Method and apparatus for forming nitrogen fertilizer granules

Abstract

The group of inventions relates to the chemical industry, and more particularly to the production of nitrogen fertilizers, and can be used for producing granules of fertilizers such as, inter alia, ammonium nitrate, urea and ammonium nitrate-phosphate fertilizers, by prilling. What is proposed is a method for forming nitrogen fertilizer granules by prilling using a closed air circulation loop, in which cooling air is fed into the lower part of a prilling tower, a nitrogen fertilizer melt is sprayed into the upper part of the prilling tower, and granules are removed from the lower part of the tower. By means of at least one closed circulation loop, air is removed from the upper part of the prilling tower for preparation by purification and cooling and is returned to the lower part of the prilling tower as cooling air, wherein before being returned to the prilling tower, at least a portion of the air is sent for additional preparation by aftercooling, with the separation and removal of condensate and subsequent warming of the air. Also proposed is an apparatus for carrying out the claimed method. The technical result of the group of inventions consists in increasing the efficiency of a prilling process entailing a closed loop for the circulation of cooling air by improving the quality of the fertilizer produced, increasing operational reliability and reducing the overall dimensions of the equipment used, while maintaining a complete absence of prilling process emissions and obviating the need for the inspiration of external air.

Description

[0001] METHOD AND APPARATUS FOR FORMING NITROGEN FERTILIZER GRANULES

[0002] Field of technology

[0003] The group of inventions relates to the chemical industry, namely to the production of nitrogen fertilizers, and can be used to obtain fertilizers such as ammonium nitrate, urea, nitroammophos and others by the prilling method.

[0004] State of the art

[0005] A method for forming nitrogen fertilizer granules by prilling and an apparatus for implementing the same are known from the prior art (RU 2629055 C1, published 24.08.2017). The method comprises the steps of supplying cooling air to the lower portion of a prilling tower to form an ascending flow, spraying a nitrogen fertilizer melt in the upper portion of the prilling tower to form melt droplets and solidify them in free fall in the ascending flow of cooling air, removing the granules formed from the melt droplets from the lower portion of the tower, and, via a partially closed circulation circuit, removing air from the upper portion of the tower for preparation by cooling without purification and returning it to the tower as cooling air. Before returning, the air is pre-mixed with another air stream from a post-evaporation apparatus, previously cooled and dried. In addition, a third stream draws atmospheric air directly into the prilling tower without treatment.To maintain the required amount of air during the solidification of melt droplets, part of the flow from the circulation circuit is diverted for cleaning into a wet scrubber and released into the atmosphere.

[0006] The unit comprises a prilling tower equipped with means for feeding the smelt, spraying it, and removing nitrogen fertilizer granules, as well as windows around the perimeter for drawing in atmospheric air. Furthermore, the unit contains a partially closed air circulation loop, including an air cooler and a fan-type blower, a duct for supplying cooled and dried air from the post-evaporation unit to the circulation loop, and an air bleed duct from the circulation loop for exhaust to the atmosphere, complete with a scrubber.

[0007] The disadvantages of this solution are as follows. Firstly, the air circulation circuit is not completely closed, since some is released into the atmosphere, and despite the fact that

[0008] SUBSTITUTE SHEET (RULE 26): The exhaust air is pre-cleaned in a scrubber, and the emissions cannot be considered safe. Secondly, untreated cooling air, contaminated with nitrogen fertilizer dust particles, is supplied to the prilling tower, which not only fouls the fan but also causes dust contamination of the product and dust adhesion to the inner walls of the tower and the circulation circuit ducts.

[0009] A method for forming nitrogen fertilizer granules by prilling and an apparatus for implementing the same are known (RU 2147554 C1, published 20.04.2000). The method includes the steps of supplying cooling air to the lower portion of a prilling tower to form an upward flow, spraying a nitrogen fertilizer melt in the upper portion of the prilling tower, removing granules formed from melt droplets from the lower portion of the tower for further cooling in a fluidized bed, and removing air from the upper portion of the tower via at least one circulation circuit for preparation by cleaning and cooling and returning it to the tower as cooling air.In this case, the air-steam mixture from the post-evaporation apparatus is mixed with the air removed from the tower, and the cooled and purified air flow is divided into two streams: the first stream is directed by ejection into the prilling tower, and the second stream is heated to reduce the relative humidity and pumped for post-cooling of the granules in the fluidized bed, then both air streams are mixed during the process of solidification of the melt droplets.

[0010] The setup comprises a prilling tower equipped with means for feeding the melt, spraying it, and removing nitrogen fertilizer granules. It also comprises an air circulation circuit comprising an air exhaust duct from the top of the prilling tower, an air preparation unit for cleaning and cooling, a duct for returning a portion of the air to the bottom of the tower, and a duct for feeding the remaining air to a fluidized bed granule post-cooling unit and subsequent return to the tower. Connected to the air exhaust duct is a duct for feeding a steam-air mixture from a post-evaporation unit. The cleaning and cooling unit forms two ducts, the purified and cooled air from which is subsequently combined: one duct goes to the prilling unit, the other to the granule post-cooling unit through a heater to reduce relative humidity and a blower in the form of a fan. This completes the air circulation circuit.

[0011] The disadvantages of these solutions are primarily that the air circulation loop cannot be closed, since, according to the diagram, the steam-air mixture from the post-evaporation unit is mixed with the exhaust air and sent to the cooling and purification unit. However, it is unclear what is done with the excess air that forms in the circulation loop. It is obvious to a person skilled in the art that the diagram must

[0012] SUBSTITUTE SHEET (RULE 26) there is an air emission in an amount proportional to the amount of supplied steam-air mixture, which in turn makes this circuit unclosed and leads to the appearance of the previously described deficiencies.

[0013] Furthermore, disadvantages include reduced equipment reliability, as dust can accumulate in the lower part of the tower due to the high relative humidity of the cooling air. The first portion of the airflow, still moist after the cooling and cleaning unit, enters the prilling unit directly, without a drying step. The second portion of the airflow passes through a heater for drying, without pre-cooling, into the integrated fluidized bed granule aftercooling unit. The two airflows then mix in the prilling tower, and the overall relative humidity decreases, but remains quite high.

[0014] The known method for forming nitrogen fertilizer granules by prilling with a closed air circulation loop and the apparatus for implementing the same (RU 2680686 C1, published 25.02.2019), selected as prototypes, are free from the disadvantages associated with air emissions into the atmosphere and air suction from outside, as well as the supply of unpurified air to the tower. The method includes the steps of supplying cooling air to the bottom of the prilling tower to form an upward flow, spraying a nitrogen fertilizer melt in the upper part of the prilling tower, removing granules formed from melt droplets from the bottom of the tower, and, via at least one closed circulation loop, removing air from the upper part of the tower for treatment by cleaning and cooling and returning it to the tower as cooling air.

[0015] The setup comprises a prilling tower equipped with means for feeding the smelt, spraying it, and removing nitrogen fertilizer granules. It also comprises a closed air circulation system, including an air exhaust duct from the top of the prilling tower, an air preparation unit for cleaning and cooling, and an air return duct to the bottom of the tower. The air preparation unit is designed as a hydro-blowing chamber within the tower with a co-current flow of washing liquid. Air returns to the prilling tower under pressure created by the flow of falling drops of said washing liquid, while fans installed in the upper part of the hydro-blowing chamber provide only additional draft.

[0016] The described solutions have the following disadvantages:

[0017] SUBSTITUTE SHEET (RULE 26) - a complex design of the prilling tower - it is equipped with a hydraulic blast cavity with a co-current flow of washing liquid for cooling and cleaning the exhaust air;

[0018] Returning air to the prilling tower at an insufficiently low temperature and 100% relative humidity due to direct contact with the cooling wash liquid reduces the quality of the resulting product (nitrogen fertilizer granules), leads to dust buildup on the tower walls, increases air consumption, and increases the size of the equipment used, particularly the flue ducts (channels) and the prilling tower. Moreover, the higher the temperature of the cooling air supplied to the tower, the larger its working area is required to ensure the solidification of the melt droplets in free fall in contact with this air.

[0019] Disclosure of the essence of the invention

[0020] The following terms and definitions are used to describe the proposed group of inventions:

[0021] Prilling is the process of producing nitrogen fertilizer granules by spraying a melt and solidifying the resulting droplets as they fall freely in an ascending flow of cooling gas.

[0022] Cooling air is air used to cool the melt droplets and facilitate their solidification during the prilling process.

[0023] A closed air circulation circuit is a circuit in which there is no provision for air discharge into the atmosphere or its suction from the outside to compensate for the discharge.

[0024] The problem that the present group of inventions is aimed at solving is the creation of a method for forming nitrogen fertilizer granules by prilling with a closed air circulation circuit and an installation for its implementation, devoid of the above-described disadvantages of analogues and the prototype.

[0025] The technical result of the group of inventions consists in increasing the efficiency of the prilling process with a closed cooling air circulation circuit by improving the quality of the resulting fertilizer, increasing operational reliability and reducing the dimensions of the equipment used while maintaining a complete absence of emissions from the prilling process and eliminating the need for air suction from the outside.

[0026] The said result is achieved in a method for forming nitrogen fertilizer granules by a prilling method with a closed air circulation loop, in which cooling air is supplied to the lower part of the prilling tower, the nitrogen fertilizer melt is sprayed in the upper part of the prilling tower and granules are removed from its lower part, wherein by means of at least one closed circulation loop the air is removed from the upper part of the prilling tower for preparation by cleaning and cooling and returned to the lower part of the prilling tower as cooling air, wherein at least part of the air before being returned to the prilling tower is sent for additional preparation by additional cooling of the air with the release of condensate, removal of condensate and subsequent heating of the air.

[0027] The use of the described additional air preparation in the method and the corresponding unit in the installation ensures an increase in the quality of the resulting product, an increase in operational reliability and a reduction in the dimensions of the equipment used while maintaining a complete absence of emissions from the prilling process due to the following:

[0028] - due to the reduction in the relative humidity of the cooling air, the possibility of moisture being captured by droplets of the melt is reduced, which improves the quality of the resulting product, and also reduces the possibility of moisture condensation on the walls of the tower and elsewhere, which increases the operational reliability of the equipment;

[0029] - due to the ability to further lower and maintain the temperature of the cooling air using the additional preparation unit, it becomes possible to reduce the amount of circulating air and use smaller equipment, in particular the prilling tower and channels in the air circulation circuit.

[0030] In a preferred embodiment, air having a relative humidity of no more than 86% and a temperature of no more than 36°C is returned to the prilling tower.

[0031] In particular, air with a relative humidity in the range of 75–80% and a temperature in the range of 30–35°C is returned to the prilling tower.

[0032] The above-mentioned temperature and relative humidity of the cooling air allow for a better efficiency of the prilling process, since under such conditions heat exchange is improved, leading to more efficient solidification of the melt droplets, and the possibility of moisture being trapped by the melt droplets is reduced, which improves the quality of the resulting fertilizer.

[0033] Preferably, at least 50% of the air is sent for post-conditioning before being returned to the prilling tower. The greater the proportion of air sent for post-conditioning, the easier it is to maintain low cooling air temperature and relative humidity with lower energy consumption, as a corresponding post-conditioning unit with lower power consumption is required, thereby increasing the overall efficiency of the prilling process.

[0034] Preferably, air is returned to the prilling tower by means of a fan.

[0035] In this case, it is preferable to pump air before its additional preparation or after additional preparation.

[0036] The use of a fan and its proposed location allow for a more uniform flow of cooling air in the prilling tower with minimal energy consumption, thereby increasing the efficiency of solidification of melt droplets.

[0037] In the preferred embodiment, when the air is cooled, its temperature is brought to 18-32°C.

[0038] In the preferred embodiment, air is returned to the prilling tower at a temperature that is 3 - 12°C higher than the air temperature after post-cooling.

[0039] The above parameters allow for further improvement of the efficiency of the prilling process, as they allow for the best cooling air characteristics and improve the quality of the resulting fertilizer.

[0040] In a preferred embodiment, ammonium nitrate or urea melt is sprayed into the top of the tower.

[0041] The proposed method is particularly effective for the specified fertilizers.

[0042] In a preferred embodiment, the volumetric flow rate of the portion of air that is sent for additional preparation is controlled remotely by means of at least one means for controlling the volumetric flow rate.

[0043] This further improves the efficiency of the prilling process, as it allows flexible adjustment of the closed-loop air circulation system without having to access the volumetric flow control device. This allows for optimal cooling air performance and improved fertilizer quality while reducing time and labor costs. Furthermore, remote control allows for automation of the process and increased control flexibility due to the faster response of the volumetric flow control system, thereby ensuring the most favorable operating conditions.The claimed technical result is also achieved by using a device for forming nitrogen fertilizer granules by a prilling method with a closed air circulation circuit, including: a prilling tower having in its upper part a means for spraying a nitrogen fertilizer melt and in its lower part a means for removing granules, one or more closed air circulation circuits, each of which contains a channel for removing air from the upper part of the prilling tower into an air preparation unit by cleaning and cooling it and a channel for returning cooling air to the lower part of the prilling tower, wherein at least one closed circulation circuit contains an additional air preparation unit located after the air preparation unit, including sections for additional air cooling with the release of condensate, condensate removal and air heating.

[0044] In one preferred embodiment, at least one closed circulation circuit is configured to provide conditions in which the cooling air returned to the bottom of the prilling tower has a relative humidity of no more than 86% and a temperature of no more than 36°C.

[0045] In a more preferred embodiment, at least one closed circulation circuit is configured to provide conditions in which the cooling air returned to the bottom of the prilling tower has a relative humidity in the range of 75 - 80% and a temperature in the range of 30 - 35°C.

[0046] In a preferred embodiment, the air preparation unit is a wet scrubber.

[0047] In a preferred embodiment, at least one closed circulation circuit is designed with the possibility of directing at least 50% of the air to the additional preparation unit.

[0048] In a preferred embodiment, each closed air circulation circuit used comprises a blower in the form of a fan.

[0049] In the preferred embodiment, the supercharger is placed before or after the additional preparation unit.

[0050] Preferably, the air aftercooling section is designed to provide conditions in which the air at the outlet has a temperature of 18 to 32°C.

[0051] It is also preferable that at least one closed circulation circuit is designed to provide conditions in which the cooling air at the inlet to the prilling tower has a temperature of 3 - 12°C higher than at the outlet from the air post-cooling section.

[0052] In a preferred embodiment, at least one closed circulation circuit is configured to remotely regulate the volumetric flow rate of a portion of the air that is directed to the additional preparation unit by means of at least one means for regulating the volumetric flow rate.

[0053] All of the above, taken separately and together, allow for increased efficiency in the prilling process with a closed-loop cooling air circulation system by improving the quality of the resulting fertilizer, increasing operational reliability, and reducing the size of the equipment while maintaining a complete absence of emissions from the prilling process and eliminating the need for external air intake.

[0054] Moreover, in the above-described particular and preferred embodiments of the inventions, the claimed technical result is achieved to a better extent than in other embodiments.

[0055] Brief description of the drawings

[0056] The group of inventions is explained using Figures 1-2, which are provided solely to illustrate embodiments. It will be obvious to those skilled in the art that other embodiments of the inventions are also possible.

[0057] Fig. 1 shows a basic diagram of an installation for forming nitrogen fertilizer granules using the prilling method with one circulation circuit and an additional preparation unit for all air.

[0058] Fig. 2 shows a diagram of an installation for the formation of nitrogen fertilizer granules using the prilling method with two circulation circuits and additional preparation units for part of the air.

[0059] The figures show:

[0060] 1 - prilling tower;

[0061] 11 - means for delivering floating material to the upper part of tower 1;

[0062] 12 - means for spraying the melt in the upper part of tower 1 (priller);

[0063] 13 - distribution (receiving) cones in the lower part of tower 1

[0064] 14 - means for removing granules formed from melt drops from the lower part of tower 1;

[0065] 2 - air preparation unit;

[0066] 21 - supercharger; 22 - refrigerator;

[0067] 3 - additional training block;

[0068] 31 - post-cooling section of additional preparation block 3;

[0069] 32 - condensate drain section of additional preparation unit 3;

[0070] 33 - heating section of block 3 for additional preparation;

[0071] 4 - channel for supplying air bypassing the additional preparation block 3;

[0072] 41 - means for regulating volumetric flow;

[0073] 5 - supercharger.

[0074] Abbreviations in the drawings: melt nitrogen, fertilizers - melt nitrogen fertilizer. solution in production - solution in production.

[0075] Condensate air - condensate obtained from air.

[0076] Steam condensate is a condensate obtained from steam.

[0077] Implementation of the invention

[0078] The proposed group of inventions can be used to obtain, by the method of prilling granules, such nitrogen fertilizers as ammonium nitrate, urea, nitroammophos and others, while the use of the invention is most effective for ammonium nitrate and urea.

[0079] 1. Description of the method

[0080] In the method for forming fertilizer granules using prilling with a closed air circulation loop, the solidification of smelt droplets as they freely fall in an ascending flow of cooling air is achieved, i.e., prilling. This stage occurs in vertically oriented devices—prilling towers 1—in which the fertilizer smelt is fed in a stream to the top, where it is sprayed, forming smelt droplets that freely fall within the tower 1. Cooling air is fed to the bottom of the tower to form a counter-current flow against the falling smelt droplets, cooling and solidifying them.

[0081] Fertilizer granules formed and shaped from the melt droplets fall into the lower portion of tower 1 and are then removed, for example, for further cooling, sorting, and packaging, or to another stage, depending on the process flow diagram used. Figures 1-2 illustrate towers 1 in which the granules fall onto receiving cones to be subsequently conveyed onto product conveyors. Other embodiments are also possible, such as one in which the granules fall into an integrated fluidized bed cooler.

[0082] To prevent pollutants and thermal emissions into the atmosphere, air moves through one or more closed circulation loops, where it undergoes the necessary treatment before returning to Tower 1. Typically, the design of Tower 1 is not complicated or modified, and the air circulation loop is installed separately from it, unlike in the prototype, but the opposite is also possible.

[0083] Thus, when using a closed circulation loop, heated and contaminated air is removed from the upper part of tower 1 and sent to preparation stage 2, where it is cleaned of dust particles of nitrogen fertilizer and cooled, for example, by contact with a cooling washing liquid, in order to then return all the air back to tower 1, namely to its lower part, as a cooling droplet of air.

[0084] Preparation 2 of the air removed from the tower 1 by contact with the cooling washing liquid can be carried out in one or several units, where the circulating solution of the resulting fertilizer is used as the said liquid.

[0085] In a particular example of the implementation of the present group of inventions, shown in Fig. 1, the cooling flushing liquid is directed by means of a compressor 21 into a refrigerator 22, where it is brought to the operating temperature by cooling water or another coolant.

[0086] One (Fig. 1) or several air circulation circuits (Fig. 2) can be used, with each such circuit including an air preparation stage 2.

[0087] Further, for all the removed air and the air that has undergone treatment 2, or only a portion of it, before returning to the tower 1, additional treatment 3 is carried out by its additional cooling 31 with the separation of condensate, the removal of condensate 32, and subsequent heating 33 of the air to reduce its relative humidity. Such additional treatment (additional treatment) 3, when using several circulation circuits, can be carried out in all circuits or some of them, while in one or more circuits with additional treatment 3, a channel 4 can be implemented bypassing the additional treatment unit 3 for a portion of the air. The volumetric flow rate of the portion of the air that is sent for additional treatment is regulated remotely by at least one means 41 for regulating the volumetric flow rate. Appropriate regulators, valves, or remote control dampers can be used as means 41 for regulating the volumetric flow rate.The means 41 can be installed at the junction of the channel 4 for supplying air bypassing stage 3 of additional preparation and the channel connecting stages 2 and 3, or in the channel 4 itself and / or on the part of the channel located between the mentioned junction and stage 3.

[0088] Preferably, at least 50% of all circulated air should be directed to post-treatment unit 3. However, it is possible to achieve the desired technical result by treating less than 50% of the air. The specific portion of air directed to post-treatment unit 3 depends on the current conditions and the equipment used in the process flow. A specialist will understand the criteria for selecting the required portion of air.

[0089] Post-cooling 31 at post-conditioning stage 3 is typically performed in heat exchange units that use a refrigerant such as liquid ammonia, chilled water, or freon. To achieve a positive effect at this stage, the air is post-cooled to the required temperature, which is selected based, among other things, on the volume of air being post-cooled. Thus, it is clear that if only a portion of the air in the circulation loop is post-conditioned, that portion will be cooled more than if all the air in the loop is post-conditioned. For example, in preferred embodiments, the air is cooled to 18 to 32°C.

[0090] Next, at the stage of additional preparation 3, the separated condensate is collected (pos. 32 in Fig. 1-2) and removed.

[0091] Aftercooling 31 with the release of condensate and its subsequent removal 32 allows to reduce the total moisture content in the air.

[0092] After the condensate has been removed, the air is preheated (item 33 in Figs. 1-2) by several degrees, approximately from 3 to 12°C, to reduce its relative humidity to a value less than or equal to 86%. Preheating 33 at the post-treatment stage 3 can be accomplished by various known methods, for example, by interaction with water vapor or water in a heat exchange unit. It is further taken into account that, in the embodiment of the invention with air injection into the lower portion of tower 1 for solidification of melt droplets, the injection means in the form of fan 5 is also capable of heating the air, for example, by 1-2°C or more; therefore, at the post-treatment stage, preheating 33 is performed to a correspondingly lower value. Air is returned to tower 1 by injection by fan 5 in each circulation circuit before or after post-treatment 3.Unlike ejection, injection increases the intensity of the air flow's interaction with the melt droplets, accelerating their solidification and transformation into granules. This injection in the circulation circuit is sufficient to create the draft necessary, among other things, for exhausting air from the top of tower 1.

[0093] The use of post-cooling stage 3 allows for the reduction and maintenance of low relative humidity and temperature of all air returned to the solidification process. For overall process efficiency, it is preferable for the cooling air to have a relative humidity of no more than 86%, preferably in the range of 75-80%, and a temperature of no more than 36°C, preferably in the range of 30-35°C. These parameters provide the best technical results. A specialist will recognize that lower temperatures and relative humidity of the cooling air will improve the cooling and solidification of the melt droplets and reduce the potential for moisture entrapment by the droplets, thereby further enhancing the technical result. However, this will require a more complex, metal-intensive, and energy-intensive post-cooling unit (stage 3).

[0094] In general, additional cooling 31, condensate removal 32 and air heating 33 at the stage of additional preparation 3 allow for its low relative humidity, which has a positive effect on the quality of the product - nitrogen fertilizer, since the possibility of moisture capture from the air by fertilizer granules is reduced, and allows for a low temperature of the cooling air, which improves the efficiency of cooling and solidification of melt droplets, and also makes it possible to reduce the amount of circulating air and use equipment of smaller dimensions while maintaining a complete absence of emissions from the prilling process and the absence of the need for air suction from the outside.

[0095] 2. Description of the device

[0096] The installation for forming nitrogen fertilizer granules (Fig. 1-2) is designed to implement the above-described method.

[0097] The installation includes a prilling tower 1 having means 12 for spraying the melt in the upper part of the tower 1. Prilling towers 1 are known from the prior art and can have different designs depending on the type of fertilizer being produced and the features of the process flow diagram, and it will be clear to a specialist that in addition to the means 12 for spraying the melt, they contain other components, for example, means 11 for feeding the melt into the upper part of the tower 1, means 13 for collecting granules formed from melt drops in the lower part of the tower 1, means 14 for removing granules from the lower part of the tower 1.

[0098] Through a pipeline included in means 11, the nitrogen fertilizer melt is fed to a priller (disperser) included in means 12 in the upper part of tower 1, which sprays the melt into drops into the space of tower 1. The drops of melt, cooled by the air flow, and the granules formed from them fall into the lower part of tower 1 onto means 13 containing receiving cones or a built-in cooler with a fluidized bed, then, due to means 14, for example, conveyors, the granules are removed for subsequent cooling or sorting and packaging.

[0099] The unit also includes one or more closed air circulation circuits 2, each comprising a channel for removing heated and contaminated air from the upper portion of the tower 1, an air preparation unit 2 for cleaning and cooling, and a channel for returning air to the lower portion of the prilling tower 1 as cooling air. A blower 5, in the form of a fan, is preferably installed in said return channel.

[0100] Air preparation unit 2 can be a single unit or comprise separate units. In most cases, a unit that combines cleaning and cooling processes by flushing the air with a cooling liquid, such as a wet scrubber, is used.

[0101] Unit 2, in the form of a wet scrubber, contains channels for the supply and discharge of cooling wash fluid, which is a solution of the resulting nitrogen fertilizer, such as a urea solution, ammonium nitrate solution, or another solution. In the preferred embodiment of the present group of inventions, shown in Fig. 1, the cooling wash fluid is directed by a blower 21 to a cooler 22, where it is brought to operating temperature by cooling water or another coolant. In the examples shown in Figs. 1-2, cooler 22 is a shell-and-tube heat exchanger.

[0102] The installation may use one (Fig. 1) or several air circulation circuits (Fig. 2), with each circuit containing the mentioned preparation unit 2.

[0103] At least one used air circulation circuit contains, before the air return channel to the tower 1, a block 3 for additional preparation (additional preparation) of all the air in this circuit or part thereof, wherein the block 3 includes a section 31 for additional cooling of the air with the release of condensate, a section 32 for removing condensate for disposal, for example, by draining into the sewer or by directing it for use somewhere in production, and a section 33 for heating the air to reduce its relative humidity.

[0104] When implementing the invention with one or more circulation circuits, a channel 4 can be made bypassing the additional preparation unit 3 for part of the air in this circuit.

[0105] At least one closed circulation circuit is configured to remotely regulate the volumetric flow rate of a portion of the air that is directed to the post-treatment unit 3 by means of at least one means 41 for regulating the volumetric flow rate, i.e. the circulation circuit is configured to change the volumetric flow rate of the air flow between the channel 4, bypassing the post-treatment unit 3, and the channel for supplying air to the unit 3. The means for regulating 41 can be installed at the junction of the channel 4 and the channel between the units 2 and 3, or in the channel 4 itself and / or on the part of the channel located between the mentioned junction of the channels and the post-treatment unit 3. The means 41 can be a volumetric flow rate regulator, a valve, preferably a remote control damper.Remote control of the volumetric flow rate allows for flexible adjustment of the closed air circulation circuit while reducing time and labor costs, thereby achieving the best cooling air characteristics and improving the quality of the resulting fertilizer, which further increases the efficiency of the prilling process.

[0106] Preferably, at least 50% of the air in the circulation circuit is directed to post-treatment unit 3. However, embodiments are possible in which post-treatment unit 3 is designed for less than 50% of the air, and the technical result is still achieved. The specific portion of air directed to post-treatment unit 3 depends on the current conditions and the equipment used in the process flow. A specialist will understand the criteria for selecting the required portion of air.

[0107] The aftercooling section 31 of the air aftertreatment unit 3 is typically implemented as heat exchange units and includes refrigerant supply and discharge channels, which may be liquid ammonia, chilled water, or freon. Thus, in some embodiments, the aftercooling section 31 of unit 3 is a cooler with circulating liquid ammonia or circulating chilled water. The condensate drainage section 32, installed downstream of the aftercooling section 31, is implemented as a drip collector and condensate drainage device. Such drip collectors are known in the art and are used at the outlet of various air cooler or recuperator units, as well as in gas purification units, liquid degassers, etc. And the heating section 33 is usually implemented by means of various known heat exchange units, for example, by using steam or water heaters; it is also possible to use electric heaters.In general, the air pre-treatment unit 3 is manufactured from means known from the prior art using methods known to specialists.

[0108] To achieve an additional positive effect, the air leaving the after-cooling section 31 has a temperature of 18 to 32°C. Moreover, at least one closed circulation circuit, in which the after-cooling unit 3 is used, is designed to ensure conditions under which the cooling air at the inlet to the tower 1 has a temperature 3 to 12°C higher than at the outlet from the after-cooling section 31, which allows for a reduction in relative humidity from 100% to 86% or less.

[0109] For the embodiment of the invention with pumping air into the prilling tower 1 by means of a pumping unit in the form of a fan 5, which is also capable of heating the air, heating 33 at the stage of additional preparation 3 is carried out to a correspondingly lower value.

[0110] Using post-treatment unit 3, even for a portion of the air, allows for a reduction in the relative humidity and temperature of all air returned to prilling tower 1. It is intended that the cooling air in tower 1 will have a relative humidity of no more than 86%, preferably in the range of 75-80%, and a temperature of no more than 36°C, preferably in the range of 30-35°C.

[0111] Low humidity has a positive effect on the quality of the product - nitrogen fertilizer and the efficiency of the prilling process as a whole, since the possibility of trapping moisture from the air by fertilizer granules is reduced, and a lower temperature allows for a reduction in the amount of circulating air and the use of smaller-sized equipment, in particular the prilling tower 1, gas ducts (channels) in the circulation circuit, for example, channels for removing heated and contaminated air and supplying prepared air as cooling, and the most preferred implementation options facilitate the use of a small-sized additional preparation unit 3 with low energy and resource consumption.

[0112] Air is returned to prilling tower 1 via a pump unit 5, such as a fan 5 installed in each circulation circuit before or after the pretreatment unit 3. Pumping by fan 5, unlike ejection, increases the intensity of the air flow's interaction with the melt droplets, accelerating their solidification and transformation into granules.

[0113] In general, the selection and placement of each specific equipment, material or environment will be clear to a specialist in this field of technology based on the specified conditions in the form of a specific nitrogen fertilizer and the parameters of the technological scheme for its production.

[0114] The operating principle of the proposed installation is characterized by the method of forming nitrogen fertilizer granules using the prilling method with a closed air circulation circuit, described above.

[0115] As can be seen, the use of the proposed group of inventions not only provides the possibility of supplying cooler and less humid air to the tower 1, which increases the efficient operation of the finished product production unit, but also provides the possibility of wide regulation of the air temperature and humidity due to two-stage cooling, which will ensure the constancy of the process mode when changing, for example, the float load and / or the temperature of the circulating water, intended to reduce the temperature of the cooling washing liquid in the refrigerator 22, while maintaining a complete absence of emissions from the prilling process and the absence of the need for air suction from the outside.

[0116] Below in Tables 1 and 2 are presented the experimental data obtained during the implementation of the inventions according to the most preferred variants.

[0117] The experiments were conducted as follows. Ammonium nitrate or urea melt, after being cleaned of mechanical impurities, was fed at a rate of 63 tons per hour into prilling tower 1, 9-11 meters in diameter, and uniformly sprayed across its cross-section in the form of droplets by priller 12 (disperser, sprinkler). The droplets of melt, falling into the tower 1 space in a counter-current of cooling air at a specified flow rate and a temperature of 30-35°C, cooled and crystallized.

[0118] Heated air contaminated with ammonium nitrate or urea dust particles from the top of prilling tower 1 was fed through one or more circulation loops to wet scrubber 2, where it was purified of these particles and cooled by water evaporation and contact with a circulating solution, either an ammonium nitrate solution acidified with nitric acid or a urea solution, respectively. A portion of the solution from this circulation loop was diverted to the process, while fresh water was fed into the loop to maintain concentration.

[0119] Then, due to remote regulation of the volumetric flow rate, all the air (Table 1) or part of it (Table 2) with 100% humidity entered the additional preparation block 3, the after-cooling section 31 of which was a cooler, where liquid ammonia or chilled water was used as a coolant, the condensate drainage section 32 was a drip collector, and the heating section 33 was a steam or water heater.

[0120] The air was then combined into a single flow in one or more circulation loops (for the case of additional processing of only part of the air) or, as a single flow, was further heated slightly by fan 5 and pumped into the lower section of tower 1, where it was reused. The air leaving fan 5 had a temperature of 30-35°C and a relative humidity of 75-86%.

[0121] Ammonium nitrate or urea granules with a moisture content of no more than 0.45% were poured onto distribution cones 13 at the bottom of the tower. The ammonium nitrate granules then entered feeder 14, where they were discharged from the tower and subsequently cooled in a fluidized bed. Urea granules were discharged from the tower for cooling in a plate cooler. The ammonium nitrate or urea granules then traveled down the process line for final processing.

[0122] In all cases, the achievement of the stated technical result and other advantages when using the proposed technical solution was confirmed.

[0123] Table 1. Experimental data obtained during the implementation of inventions using schemes with the direction of all air for additional processing in one or several circulation circuits.

[0124] Table 2. Experimental data obtained during the implementation of inventions using schemes with the direction of part of the air for additional processing in one or more circulation circuits.

[0125] These examples show that a 5°C reduction in cooling air temperature allowed for a reduction in its quantity by approximately 20%, and a 10% reduction in the diameter of the prilling tower, with a complete absence of emissions from the prilling process and no need for external air intake, which confirms the achievement of the stated technical result.

[0126] The presented embodiment examples are provided for illustrative purposes only. Those skilled in the art will readily recognize that other embodiments of the invention are possible without altering its essence. Thus, the use of the inventions improves the efficiency of the prilling process with a closed-loop cooling air circulation system due to the following:

[0127] - improving the quality of the resulting fertilizer by reducing the possibility of granules capturing moisture and dust particles from the cooling air due to the use of preparation stages with cleaning and cooling and additional preparation with post-cooling, condensate removal and air heating to reduce the relative humidity;

[0128] - the possibility of lowering the temperature of the cooling air, which allows for a reduction in its quantity and the use of smaller equipment, in particular the prilling tower and channels in the circulation circuit;

[0129] - increased operational reliability due to a reduced possibility of dust sticking to the tower walls due to a reduction in the relative humidity of the air at the stage of additional preparation and cleaning at the preparation stage;

[0130] - air injection by a fan, which, unlike ejection, increases the intensity of interaction of the cooling air flow with the melt droplets, which accelerates their solidification and transformation into granules;

[0131] - maintaining a closed air circulation circuit, therefore there is no emission of exhaust air into the atmosphere.

Claims

Invention formula 1. A method for forming nitrogen fertilizer granules by prilling with a closed air circulation loop, in which cooling air is supplied to the lower part of the prilling tower, the nitrogen fertilizer melt is sprayed in the upper part of the prilling tower and granules are removed from its lower part, wherein by means of at least one closed circulation loop the air is removed from the upper part of the prilling tower for preparation by cleaning and cooling and returned to the lower part of the prilling tower as cooling air, characterized in that at least part of the air before returning to the prilling tower is sent for additional preparation by additional cooling of the air with the release of condensate, removal of condensate and subsequent heating of the air.

2. The method according to paragraph 1, characterized in that air having a relative humidity of no more than 86% and a temperature of no more than 36°C is returned to the prilling tower.

3. The method according to paragraph 1 or 2, characterized in that air having a relative humidity in the range of 75 - 80% and a temperature in the range of 30 - 35 °C is returned to the prilling tower.

4. The method according to paragraph 1, characterized in that before returning to the prilling tower, at least 50% of the air is sent for additional preparation.

5. The method according to paragraph 1, characterized in that the return of air to the prilling tower is carried out by pumping it using a fan.

6. The method according to item 5, characterized in that the air injection is performed before its additional preparation or after additional preparation.

7. The method according to paragraph 1, characterized in that during additional cooling of the air, its temperature is brought to 18-32°C.

8. The method according to any of paragraphs 1-7, characterized in that air is returned to the prilling tower at a temperature that is 3 - 12°C higher than the temperature of the air after post-cooling.

9. The method according to any of paragraph 1, characterized in that a melt of ammonium nitrate or urea is sprayed into the upper part of the prilling tower.

10. The method according to paragraph 1 or paragraph 4, characterized in that the volumetric flow rate of the portion of air that is sent for additional preparation is regulated remotely by means of at least one means for regulating the volumetric flow rate.

11. An installation for forming nitrogen fertilizer granules by the prilling method with a closed air circulation circuit, comprising: a prilling tower having in its upper part a means for spraying the nitrogen fertilizer melt and in its lower part a means for removing granules, one or more closed air circulation circuits, each of which contains a channel for removing air from the upper part of the prilling tower into an air preparation unit by cleaning and cooling it and a channel for returning cooling air to the lower part of the prilling tower, characterized in that at least one closed circulation circuit contains an additional air preparation unit located after the air preparation unit, including sections for additional air cooling with the release of condensate, condensate removal and air heating.

12. The installation according to item 11, characterized in that at least one closed circulation circuit is designed to provide conditions under which the cooling air returned to the lower part of the prilling tower has a relative humidity of no more than 86% and a temperature of no more than 36°C.

13. The installation according to item 11 or 12, characterized in that at least one closed circulation circuit is designed to provide conditions in which the cooling air returned to the lower part of the prilling tower has a relative humidity in the range of 75 - 80% and a temperature in the range of 30 - 35°C.

14. The installation according to item 11, characterized in that the air preparation unit is a wet scrubber.

15. The installation according to item 11, characterized in that at least one closed circulation circuit is designed with the possibility of directing at least 50% of the air into the additional preparation unit.

16. The installation according to item 11, characterized in that each closed circulation circuit used contains a blower in the form of a fan.

17. The installation according to item 16, characterized in that the supercharger is placed before or after the additional preparation unit.

18. The installation according to item 11, characterized in that the section for air post-cooling is designed to provide conditions under which the air at the outlet has a temperature of 18 to 32°C.

19. The installation according to claim 18, characterized in that at least one closed circulation circuit is configured to provide conditions under which the cooling air at the inlet to the prilling tower has a temperature of 3 - 12°C higher than at the outlet from the air post-cooling section.

20. The installation according to claim 11, characterized in that at least one closed circulation circuit is configured to remotely regulate the volumetric flow rate of a portion of the air that is directed to the additional preparation unit, by means of at least one means for regulating the volumetric flow rate.

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