JPH0263124B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a combustion method, and particularly to a combustion method such as a boiler device that does not cause an increase in nitrogen oxides (hereinafter referred to as _NOx ) in exhaust gas even under low load. It concerns driving methods.

Since NO _x is considered to be one of the causative substances of photochemical oxidants, there has been a demand in recent years for the development of a combustion method that effectively suppresses its generation. The following combustion methods are known as combustion methods that meet these objectives: (1) exhaust gas recirculation method, (2) water injection method, (3) two-stage combustion method, and (4) denitrification combustion method. The two-stage combustion method is attracting particular attention because of its excellent NO _x reduction effect and operability.

As shown in FIGS. 1 and 2, the device applied to the conventional two-stage combustion method includes a lower burner 3, a middle burner 4, and an upper burner, which are sequentially provided from the bottom to the top on the front side wall of the furnace 1. 5, and a front after-air port 6 provided above the upper stage burner 5.
, a rear after-air port 7 provided on the rear wall of the furnace 1 , and a hopper port 2 provided at the bottom of the furnace 1 for regulating exhaust gas.

In the above configuration, the air ratio (actually supplied air amount/theoretically required air amount) in the burner section is
For example, 0.8 to 1.0 for lower burner 3, and 0.8 to 1.0 for middle burner 4.
The upper stage burner 5 is set at 0.6 to 0.8, and the upper stage burner 5 is set at 0.4 to 0.6, and combustion is performed under these conditions. In this _{case NO} is reduced to N ₂ by contact with reducing radicals, thereby achieving low NO _x levels. Note that the above-mentioned combustion gas contains a large amount of unburned matter, but it is not preferable from the standpoint of environmental conservation and thermal efficiency to discharge it as is. Efforts are being made to ensure complete combustion of fuel. The high-temperature exhaust gas 8 after complete combustion passes through the flue at the top of the furnace 1, recovers heat in a heat exchanger (not shown) provided as necessary, and then is discharged into the atmosphere.
On the other hand, the heat generated by each combustion is used as a heat source for evaporating boiler feed water.

Conventional combustion equipment achieves good combustion and low NO _x as described above, but these effects are
Obtained during full load or rated load operation, but not necessarily during low load or partial load operation. In other words, when operating at low loads, conventionally the flow velocity of the material passing through the burner throat is reduced simultaneously across all burners depending on the load, but when this method is used, the flow rate of the material passing through the burner throat is reduced simultaneously across all burners. Since the axial velocity of the reducing flame decreases, the reducing flame and the NO _x -containing combustion gas generated below the furnace 1 are insufficiently mixed, resulting in a disadvantage that NO _x is not sufficiently reduced.

The purpose of the present invention is to eliminate the _drawbacks of the prior art described above, and to achieve
It is an object of the present invention to provide a combustion method for a multistage burner that enables combustion in accordance with a decrease in fuel supply amount, that is, a decrease in load.

The inventors of the present invention have investigated an operating method that does not cause a decrease in flow velocity at the burner throat even under low loads, and thus does not have the above drawbacks.
It is effective to cut the burner according to the load, and to cut the burner in such a way as to avoid flame interference from adjacent burners, it is effective to shorten the flame length and reduce the generation of soot and dust. I found something very interesting.

The present invention has been made based on the above findings, and is a method for burning fuel by changing the amount of fuel supplied (load) in a combustion apparatus equipped with a multi-stage burner and an after-air port above the burner. ), among the middle stage burners excluding the lower stage burner and the upper stage burner, the burner is cut downward in sequence from the burner closest to the upper stage burner, and when the load is further reduced, according to the load. Among the lower burners and upper burners, the burners adjacent to both end burners and the burners inside these burners are sequentially cut in consideration of left and right balance.

The burner (main burner) in the middle section is usually composed of only one stage, but may be provided with two or more stages. When two or more stages are provided, according to the present invention, it is preferable to sequentially cut the burners from the stage closest to the upper stage burner according to the load reduction (partial load).

It is desirable to cut the lower burners and upper burners as uniformly as possible from the viewpoint of horizontal balance of the boiler, but if the number of rows is even, cut every two rows,
Alternatively, a mixed cut of this and every other row may be used. This degree of non-uniform cutting does not pose a particular problem to the essence of the present invention.

In the present invention, the reason why the burners at both ends of the lower stage burner and the upper stage burner are not cut is to limit the concentration of unburned matter, since unburned matter tends to be concentrated near the furnace wall surface adjacent to the both end burners.

The burner can be cut by any known method that allows cutting, but in particular, each stage burner and after-air port is provided with an independent damper for adjusting the air flow rate and a wind box following the damper, and the middle stage burner is cut. When cutting the burner, it is desirable to reduce the corresponding damper to the extent that the burner does not burn out.

Hereinafter, the present invention will be explained in more detail with reference to embodiments shown in the drawings.

Embodiment 1 FIG. 3 and FIG. 4 show an example of a combustion device to which the present invention is applied, and this device includes the symbols 1 to 8 of the device shown in FIGS. is similarly referred to, and the lower burner 3,
A lower wind box 9, a middle wind box 10, an upper wind box 11, a front after air wind box 12, and a rear wind box are provided independently on the outside of the middle burner 4, the upper burner 5, the front after-air port 6, and the rear after-air port 7. It mainly consists of a side after-air wind box 13. Incidentally, on the upstream side of each of the above-mentioned wind boxes 9 to 12, an independent damper for adjusting air flow rate (not shown) is provided respectively.

In the apparatus having the above configuration, when the burner 40 indicated by a black circle in FIG. 5 is cut by restricting the damper corresponding to the middle stage burner 4, the burner 40 is cut out.
The load operation was approximately 1/2 of the rated value. At this time, the flow velocity at the throats of the lower burner 3 and upper burner 5 that are in operation does not decrease, so the _NOx- containing fuel gas generated in the lower burner 3 and the reducing flame formed in the upper burner 5 are mixed well. As a result, the conventional problem of insufficient reduction of NO _x has been resolved. Further, since the flames of the lower stage burner 3 and the flames of the upper stage burner 5 do not interfere with the flames of the adjacent stage burners, the generation of soot and dust is reduced.

Example 2 The burners were constructed in the same manner as in Example 1, except that the burners adjacent to both end burners of the lower burner 3 and the upper burner 5 were additionally cut out as burners 30 and 50 indicated by black circles in FIG. It was cut.

By making the above cuts, load operation at approximately 1/4 of the rated load was achieved while maintaining the horizontal load balance of the boiler.

According to this example, the same NO _x reduction effect and reduction in soot and dust generation as in Example 1 can be achieved, and in the lower burner and upper burner, there is less flame interference between adjacent burners in each stage. As a result, soot and dust generation is further reduced.

Embodiment 3 The structure is similar to that shown in FIGS. 3 and 4, except that instead of the one-stage middle stage burner 4, a two-stage middle stage lower stage burner 4A and middle stage upper stage burner 4B are provided as shown in FIG. In the apparatus constructed as above, the middle upper stage burner 4B was cut like the burner 40B indicated by a black circle in FIG. 8 by squeezing the corresponding damper.

With the above cut, the load operation was approximately 3/4 of the rated load, and the same NO _x reduction effect and reduction in soot and dust generation as in Example 1 were achieved.

Example 4 Except for additionally cutting the lower middle stage burner 4A as shown in the burner 40A indicated by the black circle in Fig. 9,
When the burner was cut in the same manner as in Example 3, the load operation was approximately 1/2 of the rated value.

With the above cut, the same NO _x
A reduction effect and a reduction in soot and dust generation were achieved.

Example 5 The procedure was the same as in Example 4, except that burners adjacent to both end burners of the lower burner 3 and the upper burner 5 were additionally cut as shown in the black circles in FIG. 10. When the burner was cut off, the load was reduced to approximately 1/4 of the rated load.

According to this example, the same NO _x reduction effect and reduction in soot and dust generation as in Example 4 are achieved, and in the lower and upper burners, there is less flame interference between adjacent burners within each stage. As a result, soot and dust generation is further reduced.

Example 6 Figures 3 and 4 except that there are 5 burner rows.
In an apparatus having a configuration similar to that shown in the figure, the middle stage burner and the burners adjacent to both end burners of the lower stage burner 3 and the upper stage burner 5 are arranged as shown by black circles 40, 30 and 50 in FIG. 11, respectively. It was cut.

By making the above cuts, the load operation was reduced to about 1/4 of the rated load, and the same NO _x reduction effect and reduction in soot and dust generation as in Example 2 were achieved.

As described above, according to the present invention, according to the load reduction, the middle burner is moved from the upper burner to the lower burner, and then the burners adjacent to both end burners of the lower burner and the upper burner and the burners inside them are balanced horizontally. By cutting the pieces at equal intervals while maintaining the same, it is possible to achieve efficient combustion in response to load reduction, and the flow velocity at the throat of each operating burner is maintained at a high level, reducing the amount of NO _x contained in the lower part of the furnace. Combustion gas and the reducing flame generated in the upper burner are better mixed, which makes it possible to reduce _NOx , and because flame interference between adjacent burners is reduced, soot and dust generation can also be reduced. can.

[Brief explanation of the drawing]

Figure 1 is a side view showing a conventional combustion device, Figure 2 is a side view showing a conventional combustion device;
The figures are a view as viewed from direction A in FIG. 1, FIG. 3 is a side view showing an example of a combustion device applied to the present invention, and FIG.
A cross-sectional view in the direction of arrows along line B-B in Fig. 3, No. 5
6 and 6 are state diagrams of a burner cut according to an embodiment of the present invention, FIG. 7 is a layout diagram of a burner to be cut in another embodiment of the present invention, and FIGS. FIG. 7 is a diagram illustrating the cut state of the burner according to another embodiment of the present invention, and FIG. 11 is a state diagram of the burner cut according to another embodiment of the present invention. 3...lower burner, 4...middle burner, 4A...
...Middle stage lower burner, 4B...Middle stage upper burner, 5...Upper burner, 6...Front side after air port, 7...Rear side after air port, 9...Lower wind box,
10...middle wind box, 11...upper wind box, 12...
Front after-air wind box, 13...Rear after-air wind box, 30...Lower cut burner, 40...Middle cut burner, 40A...Middle lower cut burner, 40B...Middle upper cut burner, 50...
...Upper Katsutobana.

Claims (1)

[Claims] 1 In a method of burning by changing the amount of fuel supplied in a combustion device equipped with multi-stage burners, depending on the decrease in the amount of fuel supplied, among the middle-stage burners excluding the lower-stage burners and the upper-stage burners, from the burner in the stage closest to the upper-stage burner A combustion method characterized by sequentially cutting and burning the fuel, and further, as the amount of fuel supplied decreases, sequentially cutting and burning from the burners adjacent to the burners at both ends in the direction of the burner row, taking into account the left and right balance. .