Control method and control device for boiler

Abstract

To provide a control method and a control device for a boiler capable of suppressing an air amount of the entire boiler even when using fuel gas of which calorie variation is large and a theoretical air amount changes.SOLUTION: A control method is for a boiler that simultaneously burns a plurality of fuel gases with calories different from each other. The control method for the boiler includes a control step of controlling an air amount to be supplied to each of the fuel gases on the basis of a measurement value of an oxygen concentration in exhaust gas of the boiler and a set value of a predetermined target oxygen concentration. The control step includes a step of increasing the air amount to be supplied to the fuel gas with low calorie when the measurement value is below the set value and reducing the air amount to be supplied to the fuel gas with high calorie when the measurement value exceeds the set value.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method and a device for controlling a boiler that simultaneously burns a plurality of fuel gases having different calories. [Background technology]

[0002] Patent Document 1 describes a technology in which, in a boiler that uses multiple types of fuel gases, a target value for oxygen concentration is set taking into consideration the calorific fluctuations and mixed-firing ratio of each fuel gas, and the air ratio of each fuel gas is corrected based on the set target value for oxygen concentration. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2014-214942 A Summary of the Invention [Problem to be solved by the invention]

[0004] The technology described in Patent Document 1 corrects the air ratio of each fuel gas according to a function based on a theoretical air volume previously determined for each type of fuel gas. Therefore, when using a fuel gas with a large calorific value and a variable theoretical air volume, such as by-product gas from a steelworks, it becomes difficult to suppress the air volume of the entire boiler.

[0005] The present invention has been made in consideration of the above-mentioned problems, and its object is to provide a boiler control method and control device that can suppress the overall air volume of the boiler, even when using fuel gas that has large calorific fluctuations and a change in theoretical air volume. [Means for solving the problem]

[0006] The boiler control method of the present invention is a method for controlling a boiler that simultaneously burns multiple fuel gases having different calorie contents, and includes a control step of controlling the amount of air supplied to each fuel gas based on a measured value of the oxygen concentration in the boiler exhaust gas and a predetermined set value of a target oxygen concentration, the control step including a step of increasing the amount of air supplied to the low-calorie fuel gas when the measured value is below the set value, and decreasing the amount of air supplied to the high-calorie fuel gas when the measured value exceeds the set value.

[0007] The control step may include a step of increasing the amount of air supplied to the high-calorie fuel gas when the measured value is below the set value and the amount of air supplied to the low-calorie fuel gas is increased to a predetermined upper limit value, but the measured value is still below the set value.

[0008] The control step may include a step of reducing the amount of air supplied to the low-calorie fuel gas when the measured value exceeds the set value and the amount of air supplied to the high-calorie fuel gas is still greater than the set value even after reducing the amount of air supplied to the high-calorie fuel gas to a predetermined lower limit value.

[0009] The boiler control device of the present invention is a boiler control device that simultaneously burns multiple fuel gases each having a different calorie content, and is equipped with a control means for controlling the amount of air supplied to each fuel gas based on a measured value of the oxygen concentration in the boiler exhaust gas and a predetermined set value of a target oxygen concentration, and the control means increases the amount of air supplied to the low-calorie fuel gas when the measured value is below the set value, and decreases the amount of air supplied to the high-calorie fuel gas when the measured value exceeds the set value.

[0010] When the measured value falls below the set value, the control means increases the amount of air supplied to the low-calorie fuel gas up to a predetermined upper limit value, and if the measured value falls below the set value, the control means increases the amount of air supplied to the high-calorie fuel gas.

[0011] When the measured value exceeds the set value, the control means preferably reduces the amount of air supplied to the high-calorie fuel gas to a predetermined lower limit value, and if the measured value still exceeds the set value, the control means preferably reduces the amount of air supplied to the low-calorie fuel gas. Effect of the Invention

[0012] According to the boiler control method and control device of the present invention, even when a fuel gas with large calorific value fluctuations and a change in theoretical air volume is used, the total air volume of the boiler can be suppressed. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram showing a configuration example of a boiler to which a boiler control device according to one embodiment of the present invention is applied. [Diagram 2] FIG. 2 is a diagram showing the flow of the air ratio adjustment process when the oxygen concentration in the combustion exhaust gas is lower than the set value of the target oxygen concentration. [Diagram 3] FIG. 3 is a diagram showing the flow of the air ratio adjustment process when the oxygen concentration in the combustion exhaust gas is higher than the set value of the target oxygen concentration. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, the configuration and operation of a boiler control device according to one embodiment of the present invention will be described with reference to the drawings.

[0015] [Boiler configuration] FIG. 1 is a schematic diagram showing a configuration example of a boiler to which a boiler control device according to one embodiment of the present invention is applied. As shown in FIG. 1, the boiler 1 of this embodiment is equipped with opposed burners 2a to 2d that burn a plurality of types of fuel gases having different calories, including steelworks by-product gas. Here, the arrows shown in FIG. 1 indicate the flow of the combustion exhaust gas generated by burning the fuel gas. It is known from past experience that the combustion exhaust gas generated from the opposed burners flows through the flue forming layers according to the position of combustion. For this reason, in this embodiment, four layers of combustion exhaust gas are formed.

[0016] The boiler 1 of this embodiment includes, as a control system, oxygen concentration meters 3a-3d and a control device 4. The oxygen concentration meters 3a-3d are arranged in accordance with the positions of the four combustion exhaust gas layers along the cross-sectional height direction of the flue of the boiler 1, and measure the oxygen concentration in the combustion exhaust gas generated by burning the fuel gas for each layer. The control device 4 is configured with an information processing device such as a computer, and executes an air ratio adjustment process that adjusts the air ratio of each opposed burner in accordance with the oxygen concentration measured by the oxygen concentration meters 3a-3d so that the oxygen concentration in the combustion exhaust gas of each layer becomes a preset target oxygen concentration setting value.

[0017] [Air ratio adjustment process] Next, a specific example of the air ratio adjustment process executed by the control device 4 will be described with reference to FIGS.

[0018] FIG. 2 shows the flow of the air ratio adjustment process when the oxygen concentration in the flue gas is lower than the set value of the target oxygen concentration. As shown in FIG. 2, when the oxygen concentration in the flue gas (exhaust gas O2) is lower than the set value of the target oxygen concentration (target O2), the control device 4 selectively increases the air ratio of the opposed burner that burns a low-calorie fuel gas (low-heating gas) (time T=T1 to T2). In addition, when the oxygen concentration in the flue gas is lower than the set value of the target oxygen concentration even if the air ratio is increased to a predetermined upper limit, the control device 4 increases the air ratio of the opposed burner that burns a high-calorie flue gas (high-heating gas) (time T2 to T3). This increases the amount of air supplied to the poorly combustible calorific gas, and suppresses the increase in the amount of air supplied to the highly combustible calorific gas. This enables complete combustion of the fuel gas while suppressing the amount of air in the entire boiler 1, and the target oxygen concentration can be achieved without generating unburned fuel gas.

[0019] The control device 4 may monitor the individual oxygen concentrations measured by the oxygen concentration meters 3a-3d and the total value of the individual oxygen concentrations measured by the oxygen concentration meters 3a-3d. In this case, if the total oxygen concentration is lower than the set value of the target oxygen concentration, it can be calculated from the measurement results of the individual oxygen concentrations that the set value of the target oxygen concentration will not be reached by simply increasing the amount of air supplied to the low-calorie gas. In that case, the control device 4 may increase the amount of air supplied to both the low-calorie fuel gas and the high-calorie fuel gas.

[0020] FIG. 3 shows the flow of the air ratio adjustment process when the oxygen concentration in the flue gas is higher than the set value of the target oxygen concentration. As shown in FIG. 3, when the oxygen concentration in the flue gas is higher than the set value of the target oxygen concentration, the control device 4 selectively reduces the air ratio of the opposed burner that burns the high-calorie fuel gas (time T=T4 to T5). In addition, when the oxygen concentration in the flue gas is higher than the set value of the target oxygen concentration even after reducing the air ratio to the predetermined lower limit, the control device 4 reduces the air ratio of the opposed burner that burns the low-calorie flue gas (time T5 to T6). This maintains the amount of air supplied to the poorly combustible calorie gas and suppresses the amount of air supplied to the highly combustible calorie gas. This allows complete combustion of the fuel gas while suppressing the amount of air in the entire boiler 1, and the target oxygen concentration can be achieved without generating unburned fuel gas.

[0021] A carbon monoxide concentration meter may be installed near the oxygen concentration meters 3a to 3d to measure the concentration of monoxide in the combustion exhaust gas for each layer of the combustion exhaust gas. In this case, if a predetermined concentration of monoxide is detected while the air ratio adjustment process shown in Fig. 3 is being performed, the control device 4 increases the air ratio being reduced until carbon monoxide is no longer detected. This enables safe combustion of the fuel gas without causing unburned fuel gas.

[0022] Although the embodiments of the present invention have been described above, the present invention is not limited by the descriptions and drawings that form part of the disclosure of the present invention according to the present embodiments. In other words, other embodiments, examples, and operation techniques, etc., made by those skilled in the art based on the present embodiments are all included in the scope of the present invention. [Explanation of symbols]

[0023] 1. Boiler 2a~2d Opposed burners 3a~3d Oxygen concentration meter 4. Control device

Claims

1. A method for controlling a boiler that simultaneously burns a plurality of fuel gases having different calories, comprising the steps of: a control step of controlling an amount of air to be supplied to each fuel gas based on a measured value of an oxygen concentration in an exhaust gas of the boiler and a preset value of a target oxygen concentration; A boiler control method, wherein the control step includes a step of increasing the amount of air supplied to the low-calorie fuel gas when the measured value is below the set value, and decreasing the amount of air supplied to the high-calorie fuel gas when the measured value exceeds the set value.

2. 2. A boiler control method as described in claim 1, wherein the control step includes a step of increasing the amount of air supplied to the high-calorie fuel gas when the measured value is below the set value even after increasing the amount of air supplied to the low-calorie fuel gas to a predetermined upper limit value.

3. 3. A boiler control method as described in claim 1 or 2, wherein the control step includes a step of reducing the amount of air supplied to the low-calorie fuel gas when the measured value exceeds the set value and the measured value exceeds the set value even after reducing the amount of air supplied to the high-calorie fuel gas to a predetermined lower limit value.

4. A control device for a boiler that simultaneously burns a plurality of fuel gases having different calories, a control means for controlling an amount of air to be supplied to each fuel gas based on a measured value of an oxygen concentration in the exhaust gas of the boiler and a preset target oxygen concentration value; A boiler control device, wherein the control means increases the amount of air supplied to the low-calorie fuel gas when the measured value is below the set value, and decreases the amount of air supplied to the high-calorie fuel gas when the measured value exceeds the set value.

5. 5. A boiler control device as described in claim 4, wherein the control means increases the amount of air supplied to the high-calorie fuel gas when the measured value is below the set value even after increasing the amount of air supplied to the low-calorie fuel gas up to a predetermined upper limit value, and when the measured value is below the set value.

6. 6. A boiler control device as described in claim 4 or 5, wherein the control means reduces the amount of air supplied to the low-calorie fuel gas when the measured value exceeds the set value even after reducing the amount of air supplied to the high-calorie fuel gas to a predetermined lower limit value when the measured value exceeds the set value.

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