JPS6321406A - Powdered fuel backfire inhibiting device - Google Patents

Abstract

PURPOSE:To prevent a backfire into a fuel pipe and at the same time reduce unburnt components in the exhaust gas by disposing a throttled part on the upstream side of the fuel pipe outlet and a conical object in the center on the downstream side of said throttled part, their relationship being specially set. CONSTITUTION:The powdered coal carried by conveying air passes in a fuel pipe 1, is throttled by a throttled part 7 at the entrance of a windbox 3, is expanded outwardly by a conical object 8, and then is injected into a furnace 5 out of the fuel pipe 1. The burning air is supplied from the windbox 3 to an air resistor 2 to be injected into the furnace 5 from the furnace wall 4. If the relationship between the location of minimum inner diameter of the throttled part and the axial distance DELTAL of the location of maximum diameter of the conical object is set 0.25<DELTAL/D<1.0, where D is the diameter of the fuel pipe 1, the ignition starts from coarse powders concentrated in the outer periphery, ensuring an adequate burning time and reducing unburnt components in the exhaust gas.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a combustion device for pulverized fuel, and is particularly suitable for preventing flashback to a fuel pipe that injects fuel and reducing unburned content in exhaust gas. Regarding boiler equipment.

[Conventional technology]

After the oil crisis that occurred in the 1970s, a review of the oil-dependent energy format began, and even the power generation industry, which consumed large amounts of oil, took this as an opportunity to switch to coal, gas, and nuclear energy. ing. Among them, coal energy has abundant reserves and is inexpensive, so it is currently being utilized.

In addition to conventional pulverized coal combustion, coal can be used by
New methods such as COM, CWM, and gasification are under development. However, pulverized coal combustion, in which coal is pulverized and combusted as is, is currently overwhelmingly popular.

In this widely used pulverized coal combustion system, coal is sent from a coal bunker to a mill, where it is pulverized and turned into pulverized coal, which is then sent to a burner along with conveying air through a fuel pipe. It is often supplied to multiple burners in a mill.

Pulverized coal combustion has poor combustibility compared to conventional oil fuel, and because it uses a mill, it responds poorly to load changes, but the biggest difference lies in handling. First, in the case of oil fuel, once the pressure is increased with a pump, it can then be freely supplied to the burner via piping. on the other hand,
In the case of pulverized coal, it is transported by air, so
If the piping is too curved, the pulverized coal will accumulate, and if the pipe is long horizontally, the pulverized coal will settle. In this case, there is a risk of fire due to spontaneous combustion.

Various measures have been taken to deal with such problems in handling pulverized coal. One of these is a pulverized coal flashback prevention device installed inside the fuel pipe.

[Problem to be solved by TAMI] The pulverized coal flashback prevention device will be explained with reference to FIG.

Pulverized coal transported from the mill enters the air register 2 through a fuel pipe r. On the other hand, combustion air enters the wind box 3 and is guided to the air register 2. Then, these are ejected through the furnace wall 4 into the furnace 5, ignited,
form a flame. At this time, the pulverized coal 6 on the conveying air
The pulverized coal passes through the pulverized coal flashback prevention device 7 and enters the air register 2. However, as already mentioned, if there is a horizontal section in the piping such as the fuel pipe 1, the pulverized coal 6 tends to accumulate and prevents heat from the furnace 5 side. If this occurs, the flames may propagate within the fuel pipe 1, potentially resulting in a major fire. Therefore, this backfire can be prevented by providing an aperture that exceeds the flame propagation speed. That is the flashback prevention device 7. Fuel pipe 1 from the beginning
It would seem that it would be better to make the diameter smaller, but in that case the flame would not reach the burner and would be blown off, causing an inconvenience on the combustion side.

This flashback prevention device 7 also has another function.

As already explained, if there are bends or horizontal sections in the piping, separation of pulverized coal and conveying air and uneven flow will occur. The flashback prevention device also serves to prevent this, and is absolutely necessary for stable combustion.

However, most of the conventional flashback prevention devices have a restriction installed inside the fuel pipe 1 as shown in Figure 2. According to this method, the concentration distribution of the fuel transported from the mill is uneven and the flow is uneven. The generated pulverized coal flow is partially rectified, but the pulverized coal concentration becomes uneven again at the widening part. In other words, when leaving the constriction part, the conveying air is spread almost uniformly by adjusting the angle on the downstream side of the constriction part to an extent that does not cause separation.
However, since pulverized coal has a specific gravity of 2,000 compared to air, it does not spread outwards, but instead gathers toward the center due to the upstream effect of the throttle. This tendency is caused by coarse coal with a large inertial force. The more powdery the powder, the more noticeable it becomes.

Coarse powder takes longer to complete combustion than fine powder, but since the flame progresses from the outside to the inside, the start of ignition is delayed compared to fine powder, and sufficient combustion time cannot be secured. As a result, the amount of unburned particles due to coarse particles increases in the boiler exhaust gas, significantly reducing combustion efficiency.

As a conventional technique for dealing with this decrease, as shown in FIG. Because the rectifying effect that eliminates concentration unevenness decreases,
It has not been very effective in reducing the amount of unburned gas.

As described above, in the flashback prevention device according to the conventional technology, coarse powder with poor combustibility gathers in the center and ignition in the flame is delayed, so that it is not possible to reduce the unburned content in the exhaust gas.

[Means for solving problems]

Through experiments, it has been found that in order to eliminate the above-mentioned drawbacks, the mutual relationship between the position of the constricted portion and the position of the substantially conical object can be appropriately adjusted. That is, if the axial distance ΔL between the minimum inner diameter position of the throttle part and the maximum diameter position of the substantially conical part is 0.25<ΔL/D<1.0 with respect to the diameter of the fuel pipe, then (See Figure 6).

[Effect]

The pulverized coal flow, which has uneven concentration of fine particles and drifts, is made uniform by being squeezed from the outside in front of the throttle section. Then, when it enters the enlarged part behind the constriction part, it is pushed outward by the substantially conical object 8. As a result, pulverized coal is more concentrated on the outside than air, and in particular, coarse powder is concentrated on the outside. Therefore, at the outlet of the fuel pipe 1, a uniform distribution in the circumferential direction and a high concentration of pulverized coal on the outside in the radial direction can be obtained. Since ignition starts from the coarse powder concentrated on the outside, sufficient combustion time can be ensured, and it is thought that the amount of unburned matter in the exhaust gas can be reduced.

In order to confirm the numerical values of the present invention, a small 50 kg/hr
When tested with a burner, the unburned content was 10% lower than before. Furthermore, NOx in exhaust gas is necessary for low NOx combustion.
The value did not change.

The situation is shown in FIG. As shown in Fig. 1, the horizontal axis in Fig. 6 is the position L□ where the throttle, which is a flashback prevention device, is at its minimum.
, and the position L2 where the substantially conical structure 8 has its maximum diameter ΔL
is made dimensionless by dividing by the fuel pipe diameter. In other words, it means the displacement of the substantially conical object 8. On the other hand, the vertical axis shows NO in the exhaust gas sampled at the fuel pipe outlet.
The x'a degrees and the amount of unburned matter in the ash are shown in relative terms for comparison, with ΔL/D=O, that is, the conventional type being taken as 100%. Even if ΔL/D is increased, there is almost no change in the NoxtA degree in the exhaust gas, whereas the unburned content rapidly decreases with only a slight change. However, the reason why it increases on the contrary after that is because, based on the principle already mentioned, if ΔL/D becomes too large, the effect of the present invention will deteriorate.

It is believed that even in large commercial boilers, the amount of unburned matter can be reduced by about 10% without increasing the NOx value.

[Embodiments of the invention]

The overall configuration of the combustion system according to the embodiment of the present invention is shown in the fourth example.
As shown in the figure. Coal 11 is transferred from coal bunker 12 to feeder 1
3 and is sent to Mill 14. The crushed pulverized coal is sent from the fuel pipe 1 to each burner by conveying air. On the other hand, combustion air is sent to the wind box 3 by the fan 15 and distributed to each burner. Then, they are ejected from the furnace wall 4 into the furnace 5, burned, and exit as exhaust gas 64 from a chimney (not shown).

Note that a part of the air 61 sent out from the fan 15 flows as combustion air 62 and a part flows as transport air 63 to form a flow of pulverized coal 6 .

Next, FIG. 5 shows a burner embodying the present invention.

The pulverized coal carried by the conveying air passes through the fuel pipe 1,
At the inlet of the wind box 3, the fuel is squeezed inward by the constrictor 7, first expanded outward by the substantially conical member 8 of the present invention, and then ejected from the fuel pipe 1 into the furnace 5. On the other hand, combustion air is supplied from the wind box 3 to the air register 2.
and is ejected from the furnace wall 4 to the furnace 5 side. The pulverized coal and combustion air ejected into the furnace gradually begin to mix, receive heat from the furnace, ignite, and begin combustion.

In addition, the fuel pipe 16 for oil in the center of the fuel pipe 1
is a pipe for supplying warm-up oil until pulverized coal combustion starts, and the oil is stopped during pulverized coal combustion.

The effects of this embodiment will be explained. Δ in Fig. 5 above
The value of L/D is 0.5. First, the pulverized coal and conveying air are squeezed from the outside to the inside by the throttle section 7. As a result, it occurred in the piping from the mill 14 to the burner.

Unevenness and drift in pulverized coal concentration are eliminated.

Next, it was provided downstream of this aperture 7. The substantially conical object 8 forces the pulverized coal and the conveying air to the outside. After that, the diameter of the substantially conical object 8 gradually decreases again, so
The conveying air having a small inertial force becomes uniform within the Tsuyuel Vibe 1. However, the inertia of pulverized coal is 2,
Since it is about 1,000 times larger, it heads toward the spout while being pressed outward.

In particular, coarse powder with a large particle size has this tendency even more.

In order to confirm the effect of this example, during non-combustion.

FIG. 8 shows the results of measuring the pulverized coal concentration at the fuel pipe 1 outlet. The vertical axis is the radial position of fuel pipe 1 divided by the pipe radius, with 0 being the center,
1 corresponds to the fuel pipe diameter. The horizontal axis is a dimensionless quantity obtained by dividing the sampled pulverized coal concentration by the maximum pulverized concentration. 0 is the area where there is no pulverized coal, and 1 is the maximum concentration. In FIG. 8, B shows the case of the conventional type shown in FIG. 2, and A shows the case of FIG. 5.

As is clear from FIG. 8, in the case of the conventional type, the maximum concentration of fine powder is at the center of the fuel pipe 1, and it can be seen that the fine powder is concentrated at the center due to the throttling effect of the flashback prevention device. On the other hand, in the case of B, which is a one-piece embodiment, on the contrary, the position where the fine powder concentration is maximum is on the outside, and the concentration is low in the center.

This result demonstrated the effect of this example.

FIG. 7 shows another embodiment. The difference from the example in Figure 5 is that
A substantially conical member 8 is attached to the sleeve 21 and is configured to slide in the axial direction of the fuel pipe. If a substantially conical object is placed in the constriction part, it will be similar to the conventional example (FIG. 3), but if the sleeve 21 is pushed into the furnace side, the value of ΔL/D according to the present invention can be obtained. This sleeve 21 moves within an outer cylinder 22 extending from the fuel pipe 1 and is fixed by a stopper.

In addition, as another embodiment, the shape of the substantially conical object may be streamlined, but the effect is the same.

〔Effect of the invention〕

According to the pulverized fuel flashback prevention device of the present invention, flashback into the fuel pipe can be prevented, and at the same time, an increase in the amount of unburned components in the exhaust gas can be suppressed.

[Brief explanation of drawings]

FIG. 1 is an enlarged view of the main part of FIG. 5, FIG. 2 is a side sectional view of a conventional burner, and FIG. 3 is a side sectional view showing another example of the conventional burner. Fig. 4 is a system diagram of a pulverized coal-fired boiler embodying the present invention, Fig. 5 is a side sectional view of a burner embodying the present invention, and Fig. 6
The figure is a graph showing the effects of the present invention.
FIG. 7 is a side sectional view of a burner showing another embodiment, and FIG. 8 is a diagram showing pulverized coal concentration measurement results showing the effects of the present invention. 1...Fuel pipe. 5... Furnace. 6... Crushed solid fuel (pulverized coal), 7... Squeezing section. 8... Substantially conical object, 63... Conveying air.

Claims (4)

[Claims] (1) In a combustion device that has a fuel pipe that injects pulverized solid fuel into the furnace together with conveying air, there is a pipe on the upstream side of the fuel pipe's jet opening, where the inner diameter of the fuel pipe gradually decreases from upstream to downstream. A substantially conical object is provided with a constricted portion that gradually increases in size after reaching a minimum inner diameter, and is located at a central position on the downstream side of the constricted portion and whose diameter gradually increases from upstream to downstream and gradually decreases after reaching the maximum diameter. is provided, and the distance ΔL between the minimum inner diameter position of the constricted part and the maximum diameter position of the substantially conical part in the axial direction of the fuel pipe is 0.25< with respect to the diameter D of the fuel pipe.
A pulverized fuel flashback prevention device characterized by having a relationship of ΔL/D<1.0. (2) In claim 1, the substantially conical object is formed by the outer diameter of the oil fuel pipe provided coaxially at the center of the fuel pipe changing from upstream to downstream. Has pulverized fuel flashback prevention device. (3) In claim 1, the substantially conical object is an outer part of a cylindrical sleeve that slidably covers the outer periphery of an oil fuel pipe that is coaxially provided at an internal center position of the fuel pipe. A pulverized fuel flashback prevention device having a cylindrical sleeve whose diameter changes from upstream to downstream and configured to be slidable from the outside of a fuel pipe. (4) In any one of claims 1, 2, or 3, the substantially conical object is a pulverized fuel inverter whose diameter changes in a curved manner and has a streamlined shape as a whole. Fire prevention device.