JPH0122526B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pulverized coal combustion burner that can use various coals with different fuel ratios as fuel.

A conventional burner combustion device for a pulverized coal-fired boiler has a structure as shown in Fig. 1, in which a mixed phase mixture of pulverized coal and primary air for combustion is injected from a fuel-air compartment nozzle 1, and this is injected into auxiliary air nozzles 2, 2'. Combustion was completed by mixing with secondary combustion air ejected from the combustion chamber. In this case, the position of the ignition point is an important factor governing stable combustion; if it is too far away, so-called combustion breathing, pressure fluctuations, and misfires may occur. Additionally, if the coal used is flame-retardant (generally contains a lot of fixed carbon and has a low volatile content), the ignition point becomes further away, making stable combustion more difficult. In other words, as shown in FIG. 2, flame-retardant coal has a small flame propagation velocity Vp, while easily combustible coal has a large flame propagation velocity Vp.

FIG. 3 is an explanatory diagram showing the state of combustion flame behind the burner. The distance Ip from the rear end of the burner to the ignition point is determined by the following equation from the relationship with the secondary air flow velocity Va (m/s).

Ip (m) = 0.182Va/Vp−0.6 As is clear from this equation, the flame propagation velocity Vp
If Vp is large, the ignition point distance Ip will be small, and conversely, if Vp is small, Ip will be large. In other words, when easily flammable coal is used as fuel, the ignition point approaches the burner,
When flame-retardant coal is used as fuel, the ignition point is moved away from the burner.

Note that if the ignition point is too close to the burner, clinker trouble may occur due to overheating of the nozzle or ash adhesion, so care must be taken.

Coal-fired boilers have recently come into the spotlight again in Japan, but recent coal-fired power plants differ from conventional ones in the following ways.

(1) The properties of the coal used are extremely diverse. This is partly due to the diversification of energy sources.
Coal imported into Japan is extremely diverse, ranging from relatively good combustible coal from the western United States, to fire-retardant coal such as Australian coal, Chinese coal, and even South African coal. It is not possible to ensure such good combustibility and stability with conventional burners.

(2) Recent coal-fired power plants have large load fluctuations due to the increased density of nuclear power, and the required minimum load has become lower. Generally, when the load becomes low, the combustion load inside the furnace decreases, and the stability of the flame deteriorates.

The present invention has been made with the object of providing a pulverized coal combustion burner that satisfies these conditions required of recent coal-fired boilers and ensures good performance.

Therefore, the present invention provides a flame holder that forms a vortex in a part of the burner nozzle for burning pulverized coal to maintain fire, and also makes it possible to freely change the flame holding capacity according to the properties of the coal and the load of the boiler. Examples of the present invention will be described in detail below.

The structure of an embodiment of the present invention is shown in FIG. 4, and a bird's-eye view thereof is shown in FIG. Both figures show examples of the tangential combustion method, which is widely used in the combustion of pulverized coal.

1 is a fuel air compartment nozzle and 2 is an auxiliary air nozzle. The mixed fluid of pulverized coal/primary air pulverized by the pulverizer is supplied to the pulverized coal supply pipe 3.
through the burner and is injected into the boiler through the injection nozzle tip 6. On the other hand, the secondary air that supplements the combustion is supplied to the secondary air nozzle flow path 5 around the supply pipe 3 in the fuel-air compartment nozzle 1.
It is supplied from around the pulverized coal/primary air jet injected into the boiler through the auxiliary air nozzle 2 to maintain and complete the combustion. 4 is a partition wall.

The feature of the present invention is that the injection nozzle tip 6 has a decisive influence on the shape of the pulverized coal flame, especially the position of the ignition point.
The angle is variable and can be freely controlled depending on the purpose.

That is, the injection nozzle tip 6 is attached by support pins 7 to each of the four sides of a rectangular ejection port that ejects a multiphase flow of primary air and pulverized coal. The chips 6 on each side can be freely rotated about a support pin 7 by a drive lever 9 via a connecting pin 8.

Next, the functions and effects of the present invention will be explained. Figures 6 and 7 show the fuel air compartment nozzle 1.
This is an enlarged view of the box shown in Figure 6. Figure 6 shows the case when burning coal types with a high fuel ratio (fixed carbon/volatile matter), such as South African coal, which has little volatile matter in the coal and a lot of fixed carbon. The state of the injection nozzle tip 6 and its configuration under flame are shown. In this case,
The drive lever 9 is pulled in the direction opposite to the inside of the furnace (in the direction of arrow A), the angle of the injection nozzle tip 6 is set up, and a violent vortex of secondary air is formed behind the nozzle tip 6. This vortex holds the flame in this region even if the flame propagation speed is high, and this radiant heat is given to the flame, so that the main flame is also ignited very close to the nozzle, and the ignition point distance Ip can be kept small. As a result, even flame-retardant coal can be stably ignited, resulting in numerous benefits such as increased combustion stability and reduced unburned content in the ash.
This type of operation is also extremely effective for burning so-called low-grade ash, which has a high ash content and low volatile content in the fuel.

It goes without saying that such operation can be used not only when flame retardance is desired, but also when the combustion load is low, such as when the boiler load is low, and flame stability is generally poor.

Next, a case will be described in which a type of coal with a low fuel ratio such as coal from the western United States (Colorado, Utah, etc.) is used. These charcoals are too combustible for conventional burners, and their ignition points are very close together, sometimes drawing flame into the nozzle, causing overheating and burnout of the nozzle. In the present invention, as shown in Fig. 7, the drive lever 9 is pushed into the furnace (in the direction of arrow B), and the injection nozzle tip 6 is set horizontally so that the secondary air flows smoothly around the pulverized coal/primary air jet. This is to maintain the ignition point position at an appropriate interval Ip. Of course, such operation can be used not only when the furnace is easily flammable, but also when the furnace is filled with flame under high load and the flame stability is originally good.

Further, such nozzle changes can be made manually, or a control system can be attached to automatically set the nozzle according to the coal type and load.

FIG. 8 shows an example of a low NOx burner that has recently attracted attention, in which a recirculating gas nozzle 10 for passing inert gas is installed between the fuel air compartment nozzle 1 and the auxiliary air nozzle 2. It goes without saying that it can also be bonded to burners such as these and exhibit its effects.

FIGS. 9 and 10 are examples in which the present invention is applied to a circular burner (so-called R burner) that is often used in front combustion and opposing combustion systems. The pulverized coal/primary air mixture is sent by a pulverized coal supply nozzle 20, and is completely combusted by the secondary combustion air coming out from around this nozzle 20. Secondary combustion air is divided into an inner cylinder 22 and an outer cylinder 23 by a secondary air nozzle 21. 25 is a flame retaining vane according to the present invention, and 24 is a rotating shaft. A plurality of vanes 25 rotated by the rotating shaft 24 are installed in the radial direction,
Further, the vane 25 is installed only on the side closer to the center.

Fig. 9 shows a case where easily combustible coal type is burned, and the vane 25 is oriented in the direction of the tube axis, so that the secondary air flow smoothly flows into the main stream without causing any disturbance to the secondary air flow injected from the inner tube 22. The flame flows along the bottom of the flame, and therefore the ignition point position Ip can be kept at a certain distance from the nozzle tip.

Figure 10 shows the case of burning flame-retardant coal types.
The vanes 25 are oriented perpendicularly to the tube axis, forming a circular ring shape that appears to be continuous.
This obstructs the secondary air flow near the pulverized coal supply nozzle 20. On the other hand, since the position near the wall of the secondary air nozzle 21 is open, the secondary air flow constricts in this part and generates a strong trailing vortex on the back side of the flow vane 25, thereby holding the flame. The ignition point position Ip can be kept sufficiently close.

As described above in detail, the present invention provides a pulverized coal combustion burner that can maintain an optimal combustion state depending on the type of coal used as fuel and the load condition.

[Brief explanation of drawings]

Fig. 1 shows a conventional pulverized coal combustion burner, a is a front view as seen from the boiler side, b is a side sectional view, Fig. 2 is a characteristic diagram showing combustion characteristics depending on the type of coal in this type of burner, and Fig. 3 4 is an explanatory diagram showing the state of the combustion flame at the rear of the burner, FIG. 4 is a side sectional view showing an embodiment of the pulverized coal combustion burner according to the present invention, FIG. 5 is a bird's eye view of the one in FIG. 4, and FIG. 7 and 7 are explanatory diagrams respectively shown to explain the action of the present invention, FIG. 8 is a diagram to explain the action when the present invention is applied to another combustion burner, and FIG. 9 and FIG. FIG. 10 shows another embodiment of the present invention, in which a is a side sectional view and b is a front view seen from the boiler side. 1... Fuel air compartment nozzle, 2...
...Auxiliary air nozzle, 3... Supply pipe, 5... Secondary air nozzle flow path, 6... Injection nozzle chip, 7...
Support pin, 8... Connection pin, 9... Drive lever.

Claims (1)

[Claims] 1. In a pulverized coal combustion burner in which a secondary air nozzle for ejecting secondary air is arranged at least in part around the multiphase flow nozzle for ejecting a multiphase flow of primary air and pulverized coal, A pulverized coal combustion burner characterized in that a member is provided in the secondary air nozzle near the outlet and is driven from the outside to change the shape of the flow path of the secondary air.