JPS6237604A - Method and device for cooling boiler - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a steam generator having a superheater and a reheater,
In particular, it relates to cooling of tubes constituting superheaters and reheaters.

[Background of the invention]

Recently, accidents have occurred on power transmission lines at thermal power plants.
In the event that power transmission becomes unavailable, a function is required to rapidly reduce the load and supply only the amount of power for the on-site electrical load. A steam turbine can rapidly reduce its load using a steam control valve, but when operating in this way, the inside of the superheater and reheater of the steam generator: flowing steam. The amount will be drastically reduced. On the other hand, the steam generator has a large amount of heat and it is difficult to quickly squeeze out the fuel, so the pipes of the superheater and reheater end up overheating. It is generally known that this phenomenon is noticeable in boilers that burn coal. Turbine bypass systems are known to prevent this phenomenon. (Japanese Patent Publication No. 59-26765) A conventional method for preventing burnout of superheaters and reheaters will be explained with reference to FIG.

Water is supplied to the economizer 2 of the steam generator 1 and enters the drum 3 after exchanging heat with the exhaust gas.

The drum water becomes a mixed stream of brackish water in the evaporator tube 4, returns to the drum via the pipe 5, and is then separated into steam and water in the drum. The steam is turned into superheated steam through a pipe 6, a heater 7 and a final superheater 8, and is expanded in a high-pressure turbine 10 via a control valve 9, then reheated in a reheater 11, and then passed through a reheat valve 12. Then, the medium and low pressure turbine 13 performs expansion work again. The exhaust gas of the turbine is condensed in a condenser 14, then boosted in pressure by a condensate pump 15, and then heated in a feed water heater 16. Heated steam is supplied to the feedwater heater through a bleed pipe 17. The heated water supply is carried out by the water supply pump 18.
Water is sent to the energy saver 2. In this steam power plant, if the steam turbine reduces the load by rapidly throttling the control valve 9, the steam flowing through the superheaters 7 and 8 and the reheater 11 will rapidly decrease, causing overheating of the pipes and Burnout will occur. To prevent this, when there is a rapid load drop in the steam turbine, the high-pressure turbine bypass valve 19 and the low-pressure turbine bypass valve 20 are opened to dump the steam that no longer flows into the steam turbine into the condenser 14.
The steam flow rate inside the superheaters 7 and 8 and the reheater 11 is ensured to prevent overheating of the pipes.

Since the steam exiting the low-pressure turbine bypass valve 20 is at a high temperature, it is lowered in temperature by the water discharged from the condensate pump 15 in the desuperheater 21, and then expanded in the damper 22 in the condenser.

In order to prevent burnout of the superheater and reheater using such a system, a series flow path is formed in the order of the superheater, high pressure turbine bypass valve, reheater, and low pressure turbine bypass valve, so the low pressure If the bypass valve does not open at the time of failure and only the high-pressure turbine opens, the pressure inside the reheater will rise and the safety valve 23 will operate, and the safety valve must be disassembled and inspected every time it operates. The problem was that it didn't. Furthermore, if the high-pressure turbine bypass valve fails to open due to a failure, there is a problem in that steam does not reach the reheater and the reheater tubes burn out.

[Purpose of the invention]

An object of the present invention is to prevent burnout of a superheater and a reheater of a steam generator when the load of a steam turbine rapidly decreases.

[Summary of the invention]

The gist of the present invention is to prevent burnout of the reheater by injecting cooling steam or cooling water to the outside of the superheater and reheater using cooling devices installed in parallel.

[Embodiments of the invention]

An embodiment of the present invention will be described in detail in FIG. Superheater 7 and 8
．． The steam generated by the steam generator R1 having the reheater 11 undergoes expansion work in the high-pressure turbine 10 and the medium-low pressure turbine 13, and then condenses in the condenser 14, and is then sent to the condensate pump 15.
In a steam power plant, where the pressure is raised by the feed water pump and then returned to the steam generator by the feed pump, as mentioned above, when the load of the steam turbine rapidly drops, the superheaters 7 and 8. It is necessary to cool the tubes of the reheater 11. The cooling device according to the present invention includes a pipe line 25 branched from a steam pipe line 24 connecting an upstream superheater 7 and a downstream superheater 8, a valve 26, and installed outside the pipes of the superheater and reheater. It is constituted by a nozzle 27. When the steam turbine undergoes a rapid load drop, the regulating valve 9 rapidly closes or shifts to a small opening. As a result, the steam flow rate in the tubes of the superheaters 7 and 8 and the reheater 11 becomes extremely small. The gas temperature passing through the superheater and reheater is 10
Since the temperature is above 00°C, the pipe will be overheated, but if the steam turbine performs a rapid load drop, by opening the valve 26, the steam rapidly increasing in pressure in the drum 3 will be transferred to the pipe line 6, It is injected from a nozzle 27 via a superheater 7, pipes 24 and 25, and a valve 26. The temperature of this steam is approximately 450℃
However, it has a cooling effect because it is lower than the gas temperature and lower than the temperature resistance of the tube materials that make up the superheater and reheater. Thereby, overheating of the superheater and reheater can be prevented. In this embodiment, steam extracted from the middle of multiple superheaters was used as the cooling steam source, but the temperature of the exit steam of the final superheater 8 and the steam of the steam turbine bleed pipe 17 is also below 600°C. It is possible to use it as cooling steam. Furthermore, the object of the present invention can also be achieved by supplying cooling steam from this steam source through a hesogoo. It goes without saying that the diameters of the pipes 24 and valves 25 of this cooling device need to be such that sufficient cooling steam can flow through them to cool the pipes.

FIG. 2 shows a method of controlling the valve 26 in the embodiment shown in FIG. The valve 26 is an automatic valve, the temperature detector 28 detects the pipe wall temperature of the superheater and the reheater, and the valve 26 is controlled by a temperature controller 29 whose set value is set to a temperature below the limit temperature of the pipe. do. According to such a valve control device, when the pipes of the superheater and reheater overheat due to a rapid load drop and the pipe wall temperature rises and becomes higher than the set value of the temperature controller, the valve control device 26 will open and cooling steam will be injected. The PCB signal 30 is, for example, a rapid load drop signal generated by detecting a signal indicating that the main circuit breaker is open, and this signal can also be used to cool the pipe wall by opening the valve 26. In this example, the tube wall temperature was detected, but the superheater and reheater outlet temperatures can also be detected by determining the relationship between the outlet steam temperature of the superheater and reheater and the tube wall temperature. , can prevent overheating of the tube.

Furthermore, although steam was used as the cooling fluid in the embodiment shown in FIG. 1, it is clear that water could be used instead of steam. FIG. 3 shows an embodiment in which a superheater and a reheater are cooled by condensate pump outlet water. Extracting condensate from a pipe line downstream of the condensate pump 15,
Cooling water is sprayed from a nozzle 27 through a pipe 25 and a valve 26.

The temperature of the condensate at the outlet of the condensate pump 21 is approximately 40°C,
It can be used as a cooling fluid because it is lower in temperature than the gas flowing outside the superheater and reheater.

The valve 26 in FIG. 3 is controlled by a temperature detector 28 that detects the tube wall temperature of the superheater and reheater and a temperature controller 29, and is controlled so that the tube wall temperature of the superheater and reheater is below the limit temperature. open and close. Incidentally, as described above, burning out of the tube can be prevented by detecting the steam temperature at the outlet of the superheater and reheater instead of detecting the tube wall temperature. In the embodiment shown in Fig. 3, discharge water from the condensate pump was used, but a condensate desalination device (not shown) was installed in the condensate pump outlet pipe, and the condensate desalination device (not shown) was installed downstream of the condensate desalination device. Water boost pump (not shown) 1: If installed, it is also possible to use the condensate boost pump discharge water as the cooling fluid.

〔Effect of the invention〕

According to the present invention, it is possible to prevent the superheater and reheater of the steam generator from burning out when the load of the steam turbine rapidly decreases.

[Brief explanation of drawings]

Fig. 1 is a system diagram of a boiler cooling system according to an embodiment of the present invention, Fig. 2 is a system diagram of a boiler cooling system of the invention showing a control method, and Fig. 3 is a system diagram of a boiler cooling system of the invention using water. FIG. 4 is a system diagram of a conventional boiler cooling system.

Claims (1)

[Claims] 1. In a steam generator equipped with a superheater and a reheater in which steam flows inside a pipe, cooling fluid is injected outside the pipe of at least one of the superheater or the reheater. A boiler cooling method characterized in that the temperature of the tube wall or the steam temperature inside the tube is cooled to a target temperature or lower. 2. In a steam generator equipped with a plurality of superheaters and reheaters connected in series, a steam pipe line upstream of the hottest heater of the steam generator;
Alternatively, a boiler cooling device characterized in that a pipe line having a cooling steam end is provided outside the pipe of at least one of the superheater or the reheater through which steam extracted from the header is passed through a valve. 3. In claim 2, the valve is an automatic valve, and a temperature detector is installed on a pipe wall of at least one of the superheater or the reheater, so that the temperature of the pipe wall is below a limit value. A boiler cooling device characterized by comprising means for controlling a drive device for the valve. 4. In claim 2, the valve is an automatic valve, and a temperature detector is installed to detect the steam temperature of at least one of the steam at the outlet of the superheater or the steam at the outlet of the reheater, A boiler cooling device characterized by comprising means for controlling the temperature to be equal to a set value. 5. A boiler cooling system according to claim 2, characterized in that the valve is an automatic valve, and means is provided for opening the valve in response to a signal that the plant performs a rapid load drop.