JP3621478B2 - Steam turbine warming equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a steam turbine warming device for warming a high-pressure / intermediate-pressure casing of a steam turbine at the time of starting a power plant.
[0002]
[Prior art]
In general, in a steam turbine plant, when the steam turbine cooler is started (cold start), the high-pressure / medium-pressure casing of the steam turbine is pre-warmed, and then the steam control valve casing is warmed, and then the turbine is started. It is carried out.
[0003]
Pre-warming of the above high-pressure / medium-pressure casing reduces the temperature difference between the starting steam temperature and the casing, rotor surface and internal metal temperature, so-called mismatch temperature difference, by preheating the turbine when the steam turbine cooler is started. By controlling excessive thermal stress in the starting process, cracks are prevented from occurring in the turbine casing and the rotor.
[0004]
FIG. 14 is a schematic view showing a general turbine casing. As shown in FIG. 14, the turbine casing includes an outer casing upper half 1 and an outer casing lower half 2, and the outer casing upper half 1 is a high-pressure inner casing upper half 1a and a medium-pressure inner casing upper half 1b. On the other hand, the outer casing lower half 2 has a high pressure inner casing lower half 2a and an intermediate pressure inner casing lower half 2b.
[0005]
The turbine casing is provided with a plurality of pipe portions as steam inlets and flows into the outer casing upper half 1 and the outer casing lower half 2 from the main steam inlet pipe upper part 3a and the main steam inlet pipe lower part 3b. After the steam expands and works inside the casing, the steam is discharged from the high-pressure exhaust pipe 4 provided in the lower half 2 of the outer casing, returned to a boiler (not shown), and reheated. The reheated steam again flows into the outer casing lower half 2 from the reheat inlet pipe 5, expands again and works, and is then exhausted from the intermediate pressure exhaust pipe 6 and sent to a low-pressure turbine (not shown).
[0006]
During pre-warming, pre-warming steam flows in the high pressure inner casing upper half 1a and the high pressure inner casing lower half 2a, and passes through the intermediate gland 7 so that the medium pressure inner casing upper half 1b and the medium pressure inner casing lower half It flows into the body 2b and flows into the low-pressure turbine (not shown) through the intermediate pressure exhaust pipe 6.
[0007]
Further, during pre-warming, pre-warming is performed in the high-pressure inner casing upper half 1a and the high-pressure inner casing lower half 2a by the auxiliary steam line 9 branched from the middle of the low-temperature reheat pipe 8 connected to the high-pressure exhaust pipe 4. Warming steam is supplied from an auxiliary steam header (not shown) through the valve 10.
[0008]
Further, each of the thermocouples 11a and 11b measures the metal temperatures of the inner surface and the outer surface of the lower half body 2a of the high-pressure inner casing, and also monitors the steam temperature during pre-warming.
[0009]
The pre-warming is carried out immediately after the boiler is ignited, when the metal temperature of the first stage casing inner surface of the high-pressure turbine is measured by the thermocouple 11a, and the measured temperature is equal to or lower than a predetermined value (150 ° C.). It takes about 6 hours from the start of warming to completion.
[0010]
In general, the casing has a much larger heat capacity than the rotor and is less likely to be warmed. Therefore, the prewarming completion time may be determined by the required heating time of the casing.
[0011]
Further, after the pre-warming of the turbine casing is completed, the warming of the steam control valve casing is performed. This is because the main steam stop valve on the upstream side of the steam control valve is opened and closed before the turbine is started, and the metal temperature on the inner and outer surfaces of the steam control valve is increased. This is carried out in order to reduce excessive thermal stress generated in the steam control valve casing by reducing the rate of increase. Generally, this warming is completed when the outer surface metal temperature of the steam control valve approaches the saturation temperature of the main steam pressure at the time of startup, but it takes about one hour at the shortest.
[0012]
As described above, in the steam turbine plant, it takes 7 hours or more in total for warming in the cold start process.
[0013]
[Problems to be solved by the invention]
In this way, when the steam turbine plant is cold-started, in order to reduce the thermal stress of the steam turbine, in addition to about 6 hours until the completion of the pre-warming, the warming of the steam control valve casing takes at least one hour. It takes more than 7 hours to warm up alone. This hinders the prompt start-up of the plant for power demand, and at the same time leads to deterioration of the working conditions of power plant workers who must enter the plant start-up preparation at midnight in response to the power demand time zone. There is a problem.
[0014]
On the other hand, when the auxiliary steam boiler is operated for a long period of time for pre-warming, there is also a problem that the economic efficiency of the power plant is reduced at the plant start-up stage.
[0015]
The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide a steam turbine warming device that can reduce the warming time of the steam turbine and reduce the thermal stress when the power plant is started up. And
[0016]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, claim 1 of the present invention is that the high- and medium-pressure casings of the high-pressure / medium-pressure casing, the portion where steam flow tends to stay, and the occurrence of cracks empirically at the start of the steam turbine cooler A heater is attached to a portion that is easy to perform, and a temperature measuring means for measuring the inner and outer surface metal temperatures of the casing is provided at the heater attaching portion, and temperature data by the temperature measuring means and a predetermined target preheating completion temperature are provided. A comparator for calculating a temperature difference and calculating whether the temperature difference is greater than a predetermined plus-side allowable deviation or a minus-side allowable deviation, and the heater with the temperature difference being a plus-side allowable deviation If it is larger, the off operation is performed, and if it is larger than the negative tolerance, the on operation is performed to warm the steam turbine. In the forming device, the signal from the comparison operation unit is branched, and only when the temperature difference is within the allowable deviation on the plus side and the minus side, the signal is input to the timer, and this timer determines in advance After the elapsed time, the valve is opened to introduce steam into the casing .
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0023]
FIG. 1 is a perspective view showing a first embodiment of a warming device for a steam turbine according to the present invention. Parts that are the same as or correspond to those in the conventional configuration will be described using the same reference numerals as in FIG.
[0024]
As shown in FIG. 1, the turbine casing includes an outer casing upper half 1 and an outer casing lower half 2, and has a structure that can be horizontally divided into two in consideration of maintainability. It is concluded by.
[0025]
The turbine casing is provided with a plurality of pipes as steam inlets and outlets, and the steam flowing into the outer casing upper half 1 and the outer casing lower half 2 from the main steam inlet pipe upper part 3a and the main steam inlet pipe lower part 3b Then, after expanding and working inside the casing, it is discharged from the high-pressure exhaust pipe 4 provided in the lower half 2 of the outer casing, returned to a boiler (not shown), and reheated. The reheated steam again flows into the outer casing lower half 2 from the reheat inlet pipe 5, expands again and works, and is then exhausted from the intermediate pressure exhaust pipe 6 and sent to a low-pressure turbine (not shown).
[0026]
In the outer casing upper half 1, electrical resistance heaters 13a, 13b, and 13c are attached to uneven thick portions, portions where steam flow tends to stay, and portions where cracks are likely to occur empirically, respectively. It is fixed by existing heat insulation fixing brackets.
[0027]
In the high-pressure turbine shown in FIG. 2, the uneven thickness portion is a welded connection between a casing cylinder and a casing flange curvature portion A, a casing cylinder and a casing cylinder (or a casing cylinder and a casing flange, a casing cylinder and a short pipe). Part B, a pipe opening (short pipe connecting part protruding from the casing) C in the intermediate pressure turbine shown in FIG.
[0028]
Further, the portion where the steam flow is likely to stay is, for example, a space formed between the outer casing and the inner casing, or a portion in which irregularities are formed on the inner surface of the casing in the steam passage portion. Furthermore, the part where cracks are likely to occur is a part specifically mentioned in the above-mentioned uneven thick part and part where steam flow tends to stay.
[0029]
4 schematically shows a longitudinal section of the overall structure of FIG. 1, wherein the outer casing upper half 1 has a high pressure inner casing upper half 1a and a medium pressure inner casing upper half 1b, while the outer casing lower half. The body 2 has a high pressure inner casing lower half 2a and a medium pressure inner casing lower half 2b.
[0030]
At the time of pre-warming, pre-warming steam first flows in the high pressure inner casing upper half 1a and the high pressure inner casing lower half 2a according to the arrows in FIG. It flows into the inner casing upper half 1b and the medium pressure inner casing lower half 2b, and flows into the low pressure turbine (not shown) through the medium pressure exhaust pipe 6.
[0031]
Further, each of the thermocouples 11a and 11b measures the metal temperatures of the inner surface and the outer surface of the lower half body 2a of the high-pressure inner casing, and also monitors the temperature during pre-warming. Then, warming steam is supplied from an auxiliary steam header (not shown) through an auxiliary steam line 9 branched from the middle of a low-temperature reheat pipe 8 connected to the high-pressure exhaust pipe 4 via a pre-warming valve 10.
[0032]
FIG. 5 shows electric resistance type heaters 13a, 13b and 13c, and heaters 15 made of nichrome wire or the like are woven into heat-resistant cloth 14 having flexibility, respectively. Each of these heater elements 15 is electrically connected to a terminal box 17 via a heater cable 16, and the terminal box 17 is energized by a power source (not shown).
[0033]
Next, the operation of the first embodiment will be described with reference to FIG.
[0034]
After plant shutdown, the cooling immediately turbine components as shown in the natural cooling curve t _N in FIG. 6 starts, the heater power is turned on timing that is provided on the next reboot, locally heating the casing each section, Keep warm.
[0035]
That is, the operation timing of the heaters 13a, 13b and 13c depends on the time until the restart, and in FIG. 6, in the state of being completely cooled to room temperature, that is, in the case of restart after a relatively long stop, The heaters 13a, 13b and 13c are operated prior to the start of the ming. As a result, the metal surface temperature can be raised along the temperature rise curve t _h from the metal temperature t ₁ at normal temperature on both the inner and outer surfaces to the temperature rise value t ₂ by the heater, and warming can be started from this temperature. Therefore, the conventional warming time T1 (6 hours as the conventional example) is shortened to T2. Here, t _w is the warming completion temperature.
[0036]
At this time, the metal inner surface temperature t _im and the metal outer surface temperature t _om in the prior art are shown in the drawing in comparison with the same temperatures t _im 1 and t _om 1 in the present embodiment. As is clear from this, the difference dt1 (= t _im 1−t _om 1) between the metal inner surface temperature t _im 1 and the metal outer surface temperature _tom 1 during warming is equal to the difference dt (= t _im −t in the prior art). _om ), which is smaller than that of the conventional thermal stress σ1 due to the temperature difference between the inner and outer surfaces proportional to the temperature difference.
[0037]
In the present embodiment, since the heaters 13a, 13b and 13c are locally arranged on the casing, if the capacity is increased, the temperature difference with other parts increases, which is not preferable. It needs to be adjusted.
[0038]
As described above, according to the first embodiment, the warming start temperature is increased by the preheating by the heaters 13a, 13b, and 13c from the start of the complete cooler, so that the warming time is shortened and the warming time is increased. Thermal fatigue damage due to repeated loading at every start-up, that is, generation of cracks and their progress can be prevented.
[0039]
FIG. 7 is a perspective view showing a second embodiment of a warming device for a steam turbine according to the present invention, and FIG. 8 is a cross-sectional view taken along line AA in FIG. In addition, the same code | symbol is attached | subjected and demonstrated to the part which is the same as that of the said 1st Embodiment, or respond | corresponds. The same applies to the following embodiments.
[0040]
In the second embodiment, the electric resistance heater 13 is attached to almost the entire high temperature portion of the outer casings 1 and 2. Thereby, since the whole casing can be preheated uniformly, preheat temperature can be raised further.
[0041]
This operation will be described with reference to FIG.
[0042]
In FIG. 9, the difference dt2 (= t _im 2−t _om 2) between the metal inner surface temperature t _im 2 and the metal outer surface temperature t _om 2 during warming, and the thermal stress due to the temperature difference between the inner and outer surfaces proportional to these temperature differences. FIG. 5 shows a comparison of σ2 with the conventional internal / external surface temperature difference dt (= t _im −t _om ) and the thermal stress σ due to the internal / external surface temperature difference proportional to the temperature difference, as in FIG.
[0043]
As shown in FIG. 9, the warming time can be further shortened, the thermal stress during warming can be reduced, and if the capacity of the electric resistance heater 13 is increased in some cases, the steam warming can be completely achieved. Can be omitted.
[0044]
FIG. 10 is a sectional view showing a heater in a third embodiment of the warming device for a steam turbine according to the present invention. Whereas in the first and second embodiments, the electric resistance heater 13 is attached to the casing surface, the electric resistance heater 13 of this embodiment is attached to the inner surface of the heat insulating material 18 by a fixing bracket 19. Thereby, disassembly and inspection of the electric resistance heater 13 can be facilitated, and maintainability can be improved.
[0045]
FIG. 11 is an explanatory view showing a fourth embodiment of the steam turbine warming device according to the present invention. In the present embodiment, the temperature measurement is performed in order to measure the inner and outer surface metal temperatures of the outer casing upper half 1 or the outer casing lower half 2 at the attachment portions of the electric resistance heaters 13a, 13b and 13c in the first embodiment. A thermocouple 20a for measuring the metal inner surface temperature and a thermocouple 20b for measuring the metal outer surface temperature are attached as means. Note that the temperature measuring means is not limited to a thermocouple, and other means may be used.
[0046]
Therefore, according to this embodiment, by attaching the thermocouple 20a for measuring the metal inner surface temperature and the thermocouple 20b for measuring the metal outer surface temperature, the above-mentioned non-uniformity which is the attachment site of the heaters 13a, 13b, and 13c. It is possible to monitor and control that the metal temperature difference between the inner and outer surfaces of the thick-walled part, the part where the internal steam flow tends to stay, and the part where the crack is likely to occur empirically, and the heater preheating starts. It becomes possible to grasp the end time reliably. As a result, the reliability as a device can be improved.
[0047]
FIG. 12 is an explanatory view showing a fifth embodiment of the warming device for a steam turbine according to the present invention. In this embodiment, as compared with the target completion of preheating temperature t ₂ of the heater to a preset temperature data t _h from the fourth embodiment of the metal inner surface temperature thermocouple 20a of the measurement and the metal outer surface temperature measurement of the thermocouple 20b , T _h -t ₂ and a certain allowable deviation δt and the comparison calculators 21 and 21 as calculation means are operated to operate the servo motor 22 to automatically turn on and off the switch 23, so that the electric resistance type The heater 13 is turned on and off. As long as this servo motor 22 is a bidirectional type, any of a hydraulic drive, an air drive, and an electric valve type may be sufficient.
[0048]
Therefore, according to the present embodiment, the electric resistance heater 13 can be provided with a power on / off function to automatically maintain a predetermined holding temperature, that is, a target warming start temperature. As a result, unmanned operations until the start of warming can be performed, and labor saving can be achieved.
[0049]
FIG. 13 is an explanatory view showing a sixth embodiment of a warming device for a steam turbine according to the present invention. In this embodiment, the warming device using auxiliary steam is linked to the automation of the heater preheating system of the fifth embodiment.
[0050]
As shown in FIG. 13, the comparison operation units 21 and 21 and the servo motor 22 are branched to connect negative operation units 24 and 24, and these negative operation units 24 and 24 are connected to an AND circuit 25. Is done. The AND circuit 25 is connected to a timer 26, and the prewarming valve 10 is opened based on a set time DT of the timer 26.
[0051]
That is, compared with a target completion of preheating temperature t ₂ of the heater set to a temperature data t _h from the thermocouple 20a and the metal outer surface temperature thermocouple 20b of the measuring of the metal inner surface temperature measurement in advance, certain t _h -t ₂ The servomotor 22 is operated by processing the allowable deviation δt and the comparison calculators 21 and 21, and the switch 23 is automatically turned on and off.
[0052]
The start time Tb of the pre-warming is when it reaches the target completion of preheating temperature t ₂ which is set in the operation starting time Ta of the heater preheating system, the pre-warming valve 10 is opened by the completion of preheating signals S1, Warming starts. Here, the preheating completion signal S1 is generated after confirming that the preheating temperature t _h by the electric resistance type heater 13 was settled falls within the allowable deviation δt of its final target value t _2.
[0053]
More specifically, if the electric resistance heater 13 is not turned on / off during the set time DT of the timer 26, it is determined that the electric heater has settled and the pre-warming valve 10 is automatically opened. In order to make this determination, the above two negation calculators 24 and 24 as control means and an AND circuit 25 that takes these AND conditions are provided.
[0054]
Therefore, according to the present embodiment, since the start-up preparation including the warming start is automated and optimized / minimized, it is possible to improve reliability and save labor.
[0055]
【The invention's effect】
As described above, according to claim 1 of the present invention, a heater is attached to an uneven thick wall portion of a casing, a portion where steam flow is likely to stay, and a portion where cracks are likely to occur empirically. Suppressing the decrease in casing temperature due to long-term shutdown or maintaining a constant value can shorten the warming time and reduce the thermal stress during warming. Reliability can be increased.
Further, according to claim 1 of the present invention, by providing the control means for controlling the preheating by the heater and the warming by the auxiliary steam to be interlocked, the start-up preparation including the warming start is automated and optimized. Therefore, it is possible to improve the reliability and save labor.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a first embodiment of a warming device for a steam turbine according to the present invention.
FIG. 2 is a configuration diagram showing an uneven thick portion in a high-pressure turbine.
FIG. 3 is a configuration diagram showing an uneven thick portion in an intermediate pressure turbine.
4 is a schematic diagram showing a longitudinal sectional structure of the entire structure of FIG.
5 is a configuration diagram showing the electric resistance heater of FIG. 1. FIG.
FIG. 6 is an explanatory diagram showing metal surface temperature and thermal stress when preheating is performed in the first embodiment.
FIG. 7 is a perspective view showing a second embodiment of the steam turbine warming device according to the present invention.
8 is a cross-sectional view taken along line AA in FIG.
FIG. 9 is an explanatory diagram showing metal surface temperature and thermal stress when preheating is performed in the second embodiment.
FIG. 10 is a sectional view showing a heater in a third embodiment of a steam turbine warming device according to the present invention.
FIG. 11 is an explanatory view showing a fourth embodiment of the steam turbine warming device according to the present invention.
FIG. 12 is an explanatory view showing a fifth embodiment of a warming device for a steam turbine according to the present invention.
FIG. 13 is an explanatory view showing a sixth embodiment of a warming device for a steam turbine according to the present invention.
FIG. 14 is a schematic view showing a general turbine casing.
[Explanation of symbols]
1 External casing upper half 1a High pressure inner casing upper half 1b Medium pressure inner casing upper half 2 External casing lower half 2a High pressure inner casing lower half 2b Medium pressure inner casing lower half 3a Main steam inlet pipe upper part 3b Main Steam inlet pipe lower part 4 High pressure exhaust pipe 5 Reheat inlet pipe 6 Medium pressure exhaust pipe 7 Intermediate ground 8 Low temperature reheat pipe 9 Auxiliary steam line 10 Prewarming valves 11a, 11b Thermocouple 12 Nuts 13a, 13b, 13c Electric resistance heater 14 Heat-resistant cloth 15 Heater element 16 Heater cable 17 Terminal box 18 Insulating material 19 Fixing bracket 20a Thermocouple for temperature measurement of metal inner surface (temperature measuring means)
20b Thermocouple for temperature measurement of metal outer surface (temperature measuring means)
21 Comparison calculator (calculation means)
22 Servo motor 23 Switch 24 Negative calculator (control means)
25 AND circuit (control means)
26 Timer

Claims (1)

At the start of the steam turbine cooler, heaters are attached to the uneven and thick parts of the high-pressure / medium-pressure casing, the part where steam flow tends to stay, and the part where cracks are likely to occur empirically,
A temperature measuring means for measuring the inner and outer surface metal temperature of the casing is provided at the heater mounting site,
Find the temperature difference between the temperature data from this temperature measurement means and the predetermined target preheating completion temperature, and calculate whether this temperature difference is greater than the predetermined plus or minus tolerance A comparison operation unit,
In the warming device for a steam turbine, the heater is turned off when the temperature difference is larger than the plus-side allowable deviation, and is turned on when the temperature difference is larger than the minus-side allowed deviation.
Branch the signal from the comparator and input the signal to the timer only when the temperature difference is within the plus and minus tolerances,
After a predetermined elapsed time with this timer, the valve is opened to introduce steam into the casing
A warming device for a steam turbine.

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