JPS62251408A - Steam turbine casing - Google Patents

Abstract

PURPOSE:To reduce irregular thermal stress of a casing and to decrease the starting time, by providing the first internal casing, which surrounds the first stage of a turbine, while the second internal casing, which surrounds the final stage, and forming intermediate chambers between the internal casings and an external casing. CONSTITUTION:An internal casing of a high pressure turbine is divided into the first internal casing 7, which surrounds the first stage, and the second internal casing 8 which surrounds the final stage. And space between the internal casing and an external casing 1 is divided by a partitioning wall 10 into the first intermediate chamber 11 and the second intermediate chamber 12. In this way, one part of a flow of steam from the first stage of the turbine to its final stage is allowed to flow out into the first intermediate chamber 11 from a clearance 9 in the internal casing, and thermal stress, when the turbine is started, can be reduced by heating an external wall of the first internal casing 7.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a double casing II steam turbine casing, and more particularly to a casing for an ultra-8 temperature/ultra-high pressure turbine in which the inner casing is divided.

(Prior Art) Power plants using steam turbines are required to greatly improve thermal efficiency due to energy constraints, and for this reason, efforts are being made to make the turbines extremely high temperature and high pressure.

As such ultra-high temperature/high pressure steam turbine plans 1~, those with steam conditions of 649° C. and 352 atg have been constructed so far. The ultra-high temperature and high pressure section of this steam turbine plant is described in △SM IE 195 [rThe [ddystone 5upcr-p] of the August newsletter.
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It No., IJ, and according to this disclosure, it has a double casing structure consisting of an inner casing and an outer casing. This inner casing is made of high-grade heat-resistant steel with high high-temperature creep strength, specifically Ni1
Austenitic heat-resistant steel containing a large amount of Cr, etc. is used for the outer casing, and the outer casing is made of heat-resistant steel that is relatively inexpensive and has a lower service temperature limit than austenitic heat-resistant steel, specifically a small amount of Cr, etc. Ferritic heat-resistant steel containing MO and the like and having a service limit temperature of 593°C was used.

FIG. 4 shows a high temperature/high pressure section of a steam turbine having such a double casing structure, in which an inner casing 2 is disposed inside an outer casing 1. Inside this internal casing 2, there are a nozzle box 3, a first stage nozzle (Shizuoka) 4a and blades (moving blades) 5a, a second stage nozzle 4b and blades 5b, a third stage nozzle 4C, etc. A blade 5C, a fourth stage nozzle 4d, and a blade 5d are installed, respectively. Steam flowing in from a steam inlet pipe (not shown) passes through the nozzle box 3 and flows through each stage in the direction of the arrow. In this way, the steam t whose temperature and pressure have been reduced by performing work in each stage is discharged from the exhaust pipe 6, and a portion thereof fills the gap between the outer casing 1 and the inner casing 2.

In the structure of JP-A-60-159310, this filled steam is discharged to the outside as cooling air using the steam pipe inlet.

In this double casing structure, the inner casing 2 is made of austenitic heat-resistant steel to improve high-temperature creep strength, while the outer casing 1, which is in contact with relatively low-temperature and low-pressure steam, is made of relatively inexpensive ferritic heat-resistant steel. is used.

(Problem to be solved by the invention) However, in recent years, steam turbines in thermal power plants have been subject to startup and shutdown and load fluctuations once or twice a day, for example, in response to the widening disparity in electricity demand between day and night. ing. Due to the inflow of steam and the stoppage of the inflow of steam when the turbine is started and stopped, a large temperature difference occurs between the inner and outer walls of each turbine casing, resulting in generation of unsteady thermal stress. This unsteady stress is much larger than the thermal stress generated during steady operation, and unless it is suppressed to 1ζ below the allowable stress, safe starting and stopping cannot be achieved. However, although the Austenite 1 heat-resistant steel used for the internal casing of this ultra-high temperature/high-pressure turbine has lower high-temperature creep strength than ferritic heat-resistant steel, it has lower thermal conductivity and a smaller coefficient of thermal expansion. It also has poor yield strength, so thermal stress is likely to occur.
It has the disadvantage that the allowable stress of the material is small. For this reason, in conventional high-temperature, high-pressure steam turbines, it is necessary to increase the turbine startup and shutdown times in order to avoid operations that would cause sudden temperature changes in the internal casing when the turbine is started and stopped. The drawback was that it was not possible to operate in a timely manner.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a steam turbine casing that can suppress the occurrence of an unsteady thermal response of 7 J during startup and shutdown of a turbine, thereby shortening startup and shutdown times.

(Means for Solving the Problems) The internal casing surrounding each stage of the ultra-high temperature/high pressure turbine is divided into a first internal casing and a second internal casing. The first inner casing surrounds at least the first stage of the ultra-high temperature/high pressure turbine and forms a first intermediate casing between it and the outer casing, and the second inner casing surrounds the last stage of the ultra-high temperature/high pressure turbine and A second intermediate compartment is formed between the outer casing and the outer casing.

A partition wall projects from the second inner casing to partition the first intermediate compartment and the second intermediate compartment. An initial trachea and an auxiliary exhaust pipe communicate with the second intermediate compartment and the first intermediate compartment, respectively.

(Function) After passing through each stage of the turbine, the ultra-high temperature and high pressure steam flow flows into the second intermediate casing and is discharged from there via the exhaust pipe. At this time, part of the steam flow flows from the gap between the first internal casing and the second internal casing into the first intermediate casing on the way from the first stage to the final stage of the turbine, heating the outer wall of the first internal casing. After that, it is discharged through the auxiliary exhaust pipe.

In this way, even if the inner wall of the first inner casing is heated in an extremely high temperature and high pressure steam atmosphere, the outer wall is also heated by the relatively high temperature and high pressure steam that has flowed into the first intermediate chamber, so the temperature difference between the inner and outer walls is reduced. decreases rapidly, making it possible to suppress the occurrence of unsteady thermal stress in a short time.

(Embodiment) An embodiment of a steam turbine casing according to the present invention will be described below with reference to FIGS. 1 to 3, in which the same parts as in FIG. 4 are denoted by the same reference numerals. .

In FIG. 1, a first inner casing 7 made of austepite heat-resistant steel and a second inner casing 8 made of ferritic heat-resistant steel are disposed inside an outer casing 1 made of ferritic heat-resistant steel. , a second inner casing 7.8 (separated from each other by a gap 9 and held together in the outer casing 1). 48 and vane (dynamic 5 lit) 5a, the second stage nozzle 4b and vane 5b, respectively, and the second internal casing 8 surrounds the third stage nozzle 4C and vane 5C, and the fourth stage nozzle 4C and vane 5C. The outer casing 1 and the inner casing 7 surround the nozzle 4d and the blade 5d, respectively.
8 is divided into a first intermediate compartment 11 and a second intermediate compartment 12 by a ring-shaped partition wall 10 projecting from the second inner casing 8. That is, the first intermediate compartment 1 is formed by the outer casing 1 and the first inner casing 7.
1 is formed, and a second intermediate compartment 12 is formed by the outer casing 1, the first inner casing 8, and the partition wall 10. These first intermediate compartment 11 and second intermediate compartment 12
An auxiliary exhaust pipe 13 and an exhaust pipe 6, which pass through the outer casing 1, communicate with each other. This auxiliary exhaust pipe 1
3 is connected to the exhaust pipe 6, and this auxiliary exhaust pipe 13 has a 1f
An fi adjustment valve 14 is provided. This flow m adjustment valve 14
The valve opening degree is υ controlled by a11 control @'a15. As shown in FIG. 2, this control device 15 includes a lambda power device 16 that inputs temperature signals SS and S3 of the inner wall 7a, inner wall 7b1, and outer wall 7C of the first inner casing 7, and a It is comprised of a thermal stress calculation device 2?17 that determines the degree of Wi of the flow ffi adjustment valve 14 by calculating the thermal stress of the flow ffi adjustment valve 14, and an outlet device 18 that indicates the degree of opening. Above mentioned inner wall temperature No. 45 S1 and internal temperature signal @S2 and outside 1
! I! The temperature α signal S3 is generated from a plurality of temperature sensors (not shown) attached to the first inner casing 7.

Next, the operation of this embodiment will be explained.

When starting the turbine after pre-warming,
Nozzle box 3 via a steam inlet pipe (not shown)
The ultra-high temperature and high pressure hot air that flowed into the first, second and third stages
Each of the stage and fourth stage nozzles 48 to 4d and each blade 5a to 5
d sequentially.

As a result of the work done in each stage, the steam, which has become low temperature and low pressure, flows into the second intermediate casing 12 after passing through the final stage vane 5d and is discharged from the exhaust gas 126. At this time, the second stage blade 5b7! i: A part of the steam that has flowed out flows into the first intermediate chamber 11 through the gap 9 between the first inner casing 7 and the second inner casing 8, and flows out of the first inner casing 7! ! 7C is heated so that the difference in tQWl with respect to the inner wall 7a becomes small, and then flows out from the auxiliary exhaust pipe 13 to the exhaust pipe 6 via the flow ffi adjustment valve 14 and is discharged. This first
Since m of the high-pressure steam at a temperature flowing into the black market chamber 11 can be controlled by the opening degree of the flow m adjustment valve 14, the opening degree of the first inner casing 7 can be controlled by adjusting the opening degree of the flow m adjustment valve 14. The generation of unsteady thermal stress can be rapidly suppressed.

a, 11 The input device 16 of the In equipment 15 receives information from the inner wall of the first inner casing, the inside,
Each temperature signal S S , S3 of the outer wall is inputted.
2. The thermal stress calculation device 17 receives these temperature signals S1.
S2. Based on S3, calculate T for each temperature difference between the inner and outer walls of the first inner casing 7 and calculate the thermal stress of the first inner casing 7, and roughly calculate the flow R for this calculated thermal stress.
Determine the optimal opening degree of the regulating valve. Specifically, the relationship between the temperature difference ΔK between the inner and outer walls and the inside and the absolute value of thermal stress at this time, and the relationship between this absolute value of thermal stress and the optimal flow rate adjustment valve opening for this are calculated in advance or Determined by experiment. These relationships are shown in Figure 3(a) and (
b> can be expressed as a graph. The thermal stress calculation device 17 stores the relationship between these graphs as a table, and receives temperature signals 31 and S2 from the input device 16.
．． 33, determine the optimum flow rate regulating valve 1;4 degree for that crest. The output device 18 adjusts the valve opening of the flow h1 regulating valve 14 according to the determined optimal flow regulating valve opening.
do.

In this way, when ultra-high temperature and high pressure steam starts to flow in during the turbine orbit, the inner wall 7 a 4 of the first inner casing 7
This inner wall 7a and outer wall 7 are directly heated and become high temperature.
However, this temperature difference is immediately detected, and in response to this, the control device 15 fully opens the & amount adjustment valve 14, so that the relatively high temperature flowing out from the second stage vane 5b - High-pressure steam flows into the first intermediate casing 11 at high speed. In general, heat transfer between a fluid and a stationary object increases as the fluid velocity increases, so the steam flow at P4 speed
C is heated to reduce the temperature difference between the inner and outer walls and reduce thermal stress.
Relax in time. In this way, when the temperature of the inner and outer walls decreases, the 111 control device 15 reduces the valve opening degree of the flow rate regulating valve 14 in response to this, and directs the g-temperature and high-pressure steam from the second stage vane 5b to the first intermediate compartment 11. decrease the amount of inflow.

Further, the steam flowing into the first intermediate casing 11 is from the second stage vane 5b and is still at a fairly high pressure, so the pressure difference between the inner and outer walls of the first inner casing 7 is small. Therefore, the first inner casing 7 can be made thinner, and this thinning t further promotes rapid relaxation of thermal stress in the first inner casing.

The first internal casing 7 is made of austenitic heat-resistant steel that has excellent high-temperature creep strength since it is in an atmosphere of ultra-high temperature and high-pressure steam. Since the work is performed in the second stage in a steam atmosphere with a resulting drop in temperature and pressure, relatively inexpensive ferritic heat-resistant steel can be used.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, the inner casing is divided into a first inner casing and a second inner casing, and a first intermediate compartment is also provided between the first inner casing and the outer casing. Second inner casing and outer n1
A second intermediate casing is formed between each of the casings, and a partition wall that roughly partitions the first intermediate casing and the second intermediate casing is provided protruding from the second internal casing. A part of the steam flow flowing to the final stage passes through the opening between the first inner casing and the second inner casing.
) flows into the first intermediate casing and heats the outer wall of the first inner casing, rapidly reducing the temperature difference between the inner and outer walls of the first inner casing. Therefore, the occurrence of unsteady thermal stress in the first inner casing can be rapidly alleviated, and the time for starting and stopping the turbine can be significantly shortened, making it possible to operate the turbine according to the power supply and demand situation.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of a steam turbine casing according to the present invention, and FIG.
FIG. 3(a) is a block diagram showing the configuration of the device. (b) is a graph diagram showing the relationship between the temperature difference between the inner and outer walls and inside of the first inner casing and the absolute value of thermal stress, and the relationship between the absolute value of thermal stress and the opening degree of the flow rate regulating valve, respectively;
The figure is a sectional view C showing a conventional double casing type steam turbine casing. 1... External casing, 4a to 4d... Nozzle, 5
a to 5d...Blade, 6...Exhaust pipe, 7...First internal casing, 8...: J12 internal casing, 10
...Partition wall, 11...First intermediate compartment, 12...Second intermediate compartment, 13...Auxiliary exhaust pipe, 14...Flow rate adjustment valve. Applicant's representative Sato - Yukatsu 1, 1, bribe 2

Claims (1)

[Claims] 1. An outer casing, a first inner casing that surrounds at least the first stage of the ultra-high temperature/ultra-high pressure turbine and forms a first intermediate casing between the outer casing and the ultra-high temperature/high pressure turbine; a second inner casing that surrounds at least the final stage of the turbine and is arranged so as to form a gap with the first inner casing and forms a second intermediate casing between the second inner casing and the outer casing; 2. A partition wall projecting from the internal casing and partitioning the vehicle from the second intermediate compartment, an exhaust pipe communicating with the second intermediate compartment, and an auxiliary exhaust pipe communicating with the first intermediate compartment. A steam turbine casing featuring: 2. The steam turbine casing according to claim 1, wherein the material of the first inner casing has higher high temperature creep strength than the material of the second inner casing. 3. The steam turbine casing according to claim 2, wherein the material of the first inner casing is austenitic heat-resistant steel, and the material of the second inner casing is ferritic turbine steel. 4. Claim 1, characterized in that the auxiliary exhaust pipe is provided with a flow rate regulating valve whose opening degree is controlled according to the temperature difference between the inner and outer walls of the first inner casing. The steam turbine casing described in .