Boiler forced cooling method

Abstract

To provide a boiler forced cooling method which enables reduction of drain water.SOLUTION: A thermal power generation facility 1 includes: a boiler 2 which heats water to generate steam; a water supply pump 43 which sends water from a deaerator 41 to the boiler 2; a water supply flow rate regulating valve 44 which regulates a flow rate of the water from the water supply pump 43 to the boiler 2; a minimum passage 51 which returns the water from the water supply pump 43 to the deaerator 41; and a forced draft fan 7 which air-cools the boiler 2. At the thermal power generation facility 1, in a state that the water supply flow rate regulating valve 44 is closed, the boiler 2 is air-cooled by the forced draft fan 7 until a temperature of the boiler 2 reaches a predetermined temperature.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a boiler forced cooling method for forcedly cooling a boiler in a thermal power plant. [Background technology]

[0002] In thermal power plants, water is heated in a boiler and the steam is sent to a steam turbine to rotate the steam turbine and generate electricity. Such thermal power plants may be shut down depending on the load or for inspection, and in such cases, it is necessary to stop the fuel supply to the boiler, extinguish the fire, and forcibly cool the boiler (see, for example, Patent Document 1).

[0003] Specifically, conventionally, the boiler is cooled and air-cooled using a ventilation system. Then, when the boiler drum pressure drops to a predetermined value, the boiler drum's blowdown valve is opened and the boiler water is replaced to cool and water-cool the boiler. In other words, water from the deaerator is sent to the boiler drum using a feedwater pump to water-cool the boiler, while air-cooling via the ventilation system continues. In this case, if all of the water discharged from the feedwater pump were sent to the boiler drum, not only would a large amount of water have to be disposed of, but if the blowdown valve's capacity (maximum discharge rate) is small, the water would not be able to be discharged from the blowdown valve. For this reason, minimum flow operation was adopted, in which only a portion of the water from the feedwater pump is sent to the boiler drum and the remainder is returned to the deaerator. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-112017 Summary of the Invention [Problem to be solved by the invention]

[0005] As described above, conventionally, when a boiler is forcedly cooled, the boiler water is replaced in addition to air cooling, which generates a large amount of wastewater and places a heavy load on the wastewater treatment device.

[0006] Therefore, an object of the present invention is to provide a boiler forced cooling method that can reduce wastewater. [Means for solving the problem]

[0007] In order to solve the above problems, the invention of claim 1 provides a boiler forced cooling method for forcedly cooling the boiler in a thermal power plant including a boiler that heats water to generate steam, a feedwater pump that sends water from a deaerator to the boiler, a feedwater flow rate control valve that adjusts the flow rate of water from the feedwater pump to the boiler, a minimum flow path that returns water from the feedwater pump to the deaerator, and an air-cooling device that air-cools the boiler, comprising: After the boiler is extinguished, With the water supply flow control valve closed Without replacing the water in the boiler The boiler is cooled by the air-cooling device until the temperature of the boiler reaches a desired temperature. only It is characterized by:

[0008] The invention of claim 2 is characterized in that, in the boiler forced cooling method of claim 1, the feedwater pump is stopped and the feedwater flow rate adjustment valve is closed. [Effects of the Invention]

[0009] The present inventors discovered and confirmed that water-cooling a boiler by replacing boiler water has little or no cooling effect. Specifically, when replacing boiler water using minimum flow operation, in which only a portion of the water from the feedwater pump is sent to the boiler and the remaining amount is returned to the deaerator via the minimum flow path, the temperature of the water returned to the deaerator (the temperature of the water stored in the deaerator) rises due to the rotational heat input of the feedwater pump (the amount of heat transferred to the water as it circulates through the pump). As a result, high-temperature water is sent to the boiler, resulting in little or no cooling effect for the boiler. Furthermore, the present inventors tested a boiler using air cooling alone, without sending water to the boiler, and confirmed that the time it took for the boiler (boiler water) to reach the desired temperature was approximately the same as that of conventional cooling methods using both air and water cooling.

[0010] According to the invention described in claim 1, the boiler is cooled and air-cooled only by the air-cooling device until the boiler temperature reaches the desired temperature while the feedwater flow control valve is closed, that is, without sending water to the boiler (without replacing the boiler water).This ensures a cooling effect equivalent to that of the conventional cooling method using air and water cooling (while maintaining the same time required to reach the desired temperature as before), and allows for a significant reduction in wastewater.

[0011] According to the invention recited in claim 2, the feedwater pump is stopped and the feedwater flow rate adjustment valve is closed, so that the power required to drive the feedwater pump can be reduced. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic configuration diagram showing a thermal power generation facility according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described below based on the illustrated embodiments.

[0014] 1 is a schematic diagram showing a thermal power plant 1 according to an embodiment of the present invention. This thermal power plant 1 has a configuration similar to that of existing thermal power plants that are widely used, and is generally configured as follows.

[0015] The boiler 2 generates steam by heating water using a fossil fuel or the like, and sends the steam to a steam turbine 31, which rotates the steam turbine 31 and generates electricity in a generator 32. The steam discharged from the steam turbine 31 is condensed in a condenser 33, and stored in a deaerator 41 by a condensate pump 34.

[0016] The deaerator 41 is a device that removes dissolved oxygen, carbon dioxide, and the like from the condensate that cannot be completely removed by the condenser 33. A feedwater pump 43, a feedwater flow control valve 44, and a high-pressure feedwater heater 45 are arranged in this order from the upstream side (the deaerator 41 side) in a feedwater path 42 for sending water from the deaerator 41 to the boiler 2.

[0017] The feedwater pump 43 is a pump that sends water from the deaerator 41 to the boiler 2, and its capacity and flow rate are set large so that the water required for operation and power generation of the thermal power plant 1 can be supplied to the boiler 2 in sufficient quantity. Therefore, the minimum flow rate is also set large (for example, 100), which is larger than the maximum flow rate (for example, 50) from the boiler drum blow valve 62 described later.

[0018] The feedwater flow control valve 44 is a valve that adjusts the flow rate of water from the feedwater pump 43 to the boiler 2 (controlling the boiler drum level at a constant level), and when this valve is closed, water is not supplied to the boiler 2. The high-pressure feedwater heater 45 is a heater that heats the water sent from the feedwater pump 43 and sends it to the boiler 2, and heats the water using high-pressure steam extracted from the steam turbine 31, etc.

[0019] Meanwhile, a minimum flow path 51 is provided extending from the water supply path 42 between the water supply pump 43 and the water supply flow rate control valve 44 to the deaerator 41, and a minimum flow valve 52 is disposed in this minimum flow path 51. When the minimum flow valve 52 is opened, water from the water supply pump 43 is returned to the deaerator 41 via the minimum flow path 51.

[0020] For example, when starting up thermal power plant 1 and supplying boiler 2 with water at a rate less than the minimum flow rate of feedwater pump 43, opening feedwater flow rate control valve 44 and minimum flow valve 52 sends some of the water from feedwater pump 43 to boiler 2, and the remaining amount is returned to deaerator 41. Furthermore, to protect feedwater pump 43, closing feedwater flow rate control valve 44 and opening minimum flow valve 52 causes all of the water from feedwater pump 43 to be returned to deaerator 41. Furthermore, when boiler 2 is conventionally forcibly cooled (boiler water is replaced), the minimum flow rate of feedwater pump 43 is greater than the maximum flow rate of boiler drum blow valve 62, so opening feedwater flow rate control valve 44 and minimum flow valve 52 sends some of the water from feedwater pump 43 (water at or below the maximum flow rate of boiler drum blow valve 62) to boiler 2, and the remaining amount is returned to deaerator 41.

[0021] In addition, an FDF (Forced Draft Fan) 7 is provided as an air-cooling device that sends air to the boiler 2 to cool and air-cool it. Furthermore, a boiler drum blow valve 62 is provided in a drainage channel 61 that sends wastewater from the boiler 2 to a wastewater treatment device 63, and the maximum flow rate (maximum discharge rate) from the drainage channel 61 and the boiler drum blow valve 62 is smaller than the minimum flow rate of the feedwater pump 43.

[0022] Next, a boiler forced cooling method for forcibly cooling the boiler 2 in the thermal power plant 1 having such a configuration will be described.

[0023] First, the inventors of the present application discovered and confirmed that water-cooling the boiler 2 by replacing the boiler water as in the past has little or no cooling effect. That is, when replacing the boiler water, as described above, because the minimum flow rate of the feedwater pump 43 is greater than the maximum flow rate of the boiler drum blow valve 62, it is necessary to perform minimum flow operation, in which the feedwater flow control valve 44 and the minimum flow valve 52 are opened to send only a portion of the water from the feedwater pump 43 to the boiler 2, i.e., the boiler drum, and the remaining amount is returned to the deaerator 41 via the minimum flow path 51. However, the rotational heat input of the feedwater pump 43 (the amount of heat transferred to the water as it circulates through the pump) increases the temperature of the water returned to the deaerator 41 (the temperature of the water stored in the deaerator 41). As a result, high-temperature water is sent to the boiler 2, and the inventors discovered and confirmed that the cooling effect of the boiler 2 is little or no. Furthermore, the inventors of the present application cooled boiler 2 using only air cooling with FDF7 without supplying water to boiler 2, and confirmed that the time it took for the temperature of boiler 2, i.e., the boiler water, to reach the desired temperature (e.g., 90°C) was approximately the same as that of conventional cooling methods that use both air and water cooling.

[0024] For this reason, in this boiler forced cooling method, after the boiler 2 is extinguished, the feedwater flow control valve 44 and the boiler drum blow valve 62 are closed, and the boiler water is not replaced, but the boiler 2 is air-cooled using only the FDF 7 until the temperature of the boiler 2 and boiler water reaches the desired temperature (for example, until it drops to 90°C or below). In other words, during forced cooling, the boiler 2 is cooled and air-cooled using only the FDF 7 from start to finish. At this time, the feedwater pump 43 is stopped and the feedwater flow control valve 44 is closed. The high-pressure feedwater heater 45 is also stopped.

[0025] As described above, according to this boiler forced cooling method, the boiler 2 is cooled and air-cooled only by the FDF 7 while the feedwater flow rate control valve 44 is closed, that is, without sending water to the boiler 2 (without replacing the boiler water). This ensures a cooling effect equivalent to that of conventional cooling methods using air and water cooling (while maintaining the same time required to reach the desired temperature as before), while significantly reducing wastewater (for example, by about 600 tons). Moreover, because the feedwater pump 43 is stopped and the feedwater flow rate control valve 44 is closed, the power required to drive the feedwater pump 43 can be reduced.

[0026] Although the embodiments of the present invention have been described in detail above, the specific configuration is not limited to these embodiments, and the present invention also encompasses design changes and the like that do not deviate from the gist of the present invention. For example, while the above embodiments have been described with reference to an FDF7 as the air-cooling device, other air-cooling devices may be used, and the airflow rate of the FDF7 may be changed. For example, the airflow rate of the FDF7 may be increased compared to conventional cooling methods that combine air and water cooling.

[0027] Furthermore, a boiler forced cooling system that controls the feedwater pump 43, the feedwater flow rate control valve 44, the FDF 7, etc. may be incorporated into the thermal power generation facility 1. Then, when the boiler 2 is forcedly cooled, this boiler forced cooling system may automatically close the feedwater flow rate control valve 44 and the boiler drum blow valve 62 to stop the feedwater pump 43, and may continue to operate the FDF 7 until the temperature of the boiler 2 (boiler water) reaches a desired temperature. [Explanation of symbols]

[0028] 1. Thermal power generation facilities 2 boilers 31 Steam turbine 32 Generator 33 Condenser 34 Condensate pump 41 Deaerator 42 Water supply route 43 Water supply pump 44 Water supply flow control valve 45 High-pressure water heater 51 Minimum flow path 52 Minimum flow valve 61 Drainage Channel 62 Boiler drum blow valve 63 Wastewater treatment equipment 7 FDF (air cooling device)

Claims

1. A boiler for heating water to generate steam; a feed water pump for sending water from the deaerator to the boiler; a feedwater flow rate control valve for controlling the flow rate of water from the feedwater pump to the boiler; a minimum flow path for returning water from the feed water pump to the deaerator; an air-cooling device for air-cooling the boiler; A boiler forced cooling method for forcibly cooling the boiler in a thermal power generation facility comprising: After the boiler is turned off, the water in the boiler is not replaced with the water supply flow rate control valve closed, and the boiler is only air-cooled by the air-cooling device until the temperature of the boiler reaches a desired temperature. A method for forced cooling of a boiler.

2. Stopping the water supply pump and closing the water supply flow rate control valve; 2. The method for forced cooling of a boiler according to claim 1.

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