JPS637108B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for transporting and classifying coal ash in a combustion device that uses coal as fuel, such as a coal-fired boiler.

Conventionally, when processing coal ash in a coal-fired boiler, etc., the ash (raw powder) collected by a dust collection device such as an electrostatic precipitator is collected in a powder silo using a vacuum blower, and then passed through a classifier. Generally, an ash treatment method is adopted in which the raw powder is classified into coarse powder and fine powder by indirect classification using a so-called raw powder silo as a relay. FIG. 1 shows an example of a conventional high-vacuum type ash processing apparatus, in which the part surrounded by broken lines shows the ash collection and relay part, and the other part shows the ash classification part. 1 is a vacuum blower, which is a high vacuum power source for vacuum transporting ash. Ash collected by a dust collector 2 such as an electrostatic precipitator and stored in a hopper 3 (usually called fly ash)
is supplied from the ash supply valve 4 into the ash transport pipe 5 and rides on the atmospheric air flow sucked from the air intake valve 6,
The ash is pneumatically transported through the ash transport pipe 5 to the receiver 7. The diameter of the ash transport pipe 5 is usually 150 to 250 mm, the air velocity inside the pipe is 20 m/sec, and the pressure inside the ash transport pipe during ash transport requires a high vacuum of -5000 mmAq at the vacuum blower inlet. The mixing ratio of air and ash in the ash transport pipe during transportation is 8 to 12 parts air to 1 part ash on a weight ratio basis. The ash is centrifuged in the receiver 7 and stored in the raw powder silo 10 through a double damper 8 provided to isolate the high vacuum region from the atmospheric region. The dust-containing air that has passed through the receiver 7 is removed by a bag filter 11. The cleaned air passes through the vacuum blower 1 and is returned to the dust collector inlet duct 12. On the other hand, the ash collected by the bag filter 11 is stored in the raw powder silo 10 through the double damper 13.

The raw powder stored in the raw powder silo 10 is supplied from the rotary feeder 14 into the ash transport pipe 15. A fan 16 is connected to the ash transport pipe 15, and the fan 16 generates an air flow inside the ash transport pipe 15, and the ash (raw powder) stored in the raw powder silo 10 is divided into fine powder by a classifier 17 and a cyclone. It is pneumatically transported to the collector 18. That is, the fan 16 is a low vacuum power source. The raw powder supplied into the ash transport pipe 15 rides on the air flow and is pneumatically transported to the classifier 17 through the ash transport pipe. The diameter of the ash transport pipe 15 is usually 400 mm.
-500 mm, and the internal pressure of the ash transport pipe 15 during ash transport is a low vacuum of -500 to -700 mmAq at the inlet of the fan 16. Further, the mixing ratio of air and ash in the ash transport pipe 15 during transportation is a low concentration of 1 part air to 1 part ash on a weight ratio basis. This concentration is set to be low because it is necessary to improve classification accuracy. The raw powder is classified into coarse powder and fine powder by a classifier 17, and the classified coarse powder is fed into a coarse powder silo 21 through a rotary feeder 20 attached to the lower part of the classifier 17 and stored as ash. The fine powder that has passed through the classifier 17 is collected by a fine powder collector 18, and fed into a fine powder silo 23 through a rotary feeder 22 attached to the lower part of the fine powder collector, where it is stored as ash. The dust-containing air that has passed through the fine powder collector 18 passes through the fan 16 , and then passes through the rotary feeder 14 attached to the bottom of the raw powder silo 10 again to the classifier 17 , the fine powder collector 18 , and the fan 16 . are cycled in the order of
Once the dust concentration in the circulation duct 19 between the fan 16 and the rotary feeder 14 at the bottom of the raw flour silo 10 reaches a saturation point, the dust concentration does not increase any further. Normally, the dust concentration during this period is 20
~30g/ ^Nm3 . In order to release a small amount of leak air that leaks into the circulation system from the outside, the fan 16
An exhaust valve 24 branched on the downstream side is opened, and leak air (air containing dust) is returned to the dust collector inlet duct 12 through an exhaust pipe 25.

The functions of the classifier 17 are roughly as follows.

Fineness of coarse powder and yield: Fineness of raw powder -900 ~
−1000cm ² /g, 50% Fineness and yield of fine powder: Fineness of raw powder +900~
+1000cm ² /g, 50% The coarse powder stored in the coarse powder silo 21 is transported to an ash dump and disposed of in a landfill, and some of it may be recovered for effective use. The fine powder stored in the fine powder silo 23 is recovered for effective use as a cement admixture.

In this way, conventional ash processing equipment is complicated and expensive, and all raw powder is stored in the raw powder silo regardless of the properties of the raw powder.
The ash becomes indistinguishable. Furthermore, the mixing ratio during ash transport in the ash transport pipe is 1:8 to 12 (weight ratio), which is a high ash concentration, so to prevent wear, the pipe is thick at 14 to 15 mm and requires high-grade wear-resistant material. There were drawbacks such as:

The present invention has been made to solve the above-mentioned drawbacks, and the coal ash collected by the dust collector is guided directly to the classifier at low vacuum and low concentration through the ash transport pipe using circulating air to powder it into coarse particles. The coarse powder is charged into a coarse powder silo, and the fine powder is introduced into a fine powder silo via a fine powder collector.When classification is not necessary, the fine powder collector is By switching and feeding the fine powder collected in the container into the coarse powder silo, or the coarse powder collected in the classifier into the fine powder silo, it is possible to simplify the equipment and reduce costs. It is an object of the present invention to provide a method and apparatus for treating coal ash.

Hereinafter, the configuration of the present invention will be explained based on the drawings. FIG. 2 shows an embodiment of the coal ash processing apparatus of the present invention. The present invention is an application of the ash classification section shown in FIG. The coarse powder outlet of the classifier 17 is connected to the coarse powder silo 21 via the rotary feeder 20, and the exhaust outlet of the classifier 17 is connected to a fine powder collector 18 such as a cyclone. A low-vacuum induction fan 16 is connected to the downstream side of the collector 18, and a fine powder silo 23 is connected to the fine powder outlet of the fine powder collector 18 via a rotary feeder 22. 18 and a coarse powder silo 21 are connected via a switching/feeding device 27 such as an air slider, a conveyor, or a chute. Reference numeral 28 denotes a switching valve provided in the switching/feeding device 27, which is connected to the fine powder silo 23. 30 is a circulation duct connecting the outlet of the fan 16 and the ash transport pipe 26, and 31 is an exhaust pipe.

As described above, in the ash processing apparatus of the present invention, the ash collected by the dust collector 2 and stored in the hopper 3 is directly guided to the classifier 17. Rotary feeder 1 at the bottom of the raw powder silo in the conventional device shown in Figure 1
4 and the classifier 17 are generally installed close to each other, so the ash transportation distance is short. On the other hand, the ash supply valve 4 and the classifier 1 at the bottom of the dust collector in the apparatus of the present invention
Generally speaking, the ash transport distance between fan 1 and fan 1 is longer due to equipment layout, so fan 1
This will be dealt with by increasing the pressure of 6. In the prior art device shown in FIG. 1, the suction pressure is -500 to -700 mmAq, but in the device of the present invention, it is approximately -1000 to -1200 mmAq. The switching/feeding device 27 at the bottom of the fine powder collector 18 is installed to correspond to the quality of the raw powder. In other words, the types of coal used in recent coal-fired power plants are often more than 10 types at a single power plant. For this reason, ash of different quality is inevitably generated, and there is a large amount of unburned content in the raw powder, and even if it is passed through a classifier, the unburned content in the fine powder exceeds 5%, making it difficult to use the ash effectively. may occur. When this raw powder of poor quality is generated, the switching valve 28 is closed and the switching is switched to the coarse powder silo 21 side, and the fine powder collected by the fine powder collector 18 is also passed through the switching/feeding device 27 to the coarse powder silo. Put it in on 21.

In the present invention, the shape of the impeller of the induction fan 16, which is a low-vacuum power source for low-vacuum, low-concentration pneumatic transportation of coal ash, is a radial blade (plate). The radial blades (plates) are difficult to attract dust and can be easily prevented from wearing, so the dust concentration in the handled gas can be reduced to 50g/N instantaneously.
m ³ and continuous 30 g/Nm ³ , it can be used under the conditions of soot and dust concentration, which is the case in the present invention. That is, in the present invention, the soot and dust concentration at a mixing ratio of 1:1 (weight ratio) during pneumatic transport is approximately 1300 g/Nm ³ . The overall efficiency of the classifier 17 and fine powder collector 18 is around 98%.
The soot and dust concentration at the outlet of the fine powder collector 18, that is, at the inlet of the fan 16, is about 26 g/Nm ³ . Under this dust concentration (26g/ ^Nm3 ), fan 16 is 1
It is only necessary to carry out regular inspections once a year.
In addition, if the mixing ratio (weight ratio) is 1 ash to 1 air, the pressure loss of the entire device will increase, and the suction pressure of the fan 16 will exceed -1200 mmAq, exceeding the specification limit of the fan 16. This is not possible because the classification accuracy will decrease.

On the other hand, by reducing the mixing ratio (weight ratio) of ash to 1 part of air to less than 1, the pressure loss of the entire device will be reduced, but the classification accuracy will not be improved and the equipment will become redundant. On the contrary, it becomes an uneconomical facility.
At a mixing ratio of 1:1 (weight ratio), the fluidity of the powder in the pneumatic transport pipe is close to that of a floating flow, and the concentration is low, so there is far less wear compared to conventional high-vacuum transport, and the pipe thickness can be reduced. The material may be as thin as 4.5 to 6 mm, and ordinary carbon steel pipes can be used. In contrast, in the conventional high-vacuum transport method, the dust concentration in the pneumatic transport pipe is 8 to 12 times that in the present invention, so the fluidity state of the powder in the pneumatic transport pipe is close to that of a bottom flow, and This overlaps with the concentration, leading to increased wear, and the pipe thickness also increases.
It must be as thick as 14 to 15 mm, and requires high-grade wear-resistant material.

FIG. 3 shows another embodiment of the coal ash processing apparatus of the present invention. The apparatus of this example is constructed by connecting a classifier 17 and a fine powder silo 23 via a switching/charging device 32. 33 is a switching valve provided in the switching/feeding device 32, and is connected to the coarse powder silo 21. Therefore, when the raw powder is so fine that classification is not necessary, the coarse powder collected by the classifier 17 can be switched to and fed into the fine powder silo 23. The other configurations are the same as those in FIG. 2. Note that the switching valves 28 and 33 in FIGS. 2 and 3
For example, a structure as shown in FIG. 4 is used.

In addition, in Figures 2 and 3, an induction fan 1 is installed so that circulating air can be used for transporting coal ash.
6 is connected to the ash transport pipe 26 via the circulation duct 30, so air is not taken in from the outside.
Coal ash can be transported with circulating air. That is, the transport air circulates through the ash supply valve 4 at the bottom of the hopper, the classifier 17, the fine powder collector 18, the fan 16, and the ash supply valve 4 again. Since no air is taken in from the outside in this way, theoretically no exhaust air is emitted. In reality, only the leakage is exhausted, but it is only a very small amount. Further, the area from the ash supply valve 4 to the fan 16 via the classifier 17 and the fine powder collector 18 is operated at a pressure below atmospheric pressure. As a pressure control method that allows operation at a pressure below atmospheric pressure, the circulation duct 30 leading to the ash supply valve 4 is provided with pressure adjustment means such as a nozzle, orifice, and control valve. Furthermore, an exhaust pipe 31 connected to the inlet flue of the dust collector 2 is provided upstream of the ash supply valve 4 to enable exhaust, and a control valve and a reverse valve are installed to prevent the flue gas from flowing back into the circulation system. Provide backflow prevention means such as a stop valve.

As explained above, the present invention uses a low-vacuum method featuring direct classification to transport and transport flyash.
By using a direct classification method,
This eliminates the need for the ash collection and relay section consisting of a raw powder silo, receiver, bag filter, double damper, air intake valve, and ash transport pipe that was previously required.
The entire device is simplified, installation space is reduced, and construction costs are reduced. Furthermore, since a switching/feeding device is provided, operations can be carried out in response to the properties of the raw powder. In the conventional method, the mixing ratio during ash transport in the ash transport pipe was 1:8 to 12 (weight ratio), which resulted in a thick pipe of 14 to 15 mm and required high-grade wear-resistant material. The mixing ratio is 1:1 (weight ratio), which is a low concentration.
Therefore, the tube thickness may be as thin as 4.5 to 6 mm, and a steel tube made of ordinary carbon steel can be used. Furthermore, since the concentration is low, equipment other than piping is less likely to be damaged by wear, and running costs can be reduced. (50 to 60 in the conventional method)
%). Another advantage is that almost no exhaust gas is discharged into the dust collector inlet duct (less than 50% of the conventional method).

[Brief explanation of the drawing]

FIG. 1 is a systematic explanatory diagram of a conventional coal ash processing device, FIG. 2 is a systematic explanatory diagram showing an embodiment of the coal ash processing device of the present invention, and FIG. 3 is a systematic explanatory diagram showing an embodiment of the coal ash processing device of the present invention. FIG. 4 is an explanatory diagram showing an example of a switching valve. 1... Vacuum blower, 2... Dust collection device, 3...
Hopper, 4... Ash supply valve, 5... Ash transport pipe, 6...
... Air intake valve, 7 ... Receiver, 8 ... Double damper, 10 ... Raw powder silo, 11 ... Bag filter, 12 ... Dust collector inlet duct, 13 ... Double damper, 14 ... Rotary lift Ida, 15...
Ash transport pipe, 16...fan, 17...classifier, 1
8...Fine powder collector, 19...Circulation duct, 20...
...Rotary feeder, 21...Coarse powder silo, 22
...Rotary feeder, 23...Fine powder silo, 2
4...Exhaust valve, 25...Exhaust pipe, 26...Ash transport pipe, 27...Switching/injection device, 28...Switching valve,
30...Circulation duct, 31...Exhaust pipe, 32...
Switching/throwing device, 33... switching valve.

Claims (1)

[Claims] 1 Coal ash collected by a dust collector is guided directly to a classifier at low vacuum and low concentration through an ash transport pipe using circulating air to classify it into coarse powder and fine powder. Powder is fed into a coarse powder silo, and fine powder is fed into the fine powder silo via a fine powder collector.When classification is not necessary, coarse powder is added to the fine powder collected by the fine powder collector. A method for processing coal ash characterized by switching to a powder silo or switching and charging coarse powder collected by a classifier to a fine powder silo. 2 Connect the hopper at the bottom of the dust collector to the classifier via the ash transport pipe, connect the coarse powder outlet of this classifier to the coarse powder silo, and connect the exhaust outlet of the classifier to the fine powder collector. , connect a low vacuum induction fan to the downstream side of this fine powder collector, and connect a fine powder silo to the fine powder outlet of this fine powder collector, and connect the classifier and the fine powder silo, or A coal ash processing device characterized in that a powder collector and a coarse powder silo are connected via a switching/feeding device. 3 Connect the hopper at the bottom of the dust collector to the classifier via the ash transport pipe, connect the coarse powder outlet of this classifier to the coarse powder silo, and connect the exhaust outlet of the classifier to the fine powder collector. , connect a low vacuum induction fan to the downstream side of this fine powder collector, and connect a fine powder silo to the fine powder outlet of this fine powder collector, and connect the classifier and the fine powder silo, or The powder collector and the coarse powder silo are connected via a switching/feeding device, and the induction fan is connected to the ash transport pipe so that circulating air can be used for transporting coal ash. Coal ash processing equipment. 4. The coal ash processing device according to claim 2 or 3, wherein the switching/feeding device is an air slider having a switching valve.