Boiler control system

Abstract

This invention provides a boiler control system that can continuously control the combustion rate while avoiding unintended combustion shutdowns of the boiler. [Solution] The boiler control system comprises a plurality of boilers, a steam header into which the steam generated by each boiler is collected, steam piping connecting each boiler to the steam header, and a number control device that controls the combustion rate of each boiler based on the steam pressure in the steam header. Each boiler has a boiler control unit, which calculates the amount of combustion required for the boiler based on the steam pressure of the corresponding boiler, obtains a predetermined upper limit for the combustion rate of the boiler, and prevents the combustion rate from increasing further when the combustion rate of the boiler reaches the upper limit.

Description

Technical Field

[0001] This application relates to a boiler control system inside a boiler when controlling the state of a boiler outside the boiler, such as a unit control device for controlling a plurality of boilers.

Background Art

[0002] Conventionally, the combustion amount control of a boiler is performed, for example, by PID control or the like so that the steam pressure of the boiler itself is maintained at a predetermined value by a control device provided for each boiler. On the other hand, in recent years, as disclosed in Patent Documents 1 and 2 for example, the combustion amount control (unit control) of each boiler is mainly performed by a unit control device so that the pressure of a steam header to which steam generated by a plurality of boilers is collected via a steam pipe is maintained at a predetermined value.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, a pressure difference (pressure loss) occurs between the pressure of the steam header that is the control target and the pressure of each boiler. This pressure difference varies depending on the state of the steam pipe (for example, length, diameter, or bending, etc.) and the steam flow rate (in other words, the combustion amount of the boiler). For example, as shown in FIGS. 7A and 7B, as the steam load increases, the pressure difference between the pressure of the steam header and the pressure of each boiler tends to increase in the region RL of FIG. 7A. Due to such a pressure difference and a response delay regarding the steam pressure, there has been a current situation where it is difficult to maintain the steam pressure in the steam header at the target value.

[0005] Furthermore, boilers are equipped with a safety function that stops combustion when the steam pressure rises excessively. When controlling the boiler's combustion rate with the steam pressure in the steam header as the control target, the steam pressure in the boiler may unintentionally rise to the safety function activation point due to the aforementioned pressure difference. As a result, the boiler may suddenly stop combustion unintentionally, leading to a drop in the steam header pressure or control hunting, and in the worst case, affecting the load-side equipment. Such situations occur not only when the combustion rate increases, but also when the steam load decreases rapidly. This is due to the response delay of the steam header pressure control. As a measure to address these issues, it is conceivable to perform operational control for each boiler without performing the above-mentioned multi-boiler control. However, due to the aforementioned pressure loss, the steam pressure in the steam header that is to be used as the control target is not the same as the steam pressure in each boiler, making it difficult to maintain the steam pressure in the steam header at the target value.

[0006] The purpose of this application is to provide a boiler control system that can perform continuous combustion rate control while avoiding unintended combustion shutdowns of the boiler. [Means for solving the problem]

[0007] This application provides a boiler control system comprising: a plurality of boilers; a steam header from which steam generated by each boiler is collected; steam piping connecting each boiler to the steam header; and a unit control device that controls the combustion rate of each boiler based on the steam pressure in the steam header, wherein each boiler has a boiler control unit, and the boiler control unit calculates the amount of combustion required for the boiler based on the steam pressure of the corresponding boiler, obtains a predetermined upper limit of combustion rate for the boiler, and prevents the combustion rate of the boiler from increasing further when it reaches the upper limit of combustion rate. [Effects of the Invention]

[0008] This application provides a boiler control system that can perform continuous combustion rate control while avoiding unintended combustion shutdowns of the boiler. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a block diagram showing a schematic configuration of a boiler control system according to one embodiment. [Figure 2] Figure 2 is a block diagram showing an example of the configuration of the boiler control unit in each boiler shown in Figure 1. [Figure 3] Figure 3A is a graph showing an example of the change in steam load over time and an example of the change in combustion rate controlled by the number control device over time, while Figure 3B is a graph showing an example of the change in boiler pressure over time and an example of the change in steam header pressure over time. [Figure 4] Figure 4A is a graph showing an example of the change over time of the combustion rate controlled by the unit control device and an example of the change over time of the calculated combustion rate upper limit, while Figure 4B is a graph showing an example of the change over time of the boiler's combustion rate. [Figure 5] Figure 5A is an example of a line table, and Figure 5B is an example of a graph showing the relationship between boiler pressure and the upper limit of combustion rate corresponding to that pressure. [Figure 6] Figure 6A is a graph showing an example of the change over time of the combustion rate controlled by the unit control device and an example of the change over time of the acquired combustion rate upper limit, while Figure 6B is a graph showing an example of the change over time of the boiler's combustion rate. [Figure 7] Figure 7A is a graph showing an example of the time-dependent changes in the steam header pressure and the pressure of each boiler, and Figure 7B is a graph showing an example of the time-dependent changes in the combustion rate controlled by the steam load and the number of boilers control device. [Modes for carrying out the invention]

[0010] The boiler control system according to the embodiments of this application will be described below with reference to the drawings. The boiler control system described below is only one embodiment of this application. Therefore, this application is not limited to the following embodiments, and additions, deletions, and modifications are possible without departing from the spirit of this application.

[0011] (First Embodiment) Figure 1 is a block diagram showing the schematic configuration of the boiler control system 100 according to this embodiment. As shown in Figure 1, the boiler control system 100 includes a steam header 1, a pressure sensor 2, a unit control device 3, a plurality of boilers 4, a plurality of pressure sensors 5, a plurality of steam pipes 6, and a supply pipe 7.

[0012] Multiple boilers 4, namely N boilers 4, are provided. Specifically, in Figure 1, examples of N boilers 4 include boiler 1 4a, boiler 2 4b, boiler 3 4c, ..., and boiler N 4n. The number of boilers 4 can be changed as appropriate. Boilers 4 heat water to generate steam using a combustion device (not shown).

[0013] Steam piping 6 connects each boiler 4 to the steam header 1. Steam piping 6 is provided corresponding to each boiler 4. Multiple steam piping 6, namely N steam piping 6, are provided. Specifically in Figure 1, steam piping 6a, 6b, 6c, ..., 6n are shown as examples of N steam piping 6. Steam piping 6a connects boiler 1 4a to steam header 1. Steam piping 6b connects boiler 2 4b to steam piping 6a, thereby connecting boiler 2 4b to steam header 1. Steam piping 6c connects boiler 3 4c to steam piping 6a, thereby connecting boiler 3 4c to steam header 1. Steam piping 6n connects boiler N 4n to steam piping 6a, thereby connecting boiler N 4n to steam header 1. In addition, supply piping 7 is connected to steam header 1. In the above configuration, the steam generated in each boiler 4 is collected in the steam header 1, and the collected steam is then supplied from the steam header 1 to an external supply destination via the supply piping 7.

[0014] The pressure sensor 5 is connected to the boiler 4. The pressure sensor 5 is installed in accordance with the boiler 4. Multiple pressure sensors 5, namely N pressure sensors 5, are provided. Specifically in Figure 1, pressure sensors 5a, 5b, 5c, ..., 5n are shown as examples of N pressure sensors 5.

[0015] The pressure sensor 5a is connected to the No. 1 boiler 4a, detects the steam pressure in the No. 1 boiler 4a, and transmits the detection result to the boiler control unit 40 described later. Details of the boiler control unit 40 will be described later. Also, the pressure sensor 5b is connected to the No. 2 boiler 4b, detects the steam pressure in the No. 2 boiler 4b, and transmits the detection result to the boiler control unit 40. The pressure sensor 5c is connected to the No. 3 boiler 4c, detects the steam pressure in the No. 3 boiler 4c, and transmits the detection result to the boiler control unit 40. The pressure sensor 5n is connected to the No. N boiler 4n, detects the steam pressure in the No. N boiler 4n, and transmits the detection result to the boiler control unit 40.

[0016] The pressure sensor 2 is connected to the steam header 1, detects the steam pressure in the steam header 1, and transmits the detection result to the unit control device 3.

[0017] The unit control device 3 can be constituted by a microcontroller including a CPU (Central Processing Unit) and a memory (ROM (Read Only Memory) and RAM (Random Access Memory)) storing a program, or an ASIC (Application Specific Integrated Circuit) or the like. The unit control device 3 has a PID (Proportional Integral Derivative) control unit 3a. The unit control device 3 controls the startup and stop of each boiler 4. In this case, the unit control device 3 determines the operation priority order for each boiler 4, and executes control of starting and stopping a predetermined number of boilers 4 (that is, unit control) based on the operation priority order. Also, the PID control unit 3a controls the combustion amount of each boiler 4 based on the steam pressure in the steam header 1 received from the pressure sensor 2.

[0018] Next, FIG. 2 is a block diagram showing an example of the configuration of the boiler control unit 40 in each boiler 4 of FIG. 1. As shown in FIG. 2, the boiler 4 has a boiler control unit 40. The boiler control unit 40 can be constituted by a microcontroller including a CPU and a memory (ROM and RAM) storing a program, or an ASIC or the like. The boiler control unit 40 has a combustion amount upper limit value acquisition unit 41, a PID calculation unit 42, a low selector 43, a switch 44, and a storage unit 45.

[0019] The combustion amount upper limit value acquisition unit 41 acquires the upper limit value of the combustion amount in the boiler 4. Specifically, the combustion amount upper limit value acquisition unit 41 starts acquiring the upper limit value of the combustion amount of the boiler 4 when the steam pressure of the boiler 4 is lower than a predetermined safety function operating pressure. In the present embodiment, the combustion amount upper limit value acquisition unit 41 acquires the combustion amount upper limit value by calculation based on the steam pressure of the boiler 4 and the above-mentioned safety function operating pressure. Details of the calculation of the combustion amount upper limit value will be described later.

[0020] The PID calculation unit 42 calculates the combustion amount (first combustion amount) required in the boiler 4 based on the steam pressure in the boiler 4 detected by the pressure sensor 5. Then, the PID calculation unit 42 outputs a signal regarding the first combustion amount to the switch 44. The first combustion amount is the combustion amount controlled based on the normal boiler pressure when not in unit control.

[0021] The low selector 43 receives a signal regarding the combustion amount upper limit value output by the combustion amount upper limit value acquisition unit 41 and a signal regarding the combustion amount (that is, the combustion amount in unit control) output by the PID control unit 3a of the unit control device 3. Then, the low selector 43 outputs a signal regarding the second combustion amount, which is the smaller of the combustion amount upper limit value and the combustion amount in unit control, to the switch 44 as the second combustion amount. The second combustion amount is a combustion amount different from the first combustion amount and is the combustion amount during the execution of unit control.

[0022] The switch 44 sets either the first or second combustion rate described above as the combustion rate for the boiler 4. In this case, the switch 44 normally switches to the first fuel rate and switches to the second combustion rate when the number of boilers is controlled.

[0023] The storage unit 45 stores various information and also pre-stores a polyline table Tf, described later, which stores the steam pressure of the boiler 4 and the combustion rate upper limit corresponding to that steam pressure. The combustion rate upper limit acquisition unit 41 can acquire the combustion rate upper limit corresponding to the steam pressure of the boiler 4 by reading it from the polyline table Tf, instead of acquiring the combustion rate upper limit by calculation. Further details about the polyline table Tf will be explained in the second embodiment.

[0024] Next, the process of obtaining the combustion rate upper limit through calculation will be explained. Figure 3A is a graph showing an example of the change in steam load over time and an example of the change in the combustion rate controlled by the unit control device 3 over time, and Figure 3B is a graph showing an example of the change in the pressure of boiler 4 over time and an example of the change in the pressure of steam header 1 over time. Furthermore, Figure 4A is a graph showing an example of the change in the combustion rate controlled by the unit control device 3 over time and an example of the change in the calculated combustion rate upper limit over time, and Figure 4B is a graph showing an example of the change in the combustion rate of boiler 4 over time. Note that the change in the combustion rate controlled by the unit control device 3 shown in Figure 3A is consistent with the change in the combustion rate controlled by the unit control device 3 over time shown in Figure 4A.

[0025] Figure 3A shows the change in steam load over time and the change in combustion rate controlled by the unit control device 3 over time. Figure 3B shows examples of steam pressure in boiler 4 and steam pressure in steam header 1, corresponding to the steam load and combustion rate shown in Figure 3A.

[0026] In Figure 3B, pressure P1 is lower than the safety function activation pressure P2 described below, and is the pressure at which the calculation of the combustion rate upper limit begins; for example, it is 2.14 MPa. Pressure P1 can be set in advance. Pressure P2 is the safety function activation pressure; for example, it is 2.22 MPa. The safety function activation pressure is the pressure at which the safety function that forcibly stops combustion is activated when the steam pressure of the boiler 4 reaches the safety function activation pressure.

[0027] The combustion rate limit acquisition unit 41 starts calculating the combustion rate limit when the steam pressure of the boiler 4 reaches 2.14 MPa, which is an example of pressure P1. In this case, the combustion rate limit acquisition unit 41 calculates the combustion rate limit using the following formula 1. In the following formula 1, Pb is the steam pressure of the boiler 4 at the time of the calculation.

[0028] (Math 1) Upper limit of combustion rate [%] = 100 - (Pb - P1) / (P2 - P1) × 100

[0029] To illustrate with a specific example of Equation 1, at time t1, when the steam pressure Pb of boiler 4 is, for example, 2.15 MPa, the upper limit of the combustion rate is 100 - (2.15 - 2.14) / (2.22 - 2.14) × 100, which is 87.5%. Thus, Figure 4A shows the change over time of the upper limit of the combustion rate calculated using Equation 1 above, using the steam pressure of boiler 4 shown in Figure 3B. Note that in Figure 4A, 100% is shown as an example of the upper limit of the combustion rate before the calculation of the upper limit of the combustion rate begins.

[0030] However, the above formula 1 for calculating the upper limit of combustion rate is just one example and is not the only one that is applicable. The formula for calculating the upper limit of combustion rate should be based on the steam pressure of boiler 4 and the safety function activation pressure.

[0031] The low selector 43 determines the second combustion amount as the smaller of the combustion amount upper limit calculated by the combustion amount upper limit acquisition unit 41 and the combustion amount output by the PID control unit 3a of the unit control device 3. Figure 4B shows the change in this second combustion amount over time. The boiler control unit 40 controls the combustion amount of boiler 4 to achieve the second combustion amount shown in Figure 4B during unit control. As a result, the combustion amount of boiler 4 does not exceed the combustion amount upper limit, thus preventing the above-mentioned safety function from being activated.

[0032] As described above, according to the boiler control system 100 of this embodiment, when the combustion rate of the boiler 4 reaches the upper limit of the combustion rate, the combustion rate does not increase further, thus preventing the above-mentioned safety function from activating. Therefore, it becomes possible to perform continuous combustion rate control while avoiding unintended combustion shutdown of the boiler 4.

[0033] (Second Embodiment) Next, a second embodiment will be described. In the second embodiment, the same reference numerals will be used for components that are the same as or corresponding to those in the first embodiment, and redundant descriptions will be omitted unless otherwise noted.

[0034] Figure 5A is a diagram showing an example of a polyline table Tf, and Figure 5B is a graph showing an example of the relationship between the steam pressure of boiler 4 and the combustion rate upper limit corresponding to that steam pressure. Furthermore, Figure 6A is a graph showing an example of the change in combustion rate over time controlled by the unit control device 3 and an example of the change in the acquired combustion rate upper limit over time, and Figure 6B is a graph showing an example of the change in combustion rate over time of boiler 4.

[0035] In the second embodiment, instead of obtaining the combustion rate limit by calculation as in the first embodiment, the combustion rate limit acquisition unit 41 reads and obtains the combustion rate limit corresponding to the steam pressure of the boiler 4 from the polyline table Tf. The polyline table Tf corresponds to the combustion rate limit table of this application. As shown in Figure 5A, the polyline table Tf stores the steam pressure of the boiler 4 and the combustion rate limit corresponding to that steam pressure. The steam pressure and combustion rate limit shown in Figure 5A are just examples and are not limited thereto. Figure 5B is a graph of the steam pressure of the boiler 4 and the combustion rate limit in the polyline table Tf of Figure 5A.

[0036] In the second embodiment, the combustion rate upper limit acquisition unit 41 reads the combustion rate upper limit corresponding to each steam pressure of the boiler 4 from the polyline table Tf. For example, when the steam pressure of the boiler 4 is 2.13 MPa, the combustion rate upper limit acquisition unit 41 reads 80% as the combustion rate upper limit from the polyline table Tf. Figure 6A shows the change in the combustion rate upper limit in the polyline table Tf over time.

[0037] The low selector 43 then sets the second combustion amount to the smaller of the combustion amount upper limit obtained by the combustion amount upper limit acquisition unit 41 and the combustion amount output by the PID control unit 3a of the unit control device 3. Figure 6B shows the change in this second combustion amount over time. The boiler control unit 40 controls the combustion amount of boiler 4 to achieve the second combustion amount shown in Figure 6B during unit control. As a result, the combustion amount of boiler 4 does not exceed the combustion amount upper limit, thus preventing the activation of the safety function described above.

[0038] As described above, the boiler control system 100 of the second embodiment also prevents the combustion rate of the boiler 4 from increasing further when it reaches the upper limit of the combustion rate, thus avoiding the activation of the safety function described above. Therefore, it becomes possible to perform continuous combustion rate control while avoiding unintended combustion shutdown of the boiler 4.

[0039] This application is not limited to the embodiments described above, and the following modifications are possible without departing from the spirit of this application.

[0040] As mentioned above, methods for obtaining the upper limit of combustion rate include calculation using a mathematical formula or determination using a polyline table Tf, but these are merely examples. By adding a coefficient related to the pressure loss of the steam piping as a judgment factor when obtaining the upper limit of combustion rate, it is possible to calculate a more controllable upper limit of combustion rate without activating the safety function due to the pressure rise of boiler 4.

[0041] Furthermore, while the above embodiment describes a configuration in which the combustion rate of the boiler 4 is controlled by the unit control device 3, the invention is not limited to this. That is, instead of adopting a configuration in which the boiler 4 receives a command related to the combustion rate from the unit control device 3, or in combination with such a configuration, the essence of the present invention is also effectively applied to configurations in which the boiler 4 receives a combustion rate command from outside the boiler 4, such as an AI (artificial intelligence) load prediction system or remote manual instruction of the combustion rate to the boiler 4.

[0042] Furthermore, in addition to the configuration in which the PID calculation unit 42 continuously controls the combustion amount of the boiler 4 as in each of the embodiments described above (i.e., a configuration that performs continuous control from 0 to 100% by PID calculation so that the pressure value becomes a set value), there is also a multi-position control method that controls the combustion amount in steps depending on how far the pressure value is from the set value. To give an example of multi-position control, when the pressure set value is 0.70 MPa, low combustion is set to 30% when the pressure value is 0.75 MPa or higher, medium combustion is set to 65% when the pressure value is greater than 0.65 MPa but less than 0.75 MPa, and high combustion is set to 100% when the pressure value is 0.65 MPa or lower. In this multi-position control, in the above example, there are no combustion amounts other than 30%, 65%, and 100%, and the combustion amount is changed in steps. Even in the case of multi-position control as described above, the spirit of the present invention can be effectively applied. For example, in the case of four-position control of combustion stop, low combustion, medium combustion, and high combustion, if the acquired combustion amount upper limit is, for example, 100%, then the four-position control of combustion stop, low combustion, medium combustion, and high combustion is effective. Also, if the combustion amount upper limit is, for example, 75%, and the command regarding the combustion amount from the unit control device 3 is high combustion, then it is possible to set it to medium combustion. Furthermore, if the combustion amount upper limit is 25%, and the command regarding the combustion amount from the unit control device 3 is medium combustion or high combustion, then it is possible to set it to low combustion.

[0043] <Summary> In a first aspect, the present application provides a boiler control system comprising: a plurality of boilers; a steam header from which steam generated by each of the boilers is collected; steam piping connecting each of the boilers to the steam header; and a unit control device that controls the combustion rate of each boiler based on the steam pressure in the steam header, wherein each boiler has a boiler control unit, the boiler control unit calculates the amount of combustion required for the boiler based on the steam pressure of the corresponding boiler, obtains a predetermined upper limit of combustion rate for the boiler, and prevents the combustion rate of the boiler from increasing further when it reaches the upper limit of combustion rate.

[0044] With the above configuration, when the boiler's combustion rate reaches the upper limit, the combustion rate will not increase further, thus preventing the aforementioned safety function from activating. Therefore, it becomes possible to control the combustion rate continuously while avoiding unintended shutdowns of the boiler.

[0045] In a second embodiment, in the first embodiment, the boiler control unit starts obtaining the combustion limit value by calculation based on the boiler's steam pressure and the safety function activation pressure when the steam pressure of the boiler is lower than a predetermined safety function activation pressure. With this configuration, there is no need to prepare a combustion limit value table in advance that stores the boiler's steam pressure and the combustion limit value corresponding to that steam pressure, thus saving labor.

[0046] In a third embodiment, in the first embodiment, each boiler further has a storage unit that stores in advance a combustion rate limit table that stores the steam pressure of the boiler and the combustion rate limit corresponding to the steam pressure, and the boiler control unit obtains the combustion rate limit corresponding to the steam pressure of the boiler from the combustion rate limit table. With this configuration, there is no need to calculate the combustion rate limit based on the steam pressure of the boiler and the safety function activation pressure, so the processing load on the boiler control unit is reduced. [Explanation of Symbols]

[0047] 1. Steam Header 2. Pressure sensor 3 Unit Control Device 4 Boiler 5. Pressure Sensor 6. Steam piping 40 Boiler Control Unit 41. Unit for obtaining the upper limit of combustion amount 45 Storage section 100 Boiler Control System 140 boilers Tf folding table

Claims

1. Multiple boilers, A steam header collects the steam generated by each of the boilers, Steam piping connecting each of the boilers and the steam header, The system includes a control device that controls the combustion rate of each boiler based on the steam pressure in the steam header, Each of the aforementioned boilers has a boiler control unit, The boiler control unit is: Based on the steam pressure of the corresponding boiler, the amount of combustion required in the boiler is calculated. When the steam pressure of the boiler is lower than a predetermined safety function activation pressure, the acquisition of a predetermined combustion rate upper limit for the boiler is started by calculation based on the steam pressure of the boiler and the safety function activation pressure. A boiler control system that prevents the combustion rate of the boiler from increasing further when the combustion rate reaches the upper limit of the combustion rate.

2. Multiple boilers, A steam header collects the steam generated by each of the boilers, Steam piping connecting each of the boilers and the steam header, The system includes a control device that controls the combustion rate of each boiler based on the steam pressure in the steam header, Each of the boilers has a boiler control unit and a storage unit that stores in advance a combustion rate upper limit table which stores the steam pressure of the boiler and a predetermined combustion rate upper limit corresponding to the steam pressure. The boiler control unit is, Based on the steam pressure of the corresponding boiler, the amount of combustion required in the boiler is calculated. The combustion rate upper limit value corresponding to the steam pressure of the boiler is obtained from the combustion rate upper limit value table. A boiler control system that prevents the combustion rate of the boiler from increasing further when the combustion rate reaches the upper limit of the combustion rate.

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