JPH0712432B2 - How to regenerate activated carbon - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for regenerating granular activated carbon used for water treatment or the like, and particularly to a method for regenerating activated carbon using a two-stage fluidized bed type activated carbon regenerating apparatus. Is.

<Prior art> Conventionally, various regenerators that use vertical multistage furnaces, rotary kilns, fluidized bed furnaces, moving bed furnaces, etc. have been developed for regenerating activated carbon. There are two types, one is directly heated and regenerated, and the other is indirectly heated and regenerated. When using these regenerators to regenerate the activated carbon that has adsorbed organic substances for water treatment or the like, the activated carbon is regenerated through the following processes.

That is, as the temperature of activated carbon rises, the step of drying wet activated carbon (about 180 ° C or less), and then the step of desorption from activated carbon by evaporation and thermal decomposition of adsorbed organic matter (about 200-500
℃), carbonization by the thermal condensation of the adsorbed organic matter remaining in the activated carbon without desorption, and oxidative decomposition of the produced carbon and desorption by gasification (about 500 ° C or higher). Regeneration is carried out through these steps in order. . However, in the actual playback device, the above steps are not clearly distinguished,
There is some overlap between and or.

Among the above regenerators, the regenerator using a fluidized bed furnace has a better contact efficiency between gas (combustion gas) and solid (activated carbon), so it is more compact than other regenerators and consumes less fuel. It has the advantage of being small. Regarding the fluidized bed type regenerator, there are various proposals such as a one-stage type, a two-stage type, and a multi-stage type having two or more stages, which are fluidized on the fluidized bed plate. Despite the advantages mentioned above because they are very difficult, they are not so popular in reality.

A conventional direct heating type two-stage fluidized bed type activated carbon regenerating apparatus is as shown in FIG. 2. When regenerating used activated carbon, it is carried out as follows.

That is, the combustion gas is supplied to the primary combustion chamber 6 at the bottom of the regenerator body 1 by the burner 25 in which the fuel supply pipe 26 for fuel oil or fuel gas and the air supply pipe 27 for combustion are connected and the steam supply port 15 The steam necessary for further promoting the gasification of the carbide is supplied.

At this time, the supply amount of the combustion air is strictly controlled so as to supply the minimum amount necessary for combustion of the fuel, that is, the oxygen concentration in the combustion gas is, for example, 0.5% by volume or less. When the oxygen concentration is high, the lower fluidized bed portion 5 above it
This is because the activated carbon itself burns and the combustion loss increases.

Next, the combustion gas having a temperature of 800 to 1000 ° C. mixed with steam is raised to the lower fluidized bed section 5 through the porous lower fluidized bed plate 8. In the lower fluidized bed section 5, it is transferred from the upper fluidized bed section 2 through a transfer pipe 10 provided outside the regenerator body 1. Spent activated carbon previously dried in the upper fluidized bed section 2 is heated while being fluidized by the combustion gas to be desorbed by volatilization and thermal decomposition of the adsorbed organic matter, and carbonization of the adsorbed organic matter remaining without desorption Desorption by gasification is carried out to reactivate activated carbon. The recycled activated carbon is taken out of the regeneration furnace through the recycled activated carbon outlet 11. On the other hand, the combustion gas that has passed through the lower fluidized bed section 5 rises to the secondary combustion section 4 which is openly connected thereto. In the secondary combustion section 4, the combustion gas whose temperature has dropped after passing through the lower fluidized bed section 5 is reheated by the burner 22 connected to the fuel supply pipe 23 and the air supply pipe 24 to bring the temperature to 700 to 900 ° C. Maintain the lower fluidized bed section 5
The organic substances desorbed from the activated carbon in the above, carbon monoxide generated during the gasification of the carbide, and a small amount of low boiling point contained in the dry exhaust gas circulated from the upper fluidized bed section 2 through the circulation pipe 16. Completely burns organic substances. Part of the combustion gas completely combusted in the secondary combustion section 4 is a porous upper fluidized bed plate 7
Through the flue gas through the flue gas exhaust port 13 to the outside of the regenerator, but as described above, since this flue gas has been completely burned, It does not require a post-combustion device installed separately from the regeneration furnace for detoxification, and can be discharged as it is. On the other hand, in the upper fluidized bed section 2, the activated carbon that has been infiltrated continuously supplied from the used activated carbon supply port 9 is fluidized by the combustion gas raised from the secondary combustion section 4 while drying the activated carbon. I will do this
In order to lower the temperature in the upper fluidized bed A to about 110 to 175 ° C., cooling water is sprayed from the cooling water supply pipe Q to the upper fluidized bed section 2 S.
Spray through. The supply amount of the cooling water is controlled by a flow rate control valve P that works in conjunction with a temperature detector 20 attached to detect the temperature in the upper fluidized bed. The purpose is to control the temperature in the upper fluidized bed A within the above range so that the organic matter adsorbed on the used activated carbon is not desorbed by volatilization or thermal decomposition and is adsorbed as much as possible to the next lower stage. The heat of combustion is transferred to the fluidized bed section 5, where the adsorbed organic matter is volatilized and thermally decomposed and desorbed, and these organic matter are burned in the secondary combustion section 4 provided on the adsorbed organic matter. 4 is intended to be used for heating. As described above, the dry exhaust gas that has passed through the upper fluidized bed section 2 is circulated to the secondary combustion section 4 by the recycle fan 17 through the circulation pipe 16 to completely burn the low-boiling-point organic matter contained in the dry exhaust gas.

<Problems to be Solved by the Invention> Regeneration of activated carbon is performed through the above-mentioned steps,
Among the regeneration steps, the step of oxidatively decomposing and gasifying the carbide to desorb it from the activated carbon is the most difficult step. Therefore, in the regeneration of activated carbon, it is effective to regenerate the activated carbon by devising it so that the adsorbed organic matter is desorbed from the activated carbon by volatilization and thermal decomposition as much as possible, and the amount of the remaining carbide without desorption is minimized. This is an important point.

For example, in the case of activated carbon used for the tertiary treatment of sewage secondary treated water and the treatment of water containing low concentrations of adsorbed organic substances such as decolorization and deodorization of tap water, the amount of organic substances adsorbed on activated carbon is
It is a low load such as about 100 mg or less per 1 g, and in this case, the total amount of adsorbed organic matter is small, so there is no problem with the amount of residual carbides during regeneration, but 200 to 300 mg per 1 g of organic matter is adsorbed Activated carbon or organic matter to be adsorbed is easily adsorbed, and the amount of adsorbed organic matter is 50
When the activated carbon that exceeds 0 mg is regenerated, the amount of the remaining carbides increases. For example, the regeneration cannot be sufficiently performed unless measures such as enlarging the regeneration device and lengthening the regeneration time are taken. There is.

Further, the amount of the remaining carbides is also related to the heating rate of the activated carbon, and if the heating rate is too fast, some thermally unstable organic substances that would otherwise be thermally decomposed and desorbed are carbonized. As a result, the amount of carbide is further increased.

In the conventional regeneration method, the temperature in the upper fluidized bed is controlled by
The activated carbon is mainly dried by controlling at 110 to 175 ° C, and here, volatilization and thermal decomposition of the adsorbed organic matter are prevented as much as possible. Then, the dry coal is transferred to the lower fluidized bed to rapidly raise the temperature, and volatilization and thermal decomposition of the adsorbed organic matter, and further gasification of the charcoal are performed all at once. Therefore, when the used activated carbon having a large amount of adsorbed organic matter is regenerated by the conventional regeneration method, the total amount of the organic matter to be desorbed and removed in the lower fluidized bed is large, and the amount of the generated carbide is also large. Therefore, regeneration is performed by making the residence time in the lower fluidized bed portion longer than in the case of regenerating activated carbon having a small amount of adsorbed organic matter. That is, unless the residence time is increased, desorption of adsorbed organic substances and gasification of carbides are not sufficiently performed, and as a result, regeneration cannot be sufficiently performed. Therefore, when regenerating activated carbon that adsorbs a large amount of organic matter, the device must be made larger than when regenerating the same amount of activated carbon with a small amount of adsorbed organic matter, which increases equipment costs and prolongs residence time. As a result, there is a problem that wear of activated carbon and combustion loss also increase.

Further, in the conventional regeneration method, in order to control the temperature in the upper fluidized bed to about 110 to 175 ° C., the upper fluidized bed is sprayed with cooling water, but the fluidized bed is uniformly sprayed. Spraying is difficult, and as a result, lumps of wet activated carbon are liable to form in the fluidized bed, and there is also a problem in that the lumps must be removed by frequently interrupting the operation.

The present invention is intended to solve the above-mentioned problems associated with the conventional two-stage fluidized bed type activated carbon regeneration method, and it is possible to efficiently regenerate used activated carbon having a large amount of adsorbed organic matter. The present invention provides a method for regenerating the activated carbon.

<Means for Solving Problems> In heating regeneration of activated carbon, particularly in regeneration of activated carbon having a large amount of adsorbed organic matter, as described above, the adsorbed organic matter is desorbed from activated carbon by volatilization and thermal decomposition as much as possible, Reducing the amount of carbides remaining on activated carbon as much as possible is an important point that facilitates regeneration. The present inventor, in the two-stage fluidized bed type regenerator, without spraying the cooling water to the upper fluidized bed portion, by other means to control the temperature in the upper fluidized bed higher than before and within a certain range. At the same time, by controlling the combustion gas composition to a certain range, it is possible to desorb the adsorbed organic matter to the maximum extent by volatilizing and thermally decomposing and further oxidizing and decomposing the adsorbed organic matter in the upper fluidized bed while drying the activated carbon. Therefore, it has been found that even when the activated carbon having a large amount of adsorbed organic substances is regenerated, the regeneration can be efficiently activated by slightly raising the regeneration furnace without increasing the size of the apparatus.

The present invention has been made based on this finding.

The present invention will be described below with reference to the drawings.

FIG. 1 is an explanatory view showing an example of a two-stage fluidized bed type activated carbon regenerator used in the present invention, and has the following constitution.

That is, a primary combustion chamber 6 is provided at the bottom of the regenerator body 1, a lower fluidized bed portion 5, a secondary combustion portion 4, a mixing portion 3 and an upper fluidized bed portion 2 at the top are provided in that order, and the primary combustion chamber 6 is provided.
And the lower fluidized bed section 5, and the mixing section 3 and the upper fluidized bed section 2
And lower porous fluidized bed plate 8 and upper fluidized bed plate 7, respectively, which are porous
It is divided by. In addition, a temperature control gas selected from steam, nitrogen gas or carbon dioxide gas, for example, steam supply pipe 12 for supplying steam is connected to the mixing section 3 and the upper flow is applied to the steam supply pipe 12. A flow rate control valve 21 that works in conjunction with a temperature detector 20 for detecting the temperature in the upper fluidized bed A attached to the bed portion 2 is attached. Further, an oxygen-containing gas supply pipe 14 such as air is connected to the secondary combustion unit 4, and the oxygen-containing gas supply pipe 14 is linked with an oxygen concentration detector 18 attached to the mixing unit 3 to control the flow rate.
19 is attached. The other parts are the same as the above-mentioned conventional regenerator except that the cooling water supply means is omitted in the upper fluidized bed part 2, and therefore the description of each part is omitted.

The activated carbon regeneration method of the present invention uses the above-mentioned two-stage fluidized bed type activated carbon regenerator to generate regeneration combustion gas from the primary combustion chamber 6 to the lower fluidized bed section 5, the secondary combustion section 4, and the mixing section 3. In order to regenerate and activate the used activated carbon from the upper fluidized bed portion 2 through the transfer pipe 10 provided outside the regenerator body 1 to the lower fluidized bed portion 5 while sequentially ascending to the upper fluidized bed portion 2. The temperature in the upper fluidized bed A is controlled to 300 to 450 ° C. by supplying steam to the mixing section 3 via the steam supply tube 12, and the secondary combustion section 4 is supplied to the mixing section 3 via the oxygen-containing gas supply tube 14. The oxygen concentration in the combustion gas in the mixing section 3 is controlled to 1 to 5% by volume by supplying the oxygen-containing gas.

In the present invention, as means for controlling the oxygen concentration in the combustion gas in the mixing section 3 to 1 to 5% by volume, for example, a burner provided for supplying the combustion gas to the secondary combustion section 4 is used.
It is also possible to do this by adjusting the amount of air supplied from an air supply pipe 24 connected to 22. However,
The supply amount of the air is the fuel supply pipe 23 connected to the burner 22.
It is closely related to the amount of fuel supplied from the air source, and usually there is an optimum air-combustion ratio for stable combustion, and it is difficult to freely change only the amount of air supplied. That is, it is technically difficult to strictly control the oxygen concentration in the mixing section 3 within the above range by adjusting the amount of air supplied from the air supply pipe 24.

Therefore, as described above, the oxygen-containing gas supply pipe 14 such as air is separately provided in the secondary combustion section 4, and the oxygen-containing gas supply pipe 14 is provided.
The method of controlling the supply amount of the oxygen-containing gas by the flow rate control valve 19 by interlocking the flow rate control valve 19 attached to the oxygen concentration meter 18 attached to the mixing section 3 is easy and precise control. Can be done.

<Operation> When the used activated carbon is regenerated by the regenerating apparatus as shown in FIG. 1, it is performed as follows.

That is, the primary combustion chamber 6 provided at the bottom of the regenerator body 1
A burner in which a fuel supply pipe 26 and an air supply pipe 27 are connected to
The combustion gas is supplied by 25 and the steam is supplied from the steam supply port 15. Next, steam mixed temperature 800-1000
The combustion gas at ℃ rises to the lower fluidized bed section 5 through the porous lower fluidized bed plate 8. In the lower fluidized bed section 5, it is transferred from the upper fluidized bed section 2 via a moving pipe 10 provided outside the regenerator body 1. In the upper fluidized bed portion 2 as described below, the used activated carbon that has been dried and further desorbed by volatilization and thermal decomposition or oxidative decomposition of the adsorbed organic matter is heated while being fluidized by the combustion gas, Upper fluidized bed section 2
Desorption due to thermal decomposition of adsorbed organic matter that could not be desorbed by
The activated carbon is regenerated and activated by carbonization and desorption of the generated carbon by gasification. Regenerated activated carbon is recycled activated carbon outlet 11
From outside the regeneration furnace. The combustion gas that has passed through the lower fluidized bed section 5 rises to the secondary combustion section 4 that is openly connected thereto. In the secondary combustion section 4, the combustion gas, which has passed through the lower fluidized bed section 5 and whose temperature has decreased, is supplied to the fuel supply pipe 23 and the air supply pipe.
Reheat by burner 22 with 24 to 700
Maintaining the temperature at ~ 900 ° C, pyrolysis and desorption from the activated carbon in the lower fluidized bed section 5, carbon monoxide generated during gasification of the charcoal, and the circulation pipe 16 from the upper fluidized bed section 2 The organic matter contained in the high-temperature exhaust gas circulated through is completely burned. Further, an oxygen-containing gas such as air is supplied to the secondary combustion section 4 from the oxygen-containing gas supply pipe 14, and at this time, by a flow rate control valve 19 linked with an oxygen concentration detector 18 attached to the mixing section 3. The supply amount of the oxygen-containing gas is controlled, and as a result, the oxygen concentration in the combustion gas in the mixing section 3 is set to 1
It is controlled to be about 5% by volume, preferably about 3%. It is also possible to supply the oxygen-containing gas directly to the mixing section 3 to control the acidity concentration, but in the secondary combustion section 4, it is generated during the gasification of the organic substances desorbed from the activated carbon and the carbides. Oxygen is required to completely burn carbon monoxide and the like, so that oxygen can be supplied at the same time, and when an oxygen-containing gas is supplied to the mixing section 3,
It is preferable to supply the oxygen-containing gas to the secondary combustion section 4, because the supplied oxygen-containing gas may not be uniformly mixed with the combustion gas unless the mixing section is enlarged to increase the residence time. A part of the combustion gas supplied with the oxygen-containing gas is raised to the mixing section 3, and the other part is discharged as combustion exhaust gas to the outlet 13.
It is discharged to the outside of the regeneration furnace. In the mixing section 3, steam is supplied to the combustion gas whose acidity concentration is adjusted to 1 to 5% by volume through the steam supply pipe 12 as described above. At this time, a temperature detector attached to the upper fluidized bed section 2 is used. The flow rate control valve 21 interlocking with 20 controls the amount of steam supply, and as a result, the temperature in the upper fluidized bed A is controlled to 300 to 450 ° C, preferably around 400 ° C. In this way, the temperature in the upper fluidized bed A should be kept at 300-4
The temperature is controlled at 50 ° C, and the mixing part 3 to the upper fluidized bed part 2
By detecting the oxygen concentration in the combustion gas to be increased to 1 to 5% by volume as described above, the adsorbed organic matter is volatilized and thermally decomposed or oxidatively decomposed in the upper fluidized bed section 2. It can be detached to the maximum. In addition,
At this time, if the temperature in the upper fluidized bed A is 300 ° C. or lower, the above-mentioned thermal decomposition or oxidative decomposition becomes insufficient regardless of the oxygen concentration, and the adsorbed organic substances cannot be sufficiently desorbed, which is not preferable. Even if the temperature is 300 to 450 ° C, if the oxygen concentration detected in the mixing section 3 is 1% or less,
In particular, the oxidation reaction hardly occurs, and when the content is 5% or more, the activated carbon itself burns to increase the combustion loss, which is not preferable. Further, when the temperature is 450 ° C. or higher, the activated carbon itself burns to increase the combustion loss unless the oxygen concentration is set to 1% or less. However, if it is set to 1% or less, the oxidation reaction hardly occurs, which is not preferable. . The combustion gas that has passed through the mixing section 3 is further raised to the upper fluidized bed section 2 through the porous upper fluidized bed plate 7. In the upper fluidized bed section 2, while the activated carbon in a wet state continuously supplied from the used activated carbon supply port 9 is fluidized by the combustion gas raised from the mixing section 3, the activated carbon is dried and the adsorbed organic matter is adsorbed. A part is volatilized, pyrolyzed, and further oxidatively decomposed to be desorbed from the activated carbon. The high-temperature exhaust gas that has passed through the upper fluidized bed section 2 is circulated by the recycle fan 17 to the secondary combustion section 4 via the circulation pipe 16 to completely combust organic substances and the like contained in the high-temperature exhaust gas.

In the regeneration method of the present invention, as described above, the temperature in the upper fluidized bed A is controlled to 300 to 450 ° C. and the oxygen concentration in the combustion gas to be increased from the mixing portion 3 to the upper fluidized bed portion 2 is 1 to 5 By controlling the volume%, the upper fluidized bed section 2
In (1), the adsorbed organic matter can be volatilized and pyrolyzed and desorbed, and at the same time, a part of the adsorbed organic matter can be reacted with oxygen to be oxidized and desorbed from the activated carbon, or can be depolymerized to the maximum extent.

That is, in the conventional regeneration method, even what should remain as a carbide due to thermal decomposition can be partially desorbed in the upper fluidized bed section 2 in the method of the present invention, and thus moved to the lower fluidized bed section 5. The amount of organic matter remaining on the activated carbon is reduced as compared with the conventional regeneration method, and thus activated carbon having a large amount of adsorbed organic matter can be efficiently regenerated.

Although steam was used as the gas to be supplied to the mixing unit 3 in the above-described embodiment, nitrogen gas or carbon dioxide gas can be used instead of steam. However, steam is optimal in that the temperature can be lowered with a small amount of gas, temperature control is easy, manpower is easy, and inexpensive.

<Effects of the Invention> As described above, the method for regenerating activated carbon of the present invention does not need to enlarge the device and lengthen the residence time as in the conventional case even when regenerating activated carbon having a large amount of adsorbed organic matter, Only by slightly raising the temperature of the regenerating furnace, it is possible to efficiently regenerate the activated carbon having a small amount of adsorbed organic substances with a regenerating device having almost the same size. Therefore, it is an excellent regeneration method without increasing wear and burning loss of activated carbon.

Further, in the present invention, since cooling water is not supplied to the upper fluidized bed portion unlike the conventional regeneration method, and the temperature in the upper fluidized bed is also higher than that in the conventional regeneration method, the upper fluidized bed is wet. It has an effect that the activated carbon can be maintained in a good fluidized state without being solidified.

Further, in the regeneration method of the present invention in which the adsorbed organic matter is volatilized and pyrolyzed in the upper fluidized bed portion, and further desorption due to oxidative decomposition and the like is performed to the maximum extent, high-temperature exhaust gas containing these desorbed organic matter Is circulated from the upper fluidized bed section to the secondary combustion section and completely burned there, so that the combustion heat can be effectively utilized in the secondary combustion section as in the conventional regeneration method, and No harmful substances such as organic matter and carbon monoxide will remain.

The present invention is not limited to the regeneration of activated carbon having a large amount of adsorbed organic matter, and it goes without saying that the regeneration of low-load activated carbon can be efficiently performed.

<Examples> Examples will be described below in order to clarify the effects of the present invention.

Wastewater from a dye manufacturing plant was treated with granular activated carbon to adsorb 300 mg of organic pollutants (COD) per 1 g of activated carbon. Using the two-stage fluidized bed regenerator as shown in Fig. 1, the following was performed. Regeneration was continuously performed under the conditions.

Regeneration capacity (DeyBase) 12.0kg / H Temperature in the upper fluidized bed 400 ℃ (residence time 20 minutes) Oxygen concentration in mixing part 3% Lower fluidized bed part residence time 30 minutes Combustion gas temperature in primary combustion chamber 950 ℃ Primary combustion The amount of steam supplied to the chamber was 12.5 kg / H. For comparison, a conventional regenerator such as that shown in Fig. 2 was used, except for the fact that there was no mixing part Regeneration was carried out by the method. The regeneration conditions at this time were that the cooling fluid was supplied to the upper fluidized bed section to control the temperature inside the fluidized bed to 150 ° C and the oxygen concentration in the combustion gas supplied from the secondary combustion section to the upper fluidized bed section. Except for the fact that no particular control was performed, the other conditions are the same as the above-mentioned regeneration conditions of the present invention.

The reproduction results are shown in Table 1. For comparison, Table 1 also shows the quality of new activated carbon.

(Note that the regeneration yield in the regeneration method of the present invention was 97%.) As described above, according to the regeneration method of the present invention, a large amount of organic substances that cannot be sufficiently regenerated and activated by the conventional regeneration method are used. The used activated carbon adsorbed on was able to be efficiently regenerated.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an example of an embodiment of a two-stage fluidized bed type activated carbon regenerator used in the regeneration method of the present invention, and FIG. 2 is a description of a conventional two-stage fluidized bed type activated carbon regenerator. It is a figure. 1 ... Regeneration furnace main body, 2 ... Upper fluidized bed section 3 ... Mixing section, 4 ... Secondary combustion section 5 ... Lower fluidized bed section, 6 ... Primary combustion chamber 7 ... Upper fluidized bed plate, 8 ... … Lower fluidized bed plate 9 …… Spent activated supply port 10 …… Transfer pipe, 11 …… Regenerated activated carbon outlet 12 …… Steam supply pipe, 13 …… Combustion exhaust gas discharge port 14 …… Oxygen-containing gas supply pipe 15… … Steam supply port, 16 …… Circulation pipe 17 …… Recycling fan 18 …… Oxygen concentration detector 19,21 …… Flow control valve 20 …… Temperature detector, 22,25 …… Burner 23,26 …… Fuel supply Pipes 24, 27 ... Air supply pipe A ... Upper fluidized bed, S ... Spray P ... Flow control valve, Q ... Cooling water supply pipe

Claims (2)

[Claims] 1. A primary combustion chamber is provided at the bottom, a lower fluidized bed portion, a secondary combustion portion, and a mixing portion are provided thereon, and an upper fluidized bed portion is provided at the top in that order, and the primary combustion chamber and the lower fluidized bed portion are provided. In addition, using a two-stage fluidized bed type activated carbon regenerator having a structure in which the mixing section and the upper fluidized bed section are each partitioned by porous fluidized bed plates, the combustion gas for regeneration is fed from the primary combustion chamber to the lower fluidized bed section and the secondary combustion bed. When the activated carbon is used to transfer from the upper fluidized bed to the lower fluidized bed to regenerate and activate it, the vapor, nitrogen gas, or carbon dioxide gas is added to the mixing section. Is supplied to control the temperature in the upper fluidized bed to 300 to 450 ° C. and to control the oxygen concentration in the combustion gas in the mixing section to 1 to 5% by volume. 2. The oxygen concentration in the combustion gas in the mixing section is set to 1-5.
The means for controlling the volume% is by supplying an oxygen-containing gas such as air to the secondary combustion chamber, and the supply amount of the oxygen-containing gas is the oxygen concentration in the combustion gas in the mixing section. The method for regenerating activated carbon according to claim 1, wherein the activated carbon is controlled by a flow rate control valve that works in conjunction with an oxygen concentration detector for detection.