RU2240975C2 - Method and apparatus for manufacture of granulated percarbonate - Google Patents

Abstract

FIELD: industries inorganic synthesis and household chemical goods.

SUBSTANCE: seal percarbonate particles 0.1-0.4 mcm in size are loaded into double-screw mixer 2 and into dryer 3 provided with gas-distribution grate 4. Fluidized bed is formed in fryer 3 by means of flue gases heated to 200^oC. Hydrogen peroxide and soda ash solutions are fed into reactor 1 and resulting sodium percarbonate solution is then fed into mixer 2 to moisten seed particles, which, when being moistened, are vigorously stirred and displaced. Wet product is passed on grate 4 of dryer 3. Casing of the latter has variable cross section along its height caused by inclination of at last one of the side walls to an angle 10-20^o to vertical. Variable cross section changes velocity of flue gases and provides size separation of the dried particles: fine fraction in upper layer and coarse fraction in lower layer. Coarse fraction is withdrawn from dryer 3 through line 12 and sent to electrifier 5. Commercial fraction is discharged over line 13, whereas coarse fraction is transferred over line 14 to mill 15 wherein it is combined with fine fraction and fed over line 11 into mixer 2 as recycle.

EFFECT: increased proportion of commercial fraction relative to total amount of granules with drown from dryer to be classified.

2 cl, 2 dwg

Description

The invention relates to the chemical industry, in particular to household chemicals, and can be used in the production of sodium percarbonate and other chemical products, where the synthesis process is combined with granulation of the synthesized product.

A known method of producing granular sodium percarbonate, which consists in the fact that solutions of hydrogen peroxide and soda are brought into contact with retur in the form of granules of sodium percarbonate, mix them and subjected to drying. The dried granules are separated by particle size to obtain the desired product. At the same time, a finely dispersed product carried away by the used heat carrier and separated from it in a cyclone, a fine fraction of granules after their size separation, and also a product of crushing a large fraction (patent DE No. 2250720, class C 01 B 15/10, 1973 )

Also known is an installation for implementing this method, which includes serially connected reagent supply system, mixer, dryer and classifier (see ibid.).

A known method of producing granular sodium percarbonate, which consists in the fact that solutions of hydrogen peroxide and soda or the product of their interaction are brought into contact with retur in the form of granules of sodium percarbonate, mixed and subjected to drying, part of the dried granules are separated by particle size to obtain the target product, the rest part is used as a reture immediately after drying (patent RU 2164215, class C 01 B 15/10, 1999).

There is also known an installation for implementing this method, containing a series-connected reagent supply system in the form of a reactor, a mixer and a dryer communicated with each other in the discharge zone of dried granules, a means for separating granules into fractions, the discharge line of one of the fractions of which is the exhaust line of the finished product ( see there).

With this technical solution, considerable energy is required for moving the reture, for crushing large particles of sodium percarbonate, for heating the particles trapped in the cyclone and returned with the retur. To obtain the finished product, less than 1/20 of all the granules dried on the dryer are taken from the dryer. Of this number of granules after classification, only particles ranging in size from 0.1 to 1.0 mm are used as a marketable product. Large granules are subjected to additional crushing in a mill and, together with fine particles, are used as retur in the synthesis and granulation of sodium percarbonate.

The technical result of the proposed method and device is to increase the proportion of granules of the product fraction in relation to the total number of granules selected from the dryer for classification.

The specified technical result is achieved by the fact that in the method for producing granular sodium percarbonate, which consists in the fact that solutions of hydrogen peroxide and soda or the product of their interaction are brought into contact with reture in the form of granules of sodium percarbonate, mixed, dried, part of the dried granules are separated by size particles, and the rest of the dried granules are used as retur, in the drying process, the granules are classified according to the size of the particles by the height of the dryer so that small granules are located reimuschestvenno in the upper layer of the dried granules, and preferably in the lower large, and the separation of granules withdrawn from the lower layer of the dried granules.

This solution allows you to reduce the cost of separating the product fraction from the pulverulent product, the crushing of large substandard granules, their classification and movement. The share of granules selected as a commodity fraction, in relation to the total number of granules entering the classification, increases more than 1/20 of the part.

The specified technical result is also achieved by the fact that the installation for producing granular sodium percarbonate, containing serially connected reagent supply system, mixer, dryer, means for separating granules into fractions, the line of withdrawal of one fractions of which is the line of removal of the target product, means for returning part of the dried product in the mixer, the dryer body has a variable cross-section in height, which is ensured by tilting at least one wall of the body by 10-20 ° to the vertical.

Figure 1 shows a diagram of an installation for producing granular sodium percarbonate. Figure 2 shows the cross section of the dryer, view A.

The granular sodium percarbonate production unit includes a reactant feed system in series in the form of a reactor 1, a twin-screw mixer 2, a fluidized bed dryer 3 with a gas distribution grid 4, classifier 5. The reactor 1 has a housing with upper fittings for introducing liquid reagents and a fitting for withdrawing the reaction mixture with film type spreader. The mixer 2 is a twin-screw conveyor equipped with an engine with an adjustable speed of screws. The mixer 2 is adjacent directly to the dryer 3 and communicated with the dryer with a nozzle 6 for introducing the dried granules as a retur and a nozzle 7. The dryer body 3 has a variable cross-section along the height of the apparatus and is equipped with adjustable gates 8 and 9. The gate 8 is designed to take part of the dried product particle size separation to isolate the product fraction from the lower layers of the product transported through the dryer. The gate 9 is designed to output the upper layers of the dried product into the mixer 2 on the retur. The dryer 3 is equipped with a gas distribution grill 4 of non-failure type, which is designed in such a way that the living cross section decreases as the product dries and moves to the discharge zone, which ensures the granules move to the discharge place. The variable cross-section of the dryer along the height of the apparatus provides a decrease in the speed of the gas stream as it moves away from the gas distribution grill. Smaller particles of sodium percarbonate are carried by the gas stream into the upper layers, and larger granules accumulate near the gas distribution grid. The installation is equipped with a dust collection unit connected to a dryer 3 and including a cascade of dust gas purification devices, from which dry dusty sodium percarbonate after collection is returned to the mixer 2 along lines 10 and 11 and used as a retura, and the purified air is discharged into the atmosphere. Classifier 5 is a two-stage vibrating screen, which is connected by line 12 to the dryer 3 in the pellet discharge zone, from which the commercial fraction is taken along line 13, and the coarse fraction is fed to mill 15 via line 14, then connected to the fine fraction and fed to line 16 mixer 2 as a retur.

The method of obtaining granular sodium percarbonate in this installation is as follows.

Granulation of sodium percarbonate is carried out by building up the product layers on the seed particles, which will fill the mixer 2 and dryer 3. As the seed particles (retur), a part of the dried granules from the dryer, a finely dispersed product trapped in cyclones and the product after grinding in a mill are used.

In dryer 3, moisture is removed from the sodium percarbonate particles by a stream of hot air in a fluidized bed mode. Exhaust air is passed through a gas duct to the dust collection unit 10, and the cleaned air is discharged into the atmosphere, and the captured dust is returned to the mixer 2. Sodium percarbonate, which mixes with dusty sodium percarbonate, also enters the mixer 2, forming seed particles.

Streams of suitably prepared aqueous solutions of soda ash and hydrogen peroxide are fed into the reactor 1 through fittings. Obtained by mixing the reaction mass into the mixer 2. In the mixer, the reaction mass is distributed over the surface of the seed particles of sodium percarbonate and moistens them. From the mixer 2, the wet granules enter dryer 3.

The gas distribution grid 4 of the dryer 3 at the inlet section has an increased live section and additional flue gas blowing, which contributes to the rapid distribution of the moistened material across the width of the dryer 3. The increased live section of the gas distribution grid 4 at the inlet section of the dryer 3 prevents the accumulation of large particles at the entrance to the dryer 3. Due to the change in the gas flow velocity along the height of the dryer, the particles of the dried product are redistributed along the height of the transported layer. Fine particles are carried by a gas stream into the upper layers of a moving product. In the lower layer adjacent directly to the gas distribution grid, large particles of sodium percarbonate remain.

The dried granules of the upper layer from the dryer 3 through the adjustable gate 9 are returned as retur to the mixer 2, and the granules of the lower layer through the adjustable gate 8 are fed into the classifier 5. From the intermediate part of the classifier 5, the middle fraction enters the injector 17, from where it is directed by the flow of compressed air to the accumulator commercial product.

The fraction of large particles from the classifier 5 is sent to the mill 15, where, after mixing with the fraction of small particles by the flow of compressed air through the injector 18, it is returned to the mixer 2.

The method of obtaining granular sodium percarbonate includes the following operations in the following modes.

An aqueous solution of soda ash stabilized with sodium polyphosphate and dry magnesium sulfate is prepared at 50-70 ° C, filtered and mixed with a solution of water glass at 50-70 ° C.

Sodium percarbonate is obtained in reactor 1 by reacting a stabilized soda solution with a 30-50% hydrogen peroxide solution at a molar ratio of soda: hydrogen peroxide of 1.0: 1.5.

Then crystallization and granulation of sodium percarbonate are carried out. To do this, the sodium percarbonate solution is fed into the mixer 2, filled with dry hot retur. Retura granules are wetted with sodium percarbonate solution to a moisture content of 3-5%, mixed, increased in size due to the build-up of the shell and moved to the drying zone. The resulting wet granules are continuously fed to a fluidized bed dryer 3. The gas temperature at the inlet to the dryer is 170-400 ° C, the vacuum in the dryer is 0.1-0.5 kPa. In the dryer, the granules are dried, while being separated by granulometric composition according to the height of the layer due to the variable velocity of the gas flow along the height of the apparatus, due to its variable cross-section along the height. The lower part of the layer of dried granules (from 1 to 5% of the total mass) is removed from the dryer and sent to the classifier 5. The remaining part of the granules (upper layer) is returned to the mixer 2 as a reture immediately after the dryer.

On classifier 5, the dried product is divided into fractions, from which the middle fraction is selected as the finished product. Larger particles enter the mill, after which they are mixed with the finer fraction and returned to mixer 2. The commercial fraction is sent for packaging.

The following are examples of the method.

Example 1

Prepare an aqueous solution of soda ash with the addition of stabilizers - sodium polyphosphate, magnesium sulfate and water glass (sodium silicate) of the following composition, wt. %:

Soda Ash 20

Magnesium Sulfate 0.06

Sodium Polyphosphate 0.2

Sodium Silicate 0.8

Water Else

Prepare an aqueous 35% hydrogen peroxide solution.

In a twin-screw mixer 2 of a sodium percarbonate production unit and a 2.5 m ² fluidized bed dryer, 800 kg of seed particles 0.1-0.4 mm in size, which are ready-made sodium percarbonate, are loaded. A vacuum is created in the dryer using a fan, and flue gases with a temperature of 200 ° C are fed into the dryer through a gas distribution grid.

To obtain sodium percarbonate reactor 1, a hydrogen peroxide solution with a volumetric flow rate of 116 dm ³ / h and a soda ash solution with a volumetric flow rate of 420 dm ³ / h are supplied, where sodium percarbonate is formed within 5-8 seconds. The sodium percarbonate solution is fed through a special distributor to mixer 2. In the mixer, the seed particles are moistened with an aqueous solution of sodium percarbonate to a moisture content of 3 - 8%, intensively mixed moistened sodium percarbonate and moved to the drying zone. Through the loading pipe 7, the wet product is fed to the grate 4 of the dryer 3, where sodium percarbonate is dried in a flue gas stream. The longitudinal movement of the product through the dryer is ensured by the directed movement of the flue gases and the change in the living cross-section of the grate, and the separation into particle size distribution along the height of the apparatus is ensured by changing the cross-section of the dryer casing in height. The dried particles from the lower layer of the product moved through the dryer are removed from the drying zone and sent for classification. On classifier 5, the sodium percarbonate stream is divided into three fractions. Particles of a fraction of more than 1.0 mm are sent to a crusher, after which they are mixed with a fraction of particles of less than 0.1 mm and returned to mixer 2. Particles of a fraction of 0.1-1.0 mm are selected as a commercial product and sent for packaging. The top layer of the product moved through the dryer is sent as a retura to the mixer 2.

When using a dryer with a variable cross-section along the height of the apparatus with a device providing the selection of the lower layer to obtain a product fraction and the upper layer for retour, the yield of a product fraction was 160 kg / h. At the same time, 0.8 kg / h of granules larger than 1.2 mm were sent for crushing.

When using a dryer of the same type, but with an angle of inclination of the side wall of less than 10 °, the yield of the product fraction is reduced to 155 kg / h with the same technological parameters. At the same time, substandard dry sodium percarbonate in an amount of more than 8 kg / h is sent for crushing. When using the dryer of the same type, but with an angle of inclination of the side wall of more than 20 °, it is difficult to move the product to the unloading of the dryer.

Thus, the use of a dryer with a variable cross-section along the height of the apparatus and an angle of inclination of the side wall of 10 ° -20 ° to the vertical, together with a device that allows you to select the lower layer of dried sodium percarbonate to isolate a marketable product, brings the particle size distribution of the selected portion of the dried product closer to the particle size distribution the composition of the commercial fraction and thereby reduces energy costs for crushing large particles, separation and movement of the reture.

Claims (2)

1. The method of producing granular sodium percarbonate, which consists in the fact that solutions of hydrogen peroxide and soda or the product of their interaction are brought into contact with reture in the form of granules of sodium percarbonate, mixed and dried, part of the dried granules are separated by particle size to obtain the target product, and the rest of the dried granules are used as retur, characterized in that during the drying process the granules of sodium percarbonate are classified according to the height of the dryer according to particle sizes so that small Ranuli arranged predominantly in the top layer of the dried granules, and large - preferably in the bottom, and on the separation of granules withdrawn from the lower layer of the dried granules. 2. Installation for producing granular sodium percarbonate, containing serially connected reagent supply system, mixer, dryer communicated with the mixer in the areas of supply of wet granules and unloading of dry granules and means for separating granules into fractions, the discharge line of one of the fractions of which is the target discharge line product, characterized in that the dryer casing has a variable cross-section in height, which is ensured by tilting at least one side wall of the casing at an angle of 10-20 ° to the vertical.

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