JPS6128582A - Pretreatment of coal for liquefaction - Google Patents

Abstract

PURPOSE:To obtain coal for liquefaction, which has a low ash content, by removing free minerals by dehydrating and drying up-graded coal froth obtd. by feeding a liquefied product from a coal liquefaction process as a collector to a pulverized coal/water slurry and carrying out flotation. CONSTITUTION:A pulverized coal 11 having such a particle size distribution that at least 80% of the coal powder is composed of particles having a particle size of 3mm. or below, and water are introduced into a wet-process grinder 15, where coal is ground to form a coal power/water slurry which has a coal content of 3-15% and in which coal powder has such a particle size distribution that 70-80% of the powder is composed of particles having a particle size of 200 mesh or below. If necessary, the sluury is diluted with water. The slurry is then fed to a flotator 25. A recycling solvent 21, which is a liquefied product from a coal liquefaction process, is fed as a collector in a quantity of 300-2,500g per ton of coal. Further, a foaming agent and optionally, a pH adjustor are fed through a line 25 to adjust the pH of the slurry to 3-6 and coal is recovered by flotation as up-graded coal froth 29 having a coal content of 6-30%, and liberated ash is separated as flotation tail 27. The froth 29 is dehydrated in a dehydrator 30 and the dehydrated cake 31 having a high coal content and a water content of 20-40% is dried in a dryer 32 to a water content of 10% or below, thus obtaining coal for liquefaction, which has a low ash content.

Description

[Detailed description of the invention] The present invention relates to a method for pre-treating coal for liquefaction.

The energy crisis has sparked interest in energy diversification, particularly in the effective use of coal, and in addition to fuel conversion to coal, technological developments such as gasification and liquefaction are being developed.

When converting coal into a liquid fuel comparable to petroleum, it is necessary to pay attention to the chemical composition of both and the content of impurities such as minerals. As is clear from comparing the hydrogen and carbon ratios of coal and petroleum based on their chemical compositions, coal has a high carbon content and a low hydrogen content. Because of this relationship, the process of liquefying coal includes a hydrogenation step. Many coal liquefaction processes have been proposed, each with its own unique process characteristics, and research and development is being conducted in Japan on such methods as solvent extraction, direct hydrogenation, and solvolysis liquefaction. All of these processes adopt a circulating solvent system, in which medium oil or heavy oil fractionated in the final step of the liquefaction process is recycled as a solvent, and pulverized coal slurry (catalyst) is produced using this circulating solvent as a medium. ) is preheated at 400 to 500°C, and then liquefied in a high-pressure reactor. After that, through gas-liquid separation, and in some cases solid-liquid separation, light and medium 1
into heavy and residual fractions. In this case, the coal in the coal slurry using a circulating solvent as a medium is usually finely pulverized to about 70 to 80% of 200 mesh or less.

Also, when comparing the mineral content, even heavy oil, which has a high content of petroleum, has an ash content of 0. [While it is less than %,
The content of mineral substances in coal is in the range of 5 to 40%, although it varies depending on the coal's endowment state and mining conditions. If the content of mineral substances is high, a coal washing process is performed to remove the mineral substances contaminating the coal, but even clean coal that has been cleaned contains 5 to 10% mineral substances. For this reason, the handling of mineral substances is also an issue in coal liquefaction, and conventional methods have been to remove mineral substances from the liquefied oil obtained in the liquefaction process using a centrifuge, or to remove the mineral substances from the heavy distillate separated in the distillation process. The content of mineral substances in the target light distillate is reduced by transferring the mineral substances, especially the unliquefied fraction (residue). However, such a mineral removal operation is complicated, and further improvements have not been made.

As mentioned earlier, even in clean coal after coal preparation, mineral substances are
It contains about 10%, but this coal cleaning treatment usually reduces the coal content to 1.0-1.
Since it is carried out in the form of a block of 0.00 mm or less, in reality, only the contaminant minerals are removed. Most of the mineral substances contained in clean coal are present inside the lump coal, and these can be separated from the coal particles by crushing the coal particles to make the particle size finer. The degree of this liberation varies depending on the formation of the coal and the conditions in which it is provided, but the degree of liberation increases as the coal is made into smaller pieces.

Generally, in the fine powder slurry input to the above-mentioned liquefaction process, 1 coal usually costs 200. Metshu and below 70~
It is finely pulverized to about 80%, and from this particle size, in the circulating solvent coal slurry of the liquefaction process, 30 to 60% of the mineral substances contained in the raw coal are already in a free state. As mentioned above, this slurry is preheated in a preheater and then led to a high-pressure reactor, so wear of free minerals in the preheater and reactor is a serious problem, and furthermore, the subsequent separation of minerals, especially Reducing solid-liquid separation operations is also an important issue in the coal liquefaction process.

In addition to this mineral substance, special consideration must be given to the water content of the circulating solvent coal slurry used for liquefaction from the reaction aspect of coal liquefaction. That is, it is generally desirable to reduce the surface moisture contained in coal as much as possible.

The present invention has been made from this viewpoint, and solves the above problems by flotation treatment in the state of fine powder slurry, removing free minerals from coal for liquefaction, and further reducing the water content. In this flotation coal treatment, the liquefaction product from the liquefaction process is used to simplify the process and make effective use of the circulating solvent.

That is, the present invention supplies a liquefied product from a coal liquefaction process to a water slurry of pulverized coal, performs coal flotation using this liquefied product as a scavenger, and dehydrates the clean coal floss obtained by flotation. This is a pretreatment method for coal for liquefaction, which is characterized by drying and recovering low ash coal.

The present invention will be explained in more detail below.

The figure is a flow diagram showing an embodiment of the present invention.

Coal 11 is crushed to a suitable particle size, usually 80% or less, and is fed into a wet pulverizer 15 together with water 13 to form a pulverized coal/water slurry 17. The particle size of this pulverized coal depends on the liquefaction conditions. determined, usually 200
It is 70 to 80% below mesh. In addition, the coal concentration of the slurry is within a range suitable for the next flotation process, for example, 3 to 15%.
%, and is introduced into the flotation machine 25 after being diluted with water 19 as necessary depending on the grinding conditions of the wet grinder 15.

A collection agent 21 is supplied to the flotation machine 25, and a foaming agent,
A pH adjuster is introduced from line 23 as needed.

Although either the heavy fraction or the heavy fraction of the coal liquefaction product may be used as the collecting agent, it is particularly preferable to use a circulating solvent. In addition to the liquefied product, light oils such as kerosene and kerosene, which are commonly used in flotation, can also be used as the collecting agent. The amount of collector added is usually 30 per ton of coal.
About 0-2500g is good.

In this flotation machine, the coal content is recovered as clean coal floss 29 by flotation operation, and the liberated ash content is recovered as flotation tail 27.
Separated as The coal concentration of this clean coal floss is 6 to 3
This is in the range of 0%, which results in a dehydrated cake 31 with a high coal concentration in the dehydrator 30. A belt press is used as a dehydrator.
A drum or belt type type can be used as an external vacuum dehydrator for a filter press. In this dehydration step, it is desirable to reduce the moisture content of the dehydrated cake as much as possible in order to reduce the load on the subsequent drying step. For this purpose, it is preferable to adjust the pH of the pulverized coal/water slurry to 3 to 6 and then dehydrate it.

In the above dehydration method, the moisture content of the dehydrated 9 cake 31 is 20
Since the content is in the range of ˜40%, this cake is introduced into a dryer 32 to further evaporate water. This dryer can be constructed to handle the pulverized coal that makes up the dehydrated cake, and it is well known that, for example, an indirect heating disc type can be used to dry coal of this kind of particle size. ing. In this drying process, the moisture content is reduced to 10% or less.

The pulverized coal 33 dried in the dryer 32 is put into a stirring tank 34. Appropriate amounts of circulating solvent and liquefaction catalyst are introduced into this stirring tank through line 35 and mixed uniformly with dry pulverized coal to form a coal/circulating solvent slurry that is the base material for liquefaction.

The flotation tail 27 containing ash during deashing is treated in a wastewater treatment device 35, and the purified water is recycled and used as make-up water for the wet crusher and flotation machine. The tail of the dehydrator can also be treated with this wastewater treatment equipment.

According to the present invention, finely pulverized coal for liquefaction is deashed in a flotation process, and the deashed coal is dehydrated and dried, using a circulating solvent that has been dehydrated to a moisture value acceptable for the liquefaction process as a medium. You can get slurry. Moreover, it has the advantage of effectively using the liquefied product as a trapping agent in the flotation process.

Example Coal was pulverized to about 70% of 200 mesh or less using a wet pulverizer, and then a coal/water slurry having a concentration shown in the table below was prepared. To this slurry, a W-ring solvent obtained by the solvent drawing method and methyl isobutylcarbinol as a foaming agent were added as shown in the table below, and a selective deashing treatment was performed. 4゜The results are shown in the table below. The table also shows an example when heavy oil was used as the scavenger.

As can be seen from these results, flotation deashing using a circulating solvent showed better performance than flotation deashing using heavy oil, with an ash content of 11.
It is possible to reduce the ash content of 1% coal to about 8% at a combustible recovery rate of 90%. If a lower recovered coal ash content is desired as required by the liquefaction process, this can be achieved by making the particle size of the pulverized coal finer.

[Brief explanation of drawings]

The figure is a flow diagram showing an embodiment of the present invention.

Claims (1)

[Claims] 1. Supply the liquefied product from the coal liquefaction process into the water slurry of pulverized coal, perform coal flotation using this liquefied product as a scavenger, and dehydrate and dry the clean coal floss obtained by flotation. 1. A method for pretreatment of coal for liquefaction, characterized by recovering low ash coal.