This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2014-012623, filed on Jan. 27, 2014; the entire contents of which are incorporated herein by reference.
Embodiments described herein relate generally to a steam turbine pipe.
In a steam turbine pipe system, a main steam pipe is provided which leads steam generated in a boiler to a steam turbine. The main steam pipe is provided with a main steam control valve for regulating the flow rate of the steam.
The main steam control valve is provided with a drain pipe that discharges drain generated in the main steam pipe on the downstream side of the main steam control valve when performing warming for operating the steam turbine. The drain pipe is provided with a shutoff valve, and the drain is led to a condenser by opening the shutoff valve. Then, the shutoff valve is closed after completion of the warming.
In the above-described drain pipe provided at the conventional main steam control valve, when increasing a load up to a rated operation of the steam turbine in a state that the shutoff valve is closed, the temperature of the drain pipe between the main steam control valve and the shutoff valve sometimes abnormally increases. Consequently, the abnormal increase in temperature may cause breakage of the drain pipe.
In one embodiment, a steam turbine pipe in a steam turbine facility, includes: a steam passage that leads steam from a boiler to a steam turbine; a branching passage that branches off from the steam passage; and a shutoff valve that intervenes in the branching passage. The steam turbine pipe further includes a reduced part that is provided at a part of the branching passage between the steam passage and the shutoff valve and made by reducing a passage cross section of the branching passage.
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
As illustrated in
The main stop valves 20 that shut off the steam to be led to the high-pressure turbine 200 intervene in the upper half side main steam pipes 11 and the lower half side main steam pipes 12. Further, the main steam control valves 30 that regulate the flow rate of the steam to be led to the high-pressure turbine 200 intervene on the downstream side of the main stop valves 20.
As illustrated in
As illustrated in
Each of the drain pipes is provided with a shutoff valve (not illustrated), and the end of each drain pipe communicates with, for example, a condenser. By opening the shutoff valve of each drain pipe, the drain is led to the steams condenser. The shutoff valve of each drain pipe is opened in warming the high-pressure turbine 200 to lead, for example, the drain generated in the upper half side main steam pipes 11 and the lower half side main steam pipes 12 to the condenser. The shutoff valve of each drain pipe is closed after completion of the warming.
Next, a pipe configuration of the post-valve seat drain pipe 31 of the main steam control valve 30 in the steam turbine pipe 1 of the first embodiment will be described.
The post-valve seat drain pipe 31 is provided with a shutoff valve 32 as illustrated in
As described above, a part of the branching passage 40 is provided, for example, in a pipe wall of a pipe constituting the steam passage 30a. Further, the branching passage 40 is extended perpendicularly to the flow direction of steam and in an almost horizontal direction, for example, from a lower part of the steam passage 30a as illustrated in
The post-valve seat drain pipe 31 has a pipe part 31a having the same passage cross-sectional shape as a passage cross-sectional shape of the through hole 30b, and a reduced pipe part 31b having a passage cross section reduced from a passage cross section of the pipe part 31a. In short, the passage cross section of the reduced pipe part 31b is smaller than the passage cross section of the pipe part 31a. As described above, the reduced pipe part 31b is provided at a part of the branching passage 40 between the steam passage 30a and the shutoff valve 32. More specifically, the reduced pipe part 31b is provided at a part of the branching passage 40 on the side closer to the other end (the shutoff valve 32) than is one end side (the steam passage 30a side) of the branching passage 40. For example, as illustrated in
The reduced pipe part 31b functions as a reduced part. Here, as the reduced pipe part 31b, an example which is connected to the middle of an end part on the shutoff valve 32 side of the pipe part 31 is illustrated. Note the passage cross section is a cross section of the passage, perpendicular to the flow direction (the same applies hereinafter).
Here, assuming that a passage cross-sectional area of the pipe part 31a is 1, a passage cross-sectional area of the reduced pipe part 31b is preferably set to about 1/25 to ¼ in order that drain smoothly flows even when its flow rate is maximum. Further, the branching passage 40 is inclined downward, for example, at about 0.5 to 1 degree in order to make the drain to flow down toward the shutoff valve 32. The above-described almost horizontal direction includes a direction extended at the downward inclination angle in addition to the horizontal direction (the same applies hereinafter).
Note that at least a part of the branching passage 40 only needs to be extended perpendicularly to the flow direction of steam and in the almost horizontal direction from the lower part of the steam passage 30a. Therefore, the branching passage 40 on a further downstream side may be bent, for example, in a vertically downward direction.
Besides, the branching passage 40 is not limited to be provided in the direction perpendicular to the flow direction of steam. The branching passage 40 only needs to be in a direction almost perpendicular to the flow direction of steam. The almost perpendicular direction includes, for example, a direction inclined at about ±45 degrees with respect to the perpendicular direction in addition to the perpendicular direction (the same applies hereinafter).
Provision of the reduced pipe part 31b as described above makes it possible to reduce resonant vibration in the post-valve seat drain pipe 31 between the steam passage 30a and the shutoff valve 32. This makes it possible to suppress an abnormal increase in temperature of the post-valve seat drain pipe 31 even after the shutoff valve 32 is closed, and prevent breakage of the post-valve seat drain pipe 31.
Though the example in which the reduced pipe part 31b is connected to the middle of an end part on the shutoff valve 32 side of the pipe part 31a is illustrated in
For example, the reduced pipe part 31b may be connected to a portion lower than the middle of the end part on the shutoff valve 32 side of the pipe part 31a. More specifically, the reduced pipe part 31b may be connected to the end part on the shutoff valve 32 side of the pipe part 31a so that a lower part of an inner wall surface of the reduced pipe part 31b becomes flush with a lower part of an inner wall surface of the pipe part 31a in the cross sections illustrated in
Connecting the reduced pipe part 31b as described above makes it possible to prevent the drain from staying at a connection part between the pipe part 31a and the reduced pipe part 31b. This makes it possible to suppress an abnormal increase in temperature of the post-valve seat drain pipe 31 and prevent occurrence of hammering in the branching passage 40.
Though the case in which the branching passage 40 is extended perpendicularly to the flow direction of steam and in the almost horizontal direction is illustrated in
As illustrated in
Here, it is only necessary to allow the drain to fall with the force of gravity to thereby prevent the drain from staying on the upstream side of the reduced pipe part 31b in the configuration illustrated in
In the second embodiment, the configuration of a post-valve seat drain pipe 50 is different from the configuration of the post-valve seat drain pipe 31 of the first embodiment. Therefore, the different configuration will be mainly described here.
The post-valve seat drain pipe 50 is provided with a shutoff valve 32 as illustrated in
A part of the branching passage 41 is provided, for example, in a pipe wall of a pipe constituting the steam passage 30a. Further, the branching passage 41 is extended perpendicularly to the flow direction of steam and in an almost horizontal direction, for example, from a lower part of the steam passage 30a as illustrated in
The post-valve seat drain pipe 50 has a pipe part 31a having the same passage cross-sectional shape as a passage cross-sectional shape of the through hole 30b, a reduced pipe part 31b having a passage cross section reduced from a passage cross section of the pipe part 31a, and a pipe part 31c having a passage cross section enlarged from that of the reduced pipe part 31b. In short, the passage cross section of the reduced pipe part 31b is smaller than the passage cross section of the pipe part 31a. The passage cross section of the pipe part 31c is larger than the passage cross section of the reduced pipe part 31b. The reduced pipe part 31b is provided to have a predetermined length on the shutoff valve 32 side of the pipe part 31a. Further, the pipe part 31c is provided on the shutoff valve 32 side of the reduced pipe part 31b. In short, the pipe part 31c is provided between the reduced pipe part 31b and the shutoff valve 32.
A passage cross-sectional area of the pipe part 31c only needs to be larger than a passage cross-sectional area of the reduced pipe part 31b. Assuming that the passage cross-sectional area of the reduced pipe part 31b is 1, the passage cross-sectional area of the pipe part 31c is preferably about 4 to 25 times in order that drain smoothly flows even when its flow rate is maximum. As long as the passage cross-sectional area of the pipe part 31c is larger than the passage cross-sectional area of the reduced pipe part 31b, the passage cross-sectional area of the pipe part 31c may be larger or smaller than, for example, the passage cross-sectional area of the pipe part 31a. Further, the passage cross-sectional area of the pipe part 31c may be made the same as the passage cross-sectional area of the pipe part 31a.
As described above, the reduced pipe part 31b is provided at a part of the branching passage 41 between the steam passage 30a and the shutoff valve 32. Note that the reduced pipe part 31b functions as a reduced part. As the reduced pipe part 31b, an example which is connected to the middle of an end part on the shutoff valve 32 side of the pipe part 31a and the middle of an end part on the steam passage 30a side of the pipe part 31, is illustrated here.
Provision of the reduced pipe part 31b as described above makes it possible to reduce resonant vibration in the post-valve seat drain pipe 50 between the steam passage 30a and the shutoff valve 32. This makes it possible to suppress an abnormal increase in temperature of the post-valve seat drain pipe 50 even after the shutoff valve 32 is closed, and prevent breakage of the post-valve seat drain pipe 50.
Note that the reduced pipe part 31b may be connected between the pipe part 31a and the pipe part 31c so that a lower part of an inner wall surface of the reduced pipe part 31b becomes flush with lower parts of inner wall surfaces of the pipe part 31a and the pipe part 31c also in the second embodiment as in the configuration in
Besides, the branching passage 41 may be extended in an almost vertically downward direction from a lower part of the steam passage 30a also in the second embodiment as in the configuration in
The branching passage 42 that branches off from the steam passage 30a of the main steam control valve 30 is composed of a through hole 60 communicating with the steam passage 30a and a post-valve seat drain pipe 70 (passage in the post-valve seat drain pipe 70) provided to communicate with an outside opening of the through hole 60 as illustrated in
The branching passage 42 is extended perpendicularly to the flow direction of steam and in an almost horizontal direction, for example, from a lower part of the steam passage 30a as illustrated in
The through hole 60 is composed of a through hole 30b provided in a pipe wall of a pipe constituting the steam passage 30a and a through hole 80 formed in a heat conduction member 90 provided between the post-valve seat drain pipe 70 and the pipe constituting the steam passage 30a. The shape of the cross section perpendicular to the flow direction of the through hole 30b is formed to be the same, for example, as the shape of the cross section perpendicular to the flow direction of the through hole 80. In short, the through hole 30b and the through hole 80 constitute a part of the branching passage 42 having the same cross-sectional shape.
One end part of the heat conduction member 90 is joined to the pipe constituting the steam passage 30a, for example, by welding. The post-valve seat drain pipe 70 is connected to the other end part of the heat conduction member 90 (the end part on the shutoff valve 32 side). A passage cross section of the post-valve seat drain pipe 70 is reduced to be smaller than a passage cross section formed by the through hole 60. In other words, the post-valve seat drain pipe 70 constitutes a reduced pipe part to function as a recued part.
Here, the heat conduction member 90 conducts heat generated in the branching passage 42 located on the side closer to the steam passage 30a than is the post-valve seat drain pipe 70, to the pipe (main steam control valve 30) constituting the steam passage. Therefore, the heat conduction member 90 is preferably made of for example, a material having good heat resistance. Further, the heat conduction member 90 is preferably made of, for example, a material better in heat conduction than the material making the pipe (main steam control valve 30) constituting the steam passage 30a. Here, the pipe (main steam control valve 30) constituting the steam passage has a heat capacity enough to absorb the heat quantity conducted thereto via the heat conduction member 90.
The heat conduction member 90 is formed of, for example, a metal material. As the metal material forming the heat conduction member 90, a metal having a high heat conductivity such as copper, carbon steel or the like.
Provision of the heat conduction member 90 as described above allows the heat generated on the side closer to the steam passage 30a than is the post-valve seat drain pipe 70 functioning as a recued part to escape to the pipe (main steam control valve 30) constituting the steam passage. In other words, it is possible to achieve both of an effect of suppressing an abnormal increase in temperature attained by providing the reduced part and an effect of allowing heat to escape attained by providing the heat conduction member 90 in the steam turbine pipe 3 of the third embodiment.
Here, the configuration for allowing the heat generated on the side closer to the steam pipe 30a than is the reduced part to escape to the pipe (main steam control valve 30) constituting the steam passage is not limited to this configuration.
As illustrated in
Besides, as the heat conduction member 90, for example, a double pipe structure having an inner hollow part filled with liquid or the like may be provided. In this case, the heat generated in the pipe part 31a is allowed to escape to the pipe (main steam control valve 30) constituting the steam passage.
Note that the configuration provided with the above-described heat conduction member 90 is also applicable to the case in which the branching passage 40 is extended in the almost vertically downward direction from a lower part of the steam passage 30a. Besides, the configuration provided with the above-described heat conduction member 90 is also applicable to the steam turbine pipe 2 of the second embodiment. In these cases, the same effects as those described above can be achieved.
Here, though the passage including the post-valve seat drain pipe of the main steam control valve 30 has been described as an example of the branching passage that branches off from the steam passage in the above embodiments, the branching passage is not limited to this. For example, the above-described configuration may be applied, for example, to a branching passage (branching pipe) that branches off from a steam passage leading steam from the boiler to the high-pressure turbine 200 and has a shutoff member such as a shutoff valve or the like. Also in this case, it is possible to suppress occurrence of the resonant vibration in the branching passage between the steam passage and the shutoff member and suppress an abnormal increase in temperature in the branching passage.
As described above, provision of the reduced part reduced in passage cross section in the branching passage 40, 41, 42 that branches off from the steam passage 30a of the main steam control valve 30 makes it possible to suppress an abnormal increase in temperature in the branching passage 40, 41, 42 in the above-described embodiments. This can prevent breakage of the branching passage 40, 41, 42.
Here, the reason why provision of the reduced part in the branching passage 40, 41, 42 makes it possible to suppress an abnormal increase in temperature in the branching passage 40, 41, 42 is described.
Here, it is assumed that the frequency of the pressure fluctuation in the pipe of a cylinder with an inside diameter of R is f (Hz). According to Document 1 (Arakawa, Kawahashi, Transaction of the Society of Mechanical Engineers, Vol. 62 No. 598, B (1996), pp. 2238-2245), a heat flux q (W/m2) generated by the thermoacoustic effect due to the pressure fluctuation in a boundary layer near a pipe wall can be obtained by Expression (2) using the relation of Expression (1) made by dividing a pressure fluctuation amplitude in the pipe P by an average pressure in the pipe P0 and making the dimensionless.
Here, P1 is a dimensionless pressure amplitude, K is a constant decided by a pipe shape, γ is a specific heat ratio, μ is a viscosity coefficient, a is a sound speed, δ is a thickness of the boundary layer, and R is an inside diameter of the cylinder.
Since the inner perimeter of the cylinder is πR, a heating value Q (W/m) per unit length of the cylinder is obtained by Expression (3).
Assuming here that an angular frequency ω is 2 πf, the thickness δ of the boundary layer is obtained by Expression (4).
Here, ν is a kinematic viscosity coefficient.
Namely, as is clear from Expression (3), the heat generation due to pressure fluctuation in the pipe (thermoacoustic effect) is proportional to the square of the dimensionless pressure amplitude. Therefore, it is found that the heat generation is suppressed by suppressing the pressure fluctuation in the pipe.
(2) Explanation that Provision of the Reduced Part in the Branching Passage Makes it Possible to Suppress the Pressure Fluctuation in the Pipe
Next, the fact that provision of the reduced part in the branching passage 40, 41, 42 makes it possible to suppress the pressure fluctuation in the pipe is explained referring to
As illustrated in
The passage cross-sectional area of the pipe part 31a is S1, and the length of the pipe part 31a is L1. The passage cross-sectional area of the reduced pipe part 31b is mS1, and the length of the reduced pipe part 31b is L2. Note that m is a constant smaller than 1. The pressure fluctuation at the end part on the shutoff valve 32 side of the reduced pipe part 31b is P2.
Regarding the pressure fluctuation and the speed fluctuation of steam, portions flowing from the upstream side of the steam passage 30a into the connection part between the pipe part 31a and the steam passage 30a are Pi, Ui, portions reflected to the upstream side of the steam passage 30a from the connection part are Pr, Ur, portions flowing out to the downstream side of the steam passage 30a from the connection part are Pt, Ut, and portions flowing out to the steam passage 30a from the pipe part 31a via the connection part are P1, U1.
A region on the upstream side of the connection part of the steam passage 30a is I and a region on the downstream side of the connection part of the steam passage 30a is II. The pressure fluctuation and the speed fluctuation of steam in the region I are PI, UI, and the pressure fluctuation and the speed fluctuation of steam in the region II are PII, UII.
Assuming that the pressure fluctuation in the steam passage 30a is a plane progressive wave, a steam density is ρ0, and a steam sound speed is C0, U=P/(ρ0C0) is established. Therefore, the relations in the following Expression (5) to Expression (8) can be obtained.
Here, the sound pressures on the upstream side and the downstream side of the connection part are equal. Further, regarding the volume velocity, the relations in the following Expression (9) and Expression (10) are obtained in consideration of a portion (S1U1) flowing out to the steam passage 30a from the pipe part 31a via the connection part.
Here, Z1 is an acoustic impedance (P1/(S1U1)) including the reflection in the pipe part 31a at the opening part of the pipe part 31a.
From Expression (6), the following Expression (11) is established.
The pressure fluctuation P1 in the connection part is expressed by Expression (12) from the relation of P1=P1=(Pi+Pr).
Then, in the pipe configuration illustrated in
According to Document 2 (Ichikawa, Takayama, Transaction of the Society of Mechanical Engineers, Vol. 39 No. 325, (1973), pp. 2807-2815), a propagation constant γi (i=1, 2, 3) is approximated by the following Expression (14), Expression (15) approximating the viscos friction of flow in the pipe part 31a.
Here, j is an imaginary unit and ω is an angular frequency.
Further, a characteristic impedance Zi (i=1, 2, 3) is approximated by the following Expression (16), Expression (17).
Then, a propagator matrix T is defined as in the following Expression (18).
Further, from Expression (13), Z1=t11/t21 is obtained. T′ being an inverse of the matrix T is expressed by the following Expression (19).
Then, the relation of the following Expression (20) is obtained.
From Expression (20), a ratio (P2/Pi) between the pressure fluctuation Pi in the steam passage 30a on the upstream side of the connection part and the pressure fluctuation P2 at the end part on the shutoff valve 32 side of the reduced pipe part 31b is obtained as the following Expression (21).
Note that the above Expression (21) is obtained using the branching passage 40 of the first embodiment illustrated in
Besides, the ratio (P2/Pi) can also be obtained similarly to the above even using the branching passage 41 of the second embodiment illustrated in
A passage cross-sectional area of the pipe part 31c provided between the reduced pipe part 31b and the shutoff valve 32 is larger than a passage cross-sectional area of the reduced pipe part 31b in
As steam conditions, the temperature was set to 350° C., the pressure was set to 5 MPa, the density ρ0 was set to 19.2 kg/m3, the sound speed was set to 578 m/s, and the kinematic viscosity coefficient ν was set to 1.1×10−6 m2/s.
As the pipe shape of the model illustrated in
In the pipe shape of the model illustrated in
In the pipe shape of the branching passage without the reduced pipe part 31b used as Comparative Example, the passage cross-sectional area was uniformly set to 0.0016 m2 (corresponding to an inside diameter of 0.045 m), its length was set to 5 m. Note that in the pipe shape in Comparative Example, when it is used under the aforementioned steam conditions, an abnormal increase in temperature in the branching passage arises to break the pipe.
As illustrated in
About 29 Hz that is the value obtained by dividing the sound speed C0 (578 m/s) by 20 m that is the quadruple of the branching passage total length (5 m) is the fundamental frequency. In Comparative Example, the odd multiple of the fundamental frequency is the standing wave frequency and is found to coincide with the maximized frequency illustrated in
Here, it is known that the heat generation by the fundamental standing wave is largest in the heat generation by the thermoacoustic effect. This is shown as characteristics of Haltman tube in the aforementioned Document 1 and Document 3 (Sprenger, H., “On thermal effects in resonance tubes”, NTRS, 1964).
In Example 1, as illustrated in
In Example 2, as illustrated in
Here, it is considered that breakage due to overheating can be normally avoided if the heat generation is about 1/9 to 1/10 though depending on the heat-insulating condition of the pipe part 31a. Therefore, suppression of the pressure fluctuation to ⅓ or less of the pressure fluctuation of Comparative Example causing breakage is considered to be sufficient. Consequently, in order to prevent breakage of the pipe due to an abnormal increase in temperature, it is only necessary to decide the specifications of the branching passage so that the ratio (P2/Pi) of the pressure fluctuation obtained from the aforementioned Expression (21) becomes, for example, ⅓ or less.
Here, temperature changes of the pipe surfaces of the branching passages in the case with the reduced part and the case without the reduced part were evaluated.
Note that
The pipe with the reduced part was made to have an inside diameter of 30 mm to a position of a length of 0.5 m from the opening part (corresponding to the connection part) and to have an inside diameter of 10 mm on the downstream side (the closed end side) of the position. A portion with the smaller inside diameter is the reduced part. The total length of the pipe was 2 m.
The pipe without the reduced part was made to have an inside diameter of 30 mm from the opening part (corresponding to the connection part) to the closed end part. The total length of the pipe was 2 m. The temperature of the jet flow jetted to the opening part was the same both in the case with the reduced part and the case without the reduced part.
As illustrated in
On the other hand, in the pipe with the reduced part, any temperature increase is not recognized in the reduced part and overheating is prevented. However, at the portion from the opening part to the reduced part, the temperature increase is large. This is considered to be caused by the following reasons. At the closed end part in the case with the reduced part, overheating due to the thermoacoustic effect can be prevented by suppressing the pressure fluctuation as expressed in Expression (21). In contrast, the portion from the opening part to the reduced part, the pressure reflection at the reduced part returns to the opening part side, so that the pressure fluctuation increases to cause heat generation due to the thermoacoustic effect.
Here, even when the temperature increase is large at the portion from the opening part to the reduced part, an abnormal temperature increase can be suppressed by deciding the specifications of the branching passage so that the ratio (P2/Pi) of the pressure fluctuation obtained from the aforementioned Expression (21) becomes, for example, ⅓ or less.
Further, provision of the heat conduction member 90 in the third embodiment allows the heat generated in the portion from the opening part to the reduced part to escape to the pipe (main steam control valve 30) constituting the steam passage.
According to the above-described embodiments, it becomes possible to provide a steam turbine pipe that prevents an abnormal increase in temperature in a steam turbine pipe system and has a high reliability.
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
Number | Date | Country | Kind |
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2014-012623 | Jan 2014 | JP | national |