JP5183649B2 - Forced cooling method for once-through boiler - Google Patents

Description

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

  In a thermal power generation facility, feed water is heated and superheated by a boiler, and superheated steam is sent to the steam turbine to cause the steam turbine to work to generate power. Here, the thermal power generation facility may perform low-load operation or suspension of operation according to the amount of power consumption, and may suspend operation at regular intervals in order to perform periodic inspections or the like. When the thermal power generation facility is shut down, the supply of fossil fuel into the boiler is stopped and the fire is extinguished, and then the boiler is forcibly cooled by blowing air and supplying water to the water pipe. When performing forced cooling of the boiler, it is necessary to keep the temperature drop rate below a certain level in order to prevent damage to the overheated equipment.

  By the way, as a boiler used in a thermal power generation facility, a once-through boiler, a circulation boiler, and the like are known, but the boiler most frequently used in recent years is a once-through boiler. The once-through boiler is a boiler having a structure in which feed water is supplied from one end of a water pipe provided in the boiler, the feed water is preheated, evaporated, then superheated, and superheated steam is discharged from the other end. Since the once-through boiler does not have a steam drum for performing brackish water separation in the boiler, surplus water that has reached the primary superheater is transferred to the flash tank and then to the condenser without passing through the steam turbine. A startup bypass path is provided for distribution.

  Regarding the forced cooling of the boiler described above, the method differs depending on the type of boiler. For example, as a forced cooling method for a recirculating boiler, Patent Document 1 discloses that a boiler path outlet temperature of a boiler is detected at the time of boiler forced cooling of the recirculating boiler, and the boiler recirculation flow path is determined from the furnace path outlet temperature. Boiler forced cooling, wherein the opening of the Q valve is set to control the recirculation flow rate, and the opening of the Q valve is adjusted so that the furnace path outlet temperature has a set temperature decrease rate A control method is disclosed.

  According to the boiler forced cooling control method described in Patent Document 1, the recirculation flow rate is controlled by adjusting the opening of the Q valve so that the furnace path outlet temperature becomes the set temperature decrease rate. The boiler can be effectively cooled in the shortest time while the forced cooling of the boiler is stabilized and the safety can be maintained.

Japanese Patent Publication No. 8-006981

  However, the invention described in Patent Document 1 controls the forced cooling of the boiler by controlling the recirculation flow rate and the feed water flow rate. For the once-through boiler that does not recirculate the feed water in the first place. It is not applicable. Moreover, although the invention described in Patent Document 1 controls the recirculation flow rate and the feed water flow rate so that the temperature decrease rate of the boiler is below a certain level, the feed water flow rate is specifically controlled to any value. This is not disclosed to the extent that it can be implemented, and further consideration is required in this respect.

  The present invention has been made in view of the above problems, and is a forced cooling method for a boiler implemented in a once-through boiler, in which the temperature drop rate of the boiler is controlled to be a certain level or less. It aims to provide a method.

  In the boiler provided in the thermal power generation facility, when the boiler is forcibly cooled by air cooling and water cooling, the flow rate of the feed water circulated in the water pipe is changed to a predetermined value, thereby stably. The present inventors have found that the boiler can be forcibly cooled and have completed the present invention.

  Specifically, the present invention has the following objects.

  (1) A boiler that burns fossil fuel to generate combustion heat, a economizer that is provided in the boiler and circulates water for heating, and is provided in the boiler and circulates through the economizer A boiler water wall for circulating the heated feed water and heating it, a primary superheater provided in the boiler for overheating the feed water flowing through the boiler water wall to generate steam, and steam generated by seawater A condenser for generating condensate by cooling, a start-up bypass path for distributing feed water from the primary superheater to the condenser, and condensing from the condenser to the economizer In a thermal power generation facility comprising a condensate / water supply pipe for circulating water supply and an air supply fan for supplying air for assisting combustion to the boiler, forced cooling of the boiler performed after extinguishing the boiler A method wherein the air Under the condition that the supply fan is operated to supply a constant amount of air continuously and the boiler temperature is 180 ° C. or higher, the first flow rate of water is supplied to the economizer, the boiler water wall, and In a condition where the primary superheater, the startup bypass path, and the condensate / feed water pipe are circulated and the boiler temperature is less than 180 ° C., the second flow rate of water smaller than the first flow rate is A forced boiler cooling method for circulating through a economizer, the boiler water wall, the primary superheater, the startup bypass path, and the condensate / water supply pipe.

  Here, the first flow rate is, for example, 150 T / H or more and 250 T / H or less, and the second flow rate is, for example, 130 T / H.

  The invention described in (1) particularly relates to a forced cooling method in a once-through boiler. In the once-through boiler, in order to prevent damage to the water pipe, the water supply must be circulated through the economizer, boiler water wall, and primary superheater even after the boiler is extinguished. On the other hand, in the secondary superheater for superheating the steam generated in the primary superheater and the steam turbine rotating by the pressure of the steam generated in the secondary superheater, only steam is circulated. It is necessary to prevent inflow. In order to prevent the inflow of feed water to the economizer, boiler water wall, and primary superheater and to prevent the inflow of feedwater to the secondary superheater and steam turbine with the boiler extinguished, from the primary superheater It is necessary to distribute the water supply to the start-up bypass route leading to the condenser and the flash tank for performing brackish water separation.

  That is, in the invention described in (1), after the boiler is extinguished, the boiler is forcibly cooled using various heat exchangers and feed water circulated to the startup bypass path. According to this, existing equipment can be used to implement the forced cooling method of the boiler, and the circulation rate can be reduced by using a control mechanism that is used during normal operation or low-load operation when supplying water. Since it can be controlled, the cost of capital investment can be reduced. In addition, since the air cooling of the boiler that is performed simultaneously with the water cooling of the boiler uses an air supply fan that is usually provided in the boiler, the cost of capital investment can be reduced also in this respect.

  In the invention described in (1), under conditions where the boiler temperature is 180 or more, the flow rate of the feed water flowing through the various heat exchangers, the startup bypass path, and the condensate / feed water pipe is set as the first flow rate, Under the condition of less than 180 ° C., the flow rate of the feed water flowing through the various heat exchangers, the startup bypass path, and the condensate / feed water pipe is set to a second flow rate smaller than the first flow rate. When the boiler is forcibly cooled, under conditions where the temperature drops, reducing the flow rate of the feed water that circulates the various heat exchangers at this time reduces the boiler load without increasing the burden on the various regulating valves of the feed water system. Can be cooled.

  (2) The forced cooling method for a boiler according to (1), wherein the first flow rate is increased stepwise under a condition where the temperature of the boiler is 180 ° C. or higher.

  When a large amount of feed water is circulated inside various heat exchangers with a decrease in the temperature of the boiler, there is a risk that the rate of decrease in the temperature of the boiler increases rapidly. In such a case, the water pipe provided in the boiler is distorted due to a local temperature difference, which may damage the water pipe. By increasing the first flow rate stepwise, it is possible to prevent a rapid fluctuation in the temperature drop rate of the boiler and to safely perform forced cooling of the boiler.

  (3) Under the condition that the boiler temperature is 180 ° C. or higher, the water pressure for supplying feed water is the first water pressure, and under the condition for the boiler temperature being less than 180 ° C., the water pressure for supplying feed water is the first water pressure. The forced cooling method for a boiler according to (1) or (2), wherein the second water pressure is smaller than the water pressure.

  (4) The forced cooling method of the boiler according to any one of (1) to (3), wherein the first water pressure is a boiler rated pressure and the second water pressure is 3.5 MPa.

  The inventions described in (3) and (4) define a specific method for carrying out the invention described in (1). For this reason, according to the invention as described in (3) and (4), the effect similar to the invention as described in (1) can be acquired.

  In the invention described in (4), the boiler rated pressure is 15 Mpa or more and 25 Mpa or less in a normal thermal power generation facility.

  (5) The forced cooling method of the boiler according to any one of (1) to (4), wherein a flow rate of air supplied by the air supply fan is 40% of a total output of the air supply fan.

  When the boiler is forcibly cooled, it is preferable to perform air cooling of the boiler by an air supply fan in addition to water cooling of the boiler by circulating feed water in the water pipe. According to the invention described in (6), the flow rate of the air supplied by the air supply fan during air cooling of the boiler is set to 40% of the total output of the air supply fan. Thereby, while being able to cool the inside of a boiler efficiently, damage to piping etc. inside a boiler by overcooling the inside of a boiler can be prevented beforehand. Further, it is preferable that the flow rate of the air to be blown is the above flow rate also from the aspect of the output of the normally used air supply fan.

  Note that the total output of the air supply fan used in a normal thermal power generation facility is about 1.1 times the amount of air necessary for burning the fuel necessary for the thermal power generation facility to generate power at the rated output. Is the output required to supply

  The present invention is a forced boiler cooling method that can be carried out in a once-through boiler, and according to the present invention, the boiler can be cooled safely without placing a burden on various regulating valves of the water supply system.

It is drawing which shows the thermal power generation equipment which concerns on this invention. It is drawing which shows the outline of the forced cooling method of the boiler which concerns on this invention. It is drawing which shows the outline of the forced cooling method of the boiler which concerns on this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<Thermal power generation equipment>
First, before describing the forced cooling method for the boiler according to the present embodiment, the thermal power generation facility according to the present embodiment will be described.

[Configuration of thermal power generation facilities]
FIG. 1 shows a thermal power generation facility according to this embodiment. The thermal power generation facility according to the present embodiment includes a boiler 1 that burns fossil fuel to generate combustion heat, a boiler 1 that is provided with a economizer 2 that circulates water and heats it, and a boiler 1. A boiler water wall 3 is provided for circulating and heating the feed water circulated through the economizer 2, and the feed water provided in the boiler 1 and circulated through the boiler water wall 3 is heated to generate steam. A primary superheater 4 for cooling, a condenser 9 for cooling the steam with seawater to generate condensate, and a startup bypass path 18 for distributing feed water from the primary superheater 4 to the condenser 9; A condenser pipe 12 (a path from the condenser 9 to a deaerator 13 to be described later), which is a part of the condenser / feed water pipe, for circulating the condenser / feed water from the condenser 9 to the economizer 2; , A water supply pipe 16 which is a part of the condensate / water supply pipe (the process from the deaerator 13 described later to the economizer 2 Comprising a), an air supply fan for supplying air to support combustion in the boiler 1 (not shown).

  The startup bypass path 18 will be described in detail. The startup bypass path 18 primarily supplies water without passing through the secondary superheater 5, the high-pressure / intermediate-pressure turbine 6, the reheater 7, and the low-pressure turbine 8. This is a path that circulates from the superheater 4 to the condenser 9. On the startup bypass system path, a startup bypass path valve 17 for preventing inflow of water supply to the startup bypass path 18 during normal operation and brackish water separation are performed. A flash tank (not shown).

  Furthermore, the thermal power generation facility according to the present embodiment has a secondary superheater 5 for heating the steam generated in the primary superheater 4 and a high pressure rotating using the pressure of the steam generated in the secondary superheater 5. Utilizing the intermediate pressure turbine 6, the reheater 7 that reheats the steam discharged from the high pressure / intermediate pressure turbine 6 by the heat generated in the boiler 1, and the pressure of the reheated steam in the reheater 7 The rotating low pressure turbine 8, the deaerator 13 for removing air mixed in the condensate, and the low pressure feed water heating for exchanging heat between the extracted steam extracted from the low pressure turbine 8 and the condensed water A high pressure feed water heater 15 for exchanging heat between the extracted steam extracted from the high pressure / intermediate pressure turbine 6 and the condensate, and a condensate pump 10 for sending the condensate to the condensate pipe 12. And a water supply pump 14 for sending water supply to the water supply pipe 16.

[Operation of thermal power generation equipment]
Here, the operation of the thermal power generation facility according to the present embodiment will be described. When fossil fuel such as oil and coal is burned in the boiler 1 to generate combustion heat, the feed water is supplied from the feed water pipe 16 by the feed water pump 14. 1 is sequentially sent to a economizer 2, boiler water wall 3, primary superheater 4, and secondary superheater 5, and is heated (superheated) by combustion heat. The feed water that has reached the primary superheater 4 is boiled by the fossil fuel combustion heat to become steam, which is sent to the secondary superheater 5 where it is further heated. The superheated steam is first sent to the high-pressure / intermediate-pressure turbine 6 and rotated at a high speed. The steam that has finished its work in the high-pressure / intermediate-pressure turbine 6 is once returned to the reheater 7 in the boiler 1, where it is superheated again and sent to the low-pressure turbine 8 to rotate the low-pressure turbine 8 at high speed. . The steam that has finished its work in the low-pressure turbine 8 is sent to the condenser 9 and cooled by seawater to become condensate. This condensate is sent again to the condensate pipe 12 by the condensate pump 10 and reaches the heat exchanger in the boiler 1.

  Here, in order to prevent the water pipe in the boiler 1 from being damaged, it is necessary to constantly circulate a water supply of a certain amount or more. On the other hand, for the high-pressure / medium-pressure turbine 6 and the low-pressure turbine 8, the flow rate of steam must be adjusted according to the required power generation amount. For this reason, at the time of starting the thermal power generation facility or during low-load operation, the flow rate of steam flowing through the high-pressure / intermediate-pressure turbine 6 or the low-pressure turbine 8 is higher than the flow rate of the feed water circulating through the water pipe in the boiler 1. It is assumed that there will be fewer situations. In such a case, surplus water supplied to the water pipe in the boiler 1 is sent to the condenser 9 or the like by the startup bypass path 18 by opening the startup bypass path valve 17.

  This will be described in more detail. First, surplus water that has reached the primary superheater 4 is sent to the flash tank through the startup bypass path 18. In the flash tank, the pressure is set lower than that of the primary superheater 4, and a part of the hot water supply becomes steam here and is sent to the secondary superheater 5. The remaining water that has not evaporated in the flash tank is further sent to the condenser 9 via the startup bypass path 18 and mixed with the condensate.

<Forced boiler cooling method>
In the forced cooling method for the boiler 1 according to the present embodiment, the air supply fan is operated to continuously supply a constant amount of air, and the first flow rate is set under the condition that the temperature of the boiler 1 is 180 ° C. or higher. In the condition where the temperature of the boiler 1 is 180 ° C. or less, the feed water is circulated through the economizer 2, the boiler water wall 3, and the primary superheater 4, and the startup bypass path 18, the condensate pipe 12, and the feed water pipe 16. The feed water having a second flow rate smaller than the first flow rate is circulated through the economizer 2, the boiler water wall 3, the primary superheater 4, and the startup bypass path 18, the condensate pipe 12, and the feed water pipe 16. .

  Here, the forced cooling method of the boiler 1 which concerns on this embodiment is related with the forced cooling method in a once-through boiler especially. In the once-through boiler, in order to prevent damage to the water pipe, the water supply must be circulated through the economizer 2, the boiler water wall 3, and the primary superheater 4 even after the boiler 1 is extinguished. On the other hand, in the secondary superheater 5 for superheating the steam generated in the primary superheater 4 and the steam turbine rotating by the pressure of the steam generated in the secondary superheater 5, only the steam is circulated. It is necessary to prevent the inflow of water supply. In order to prevent the inflow of feed water to the economizer 2, the boiler water wall 3, and the primary superheater 4 and further to the secondary superheater 5 and the steam turbine with the boiler 1 extinguished. It is necessary to distribute the feed water to the start-up bypass path 18 leading to the flash tank for performing brackish water separation from the primary superheater 4 and further to the condenser 9.

  The forced cooling method of the boiler 1 which concerns on this embodiment is the forced cooling of the boiler 1 using the various heat exchangers and the feed water circulated to the starting bypass path 18 after the fire extinguishing of the boiler 1. According to this, existing equipment can be used when the forced cooling method of the boiler 1 is carried out, and further, the circulation amount is circulated using a control mechanism that is performed during normal operation or low-load operation when circulating the water supply. Therefore, the cost of capital investment can be reduced. In addition, since the air cooling of the boiler 1 that is performed simultaneously with the water cooling of the boiler 1 uses an air supply fan that is normally provided in the boiler 1, the cost of capital investment can be reduced also in this respect.

[Air supply by air supply fan]
The air supply fan is for supplying air for assisting combustion of fossil fuel or the like, and is called a forced blower or the like. The air supply fan blows air at a constant flow rate from the time when the boiler 1 is extinguished to the time when forced cooling ends, and thereby the inside of the boiler 1 is air-cooled. The flow rate of air blown into the boiler 1 by the air supply fan is preferably 40% of the total output of the air supply fan. Thereby, while being able to cool the inside of the boiler 1 efficiently, damage to piping etc. inside the boiler 1 by overcooling the inside of the boiler 1 can be prevented beforehand. It should be noted that the total output of the air supply fan is necessary for supplying air that is about 1.1 times the amount of air necessary for burning the fuel necessary for the thermal power generation facility to generate power at the rated output. Is the output.

[Distribution of water supply]
In the forced cooling method for the boiler 1 according to the present embodiment, air is supplied by the above-described air supply fan, and the boiler 1 is cooled by supplying water to the water pipe in the boiler 1. That is, when the boiler 1 is forcibly cooled, the start-up bypass passage valve 17 is opened to supply water to the economizer 2, the boiler water wall 3, the primary superheater 4, the start-up bypass passage 18, Although it distribute | circulates to the water pipe 12 and the water supply pipe | tube 16, according to the temperature of the boiler 1, the flow volume at the time of distribute | circulating water supply is controlled. As shown in FIG. 2, under conditions where the temperature of the boiler 1 is 180 ° C. or higher (corresponding to before the time a in FIG. 2), the flow rate of the feed water is the first flow rate, and the temperature of the boiler 1 is less than 180 ° C. Under the condition (corresponding to after time b in FIG. 2), the flow rate of the feed water is a second flow rate smaller than the first flow rate.

  Here, under the condition that the temperature of the boiler 1 is 180 ° C. or higher, the flow rate of the feed water flowing through the various heat exchangers, the startup bypass path 18, the condensate pipe 12, and the feed water pipe 16 is set as the first flow rate, Under the condition that the temperature of the water is less than 180 ° C., the flow rate of the feed water flowing through the various heat exchangers, the startup bypass path 18, the condensate pipe 12, and the feed water pipe 16 is smaller than the first flow rate, By doing so, when performing forced cooling of the boiler 1, the boiler can be cooled without increasing the burden on various regulating valves of the water supply system under the condition that the temperature is lowered.

  The means for controlling the flow rate of the feed water is not particularly limited, and examples thereof include a feed water pump 14 provided on the feed water pipe 16 and various control valves. By adjusting the output of the feed water pump 14 and the opening of various control valves, the feed water at a desired flow rate can be circulated through the water pipe in the boiler 1.

  Here, the feed water flow rate of the feed water supplied to the water pipe in the boiler 1 varies depending on the output of the thermal power generation facility provided in the boiler 1, but in a general thermal power generation facility, The flow rate is preferably 150 T / H or more and 250 T / H. Further, the value of the second flow rate is preferably set to 130 T / H, for example. Here, as shown in FIG. 3 (before time a), the first flow rate preferably increases the flow rate stepwise within the range of the flow rate. That is, by suppressing the rapid increase in the flow rate of the feed water, the temperature effect rate of the boiler 1 can be maintained more stably and at a certain level.

(Water pressure when distributing water supply)
The water pressure when the feed water is circulated is the first water pressure when the temperature of the boiler 1 is 180 ° C. or higher, and is lower than the first water pressure when the temperature of the boiler 1 is less than 180 ° C. Second water pressure. The boiler can be cooled without increasing the burden on the various regulating valves of the water supply system by reducing the water pressure for circulating the water supply as the temperature of the boiler 1 decreases.

  The first water pressure is preferably a boiler rated pressure. The second water pressure is preferably 3.5 MPa. The boiler rated pressure is, for example, 15 Mpa or more and 25 Mpa or less in a normal thermal power generation facility.

  The means for controlling the water pressure of the feed water is not particularly limited, and examples thereof include a feed water pump 14 provided on the feed water pipe 16. By adjusting the output of the feed pump 14, feed water having a desired water pressure can be circulated through the water pipe in the boiler 1.

(Temperature drop rate)
By the forced cooling method of the boiler 1 implemented as mentioned above, the boiler 1 can be cooled at a stable temperature drop rate. The temperature drop rate when forcibly cooling the boiler 1 is appropriately determined according to the output of the boiler 1 provided in the thermal power generation facility, the constituent material of the boiler 1, and the structure of the boiler 1, but is 80 ° C. / H or higher, preferably about 110 ° C./h. In the forced cooling method of the boiler 1 according to the present embodiment, the flow rate of the feed water to be circulated through the various heat exchangers, the startup bypass path 18, the condensate pipe 12, and the feed water pipe 16 so that the temperature drop rate becomes the above value. This is set as appropriate.

(Target cooling temperature)
The boiler 1 cooled by the forced cooling method of the boiler 1 according to the present embodiment is preferably cooled to 100 ° C. or lower at the inlet of the primary superheater 4, and is cooled to 60 ° C. or lower. Further preferred. By cooling to 60 ° C. or lower, for example, even during regular inspection, an operator can perform work in the boiler 1.

  In the present specification, the forced cooling method of the once-through boiler has been described as an example, but the forced cooling method of the boiler has been described, but is not limited to the forced cooling method in the once-through boiler, and in a drum boiler having a different configuration from the once-through boiler, By cooling in the same manner while paying attention to the temperature difference between the top and bottom of the drum and the inside and outside of the drum, the forced cooling method of the boiler can be implemented by blowing at a precipitation pipe temperature of about 130 ° C.

1 boiler 2 economizer 3 boiler water wall 4 primary superheater 5 secondary superheater 6 high pressure / medium pressure turbine 7 reheater 8 low pressure turbine 9 condenser 10 condensate pump 11 low pressure feed water heater 12 condensate pipe 13 desorption Ventilator 14 Water supply pump 15 High-pressure feed water heater 16 Water supply pipe 17 Startup bypass path valve 18 Startup bypass path

Claims (5)

A boiler that burns fossil fuels and generates combustion heat;
A economizer that is provided in the boiler and that heats the feed water by circulating it;
A boiler water wall provided in the boiler for circulating and heating the feed water that has been circulated through the economizer;
A primary superheater that is provided in the boiler and generates steam by superheating water supplied through the boiler water wall;
A condenser for cooling steam with seawater to produce condensate,
A start-up bypass path for circulating water from the primary superheater to the condenser;
A condensate / water supply pipe for circulating condensate / water supply from the condenser to the economizer;
In a thermal power generation facility comprising an air supply fan for supplying air for assisting combustion to the boiler, a forced cooling method for a once- through boiler performed after extinguishing the boiler,
The air supply fan is operated to supply a constant amount of air continuously,
Under the condition that the temperature of the boiler is 180 ° C. or higher, feed water at a first flow rate to the economizer, the boiler water wall, the primary superheater, the startup bypass path, and the condensate / feed pipe. Circulate,
Under the condition that the temperature of the boiler is 180 ° C. or less, the feed water at a second flow rate smaller than the first flow rate is supplied to the economizer, the boiler water wall, the primary superheater, and the startup bypass path, and A forced cooling method for a once-through boiler, which is circulated through the condensate / water supply pipe. The forced cooling method for a once- through boiler according to claim 1, wherein the first flow rate is increased stepwise under a condition where the temperature of the boiler is 180 ° C or higher. Under the condition that the temperature of the boiler is 180 ° C. or higher, the water pressure for circulating the feed water is the first water pressure,
The forced cooling method of the once- through boiler according to claim 1 or 2 which makes the water pressure which distributes feed water into the 2nd water pressure smaller than the 1st water pressure on the conditions that the temperature of said boiler is less than 180 ° C. The forced cooling method for a once- through boiler according to claim 3 , wherein the first water pressure is a boiler rated pressure and the second water pressure is 3.5 MPa. The forced cooling method for a once- through boiler according to any one of claims 1 to 4, wherein a flow rate of air supplied by the air supply fan is 40% of a total output of the air supply fan.

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