JPH08323112A - Treatment of bottom ash of coal firing furnace and device therefor - Google Patents

Abstract

PURPOSE: To remove fine particles in circulating water causing wear of a pump or the like and damage to a shaft seal part in a method for treating bottom ash of a coal firing furnace of intermittent ash flowing water flow system. CONSTITUTION: In order to recover water from a bottom ash slurry, a filter system using bottom ash as a filter medium is adopted. A filter tank 8 having a filtrate water outlet 11 equipped with a grid or a screen, a blow port 12 for blowing water into the filter and an ash discharge gate 13 in the bottom part is provided. A bottom ash slurry intermittently sent from a clinker hopper 2 is stored in the filter tank 8, and is filtered to separate bottom ash from water by using the ash settled in the filter tank as a filter medium. After water is jetted into the filter tank to perform agitation, when the ash is re-settled and turned into the filter medium, filter efficiency is favorably improved. An amt. of fine particles in circulating water is reduced to one-several hundredths. Replacement frequency of a pump, a valve, piping or the like is largely reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for treating bottom ash of a coal combustion furnace mainly for large boilers. Particularly, it is useful for treating bottom ash of a coal combustion furnace for large-scale thermal power generation.

[0002]

2. Description of the Related Art Ash attached to the surface of a water pipe or a furnace wall of a coal burning furnace for a boiler successively drops to the bottom of the furnace, which is generally called bottom ash (also called clinker ash). In Japan and the United States, the intermittent ash flow method is generally used for the treatment of bottom ash. This method usually uses a large amount of water, so recently, in order to save water and prevent environmental pollution, the method of separating the water used for the bottom ash transportation processing in a dehydration tank and recycling it is adopted. . FIG. 2 shows the basic flow sheet. A clinker hopper 22 filled with water is provided below the combustion furnace 21, and receives a falling bottom ash 23. The bottom ash is rapidly cooled with water, crushed, and stored in the clinker hopper 22. The stored bottom ash is intermittently discharged by opening the ashing gate 24 at the bottom of the hopper. The discharged bottom ash passes through the clinker crusher 25, is crushed to a size of about 40 mm at maximum, and is slurried as a slurry by a water flow pump (also called a jet pump or a high ejector) 26 as the ash flow pipe 2
It is sent to the dehydration tank 28 via 7 and drained.

The dehydration tank 28 is usually a gravity drainage type having a cylindrical upper portion and a cone lower portion, and a dehydration louver or screen for separating and discharging water is attached to the peripheral wall. The ash in the slurry gravity settles and remains in the tank, and the supernatant water is separated from the ash by the dehydrating louver or screen and sent to the settling tank 29 through the dehydrating trough. The water sent to the settling tank 29 precipitates and separates fine ash, and the supernatant water passes through the water storage tank 30 and is circulated and used as ash drainage water. The water at the bottom with high ash concentration is dehydrated tank 28
Reflux to. The ash settled on the bottom of the dehydration tank is taken out from the ash discharge gate 31 and carried out of the system by a conveyor or a truck. Reference numeral 32 is a circulation pump for sending the recovered water to the clinker hopper, 33 is a drive pump for sending the recovered water to drive the water flow pump, and 34 is a sludge pump for returning the sludge to the dewatering tank 28.

Since dehydration requires a long time, two dehydration tanks are usually used in combination. The dehydration tank accepts the slurry intermittently, gravity settles the solid content in the slurry, drains water, and repeatedly removes the solid content.When one of the dehydration tanks is full, the slurry is switched to the other dehydration tank. After being sent, the dehydration operation of one of the dehydration tanks is completed during this period, the ash content is discharged, and the reception and the dehydration are alternately repeated. The above-mentioned conventional technology is “Coal ash processing system and effective utilization technology” (Shigeru Tamanuki et al., Published by Fuji Techno System (19
81)) and is described in detail.

In the above treatment method, when the slurry is intermittently supplied one after another and then drained, the ash repeatedly accumulates in layers according to the particle size distribution and prevents rapid dewatering. Therefore, the water injection port is provided near the tip of the bottom. A blockage prevention method (described in Japanese Patent Laid-Open No. 6-31114) in which water and air are sent back to the tank from time to time to stir the slurry, or means for using an economically efficient ash pump instead of the water pump (Described in JP-A-6-82029) has been put to practical use.

[0006]

As described above, in many large coal-fired power plants, the water used for the bottom ash treatment is circulated and reused to save water. However, problems associated with circulation occur. There is. That is, in gravity settling separation, ash having a small particle size, particularly small ash having a particle size of 30 μm or less, is not separated but is circulated together with water, and the solid content concentration in the circulating water increases. Depending on the device, in most cases 300-100
Equilibrium is reached in the range of 0 ppm. These fine particles cause wear of pumps and pipes and damage of shaft seals.
To increase the solid content concentration, it is technically possible to increase the size of the settling tank to increase the settling time, or to perform filtration separation using conventional filtration means. Not realistic in terms. Therefore, as a result of examining the method of effectively using the conventional equipment and reducing the solid content concentration in the circulating water, the present inventor can complete the present invention having a epoch-making effect. did it.

[0007]

According to the present invention, in a method for treating bottom ash of an intermittent ash flow water flow type coal combustion furnace, a bottom ash slurry intermittently sent from a clinker hopper 2 is attached to a grid or screen. The filtered water outlet 11 is stored in the filtration tank 8 provided at the bottom,
Provided is a method for treating bottom ash in a coal combustion furnace, characterized in that the bottom ash settled in the filtration tank is used as a filtration bed to filter water in the filtration tank to separate the bottom ash and the water. When the ash that has settled in the filter tank is blown with water or air from the bottom and stirred and then re-precipitated to form a filter bed, ash with a larger particle size is deposited toward the bottom, which is preferable because the filtration efficiency is improved.

Further, the present invention provides a bottom ash treatment apparatus for an intermittent ash-flowing water flow type coal combustion furnace, which has a grid or screen and a shut-off valve as a tank for the bottom ash slurry intermittently discharged from the clinker hopper 2. A filter tank 8 having a filtered water outlet 11 attached, a nozzle 12 for blowing water or air into the tank, and an ashing gate 13 for discharging bottom ash is provided at the bottom. The present invention provides a bottom ash treatment device for a coal combustion furnace.

That is, the present invention replaces the conventional gravity sedimentation separation system in which the solid content in the recovered water cannot be completely separated,
The bottom ash is found to be a material suitable for constituting the filter bed, particularly the particle size distribution, and the bottom ash itself is used as the filter bed to obtain recovered water with extremely low solid content from the bottom ash slurry. It was completed by adopting a filtration method.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [Examples and Functions] With reference to the drawings, a method and an apparatus for treating bottom ash of a coal combustion furnace according to the present invention will be specifically described with reference to examples of embodiments. Figure 1
It is a flow sheet which shows the example of an embodiment of the present invention. FIG.
Shows an example in which an ash pump is used to send the bottom ash slurry to the filtration tank 8, but it goes without saying that a water flow pump or the like can be used in the present invention.

Also in the bottom ash treatment method of the present invention, as in the conventional treatment method, the bottom ash 3 discharged from the combustion furnace 1 is once stored in the water-filled clinker hopper 2 and a part thereof is stored. In the slurry state, for example, once every 8 hours, for about 1 hour, it is sent from the ashing gate 4 through the clinker crusher 5 and the ashing tube 7 to the filtration tank 8 by the water flow pump or the ash pump 6.
The shape of the filtration tank 8 used in the present invention is not particularly limited, but a filtered water outlet 11 and an ashing gate 13 are provided at the bottom. In the filtration tank of the present invention, separation of water on the peripheral wall, it is not necessary to provide a dehydration trough including a screen or a louver for discharging, but in order to divert the dehydration tank of the conventional device or to use the conventional method together, It does not matter if these members are attached.

The filtered water outlet 11 has an opening of 0.5 to 4 m to prevent the bottom ash in the slurry from flowing out.
Install a grid or screen of about m and a stop valve for opening and closing and control. If the mesh size is too small, clogging will occur, and fine particles will accumulate in the lower layer, resulting in poor filtration performance. As a type of grid or screen, usually more than the common wire mesh or punching plate,
It is preferable to attach a wedge wire screen in which bars having triangular cross sections are arranged in parallel so that the bottom side of the triangle faces the inside of the tank. The wedge wire screen has extremely small holding power even if particles of the same size as the opening are clogged, so
If it is backwashed, it can be easily removed and the problem is unlikely to occur.

After the bottom ash slurry has been fed into the filter tank 8, the ash is allowed to settle for an appropriate natural settling time to form a filter bed. Fortunately,
The properties of ash in the slurry are extremely suitable as a filtering material. After the filtration bed is formed, the valve attached to the filtrate outlet 11 is opened appropriately to start the filtration operation. A relatively small amount of ash is deposited on the upper layer portion of the filtration layer, and fine particles can be separated by filtration, and the solid content remaining in the filtered water can be greatly reduced as compared with the conventional method of sedimentation separation.

Now, preferably, a water or air blowing port 12 is further provided at the bottom of the filtration tank 8 so that a fluid such as water or air can be blown into the tank to agitate the slurry and re-precipitate the ash. Leave. The preferable reason will be explained. The ash slurry sent to the filtered water tank contains ash having a wide particle size distribution, which consists of particles having different particle sizes of submicron to ten and several mm, which are continuously crushed by the clinker crusher 5 during the liquid sending. In addition to the difference in sedimentation speed due to the size of the particles, the bottom ash that has been fed first tends to deposit in the lower layer and the later ash tends to deposit in the upper layer, depending on the timing of the slurry feeding. However, since the ash in the slurry has a wide and continuous particle size distribution, when the slurry is agitated to re-precipitate the ash, coarse particles, fine particles, and ultrafine particles of clay are settled and deposited in this order, It is possible to form a filter bed that is convenient for filtering fine particles efficiently. The water or air blowing port can be shared with the ashing gate or the filtered water outlet. The ash filter bed thus formed in the order of particle size has a high filtration rate and can efficiently separate fine particles.

In the present invention, it is not necessary to store the entire amount of the slurry intermittently sent from the clinker hopper 2 in the filtration tank 8. The filtration tank 8 requires a certain height and the equipment cost is high. In order to save the facility cost, a small economical filtration tank 8 is installed, a receiving tank 9 is separately provided to store the overflowing slurry, and the circulating pump 14 returns the slurry to the filtration tank 8 for filtration at appropriate time. You can Further, as in a conventional dehydration tank, a screen or a louver is provided on the peripheral wall, the separated water is stored in the receiving tank 9, and when appropriate, returned to the filtration tank by the circulation pump 14 to filter and separate the accompanying relatively fine particles. it can. That is, the conventional device can be advantageously improved to the device of the present invention. The detailed filtration conditions differ depending on the particle size distribution of the slurry solids, the specific gravity of the particles, etc., and are therefore determined by conducting a preliminary test. The water taken out from the filtered water outlet 11 is stored in the water storage tank 10 and is circulated and used for water filling of the clinker hopper 2, driving water of the water flow pump 6, blowing water to the filtering tank 8 and the like at appropriate times.

[0016]

EXAMPLE A method for treating bottom ash of a coal combustion furnace according to the present invention was carried out on a test basis by using substantially the same apparatus as shown in FIG. The test has a cylindrical upper part and a conical lower part with a maximum inner diameter of about 9.7.
The bottom ash slurry was almost completely filled in a filtration tank having a volume of m, a height of approximately 10.8 m, and an internal volume of approximately 360 m ³ , and the overflowed slurry which did not fully enter was stored in a receiving tank. In addition to the ashing gate, the bottom of the filtration tank was provided with a filtrate outlet port equipped with a wedge wire screen having a mesh opening of 2 mm and a fluid (water) inlet port. The procedure of the test is Step I. Filtration state before water is injected from the water inlet Step II. Filtration state after water injection Step III The filtration was performed in the order of clogging by continuous filtration. The filtered water was measured by measuring the pH (hydrogen ion concentration), SS (amount of suspended solids) and COD (chemical oxygen demand) according to JIS K 0102 (factory wastewater test method), and the transparency by the sewer test method (Japan Waterworks Association). Enacted). Samples are filtered water except as noted.

Step I. First, place the bottom
Approximately 1 hour after the completion of feeding the slurry, the filtrate was discharged.
The outlet stop valve of the mouth was opened and the filtered water was discharged. Initial
The transparency of the filtered water was 150 mm, but after a few minutes (sample
400mm or more in 1), 400 after 55 minutes (Sample 2)
mm was held. The amount of filtered water during this period is 18.5 m ³
Was / H. The present invention is effective in removing solids in circulating water
Was found.

Step II. Next, water was blown into the filtration tank from the water blowing port at a rate of 400 m ³ / H for about 5 minutes to stir the inside of the tank. Ten minutes after the end of the water injection, when the outlet stop valve of the filtrate outlet was fully opened, about 280 m ³ / H of filtered water was discharged. The transparency of the filtered water is 20 mm, and 50 minutes after 3 minutes.
mm. Therefore, the opening amount of the outlet stop valve was set to 1/4 and the amount of filtered water was reduced to 17.5 m ³ / H. The transparency of the filtered water increased to 100 mm. After that, the transparency gradually increased, and the transparency was 280 mm 8 minutes after the closing valve adjustment, exceeded 400 mm after about 20 minutes, and continued as it was (50 minutes after the closing valve adjustment: sample 4). Next, set the opening of the stop valve to 1
The amount of filtered water was adjusted to 65 m ³ / H. The transparency was once 330 mm, but after a few minutes it was 400 m.
Recovered over m. Approximately 20 minutes later, sample 5 was sampled and the test was suspended. It was confirmed that stirring in the tank and re-sedimentation of bottom ash were effective in improving the filtration efficiency.

Step III After half a day, the test was restarted with the closing valve opening kept at 1/3. The flow rate of the filtered water after restarting was about 66 m ³ / H, and the transparency exceeded 400 mm. Simultaneously, the transparency of the slurry return water from the receiving tank and the raw water of the filtering tank were measured and found to be 25 mm and 15 mm (Sample 3). After about 4 hours from the restart of the test, the opening degree of the shutoff valve was halved. The amount of filtered water was about 122 m ³ / H, and the transparency, which initially dropped to 300 mm, recovered to 400 mm or more in about 15 minutes (Sample 6). The opening degree of the shutoff valve was returned to 1/3 (Sample 7), and the filtration was continued for about two and a half hours with the filtered water amount of about 66 m ³ / H and the transparency of 400 mm or more.

However, since the amount of filtered water gradually decreased (Sample 8), the opening degree of the stop valve was adjusted so as to maintain the amount of filtered water of about 68 m ³ / H, and the filtering operation was continued for about 48 hours and a half. . After about 17 hours and a half, the transparency of the slurry return water and the raw water in the filtration tank was measured and found to be 60 mm and 30 mm. Sample 9 (raw water in the filtration tank) and sample 10 were collected at approximately the same time. Then, after about 48 hours and a half, the sample 11 was sampled and the test was completed. It was confirmed that the present invention was sufficiently practical. Table 1 shows the measurement results of the characteristics of each sample.

[0021]

[Table 1]

[0022]

By using the bottom ash treatment method or treatment apparatus of the present invention, the solid content in the circulating water can be reduced to several hundredths. As a result, the frequency of replacement of pumps, valves and pipes used in the circulation system is reduced. Moreover, the facility cost and running cost required for this are almost the same as the conventional ones, and it is easy to modify the conventional facilities and use the present invention. Further, stirring in the filtration tank and re-sedimentation of the bottom ash are effective for forming a preferable filtration bed, and the filtration operation can be efficiently performed.

[Brief description of drawings]

FIG. 1 is a flow sheet showing an embodiment of the present invention.

[Fig. 2] A basic flow sheet of a conventional bottom ash treatment device of an intermittent ash flow water flow system

[Explanation of symbols]

1: Combustion furnace 2: Clinker hopper 3: Bottom ash 4: Ashing gate 5: Clinker crusher 6:
Ash pump 7: Ash extraction pipe 8: Filtration tank 9: Receiving tank 10: Water storage tank 11: Filtration water outlet 12: Fluid (water or air etc.)
Blow-in port 13: Ash discharge gate 14: Circulation pump 21: Combustion furnace 22: Clinker hopper 23: Bottom ash 24: Ash discharge gate 25: Clinker crusher
26: water flow pump 27: ashing pipe 28: dehydration tank 29: precipitation tank
30: Water storage tank 31: Ash discharge gate 32: Circulation pump 33: Drive pump 34: Sludge pump

Claims (3)

[Claims] 1. A method for treating bottom ash of a coal combustion furnace of an intermittent ash-flowing water flow system, wherein bottom ash slurry intermittently sent from a clinker hopper 2 is supplied to a bottom of a superfluid outlet 11 equipped with a grid or a screen. A bottom of a coal combustion furnace, characterized in that the bottom ash stored in the provided filtration tank 8 and settled in the filtration tank is used as a filtration bed to filter the water in the filtration tank to separate the bottom ash from the water. How to treat ash. 2. The bottom of a coal combustion furnace according to claim 1, wherein the bottom ash settled in the filtration tank is blown with water or air from the bottom to stir it and then settled again to form a filter bed. How to treat ash. 3. An apparatus for treating bottom ash of a coal combustion furnace of an intermittent ash-flowing water flow system, wherein filtered water having a grid or a screen and a valve attached as a tank for receiving the bottom ash slurry intermittently discharged from the clinker hopper 2. An outlet 11, an inlet 12 for injecting water or air into the tank, and an ashing gate 13 for discharging the filtered and separated bottom ash are provided in the bottom of the filter tank 8. A feature is a bottom ash treatment device for a coal combustion furnace.