam supply pipe 46. The superheated steam obtained after rotationally driving the ahead medium-pressure turbine 40 passes through the exhaust steam pipe 48, and joins the exhaust steam guided from the ahead high-pressure turbine 7 at the junction 50. The superheated steam then flows through the first supply pipe 29 and the second supply pipe 31 provided in parallel with each other. The superheated steam flowing through the first supply pipe 29 and the check valve 29 is guided to the ahead first low-pressure turbine 11 to rotationally drive the ahead first low-pressure turbine 11. Similarly, the superheated steam flowing through the second supply pipe 31 is guided to the ahead second low-pressure turbine 13 to rotationally drive the ahead second low-pressure turbine 13.

[0046] The pressure of the superheated steam supplied to the respective low-pressure turbines 11 and 13 as described above is adjusted by the pressure reducing valve 35 provided in the steam dump pipe 33. That is, the opening degree of the pressure reducing valve 35 is adjusted so as to obtain the set pressure value SV by the second control section 58 that controls the opening degree based on the measurement pressure value PV of the pressure sensor 56. To be more specific, the amount of steam guided to the condenser 60 through the steam dump pipe 33 is increased by increasing the opening degree of the pressure reducing valve 35, so that the pressure of the superheated steam guided to the respective low-pressure turbines 11 and 13 is lowered. Conversely, the amount of steam guided to the condenser through the steam dump pipe 33 is reduced by decreasing the opening degree of the pressure reducing valve 35, so that the pressure of the superheated steam guided to the respective low-pressure turbines 11 and 13 is raised. The set pressure value SV given to the second control section 58 may be set to a variable value so as not to unnecessarily dump the steam.

[0047] When the ahead first low-pressure turbine 11 and the ahead second low-pressure turbine 13 are rotationally driven, the propeller shaft 25 is driven via the second drive shaft 14 and the speed reducer 21, and the port-side propeller is rotated. An ahead thrust is thereby generated. The output power of the port-side propeller is adjusted by the opening degree of the pressure reducing valve 35 as described above.
When the output power of the port-side propeller is insufficient, the low-pressure drive steam guided from the low-pressure drive steam pipe 37 is supplied to the ahead first low-pressure turbine 11. The pressure of the supplied low-pressure drive steam is adjusted by the low-pressure drive steam valve 38 controlled by the third control section 68.
The steam obtained after rotationally driving the ahead first low-pressure turbine 11 and the ahead second low-pressure turbine 13 is guided to the condenser 60 as exhaust steam.

[0048] In the astern motion, the main steam valve 10 and the low-pressure drive steam valve 38 for the ahead motion are fully closed.
Since the same operation as that in the ahead motion is performed in the astern motion, the description thereof is omitted. That is, the operation is similar to that in the ahead motion in that the high-pressure astern turbine 70 is driven by the main drive steam and the low-pressure astern turbine 72 is driven by the exhaust steam from the high-pressure astern turbine 70, in that the pressure control is performed by the steam dump pipe 80, the pressure reducing valve 83, the pressure sensor 84, and the fifth control section 86, and in that the low-pressure astern turbine 72 is assist-driven by the low-pressure drive steam adjusted by the low-pressure drive steam valve 98.

[0049] Following effects are obtained by the present embodiment described above.
A configuration in which two shafts using a single steam flow are provided is enabled by employing the first drive shaft 4 driven by the ahead high-pressure turbine 7 and the ahead medium-pressure turbine 40, and the second drive shaft 14 driven by the ahead first low-pressure turbine 11 and the ahead second low-pressure turbine 13 that are driven by supply of the steam discharged from the high-pressure turbine 7. Accordingly, the configuration with two shafts can be achieved without causing an increase in installation space.

[0050] The steam dump pipe 33 and the pressure reducing valve 35 are provided so as to control the pressure of the steam discharged from the ahead high-pressure turbine 7 and the ahead medium-pressure turbine 40 and supplied to the ahead first low-pressure turbine 11 and the ahead second low-pressure turbine 13. Accordingly, the pressure of the steam flowing into the ahead first low-pressure turbine 11 and the ahead second low-pressure turbine 13 can be set without being affected by operating conditions of the ahead high-pressure turbine 7. Consequently, the output power of the ahead high-pressure turbine 7, and the output power of the ahead first low-pressure turbine 11 and the ahead second low-pressure turbine 13 can be independently controlled. The independent control of the two shafts can be achieved with a simple configuration in which the steam dump pipe 33, the pressure reducing valve 35, and the control section that controls the pressure reducing valve are added as described above.
With regard to the astern turbines 70 and 72, the steam dump pipe 80 and the pressure reducing valve 82 are provided so as to control the pressure of the steam supplied to the low-pressure astern turbine 72 in a similar manner to the ahead turbines. The same effects as those of the ahead turbines are thereby obtained.

[0051] The low-pressure drive steam is supplied from the low-pressure drive steam pipe 37 as a separate superheated steam supply system from the first supply pipe 29 and the second supply pipe 31 in which the exhaust steam from the ahead high-pressure turbine 7 and the ahead medium-pressure turbine 40 is guided. The output power of the ahead first low-pressure turbine 11 can be thereby increased independently from a main steam system guided to the ahead high-pressure turbine 7 and the ahead medium-pressure turbine 40. Accordingly, the port engine 5 driven by the ahead first low-pressure turbine 11 and the ahead second low-pressure turbine 13 can be stably controlled.
Also, the low pressure-side turbine is divided into the two low-pressure turbines (the ahead first low-pressure turbine 11 and the ahead second low-pressure turbine 13), and the steam is supplied only to the ahead first low-pressure turbine 11 from the low-pressure drive steam pipe 37. Accordingly, the controllability of the low pressure-side turbine (the ahead first low-pressure turbine 11 and the ahead second low-pressure turbine 13) is improved.
Moreover, the pressure of the low-pressure drive steam supplied to the first low-pressure turbine 11 may become relatively higher than the pressure of the superheated steam discharged from the high pressure-side turbines 7 and 40 depending on pressure conditions of the superheated steam (that is, depending on the set pressure value SV of the second control section 58), thereby possibly causing the steam to flow reversely from the first low-pressure turbine 11 toward the high pressure-side turbines 7 and 40. Thus, the check valve 62 is provided in the first supply pipe 29. Accordingly, stable operation is achieved.

{Third Embodiment}

[0052] Next, a third embodiment of the present invention will be described based on Fig. 3. In the first embodiment and the second embodiment, it is premised that the steam turbine drivers 1A and 1B are applied to the twin-screw marine vessel. In the present embodiment, a gas liquefaction apparatus 100 will be described as another application of the steam turbine driver.
The gas liquefaction apparatus 100 cools and liquefies natural gas (NG) as a raw material of liquefied gas such as LNG (liquefied natural gas). The gas liquefaction apparatus 100 uses the aforementioned steam turbine drivers 1A and 1B as a drive source of a compressor that constitutes a refrigeration cycle. Although the steam turbine drivers 1A and 1B are schematically shown in the drawing, a high pressure-side turbine 102, a low pressure-side turbine 103, a pressure control means (not shown), an assist drive (not shown) using low-pressure drive steam, a first drive shaft 105, and a second drive shaft 107 have the same configurations as those of the first embodiment and the second embodiment.

[0053] The gas liquefaction apparatus 100 includes a first compressor 109 that is rotationally driven by the first drive shaft 105, and a second compressor 111 that is rotationally driven by the second drive shaft 107. Each of the compressors 109 and 111 includes a coaxial two-stage compression section rotationally driven by each of the drive shafts 105 and 107. A compressed refrigerant (e.g., nitrogen) is guided to the unillustrated refrigeration cycle.

[0054]  In the unillustrated refrigeration cycle, a first cold energy output section that obtains cold energy by expanding the refrigerant compressed by the first compressor 109, and a second cold energy output section that obtains cold energy by expanding the refrigerant compressed by the second compressor 111 are provided (a so-called double expansion cycle). The first cold energy output section and the second cold energy output section cool and liquefy natural gas as a raw material of LNG.

[0055] By applying the steam turbine drivers 1A and 1B capable of independently controlling the two shafts so as to achieve a refrigeration cycle having two expansion sections as in the present embodiment, a gas liquefaction apparatus having excellent installability and cost advantages can be provided. Also, since the respective drive shafts can be independently controlled, one of the compressors can be used as a high-pressure compressor, and another of the compressors can be used as a low-pressure compressor. Accordingly, highly efficient liquefaction can be achieved.

{Fourth Embodiment}

[0056] Next, a fourth embodiment of the present invention will be described based on Fig. 4. In the first embodiment and the second embodiment, it is premised that the steam turbine drivers 1A and 1B are applied to the twin-screw marine vessel. In the present embodiment, an example in which the steam turbine driver used as a marine vessel propulsion unit is converted into a power-generating driver is described as another application of the steam turbine driver.

[0057] In an existing single-screw steam turbine marine vessel, an output mechanism section 201 composed of a speed reducer, a propeller shaft or the like is provided at an output destination of a steam turbine driver, that is, on the output sides of respective drive shafts 205 and 207. When the steam turbine marine vessel is changed into a floating body such as an FSRU (floating storage and regasification unit) that requires no propeller, the output mechanism section 201 becomes unnecessary.
Thus, in the present embodiment, the output mechanism section 201 is removed, and the steam turbine driver is converted into the steam turbine drivers 1A and 1B similar to the first embodiment and the second embodiment. To be more specific, a pressure control means such as the steam dump pipe 33 and the pressure reducing valve 35, and an assist-drive system such as the low-pressure drive steam pipe 37 and the low-pressure drive steam valve 38 for guiding low-pressure drive steam such as utility steam are added between an existing high pressure-side turbine 202 and an existing low pressure-side turbine 203. The first drive shaft 205 and the second drive shaft 207 are also respectively connected with a first power generator 209 and a second power generator 211 driven by the rotation thereof.

[0058] Even when the existing single-screw steam turbine marine vessel is changed into the floating body such as the FSRU as in the present embodiment, the existing propulsion unit can be converted so as to drive the power generator. Also, since the respective drive shafts 205 and 207 can be independently controlled, the steam turbine drivers 1A and 1B can freely adjust the electric power generations of the respective power generators 209 and 211, and can thereby flexibly respond to a demand for electric power.

{Reference Signs List}

[0059] 

1A, 1B Steam turbine driver

4 First drive shaft

7 Ahead high-pressure turbine (high pressure-side turbine)

11 Ahead first low-pressure turbine (low pressure-side turbine)

13 Ahead second low-pressure turbine (low pressure-side turbine)

14 Second drive shaft

33, 80 Steam dump pipe (pressure control means)

35, 82 Pressure reducing valve (pressure control means)

37 Low-pressure drive steam pipe

56, 84 Pressure sensor (pressure control means)

58 Second control section (pressure control means)

62 Check valve

86 Fifth control section (pressure control means)

Claims

1. A steam turbine driver comprising:

a high pressure-side turbine that is driven upon supply of steam;

a first drive shaft that is driven by the high pressure-side turbine;

a low pressure-side turbine that is driven upon supply of steam discharged from the high pressure-side turbine; and

a second drive shaft that is driven by the low pressure-side turbine,

the steam turbine driver further comprising a pressure control means that controls a pressure of the steam discharged from the high pressure-side turbine and supplied to the low pressure-side turbine.

2. The steam turbine driver according to claim 1, wherein the pressure control means includes:

a steam dump path that branches a portion of the steam discharged from the high pressure-side turbine and guides the portion to a condenser;

a pressure reducing valve that reduces the pressure of the steam flowing through the steam dump path; and

a control section that controls the pressure reducing valve such that the steam flowing into the low pressure-side turbine has a predetermined pressure.

3. The steam turbine driver according to claim 1 or 2, wherein steam guided from a separate system from an exhaust system of the high pressure-side turbine is supplied to the low pressure-side turbine.

4. The steam turbine driver according to claim 3, wherein the low pressure-side turbine is composed of two low-pressure turbines of a first low-pressure turbine and a second low-pressure turbine provided in parallel with respect to the superheated steam supplied from the high pressure-side turbine,
the steam from the separate system being supplied only to the first low-pressure turbine.

5. The steam turbine driver according to claim 4, wherein a check valve that prevents the steam from flowing reversely from the first low-pressure turbine toward the high pressure-side turbine is provided in a steam supply path that connects an inlet side of the first low-pressure turbine and an exhaust side of the high pressure-side turbine.

6. A marine vessel comprising:

the steam turbine driver according to any one of claims 1 to 5;

a first propeller that is rotationally driven by the first drive shaft; and

a second propeller that is rotationally driven by the second drive shaft.

7. A gas liquefaction apparatus comprising:

the steam turbine driver according to any one of claims 1 to 5;

a first compressor that is rotationally driven by the first drive shaft;

a second compressor that is rotationally driven by the second drive shaft;

a first cold energy output section that obtains cold energy by expanding a refrigerant compressed by the first compressor; and

a second cold energy output section that obtains cold energy by expanding a refrigerant compressed by the second compressor,

wherein the first cold energy output section and the second cold energy output section cool and liquefy gas.

Drawing