JP2541936B2 - Combustion device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a combustion device using fine powder of solid fuel such as pulverized coal, and particularly to stable combustion even at boiler startup and low load. The present invention relates to a combustion device that can maintain the state, enhance the use efficiency of solid fuel, and reduce the consumption of oil fuel.

[Background of the Invention]

Along with the transition of the fuel supply and demand situation, there are an increasing number of cases where solid fuels, mainly coal, are applied to large-capacity power generation boilers. Hereinafter, the background of the present invention will be described by taking coal as an example.

Conventional coal-fired boilers often have a so-called pulverizer direct connection type, which has a coal combustion facility system mainly composed of a pulverizer such as a ball mill and a burner directly connected to the pulverizer. For the reason, the fineness of 74 μm is used in 70 to 85% pass.

Further, the pulverized coal pulverized by the pulverizer is transported by the primary air and ejected from the burner nozzle into the furnace, but the primary air amount is determined due to the performance of the pulverizer. Therefore, the ratio of air to pulverized coal (pulverized coal concentration) changes depending on the load of the pulverizer, and the pulverized coal concentration decreases as the fineness is improved and the load is reduced. Due to the influence of flammability, furnace ambient temperature and combustion air temperature, coal cannot be burnt at low load in the boiler, and oil must be supplemented. Also,
In the initial stage of startup, in addition to the above, there is a problem that coal cannot be used due to a lack of a heat source for drying the coal in the crusher.

Further, recently, the ratio of nuclear power generation to the total amount of power generation has been increasing, so that the operation of the pulverized coal combustion boiler is also affected by it. That is, in nuclear power generation, it is difficult to change the load and it is also inefficient, so that the pulverized coal boiler has come to be operated at an intermediate load with the nuclear power generation as a base load. For this reason, the load fluctuation of the pulverized coal boiler is large, and the flexibility of the system capable of coping with this is now required.

Under such circumstances, for example, at the time of starting the pulverized coal boiler, or in the minimum load zone at the limit of possible load, or in other rapid load change zones, it is a so-called crusher to always maintain an optimum combustion state. It is extremely difficult as long as there is a large capacity, poorly responsive buffer tank in the combustion system.

In contrast to the combustion system directly connected to the crusher, there is a once-storage type combustion system. With this method, pulverized coal that has been crushed with a crusher and adjusted to a desired particle size is stored in a bottle regardless of load fluctuations, and then pulverized coal is taken out of the bottle according to load fluctuations and transported by air to a burner. It is a system that is used for combustion.

This method is suitable under conditions where responsiveness is required, such as at startup or during low load or sudden load changes, but when the boiler load is large and relatively stable, the amount of coal used is large. Moreover, since there are problems such as ignition and dust explosion when storing a large amount of coal, the crusher direct connection method described above is more preferable.

[Object of the Invention]

The present invention has been made in view of the above circumstances, and can maintain a stable combustion state even at the time of starting the boiler and at the time of low load, while increasing the use efficiency of solid fuel such as coal and using the amount of oil fuel. It is an object of the present invention to provide a combustion device with reduced fuel consumption.

[Outline of Invention]

In order to achieve the above-mentioned object, the present invention provides a first solid fuel crushing means which is driven, for example, a ball mill and which is driven at start-up and low load, and, for example, coal which is crushed by the first solid fuel crushing means. The solid fuel of (1) is entrained in a high-temperature gas such as a mixed gas of air and exhaust gas and transported by air flow to obtain a fine powder solid fuel having a predetermined particle size distribution and an ultrafine powder having a smaller particle size than the fine powder solid fuel. Separation means such as a cyclone separator for separating into powdery solid fuel, first storage means such as a bottle for storing the fine powdery solid fuel having the predetermined particle size distribution, and the ultrafine powdery solid fuel A second storage means, such as a bag filter, for storing the fuel, and a start-up for transporting the fine pulverized solid fuel taken out from the first storage means by air flow and burning it. A load burner, a steam type gas heater for sending a high temperature gas to the first solid fuel crushing means, and a first solid by burning the ultrafine powder solid fuel stored in the second storage means. Second solid fuel crushing means including a hot-air stove provided adjacent to the steam gas heater for feeding high-temperature gas to the fuel crushing means, and a ball mill or the like driven at normal load other than startup and low load And a load main burner which directly combusts the fine powdery solid fuel pulverized by the second solid fuel pulverizing means by air flow transportation by a high temperature gas.

〔Example〕

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of a main part of a combustion apparatus according to an embodiment.

Coarse-grained coal 2 in the startup-low load coal bunker 1 passes through a coal feeder 3 and each startup pulverizer (for example, a ball tube mill, a vertical roll race pulverizer with a built-in rotary classifier, etc.) 4 It is thrown into and crushed. This crusher 4
The pulverized coal 5 pulverized by the above and adjusted to a predetermined particle size (74 μm 90% or more pass) is transported by air, and the pulverized coal 5 is separated from the air by passing through each cyclone separator 6,
After that, they are distributed and put into the respective bins 8 by the distributor 7 composed of a chain conveyor. On the other hand, the air containing the ultrafine coal 46 separated by the cyclone separator 6 is introduced into the bag filter 9, where it is separated into ultrafine coal 46 and air. A static eliminator 12 is installed in the middle of the connecting pipe 10 connecting the cyclone separator 6 and the distributor 7 and the connecting pipe 11 connecting the distributor 7 and the bottle 8.

As shown in FIG. 2, this static eliminator 12 is composed of a mesh body 13 in which conductive thin wires such as copper and nickel are woven at intervals of about 5 to 20 mm, and as shown in FIG. Are arranged along the falling direction of the pulverized coal 5 at predetermined intervals, and each net 13 is grounded.

FIG. 4 shows another example of the static eliminator 12, which is composed of a grid body 14 in which conductive plates such as copper and nickel are combined at intervals of about 20 to 30 mm.

The pulverized coal 5 is rubbed against each other during transportation or the like to generate static electricity. On the other hand, since a part of the pulverized coal 5 floats in the hollow portion of the bottle 8, when the static electricity of the pulverized coal 5 is discharged in the hollow portion to generate fireworks, a dust explosion occurs. Therefore, the static electricity of the pulverized coal 5 is removed by the above-mentioned static eliminator 12 to prevent the dust explosion.

As shown in FIGS. 5 and 6, a large number of cooling pipes 15 are embedded in the layer of the pulverized coal 5 formed in the bottle 8. Each cooling pipe 15 is inserted from the outside to the inside of the bottle 8 and is attached at a slight inclination (inclination angle of about 10 to 30 degrees) so that its tip end faces downward. In this embodiment, eight cooling pipes 15 are arranged at equal intervals along the circumferential direction, and the cooling pipes 15 are provided in three stages along the height direction of the bottle 8.

As the cooling pipe 15, a natural circulation type shown in FIG. 7,
Alternatively, the forced circulation type shown in FIG. 8 is used.
The natural circulation type cooling pipe 15 is a double pipe as shown in FIG. 7, and a cooler 16 is individually attached to the outside of the bottle 8,
The cooling system is filled with a coolant (not shown) such as water. The forced circulation type cooling pipe 15 has 2 as shown in FIG.
It has a heavy pipe structure, and a cooler 16, a refrigerant tank 17 and a pump 18 are attached to the outside of the bottle 8. The cooler 16, the refrigerant tank 17 and the pump 18 are connected to the other cooling pipes 15.
It is shared with.

A temperature detector 19 such as a thermocouple is attached to the outer periphery of the cooling pipe 15, whereby the pulverized coal 5
The temperature in the bed of is monitored and recorded in the recorder 20.
When the temperature in the layer exceeds 150 ° C., for example, the alarm device 21 including a buzzer, a lamp and the like operates to warn the temperature rise in the layer.

The above-mentioned natural circulation type cooling pipe 15 allows the refrigerant to naturally circulate in the system due to the difference in specific gravity, and cools the refrigerant that has reached a high temperature.
It is designed to be reused after being cooled to a predetermined temperature at 16. On the other hand, the forced circulation type cooling pipe 15 monitors the temperature inside the bed with the temperature detector 19, and when the temperature exceeds a predetermined temperature (for example, 150 ° C.), the pump 18 is activated to forcibly circulate the refrigerant, and It is designed to lower the temperature. Further, the pump 18 may be started up every predetermined time, apart from the case of the temperature rise described above.

Further, a heat pipe can be used as the cooling pipe 15. In this case, the evaporating portion of the heat pipe is pulverized coal
Is buried in the bed of the container and the condensation side is arranged outside the bottle 8. In any case, the temperature inside the bed of the pulverized coal 5 is maintained below a predetermined temperature by the cooling pipe 15.

There is a concern that the pulverized coal 5 stored in the bottle 8 will generate heat due to natural oxidation, and heat will not be dissipated in the inside of the bed, and it will be accumulated inside, which will raise the temperature in the bed and may cause ignition. There is. By embedding a large number of cooling pipes 15 in the layer of the pulverized coal 5 as described above, it is possible to lower the temperature in the layer and prevent ignition.

When the cooling pipes 15 are arranged horizontally in the bed, the blockage of the pulverized coal 5 and the bridging are formed in the bottle 8 due to that, and the pulverized coal 5 may not be smoothly supplied. In the embodiment of the present invention, the pulverized coal 5 is smoothly supplied by inclining the cooling pipes 15 to each other.

The distributor 7 is a hermetically sealed type, and the inside of the distributor 7 is filled with an inert gas such as carbon dioxide gas or nitrogen gas so that the oxygen concentration is suppressed to about 12% or less. The inert gas is of a circulation type, and as shown in FIG. 1, a dust remover 23, a dehumidifier 24, an oxygen concentration detector 25, an inert gas cylinder 26 and a fan 27 are provided in the inert gas circulation system 22. It is provided.

The pulverized coal 5 moving along with the circulating inert gas is collected by the dust remover 23 and returned to the distributor 7. If the pulverized coal 5 contains water, it may cause blockage or bridging, so that the dehumidifier 24 is provided to remove water as described above. Also, the oxygen concentration in the circulating inert gas is constantly monitored by the oxygen concentration detector 25,
When the actually measured oxygen concentration exceeds the set oxygen concentration (for example, 12%), the inert gas is supplied from the inert gas cylinder 26, and the ignition is prevented by lowering the oxygen concentration.
As shown in the figure, an inert gas such as carbon dioxide gas or nitrogen gas is also supplied to the inside of the bottle 8 to form a low oxygen concentration atmosphere.

In the lower part of the bin 8, for example, a metering coal feeder 28 such as a vertical rotary blade feeder or a feeder with an impact meter is installed. Then, the pulverized coal 5 stored in the bottle 8 is sequentially taken out from the metering and feeding machine 28 according to the boiler load, and heated to a predetermined temperature (for example, about 80 ° C.) by an air preheater (not shown). The air is carried along with the primary air 29 to each starter-low load burner 30 and used for combustion when the boiler starts up, when the load is low, or when the load fluctuation rate is large.

An air amount measuring device 31 and a primary air blower 32 are provided in the supply system of the primary air 29.

FIG. 9 is a schematic configuration diagram of the starter-low load burner 30 used in this embodiment.

As shown in the figure, the starter-low load burner 30 has a primary sleeve 33 for supplying primary air 29 in which the pulverized coal 5 is mixed at a predetermined ratio, and a tip portion of the primary sleeve 33. The provided flame stabilizer 34 and the flame stabilizer in the primary sleeve 33
A swirl vane 35 made of, for example, ceramic, which is provided slightly ahead of 34 and is excellent in heat resistance and wear resistance that swirls the mixed air flow of the pulverized coal 5 and the primary air 29 to give a non-uniform distribution of density Have

Further, the starter-low load burner 30 has an opening degree adjuster 36 for adjusting the opening degree of the swirl vane 35, and the swirl vane 35 allows the mixed air flow of the pulverized coal 5 and the primary air 29 to flow. The pulverized coal concentration (the pulverized coal / air or less, abbreviated as C / A) where the density distribution is given by swirling with the C / A detector 37 for detecting by using a laser, for example. A heating element 38 for igniting the pulverized coal 5, a power supply device 39 for supplying power to the heating element 38, and a control signal for adjusting the opening degree of the swirl vane 35 according to the detection signal from the C / A detector 37. The opening controller 36
And a control unit 40 for outputting an ignition command signal to the power supply device 39.

FIG. 10 is an ignition characteristic diagram when a ZrBz / SiC type conductive ceramic is used as the heating element 38 and is inserted in a mixed air flow of the pulverized coal 5 and the primary air 29. This experiment
Use three types of coal supply amount A, B, C different from each other,
This is an experiment in which the stable ignition region, the unstable ignition region, and the non-ignition region were investigated by varying the primary air flow velocity at the nozzle outlet and the pulverized coal concentration (C / A).

As is clear from this figure, the pulverized coal concentration (C / A) is regulated to 0.5 or more and the primary air velocity is regulated to 10 m / s or less in order to stably ignite and hold flames at startup or under low load. I know I need.

On the other hand, in an actual pulverized coal burning combustor, it is known that the pulverized coal piping cannot be reliably handled and transported unless the C / A is set to 0.5 or more because of the specific gravity of the pulverized coal. ing. In addition, the air flow velocity at the fuel injection port must be maintained at 15 m / s or higher to prevent flashback.

In FIG. 9, the inside of the primary sleeve 33 is about 15 to 20 m /
The mixed air flow of the pulverized coal 5 and the primary air 29 supplied at a flow rate of s is swirled by the swirl vanes 35, and as shown in the same figure, the pulverized coal near the tip inner peripheral portion of the primary sleeve 33. A high concentration (C / A) region is formed.

For stable ignition, it is necessary to set an appropriate C / A according to the amount of coal supply, as shown in Fig. 10. In this embodiment, the pulverized coal concentration (C / A) is detected by using the C / A detector 37, and the opening of the swirl vane 35 is adjusted by the controller 40 based on the detection signal so that the C / A becomes appropriate. Is adjusted. If you turn too much, pressure loss will increase, so C / A will be 0.5.
The opening degree of the swirl vane 35 may be adjusted so as to be restricted to the range of 2.0 to 2.0, preferably 1.0 to 2.0.

Another factor for stable ignition and flame holding is the condition of air velocity. In this embodiment, as shown in FIG. 9, the large-diameter portion 41 is provided at the tip of the primary sleeve 33 to reduce the flow velocity of 15 to 20 m / s described above to 10 m / s or less. Further, by causing the mixed airflow to collide with the flame stabilizer 34, a circulation vortex 42 is formed in the vicinity of the flame stabilizer 34. Since the air velocity of the circulating vortex 42 is a low velocity region of 5 m / s or less in absolute value, a region suitable for ignition and flame holding is formed. For this reason, an area suitable for direct ignition of pulverized coal having a high concentration of pulverized coal and a low flow velocity is formed near the outlet of the burner.

Then, when the pulverized coal collides with the heating element 38 installed in this area and heated to about 1000 to 1200 ° C., the volatile components in the pulverized coal are continuously ignited, and a flame is formed in the circulation vortex flow. . Further, due to the propagation of this flame, the entire supplied pulverized coal is ignited.

Referring back to FIG. 1, the system of the combustion device will be described. The exhaust gas introduced from the boiler chimney inlet gas conduit 43 is mixed with the air decomposed by the bag filter 9 at a predetermined ratio, and the exhaust gas pushing fan 44 allows the steam exhaust gas heater.
Introduced into 45, it is heated up to a predetermined temperature by high-pressure steam 46 from, for example, a local boiler (not shown). The exhaust gas whose temperature has been raised in this way passes through the exhaust gas amount measuring device 47, and is thereafter supplied to each of the startup-low load crushers 4.

In addition to the steam type exhaust gas heater 45, a hot-air stove 48 is also provided, and as the fuel for the hot-air stove 48, ultra-fine coal 49 with a very small particle size collected by the bag filter 9 is used, and it is directly ignited. To be done.

Fig. 11 shows the relationship between the particle size of pulverized coal and the ignition energy. As is clear from this figure, when the particle size of pulverized coal becomes ultrafine coal of 10 μm or less, the specific surface area increases and combustion Since the speed is increased, it is possible to ignite with an extremely small energy, and therefore it is possible to directly burn the ultrafine coal 46 without using oil or gas.

As shown in FIG. 1, this ultra-fine coal 46 is mixed not only with the hot air stove 48 but also with the pulverized coal 5 and is supplied to the starter-low load burner 30. Although not shown, a sensor such as a load cell is provided below the bag filter 9, and the ultra-fine coal powder stored in the bag filter 9 is
The amount of 46 can be detected. Then, normally, the ultrafine coal 46 is used for starting-low load of the boiler, and when the storage amount of the ultrafine coal 46 in the bag filter 9 exceeds a predetermined value, it is also supplied to the hot air stove 48, or On the contrary, normally, the pulverized coal 46 is supplied to the hot blast stove 48 and used, and when the storage amount of the pulverized coal 46 in the bag filter 9 exceeds a predetermined amount, it is also supplied to the starter-low load burner 30. It is about to do.

The coarse-grained coal 2 in the load coal bunker 50 passes through the coal feeder 3 and is charged into each load crusher (for example, a crusher such as a ball mill) 51 to be crushed. This load crusher
The pulverized coal pulverized by 51 and adjusted to a predetermined particle size (the pulverized coal having a particle size slightly larger than that of the pulverized coal pulverized by the starting pulverizer 4 may be used in the air preheater (not shown). Therefore, it is transported by air while being dried by the hot air 52 whose temperature has been raised in advance, and is directly introduced into the main load burner 53 for combustion.

When the boiler is started, when the load is low at about 10 to 30%, or when the load fluctuation rate is large, start the required number of units-Drive the crusher 4 for low load to make the pulverized coal 5 and the ultra-fine coal 46. , Start-up-supplies to the low-load burner 30 to cope with the start-up of the boiler, low load, or high load fluctuation rate. If the boiler load is large or the load fluctuation rate is comparatively small, the required number of load crushers 51
Is driven to produce pulverized coal, which is supplied to the main load burner 53 to meet the required load. In a certain load region, the start-low load burner 30 and the load main burner 53 can be used together as needed.

〔The invention's effect〕

Since the present invention has the above-described configuration, when the combustion apparatus is started, when the load is low, or when the load fluctuation is large, the temporary storage method with excellent responsiveness can be applied and the concentration of the solid fuel can be maintained high. No need for auxiliary combustion of oil and low NOx
Efficient combustion including conversion can be performed. Further, when the load of the combustion device is large and relatively stable, the pulverizer direct connection system, which does not cause a trouble due to the storage of the fine powdered solid fuel, can be applied, so that the safety of the combustion device can be secured.

Furthermore, since the ultra-fine powdered solid fuel generated when producing the fine powdered solid fuel to be supplied to the starter-low load burner is collected and used as the fuel for the hot stove, the use efficiency of the solid fuel is high. The amount of oil fuel used as fuel for the steam gas heater can be reduced. In addition, since the ultrafine powdery solid fuel has an extremely large specific surface area and a high burning rate, it is possible to directly ignite the ultrafine powdery solid fuel, which also reduces the amount of oil fuel used. .

[Brief description of drawings]

The drawings are all for explaining a combustion apparatus according to an embodiment of the present invention, and FIG. 1 is a schematic configuration diagram of a main portion of the combustion apparatus,
2 and 3 are a plan view and a cross-sectional view of the static eliminator, FIG. 4 is a perspective view of another static eliminator, and FIGS. 5 and 6 are vertical cross-sectional views showing the arrangement of the cooling pipes in the bottle. And a plan view, FIG. 7 is an explanatory diagram of a natural circulation type cooling pipe, FIG. 8 is an explanatory diagram of a forced circulation type cooling pipe, FIG. 9 is a schematic configuration diagram of a starter-low load burner, and FIG. 10 is coal. Fig. 11 is a characteristic diagram showing the ignition state of Fig. 11, and Fig. 11 is a characteristic diagram showing the relationship between the particle size of pulverized coal and the ignition energy. 4 ... Startup-low load crusher, 5 ... Pulverized coal, 6 ... Cyclone separator, 8 ... Bottle, 9 ... Bag filter, 15 ... Cooling pipe, 30 ... Startup-low load burner, 38 …
Heating element, 45 …… Steam exhaust gas heater, 48 …… Hot air stove, 49
…… Ultra-fine coal, 51 …… Load crusher, 53 …… Load main burner.

Claims (6)

(57) [Claims] 1. A first solid fuel crushing means that is driven at startup and under a low load, and a solid fuel crushed by the first solid fuel crushing means is entrained in a high temperature gas and is transported by air flow to have a predetermined particle size distribution. Means for separating into a pulverized solid fuel having a particle size smaller than that of the pulverized solid fuel, and a first storage for storing the pulverized solid fuel having the predetermined particle size distribution Means, a second storage means for storing the ultra-fine powdery solid fuel, a starter-low load burner for transporting and burning the fine powdery solid fuel taken out from the first storage means by air flow, No. 1 steam type gas heater for sending high temperature gas to the solid fuel crushing means, and hot air for sending high temperature gas to the first solid fuel crushing means by burning the ultrafine powdery solid fuel stored in the second storage means. Furnace and usually negative A second solid fuel crushing unit that is driven during loading, and a load main burner that directly transports the fine pulverized solid fuel crushed by the second solid fuel crushing unit by high-temperature gas to directly burn it, First solid fuel crushing means, separating means, first storage means, second storage means, start-up system-system comprising low load burner, steam gas heater and hot stove, and second solid fuel crushing means And a main burner for load are separate systems. 2. In the claim (1),
A combustion device, wherein a cooling pipe is embedded in the solid fuel layer of the first storage means. 3. In claim (1),
The startup-low load burner is provided with a heating element made of a conductive ceramic, and the fine powder solid fuel supplied to the startup-low load burner is directly ignited by the heating element. Combustion device. 4. In claim (1),
A combustion device, wherein the mixing ratio C / A of the solid fuel C and the air A passing through the start-up / low load burner is regulated within a range of 0.5 to 2.0. 5. In the claim (1),
A combustion apparatus, comprising: an ultra-fine powdery solid fuel transport path for supplying the ultra-fine powdery solid fuel stored in the second storage means to the starter-low load burner. 6. In the claim (1),
A sensor for detecting the storage amount of the ultrafine powdery solid fuel in the second storage means is provided, and switching of the ultrafine powdery solid fuel to be supplied to the hot air stove and the starter-low load burner by the detection signal is provided. Combustion device characterized by being configured to perform.