JPH01167591A - Furnace combustion method - Google Patents

Abstract

PURPOSE:To reduce generation of nitrogen oxides to a low level by providing air supply-exhaust devices in a pair each forming a regenerative chamber in part and in an arrangement having a fuel feeding means interposed therebetween. CONSTITUTION:The air from a blower 5 is channeled as shown by a solid arrow line by a switching valve to feed into an air supply-exhaust device 1 on the left while fuel is constantly fed into the furnace 7 through a fuel feeding means 4 so that the fuel and the air burn after mixing with the combustion gas in the furnace. The exhaust gas goes into an air supply-exhaust device 1 on the right and is cooled as it passes through a regenerator 3 and, drawn by an exhaust fan 8 as shown by a broken arrow line, is let out. After an interval of time, the switching valve shifts the channel for the supply of the air for combustion to the opposite one. Thus the function of the air supply-exhaust devices 1 during combustion is alternated between the supply and the exhaust while the fuel is in continuous supply. With the above-mentioned setup, the fuel feeding means 4 and the air supply-exhaust devices 1 are so disposed mutually as not to allow easy mixing but to allow the fuel and the air to separately mix with the gas in the furnace rather than to mix directly so that the combustion can be prevented from being locally overheated.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates primarily to an in-furnace combustion method used in high-temperature industrial furnaces.

(Prior art and its problems) As an energy-saving combustion method in a high-temperature furnace such as a glass melting furnace, a method is known in which a regenerator is used to recover waste heat and preheat combustion air. Figure 1 shows an example of a tank kiln for melting glass, which is equipped with two glue generators using checker bricks as heat storage bodies. Each glue generator has a boat that acts as an air outlet or exhaust port. Preheated air and fuel are ejected from one boat and during combustion are exhausted from the other, heating the checker bricks. It is switched after a certain period of time, and the combustion boat and exhaust port take turns. At this time, fuel injection is also switched at the same time. This is a combustion method in which this process is repeated alternately. This combustion method has a high effect of preheating the combustion air in the heat storage chamber, so a high exhaust heat recovery rate can be achieved. With such a heat storage system, a high exhaust heat recovery rate of 80% can be obtained, compared to around 40% with a general regulator. However, a major drawback of such a combustion system is that, due to the high exhaust heat recovery rate, the combustion air is preheated to an extremely high temperature, resulting in a very high level of nitrogen oxide generation. It is an object of the present invention to suppress the generation level of nitrogen oxides to an extremely low level in the conventional combustion system. The details of the figure are as follows.

(Structure and operation of the invention) An example in which the present invention is applied to a rectangular parallelepiped furnace is shown in FIGS. 2 and 3.
As shown in the figure. In the figure, reference numeral 1 denotes a member for both air supply and exhaustion, and two of these members 1 for air supply and exhaustion are attached to the furnace body 2. The case of FIG. 2 is an example in which they are arranged side by side, and the case in FIG. 3 is an example in which they are arranged facing each other.

Each of the air supply/exhaust members 1 is provided with a heat storage chamber 3, and a fuel supply member 4 is interposed between the two air supply/exhaust members 1. First, an embodiment corresponding to the first invention will be explained based on FIG. 2. Air supplied from the blower 5 is passed through the switching valve 6, as indicated by the solid line arrow in the figure, and is used for both supply and exhaust on the left side. At this time, since fuel is constantly being supplied to the furnace 7 from the fuel supply member 4, this fuel and air are mixed with the combustion gas in the furnace and combusted. At this time, the exhaust gas is transferred to the other supply/exhaust member 1,
That is, as shown by the broken line arrow from the member 1 on the right side of the figure, it passes through the heat storage chamber 3, becomes low temperature, is sucked into the exhaust fan 8, and is discharged. After a certain period of time, the flow of the combustion air described above is reversed by the switching valve 6. That is, the air from the blower 5 passes through the switching valve 6 to the heat storage chamber 3 of the supply/exhaust member 1 on the left side of the figure, where it is preheated and then ejected from the supply/exhaust member 1 into the furnace interior 7, where it is blown out as fuel. It mixes with the fuel and furnace gas ejected from the supply member 4 and burns. At this time, the combustion exhaust gas passes through the heat storage chamber 3 of the supply/exhaust member 1 on the left side of the figure, stores heat, becomes low temperature, and is discharged by the exhaust fan 8. Combustion is thus carried out in the fuel supply state by alternately supplying and exhausting air through the supply and exhaust member 1. In addition,
The fuel supply member 4 may be freely selected such as a single hole or a plurality of radially arranged nozzles in order to adapt the flame to the shape of the furnace body 2 or to adjust the mixing state.

Next, an embodiment corresponding to the second invention will be explained based on FIG. The instability of combustion is exposed. Therefore, at low temperatures, the fuel supply member 4 does not supply fuel, but instead guides fuel to the air supply/exhaust member 1 shown on the left side of the figure, as shown by the imaginary line in the figure, and the fuel is sent from the blower 5. Mix with air and burn.

Then, the exhaust at that time is from another air supply/exhaust member 1,
That is, the gas is discharged from the supply/exhaust member 1 on the left side of the figure through the heat storage chamber 3 at a low temperature. In this case, the supply/exhaust member 1 is alternately switched as necessary. In this state, the temperature inside the furnace is 7.
When the temperature reaches a high temperature of 50° C. or higher, the injection of fuel supplied from the air supply/exhaust member 1 together with the combustion air is stopped,
Fuel is supplied into the furnace only from the fuel supply member 4, mixed with combustion air and furnace gas supplied into the furnace from one of the above-mentioned supply/exhaust members, and combusted. Air is discharged from the dual-purpose member 1, and at this time, the air supply/exhaust member 1 alternately and repeatedly performs air supply and exhaust.

(Effects of the Invention) When the combustion state in the furnace of the present invention is compared with the conventional combustion system, there is a marked difference. That is, in the conventional system, the fuel is directly injected into the preheated air at the boat outlet or the fuel is directly injected inside the boat and mixed with the air, resulting in an extremely good mixing state. In this case, the air supply/exhaust members and the fuel supply member 4 are located far apart, resulting in poor mixing.Furthermore, before the air and fuel are directly mixed, they are mixed with the furnace gas, resulting in a decrease in oxygen concentration. - Slow combustion of the layer results in a combustion state without local high temperatures. In addition, in conventional combustion systems, combustion starts inside an insulated burner, resulting in high flame temperature, but in the present invention, fuel is injected directly into the furnace, so combustion starts and heat is generated. At the same time, heat is transferred from the flame to the object to be heated or the surrounding furnace wall, the flame temperature is further lowered, and nitrogen oxides can be significantly reduced.

Furthermore, in the second aspect of the invention, since combustion is performed using the supply/exhaust member only at low temperatures, the preheated air temperature is also low, combustion can be achieved at a low furnace temperature, and nitrogen oxides can be suppressed to a sufficiently low level. When the temperature is high, the method is switched to the same method as above,
A similar effect can be obtained.

In the experiment, nitrogen oxides were 1000 ppn+ (0□11%) at a furnace temperature of 1300°C and a preheated air temperature of 1050°C, but under the same conditions, the combustion method of the present invention reduced the nitrogen oxides to 1000 ppn+ (0□11%).
It became 100 pp or less, and a reduction rate of 90% or more was obtained.

As described above, according to the present invention, a large effect of reducing nitrogen oxides can be achieved through self-exhaust gas recirculation in the furnace, slow combustion, and heat dissipation from the flame.

[Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram of a conventional combustion system, and FIGS. 2 and 3 are schematic explanatory diagrams of a combustion method according to the present invention. Code 1... Member for both supply and exhaust, 2... Furnace body, 3...
Heat storage chamber, 4...Fuel supply member, 5...Blower, 6.
...Switching valve, 7...Furnace interior, 8...Exhaust fan.

Claims (2)

[Claims] (1) Two air supply/exhaust members are installed in the furnace body, each of the air supply/exhaust members is provided with a heat storage chamber, a fuel supply member is provided between the two air supply/exhaust members, and the fuel Fuel is constantly supplied into the furnace from the supply member, and combustion air is supplied from one of the supply/exhaust members to cause combustion in the furnace to occur while mixing the fuel and air together with the gas in the furnace. An in-furnace combustion method, characterized in that the air is discharged from the other one of the air supply/exhaust members, and the air supply/exhaust members alternately perform air supply and exhaust. (2) Two air supply/exhaust members are installed in the furnace body, a heat storage chamber is provided in each of the air supply/exhaust members, a fuel supply member is provided between the two air supply/exhaust members, and when the temperature is low, , without supplying fuel from the fuel supply member, the fuel is ejected and mixed with air from the one air supply/exhaust member to perform combustion in the furnace, and the exhaust gas at that time is not supplied from the other air supply/exhaust member. When the temperature inside the furnace reaches a high temperature of 750°C or higher, the fuel is ejected from the member together with combustion air by switching the supply/exhaust member as necessary. The fuel is supplied into the furnace only from the fuel supply member, mixed with combustion air and furnace gas supplied from one of the supply/exhaust members, and burned in the furnace. An in-furnace combustion method, characterized in that air is discharged from a member that also serves as an exhaust gas, and in this case, the member that serves as an air supply and exhaust gas alternately performs air supply and exhaust.