JPH0220888B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention provides a coal that can reduce losses due to flying out of unburned pulverized coal, significantly reduce the dust collection load of combustion exhaust gas, and also allows the use of inferior quality coal with a high ash content. This relates to the method of combustion. [Conventional technology] In recent years, due to the instability of oil supply, the development of technology to effectively utilize coal has been progressing. As one of these, research is being put into practical use using a coal/oil mixed fuel made by mixing coal and oil into a slurry. However, conventional coal/oil mixed fuel is usually produced by pulverizing coal into fine powder and mixing it with heavy oil, so the ash contained in the coal is also contained in the coal/oil mixed fuel, reducing the calorific value. There are disadvantages such as: the dust collection load of combustion exhaust gas increases, a large amount of ash must be disposed of, there is a lot of loss due to the flying out of unburned pulverized coal, and inferior quality coal with a high ash content cannot be used. Ta. Furthermore, in order to reduce the cost of transporting coal, it is effective to transport coal as a slurry, and therefore there is a current demand for the development of a method for efficiently recovering coal particles transported as a slurry. Conventionally, a method of transporting slurry of coal directly from a coal-producing area has been carried out in the United States and the Soviet Union, and has been reported in the literature. However, in these methods, the separation of coal particles and water after slurry transportation is performed using a centrifugal separator, and although the energy consumption is large, the water content in the coal particles after dehydration is large (approximately 25 to 39 %). Conventionally, in JP-A-53-70076, an aqueous emulsion of an oil fraction is added to a coal slurry, the mixture is stirred in a container 2, the generated aggregates are separated by a vibrating sieve 4, and coal A method is described in which the ash and coal contained in the fine powder are separated and the above addition and subsequent treatment are repeated at least once on the remaining slurry. Furthermore, in JP-A-56-42004, fluidized bed boiler combustion gas is introduced into a cyclone collector 4, and the collected dust is then introduced into a classifier 5 to classify it into fine ash and phase ash. , a fluidized bed boiler device is described which is configured to supply fine ash to a fluidized bed 8, and selectively return only the fine ash with a high unburnt carbon content to the fluidized bed for re-combustion. . [Problems to be Solved by the Invention] In the above-mentioned Japanese Patent Application Laid-Open No. 53-70076, an aqueous emulsion of an oil fraction is added to coal slurry, the mixture is stirred, and the resulting aggregates are passed through a vibrating sieve. A technique for separating the ash and coal contained in fine coal powder has been described, but as in the present invention, the coal aggregate obtained after deashing is combusted, and the coal is removed from the combustion exhaust gas. There is no mention or suggestion of combustion technology that reduces the amount of soot and dust, reduces the load on the soot and dust collection equipment, and recovers and utilizes the unburned coal in the obtained soot and dust. In addition, in the above-mentioned Japanese Patent Application Laid-open No. 56-42004, after collecting combustion ash (dust) in combustion gas discharged from a fluidized bed boiler, the distribution of unburned carbon content based on the particle size distribution of combustion ash is disclosed. Using
A fluidized bed boiler device is described in which coarse particles and fine particles are separated and the fine particles with a high unburned carbon content are circulated to a fluidized bed and re-burned. However, regarding the removal of ash from fuel as in the present invention, , nothing is stated or suggested. Originally, the ash contained in the combustion exhaust gas is classified,
It is difficult to reduce the amount of collected combustion ash or maintain combustion with inferior quality coal simply by re-burning fine particles containing a large amount of unburned carbon. This can only be achieved by recovering and reusing the unburned coal in the collected soot and dust. The inventors of the present invention have conducted extensive research to solve the above disadvantages, and have conducted various tests on underwater granulation and deashing of coal particles. Therefore, it was discovered that the ash content in coal can be separated and removed, and that the finer the coal is pulverized, the better the deashing rate is, and that it is advantageous to apply this to a fluidized bed boiler. The present invention was developed in view of the above points, and can reduce loss due to unburned fine powder flying out of the system, significantly reduce the dust collection load of combustion exhaust gas,
Another object of the present invention is to provide a coal combustion method that allows the use of inferior quality coal with a high ash content. [Means for Solving the Problems] In order to achieve the above-mentioned object, the coal combustion method of the present invention finely pulverizes coal and mixes it with water.
After preparing the water slurry, the coal is granulated underwater while mixing this coal/water slurry with heavy oil and a granulating agent to separate and remove the ash content in the coal, and after deashing, the coal is granulated. The granular coal is supplied to a fluidized bed boiler and burned, and the combustion gas is introduced into a cyclone to collect soot and dust containing unburned coal in the combustion gas.
Next, the soot and dust containing this unburned coal is
The feature is that the coal content in soot and dust is recovered and used as granulated coal by recycling it into the water slurry. [Operation] Coal and water are supplied to the wet mill 1, and the coal is pulverized to prepare a coal/water slurry. Next, the coal/water slurry is sent to a mixing tank 7 together with heavy oil and a granulating agent to be stirred and mixed, and then this mixed slurry is sent to an underwater granulation/deashing tank 11. This tank 11
In the mixing slurry, a rotating body is rotated at high speed to granulate coal particles into pellet-like granulated coal and separate the ash content. Next, the wastewater containing the granulated pellets and ash is passed through the first solid-liquid separator 1.
5, where it is separated into pellets and wastewater containing ash. The pellets are put into a fluidized bed boiler 23 and burned. The exhaust gas from the fluidized bed boiler 23 is introduced into cyclones 25, 27, which collect relatively large particles ejected from the fluidized bed, and are returned to the deashing process. [Example] Hereinafter, an example of the present invention will be described based on the drawings. The drawing shows an example of a device for carrying out the method of the invention. 1 is a wet mill such as a ball mill,
This wet mill 1 includes a coal input pipe 2, a water supply pipe 3,
An alkaline agent supply pipe 4 is connected. The wet mill 1 is connected to an agitator 6 via a coal/water slurry extraction pipe 5.
A heavy oil supply pipe 8 and a granulating agent supply pipe 10 are connected to this mixing tank 7. The heavy oil supply pipe 8 and the granulating agent supply pipe 10 may be provided individually as shown in the drawings, or may be provided in a group. Furthermore, instead of connecting to the mixing tank 7, it may be connected to the wet mill 1, the coal/water slurry extraction pipe 5, or the underwater granulation/deashing tank 11. The mixing tank 7 is connected to an underwater granulation/deashing tank 11 via a mixed slurry extraction pipe 12. This underwater granulation/deashing tank 11 is equipped with one or more rotating bodies (not shown) that rotate at high speed. The rotating body consists of a rotating shaft connected to a motor and rotating blades, and the rotation speed of the rotating body is 200 rpm or more, especially 300 rpm.
It is preferable to set it as 900 rpm. In addition, underwater granulation
In the deashing tank 11, a baffle plate that satisfies the complete baffle condition is generally provided. Note that the baffle plate is not necessarily necessary and may not be provided. Further, although the drawing shows a horizontal underwater granulation/deashing tank, a vertical underwater granulation/deashing tank may also be used. Underwater granulation/
The outlet of the deashing tank 11 is connected to a first solid-liquid separator 15 consisting of a vibrating sieve, a bucket conveyor type discharger, etc., and this first solid-liquid separator 15 is connected to a thickener through an ash/wastewater extraction pipe 16. It is connected to a second solid-liquid separator 17 including a filter and the like. 18 is a pellet extraction line, 20 is a dehydrated cake (ash) extraction pipe, and 21 is a waste water extraction pipe. A waste water discharge pipe 21 is connected to the wet mill 1 via a circulation line 22. Pellet extraction line 18 is connected to fluidized bed boiler 23. As the fluidized medium of this fluidized bed boiler 23, an inert medium such as sand or an active medium that reacts with sulfur oxides such as coal stone is used. The fluidized bed boiler 23 is connected to a first cyclone 25 via a combustion gas duct 24, and further connected to the first cyclone 25.
5 is the second cyclone 2 via the exhaust gas duct 26
Connected to 7. The first cyclone 25 and the second
Unburned coal and dust extraction pipes 28 and 30 at the lower part of the cyclone 27 join together and are connected to the mixing tank 7 and the fluidized bed boiler 23. 31 is an air supply pipe. In some cases, only one cyclone is installed. In the apparatus configured as described above, coal, water, and, if necessary, an alkaline agent for pH adjustment are supplied to the wet mill 1, and the coal is pulverized to prepare a coal/water slurry. In this case, 200 mesh or less (particle size
It is desirable to crush the particles so that the particle size (74 μm or less) is around 50% or more. Next, the coal/water slurry is sent to mixing tank 7 along with heavy oil and granulating agent, where it is stirred and
After mixing (premixing), this mixed slurry is sent to an underwater granulation/deashing tank 11. Note that the coal/water slurry prepared in the wet mill 1 may be directly sent to the underwater granulation/deashing tank 11 without providing the premixing step. In this case, the heavy oil and granulating agent are added to the wet mill 1 or the underwater granulating/deashing tank 11. In the underwater granulation/deashing tank 11, a rotating body is rotated at high speed in the mixed slurry to granulate coal particles into pellet-shaped granulated coal (hereinafter referred to as pellets) and separate the ash content. That is, when granulation occurs by mixing the coal/water slurry, heavy oil, and granulating agent, the coal content in the coal is separated into the pellet side, and the ash content in the coal is separated into the waste water side. This phenomenon is understood to be due to the fact that oil easily adheres to coal and is difficult to adhere to ash. The deashing rate is 40 to 80 depending on the coal type.
It is about %. The granulated pellets and wastewater containing ash are then sent to the first solid-liquid separator 15 where they are separated into pellets and wastewater containing ash, and the pellets are taken out of the system through a pellet extraction line 18. Wastewater containing ash is passed through the second solid-liquid separator 1
7 and separated into dehydrated cake (ash) and waste water. The dehydrated cake (ash content) is taken out of the system through the dehydrated cake (ash content) extraction pipe 20, and the waste water is circulated to the wet mill 1 via the waste water extraction pipe 21 and the circulation line 22, and is reused as water for slurry preparation. be done. The pellets produced by the above deashing process are fed into the fluidized bed boiler 23 and then reduced to a pressure of 1 to 1.
30atm, air flow rate 0.5~5m/sec, temperature 750~
Burns under conditions of 1100℃. Fluidized bed boiler 2
After recovering heat from the combustion gas in the fluidized bed in 3, the exhaust gas is introduced into cyclones 25, 27,
Relatively large particles (consisting of unburned coal and soot) ejected from the fluidized bed are collected, and the collected particles are returned to the deashing process. The heavy oil used in the present invention must have a viscosity necessary as a binder during granulation and must be relatively inexpensive. From this meaning, C
Heavy oil, B heavy oil, atmospheric distillation column bottom oil, etc. are suitable. Also, the amount of heavy oil added is 6% of that of coal on a dry basis.
-50% by weight, preferably 10-40% by weight. The granulating agent used in the present invention may be anionic, nonionic, cationic surfactants, etc., used alone or in combination, and is appropriately selected depending on the type of coal. Specifically, anionic surfactants include alkylbenzene sulfonates, alkyl sulfate ester salts, polyoxyethylene alkyl (alkylphenol) sulfate ester salts, alkyl phosphate ester salts, dialkyl sulfosuccinate ester salts, acrylic acid and/or
and maleic anhydride copolymers, polycyclic aromatic sulfonates, or formalin compounds, etc. As cationic surfactants, alkyl amine salts, quaternary amine salts, etc. are used, and nonionic surfactants Polyoxyalkyl ethers, polyoxyethylene alkyl phenol ethers, oxyethylene/oxypropylene block polymers, polyoxyethylene alkyl amines, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, etc. are used as amphoteric surfactants. For example, alkyl betaines are used, and 1,2,3 monoamines,
Amine compounds such as diamines are used. In addition, the amount of granulating agent added is 0.01 to 0.01 of coal on a dry basis.
5.0% by weight, preferably 0.05-2.0% by weight. Some types of coal, such as Blairsall coal from Australia, are acidic, and in such cases, the alkali supply pipe 4
Add a neutralizing agent such as Ca(OH) ₂ to the coal-water slurry to adjust the pH to 6.5~11, preferably 7~
After adjusting to 10, add heavy oil and granulating agent.
Note that while adding heavy oil and a granulating agent to the coal/water slurry, a neutralizing agent such as Ca(OH) ₂ may be further added to adjust the pH to 6.5 to 11, preferably 7 to 10. It is thought that granulation in the present invention is carried out by the following process. First, the heavy oil and granulating agent added to the coal/water slurry are dispersed, and the granulating agent adsorbs onto the surface of the coal particles to modify the surface of the coal particles.Then, the heavy oil adheres to the surface of the coal particles. An oil film is formed, and then the coal particles adsorbed with the heavy oil and granulating agent collide and come into contact, coagulating with the oil as a binder.
They combine to form flocs, grow, and are further compacted to form pellets. Next, an experimental example will be explained. Experimental example: Breastall charcoal was mixed with three different particle sizes: 6 mm or less, 2 mm or less, and 74 μm or less (200 mesh or less)
After adjusting to 75%, 1 kg each was weighed on a dry basis, granulated under the conditions shown in Table 1, and separated into pellets, waste water containing ash, and waste water using a sieve. As a result, it was possible to separate and remove 40% of the ash from particles with a particle size of 75% below 74 μm.
Note that this example was conducted using a 5-tall beaker and a stirrer. In addition, as Middle Eastern C heavy oil, the viscosity at 50℃ is 137.3 centistokes, and the specific gravity (15/4
°C) 0.9515, and an anionic surfactant was used as a granulating agent.

【table】

〔Effect of the invention〕

As explained above, according to the method of the present invention,
The ash content in coal can be separated and removed with a high deashing rate, and the ash content can be reduced by burning the resulting pellets in a fluidized bed boiler, collecting unburned coal from the combustion gas, and recovering it again as pellets. It is now possible to use even poor quality coal with a high content of coal, and since there is less ash in the combustion gas discharged from the fluidized bed boiler, the dust collection load of the flue gas is significantly reduced, making it possible to use a dust collector installed downstream of the cyclone. The device can be downsized, and the amount of unburned pulverized coal taken out of the system is reduced, so it is extremely economical.

[Brief explanation of drawings]

The drawing is a systematic explanatory diagram showing an example of an apparatus for carrying out the method of the present invention. 1... Wet mill, 2... Coal input pipe, 3... Water supply pipe, 6... Stirrer, 7... Mixing tank, 8... Heavy oil supply pipe, 10... Granulating agent supply pipe, 11 ...Underwater granulation/deashing tank, 15...First solid-liquid separation device, 1
7... Second solid-liquid separator, 18... Pellet extraction line, 20... Dehydrated cake (ash content) extraction pipe, 2
1...Wastewater extraction pipe, 22...Circulation line, 23...
...Fluidized bed boiler, 25...First cyclone, 27
...Second cyclone, 28,30...Unburned coal
Dust extraction pipe.

Claims (1)

[Claims] 1. After finely pulverizing coal and mixing it with water to prepare a coal/water slurry, the coal is granulated underwater while mixing this coal/water slurry with heavy oil and a granulating agent. The ash content is separated and removed, the deashed granulated coal is supplied to a fluidized bed boiler for combustion, the combustion gas is introduced into a cyclone to collect the soot and dust containing unburned coal in the combustion gas, and then A method for burning coal, characterized in that the soot and dust containing this unburned coal is recirculated into the coal/water slurry, and the coal content in the soot and dust is recovered and used as granulated coal.