Combustion control method of burner and burner facility

Abstract

To provide a combustion control method of a burner capable of suppressing the generation of NOx and soot.SOLUTION: The combustion control method of a burner comprises a primary combustion step of mixing combustion gas supplied from a gas nozzle with primary mixed air supplied from a primary mixed air feed port to combust the mixture, and a secondary combustion step of mixing the combustion gas after the primary combustion step with secondary mixed air supplied from a secondary mixed air feed port to combust the mixture. The method further includes a premixed air mixing step of mixing the combustion gas with premixed air according to the flow rate of the combustion gas in the gas nozzle before the primary combustion step.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a combustion control method for a burner and burner equipment that can suppress the generation of NOx and soot by combustion.

Background Art

[0002] In a heat treatment furnace or the like used for quenching thick steel plates using combustion gas, a combustion device using a burner is used. In these combustion devices, in order to reduce the environmental load, a burner of a two-stage combustion method in which mixed air is divided into two stages and mixed with combustion gas is used.

[0003] However, when using a burner of the two-stage combustion method, natural gas such as city gas generally used has a narrow combustion range, and various combustion problems such as unstable combustion, misfire, and an increase in NOx and soot occur. As a technique for solving this problem, Patent Document 1 discloses a technique for controlling the supply ratio of primary mixed air and secondary mixed air.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] According to the technique disclosed in Patent Document 1, combustion can be stabilized by controlling the supply ratio of primary mixed air and secondary mixed air. However, even in this case, there is still room for improvement from the viewpoint of suppressing the generation of NOx and soot. The present invention has been made in view of such conventional techniques, and an object thereof is to provide a combustion control method for a burner and burner equipment that can suppress the generation of NOx and soot.

Means for Solving the Problems

[0006] The means for solving the above problems are as follows. [1] A combustion control method for a burner having a primary combustion step of mixing and burning combustion gas supplied from a gas nozzle and primary mixed air supplied from a primary mixed air port, and a secondary combustion step of mixing and burning the combustion gas after the primary combustion step and secondary mixed air supplied from a secondary mixed air port, the method comprising a pre-mixed air mixing step of mixing pre-mixed air with the combustion gas according to the flow rate of the combustion gas in the gas nozzle before the primary combustion step. [2] In the pre-mixed air mixing step, when the flow rate of the combustion gas is equal to or less than a predetermined threshold value, the pre-mixed air is mixed with the combustion gas, and when the flow rate of the combustion gas exceeds the threshold value, the pre-mixed air is not mixed with the combustion gas. The combustion control method for a burner according to [1]. [3] In the pre-mixed air mixing step, the pre-mixed air is mixed with the combustion gas so that the pre-mixed air ratio is in the range of 60% or more and 70% or less. The combustion control method for a burner according to [1] or [2]. [4] In the pre-mixed air mixing step, the pre-mixed air is mixed with the combustion gas at a position upstream of the primary mixed air port and within a range of 1000 mm or less from the tip of the gas nozzle. The combustion control method for a burner according to any one of [1] to [3]. [5] The volume ratio of the primary mixed air and the secondary mixed air is in the range of 20:80 to 40:60. The combustion control method for a burner according to any one of [1] to [4]. [6] A burner having a gas nozzle for supplying combustion gas, a mixed air inlet for introducing mixed air to be mixed with the combustion gas, a primary mixed air port for supplying primary mixed air to a primary combustion chamber, and a secondary mixed air port for supplying secondary mixed air to a secondary combustion chamber for burning the combustion gas burned in the primary combustion chamber, a pre-mixed air supply device for supplying pre-mixed air to the gas nozzle, a flow meter for measuring the flow rate of the combustion gas, and a control device for controlling the supply of the pre-mixed air by the pre-mixed air supply device based on the flow rate of the combustion gas measured by the flow meter.

Advantages of the Invention

[0007] According to the present invention, by mixing pre-mixed air with the combustion gas according to the flow velocity of the combustion gas in the gas nozzle, the generation of NOx and soot due to combustion can be suppressed.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0009] Hereinafter, the present invention will be specifically described through embodiments of the present invention. However, the following embodiments show a preferred example of the present invention, and the present invention is not limited by these embodiments.

[0010] FIG. 1 is a schematic cross-sectional view showing a configuration example of burner equipment 70 in which the combustion control method of the burner according to the present embodiment can be implemented. Further, FIG. 2 is a schematic cross-sectional view showing the burner equipment 70 in a state where the combustion gas is burned. The configuration of the burner equipment 70 will be described with reference to FIGS. 1 and 2.

[0011] The burner facility 70 according to this embodiment is connected to the end face of the radiant tube 80 and is used to heat the radiant tube 80. However, the burner facility 70 is not limited to the radiant tube 80 and may be used for heating other facilities. The burner facility 70 includes a burner 10, a flow meter 14, a premixed air supply pipe 30, a shut-off valve 32 for opening and closing the premixed air supply pipe 30, and a control device 34 for controlling the shut-off valve 32. In this embodiment, the premixed air supply device is configured to include the premixed air supply pipe 30 and the shut-off valve 32.

[0012] The burner 10 has a gas nozzle 12 and a burner body 20. The gas nozzle 12 is a pipe that supplies a predetermined flow rate of combustion gas to the burner 10. One end side of the gas nozzle 12 is provided to penetrate the burner body 20, and the other end side is connected to a combustion gas supply source (not shown) provided with a flow rate adjustment valve. The burner body 20 is provided with a mixed air inlet 22 for introducing mixed air therein, a primary mixed air port 26 for supplying primary mixed air from around the gas nozzle 12 to the primary combustion chamber 40, and a secondary mixed air port 28 for supplying secondary mixed air from around the primary mixed air port 26 to the secondary combustion chamber 42. The mixed air inlet 22 is connected to a mixed air supply source (not shown) provided with a flow rate adjustment valve.

[0013] The gas nozzle 12 is provided in the burner body 20 such that one end side of the gas nozzle 12 is inside the primary combustion chamber 40. The primary combustion chamber 40 is formed by a partition wall 24. Around the primary combustion chamber 40, a secondary combustion chamber 42 is formed by the partition wall 24 and the radiant tube 80. By providing the partition wall 24 in this way to form the primary combustion chamber 40 and the secondary combustion chamber 42, two-stage combustion can be realized, which is the primary combustion of combustion gas and primary mixed air and the secondary combustion of the combustion gas after the primary combustion and secondary mixed air. In this embodiment, the step of mixing the combustion gas with the primary mixed air for primary combustion is the primary combustion step, and the step of mixing the combustion gas after the primary combustion with the secondary mixed air for secondary combustion is the secondary combustion step.

[0014] The premixed air supply pipe 30 has one end connected to the gas nozzle 12 and the other end connected to a premixed air supply source (not shown) provided with a flow rate adjustment valve. A shut-off valve 32 is provided in the premixed air supply pipe 30. By opening the shut-off valve 32 provided in the premixed air supply pipe 30, premixed air at a predetermined flow rate is supplied into the gas nozzle 12, and by closing the shut-off valve 32, the supply of premixed air into the gas nozzle 12 is stopped. In the present embodiment, the step of supplying premixed air from the premixed air supply pipe 30 to the gas nozzle 12 is the premixed air mixing step, and this premixed air mixing step is carried out before the primary combustion step of mixing the primary air with the combustion gas and causing primary combustion.

[0015] The connection position between the premixed air supply pipe 30 and the gas nozzle 12 is preferably within a range that is upstream of the primary air inlet 26 and 1000 mm or less from the tip (one end) of the gas nozzle 12. By connecting the premixed air supply pipe 30 to the gas nozzle 12 upstream of the primary air inlet 26, the premixed air can be mixed with the combustion gas, and incomplete combustion and misfire due to insufficient mixing of the combustion gas and the premixed air can be suppressed. On the other hand, even if the connection position of the premixed air supply pipe 30 is made longer than 1000 mm from the tip of the gas nozzle 12, there is no difference in the degree of mixing between the combustion gas and the premixed air, and instead, the range accompanied by the risk of ignition is expanded, which is not preferable. Incidentally, the connection position between the premixed air supply pipe 30 and the gas nozzle 12 is more preferably within a range that is separated from the upstream side of the primary air inlet 26 by 500 mm or more and is 1000 mm or less from the tip of the gas nozzle 12.

[0016] The flowmeter 14 is provided in the gas nozzle 12 or in the conveyance path that conveys combustion gas to the gas nozzle 12, and measures the flow rate of the combustion gas flowing through the gas nozzle 12. The control device 34 controls the supply of premixed air to the gas nozzle 12 according to the flow velocity of the combustion gas in the gas nozzle 12. When the flow velocity of the combustion gas is equal to or lower than a predetermined threshold value, the control device 34 opens the shut-off valve 32 to supply premixed air to the gas nozzle 12 and mixes the premixed air with the combustion gas. On the other hand, when the flow velocity of the combustion gas exceeds the predetermined threshold value, the control device 34 closes the shut-off valve 32 and does not supply premixed air to the gas nozzle 12, and does not mix the premixed air with the combustion gas.

[0017] The premixed air is mixed with the combustion gas so that the premixed air ratio is 60% or more and 70% or less. The premixed air ratio is a value calculated by the following formula (1).

[0018] Premixed air ratio (%) = Premixed air flow rate (m 3 N / h) × 100 / [Combustion gas flow rate (m 3 N / h) + Premixed air flow rate (m 3 N / h)] ··· (1)

[0019] By mixing the premixed air with the combustion gas so that the premixed air ratio is 60% or more and 70% or less, the generation of NOx and soot can be suppressed. On the other hand, when the premixed air ratio is less than 60%, the combustion gas and the premixed air are not sufficiently mixed, and a part of the combustion gas becomes unburned, making it easy to generate soot, which is not preferable. Further, when the premixed air ratio is higher than 70%, the risk of ignition increases, which is not preferable.

[0020] Further, the volume ratio of the primary mixed air and the secondary mixed air is preferably in the range of 20:80 to 40:60. By setting the volume ratio of the primary mixed air and the secondary mixed air within the range of 20:80 to 40:60, the combustion gas can be stably combusted, and the generation of NOx and soot can be suppressed. The volume ratio of the primary mixed air and the secondary mixed air can be adjusted by changing the area ratio of the primary mixed air port 26 and the secondary mixed air port 28. When premixed air is mixed with the combustion gas, the mixing amount of the premixed air may be reduced according to the ratio of the primary mixed air and the secondary mixed air. For example, when the primary mixed air:secondary mixed air = 20:80 and 10 equivalent parts thereof are mixed with the combustion gas as premixed air, the volume ratio of each mixed air is primary mixed air:secondary mixed air:premixed air = 18:72:10.

[0021] Furthermore, it is preferable to mix the primary mixed air, the secondary mixed air, and the premixed air with the combustion gas so that the air ratio, which is the ratio of the actual mixed air amount to the theoretical air amount, is in the range of 1.3 or more and 3.0 or less. Thereby, the combustion gas can be stably combusted, and furthermore, the generation of NOx and soot can be suppressed.

[0022] Next, the control of the supply of the premixed air by the control device 34 will be described. FIG. 3 is a schematic diagram showing a configuration example of the control device 34. The control device 34 is a general-purpose computer such as a workstation or a personal computer, for example. The control device 34 includes a control unit 50, an input unit 52, an output unit 54, and a storage unit 56.

[0023] The control unit 50 is, for example, a CPU or the like, and functions as an acquisition unit 58 and a determination unit 60 by executing various programs stored in the storage unit 56. The input unit 52 is, for example, a keyboard, a touch panel provided integrally with a display, or the like. The output unit 54 is, for example, an LCD or a CRT display. The storage unit 56 is, for example, a rewritable flash memory, a hard disk built-in or connected by a data communication terminal, an information recording medium such as a memory card, and a reading / writing device thereof. Programs and data used to control the opening and closing of the shut-off valve 32 based on the flow rate of the combustion gas are stored in the storage unit 56 in advance. Further, a threshold value of the flow rate of the combustion gas used to control the opening and closing of the shut-off valve 32 is also stored in the storage unit 56. In this embodiment, the threshold value of the flow rate of the combustion gas is 1.5 m / s. The threshold value of the flow rate of the combustion gas is determined in advance, for example, by changing the flow rate of the combustion gas and performing a combustion experiment in which premixed air is mixed with the combustion gas and burned, and checking the generation amounts of soot and NOx in the combustion experiment. The predetermined threshold value may be input to the storage unit 56 by an operator through the input unit 52.

[0024] Next, the processes executed by the acquisition unit 58 and the determination unit 60 will be described. The acquisition unit 58 acquires the flow rate data of the combustion gas from the flow meter 14 at a predetermined sampling rate. The predetermined sampling rate is, for example, once per second. The acquisition unit 58 outputs the acquired flow rate data of the combustion gas to the determination unit 60.

[0025] When the determination unit 60 acquires the flow rate data of the combustion gas, it calculates the flow velocity data of the combustion gas by dividing the flow rate data by the cross-sectional area of the gas nozzle 12. The determination unit 60 reads out 1.5 m / s, which is the threshold value of the flow velocity of the combustion gas, from the storage unit 56, and compares the threshold value with the calculated flow velocity data of the combustion gas. When the flow velocity data of the combustion gas is 1.5 m / s or less, the determination unit 60 determines that the flow velocity of the combustion gas is below the threshold value, and outputs a signal to open the shut-off valve 32. As a result, the shut-off valve 32 is opened, the premixed air is supplied to the gas nozzle 12, and the premixed air is mixed with the combustion gas. When a signal to open the shut-off valve 32 is output while the shut-off valve 32 is already open, the shut-off valve 32 maintains the open state of the valve.

[0026] On the other hand, when the calculated flow velocity data of the combustion gas exceeds 1.5 m / s, the determination unit 60 determines that the flow velocity of the combustion gas exceeds the threshold value, and outputs a signal to close the shut-off valve 32. As a result, the shut-off valve 32 is closed, and the supply of the premixed air is stopped. When a signal to close the shut-off valve 32 is output while the shut-off valve 32 is closed, the shut-off valve 32 maintains the closed state of the valve.

[0027] In this way, the determination unit 60 determines whether to mix the premixed air with the combustion gas according to the flow velocity of the combustion gas in the gas nozzle 12, and performs the premixed air mixing step. That is, in the premixed air mixing step, when the flow velocity of the combustion gas in the gas nozzle 12 is below the threshold value, the premixed air is mixed with the combustion gas, and when the flow velocity of the combustion gas exceeds the threshold value, the premixed air is not mixed with the combustion gas.

[0028] When the flow rate of the combustion gas in the gas nozzle 12 is below the threshold value, the combustion gas, the primary mixed air, and the secondary mixed air are not sufficiently mixed, and a part of the combustion gas becomes unburned and soot is generated. On the other hand, when the flow rate of the combustion gas in the gas nozzle 12 exceeds the threshold value, the mixing of the combustion gas with the primary mixed air and the secondary mixed air is promoted, so that the combustion gas can be properly burned without mixing the premixed air with the combustion gas. Thus, when the flow rate of the combustion gas in the gas nozzle 12 is high and the premixed air is mixed, the air becomes excessive and excessive N and O enter during combustion, and conversely, the generation amount of NOx increases.

[0029] Therefore, in the burner equipment 70 and the combustion control method of the burner according to the present embodiment, when the flow rate of the combustion gas is below the threshold value, the premixed air is mixed with the combustion gas, and when the flow rate of the combustion gas exceeds the threshold value, the premixed air is not mixed with the combustion gas. Thereby, the combustion gas can be properly burned, and the generation of NOx and soot can be suppressed. Specifically, the generation amount of NOx in terms of O2 11% can be reduced to 70 ppm or less (O2 11% conversion: O2 11% conversion means the upper limit of the dilution amount of air), and the generation amount of soot can be reduced to 1 or less in terms of the Backer Raccoon index.

[0030] If the combustion gas can be properly burned in this way, even if the combustion gas is changed from the by-product gas of the steelworks with high combustibility to the city gas with low combustibility, the combustion gas can be properly burned by mixing the premixed air with the combustion gas. Thereby, with respect to the change of the combustion gas (by-product gas of the steelworks → city gas), the burner body 20 used with the by-product gas can be used as it is, and it becomes possible to cope with a relatively small-scale modification. The by-product gas of the steelworks is coke oven gas, converter gas, blast furnace gas, or a mixed gas thereof.

[0031] FIG. 4 is a schematic diagram showing another example of the burner equipment according to the present embodiment. In the burner equipment 72 shown in FIG. 4, the same components as those of the burner equipment 70 shown in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted. The burner equipment 72 shown in FIG. 4 is different from the burner equipment 70 shown in FIG. 1 in that the premixed air supply device has an orifice nipple 36 and a flow meter 38.

[0032] The orifice nipple 36 is provided in the premixed air supply pipe 30 at a position closer to the connection position with the gas nozzle 12 than the shut-off valve 32 and the flow meter 38. The orifice nipple 36 is provided to prevent the combustion gas from flowing into the premixed air supply pipe 30. The flow meter 38 is a device for measuring the supply amount of the premixed air. By providing the flow meter 38, it is possible to confirm whether the premixed air of the intended flow rate is supplied to the gas nozzle 12. Note that the flow rate data of the premixed air measured by the flow meter 38 may be output to the control device 34, and the flow rate of the premixed air may be displayed on the output unit 54 to monitor the flow rate of the premixed air.

[0033] As described above, the burner equipment according to the present embodiment may have an orifice nipple 36 and a flow meter 38 for measuring the flow rate of the premixed air. Thereby, the combustion gas can be burned more stably and appropriately.

Example

[0034] Next, an example in which the amounts of soot and NOx generated when the combustion gas is burned using the burner equipment 70 shown in FIG. 1 are measured will be described. In the example, when city gas is used as the combustion gas and the flow velocity of the city gas is 1.3 m / s, 5 m 3 N / h or 12 m 3 N / h of premixed air is supplied to the gas nozzle 12, and the amounts of soot and NOx generated are measured when premixed air is not supplied. Similarly, when the flow velocity of the city gas is 4.1 m / s, 5 m 3 N / h or 12 m 3The generation amounts of NOx and soot were measured when premixed air of N / h was supplied to the gas nozzle 12 and when premixed air was not supplied.

[0035] The generation amount of NOx (ppm) is the value converted to O2 11%. In addition, the Bacharach smoke index was used as an index for evaluating the generation amount of soot. The Bacharach smoke index is obtained by measuring the exhaust gas generated by the combustion of the combustion gas with a Bacharach smoke tester. The smaller the value of the Bacharach smoke index, the less soot there is. The Bacharach smoke index is preferably 3 or less, and more preferably 1 or less. The measurement results of the generation amount of NOx and the Bacharach smoke index are shown in Table 1 below. The threshold value of the flow rate of the city gas in the examples is 1.5 m / s.

[0036]

Table 1

[0037] As shown in Table 1, when the flow rate of the city gas is 4.1 m / s, which exceeds the threshold value of 1.5 m / s, when premixed air is supplied to the gas nozzle 12, the amount of air mixed into the combustion gas increases, and the generation amount of NOx, which was 66 ppm when premixed air was not supplied to the combustion gas, becomes more than 70 ppm by supplying premixed air. From this result, it was confirmed that when premixed air is supplied to the gas nozzle 12 and mixed into the combustion gas when the flow rate of the combustion gas exceeds the threshold value of 1.5 m / s, the generation amount of NOx rather increases.

[0038] On the other hand, when the flow velocity of the city gas, which is the combustion gas, is 1.3 m / s, which is equal to or less than the threshold value of 1.5 m / s, by supplying premixed air to the gas nozzle 12 and mixing it with the combustion gas, the Backalakusmoke index "9" becomes "0", and the amount of soot generation is greatly reduced. Also, by supplying premixed air to the gas nozzle 12 and mixing it with the combustion gas, although the amount of NOx generation increased compared to the case where no premixed air was supplied, the amount of NOx generation was less than 50 ppm. From these results, it was confirmed that by implementing a premixed air mixing step of mixing premixed air with the combustion gas according to the flow velocity of the combustion gas, the generation of NOx and soot due to the combustion of the combustion gas can be suppressed.

Explanation of symbols

[0039] 10 Burner 12 Gas nozzle 14 Flow meter 20 Burner body 22 Premixed air inlet 24 Partition wall 26 Primary premixed air port 28 Secondary premixed air port 30 Premixed air supply pipe 32 Shut-off valve 34 Control device 40 Primary combustion chamber 42 Secondary combustion chamber 50 Control unit 52 Input unit 54 Output unit 56 Storage unit 58 Acquisition unit 60 Judgment unit 70 Burner equipment 72 Burner equipment 80 Radiant tube

Claims

1. A primary combustion step of mixing and burning combustion gas supplied from a gas nozzle and primary mixing air supplied from a primary mixing air port; A secondary combustion step of mixing and burning the combustion gas after the primary combustion step and secondary mixing air supplied from a secondary mixing air port, the combustion control method of a burner having: A pre-mixed air mixing step of mixing pre-mixed air with the combustion gas according to the flow velocity of the combustion gas in the gas nozzle before the primary combustion step, the combustion control method of a burner.

2. In the pre-mixed air mixing step, when the flow velocity of the combustion gas is equal to or less than a predetermined threshold value, the pre-mixed air is mixed with the combustion gas, and when the flow velocity of the combustion gas exceeds the threshold value, the pre-mixed air is not mixed with the combustion gas, the combustion control method of the burner according to Claim 1.

3. In the pre-mixed air mixing step, the pre-mixed air is mixed with the combustion gas so that the pre-mixed air ratio is in the range of 60% or more and 70% or less, the combustion control method of the burner according to Claim 1 or Claim 2.

4. In the pre-mixed air mixing step, the pre-mixed air is mixed with the combustion gas at a position upstream of the primary mixing air port and within a range of 1000 mm or less from the tip of the gas nozzle, the combustion control method of the burner according to Claim 1 or Claim 2.

5. In the pre-mixed air mixing step, the pre-mixed air is mixed with the combustion gas at a position upstream of the primary mixing air port and within a range of 1000 mm or less from the tip of the gas nozzle, the combustion control method of the burner according to Claim 3.

6. The volume ratio of the primary mixing air and the secondary mixing air is in the range of 20:80 to 40:60, the combustion control method of the burner according to Claim 1 or Claim 2.

7. The volume ratio of the primary mixing air and the secondary mixing air is in the range of 20:80 to 40:60, the combustion control method of the burner according to Claim 3.

8. The volume ratio of the primary mixing air and the secondary mixing air is in the range of 20:80 to 40:60, the combustion control method of the burner according to Claim 4.

9. The volume ratio of the primary mixing air and the secondary mixing air is in the range of 20:80 to 40:60, the combustion control method of the burner according to Claim 5.

10. A burner having a gas nozzle for supplying combustion gas, a mixed air inlet for introducing mixed air to be mixed with the combustion gas, a primary mixed air port for supplying primary mixed air to a primary combustion chamber, and a secondary mixed air port for supplying secondary mixed air to a secondary combustion chamber for burning the combustion gas burned in the primary combustion chamber. A premixed air supply device for supplying premixed air to the gas nozzle. A flow meter for measuring the flow rate of the combustion gas. A control device for controlling the supply of the premixed air by the premixed air supply device based on the flow rate of the combustion gas measured by the flow meter. A burner facility having the above components.

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