What is saltpeter made from? Production of ammonium nitrate
Ammonium nitrate is obtained by neutralizing nitric acid with gaseous ammonia according to the reaction:
NH 3 (g) + НNO 3 (l) NH 4 NO 3 +144.9 kJ
This almost irreversible reaction proceeds at a high rate and with the release of a significant amount of heat. Usually it is carried out at a pressure close to atmospheric; in some countries, neutralization plants operate at a pressure of 0.34 MPa. In the production of ammonium nitrate, dilute 47-60% nitric acid is used.
The heat of the neutralization reaction is used to evaporate the water and concentrate the solution.
Industrial production includes the following stages: neutralization of nitric acid with gaseous ammonia in the ITN apparatus (use of neutralization heat); saltpeter solution evaporation, saltpeter melt granulation, granule cooling, surfactant granule processing, saltpeter packaging, storage and loading, gas emissions and wastewater treatment. Additives are introduced during the neutralization of nitric acid.
Figure 1 shows a diagram of a modern large-tonnage AS-72 unit with a capacity of 1360 t/day.
Rice. one.
1 - acid heater; 2 - ammonia heater; 3 - ITN devices; 4 - 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
The incoming 58-60% nitric acid is heated in the heater 1 to 70-80 o C with juice vapor from the apparatus ITN 3 and is fed to neutralization. Before apparatus 3, thermal phosphoric and sulfuric acids are added to nitric acid in an amount of 0.3-0.5% P 2 O 5 and 0.05-0.2% ammonium sulfate, counting on the finished product.
Sulfuric and phosphoric acids are supplied by plunger pumps, the performance of which is easily and precisely regulated. The unit is equipped with two neutralization devices operating in parallel. Gaseous ammonia is also supplied here, heated in the heater 2 by steam condensate to 120-130 ° C. The amount of nitric acid and ammonia supplied is regulated so that the solution has a slight excess of nitric acid at the outlet of the ITN apparatus, ensuring the complete absorption of ammonia.
In the lower part of the apparatus is the neutralization of acids at a temperature of 155-170°C to obtain a 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 HN0 3 vapor. Part of the heat from the juice vapor is used to heat the nitric acid. Next, the juice steam is sent for cleaning in washing scrubbers and then released into the atmosphere.
An acid solution of ammonium nitrate is sent to the neutralizer 4, where ammonia is supplied in the amount necessary to neutralize the solution. Then the solution is fed into the evaporator 5 on the doupar, which is conducted by water vapor at a pressure of 1.4 MPa and air heated to about 180°C. The resulting melt, containing 99.8-99.7% of saltpeter, passes through a filter 21 at 175 ° C and is fed by a centrifugal submersible pump 20 into a pressure tank 5, and then into a rectangular metal granulation tower 16 with a length of 11 m, a width of 8 m and a height of top to the cone 52.8 m.
In the upper part of the tower are granulators 7 and 8; air is supplied to the lower part of the tower, cooling drops of saltpeter, which turn into granules. The drop height of saltpeter particles is 50--55m. The design of the granulators ensures the production of granules of a uniform granulometric composition with a minimum content of small granules, which reduces the entrainment of dust from the tower by air. The temperature of the granules at the outlet of the tower is 90--110°C, so they are sent for cooling to the fluidized bed apparatus 15. The fluidized bed apparatus is a rectangular apparatus having three sections and equipped with a grate with holes. Air is supplied under the grate by fans, thus creating a fluidized layer of saltpeter granules 100--150 mm high, which come through the conveyor from the granulation tower. There is an intensive cooling of the granules to a temperature of 40°C (but not higher than 50°C), corresponding to the conditions for the existence of modification IV. If the temperature of the cooling air is below 15°C, then before entering the fluidized bed apparatus, the air is heated in the heat exchanger to 20°C. In the cold period of time, 1-2 sections can be in operation.
The air from the apparatus 15 enters the granulation tower for the formation of granules and their cooling.
Ammonium nitrate granules from the fluidized bed apparatus are fed by conveyor 14 for treatment with a surfactant into a rotating drum 11. Here, the granules are sprayed with a sprayed 40% aqueous solution of the NF dispersant. After that, the saltpeter passes through an electromagnetic separator to separate accidentally trapped metal objects and is sent to the bunker, and then for weighing and packaging in paper or plastic bags. Bags are conveyed by a conveyor for loading into wagons or to a warehouse.
The air leaving the upper part of the granulation tower is contaminated with ammonium nitrate particles, and the juice vapor from the neutralizer and the vapor-air mixture from the evaporator contain unreacted ammonia and nitric acid and particles of entrained ammonium nitrate. For cleaning in the upper part of the granulation tower, six parallel-operating washing plate-type scrubbers 10 are installed, irrigated with a 20-30% solution of ammonium nitrate, which is supplied by a pump 18 from the tank. Part of this solution is diverted to the ITN neutralizer for washing the juice steam, and then mixed with the ammonium nitrate solution and, therefore, goes to the production of products.
Part of the solution (20-30%) is continuously withdrawn from the cycle, so the cycle is depleted and replenished with the addition of water. At the outlet of each scrubber, a fan 9 with a capacity of 100,000 m 3 / h is installed, which sucks air from the granulation tower and releases it 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 nitric acid and ammonia supplied 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.
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 device 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 processing 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.
INTRODUCTION
The nitrogen industry is one of the fastest growing industries.
Nitric acid is one of the starting products for the production of most nitrogen-containing substances and is one of the most important acids.
In terms of production scale, nitric acid ranks second among various acids after sulfuric acid. The large scale of production is explained by the fact that nitric acid and its salts have become very important in the national economy.
The consumption of nitric acid is not limited to the production of fertilizers. It finds wide application in the production of all types of explosives, a number of technical salts, in the organic synthesis industry, in the production of sulfuric acid, in rocket technology, and in many other branches of the national economy.
The industrial production of nitric acid is based on the catalytic oxidation of ammonia with atmospheric oxygen, followed by the absorption of the resulting nitrogen oxides by water.
The purpose of this course project is to consider the first stage of the production of nitric acid - the contact oxidation of ammonia, as well as the calculation of the material and heat balances of the reactor.
In technological schemes for the production of nitric acid, the process of catalytic oxidation of ammonia is important, since it determines three main indicators - ammonia consumption, investments and losses of platinum metals, as well as the energy capabilities of the scheme. In this regard, the improvement of the process of catalytic oxidation of ammonia is of great importance for the production of nitric acid and mineral fertilizers in general.
1. CHARACTERISTICS OF NITRIC ACID
1.1 Varieties of nitric acid
In industry, 2 grades of nitric acid are used: dilute (weak) with a content of 30-60% HNO3 and concentrated, containing 97-99% HNO3, as well as a relatively small amount of reactive and highly pure nitric acid. The quality of the produced nitric acid must meet the established standards.
According to physicochemical parameters, concentrated nitric acid must meet the standards specified in table 1.
Table 1 - Requirements for the quality of concentrated nitric acid (GOST 701-89)
The quality of the produced nitric acid must comply with the established standards indicated in tables 2 and 3.
Table 2 - Quality requirements for non-concentrated nitric acid (OST 6-03-270-76)
Table 3 - Requirements for the quality of nitric acid (GOST 4461-67)
Content in %, not more 005Sulfates (SO42)-0.00020.00050.002Phosphates (PO43-)0.000020.00020.002Chlorides (Cl-)0.000050.00010.0005Iron (Fe)0.000020.00010.0003Calcium (Ca)0.00050 .0010.002Arsenic (As)0.0000020.0000030.00001Heavy metals (Pb)0.000020.00050.0005
1.2 Use of nitric acid
Nitric acid is used in various fields of activity:
1)at galvanization and chromium plating of details; )for the production of mineral fertilizers; )to obtain explosives (military industry); )in the production of medicines (pharmaceuticals); )obtaining silver nitrate for photography; )for etching and engraving of metal forms; )as a raw material for obtaining concentrated nitric acid; )in hydrometallurgy; )in jewelry - the main way to determine gold in a gold alloy; )to obtain aromatic nitro compounds - precursors of dyes, pharmacological preparations and other compounds used in fine organic synthesis; )to obtain nitrocellulose. 1.3 Properties of nitric acid 3.1 Physical properties of nitric acid Nitric acid is one of the strong monobasic acids with a pungent suffocating odor, is sensitive to light and, in bright light, decomposes into one of the nitrogen oxides (also called brown gas - NO2) and water. Therefore, it is desirable to store it in dark containers. In a concentrated state, it does not dissolve aluminum and iron, so it can be stored in appropriate metal containers. Nitric acid - is a strong electrolyte (like many acids) and a very strong oxidizing agent. It is often used in reactions with organic substances. Nitrogen in nitric acid is tetravalent, oxidation state +5. Nitric acid is a colorless liquid fuming in air, melting point -41.59 , boiling point +82.6 with partial expansion. The solubility of nitric acid in water is not limited. Aqueous solutions of HNO3 with a mass fraction of 0.95-0.98 are called "fuming nitric acid", with a mass fraction of 0.6-0.7 - concentrated nitric acid. Forms an azeotropic mixture with water (mass fraction 68.4%, d20 = 1.41 g/cm, Tboil = 120.7 )
When crystallized from aqueous solutions, nitric acid forms crystalline hydrates: ) HNO3 H2O monohydrate, Tmelt = -37.62 ;
2) HNO3 3H2O trihydrate, Tmelt = -18.47 .
Nitric acid, like ozone, can be formed in the atmosphere during lightning flashes. Nitrogen, which makes up 78% of atmospheric air, reacts with atmospheric oxygen to form nitric oxide NO. Upon further oxidation in air, this oxide turns into nitrogen dioxide (brown gas NO2), which reacts with atmospheric moisture (clouds and fog), forming nitric acid. But such a small amount is completely harmless to the ecology of the earth and living organisms. One volume of nitric acid and three volumes of hydrochloric acid form a compound called aqua regia. It is able to dissolve metals (platinum and gold) that are insoluble in ordinary acids. When paper, straw, cotton are introduced into this mixture, vigorous oxidation will occur, even ignition. 1.3.2 Chemical properties of nitric acid Nitric acid exhibits different chemical properties depending on the concentration and the substance with which it reacts. If nitric acid is concentrated: 1) with metals - iron (Fe), chromium (Cr), aluminum (Al), gold (Au), platinum (Pt), iridium (Ir), sodium (Na) - does not interact due to the formation of a protective film on their surface , which does not allow further oxidation of the metal. With all other metals<#"justify">HNO3 conc + Cu = Cu(NO3)2 + 2NO2 + H2O (1)
2) with non-metals<#"justify">HNO3 conc. + P = H3PO4 + 5NO2 + H2O (2)
If nitric acid is dilute: 1) when interacting with alkaline earth metals, as well as with zinc (Zn), iron (Fe), it is oxidized to ammonia (NH3) or to ammonium nitrate (NH4NO3). For example, when reacting with magnesium (Mg): HNO3 diluted + 4Zn = 4Zn(NO3)2 + NH4NO3 + 3H2O (3)
But nitrous oxide (N2O) can also be formed, for example when reacting with magnesium (Mg): HNO3 diluted + 4Mg = 4Mg(NO3)2 + N2O + 3H2O (4)
Reacts with other metals to form nitric oxide (NO), for example, dissolves silver (Ag): HNO3 diluted + Ag = AgNO3 + NO + H2O (5)
2) reacts similarly with non-metals, such as sulfur<#"justify">HNO3 diluted + S = H2SO4 + 2NO (6)
Oxidation of sulfur to the formation of sulfuric acid and the release of gas - nitrogen oxide; 3) chemical reaction with metal oxides, for example, calcium oxide: HNO3 + CaO = Ca(NO3)2 + H2O (7)
Salt (calcium nitrate) and water are formed; ) chemical reaction with hydroxides (or bases), for example, with slaked lime: HNO3 + Ca(OH)2 = Ca(NO3)2 + H2O (8)
Salt (calcium nitrate) and water are formed - a neutralization reaction; ) chemical reaction with salts, for example with chalk: HNO3 + CaCO3 = Ca(NO3)2 + H2O + CO2 (9)
A salt (calcium nitrate) and another acid (in this case, carbonic acid, which decomposes into water and carbon dioxide) is formed. 6) depending on the dissolved metal, the decomposition of salt at temperature occurs as follows: a) any metal (denoted as Me) up to magnesium (Mg): MeNO2 + O2 (10)
b) any metal from magnesium (Mg) to copper (Cu): 3 = MeO + NO2 + O2 (11)
c) any metal after copper (Cu): 3 = Me + NO2 + O2(12) 2. METHODS FOR OBTAINING NITRIC ACID nitric acid catalyst ammonia Industrial methods for producing dilute nitric acid include the following steps: ) obtaining nitric oxide (II); 2) its oxidation to nitric oxide (IV); 3) absorption of NO2 by water; 4) purification of exhaust gases (mainly containing molecular nitrogen) from nitrogen oxides. Concentrated nitric acid is obtained in two ways: 1) the first method consists in the rectification of ternary mixtures containing nitric acid, water and water-removing substances (usually sulfuric acid or magnesium nitrate). As a result, vapors of 100% nitric acid (which condense) and aqueous solutions of the dewatering agent are obtained, the latter is evaporated and returned to production; 2) the second method is based on the reaction: N2O4(t) + 2H2O(l) + O2(g) = 4HNO3(l) + 78.8 kJ (13)
At a pressure of 5 MPa and using pure O2, 97-98% acid is formed, containing up to 30% by weight of nitrogen oxides. Target product is obtained by distillation of this solution. High purity nitric acid is obtained by distillation with 97-98.5% nitric acid in silicate or quartz glass equipment. The content of impurities in such an acid is less than 110-6% by weight. 3. RAW MATERIAL BASE IN THE PRODUCTION OF NON-CONCENTRATED NITRIC ACID The main raw materials for the production of non-concentrated nitric acid are currently ammonia, air and water. Auxiliary material and energy resources are catalysts for ammonia oxidation and exhaust gas purification, natural gas, steam and electricity. 1. Ammonia. Under normal conditions, it is a colorless gas with a pungent odor, readily soluble in water and other solvents, forms hemi- and monohydrates. A turning point in the development of synthetic ammonia production was the use of the currently dominant method in industry for producing hydrogen by converting methane contained in natural gas into associated petroleum gases and refined petroleum products. The content of impurities in liquid ammonia is regulated by GOST 6221-82. The most typical impurities are: water, lubricating oils, catalyst dust, scale, ammonium carbonate, dissolved gases (hydrogen, nitrogen, methane). If GOST is violated, impurities contained in ammonia can get into the ammonia-air mixture and reduce the output of nitrogen oxide (II), and hydrogen and methane can change the explosive limits of the ammonia-air mixture. Air. For technical calculations, it is assumed that dry air contains [%, (vol.)]: N2 = 78.1, O2 = 21.0, Ar2 = 0.9, H2O = 0.1-2.8. There may also be traces of SO2, NH3, CO2 in the air. In the area of industrial sites, the air is polluted with dust of various origins, as well as various components of fugitive gas emissions (SO2, SO3, H2S, С2H2, Cl2, etc.). The amount of dust in the air is 0.5-1.0 mg/m3. 3. Water. It is used in the production of nitric acid for irrigation of the absorption column, for generating steam during heat recovery in waste heat boilers, for cooling reaction apparatuses. For the absorption of nitrogen oxides, steam condensate and chemically purified water are most often used. In some schemes, it is allowed to use ammonium nitrate juice vapor condensate. In any case, the water used to irrigate the columns should not contain free ammonia and solid suspensions, the content of chloride ion should not exceed 2 mg/l, oils should not exceed 1 mg/l, NH4NO3 should not exceed 0.5 g/l . Chemically purified water for waste heat boilers must comply with the requirements of GOST 20995-75. Process water intended for heat removal in heat exchangers and equipment cooling (circulating water) must meet the following requirements: carbonate hardness not more than 3.6 meq/kg, suspended solids content not more than 50 mg/kg, pH value 6.5-8 ,5. 4. Oxygen. It is mainly used in the production of concentrated nitric acid by direct synthesis. In some cases, it is used to enrich the ammonia-air mixture when obtaining non-concentrated nitric acid. 4. CONTACT OXIDATION OF AMMONIA 4.1 Physical and chemical bases of the process Modern methods for the production of nitric acid are based on the contact oxidation of ammonia. During the oxidation of ammonia on various catalysts and depending on the conditions, the following reactions occur: NH3 + 5O2 = 4NO + 6H2O + 907.3 kJ (14)
4NH3 + 4O2 = 2N2O + 6H2O + 1104.9 kJ (15)
4NH3 + 3O2 = 2N2 + 6H2O + 1269.1 kJ (16)
In addition to reactions (14-16), others are also possible, occurring in the near-surface layers of the catalyst. For example, the decomposition of NO, the interaction of N2O, NO2 and NH3: NO N2+O2 (17)
2NH3 + 3N2O = 4N2 + 3H2O (18)
NH3 + 6NO2 = 7N2 + 12H2O (19)
Naturally, reaction (14) will be "useful". Thermodynamic calculations show that reactions (14-16) practically proceed to completion. The equilibrium constants for reverse reactions (14-16) at 900°C have the following values (20)
(21)
(22)
K1 = ,(23)
where k1 - NO + H2O; k2 - NH3 + O2. At 900 the catalytic conversion of ammonia into final products reaches 100%, i.e. the process is practically irreversible. However, equations (14-16) do not reflect the actual mechanism of the process, since in this case nine molecules would have to collide simultaneously in reaction (14); in reaction (16) - seven molecules. It's almost unbelievable. Several mechanisms of ammonia oxidation on catalysts have been proposed. Differences in ideas about the mechanisms are as follows: 1) the formation of NO and N2 through an intermediate on the catalyst; 2) the formation of NO occurs on the catalyst, and the formation of N2 on the catalyst and in the volume of gas. Based on the above (about the equilibrium constant and oxidation mechanisms), it can be stated that the chosen catalyst must have high activity (high reaction rate and short contact time: as it increases, the probability of N2 formation increases) and selectivity with respect to reaction (14). Among several mechanisms proposed by our and foreign scientists, the mechanism proposed by L.K. Androsov, G.K. Boreskov, D.A. Epstein. The mechanism can be presented step by step as follows: Stage 1 - oxidation of the platinum surface. A peroxide catalyst-oxygen complex is formed (Figure 1). Figure 1 - Structure of the peroxide catalyst-oxygen complex stage - diffusion and adsorption of ammonia on the surface of platinum covered with oxygen. A catalyst-oxygen-ammonia complex is formed (Figure 2). Figure 2 - Structure of the catalyst-oxygen-ammonia complex the stage is the redistribution of electronic bonds, the breaking of old bonds and the strengthening of new bonds. stage - desorption of products and diffusion into the gas flow (stable NO and H2O compounds are removed from the surface). The liberated centers adsorb oxygen again, since the diffusion rate of oxygen is higher than that of ammonia, etc. According to scientists, oxygen entering the catalyst lattice (non-platinum contact) does not participate in the ammonia oxidation reaction (proved using the method of labeled atoms). The conversion of ammonia into nitrogen, according to I.I. Berger and G.K. Boreskov, can occur in volume as a result of reactions of ammonia, both with oxygen and with nitric oxide. There are kinetic, transition and diffusion regions of the process. The kinetic region is characteristic of low temperatures: it is limited by the ignition temperature of the catalyst, at which rapid spontaneous heating of its surface is noted, i.e., up to the ignition temperature, the rate is limited by the rate of the chemical reaction at the contact. At T > Tzazh already diffusion controls the process - the chemical reaction is fast. The process passes into the diffusion region. It is this area (600-1000 ) is typical for a stationary autothermal process under industrial conditions. This implies an indispensable increase in the volumetric velocity of the gas and a decrease in the contact time. The oxidation reaction of ammonia on active catalysts starts earlier: on palladium (Pd) at 100 , on platinum (Pt) at 145 , on iron (Fe) at 230 , on metal oxides, the temperature of the onset of the reaction varies widely. At the same time, it reaches a sufficient rate and degree of transformation at T > 600 .
4.2 Ammonia oxidation catalysts Almost all nitric acid plants use platinum or its alloys as a catalyst for the oxidation of ammonia. Platinum is an expensive catalyst, but it retains high activity for a long time, has sufficient stability and mechanical strength, and is easily regenerated. Finally, with the modern network form of the catalyst, the use of platinum makes it possible to use the simplest type of contact apparatus. It is easily ignited, and its consumption per unit of production is negligible. In the production of nitric acid, carriers for platinum and its alloys are not used, since in the presence of carriers, the activity of the catalyst decreases relatively quickly and its regeneration becomes more difficult. At modern plants, platinum for catalysts is used in the form of grids. The mesh form creates a large catalyst surface in the contact apparatus at a relatively low consumption of platinum. Grids are usually used in which the wire diameter is 0.045-0.09 mm with dimensions on the cell side of 0.22 mm. The area of nets not occupied by wire is approximately 50-60% of its total area. When using threads of a different diameter, the number of weaves is changed so that the free area not occupied by the wire remains within the specified limits. In contact devices operating under atmospheric pressure. install from 2 to 4 grids, mostly 3, and in devices operating under pressure up to 8 atm - from 13 to 16 grids. When one grid is installed, some of the ammonia molecules do not come into contact with the catalyst, which reduces the yield of nitric oxide. Under the best conditions, the degree of contact can reach 86-90% on one mesh, 95-97% on two meshes, and 98% on three meshes. When working under atmospheric pressure, more than 4 grids are not used, since with a large number of grids, although the performance of the contact apparatus increases, the resistance to gas flow increases greatly. Grids should fit snugly to each other, because, otherwise, in the free space between the grids, a number of homogeneous reactions occur, reducing the output of nitric oxide. In the process of work, platinum grids are greatly loosened. Their smooth and shiny threads become spongy and matte, elastic nets become brittle. The formation of a spongy, loosened surface increases the thickness of the threads. All this creates a highly developed network surface, which increases the catalytic activity of platinum. Only poisoning of the catalyst with impurities coming with gases can subsequently cause a decrease in its activity. The loosening of the surface of platinum gauzes over time leads to a strong destruction of the gauzes, which causes large losses of platinum. Platinum intended for the manufacture of a catalyst should not contain iron, which already at 0.2% significantly reduces the yield of nitrogen oxide. Pure platinum is rapidly destroyed at high temperatures, and its smallest particles are carried away with the gas flow. Other metals of the platinum group in their pure form are not used as catalysts. Palladium breaks down quickly. Iridium and rhodium are not very active. Osmium is easily oxidized. Platinum alloys have been studied and applied, which have greater strength and no less activity than pure platinum. In practice, alloys of platinum with iridium or with rhodium and sometimes with palladium are used. Grids made of an alloy of platinum with 1% iridium at high temperatures are more active than platinum ones. Significantly greater activity and, in particular, mechanical strength are characteristic of platinum-rhodium alloys. The best yield of nitric oxide is obtained when working on platinum alloys, which contain 10% rhodium. However, given the higher cost of rhodium compared to platinum, its content in alloys is usually reduced to 7-5%. When ammonia is oxidized under pressure on platinum-rhodium grids, a significantly higher yield of nitric oxide is obtained than on pure platinum grids. Platinum catalysts are sensitive to certain impurities contained in the feed gas. Thus, the presence of 0.00002% phosphine (РН3) in the gas reduces the degree of conversion to 80%. Less powerful poisons are hydrogen sulfide, acetylene vapors, lubricating oils, iron oxides and other substances. Grids are regenerated by treating them with a 10-15% hydrochloric acid solution at 60-70°C for 2 hours. Then the grids are thoroughly washed with distilled water, dried and calcined in a hydrogen flame. In the course of operation, the physical structure of the grids changes and the mechanical strength of the alloy decreases, which increases the loss of metal and reduces the service life of the catalyst. 4.3 Composition of the gas mixture. Optimal ammonia content in the ammonia-air mixture Air is mainly used to oxidize ammonia. The oxygen consumption for the oxidation of ammonia according to reaction (24) with the formation of NO can be calculated as follows: NH3 + 5O2 = 4NO + 6H2O (24)
According to reaction (24), 1 mole of NH3 accounts for 1.25 moles of O2 = , then - the content of NH3 can be expressed as follows:
where - amount of NH3 mixed with air; 100 - the total amount of the mixture (%). However, this is theoretical. For practical purposes, a certain excess of oxygen is used, then the ammonia concentration will be less than 14.4% (vol.). The optimal concentration of ammonia in the ammonia-air mixture is its highest content, at which a high NO output is still possible at a ratio of O2:NH3< 2. A sharp decrease in the degree of conversion is observed with a decrease in the ratio of O2:NH3< 1,7 и содержании NH3 в смеси равном 11,5 % (об.). Если увеличивать соотношение O2:NH3, например, >2, the conversion rate increases significantly. So the important point is: 1) on the one hand, an increase in the NH3 content in the ammonia-air mixture, i.e., a decrease in the O2:NH3 ratio, leads to a decrease in the degree of ammonia conversion; 2) on the other hand, with an increase in the content of NH3 in the ammonia-air mixture, the temperature of the system increases, since more heat is released according to reactions (14-16), and the degree of conversion increases, as can be seen from table 4. Table 4 - Dependence of the degree of conversion of ammonia on its content in the ammonia-air mixture (P = 0.65 MPa) NH3 content in the mixture, % (vol.) O2:NH3 ratio Conversion temperatures, NH3 conversion rate, %9.531.9874391.8810.421.7878693.1610.501.7678993.3011.101.6782894.2111.531.5983495.30 From Table 4 it follows that an increase in temperature from 740 to 830°C at a ratio of O2:NH3 in the range of 1.6-2 favorably affects the process. At a ratio of O2:NH3< 1,35 лимитирующая стадия процесса - диффузия кислорода. An excess of O2 is necessary to ensure that the surface of platinum is always covered with oxygen in order to carry out the oxidation process according to the mechanism considered earlier and to exclude the formation of N2 and N2O (with a lack of oxygen). It must be more than 30%, i.e. O2:NH3 ratio > 1.62. The composition of the gas will also depend on the flow of the second stage of obtaining nitric acid (oxidation of NO) 2NO + 1.5O2 + H2O = 2HNO3 (25)
It also requires an excess of oxygen: 1) for systems operating under pressure - 2.5%; 2) for systems operating at atmospheric pressure - 5%. The overall reaction that determines the oxygen demand for the production of nitric acid is written as follows NH3 + 2O2 = HNO3 + H2O (26)
There is one more circumstance, due to which it is undesirable to increase the concentration of ammonia above 9.5% (vol.). In this case, there is a decrease in the concentration of nitrogen oxides in the absorption towers due to the introduction of additional oxygen (i.e., NO is being diluted). Thus, 9.5% (vol.) is the optimal ammonia content for all stages of obtaining dilute nitric acid. You can use oxygen instead of air for oxidation. Then, in accordance with the overall reaction (26), it is necessary to increase the concentration of ammonia to 33.3% (vol.). However, safety precautions come into play here, since a mixture with such a concentration of ammonia becomes explosive (table 5). Table 5 - Lower (LEL) and upper (URL) explosive limits for ammonia-oxygen-nitrogen mixtures With an increase in gas humidity, the explosive limits narrow, i.e., it is possible to use steam-oxygen conversion of ammonia. Mixtures of ammonia with oxygen ignite with an explosion (Tflax = 700-800 ). Within these temperature limits, self-ignition occurs at any ammonia content in the ammonia-oxygen mixture. Practically used ammonia-air mixtures (ammonia concentration 9.5-11.5% (vol.)) are not explosive (table 5). There are dependences of the explosive limits of the ammonia-air mixture on the content of ammonia and oxygen at various pressures. However, it should be noted that the speed of propagation of the explosion is low and for the ammonia-air mixture is 0.3-0.5 m/s. That is, to eliminate the possibility of explosion propagation, it is necessary to create a gas velocity greater than this value (0.5 m/s). This is exactly what is achieved by using active platinoid catalysts in the process, where the contact time is 10-4 sec and, consequently, the linear velocity is more than 1.5 m/s. 4.4 Oxidation of ammonia under pressure The purpose of pressurization is: 1) the need to increase the speed of the process; 2) compact installations. It has been thermodynamically proven that even at high pressures the NO yield is close to 100%. The performance of the converter increases with increasing pressure and increasing the number of grids of the platinoid catalyst. With increasing pressure, the process temperature also increases above 900 . However, with increasing pressure, in order to achieve a high degree of NH3 conversion, it is necessary to increase the residence time of the gas in the converter which in turn leads to an increase in the number of grids. The main disadvantage is the increased loss of platinum (Pt) catalyst at high temperatures. These shortcomings (loss of platinum, decrease in the degree of conversion) can be eliminated by resorting to a combined production scheme, i.e., carrying out the process of NH3 oxidation at atmospheric pressure or close to it, and NO oxidation and absorption at elevated pressure. This approach is often implemented in the technological schemes of many countries. At the same time, energy costs for gas conditioning increase the cost of nitric acid. 4.5 Optimum conditions for ammonia oxidation Temperature. The reaction of ammonia on platinum begins at 145 , but proceeds with a low NO yield and the formation of predominantly elemental nitrogen. An increase in temperature leads to an increase in the yield of nitric oxide and an increase in the reaction rate. In the range of 700-1000 NO yield can be increased to 95-98%. Contact time at temperature increase from 650 to 900 is reduced by about five times (from 5 10-4 to 1.1 10-4 sec). The required temperature regime of the process can be maintained by the heat of the oxidation reactions. For a dry ammonia-air mixture containing 10% NH3, at a conversion rate of 96%, the theoretical gas temperature rise is approximately 705 or about 70 for each percentage of ammonia in the initial mixture. Using an ammonia-air mixture containing 9.5% ammonia, it is possible, due to the thermal effect of the reaction, to reach a temperature of about 600 , to further increase the conversion temperature, preheating of the air or ammonia-air mixture is necessary. It should be borne in mind that the ammonia-air mixture can only be heated to a temperature not exceeding 150-200 at a heating gas temperature of not more than 400 . Otherwise, the dissociation of ammonia or its homogeneous oxidation with the formation of elemental nitrogen is possible. The upper limit of the increase in the temperature of the contact oxidation of ammonia is determined by the loss of the platinum catalyst. If up to 920 Since the loss of platinum is to some extent compensated by an increase in the activity of the catalyst, then above this temperature, the increase in catalyst losses significantly outpaces the increase in the reaction rate. According to factory data, the optimum conversion temperature of ammonia under atmospheric pressure is about 800 ; on installations operating under a pressure of 9 atm, it is equal to 870-900 .
Pressure. The use of increased pressure in the production of dilute nitric acid is mainly associated with the desire to increase the rate of oxidation of nitric oxide and the processing of the resulting nitrogen dioxide into nitric acid. Thermodynamic calculations show that even at elevated pressure the equilibrium NO yield is close to 100%. However, a high degree of contact in this case is achieved only with a large number of catalyst gauzes and a higher temperature. Recently, under industrial conditions on multilayer catalysts with thorough gas purification and a temperature of 900 managed to bring the degree of conversion of ammonia to 96%. When choosing the optimal pressure, it should be borne in mind that an increase in pressure leads to an increase in platinum losses. This is explained by an increase in the temperature of catalysis, the use of multilayer networks, and an increase in their mechanical destruction under the action of a high gas velocity. 3. The content of ammonia in the mixture. Air is usually used to oxidize ammonia, so the ammonia content in the mixture is determined by the oxygen content in the air. At a stoichiometric ratio of O2:NH3 = 1.25 (ammonia content in a mixture with air is 14.4%), the yield of nitrogen oxide is not significant. To increase the NO yield, some excess of oxygen is required; therefore, the ammonia content in the mixture should be less than 14.4%. In factory practice, the ammonia content in the mixture is maintained within the range of 9.5-11.5%, which corresponds to the ratio O2:NH3 = 21.7. The overall reaction (26), which determines the need for oxygen during the processing of ammonia into nitric acid, gives the ratio O2:NH3 = 2, which corresponds to the ammonia content in the initial mixture of 9.5%. This suggests that an increase in the ammonia concentration in the mixture above 9.5% will ultimately not lead to an increase in the NO concentration, since in this case additional air will have to be introduced into the adsorption system. If an ammonia-oxygen mixture is used as initial reagents, then, in accordance with the equation of the overall reaction, it would be possible to increase the concentration of ammonia in it to 33.3%. However, the use of high concentrations of ammonia is difficult because such mixtures are explosive. Influence of impurities. Platinum alloys are sensitive to impurities contained in the ammonia-air mixture. In the presence of 0.0002% hydrogen phosphide in the gas mixture, the degree of ammonia conversion is reduced to 80%. Less strong contact poisons are hydrogen sulfide, acetylene, chlorine, lubricating oil vapors, dust containing iron oxides, calcium oxide, sand, etc. Preliminary purification of gases increases the duration of the catalyst. However, over time, the catalyst is gradually poisoned and the NO yield decreases. To remove poisons and contaminants, the grids are periodically regenerated by treating them with a 10-15% hydrochloric acid solution. 5. Contact time. The optimal contact time is determined by the rate of ammonia oxidation. Most often, the oxidation rate is defined as the amount of oxidized ammonia (kg) per unit area (m2) per day (catalyst intensity). The duration of contact of the gas with the catalyst, or the contact time, is determined by the equation: Vsv / W where t is the residence time of the gas in the catalyst zone, sec; Vw is the free volume of the catalyst, m3; W - volumetric velocity in contact conditions m3 sec-1. The maximum degree of conversion of ammonia into nitric oxide is achieved at a well-defined time of contact of the gas with the catalyst. The optimal contact time should be considered not the one at which the maximum NO yield is achieved, but somewhat shorter, since it is economically advantageous to work at a higher productivity even at the expense of a decrease in the product yield. Under practical conditions, the contact time of ammonia with the catalyst ranges from 1 10-4 to 2 10-4 sec. Mixing ammonia with air. The complete homogeneity of the ammonia-air mixture entering the contact zone is one of the main conditions for obtaining a high yield of nitric oxide. Good mixing of gases is of great importance not only to ensure a high degree of contact, but also to protect against the risk of explosion. The design and volume of the mixer must fully ensure good mixing of the gas and exclude the slip of ammonia in separate jets onto the catalyst. 5. CONTACT DEVICES The most complex and undergone significant improvements is the design of the contact apparatus itself. Figure 3 - Ostwald contact apparatus: 1 - ammonia-air mixture collector; 2 - platinum spiral; 3 - viewing window; 4 - nitrous gas collector The first industrial contact apparatus was the Ostwald apparatus (Figure 3), consisting of two concentric pipes: an outer cast-iron pipe with a diameter of 100 mm, enameled on the inside, and an inner one made of nickel with a diameter of 65 mm. The ammonia-air mixture entered the apparatus from below through the outer pipe and fell on the catalyst located in the upper part of the inner pipe. The nitrous gases were directed down through the inner pipe to the collector, giving off heat to the incoming mixture. The catalyst consisted of strips of platinum foil 0.01 mm thick and 20 mm wide coiled together into a spiral. One of the tapes is smooth, the second is corrugated with 1 mm bends. The degree of ammonia conversion reached 90-95%, the mixture with air contained NH3 8% (vol.), the productivity of the apparatus was 100 kg of nitric acid per day. This form of the catalyst did not allow increasing the productivity of the apparatus by increasing its size. In the Ostwald apparatus, the uniform supply of the gas mixture was not ensured, since before entering the catalyst, the gas flow changed its direction by 180° and only then entered it. In addition, the design of the apparatus did not allow the rapid removal of nitrogen (II) oxides from the high temperature zone. In subsequent designs of the contact apparatus, a catalyst was used in the form of a grid of filaments with a diameter of 0.06 mm. Figure 4 - Andreev's contact apparatus: 1 - platinum grids; 2 - viewing window The first nitric acid production in Russia was equipped with Andreev's contact apparatus, which produced 386 kg of nitric acid per day and was considered the most advanced in the world. The cylindrical apparatus with a diameter of 300 mm and a height of 450 mm was made of cast iron. The mixture of gases came from below (Figure 4). The grid of the platinum catalyst was located across the apparatus, in the middle of it. The use of cast iron for the manufacture of this apparatus had a number of disadvantages: the occurrence of side reactions, contamination of platinum with scale. The degree of conversion in it did not exceed 87%. Figure 5 - Fisher's contact apparatus: 1 - nozzle; 2 - platinum grid; 3 - isolation The Fisher apparatus was made of aluminum, its diameter was 1000 mm, height 2000 mm (Figure 5). From below, the apparatus was filled with porcelain Raschig rings, and the upper part was lined with refractory bricks. The design of the apparatus did not provide a uniform supply of the ammonia-air mixture to the catalyst, the yield of oxides was 89–92% at a contact temperature of 700–720°C. Productivity of the device on ammonia is 600-700 kg/days. Particles of refractory bricks, falling on the catalyst, reduced its activity. Figure 6 - Apparatus Bamag: 1 - nozzle; 2 - platinum grid; 3 - viewing window The apparatus proposed by Bamag (Figure 6) consisted of two truncated cones connected by wide bases, between which catalyst grids were placed. The diameter of the apparatus in the widest part was 1.1 m or 2.0 m. The ammonia-air mixture was fed into the apparatus from below. Initially, the apparatus was made of aluminum, then its upper, hot part was made of stainless steel. For better mixing of the mixture, Raschig rings were poured into the lower part of the apparatus. The main disadvantage of these devices was the direction of the gas mixture on the catalyst from below, which led to the vibration of the grids and to an increase in the loss of platinum. Studies of the design of the contact apparatus have shown that the direction of the gas mixture from top to bottom stabilizes the operation of catalyst networks, reduces the loss of an expensive scarce platinum catalyst, increases the degree of conversion by 1.0-1.5% and allows the use of a two-stage catalyst, in which the second stage is used oxide non-platinum catalyst. When a gas mixture is supplied to the apparatus from above, in its lower part, a layer of insulating material can be placed, as well as coils of a steam boiler and a superheater without the risk of contamination of the catalyst with refractory dust and iron scale. This reduces the loss of reaction heat to the environment. A study of the temperature distribution over the catalyst surface showed that the edges of the catalyst adjacent to the walls have a lower temperature, and the degree of contact decreases accordingly, reducing the total yield of nitric oxide (II). In this regard, the geometry of the inlet part of the contact apparatus is of great importance; it should be a smoothly divergent cone with an angle at the top of not more than 30°. Figure 7 - Parsons apparatus: 1 - cylindrical platinum mesh; 2 quartz bottom; 3 - viewing window; 4 - isolation In the United States, a Parsons apparatus was created with a vertical arrangement of a catalyst grid rolled up in the form of a four-layer cylinder 33 cm high and 29 cm in diameter (Figure 7). The platinum cylinder was placed in a metal casing lined with refractory bricks, which ensured good heat exchange with the hot catalyst. The productivity of such an apparatus was up to 1 ton of ammonia per day, the degree of conversion was 95-96%. The advantage of this device is a large catalyst surface compared to the volume of the device. Its disadvantage is the uneven supply of the ammonia-air mixture to the catalyst. More mixture flows through the bottom of the sieve catalyst than through the top. A number of devices of various shapes were tested: in the form of two hemispheres, a cone and a hemisphere with the direction of the gas flow from bottom to top. These devices did not have any special advantages even when the process was carried out up to 0.51 MPa, the degree of conversion did not exceed 90%. Figure 8 - Dupont apparatus: 1 - platinum grids; 2 - grate; 3 - water jacket When carrying out the process at elevated pressure, the DuPont apparatus (Figure 8) became widespread, consisting of cones: the upper one is made of nickel and the lower one is made of heat-resistant steel. The lower case was provided with a water jacket for cooling. The catalyst placed on the grate is made in the form of a package of rectangular grids. Now all over the world they are designing and building units for the production of dilute nitric acid with a large unit capacity - up to 400-600 tons / year. Contact devices with flat layers of grids or a layer of granular material located across the gas flow for such units should have a large diameter of up to 5-7 m. However, with an increase in the diameter of the apparatus, the uniformity of the distribution of the ammonia-air mixture over the cross section of the apparatus deteriorates, and the metal consumption per unit of productivity increases , difficulties in sealing flanged joints increase. Apparatuses of large diameters (over 4 m) cannot be transported by rail, their manufacture at the factory site is associated with serious difficulties. In this regard, the most promising is a converter with a radial flow of the gas mixture through the catalyst, made in the form of a cylinder or cone. With such an arrangement of the catalyst, it is possible, without changing the diameter of the apparatus, to increase its height and, accordingly, its productivity. Designs of devices with a cylindrical arrangement of the catalyst have been known for a long time (Parsons devices), but with an increase in their productivity from 4.5 kg/h to 14.3 t/h of ammonia, problems arose in the distribution of gas mixture flows, heat transfer, catalyst attachment, etc. Figure 9 - Parsons' improved apparatus: 1 - body; 2 - covers; 3 - coolant collector; 4 - support device; 5 - fitting for the output of nitrous gases; 6 - catalyst grids; 7 - channels for refrigerant; 8 - channels for gases One of the new devices is the improved Parsons apparatus (Figure 9). It consists of a body with covers, fittings for the input of the ammonia-air mixture and the output of nitrous gases. The catalyst is platinum grids arranged vertically along the cylindrical surface and fixed under the caps. The grids are stretched on a ceramic support device, which has horizontal channels for supplying the ammonia-air mixture to the contact grids and vertical channels for supplying a coolant. The disadvantage of such a support device is the distribution of the gas entering the catalyst in the form of separate jets, as a result of which the catalyst area does not work completely. Figure 10 - Contact apparatus with radial gas flow: 1 - housing; 2 - cover; 3 - system of supporting elements; 4 - catalyst; 5 - lattice; 6 - blind bottom A device with a radial gas flow is proposed (Figure 10), which consists of a body 1 and a cover with a fitting for introducing an ammonia-air mixture. In the lower part of the housing there is a fitting for introducing nitrous gases. Catalyst gauzes in the form of a cylinder and a cone are arranged vertically. However, this device also does not provide a uniform supply of gases to the catalyst. Figure 11 - Contact device with granular catalyst: 1 cylindrical body; 2 - cover with a central hole; 3, 4 - coaxial cylindrical perforated distribution grids; 5 - annular bottom; 6 - outlet fitting An apparatus with a radial gas flow and a granular catalyst is proposed. As catalysts, platinum metals deposited on a carrier or tablets of a non-platinum catalyst are used (Figure 11). The apparatus in Figure 11 consists of a cylindrical body 1, in the upper part of which an ammonia-air mixture is introduced, and in the lower part nitrous gases are removed. Inside there are two coaxial cylindrical perforated distribution grids 3 and 4, between which a layer of granular catalyst 7 is placed. fitting 6. The ammonia-air mixture at the entrance to the apparatus is divided into two streams. The main part passes into the annular gap between the walls of the housing and the outer distribution cylinder and enters radially on the catalyst. The second, smaller part passes through the hole in the cover and enters the catalyst along the axis. Uniform distribution of the gas mixture in the catalyst is not ensured. The disadvantage of these designs is the overheating of the ammonia-air mixture over 200 near a blind bottom due to a decrease in gas velocity to zero. Overheating of the gas causes overheating of the catalyst gauzes and their increased wear. Figure 12 - Apparatus with a catalyst in the form of a cone: 1 - a shirt for heating gas; 2 - catalyst; 3 - support pipe device; 4 - water jacket The apparatus (Figure 12) contains a catalyst in the form of several layers of a platinum mesh, welded from pieces of a triangular shape into a cone with an apex angle of about 60°. The grid package is based on a structure consisting of 6-12 pipes along the generatrix of the cone, through which the coolant passes. This form of catalyst has a large specific surface (in relation to the volume of the apparatus) compared to a flat catalyst located across the gas flow. However, compared to a cylindrical catalyst, its specific surface area is smaller. Figure 13 - Contact apparatus for the oxidation of ammonia under high pressure: 1 - body; 2 - inner cone; 3 - switchgear; 4 - igniter; 5 - catalyst grids; 6 - superheater; 7 - steam boiler packages; 8 - economizer Figure 13 shows a contact apparatus for the oxidation of ammonia under a pressure of 0.71 MPa. The apparatus consists of two cones inserted into each other. The ammonia-air mixture enters from below into the space between the inner and outer cones, rises and from there descends down the inner cone. On the way to the platinum catalyst, made in the form of grids, the mixture is well mixed in the distribution device of the Raschig rings. To measure the temperatures of the incoming gas mixture and the conversion process, the apparatus is equipped with thermocouples: four before the catalyst and four after it. For gas sampling, there are vapor sampling tubes: four before the catalyst and four after it. The catalyst is ignited with a nitric-hydrogen mixture supplied by means of a rotary burner (igniter). Figure 14 - Grand Paroiss contact apparatus: 1 - case; 2 lattice; 3 - platinum catalyst; 4 - armored mesh; 5 - layer of rings; 6 perforated plate; 7 - superheater; 8 - waste heat boiler Among the devices operating at an average pressure of 0.40-0.50 MPa, the apparatus of the company Grande Paroiss, made of stainless steel, is of interest (Figure 14). It consists of a body, closed on top with an elliptical lid, with an inlet fitting for introducing a gas mixture. Under the cover there is a perforated cone, then a baffle. A distribution grid is placed above the platinum grids, on which lies a layer of six grids that act as a damper for flow velocity pulsations. The disadvantage of the device is the presence of stagnant zones in the region of high temperatures of the catalyst, where the incoming ammonia can decompose. 6. SELECTION AND DESCRIPTION OF THE TECHNOLOGICAL SCHEME FOR THE PRODUCTION OF NON-CONCENTRATED NITRIC ACID Depending on the conditions of the production process, the following types of nitric acid systems are distinguished: 1) systems operating at atmospheric pressure; 2) systems operating at elevated pressure (4-8 atm); 3) combined systems in which the oxidation of ammonia is carried out at a lower pressure, and the absorption of oxides - at a higher pressure. Consider these technological schemes. 1) systems operating at atmospheric pressure; Figure 15 - Scheme of the installation for the production of dilute nitric acid at atmospheric pressure: 1 - water scrubber; 2 - cloth filter; 3 - ammonia-air fan; 4 - cardboard filter; 5 - converter; 6 - steam recovery boiler; 7 - high-speed refrigerator; 8 - refrigerator-condenser; 9 - fan for nitrous gases; 10 - absorption towers; 11 - oxidation tower; 12 - tower for absorption of nitrogen oxides by alkalis; 13 - acid refrigerator; 14, 15 - pumps These systems (Figure 15) are no longer in operation due to the bulkiness of the equipment (a large number of acid and alkaline absorption towers), low productivity, and the accumulation of a certain amount of chlorine, which in acid and alkaline absorption systems has a strong corrosive effect on the equipment, which constantly have to be replaced, and this leads to large economic costs. 2) combined systems; Figure 16 - Obtaining nitric acid by a combined method: 1 - high-speed refrigerator; 2 - refrigerator; 3 - turbocharger engine; 4 - reducer; 5 - turbocompressor of nitrous gases; 6 - turbine for irrigation of exhaust gases; 7 - oxidizer; 8 - heat exchanger; 9 - refrigerator-condenser; 10 - absorption column; 11 - acid valve; 12 - condensate collector; 13, 14 - nitric acid collectors The main advantages of this scheme are: 1. These systems (Figure 16) operate without external energy consumption, since the heat of ammonia oxidation and nitrogen oxide oxidation is sufficient to obtain energy for compressing air and nitrous gases to the required pressures; 2. Compactness of the equipment. 3. The productivity of such units is 1360 tons/day. The disadvantages of the scheme: The main disadvantage of this scheme is that when ammonia is oxidized at a pressure of 9 atm, the degree of conversion is 2–3% less than at atmospheric pressure, and the loss of the platinum catalyst is 2–3 times greater. Thus, this process is more advantageous to carry out under atmospheric pressure. But for modern powerful workshops that produce nitric acid, in this case, a large number of large-sized devices will be required and, consequently, an increase in the cost of construction and installation work. These considerations make it necessary to resort to increasing the pressure in the ammonia conversion process. In this regard, a pressure of about 2.5 atm is acceptable, since the volume of the apparatus is reduced by a factor of 2.5 compared to the volume in systems operating at atmospheric pressure, with moderate losses of ammonia and catalyst. 3) systems operating under high pressure. Advantages of the circuit (Figure 17): 1. The unit is compact, all devices are transportable. The power cycle of the unit is autonomous and, when the chemical production is turned off, remains in operation until it is turned off from the control panel. This allows you to quickly put the unit into operation in case of accidental shutdowns of the chemical process. The control of the unit in the operating mode is automated. 2. The actual cost and energy intensity of nitric acid, produced on units of a single pressure of 0.716 MPa, remains the lowest in comparison with the AK-72 unit and the unit operating according to the combined scheme. 3. Instead of a waste heat boiler, a high-temperature heat exchanger is installed behind the contact apparatus to heat the exhaust gases in front of the turbine up to 1120 K. At the same time, due to the increase in the power of the gas turbine, the power output increased by 274 compared to the AK-72 unit. 4. In the scheme, a constantly switched on combustion chamber is installed in parallel with the technological apparatus, which makes it possible to make the operation of the machine unit independent of the production line, as well as to ensure a smooth transition from the operation of the machine in idle mode to the operation of the machine with the technology process turned on. The disadvantages of the scheme: 1. The process proceeds at elevated temperatures in the unit, which places very large loads on the palladium catalyst and it fails. According to the literature, the specific irretrievable losses per 1 ton of nitric acid are 40-45 mg for the process at atmospheric pressure, 100 mg at 0.3-1.6 MPa, and 130-180 mg at 0.7-0.9 MPa. That is, the loss of platinum in plants operating under pressure increases due to higher catalysis temperatures compared to the temperature in plants operating at atmospheric pressure. 2. A very high degree of air purification is required before entering the gas turbine, since the compressor air capacity can be reduced by up to 10% and efficiency by up to 6%. In this course project, a scheme for the production of nitric acid under pressure with a compressor driven by a gas turbine is considered in detail (Figure 17). The production capacity of nitric acid according to the scheme operating at a pressure of 0.716 MPa is determined by the number of units. The capacity of one unit is 120 thousand tons/year (100% HNO3). The number of units in the scheme is determined by the need for nitric acid processing shops. In each unit, the following is carried out: preparation of the ammonia-air mixture (cleaning and compression of air, evaporation of liquid ammonia, purification of gaseous ammonia and ammonia-air mixture); ammonia conversion; utilization of heat of formation of nitrogen oxides; cooling of nitrous gases; obtaining nitric acid; off-gas heating; purification from nitrogen oxides and recovery of gas energy in the gas turbine and waste heat boiler. In addition, the scheme includes units for preparing feed water to feed waste heat boilers, cooling condensate or demineralized water for irrigation of absorption columns, reducing steam to the required parameters, storing the generated nitric acid and distributing it to consumers. Figure 17 - Diagram of the production of nitric acid under pressure with a compressor drive from a gas turbine: 1 - air filter; 2 - turbocharger of the first stage; 3 - intermediate refrigerator; 4 - turbocharger of the second stage; 5 - gas turbine; 6 - gearbox; 7 - motor-generator; 8 - air heater; 9 - ammonia mixer with air; 10 - air heater; 11 - porous filter; 12 - converter; 13 - waste heat boiler; 14 - a vessel for the oxidation of nitrous gases; 15 - refrigerator - condenser; 16 - absorption column; 17 - converter; 18 - waste heat boiler Atmospheric air is sucked in through the filter 1 by the turbocharger of the first stage 2 and compressed to 0.2-0.35 MPa. Due to compression, the air is heated to 175 . After cooling down to 30-45 in the refrigerator 3, the air enters the turbocharger of the second stage 4, where it is compressed to a final pressure of 0.73 MPa and heated to 125-135 . Further air heating up to 270 occurs in the heater 8 due to the heat of hot nitrous gases leaving the converter. Hot air enters further into the mixer 9. Ammonia under pressure of 1.0-1.2 MPa is heated to 150 in the heater 10 with water vapor and enters the mixer 9, where it mixes with air. The resulting ammonia-air mixture, containing 10-12% NH3, is filtered in the porolith filter 11 and enters the converter 12, where on a platinum-rhodium catalyst at a temperature of 890-900 ammonia is oxidized to nitric oxide. The heat of the gases leaving the converter is used in the waste heat boiler 13 to produce steam, while the gases are cooled to 260 .
Next, the gases pass through a filter for trapping platinum, located in the upper part of the empty vessel 14. In vessel 14, NO is oxidized to NO2 (oxidation degree 80%), as a result of which the gas mixture is heated to 300-310 and enters the air heater 8, where it is cooled to 175 . Further use of the heat of nitrous gases becomes unprofitable, so they are cooled with water in the refrigerator 16 to 50-55 . Simultaneously with the cooling of the gas in the refrigerator 16 is the condensation of water vapor and the formation of nitric acid as a result of the interaction of water with nitrogen dioxide. The concentration of the resulting acid does not exceed 52% HNO3, the yield is about 50% of the total capacity of the plant. From the cooler 15, nitrous gases enter the absorption column 16 with sieve plates, where NO2 is absorbed by water to form nitric acid (concentration up to 55%). On the plates of the absorption column 16 coils (refrigeration elements) are laid, through which water circulates to remove heat released during the formation of nitric acid. To clean the exhaust gases from nitrogen oxides, they are heated to 370-420 ° C, a small amount of natural gas is added to them and sent to the converter (reactor) 17. Here, in the presence of a palladium catalyst, the following reactions occur: CH4 + O2 2CO + 4H2 + Q (27)
2NO2 + 4H2 = N2 + 4H2O + Q (28)
2NO + 2H2 = N2 + 2H2O + Q (29)
Since these reactions proceed with the release of heat, the temperature of the gases rises to 700-730 . These gases enter the turbine 5 at a pressure of 0.5-0.6 MPa, which drives the turbochargers 2 and 4, which compress the air. After that, gases at a temperature of about 400 enter the waste heat boiler 19, which receive low-pressure steam. Turbochargers of the first and second stages 2 and 4, as well as gas turbine 5 are a single unit. The turbine of the first stage 2 and the gas turbine 5 are located on a common shaft and are connected by a gearbox 6 to the second stage turbine 4 and an electric motor 7. This unit allows you to use the bulk of the energy spent on compressing the air, and thus significantly reduce power consumption. 7. CALCULATION OF THE MATERIAL AND THERMAL BALANCES OF THE REACTOR 7.1 Calculation of the material balance of the reactor 1) Calculate the required volume of air: 2) Volumes supplied with air, nm3: a) water vapor b) dry air 3) Calculate the volumes of oxygen, nitrogen and argon, coming with the air, based on their percentage in the air ) Find the volumes formed by reaction (14), nm ³ /h: a) nitric oxide b) water vapor 5) Determine the volumes formed by reaction (15), nm ³ /h: a) nitrogen b) water vapor c) oxygen consumed during this reaction 6) We calculate the volumes in the gas after the oxidation of ammonia, nm ³ /h: a) oxygen b) nitrogen c) argon
d) water vapor 7) The actual material balance can be calculated if the volumes of flows at the inlet to the contact apparatus and at the outlet of it are recalculated into masses, while the material balance must be observed. Coming: Consumption: Let's fill in the table for the material balance (Table 6). Table 6 Income Flow Component Quantity Component Quantity kg/hm ³ /hkg/hm ³ /чNH34477,6795900NO7348,6615487O215608,57110926O25367,8573757,5N250729,69140583,755N250987,81640790,255Ar929,116520,305Ar928520H2O1827,022273,625H2O8938,62711123,625Всего73572,07760203,68Всего73570,96161678,38 Balance discrepancy
7.2 Calculation of the heat balance of the reactor Let us find the temperature tx to which it is necessary to heat the ammonia-air mixture to ensure the autothermal nature of the ammonia oxidation process. 1) Calculate the total volume of the ammonia-air mixture ) Determine the concentration of the components of the ammonia-air mixture,% (vol.): a) ammonia b) dry air c) water vapor 3) Calculate the average heat capacity of the ammonia-air mixture Cav = 0.01 (35.8 Pam + 28.7 Psv + 32.6 PN2O) (59) Сav = 0.01 (35.8 9.8 + 28.7 86.4 + 32.6 3.8) = 29.544 kJ/(kmol K), where 35.8; 28.7 and 32.6 - heat capacities of ammonia, dry air and water vapor, kJ/(kmol K). ) Determine the heat introduced by the ammonia-air mixture ) We calculate the heats released during the reaction (14) and (16) or 17030 kW, where 905800 and 126660 are the heats released during the formation of nitrogen oxide and nitrogen according to reactions (14) and (16). ) Find the total volume of nitrous gas entering the waste heat boiler 7) Determine the concentration of the components of nitrous gas,% (vol.): a) nitric oxide b) oxygen c) argon d) nitrogen e) water vapor 8) Calculate the average heat capacity of nitrous gas: Snav = 0.01(31.68 PNO + 32.3 P2 + 20.78 Steam 30.8 PN2 + 37.4 Pvod 3(68) Sav=0.01(31.68 8.9+32.3 6.1+20.78 0.84+30.8 66.1+37.4 18.0) = 32.17 kJ/(kmol K) where 31.68; 32.3; 20.78; 30.8 and 37.4 - heat capacities of nitrous gas components at a temperature of 900 , kJ/(kmol K). 9) For steam heating from 198 up to 250 in the superheater it is necessary to take away the heat: 1880 kW, where 800 10 ³ and 1082 10 ³ J/kg - specific enthalpies of superheated steam at temperatures of 198 and 250 and pressures of 1.5 MPa and 3.98 MPa. 10) The temperature of nitrous gases at the outlet of the contact apparatus is determined from the heat balance equation for this section: 6768 106 = 64631 1.66 10³(900 - t2) 11) We calculate the heat carried away by nitrous gases. Consider the case when the contact apparatus and the waste heat boiler are mounted as a single apparatus: 12) Determine the heat loss to the environment Equating the heat input to the flow rate, we compose the heat balance equation and solve it with respect to tx: Fill in the table for heat balance (Table 7). Table 7 Input, kWConsumption, kWHeat introduced by the ammonia-air mixture6369.2Heat for heating water vapor in the superheater1880Heat carried away by nitrous gases20584.3Heat released during the reaction (14) and (16)17030.6Losses to the environment935.9Total23399.8Total23400.2 Balance discrepancy: 8. SAFETY AND INDUSTRIAL ENVIRONMENT To ensure a safe mode of operation in the production of non-concentrated nitric acid under high pressure, it is necessary to strictly comply with the technological regulations, labor protection instructions for workplaces, instructions for labor protection and industrial safety of the department, instructions for certain types of work. Service personnel are allowed to work in the work clothes and safety shoes prescribed by the norms, they are obliged to have serviceable personal protective equipment with them. Protective equipment (individual gas mask) must be checked every shift before starting work. Persons servicing the mechanisms must know the rules of Gosgortekhnadzor related to the equipment being serviced. Persons serving boiler supervision equipment - boiler supervision rules. Prevent violations of the normal technological regime at all stages of the process. Carry out work only on serviceable equipment, equipped with all necessary and properly functioning safety devices, instrumentation and control devices, alarms and interlocks. When handing over equipment and communications for repair, in which ammonia accumulation is possible, purge the equipment and communications with nitrogen until there are no combustibles in the purge nitrogen. Before filling the apparatuses and communications with ammonia after their repair, purge with nitrogen until the oxygen content in the purge nitrogen is not more than 3.0% (vol.). Do not allow repair of communications, fittings, equipment under pressure. Repairs should be carried out after depressurizing and shutting off the repaired area with plugs. Equipment, communications to be repaired must be blown or washed. To avoid hydraulic shocks, steam should be supplied to cold steam pipelines slowly, ensuring sufficient heating with condensate discharge along the entire length of the pipeline. The exit of dry steam from the drainage indicates sufficient heating of the pipeline. Do not turn on electrical equipment with faulty grounding. Do not allow repair of equipment with an electric drive, without removing the voltage from the electric motors. Repair and adjustment of control and measuring instruments and electrical equipment should be carried out only by the services of the department of the chief instrument operator and electricians. It is forbidden to use open fire in production and storage facilities: smoking is allowed in the places designated for these purposes. All rotating parts of the equipment (coupling halves), impellers of rotating fans, on the shafts of electric motors must be securely fastened and fenced, and painted red. Flanged connections of acid lines must be protected by protective covers. Tightening bolts of flange connections of pipelines, as well as work on equipment under pressure, is not allowed. Apparatus operating under pressure must meet the requirements set forth in the technical specifications and rules for the design and safe operation of vessels and communications operating under pressure. Works in closed vessels should be carried out in the presence of a work permit for carrying out gas hazardous work. Ventilation must be in good condition and be constantly in operation. Maintenance of lifting mechanisms, pressure vessels is carried out only by persons specially trained and having a special certificate. Approaches to emergency cabinets, fire detectors, telephones, fire equipment are not allowed to be cluttered with foreign objects, they must be kept clean and in good condition. Open openings in ceilings, platforms, walkways should have fences 1 m high. At the bottom of the fence there should be a side or a protective strip 15 cm high. All instrumentation and automation and blocking systems must be in good condition. To prevent the deposition of nitrite-nitrate salts on the internal surfaces of apparatuses and pipelines, rotor blades, walls of nitrous gas compressors and other parts and apparatuses, prevent prolonged ignition of contact apparatuses (more than 20 minutes), lowering the temperature of catalyst gauzes, rupturing them, leading to slips of ammonia , termination of irrigation of surfaces, which leads to the deposition of nitrite-nitrate salts. Timely perform wiping, cleaning equipment from spills of process products, topping up oil in pump crankcases. Workplaces for repair and other work and passages to them at a height of 1.3 m or more must be fenced. If it is impossible or inexpedient to install fences for work at a height of 1.3 m and above, as well as when working from a ladder at a height of more than 1.3 m, it is necessary to use safety belts, while at the place of work there must be auxiliary workers who are ready to assist the worker. on high. The place of fastening of the carabiner is determined by the head of work. Safety belts are tested before commissioning, as well as during operation every 6 months. The safety belt must be tagged with the registration number and the date of the next test. When working with nitric acid (sampling, inspection of communications, starting production acid pumps, etc.), it is necessary to use individual respiratory and eye protection (filtering gas mask with an M brand box, goggles with a rubber half mask or a protective shield made of plexiglass, or a gas mask helmet), rubber acid-proof gloves, special acid-proof clothing. If any malfunctions in the operation of the equipment, defects in supports, walls, etc. are detected. timely inform the head of the department, the shop mechanic. If necessary, stop the equipment and prepare it for delivery for repair. At each stop of the unit for repair, open the lower hatch of the oxidizer and, in the presence of ammonium salts on the distribution grid, along the walls and bottom, steam it with live steam, drain the condensate. Work with steam, steam condensate should be carried out in overalls, footwear, gloves. To prevent occupational poisoning and diseases in the department, the following sanitary and hygienic requirements must be observed: a) the air temperature should be: 23- transitional and winter period; 18-27- summer period. b) relative air humidity: in summer - no more than 75%; in winter - no more than 65%. c) noise - no more than 65 dBA in soundproof cabins, in other places no more than 80 dBA; d) vibration - no more than 75 dB in soundproof cabins, in engine and contact rooms no more than 92 dB; e) illumination of workplaces: soundproof booths - at least 200 lux; at the sites of absorption columns - at least 50 lux; in the engine and contact rooms - at least 75 lux. f) the maximum permissible concentration of harmful substances in the air of the working area of the premises: ammonia - no more than 20 mg/m3; nitrogen oxides - no more than 5 mg/m3. In addition to individual gas masks, the department has an emergency supply of filtering and isolating gas masks. Emergency gas masks are stored in emergency cabinets. CONCLUSION In the course of the course work, a reactor for the catalytic oxidation of ammonia was designed to produce nitrogen oxides in the production of non-concentrated nitric acid. The physical and chemical foundations of the process were considered. The characteristics of the initial raw material and the finished product are given. The required volume of air for oxidation was calculated as 5900 m ³ / h of ammonia, it amounted to 54304 m ³ /h The volumes of oxygen, nitrogen and argon supplied with air were calculated based on their percentage in the air. The volumes of oxygen, nitrogen, argon, and water vapor in the gas after oxidation of ammonia were also calculated. The heat balance was calculated, as a result of which all heat flows were calculated. The temperature to which it is necessary to heat the ammonia-air mixture to ensure the autothermal process of ammonia oxidation was calculated; it was 288 . The temperature of the nitrous gas after the superheater was calculated, it was 836.7 . Heat losses to the environment are determined. A review of the literature was made on the most efficient scheme for the production of non-concentrated nitric acid. A system operating under high pressure was chosen, since this unit is compact, all devices are transportable, the energy cycle of the unit is autonomous. In the considered scheme, electricity is not consumed for technological needs. Electricity is consumed in a small amount only to drive the pumps necessary for pumping acid, supplying feed water to the boilers. Work according to this scheme is carried out without emissions of harmful gases into the atmosphere. REFERENCES 1. Atroshchenko V.I., Kargin S.I. Technology of nitric acid: Proc. Allowance for universities. - 3rd ed., revised. and additional - M.: Chemistry, 1970. - 496 p. Egorov A.P. Shereshevsky A.I., Shmanenko I.V. General chemical technology of inorganic substances: Textbook for technical schools. - Ed. 4th revision - Moscow, Leningrad: Chemistry, 1965 - 688s. Karavaev M.M., Zasorin A.P., Kleschev N.F. Catalytic oxidation of ammonia / Ed. Karavaeva M.M. - M.: Chemistry, 1983. - 232 p. Catalysts in the nitrogen industry./Ed. Atroshchenko V.I. - Kharkov: Vishcha school, 1977. - 144 p. General chemical technology. Under the editorship of prof. Amelina A.G. Moscow: Chemistry, 1977. - 400 s. Pavlov K.F., Romankov P.G., Noskov A.A. Examples and tasks in the course of processes and apparatuses of chemical technology. L .: Chemistry, 1976 - 552s. Perlov E.I., Bagdasaryan V.S. Optimization of nitric acid production. M.: Chemistry, 1983. - 208 p. Calculations for the technology of inorganic substances: Proc. Manual for universities / Pozin M.E., Kopylev B.A., Belchenko G.V. and etc.; Ed. Pozina M.E. 2nd ed. revised and additional - L.: Chemistry. Leningrad. department, 1977 - 496 p. Rumyantsev O.V. Equipment for high-pressure synthesis shops in the nitrogen industry; Proc. for universities. - M.: Chemistry, 1970 - 376 p. 10. Sokolov R.S. Chemical technology: textbook. allowance for students. higher textbook institutions: In 2 T. - M .: Humanit ed. center VLADOS, 2000. - V.1: Chemical production in anthropogenic activity. Basic questions of chemical technology. Production of inorganic substances. - 368 p. Azotchik's Handbook./Ed. Melnikova E.Ya. - V.2: Production of nitric acid. Production of nitrogen fertilizers. Materials and basic special equipment. Energy supply. Safety engineering. - M.: Chemistry - 1969. - 448s. Chemical technology of inorganic substances: In 2 books. Book 1. Textbook / T.G. Akhmetov, R.G. Porfiryeva, L.G. Gysin. - M.: Higher. school, 2002. 688s.: ill. Korobochkin V.V. Nitric acid technology. - Publishing house of the Tomsk Polytechnic University. 2012.
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