RU2411184C1 - Method of producing granular ammonium nitrate - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: disclosed is a method of producing granular ammonium nitrate which involves neutralisation of nitric acid with gaseous ammonia, evaporation of the obtained solution until obtaining a highly concentrated melt which contains ammonium nitrate in amount of not less than 99.5%, spraying the melt into a granulation tower having at least one vibrogranulator, while feeding air in a counterflow at a rate of 7.0-7.8 t/h per m² of the cross-section of the tower and output of the obtained granules in amount of 1.0-1.2 t/h per m² of the cross-section of the tower, cooling the obtained granules with air in fluidised bed apparatus, where after cooling the granules to temperature not over 45°C, spent air at temperature 60 - 70°C comes out of the fluidised bed apparatus into the bottom part of the granulation tower, where it mixes with air sucked from the atmosphere in volume ratio of 1:1, spent air and juice vapour from the neutralisation and evaporation steps are mixed with spent air from the granulation tower, the vapour-air mixture formed is washed in a gas cleaner, while sprinkling the trays of the gas cleaner with a circulating ammonium nitrate solution and further filtered through a multilayer fibrous non-woven material which contains ultrafine fibre, while sprinkling the front layer of the material with condensate of the juice vapour.

EFFECT: invention enables to intensify the process while improving the quality of the end product and reducing harmful emissions into the atmosphere.

3 cl, 1 dwg, 1 ex

Description

The invention relates to the field of inorganic chemistry and can be used to obtain ammonium nitrate (ammonium nitrate).

The main method for producing ammonium nitrate is a method involving the interaction of nitric acid with ammonia.

A known method, for example, comprising neutralizing nitric acid with ammonia at elevated pressure and a temperature of 180-190 ° C, evaporating the resulting production solution of ammonium nitrate to a concentration of 96-99.8% using the heat of the neutralization reaction, the production solution of ammonium nitrate being evaporated first to concentration of 92-96% due to the heat of the juice vapor removed from the boiling solution from the neutralization zone in an amount that ensures concentration of the solution, then evaporated to a concentration of 96-99.8% using heat boiling solution, withdrawn from the neutralization zone through the heat sink surface at a pressure of 0.07-0.30 atm, unused heat is removed by a circulating solution of ammonium nitrate (RU 2049725, 1995).

For consumers of ammonium nitrate, for example, in agriculture, the main requirement is the possibility of obtaining ammonium nitrate in granular form. An important indicator of the quality of a commercial product is the strength of the granules, their friability and lack of caking during long-term storage.

The closest in technical essence and the achieved result is a method for the production of granular ammonium nitrate, including the neutralization of nitric acid with gaseous ammonia, evaporation of the resulting solution to obtain a highly concentrated melt containing ammonium nitrate in an amount of at least 99.5%, spraying the melt into the granulation tower, cooling the resulting granules with air up to 110-120 ° C in a fluidized bed apparatus, mixing of exhaust air and juice steam removed from the stages of neutralization and evaporation, washing the resulting vapor-gas mixture in a scrubber during irrigation of the scrubber plates with a circulating 10-20% solution of ammonium nitrate (Nitrochik Handbook, Moscow, Chemistry, 1987, pp. 164-169).

However, the known method is characterized by the heterogeneity of the granules, the insufficient productivity of the process and the low degree of purification of gas emissions.

The objective of the present invention is to increase the productivity of the process by intensifying the granulation stage while ensuring high product quality and low levels of harmful emissions into the atmosphere.

The problem is solved by the described method for the production of granular ammonium nitrate, which includes the neutralization of nitric acid with gaseous ammonia, evaporation of the resulting solution to obtain a highly concentrated melt containing ammonium nitrate in an amount of at least 99.5%, spraying the melt into a granulation tower equipped with at least one vibro-granulator when air supply is countercurrent with a flow rate of 7.0-7.8 tons / hour per 1 m ^{2 of} tower cross-section and output of the obtained granules in an amount of 1.0-1.2 tons / hour per 1 m ^{2 of} cross-section I tower, cooling the obtained granules with air in a fluidized bed apparatus, and after cooling the granules to a temperature not exceeding 45 ° C, exhaust air is removed from the fluidized bed apparatus at a temperature of 60-70 ° C and fed to the lower part of the granulation tower, where it is mixed in a volume ratio of 1: 1 with outdoor air drawn in from the atmosphere, air and juice vapor removed from the neutralization and evaporation stage are mixed with exhaust air from the granulation tower, and the resulting vapor-air mixture is washed s in a scrubber with irrigation plates scrubber circulating solution of ammonium nitrate and was then filtered through a layered fibrous nonwoven fabric comprising ultrafine fibers at reflux front layer material juice steam condensate.

Preferably, the granules are cooled in a three-section apparatus with the supply of at least one section of the conditioned air apparatus with a temperature of 15-20 ° C. and a relative humidity of 40-60%.

Preferably, washing the steam-air mixture in a scrubber is carried out with a solution of ammonium nitrate with a concentration of 15-40 wt.%.

The installation with which this method is carried out is shown in the drawing. It includes an apparatus for neutralizing nitric acid with gaseous ammonia 1; apparatus for evaporating the resulting solution of ammonium nitrate 2; a collection with a submersible pump for pumping highly concentrated melt of ammonium nitrate 3; a vibration granulator to even out the size of drops of melt 4; granulation tower, providing crystallization of drops of melt, 5; apparatus for cooling hot granules 6; exhaust fans providing a certain amount of air entering the granulation tower, 7; apparatus for air conditioning 8; scrubber - washer for wet cleaning of steam-air mixture 9; filtration compartment for deep purification of exhaust into the atmosphere 10.

The drawing shows the following abbreviations for the flows:

AMG - gaseous ammonia;

CAS - non-concentrated nitric acid;

CAP - ammonium nitrate solution;

PS - juice steam;

PVA - vapor-air mixture;

To the air;

PN - saturated steam;

KN - condensate of saturated steam;

SAP - ammonium nitrate melt;

KSP - condensate juice steam.

The following is a specific example of the method.

In the apparatus 1 serves nitric acid in an amount of 70.65 t / h in terms of 100% HNO ₃ and gaseous ammonia in an amount of 19.17 t / h with obtaining a solution of ammonium nitrate and juice steam. Juice vapor is partially condensed to heat nitric acid, and the unused portion is sent to the atmosphere, previously mixed with air from the granulation tower 5 before the stage of purification of the vapor-air mixture from NH ₄ NO ₃ and ammonia impurities. The solution of ammonium nitrate is sent to the apparatus 2 for evaporation in a stream of atmospheric air with further supply of a steam-air mixture from the evaporator for mixing with air from the granulation tower 5 and juice from the neutralization stage before cleaning the exhaust into the atmosphere. The highly concentrated melt resulting from evaporation contains ammonium nitrate in an amount of 99.5-99.7%. Highly concentrated melt of ammonium nitrate in the amount of 90 t / h in terms of 100% NH ₄ NO _{3 is} fed to high-performance vibro-granulators 4, which ensure the maximum aligned size of the drops of melt, and also ensures the absence of drops with a diameter of less than 1 mm. The melt is sprayed into the granulation tower 5 with a round or rectangular cross-section, the area of which is 88 m ² , and with a height that crystallizes melt drops with an average diameter of ~ 2.5 mm until they come into contact with the solid surface of the tower bottom, mainly conical, and cool the frozen granules to temperature not higher than 125 ° С. Hot granules are obtained in an amount of 1.0-1.2 tons / hour per 1 m ² section of a granulation tower.

Hot granules from the tower 5 enter the cooling apparatus 6, which is a sectioned cooling apparatus in a "fluidized bed".

The cooling apparatus and the granulation tower form a single complex by air, since the exhaust air from the cooling apparatus 6 is fed to the bottom of the tower 5, where it is mixed with air sucked directly from the atmosphere at a volume ratio of 1: 1.

The total amount of air entering the granulation tower is 7-7.8 tons per 1 m ^{2 of} tower cross-section, depending on the time of year, this flow rate is provided by exhaust fans 7 installed on the granulation tower after cleaning the air-vapor mixture from NH ₄ NO ₃ and NН ₃ .

In the warm season, the total amount of air entering the granulation tower is averaged 670-680 tons / hour (~ 530-540 thousand nm ³ / hour, calculated on the pressure of 760 mm Hg and ± 0 ° С). Of the total amount of air through the pellet cooling apparatus, at least 45-50%, i.e. up to 340 t / h.

The air temperature from the cooling apparatus is in the range of 60-70 ° C, which in the hot season is provided by conditioning part of the air supplied to one or two end sections of the apparatus.

Air conditioning is carried out in the apparatus 8 by cooling it to 5-8 ° C with evaporating liquid ammonia and subsequent heating to 15-20 ° C to ensure its relative humidity in the range of 40-60%.

Air conditioning is turned off when the temperature of the granules at the outlet of the end section of the cooling apparatus is not more than 45 ° C without it, for example, at an outdoor temperature of + 20-25 ° C and a relative humidity of 60% at this temperature.

In the cold season and at high relative humidity of the outside air (above 60-70%), the air is heated to reduce the relative humidity.

The air entering the tower is heated during cooling and crystallization of the melt drops to 50-80 ° C, depending on the time of year (outdoor temperature), the speed of the heated air in the upper part of the tower reaches 2-2.2 m / s.

The air at the exit of the tower is dusty with small particles of ammonium nitrate (<0.5 mm) and aerosol particles (2-5 microns), which are formed from fumes of ammonium nitrate.

At the exit of the tower in front of the purification apparatus, the air is mixed with the juice vapor from the converter and the vapor-air mixture from the evaporator.

The steam-air mixture (PVA) before cleaning contains 8-12% vol. water vapor, and the temperature reaches 70-90 ° C.

The first stage of PVA cleaning is wet cleaning in a dish scrubber - washer 9 with a circulating solution of ammonium nitrate, acidified with nitric acid to trap and neutralize ammonia.

At the first stage of purification, relatively large particles of NH ₄ NO _{3 are} captured, and aerosol particles are insignificantly captured.

The concentration of the circulating solution is maintained within the range of 15-40% NH ₄ NO ₃ depending on the time of the year, and the upper limit refers to the hot season, when the evaporation of water from the solution to saturate the hot PVA increases in the scrubber-washer, and the lower limit refers to the cold season, when evaporation decreases sharply and it is necessary to close in the production cycle all the condensate of the juice vapor generated in the installation, without issuing it to the side.

Deep cleaning of the exhaust into the atmosphere is achieved in the 2nd stage in the filtration compartment of the PVA 10 through non-woven material from ultrafine fibers. The number of layers of filter material is determined by the permissible content of NH ₄ NO ₃ in the exhaust of PVA into the atmosphere.

An increase in the degree of purification and the service life of the filter material is achieved by using a constant or periodic supply of juice vapor condensate to the front layer through spray nozzles.

The implementation of the process with the stated parameters allows to obtain 2160 tons of the finished product per day, i.e. to increase the productivity of the process by at least 40% compared with the prototype (1540 t / day with a tower section of 88 m ² ). The use of a vibro-granulator in the granulation tower ensures a spray of melt drops, in which there is no sticking of melt on the walls of the granulation tower up to the cone and intersection of the jets of melt drops, which leads to improved quality of the granules and a stable fractional composition. In the finished product, the content of the fine fraction (<1 mm) does not exceed 0.5 wt.%, And more than 4 mm does not exceed 2 wt.%, Which eliminates the stage of classification of the finished product on sieves before being sent to the consumer. The implementation of the cleaning process by spraying the juice vapor condensate onto the multilayer filtering material makes it possible to dilute the concentration of trapped droplets of the solution and aerosol particles of ammonium nitrate and to intensify the process of washing them off. The combination of the claimed features allows you to dramatically intensify the production of ammonium nitrate in the granulation tower and at the same time increase the degree of purification of emissions into the atmosphere to the content of ammonium nitrate below 50 mg / m ³ and ammonia below 15 mg / m ³ .

Claims (3)

1. A method of producing granular ammonium nitrate, including neutralizing nitric acid with gaseous ammonia, evaporating the resulting solution to obtain a highly concentrated melt containing ammonium nitrate in an amount of at least 99.5%, spraying the melt into a granulation tower, cooling the obtained granules with air in a fluidized bed apparatus, mixing of exhaust air and juice steam removed from the stages of neutralization and evaporation, washing the formed steam-air mixture in a scrubber during irrigation of scrub plates ammonia nitrate circulating solution of ammonium nitrate and filtering emissions, characterized in that the granulation process is carried out in a granulation tower equipped with at least one vibratory granulator when air is supplied countercurrent with a flow rate of 7.0-7.8 t / h per 1 m ² tower section and the withdrawal of the obtained granules in an amount of 1.0-1.2 t / h per 1 m ² tower section, after cooling the granules to a temperature not exceeding 45 ° C, exhaust air is removed from the fluidized bed apparatus at a temperature of 60-70 ° C and feed it to the bottom of the granulation tower, mix it with air drawn in from the atmosphere in a volume ratio of 1: 1, the air exhausted in the granulation tower is mixed with juice vapor and air from the stages of solution neutralization and evaporation, and then the vapor-air mixture is cleaned of ammonium nitrate and ammonia impurities by washing with a solution of ammonium nitrate and then filtering through a multilayer fibrous nonwoven material containing ultrafine fibers upon irrigation of the front layer of the material with juice vapor condensate. 2. The method according to claim 1, characterized in that the granules are cooled in a three-section apparatus with the supply of at least one section of an air-conditioned apparatus with a temperature of 15-20 ° C and a relative humidity of 40-60%. 3. The method according to claim 1, characterized in that the washing of the steam-air mixture in the scrubber is carried out with a circulating solution of ammonium nitrate with a concentration of 15-40 wt.%.

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