JPS62288406A - Fine coal burner - Google Patents

Abstract

PURPOSE:To enable a nitrogen oxide to be decreased without increasing unburnt portion in discharged gas by a method wherein a diameter of a pipe injecting fine coal is expanded and a peeled eddy flow of injection flow is generated. CONSTITUTION:An inlet diameter R1 is increased up to an outlet diameter R2, an opening angle is set as theta and an axial length of an enlarged part is difined as l. Factors 2theta and l/R1 are defined in Y-axis and X-axis, respectively, a flowing condition at an injecting flow is expressed. At portions located at lines c-c and a-a, a peeled eddy flow is substantially varied. Due to this fact, hot temperature gas at an outlet is not continuous with time. However, the gas flows to a root part of the expanded part. Therefore, a flame can be ignited at a root part of the expanded pipe. The values theta and l/R1 which are present in this area are employed to make a fine coal burner. In order to assure an action to expand a flow passage, an internal obstacle 22 having a conical shape is placed in the expanded pipe 21. For example, if an opening angle theta of the expanded pipe 21 is 8 deg. and l/R1 is 10, the eddy flow through peeling-off 24 is generated, combustion air 8 is entrapped when the eddy flow exits the expanded pipe 21 and then an amount of air required for maintaining the ignition and the combustion is assured.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Field of Application of the Invention] The present invention relates to a combustion device, and in particular to a pulverized coal suitable for reducing nitrogen oxides without increasing unburned matter in exhaust gas. This relates to the structure of the burner.

[Conventional technology]

In recent years, due to the high availability of oil, coal and natural gas have come to be used as alternative energy in both commercial and industrial boiler equipment.

In particular, coal is an important source of thermal energy because it is cheap and has abundant reserves.

Recently, methods for using coal as a combustion source in boiler equipment include burning pulverized coal slurried with oil called COM in an oil burner, or blowing air upward from the bottom of the furnace and pulverized coal there. A method of combustion in a suspended so-called fluidized bed is being developed. and,
Currently, pulverized coal combustion is the mainstream, in which pulverized coal is transported to a burner using conveying air, and then pulverized coal is ejected into a furnace for combustion.

At the same time that coal combustion became important,
On the other hand, environmental issues are becoming more important. In particular, since boiler equipment emits large amounts of exhaust gas, there are strict environmental regulations regarding the harmful substances contained therein, such as nitrogen oxides (NOx), sulfur oxides (SOx), and carbon oxides (CO). It looks like this. Therefore, there is a need for a combustion method that reduces the amount of these harmful substances.

Furthermore, when coal is used as a fuel, its flammability is poorer than that of gas or oil, so the ash inevitably contains unburned matter. In order to increase combustion efficiency, it is required to reduce this unburned content in the ash.

As mentioned above, in boilers that burn pulverized coal.

Low-pollution and highly efficient combustion is required. Currently, sulfur oxides are being dealt with by installing desulfurization equipment downstream of the boiler. On the other hand, regarding nitrogen oxidation, there are two methods: installing a denitrification device downstream of the boiler, and reducing the amount of NOx produced by burning it with a burner called a pulverized coal burner without installing such ancillary equipment. be.

Figure 3 shows a conventional example of a low NOx pulverized coal burner.

Pulverized coal 1 pulverized by a mill (coal pulverizer) to an average particle size of about 50 microns is ejected into a furnace 4 through a fuel supply pipe 3 together with conveying air 2 .

A throttle 5 in the fuel supply pipe 3 increases the speed of the pulverized coal 1 to prevent backfire. The impeller 7 supported at the tip of the support rod 6 creates a small-scale backflow area of air at the pulverized coal spouting part, thereby stably maintaining the flame. On the other hand, combustion air 8 is supplied to the burner from a wind box 9, separated into secondary air and tertiary air, each given a swirl by a secondary swirler 10 and a tertiary swirler 11, and sent from a throat 12 to the furnace 4. gush.

The pulverized coal 1 ejected from the fuel supply pipe 3 into the furnace 4 gradually mixes with the combustion air 8, while its temperature begins to rise as it receives radiation from the furnace. At this time, the pulverized coal 1 generates volatile gas, and this gas starts combustion. However, since the combustion air 8 is swirled and widely spread, the pulverized coal 1 is separated from the combustion air 8 and heated in an air-deficient state. Therefore, NOx generated by combustion of volatile matter is reduced by pulverized coal (char) from which volatile matter has been removed, and converted into N2. This effect is important for low NOx burners. From then on,
Char is mixed with air and burns gradually until complete combustion occurs.

Due to this reduction effect, the NOx concentration in the exhaust gas is reduced to 172 to 1/3 of that of a normal burner. When NOx is reduced to this level, a denitrification device becomes unnecessary, and equipment costs can be reduced significantly.

[Problem that the invention seeks to solve]

However, even this low NOx burner does not completely eliminate the need for a denitrification device. This is the problem of unburned matter that occurs as a reaction to lower NOx emissions. This problem can be solved in the fourth
The behavior of the pulverized coal 1 in the furnace 4 is schematically shown in the figure and will be explained. As already mentioned, the powdered coal 1 is initially separated from the combustion air 8 in the vicinity of the burner. Therefore, the incompletely burned char is cooled by the opposing wall (water wall 13) and further cooled by radiation. After that, combustion air 8
However, combustion progresses by mixing with

The combustion will be much slower than that of a burner that is not a low NOx burner.

If you want to avoid this, you can increase the height of the furnace, but this will increase the price of the furnace and is not a definitive solution. Also, the burners were provided facing each other. If I use a facing combustion furnace, I wonder if there will be no cooling due to collision with the water wall, or since there will still be cooling by radiation.
This is also not a definitive method.

In other words, although it is essential for a low NOx burner to burn char quickly, it must be separated from combustion air in the vicinity of the burner to suppress combustion, which creates a contradiction.

Low NOx burners, which suffer from such contradictions, still have room for improvement. The first is to ensure the ignition of volatile matter and to speed up combustion. In the conventional burner shown in FIG. 3, the ignition of volatile matter is not reliable, and a non-combustion zone called a black skirt is formed. Therefore, the combustion of pulverized coal begins with considerable light in the burner section. Therefore, the combustion of the pulverized coal starts from the burner section without fail to ignite the volatile matter, and the unburned matter can be reduced.

The second is to lower the transport speed of the pulverized coal itself. If the ejection speed becomes slower, it takes longer for the pulverized coal to reach the opposing wall, resulting in a longer residence time in the furnace and a reduction in unburned coal. deer.

However, if the conveyance speed of pulverized coal is lowered and the jetting speed itself is lowered, the pulverized powder will accumulate in the fuel supply pipe, causing flashback. Therefore, it is currently difficult to reduce the ejection speed itself.

As shown in Fig. 5, a method has also been proposed in which a swirling vane 14 is inserted into the fuel supply pipe 3 to diffuse the pulverized coal by centrifugal force to solve the above-mentioned drawbacks. The current situation is that no effective countermeasures have been taken for the rapid mixing of NOx with NOx and the generation of large amounts of NOx.

An object of the present invention is to eliminate the drawbacks of the prior art described above, and to eliminate nitrogen oxides (NO) without increasing the unburned content in exhaust gas.
An object of the present invention is to provide a boiler device capable of reducing x).

[Means for solving problems]

In short, the present invention expands the diameter of the tube through which pulverized coal is ejected so that a separation vortex is generated in the ejected flow, so that the high-temperature gas in the furnace flows to the base of the expansion tube and the flame is ignited from the base. It is something.

Next, the structural dimensions of the expansion tube for causing large fluctuations in the separation vortex will be explained below.

First, FIG. 8 shows the dimensional definition of the expansion tube. Inlet side diameter R1
The outlet side (spouting end side) is expanded to a diameter R2. The opening angle at this time is O. Let Q be the length of the enlarged portion in the axial direction.

FIG. 9 shows the opening angle 20 on the horizontal axis and the pressure loss coefficient on the vertical axis. There is a minimum value at 20-5'', and it increases from there as the opening angle increases.

On the other hand, from 20″=!60°, the pressure loss coefficient becomes independent of θ.This means that it is expected that there are roughly three states in the jet flow from the expansion tube.

Therefore, in Fig. 1o, 20 and Q/R1 are taken as the vertical and horizontal axes to show the flow situation of the jet flow. a in the diagram
Below -a, the flow is such that no separation occurs. In this state, as shown in FIG. 11(a), no separation occurs, so high temperature gas from the outlet side (inside the furnace) does not flow into the enlarged portion.

Next, above a-a in FIG. 10, the flow is a so-called free jet as shown in FIG. 11(c), and fixed ring-shaped vortices are formed on both sides of the jet. In this case, the hot gas on the outlet side can reach the outside of this vortex.

On the other hand, the portion between cc and aa in FIG. 10 corresponds to the middle of these, and the separated vortices vary greatly as shown in FIG. 11(b). Therefore, the high-temperature gas on the outlet side flows up to the root of the enlarged portion, although it is not continuous over time. Therefore, the flame can be ignited from the base of the expanding tube.

The present invention is based on this phenomenon. However, since the spreading angle as shown in FIG. 11(b) is small and the efficiency of reducing the flow velocity of pulverized coal is poor, it is desirable to insert a conical object inside the expansion tube.

〔Example〕

An embodiment of the invention is shown in FIG. The pulverized coal 1 carried to the burner by the conveying air 2 expands its flow path in the expanding tube 21 which expands into a widening shape. In order to ensure this effect, a conical internal obstruction 22 is placed inside the expansion tube 21.

As a result, the jetting speed of the pulverized coal 1 at the jetting end is greatly reduced.

On the other hand, the combustion air 2 enters the swirl generator 23 from the wind box 9, is given a swirl, and is ejected into the furnace 4.
It is expanded outwardly by a widening expansion tube 21.

The decelerated pulverized coal 1 is rectified by the downstream parallel portion of the widening expanding tube 21 so as to travel straight. And pulverized coal 1
received radiation from the furnace 4 side.

It generates volatile matter with good ignitability, but the jetting speed at the jetting end is lower than that of conventional ones, so it ignites immediately. Further, when the flow path is expanded by the widening tube 21, the opening angle θ of the tube 21 is set to 8 degrees, and Q/R□ is set to 10. This generates a vortex 24 due to separation.

When this vortex flow 24 exits the wide-spread expansion tube 21, it effectively entrains the combustion air 8, ensuring the amount of air necessary to maintain ignition and combustion.

On the other hand, since the combustion air 8 is expanded outward by the widening expansion tube 21 and swirling, the pulverized coal 1 is exposed to a high-temperature reducing atmosphere, and the NO generated by the combustion of volatile matter is
Reduce x to N2.

Thereafter, the pulverized coal 1 is gradually mixed with the combustion air 8 and combusted, but since one ignition is faster than in a conventional burner, the pulverized coal 1 can be ignited faster by that amount. In other words, since the generation and reduction of NOx is faster, the pulverized coal 1 and air can be mixed more quickly than in the conventional burner.

Furthermore, since the ejection velocity of the pulverized coal 1 at the ejection end is reduced by the conventional burner, combustion is almost completed until reaching the opposing wall.

FIG. 7 shows the results of a combustion comparison test between the burner of the present invention shown in FIG. 1 and the conventional burner shown in FIG. 3. The burners used in the test had a coal consumption of 50 kg/hr and had a common throat section and wind box. The throat diameter is 80 m, the furnace has a cross section of 0.6 m x 0.6 m, and is 5 m long.
It is. The residence time in the furnace required for combustion is approximately 2 seconds, which is equivalent to a large commercial boiler. The coal used was Pacific coal.

In FIG. 7, the vertical axis represents the NOx value at the furnace outlet, and the horizontal axis represents the unburned matter sampled at the furnace outlet.

As a parameter, the angle of the swirl vane is changed to 15 degrees (strong swirl), 30 degrees, and 45 degrees (weak swirl). In addition,
The NOx value in the exhaust gas is maintained at 0□ concentration at 3%.

As the turning becomes stronger, NOx decreases, but on the contrary, unburned fuel increases. This is a characteristic of the low-Nos pulverized coal burner mentioned above; when the swirl is strengthened, the combustion air is largely separated from the pulverized coal, and as a result, although the NOx reduction effect is ensured, the combustion of pulverized coal is It gets worse because it slows down the mixing with the commercial air.

The solid line in FIG. 7 shows the combustion results of the burner according to the present invention, and it is clear that the conventional burner has improved combustibility. When compared with the same NOx value, the unburned content has decreased by about 20%.

Another embodiment based on the same inventive idea is shown in FIG.

In FIG. 2, another widening tube 25 is attached to the outside of the widening tube 21 shown in FIG. 1. Note that the inner expansion tube 21 is provided with a large number of holes 26.

FIG. 6 is an enlarged view of this portion.

Between the outer expansion tube 25 and the inner expansion tube 21.

The ejector is effective due to the expansion action of the inner expansion tube 21, and the pressure is lower than that on the furnace side.

Therefore, the high-temperature gas 27 on the furnace 4 side is drawn into this space, and further enters the inner expansion tube 21 through the hole 26.
It rapidly mixes with pulverized coal 1, increasing the ignitability of the pulverized coal. However, since this gap is very narrow, a large amount of air does not enter, and there is almost no rise in NOx.

A comparison of combustion in the previous test furnace showed that unburned matter was further reduced by 5% compared to the burner shown in Figure 1.

〔Effect of the invention〕

According to the pulverized coal burner of the present invention, a separation vortex is generated in the ejected flow within the expansion tube, so that high-temperature gas in the furnace flows to the base of the expansion tube, thereby improving the ignitability of the pulverized coal.

Incidentally, the structure of the present invention is very simple and requires only modification of a conventional burner, so the implementation cost can be ignored.

[Brief Description of the Drawings] Fig. 1 is a side view showing an embodiment of a pulverized coal burner according to the present invention, Fig. 2 is a side view showing another embodiment of the present invention, and Fig. 3 is a conventional burner device. Figure 4 is a side view of a furnace equipped with a conventional burner, Figure 5 is a side view of an improved conventional burner, and Figure 6 is a partially enlarged view of Figure 2. The side view shown, FIG. 7, is a graph showing the combustion results. Figure 8 is a diagram for defining the dimensions of each part of the pulverized coal burner of the present invention, Figures 9 and 10 are graphs for explaining the invention in detail, and Figure 11 is for each state in Figure 10. FIG. 2 is a schematic diagram of a hail burner. 1...Pulverized coal, 2...Air for conveyance, 4...
・Furnace, 21.25... Expansion tube.

Claims (3)

[Claims] (1) A burner in which pulverized coal is injected into the furnace together with conveying air from the center tube of a double tube or multiple tubes with two or more layers, and the combustion air is swirled and injected into the furnace from the outer tube. The pipe for ejecting the pulverized coal forms an expanding pipe whose diameter increases toward the jetting end of the pipe, and the jetting end has a parallel portion whose diameter does not change, and the opening angle of the expanding pipe is 0, the length in the axial direction of the expanding tube is l, and the diameter on the inlet side of the expanding tube is R_1, and the vertical and horizontal axes are 2θ and l/R_1, respectively, to graph the area where the separation vortex of the jet flow occurs. Expression: θ, l/ existing in this region
A pulverized coal burner characterized by adopting R_1. (2) A pulverized coal burner according to claim 1, in which an obstacle having a narrow upstream side of the jet flow and a thicker downstream side is placed coaxially with the expanded portion in the expanded portion. (3) The pulverized coal burner according to claim 1, wherein another expansion tube is attached to the outer periphery of the expansion tube, and a plurality of holes are provided in the inner one of these two expansion tubes.