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• Introduction
• 1. Production of ammonium nitrate
• 2. Raw materials
• 3. Ammonia synthesis
• 4. Characteristics of the target product
• 5. Physical and chemical substantiation of the main processes of production of the target product and environmental safety of production

Introduction

The most important type of mineral fertilizers are nitrogen fertilizers: ammonium nitrate, urea, ammonium sulfate, aqueous solutions of ammonia, etc. Nitrogen belongs exclusively to important role in the life of plants: it is part of chlorophyll, which is an acceptor of solar energy, and protein necessary for the construction of a living cell. Plants can only consume fixed nitrogen - in the form of nitrates, ammonium salts or amides. Relatively small amounts of fixed nitrogen are formed from atmospheric nitrogen due to the activity of soil microorganisms. However, modern intensive agriculture can no longer exist without additional application of nitrogen fertilizers to the soil, obtained as a result of the industrial fixation of atmospheric nitrogen.

Nitrogen fertilizers differ from each other in their nitrogen content, in the form of nitrogen compounds (nitrate, ammonium, amide), phase state (solid and liquid), and there are also physiologically acidic and physiologically alkaline fertilizers.

1. Production of ammonium nitrate

Ammonium nitrate, or ammonium nitrate, NH 4 NO 3 - a white crystalline substance containing 35% nitrogen in ammonium and nitrate forms , both forms of nitrogen are easily absorbed by plants. Granulated ammonium nitrate is used on a large scale before sowing and for all types of fertilizing. On a smaller scale, it is used to produce explosives.

Ammonium nitrate is highly soluble in water and has high hygroscopicity (the ability to absorb moisture from the air). This is the reason that fertilizer granules spread out, lose their crystalline shape, caking of fertilizers occurs - bulk material turns into a solid monolithic mass.

Ammonium nitrate is produced in three types:

A and B - used in industry; used in explosive mixtures (ammonites, ammonials)

B is the effective and most common nitrogen fertilizer, containing about 33-34% nitrogen; has physiological acidity.

2. Raw materials

The starting materials for the production of ammonium nitrate are ammonia and nitric acid.

Nitric acid . Pure nitric acid HNO is a colorless liquid with a density of 1.51 g/cm3 at - 42 °C, solidifying into a transparent crystalline mass. In the air, it, like concentrated hydrochloric acid, “smoke”, since its vapors form small droplets of fog with the moisture in the air. Nitric acid is not durable, and already under the influence of light it gradually decomposes:

The higher the temperature and the more concentrated the acid, the faster the decomposition occurs. The released nitrogen dioxide dissolves in the acid and gives it a brown color.

Nitric acid is one of the most powerful acids; in dilute solutions, it completely decomposes into H and -NO ions. Nitric acid is one of the most important nitrogen compounds: it is used in large quantities in the production of nitrogen fertilizers, explosives and organic dyes, serves as an oxidizing agent in many chemical processes, and is used in the production of sulfuric acid. acids using the nitrous method, used for the manufacture of cellulose varnishes and film .

Industrial production of nitric acid . Modern industrial methods for producing nitric acid are based on the catalytic oxidation of ammonia with atmospheric oxygen. When describing the properties of ammonia, it was indicated that it burns in oxygen, and the reaction products are water and free nitrogen. But in the presence of catalysts, the oxidation of ammonia with oxygen can proceed differently. If a mixture of ammonia and air is passed over the catalyst, then at 750 ° C and At a certain composition of the mixture, almost complete conversion occurs

The resulting mixture easily passes into, which, with water in the presence of atmospheric oxygen, gives nitric acid.

Platinum-based alloys are used as catalysts for the oxidation of ammonia.

The nitric acid obtained by the oxidation of ammonia has a concentration not exceeding 60%. If necessary, it is concentrated,

The industry produces diluted nitric acid with a concentration of 55, 47 and 45%, and concentrated nitric acid - 98 and 97%. Concentrated acid is transported in aluminum tanks, diluted - in acid-resistant steel tanks.

3. Ammonia synthesis

ammonia nitrogen nitrate raw materials

Ammonia is a key product of various nitrogen-containing substances used in industry and agriculture. D.N. Pryanishnikov called ammonia “alpha and omega” in the metabolism of nitrogenous substances in plants.

The diagram shows the main applications of ammonia. The composition of ammonia was established by C. Berthollet in 1784. Ammonia NH 3 is a base, a moderately strong reducing agent and an effective complexing agent with respect to cations with vacant bonding orbitals.

Physico-chemical basis of the process . The synthesis of ammonia from elements is carried out according to the reaction equation

N 2 +3H 2 =2NH 3; ?H<0

The reaction is reversible, exothermic, characterized by a large negative enthalpy effect (?H = -91.96 kJ/mol) and at high temperatures becomes even more exothermic (?H = -112.86 kJ/mol). According to Le Chatelier's principle, when heated, the equilibrium shifts to the left, towards a decrease in the yield of ammonia. The change in entropy in this case is also negative and does not favor the reaction. With a negative value of ?S, an increase in temperature reduces the probability of a reaction occurring,

The reaction of ammonia synthesis proceeds with a decrease in volume. According to the reaction equation, 4 moles of initial gaseous reactants form 2 moles of gaseous product. Based on Le Chatelier's principle, we can conclude that, under equilibrium conditions, the ammonia content in the mixture will be greater at high pressure than at low pressure.

4. Characteristics of the target product

Physicochemical characteristics . Ammonium nitrate (ammonium nitrate) NH4NO3 has a molecular weight of 80.043; the pure product is a colorless crystalline substance containing 60% oxygen, 5% hydrogen and 35% nitrogen (17.5% each in ammonia and nitrate forms). The technical product contains at least 34.0% nitrogen.

Basic physical and chemical properties of ammonium nitrates:

Ammonium nitrate, depending on temperature, exists in five crystalline modifications that are thermodynamically stable at atmospheric pressure (table). Each modification exists only in a certain temperature range, and the transition (polymorphic) from one modification to another is accompanied by changes in the crystal structure, release (or absorption) of heat, as well as an abrupt change in specific volume, heat capacity, entropy, etc. Polymorphic transitions are reversible - enantiotropic.

Table. Crystal modifications of ammonium nitrate

The NH 4 NO 3 -H 2 O system (Fig. 11-2) refers to systems with simple eutectics. The eutectic point corresponds to a concentration of 42.4% MH 4 MO 3 and a temperature of -16.9 °C. The left branch of the diagram—the liquidus line of water—corresponds to the conditions for the release of ice in the system NN 4 MO 3 -H 2 O. The right branch of the liquidus curve is the solubility curve of MH 4 MO 3 in water. This curve has three break points corresponding to the temperatures of modification transitions NH 4 NO 3 1 = 11 (125.8 ° C), II = III (84.2 ° C) and 111 = IV (32.2 ° C). Melting point (crystallization) of anhydrous ammonium nitrate is 169.6 ° C. It decreases with increasing moisture content of salt.

Dependence of crystallization temperature of NH 4 NO 3 (Tcrystal, "C) on moisture content (X,%) up to 1.5% is described by the equation:

t crist = 169.6 - 13, 2x (11.6)

Dependence of the crystallization temperature of ammonium nitrate with the addition of ammonium sulfate on moisture content (X,%) up to 1.5% and ammonium sulfate (U, %) up to 3.0% is expressed by the equation:

t crystal = 169.6 - 13.2X+2, OU. (11.7).

Ammonium nitrate dissolves in water and absorbs heat. Below are the values ​​of the heats of dissolution (Q dist) of ammonium nitrate of various concentrations in water at 25 ° C:

C(NH4NO3) % masses 59,69 47.05 38,84 30,76 22,85 15,09 2,17
Q solution kJ/kg. -202.8 -225.82 -240.45 -256.13 -271.29 -287.49 -320.95

Ammonium nitrate is highly soluble in water, ethyl and methyl alcohols, pyridine, acetone, and liquid ammonia.

Rice. 11-2. System State DiagramN.H.4 N03 - H20

Thermal decomposition . Ammonium nitrate is an oxidizing agent that can support combustion. When heated in a confined space, when thermal decomposition products cannot be freely removed, saltpeter can, under certain conditions, explode (detonate). It can also explode under the influence of strong impacts, for example when initiated by explosives.

During the initial period of heating at 110°C, endothermic dissociation of nitrate into ammonia and nitric acid gradually occurs:

NH 4 NO 3 > NH 3 + HNO 3 - 174.4 kJ/mol. (11.9)

At 165 °C, weight loss does not exceed 6%/day. The rate of dissociation depends not only on temperature, but also on the ratio between the surface of nitrate and its volume, the content of impurities, etc.

Ammonia is less soluble in the melt than nitric acid, so it is removed faster; the concentration of nitric acid increases to an equilibrium value determined by temperature. The presence of nitric acid in the melt determines the autocatalytic nature of thermal decomposition.

In the temperature range 200-270 °C, a mainly weakly exothermic reaction of the decomposition of nitrate into nitrous oxide and water occurs:

NH 4 NO 3 > N 2 O+ 2H 2 O + 36.8 kJ/mol. (11.10)

A noticeable effect on the rate of thermal decomposition is exerted by nitrogen dioxide, which is formed during the thermal decomposition of nitric acid, which is a product of the dissociation of ammonium nitrate.

When nitrogen dioxide reacts with nitrate, nitric acid, water and nitrogen are formed:

NH 4 NO 3 + 2NO 2 > N 2 + 2HNO 3 + H 2 O + 232 kJ/mol. (11.11 )

The thermal effect of this reaction is more than 6 times higher than the thermal effect of the reaction of the decomposition of nitrate into N 2 O and H 2 O. Thus, in acidified nitrate, even at ordinary temperatures, due to a significant exothermic reaction of interaction with nitrogen dioxide, spontaneous thermal decomposition occurs, which, with a large mass ammonium nitrate can lead to its rapid decomposition.

When nitrate is heated in a closed system at 210-220 °C, ammonia accumulates, the concentration of nitric acid decreases, and therefore the decomposition reaction is strongly inhibited. The thermal decomposition process practically stops, despite the fact that most of the salt has not yet decomposed. At higher temperatures, ammonia oxidizes faster, nitric acid accumulates in the system and the reaction proceeds with significant self-acceleration, which can lead to an explosion.

Additive to ammonium nitrate of substances that can decompose with the release of ammonia (for example, urea and acetamide) inhibits thermal decomposition. Salts with silver or thallium cations significantly increase the reaction rate due to the formation of complexes with nitrate ions in the melt. Chlorine ions have a strong catalytic effect on the thermal decomposition process. When a mixture containing chloride and ammonium nitrate is heated to 220-230 ° C, very rapid decomposition begins with the release of large quantities of gas. Due to the heat of reaction, the temperature of the mixture increases greatly, and decomposition is completed within a short time.

If the chloride-containing mixture is maintained at a temperature of 150-200 ° C, then in the first period of time, called induction, decomposition will proceed at a rate corresponding to the decomposition of nitrate at a given temperature. During this period, in addition to decomposition, other processes will also occur, the result of which is, in particular, an increase in the acid content in the mixture and the release of a small amount of chlorine. After the induction period, decomposition proceeds at high speed and is accompanied by strong heat release and the formation of large amounts of toxic gases. With a high chloride content, the decomposition of the entire mass of ammonium nitrate quickly ends. In view of this, the chloride content in the product is strictly limited.

When operating mechanisms used in the production of ammonium nitrate, lubricants should be used that do not interact with the product and do not reduce the initial temperature of thermal decomposition. For this purpose, for example, VNIINP-282 lubricant (GOST 24926-81) can be used.

The temperature of the product sent for storage in bulk or for packaging in bags should not exceed 55 °C. Polyethylene or kraft paper bags are used as containers. The temperatures at which active processes of oxidation of polyethylene and kraft paper with ammonium nitrate begin are 270-280 and 220-230 °C, respectively. Empty plastic and kraft paper bags must be cleaned of product residues and, if they cannot be used, must be incinerated.

In terms of explosion energy, ammonium nitrate is three times weaker than most explosives. A granular product can, in principle, detonate, but initiation with a detonator capsule is impossible; this requires large charges of powerful explosives.

The explosive decomposition of nitrate proceeds according to the equation:

NH 4 NO 3 > N 2 + 0.5 O 2 + 2H 2 O + 118 kJ/mol. (11.12)

According to equation (11.12), the heat of the explosion should be 1.48 MJ/kg. However, due to the occurrence of side reactions, one of which is endothermic (11.9), the actual heat of explosion is 0.96 MJ/kg and is small compared to the heat of explosion of hexogen (5.45 MJ). But for such a large-scale product as ammonium nitrate, taking into account its explosive properties (albeit weak) is important for ensuring safety.

Consumer requirements for the quality of ammonium nitrate produced by industry are reflected in GOST 2-85, according to which two grades of commercial product are produced.

The strength of granules is determined in accordance with GOST-21560.2-82 using IPG-1, MIP-10-1 or OSPG-1M devices.

The friability of granulated ammonium nitrate packed in bags is determined in accordance with GOST-21560.5-82.

GOST 14702-79-" waterproof"

5. Physical and chemical substantiation of the main processes of production of the target product and environmental safety of production

To obtain practically non-caking ammonium nitrate, a number of technological methods are used. An effective means of reducing the rate of moisture absorption by hygroscopic salts is their granulation. The total surface of homogeneous granules is less than the surface of the same amount of fine-crystalline salt, so granular fertilizers absorb moisture from the air more slowly. Sometimes ammonium nitrate is fused with less hygroscopic salts, for example ammonium sulfate.

Ammonium phosphates, potassium chloride, and magnesium nitrate are also used as similarly acting additives. The process of producing ammonium nitrate is based on a heterogeneous reaction between gaseous ammonia and a solution of nitric acid:

NH 3 + HNO 3 = NH 4 NO 3

?H = -144.9 kJ (VIII)

The chemical reaction occurs at high speed; in an industrial reactor it is limited by the dissolution of gas in liquid. To reduce diffusion inhibition, mixing of the reagents is of great importance.

Intensive conditions for carrying out the process can be ensured to a large extent when developing the design of the apparatus. Reaction (VIII) is carried out in a continuously operating ITN apparatus (using the heat of neutralization). The reactor is a vertical cylindrical apparatus consisting of reaction and separation zones. In the reaction zone there is a glass /, in the lower part of which there are holes for circulation of the solution. A bubbler is located slightly above the holes inside the glass 2 for supplying ammonia gas, above it there is a bubbler 3 for supplying nitric acid. The reaction vapor-liquid mixture exits from the top of the reaction glass; part of the solution is removed from the ITN apparatus and enters the final neutralizer, and the rest (circulation) goes down again. The juice vapor released from the vapor-liquid mixture is washed on cap plates 6 from splashes of ammonium nitrate solution and nitric acid vapor with a 20% nitrate solution, and then juice steam condensate.

The heat of reaction (VIII) is used to partially evaporate water from the reaction mixture (hence the name of the apparatus - ITN). The difference in temperatures in different parts of the apparatus leads to more intense circulation of the reaction mixture.

Technological process production of ammonium nitrate includes, in addition to the stage of neutralization of nitric acid with ammonia, also the stages of evaporation of the nitrate solution, granulation of the melt, cooling of the granules, treatment of the granules with surfactants, packaging, storage and loading of nitrate, purification of gas emissions and Wastewater.

In Fig. a diagram of a modern large-capacity unit for the production of ammonium nitrate AS-72 with a capacity of 1360 tons/day is shown. The initial 58-60% nitric acid is heated in a heater / up to 70-80 With juice steam from the ITN apparatus 3 and is sent for neutralization. In front of the devices 3 Phosphoric and sulfuric acids are added to nitric acid in such quantities that the finished product contains 0.3-0.5% P 2 O 5 and 0.05-0.2% ammonium sulfate.

The unit contains two ITN devices operating in parallel. In addition to nitric acid, they are supplied with ammonia gas, preheated in a heater 2 steam condensate up to 120-130 °C. The amounts of supplied nitric acid and ammonia are adjusted so that at the exit from the pumping apparatus the solution has a slight excess of acid (2-5 g/l), ensuring complete absorption of ammonia.

Nitric acid (58-60%) is heated in the apparatus 2 up to 80-90 °C with juice steam from an ITN apparatus 8. Ammonia gas in the heater 1 heated by steam condensate to 120-160°C. Nitric acid and gaseous ammonia in an automatically controlled ratio enter the reaction parts of two ITN 5 apparatuses operating in parallel. The 89-92% NH 4 NO 3 solution leaving the ITN apparatus at 155-170 °C has an excess of nitric acid in the range of 2-5 g/l, ensuring complete absorption of ammonia.

In the upper part of the apparatus, juice steam from the reaction part is washed away from splashes of ammonium nitrate; vapors of HNO 3 and NH 3 with a 20% solution of ammonium nitrate from a washing scrubber 18 and juice steam condensate from the nitric acid heater 2, which are served on the cap plates of the upper part of the apparatus. Part of the juice steam is used to heat nitric acid in heater 2, and the bulk of it is sent to the washing scrubber 18, where it is mixed with air from the granulation tower, with a steam-air mixture from the evaporator 6 and washed on scrubber wash plates. The washed steam-air mixture is released into the atmosphere by a fan 19.

Solution from ITN devices 8 sequentially passes through the neutralizer 4 and control neutralizer 5. To the neutralizer 4 sulfuric and phosphoric acids are dosed in an amount ensuring that the finished product contains 0.05-0.2% ammonium sulfate and 0.3-0.5% P20s. The dosage of acids by plunger pumps is adjusted depending on the load of the unit.

After neutralization of excess NMO3 in a solution of ammonium nitrate from ITN devices and introduced sulfuric and phosphoric acids in after-neutralizer 4, the solution passes the control after-neutralizer 5 (where ammonia is automatically supplied only in case of acid leakage from the neutralizer 4) and enters the evaporator 6. Unlike the AS-67 unit, the upper part of the evaporator 6 equipped with two sieve washing plates, onto which steam condensate is supplied, washing the steam-air mixture from the evaporator from ammonium nitrate

Nitrate melt from the evaporator 6, passing through the water seal and neutralizer 9 and filter 10, enters the tank 11, where does it come from submersible pump 12 through a pipeline with an anti-knock nozzle is supplied to pressure tank 15, and then to the granulators 16 or 17. The safety of the melt pumping unit is ensured by a system of automatic maintenance of the melt temperature during its evaporation in the evaporator (not higher than 190 °C), control and regulation of the melt environment after the neutralizer 9 (within 0.1-0.5 g/l NH 3), by controlling the temperature of the melt in the tank 11, pump housing 12 And pressure pipeline. If the regulatory parameters of the process deviate, the pumping of melt automatically stops, and the melt in the tanks 11 and evaporator 6 when the temperature rises, dilute with condensate.

Granulation is provided by two types of granulators: vibroacoustic 16 and monodisperse 17. Vibroacoustic granulators, which are used on large-capacity units, have proven to be more reliable and convenient to use.

The melt is granulated in a rectangular metal tower 20 with plan dimensions of 8x11 m. The flight height of the granules is 55 m, ensuring the crystallization and cooling of granules with a diameter of 2-3 mm to 90-120 ° C with a counter air flow in summer up to 500 thousand m3/h and in winter (at low temperatures) up to 300- 400 thousand m/h. At the bottom of the tower there are receiving cones from which the granules are conveyed by a belt conveyor 21 sent to the CC cooling apparatus 22.

Cooling apparatus 22 divided into three sections with autonomous air supply under each section of the fluidized bed grate. In its head part there is a built-in screen, which sifts out lumps of nitrate formed as a result of disruption of the granulators’ operating mode. The lumps are sent for dissolution. Air supplied to the cooling apparatus sections by fans 23, heated in the apparatus 24 due to the heat of juice steam from ITN devices. Heating is carried out when the atmospheric humidity is above 60%, and in winter to avoid sudden cooling of the granules. Ammonium nitrate granules sequentially pass through one, two or three sections of the cooling apparatus, depending on the load of the unit and the ambient air temperature. The recommended cooling temperature for the granular product in winter is below 27 °C, in summer up to 40-50 °C. When operating units in southern regions, where a significant number of days the air temperature exceeds 30 °C, the third section of the cooling apparatus operates on pre-cooled air (in an evaporative ammonia heat exchanger). The amount of air supplied to each section is 75-80 thousand m³/h. Fan pressure 3.6 kPa. Exhaust air from sections of the apparatus at a temperature of 45-60°C, containing up to 0.52 g/m 3 of ammonium nitrate dust, is sent to the granulation tower, where it is mixed with atmospheric air and enters the washing scrubber for washing 18.

The cooled product is sent to a warehouse or for treatment with a surfactant (NP dispersant), and then for shipment in bulk or for packaging in bags. Treatment with NF dispersant is carried out in a hollow apparatus 27 with a centrally located nozzle spraying an annular vertical stream of granules, or in a rotating drum. The quality of processing of the granular product in all used devices satisfies the requirements of GOST 2-85.

Granulated ammonium nitrate is stored in a warehouse in piles up to 11 m high. Before shipping to the consumer, the nitrate is sent from the warehouse to sieving. The non-standard product is dissolved, the solution is returned to the park. The standard product is treated with an NF dispersant and shipped to consumers.

Tanks for sulfuric and phosphoric acids and pumping equipment for their dosing are arranged in a separate unit. The central control point, electrical substation, laboratory, service and household premises are located in a separate building.

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9.4. PRODUCTION OF AMMONIUM NITERATE

Ammonium nitrate is one of the main types of nitrogen fertilizers; contains at least 34.2% nitrogen. The raw materials for producing granulated ammonium nitrate are unconcentrated 58-60% nitric acid and gaseous ammonia.

92.5% sulfuric acid is used as a conditioning additive, which is neutralized with ammonia together with nitric acid to ammonium sulfate. To spray the finished granules, a surfactant is used - a 40% aqueous solution of the “NF” dispersant.

The main stages of ammonium nitrate production are: neutralization of nitric acid with ammonia gas; obtaining highly concentrated ammonium nitrate melt; melt granulation; cooling of ammonium nitrate granules; treatment of granules with a surfactant - dispersant "NF"; purification of air and juice steam before release into the atmosphere; packaging and storage of the finished product.

Below we consider the automation of the first stage - neutralization of nitric acid with ammonia - which largely determines the operating modes of subsequent stages.

Technological diagram of the process. Nitric acid is preheated in a heat exchanger 1 (Fig. 9.8) to a temperature of 70-80 °C with juice steam from the apparatus 2 neutralization (ITN), ammonia gas is heated in a heat exchanger 3 and then enters the apparatus 2. The heated nitric acid enters the mixer 4, where sulfuric and phosphoric acids are also supplied. Sulfuric acid is dosed in such a way that the content of ammonium sulfate in the finished product is in the range of 0.3-0.7%. The mixture of acids then enters the heating apparatus, where, under pressure close to atmospheric, at a temperature of 155-165 °C, the process of neutralizing nitric acid with ammonia is carried out:

Nitric acid and ammonia are dosed in such a way that at the exit from the ITN apparatus the solution has a certain excess of nitric acid (within 2-5 g/l), which is necessary to ensure complete absorption of ammonia in the reaction zone. In the separation zone of the ITN apparatus, juice steam is separated from the boiling solution and is supplied for cleaning to the washing zone of the ITN apparatus, which consists of four plates and a splash trap. Juice steam condensate is supplied to the upper plate. At the exit from the ITN apparatus, juice steam contains 2-5 g/l NH 4 NO 3, 1-2 g/l HNO 3; If the washing process is carried out correctly, there is no ammonia in steam.

The 92-93% ammonium nitrate solution formed in the ITN apparatus is slightly diluted with solutions from the washing part of the apparatus and, at a concentration of 89-91%, is sent to the final neutralizer 5 , where ammonia is supplied to neutralize excess acid and create an alkaline solution (excess ammonia must be maintained within 0.1 g/l of free NH 3). Next, the ammonium nitrate solution is sent to the evaporation department.

Process automation. At the neutralization stage, the task of the automatic process control system is to maintain the ratio of ammonia and nitric acid flows into the ITN apparatus; maintaining a given pH of the ammonium nitrate solution in the ITN apparatus; ensuring an alkaline reaction of the ammonium nitrate solution after complete neutralization at the inlet to the evaporator.

For the control system, the leading parameters are the parameters of ammonia gas. To avoid the influence of fluctuations in ammonia pressure in the external network on the quality of regulation of the neutralization process, the pressure of ammonia gas is automatically maintained at the entrance to the ammonium nitrate unit. The ammonia flow into the ITN apparatus is maintained automatically using a flow regulator 6, by acting on the control valve 7 .

The supply of nitric acid to the pumping apparatus is automatically regulated in a given ratio with the ammonia flow rate using a flow ratio regulator 8 influence on the control valve 9. The supply of sulfuric and phosphoric acids is automatically adjusted in a given ratio with the consumption of nitric acid using flow ratio regulators 10 And 11 and control valves 12 And 13 .

The ratio of the consumption of nitric acid and ammonia predetermines a certain excess of acid, to control and regulate which the pH of the ammonium nitrate solution is continuously monitored at the output of the pumping apparatus. The specified excess of nitric acid in the solution is automatically maintained by the pH regulator 14 , adjusting the supply of ammonia to the pumping station using a control valve 15 installed on the ammonia bypass line, which carries a small amount of ammonia (a few percent of the total flow). Such a system provides good quality control of the neutralization process.

To ensure the maximum possible purification of juice steam in the washing part of the ITN apparatus, the supply of juice steam condensate to the upper plate is automatically regulated. A large supply of condensate is undesirable in order to avoid dilution of nitrate solutions before they are evaporated, and an insufficient supply of condensate will expose the plates, since the juice steam is overheated. The supply of juice steam condensate is regulated using a temperature controller 16 influence on the control valve 17 . Since acidic solutions of ammonium nitrate cannot be fed into the evaporator, excess acidity is neutralized in the neutralizer 5 . The supply of ammonia into it is regulated using a regulator 18 pH of the solution at the outlet of the pre-neutralizer acting on the control valve 19 .

The automatic control system provides for regulation of the heating of ammonia and nitric acid using temperature controllers 20 And 21 influence on control valves 22 And 23 supply of coolant to heat exchangers 1 And 2 .

Ammonium nitrate, or ammonium nitrate, NH 4 NO 3 is a white crystalline substance containing 35% nitrogen in ammonium and nitrate forms, both forms of nitrogen are easily absorbed by plants. Granulated ammonium nitrate is used on a large scale before sowing and for all types of fertilizing. On a smaller scale, it is used to produce explosives.

Ammonium nitrate is highly soluble in water and has high hygroscopicity (the ability to absorb moisture from the air), which is the reason that fertilizer granules spread out, lose their crystalline shape, and fertilizer caking occurs - bulk material turns into a solid monolithic mass.

Schematic diagram of ammonium nitrate production

To obtain practically non-caking ammonium nitrate, a number of technological methods are used. An effective means of reducing the rate of moisture absorption by hygroscopic salts is their granulation. The total surface of homogeneous granules is less than the surface of the same amount of fine-crystalline salt, therefore granular fertilizers absorb moisture from

Ammonium phosphates, potassium chloride, and magnesium nitrate are also used as similarly acting additives. The process of producing ammonium nitrate is based on a heterogeneous reaction between gaseous ammonia and a solution of nitric acid:

NH 3 +HNO 3 = NH 4 NO 3; ΔН = -144.9 kJ

The chemical reaction occurs at high speed; in an industrial reactor it is limited by the dissolution of gas in liquid. To reduce diffusion inhibition, stirring the reagents is of great importance.

The technological process for the production of ammonium nitrate includes, in addition to the stage of neutralization of nitric acid with ammonia, also the stages of evaporation of the nitrate solution, granulation of the melt, cooling of the granules, treatment of the granules with surfactants, packaging, storage and loading of nitrate, purification of gas emissions and wastewater. In Fig. Figure 8.8 shows a diagram of a modern large-scale unit for the production of ammonium nitrate AS-72 with a capacity of 1360 tons/day. The initial 58-60% nitric acid is heated in a heater to 70 - 80°C with juice steam from the ITN 3 apparatus and supplied for neutralization. Before apparatus 3, phosphoric and sulfuric acids are added to nitric acid in such quantities that the finished product contains 0.3-0.5% P 2 O 5 and 0.05-0.2% ammonium sulfate. The unit contains two ITN devices operating in parallel. In addition to nitric acid, they are supplied with ammonia gas, preheated in heater 2 by steam condensate to 120-130°C. The amounts of supplied nitric acid and ammonia are regulated so that at the exit from the pumping apparatus the solution has a slight excess of acid (2-5 g/l), ensuring complete absorption of ammonia.

In the lower part of the apparatus, a neutralization reaction occurs at a temperature of 155-170°C; this produces a concentrated solution containing 91-92% NH 4 NO 3 . In the upper part of the apparatus, water vapor (so-called juice steam) is washed away from splashes of ammonium nitrate and nitric acid vapor. Part of the heat from the juice steam is used to heat the nitric acid. The juice steam is then sent for purification and released into the atmosphere.

Fig. 8.8. Diagram of the ammonium nitrate unit AS-72:

1 – acid heater; 2 – ammonia heater; 3 – ITN devices; 4 – pre-neutralizer; 5 – evaporator; 6 – pressure tank; 7.8 – granulators; 9.23 – fans; 10 – washing scrubber; 11 – drum; 12,14 – conveyors; 13 – elevator; 15 – fluidized bed apparatus; 16 – granulation tower; 17 – collection; 18, 20 – pumps; 19 – swimming tank; 21 – filter for water; 22 – air heater.

The acidic solution of ammonium nitrate is sent to the neutralizer 4; where ammonia is supplied, which is necessary to react with the remaining nitric acid. Then the solution is fed into the evaporator 5. The resulting melt, containing 99.7-99.8% nitrate, passes through a filter 21 at 175°C and is fed by a centrifugal submersible pump 20 into a pressure tank 6, and then into a rectangular metal granulation tower 16.

In the upper part of the tower there are granulators 7 and 8, into the lower part of which air is supplied, cooling the drops of nitrate falling from above. When drops of nitrate fall from a height of 50-55 m and air flows around them, fertilizer granules are formed. The temperature of the granules at the exit from the tower is 90-110°C; hot granules are cooled in a fluidized bed apparatus 15. This is a rectangular apparatus having three sections and equipped with a grid with holes. Fans supply air under the grille; in this case, a fluidized layer of nitrate granules is created, arriving via a conveyor from the granulation tower. After cooling, the air enters the granulation tower. Ammonium nitrate granules are fed by conveyor 14 into a rotating drum for treatment with surfactants. Then the finished fertilizer is sent to packaging by conveyor 12.

The air leaving the granulation tower is contaminated with particles of ammonium nitrate, and the juice steam from the neutralizer and the steam-air mixture from the evaporator contain unreacted ammonia and nitric acid, as well as particles of entrained ammonium nitrate.

To clean these flows, in the upper part of the granulation tower there are six parallel operating washing scrubbers of the plate type 10, irrigated with a 20-30% solution of ammonium nitrate, which is supplied by pump 18 from the collection 17. Part of this solution is discharged to the ITN neutralizer for washing juice steam, and then mixed with a solution of nitrate, and, therefore, used for the production of products. The purified air is sucked out of the granulation tower by fan 9 and released into the atmosphere.

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Production of ammonium nitrate

• Content

Introduction

2. Production methods

3. The main stages of the production of ammonium nitrate from ammonia and nitric acid

3.1 Preparation of ammonium nitrate solutions

3.1.1 Basics of the neutralization process

3. 1 5 Main equipment

4. Material and energy calculations

5. Thermodynamic calculation

6. Recycling and neutralization of waste in the production of ammonium nitrate

Conclusion

List of sources used

Appendix A

Introduction

In nature and in human life, nitrogen is extremely important. It is part of protein compounds (16-18%), which are the basis of the plant and animal world. A person consumes 80-100 g of protein daily, which corresponds to 12-17 g of nitrogen.

For normal plant development, many chemical elements. The main ones are carbon, oxygen, hydrogen, nitrogen, phosphorus, magnesium, sulfur, calcium, potassium and iron. The first three elements of a plant are obtained from air and water, the rest are extracted from the soil.

Nitrogen plays a particularly important role in the mineral nutrition of plants, although its average content in plant mass does not exceed 1.5%. Without nitrogen, no plant can live or develop normally.

Nitrogen is a component not only of plant proteins, but also of chlorophyll, with the help of which plants, under the influence of solar energy, absorb carbon from carbon dioxide CO2 in the atmosphere.

Natural nitrogen compounds are formed as a result of chemical processes of decomposition of organic residues, during lightning discharges, as well as biochemically as a result of the activity of special bacteria - Azotobacter, which directly absorb nitrogen from the air. The same ability is possessed by nodule bacteria that live in the roots of leguminous plants (peas, alfalfa, beans, clover, etc.).

A significant amount of nitrogen and other nutrients necessary for the development of agricultural crops is annually removed from the soil with the resulting harvest. In addition, some nutrients are lost as a result of their leaching by groundwater and rainwater. Therefore, to prevent a decrease in yield and depletion of the soil, it is necessary to replenish it with nutrients by applying various types fertilizers

It is known that almost every fertilizer has physiological acidity or alkalinity. Depending on this, it can have an acidifying or alkalizing effect on the soil, which is taken into account when using it for certain agricultural crops.

Fertilizers, the alkaline cations of which are more quickly extracted by plants from the soil, cause acidification; Plants that consume acidic anions from fertilizers more quickly contribute to soil alkalization.

Nitrogen fertilizers containing the ammonium cation NH4 (ammonium nitrate, ammonium sulfate) and the amide group NH2 (urea) acidify the soil. The acidifying effect of ammonium nitrate is weaker than ammonium sulfate.

Depending on the nature of the soil, climatic and other conditions, different amounts of nitrogen are required for different crops.

Ammonium nitrate (ammonium nitrate, or ammonium nitrate) occupies a significant place in the range of nitrogen fertilizers, the global production of which amounts to millions of tons per year.

Currently, approximately 50% of nitrogen fertilizers used in agriculture in our country are ammonium nitrate.

Ammonium nitrate has a number of advantages over other nitrogen fertilizers. It contains 34-34.5% nitrogen and in this respect is second only to urea CO(NH2) 2, containing 46% nitrogen. Other nitrogen and nitrogen-containing fertilizers have significantly less nitrogen (nitrogen content is given in terms of dry matter):

Table 1 - Nitrogen content in compounds

Ammonium nitrate is a universal nitrogen fertilizer, as it simultaneously contains ammonium and nitrate forms of nitrogen. It is effective in all zones, for almost all crops.

It is very important that the nitrogen forms of ammonium nitrate are used by plants in different time. Ammonium nitrogen, directly involved in protein synthesis, is quickly absorbed by plants during the growth period; Nitrate nitrogen is absorbed relatively slowly, so it lasts longer. It has also been established that the ammonia form of nitrogen can be used by plants without prior oxidation.

These properties of ammonium nitrate have a very positive effect on increasing the yield of almost all agricultural crops.

The high nitrogen content in ammonium nitrate, the relatively simple method of its production and the relatively low cost per unit of nitrogen create good preconditions for the further development of this production.

Ammonium nitrate is part of a large group of stable explosives. Explosives based on ammonium nitrate and ammonium nitrate, pure or treated with certain additives, are used for blasting operations.

A small amount of saltpeter is used to produce nitrous oxide, used in medicine.

Along with increasing the volume of ammonium nitrate production by modernizing existing production facilities and constructing new ones, measures are being taken to further improve the quality of the finished product (obtaining a 100% friable product and preserving granules after long-term storage of the product).

1. Physico-chemical properties of ammonium nitrate

In its pure form, ammonium nitrate is a white crystalline substance containing 35% nitrogen, 60% oxygen and 5% hydrogen. The technical product is white with a yellowish tint and contains at least 34.2% nitrogen.

Ammonium nitrate is a strong oxidizing agent for a number of inorganic and organic compounds. It reacts violently with the melts of some substances, even to the point of explosion (for example, with sodium nitrite NaNO2).

If gaseous ammonia is passed over solid ammonium nitrate, a very mobile liquid is quickly formed - ammonia 2NH4NO3*2NH3 or NH4NO3*3NH3.

Ammonium nitrate is highly soluble in water, ethyl and methyl alcohols, pyridine, acetone and liquid ammonia. With increasing temperature, the solubility of ammonium nitrate increases significantly.

When ammonium nitrate is dissolved in water, a large amount of heat is absorbed. For example, when 1 mole of crystalline NH4NO3 is dissolved in 220-400 moles of water and a temperature of 10-15 °C, 6.4 kcal of heat is absorbed.

Ammonium nitrate has the ability to sublimate. When storing ammonium nitrate under conditions elevated temperatures and air humidity, its volume approximately doubles, which usually leads to rupture of the container.

Under a microscope, pores and cracks are clearly visible on the surface of ammonium nitrate granules. The increased porosity of nitrate granules has a very negative effect on the physical properties of the finished product.

Ammonium nitrate is highly hygroscopic. In the open air, in a thin layer of saltpeter, it quickly becomes moistened, loses its crystalline shape and begins to blur. The degree to which salt absorbs moisture from the air depends on its humidity and the vapor pressure above a saturated solution of a given salt at a given temperature.

Moisture exchange occurs between air and hygroscopic salt. Relative air humidity has a decisive influence on this process.

Calcium and lime-ammonium nitrate have a relatively low water vapor pressure over saturated solutions; at a certain temperature they correspond to the lowest relative humidity. These are the most hygroscopic salts among the above nitrogen fertilizers. Ammonium sulfate is the least hygroscopic and potassium nitrate is almost completely non-hygroscopic.

Moisture is absorbed only by a relatively small layer of salt immediately adjacent to the surrounding air. However, even such moistening of saltpeter greatly deteriorates the physical properties of the finished product. The rate at which ammonium nitrate absorbs moisture from the air increases sharply with increasing temperature. Thus, at 40 °C the rate of moisture absorption is 2.6 times greater than at 23 °C.

Many methods have been proposed to reduce the hygroscopicity of ammonium nitrate. One such method is based on mixing or fusing ammonium nitrate with another salt. When choosing a second salt, proceed from the following rule: to reduce hygroscopicity, the pressure of water vapor above a saturated solution of a mixture of salts must be greater than their pressure above a saturated solution of pure ammonium nitrate.

It has been established that the hygroscopicity of a mixture of two salts having a common ion is greater than the most hygroscopic of them (the exception is mixtures or alloys of ammonium nitrate with ammonium sulfate and some others). Mixing ammonium nitrate with non-hygroscopic but water-insoluble substances (for example, limestone dust, phosphate rock, dicalcium phosphate, etc.) does not reduce its hygroscopicity. Numerous experiments have shown that all salts that have the same or greater solubility in water than ammonium nitrate have the property of increasing its hygroscopicity.

Salts that can reduce the hygroscopicity of ammonium nitrate must be added in large quantities (for example, potassium sulfate, potassium chloride, diammonium phosphate), which sharply reduces the nitrogen content in the product.

The most effective way to reduce the absorption of moisture from the air is to coat the nitrate particles with protective films of organic substances that are not wetted by water. The protective film reduces the rate of moisture absorption by 3-5 times and helps improve the physical properties of ammonium nitrate.

A negative property of ammonium nitrate is its ability to cake - to lose its flowability (crumbly) during storage. In this case, ammonium nitrate turns into a solid monolithic mass, difficult to grind. Caking of ammonium nitrate is caused by many reasons.

Increased moisture content in the finished product. Particles of ammonium nitrate of any shape always contain moisture in the form of a saturated (mother) solution. The NH4NO3 content in such a solution corresponds to the solubility of the salt at the temperatures at which it is loaded into the container. As the finished product cools, the mother liquor often becomes supersaturated. With a further decrease in temperature, a large number of crystals with sizes of 0.2-0.3 mm fall out of the supersaturated solution. These new crystals cement the previously unbound particles of nitrate, causing it to turn into a dense mass.

Low mechanical strength of saltpeter particles. Ammonium nitrate is produced in the form of round particles (granules), plates or small crystals. Particles of granular ammonium nitrate have a smaller specific surface area and a more regular shape than flake and fine-crystalline ones, so the granules cake less. However, during the granulation process, a certain amount of hollow particles are formed, which have low mechanical strength.

When storing, bags with granulated saltpeter are placed in stacks 2.5 m high. Under the pressure of the upper bags, the least durable granules are destroyed with the formation of dust-like particles, which compact the mass of saltpeter, increasing its caking. Practice shows that the destruction of hollow particles in a layer of granular product sharply accelerates the process of caking. This is observed even if, when loaded into the container, the product was cooled to 45 °C and the bulk of the granules had good mechanical strength. It has been established that hollow granules are also destroyed due to recrystallization.

As the ambient temperature increases, saltpeter granules almost completely lose their strength, and such a product cakes heavily.

Thermal decomposition of ammonium nitrate. Explosion hazard. Fire resistance. From the point of view of explosion safety, ammonium nitrate is relatively little sensitive to shocks, friction, impacts, and remains stable when hit by sparks of varying intensity. Admixtures of sand, glass and metal impurities do not increase the sensitivity of ammonium nitrate to mechanical stress. It is capable of exploding only under the influence of a strong detonator or during thermal decomposition under certain conditions.

With prolonged heating, ammonium nitrate gradually decomposes into ammonia and nitric acid:

NH4NO3=NH3+HNO3 - 174598.32 J (1)

This process, which occurs with heat absorption, begins at temperatures above 110°C.

With further heating, ammonium nitrate decomposes to form nitrous oxide and water:

NH4NO3= N2O + 2H2O + 36902.88 J (2)

The thermal decomposition of ammonium nitrate occurs in the following successive stages:

· hydrolysis (or dissociation) of NH4NO3 molecules;

· thermal decomposition of nitric acid formed during hydrolysis;

· interaction of nitrogen dioxide and ammonia formed in the first two stages.

When ammonium nitrate is intensively heated to 220--240 °C, its decomposition may be accompanied by outbreaks of a molten mass.

It is very dangerous to heat ammonium nitrate in a closed volume or in a volume with a limited release of gases formed during the thermal decomposition of nitrate.

In these cases, the decomposition of ammonium nitrate can proceed through many reactions, in particular, through the following:

NH4NO3 = N2+2H2O + S 02 + 1401.64 J/kg (3)

2NH4NO3 = N2 + 2NO+ 4H20 + 359.82 J/kg (4)

3NH4NO3= 2N2 + N0 + N02 + 6H20 + 966.50 J/kg (5)

From the above reactions it is clear that ammonia, formed during the initial period of thermal decomposition of nitrate, is often absent in gas mixtures; Secondary reactions take place in them, during which ammonia is completely oxidized to elemental nitrogen. As a result of secondary reactions, the pressure of the gas mixture in a closed volume sharply increases and the decomposition process can end in an explosion.

Copper, sulfides, magnesium, pyrites and some other impurities activate the decomposition process of ammonium nitrate when it is heated. As a result of the interaction of these substances with heated nitrate, unstable ammonium nitrite is formed, which at 70-80 ° C rapidly decomposes with an explosion:

NH4NO3=N2+ 2H20 (6)

Ammonium nitrate does not react with iron, tin and aluminum even in a molten state.

With increasing humidity and increasing particle size of ammonium nitrate, its sensitivity to explosion greatly decreases. In the presence of approximately 3% moisture, saltpeter becomes insensitive to explosion even when exposed to a strong detonator.

The thermal decomposition of ammonium nitrate increases with increasing pressure to a certain limit. It has been established that at a pressure of about 6 kgf/cm2 and the corresponding temperature, the entire molten nitrate decomposes.

Crucial to reducing or preventing the thermal decomposition of ammonium nitrate is maintaining an alkaline environment when evaporating solutions. Therefore, in the new technological scheme for the production of non-caking ammonium nitrate, it is advisable to add a small amount of ammonia to the hot air.

Considering that, under certain conditions, ammonium nitrate can be an explosive product, during its production, storage and transportation, the established technological regime and safety regulations must be strictly observed.

Ammonium nitrate is a non-flammable product. Only nitrous oxide, formed during the thermal decomposition of salt, supports combustion.

A mixture of ammonium nitrate with crushed charcoal can spontaneously ignite when heated strongly. Some easily oxidized metals (such as powdered zinc) in contact with wet ammonium nitrate with slight heat can also cause it to ignite. In practice, cases of spontaneous ignition of mixtures of ammonium nitrate with superphosphate have been observed.

Paper bags or wooden barrels that contained ammonium nitrate can catch fire even when exposed to sunlight. When a container containing ammonium nitrate ignites, nitrogen oxides and nitric acid vapors may be released. In case of fires arising from an open flame or due to detonation, ammonium nitrate melts and partially decomposes. The flame does not spread into the depth of the saltpeter mass.

2 . Production methods

ammonium nitrate neutralization acid

In industry, only the method of producing ammonium nitrate from synthetic ammonia (or ammonia-containing gases) and dilute nitric acid is widely used.

The production of ammonium nitrate from synthetic ammonia (or ammonia-containing gases) and nitric acid is multi-stage. In this regard, they tried to obtain ammonium nitrate directly from ammonia, nitrogen oxides, oxygen and water vapor by the reaction

4NH3 + 4NO2 + 02 + 2H20 = 4NH4NO3 (7)

However, this method had to be abandoned, since along with ammonium nitrate, ammonium nitrite was formed - an unstable and explosive product.

A number of improvements have been introduced into the production of ammonium nitrate from ammonia and nitric acid, which have made it possible to reduce capital costs for the construction of new plants and reduce the cost of the finished product.

To radically improve the production of ammonium nitrate, it was necessary to abandon the ideas that had prevailed for many years about the impossibility of working without appropriate reserves of basic equipment (for example, evaporators, granulation towers, etc.), about the danger of obtaining almost anhydrous ammonium nitrate melt for granulation.

It is firmly established in Russia and abroad that only the construction of high-power units, using modern achievements of science and technology, can provide significant economic advantages compared to existing ammonium nitrate production.

A significant amount of ammonium nitrate is currently produced from the ammonia-containing off-gases of some urea synthesis systems. According to one of the methods of its production, 1 ton of urea produces from 1 to 1.4 tons of ammonia. From this amount of ammonia, 4.6-6.5 tons of ammonium nitrate can be produced. Although more advanced schemes for the synthesis of urea are also working, ammonia-containing gases - waste from this production - will serve as raw materials for the production of ammonium nitrate for some time.

The method for producing ammonium nitrate from ammonia-containing gases differs from the method for producing it from gaseous ammonia only at the neutralization stage.

Ammonium nitrate is obtained in small quantities by exchange decomposition of salts (conversion methods).

These methods for producing ammonium nitrate are based on the precipitation of one of the resulting salts or on the production of two salts with different solubilities in water. In the first case, ammonium nitrate solutions are separated from sediments on rotating filters and processed into a solid product according to conventional procedures. In the second case, the solutions are evaporated to a certain concentration and separated by fractional crystallization, which boils down to the following: when cooling hot solutions, most of the ammonium nitrate is isolated in its pure form, then crystallization is carried out in separate equipment from the mother solutions to obtain a product contaminated with impurities.

All methods for producing ammonium nitrate by exchange decomposition of salts are complex and involve high steam consumption and loss of bound nitrogen. They are usually used in industry only when it is necessary to utilize nitrogen compounds obtained as by-products.

The modern method of producing ammonium nitrate from gaseous ammonia (or ammonia-containing gases) and nitric acid is constantly being improved.

3 . The main stages of the production of ammonium nitrate from ammonia and nitric acid

The ammonium nitrate production process consists of the following main stages:

1. Preparation of ammonium nitrate solutions by neutralizing nitric acid with gaseous ammonia or ammonia-containing gases.

2. Evaporation of ammonium nitrate solutions to a melt state.

3. Crystallization from melted salt in the form of round-shaped particles (granules), flakes (plates) and small crystals.

4. Cooling or drying salt.

5. Packaging of the finished product.

To obtain low-caking and water-resistant ammonium nitrate, in addition to the indicated stages, a stage of preparation of appropriate additives is also necessary.

3.1 P Preparation of ammonium nitrate solutions

3.1.1 Neutralization Process Basics

Ammonium nitrate solutions ry are obtained by reacting ammonia with nitric acid according to the reaction:

4NH3 + HNO3 = NH4NO3 + Q J (8)

The formation of ammonium nitrate is irreversible and is accompanied by the release of heat. The amount of heat released during the neutralization reaction depends on the concentration of nitric acid used and its temperature, as well as on the temperature of the ammonia gas (or ammonia-containing gases). The higher the concentration of nitric acid, the more heat is generated. In this case, water evaporates, which makes it possible to obtain more concentrated solutions of ammonium nitrate. To obtain solutions of ammonium nitrate, 42-58% nitric acid is used.

The use of nitric acid with a concentration higher than 58% to obtain ammonium nitrate solutions with the existing design of the process is not possible, since in this case a temperature develops in the neutralizer apparatus that significantly exceeds the boiling point of nitric acid, which can lead to its decomposition with the release of nitrogen oxides. When ammonium nitrate solutions are evaporated, juice steam is formed due to the heat of reaction in neutralizer apparatuses, having a temperature of 110-120 °C.

When obtaining ammonium nitrate solutions of the highest possible concentration, relatively small heat exchange surfaces of evaporators are required, and a small amount of fresh steam is consumed for further evaporation of the solutions. In this regard, together with the feedstock, they strive to supply additional heat to the neutralizer, for which they heat ammonia to 70 ° C and nitric acid to 60 ° C with juice steam (at a higher temperature of nitric acid, its significant decomposition occurs, and the heater pipes are subjected to strong corrosion if they are not made of titanium).

Nitric acid used in the production of ammonium nitrate must contain no more than 0.20% dissolved nitrogen oxides. If the acid is not sufficiently purged with air to remove dissolved nitrogen oxides, they form ammonium nitrite with ammonia, which quickly decomposes into nitrogen and water. In this case, nitrogen losses can amount to about 0.3 kg per 1 ton of finished product.

Juice vapor, as a rule, contains impurities NH3, NHO3 and NH4NO3. The amount of these impurities strongly depends on the stability of the pressures at which ammonia and nitric acid must be supplied to the neutralizer. To maintain a given pressure, nitric acid is supplied from a pressure tank equipped with an overflow pipe, and ammonia gas is supplied using a pressure regulator.

The neutralizer load also largely determines the loss of bound nitrogen with juice steam. Under normal load, losses with juice steam condensate should not exceed 2 g/l (in terms of nitrogen). When the neutralizer load is exceeded, flows occur between ammonia and nitric acid vapors. adverse reactions, as a result of which, in particular, fog-like ammonium nitrate is formed in the gas phase, polluting juice steam, and the loss of bound nitrogen increases. The ammonium nitrate solutions obtained in the neutralizers are accumulated in intermediate containers with stirrers, neutralized with ammonia or nitric acid, and then sent for evaporation.

3.1.2 Characteristics of neutralization installations

Depending on the application required pressure, modern installations for producing ammonium nitrate solutions using neutralization heat are divided into installations operating at atmospheric pressure; in rarefaction (vacuum); at elevated pressure (several atmospheres) and combined installations operating under pressure in the neutralization zone and under vacuum in the zone of separation of juice vapors from the ammonium nitrate solution (melt).

Installations operating at atmospheric or slight excess pressure are characterized by simplicity of technology and design. They are also easy to maintain, start and stop; accidental violations of the specified operating mode are usually quickly eliminated. Installations of this type are most widely used. The main apparatus of these installations is the neutralizer apparatus ITN (use of neutralization heat). The ITN apparatus operates under an absolute pressure of 1.15--1.25 atm. Structurally, it is designed in such a way that almost no boiling of solutions occurs - with the formation of foggy ammonium nitrate.

The presence of circulation in the heat pump apparatus eliminates overheating in the reaction zone, which allows the neutralization process to be carried out with minimal losses of bound nitrogen.

Depending on the operating conditions of the production of ammonium nitrate, the juice steam of the ITN apparatuses is used for preliminary evaporation of nitrate solutions, for the evaporation of liquid ammonia, heating of nitric acid and gaseous ammonia sent to the ITN apparatuses, and for the evaporation of liquid ammonia when obtaining gaseous ammonia used in the production of diluted nitric acid.

Solutions of ammonium nitrate are produced from ammonia-containing gases in installations whose main apparatus operates under vacuum (evaporator) and at atmospheric pressure (scrubber-neutralizer). Such installations are bulky and it is difficult to maintain a stable operating mode in them due to the variability of the composition of ammonia-containing gases. The latter circumstance negatively affects the accuracy of regulation of excess nitric acid, as a result of which the resulting solutions of ammonium nitrate often contain an increased amount of acid or ammonia.

Neutralization installations operating under an absolute pressure of 5-6 atm are not very common. They require significant energy consumption to compress ammonia gas and supply pressurized nitric acid to the neutralizers. In addition, at these installations, increased losses of ammonium nitrate are possible due to the entrainment of splashes of solutions (even in separators of complex design, splashes cannot be completely captured).

In installations based on the combined method, the processes of neutralizing nitric acid with ammonia are combined and producing ammonium nitrate melt, which can be directly sent for crystallization (i.e., evaporators for concentrating nitrate solutions are excluded from such installations). Installations of this type require 58-60% nitric acid, which industry still produces in relatively small quantities. In addition, some of the equipment must be made of expensive titanium. The neutralization process to obtain saltpeter melt has to be carried out at very high temperatures (200-220 ° C). Considering the properties of ammonium nitrate, to carry out the process at high temperatures it is necessary to create special conditions that prevent thermal decomposition of the nitrate melt.

3.1.3 Neutralization plants operating at atmospheric pressure

These installations include They include ITN neutralizer devices (using the heat of neutralization) and auxiliary equipment.

Figure 1 shows one of the designs of the ITN apparatus used in many existing ammonium nitrate production plants.

Z1 - swirler; BC1 - external vessel (reservoir); VTs1 - inner cylinder (neutralization part); U1 - device for distributing nitric acid; Ш1 - fitting for draining solutions; O1 - windows; U2 - device for ammonia distribution; G1 - water seal; C1 - separator-trap

Figure 1 - ITN neutralizer apparatus with natural circulation of solutions

The ITN apparatus is a vertical cylindrical vessel (reservoir) 2, in which a cylinder (glass) 3 with shelves 1 (swirler) is placed to improve the mixing of solutions. Pipelines for introducing nitric acid and ammonia gas are connected to cylinder 3 (the reagents are supplied in countercurrent); the pipes end with devices 4 and 7 for better distribution of acid and gas. In the inner cylinder, nitric acid reacts with ammonia. This cylinder is called the neutralization chamber.

The annular space between vessel 2 and cylinder 3 serves for circulation of boiling solutions of ammonium nitrate. In the lower part of the cylinder there are 6 holes (windows) connecting the neutralization chamber with the evaporation part of the heat pump. Due to the presence of these holes, the productivity of the ITN apparatus is somewhat reduced, but intensive natural circulation of solutions is achieved, which leads to a reduction in the loss of bound nitrogen.

The juice steam released from the solution is discharged through a fitting in the cover of the ITN apparatus and through a trap-separator 9. The solutions of nitrate formed in cylinder 3 in the form of an emulsion - mixtures with juice steam enter the separator through a water seal 5. From the fitting of the lower part of the trap-separator, ammonium solutions The nitrate is sent to the final neutralizer-mixer for further processing. The water seal located in the evaporation part of the apparatus allows you to maintain a constant level of solution in it and prevents juice steam from escaping without flushing from the splashes of solution entrained by it.

Steam condensate is formed on the separator plates due to partial condensation of juice steam. In this case, the heat of condensation is removed recycled water, passing along coils laid on plates. As a result of partial condensation of juice steam, a 15--20% solution of NH4NO3 is obtained, which is sent for evaporation along with the main flow of ammonium nitrate solution.

Figure 2 shows a diagram of one of the neutralization units operating at pressure close to atmospheric.

NB1 - pressure tank; C1 - separator; I1 - evaporator; P1 - heater; SK1 - collection for condensate; ITN1 - ITN apparatus; M1 - stirrer; TsN1 - centrifugal pump

Figure 2 - Diagram of a neutralization installation operating at atmospheric pressure

Pure or with additives nitric acid is supplied to a pressure tank equipped with a constant overflow of excess acid into storage.

From pressure tank 1, nitric acid is directed directly into the glass of apparatus ITN 6 or through a heater (not shown in the figure), where it is heated by the heat of juice steam removed through separator 2.

Gaseous ammonia enters the liquid ammonia evaporator 3, then into the heater 4, where it is heated by the heat of secondary steam from the expander or by the hot condensate of the heating steam of the evaporators, and is then sent through two parallel pipes into the glass of the apparatus ITN 6.

In the evaporator 3, the liquid ammonia spray evaporates and the contaminants usually associated with gaseous ammonia are separated. In this case, weak ammonia water is formed with an admixture of lubricating oil and catalyst dust from the ammonia synthesis workshop.

The ammonium nitrate solution obtained in the neutralizer continuously flows through a hydraulic seal and a splash trap into the final neutralizer mixer 7, from where, after neutralizing the excess acid, it is sent for evaporation.

The juice steam released in the heating apparatus, having passed through separator 2, is sent for use as heating steam to the first stage evaporators.

Juice steam condensate from heater 4 is collected in collector 5, from where it is spent on various production needs.

Before starting the neutralizer, the preparatory work provided for in the operating instructions is carried out. Let us note only some of the preparatory work related to the normal conduct of the neutralization process and ensuring safety precautions.

First of all, you need to pour ammonium nitrate solution or steam condensate into the neutralizer up to the sampling valve.

Then it is necessary to establish a continuous supply of nitric acid to the pressure tank and its overflow into the warehouse storage area. After this, it is necessary to receive gaseous ammonia from the ammonia synthesis workshop, for which it is necessary to briefly open the valves on the line for releasing juice steam into the atmosphere and the valve for the solution outlet into the mixer-neutralizer. This prevents the creation of high pressure in the pumping apparatus and the formation of an unsafe ammonia-air mixture when starting the device.

For the same purpose, before start-up, the neutralizer and the communications connected to it are purged with steam.

After reaching normal operating mode, juice steam from the heating apparatus is sent for use as heating steam].

3.1.4 Neutralization plants operating under vacuum

Co-processing of amm ammonia-containing gases and gaseous ammonia is impractical, as it is associated with large losses of ammonium nitrate, acid and ammonia due to the presence of a significant amount of impurities in ammonia-containing gases (nitrogen, methane, hydrogen, etc.) - These impurities bubbling through the resulting boiling solutions of ammonium nitrate , would carry away bound nitrogen with the juice steam. In addition, juice steam contaminated with impurities could not be used as heating steam. Therefore, ammonia-containing gases are usually processed separately from ammonia gas.

In installations operating under vacuum, the heat of reaction is used outside the neutralizer - in a vacuum evaporator. Here, hot solutions of ammonium nitrate coming from the neutralizer are boiled at a temperature corresponding to the vacuum in the apparatus. Such installations include: a scrubber-type neutralizer, a vacuum evaporator and auxiliary equipment.

Figure 3 shows a diagram of a neutralization installation operating using a vacuum evaporator.

HP1 - scrubber-type neutralizer; H1 - pump; B1 - vacuum evaporator; B2 - vacuum separator; NB1 - nitric acid pressure tank; B1 - tank (gate mixer); P1 - washer; DN1 - pre-neutralizer

Figure 3 - Scheme of a neutralization installation with a vacuum evaporator

Ammonia-containing gases at a temperature of 30--90 °C under a pressure of 1.2--1.3 atm are supplied to the lower part of the scrubber-neutralizer 1. A circulating solution of nitrate enters the upper part of the scrubber from the seal tank 6, which is usually continuously supplied from tank 5 nitric acid, sometimes preheated to a temperature not exceeding 60 °C. The neutralization process is carried out with an excess of acid in the range of 20-50 g/l. Scrubber 1 usually maintains a temperature 15-20 °C below the boiling point of solutions, which helps prevent acid decomposition and the formation of ammonium nitrate mist. The set temperature is maintained by irrigating the scrubber with a solution from a vacuum evaporator, which operates at a vacuum of 600 mm Hg. Art., so the solution in it has a lower temperature than in the scrubber.

The nitrate solution obtained in the scrubber is sucked into vacuum evaporator 5, where at a vacuum of 560-600 mm Hg. Art. partial evaporation of water occurs (evaporation) and an increase in the concentration of the solution.

From the vacuum evaporator, the solution flows into the water seal tank 6, from where most of it again goes to irrigate the scrubber 1, and the rest is sent to the after-neutralizer 8. The juice steam generated in the vacuum evaporator 3 is sent through the vacuum separator 4 to the surface condenser (not shown in the figure) or into a mixing-type capacitor. In the first case, juice steam condensate is used in the production of nitric acid, in the second - for various other purposes. The vacuum in the vacuum evaporator is created due to the condensation of juice steam. Non-condensed vapors and gases are sucked out of the condensers by a vacuum pump and discharged into the atmosphere.

Exhaust gases from scrubber 1 enter apparatus 7, where they are washed with condensate to remove drops of nitrate solution, after which they are also removed into the atmosphere. In the final neutralizer mixer, the solutions are neutralized to a content of 0.1--0.2 g/l of free ammonia and, together with the flow of nitrate solution obtained in the ITN apparatus, are sent for evaporation.

Figure 4 shows a more advanced vacuum neutralization scheme.

XK1 - refrigerator-condenser; CH1 - scrubber-neutralizer; C1, C2 - collections; TsN1, TsN2, TsN3 - centrifugal pumps; P1 - gas washer; G1 - water seal; L1 - trap; B1 - vacuum evaporator; BD1 - neutralizer tank; B2 - vacuum pump; P2 - juice machine washer; K1 - surface capacitor

Figure 4 - Vacuum neutralization diagram:

Distillation gases are directed to the lower part of the neutralizer scrubber 2, irrigated with a solution from the collector 3 using a circulation pump 4.

The collection 3, through the water seal 6, receives solutions from the scrubber-neutralizer 2, as well as solutions after the trap of the vacuum evaporator 10 and the juice steam washer 14.

Through a pressure tank (not shown in the figure), nitric acid solution from gas washer 5, irrigated with juice steam condensate, is continuously fed into collection 7. From here, the solutions are supplied by circulation pump 8 to washer 5, after which they are returned to collection 7.

Hot gases after the washer 5 are cooled in the refrigerator-condenser 1 and released into the atmosphere.

Hot solutions of ammonium nitrate from water seal 6 are sucked using vacuum pump 13 into vacuum evaporator 10, where the concentration of NH4NO3 increases by several percent.

The juice vapors released in the vacuum evaporator 10, having passed through the trap 9, the washer 14 and the surface condenser 15, are released into the atmosphere by the vacuum pump 13.

An ammonium nitrate solution with a given acidity is discharged from the discharge line of pump 4 into the neutralizer tank. Here the solution is neutralized with ammonia gas and pump 12 is sent to the evaporation station.

3.1. 5 Main equipment

ITN neutralizers. Several types of neutralizers are used, differing mainly in the size and design of devices for distributing ammonia and nitric acid inside the apparatus. Devices of the following sizes are often used: diameter 2400 mm, height 7155 mm, glass - diameter 1000 mm, height 5000 mm. Devices with a diameter of 2440 mm and a height of 6294 mm and devices from which the previously provided mixer has been removed are also used (Figure 5).

LK1 - hatch; P1 - shelves; L1 - sampling line; L2 - solution output line; BC1 - inner glass; C1 - external vessel; Ш1 - fitting for draining solutions; P1 - ammonia distributor; P2 - nitric acid distributor

Figure 5 - ITN neutralizer device

In some cases, for the processing of small quantities of ammonia-containing gases, ITP devices with a diameter of 1700 mm and a height of 5000 mm are used.

The ammonia gas heater is a shell-and-tube apparatus made of carbon steel. Case diameter 400--476 mm, height 3500--3280 mm. The tube often consists of 121 tubes (tube diameter 25x3 mm) with a total heat transfer surface of 28 m2. Gaseous ammonia enters the tubes, and heating steam or hot condensate enters the inter-tube space.

If juice steam from heating equipment is used for heating, then the heater is made of stainless steel 1Х18Н9Т.

The liquid ammonia evaporator is a carbon steel apparatus, in the lower part of which there is a steam coil, and in the middle there is a tangential input of gaseous ammonia.

In most cases, the evaporator operates on fresh steam with a pressure (excess) of 9 atm. At the bottom of the ammonia evaporator there is a fitting for periodic purging from accumulated contaminants.

The nitric acid heater is a shell-and-tube apparatus with a diameter of 400 mm and a length of 3890 mm. Tube diameter 25x2 mm, length 3500 mm; total heat exchange surface 32 m2. Heating is carried out by juice steam with an absolute pressure of 1.2 atm.

The scrubber-type neutralizer is a vertical cylindrical apparatus with a diameter of 1800-2400 mm and a height of 4700-5150 mm. Devices with a diameter of 2012 mm and a height of 9000 mm are also used. Inside the apparatus, for uniform distribution of circulating solutions across the cross-section, there are several perforated plates or a nozzle made of ceramic rings. In the upper part of the devices equipped with plates, a layer of rings with dimensions of 50x50x3 mm is laid, which acts as a barrier against splashes of solutions.

The gas velocity in the free section of the scrubber with a diameter of 1700 mm and a height of 5150 mm is about 0.4 m/sec. Irrigation of the scrubber-type apparatus with solutions is carried out using centrifugal pumps with a capacity of 175-250 m3/h.

Vacuum evaporator is a vertical cylindrical device with a diameter of 1000-1200 mm and a height of 5000-3200 mm. The nozzle is ceramic rings measuring 50x50x5 mm, laid in regular rows.

The gas washer is a vertical cylindrical apparatus made of stainless steel with a diameter of 1000 mm and a height of 5000 mm. The nozzle is ceramic rings measuring 50x50x5 mm.

Stirrer-neutralizer - a cylindrical apparatus with a stirrer rotating at a speed of 30 rpm. The drive is carried out from an electric motor through a gearbox (Figure 6).

Ш1 - fitting for installing a level meter; B1 - air vent; E1 - electric motor; P1 - gearbox; VM1 - mixer shaft; L1 - manhole

Figure 6 - Stirrer-neutralizer

The diameter of frequently used devices is 2800 mm, height 3200 mm. They operate under atmospheric pressure, serve for the final neutralization of ammonium nitrate solutions and as intermediate containers for solutions sent for evaporation.

Surface condenser is a vertical shell-and-tube two-pass (through water) heat exchanger designed to condense juice steam coming from a vacuum evaporator. Device diameter 1200 mm, height 4285 mm; heat transfer surface 309 m2. It operates at a vacuum of approximately 550-- 600 mm Hg. Art.; has tubes: diameter 25x2 mm, length 3500 m, total number 1150 pcs.; the weight of such a capacitor is about 7200 kg

In some cases, to eliminate emissions of juice steam into the atmosphere, discharged during purging from evaporators, traps of heating equipment and water seals, a surface condenser is installed with the following characteristics: case diameter 800 mm, height 4430 mm, total number of tubes 483 pcs., diameter 25x2, total surface 125 m2.

Vacuum pumps. Different types of pumps are used. The VVN-12 type pump has a capacity of 66 m3/h, shaft rotation speed is 980 rpm. The pump is designed to create a vacuum in a vacuum neutralization unit.

Centrifugal pumps. To circulate ammonium nitrate solution in a vacuum neutralization installation, 7ХН-12 pumps with a capacity of 175-250 m3/h are often used. Installed power of the electric motor is 55 kW.

4 . Material and energy calculations

Let us calculate the material and thermal balance of the process. I calculate the neutralization of nitric acid with ammonia gas per 1 ton of product. I take the initial data from Table 2, using the methodology of manuals , , .

We accept that the neutralization process will proceed under the following conditions:

Initial temperature, °C

ammonia gas................................................... ...........................50

nitric acid........................................................ ......................................20

Table 2 - Initial data

Material calculation

1 To obtain 1 ton of nitrate by the reaction:

NH3+HNO3=NH4NO3 +Q J (9)

theoretically the following amount of raw materials is required (in kg):

ammonia

17 - 80 x = 1000*17/80 = 212.5

x - 1000

nitric acid

63 - 80 x = 1000*63/80 = 787.5

x - 1000

Where 17, 63 and 80 are the molecular weights of ammonia, nitric acid and ammonium nitrate, respectively.

The practical consumption of NH3 and HNO3 is slightly higher than the theoretical one, since during the neutralization process, losses of reagents with juice steam are inevitable through leaks in communications due to slight decomposition of the reacting components and nitrate, etc.

2. Determine the amount of ammonium nitrate in the commercial product: 0.98*1000=980 kg/h

or

980/80=12.25 kmol/h,

and also the amount of water:

1000-980=20 kg/h

3. I will calculate the consumption of nitric acid (100%) to produce 12.25 kmol/h of nitrate. According to stoichiometry, the same amount of it is consumed (kmol/h) as nitrate is formed: 12.25 kmol/h, or 12.25*63=771.75 kg/h

Since the conditions set the complete (100%) conversion of the acid, this will be the amount supplied.

The process involves diluted acid - 60%:

771.75/0.6=1286.25 kg/h,

including water:

1286.25-771.25=514.5 kg/h

4. Similarly, ammonia consumption (100%) to produce 12.25 kmol/h, or 12.25*17=208.25 kg/h

In terms of 25% ammonia water, this will be 208.25/0.25 = 833 kg/h, including water 833-208.25 = 624.75 kg/h.

5. I will find the total amount of water in the neutralizer supplied with the reagents:

514.5+624.75=1139.25 kg/h

6. Let us determine the amount of water vapor formed by evaporation of the nitrate solution (20 kg/h remains in the commercial product): 1139.25 - 20 = 1119.25 kg/h.

7. Let’s draw up a table of the material balance of the ammonium nitrate production process.

Table 3 - Material balance of the neutralization process

8. Let's calculate technological indicators.

· theoretical expense coefficients:

for acid - 63/80=0.78 kg/kg

for ammonia - 17/80=0.21 kg/kg

· actual expense ratios:

for acid - 1286.25/1000=1.28 kg/kg

for ammonia - 833/1000=0.83 kg/kg

During the neutralization process, only one reaction took place, the conversion of the raw material was equal to 1 (i.e., complete conversion occurred), there were no losses, which means that the actual yield is equal to the theoretical one:

Qf/Qt*100=980/980*100=100%

Energy calculation

The arrival of warmth. During the neutralization process, the heat input consists of the heat introduced by ammonia and nitric acid, and the heat released during neutralization.

1. The heat contributed by ammonia gas is:

Q1=208.25*2.18*50=22699.25 kJ,

where 208.25 is ammonia consumption, kg/h

2.18 - heat capacity of ammonia, kJ/(kg*°C)

50 - ammonia temperature, °C

2. Heat introduced by nitric acid:

Q2=771.75*2.76*20=42600.8 kJ,

where 771.25 is the consumption of nitric acid, kg/h

2.76 - heat capacity of nitric acid, kJ/(kg*°C)

20 - acid temperature, °C

3. The heat of neutralization is preliminarily calculated per 1 mole of ammonium nitrate formed according to the equation:

HNO3*3.95H2O(liquid) +NH3(gas) =NH4NO3*3.95H2O(liquid)

where HNO3*3.95H2O corresponds to nitric acid.

The thermal effect Q3 of this reaction is found from the following quantities:

a) heat of dissolution of nitric acid in water:

HNO3+3.95 H2O=HNO3*3.95H2O (10)

b) heat of formation of solid NH4NO3 from 100% nitric acid and 100% ammonia:

HNO3 (liquid) + NH3 (gas) = ​​NH4NO3 (solid) (11)

c) the heat of dissolution of ammonium nitrate in water, taking into account the reaction heat consumption for evaporation of the resulting solution from 52.5% (NH4NO3 *H2O) to 64% (NH4NO3 *2.5H2O)

NH4NO3 +2.5H2O= NH4NO3*2.5H2O, (12)

where NH4NO3*4H2O corresponds to a concentration of 52.5% NH4NO3

The value of NH4NO3*4H2O is calculated from the ratio

80*47.5/52.5*18=4H2O,

where 80 is the molar weight of NH4NO3

47.5 - HNO3 concentration, %

52.5 - NH4NO3 concentration, %

18 - molar weight of H2O

The value of NH4NO3*2.5H2O corresponding to a 64% solution of NH4NO3 is calculated similarly

80*36/64*18=2.5H2O

According to reaction (10), the heat of dissolution q of nitric acid in water is 2594.08 J/mol. To determine the thermal effect of reaction (11), it is necessary to subtract the sum of the heats of formation of NH3 (gas) and HNO3 (liquid) from the heat of formation of ammonium nitrate.

The heat of formation of these compounds from simple substances at 18°C ​​and 1 atm has the following values ​​(in J/mol):

NH3(gas):46191.36

HNO3 (liquid): 174472.8

NH4NO3(s):364844.8

The overall thermal effect of a chemical process depends only on the heats of formation of the initial interacting substances and final products. It follows from this that the thermal effect of reaction (11) will be:

q2=364844.8-(46191.36+174472.8)=144180.64 J/mol

The heat q3 of dissolution of NH4NO3 according to reaction (12) is equal to 15606.32 J/mol.

The dissolution of NH4NO3 in water occurs with the absorption of heat. In this regard, the heat of solution is taken in the energy balance with a minus sign. The concentration of the NH4NO3 solution proceeds accordingly with the release of heat.

Thus, the thermal effect of Q3 reaction

HNO3 +*3.95H2O(liquid)+ NH3(gas) =NH4NO3*2.5H2O(liquid)+1.45 H2O(steam)

will be:

Q3=q1+q2+q3= -25940.08+144180.64-15606.32=102633.52 J/mol

When producing 1 ton of ammonium nitrate, the heat of the neutralization reaction will be:

102633.52*1000/80=1282919 kJ,

where 80 is the molecular weight of NH4NO3

From the above calculations it is clear that the total heat gain will be: with ammonia 22699.25, with nitric acid 42600.8, due to the heat of neutralization 1282919 and a total of 1348219.05 kJ.

Heat consumption. When neutralizing nitric acid with ammonia, heat is removed from the apparatus by the resulting ammonium nitrate solution, spent on evaporating water from this solution and lost into the environment.

The amount of heat carried away by the ammonium nitrate solution is:

Q=(980+10)*2.55 tkip,

where 980 is the amount of ammonium nitrate solution, kg

10 - losses of NH3 and HNO3, kg

tboil - boiling temperature of ammonium nitrate solution, °C

The boiling point of the ammonium nitrate solution is determined at an absolute pressure in the neutralizer of 1.15 - 1.2 atm; This pressure corresponds to a temperature of saturated water vapor of 103 °C. at atmospheric pressure, the boiling point of the NH4NO3 solution is 115.2 °C. temperature depression is equal to:

?t=115.2 - 100=15.2 °C

Calculate the boiling point of a 64% NH4NO3 solution

tboil = tsat. steam+?t*з =103+15.2*1.03 = 118.7 °С,

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Ammonium nitrate is one of the most common fertilizers.

Ammonium nitrate (otherwise known as ammonium nitrate) is produced in factories from nitric acid and ammonia by chemical interaction of these compounds.

The production process consists of the following stages:

1. Neutralization of nitric acid with ammonia gas.
2. Evaporation of ammonium nitrate solution.
3. Crystallization of ammonium nitrate.
4. Drying salt.

The figure shows a simplified process flow diagram for the production of ammonium nitrate. How does this process take place?

The feedstock - gaseous ammonia and nitric acid (aqueous solution) - enters the neutralizer. Here, as a result of the chemical interaction of both substances, a violent reaction occurs with the release of a large amount of heat. In this case, part of the water evaporates, and the resulting water vapor (so-called juice vapor) is discharged outside through the trap.

The incompletely evaporated ammonium nitrate solution flows from the neutralizer to the next apparatus - the final neutralizer. In it, after adding an aqueous solution of ammonia, the process of neutralization of nitric acid ends.

From the pre-neutralizer, the ammonium nitrate solution is pumped into an evaporator - a continuously operating vacuum apparatus. The solution in such devices is evaporated at reduced pressure, in this case at a pressure of 160-200 mm Hg. Art. Heat for evaporation is transferred to the solution through the walls of tubes heated by steam.

Evaporation is carried out until the concentration of the solution reaches 98%. After this, the solution goes for crystallization.

According to one method, crystallization of ammonium nitrate occurs on the surface of a drum, which is cooled from the inside. The drum rotates, and a crust of crystallizing ammonium nitrate up to 2 mm thick is formed on its surface. The crust is cut off with a knife and sent through a chute for drying.

Ammonium nitrate is dried with hot air in rotating drying drums at a temperature of 120°. After drying, the finished product is sent for packaging. Ammonium nitrate contains 34-35% nitrogen. To reduce caking, various additives are added to its composition during production.

Ammonium nitrate is produced by factories in granular form and in the form of flakes. Flake saltpeter strongly absorbs moisture from the air, so during storage it spreads and loses its friability. Granulated ammonium nitrate has the form of grains (granules).

Granulation of ammonium nitrate is mostly carried out in towers (see figure). The evaporated solution of ammonium nitrate - melt - is sprayed using a centrifuge mounted in the ceiling of the tower.

The melt flows in a continuous stream into the rotating perforated drum of the centrifuge. Passing through the holes of the drum, the spray turns into balls of the appropriate diameter and hardens as it falls down.

Granulated ammonium nitrate has good physical properties, does not cake during storage, disperses well in the field and slowly absorbs moisture from the air.

Ammonium sulfate - (otherwise - ammonium sulfate) contains 21% nitrogen. Most of the ammonium sulfate is produced by the coke industry.

In the coming years, the production of the most concentrated nitrogen fertilizer - urea, or urea, which contains 46% nitrogen, will receive great development.

Urea is produced under high pressure by synthesis from ammonia and carbon dioxide. It is used not only as fertilizer, but also for feeding livestock (supplements protein nutrition) and as an intermediate for the production of plastics.

Liquid nitrogen fertilizers - liquid ammonia, ammonia and ammonia water - are also of great importance.

Liquid ammonia is produced from gaseous ammonia by liquefaction under high pressure. It contains 82% nitrogen. Ammonia compounds are solutions of ammonium nitrate, calcium nitrate or urea in liquid ammonia with a small addition of water. They contain up to 37% nitrogen. Ammonia water is an aqueous solution of ammonia. It contains 20% nitrogen. In terms of their effect on the crop, liquid nitrogen fertilizers are not inferior to solid ones. And their production is much cheaper than solid ones, since the operations of evaporating the solution, drying and granulating are eliminated. Of the three types of liquid nitrogen fertilizer, ammonia water is the most widely used. Of course, the application of liquid fertilizers to the soil, as well as their storage and transportation, require special machines and equipment.

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