JPS60251315A - Catalytic combustion heating furnace and method of controlling same - Google Patents

Abstract

PURPOSE:To keep a uniform heating function and reduce the coefficient of excess air to improve the thermal efficiency by installing a number of catalytic burner on the side surface of combustion furners on the side surface of combustion furnace and providing a radiation heating plate on the front surface of each catalytic burner. CONSTITUTION:A fuel (d) and air (e) are mixed in a diffuser 26 and burn at a combustion catalyst 21 through an igniter 19. A gas emitted from the combustion catalyst layer 21 heats a radiation heating plate 22 to a high temperature to increase a furnction to conduct rediation heat. Further, the combustion high-temperature gas is uniformly flowed into the furnace. In this manner, the provision of the radiation heating plate 22 causes the burner outlet gas to have a high temperature and shortens the flame length. Hence, it becomes possible to largely shorten the interval between the heating pipe 2 and the furnace wall and to make the construction of the furnace compact. This interval can be determined by the number of the catalytic burners 13. The gas flowing into the furnace heats the convection heating pipe 2 and a heat recovery heating pipe 4, and thereafter is exhausted as a combustion exhaust gas (a).

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Application of the Invention) The present invention relates to a catalytic combustion heating furnace and a method for controlling the same, and particularly to a heating furnace and a heating furnace that suppress the generation of NOx, increase thermal efficiency, and can use low-calorie fuel. The present invention relates to a combustion control method.

(Background of the Invention) Heating furnaces range from those used simply for heating incineration fluids made of flammable gas to those used as reaction furnaces such as cracking furnaces and reforming furnaces, and those used as reaction furnaces such as heat treatment furnaces and soaking furnaces. Various types of furnaces for heating objects are known, and depending on the purpose of use, there are box-shaped, upright cylindrical, cell-shaped, and other shapes. In any type of heating furnace, fuel is combusted in a burner and heating is performed using the heat of combustion. With the advancement of industrial technology, the conditions for heating furnaces are becoming higher in temperature and pressure, and the performance required of heating furnaces is to ensure uniform heating and to prevent the rise in temperature of the heating tube from exceeding its usage limit. In order to reduce the amount of nitrogen oxides that are generated in high temperature ranges, it is possible to reduce the amount of nitrogen oxides that are generated in high temperature ranges in order to prevent pollution. There are demands to suppress it.

In typical heating furnaces such as ethylene cracking furnaces and hydrogen operating reforming furnaces, the temperature of the fluid to be heated (raw material fluid) is desired to be 800°C to 850°C, or even higher. This is a cell-type furnace as shown in the figure, with a large number of burners 5 arranged on the side of the furnace, and short-flame radiation type burners with short flames. In addition, 2 in the figure 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 pipe, 8 is a combustion exhaust gas, 9 is a fuel control valve, 10 is an air control valve, 11 is a temperature controller, and 12 is a proportional setting device.

On the other hand, the largest loss in thermal efficiency in a heating furnace is the amount of heat taken out by the combustion exhaust gas, so-called stack loss, but this loss is influenced by the excess air content of the combustion air and increases as the excess air content increases. For this reason, improving thermal efficiency depends on how to perform combustion with low excess air. Combustion at this low excess air ratio has the effect of suppressing the generation of NOx, but when the excess air ratio is reduced, the flame inevitably becomes longer and uniform heating becomes impossible. For this reason, the first
The short flame radiant burner of the heating furnace shown in the figure requires an air ratio of at least 1.10, and generally about 1.20.

On the other hand, it is known to recirculate combustion exhaust gas as a measure to improve thermal efficiency, but it is not an effective means because uniform heating cannot be achieved due to the low excess air ratio.

Also, if the fuel used does not have a calorific value of 1200Kca1/Nffr or more, misfires will occur and stable combustion will not be possible.If the excess air ratio is low, combustion will become even more unstable, and the fuel will not be of good quality. Something is needed.

On the other hand, in heat treatment furnaces, etc., it is necessary to change the temperature inside the furnace over time. There is a problem that it is difficult and insufficient heat recovery is carried out.

(Objective 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, reduce fuel amount, and use low-quality fuel. The object of the present invention is to provide a heating furnace that can also be used.

(Summary of the invention) In short, the present invention has a large number of catalytic combustors installed on the side of the combustion furnace, and a radiant heating plate provided in front of the catalytic combustors to maintain uniform heating performance and make it possible to reduce the excess air ratio. It is.

In addition, the present invention enables recirculation of exhaust gas by installing the above-mentioned catalytic combustor, and enables low NOx and high efficiency combustion by controlling 0□ in the exhaust gas and adjusting the amount of recirculated gas.
The aim is to reduce fuel consumption. That is, the method for controlling a catalytic combustion heating furnace of the present invention is a method for controlling a heating furnace having a catalytic combustion reactor and a combustion exhaust gas recirculation system, by detecting the amount of oxygen in the combustion exhaust gas and the temperature of the combustion gas, and detecting the amount of oxygen in the combustion exhaust gas and the temperature of the combustion gas. The combustion air amount is adjusted so that the combustion gas temperature and combustion gas temperature reach the set values, and the exhaust gas is It is characterized by controlling the amount of circulation.

(Embodiments 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 exchanger tube 3 through which a fluid to be heated flows, a radiant heating tube 2, and a heating tube 4 for improving thermal efficiency. Catalytic combustion burners 13 are arranged in multiple stages on both inner walls. Fuel and combustion air are fed into 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 this combustor includes a funnel-shaped diffuser 26 into which fuel and air are introduced, and a flashback prevention plate 20 that is sequentially provided in the combustion gas flow path. , ignition device 19, combustion catalyst (layer) 21, and radiant heating plate 2
2, and has an ignition control device that activates the ignition device 19 with the ignition device plate 24 when the outlet temperature of the combustion catalyst 21 detected by the temperature detector 25 becomes below a predetermined temperature. In such a configuration, fuel and air are mixed in the diffuser 26, passed through the igniter 19,
It is combusted by a combustion catalyst 21. As the ignition device 19, a ceramic heater is preferably used, but a general ignition device may be used depending on the fuel, such as ignition using a spark plug or ignition using a pyro-nodburner. In the fuel catalyst 21, the catalyst temperature is 100 to 3 when using fuel containing a large amount of H2 gas.
Since the stable combustion range is reached at 00° C. and 300 to 500° C. for other gases, the ignition device 19 may be stopped when the temperature rises to these predetermined temperatures. When using liquid fuel, it is desirable to supply startup gas to raise the temperature of the catalyst.

As the combustion catalyst 21, for example, Al2O, 0.5% on the plate
Although plate-shaped catalysts on which palladium is supported are stacked along the gas flow, the present invention is not limited to the catalyst type or structure. Since such catalysts are already in the practical stage, a variety of catalysts can be selected. The gas leaving the combustion catalyst layer 21 is transferred to the radiant heating plate 2
2 to a high temperature to increase the radiation heat transfer performance to the heating tube 2 and to uniformly flow the combustion hot gas into the furnace. The radiant heating plate 21 is preferably made of a ceramic layer, 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 high temperature and the flame becomes short (as a result, the distance between the heating tube 2 and the furnace wall can be significantly shortened, making the furnace more compact. This interval can be
It can be determined by the number 3, and can be determined simply by considering the cost, without being affected by the flame length as in conventional burners. The gas flowing into the furnace heats the convection heating tube 2 and the heat recovery heating tube 4 in the convection section, and then is exhausted as fuel exhaust gas 8.

Generally, the thermal efficiency of a heating furnace is about 80%, and the exhaust gas temperature is between 250°C and 300°C, but if there is no object to be heated for heat recovery, the exhaust gas temperature will be even higher.
In an annealing furnace, etc., the exhaust gas temperature is 800℃, and the thermal efficiency is 3.
It may be less than 0%. Therefore, in the control method of the present invention, a part of the exhaust gas 8 is recirculated, air necessary for fuel is mixed with this recirculated gas, and the mixed gas is used as combustion air for the catalytic combustion burner. . This exhaust gas recirculation is possible because a catalytic combustion device is used in the burner, which allows combustion even at a low excess air ratio. Because the air mixed with recirculated gas has a lower oxygen concentration than air, it has a larger capacity than air combustion in a general burner, causing burner blowout or flame extension, but in the case of a catalytic combustion burner. Since this is compensated for by the contact area of the catalyst, such troubles disappear. According to the test results of the present inventors, the amount of combustion heat per catalyst area in the present invention is, for example, 30×10 Kcal/at 600°C.
n(h or more), and the size of the catalyst layer can be made extremely small.

To effectively carry out the present invention, oxygen (0□
) is detected by the 02 measuring device 23, and the amount of combustion air is controlled by the air control valve 16 so that this 0□ concentration is constant. The set value of 02 is set depending on the fuel type, the temperature inside the furnace, and the amount of heat absorbed by the object to be heated, but in the case of high temperature and high amount of absorbed heat such as in an ethylene decomposition furnace, it is about 1 to 2%, and in the case of an annealing furnace, etc. 4 to 5 when the temperature is relatively low and the amount of absorbed heat is small.
% is preferable.

In the present invention, the outlet temperature of the heated fluid passing through the heating pipe 2 or the combustion gas temperature 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.
At the same time, the computer recirculating gas amount controller 15 programmed in advance calculates the amount of recirculating gas that minimizes the amount of fuel based on this temperature, and at the same time controls the amount of fuel. Control the amount of recirculation.

The concept of recirculation gas amount control in the present invention will be explained with reference to FIG. FIG. 4 qualitatively shows changes in the 02 concentration in the fuel gas, the amount of combustion air, and the amount of fuel depending on the amount of exhaust gas recirculation.

When the circulation amount is increased under the condition that the fuel gas temperature is constant, 0□
This results in a decrease in concentration, a decrease in the amount of fuel air, and a decrease in the amount of fuel. When the 02 concentration falls to the set value level, the control system is activated to control the 0□ concentration to the minimum value, causing an increase in the amount of air. However, in a range where the increase in the amount of heat brought in by the circulating gas is greater than the increase in the amount of heat required to preheat the amount of air, the amount continues to decrease, and after reaching a minimum value, begins to increase. The circulation amount that provides this minimum value can be predicted in advance by calculation based on the heat balance and 02 balance of the furnace. In other words, from 0□balance here, the amount of combustion gas =
Circulating gas amount + f (air amount, fuel amount)... (2) Fuel consumption 02 amount = f (fuel amount, fuel type)... (3) Combustion gas temperature from heat balance = ((air carry-in heat amount + Combustion heat amount + circulating gas brought in heat amount) - (heated object absorption heat quantum heat gas))
/(Heat capacity per unit amount of combustion gas)... (4) Air carry-in heat amount = f (air amount, air temperature)... (5) Fuel heat amount = f (fuel amount, fuel type)... (6 ) Calorific value brought in by circulating gas = f (circulating gas amount, circulating gas temperature) (7), and the operation control variables are the air amount, circulating gas amount, and fuel amount, and the other factors are the operating conditions. It is set or determined by Among the above three variables, the air amount is constantly controlled by 02% control so as to satisfy equation (1).

When the amount of air is controlled first, the variables are the amount of circulation and the amount of fuel, and determining one will determine the other, and the amount of recirculation that minimizes the fuel is calculated using the relational expressions (1) to (6). be able to.

The exhaust gas circulation amount for this minimum fuel is set at 02%,
Since it changes depending on the combustion gas temperature, etc., by calculating the optimum point for each set value and controlling the circulation amount, the amount of fuel can always be kept at the minimum amount.

In particular, if there are fluctuations in the temperature setting in a heat treatment furnace, etc.
The effect of reducing fuel consumption by changing this temperature setting value is large.

FIG. 4 is a diagram showing the relationship between the exhaust gas circulation amount and control elements of the heating furnace control system according to the present invention, and FIG. 5 is a diagram showing the temperature maintenance diagram of the annealing furnace in the above control. The optimum circulation amount in this case is point (a) in FIG. 4, and in the case of high temperature maintenance, it is point (b). Since the optimal point of the circulation amount varies depending on fluctuations in the combustion gas set temperature, the amount of fuel can be minimized by always calculating the circulation amount at the optimal point and controlling the setting to that amount. In addition, as shown in Fig. 4 (C
) is the amount when conventional circulation is not performed, and it is clear that compared to this amount, the amount of fuel can be reduced by 50% or more in the annealing furnace.

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 the apparatus shown in FIG. 2, except that the air preheating pipe 2 and the catalytic combustion furnace 29 are separately provided, and the explanations of the reference numerals in FIG. 2 are similarly referred to for the same parts. Note that the catalytic combustor 29 may be integrated with the annealing device 27, and the structure and number of catalytic combustors are not particularly limited. By employing this system, fuel consumption can be reduced by approximately 50% compared to the case without recirculation.

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

According to this device, the combustor can be installed closer to the object to be heated than in the case of flameless combustion, so the device is compact and can perform highly efficient heating. In addition, if the object to be heated does not contain 0□, for example, a scorching furnace for manufacturing carbon fiber is used to produce fiber materials such as ester or acrylic by steaming at high temperatures, but in this case, 0□ should not be mixed in. Therefore, when used for carbon fiber manufacturing, the setting of 02 is 0, and the air control valve 16 is adjusted using the gas analyzer 35 so that the CO/GO□ ratio becomes the set value. The amount of recirculated gas and fuel will be controlled depending on the temperature inside the thermal furnace. In this case as well, the computer can calculate the optimum circulation amount from the heat balance and 02 balance.

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

It becomes possible to recirculate +11 waste gas, making it possible to significantly reduce fuel consumption. For example, there is a change in temperature setting in an annealing furnace, and compared to when waste heat recovery is not performed, approximately 5
A reduction of 0% or more is possible.

(2) As the fuel, it is possible to use a low-calorie fuel that has a low calorific value and cannot be used in a general combustor.

(3) Since the vehicle is always operated with the minimum amount of fuel, unnecessary fuel consumption can be eliminated.

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

(5) Low 02 combustion and NOx generation can be controlled.

(6) Since it is possible to make 02 less than zero and has excellent heat uniformity, it can be used for carbon fiber manufacturing equipment.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of a cell-type heating furnace showing an example of a conventional heating furnace, Fig. 2 is a schematic diagram showing an embodiment of a heating furnace system according to the present invention, and Fig. 3 is a schematic diagram showing an embodiment of a heating furnace system according to the present invention. FIG. 4 is a schematic diagram of a catalytic combustion burner for a heating furnace, and FIG. Temperature holding diagram in an annealing furnace, Figure 5-a is a flow sheet of a conventional annealing furnace, and Figure 6-b is a flowchart showing an example of applying the heating furnace system according to the present invention to an annealing furnace. FIG. 7 is a flow sheet showing an embodiment in which the heating furnace system according to the present invention is applied to a soaking furnace. ■...Heating furnace body, 2...Radiation heating tube, 3...
・Convection heating tube, 4...Heat recovery heating tube, 5...Burner, 6...Combustion air pipe, 7...Fuel pipe,
8... Combustion exhaust gas, 9... Fuel control valve, lO・
...Air control valve, 11...Temperature controller, 12...
Proportional setting device, 13...Catalytic combustion burner, 14...
・Recirculation gas control valve, 15... Recirculation gas controller,
16... Air control valve, 17... Recirculation floor,
18... Air supply floor, 19... Ignition device,
20... Flashback prevention plate, 21... Combustion catalyst, 22
...Radiation heating plate, 23...0□ measuring device, 24.
...Ignition device panel, 25...Temperature detector, 26...
・Diffuser. Agent Patent Attorney Takenaga Kawakita Figure 1 I51U A Bond Review Axis Figure 4 Tsuba Figure 6a Figure 6b

Claims (2)

[Claims] (1) A catalytic combustion-resistant heating furnace characterized in that catalytic combustors having radiant heating plates on the front are arranged in multiple stages on the furnace side wall. (2) In a method for controlling a heating furnace having a catalytic combustion reactor and a combustion exhaust gas recirculation system, the amount of oxygen in the flue gas and the temperature of the combustion gas are detected, and the amount of oxygen and the temperature of the combustion gas are adjusted to a set value. The catalyst is characterized in that the amount of combustion air is adjusted and the amount of exhaust gas circulation is controlled so that the amount of fuel is minimized based on the preprogrammed relationship between the amount of oxygen, the amount of combustion air, and the amount of fuel. Control method for combustion heating furnace.