JPS62190316A - Combustion method for coal - Google Patents

Abstract

PURPOSE:To enable separation and removal of an ash content from coal with high ash removal efficiency, by a method wherein coal is granulated in water as coal and water slurry, prepared by pulverizing coal, heavy oil, and a granulating agent are mixed together. CONSTITUTION:Coal, water, and alkali agent for regulating pH are fed in a wet type mill 1 and the coal is pulverized to prepare coal and water slurry. In this case, it is desirable that the coal is pulverized so that the coal having a grain size of 200 meshes or less amounts for about 50% The coal and water slurry is fed through a mixing tank 7 to a granulating-in-water and ash-removing tank 11 together with heavy oil and a granulating agent. In the granulating-in- water and ash-removing tank 11, coal particle is granulated through high speed rotation of a rotary body to produce pelletlike granulated coal and separate an ash content. An ash removing rate is about 40-80% although it depends upon a kind of coal. This processing enables the use of a coal even if it is of poor quality having a large amount of an ash content, and sharply reduces a dust collecting load for exhaust gas, resulting in the possibility to reduce the size of a dust collecting device mounted down a line from a cyclone.

Description

[Detailed description of the invention] [Industrial application field] The present invention reduces loss due to unburned pulverized coal flying out,
The present invention also relates to a coal combustion method that can significantly reduce the dust collection load of combustion exhaust gas and that allows the use of inferior quality coal with a high ash content.

[Conventional technology]

In recent years, due to the instability of oil supplies, technological development for effectively utilizing 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. 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 unburned pulverized coal flying out, inferior quality coal with a high ash content cannot be used.
There were problems such as:

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, the method of transporting slurry of coal directly from coal producing areas was
It was carried out in the United States and the Soviet Union, and is also reported in the literature.

[Problem that the invention seeks to solve]

However, in these methods, the separation of coal particles and water after transporting the slurry 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 %).

The present inventors have conducted intensive research to solve the above problems,
As a result of various tests conducted on underwater granulation and deashing of coal particles, it was found that by performing underwater granulation after finely pulverizing coal, it was possible to separate and remove the natural elements in the coal, and the coal It was found that the finer the grinding, the better the deashing rate.

The present invention has been devised in view of the above-mentioned points, and provides a coal combustion method that solves the above problems.

[Means and actions for solving the problem] - While combining water slurry with heavy weight and "6 grains"
[Embodiment] Hereinafter, the method of the present invention will be explained based on the drawings.The drawing shows an example of an apparatus for carrying out the method of the present invention. 1 is a wet mill such as a ball mill, and a coal input pipe 2, a water supply pipe 3, and an alkali supply pipe 4 are connected to this wet mill 1. The wet mill 1 is connected to a mixing tank 7 equipped with an agitator 6 via a coal/water slurry extraction pipe 5, and a heavy oil supply pipe 8 and a granulating agent supply pipe 10 are connected to this mixing tank 7. The zero heavy oil supply pipe 8 and the granulating agent supply pipe 10 may be provided individually as shown in the drawing, or may be provided in a group.Furthermore, instead of being connected to the mixing tank 7, the wet mill 1, coal/ It may be connected to the 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 rotation speed of the rotating body is 20 Orpm or more, especially 300 to 900 rpm.
It is preferable to set it to +. In addition, a baffle plate that satisfies the perfect baffle plate condition is generally provided in the underwater granulation/deashing tank 11. 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. The outlet of the underwater granulation/deashing tank 11 is connected to a first solid-liquid separator 15 consisting of a vibrating sieve, a packet conveyor-like discharger, etc., and this first solid-liquid separator NS is connected to an ash/wastewater extraction pipe 16.
A second solid-liquid separator consisting of a thickener, filter plate, etc. +7 is connected.

18 is pellet extraction line, 2o is dehydrated cake (ash content)
The extraction pipe 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 limestone is used. Fluidized bed boiler 23 has combustion gas duct 2
4 to the first cyclone 25, and further connected to the first cyclone 25 via
Cyclone 25 is connected to a second cyclone 27 via an exhaust gas duct 26. The first cyclone 25 and the second
Unburned coal and dust extraction pipe 28 at the bottom of cyclone 27
．． 30 join together to form the mixing tank 7 and the fluidized bed boiler 23.
connected to. 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 adjusting pn are supplied to the wet mill 1, and the coal is pulverized to prepare a coal/water slurry. In this case, 50% of the particles are 200 mesh or less (particle size 74 μm or less).
It is preferable to crush it so that it is more than the front and back. Next, the coal/water slurry is mixed with heavy oil and a granulating agent in a mixing tank 7.
After stirring and mixing (premixing), the 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 a 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. Underwater granulation/deashing tank 1
In step 1, the rotating body is rotated at high speed in the mixed slurry to form coal particles into pellet-like granulated coal (hereinafter referred to as pellets).
The ash is granulated and the ash is separated. That is, when granulation occurs by mixing coal/water slurry, heavy oil, and a 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 caused by oil adhering to coal.
This is thought to be due to the fact that it is difficult to adhere to ash. The deashing rate is about 40 to 80%, depending on the type of coal. Next, the wastewater containing the granulated pellets and ash is transferred to the first solid-liquid separator 1.
5 and are separated into pellets and wastewater containing ash, and the pellets are taken out of the yarn through a pellet extraction line 18. The wastewater containing natural components is sent to the second solid-liquid separator 17 and separated into a dehydrated cake (ash) and wastewater. The dehydrated cake (temperature) is taken out of the yarn through the dehydrated cake (ash) extraction pipe 20, and the wastewater is circulated to the wet mill 1 via the wastewater extraction pipe 21 and the circulation line 22, where it is recycled as water for slurry preparation. used.

After the pellets produced by the above deashing process are input into the fluidized bed boiler 23, the pressure is 1 to 30 atm, the air flow rate is 0.5 to 5 m/see, and the temperature is 750 to 11 m/see.
Burns under conditions of 00℃. After recovering heat from the combustion gas in the fluidized bed in the fluidized bed boiler 23, the exhaust gas is introduced into the cyclone 25.27, where relatively large particles (consisting of unburned coal and soot) ejected from the fluidized bed are collected.
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. In this sense, C heavy oil, B heavy oil, atmospheric distillation column bottom oil, etc. are suitable. The amount of heavy oil added is 6 to 50% by weight of the coal on a dry basis, preferably 10 to 4% by weight.
It is 0% 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 sulfates, polyoxyethylene alkyl (alkylphenol) sulfates, alkyl phosphates, dialkyl sulfosuccinates, acrylic acid and/or Maleic anhydride copolymers, polycyclic aromatic sulfonates, formalin compounds, etc. are used, and as cationic surfactants, alkyl amine salts, quaternary amine salts, etc. are used, and as nonionic surfactants, Polyoxyalkyl ether, polyoxyethylene alkylphenol ether, oxyethylene/oxypropylene block polymer, polyoxyethylene alkylamine, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, etc. are used as amphoteric surfactants. Alkyl betaines and the like are used, and amine compounds such as 1, 2.3 monoamines and diamines are also used. The amount of the granulating agent added is 0.01 to 5.0% by weight of the coal on a dry basis, preferably 0.05 to 2% by weight of the coal.
．． It is 0% by weight.

Some types of coal, such as Australian Preasol coal, exhibit acidity, and in such cases, the alkali agent supply pipe 4 is used to add Ca(OH)t, etc. to the coal/water slurry. Add Japanese additives and p
After adjusting H to 6.5-11, preferably 7-10, heavy oil and granulating agent are added.

In addition, while adding heavy oil and a granulating agent to the coal/water slurry, a neutralizing agent such as Ca (OR)
o may be adjusted to 6.5-11, preferably 7-10.

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 heavy oil and granulating agent collide and come into contact with each other, coagulate and combine with oil as a binder, form and grow flocs, and are further consolidated to form pellets.

Next, an experimental example will be explained.

Experimental example Preassol charcoal was adjusted to three different particle sizes: 61 or less, 2N or less, and 74 μm or less (200 mesh or less) to 75%, then weighed 1 kg each on a dry basis and granulated under the conditions shown in the following table. After that, the pellets were separated into pellets and wastewater containing ash using a sieve. As a result, 74 μm or less 7
With a particle size of 5%, 40% of ash could be separated and removed. Note that this example was carried out using a 5E tall beaker and a stirrer. In addition, 50℃ as Middle Eastern C heavy oil
Viscosity at 137.3 centistokes, specific gravity (15
/4°C) 0.9515, and an anionic surfactant was used as a granulating agent.

〔Effect of the invention〕

The above experiments have shown that ash in coal can be separated and deashed with a high deashing rate.
By burning the obtained pellets in a fluidized bed boiler, collecting the unburned coal from the combustion gas and recovering it as pellets again, it is possible to use even poor quality coal with a high ash content. In addition, since there is less ash in the combustion gas discharged from the fluidized bed boiler, the dust collection load of the exhaust gas is significantly reduced, making it possible to downsize the dust collection equipment installed downstream of the cyclone, and furthermore, Since the amount of unburned pulverized coal extracted during the process is reduced, 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
- Granulation agent supply pipe, 11- Underwater granulation/deashing tank, 15-
First solid-liquid separator, 17--Second solid-liquid separator, 18
- Pellet extraction line, 20... Dehydrated cake (ash) extraction pipe, 21 - Waste water extraction pipe, 22 - Circulation line,
23...-Fluidized bed boiler, 25-...-First cyclone,
27...-Second cyclone, 28.30...Unburned coal and 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 is separated and removed, the deashed granulated coal is fed to a fluidized bed boiler for combustion, the combustion gas is introduced into a cyclone, and the soot and dust containing unburned coal in the combustion gas is collected.
A method for burning coal, characterized in that the soot and dust containing this unburned coal is then recirculated into the coal/water slurry, and the coal content in the soot and dust is recovered and used as granulated coal.