JP2015174980A - Method of burning removal of deposit carbon in carbonization chamber of coke oven - Google Patents

Abstract

PROBLEM TO BE SOLVED: To blow air in a blowing condition in which a deposit carbon layer after burning is made appropriate in thickness by considering the thickness of carbon deposits for each carbonization chamber.SOLUTION: In a method of burning removal of deposit carbon in a carbonization chamber of a coke oven, carbon attached inside the carbonization chamber of the coke oven is burned and removed by blowing air from injection nozzles into the carbonization chamber, and when the total air volume blown into the carbonization chamber is V1, a blowing condition is set so as to satisfy the following formula: V1=V0+(A-B)/(▵CO/▵V), where V1 is the total flow rate of blown air; V0 is the total flow rate of air blown the last time; A is an average value of concentration of COin a flue gas at the latest N-times (N is 1 or more); B is a target value of concentration of COin a flue gas; and ▵CO/▵V is an average value of a ratio of COto an air volume after a COconcentration at the completion of the blowing at the latest M-times (M is more than 1).

Description

  The present invention relates to a method for burning and removing carbon adhering to a wall surface of a coking chamber of a coke oven.

  In the coke oven carbonization chamber, carbon generated by pyrolysis of the dry distillation product gas and pulverized coal scattered at the time of charging the coal adhere to the furnace wall and coke, thereby generating carbon attached to the furnace wall. The carbon attached to the furnace wall lowers the thermal conductivity of the furnace wall as it grows on the furnace wall surface, and reduces the effective volume of the carbonization chamber, thereby reducing the productivity of the coke oven. Furthermore, since the extrusion load at the time of extruding coke from a carbonization chamber becomes large and causes clogging, periodic removal work is necessary.

  As a method of removing the carbon adhering to the furnace wall, there is known a method of burning and removing the carbon adhering to the furnace wall by injecting air from an injection nozzle inserted into the carbonization chamber. Here, if all of the furnace wall adhering carbon is burned and removed, the preferable adhering carbon that has filled the joints is also removed. For this reason, the load at which coke slides on the furnace wall during extrusion increases, and on the contrary, the furnace wall may be damaged. Furthermore, when the joint portion is exposed in the furnace, the coal dust generated at the time of charging the coal easily flows from the carbonization chamber into the combustion chamber through the crack formed in the joint portion. In other words, there is an appropriate value for the amount of combustion of the carbon adhering to the furnace wall, and the injection conditions (hereinafter referred to as “appropriate It is necessary to inject gas.

  Patent Document 1 discloses a method of stopping gas injection when the oxygen concentration of combustion exhaust gas reaches a target value, with the oxygen concentration at which a predetermined extrusion load is minimized as a target value. Further, in Patent Document 1, as long as the same injection nozzle and the same gas are used in the same coke oven, if the gas injection is stopped when the predetermined oxygen concentration target value (14%) is reached, extrusion is performed. It is described that the resistance value is minimized, and it is not necessary to individually obtain data for each carbonization chamber (see paragraph 0017 of the specification).

In Patent Document 2, when the O ₂ concentration of the combustion exhaust gas is higher than a predetermined value, the air blowing time at the next and subsequent carbon incineration is shortened, and when it is lower than the predetermined value, the air blowing time at the next and subsequent carbon incineration is extended. A method is disclosed.

These Patent Documents 1 and 2 are common in that they focus on the O ₂ concentration of combustion exhaust gas, which is an index representing the smoothness of carbon adhering to the furnace wall (see paragraph 0014 of the specification of Patent Document 1). (See paragraph 0010 of the specification of Patent Document 2)

JP 2008-201925 A JP 2008-95030 A

  The measurement data of FIG. 6 is the furnace wall temperature for each carbonization chamber (kiln) in the coke oven, the horizontal axis indicates the furnace number, and the vertical axis indicates the furnace wall temperature. PS means the pusher side, and corresponds to the side where the extruder is arranged. CS means coke side and corresponds to the coke discharge side. As shown in the figure, the temperatures of the carbonizing chambers are not the same. For example, there is a temperature difference of about 100 ° C. between the carbonizing chamber of the kiln number 42 and the carbonizing chamber of the kiln number 57. Even in the same carbonization chamber, the furnace wall temperature may be different from that in the past coke production due to adjustment of the production amount. On the other hand, there is a correlation between the amount of carbon wall deposited on the furnace wall and the furnace temperature, and the amount of carbon wall deposited on the furnace wall increases as the furnace temperature increases.

FIG. 7 and FIG. 8 are enlarged views of the furnace wall schematically showing the carbon adhesion state of two carbonization chambers having different furnace wall temperatures. FIG. 7 corresponds to a carbonization chamber having a relatively high furnace wall temperature, and FIG. 8 corresponds to a carbonization chamber having a relatively low furnace wall temperature. The combustion removal methods of Patent Documents 1 and 2 are removal methods that stop gas injection when the O ₂ concentration target value set based on the relationship between the smoothness of carbon and the O ₂ concentration of combustion exhaust gas is reached. is there. The O ₂ concentration is an index reflecting the burning rate of the attached carbon layer, that is, the smoothness, and does not provide any information on the thickness of the attached carbon. That is, the methods of Patent Documents 1 and 2 are intended to burn and remove the convex carbon formed on the surface of the adhered carbon layer, and the thickness of the carbon layer interposed between the convex carbon and the furnace wall. No consideration is given to.

  For example, if the smoothness after the previous combustion process is the same as that of the current target, the amount of blown air is not corrected. However, if there is a change in the thickness of attached carbon before combustion between the previous time and this time, if the thickness of the carbon layer before combustion removal is thick (see FIG. 7A), the thickness of the carbon layer remaining after combustion is the appropriate thickness. It becomes Tr1 thicker than To (refer FIG. 7B), and there exists a possibility that the effective volume of a carbonization chamber may reduce. On the other hand, when the thickness of the carbon layer is thin (see FIG. 8A), the thickness of the carbon layer remaining after combustion becomes Tr2 thinner than the appropriate thickness To (see FIG. 8B), and protects the furnace wall during coke extrusion, There is a risk of losing the thin carbon layer that prevents the inflow of coal dust into the combustion chamber.

  Then, this invention aims at making the thickness of the adhesion carbon layer after combustion approach appropriate thickness by setting the blowing conditions which considered the carbon adhesion thickness for every carbonization chamber.

The inventor diligently studied the injection conditions based on the carbon deposition thickness for each carbonization chamber, and obtained the following knowledge. The curve shown in the graph of FIG. 1 shows the relationship between the blowing time and the CO ₂ concentration when two carbon layers having different thicknesses are burned. The right end of the curve indicates the end of blowing. The blowing flow rate (m ³ / t) was constant. The solid line I shows the CO ₂ concentration variation characteristic when the carbon layer deposited is relatively thick, broken line II indicates the CO ₂ concentration variation characteristic when the carbon layer deposited is relatively thin.

As shown in FIG. 1, when the carbon layer is thin, the carbon burns early, so that the slope of the curve becomes relatively large. On the other hand, when the carbon layer is thick, carbon does not burn early, so the slope of the curve becomes relatively small. The slope of the curve is the slope after the CO ₂ concentration has changed from increasing to decreasing. In other words, there is a correlation between the thickness of the slope and the carbon layer of the curve, on the basis of this correlation, that the CO ₂ concentration is set the blowing time of the air so that the target CO ₂ concentration, after combustion The thickness of the carbon layer can be made closer to the appropriate thickness.
In the above example, the removal of carbon is expressed as a time change when the air flow rate is constant. If this knowledge is converted into a higher level concept, it can be expressed by the total amount of air blown. That is, when the carbon layer is thick, the thickness of the carbon layer after combustion can be made closer to the appropriate thickness by increasing the total amount of blown air. Further, when the carbon layer is thin, the thickness of the carbon layer after combustion can be made closer to the appropriate thickness by further reducing the total amount of blown air.

That is, according to one aspect of the present invention, in an attached carbon combustion removing method, carbon adhering to a carbonizing chamber of a coke oven is burned and removed by blowing air into the carbonizing chamber from an injection nozzle. The blowing condition is set so as to satisfy the formula (A) when the total air volume is V1.
V1 = V0 + (A−B) / (ΔCO ₂ / ΔV) (A)
V0 is the total blowing flow rate at the previous blowing time. A is an average value of the CO ₂ concentration of the combustion exhaust gas at the end of the last N times (N is plural). B is a target value of the CO ₂ concentration of the combustion exhaust gas. ΔCO ₂ / ΔV is an average value of the ratio between the air volume and CO ₂ after the CO ₂ concentration has changed from increasing to decreasing at the end of the last M times (M is plural).

Another aspect of the present invention is that, in another method, the carbon adhering to the carbonization chamber of the coke oven is burned and removed by blowing air from the injection nozzle into the carbonization chamber. The blowing condition is set so as to satisfy the formula (A) when the total air volume is V1.
V1 = V0 + (A−B) / (ΔCO ₂ / ΔV) (A)
V0 is the total blowing flow rate at the previous blowing time. A is the CO ₂ concentration of the combustion exhaust gas at the end of the previous blowing. B is a target value of the CO ₂ concentration of the combustion exhaust gas. ΔCO ₂ / ΔV is the ratio of the air volume and CO ₂ after the CO ₂ concentration at the end of the previous blowing has changed from increasing to decreasing.

  According to the present invention, the thickness of the deposited carbon layer after combustion can be brought close to an appropriate thickness by setting the blowing conditions in consideration of the carbon deposited thickness for each carbonization chamber.

Thickness is a graph showing the relationship between the blowing time and the concentration of CO ₂ upon combustion of two different carbon layer. It is a schematic block diagram in a part of coke manufacturing equipment. It is the flowchart which showed the process which a system controller performs. It is a graph for demonstrating the meaning of (1) Formula. Extrusion torque is a graph showing the relation between dust concentration and CO ₂ concentration. It is the graph which showed the furnace wall temperature for every carbonization chamber (kiln). It is the furnace wall enlarged view which showed typically the adhesion state of the carbon in the carbonization chamber with a relatively high furnace wall temperature. It is the furnace wall enlarged view which showed typically the adhesion state of the carbon in the carbonization chamber with a relatively low furnace wall temperature.

  The attached carbon combustion removal method of the present embodiment will be described with reference to the drawings. In this embodiment, in order to make the thickness of the carbon layer after combustion approach an appropriate thickness (corresponding to the minimum thickness), the blowing time is controlled under the condition that the blowing flow rate is constant. FIG. 2 is a schematic configuration diagram of a part of a coke production facility for effectively carrying out the method of burning and removing attached carbon.

Referring to the figure, the coke production facility includes a carbonization chamber 1, a riser pipe 2, a connection pipe 3, a dry main 4, an O ₂ concentration meter 5, a charging vehicle 6, a system controller 7, A storage unit 8 and a timer 9 are included. The carbonization chamber 1 dry-distills the blended coal charged from the charging vehicle 6. The ascending pipe 2 extends in the vertical direction, and discharges dry distillation gas generated from the blended coal during dry distillation to the dry main 4 via the connecting pipe 3. The dry main 4 extends in the direction in which the carbonization chambers 1 are arranged, and transfers the dry distillation gas discharged from the carbonization chambers 1 to a dry distillation gas storage facility (not shown).

  The charging vehicle 6 is equipped with a plurality of injection nozzles 6a and blowers 6b. When the blower 6b is operated, combustion air is blown into the carbonization chamber 1 through the injection nozzle 6a. By burning combustion air into the carbonization chamber 1, carbon adhering to the furnace wall of the carbonization chamber 1 can be removed by combustion. In the present embodiment, the number of the injection nozzles 6a is three. However, the number of the injection nozzles 6a may be appropriately increased or decreased according to the volume of the carbonization chamber 1 or the number of charging ports (holes for charging coal into the carbonization chamber). it can.

The system controller 7 controls the entire charging vehicle 6 including the injection nozzle 6a and the blower 6b. Specifically, the system controller 7 operates the injection nozzle 6a for a predetermined time so that the thickness of the carbon layer remaining on the furnace wall after combustion becomes an appropriate thickness. The O ₂ concentration meter 5 is provided in the pipeline of the ascending pipe 2, acquires the O ₂ concentration of the exhaust gas, and transmits the acquisition result to the system controller 7.

However, the O ₂ concentration meter 5 may be installed inside another pipe (not shown) extending in parallel with the insertion port of the injection nozzle 6a. A zirconia sensor can be used for the O ₂ concentration meter 5. Since the zirconia sensor is strong against vibration as mounted on an automobile and can be used as it is exposed, it has an advantage of easy visual inspection and a small maintenance load. The system controller 7, based on a predetermined calculation formula (21% -O ₂ concentration), and calculates the CO ₂ concentration of the exhaust gas from the _{O 2 concentration O 2} concentration meter 5 is acquired.

The storage unit 8 stores the CO ₂ concentration (past performance) at the end of blowing in each carbonizing chamber 1 and the previous blowing time T0. The past results may be, for example, the latest three times. The CO ₂ concentration and the previous blowing time T0 are associated with the kiln number of each carbonization chamber 1. That is, the storage unit 8 stores the CO ₂ concentration and the previous blowing time T0 for each carbonization chamber 1.

Next, processing performed by the system controller 7 will be described with reference to the flowchart of FIG. This flowchart is started after completion of the coke pushing operation. In step S101, the system controller 7 blows air into the carbonization chamber 1 from the injection nozzle 6a by operating the blower 6b. In step S102, the system controller 7 starts the O ₂ concentration detection by the O ₂ concentration meter 5 and activates the timer 9. Note that the processes in steps S101 and S102 are started simultaneously.

When air is blown into the carbonization chamber 1, as shown in FIG. 1, the CO ₂ concentration rapidly increases at the initial stage of blowing. This is because the gas remaining during dry distillation at the initial stage of blowing is rapidly replaced by the carbon combustion gas. After turning to decrease, it can be considered that the remaining gas is completely eliminated and the change in the composition of the combustion gas is directly reflected. Here, since the convex portion is preferentially burned on the surface of the carbon layer and becomes smooth gradually, the combustion speed gradually decreases. Furthermore, if the combustion removal is excessively performed and the carbon adhering to the brick surface is removed and only the joint portion is formed, the combustion rate is further reduced and the CO ₂ concentration is reduced.

In step S103, the system controller 7 determines whether or not the CO ₂ concentration has changed from increasing to decreasing. If the CO ₂ concentration has changed from increasing to decreasing, the process proceeds to step S104. Conventionally, since the main purpose was to smooth the surface of the carbon layer, the blowing of air was stopped when the CO ₂ concentration reached a predetermined value. On the other hand, in this embodiment, the air blowing time is adjusted so that the thickness of the carbon layer becomes an appropriate thickness.

In step S104, the system controller 7 calculates the blow end time. Specifically, the blow end time is calculated based on the following formula (1).
T1 = T0 + (A−B) / (ΔCO ₂ / ΔT) (1)
The significance of equation (1) will be described with reference to FIG.

  T1 is the current blowing time, and obtaining this is the purpose of step S104. T0 is the previous blowing time in the same coking chamber 1. For example, when the carbonization chamber 1 with the kiln number 5 is the blowing target, the system controller 7 reads the previous blowing time T0 with the kiln number 5 from the storage unit 8.

A is an average value of the CO ₂ concentration at the end of blowing in the same carbonization chamber 1 in the past three times. The system controller 7 reads the past three CO ₂ concentrations from the storage unit 8 and averages these CO ₂ concentrations, thereby calculating A, which is an average value of the CO ₂ concentrations. For example, the CO ₂ concentration at the end of the previous blow is 7.2%, the CO ₂ concentration at the end of the previous blow is 6.8%, and the CO ₂ concentration at the end of the third blow is 7. When it is 9%, A is 7.3%. However, the past performance when calculating A is not limited to three times, and may be N times other than three times (N is a plurality other than 3). By making the past results when calculating A a plurality of times, the blowing process based on the carbon adhesion thickness in each carbonization chamber 1 can be accurately performed.

  Here, the operation state of the coke oven includes an unsteady operation state different from the normal operation state. The unsteady operation is an operation state including a planned suspension or an operation state including a long-time operation stop due to a trouble. The planned suspension is, for example, a maintenance operation performed once a month, and the operation is temporarily suspended for about 8 hours. The operation stop is to stop the coke extrusion work and the coal charging work. Usually, coke is extruded after about 1 to 2 hours have passed after the dry distillation. In the case of the operation stop, coke is extruded after 2 hours have passed after dry distillation, so that almost no gas is generated and the inside of the furnace becomes negative pressure. When the pressure in the furnace becomes negative, the attached carbon in the furnace is combusted by the outside air flowing in from the kiln opening or the like, and therefore data that does not reflect the original carbon attached thickness is included.

In this embodiment, the past performance when calculating the average CO ₂ concentration A is set to a plurality of times, thereby mitigating adverse effects (decrease in thickness control accuracy) due to the inclusion of unsteady operations in the past performance. be able to. Although the method of excluding the data of unsteady operation from the basis of calculation is also considered, the system management in actual operation becomes complicated. By making the past results when calculating the average CO ₂ concentration A a plurality of times, it is not necessary to consider the presence or absence of unsteady operation, and thus the complexity of system management in actual operation can be prevented.

B is a CO ₂ concentration corresponding to the appropriate smoothness of the deposited carbon layer, and is determined individually for each carbonization chamber 1 reflecting the state of the furnace wall of the carbonization chamber 1. That is, since the carbonization chambers 1 have different degrees of aging, the appropriate smoothness needs to be obtained individually for each carbonization chamber 1.

A method for calculating the CO ₂ concentration corresponding to the appropriate smoothness will be described with reference to FIG. The graph of FIG. 5 shows the relationship between the extrusion torque, the dust concentration, and the CO ₂ concentration. The amount of coal charged into the coke oven is basically quantitative. Therefore, when the same amount of coal is charged into the same volume of the carbonization chamber, the extrusion load after dry distillation becomes smaller as the thickness of the carbon adhering to the furnace wall becomes thinner. On the other hand, when the carbon adhering to the furnace wall becomes thin, a leakage phenomenon in which dust generated at the time of charging coal enters the adjacent combustion chamber through a crack in the joint portion is likely to occur. When the leakage increases, the dust concentration increases and the possibility of environmental impact increases. Further, when the leakage into the combustion chamber increases, clogging of the duct or the like occurs in the long term, and the combustion function is lowered. Therefore, it is necessary to set the CO ₂ concentration at which the extrusion load and the dust concentration are both low as the target CO ₂ concentration B.

In the present embodiment, the CO ₂ concentration at which the change curves of the extrusion load (torque) and the dust concentration intersect is set as the target CO ₂ concentration B. Although it is not necessary to change the target CO ₂ concentration every time it is blown, it is desirable to review it at a predetermined cycle according to the degree of aging of each carbonization chamber 1.

ΔCO ₂ / ΔT is the average value of the slope after the CO ₂ concentration has changed from increasing to decreasing at the end of the most recent M times (M is plural), that is, the amount of change in CO ₂ concentration per unit time Is defined as the average value of This is synonymous with the time change of the burning rate of carbon. At this time, when the carbon layer is thick / thin, ΔCO ₂ / ΔT is small / large. The present application is characterized in that it has been found that ΔCO ₂ / ΔT reflects information on the thickness of the carbon adhesion layer.

Since A, which is the average value of the CO ₂ concentration, changes according to the amount of carbon adhering to the furnace wall (changes according to the operating state), (A-B) differs at the time of blowing. When (A-B) is positive, that is, A> B, if blowing is performed at the previous blowing time T0, blowing is insufficient, and thus the thickness of the carbon layer after combustion becomes thicker than the appropriate thickness. When (AB) is negative, that is, A <B, if blowing is performed at the previous blowing time T0, excessive blowing occurs, and thus the thickness of the carbon layer after combustion becomes thinner than the appropriate thickness.
Therefore, an appropriate blowing time can be set by using (AB) / (ΔCO ₂ / ΔT) reflecting the adhesion thickness of each carbonizing chamber 1 as a correction value.

  In step S105, the system controller 7 determines whether or not the count time by the timer 9 has reached the blowing time T1. If the count time reaches the blowing time T1, the process proceeds to step S106. In step S106, the system controller 7 stops the blower 6b and stops blowing air.

  Thus, in this embodiment, the thickness of the carbon layer after combustion can be brought close to the appropriate thickness by stopping the air blowing at an appropriate timing in consideration of the carbon adhesion thickness for each carbonization chamber 1. . Thereby, the furnace wall damage by coke sliding can be prevented, preventing the corrosion of the volume of the carbonization chamber 1. As a result, an appropriate carbon removal operation can be performed over a long period of time.

(Modification 1)
In the above embodiment, the carbon layer after combustion is controlled to an appropriate thickness by fixing the air blowing flow rate (m ³ / t) and changing the blowing time. However, the present invention is not limited to this. . For example, the carbon layer after combustion may be controlled to an appropriate thickness by making the blowing time constant and changing the air blowing flow rate (m ³ / t). That is, the system controller 7, after the CO ₂ concentration is turned from increase to decrease, if the current blowing flow rate (m 3 ^{/ t),} the CO ₂ concentration in the blowing time was determined not drop to the target CO ₂ concentration The blowing flow rate (m ³ / t) can be increased.

In addition, when the system controller 7 determines that the current blowing flow rate (m ³ / t) decreases to the target CO ₂ concentration in a time shorter than the blowing time, the blowing flow rate (m ³ / t) Can be reduced. The blowing flow rate (m ³ / t) can be changed, for example, by adjusting the valve opening degree of the air blown from the blower 6b. According to the above-described configuration, it is possible to blow in as much air as necessary to leave an appropriate thickness. Thereby, the furnace wall damage by coke sliding can be prevented, preventing the corrosion of the volume of the carbonization chamber 1.

That is, since the CO ₂ concentration decreases as the total air flow rate (m ³ ) increases, the target time can be changed by changing the blow time or changing the flow rate (m ³ / t) as described above. CO ₂ can be brought close to the density. When the total flow rate of air blowing (m ³ ) is used as a reference, the above formula (1) can be rewritten as the following formula (2).
V1 = V0 + (A−B) / (ΔCO ₂ / ΔV) (2)
V1 is the current total flow rate (m ³ ). V0 is the previous total blow-in flow rate (m ³ ). The description of A and B will not be repeated. However, controlling the total flow rate (m ³ ) based on the blowing time instead of the flow rate (m ³ / t) is simpler and improves the reliability.

(Modification 2)
In the above-mentioned embodiment, although the average value of the CO ₂ concentration in the same carbonization chamber 1 in the past three times is A, it is not limited to three times and may be one time. The calculation conditions of A 1 time (i.e., the last time only) if the average value of CO ₂ concentration is the previous blowing at the end of the CO ₂ concentration itself. In this case, ΔCO ₂ / ΔV is the slope after the CO ₂ concentration has changed from increasing to decreasing at the end of the previous blowing, that is, the amount of change per unit time of the CO ₂ concentration corresponding to the previous blowing. Can do. Moreover, when the operation state of the carbonization chamber at the previous blowing is an unsteady operation different from the steady operation, it is desirable to use the CO ₂ concentration at the end of the previous blowing as A. Thereby, the bad influence (decrease in the precision of thickness control) by including unsteady operation can be eased.

1 4 carbonization chamber 2 uprising pipe 3 connecting pipe dry Maine 5 _{O 2} concentration meter 6 Sonyukuruma 6a injection nozzle 6b blower 7 system controller 8 storage unit 9 Timer

Claims (6)

In the adhering carbon combustion removing method, the carbon adhering to the carbonizing chamber of the coke oven is burned and removed by blowing air into the carbonizing chamber from an injection nozzle.
The adhering carbon combustion removing method is characterized in that the blowing condition is set so as to satisfy the formula (A) when the total air volume of the air blown into the carbonization chamber is V1, V1 = V0 + (A−B) / (△ CO ₂ / △ V) (A)
V0 is the total blowing flow rate at the previous blowing time.
A is an average value of the CO ₂ concentration of the combustion exhaust gas at the end of the last N times (N is plural).
B is a target value of the CO ₂ concentration of the combustion exhaust gas.
ΔCO ₂ / ΔV is an average value of the ratio between the air volume and CO ₂ after the CO ₂ concentration has changed from increasing to decreasing at the end of the last M times (M is plural). In the adhering carbon combustion removing method, the carbon adhering to the carbonizing chamber of the coke oven is burned and removed by blowing air into the carbonizing chamber from an injection nozzle.
The adhering carbon combustion removing method is characterized in that the blowing condition is set so as to satisfy the formula (A) when the total air volume of the air blown into the carbonization chamber is V1, V1 = V0 + (A−B) / (△ CO ₂ / △ V) (A)
V0 is the total blowing flow rate at the previous blowing time.
A is the CO ₂ concentration of the combustion exhaust gas at the end of the previous blowing.
B is a target value of the CO ₂ concentration of the combustion exhaust gas.
ΔCO ₂ / ΔV is the ratio of the air volume and CO ₂ after the CO ₂ concentration at the end of the previous blowing has changed from increasing to decreasing. The CO ₂ concentration of the combustion exhaust gas at the end of the previous blowing is used as the A when the operating state of the carbonization chamber at the previous blowing is an unsteady operation different from the steady operation. The method for removing burnt carbon described in 1. B is an adhesion necessary to prevent coal dust generated in the carbonization chamber from flowing into the combustion chamber of the coke oven through a gap formed in a joint portion of a brick constituting the carbonization chamber. 4. The method according to claim 1, wherein the CO ₂ concentration corresponds to the minimum thickness of carbon.   5. The method according to claim 1, wherein an air blowing time is controlled so as to satisfy the V <b> 1. 5. The method according to claim 1, wherein an air blowing flow rate is controlled so as to satisfy the V <b> 1.