Boiler control method and control device

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 control method and a control device for a boiler that simultaneously burns a plurality of fuel gases having different calorific values from each other.

Background Art

[0002] Patent Document 1 describes a technique for setting a target value of oxygen concentration in consideration of the calorific value variation and the co-combustion ratio of each fuel gas in a boiler using a plurality of types of fuel gases, and correcting the air ratio of each fuel gas based on the set target value of oxygen concentration.

Prior Art Document

Patent Document

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The technique described in Patent Document 1 corrects the air ratio of each fuel gas according to a function based on the predetermined theoretical air quantity for each of the plurality of types of fuel gases. Therefore, when using a fuel gas with a large calorific value variation and a changing theoretical air quantity, such as the by-product gas of a steel mill, it becomes difficult to suppress the air quantity of the entire boiler.

[0005] The present invention has been made in view of the above problems, and an object thereof is to provide a control method and a control device for a boiler capable of suppressing the air quantity of the entire boiler even when using a fuel gas with a large calorific value variation and a changing theoretical air quantity.

Means for Solving the Problems

[0006] The boiler control method according to the present invention is a boiler control method for simultaneously burning a plurality of fuel gases with different calorific values, 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 exhaust gas of the boiler and a predetermined set value of the target oxygen concentration, wherein the control step includes 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 is above the set value.

[0007] The control step may include, if the measured value falls below the set value, increasing the amount of air supplied to the high-calorie fuel gas if the measured value still falls below the set value even after increasing the amount of air supplied to the low-calorie fuel gas to a predetermined upper limit.

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

[0009] The boiler control device according to the present invention is a boiler control device for simultaneously burning multiple fuel gases with different calorific values, and includes 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 exhaust gas of the boiler and a predetermined set value of the target oxygen concentration, wherein the control means increases the amount of air supplied to the low-calorie fuel gas when the measured value falls 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] If the measured value falls below the set value, the control means may increase the amount of air supplied to the high-calorie fuel gas if the measured value still falls below the set value even after increasing the amount of air supplied to the low-calorie fuel gas to a predetermined upper limit.

[0011] If the measured value exceeds the set value, the control means may reduce the amount of air supplied to the low-calorie fuel gas if the measured value still exceeds the set value even after reducing the amount of air supplied to the high-calorie fuel gas to a predetermined lower limit. [Effects of the Invention]

[0012] According to the boiler control method and control device of the present invention, even when using a fuel gas that exhibits large calorific fluctuations and changes in theoretical air volume, the total amount of air in the boiler can be suppressed. [Brief explanation of the drawing]

[0013] [Figure 1] Figure 1 is a schematic diagram showing an example of a boiler configuration to which a boiler control device, which is one embodiment of the present invention, is applied. [Figure 2] Figure 2 shows the flow of the air-fuel ratio adjustment process when the oxygen concentration in the combustion exhaust gas is lower than the set value for the target oxygen concentration. [Figure 3] Figure 3 shows the flow of the air-fuel ratio adjustment process when the oxygen concentration in the combustion exhaust gas is higher than the set value for the target oxygen concentration. [Modes for carrying out the invention]

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

[0015] [Boiler configuration] Figure 1 is a schematic diagram showing an example of the configuration of a boiler to which a boiler control device, which is one embodiment of the present invention, is applied. As shown in Figure 1, the boiler 1 of this embodiment is equipped with opposing burners 2a to 2d that burn multiple types of fuel gases with different calorific values, including by-product gases from a steel mill. Here, the arrows shown in Figure 1 indicate the flow of combustion exhaust gas generated by the combustion of fuel gas. From practical experience, it is known that the combustion exhaust gas generated from opposing burners flows through the flue in layers according to the location of combustion. For this reason, in this embodiment, four layers of combustion exhaust gas are formed.

[0016] The boiler 1 of this embodiment is equipped with an oxygen concentration meter 3a to 3d and a control device 4 as a control system. The oxygen concentration meter 3a to 3d are positioned along the cross-sectional height direction of the flue of the boiler 1, corresponding to the positions of the four combustion exhaust gas layers, and measure the oxygen concentration in the combustion exhaust gas generated by the combustion of fuel gas for each layer. The control device 4 is composed of an information processing device such as a computer, and performs an air ratio adjustment process to adjust the air ratio of each opposing burner so that the oxygen concentration in the combustion exhaust gas of each layer becomes a predetermined target oxygen concentration setting value according to the oxygen concentration measured by the oxygen concentration meter 3a to 3d.

[0017] [Air ratio adjustment process] Next, with reference to Figures 2 and 3, a specific example of the air ratio adjustment process performed by the control device 4 will be described.

[0018] Figure 2 shows the flow of the air ratio adjustment process when the oxygen concentration in the combustion exhaust gas is lower than the set value for the target oxygen concentration. As shown in Figure 2, when the oxygen concentration in the combustion exhaust gas (exhaust gas O2) is lower than the set value for the target oxygen concentration (target O2), the control device 4 selectively increases the air ratio of the opposing burner that burns the low-calorie fuel gas (low calorific value gas) (time T=T1~T2). Furthermore, if the oxygen concentration in the combustion exhaust gas is still lower than the set value for the target oxygen concentration even after increasing the air ratio to a predetermined upper limit, the control device 4 increases the air ratio of the opposing burner that burns the high-calorie combustion exhaust gas (high calorific value gas) (time T2~T3). As a result, the amount of air supplied to the less combustible calorific gas increases, while the increase in the amount of air supplied to the more combustible calorific gas is suppressed. Therefore, complete combustion of the fuel gas is possible while suppressing the total amount of air in the boiler 1, and the target oxygen concentration can be achieved without generating unburned fuel gas.

[0019] The control device 4 may also monitor the individual oxygen concentrations measured by oxygen concentration meters 3a to 3d and the sum of the individual oxygen concentrations measured by oxygen concentration meters 3a to 3d. In this case, if the sum of the oxygen concentrations is lower than the set value for the target oxygen concentration, it can be calculated from the individual oxygen concentration measurements that simply increasing the amount of air supplied to the low-calorie gas will not reach the set value for the target oxygen concentration. 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] Figure 3 shows 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. As shown in Figure 3, when the oxygen concentration in the combustion exhaust gas is higher than the set value of the target oxygen concentration, the control device 4 selectively decreases the air ratio of the opposed burners that burn high-calorie fuel gas (time T = T4~T5). Further, when the oxygen concentration in the combustion exhaust gas is still higher than the set value of the target oxygen concentration even after decreasing the air ratio to a predetermined lower limit value, the control device 4 decreases the air ratio of the opposed burners that burn low-calorie combustion exhaust gas (time T5~T6). Thereby, the amount of air supplied to the calorie gas with poor combustibility is maintained, and the amount of air supplied to the calorie gas with good combustibility is suppressed. For this reason, complete combustion of the fuel gas becomes possible 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] In addition, a carbon monoxide concentration meter may be installed near the oxygen concentration meters 3a~3d, and the carbon monoxide concentration in the combustion exhaust gas may be measured for each layer of the combustion exhaust gas. In this case, when a predetermined concentration of carbon monoxide concentration is detected while the air ratio adjustment process shown in Figure 3 is being executed, the control device 4 raises the decreasing air ratio until no carbon monoxide is detected. Thereby, safe combustion of the fuel gas becomes possible without generating unburned fuel gas.

[0022] As described above, the embodiments to which the invention made by the present inventors is applied have been described, but the present invention is not limited by the description and drawings that form a part of the disclosure of the present invention according to this embodiment. That is, all other embodiments, examples, and operation techniques made by those skilled in the art based on this embodiment are included in the scope of the present invention.

Description of Reference Numerals

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

Claims

1. A boiler control method for simultaneously burning multiple fuel gases with different calorific values, The control step includes controlling the amount of air supplied to each fuel gas based on a measurement of the oxygen concentration in the boiler exhaust gas and a predetermined target oxygen concentration setting. The control step includes increasing the amount of air supplied to the low-calorie fuel gas when the measured value falls 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. A boiler control method comprising the control step of, when the measured value falls below the set value, increasing the amount of air supplied to the high-calorie fuel gas if the measured value still falls below the set value even after increasing the amount of air supplied to the low-calorie fuel gas to a predetermined upper limit.

2. The boiler control method according to claim 1, wherein the control step includes, when the measured value exceeds the set value, reducing the amount of air supplied to the low-calorie fuel gas if the measured value still exceeds the set value even after reducing the amount of air supplied to the high-calorie fuel gas to a predetermined lower limit.

3. A method for controlling a boiler that simultaneously burns multiple fuel gases with different calorific values, The control step includes controlling the amount of air supplied to each fuel gas based on a measurement of the oxygen concentration in the boiler exhaust gas and a predetermined target oxygen concentration setting. The control step includes increasing the amount of air supplied to the low-calorie fuel gas when the measured value falls 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. A boiler control method comprising the control step of reducing the amount of air supplied to a low-calorie fuel gas if the measured value exceeds the set value, and the measured value still exceeds the set value even after reducing the amount of air supplied to the high-calorie fuel gas to a predetermined lower limit.

4. A boiler control device for simultaneously burning multiple fuel gases with different calorific values, The system includes a control means that controls 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 target oxygen concentration setting. The control means increases the amount of air supplied to the low-calorie fuel gas when the measured value falls 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. The control means is a boiler control device that, when the measured value falls below the set value, increases the amount of air supplied to the high-calorie fuel gas if the measured value still falls below the set value even after increasing the amount of air supplied to the low-calorie fuel gas to a predetermined upper limit.

5. The control means, when the measured value exceeds the set value, reduces the amount of air supplied to the low-calorie fuel gas if the measured value still exceeds the set value even after reducing the amount of air supplied to the high-calorie fuel gas to a predetermined lower limit, further reduces the amount of air supplied to the low-calorie fuel gas, as described in claim 4.

6. A boiler control device for simultaneously burning multiple fuel gases with different calorific values, The system includes a control means that controls 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 target oxygen concentration setting. The control means increases the amount of air supplied to the low-calorie fuel gas when the measured value falls 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. The control means is a boiler control device that, when the measured value exceeds the set value, reduces the amount of air supplied to the low-calorie fuel gas if the measured value still exceeds the set value even after reducing the amount of air supplied to the high-calorie fuel gas to a predetermined lower limit.

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