JPH068685B2 - Control method of catalytic combustion heating furnace - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for controlling a catalytic combustion heating furnace, and more particularly to NO.
_{The present} invention relates to a method for controlling a catalytic combustion heating furnace, which suppresses the generation of _X , improves thermal efficiency, and can use low-calorie fuel.

(Background of the Invention) A heating furnace is used for heating an incineration fluid composed of mere combustible gas, and is used as a reaction furnace such as a decomposition furnace or a reforming furnace, a heat treatment furnace, a soaking furnace, or the like. Various furnaces for heating objects are known, and there are roughly box-shaped, upright cylindrical, and cell-shaped furnaces depending on the purpose of use. In these heating furnaces, fuel of any type is burned by a burner and heated by combustion heat. With the progress of industrial technology, as the heating furnace conditions become higher in temperature and pressure, the performance required for the heating furnace should be uniform and the temperature rise of the heating tube should not exceed its usage limit. In order to reduce the amount of fuel by suppressing the heat efficiency and increasing the thermal efficiency of the furnace, making it possible to use low-quality and cheap fuel, and reducing the cost, and to prevent pollution, the generation of nitrogen oxides that occur in the high temperature range is prevented. Suppression is required.

In a typical heating furnace such as ethylene cracking furnace and hydrogen reforming furnace, the temperature of the fluid to be heated (raw material fluid) is 800 ° C to 850 ° C.
Since high temperatures of ℃ and even higher are desired,
In the cell type furnace as shown in the figure, a large number of burners 5 are installed on the side of the furnace.
, And a short flame radiation type with a short flame is used as the burner. In the figure, 2 is a radiation heating tube, 3 is a convection heating tube, 4 is a heat recovery heating tube, 6 is a combustion air tube, 7 is a fuel tube, 8 is a combustion exhaust gas, 9 is a fuel control valve, and 10 is an air control. A valve, 11 is a temperature controller, and 12 is a proportional setter.

On the other hand, the largest loss of thermal efficiency in the heating furnace is the amount of heat carried out by the combustion exhaust gas, so-called stack loss. This loss depends on the excess air ratio of the combustion air and increases with an increase in the excess air ratio. Therefore, improvement of thermal efficiency depends on how to burn with low excess air. Combustion at this low excess air ratio has the effect of suppressing the generation of NO _X , but if the excess air ratio is reduced, the flame inevitably becomes longer and uniform heating cannot be performed. For this reason, at least 1.10.
It needs an air ratio of about 1.20.

On the other hand, as a measure for improving the thermal efficiency, it is known to recirculate combustion exhaust gas, but since the excess air ratio is also low, uniform heating cannot be performed and it is not an effective means.
Also, if the fuel used does not have a calorific value of 1200 kcal / Nm ³ or more, then misfires will occur and stable combustion will not be possible. Things are needed.

On the other hand, in a heat treatment furnace or the like, it is necessary to change the temperature inside the furnace with time. Therefore, even if the heat of the combustion gas is recovered by the waste heat recovery device, the recovered heat cannot be used because it fluctuates with time. There is a problem that it is difficult and the heat recovery is not sufficient.

(Object of the Invention) The object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, maintain uniform heating performance, reduce excess air ratio to improve thermal efficiency, and reduce the amount of fuel to reduce the quality of fuel. Another object of the present invention is to provide a method for controlling a catalytic combustion heating furnace that enables the use of the same.

(Summary of the Invention) In summary, the present invention enables exhaust gas recirculation by installing a catalytic combustor, and enables low NO _x and high efficiency combustion by controlling O ₂ in the exhaust gas and adjusting the amount of recirculated gas. The fuel consumption is reduced. That is, the control method of the catalytic combustion heating furnace of the present invention, in the control method of the catalytic combustion heating furnace having a catalytic combustion reactor and a recirculation system of the combustion exhaust gas, to detect the oxygen amount and combustion gas temperature in the combustion exhaust gas, The amount of oxygen for combustion is adjusted so that the amount of oxygen and the temperature of the combustion gas are set values, and the amount of oxygen in the combustion exhaust gas of the catalytic combustion heating furnace, the amount of air for combustion, and the catalytic combustion reactor that are obtained in advance are adjusted. The following O ₂ balance equation (1) showing the relationship of the amount of fuel supplied to the engine, O ₂ % = [(circulation gas amount × O ₂ % + air amount × 0.21) −combustion consumption O ₂ amount] / combustion Gas amount (1) and the following heat balance formula (4), combustion gas temperature = [(air carry-in heat + combustion heat + circulating gas carry-in heat)-(heated material absorption heat + heat loss)] / (combustion gas Heat capacity per unit amount) …… Based on (4) The fuel quantity Te is characterized by controlling the exhaust gas circulation amount such that the small amount.

In the O ₂ balance formula (1) of the present invention, the combustion gas amount is
It is the sum of the circulating gas amount and the value obtained from the air amount and the fuel amount, and the fuel consumption O ₂ amount is the value obtained from the fuel amount and the fuel type.

Further, in the heat balance formula (4) of the present invention, the air carry-in heat quantity is a value obtained from the air quantity and the air temperature, the combustion heat quantity is a value obtained from the fuel quantity and the fuel type, and the circulating gas carry-in heat quantity is the circulating gas. It is a value obtained from the amount and the circulating gas temperature.

(Embodiment of the Invention) A preferred embodiment of the present invention will be described with reference to FIGS. 2 and 3.

In the figure, a heating furnace main body 1 includes a convection heat transfer tube 3 through which a fluid to be heated flows, a radiant heating tube 2, and a heating tube 4 for improving thermal efficiency. The catalytic combustion burners 13 are arranged in multiple stages on both inner walls. Fuel and combustion air are sent to the catalytic combustion burner 13 from the fuel pipe 7 and the combustion air pipe 6. The details of this catalytic combustion burner 13 are shown in FIG. 3, and in this combustor, a funnel-shaped diffuser 26 into which fuel and air are introduced, and a flashback prevention plate 20 sequentially provided in a combustion gas flow path 20. , Ignition device 19,
The combustion catalyst (layer) 21 and the radiant heating plate 22 are provided, and the ignition device plate 24 ignites when the outlet temperature of the combustion catalyst 21 detected by the temperature detector 25 becomes equal to or lower than a predetermined temperature.
It has an ignition control device for activating 19. In such a configuration, the fuel and air are mixed in the diffuser 26, pass through the ignition device 19, and are burned by the combustion catalyst 21. A ceramic heater is preferably used as the ignition device 19, but a general ignition device such as ignition by an ignition plug or ignition by a pilot burner may be used depending on the fuel.
The combustion catalyst 21 enters a stable combustion region at a catalyst temperature of 100 to 300 ° C. for fuel containing a large amount of H ₂ gas and 300 to 500 ° C. for other gases, so the ignition device 19 is stopped when the temperature rises to these predetermined temperatures. You may. When using a liquid fuel, it is desirable to supply a startup gas to raise the temperature of the catalyst.

As the combustion catalyst 21, for example, a plate-shaped catalyst in which 0.5% palladium is supported on an Al ₂ O ₃ plate is laminated along the gas flow, but the present invention is not limited to the catalyst species and structure. Not something. As for such a catalyst, various catalysts can be selected since it is in the stage of practical use. The gas leaving the combustion catalyst layer 21 heats the radiant heating plate 22 to a high temperature, increases the radiant heat transfer performance to the heating pipe 2, and causes the combustion high temperature gas to uniformly flow into the furnace. The radiant heating plate 22 is preferably made of ceramics, but may be made of other materials as long as it has heat resistance. By providing the radiant heating plate 22 in this way, the burner outlet gas becomes hot and the flame becomes short, so that the distance between the heating tube 2 and the furnace wall can be greatly shortened, and the furnace can be made compact. Can be converted. This interval can be determined by the number of catalytic combustion burners 13, and can be determined simply in consideration of cost without being affected by the flame length unlike the conventional burners. The gas flowing into the furnace heats the convection heating pipe 2 and the heat recovery heating pipe 4 in the convection section, and then is exhausted as the fuel exhaust gas 8.

Generally, the thermal efficiency of the heating furnace is about 80%, and the exhaust gas temperature is
Although it is 250 ℃ ~ 300 ℃, if there is no heated target for heat recovery, the exhaust gas temperature will be even higher, for example, in a combustion furnace, the exhaust gas temperature will be 800 ° C, and the thermal efficiency may be 30% or less. . Therefore, in the control method of the present invention, part of the exhaust gas 8 is recirculated, the recirculated gas is mixed with air required for fuel, and the mixed gas is used as combustion air for the catalytic combustion burner. . The reason why such exhaust gas recirculation is possible is that a burner uses a catalytic combustion device to enable combustion even at a low excess air ratio. Since the mixed air with the recirculation gas has a lower oxygen concentration than air, it has a larger capacity than air combustion in a general burner and causes blowout of the burner or extension of flame, but in the case of a catalytic combustion burner Eliminates such trouble because the contact area of the catalyst compensates for this. From the test results of the present inventors, it was found that the combustion heat amount per catalyst area in the present invention is, for example, 30 × 10 kcal / m ² h or more at 600 ° C., and the size of the catalyst layer can be very small.

In the present invention, oxygen (O ₂ ) in the combustion gas is detected by the O ₂ measuring device 23, and the air control valve 16 controls the combustion air amount so that the O ₂ concentration becomes constant. The set value of O ₂ is set depending on the fuel type, the temperature inside the furnace, and the absorbed heat amount of the object to be heated, but in the case of high temperature and high absorbed heat amount such as ethylene decomposition furnace, about 1 to 2%, annealing furnace When the amount of absorbed heat is small at a relatively low temperature such as that of 4), about 4 to 5% is preferable.

In the present invention, the temperature of the combustion gas is detected under the control of the amount of oxygen in the combustion gas, and the fuel supply amount is controlled by the control valve 9 based on this temperature. The computer recirculated gas amount controller 15 calculates the recirculated gas amount that minimizes the fuel amount, and controls the exhaust gas recirculated amount so that it becomes the value.

In the present invention, instead of the combustion gas temperature, the outlet temperature of the fluid to be heated passing through the heating pipe 2 may be detected, and the fuel supply amount may be controlled by this temperature.

The concept of recirculation gas amount control in the present invention will be described with reference to FIG. FIG. 4 qualitatively shows changes in the O ₂ concentration in the combustion gas, the combustion air amount, and the fuel amount depending on the exhaust gas recirculation amount. When the circulation amount is increased under the condition that the combustion gas temperature is constant, the O ₂ concentration decreases, the combustion air amount decreases, and the fuel amount decreases. When the O ₂ concentration decreases to the set value level, the control system is activated and the O ₂ concentration is controlled to the minimum value, so that the air amount increases. However, in the range where the increase in the quantity of heat introduced into the circulating gas is larger than the increase in the quantity of heat required for preheating the air quantity, it continues to decrease, and after reaching the minimum value,
Start increasing. The circulation amount that gives this minimum value can be predicted in advance by calculation based on the heat balance and O ₂ balance of the furnace. That is, from O ₂ balance Here, combustion gas amount = circulation gas amount + f (air amount, fuel amount) (2) Fuel consumption O ₂ = f (fuel amount, fuel type) (3) From heat balance, combustion gas temperature = {(air Carrying heat quantity + Combustion heat quantity + Circulating gas carry-in heat quantity)-(Heating object absorption heat quantity + Heat gas) /
(Heat capacity per unit amount of combustion gas) (4) Air intake heat amount = f (air amount, air temperature) ... (5) Combustion heat amount = f (fuel amount, fuel type) ... (6) Circulating gas intake heat amount = f (Amount of circulating gas, temperature of circulating gas)
(7) The operation control variables are the air amount, the circulating gas amount, and the fuel amount, and the other factors are set or determined by the operating conditions. Of the above three variables, the air amount is constantly controlled by O ₂ % control so as to satisfy the equation (1).

When the air amount is controlled first, the variables are the circulation amount and the fuel amount. If one is determined, the other is determined, and the recirculation amount that minimizes the fuel is calculated by the relational expressions (1) to (6). be able to.

The exhaust gas circulation rate for this minimum fuel is set to O ₂ %,
Since it changes depending on the combustion gas temperature and the like, the optimum fuel amount at each set value is calculated and the circulation amount is controlled, so that the minimum fuel amount can always be obtained.

Especially when there is a change in the temperature setting value in the heat treatment furnace, etc.
The effect of reducing fuel by changing the temperature set value is great.
FIG. 4 is a diagram showing the relationship between the exhaust gas circulation amount and the control elements of the heating furnace control system according to the present invention, and FIG. 5 is a temperature holding diagram of the annealing furnace in the above control. The optimum circulation amount in this case is point (a) in FIG. 4, and is the point (b) in the case of high temperature holding. Since the optimum point of the circulation amount fluctuates due to the fluctuation of the combustion gas set temperature, the fuel amount can be minimized by always calculating the circulation amount at the optimum point and controlling the setting to that amount. It should be noted that point (c) shown in FIG. 4 is the amount when the conventional circulation is not performed, and it is clear that the amount of fuel can be reduced by 50% or more in the annealing furnace as compared with this amount. is there.

Next, FIG. 6-b is a diagram showing a flow when the control method of the present invention is applied to the annealing furnace 27. In this case, the apparatus is the same as that of FIG. 2 except that the air preheating pipe 28 and the catalytic combustion furnace 29 are separately provided, and the same reference numerals are similarly referred to for the same portions. The catalyst combustor 29 may be integrated with the annealing device 27, and the structure and the number of bases of the catalyst combustor are not particularly limited. By adopting this system, it is possible to reduce the fuel consumption by about 50% compared to the case where no recirculation is performed.

FIG. 7 shows an embodiment in which the present invention is applied to a soaking furnace. A large number of catalytic combustors 13 are provided on the opposite side walls in the soaking and heating furnace body 30, and the object 31 to be heated is heated by the effect of the radiant heating plate 22 on the front side while passing between the catalytic combustors 13 on both sides. Heated evenly.

According to this device, since the combustor can be installed close to the object to be heated by flameless combustion, the device becomes compact and highly efficient heating can be performed. Also, if the object to be heated is averse to O _2, for example, burning furnace for carbon fiber production is an ester, a fiber material such as acrylic, but is intended to produce and steamed at high temperature, this time is O ₂
When used as a carbon fiber production, the O ₂ setting is 0 and the gas analyzer 35
Control valve to adjust the C0 / C0 ₂ ratio to the set value.
By adjusting 16, the amount of recirculated gas and the amount of fuel will be controlled according to the temperature in the soaking furnace. Also in this case, the optimum circulation amount can be calculated by the computer from the heat balance and the O ₂ balance.

(Effects of the Invention) According to the present invention, the following effects can be obtained.

(1) It becomes possible to recirculate waste gas, and it is possible to significantly reduce fuel consumption. For example, there is a temperature setting change in the annealing furnace, which is about 50% compared to the case where waste heat recovery is not performed.
The above reduction is possible.

(2) As a fuel, low calorie fuel, which has a low calorific value and cannot be used in a general combustor, can be used.

(3) Since the engine is always operated with a small amount of fuel, it is possible to eliminate unnecessary fuel consumption.

(4) Since the flame is short and the distance to the object to be heated can be short, the furnace width can be minimized and the uniform heating performance is improved.

(5) The combustion is low O ₂ and the generation of NO _X can be controlled.

(6) O ₂ can be made zero or less and excellent in heat uniformity, so that it can be used for a carbon fiber production apparatus.

[Brief description of drawings]

FIG. 1 is a schematic view of a cell type heating furnace showing an example of a conventional heating furnace, FIG. 2 is a schematic view showing an embodiment of a heating furnace system according to the present invention, and FIG. 3 is the present invention. FIG. 4 is a schematic diagram of a catalytic combustion burner for a heating furnace, FIG. 4 is a diagram showing the relationship between the circulation amount and the combustion gas O ₂ %, the combustion air amount, and the fuel amount in the heating furnace control system according to the present invention, FIG. Is a temperature holding diagram in an annealing furnace, FIG. 6-a is a flow sheet of a conventional annealing furnace,
FIG. 6-b is a flow sheet showing an embodiment when the heating furnace system according to the present invention is applied to an annealing furnace, and FIG.
It is a flow sheet which shows an example at the time of applying the heating furnace system by the present invention to a soaking furnace. 1 ... Heating furnace body, 2 ... Radiant heating tube, 3 ... Convection heating tube, 4
... Heat recovery heating tube, 5 ... Burner, 6 ... Combustion air tube, 7
... fuel pipe, 8 ... combustion exhaust gas, 9 ... fuel control valve, 10 ... air control valve, 11 ... temperature controller, 12 ... proportional setting device, 13 ... catalytic combustion burner, 14 ... recirculation gas control valve, 15 ... re Circulating gas controller, 16 ... Air control valve, 17 ... Recirculation floor, 18 ... Air supply floor, 19 ... Ignition device, 20 ... Flashback prevention plate, 21 ... Combustion catalyst, 22 ... Radiant heating plate, 23 ... O ₂ Measuring instrument, 24 ... Ignition panel, 25 ... Temperature detector, 26 ... Diffuser.

Claims (1)

[Claims] 1. A method for controlling a catalytic combustion heating furnace having a catalytic combustion reactor and a combustion exhaust gas recirculation system, wherein the oxygen amount and combustion gas temperature in the combustion exhaust gas are detected and the oxygen amount and combustion gas temperature are set. The amount of combustion air is adjusted so that the value becomes a value, and the relationship between the amount of oxygen in the combustion exhaust gas of the catalytic combustion heating furnace, the amount of combustion air, and the amount of fuel supplied to the catalytic combustion reactor, which are obtained in advance, is obtained. Indicates the following O
₂ balance formula (1) O ₂ % = [(circulation gas amount × O ₂ % + air amount × 0.21) -combustion consumption O ₂ amount] / combustion gas amount ... (1) and the following heat balance formula (4 ), Combustion gas temperature = [(Air carry-in heat + Combustion heat quantity + Circulating gas carry-in heat quantity)-(Heating object absorption heat quantity + Heat loss)] / (Heat capacity per unit quantity of combustion gas) ... (4) A method for controlling a catalytic combustion heating furnace, which comprises controlling an exhaust gas circulation amount so that the fuel amount is minimized.