JP3774532B2 - Storage method when turbine equipment of thermal power plant is stopped - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of using a turbine of a thermal power plant, and more particularly to a storage method and turbine equipment when the turbine equipment of the plant is stopped, which is effective for improving the reliability of the members constituting the turbine over a long period of time.
[0002]
[Prior art]
Volatile treatment (AVT), oxygen as a method to prevent corrosion of equipment components constituting the water supply system of a thermal power plant that uses steam generated by fuel combustion to rotate the turbine to obtain power Three water treatment methods are known: treatment (CWT: Combined Water Treatment) and phosphate treatment (Coodinated Phosphate Treatment).
[0003]
Among these, in the volatile substance treatment (hereinafter referred to as AVT), the feed water supplied from the condensate / feed water system is collected on the inlet side of the steam generator, and the pH of the feed water and the dissolved oxygen concentration are measured. Then, ammonia or hydrazine is injected from the inlet side of the low-pressure feed water heater so that the pH of the collected feed water is 9.0 to 9.6, and the dissolved oxygen concentration is 7 ppb or less.
[0004]
On the other hand, oxygen treatment (hereinafter referred to as CWT) collects feed water supplied from the condensate / feed water system at the inlet side of the steam generator, and has a pH of 8.0 to 9.0 and dissolved oxygen of 20 to 20%. Ammonia is injected from the inlet side of the low-pressure feed water heater so that the pressure becomes 200 ppb. In addition, oxygen is injected from the inlet side of the condensate booster pump and the inlet side of the feed water pump.
[0005]
Phosphate treatment uses caustic soda as a pH adjuster and sodium phosphate as a hardness remover, and the pH adjustment range is generally high, about 10.5 to 11.8. This system is often used for boilers with a pressure of 30 kg / cm ² or less. Since the pH is high, it is suitable for corrosion prevention of steel materials and is strong against oxygen intrusion. Also, when seawater leaks from the condenser, the pH of boiler water is prevented from lowering and corrosion is prevented. However, caustic soda concentrates at places where the heat load is large, or where the scales are attached, causing corrosion and is not used in medium and high pressure boilers.
[0006]
These water treatment methods are all techniques for the purpose of preventing corrosion of the water supply system of a thermal power plant. Examples of the three water treatments described above include, for example, JP-A-60-100688 and JP-A-4-128395. The ones described in the publication No. are known. Further, the ranges of pH and dissolved oxygen of the three water treatments described above are described in “JIS, Japanese Standards Association, 1989, Boiler Supply Water and Boiler Water Quality (JIS B 8223)”.
[0007]
[Problems to be solved by the invention]
Among the three water treatments mentioned above, the CWT water treatment method is becoming mainstream in recent water treatment in thermal power plants. In the above-described AVT water treatment, the pH of the condensate supplied to the steam generator is set to 9.0 to 9.6 (alkaline), which is effective in suppressing iron elution. Although it is possible to maintain the reliability of the evaporation pipe or the like, it has been found that, depending on the plant, a scale is generated on the inner surface of the evaporation pipe of the steam generator, and the pressure difference of the steam generator is significantly increased. In contrast, in CWT water treatment, oxygen injected into the condensate supplied to the steam generator generates hematite particles on the inner surface of the steam generator's evaporation pipe, resulting in a dense and smooth coating surface. This is because it can be formed, scale (corrosion) can be prevented, and an increase in the differential pressure of the steam generator can be suppressed.
[0008]
However, in the water treatment of CWT, when the temperature is low, the above-described production of hematite particles becomes insufficient, and there is a problem in that iron elution is increased from the steel material or the like constituting the device. In particular, in the low-pressure turbine and the feed water pump drive turbine, the temperature is low and the generation of the aforementioned hematite particles becomes insufficient because the drive source steam is in the wet steam region where the steam is condensed. Thereby, corrosion of the material which comprises a turbine is accelerated, and there exists a possibility of reducing the reliability of a turbine.
[0009]
On the other hand, crevice corrosion and stress corrosion cracking often occur in the dovetail portion at the base of the turbine rotor blade, thereby impairing the reliability of the turbine blade. This problem is a factor that affects the reliability and life of the rotor of the low-pressure turbine, and the concentration of impurities such as NaCl in the steam is managed in order to prevent corrosion and solid matter adhesion. This results in oxygen concentration cell in and around the internal clearance of the dovetail portions, Cl inside gap ^- a halogen ion such as enrichment, reduces the pH material is intended to cause active dissolution. In order to form this oxygen concentration cell, an aqueous solution with a high dissolved oxygen concentration is required around the gap in the dovetail part, and this increase in dissolved oxygen is caused by the condensation of the steam that was cooled when the plant was shut down. It is estimated that air enters the water from outside the turbine.
[0010]
By the way, when the steam turbine equipment is stopped, the gas in the turbine equipment contracts as the turbine temperature decreases, so that it is stored in a state where the pressure is smaller than the atmospheric pressure. Therefore, it is inevitable to mix outside air from bearing seals such as labyrinths in the turbine casing and condensers, thus leading to an increase in dissolved oxygen concentration in condensed water, which causes crevice corrosion and stress corrosion cracking. It is thought that there is.
[0011]
Such crevice corrosion and stress corrosion cracking cannot be dealt with only by the conventional water quality management method.
[0012]
An object of the present invention is to prevent crevice corrosion and pitting corrosion when turbine equipment of a thermal power plant is stopped, and to achieve an effective and long life for the equipment constituting the plant, particularly the dovetail portion of the turbine blade. It is to provide a highly reliable storage / stop method.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, a turbine of a thermal power plant that obtains energy by turning water into steam using thermal energy generated by combustion of fuel and rotating the turbine with the steam. In the storage method at the time of equipment stop, a storage method at the time of turbine equipment stop of a thermal power plant is provided, wherein the inside of the turbine casing is made into a non-oxidizing atmosphere and the pressure of the atmosphere is made larger than the atmospheric pressure. . The turbine casing is a container that houses a turbine blade and a turbine rotor shaft so as to be isolated from the outside. As the non-oxidizing atmosphere, argon, nitrogen, or the like that is an inert gas can be used most generally, but any gas that does not contain oxygen may be used.
[0014]
By the said structure, the increase in the dissolved oxygen concentration of the condensed water in the turbine at the time of a turbine apparatus stop can be prevented. That is, even when the turbine equipment is stopped, crevice corrosion due to dissolved oxygen does not occur in the dovetail portion connecting the turbine blade and the turbine rotor shaft, and the turbine equipment of a highly reliable thermal power plant can be provided.
[0015]
The turbine equipment of the first invention can be applied to any of a high pressure turbine, an intermediate pressure turbine, a low pressure turbine, and a feed water pump drive turbine.
[0016]
It is preferable that the non-oxidizing atmosphere gas injection method according to the first aspect of the invention injects the gas in response to a decrease in pressure inside the turbine casing accompanying a temperature decrease when the turbine is stopped. When the turbine is stopped, the gas in the turbine contracts and the pressure in the casing decreases compared to the atmospheric pressure. Injecting non-oxidizing gas in accordance with the degree of pressure drop and adjusting the pressure in the casing to always be larger than the atmospheric pressure, so that oxygen in the atmosphere is mixed into the casing. Can be prevented. Therefore, an increase in the dissolved oxygen concentration of the condensed water in the turbine can be prevented, and crevice corrosion can be suppressed. Since the pressure drop in the casing stops after the turbine returns to normal temperature, this need is eliminated, but it takes several days to return to normal temperature after the turbine stops, depending on the size of the turbine. Therefore, the above method is effective.
[0017]
The non-oxidizing atmosphere gas of the first invention may be injected into the turbine casing from an air ejection hole provided in the turbine stationary blade.
[0018]
The non-oxidizing atmospheric gas of the first invention may be injected from the inlet side of the high-pressure or low-pressure turbine or from the inlet side of the condensate booster pump and the feed water pump.
[0019]
In the first invention, an inhibitor may be added to the condensed water in the turbine casing.
[0020]
In order to achieve the above object, according to the second aspect of the present invention, a thermal power plant that uses water as steam by using heat energy generated by fuel combustion, and rotates the turbine by the steam to obtain energy. The turbine equipment of the thermal power plant having a mechanism for injecting a non-oxidizing atmosphere gas into the turbine casing when the turbine is stopped is provided.
[0021]
In a second aspect of the present invention, it is preferable to have a mechanism for controlling the injection amount of the non-oxidizing atmospheric gas into the turbine casing based on an instruction from a pressure gauge in the turbine casing. The injection amount of the non-oxidizing gas may be controlled manually based on the instruction of the pressure gauge in the casing. For example, the instruction of the pressure gauge is output as an electrical signal, and the microcomputer outputs a signal according to the output. It is most preferable to use a mechanism that controls the opening / closing amount of a non-oxidizing gas cylinder. As described above, since it takes several days for the turbine to return to normal temperature from the stop, it is difficult for a human to continuously control the injection amount during that time.
[0022]
With the above configuration, the pressure in the turbine casing after the turbine is stopped can be kept constant for a long time.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Example 1
Embodiments of the present invention will be described below with reference to the drawings.
[0024]
FIG. 1 is a system diagram showing a thermal power plant that is an embodiment of the present invention. First, the configuration of the thermal power plant will be described. The thermal power plant is roughly divided into a steam system having the steam generator 11 as an upstream side and the condenser 1 as a downstream side, and a condensate / water supply system having the condenser 1 as an upstream side and the steam generator 11 as a downstream side. It is made up of.
[0025]
Among them, the steam system is a high-pressure steam turbine 12 that uses steam generated by the steam generator 11 as a drive source, and reheat steam that is obtained by heating the exhaust steam of the high-pressure steam turbine 12 by the steam generator 11 as a drive source. And a low-pressure steam turbine 14 that uses the exhaust steam of the intermediate-pressure steam turbine 13 as a drive source.
[0026]
The steam generated by the steam generator 11 is supplied to the high-pressure steam turbine 12 via the high-pressure steam pipe to drive the turbine. The steam after driving the high-pressure steam turbine 12 is supplied to the low-pressure steam turbine 14 via the low-pressure steam pipe to drive the turbine. Then, the steam after driving the low-pressure steam turbine 14 is discharged to the condenser 1 and condensed.
[0027]
Further, the above system includes a feed water pump drive steam turbine 15 for driving a feed water pump, which will be described later, and the feed water pump drive steam turbine 15 is connected to the high pressure steam turbine 12 via a branch pipe branched from the high pressure steam pipe. A part of the supplied steam or the extraction of the intermediate pressure steam turbine 13 is supplied to drive the turbine. Then, the steam after driving the feed water pump drive steam turbine 15 is discharged to the condenser 1 through the discharge pipe and condensed as described above.
[0028]
On the other hand, the condensate / feed water system condenses the steam discharged from the steam turbine (low pressure steam turbine 14, feed water pump drive steam turbine 15) in the condenser 1 and supplies the obtained steam to the deaerator 8. It is divided into a condensate system and a water supply system that supplies the condensate degassed by the deaerator 8 to the steam generator 11.
[0029]
Of these, the condensate system is composed of a condensate pump 2 that feeds the condensate that has been condensed in the condenser 1, and iron oxide contained in the condensate that is fed from the condensate pump 2 through the ground condenser 3. The condensate filter 4 for removing corrosion products such as substances, the condensate demineralizer 5 for removing Cl ^- ions contained in the condensate, the condensate filter 4 and the condensate demineralizer 5 And a condensate booster pump 6 for feeding the condensate from which the corrosion products and impurity ions contained in the water are removed to the deaerator 8 through the low-pressure feed water heater 7.
[0030]
The water supply system also includes a water supply pump 9 that supplies the condensate desalted by the deaerator 8 to the steam generator 11 via the high-pressure water heater 10. The feed water pump 9 includes the feed water pump drive steam turbine 15 described above as a drive source.
[0031]
The condensate condensed in the condenser 1 is sent from the condensate pump 2 to the condensate filter 4 through the ground condenser 3 to remove corrosion products such as iron oxides contained in the condensate. Next, the condensate is sent to the condensate demineralizer 5 to remove impurity ions contained in the condensate. In this way, after the corrosion products and impurity ions contained in the condensate are removed, the pressure is increased by the condensate booster pump 6, heated by the low-pressure feed water heater 7 and fed to the deaerator 8. The deaerator 8 degass the fed condensate. The condensate deaerated by the deaerator 8 is fed by a feed water pump 9, heated by a high-pressure heater on the way, and fed to the steam generator 11.
[0032]
First, as a preliminary study, potential measurement was performed to determine how much the dissolved oxygen concentration in the condensed water outside the gap should be lowered. That is, at 290 ° C., the dissolved oxygen concentration in the environmental water was variously changed, and the potential of the 12Cr steel specimen was measured. The result is shown in FIG. The progress of crevice corrosion proceeds by a local battery due to a potential difference caused by a difference in oxygen concentration inside and outside the gap. Therefore, in order to prevent crevice corrosion, the potential difference inside and outside the gap should be reduced. It is considered that oxygen inside the gap is consumed by the corrosion of the metal, and it is considered that it is almost several ppb or less, so the dissolved oxygen concentration outside the gap does not differ greatly from the corrosion potential of this several ppb dissolved oxygen concentration. It only has to be. Reading this value from FIG. 2, it can be seen that the potential difference inside and outside the gap should be about 20 ppb or less, and therefore the dissolved oxygen concentration in the condensed water outside the gap should be about 20 ppb or less.
[0033]
Next, a storage stop method for this thermal power plant will be described.
[0034]
The output is gradually reduced to stop the plant at night when the output demand for power is small. Along with this, the steam temperature gradually decreases. In order to inject nitrogen as an inert gas when the high-pressure, medium-pressure, low-pressure turbine, and feed water pump drive turbine of this thermal power plant are stopped, the following measures are taken. That is, after shutting down the plant, by closing the valves between the high-pressure turbine and the boiler and between the low-pressure turbine and the condenser, only the turbine section is isolated and isolated from other systems. With the passage of time after the turbine stops, when the steam temperature in the turbine decreases and the pressure becomes lower than the external pressure, the valve of the nitrogen injection line connected to each turbine is opened. The pressure of the inert gas is initially maintained at 2 to 3 atm, the temperature is lowered, and the temperature of the vapor pressure in the turbine is sufficiently lower than the atmospheric pressure. And keep the pressure higher than the outside air by several percent to make the inside of the turbine pressurize against the outside air. The concentration of dissolved oxygen in the condensed water in the turbine at the time of stop storage was measured by collecting the condensed water from the sampling line and found it to be several tens of ppb or less. In addition, for comparison with this, after the plant was shut down, the conventional method of vacuum storage was performed, and the dissolved oxygen concentration in the condensed water was continuously measured. As a result, in the case of daily start / stop as shown in FIG. 3, the dissolved oxygen in the condensed water shows a low value of several tens of ppb for several hours after the turbine shuts down, but then rises slowly before the turbine restarts. Was a relatively high value of 1 to 2 ppm.
[0035]
On the other hand, the relationship between the pitting corrosion generated in the dovetail part and the dissolved oxygen concentration outside the dovetail was obtained. That is, a gap test piece simulating the dovetail part is exposed to steam at the same temperature as the turbine for 1-2 days, and then simulated for daily start / stop, cooled for half a day, and the dissolved oxygen level during condensation is varied. An experiment was conducted in which the temperature was increased again after the temperature was maintained. This experiment was conducted for 2000 hours, the number of pitting corrosion occurrences and the pitting corrosion depths were examined, and the progress rate of pitting corrosion was calculated from the pitting corrosion depth. As a result, as shown in FIG. 4 and FIG. 5, it was found that there is a proportional relationship between the dissolved oxygen concentration around the dovetail gap, the number of pitting corrosion, and the rate of progress of pitting corrosion. Therefore, from these results, as in this example, by reducing the dissolved oxygen concentration in the condensed water of the steam that contacts the dovetail portion, crevice corrosion in the dovetail portion due to the formation of oxygen concentration cells inside and outside the gap is caused. It is suppressed.
[0036]
(Example 2)
Another embodiment of the daily start / stop of a thermal power plant is shown. Here, the inhibitor shown in Example 1 is used in combination with the inert gas. That is, argon was injected in the same manner as in Example 1 as an inert gas when the high-pressure, medium-pressure, low-pressure turbine and feed water pump drive turbine of the thermal power plant were stopped. That is, the turbine part was isolated and isolated from the condensate system and the water supply system by closing the valve in the same manner as in Example 1, and then the inert gas was injected from the air ejection holes of the turbine vane. The pressure is initially maintained at 2 to 3 atm. When the temperature decreases and the pressure in the casing becomes smaller than the outside air pressure, the pressure of the inert gas is kept several percent higher than the outside air, and then gas injection is performed. Stop. Next, hydrazine is injected from the turbine inlet with a chemical injection pump. The concentration of dissolved oxygen in the condensed water in the turbine at the time of stop storage was measured by collecting the condensed water from the sampling line and found it to be several tens of ppb or less.
[0037]
Therefore, considering the above results together with the results of FIGS. 4 and 5, the corrosion of the dovetail part due to oxygen concentration inside and outside the gaps in the dovetail part during plant operation due to the inert gas injection during this periodic inspection is It can be greatly reduced.
[0038]
【The invention's effect】
According to the present invention, even when the turbine equipment is stopped, a crevice corrosion due to dissolved oxygen does not occur in a dovetail portion or the like that connects the turbine blade and the turbine rotor shaft, and a highly reliable turbine equipment for a thermal power plant is provided. be able to.
[Brief description of the drawings]
FIG. 1 is a system diagram of a thermal power plant showing an embodiment of the present invention.
FIG. 2 is a graph showing the relationship between dissolved oxygen concentration and corrosion potential.
FIG. 3 is a graph showing changes in dissolved oxygen concentration and turbine internal temperature after turbine shutdown.
FIG. 4 is a diagram showing the relationship between the dissolved oxygen concentration outside the gap and the number of pitting corrosion occurring in the gap.
FIG. 5 is a diagram showing the relationship between the dissolved oxygen concentration outside the gap and the progress rate of pitting corrosion occurring in the gap.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Condenser, 2 ... Condensate pump, 3 ... Grand condenser, 4 ... Condensate filter, 5 ... Condensate demineralizer, 6 ... Condensate booster pump, 7 ... Low-pressure feed water heater, 8 ... Deaeration 9 ... Feed pump, 10 ... High pressure feed heater, 11 ... Steam generator, 12 ... High pressure steam turbine, 13 ... Medium pressure steam turbine, 14 ... Low pressure steam turbine, 15 ... Feed water pump driven steam turbine, 16 ... Difference Pressure gauge, 17 ... Nitrogen injection line.

Claims (5)

In the storage method when the turbine equipment of the thermal power plant is stopped, the thermal energy generated by the combustion of the fuel is used as the steam, and the turbine is rotated by the steam to obtain the energy.
The non-oxidizing atmosphere gas turbine casing section and the non-oxidizing atmosphere, in response to a decrease in pressure inside the turbine casing due to temperature drop during turbine equipment stop injecting, and the pressure of the atmosphere to atmospheric pressure A storage method when the turbine equipment of a thermal power plant is stopped, which is characterized by being larger than that.   The storage device according to claim 1, wherein the turbine device is at least one of a high pressure turbine, an intermediate pressure turbine, a low pressure turbine, and a feed water pump drive turbine.   A non-oxidizing atmosphere gas according to claim 1 is injected into a turbine casing from an air jet hole provided in a turbine stationary blade.   A non-oxidizing atmosphere gas according to claim 1 is injected from the inlet side of a high-pressure or low-pressure turbine or from the inlet side of a condensate booster pump and a feed water pump.   2. The storage method according to claim 1, wherein an inhibitor is added to the condensed water in the turbine casing when the turbine equipment of the thermal power plant is stopped.

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