Patent Application
20140000260
This application is based upon and claims benefit of priority under 35 USC 119 from the Japanese Patent Application No. 2012-021109, filed on Feb. 2, 2012, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a protection device for turbine exhaust chambers and a condenser and a monitoring controller for the turbine exhaust chambers and the condenser.
Related Art
A power-generation plant having a steam turbine is provided with a condenser for cooling and condensing exhaust steam of the turbine. During operation of the plant, an inside of the condenser is kept at a negative pressure.
Seawater for cooling the exhaust steam of the turbine is supplied by a circulating water pump. However, the supply of the cooling water by the circulating water pump may be stopped for some reasons. As another reason for an insufficient flow rate of the cooling water, a blackout accident in the plant, which is the loss of all power supply in the power-generation plant, may occur, for example. In this case, a cooling function and a condensing function of the condenser are lost.
If such an accident occurs, a boiler and the steam turbine come to an emergency stop. However, the boiler immediately after the stop has residual heat. In order to release the residual heat, steam and heat drain water flow into the condenser via a turbine bypass valve, various drain valves, and the like.
However, since the cooling function and the condensing function of the condenser have been lost, the steam does not condense. As a result, pressures in the condenser and the turbine exhaust chamber, which is a pressure vessel integral with the condenser, gradually increase due to a steam pressure and eventually turn from negative pressures into positive pressures, i.e., pressures equal to or higher than the atmospheric pressure. The positive pressures are not suitable conditions for the condenser and the turbine exhaust chambers which are originally designed to be used at the negative pressure.
Therefore, as a protection device for the condenser and the turbine exhaust chambers, atmosphere discharge discs are used.
The atmosphere discharge discs are disposed at a ceiling portion of the turbine exhaust chambers and form parts of the turbine exhaust chambers. If the pressures in the turbine exhaust chambers turn into the positive pressures and, more specifically, if gauge pressures reaches the positive pressures of about 20 kPa to 40 kPa, the atmosphere discharge discs rupture. In this manner, the atmosphere discharge discs are designed to discharge the steam in the condenser into the atmosphere.
In other words, the atmosphere discharge discs are provided to prevent breakage of the important turbine exhaust chambers and condenser by rupturing themselves.
In lines 36 to 41 in column 5 on page 3 of the after-mentioned Patent Document 1 disclosing the prior-art protection device, there is the following description:
“Many of currently-used steam turbines have structures resistant to the negative pressure. Therefore, as in this prior art, if the outside air is forced into the steam turbine for cooling to build the positive pressure in the steam turbine, unexpected breakage such as rupture of the atmosphere discharge discs or the like occurs.
If the atmosphere discharge discs rupture, repair work of them takes a few days, which forces the power-generation plant to stop to thereby seriously affect society when demand for electricity is critically high, for example.
Moreover, for an independent power producer (IPP) running a power-generation plant under an electric power selling contract with a power company for business, this is directly linked to a large financial loss.
With the above circumstances in view, it is an object of the present invention to provide a protection device for turbine exhaust chambers and a condenser and a monitoring controller for the turbine exhaust chambers and the condenser, which can prevent breakage of the turbine exhaust chambers and the condenser without requiring much time and cost for repair.
According to one aspect of the present invention, there is provided a protection device for a turbine exhaust chamber and a condenser comprising:
a condenser for cooling and condensing steam exhausted from a steam turbine;
a turbine exhaust chamber casing integrally covering the steam turbine and the condenser;
an atmosphere discharge disc for rupturing when a pressure in the turbine exhaust chamber casing reaches a first predetermined value;
a temperature measuring means for measuring a temperature in the turbine exhaust chamber casing;
a first setter for setting a second predetermined value;
an output means for producing an external output, based on the temperature measured by the temperature measuring means and the second predetermined value set by the first setter, when a pressure corresponding to the temperature becomes higher than or equal to the second predetermined value related to pressure or when the temperature becomes equal to or higher than the second predetermined value related to temperature; and
a releasing means for releasing the steam in the turbine exhaust chamber casing to an exterior when the output means produces the external output.
According to one aspect of the present invention, there is provided a monitoring controller for a turbine exhaust chamber and a condenser comprising:
a first setter for setting a first predetermined value; and
an output means for outputting an external output, based on a measured temperature in a turbine exhaust chamber casing integrally covering a condenser for cooling and condensing steam exhausted from a steam turbine and the steam turbine and the first predetermined value set by the first setter, when a pressure corresponding to the temperature becomes higher than or equal to the first predetermined value related to pressure or when the temperature becomes higher than or equal to the first predetermined value related to temperature.
With the protection device for the turbine exhaust chambers and the condenser and the monitoring controller for the turbine exhaust chambers and the condenser according to the invention, it is possible to prevent the breakage of the turbine exhaust chambers and the condenser without requiring much time and cost for the repair.
As described above, when the pressures in the turbine exhaust chambers reach the positive pressures, the atmosphere discharge discs rupture to discharge the steam in the condenser into the atmosphere to thereby prevent breakage of the important turbine exhaust chambers and the condenser. Such atmosphere discharge discs serve the purpose by rupturing themselves. Therefore, it is necessary to have the atmosphere discharge discs as last protection means. However, if the positive pressures in the turbine exhaust chambers can be sensed and the steam in the turbine exhaust chambers can be released into the atmosphere before the atmosphere discharge discs rupture, it is possible to avoid the above-described nonproductive repair work.
An important point here is to measure a very low positive pressure close to the atmospheric pressure with high accuracy.
In general, pressure is measured by using a pressure transmitter, a pressure switch, or the like. However, if they are used in an attempt to measure the very low positive pressure with high accuracy, “the pressure transmitter and the pressure switch measure a saturated pressure of an atmospheric temperature instead of the pressures in the turbine exhaust chamber”. This phenomenon will be described below.
In general, to measure the pressure by using the pressure transmitter, actual process, i.e., steam, water, oil, or the like to be measured at a measure point is led to the pressure transmitter through a capillary tube which is also called instrumentation pipe and a pressure of the actual process is measured.
Measurement of the pressure in the vicinity of the atmosphere discharge discs by using such a pressure transmitter will be discussed.
In the vicinity of each of the atmosphere discharge discs in the turbine exhaust chambers, a basket chip, for example, for taking in the stream as the actual process is disposed. The steam in each of the turbine exhaust chambers comes into the basket chip and is led out of the turbine exhaust chamber through the capillary tube and sent to the pressure transmitter where the pressure of the steam is measured.
The steam pressure at this time is affected by an environmental temperature around the capillary tube outside the turbine exhaust chamber, i.e., an atmospheric temperature. More specifically, the pressure in the capillary tube is a saturated pressure of the atmospheric temperature or a pressure close to the saturated pressure due to an influence of the saturated pressure.
As a result, the pressure transmitter measures the saturated pressure of the atmospheric temperature outside the turbine exhaust chambers or the pressure close to the saturated pressure instead of the pressures in the turbine exhaust chambers. Such an inconvenience occurs similarly when the pressure switch, which measures the pressure by similarly leading the steam out of each of the turbine exhaust chambers through the capillary tube, is used.
This phenomenon can be ignored when the temperature and pressure of the actual process are much higher than the atmospheric temperature and pressure. However, it can not be ignored in the measurement of the actual process at the pressure and temperature close to the atmospheric pressure and reduces the measurement accuracy.
In order to suppress such a phenomenon, measures such as a heat insulator provided around the capillary tube may be taken. With such measures, however, it is extremely difficult to fundamentally improve the pressure measurement accuracy.
Therefore, in the embodiments of the invention, the inventors have noted that the steam in each of the turbine exhaust chambers is saturated steam and thought of measurement of the temperature in each of the turbine exhaust chambers instead of the measurement of the pressure. The measured temperature is converted into the saturated pressure of the steam. It is detected that the obtained pressure in each of the turbine exhaust chambers has reached a predetermined positive pressure. The embodiments are characterized in that the steam in the turbine exhaust chambers is released into the atmosphere by actuating any releasing means before the atmosphere discharge discs rupture.
The protection devices for the turbine exhaust chambers and the condenser and the monitoring controllers for the turbine exhaust chambers and the condenser according to the embodiments of the invention will be described below with reference to the drawings.
During operation of the power-generation plant, pressures in turbine exhaust chambers 101a and 101b and the condenser 107 (hereafter referred to as internal pressures) are maintained at negative pressures close to a vacuum. From exhaust of an intermediate-pressure turbine (not shown), steam a flows into a crossover pipe 108. This steam a is led into the inner casing 105 and drives the low-pressure turbine rotor 104 as driving steam b.
Pressure of the driving steam b is reduced at every stage of the low-pressure turbine rotor 104. Finally, the steam is exhausted as exhaust steams c and d into the turbine exhaust chambers 101a and 101b and the condenser 107, respectively. With cooling water sent into the condenser 107 from a circulating water pump (not shown), the exhaust steams c, d are condensed and collected in a hot well 109 at a lower portion.
In this operating state, if the circulating water pump stops due to some accident and supply of the cooling water stops or a flow rate of the cooling water becomes insufficient, the exhaust steams c, d are not condensed. As a result, the internal pressure increases. If the internal pressure reaches a protection trip value, the power-generation plant including the steam turbine and a boiler comes to an emergency stop and inflow of the exhaust steams c, d stop.
However, the boiler immediately after the stop has residual heat. This heat flows into the condenser 107 in forms of bypass steam e sent from a turbine bypass valve 110 and heat drain water f sent from a drain valve 111. As a result, the internal pressure gradually increases.
As described above, the steam in the turbine exhaust chambers 101a and 101b is the saturated steam. Therefore, between saturated steam pressure and saturated steam temperature, there is such a relationship that the pressure increases as the temperature increases as shown in
The atmosphere discharge discs 100a and 100b rupture when the internal pressure increases and turns from the negative pressure into the positive pressure, e.g., when it reaches 129.51 kPa·abs (abs stands for absolute pressure). In this way, the saturated steam in the turbine exhaust chamber casing 106 is released into the atmosphere. In the following description, the pressure at which the atmosphere discharge discs 100a and 100b rupture is defined as 129.51 kPa·abs for the sake of convenience.
A structure provided in the first embodiment in order to release the saturated steam at a stage before the rupture pressure of the atmosphere discharge discs 100a and 100b is reached will be described.
A resistance temperature detector 102a measures an internal temperature g in the vicinity of the atmosphere discharge disc 100a and a resistance temperature detector 102b measures an internal temperature h in the vicinity of the atmosphere discharge disc 100b, respectively, in the turbine exhaust chamber casing 106. The measured temperatures g and h are input to a monitoring controller 201 through cables 112a and 112b, respectively.
The internal temperatures g and h measured by the resistance temperature detectors 102a and 102b are input to the high value selector 203. Higher one of the internal temperatures g and h is output as a steam temperature j and input to the converter 204.
In the converter 204, a characteristic curve representing the relationship between the saturated steam pressure and the saturated steam temperature shown in
The output saturated steam pressure k is input to the comparators 206 and 208.
A predetermined set value m is set in the setter 205. The saturated steam pressure k and the set value m are input to the comparator 206 and compared to each other. While the saturated steam temperature k is not higher than the set value m, the output n of the comparator 206 is maintained in an OFF state. If the saturated steam pressure k exceeds the set value m, the output n is turned on. Operation of the comparator 208 will be described later.
Here, as the set value m, the vacuum breaker valve opening pressure of 105.09 kPa·abs shown in
If the external output n from the comparator 206 is generated, the external output n is produced from the monitoring controller 201 shown in
Here, if the external output n is produced from the comparator 206, the vacuum breaker valve 103 is used as a releasing means for releasing the steam in the turbine exhaust chamber casing 106 to an exterior. However, the releasing means is not limited to the vacuum breaker valve, if it can operate as a means for releasing the steam in the turbine exhaust chamber casing 106 to an exterior in response to the output from the comparator.
The vacuum breaker valve 103 is a motor-operated valve which is provided to the condenser 107 without exception. The vacuum breaker valve 103 is for carrying out what is called vacuum break which is opening of the inside of the condenser 107 into the atmospheric state when the plant stops for a long period of time.
This vacuum breaker valve 103 is disposed on the pipe 115 connecting the inside and the outside of the condenser 107 as described above. While the negative pressure is maintained in the condenser 107, the vacuum breaker valve 103 is closed. To carry out the vacuum break, the vacuum breaker valve 103 is opened and the air flows into the condenser 107.
In the first embodiment, on the other hand, the vacuum breaker valve 103 is opened when the internal pressures in the turbine exhaust chamber casing 106 and the condenser 107 reach the predetermined positive pressure. In this way, the internal steam is released into the atmosphere.
As described above, the internal pressure in the turbine exhaust chamber casing 106 is retained by the saturated steam. Therefore, by measuring the internal temperature, it is possible to obtain the internal pressure by using the characteristic curve in
To measure the internal temperature, a thermocouple may be used, for example, besides the above-described resistance temperature detector. If the temperature is measured by using the resistance temperature detector or the thermocouple, the capillary tube, which is necessary in the measurement of the internal pressure, is unnecessary. Therefore, it is possible to measure the internal temperature with high accuracy to calculate the internal pressure without being affected by the atmospheric temperature. In the first embodiment, the resistance temperature detector, which is generally considered to have higher measurement accuracy than the thermocouple, is used.
As shown by the characteristic curve in
Therefore, the vacuum breaker valve 103 is opened when the internal temperature of 101° C. which is sufficiently lower than the internal temperature 107° C. corresponding to the internal pressure at which the atmosphere discharge discs 100a and 100b rupture is detected. In this way, it is possible to protect the turbine exhaust chamber casing 106 and the condenser 107.
Here, as a means for releasing the steam in the turbine exhaust chamber casing 106 and the condenser 107, the vacuum breaker valve 103 is used. As described above, the vacuum breaker valve 103 is equipment provided to the condenser 107 without exception. Therefore, it is unnecessary to additionally provide a means for releasing the steam, which prevents an increase in cost.
The vacuum breaker valve is normally provided as a motor-operated valve which is driven by a direct-current (DC) power supply to carry out a stop of turbine rotation as an emergency measure.
In a blackout accident in the plant, an alternating-current (AC) power supply is lost. However, the direct-current (DC) power supply can always be secured even in an emergency. Therefore, by using the vacuum breaker valve 103 which can be driven by the direct-current (DC) power supply, it is possible to obtain the reliable protection device.
If the vacuum breaker valve 103 is used as the steam releasing means, there is an element to consider. When the atmosphere discharge discs 100a and 100b rupture, large areas rupture and, as a result, the internal steam is released at a burst. On the other hand, when the steam is released by using the vacuum breaker valve 103, the steam cannot be released at a burst and it takes time for the steam to be released due to restriction by dimensions of the pipe 115.
Of course opening of the vacuum breaker valve 103 has to be started at a positive pressure lower than the positive pressure at which the atmosphere discharge discs 100a and 100b rupture. However, it is necessary to consider that reduction of the internal pressure requires time when the steam is released by the vacuum breaker valve 103.
Therefore, the opening of the vacuum breaker valve 103 is preferably started at a very low positive pressure immediately after the saturated pressure turns from the negative pressure into the positive pressure. Therefore, in the first embodiment, the set value m is 105.09 kPa·abs. Such setting is possible because of high-accuracy measurement by using the resistance temperature detectors 102a and 102b.
According to the first embodiment, by opening the vacuum breaker valve 103 immediately after the saturated pressure turns from the negative pressure into the positive pressure, the residual heat flowing into the turbine exhaust chamber casing 106 after that escapes into the atmosphere. As a result, it is possible to prevent increase of the internal pressure from the pressure at the time of the valve opening.
Because the first embodiment has the structure for opening the vacuum breaker valve 103 after the saturated pressure turns from the negative pressure into the positive pressure, it may not have the atmosphere discharge discs 100a and 100b. In this case, it is possible to reduce manufacturing cost of the atmosphere discharge discs and cost required for the repair.
However, depending on various forms of accidents of the power-generation plant, the internal pressure does not necessarily increase gradually and a possibility of abrupt increase cannot be denied.
Considering all forms of accidents, it is preferable to dispose the atmosphere discharge discs 100a and 100b so as to further increase security.
As described above, preferably the set value m is set at the very low positive pressure immediately after the saturated pressure turns from the negative pressure into the positive pressure and the vacuum breaker valve 103 is opened at this pressure. However, it is also possible to allow more time by setting the set value m at a negative pressure lower than the positive pressure and opening the vacuum breaker valve 103 when the pressure is the negative pressure.
However, if the vacuum breaker valve 103 is opened at the negative pressure, the internal pressure increases toward the atmospheric pressure at that instant.
A phenomenon which can occur at this time will be considered. Seal steam is supplied to gland portions 116a and 116b where the low-pressure turbine rotor 104 passes through the turbine exhaust chamber casing 106 in order to seal clearances in the passing-through portions.
However, once the blackout accident occurs in the plant, a gland steam exhauster stops and a function of recovering the seal steam is lost. While the internal pressure is the negative pressure, the seal steam is drawn into the condenser 107. Therefore, leakage does not occur through the clearances at the passing-through portions or is suppressed if it occurs.
However, if the internal pressure reaches the atmospheric pressure, the seal steam leaks from the clearances at the passing-through portions and the steam and water mix into bearing oil. Or the bearing oil may be carried by the leaking seal steam and come in contact with a high-temperature object to cause a fire.
It is important to prevent the rupture of the atmosphere discharge discs 100a and 100b. However, while the internal pressure is the negative pressure, it is also important to maintain the negative pressure.
Therefore, considering these two points, i.e., prevention of the rupture of the atmosphere discharge discs 100a and 100b and maintenance of the internal pressure at the negative pressure, the first embodiment is configured as follows:
To be prepared for an accident in which an amount of the residual heat of the boiler is relatively small and an enough amount of heat to increase the internal pressure to the positive pressure does not flow in, the vacuum breaker valve 103 is maintained in a closed state to maintain the negative pressure as long as possible.
From this state, at a low positive pressure immediately after the internal pressure turns into the positive pressure, the vacuum breaker valve 103 is opened to release the steam. As the positive pressure at this time, as described above, the set value m is set at 105.09 kPa·abs which is slightly higher than the atmospheric pressure (101.42 kPa·abs).
If the internal pressure turns from the negative pressure into the positive pressure, it greatly affects operation of the power-generation plant. Therefore, it is important that the protection device informs an operator of this change.
Therefore, as shown in
A set value p is set in advance in the setter 207. The saturated pressure k output from the converter 204 and the set value p output from the setter 207 are given to the comparator 208. They are compared to each other in the comparator 208 and an alarm q is output when the saturated pressure k exceeds the set value p. The set value p is set at 99 kPa·abs which is the internal pressure immediately before turning from the negative pressure into the positive pressure.
As described above, according to the first embodiment, by opening the vacuum breaker valve 103 when the internal pressure turns from the negative pressure into the positive pressure and reaches 105.09 kPa, breakage of rupture of the atmosphere discharge discs 100a and 100b can be prevented and breakage of the turbine exhaust chamber and the condenser can be prevented without requiring much time and cost for the repair.
A protection device for a turbine exhaust chamber and a condenser and a monitoring controller for a turbine exhaust chamber and a condenser according to a second embodiment of the invention will be described by using the drawings.
In the second embodiment, a monitoring controller 401 has a different configuration from the monitoring controller 201 in the first embodiment. As shown in
The internal temperatures g and h are input to the high value selector 403, and higher one of the internal temperatures g and h is output as a steam temperature j and input to the comparator 406 without through converter.
In the setter 405, 101° C. is set in advance as a set value r. The set steam temperature of 101° C. corresponds to the steam pressure of 105.09 kPa at which the vacuum breaker valve 103 is opened in
The set value r is input to the comparator 406 and the steam temperature j and the set value r are compared to each other. When the steam temperature j exceeds the set value r, the output n is turned on. After that, similarly to the first embodiment, the vacuum breaker valve 103 is opened when the external output n is produced.
In this manner, in the second embodiment, the set value r is given as a set value of temperature. The steam temperature j output from the high value selector 403 is input to the comparator 406 without being converted into the steam pressure by a converter. Because the converter is unnecessary, a circuit configuration of the arithmetic section circuit 402 is simplified and cost is reduced.
However, considering review and revision of the steam pressure at which the vacuum breaker valve is opened, it is more convenient if the steam pressure is directly set in the setter 205 and the set value m and the steam pressure k are compared to each other in the comparator 206 as in the first embodiment.
As described above, according to the second embodiment, by opening the vacuum breaker valve 103 when the temperature 101° C., corresponding to the internal pressure turning from the negative pressure into the positive pressure and reaching 105.09 kPa, is reached, rupture of the atmosphere discharge discs 100a and 100b can be prevented and breakage of the turbine exhaust chamber and the condenser can be prevented without requiring much time and cost for the repair. Moreover, the configuration of the arithmetic section circuit 402 is simplified, which contributes to cost reduction.
Although a few embodiments of the invention have been described, these embodiments are shown as examples and are not intended to limit a technical scope of the invention. These novel embodiments can be carried out in other various forms and various omissions, replacement, and modifications can be made without departing from the gist of the invention. These embodiments and their variations are included in the technical scope and the gist of the invention and included in the invention described in the claims and a scope equivalent to the invention.
For example, in the first and second embodiments, the saturated pressure at which the vacuum breaker valve 103 is opened is 109.09 kPa. However, this value is merely an example and the saturated pressure is not limited to it.
In the first embodiment, the set value of 99 kPa·abs is set as the pressure at which the alarm is output. However, the pressure is not limited to this value and the set value p can be set at a desired value.
In the second embodiment, in order to output an alarm similarly to the first embodiment, it may be configured to output an alarm when the steam temperature j reaches a predetermined pressure value.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-21109 | Feb 2012 | JP | national |
