RU2233699C2 - Method of granulation of nitrogen fertilizers and device for realization of this method - Google Patents

Abstract

FIELD: production of mineral fertilizers, granulated nitrogen fertilizers in particular, such as ammonium nitrate; chemical and other industries.

SUBSTANCE: proposed method includes increasing sizes of fine granules to required level by repeated spraying the melt of nitrogen fertilizers on surfaces of granules of seeding material-tailings at temperature below crystallization temperature by 20-25 C of 96-98% of melt which is returned for repeated granulation and classification. Circulating flow of fine granules is in free fall in form of vertical screen at thickness no less than 50 mcm. Product thus formed is repeatedly directed to vertical screen for repeated spraying till required sizes of granules have been obtained; then, fraction is removed from circulating loop by means of string-type limiting sieve. Device proposed for realization of this method is made in form of multi-section apparatus; its lower section is provided with twin circulating proportioner at adjustable speed of revolutions and auger for unloading large lumps, vertical shaft, vertical transportation air duct which widens upward, settling chamber with pipe unions connected to shaft and to air duct, string-type limiting sieve, scraper chain conveyer for cleaning strings and swivel drum with flexible belt cloth wound on it. Mounted on either side of vertical shaft collectors for delivery of melt which are provided with injectors mounted at angle of 45 deg. relative to level. Sieve is mounted in inclined position below inlet of settling chamber. Chain conveyer is also inclined and is located under sieve. Length of flexible belt cloth is sufficient for complete overlapping of product passage zone; one end is secured on drum and second end is held in position parallel relative to sieve by means of two ropes provided with weights thrown through blocks on the outside of settling chamber and enclosed in protective casings. Belt cloth is located under sieve for removal of fine and commercial fractions through pipe union. Located inside connecting pipe union of settling chamber is flexible rubber apron secured on upper transversal rod and thrown through similar rod which is shifted relative to axis of pipe union.

EFFECT: possibility of obtaining homogeneous fraction; increased yield; reduced power requirements; enhanced operational reliability.

5 cl, 3 dwg

Description

The invention relates to the production of mineral fertilizers, in particular to the production of granular nitrogen fertilizers, such as ammonium nitrate (urea), and can be used in chemical and other industries.

A device and method for granulating nitrogen fertilizers by gradually increasing and enlarging the size of granules in continuously operating apparatuses with a suspended fluidized (boiling) layer of material is known. Granulation is carried out by introducing a concentrated melt into a suspended fluidized bed of retur and a granular product, followed by outputting the granules to an external classification by fractions. Granules that do not meet the grain specifications for the finished product (with finer and larger grains) are used as retur, and larger grains are pre-crushed [1. Pozin M.E. Technology of mineral fertilizers, Moscow: Chemistry, 1965, p.63-68].

The main disadvantage is the low yield of the target product, the difficulty in ensuring the required granulation mode, the increased energy intensity of the process due to the presence of a material-intensive external circulation circuit along the retur, and the large heterogeneity of the product fraction in terms of particle size distribution.

A known method of granulation and a device for its implementation, in which the device comprises an inclined belt conveyor, a shelter for the upper working branch of the belt, having side walls and a flat cover in which melt sprayers are installed, as well as a loading device for reture and unloading for the finished product. The loading device is installed in the lower part of the inclined belt conveyor and is made in the form of a funnel.

The unloading device is an overflow pipe mounted on the side wall of the shelter. The granulation process is carried out in the working space, limited by the upper working branch of the tape and shelter, and in the process, the upper working branch of the tape takes the form of a gutter. Retur particles are fed onto the working surface of the belt at the bottom of the conveyor. When moving from the bottom up, the tape carries away particles from the lower part of the layer, which, under the action of gravity, roll down, go into the upper layer, where, with a further movement down, they are sprayed by melt from sprayers [2. Patent FR 1545663, CL In 01 j 2/26, 1968].

The disadvantage is also the low yield of the target product, the difficulty of cooling due to the concentration of the bulk of the granular product in the lower part of the conveyor trough, the difficulty of removing moisture released on the surface of the granules during crystallization of the melt, the rather high energy consumption of the granulation process due to the need to organize an external circulation circuit returu and its cooling.

The closest in technical essence and the achieved effect is a method of granulating mineral fertilizers and a device for its implementation, in which granulation of nitrogen fertilizers is carried out in a rotating fluidized stream of granulated product at a temperature along the entire length of the granulation zone below the crystallization temperature of 20-25 ° C followed by cooling the resulting product to the temperature of the starting product (retur), and create a vacuum above a rotating stream to 0.0035-0.0045 MPa. The resulting product is sent to the classifier to separate it into a commercial fraction of 2-4 mm in size, a small fraction of 0.5-2 mm in size for use as a retur, a large fraction of more than 4 mm, followed by crushing to a retur size and partially commercial fraction with crushing for compensation for the lack of reture. The granulation device comprises a housing, in the lower part of which there are air supply, and in the upper part - air discharge fittings; a common air distribution grill mounted above the air supply fittings; a fitting for supplying the reture to the granulation zone and a fitting for unloading the granular product. A granulation unit is mounted centrally inside the body in a two-roll returous stream rotating towards each other, containing in the lower part a wave-like working grating with an angle of 45 ° to the horizon and 60 ° at the top of the wave. The working grid is provided with holes in horizontal and inclined sections. Above the working grate, at a distance sufficient for the passage of the fluidized rotating flow of the retura, two expanding aerial chutes expanding to the top are mounted, between the inner walls of which in the central part there are two rows of spray nozzles directed towards the inclined walls of the chute [3. RF patent №2163901, IPC С 05 C 1/02, В 01 J 2/16, publ. bull. No. 7, 2001 - prototype].

The disadvantage is the low yield of the product fraction of the product, the possibility of forming large pieces due to deviations from the normal operation of the spray nozzles, the significant energy costs associated with the need to organize an external circulation loop of the reture and, as a result, sieving the granulated product into fractions.

The basis of the invention is the task of increasing the product yield of a product fraction, reducing or completely eliminating the external circulation circuit with a screening unit for the granulated product into a product fraction, retur and coarse fraction, eliminating the additional cost of crushing granules of more than 4 mm to the quality of the retur, increasing the reliability of the installation in as a whole, by organizing in the internal maximum circulating flow possible device the freely falling retura granules in the form of a vertical curtain, on which both of the sides using spray nozzles, a melt of 97.5% ammonium nitrate solution or 95% urea solution is applied, followed by cooling of the granulated product, screening the product fraction with a string sieve limiter and removing it from the device as the granules reach the required size.

The problem is achieved in that in the method of granulation of nitrogen fertilizers, which consists in increasing the size of small granules to the desired size by repeatedly spraying a melt of nitrogen fertilizers on the surface of the granules of the seed material - reture at a temperature below the crystallization temperature of 96-98% melt at 20-25 ° C returned to re-granulation after cooling and classification, according to the invention, the circulation flow of small granules is in free fall in the form of a vertical curtain with a thickness not less than 50 mm, moreover, the resulting product is repeatedly sent for re-spraying in a vertical curtain until the granulated product reaches the size of the granules of the commercial fraction, which is then removed from the circulation circuit of the freely falling granule stream using a string sieve-granule growth restrictor; the temperature in the vertical curtain after spraying the melt 115-120 ° C and at the entrance to the vertical curtain before spraying the melt 95-100 ° C is maintained by changing the intensity of circulation of the granulated product in the circulation loop of the freely falling flow of granules, and the intensity of circulation of the granulated product in the circulation the circuit of the device is provided by changing the number of revolutions of the twin metering screw depending on the temperature of the granulated product, and in the device for granulating nitrogen fertilizers, with according to the invention, the device is made in the form of a vertical multisection apparatus and contains: a lower housing, which has air inlet fittings in the lower part and an air inlet fitting, a retura inlet fitting, a granulated product outlet fitting and nitrogen fertilizer supply manifolds according to the invention a section equipped with a twin circulating metering screw with an adjustable speed, a screw for unloading large pieces; a vertical shaft, on both sides of which there are installed collectors for supplying melt with spray nozzles installed at an angle of 45 ° to the horizontal, a vertical, expanding upward, transport duct, a precipitation chamber containing connecting fittings to a vertical shaft and a vertical duct, a string sieve growth limiter granules installed obliquely and below the entry point into the precipitation chamber of the vertical duct, a scraper chain conveyor for cleaning strings installed obliquely close to the sieve - a limiter, a rotary drum with a flexible flexible tape wrapped around it, sufficient to completely overlap the product passage through a strainer to a vertical shaft, one end of which is fixed to the drum, and the other is held parallel to the string sieve with two ropes with loads, thrown through the blocks outside the precipitation chamber and enclosed in protective casings, and the tape web is located under the sieve with the possibility of output of small and commodity fractions through the outlet fitting of the commodity product a, a flexible rubber apron located inside the connecting nozzle of the precipitation chamber to the vertical shaft, mounted on the upper transverse rod and thrown over a deflecting rod, offset to the axis of the nozzle, in such a way that its free end is launched at a certain distance into the vertical shaft, and the left the bottom wall of the precipitation chamber is extended to the apron and at a distance of 50 mm from the apron is bent down by a length similar to the apron, and the apron and the wall are made over the entire width of the vertical shaft with no a large gap to the end walls of the shaft, and the upper wall of the circulating twin metering screw inside the left air supply fitting is cut and bent to the sides in such a way that it forms two inclined partition walls that are equipped with holes for air passage, and the lower wall from the end of the screws of the screw the dispenser and before it enters the right nozzle of the air inlet into the vertical duct is also provided with openings for the passage of air from the left nozzle of the air inlet using the bypass pipe to the right nozzle in Air ode; the screw for removing large pieces is set so that its horizontal axis is located on the right vertical wall of the air inlet fitting at a height slightly lower than the lower wall of the metering screw, and the upper left part of the wall of the screw for unloading large pieces at a length equal to the width of the air inlet fitting is removed, and instead of it, from its axis and to the height to the axis of the metering screw, a vertical threshold wall is installed, the lower end of which is tangentially adjacent to the right inner side of the wall of the air inlet fitting, providing a height denie large pieces on the auger screw.

The thickness of the vertical curtain of the freely falling circulation stream of the retur should be at least 50 mm in order to exclude the through passage of the sprayed melt as a result of the operation of oppositely arranged nozzles through the vertical curtain and to prevent the formation of adhering granules during the granulation process.

Inclined baffle walls with openings for the passage of air of the twin metering screw inside the left air supply nozzle ensure reliable loading of the twin metering screw with a granulated product, prevent sticking, and its further transfer to the vertical transport duct, and the presence of holes in the lower wall from the end of the twin turns the metering screw and until it enters the right air inlet into the vertical transport duct provides a smooth and soft transfer of the granulated product to vertical transport duct using air from the left duct through the bypass pipe.

Removing the upper left part of the wall of the auger for unloading large pieces, replacing it with a vertical threshold wall, the lower end of which is tangentially adjacent to the right inner side of the wall of the right vertical duct, provide the deposition of large pieces (sinter) on the screw of the auger for unloading large pieces due to the rarefaction created air flow over the screw of the screw.

The whole range of proposed technical solutions allows to ensure reliable and long-term operation in the optimal technological mode with the achievement of the maximum yield of the target product with its high quality and homogeneous particle size distribution, reduces the cost of the finished product by minimizing the external circulation circuit along the retur and eliminating the receipt and crushing of substandard product larger than the size of the product fraction, i.e. more than 4 mm.

The proposed method of granulation of nitrogen fertilizers and a device for its implementation are shown schematically in the drawings:

figure 1 is a vertical section in the form of a diagram of the device;

figure 2 is an oblique section aa of the device across the string sieve-limiter of growth of granules;

figure 3 is a vertical section bB of the device across the circulating auger metering.

The method of granulation of nitrogen fertilizers is illustrated in figure 1, where a vertical section of the device is schematically represented. The device comprises a lower section 1, equipped with air supply fittings 2 and 3, a paired circulation metering screw 4, a screw 5 for removing large pieces; a vertical shaft 6, equipped on both sides along the width of the shaft with collectors 7 for supplying melt with nozzles 8, passed into the inside of the shaft 6 and installed downward at an angle of 45 ° to the horizontal; vertical, expanding upward transport duct 9, located in the upper part above the shaft 6 and vertical duct 9, a precipitation chamber 10 containing an air outlet 11, two connecting nipples 12 and 13, a reture defect inlet fitting 14, a string sieve limiter 15 for granule growth, scraper a chain conveyor 16 mounted above the strainer sieve 15 with the possibility of stripping the strings, a rotary drum 17 with a tape web 18 wound thereon sufficient to completely cover the product passage zone through sieve limiter 15 in a vertical shaft 6, one end of which is fixed on the drum 17, and the second is held parallel to the string sieve limiter 15 with two cables 19 with loads 20 thrown over the deflecting blocks 21, and the loads 20 are enclosed in protective casings 22 and the web 18 is installed below the sieve-limiter 15 with the possibility of withdrawing a fine fraction (retur) together with the commercial fraction through the fitting 23 of the output of the granular product outside the device. Inside the nozzle 12 connecting to the vertical shaft 6, the precipitation chamber 10 has a flexible rubber apron 24 mounted on the upper transverse rod 25 and thrown over a similar rod 26 deflecting, offset to the axis of the nozzle, so that the free end of the apron 24 is launched some distance into the vertical shaft 6, and the lower left wall 27 of the precipitation chamber 10 is extended to the apron 24 and at a distance of 50 mm from the apron 24 is bent down by a length similar to the apron 24, and the apron 24 and the wall 27 are made to the full width of the vertical mine 6 with a small gap to the end walls.

The upper wall 28 of the circulating twin metering screw 4 inside the left air inlet fitting 2 is cut and bent to the sides in such a way that it forms two inclined partition walls 29, which are provided with holes 30 for air passage, and the lower wall 31 at the end of the screws of the metering screw 4 and before it enters the vertical transport duct 9 is also provided with openings 30 for the passage of air from the left air supply fitting 2 using the bypass pipe 32.

The screw 5 for unloading large pieces is installed so that its horizontal axis is located on the right vertical wall of the air inlet fitting 3 at a height slightly lower than the lower wall of the metering screw 4, and the upper left part of the wall of the screw 5 at a length equal to the width of the nozzle 3 is removed, and on the left side of the screw 5 from its axis and to the height to the axis of the metering screw 4, a vertical wall-threshold 33 is installed, which provides the planting of large pieces on the screw of the screw 5.

A method of granulating nitrogen fertilizers in a device for its implementation is as follows.

At the beginning of the start-up of the device, external air is separately supplied to the nozzle 2 with a temperature of + 30 ° C and the nozzle 3 with a temperature of + 40 ° C, and from the nozzle 11 the air is sucked out through an external flushing system and, already cleaned, is discharged into the atmosphere. Then, the circulating metering screw 4, the auger for unloading large pieces 5, the scraper chain conveyor 16 are turned on, and the required amount of retur is fed through the nozzle 14 into the device until 100% loading of the circulating metering screw 4 occurs, and in the vertical the shaft 6 does not form a continuous free-falling vertical curtain of retura. After that, 96-98% melt of ammonium nitrate (urea) with a temperature of 150-160 ° C, which is applied by nozzles 8 to the freely falling and rotating granules of the retura in the form of a curtain, is supplied to the collector 7 under a pressure of 0.4-0.6 MPa. The granules of the retura in a free fall diverge from each other by a small distance and randomly rotate around their own axis due to friction against the incoming air; especially borderline, which received the initial rotation when passing them between the wall 27 and the apron 24 due to friction about them. As a result of this, the melt is evenly applied over the entire surface of the individual granules.

As the pellets sprayed down by melt fly down, they are cooled by the internal cold of each pellet and by the oncoming air flow to the crystallization temperature. Then, as a result of crystallization, additional heat is released, which is spent on the evaporation of the moisture contained in the melt, which is carried away by the working air. At the end of the flight, all granules are transferred using a circulating metering screw 4 to a vertical transport duct 9, where they are transported upward into a precipitation chamber 10 by a powerful stream of air, simultaneously cooled and dropped onto a string sieve-limiter 15, sieved through it and then collected back into a free-falling a stream in the form of a vertical curtain along the height of the shaft 6, where repeatedly melt is repeatedly applied to them.

The process of applying melt to small granules (retur) continues until the granules reach a commodity fraction size of 4 mm, i.e. the amount of clearance in the light between the individual strings of the sieve-limiter 15, which then through the nozzle 23 are displayed, if necessary, for external classification and then for cooling, packaging or in bulk to the warehouse. As a result of the operation of nozzles 8 installed at an angle of 45 ° to the horizontal and vertically falling flow of granules in the shaft 6, due to the different lengths of the flight path, individual particles of the melt with the longest flight length have time to crystallize before reaching a free-falling flow of granules and, thus , self-formation of retura occurs, which subsequently, due to repeated application of melt on it, increases to the size of a commodity fraction, i.e. 4 mm.

If necessary, a small amount of small granules after sifting on a string sieve-limiter 15 using the tape web 18 and the fitting 23 together with the commercial fraction is displayed on the external classification. After that, the commercial fraction is sent to after-cooling and then to the packaging or in bulk to the warehouse, and granules less than 4 mm, somewhat cooled by heat loss into the environment, are sent back through the nozzle 14 to compensate for the lack of reture. Compensation for the lack of reture can also be made by crushing a small amount of a commercial fraction. The tape web 18 can be wound on a drum 17 and thus eliminating the output of granules with a size of less than 4 mm through the nozzle 23 together with the product fraction to an external classification, as a result of which the device operates on the internal self-formation of the reture with compensation for the lack of reture due to crushing of a small amount of commodity fractions.

The coalesced large granules (agglomerate) and crystallized pieces falling from the edges of the nozzles 8 fall onto the screw 5 and are removed from the device, then crushed, sieved and sent through the nozzle 14 to compensate for the lack of reture.

The temperature regime of the granulation process is provided by changing the number of revolutions of the circulating metering screw in automatic mode. After applying the melt to the retour with nozzles 8, the temperature of the incident granule flow is maintained at 115 ° C, and after cooling it in the vertical transport duct 9 is within 95-100 ° C. When the temperature rises above 115 ° C, the revolutions of the metering screw 4 increase, and when it falls below 115 ° C, it decreases.

The device is stopped after the material is completely unloaded through the nozzle 23 due to the complete closure of the product passage zone through the string sieve-limiter 15 into the vertical shaft 6 by the web 18 and the entire mass of the product is sent for unloading into the nozzle 23.

Thus, the proposed method of granulating nitrogen fertilizers and a device for its implementation can significantly improve the quality of the granulated product, obtain a uniform particle size distribution of the product, reduce energy consumption by eliminating the external circulation circuit of the retur, and significantly increase the reliability of the device as a whole.

Claims (5)

1. The method of granulation of nitrogen fertilizers, which consists in increasing the size of small granules to the desired size by repeatedly spraying a melt of nitrogen fertilizers on the surface of the granules of the seed material - reture at a temperature below the crystallization temperature of 96-98% of the melt at 20-25 ° C, returned to re-granulation after cooling and classification, characterized in that the circulation flow of fine granules is in free fall in the form of a vertical curtain with a thickness of at least 50 mm, and the resulting product m repeatedly directed to re-spraying into a vertical curtain until the granulated product reaches the size of the granules of the commercial fraction, which is then removed from the circulation circuit using a string sieve - granule growth restrictor. 2. The granulation method according to claim 1, characterized in that the temperature in the vertical curtain after spraying the melt 115-120 ° C and at the entrance to the vertical curtain before spraying the melt 95-100 ° C is supported by changing the intensity of circulation of the granulated product in the circulation circuit a free-falling flow of granules, and the intensity of circulation of the granulated product in the circulation circuit of the device is ensured by a change in the number of revolutions of the twin metering screw depending on the temperature of the granulated product. 3. A device for granulating nitrogen fertilizers, comprising a rectangular casing, in the lower part of which there are air supply fittings, and in the upper part, an air discharge fitting, reture input fitting, outlet for granulated product and collectors for supplying nitrogen fertilizer melt, characterized in that the device is made in the form a vertical multi-sectional apparatus and contains a lower section equipped with a paired circulating metering screw with an adjustable speed, a screw for unloading large pieces, vertical a mine shaft, on both sides of which there are installed melt supply manifolds with spraying nozzles installed at an angle of 45 ° to the horizontal, a vertical transport duct expanding upwards, a precipitation chamber containing connecting fittings to a vertical shaft and a vertical duct, a string sieve limiter for granule growth, installed obliquely and below the entrance to the precipitation chamber of the vertical duct, a scraper chain conveyor for cleaning strings installed obliquely close to the sieve-limit a rotary drum with a flexible flexible tape wrapped around it that is long enough to completely overlap the product passage through a strainer to a vertical shaft, one end of which is attached to the drum, and the other is held parallel to the string sieve with two ropes with loads thrown across blocks outside the precipitation chamber and enclosed in protective casings, and the tape web is located above the sieve with the possibility of output of small and commodity fractions through the outlet fitting of the product, flexible cut a new apron located inside the connecting nozzle of the precipitation chamber to the vertical shaft, mounted on the upper transverse rod and thrown over a similar rod deflecting biased towards the nozzle axis so that its free end is launched some distance into the vertical shaft, and the lower left wall of the precipitation chamber is extended to the apron and at a distance of 50 mm from the apron is bent down to a length similar to the apron, and the apron and the wall are made over the entire width of the vertical shaft with a small gap m to the end walls of the mine. 4. The device according to claim 3, characterized in that the upper wall of the circulating twin metering screw inside the left air supply fitting is cut and bent to the sides in such a way that it forms two inclined partition walls that are provided with openings for air passage, and the lower wall from the end of the screws of the metering screw and before it enters the right air inlet fitting into the vertical duct is also provided with openings for air passage from the left air inlet fitting using the bypass pipe to the right air inlet fitting spirit. 5. The device according to claim 3, characterized in that the auger for unloading large pieces is installed so that its horizontal axis is located on the right vertical wall of the air inlet fitting at a height slightly lower than the lower wall of the metering screw, and the upper left part of the wall of the unloading screw large pieces at a length equal to the width of the air inlet fitting are removed, and instead of it, a vertical threshold wall is installed from the axis and to the height to the axis of the metering screw, the lower end of which is tangentially adjacent to the right inner side of the wall of the unit and an air input providing precipitation of large pieces on the auger screw.

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