boiler

Abstract

To provide a boiler capable of calculating the conductivity of canned water as accurately as possible by taking out canned water even when the combustion amount of the boiler is low.SOLUTION: There is provided a boiler whose combustion amount is continuously controlled at a predetermined combustion stage (e.g., low combustion stage) at a predetermined amount or less for a certain period of time or longer, and, if the electrical conductivity calculated by an electrical conductivity calculation unit has not changed and there is a risk that the canned water has not been taken out, an elevated water level control is performed to set a specific water level higher than a reference water level as a target water level.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a boiler. [Background technology]

[0002] Conventionally, there have been systems that calculate the conductivity of the water separated by a separator from the steam from the boiler body, and control the amount of water supplied to the boiler body by changing the combustion stage based on that conductivity (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-003094 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when the combustion rate of the boiler is low, boiler water in the boiler body boils slowly, making it difficult for the boiler water to be carried to the separator side. As a result, for example, it becomes difficult for the boiler water to reach the calculation unit that calculates the conductivity, which may cause a problem such as an inability to calculate the actual conductivity of the boiler water.

[0005] The present invention has been devised in view of the above circumstances, and its object is to provide a boiler that can extract boiler water and calculate the boiler water conductivity as accurately as possible even when the boiler combustion amount is low. [Means for solving the problem]

[0006] In order to achieve the above object, a boiler according to one aspect of the present invention includes a main body that heats boiler water by burning fuel to generate steam, a combustion stage control unit that controls one of a plurality of combustion stages with different combustion amounts, a feedwater control unit that controls the amount of feedwater supplied to the main body so that the boiler water level becomes a reference water level determined based on the combustion stage controlled by the combustion stage control unit, and a conductivity calculation unit that can calculate the conductivity of water corresponding to the boiler water, and the feedwater control unit performs an upper water level control to raise the boiler water level to a level higher than the reference water level determined based on the predetermined combustion stage when the boiler water level is controlled to a predetermined combustion stage among the plurality of combustion stages with a combustion amount equal to or less than a predetermined amount for a certain period of time continuously and the conductivity calculated by the conductivity calculation unit does not change.

[0007] According to the above configuration, when the boiler combustion amount is continuously controlled to a predetermined combustion stage below a predetermined amount for a certain period of time or more, and the conductivity calculated by the conductivity calculation unit does not change and there is a risk that boiler water is not being taken out, an upper water level control is performed to raise the water level above the reference water level, which makes it easier for boiler water to be taken out and allows the boiler water conductivity to be calculated as accurately as possible.

[0008] Preferably, the water supply control unit cancels the upper water level control when the combustion stage control unit controls the combustion amount to a combustion stage that exceeds the predetermined amount.

[0009] According to the above configuration, when the combustion amount is controlled to a combustion stage exceeding a predetermined amount, which makes it easier for boiler water to be taken out, the upper water level control is released, thereby preventing excessive boiler water from being taken out relative to the combustion amount, which would result in the supply of steam with a low dryness.

[0010] Preferably, the water supply control unit cancels the top water level control when the conductivity calculated by the conductivity calculation unit changes.

[0011] According to the above configuration, when the conductivity calculated by the conductivity calculation unit changes and it is estimated that boiler water has been removed, the top water level control is released, thereby preventing excessive boiler water from being removed, which would result in an extreme decrease in combustion efficiency. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram for explaining a schematic configuration of a boiler device. [Figure 2] 10 is a flowchart illustrating an example of a water supply control process. [Figure 3] 10 is a flowchart illustrating another example of the water supply control process. DETAILED DESCRIPTION OF THE INVENTION

[0013] <Overview of the configuration> Hereinafter, an embodiment of the present invention will be described with reference to the drawings. First, a schematic configuration of a boiler apparatus 1 according to this embodiment will be described with reference to Fig. 1. As shown in Fig. 1, the boiler apparatus 1 includes a boiler main body 2, a blower 3 that sends air into the boiler main body 2, and a fuel supply line 21 that supplies fuel to the boiler main body 2. An example in which the fuel is oil will be described, but the fuel is not limited to a liquid such as oil, and may be a gas such as gas.

[0014] The fuel supply line 21 is provided with a fuel regulating valve 21a that functions as a pressure regulating valve capable of adjusting the flow rate of fuel supplied to the boiler body 2 and also has a shutoff function. The fuel regulating valve 21a is configured, for example, by a motor valve, but is not limited to a motor valve and may be an air-operated control valve as long as it adjusts the flow rate of fuel. The fuel supplied from the fuel supply line 21 is supplied to the burner 20 in the boiler body 2, where it is mixed with combustion air blown from the blower 3 and burned. The flow rate of the combustion air is adjusted by the opening degree of a damper provided in the air supply path, or alternatively or additionally by using an inverter to adjust the rotation speed (frequency) of the fan of the blower 3.

[0015] The boiler body 2 is formed in a substantially cylindrical shape and includes a burner 20, water pipes 12, an upper header 13, and a lower header 11. The lower header 11 is provided at the bottom of the boiler body 2 and is connected to the lower parts of the multiple water pipes 12. The lower header 11 is connected to a water supply pipe 24. The water supply pipe 24 is provided with a water supply pump 22 and a check valve 23. Water is supplied from the water supply pump 22 to the lower header 11 via the water supply pipe 24, and the supplied water is heated in the water pipes 12. The upper header 13 is provided at the top of the boiler body 2 and is connected to the upper parts of the multiple water pipes 12. The upper header 13 collects steam generated in the multiple water pipes 12 and leads it to the separator 5 via a connecting pipe 4.

[0016] The boiler apparatus 1 generates steam by burning fuel in a burner 20 in the boiler body 2 to heat and boil boiler water. The generated steam flows into the separator 5 together with the boiled boiler water from the upper header 13 via the connecting pipe 4, where it is separated by the separator 5 and taken out from the steam pipe 6. In addition, a downcomer pipe 7 is provided connecting the lower part of the separator 5 with the lower part of the boiler body 2, and the boiler water separated by the separator 5 is returned to the lower header 11 via the downcomer pipe 7. In this way, the boiler water in the boiler body 2 is circulated.

[0017] Downstream pipe 7 is provided with conductivity calculation unit 9. Conductivity calculation unit 9 includes, for example, a sensor (electrode) that detects a resistance value, and calculates the conductivity of the water in downstream pipe 7 from the resistance value. Conductivity calculation unit 9 is electrically connected to control unit 10, and can input conductivity information to control unit 10 to specify the calculated conductivity in downstream pipe 7.

[0018] Further, a blow pipe 8 for discharging boiler water from the boiler body 2 is connected to the downcomer pipe 7. A blow valve 8a is provided on the blow pipe 8. For example, when the conductivity calculated by the conductivity calculation unit 9 exceeds a predetermined value, it is assumed that the boiler water in the boiler body is concentrated, and the boiler water in the boiler body 2 can be discharged (blow-down) by opening the blow valve 8a.

[0019] The control unit 10 is realized by a computer including an internal memory, a timer, and an arithmetic processing unit, and controls the operation and behavior of the boiler 1, for example, controlling the operation at ignition and shutdown, multiple combustion stages (e.g., low combustion stage, medium combustion stage, high combustion stage, etc.) with different combustion amounts depending on the steam load, and the operation (feedwater control) of the feedwater pump 22. The control unit 10 is electrically connected to the blower 3, fuel regulating valve 21a, blowdown valve 8a, conductivity calculation unit 9, and feedwater pump 22.

[0020] The control unit 10 also executes a water supply control process to set a target water level in the water pipe 12 based on the multiple combustion stages and changes in the conductivity of the water in the downcomer pipe 7. The control unit 10 performs a process to control the amount of water supply so that the water level in the water pipe 12 reaches the set target water level. The target water level is set to a reference water level corresponding to the combustion stage being controlled, among reference water levels defined for each of the multiple combustion stages. For example, in the low combustion stage, the low-fuel reference water level is set as the target water level. In the medium combustion stage, the medium-fuel reference water level is set as the target water level. In the high combustion stage, the high-fuel reference water level is set as the target water level. As shown in FIG. 1 , the water levels are ranked as follows: low-fuel reference water level > medium-fuel reference water level > high-fuel reference water level. The reference water levels defined for each of the multiple combustion stages are predetermined to be between the superheat limit water level and the dryness limit water level corresponding to each combustion stage.

[0021] Furthermore, in this embodiment, in order to solve problems that may arise in devices that perform predetermined processes, such as draining boiler water, based on the conductivity calculated by the conductivity calculation unit 9, a specific water level that is higher than the low-combustion reference water level is set as the target water level in the low-combustion stage. That is, in devices that perform predetermined processes based on the conductivity calculated by the conductivity calculation unit, for example, in a combustion stage where the combustion amount is low (e.g., the low-combustion stage), boiling becomes gentle, making it difficult for boiler water to be carried to the separator side by boiling, and therefore making it difficult for boiler water to reach the target location (calculation unit) where the conductivity is calculated. As a result, there is a risk that the actual conductivity of the boiler water in the main body will differ greatly from the conductivity calculated by the conductivity calculation unit, making it impossible to perform the predetermined process appropriately.

[0022] To address this issue, this embodiment defines a specific water level higher than the low-combustion reference water level. The specific water level is forcibly set as the target water level, assuming, for example, that the low-combustion stage has been continuously maintained for a certain period of time and that the conductivity of the water in the downcomer pipe 7 has not changed based on the conductivity calculated by the conductivity calculation unit 9. This allows for a feedwater control process that facilitates the transfer of boiler water from the boiler body 2 to the separator. This allows for a conductivity close to the actual conductivity of the boiler water in the boiler body (i.e., the boiler water conductivity can be calculated as accurately as possible), allowing for appropriate processing, such as the discharge of boiler water. The specific water level is defined as, for example, approximately 10 mm higher than the low-combustion reference water level. The feedwater control process in this embodiment is described in detail below.

[0023] <About water supply control treatment> 2 is a flowchart for explaining an example of the water supply control process. The control unit 10 starts the water supply control process at regular intervals (for example, every second), and executes the water supply control process once started until it is finished.

[0024] In step S01, it is determined whether the operation time (continuous operation time) during the low combustion stage has reached a predetermined time (e.g., one hour), and whether the conductivity of the water in downcomer pipe 7 has not changed over the predetermined time based on the conductivity calculated by conductivity calculation unit 9. An example in which the predetermined time is the same as a fixed time will be described. Therefore, in step S01, it is determined whether the operation time during the low combustion stage is equal to or longer than the predetermined time, and whether the conductivity has not changed over the predetermined time since the change. In step S01, when the operation time during the low combustion stage has not reached the predetermined time (e.g., when the low combustion stage is in operation but the predetermined time has not elapsed, or when the medium or high combustion stage is in operation), and it is not determined based on the conductivity calculated by conductivity calculation unit 9 that the conductivity of the water in downcomer pipe 7 has not changed over the predetermined time (e.g., when the low combustion stage is in operation but the predetermined time has not elapsed or the conductivity is changing, or when the medium or high combustion stage is in operation), the process proceeds to step S03. In step S03, it is determined whether a specific water level is set as the target water level. If it is determined in step S03 that a specific water level is not set as the target water level (for example, if any of the low, medium, or high fuel reference water levels is set), the process proceeds to step S08.

[0025] In step S08, it is determined whether the combustion stage has changed in response to the load (steam load). This determination is made regardless of the water level set as the target water level (for example, even if a specific water level is set as described below). If it is not determined in step S08 that the combustion stage has changed in response to the load, in step S10, the water supply amount (water supply pump 22) is controlled so that the water level in the water pipe 12 becomes the currently set target water level, and the water supply control process ends. As a result, water supply control is performed so that the water level becomes the reference water level corresponding to the controlled combustion stage.

[0026] On the other hand, if it is determined in step S08 that the combustion stage has changed in response to the load, the reference water level determined based on the changed combustion stage is set as the target water level in step S09. As a result, in step S10, water supply control is performed so that the reference water level corresponds to the changed combustion stage.

[0027] Returning to step S01, if it is determined in step S01 that the operating time in the low combustion stage has reached a certain time and that the conductivity of the water in downcomer pipe 7 has not changed over the predetermined time based on the conductivity calculated by conductivity calculation unit 9, the process proceeds to step S02A, where it is determined whether the low fuel reference water level is set as the target water level. If it is determined in step S02A that the low fuel reference water level is set as the target water level, the process proceeds to step S02B.

[0028] When the operating time in the low combustion stage reaches a certain time and the conductivity of the water in the downcomer pipe 7 has not changed over the predetermined time based on the conductivity calculated by the conductivity calculation unit 9, boiler water has not been removed, and there is a risk that the actual conductivity of the boiler water may differ significantly from the conductivity calculated by the conductivity calculation unit 9. Therefore, in step S02B, a specific water level higher than the low combustion reference water level is set as the target water level in the water pipe 12, and the process proceeds to step S08. Thus, when the determinations in steps S01 and S02A are YES, the specific water level is forcibly set in step S02B regardless of the conductivity value (e.g., high or low) calculated by the conductivity calculation unit 9. Note that when the specific water level is set, the operating time in the low combustion stage and the time during which the conductivity has not changed are reset. Furthermore, even after the specific water level is set, the combustion stage remains the low combustion stage.

[0029] In step S08 immediately after step S02B, it is not determined that the combustion stage has changed, and the process proceeds to step S10, where water supply control is performed so that the water level in the water pipe 12 reaches a specific water level. As a result, even in a low combustion stage, boiler water is easily carried out to the outside of the main body 2, boiler water flows into the separator 5, and a conductivity close to the actual conductivity of the boiler water in the main body can be calculated, allowing predetermined processes such as boiler water discharge to be performed appropriately. In addition, it is possible to prevent the boiler water from becoming too concentrated. The water outside the main body 2 that flows into the separator 5 is an example of water corresponding to the boiler water.

[0030] When the specific water level is set, the operating time in the low combustion stage and the time during which the conductivity remains unchanged are reset as described above. Therefore, step S01 is determined as NO, and step S03 is determined as YES, and the process proceeds to step S04. In step S04, it is determined whether the conductivity of the water in the downcomer pipe 7 has changed (e.g., compared to the conductivity before the specific water level was set) based on the conductivity calculated by the conductivity calculation unit 9. In step S04, it is indirectly determined whether boiler water has actually been delivered to the separator 5 side based on whether the conductivity of the water in the downcomer pipe 7 has changed. If it is determined in step S04 that the conductivity in the downcomer pipe 7 has changed, it is assumed that boiler water has actually been delivered to the separator 5 side, and in step S05, the low-combustion reference water level is set as the target water level in the water pipe 12. Thereafter, the process proceeds to step S08, and the feedwater amount is controlled in step S10 according to the flow described above, and the feedwater control process ends. In this way, if the conductivity calculated by the conductivity calculation unit 9 changes and it is estimated that boiler water has been taken out of the boiler body 2, the setting of the specific water level as the target water level is canceled. This makes it possible to prevent steam with a low dryness level from being supplied as much as possible.

[0031] On the other hand, if it is not determined in step S04 that the conductivity of the water in the downcomer pipe 7 has changed, the process proceeds to step S08, and the water feed rate is controlled in step S10 according to the flow described above, and the water feed control process ends. Note that in step S08, even when a specific water level is set, it is determined whether the combustion stage has changed depending on the load. Therefore, even when a specific water level is set, if the combustion stage changes to a medium combustion stage or the like depending on the load, a reference water level corresponding to the changed combustion stage is set in step S09, and the setting of the specific water level is canceled.

[0032] Furthermore, if, in step S01, the operating time in the low combustion stage has reached a certain time, and it is determined that the conductivity of the water in the downcomer pipe 7 has not changed over the predetermined time based on the conductivity calculated by the conductivity calculation unit 9, and it is not determined in step S02A that the low combustion reference water level has been set as the target water level, then the specific water level has already been set, so the process proceeds directly to step S08, and the feedwater amount is controlled in step S10 according to the flow described above, and the water feed control process ends. In other words, if the specific water level has already been set as the target water level, the specific water level will remain set as the target water level until the conductivity calculated by the conductivity calculation unit 9 changes or the combustion stage changes.

[0033] In this embodiment, as shown in steps S01, S02A, and S02B of FIG. 2 , if the boiler continues to operate at a low combustion stage (i.e., a low combustion rate) for a certain period of time or longer, and the conductivity of the water in the downcomer pipe 7 based on the conductivity calculated by the conductivity calculation unit 9 has not changed over a predetermined period of time, and there is a risk that boiler water is not being transported to the separator 5, the target water level in the water pipe 12 is set to a specific water level higher than the reference water level, regardless of the conductivity value (e.g., high or low) calculated by the conductivity calculation unit 9. This makes it easier for boiler water to be transported outside the boiler body 2. As a result, for example, the conductivity calculation unit 9 can more easily calculate the actual boiler water conductivity (calculating the actual boiler water conductivity as accurately as possible), and predetermined processes, such as boiler water discharge, can be appropriately performed based on the conductivity. Furthermore, excessive boiler water concentration can be prevented.

[0034] 2, even if a specific water level has been set, if the combustion stage changes from the low combustion stage to the medium combustion stage or the high combustion stage depending on the load, and boiler water is more likely to be taken out of the boiler body 2 than when it was in the low combustion stage, the reference water level based on the combustion stage after the change is set as the target water level, and the setting of the specific water level is canceled, regardless of the value of the conductivity calculated by the conductivity calculation unit 9. This makes it possible to prevent excessive boiler water from being taken out and steam with low dryness from being supplied as much as possible.

[0035] 2, if the conductivity of the water in the downcomer pipe 7 changes when the specific water level is set, the setting of the specific water level is canceled and the reference water level based on the low combustion stage is set as the target water level. This makes it possible to prevent as much boiler water as possible from being taken out of the boiler body 2, which would result in an extreme drop in combustion efficiency.

[0036] The present invention is not limited to the above-described embodiment, and various modifications and applications are possible. Modifications of the above-described embodiment that can be applied to the present invention will be described below.

[0037] In the above embodiment, the specific water level is set as a water level higher than the low-combustion standard water level. However, as shown in FIG. 1, a special water level higher than the specific water level may be set in addition to the specific water level. For example, during the low-combustion stage when the specific water level is set, if a predetermined time has elapsed without the conductivity of the water in the downcomer pipe 7 changing, the special water level is forcibly set as the target water level, thereby performing water supply control processing to further facilitate the transfer of boiler water from the boiler body 2 to the separator. Note that the special water level is set, for example, to a water level approximately 10 mm higher than the specific water level.

[0038] FIG. 3 is a flowchart illustrating an example of a water supply control process when a special water level is set in addition to the above embodiment. Note that the same parts as those in the above embodiment are designated by the same reference numerals, and descriptions thereof will not be repeated. In step S01, if the operation time in the low combustion stage has not reached a certain time, and it is not determined that the conductivity of the water in the downcomer pipe 7 has not changed over a predetermined time period based on the conductivity calculated by the conductivity calculation unit 9, the process proceeds to step S03A. In step S03A, it is determined whether a special water level or a special water level has been set. If it is not determined in step S03A that a special water level or a special water level has been set as the target water level, the process proceeds to step S08A.

[0039] In step S08A, it is determined whether the combustion stage has changed in response to the load (steam load). This determination is made regardless of the water level set as the target water level (for example, even if not only a specific water level but also a special water level is set). If it is not determined in step S08A that the combustion stage has changed in response to the load, the water feed rate is controlled in step S10, and the water feed control process is terminated. On the other hand, if it is determined in step S08A that the combustion stage has changed in response to the load, the process proceeds to step S09, the water feed rate is controlled in step S10, and the water feed control process is terminated.

[0040] Furthermore, if the specific water level has already been set, and if it is determined in step S01 that the plant is in the low combustion stage and the operating time in that stage has reached a certain time, and the conductivity calculated by the conductivity calculation unit 9 indicates that the conductivity of the water in the downcomer pipe 7 has not changed over the predetermined time, and the process proceeds to step S02A, it is determined that the low combustion reference water level has not been set as the target water level, and the process proceeds to step S02C, where a special water level higher than the specific water level is set as the target water level. Then, the process proceeds to step S08A, and in step S10, water supply control is performed according to the above-described flow so that the water level in the water pipe 12 reaches the special water level, and the water supply control process ends. In this way, even after setting the target water level to the specific water level, if the operating time in the low combustion stage reaches a certain time, the conductivity calculated by the conductivity calculation unit 9 does not change over a predetermined time (when the same conditions as those for setting the specific water level are met in Figure 3), and it is estimated that boiler water has not yet been removed from the boiler body 2, a special water level higher than the specific water level is set. This more reliably ensures that boiler water is removed from the boiler body 2. As a result, the conductivity calculation unit 9 can more easily calculate the actual boiler water conductivity, preventing the boiler water from becoming overly concentrated. Note that when the special water level is set, the operating time in the low combustion stage and the time during which the conductivity does not change are reset. Furthermore, even after the special water level is set, the combustion stage remains the low combustion stage.

[0041] On the other hand, if it is determined in step S03A that the specific water level or special water level is set as the target water level, the process proceeds to step S04. If it is not determined in step S04 that the conductivity of the water in the downcomer pipe 7 has changed, the process proceeds to step S08A, and the water feed rate is controlled in step S10 according to the flow described above, and the water feed control process ends. In other words, if the special water level has already been set as the target water level, the special water level will remain set as the target water level until the conductivity calculated by the conductivity calculation unit 9 changes or the combustion stage changes.

[0042] On the other hand, if it is determined in step S04 that the conductivity of the water in the downcomer pipe 7 has changed, the process proceeds to step S05A. In step S05A, it is determined whether a specific water level has been set as the target water level. If it is not determined in step S05A that a specific water level has been set as the target water level, that is, if a special water level has been set as the target water level, the process proceeds to S05C, where the specific water level is set as the target water level in the water pipe 12. Thereafter, the process proceeds to step S08A, and the water supply amount is controlled in step S10 according to the flow described above, and the water supply control process ends.

[0043] Furthermore, if it is determined in step S05A that a specific water level has been set as the target water level, the process proceeds to S05B, where the low-fuel reference water level is set as the target water level, and the process proceeds to step S08A. The feedwater volume is controlled in step S10 according to the flow described above, and the water feed control process ends. Thus, even if a specific water level is set and it is determined in step S04 that the conductivity has changed, the specific water level is first set, and then the low-fuel reference water level is set in stages according to the change in conductivity. However, this is not limiting, and if it is determined in step S04 that the conductivity has changed when the special water level is set, the low-fuel reference water level may be set without going through stages.

[0044] In addition, in step S08A, even if a special water level or the like is set, if the load changes to a medium combustion stage or the like, the setting of the special water level or the like is canceled by setting a standard water level corresponding to the combustion stage after the change in step S09.

[0045] In the above embodiment, the case where the predetermined time during which the conductivity of the water in the downcomer pipe 7 remains unchanged, which is one of the conditions for setting the specific water level, is the same as the fixed time during which the fuel is operated in the low combustion stage (S01), is exemplified. However, the predetermined time during which the conductivity of the water in the downcomer pipe 7 remains unchanged, which is one of the conditions for setting the specific water level, may be different from the fixed time during which the fuel is operated in the low combustion stage. For example, the fixed time during which the conductivity of the water in the downcomer pipe 7 remains unchanged, which is determined to be the condition satisfied, may be set to be shorter than the fixed time (e.g., one hour) during which the fuel is operated in the low combustion stage. In this case, the condition for setting the specific water level may be satisfied if the conductivity of the water in the downcomer pipe 7 changes during the initial stage of the transition to the low combustion stage, but the conductivity of the water in the downcomer pipe 7 remains unchanged for the most recent fixed time (e.g., 10 minutes) after the fixed time during which the fuel is operated in the low combustion stage has elapsed.

[0046] In addition, although the example has been described in which the fixed time, which is the operating time in the low combustion stage among the conditions for setting the specific water level, and the fixed time, which is the operating time in the low combustion stage among the conditions for setting the special water level, are the same, this is not limiting, and different times may be set for both. For example, the fixed time, which is the operating time in the low combustion stage among the conditions for setting the special water level, may be set to a time shorter than the fixed time (1 hour) that is longer than the average time required, under normal circumstances, for the water level in the water pipe 12 to reach the specific water level and for the boiler water to be removed outside after the target water level is set to the specific water level.

[0047] Furthermore, as with the fixed time in step S01 described above, an example has been described in which the predetermined time during which the conductivity of the water in the downcomer pipe 7 does not change, which is one of the conditions for setting a specific water level, and the predetermined time during which the conductivity of the water in the downcomer pipe 7 does not change, which is one of the conditions for setting a special water level, are the same time, but this is not limited to this, and different times may be set for both.For example, the predetermined time during which the conductivity of the water in the downcomer pipe 7 does not change, which is one of the conditions for setting a special water level, may be set to be shorter than the predetermined time during which the conductivity of the water in the downcomer pipe 7 does not change, which is one of the conditions for setting a specific water level.

[0048] In the above embodiment, the "low combustion stage" with the lowest combustion amount, as shown in step S01 of FIG. 2, is used as an example of a "predetermined combustion stage where the combustion amount is equal to or less than a predetermined amount" for which a water level higher than the reference water level can be set by satisfying the conditions for setting the specific water level, etc. However, this is not limited to this, and the "low combustion stage" and "medium combustion stage" may also be used as long as the combustion amount is equal to or less than the amount at which boiler water boils slowly and therefore does not easily flow into, for example, separator 5. In this case, if the operating time in the medium combustion stage reaches a certain time or more and the conductivity does not change, a water level higher than the medium combustion reference water level is set as the target water level in step S02B. Note that in the above embodiment, the "medium combustion stage" and "high combustion stage" are used as examples of a "combustion stage where the combustion amount is greater than a predetermined amount." However, as described above, if the "predetermined combustion stage where the combustion amount is equal to or less than a predetermined amount" is the "low combustion stage" or the "medium combustion stage," the "combustion stage where the combustion amount is greater than a predetermined amount" becomes the "high combustion stage."

[0049] In the above embodiment, an example has been described in which the boiler apparatus 1 is configured as a so-called four-position control boiler that can be controlled to any one of a low combustion stage, a medium combustion stage, a high combustion stage, and a combustion stop stage. However, the boiler that configures the boiler apparatus 1 is not limited to this, and for example, in addition to a four-position control boiler, it may also be a so-called three-position control boiler that can be controlled to any one of a low combustion stage, a high combustion stage, and a combustion stop stage. In the case of a three-position control boiler, the combustion stage in which the combustion amount is equal to or less than a predetermined amount is the low combustion stage, and the combustion stage in which the combustion amount is greater than the predetermined amount is the high combustion stage.

[0050] The boiler constituting the boiler apparatus 1 may be, for example, a boiler whose load factor can be proportionally controlled between 10% and 100%. In this case, the predetermined combustion amount serving as the criterion in step S01 of FIG. 2 may be, for example, the combustion amount at which the load factor is 20%, and the process may proceed to step S02A when the operation time at 20% or less reaches a certain time. In this case, when the operation time at 10% load factor reaches or exceeds the certain time (and the conductivity has not changed over the certain time), the process corresponding to step S02B sets the target water level to a water level higher than the reference water level based on 10%. When the operation time at 20% load factor reaches or exceeds the certain time (and the conductivity has not changed over the certain time), the process corresponding to step S02B sets the target water level to a water level higher than the reference water level based on 20%.

[0051] In the above embodiment, the difference between the reference water level and the specific water level, and the difference between the specific water level and the special water level described in the modified example, are both 10 mm. However, the difference between the reference water level and the specific water level and the difference between the specific water level and the special water level are not limited to this as long as they are water level differences that make it easier for boiler water to be carried out of the boiler body 2 by raising the target water level, and may be, for example, any level difference between 5 mm and 15 mm. Furthermore, both the specific water level and the special water level may be water levels that are below the dryness fraction limit water level corresponding to the combustion stage (e.g., the low combustion stage), or only the specific water level may be below the dryness fraction limit water level and the special water level may be a water level that is lower than the dryness fraction limit water level, while the special water level may be a water level higher than the dryness fraction limit water level.

[0052] In the above embodiment, one hour is exemplified as the certain time for determining whether the operating time in the low combustion stage in step S01 has reached the certain time, but the certain time may be two hours, for example. Furthermore, the certain time in step S01 may be, for example, shorter than the average time required for boiler water to become highly concentrated in the low combustion stage. In a boiler that issues an alarm to notify the user of a possible malfunction of the conductivity calculation unit 9 and prompt inspection when the conductivity calculated by the conductivity calculation unit 9 has not changed (remained constant) for a specific time (e.g., one hour), the certain time in step S01 is preferably set to a time shorter than the specific time (e.g., 50 minutes). As a result, when it is determined in step S01 that a certain time has been reached and a specific water level is set in step S02, boiler water becomes more likely to be taken out of the boiler body 2, and if the conductivity calculation unit 9 is not malfunctioning, the conductivity will change and an alarm can be avoided.However, if the conductivity does not change even after the specific water level is set, there is a higher possibility that the conductivity calculation unit 9 is malfunctioning, which can improve the accuracy of the alarm notification.

[0053] In addition, in a boiler that issues an alarm to notify a user of the possibility of a malfunction of the conductivity calculation unit 9 and to have the unit inspected, if the conductivity calculated by the conductivity calculation unit 9 does not change even after a predetermined time has elapsed since the specific water level was set in FIG. 2 (for example, a predetermined time that is longer than the average time required for the water level in the water pipe 12 to reach the specific water level and for the boiler water to be taken outside under normal circumstances), the conductivity calculation unit 9 may be malfunctioning, and a notification to that effect may be issued. Similarly, in the case of FIG. 3, if the conductivity calculated by the conductivity calculation unit 9 does not change even after a predetermined special time has elapsed since the special water level was set (for example, a predetermined time that is longer than the average time required for the water level in the water pipe 12 to reach the special water level and for the boiler water to be taken outside under normal circumstances), the conductivity calculation unit 9 may be malfunctioning, and a notification to that effect may be issued. As a result, when it is determined in step S01 that a certain time has been reached and a specific water level or the like is set in step S02B in FIG. 2 and step S02C in FIG. 3, an alarm is sounded when the conductivity does not change even though the boiler water is in a state where it is easy for the boiler water to be taken out of the boiler main body 2, thereby suggesting at an appropriate time that the conductivity calculation unit 9 may be malfunctioning.

[0054] In the above embodiment, an example was described in which the conditions for setting a specific water level include the conductivity not changing over a predetermined period of time, regardless of the value of the conductivity calculated by the conductivity calculation unit 9. However, the conditions are not limited to this, and may include the range of change in conductivity being limited to a predetermined range based on the history of conductivity within a predetermined period of time (the conductivity not changing beyond the predetermined range).

[0055] In the above embodiment, an example has been described in which it is determined in step S04 of Figure 2 whether the conductivity of the water in the downcomer pipe 7 has changed, but this is not limiting, and it may be determined, for example, whether the conductivity of the water in the downcomer pipe 7 has changed by a predetermined value (e.g., 50 S / m) or more.

[0056] In the above embodiment, as shown in steps S01 and S02B of FIG. 2 , an example was described in which the target water level is set to a water level higher than the reference water level when operation in the low combustion stage, where the boiler combustion amount is low, has continued for a certain period of time or more and the conductivity of the water in downcomer pipe 7, based on the conductivity calculated by conductivity calculation unit 9, has not changed over the predetermined period of time. However, this is not limited to this. When operation in the low combustion stage, where the boiler combustion amount is low, has continued for a certain period of time or more, the target water level may be set to a water level higher than the reference water level even if the conductivity of the water in downcomer pipe 7 has changed. Furthermore, when the conductivity of the water in downcomer pipe 7, based on the conductivity calculated by conductivity calculation unit 9, has not changed over the predetermined period of time in the low combustion stage, the target water level may be set to a water level higher than the reference water level even if operation in the low combustion stage has not continued for a certain period of time.

[0057] In the above embodiment, the conductivity sensor (sensor that detects resistance) included in the conductivity calculation unit 9 is provided in the downcomer pipe 7, enabling calculation of the conductivity of the water in the downcomer pipe 7. However, the conductivity sensor included in the conductivity calculation unit 9 may be provided in the lower header 11, enabling calculation of the conductivity of the water in the lower header 11. Water that is taken outside the main body 2 and flows into the lower header 11 through the separator 5 is an example of boiler water. In this case, the conductivity sensor included in the conductivity calculation unit 9 may be provided adjacent to the connection between the lower header 11 and the downcomer pipe 7, for example. This makes it difficult to confuse freshly supplied water with water that has passed through the downcomer pipe 7, making it possible to calculate the conductivity of the water that has flowed from the downcomer pipe 7 into the lower header 11. As a result, the actual boiler water conductivity can be calculated as accurately as possible.

[0058] In the above embodiment, an example of a boiler apparatus 1 having one boiler body 2 has been described. However, the present invention can also be applied to a multi-boiler installation system in which multiple boilers are installed. In a multi-boiler installation system, a number control method is employed to control the number of operating boilers according to the load situation. In this number control method, an operational priority is preset for each boiler body. While a boiler body with a higher priority is operating in a high combustion phase, a boiler body with a lower priority may continue to wait in a low combustion phase. In this case, for a boiler body that continues to wait in the low combustion phase, the boiler water may boil slowly, as shown in the above embodiment, and the conductivity may not be accurately determined. By applying the present invention to this boiler body, it becomes possible to accurately determine whether the boiler water in the boiler body is concentrated.

[0059] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0060] 1. Boiler equipment 2 Boiler body 3. Blower 4. Connecting pipe 5 Separator 6 Steam piping 7 Downpipe 8 Blow piping 8a Blow valve 9 Conductivity calculation section 10 Control Unit 11 Bottom Header 12 Water pipe 13 Upper Header 20 Burner 21 Fuel supply line 21a Fuel adjustment valve 22 Water supply pump 23 Check valve 24 Water supply piping

Claims

1. a main body that heats boiler water by burning fuel to generate steam; a combustion stage control unit that controls the combustion amount to one of a plurality of combustion stages having different combustion amounts; a water supply control unit that controls the amount of water supplied to the main body so that the boiler water level becomes a reference water level determined based on the combustion stage controlled by the combustion stage control unit; a conductivity calculation unit that can calculate the conductivity of water according to the boiler water, The water supply control unit performs an upper water level control to raise the boiler water level to a level higher than a reference water level determined based on the predetermined combustion stage when the combustion amount is controlled to a predetermined amount or less among the plurality of combustion stages continuously for a certain period of time or more and the conductivity calculated by the conductivity calculation unit does not change.

2. The boiler according to claim 1 , wherein the water supply control unit cancels the upper water level control when the combustion stage control unit controls the combustion amount to a combustion stage exceeding the predetermined amount.

3. 3. The boiler according to claim 1, wherein the water supply control unit cancels the top water level control when the conductivity calculated by the conductivity calculation unit changes.

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