JP7639550B2 - Boiler forced cooling method - Google Patents

Description

The present invention relates to a method for forced cooling of a boiler in a thermal power generation facility.

In thermal power plants, water is heated in a boiler and the resulting 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, in which case 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).

Specifically, conventionally, the boiler was cooled and air-cooled by the ventilation system, and then when the boiler drum pressure dropped to a specified value, the boiler drum blow valve was opened and the boiler water was replaced to cool and water-cool the boiler. In other words, water from the deaerator was sent to the boiler drum by the feedwater pump to water-cool the boiler, while air-cooling by the ventilation system continued. In this case, if all the water discharged from the feedwater pump was sent to the boiler drum, not only would a large amount of water have to be discharged, but if the capacity (maximum discharge amount) of the blow valve was small, the water would not be able to be discharged from the blow valve. For this reason, minimum flow operation was adopted, in which only a portion of the water from the feedwater pump was sent to the boiler drum and the remaining amount was returned to the deaerator.

JP 2014-112017 A

As mentioned above, conventionally, when forcibly cooling a boiler, the boiler water was replaced in addition to air cooling, which resulted in a large amount of wastewater being generated and placed a heavy burden on the wastewater treatment equipment.

Therefore, the present invention aims to provide a method for forced cooling of a boiler that can reduce wastewater.

In order to solve the above problem, the invention of claim 1 is a boiler forced cooling method for forcibly cooling the boiler in a thermal power generation facility 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, characterized in that after the boiler is extinguished, the feedwater flow rate control valve is closed and the water in the boiler is not replaced , and the boiler is only air- cooled by the air-cooling device until the temperature of the boiler reaches a desired temperature.

The invention of claim 2 is characterized in that in the boiler forced cooling method described in claim 1, the feedwater pump is stopped and the feedwater flow rate control valve is closed.

The inventors of the present application have discovered and confirmed that even if the boiler water is replaced to cool the boiler, the cooling effect is almost insignificant or small. In other words, when replacing the boiler water by performing 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 through 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, and the inventors have discovered and confirmed that the cooling effect of the boiler is almost insignificant or small. Furthermore, the inventors of the present application have confirmed that when the boiler was cooled only by air cooling without sending water to the boiler, the time it took for the temperature of the boiler (boiler water) to reach the desired temperature was almost the same as that of the conventional cooling method using air cooling and water cooling.

According to the invention described in claim 1, with the feedwater flow rate control valve closed, i.e., without sending water to the boiler (without replacing the boiler water), the boiler is cooled/air-cooled only by the air-cooling device until the boiler temperature reaches the desired temperature. 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 can significantly reduce wastewater.

According to the invention described in claim 2, the water supply pump is stopped and the water supply flow rate control valve is closed, so the power required to drive the water supply pump can be reduced.

1 is a schematic configuration diagram showing a thermal power generation facility according to an embodiment of the present invention.

The present invention will be described below based on the illustrated embodiment.

Figure 1 is a schematic diagram showing a thermal power generation facility 1 according to an embodiment of the present invention. This thermal power generation facility 1 has a configuration similar to existing thermal power generation facilities that are widely used, but is generally configured as follows.

The boiler 2 heats water using fossil fuels or the like to generate steam, and sends the steam to the steam turbine 31, which rotates the steam turbine 31 and generates electricity in the generator 32. In addition, the steam discharged from the steam turbine 31 is condensed in the condenser 33, and stored in the deaerator 41 by the condensate pump 34.

The deaerator 41 is a device that removes dissolved oxygen, carbon gas, and other contaminants from the condensate that cannot be completely removed by the condenser 33. A water supply path 42 for sending water from the deaerator 41 to the boiler 2 is provided with a water supply pump 43, a water supply flow rate control valve 44, and a high-pressure water supply heater 45, in that order from the upstream side (the deaerator 41 side).

The water supply 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 during operation and power generation of the thermal power generation facility 1 can be supplied to the boiler 2 in sufficient volume. Therefore, the minimum flow rate is also set large (e.g., 100), which is larger than the maximum flow rate (e.g., 50) from the boiler drum blow valve 62 described later.

The feedwater flow rate control valve 44 is a valve that adjusts the flow rate of water from the feedwater pump 43 to the boiler 2 (controls the boiler drum level/water 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.

Meanwhile, a minimum flow path 51 is provided that extends 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 can be returned to the deaerator 41 via the minimum flow path 51.

For example, when the thermal power generation facility 1 is started and a water amount less than the minimum flow rate of the feedwater pump 43 is supplied to the boiler 2, if the feedwater flow rate control valve 44 and the minimum flow valve 52 are opened, a part of the water from the feedwater pump 43 is sent to the boiler 2, and the remaining amount is returned to the deaerator 41. Also, to protect the feedwater pump 43, if the feedwater flow rate control valve 44 is closed and the minimum flow valve 52 is opened, the entire amount of water from the feedwater pump 43 is returned to the deaerator 41. Furthermore, in the conventional case, when the boiler 2 is forcibly cooled (the boiler water is replaced), since the minimum flow rate of the feedwater pump 43 is greater than the maximum flow rate of the boiler drum blow valve 62, by opening the feedwater flow rate control valve 44 and the minimum flow valve 52, a part of the water from the feedwater pump 43 (water less than the maximum flow rate of the boiler drum blow valve 62) is sent to the boiler 2, and the remaining amount is returned to the deaerator 41.

FDF (Forced Draft Fan) 7 is also provided as an air-cooling device that sends air to the boiler 2 to cool and air-cool it. A boiler drum blow valve 62 is provided in the drainage channel 61 that sends wastewater from the boiler 2 to the 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.

Next, we will explain the boiler forced cooling method for forcibly cooling the boiler 2 in a thermal power generation facility 1 configured as described above.

First, the inventors of the present application discovered and confirmed that even if boiler 2 is cooled by replacing boiler water as in the past, the cooling effect is almost nonexistent or small. That is, when replacing boiler water, as described above, because the minimum flow rate of feedwater pump 43 is greater than the maximum flow rate of boiler drum blow valve 62, it is necessary to perform minimum flow operation by opening feedwater flow rate control valve 44 and minimum flow valve 52 to send only a portion of the water from feedwater pump 43 to boiler 2, i.e., the boiler drum, and returning the remaining amount to deaerator 41 through minimum flow path 51. However, the temperature of the water returning to deaerator 41 (storage water temperature in deaerator 41) increases due to the rotational heat input of feedwater pump 43 (amount of heat transferred to water by circulating water through the pump). As a result, high-temperature water is sent to boiler 2, and it was discovered and confirmed that the cooling effect of boiler 2 is almost nonexistent or small. Furthermore, the inventors of the present application confirmed that when boiler 2 was cooled only by air cooling using FDF7 without feeding water to boiler 2, 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 roughly the same as that of the conventional cooling method using both air and water cooling.

For this reason, in this boiler forced cooling method, after the boiler 2 is turned off, the feedwater flow rate control valve 44 and the boiler drum blow valve 62 are closed and the boiler water is not replaced, and the boiler 2 is air-cooled using only the FDF 7 until the temperature of the boiler 2 and the boiler water reaches the desired temperature (for example, until it falls below 90°C). 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 rate control valve 44 is closed. The high-pressure feedwater heater 45 is also stopped.

As described above, according to this boiler forced cooling method, the boiler 2 is cooled and air-cooled only by the FDF 7 with the feedwater flow rate control valve 44 closed, i.e., with no water being sent to the boiler 2 (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 can significantly reduce 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.

Although the embodiment of the present invention has been described above in detail, the specific configuration is not limited to this embodiment, and the present invention includes design changes that do not deviate from the gist of the present invention. For example, in the above embodiment, the air-cooling device is an FDF7, but other air-cooling devices may be used, and the amount of air blown by the FDF7 may be changed. For example, the amount of air blown by the FDF7 may be increased compared to conventional cooling methods that use air and water cooling.

A boiler forced cooling system that controls the feedwater pump 43, the feedwater flow rate control valve 44, the FDF 7, etc. may also 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 continue to operate the FDF 7 until the temperature of the boiler 2 (boiler water) reaches the desired temperature.

REFERENCE SIGNS LIST 1 Thermal power generation facility 2 Boiler 31 Steam turbine 32 Generator 33 Condenser 34 Condensate pump 41 Deaerator 42 Feedwater path 43 Feedwater pump 44 Feedwater flow rate control valve 45 High-pressure feedwater heater 51 Minimum flow path 52 Minimum flow valve 61 Drainage path 62 Boiler drum blow valve 63 Drainage treatment device 7 FDF (air cooling device)

Claims (2)

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 water supply 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. 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.