Physical and chemical bases of production of ammonium nitrate. Overview of ammonium nitrate production technologies

Polymer recycling

The most important feature of new materials obtained on the basis of various polymers is the comparative simplicity of their transformation into finished products in the stage of a viscous-flow state, in which their plastic properties are most pronounced. This ability to be easily formed (under certain conditions, one way or another connected with heating), and then at ordinary temperature to steadfastly maintain the acquired shape, gave plastic masses their name.

From the point of view of polymer processing, they can (however, very conditionally) be divided into two main groups: thermoplastics, which include materials that change only their plasticity under the influence of heating, but retain their structure, and thermosetting plastics, in which, under the influence of heating, linear molecules as would be stitched together, forming complex spatial structures.

Thermoplastics include almost all plastic masses, which are obtained by splicing monomers into long chains by polymerization. Let us name some common plastic masses of this kind. Among them, polyethylene stands out, or polythene, which is not without reason called the “king of plastics”. With the exception of porous and foamy plastics, polythene is the lightest plastic mass. Its specific gravity differs little from that of ice, which allows it to float on the surface of the water. It is exceptionally resistant to alkalis and caustic acids and at the same time strong, easily bent, does not lose flexibility even at a sixty-degree frost. Polythene lends itself to drilling, turning, stamping, - in a word, any type of processing on those machines that are used for metal processing. Heated to 115-120 °, polythene becomes soft and plastic, and then by pressing or injection molding it is possible to produce any kind of dishes from it - from perfume bottles to huge bottles for acids and alkalis. When heated, polythene can be easily rolled into thin films that are used to wrap products that are afraid of dampness. The combination of strength and elasticity makes polythene a suitable material for the manufacture of silent gears, ventilation equipment and pipes for chemical plants, valves, gaskets.

Polyvinyl chloride (often not quite correctly called polyvinyl chloride) also belongs to common thermoplastics. On its basis, two main types of plastics are produced: rigid celluloid-like type - the so-called vinyl plastics and soft plastic compounds.

Polystyrene, a valuable insulator for high-frequency devices and special radio equipment, resembling colorless glass in appearance, and polymethyl methacrylate (organic glass) also adjoin here.

Thermoplastics include plastics made from appropriately processed natural polymers (for example, nitrocellulose obtained by treating cotton cellulose with a mixture of nitric and sulfuric acids, and cellulose acetate), and, as an exception, polyamide resins obtained by the polycondensation process and the so-called "stepped" , or multiple, polymerization.

The difference between these main groups of materials is very significant. Thermoplastic products can be crushed and recycled. For the manufacture of certain products from them, injection molding is widely used. The product hardens in a cooled mold in a few seconds; as a result, the productivity of modern injection molding machines is very high: in a day they can produce from 15 to 40 thousand medium-sized products and several hundred thousand small ones.

With thermosetting materials, the situation is more complicated: after they have hardened, it is almost impossible to return them to a viscous-flowing state in which they could become plastic again. Therefore, casting from them is difficult; they are mostly pressed under heat, and the resulting products are kept in the mold for as long as necessary for the resin to pass into an infusible state over the entire cross section of the product. But the product no longer requires cooling.

Although the method of hot pressing is somewhat less productive than injection molding, however, even it is many times faster than conventional technological processes for the manufacture of metal products. This provides a huge additional benefit when replacing metals with plastics. After all, many complex metal products require a long series of production operations for their finishing. A typical example is the manufacture of dies that require long-term efforts of the most skilled toolmakers. The Soviet automotive industry is now using stamps made from so-called epoxy resins with the appropriate filler. They are created with the help of one main operation - casting and one auxiliary - cleaning of individual, randomly formed irregularities. The industry has come close to solving the problem of forming large-sized products, such as car hulls, motor boats, etc.

Using the example of a plastic mass obtained by the method of stepwise polymerization - polycaprolactam (as nylon resin is called in the language of chemists) - one can clearly see how conditional the boundaries are that separate plastic masses from synthetic fibers in practice.

Capron resin is obtained from aminocaproic acid lactam - caprolactam, which in turn is obtained from phenol, benzene, furfural (a very promising raw material, formed, in particular, during the processing of agricultural waste) and acetylene obtained by the action of water on calcium carbide. After polymerization is completed, polycaprolactam is released from the reactor through a thin slot. At the same time, it solidifies in the form of a ribbon, which is then ground into crumbs. After additional purification from monomer residues, the polyamide resin we need is obtained. From this resin, the melting point of which is quite high (216-218 °), steamship screws, bearing shells, machine gears, etc. are made. But polyamide resins are most widely used in the production of threads from which non-rotting fishing nets are made and nylon stockings, etc.

The filaments are formed from a resin melt that passes through small holes, forming streams that solidify upon cooling into filaments. Several elementary filaments are joined into one and subjected to torsion and drawing.

Chemistry is the most reliable ally of such a decisive factor in industrial progress as automation. Chemical technology, by virtue of its most important feature, especially emphasized in the report of N. S. Khrushchev at the 21st Congress of the CPSU, namely continuity, is the most effective and desirable object for automation. If we take into account, in addition, that chemical production in its main directions is a large-tonnage and mass production, then one can clearly imagine what immense sources of labor saving and expansion of production are contained in chemistry, especially the chemistry and technology of polymers.

Recognizing the deep connections between the structure of the most important technical polymer materials and their properties and having learned to “design” polymer materials according to a kind of “chemical drawings”, chemical scientists can safely say: “The age of materials of unlimited choice has begun.”

Application of fertilizers

Socialist agriculture faces the task of creating an abundance of foodstuffs in our country and supplying industry with raw materials to the full extent.

In the coming years, the production of grain products, sugar beets, potatoes, industrial crops, fruits, vegetables and fodder plants will increase significantly. The production of basic livestock products: meat, milk, wool, etc., will increase significantly.

In this struggle for the abundance of food chemistry plays a huge role.

There are two ways to increase the production of agricultural products: first, by expanding the area under crops; secondly, by increasing the yield on already cultivated land masses. This is where chemistry comes to the aid of agriculture.

Fertilizers not only increase the quantity, but also improve the quality of crops grown with their help. They increase the sugar content in beets and starch in potatoes, increase the strength of flax and cotton fibers, etc. Fertilizers increase the resistance of plants to disease, drought and cold.

In the coming years, our agriculture will need a lot of mineral and organic fertilizers. It receives mineral fertilizers from the chemical industry. In addition to various mineral fertilizers, the chemical industry provides agriculture with pesticides for combating harmful insects, plant diseases and weeds - herbicides, as well as means for regulating growth and fruiting - growth stimulants, means for pre-harvest fall of cotton leaves, etc. (more about them application and action is described in v. 4 DE).

What are fertilizers

Fertilizers used in agriculture are divided into two main groups: organic and mineral. Organic fertilizers include: manure, peat, green manure (plants that absorb atmospheric nitrogen) and various composts. Their composition, in addition to minerals, includes organic substances.

Complex, or multilateral, fertilizers are also produced in our country. They contain not one, but two or three batteries. The use of microfertilizers in agriculture is also developing significantly. They include boron, copper, manganese, molybdenum, zinc and other elements, small amounts of which (several kilograms per hectare) are necessary for the development and fruiting of plants.

In addition, so-called indirect fertilizers are also used in agriculture: lime, gypsum, etc. They change the properties of soils: they eliminate acidity harmful to plants, enhance the activity of beneficial microorganisms, and convert the nutrients contained in the soil itself into a more accessible form for plants. soil, etc.

NITROGEN FERTILIZERS

The starting material for the production of most nitrogen fertilizers is ammonia. It is obtained by synthesis from nitrogen and hydrogen or as a by-product (by-product) during the coking of coal and peat.

The most common nitrogen fertilizers are ammonium nitrate, ammonium sulfate, calcium nitrate, sodium nitrate, urea, liquid nitrogen fertilizers (liquid ammonia, ammonia, ammonia water).

These fertilizers differ from each other in the form of nitrogen compounds. Some contain nitrogen in the form of ammonia. These are ammonia fertilizers. These include ammonium sulfate. In others, nitrogen is in the nitrate form, that is, in the form of salts of nitric acid. These are nitrate fertilizers. These include sodium nitrate and calcium nitrate. In ammonium nitrate, nitrogen is contained simultaneously in both nitrate and ammonium forms. Urea contains nitrogen in the form of an amide compound.

Nitrate forms of nitrogen fertilizers are easily soluble in water, are not absorbed by the soil and are easily washed out of it. They are absorbed by plants faster than other forms of nitrogen compounds.

Ammonia fertilizers are also easily soluble in water and are well absorbed by plants, but they act more slowly than nitrate fertilizers. Ammonia is well absorbed by the soil and weakly washed out of it. Therefore, ammonia fertilizers provide plants with nitrogen nutrition for a longer time. They are also cheaper. This is their advantage over nitrate fertilizers.

How ammonium nitrate is made

Ammonium nitrate is one of the most common fertilizers.

Ammonium nitrate (otherwise - ammonium nitrate) is obtained at 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 gaseous ammonia.
2. Evaporation of ammonium nitrate solution.
3. Crystallization of ammonium nitrate.
4. Drying salt.

The figure shows in a simplified form the technological scheme for the production of ammonium nitrate. How does this process proceed?

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 (the so-called juice vapor) is discharged through the trap to the outside.

Incompletely one stripped off solution of ammonium nitrate comes from the neutralizer into the next apparatus - the neutralizer. In it, after the addition of an aqueous solution of ammonia, the process of neutralization of nitric acid ends.

From the neutralizer, the ammonium nitrate solution is pumped into the evaporator - a continuously operating vacuum apparatus. The solution in such devices is evaporated under 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 that, the solution goes to crystallization.

According to one method, the crystallization of ammonium nitrate occurs on the surface of the 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 to the chute for drying.

The 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 introduced into its composition during production.

Ammonium nitrate is produced by factories in granular form and in the form of flakes. Saltpeter flake 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 done in towers (see figure). One stripped off solution of ammonium nitrate - melt - is sprayed with a centrifuge mounted in the ceiling of the tower.

The melt is poured into the rotating perforated drum of the centrifuge in a continuous stream. Passing through the holes of the drum, the spray turns into balls of the appropriate diameter and hardens during the fall down.

Granular 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, carbamide, or urea, which contains 46% nitrogen, will be greatly developed.

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

Of great importance are liquid nitrogen fertilizers - liquid ammonia, ammonia and ammonia water.

Liquid ammonia is produced from gaseous ammonia by high pressure liquefaction. It contains 82% nitrogen. Ammonias 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 there are no operations for evaporating the solution, drying and granulating. 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.

The technological process for the production of ammonium nitrate consists of the following main stages: neutralization of nitric acid with gaseous ammonia, evaporation of an ammonium nitrate solution, crystallization and granulation of the melt.

Gaseous ammonia from heater 1 and nitric acid from heater 2 at a temperature of 80-90 0 C enter the ITP 3 apparatus. To reduce the loss of ammonia, together with steam, the reaction is carried out in an excess of acid. The ammonium nitrate solution from the apparatus 3 is neutralized in the after-neutralizer 4 with ammonia and enters the evaporator 5 for evaporation. into a rectangular granulation tower 16.

Fig.5.1. Technological scheme for the production of ammonium nitrate.

1 - ammonia heater, 2 - nitric acid heater, 3 - ITN apparatus (using the heat of neutralization), 4 - additional 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-collector, 18,20-pumps, 19-float tank, 21-float filter, 22 - air heater.

In the upper part of the tower there are granulators 7 and 8, the lower part of which is supplied with air, which cools the saltpeter drops falling from above. During the fall of saltpeter drops from a height of 50-55 meters, when air flows around them, granules are formed, which are cooled in a fluidized bed apparatus 15. This is a rectangular apparatus having three sections and a grid with holes. Fans supply air under the grate. A fluidized bed of saltpeter granules is created, coming from the granulation tower through a conveyor. The air after cooling enters the granulation tower.

Granules of ammonium nitrate conveyor 14 is served for treatment with surfactants in a rotating drum 11. Then the finished fertilizer conveyor 12 is sent to the package.

The air leaving the granulation tower is contaminated with ammonium nitrate, and the juice vapor from the neutralizer contains unreacted ammonia and nitric acid, as well as particles of carried-away ammonium nitrate. To clean these streams in the upper part of the granulation tower, there are six parallel-operating washing plate-type scrubbers 10, irrigated with a 20-30% solution of saltpeter, which is supplied by pump 18 from collection 17. to a solution of saltpeter, and, therefore, is used to make products. The purified air is sucked out of the granulation tower by fan 9 and released into the atmosphere.

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

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

Schematic diagram of the production of ammonium nitrate

To obtain a practically non-caking ammonium nitrate, a number of technological methods are used. An effective means of reducing the rate of absorption of moisture 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 more slowly from

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

NH 3 + HNO 3 \u003d NH 4 NO 3; ΔН = -144.9kJ

The chemical reaction proceeds at a high rate; in an industrial reactor, it is limited by the dissolution of the gas in the liquid. Mixing of the reactants is of great importance to reduce diffusion retardation.

The technological process for the production of ammonium nitrate includes, in addition to the stage of neutralizing nitric acid with ammonia, the stages of evaporating the saltpeter solution, granulating the melt, cooling the granules, treating the granules with surfactants, packing, storing and loading saltpeter, cleaning gas emissions and wastewater. On fig. 8.8 shows a diagram of a modern large-capacity unit for the production of ammonium nitrate AS-72 with a capacity of 1360 tons / day. The original 58-60% nitric acid is heated in the heater to 70 - 80°C with juice vapor from the apparatus ITN 3 and is fed to 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 is equipped with two ITN devices operating in parallel. In addition to nitric acid, gaseous ammonia is supplied to them, preheated in the heater 2 with steam condensate to 120-130°C. The amounts of supplied nitric acid and ammonia are regulated in such a way that at the outlet of the ITN apparatus the solution has a slight excess of acid (2-5 g/l), which ensures the complete absorption of ammonia.

In the lower part of the apparatus, a neutralization reaction takes place 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 (the so-called juice vapor) is washed from splashes of ammonium nitrate and nitric acid vapor. Part of the heat of the juice vapor is used to heat the nitric acid. Then the juice steam is sent for purification and released into the atmosphere.

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

1 – acid heater; 2 – ammonia heater; 3 – ITN devices; 4 - after-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 - tank for swimming; 21 - filter for swimming; 22 - air heater.

An acid solution of ammonium nitrate is sent to the neutralizer 4; where ammonia enters, necessary for interaction 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 the filter 21 at 175 ° C and is fed into the pressure tank 6 by a centrifugal submersible pump 20, and then into the rectangular metal granulation tower 16.

In the upper part of the tower there are granulators 7 and 8, the lower part of which is supplied with air, which cools the saltpeter drops falling from above. During the fall of saltpeter drops from a height of 50-55 m, fertilizer granules are formed when air flows around them. The temperature of the pellets at the outlet of the tower is 90-110°C; the hot granules are cooled in a fluidized bed apparatus 15. This is a rectangular apparatus having three sections and equipped with a grate with holes. Fans supply air under the grate; this creates a fluidized bed of nitrate granules coming through the conveyor from the granulation tower. The air after cooling enters the granulation tower. Granules of ammonium nitrate conveyor 14 is served for treatment with surfactants in a rotating drum. Then the finished fertilizer is sent to the packaging by the conveyor 12.

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

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

Urea production

Carbamide (urea) among nitrogen fertilizers ranks second in terms of production after ammonium nitrate. The growth of carbamide production is due to the wide scope of its application in agriculture. It is more resistant to leaching than other nitrogen fertilizers, i.e. it is less susceptible to leaching from the soil, less hygroscopic, and can be used not only as a fertilizer, but also as an additive to cattle feed. Urea is also widely used in compound fertilizers, time-controlled fertilizers, and in plastics, adhesives, varnishes, and coatings. Carbamide CO (NH 2) 2 is a white crystalline substance containing 46.6% nitrogen. Its production is based on the reaction of the interaction of ammonia with carbon dioxide:

2NH 3 + CO 2 ↔ CO (NH 2) 2 + H 2 O; ΔН = -110.1 kJ (1)

Thus, the raw materials for the production of urea are ammonia and carbon dioxide obtained as a by-product in the production of process gas for the synthesis of ammonia. Therefore, the production of urea in chemical plants is usually combined with the production of ammonia. Reaction (I) - total; it proceeds in two stages. At the first stage, the synthesis of carbamate occurs:

2NH 3 (g) + CO2 (g) ↔ NH 2 COOHNH 4 (g); ΔН = –125.6 kJ (2)

At the second stage, an endothermic process of water splitting off from carbamate molecules occurs, as a result of which carbamide is formed:

NH 2 COOHNH 4 (l) ↔ CO (NH 2) 2 (l) + H2O (l); ΔН =15.5 kJ (3) The reaction of formation of ammonium carbamate is a reversible exothermic reaction proceeding with a decrease in volume. To shift the equilibrium towards the product, it must be carried out at elevated pressure. In order for the process to proceed at a sufficiently high rate, elevated temperatures are required. An increase in pressure compensates for the negative effect of high temperatures on the shift of the reaction equilibrium in the opposite direction. In practice, the synthesis of carbamide is carried out at temperatures of 150-190°C and a pressure of 15-20 MPa. Under these conditions, the reaction proceeds at a high rate and almost to completion. The decomposition of ammonium carbamate is a reversible endothermic reaction that proceeds intensively in the liquid phase. To prevent crystallization of solid products in the reactor, the process must be carried out at temperatures not lower than 98 ° C [eutectic point for the CO(NH 2) 2 - NH 2 COONH 4 system]. Higher temperatures shift the reaction equilibrium to the right and increase its rate. The maximum degree of conversion of carbamate to carbamide is reached at 220°C. To shift the equilibrium of this reaction, an excess of ammonia is also introduced, which, by binding the reaction water, removes it from the reaction sphere. However, it is still not possible to achieve complete conversion of carbamate into urea. The reaction mixture, in addition to the reaction products (urea and water), also contains ammonium carbamate and its decomposition products - ammonia and CO 2 .

For the full use of the feedstock, it is necessary either to provide for the return of unreacted ammonia and carbon dioxide, as well as carbon ammonium salts (intermediate reaction products) to the synthesis column, i.e., the creation of a recycle, or the separation of urea from the reaction mixture and the direction of the remaining reagents to other industries, for example for the production of ammonium nitrate, i.e. conducting an open process.

In the latter case, the melt leaving the synthesis column is throttled to atmospheric pressure; the equilibrium of reaction (2) at temperatures of 140-150°C is almost completely shifted to the left and the entire remaining carbamate decomposes. An aqueous solution of urea remains in the liquid phase, which is evaporated and sent to granulation. Recycling the resulting ammonia and carbon dioxide gases to the synthesis column would require them to be compressed in a compressor to the urea synthesis pressure. This is associated with technical difficulties associated with the possibility of carbamate formation at low temperatures and high pressure already in the compressor and clogging of machines and pipelines with solid particles.

Therefore, in closed circuits (circuits with recirculation), only liquid recycle is usually used. There are a number of technological schemes with liquid recycle. Among the most progressive are the so-called schemes with a complete liquid recycle and with the use of a stripping process. Stripping (blowing) consists in the fact that the decomposition of ammonium carbamate in the melt after the synthesis column is carried out at a pressure close to the pressure at the synthesis stage, by blowing the melt with compressed CO 2 or compressed ammonia. Under these conditions, the dissociation of ammonium carbamate occurs due to the fact that when the melt is blown with carbon dioxide, the partial pressure of ammonia sharply decreases and the equilibrium of reaction (2) shifts to the left. Such a process is distinguished by the use of the reaction heat of carbamate formation and lower energy consumption.

In Fig.8.9. a simplified diagram of a large-capacity urea synthesis unit with a liquid recycle and the use of a stripping process is given. It can be divided into a high pressure unit, a low pressure unit and a granulation system. An aqueous solution of ammonium carbamate and carbon ammonium salts, as well as ammonia and carbon dioxide, enter the lower part of the synthesis column 1 from the high pressure condenser 4. In the synthesis column at a temperature of 170-190 ° C and a pressure of 13-15 MPa, the formation of carbamate ends and the synthesis reaction proceeds carbamide. The consumption of reagents is selected so that the molar ratio of NH 3 : CO 2 in the reactor is 2.8-2.9. The liquid reaction mixture (melt) from the urea synthesis column enters the stripping column 5, where it flows down the tubes. Carbon dioxide compressed in the compressor to a pressure of 13-15 MPa is supplied countercurrently to the melt, to which air is added in an amount that provides an oxygen concentration of 0.5-0.8% in the mixture to form a passivating film and reduce equipment corrosion. The stripping column is heated with steam. The gas-vapor mixture from column 5, containing fresh carbon dioxide, enters the high-pressure condenser 4. Liquid ammonia is also introduced into it. It simultaneously serves as a working flow in injector 3, which supplies a solution of carbon-ammonium salts from scrubber 2 to the condenser and, if necessary, part

Fig.8.9. A simplified process flow diagram for the production of carbamide with a complete liquid recycle and the use of a stripping process:

1 – carbamide synthesis column; 2 – high pressure scrubber; 3 - injector; 4 – high pressure carbamate condenser; 5 – stripping column; 6 - pumps; 7 – low pressure condenser; 8 – distillation column of low pressure; 9 - heater; 10 - collection; 11 – evaporator; 12 - granulation tower.

melt from the synthesis column. Carbamate is formed in the condenser. The heat released during the reaction is used to produce steam.

From the upper part of the synthesis column, unreacted gases continuously exit, entering the high-pressure scrubber 2, in which most of them are condensed due to water cooling, forming an aqueous solution of carbamate and carbon ammonium salts. The aqueous solution of carbamide leaving the stripping column 5 contains 4-5% carbamate. For its final decomposition, the solution is throttled to a pressure of 0.3-0.6 MPa and then sent to the upper part of the distillation column 8. The liquid phase flows in the column down the nozzle countercurrently to the vapor-gas mixture rising from the bottom up; NH 3 , CO 2 and water vapor exit from the top of the column. Water vapor condenses in the low pressure condenser 7, while the main part of ammonia and carbon dioxide is dissolved. The resulting solution is sent to scrubber 2. The final purification of gases emitted into the atmosphere is carried out by absorption methods (not shown in the diagram).

A 70% aqueous solution of carbamide leaving the lower part of the distillation column 8 is separated from the vapor-gas mixture and sent, after the pressure is reduced to atmospheric, first to evaporation, and then to granulation. Before spraying the melt in the granulation tower 12, conditioning additives, such as urea-formaldehyde resin, are added to it in order to obtain a non-caking fertilizer that does not deteriorate during storage.

Schematic diagram with full recycling

Introduction

The most important type of mineral fertilizers are nitrogen: ammonium nitrate, carbamide, ammonium sulfate, aqueous solutions of ammonia, etc. Nitrogen plays an extremely important role in the life of plants: it is part of chlorophyll, which is an acceptor of solar energy, and protein, which is necessary for building a living cell. Plants can only consume bound nitrogen - in the form of nitrates, ammonium salts or amides. Relatively small amounts of bound nitrogen are formed from atmospheric nitrogen due to the activity of soil microorganisms. However, modern intensive agriculture can no longer exist without the 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), physiologically acidic and physiologically alkaline fertilizers are also distinguished.

Production of ammonium nitrate

Ammonium nitrate, or ammonium nitrate, NH4NO3 is a white crystalline substance containing 35% nitrogen in ammonium and nitrate forms , both forms of nitrogen are easily assimilated by plants. Granular ammonium nitrate is used on a large scale before sowing and for all types of top dressing. On a smaller scale, it is used for the production of 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, lose their crystalline form, caking of fertilizers occurs - loose material turns into a solid monolithic mass.

Ammonium nitrate is produced in three types:

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

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

Raw material

The feedstock in the production of ammonium nitrate is ammonia and nitric acid.

Nitric acid . Pure nitric acid HNO

-colorless liquid with a density of 1.51 g/cm at - 42 C it solidifies into a transparent crystalline mass. In air, it, like concentrated hydrochloric acid, "smokes", since its vapors form small droplets of fog with air moisture. Nitric acid does not differ in strength Already under the influence of light, it gradually decomposes:

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

Nitric acid is one of the strongest acids; in dilute solutions, it completely decomposes into ions

and - Nitric acid is one of the most important compounds of nitrogen: 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 for nitrous method, used for the manufacture of cellulose varnishes, 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 you pass a mixture of ammonia with air over the catalyst, then at 750 ° C and a certain composition of the mixture, almost complete conversion occurs

formed

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

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

Nitric acid obtained by oxidation of ammonia has a concentration not exceeding 60%. If necessary, concentrate

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

Ammonia synthesis

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 NH3 is a base, a moderately strong reducing agent and an effective complexing agent with respect to cations with vacant bonding orbitals.

Physical and chemical bases of the process . The synthesis of ammonia from the elements is carried out according to the reaction equation

N2 + ZN2 \u003d 2NHz; ∆H<0

The reaction is reversible, exothermic, characterized by a large negative enthalpy effect (∆H=-91.96 kJ/mol) and becomes even more exothermic at high temperatures (∆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 likelihood of a reaction occurring,

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

Characteristics of the target product

Physicochemical characteristics Ammonium nitrate (ammonium nitrate) NH4NO3 has a molecular weight of 80.043; pure product - 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 nitrate :

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 NH4NO3-H2O system (Fig. 11-2) belongs to systems with a simple eutectic. The eutectic point corresponds to a concentration of 42.4% MH4MO3 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 HH4MO3-H20 system. The right branch of the liquidus curve is the solubility curve of MH4MO3 in water. This curve has three breaking points corresponding to the temperatures of the modification transitions NH4NO3 1=11(125.8°C), II=III (84.2°C) and 111=IV (32.2 "C). Melting point (crystallization) anhydrous ammonium nitrate is 169.6 ° C. It decreases with increasing salt moisture content.

Dependence of the crystallization temperature of NH4NO3 (Tcryst, "C) on the moisture content (X,%) to 1.5% is described by the equation:

tcr == 169.6-13, 2x (11.6)

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

tcrist \u003d 169.6- 13.2X + 2, OU. (11.7).

Ammonium nitrate dissolves in water with heat absorption. Below are the values ​​​​of the heats of dissolution (Qsolv) of ammonium nitrate of various concentrations in water at 25 ° C:

C(NH4NO3) % mass 59,69 47.05 38,84 30,76 22,85 15,09 2,17

Qsolv 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, liquid ammonia.

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1. Technological part

1.4.1 Obtaining an aqueous solution of ammonium nitrate with a concentration

Introduction

In nature and in human life, nitrogen is extremely important; it is part of the protein compounds that are the basis of the plant and animal world. A person daily consumes 80-100 g of protein, which corresponds to 12-17 g of nitrogen.

Many chemical elements are required for the normal development of plants. The main ones are: carbon, oxygen, nitrogen, phosphorus, magnesium, calcium, iron. The first two elements of the plant are obtained from air and water, the rest are extracted from the soil.

Nitrogen plays a particularly large role in the mineral nutrition of plants, although its average content in the plant mass does not exceed 1.5%. No plant can live and develop normally without nitrogen.

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

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 in the soil - Azotobacter, which directly assimilate nitrogen from the air. Nodule bacteria that live in the roots of leguminous plants (peas, alfalfa, beans, etc.) have the same ability.

A significant amount of nitrogen contained in the soil is annually removed with the harvest of plant crops, and part is lost as a result of the washing out of nitrogen-containing substances by groundwater and rainwater. Therefore, in order to increase crop yields, it is necessary to systematically replenish nitrogen reserves in the soil by applying nitrogen fertilizers. Under different crops, depending on the nature of the soil, climatic and other conditions, different amounts of nitrogen are required.

Ammonium nitrate occupies a significant place in the range of nitrogen fertilizers. Its production has increased by more than 30% in recent decades.

As early as the beginning of the 20th century, an outstanding scientist - an agrochemist D.N. Pryanishnikov. called ammonium nitrate the fertilizer of the future. In Ukraine, for the first time in the world, they began to use ammonium nitrate in large quantities as a fertilizer for all industrial crops (cotton, sugar and fodder beets, flax, corn), and in recent years for vegetable crops. .

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 [(NH2)2CO], containing 46% nitrogen. Ammonium nitrate NH4NO3 is a universal nitrogen fertilizer, since it simultaneously contains the ammonium group NH4 and the nitrate group NO3 of the form of nitrogen.

It is very important that the nitrogen forms of ammonium nitrate are used by plants at different times. Ammonium nitrogen NH2, which is directly involved in protein synthesis, is quickly absorbed by plants during the growth period; nitrate nitrogen NO3 is absorbed relatively slowly, so it acts for a longer time.

Ammonium nitrate is also used in industry. It is part of a large group of ammonium nitrate explosives that are stable under different conditions as an oxidizing agent, decomposing under certain conditions only into gaseous products. Such an explosive is a mixture of ammonium nitrate with trinitrotoluene and other substances. Ammonium nitrate treated with a bicarbonate film of the Fe(RCOO)3 RCOOH type is used in large quantities for blasting in the mining industry, in the construction of roads, hydraulic engineering and other large structures.

A small amount of ammonium nitrate is used to produce nitrous oxide, which is used in medical practice.

Along with an increase in the production of ammonium nitrate through the construction of new and modernization of existing enterprises, the task was to improve its quality, i.e. get a finished product with 100% friability. This can be achieved by further research on various additives that affect the processes of polymer transformations, as well as through the use of available and cheap surfactants that provide hydrophobization of the surface of the granules and protect it from atmospheric moisture - the creation of slow-acting ammonium nitrate.

saltpeter production granule

1. Technological part

1.1 Feasibility study, site selection and construction site

Guided by the principles of rational economic management when choosing a construction site, we take into account the proximity of the raw material base, fuel and energy resources, the proximity of consumers of manufactured products, the availability of labor resources, transport, and the uniform distribution of enterprises throughout the country. Based on the above principles of location of enterprises, the construction of the projected shop for granulated ammonium nitrate is carried out in the city of Rivne. Since from the raw materials necessary for the production of ammonium nitrate, only natural gas used for the production of synthetic ammonia is supplied to the city of Rivne.

The Goryn river basin serves as a source of water supply. The energy consumed by production is generated by the Rivne CHPP. In addition, Rivne is a large city with a population of 270 thousand people, capable of providing the projected workshop with labor resources. Recruitment of the labor force is also envisaged to be made from the districts attached to the city. The workshop is provided with engineering personnel by graduates of the Lviv Polytechnic Institute, Dnepropetrovsk Polytechnic Institute, Kiev Polytechnic Institute, the workshop will be provided with local vocational schools.

Transportation of finished products to consumers will be carried out by rail and road.

The expediency of building the planned workshop in the city of Rivne is also evidenced by the fact that in the territories of Rivne, Volyn, Lviv regions with well-developed agriculture, the main consumer of the products of the designed workshop is granulated ammonium nitrate, as a mineral fertilizer.

Consequently, the proximity of the raw material base, energy resources, the sales market, as well as the availability of labor force, indicates the feasibility of building the planned workshop in the city of Rivne.

The proximity of a large railway station with a large branching of the railway tracks makes it possible to transport cheaply

1.2 Selection and justification of the production method

In industry, only the method of obtaining ammonium nitrate from synthetic ammonia and dilute nitric acid is widely used.

In many productions of ammonium nitrate, instead of previously used, poorly working devices, special washers were introduced. As a result, the content of ammonia or ammonium nitrate in juice vapors decreased by almost three times. Neutralizers of obsolete designs with low productivity (300 - 350 tons/day), increased losses and insufficient utilization of reaction heat were reconstructed. A large number of low-power horizontal evaporators were replaced by vertical ones with a falling or sliding film, and by devices with a larger heat exchange surface, which made it possible to almost double the productivity of the evaporator stages, reduce the consumption of secondary and fresh heating steam by an average of 20%.

In Ukraine and abroad, it is firmly established that only the construction of high-capacity units, using modern achievements in science and technology, can provide economic advantages compared to the existing ammonium nitrate production.

A significant amount of ammonium nitrate at individual plants is produced from ammonia-containing waste gases from urea systems with partial liquid recycles, where from 1 to 1.4 tons of ammonia is consumed per ton of urea produced. From the same amount of ammonia it is fashionable to produce 4.5 - 6.4 tons of ammonium nitrate.

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

In small quantities, ammonium nitrate is obtained by exchange decomposition of salts (conversion methods) according to the reactions:

Ca(NO3)2 + (NH4)2CO3 = 2NH4NO3 + vCaCO3 (1.1)

Mg (NO3) 2 + (NH4) 2CO3 \u003d 2NH4NO3 + vMgCO3 (1.2)

Ba(NO3)2 + (NH4)2SO4 = 2NH4NO3 + vBaSO4 (1.3)

These methods of obtaining ammonium nitrate are based on the precipitation of one of the resulting salts. All methods of obtaining ammonium nitrate by the exchange decomposition of salts are complex, associated with high steam consumption and loss of bound nitrogen. They are usually used in industry only if it is necessary to dispose of nitrogen compounds obtained as by-products.

Despite the relative simplicity of the technological process for obtaining ammonium nitrate, the schemes for its production abroad have significant differences, differing from each other both in the type of additives and the method of their preparation, and in the method of melt granulation.

Method "Nuklo" (USA).

A feature of this method for the production of granulated ammonium nitrate is the addition to a highly concentrated melt (99.8% of ammonium nitrate before its granulation in the tower, about 2% of a special additive called "Nuklo". It is a finely divided dry powder of concreted clay with a particle size of not more than 0.04 mm.

Method "Nitro - current".

This process was developed by the British firm Fayzone. The main difference of this method from others is that the drops of ammonium nitrate melt are simultaneously cooled, granulated and powdered first in a dust cloud of the powdering additive, and then in a fluidized bed of the same additive.

The method of the company "Ai - Si - Ai" (England).

This method of obtaining ammonium nitrate is different in that magnesium nitrate solution is used as an additive that improves the physical and chemical properties of the finished product, which makes it possible to obtain a high-quality product from ammonium nitrate melt containing up to 0.7% water.

The vacuum-free method for the production of ammonium nitrate was taken in 1951 in the USA by the "Stengel patent" and later implemented in the industry. The essence of the method lies in the fact that heated 59% nitric acid is neutralized with heated gas ammonia in a small volume under a pressure of 0.34 MPa.

In addition to the schemes described above, there are many other schemes for the production of ammonium nitrate abroad, but they differ little from each other.

It should be noted that, unlike the workshops operating and under construction in Ukraine and neighboring countries, in all foreign installations, the product after the granulation tower goes through the stage of screening and dusting, which improves the quality of the commercial product, but significantly complicates the technological scheme. At domestic plants, the absence of product sifting operation is compensated by a more advanced design of granulators, which give a product with a minimum fraction content of less than 1 mm. Bulky rotating drums for cooling granules, widely used abroad, are not used in Ukraine and have been replaced by fluidized bed cooling devices.

The production of granulated ammonium nitrate in the workshop is characterized by: obtaining a high quality product, a high utilization rate of neutralization heat, the use of a single-stage evaporation with a "sliding film", the maximum use of waste by returning it to the process, a high level of mechanization, storage and loading of products. This is a fairly high level of production.

1.3 Characteristics of raw materials and finished product

For the production of ammonium nitrate, 100% ammonia and dilute nitric acid HNO3 with a concentration of 55 - 56% are used.

Ammonia NH3 is a colorless gas with a pungent, specific odor.

A reactive substance that enters into addition, substitution and oxidation reactions.

Let's well dissolve in water.

Density in air at a temperature of 0 ° C and a pressure of 0.1 MPa - 0.597.

The maximum permissible concentration in the air of the working area of ​​industrial premises is 20 mg / m3, in the air of populated areas 0.2 mg / m3.

When mixed with air, ammonia forms explosive mixtures. The lower explosive limit of the ammonia-air mixture is 15% (volume fraction), the upper limit is 28% (volume fraction).

Ammonia irritates the upper respiratory tract, mucous membranes of the nose and eyes, getting on the skin of a person causes burns.

Hazard class IV.

Produced in accordance with GOST 6621 - 70.

Nitric acid HNO3 is a liquid with a pungent odor.

Density in air at a temperature of 0°C and a pressure of 0.1MPa-1.45g/dm3.

Boiling point 75°C.

Miscible with water in all respects with the release of heat.

Nitric acid getting on the skin or mucous membranes causes burns. Animal and plant tissues are destroyed under the influence of nitric acid. Vapors of nitric acid, similarly to nitrogen oxides, cause irritation of the internal respiratory tract, shortness of breath, and pulmonary edema.

The maximum permissible concentration of nitric acid vapors in the air of industrial premises in terms of NO2 is 2 mg/m3.

The mass concentration of nitric acid vapors in the air of populated areas is not more than 0.4 mg/m3.

Hazard class II.

Produced according to OST 113 - 03 - 270 - 76.

Ammonium nitrate NH4NO3 is a white crystalline substance produced in granular form with a nitrogen content of up to 35%

Produced in accordance with GOST 2 - 85 and meets the following requirements (see table 1.1)

Table 1.1 - Characteristics of ammonium nitrate produced in accordance with GOST 2 - 85

Name of indicator	Norm for the brand
The total mass fraction of nitrate and ammonium nitrogen in terms of:
for NH4NO3 in dry matter, %, not less than
for nitrogen in dry matter, %, not less than
Mass fraction of water, %, no more
pH 10% aqueous solution, not less than
Mass fraction of substances insoluble in 10% nitric acid solution, %, max
Grading
Mass fraction of granules size:
from 1 to 3 mm, %, not less
from 1 to 4 mm, %, not less
Including:
granules from 2 to 4 mm, %, not less than
granules less than 1 mm in size, %, no more
granules larger than 5 mm, %
Static strength of granules
N/granule (kg/granule), not less than
Friability, %, not less

Ammonium nitrate is an explosive and flammable substance. Granules of ammonium nitrate are resistant to friction, shock and shock, when exposed to detonators or in a confined space, ammonium nitrate explodes. The explosiveness of ammonium nitrate increases in the presence of organic acids, oils, sawdust, charcoal. The most dangerous metal impurities in ammonium nitrate are cadmium and copper.

Explosions of ammonium nitrate can be caused by:

a) exposure to detonators of sufficient power;

b) the influence of inorganic and organic impurities, in particular finely dispersed copper, cadmium, zinc, powdered charcoal, oil;

c) thermal decomposition in a closed space.

Dust of ammonium nitrate with an admixture of organic substances increases the explosiveness of salt. Cloth soaked in saltpeter and heated to 100°C can cause a fire. Extinguish saltpeter when sunbathing with water. Due to the fact that nitrogen oxides are formed when ammonium nitrate ignites, it is necessary to use gas masks when extinguishing.

NH4NO3 = N2O = 2H2O = 3600 kJ (1.4)

NH4NO3 \u003d 0.5N2 + NO \u003d 2H2O \u003d 28.7 kJ (1.5)

The presence of free acidity in the solution increases the capacity for chemical and thermal decomposition.

A negative property of ammonium nitrate is its ability to cake - to lose its flowability during storage.

Factors contributing to caking:

b) heterogeneity and low mechanical strength of the granules. When stored in stacks 2.5 meters high, under the pressure of the upper bags, the least durable granules are destroyed with the formation of dust particles;

c) change in crystalline modifications;

d) hygroscopicity promotes caking. The most effective way to prevent caking is to pack it in sealed containers (polyethylene bags).

The maximum permissible concentration of ammonium nitrate in the form of dust in industrial premises is not more than 10 mg/m3.

Means of protection of respiratory organs - solution.

Ammonium nitrate is used in agriculture as a nitrogen fertilizer, as well as in industry for various technical purposes.

Granular ammonium nitrate is used as a raw material in large quantities at military industry enterprises producing explosives and their semi-finished products.

1.4 Physical and chemical bases of the technological process

The process of obtaining granulated ammonium nitrate includes the following stages:

obtaining an aqueous solution of ammonium nitrate with a concentration of at least 80% by neutralizing nitric acid with gaseous ammonia;

evaporation of an 80% solution of ammonium nitrate to a state of melt;

evaporation of weak solutions of ammonium nitrate from dissolution units and capture systems;

salt granulation from melt;

cooling of granules in a "fluidized bed" with air;

treatment of granules with fatty acids;

transportation, packaging, and storage.

1.4.1 Obtaining an aqueous solution of ammonium nitrate with a concentration of at least 80% by neutralizing nitric acid with gaseous ammonia

A solution of ammonium nitrate is obtained in neutralizers that allow the heat of reaction to be used to partially evaporate the solution. He received the name of the apparatus ITN (use of neutralization heat).

The neutralization reaction proceeds at a faster rate and is accompanied by the release of a large amount of heat.

NH3 \u003d HNO3 \u003d NH4NO3 \u003d 107.7 kJ / mol (1.6)

The thermal effect of the reaction depends on the concentration and temperature of nitric acid and gaseous ammonia.

Figure 1.1 - Heat of neutralization of nitric acid with gaseous ammonia (at 0.1 MPa and 20 °)

The neutralization process in the ITN apparatus is carried out at a pressure of 0.02 MPa, the temperature is maintained at no more than 140 ° C. These conditions ensure that a sufficiently concentrated solution is obtained with a minimum entrainment of ammonia, nitric acid and ammonium nitrate with juice steam, which forms as a result of evaporation of water from the solution. Neutralization is carried out in a slightly acidic environment, since the loss of ammonia, nitric acid and saltpeter with juice vapor is less than in a slightly alkaline environment.

Due to the difference in the specific gravity of the solutions in the evaporation and neutralization parts of the ITN apparatus, there is a constant circulation of the solution. A denser solution from the opening of the neutralization chamber continuously enters the neutralization part. The presence of solution circulation promotes better mixing of the reagents in the neutralization part, increases the productivity of the apparatus and eliminates overheating of the solution in the neutralization zone. When the temperature in the reaction part rises to 145°C, a blockage is triggered with the cessation of the supply of ammonia and nitric acid and the supply of acid condensate.

1.4.2 Evaporation of 80% ammonium nitrate solution to a state of melting

Evaporation of 80 - 86% ammonium nitrate solution is carried out in evaporators due to the heat of condensation of saturated steam at a pressure of 1.2 MPa and a temperature of 190°C. steam is supplied to the upper part of the annular space of the evaporator. The evaporator operates under a vacuum of 5.0 h 6.4 104 Pa according to the principle of solution film “sliding” along the walls of vertical pipes.

A separator is located in the upper part of the apparatus, which serves to separate the ammonium nitrate melt from the juice vapor.

To obtain high quality ammonium nitrate, the ammonium nitrate melt must have a concentration of at least 99.4% and a temperature of 175 - 785°C.

1.4.3 Evaporation of weak solutions of ammonium nitrate from dissolution units and capture systems

Evaporation of weak solutions and solutions obtained as a result of starting and stopping the workshop takes place in a separate system.

Weak solutions obtained at the dissolution and trapping units are fed through a control valve to the lower part of the apparatus that evaporates only weak solutions. Evaporation of weak solutions of ammonium nitrate is carried out in a "film type" evaporator, operating on the principle of "sliding" of the film inside vertical pipes. The vapor-liquid emulsion, which forms in the tube of the evaporator, enters the separator-washer, where the juice vapor and the ammonium nitrate solution are separated. Juice vapor passes through the sieve plates of the evaporator washer, where splashes of ammonium nitrate are captured and then sent to the surface condenser.

The heat carrier is flash steam coming from the steam expander with a pressure of (0.02 - 0.03) MPa and a temperature of 109 - 112°C, supplied to the upper shell side of the evaporator. The vacuum in the evaporator is maintained at 200 - 300 mm Hg. Art. From the lower plate, a weak solution with a concentration of about 60% and a temperature of 105 - 112 ° C is discharged into a collection - an additional neutralizer.

1.4.4 Salt granulation from melt

To obtain ammonium nitrate in granular form, its crystallization from melt with a concentration of at least 99.4% is carried out in towers, which are a reinforced concrete structure, cylindrical in shape with a diameter of 10.5 meters. The melt with a temperature of 175 - 180°C and a concentration of at least 99.4% ammonium nitrate enters a dynamic granulator rotating at a speed of 200 - 220 rpm, having holes with a diameter of 1.2 - 1.3 mm. The melt sprayed through the holes, during the fall from a height of 40 meters, is formed into spherical particles.

The air for cooling the granules moves countercurrently from the bottom to the top. To create air draft, four axial fans with a capacity of 100,000 Nm3/h each are installed. In the granulation tower, the granules are slightly dried. Their humidity is 0.15 - 0.2% less than the moisture content of the incoming melt.

This is because even at 100% relative humidity of the air entering the tower, the water vapor pressure over the hot pellets is greater than the partial pressure of moisture in the air.

1.4.5 Cooling pellets in a fluidized bed with air

Granules of ammonium nitrate from the cones of the granulation tower are fed to the apparatus with a "fluidized bed" for cooling. Cooling of the granules from a temperature of 100-110°C to a temperature of 50°C takes place in the apparatus, which is located directly under the granulation tower. An overflow pipe is installed on the perforated grate to regulate the height of the "fluidized bed" and uniform unloading of saltpeter. Air up to 150,000 Nm3/h is supplied under the perforated grate, which cools the ammonium nitrate and partially dries it. The moisture content of ammonium nitrate granules is reduced by 0.05 - 0.1% compared to the granules coming from the cones.

1.4.6 Treatment of granules with fatty acids

The processing of granules with fatty acids is carried out in order to prevent caking of ammonium nitrate during long-term storage or transportation in bulk.

The treatment process consists in the fact that fatty acids finely sprayed with nozzles are applied to the surface of the granules at a rate of 0.01 - 0.03%. The design of the nozzles ensures the creation of an elliptical section of the spray jet. The mounting design of the nozzles provides the ability to move and fix them in different positions. Processing of granules with fatty acids is carried out in places where granules are transferred from conveyor belts to conveyor belts.

1.4.7 Transport, packaging, and storage

Granulated ammonium nitrate from the fluidized bed is fed through conveyors to bulkhead No. 1, processed with fatty acids and fed through second and third lift conveyors to mounted bins, from where it enters automatic scales that weigh out portions of 50 kg and then to the packaging unit. With the help of a packaging machine, ammonium nitrate is packed into polyethylene valve bags and dumped onto conveyors that send the packaged products to loading machines for loading into wagons and vehicles. Storage of finished products in warehouses is provided in the absence of wagons or vehicles.

Stored ammonium nitrate in piles must be protected from moisture and various temperature extremes. The height of the stacks should not exceed 2.5 meters, since under the pressure of the upper bags, the weakest granules in the lower bags may be destroyed with the formation of dust particles. The rate of absorption of moisture from the air by ammonium nitrate increases sharply with increasing temperature. So at 40°C, the rate of moisture absorption is 2.6 times greater than at 23°C.

In warehouses it is forbidden to store together with ammonium nitrate: oil, sawdust, charcoal, metal impurities of powders of cadmium and copper, zinc, chromium compounds, aluminum, lead, nickel, antimony, bismuth.

Storage of empty sack containers is located separately from the stored ammonium nitrate in containers in accordance with fire safety and safety requirements.

1.5 Protection of water and air basins. Production waste and their disposal

In the context of the rapid development of the production of mineral fertilizers, the widespread chemicalization of the national economy, the problems of protecting the environment from pollution and protecting the health of workers are becoming increasingly important.

The Rivne Chemical Plant, following the examples of other large chemical industries, has ensured that chemically dirty effluents are not discharged into the river, as before, but are cleaned in special facilities of the biochemical treatment plant and returned to the circulating water supply system for further use.

A number of targeted and local facilities have been put into operation for wastewater treatment, incineration of bottoms residues and disposal of solid waste. The total amount of capital investment for these purposes exceeds UAH 25 billion.

The bio-cleaning workshop is listed in the book of glory of the State Committee of the Council of Ministers of Ukraine for Nature Protection for success. The treatment facilities of the enterprise are located on an area of ​​40 hectares. In ponds filled with purified water, carps, silver carps, delicate aquarium fish frolic. They are an indicator of the quality of treatment and the best proof of the safety of wastewater.

Laboratory analyzes show that the water in the buffer ponds is no worse than that taken from the river. With the help of pumps, it is again supplied to the needs of production. The biochemical cleaning shop has been brought up to a chemical cleaning capacity of up to 90,000 cubic meters per day.

At the plant, the control service for the content of harmful substances in wastewater, soil, in the air of industrial premises, on the territory of the enterprise and in the vicinity of settlements and the city is constantly being improved. For more than 10 years, sanitary control has been actively operating, carrying out the work of an industrial sanitary laboratory. Day and night, they closely monitor the sanitary and hygienic state of the external and production environment, and the working conditions.

Wastes from the production of granulated ammonium nitrate are: steam condensate in the amount of 0.5 m3 per ton of product, which is discharged into the general plant network; juice steam condensate in the amount of 0.7 m3 per ton of product. Juice steam condensate contains:

ammonia NH3 - not more than 0.29 g/dm3;

nitric acid НNO3 - not more than 1.1 g/dm3;

ammonium nitrate NH4NO3 - no more than 2.17 g/dm3.

Juice vapor condensate is sent to the nitric acid shop for irrigation of columns in the purification department.

Emissions from the stack of axial fans into the atmosphere:

mass concentration of ammonium nitrate NH4NO3 - no more than 110 m2/m3

total volume of exhaust gases - no more than 800 m3/hour.

Emissions from the general shop pipe:

mass concentration of ammonia NH3 - no more than 150 m2/m3

mass concentration of ammonium nitrate NH4NO3 - no more than 120 m2/m3

Measures to ensure the reliability of the protection of water resources and the air basin. In the event of an emergency and shutdowns for repairs, in order to exclude contamination of the water cycle with ammonia, nitric acid and ammonium nitrate, as well as to prevent the ingress of harmful substances into the soil, the solution is drained from the absorption and evaporation section into three drainage tanks with a volume of V = 3 m3 each, in addition, leaks from the seals of the circulation pumps of the absorption and evaporation sections are collected in the same tanks. From these containers, the solution is pumped into a collection of weak solutions pos. 13 from where it then enters the department for the evaporation of weak solutions.

To prevent the ingress of harmful substances into the soil when gaps appear on the equipment and communications, a pallet made of acid-resistant material is equipped.

At the granulation tower, cleaning is carried out by washing the polluted air with a weak solution of ammonium nitrate and further filtering the steam-air flow. In the ammonium nitrate packaging department there is an air purification unit from ammonium nitrate dust after packaging semi-automatic machines and conveyors. Cleaning is carried out in a cyclone type TsN - 15.

1.6 Description of the technological scheme of production with elements of new equipment, technology and instrumentation

Nitric acid and ammonia are fed into the neutralization chamber of the ITN apparatus by countercurrent. Nitric acid with a concentration of at least 55% from the nitric acid shop is supplied through two pipelines with a diameter of 150 and 200 mm to a pressure tank (pos. 1) with an overflow through which excess acid is returned from the pressure tank to the nitric acid storage. From the tank (pos. 1), nitric acid is sent through the collector to the ITN apparatus (pos. 5). The ITN apparatus is a vertical cylindrical apparatus with a diameter of 2612 mm and a height of 6785 mm in which a glass with a diameter of 1100 mm and a height of 5400 mm is placed (neutralization chamber). In the lower part of the neutralization chamber there are eight rectangular holes (windows) 360x170 mm in size, connecting the neutralization chamber with the evaporation part of the ITN apparatus (the annular space between the walls of the apparatus and the wall of the neutralization chamber). The amount of nitric acid entering the ITN apparatus (pos. 5) is automatically adjusted by the pH meter system depending on the amount of gaseous ammonia entering the ITN apparatus (pos. 5) with correction for acidity.

Gaseous ammonia NH3 with a pressure of not more than 0.5 MPa from the factory network through the control valve after throttling to 0.15 - 0.25 MPa enters the liquid ammonia droplet separator pos. 2, where it is also separated from the oil in order to prevent them from entering the ITN apparatus (pos. 5). Then gaseous ammonia is heated to a temperature not lower than 70°C in the ammonia heater (pos. 4), where steam condensate from the steam expander (pos. 33) is used as a heat carrier. The heated gaseous ammonia from (pos. 3) through the control valve through the pipelines enters the ITN apparatus (pos. 5). Gaseous ammonia NH3 is introduced into the ITN apparatus (pos. 5) through three pipelines, two pipelines enter the neutralization chamber of the ITN apparatus in parallel flows after the control valve, where they are combined into one and end with a barbater. Through the third pipeline, ammonia is supplied through the barbater down the hydraulic seal in an amount of up to 100 Nm3/h to maintain a neutral environment at the outlet of the ITN apparatus. As a result of the neutralization reaction, a solution of ammonium nitrate and juice vapor are formed.

NH3 + HNO3 = NH4NO3 + 107.7 kJ/mol (1.6)

The solution is poured through the upper part of the neutralization chamber into the evaporation part of the apparatus, where it is evaporated to a concentration of 80 - 86%, due to the heat of the neutralization reaction, and the steam, mixing with the juice vapor obtained in the evaporation part, is removed from the apparatus at a temperature of 140 ° C to the washer (pos. . 12), intended for washing juice steam from splashes of ammonium nitrate and ammonia solution. The washer (pos. 12) is a cylindrical vertical apparatus, inside of which there are three sieve plates over which splash guards are installed. Coils are installed on two vertical plates through which cooled wash water passes. Juice steam passes through the sieve trays bubbling through the layer of solution formed on the trays as a result of cooling. A weak solution of ammonium nitrate flows from the plates to the lower part, from where it is discharged into the tank of weak solutions (pos. 13).

Uncondensed washed juice vapor enters the surface condenser (pos. 15) in the annulus. Industrial water is supplied to the pipe space of the condenser (pos. 15), which removes the heat of condensation.

The condensate (pos. 15) drains by gravity into the acid condensate collector (pos. 16), and inert gases are discharged into the atmosphere through the candle.

The solution of ammonium nitrate from the evaporator part through the water seal enters the separator - expander (pos. 6) to extract juice vapor from it and is discharged into the collector - neutralizer (pos. 7) to neutralize excess acidity (4 g / l). The collection - after-neutralizer (pos. 7) provides for the supply of gaseous ammonia. From collections - neutralizers (pos. 7) and pos. 8) a solution of ammonium nitrate with a concentration of 80 - 88% (alkaline medium no more than 0.2 g / l) and a temperature of no more than 140 ° C with pumps pos. 9 is fed into the granulation compartment into the pressure tank (pos. 11).

As a buffer tank, two additional collectors are installed - an after-neutralizer (pos. 8) to ensure the rhythmic operation of the workshop and pumps (pos. 9), and a pump (pos. 10) is also installed. The pump (pos. 10) is connected in such a way that it can supply the solution from the collector - after-neutralizer (pos. 7) to the collector - after-neutralizer (pos. 8) and vice versa.

Juice vapor condensate from the acid condensate collectors (pos. 16) is pumped out to the collector (pos. 18) from where it is pumped out by pumps (pos. 19) to the nitric acid shop for irrigation.

Steam enters the workshop at a pressure of 2 MPa and a temperature of 300°C, passes through a diaphragm and a control valve, is reduced to 1.2 MPa, and a steam humidifier (pos. 32) enters the lower part of the apparatus, inside which there are two sieve plates, and in the upper part, a fender is installed - a wavy nozzle. Here, the steam is humidified and with a temperature of 190°C and a pressure of 1.2 MPa enters the evaporator (pos. 20). Steam condensate from (pos. 32) in the form of a vapor-liquid emulsion with a pressure of 1.2 MPa and a temperature of 190 ° C through a control valve enters the steam expander (pos. 3), where, due to pressure reduction to 0.12 - 0.13 MPa secondary flash steam is formed with a temperature of 109 - 113 ° C, which is used to heat the evaporator of weak saltpeter solutions (pos. 22). Steam condensate from the bottom part of the steam expander (item 33) flows by gravity to the heating of the ammonia heater (item 4) into the annular space, from where, after heat is released at a temperature of 50 ° C, it enters the steam condensate collector (item 34), from where it is pumped ( pos. 35) is discharged through the control valve into the factory network.

The pressure tank (pos. 11) has an overflow pipe in (pos. 7). Pressure and overflow pipes are laid with steam tracers and insulated. From the pressure tank (pos. 11), the ammonium nitrate solution enters the lower pipe part of the evaporator (pos. 20), where the solution is evaporated due to the heat of condensation of saturated steam at a pressure of 1.2 MPa and a temperature of 190 ° C, supplied to the upper part of the annulus space. The evaporator (pos. 20) operates under a vacuum of 450 - 500 mm Hg. Art. according to the principle of "Sliding" of the solution film along the walls of vertical pipes. A separator is located in the upper part of the evaporator, which serves to separate the ammonium nitrate melt from the juice vapor. The melt from (pos. 20) is discharged into a water seal - an additional neutralizer (pos. 24), where gaseous ammonia is supplied to neutralize excess acidity. In case of termination of the selection, the overflow is sent to (pos. 7). Juice vapor from the evaporator (pos. 20) enters the washer with the resulting juice vapor condensate from splashes of ammonium nitrate. Inside the washer are sieve plates. On the upper two plates, coils with cooling water are laid, on which steam condenses. As a result of washing, a weak solution of ammonium nitrate is formed, which is sent through a water seal (pos. 27) to a pressure tank (pos. 28) of the neutralization compartment. Juice steam after the washer (pos. 26) is sent for condensation to the surface condenser (pos. 29) in the annulus, and the cooling water to the pipe space. The resulting condensate is directed by gravity to the acid solution collector (pos. 30). Inert gases are sucked off by vacuum pumps (pos. 37).

The melt of ammonium nitrate from the hydraulic seal - neutralizer (pos. 24) with a concentration of 99.5% NH4NO3 and a temperature of 170 - 180 ° C with an excess of ammonia of not more than 0.2 g / l is supplied by pumps (pos. 25) to the pressure tank (pos. 38) from where it flows by gravity into dynamic granulators (pos. 39) through which, spraying over the granulation tower (pos. 40), during the fall it is formulated into round particles. The granulation tower (pos. 40) is a cylindrical reinforced concrete structure with a diameter of 10.5 m and a hollow part height of 40.5 m. From the bottom of the granulation tower, air is supplied by fans (pos. 45), drawn by axial fans (pos. 44). Most of the air is sucked in through the windows and gaps in the grantower cones. Falling down the shaft, ammonium nitrate granules are cooled to 100 - 110°C and from the cones of the granulation tower they go for cooling to the apparatus with a "fluidized bed" (pos. 41) which is located directly under the granulation tower. In places where the estrus is flushed to the perforated grate, movable partitions are installed that allow you to adjust the height of the “fluidized bed” on the serk.

When cleaning the tower and apparatus "KS" from ammonium nitrate and dust deposits, the collected mass is dumped into the solvent (pos. 46), where steam is supplied at a pressure of 1.2 MPa and a temperature of 190 ° C for dissolution. The resulting solution of ammonium nitrate is drained from (pos. 46) into the collection (pos. 47) and pumped (pos. 48) into the collection of weak solutions (pos. 13). A weak solution of ammonium nitrate after the washer (pos. 12) also enters the same collection.

Weak solutions of NH4NO3 collected in (pos. 13) by pumps (pos. 14) are sent to the pressure tank (pos. 28) from where they are fed by gravity through the control valve to the lower part of the evaporator of weak solutions (pos. 22).

The evaporator works on the principle of film “sliding” inside vertical pipes. Juice vapor passes through the sieve plates of the evaporator washer, where the ammonium nitrate splashes are evaporated and is sent to the surface condenser (pos. 23), where it condenses and enters by gravity into (pos. 30). And the inert gases, having passed the trap (pos. 36), are sucked off by a vacuum pump (pos. 37). The vacuum is maintained at 200 - 300 mm. rt. pillar. From the lower plate of the evaporator (pos. 22), an ammonium nitrate solution with a concentration of about 60% and a temperature of 105 - 112 ° C is discharged into a collector (pos. 8). The heat carrier is secondary evaporation steam coming from the expander (pos. 33) with a temperature of 109 - 113°C and a pressure of 0.12 - 0.13 MPa. The steam is supplied to the upper annular part of the evaporator, the condensate is discharged into the steam condensate collector (pos. 42).

Granulated ammonium nitrate from the granulation tower (pos. 40) is fed by conveyors (pos. 49) to the transfer unit, where the granules are treated with fatty acids. Fatty acids are pumped by pumps (pos. 58) from railway tanks to a collection tank (pos. 59). Which is equipped with a coil with a heating surface of 6.4 m2. Mixing is carried out by pumps (pos. 60) and the same pumps supply fatty acids to the nozzles of the dosing unit, through which they are sprayed with compressed air at a pressure of up to 0.5 MPa and a temperature of at least 200°C. The design of the nozzles ensures the creation of an elliptical section of the spray jet. Processed granulated ammonium nitrate is poured onto conveyors (pos. 50) of the second lift from which ammonium nitrate is discharged into bunkers (pos. 54) in cases of bulk loading. From the conveyors (pos. 50), ammonium nitrate enters the conveyors (pos. 51) from where it is dumped into mounted bunkers (pos. 52). After the mounted hoppers, the amnitrate enters the automatic scales (pos. 53) weighing portions of 50 kilograms and then to the packaging unit. With the help of a packaging machine, ammonium nitrate is packed into valve plastic bags and dumped by reversible conveyors (pos. 55), from where it goes to warehouse conveyors (pos. 56), and from them to loading machines (pos. 57). From loading machines (pos. 57), ammonium nitrate is loaded into wagons or vehicles. Storage of finished products in warehouses is provided in the absence of rail transport and vehicles.

The finished product - granulated ammonium nitrate must comply with the requirements of the state standard GOST 2 - 85.

The project provides for the collection of spills of ammonium nitrate after packaging machines. An additional conveyor (pos. 62) and an elevator (pos. 63) are installed. Ammonium nitrate spilled during filling into bags through slime is poured down streams onto the conveyor (pos. 62), from where it enters the elevator (pos. 63). From the elevator, ammonium nitrate enters the mounted bins (pos. 52) where it mixes with the main flow of spent ammonium nitrate.

1.7 Material calculations of production

We expect material calculations of production for 1 ton of finished products - granulated ammonium nitrate.

Material grows neutralizing

Initial data:

The loss of ammonia and nitric acid per ton of ammonium nitrate is determined based on the neutralization reaction equation.

The process is carried out in an ITN apparatus with natural circulation of ammonium nitrate solution.

To obtain one ton of salt by the reaction

NH3 + HNO3 = NH4NO3 + 107.7 kJ/mol

Consumed 100% HNO3

Consumed 100% NH3

where: 17, 63, 80 molecular weights of ammonia, nitric acid and ammonium nitrate.

The practical consumption of NH3 and HNO3 will be somewhat higher than the theoretical one, since in the process of neutralization the loss of reagents with juice vapor is inevitable, through leaky communications, due to the greater decomposition of the reacting components. The practical consumption of reagents, taking into account losses in production, will be:

787.5 1.01 = 795.4 kg

55% HNO3 consumed will be:

Loss of acid will be:

795.4 - 787.5 = 7.9 kg

Consumption 100% NH3

212.4 1.01 = 214.6 kg

The loss of ammonia will be:

214.6 - 212.5 = 2.1 kg

1446.2 kg of 55% HNO3 contains water:

1446.2 - 795.4 = 650.8 kg

The total amount of ammonia and acid reagents entering the neutralizer will be:

1446.2 + 214.6 \u003d 1660.8 × 1661 kg

In the ITN apparatus, water evaporates due to the heat of neutralization, and the concentration of the resulting ammonium nitrate solution reaches 80%, so an ammonium nitrate solution will come out of the neutralizer:

This solution contains water:

1250 - 1000 = 250 kg

This evaporates water during the neutralization process.

650.8 - 250 = 400.8? 401 kg

Table 1.2 - Material balance of neutralization

Material calculation of the evaporation department

Initial data:

Steam pressure - 1.2 MPa

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