RU2564812C1 - Method of producing water-resistant ammonium nitrate granules (versions) - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to production of granular ammonium nitrate encapsulated with a relatively water-resistant coating, which can be used to produce industrial explosives, particularly water-resistant igdanites, granulates, grammonites, and in production of nitrogenous fertilisers used in agriculture. A method of producing water-resistant ammonium nitrate granules, wherein each granule is coated with a layer of a water-soluble combustible material, and then with a layer of a crosslinked aqueous gel of a concentrated solution of the same ammonium nitrate or a mixture of ammonium nitrate solutions and/or with a carbamide solution with equilibrium concentration at temperature of 0-20°C. The coating of the aqueous gel is then fixed by adding a gelling agent and/or crosslinking agent to the gel. Polymerisation is carried out for 2-20 minutes at 15-60°C, while simultaneously mixing components until the gel coating is fixed on the granules in the form of a film with thickness of 0.1-2 mm. According to another version of the method of producing ammonium nitrate granules, each ammonium nitrate granule is first coated with a layer of a water-resistant crosslinked aqueous gel of a concentrated solution of the same ammonium nitrate or a mixture of ammonium nitrate solutions and/or with a carbamide solution with equilibrium concentration at temperature of 0-20°C. Subsequent operations are carried out similar to the first version of the method.

EFFECT: reduced fire and explosion hazard, improved explosion and energy characteristics when used as an industrial explosive and environmental safety when used as fertiliser for agriculture.

10 cl, 1 tbl

Description

The invention relates to the production of industrial explosives (PVV), in particular to the production of waterproof igdanites, granulites, grammonites based on ammonium nitrate encapsulated with a waterproof, relatively waterproof coating, as well as the production of nitrogen-containing fertilizers used in agriculture.

The known composition of the fuel for the manufacture of explosives (BB), containing granular urea, impregnated with liquid petroleum products and coated with dispersed combustible substances, granulated polystyrene foam and 0.1-13% aqueous solution of a surface-active substance (surfactant) in the following ratio of components, wt . %:

Granular carbamide 20-70 Liquid petroleum products 1-15 Solid particulate combustibles 5-60 Granular polystyrene foam 0.9-3 0.1-13% aqueous surfactant solution 1,0-10

- RU 2343139 C2.

The disadvantages of the known composition are that the film of the suspension on fuel not only does not protect the urea and ammonium nitrate (AC) granules coated with it, but is a specially introduced solvent thereof. Moreover, the process of partial dissolution of AS and the formation of eutectics is organized directly in the well, necessarily dry or drained, because fuel not only does not protect the AS from dissolution, but partially contributes to it. When a mixture of such fuel with ammonium nitrate is charged into a flooded well, especially a flowing one, most of the AS and urea will dissolve within 15-60 minutes, and the PVV will lose working capacity due to the excessive water content and the broken fuel-oxidizer ratio.

The prototype of the invention is a method for producing waterproof granules, comprising applying an encapsulating substance to a granular substance in the form of a melt of a mixture of wax with a plasticizer by spraying it over the surface of encapsulated granules, onto the surface of which, when rolling, a melt of a mixture of polyethylene wax with paraffin or powder polyethylene with a temperature of 140-180 is sprayed ° C in a mass ratio of 3: 1-5: 1 in an amount of 0.5-2.0 wt. at a temperature of granules of 70-80 ° C, followed by a decrease in the temperature of granules to 45-50 ° C and further spraying to a total mass of encapsulating melt of 3-6 wt. Then the encapsulated granules are cooled to 20-25 ° C - RU 2038346 C1.

The disadvantage of the prototype is that when using granules of ammonia and other nitrate encapsulated with a paraffin-polyethylene alloy with a content of 3-6% by weight of fuel, which directly refers to polyethylene, paraffin and polyethylene wax, the material becomes fire and explosion hazardous with special requirements for handling it including storage, transportation.

The use of a mixture of waterproof granules as an industrial explosive obtained in a known manner cannot be considered effective, because contains insufficient fuel in order not to emit toxic nitrogen oxide emissions during the explosion or burning and to have satisfactory explosive and energy characteristics.

The use of this mixture as a fertilizer is environmentally unsafe, because the granules contain an encapsulating substance in the form of a melt of a mixture of wax with a plasticizer or a melt of a mixture of polyethylene wax and paraffin (powdered polyethylene), but neither polyethylene nor paraffin are components of the nutrition of plants or living organisms, are absorbed by nature and accumulate in the soil, clogging it up with no use (polyethylene) or even substances harmful to living organisms and plants (paraffin).

In connection with these shortcomings, the technical problem solved by the invention is to reduce fire and explosion hazard, improve explosive and energy characteristics when used as an industrial explosive and environmental safety when used as fertilizer for agriculture.

These technical results are achieved by two variants of the method of producing waterproof granules, the first of which is preferably used in the manufacture of PVV, and the second in the manufacture of fertilizers for agriculture.

The first option is a method of producing water-resistant nitrate granules, in which each nitrate granule is coated with a layer of water-soluble fuel, then it is coated with a layer of cross-linked aqueous gel of a concentrated solution of the same nitrate or a mixture of nitrate and / or urea solution with an equilibrium concentration at a temperature from 0 to 20 ° C, the specified shell of the aqueous gel is fixed by introducing into the gel gel in an amount of 2-12% of the water content in the solution and / or cross-linking agent in an amount of 4-6% o t of gelling agent content, polymerization is carried out for 2-20 minutes at a temperature of 15-60 ° C while stirring the components until the gel coating is fixed on the granules in the form of a film with a thickness of 0.1-2 mm.

When using the method, the following private executions are possible:

- apply ammonia, or potassium, or sodium, or calcium nitrate;

- water-soluble fuel contains glycols, urea, gelling agents, while all the fuel contained in the mixture is in a close to stoichiometric ratio with the oxidizing agent - from 90 to 105%;

- as a gelling agent, natural gelling agents are used - guar gum, or xanthan gum, or a mixture thereof, or polyacrylamide;

- water-soluble fuel additionally contains trinitrotoluene in the form of granules, flakes or powder in an amount of from 30% to 90% of the total content of water-soluble fuel;

- hardening cross-linked aqueous gel produce potassium pyroantimonate or potassium chromium.

The second option is a method for producing waterproof nitrate granules, in which each nitrate granule is coated with a layer of a waterproof cross-linked aqueous gel of a concentrated solution of the same nitrate or a mixture of nitrate solutions and / or with a urea solution with an equilibrium concentration at a temperature from 0 to 20 ° C, the specified shell from an aqueous gel is fixed by introducing into the gel a gel former in an amount of 2-12% of the water content in the solution and / or a cross-linking agent in an amount of 4-6% of the gel former, p oizvodyat polymerization for 2-20 minutes at 15-60 ° C while stirring the components prior to fixation of the gel coating on the granules in a dry film thickness of 0.1-2 mm.

The second variant of the method, as well as the first, involves using its private execution:

- apply ammonia, or potassium, or sodium, or calcium nitrate;

- as a gelling agent, natural gelling agents are used - guar gum, or xanthan gum, or a mixture thereof, or polyacrylamide;

- hardening cross-linked aqueous gel produce potassium pyroantimonate or potassium chromium.

The presented variants of the method for producing waterproof granules are environmentally friendly technological solutions to the problem of increasing the water resistance (decreasing the dissolution rate) of nitrate and other water-soluble salts or materials, including PVV, by protecting them with a waterproof and insoluble (for a given time) shell of water consisting of the same materials, in this case - saltpeter and water, combined into an insoluble whole with special materials and technological processes compatible with E tasks: obtaining predetermined characteristics PWV and waterproof fertilizer without impairing their basic operational properties - safety in handling and environmental security - for PWV for the nature and utility - using fertilizers.

Consider the first embodiment of the invention.

In a gravitational mixer (such as a “drunk barrel”, concrete mixer), each saltpeter granule is coated with a layer of water-soluble fuel containing, for example, glycols, urea, gelling agents, while all the fuel contained in the mixture is close to the stoichiometric ratio with the oxidizing agent - from 90 wt. % up to 105 wt. %

If the water-soluble fuel is less than 90 wt. %, then the release of carbon monoxide - CO - a toxic substance that pollutes the environment; if the water-soluble fuel is more than 105 wt. %, excess oxidizer and lack of fuel leads to an unstable reaction, i.e. loss of explosive properties and reduced energy characteristics.

When the content of water-soluble fuel in the specified range, i.e. when using an oxidizing agent at the level of 0.9-1.05 stoichiometric ratio, complete combustion of the fuel occurs, i.e. energy characteristics will have maximum value.

The indicated conclusions are based on the test results, issued as the “Report on laboratory tests for explosive industrial substances GRAMMONIT VU, TU 7276-02-13459510-2014”.

Then the granules are coated with a layer of a waterproof cross-linked aqueous gel of a concentrated solution with an equilibrium concentration at a temperature of 0 to 20 ° C of the same nitrate or a mixture of nitrate solutions and / or with a urea solution. Exceeding the temperature of the equilibrium concentration of solutions above 20 ° C will entail the crystallization of salts from the solutions at room temperature for processing (15-30 ° C), storage (0-30 ° C), which leads to breakdowns of the equipment pumping the solutions, and a decrease in the concentration of oxidizing agent with increasing the proportion of water in the water supply and, accordingly, partial or complete loss of its performance. When the temperature drops below 0 ° C, the proportion of water in the PVV increases, which leads to the loss of its explosive properties.

Shells from aqueous gels are additionally fixed on the granules by introducing into the gel an additional, strengthening cross-linking - cross-linking agent, which increases the viscosity and strength of the aqueous gel and / or additional input gel. For example, Table 1 shows the change in the viscosity (strength) value of aqueous gels of a mixture of urea and ammonium nitrate solutions depending on the amount of gelling agent (guar gum) and crosslinking agent in it, i.e. brands of the mixture. Here, the conditional viscosity (expiration time) according to GOST 8920-74, determined on a B3-246 viscometer (100 ml through an opening with a diameter of 4 mm) of a mixture of 50% AS solution and 27% urea solution:

At the same time, the minimum conditional viscosity, which allows obtaining water resistance acceptable for the considered practical applications, is 45-50 sec. The maximum viscosity (strength of the gel) and, accordingly, the amount of gelling agent and cross-linking agent are limited from the condition of preserving the flowability of the product after completion of the polymerization of the aqueous gel, as well as its acceptable cost for the considered practical applications. Technically, with a further increase in the content of gelling agent and a cross-linking agent, a rubber-like elastic material can be obtained that protects AS as much as possible, etc. from exposure to water, however, its cost will be prohibitive because of the high cost of the aforementioned gelling agents and effective crosslinking agents, as well as the need for prolonged mixing of the mixture until the aqueous gel is fully polymerized to prevent it from sticking together.

For example, granules of ammonium nitrate are coated with a cross-linked aqueous gel of a mixture of 50 wt. % AC solution and 27 wt. % urea solution. In this case, the operation of saturation (coating) of the granules of the oxidizing agent is performed - nitrate (ammonia, potassium, sodium, calcium) with water-soluble combustible or combustible (ethylene glycol, diethylene glycol, polyglycol) to a stoichiometric fuel-oxidizer ratio.

Taking into account the fuel content in the solution of nitrate (urea), all the missing water-soluble fuel (urea, urotropin, glycols) is introduced into the composition of the aqueous gel during the manufacturing process.

In this case, a gel is formed - the eutectic of the oxidizing agent, fuel, and gelling agent, which has important properties for PVW: a reduced gel freezing point - to minus 40 - minus 50 ° C, i.e. below the freezing temperature of components and their "pure" solutions (taking into account concentrations); increased sensitivity to the detonation source pulse - due to the formation of contact between fuel and oxidizing agent, including at the molecular level, as well as the partial nitration of glycols (nitric acid resulting from the partial decomposition of ammonium nitrate) with the formation of nitroglycols, which are sensitizers of explosive processes. The same process occurs with a film of glycols covering granules of ammonium nitrate. The active phase of the process of mutual diffusion of the components, and the nitration reactions associated with it, slow down as the aqueous gel is crosslinked and practically ceases with the completion of it mainly after 1 day, depending on the gelling agent used.

Given the purpose of PVV - blasting in industry - when the gelling agent is completely oxidized, turning into gaseous products of combustion during the explosion, polyacrylamide cross-linked with potassium chromic peak can be used as a gelling agent in this composition.

In order to significantly improve such an important characteristic for PVV as the critical diameter of detonation, if necessary, to improve this (to reduce the diameter of holes and boreholes for charging PVV and reduce the cost of drilling), an operation is introduced to add additional water-soluble combustible trinitrotoluene in the form of granules, flakes or powder in an amount of 30 wt. % up to 90 wt. % of the total content of water-soluble fuel (glycols, urea, gelling agents) in the mixture while maintaining a stoichiometric fuel-oxidizer ratio. At the same time, waterproof trinitrotoluene, along with nitrated glycols, serves as sensitizers of explosive transformations of PVV.

The excess content of trinitrotoluene above 90 wt. % of the fuel content will entail an unacceptable decrease in frost resistance to minus 5-10 ° C due to a decrease in the number of antifreezes - glycols and urea. With a decrease in the content of trinitrotoluene below 30 wt. % decreases the effectiveness of the sensitizer to the level of "insignificant in the main parameter" and, as a result, increases the critical diameter of the detonation of the explosives, which limits its use to the minimum allowable diameter of the holes or wells for charging.

When the content of trinitrotoluene in the specified range, i.e. 30-90 wt. % of the total content of water-soluble fuel, there is an improvement in explosive characteristics: sensitivity to initiation, detonation velocity, the critical diameter of detonation decreases.

The indicated conclusions are based on the test results, issued as the “Report on laboratory tests for explosive industrial substances GRAMMONIT VU, TU 7276-02-13459510-2014”.

Polymerization (additional cross-linking of the aqueous gel) is carried out for 2-20 minutes (depending on the temperature and the gelling agent used and its cross-linking agent) at a temperature of 15 ° C to 60 ° C while mixing the components in a gravitational or fluidized bed mixer before fixing the gel coating on the granules in the form of a film with a thickness of 0.1-2 mm, depending on the gel and on the necessary consumer properties: dissolution time, the proportion of useful shell materials necessary to achieve maxim flax effectiveness of the composition.

Exceeding the polymerization time with simultaneous stirring for more than 20 min will entail unjustified additional costs, since the intensive polymerization (crosslinking) of the gel, depending on the gelling agent, the composition of the solution and its temperature, takes 2-20 minutes (table. 1), reduction of the polymerization time at mixing after introducing a gelling agent below 2 min will lead to mass sticking in a lump despite the fact that the required quantity and size of air bubbles - sensitizers of explosive processes are not formed, which leads to the deterioration of the main characteristics of PVV - detonation ability, flowability (ability to charge).

Exceeding the polymerization temperature above 60 ° C will lead to the creation of unacceptable conditions from the point of view of the requirements for safe parameters and the operation of production facilities for the preparation of PVV for use in enterprises conducting blasting operations (SPI), in which it is most expedient to carry out PVV gelation. A decrease in the polymerization temperature below 15 ° C is unacceptable under the conditions of safe operation of the same plants. Physically, this is associated with an increase in the probability of decomposition of oxidizing agents with increasing temperature (thermal stability) and an increase in the sensitivity of the components and the PVV proper at lower temperatures due to crystallization processes.

Consider the second embodiment of the invention.

In a rotating drum (drunk barrel mixer), each nitrate granule is coated with a layer of a waterproof cross-linked aqueous gel of a concentrated solution with an equilibrium concentration at a temperature of 0 to 20 ° C of the same nitrate or a mixture of nitrate and / or urea solution. Exceeding the equilibrium temperature above 20 ° C will entail the crystallization of salts from the solution during storage (0-40 ° C) and processing (15-30 ° C) when its temperature drops below equilibrium. When the equilibrium temperature decreases below 0 ° C, nitrate dissolves during the deposition of an uncured aqueous gel on it with a sharp decrease in the temperature of the mixture, blocking the gel cross-linking (polymerization) process, which ultimately leads to an unacceptable decrease in the quality of the coating while increasing production costs.

For example, granules of ammonium nitrate are coated with a cross-linked aqueous gel of a mixture of 50 wt. % AC solution and 27 wt. % urea solution. Both substances are nitrogen fertilizers, however, optimal for different groups of plants. The best results are obtained in a mixture, a mixture of solutions is available as a complex fertilizer (UAN).

Shells of water gels are additionally fixed on the granules by introducing into the gel an additional reinforcing cross-linking that increases the viscosity and strength of the aqueous gel, and / or by the additional introduction of a gelling agent. For example, natural gelling agents - guar gum (guar gum), xanthan gum or a mixture thereof in an amount of 2-12% of the water content in the solution; cross-linking agents - potassium pyroantimonate - in the amount of 4-6% of the gum content.

Exceeding the content of gelling agents above 12% will lead to excessive gel strength and a corresponding decrease in flowability of the mixture, excessive thickness and water resistance of the fertilizer at an unacceptably high cost for agricultural purposes, given the cost of the gelling agent (20-40 times higher than granular AS). A decrease in the content of gelling agents below 2% leads to insufficient gel strength to ensure an acceptable time of gel resorption and fertilizer in the soil (at least 5-10 days).

Exceeding the content of cross-linking agents above 6% will entail excessive strength (insufficient flowability) of the gel and an unjustified increase in the cost of fertilizer, their decrease below 4% will lead to insufficient strength and water resistance of the gel, as well as an insufficient amount of gelling agent.

Polymerization (additional cross-linking of the aqueous gel) is carried out for 2-20 minutes (depending on the temperature and the gelling agent used and its cross-linking agent) at a temperature of 15 ° C to 60 ° C while mixing the components in a gravitational or fluidized bed mixer before fixing the gel coating on the granules in the form of a film with a thickness of 0.1-2 mm, depending on the gel and on the necessary consumer properties: dissolution time, the proportion of useful shell materials necessary to achieve maxim flax effectiveness of the composition.

Exceeding the polymerization time in the production process in a rotating drum for more than 20 minutes will entail unjustified costs, because the active phase of crosslinking is completed at reasonable process temperatures and dosages of crosslinking and gelling agents after 5-20 minutes (table. 1). When the polymerization time is reduced below 2 minutes, the crosslinking process is not completed, and an adherent coma ("goat") is formed.

Exceeding the polymerization temperature above 60 ° C will result in a violation of safety requirements when working with insufficiently stable oxidizing agents (ammonium nitrate). If the polymerization temperature drops below 15 ° C, unacceptable conditions for personnel work are formed, increased costs (cost) of production due to an unjustified increase in the polymerization time, inversely proportional to temperature.

Thus, the protection of hygroscopic fertilizers (saltpeter granules) is ensured by applying a waterproof gel of a solution of the same nitrate mixed with a urea solution, the properties of which are formed in fact by the flour of leguminous or pea wood (gum) mixed with microelements of plant nutrition - cross-linking agents (potassium salts and others metals). Unlike shells based on polyethylene with paraffin, a water-gel shell based on the same or compatible salt is environmentally friendly and fire and explosion safe, because contains at least 50% water.

In the manufacture of a water-gel shell from another salt (for example, potassium or sodium nitrate), the efficiency of the fertilizer increases, because it becomes, if necessary, complex. In addition, by changing the content of the gelling agent and / or the cross-linking agent in the gel, it is possible, in addition to the film thickness, to control the dissolution (resorption) time of the composition in a wide range from 15 minutes to several days or weeks.

An important advantage of this technology over the prototype is its simplicity and safety in implementation, because there are no high temperatures, fire and explosion hazardous products and intermediate products, as a result of which the technology can be implemented directly with agricultural producers, including in the field.

Claims (10)

1. A method of producing waterproof granules of nitrate, in which each granule of nitrate is covered with a layer of water-soluble fuel, then coated with a layer of cross-linked aqueous gel of a concentrated solution of the same nitrate and / or a solution of nitrate and / or with a solution of urea with an equilibrium concentration at a temperature from 0 to 20 ° C , the specified shell of an aqueous gel is fixed by introducing into the gel a gel in an amount of 2-12% of the water content in the solution and / or cross-linking agent in an amount of 4-6% of the content of the gel, p oizvodyat polymerization for 2-20 minutes at 15-60 ° C while stirring the components prior to fixation of the gel coating on the granules in a dry film thickness of 0.1-2 mm. 2. The method according to p. 1, in which ammonia, or potassium, or sodium, or calcium nitrate is used. 3. The method according to p. 1, in which the water-soluble fuel contains glycols, urea, gelling agents, while all the fuel contained in the mixture is in a close to stoichiometric ratio with the oxidizing agent - from 90 to 105%. 4. The method according to p. 1, in which natural gelling agents are used as a gelling agent - guar gum, or xanthan gum, or a mixture thereof, or polyacrylamide. 5. The method according to p. 1, in which the water-soluble fuel further comprises trinitrotoluene in the form of granules, flakes or powder in an amount of from 30% to 90% of the total content of water-soluble fuel. 6. The method according to p. 1, in which the hardening of the crosslinked aqueous gel is carried out with potassium pyroantimonate or potassium chromium. 7. A method of producing waterproof granules of nitrate, in which each granule of nitrate is coated with a layer of waterproof cross-linked aqueous gel of a concentrated solution of the same nitrate or a mixture of solutions of nitrate and / or with a solution of urea with an equilibrium concentration at a temperature of 0 to 20 ° C, the specified shell of an aqueous the gel is fixed by introducing into the gel a gelling agent in an amount of 2-12% of the water content in the solution and / or a cross-linking agent in an amount of 4-6% of the gelling agent, polymerization is carried out over 2-20 minutes at a temperature of 15-60 ° C while stirring the components prior to fixation of the gel coating on the granules in a dry film thickness of 0.1-2 mm. 8. The method according to p. 7, in which ammonia, or potassium, or sodium, or calcium nitrate is used. 9. The method according to p. 7, in which natural gelling agents are used as a gelling agent - guar gum, or xanthan gum, or a mixture thereof, or polyacrylamide. 10. The method according to p. 7, in which the hardening of the crosslinked aqueous gel is performed with potassium pyroantimonate or potassium chromium.