RU2439131C1 - Method for coal-water fuel production - Google Patents

Abstract

FIELD: power engineering. ^ SUBSTANCE: previously ground initial product is exposed in two and more stages to wet grinding in a rotor hydrodynamic cavitation device (2, 7). In a cavitation device the rotor fixed on a driving shaft comprises pump blades, and at least one concentric row of cavitators, quantity of which in the row is a prime number of at least 7 and increases in each subsequent row in direction from a driving shaft to the periphery. Each stage of wet grinding is carried out in a closed cycle with classification of coal-water suspension in size in a device for classification (5, 10). Coarse fraction from the device (10) is returned into the device (7) for grinding. Fine fraction is supplier to a thickener (11). Residue produced in the thickener is divided into two flows, one of which is sent to a mixing device (13) to produce finished fuel. The other is exposed to dehydration at the filter (12), from where it is also supplied to the stage of the finished fuel production into the device (13), where the requested quantity of a stabiliser is supplied. ^ EFFECT: when using the method, power inputs are reduced due to reduction of energy consumption for grinding. ^ 6 cl, 2 dwg

Description

The invention relates to the field of fuel energy, and in particular to methods for producing finely dispersed coal-water fuel based on fossil coal, which can be used for burning in boilers, furnaces and other installations of heat power plants when replacing gas and fuel oil, as well as in internal combustion engines.

Known methods for the preparation of water-coal fuel (hereinafter VUT) by grinding coal in an aqueous medium (USSR Patent 1375335, B02C 19/00, 1986;

USSR patent 1530099, C10L 1/32, 1985; USSR patent 1838384, C10L 1/32, 1987; RF patent 2026741, B02C 19/00, 1991; RF patent 2027744, C10L 1/32, 1991; RF patent 2183658, C10L 1/32, 2001).

The main disadvantage of the known methods for the preparation of VUT is that coal grinding is carried out, as a rule, when the solid content in the processed coal-water suspension (pulp) is at least 40-50 wt.%. With such a solid content, it is impossible to conduct an effective process of grinding a water-coal suspension in a closed cycle due to the inoperability of the classification devices (hydrocyclones, fine-mesh sieves, etc.). Therefore, the above methods for the preparation of HLF are characterized by high energy intensity (from 40 to 100 kWh / t). However, it is well known that maximum efficiency and minimum energy consumption of grinding are achieved only when the grinding equipment is operated in a closed cycle with a device for classifying the grinding product by size.

A known method of producing water-coal fuel, including crushing coal, its wet grinding to obtain a water-coal suspension, stepwise demineralization of crushed coal to reduce its ash content with the formation of primary and secondary products, their subsequent demineralization and dehydration / patent of the Russian Federation No. 2178455, class. C10L 1/32, 2002 /.

The known method includes the following operations: crushing coal, its wet grinding to obtain a water-coal suspension, stepwise demineralization of crushed coal to reduce its ash content with the formation of primary and secondary products, their subsequent demineralization and dehydration. Wet grinding of coal is carried out to a colloidal particle size to obtain a water-coal suspension with an average surface size of the dispersed phase of not more than 3 μm, the resulting suspension is diluted with water to a coal concentration of 1-3%, the demineralization of primary and secondary products is carried out jointly by combining products with similar ash values .

The specified method of producing water-carbon fuel has the following disadvantages:

1. When grinding coal at a moisture content of 55-60%, it is practically impossible to effectively operate a ball mill in a closed cycle with a classifier, which leads to a significant increase in the energy intensity of the grinding process.

2. Grinding coal in a ball mill to a colloidal particle size with an average surface size of not more than 3 microns is very problematic and requires extremely high specific energy costs.

A known method of preparation of cavitation water-coal fuel (KaVUT) and a production line for its implementation / RF Patent 2380399, cl. C10L 1/32, 2006 /.

The disadvantages of this method are:

- gross grinding of raw coal without classification of grinding products by size determines increased specific energy costs for grinding;

- an increased number of sequentially installed cavitation dispersants due to the lack of classification of grinding products by size;

- the content of 60-75% of the solid fuel component in the processed pulp reduces the intensity of cavitation.

A known method of producing water-coal fuel, according to which coal is crushed in a hammer mill to a fraction of 0-10 mm, a large grinding of the obtained solid component is carried out in a cavitation mixer, to which 0.005 wt.% Alkaline reagent is added, up to 3.5 wt.% Carbon stabilizing additives and water while maintaining the pulp of the mixer turbine in suspension with simultaneous demineralization, the resulting suspension is sent to a hydroclassifier to separate coal particles larger than 800 microns and mineral particles, separated th particles of minerals and coal are fed into the hydrocyclone to separate the coal particles and return them to the mixer, and the minerals to the dump, while the suspension after separation of the coarse fraction of coal and minerals is sent to a fine grinding disperser to obtain particles of a solid phase of 0-250 μm, times, the components of the suspension are subjected to simultaneous regrinding and mixing, followed by directing the mixture into a container for storage and storage, from which it is pumped to the boiler burners / RF Patent 2249029, C10L 1/32, 2005 /.

The disadvantage of this method is grinding in a cavitation mixer coarse grinding pulp containing 65-70% of the solid fuel component, which leads to a significant decrease in the cavitation intensity and the efficiency of the hydroclassifier in the subsequent separation of the pulp grinding product at a boundary grain of 800 microns.

In addition, the design features of cavitation grinders coarse and fine grinding, consisting in the fact that the number of holes in the rotors of the grinders is a multiple of 2, 3 or 5, contribute to the emergence of unstable pulsations of hydrodynamic resistance to rotation of their rotors and ripples of current in the circuits of their drive motors. When the gaps between such cavitators in the radial direction coincide during the rotation of the rotor, resonant pulsating flows of the treated liquid arise, leading to pulsations of hydrodynamic resistance to rotor rotation, pressure pulsations (in the range of ± 30% or more) in the outlet pipe of the apparatus and pulsations of current strength (in the range ± 30% or more) in the electric circuit of the drive motor. As a result, the effectiveness of cavitation effects on the treated suspension decreases, the energy intensity of the process increases, the conditions worsen, and the life of the grinders decreases.

The technical result from the use of the proposed method for producing water-coal fuel is to reduce energy costs by reducing the energy consumption for grinding.

The technical result is achieved due to the fact that in the method of producing water-carbon fuel, feedstock with a particle size of less than 3 mm are subjected to preliminary wet grinding in a mill or dry grinding, followed by classification of the crushed product into coarse, medium and fine fractions, preliminary wet grinding product or middle fraction of dry product grinding is served for mixing with water to obtain a water-coal suspension with a solids content of 5-30 wt.% and subjected to two or more stages of wet measurement in a rotary hydrodynamic cavitation apparatus for processing liquid media with a rotor mounted on the drive shaft containing pump blades and at least one concentric row of cavitators, the number of which in the row is a prime number of at least 7 and increases in each next row in the direction from the drive shaft to the periphery, with each stage of wet grinding is carried out in a closed cycle with classification of the coal-water suspension by size, the product obtained in the first stage of wet grinding they undergo the first stage of classification, from where the coarse fraction is returned to mixing with water, and the small fraction is sent to the second stage of wet grinding, the product obtained in the second stage of wet grinding is subjected to the second classification stage with the return of the coarse fraction to the second stage of wet grinding, and the fine fraction is fed to dehydration to obtain a condensed sludge and discharge, which is returned to mixing with the product of preliminary wet grinding or with an average fraction of the dry grinding product and water, and the precipitate thickened is fed to the step of obtaining the finished coal-water fuel, where it is mixed with a stabilizer and a fine fraction obtained by grinding the dry product classification, the coarse fraction obtained from the classification of the product of dry grinding is returned to the dry grinding.

The technical result is also achieved due to the fact that before dehydration, a fine fraction of the classification of the product of the second stage of wet grinding is sent to at least the third stage of wet grinding, followed by classification with the return of a large fraction of each stage to the corresponding stage of wet grinding.

The technical result is also achieved due to the fact that the condensed sludge is divided into two streams, one of which is sent to the stage of obtaining ready-made coal-water fuel, and the second is filtered and also sent to the stage of obtaining finished water-coal fuel, while the filtrate from dehydration of the thickened sludge is returned to mixing with the feedstock.

In particular cases, a hydrocyclone, a fine mesh sieve or a centrifugal separator can be used to classify a wet-milled product of a rotary hydrodynamic cavitation apparatus.

The fundamental difference between the proposed method and the known methods for producing water-coal fuel, which use cavitation apparatuses, is that the grinding of coal is carried out in a rotary hydrodynamic cavitation apparatus for processing liquid media with a solid content in the treated pulp in the range from 5 to 30 wt.%, And to obtain the finished HLW, the product of the final stage of wet grinding is processed in known devices for dehydration and mixed with a stabilizer.

A significant difference of the proposed method is the use for wet grinding of coal rotary hydrodynamic cavitation apparatus with a rotor mounted on the drive shaft containing pump blades and at least one concentric row of cavitators, the number of which in the row is a prime number of at least 7 and increases in each following row in the direction from the drive shaft to the periphery. The design features of the rotary hydrodynamic cavitation apparatus used in the claimed method exclude the coincidence of the gaps between the multiple cavitators in the radial direction during the rotor rotation, which leads to stabilization of the hydrodynamic resistance to the rotor rotation, while the pressure pulsation in the apparatus outlet pipe and the current pulsation in the drive electric motor circuit are not exceed ± 5%.

The method is illustrated by drawings. Figure 1 shows a schematic flow diagram of a method of producing water-coal fuel with preliminary wet grinding. Figure 2 is a flow diagram of a method of producing water-coal fuel with preliminary dry grinding using for the classification of products of wet grinding of hydrocyclones.

The source coal (Fig. 1) with a particle size <3 mm is subjected to preliminary wet grinding to a particle size <630 μm in a vibratory mill and fed to contact tank 1, where water is simultaneously supplied in the amount necessary to obtain a water-coal suspension with a solid content in the range from 5 to 30 wt.%. The water-carbon suspension from the contact tank 1 is sent to the rotary cavitation hydrodynamic apparatus 2 of the first stage of wet grinding.

The product of the apparatus 2 enters the contact tank 3, from which it is pumped 4 to the device 5 for classification by size into two fractions. The fine fraction is fed to the contact tank 6, and the large fraction is returned to the contact tank 1.

From the contact tank 6, a fine fraction of the first stage classification product is fed into the rotary cavitation hydrodynamic apparatus 7 of the second stage of wet grinding. The product of the apparatus 7 enters the contact tank 8, from which it is fed by a pump 9 to the particle size classification device 10 of the second stage.

A large fraction from the device 10 is returned to the contact tank 6, from which it is fed to the apparatus 7 for additional grinding. The fine fraction from the device 10 is fed to the thickener 11.

The precipitate obtained in the thickener 11 is divided into two streams, one of which is sent to the stage of obtaining the finished HLW in the mixing device 13, and the other is subjected to additional dehydration on the filter 12, from where it is also fed to the stage of obtaining the finished HLW in the mixing device 13, where in order to obtain a HLF with a solid content of 55-65 wt.%, the necessary amount of stabilizer is fed. The drain of the thickener 11 and the filtrate of the filter 12 are sent to the contact tank 1 as recycled water, and the finished HLW pump 14 is diverted to the consumer.

The proposed scheme can be used in the modernization of existing plants for the preparation of HLW in order to increase their efficiency and reduce energy intensity.

The initial coal (Figure 2) with a particle size <3 mm is subjected to dry grinding in a centrifugal rotary crusher to a particle size <500 μm, followed by classification of the crushed product by size into large (> 500 μm), medium (500-20 μm) and small (<20 μm) fractions. The classification product - a coarse fraction> 500 μm is returned for re-grinding into a crusher. The middle fraction of 20-500 μm is fed into the contact tank 1, and the fine fraction of the classification <20 μm is used to prepare the WCF with a solid content of 55-65 wt.%. In contact tank 1 simultaneously with coal, water is supplied in the amount necessary to obtain a water-coal suspension with a solid content in the range from 5 to 30 wt.%. The water-carbon suspension from the contact tank 1 is sent to a rotary cavitation hydrodynamic apparatus 2 for wet grinding.

The product of apparatus 2 is sent to contact tank 3, from which pump 4 is fed into the particle size classification device into two fractions - hydrocyclone unit 5. Drain of hydrocyclone unit 5 with a particle size <100 μm is fed to contact tank 6, and the sands of a hydrocyclone unit 5 with a particle size> 100 μm are returned by gravity to the contact tank 1 for additional grinding.

From the contact tank 6, a product with a particle size of <100 μm is fed into the rotary cavitation hydrodynamic apparatus 7 of the second grinding stage. The product of the apparatus 7 is sent to the contact tank 8, from which it is pumped 9 to the device for classification by size into two fractions - a hydrocyclone unit 10.

The sands of the hydrocyclone unit 10 are fed by gravity to the contact tank 6, from which they are returned to the apparatus 7 for additional grinding to a particle size <20 μm. The discharge of the hydrocyclone unit 10 with a particle size <20 μm enters the thickener 11.

The precipitate obtained in the thickener 11 is subjected to additional dehydration on the filter 12, from where it is fed to the stage of obtaining the finished HLW in the mixer 13, where a fine fraction <20 mm of dry product classification is also fed to prepare HLW with a solid content of 55-65 wt.% grinding and the required amount of stabilizer. The drain of the thickener 11 and the filtrate of the filter 12 are sent to the contact tank 1 as recycled water, and the finished HLW pump 14 is diverted to the consumer.

The proposed method can be used to obtain water-coal fuel with particles smaller than 3 microns.

If it is necessary to obtain ultrafine water-coal fuel before dehydration, additional wet grinding of a fine fraction of the product classification of the second wet grinding product in the third and subsequent stages is possible using the wet grinding in the rotary cavitation hydrodynamic apparatus as a device for classifying the wet grinding product of a centrifugal separator.

Thus, the proposed method allows to obtain water-coal fuel of a given quality at low energy costs.

Claims (6)

1. A method of producing water-coal fuel, characterized in that the feedstock with a particle size of less than 3 mm is subjected to preliminary wet grinding in a mill or dry grinding, followed by classification of the crushed product into coarse, medium and fine fractions, the preliminary wet grinding product or the middle fraction of the dry grinding product for mixing with water to obtain a water-coal suspension with a solid content of 5-30 wt.% and subjected to two or more stages of wet grinding in a rotary hydro dynamic cavitation apparatus for processing liquid media with a rotor mounted on the drive shaft containing pump blades and at least one concentric row of cavitators, the number of which in the row is a prime number of at least 7 and increases in each next row in the direction from the drive shaft to peripherals, with each stage of wet grinding is carried out in a closed cycle with classification of the coal-water suspension by size, the product obtained in the first stage of wet grinding is subjected to the first stage to classification, from where the coarse fraction is returned to mixing with water, and the coarse fraction is sent to the second stage of wet grinding, the product obtained in the second stage of wet grinding is subjected to the second classification stage, the coarse fraction is returned to the second stage of wet grinding, and the fine fraction is fed to dehydration to obtain thickened sludge and drain, which is returned to mixing with the product of preliminary wet grinding or with an average fraction of the dry grinding product and water, and the condensed sludge ok serves at the stage of obtaining the finished water-coal fuel, where it is mixed with a stabilizer and a fine fraction obtained by the classification of the dry grinding product, while the large fraction obtained by the classification of the dry grinding product is returned to dry grinding. 2. The method according to claim 1, characterized in that before dehydration, a small fraction of the classification of the product of the second stage of wet grinding is sent to at least the third stage of wet grinding, followed by classification with the return of a large fraction of each stage to the corresponding stage of wet grinding. 3. The method according to claim 1 or 2, characterized in that the condensed precipitate is divided into two streams, one of which is sent to the stage of obtaining the finished water-carbon fuel, and the second is filtered and also sent to the stage of obtaining the finished water-coal fuel, while the filtrate from dehydration of the condensed sludge is returned to mixing with the feedstock. 4. The method of producing water-coal fuel according to claim 1, characterized in that a hydrocyclone is used to classify the wet grinding product. 5. The method of producing water-coal fuel according to claim 1, characterized in that a fine-mesh sieve is used to classify the wet grinding product. 6. The method of producing water-coal fuel according to claim 1, characterized in that a centrifugal separator is used to classify the wet grinding product.

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