Sulfuric acid is produced in large quantities at sulfuric acid plants.
I. Raw materials used for the production of sulfuric acid:
II. Preparation of raw materials.
Let's analyze the production of sulfuric acid from FeS2 pyrite.
1) Grinding of pyrite.
Large pieces of pyrite are crushed in crushers prior to use. You know that when a substance is ground, the reaction rate increases, because the area of \u200b\u200bthe contact surface of the reactants increases.
2) Purification of pyrite.
After crushing the pyrite, it is purified from impurities (waste rock and earth) by flotation. To do this, crushed pyrite is dipped into huge vats of water, mixed, the waste rock floats up, then the waste rock is removed.
III. Production chemistry.
The production of sulfuric acid from pyrite consists of three stages.
FIRST STAGE - firing pyrite in a "fluidized bed" kiln.
First stage reaction equation
4FeS2 + 11O2 2Fe2O3 + 8SO2 + Q
The crushed purified wet (after flotation) pyrite is poured from above into a furnace for roasting in a "fluidized bed". Oxygen-enriched air is passed from below (counter-current principle) for a more complete firing of pyrite. The kiln temperature reaches 800 ° C. The pyrite becomes red hot and is "suspended" due to the air blown from below. It all looks like a boiling red-hot liquid.
Due to the heat released as a result of the reaction, the temperature in the furnace is maintained. The excess amount of heat is removed: pipes with water pass along the perimeter of the furnace, which heats up. Hot water used further for central heating of adjacent premises.
The formed iron oxide Fe2O3 (cinder) is not used in the production of sulfuric acid. But it is collected and sent to a metallurgical plant, where iron and its alloys with carbon are obtained from iron oxide - steel (2% carbon C in the alloy) and cast iron (4% carbon C in the alloy).
Thus, the principle of chemical production is fulfilled - waste-free production.
Furnace gas comes out of the furnace, the composition of which is SO2, O2, water vapor (the pyrite was wet!) And the smallest particles of cinder (iron oxide). Such a furnace gas must be cleaned from impurities of solid particles of cinder and water vapor.
Cleaning the furnace gas from solid cinder particles is carried out in two stages - in a cyclone (used centrifugal force, solid cinder particles hit the walls of the cyclone and are poured down) and in electrostatic precipitators (electrostatic attraction is used, the cinder particles adhere to the electrified plates of the electrostatic precipitator, with sufficient accumulation under their own weight, they are poured down), to remove water vapor in the furnace gas (drying of the furnace gas ) use sulfuric concentrated acidwhich is a very good desiccant as it absorbs water.
Drying of oven gas is carried out in a drying tower - oven gas rises from bottom to top, and concentrated sulfuric acid flows from top to bottom. At the outlet of the drying tower, the kiln gas no longer contains cinder particles or water vapor. The furnace gas is now a mixture of sulfur oxide SO2 and oxygen O2.
SECOND STAGE - oxidation of SO2 to SO3 with oxygen.
Leaks in the contact apparatus.
The reaction equation of this stage: 2SO2 + O2 2SO3 + Q
The complexity of the second stage is that the process of oxidation of one oxide to another is reversible. Therefore, it is necessary to select the optimal conditions for the direct reaction (SO3 production).
a) temperature:
The direct reaction is exothermic + Q, according to the rules for the shift of chemical equilibrium, in order to shift the equilibrium of the reaction towards an exothermic reaction, the temperature in the system must be lowered. But, on the other hand, at low temperatures, the reaction rate drops significantly. Experimentally, chemists-technologists have established that the optimal temperature for a direct reaction with the maximum formation of SO3 is 400-500 ° C. This is a fairly low temperature in chemical industries. In order to increase the reaction rate at such a low temperature, a catalyst is introduced into the reaction. It has been experimentally established that the best catalyst for this process is vanadium oxide V2O5.
b) pressure:
A direct reaction proceeds with a decrease in the volume of gases: on the left 3V gases (2V SO2 and 1V O2), and on the right - 2V SO3. Since the direct reaction proceeds with a decrease in the volume of gases, then, according to the rules for the displacement of chemical equilibrium, the pressure in the system must be increased. Therefore, this process is carried out at elevated pressure.
Before the mixture of SO2 and O2 enters the contact apparatus, it must be heated to a temperature of 400-500 ° C. Heating of the mixture begins in a heat exchanger, which is installed in front of the contact device. The mixture passes between the tubes of the heat exchanger and is heated by these tubes. Hot SO3 from the contact device flows inside the tubes. Getting into the contact device, the mixture of SO2 and O2 continues to heat up to the required temperature, passing between the tubes in the contact device.
The temperature of 400-500 ° C in the contact apparatus is maintained due to the release of heat in the reaction of the conversion of SO2 to SO3. As soon as the mixture of sulfur oxide and oxygen reaches the catalyst beds, the process of oxidation of SO2 to SO3 begins.
The formed sulfur oxide SO3 leaves the contact apparatus and enters the absorption tower through the heat exchanger.
THIRD STAGE - absorption of SO3 by sulfuric acid.
It flows in the absorption tower.
Why is sulfur oxide SO3 not absorbed by water? After all, it would be possible to dissolve sulfur oxide in water: SO3 + H2O H2SO4. But the fact is that if water is used to absorb sulfur oxide, sulfuric acid is formed in the form of a fog, consisting of tiny droplets of sulfuric acid (sulfur oxide dissolves in water with the release of a large amount of heat, sulfuric acid heats up so much that it boils and turns into steam ). In order to avoid the formation of sulfuric acid mist, use 98% concentrated sulfuric acid. Two percent water is so little that heating the liquid will be weak and harmless. Sulfur oxide dissolves very well in such an acid, forming oleum: H2SO4 · nSO3.
The reaction equation of this process is nSO3 + H2SO4 H2SO4 nSO3
The resulting oleum is poured into metal tanks and sent to the warehouse. Then the tanks are filled with oleum, the trains are formed and sent to the consumer.
Environmental protection,
associated with the production of sulfuric acid.
The main raw material for the production of sulfuric acid is sulfur. It is one of the most common chemical elements on our planet.
The production of sulfuric acid takes place in three stages; in the first stage, SO2 is obtained, by roasting FeS2, then SO3, after which sulfuric acid is obtained in the third stage.
The scientific and technological revolution and the associated intensive growth of chemical production causes significant negative changes in the environment. For example poisoning fresh water, pollution of the earth's atmosphere, extermination of animals and birds. As a result, the world found itself in the grip of an environmental crisis. Harmful emissions of sulfuric acid plants should be assessed not only by the effect of sulfur oxide contained in them on the areas located near the plant, but also take into account other factors - an increase in the number of cases of respiratory diseases in humans and animals, the death of vegetation and suppression of its growth, destruction of structures made of limestone and marble, increased corrosive wear of metals. Due to the fault of "sour" rains, architectural monuments (Taj Makal) were damaged.
In the zone up to 300 km from the source of pollution (SO2), sulfuric acid poses a hazard, in the zone up to 600 km. - sulfates. Sulfuric acid and sulfates slow down the growth of agricultural crops. Acidification of water bodies (in spring, when the snow melts, causes the death of eggs and juveniles of fish. In addition to environmental damage, there is economic damage - huge amounts are lost every year when soil is deoxidized.
Consider chemical methods for removing the most common gaseous air pollutants. More than 60 methods are known. The most promising methods are based on the absorption of sulfur oxide by limestone, a solution of sulfite - ammonium hydrosulfite and an alkaline solution of sodium aluminate. Catalytic methods for the oxidation of sulfur oxide in the presence of vanadium oxide are also of interest.
Of particular importance is the cleaning of gases from fluorine-containing impurities, which, even in low concentrations, have a harmful effect on vegetation. If the gases contain hydrogen fluoride and fluorine, then they are passed through columns with a nozzle in a countercurrent in relation to a 5-10% sodium hydroxide solution. Within one minute, the following reactions occur:
F2 + 2NaOH-\u003e O2 + H2O + 2NaF
HF + NaOH-\u003e NaF + H2O;
The resulting sodium fluoride is treated to regenerate sodium hydroxide.
Home\u003e AbstractGeneral information
Sulfuric acid is one of the main large-tonnage products of the chemical industry. It is used in various industries national economysince it has a complex special propertiesfacilitating its technological use. Sulfuric acid does not smoke, has no color or odor, at normal temperatures it is in liquid state, in concentrated form does not corrode ferrous metals. At the same time, sulfuric acid is one of the strong mineral acids, forms numerous stable salts and is cheap.Technological properties of sulfuric acid
In technology, sulfuric acid is understood as a system consisting of sulfur oxide (VI) and water of various compositions: nSO 3 . mH 2 O. At n = m \u003d 1 is sulfuric acid monohydrate (100% acid), with m > n – aqueous solutions monohydrate, at m < n - solutions of sulfur oxide (VI) in monohydrate (oleum):H 2 SO 4 · ( n - 1) SO 3 H 2 SO 4 H 2 SO 4 ( m - 1) H 2 O
oleum monohydrate aqueous acid Sulfuric acid monohydrate is a colorless oily liquid with a crystallization temperature of 10.37 ° C, a boiling point of 296.2 ° C and a density of 1.85 g / cm 3. It mixes with water and sulfur (VI) oxide in all respects, forming hydrates of the composition H 2 SO 4 . H 2 O; H 2 SO 4 . 2 H 2 O; H 2 SO 4 . 4 H 2 O and compounds with sulfur (VI) oxide composition H 2 SO 4 . SO 3 and H 2 SO 4 . 2SO 3. These hydrates and compounds with sulfur oxide have different crystallization temperatures and form a number of eutectics. Some of these eutectics have crystallization temperatures below zero or close to zero. These features of sulfuric acid solutions are taken into account when choosing its commercial grades, which, according to the conditions of production and storage, should have a low crystallization temperature. Sulfuric acid mixes with water in all respects and generates a lot of heat. For this reason, you should always dilute sulfuric acid by pouring it into water, and not vice versa. This acid hygroscopic, i.e. it is capable of absorbing moisture from the air. Therefore, it is used to dry gases that do not react with it, passing them through sulfuric acid.
The use of sulfuric acid and oleum
The high activity of sulfuric acid, combined with the relatively low cost of production, predetermined the enormous scale and extreme variety of its use. It is difficult to find a branch of the national economy in which sulfuric acid or products made from it would not be consumed in certain quantities. Sulfuric acid ranks first among mineral acids in terms of production and consumption. Over the past 25 years, its world production has more than tripled, currently amounting to more than 160 million tons per year. The production of sulfuric acid and oleum (in terms of monohydrate) in the Russian Federation amounted to 5.7 million tons in 1998. The fields of application of sulfuric acid and oleum are very diverse. A significant part of it is used in the production of mineral fertilizers (from 30 to 60%), as well as in the production of dyes (from 2 to 16%), chemical fibers (from 5 to 15%) and metallurgy (from 2 to 3%). With the help of sulfuric acid, ethyl and other alcohols, some esters, synthetic detergents, and a number of pesticides for pest control are produced agriculture and weeds. Diluted solutions of sulfuric acid and its salts are used in the manufacture of artificial silk, in the textile industry for processing fibers or fabrics before dyeing them, as well as in other branches of light industry. In the food industry, sulfuric acid is used in the production of starch, molasses and a number of other products. Transport uses lead-acid batteries. Finally, sulfuric acid is used in nitration processes and in the manufacture of most explosives. In fig. 5. shows the use of sulfuric acid and oleum in the national economy.2NOHSO 4 + H 2 O 2H 2 O + N 2 O 3 - Q
Sulfur dioxide is absorbed by water and forms sulfurous acid:
SO 2 + H 2 O H 2 SO 3 + Q
The latter reacts with nitrogen oxides in the liquid phase:
H 2 SO 3 + N 2 O 3 H 2 SO 4 + 2NO + Q
Partially SO 2 can be oxidized in the gas phase:
SO 2 + N 2 O 3 SO 3 + 2NO + Q
SO 3 absorbed by water also gives sulfuric acid:
SO 3 + H 2 O H 2 SO 4 + Q
Nitric oxide is desorbed into the gas phase and oxidized to nitrogen dioxide by atmospheric oxygen:
2NO + O 2 2NO 2 + Q
Nitrogen oxides NO + NO 2 N 2 O 3 are absorbed by sulfuric acid in the next three to four towers according to the reaction inverse to equation (a). For this purpose, cooled sulfuric acid with a low nitrose content is fed into the towers, flowing from the first towers. When oxides are absorbed, nitrosylsulfuric acid is obtained, which takes part in the process. Thus, nitrogen oxides are circulating and theoretically should not be consumed. In practice, due to incomplete absorption, there are losses of nitrogen oxides. The consumption of nitrogen oxides in terms of HNO 3 is 10-20 kg per ton of H 2 SO 4 monohydrate. The nitrous method is used to obtain contaminated with impurities and diluted 75-77% sulfuric acid, which is used mainly for the production of mineral fertilizers.
Raw materials for the production of sulfuric acid
The raw material in the production of sulfuric acid can be elemental sulfur and various sulfur-containing compounds, from which sulfur or directly sulfur (IV) oxide can be obtained. Natural deposits of native sulfur are small, although its clarke is 0.1%. Most often, sulfur is found in nature in the form of metal sulfides and metal sulfates, and is also a part of oil, coal, natural and associated gases. Significant amounts of sulfur are contained in the form of sulfur oxide in flue gases and gases of non-ferrous metallurgy and in the form of hydrogen sulphide released during the purification of combustible gases. Thus, the raw material sources for the production of sulfuric acid are quite diverse, although elemental sulfur and iron pyrite are still used as raw materials. The limited use of raw materials such as flue gases from thermal power plants and gases from copper smelting production is explained by the low concentration of sulfur (IV) oxide in them. At the same time, the share of pyrite in the balance of raw materials decreases, while the share of sulfur increases. In 1988, it already exceeded 60% of the total amount of sulfur-containing raw materials. In the general scheme of sulfuric acid production, the first two stages are essential - preparation of raw materials and their combustion or roasting. Their content and hardware design significantly depend on the nature of the raw material, which largely determines the complexity of the technological production of sulfuric acid. 1. IRON QUALITY. Natural iron pyrite is a complex rock consisting of iron sulfide FeS 2, sulfides of other metals (copper, zinc, lead, nickel, cobalt, etc.), metal carbonates and waste rock. On the territory of the Russian Federation there are pyrite deposits, in the Urals and the Caucasus, where it is mined in mines in the form of ordinary pyrite.|
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General scheme of sulfuric acid production
The production of sulfuric acid from sulfur-containing raw materials includes several chemical processes in which the oxidation state of raw materials and intermediate products changes. This can be represented as the following diagram:
where: I - stage of obtaining furnace gas (sulfur oxide (IV)) II - the stage of catalytic oxidation of sulfur oxide (IV) to sulfur oxide (VI) and its absorption (processing into sulfuric acid). In real production, these chemical processes are supplemented by the processes of preparing raw materials, cleaning furnace gas and other mechanical and physicochemical operations. In general, the scheme for the production of sulfuric acid can be expressed in the following form: Raw materials preparation of raw materials combustion (roasting) of raw materials cleaning the furnace gas contacting absorption of the contacted gas SULFURIC ACID. The specific technological scheme of production depends on the type of raw material, the features of the catalytic oxidation of sulfur (IV) oxide, the presence or absence of the stage of absorption of sulfur oxide (VI).
Sulfuric acid production from pyrites flotation
Chemical and production concept
The chemical scheme for obtaining sulfuric acid from pyrite includes three successive stages: - oxidation of iron disulfide of pyrite concentrate with atmospheric oxygen:4FeS 2 + 11O 2 \u003d 2Fe 2 O 3 + 8SO 2,
Catalytic oxidation of sulfur (IV) oxide with an excess of oxygen in the furnace gas:
2SO 2 + O 2 \u003d 2SO 3,
Absorption of sulfur (IV) oxide with the formation of sulfuric acid:
SO 3 + H 2 O \u003d H 2 SO 4
In terms of technological design, the production of sulfuric acid from iron pyrite is the most complex and consists of several successive stages.
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Oxidative burning of pyrite
Firing pyrite in a stream of air is an irreversible non-catalytic heterogeneous process that occurs with the release of heat through the stages of thermal dissociation of iron disulfide.2FeS 2 \u003d 2FeS + S 2
and oxidation of dissociation products:
S 2 + 2O 2 \u003d 2SO 2,
4FeS + 7O 2 \u003d 2Fe 2 O 3 + 4SO 2,
which is described by the general equation:
4FeS 2 + 11O 2 \u003d 2Fe 2 O 3 + 8SO 2 + 3400 kJ.
The speed of the firing process depends on the temperature, the fineness of the pyrite being fired. An increase in the driving force of the roasting process is achieved by flotation of pyrite, which increases the content of iron disulfide in the raw material, enrichment of air with oxygen and the use of excess air during roasting up to 30% above the stoichiometric amount. In practice, the firing is carried out at a temperature not higher than 1000 o C, since beyond this limit, sintering of the particles of the raw material to be fired begins, which leads to a decrease in their surface and makes it difficult to wash the particles with an air stream. Furnaces of various designs can be used as reactors for firing pyrite: mechanical, pulverized firing, fluidized bed (CC). Fluidized bed furnaces are characterized by high intensity (up to 10,000 kg m 2 / day), provide a more complete burnout of iron disulfide (the sulfur content in the cinder does not exceed 0.005 wt. Fractions) and temperature control, facilitate the process of utilizing the heat of the firing reaction. The disadvantages of KS furnaces include the increased dust content in the firing gas, which makes it difficult to clean it. At present, KS furnaces have completely replaced furnaces of other types in the production of sulfuric acid from pyrite. The products of the oxidative roasting of pyrite are roasting (furnace) gas and cinder, consisting of iron (III) oxide, waste rock, and unburnt residue of iron disulfide. In practice, when firing pyrite, the furnace gas contains 13-14% sulfur (IV) oxide, 2% oxygen and about 0.1% sulfur (VI) oxide. Since there must be an excess of oxygen in the furnace gas for the subsequent oxidation of sulfur (IV) oxide, its composition is corrected by diluting it with air to a sulfur (IV) oxide content of 7 - 9% and oxygen of 11 - 9%.
Cleaning of firing (furnace) gas
The firing gas must be cleaned of dust, sulfuric acid mist, and substances that are catalytic poisons or valuable as by-products. The firing gas contains up to 300 g m 3 of dust, which at the stage of contact clogs the equipment and reduces the activity of the catalyst, as well as the sulfuric acid mist. In addition, when pyrite is roasted, sulfides of other metals contained in pyrite are oxidized simultaneously with the oxidation of iron disulfide. In this case, arsenic and selenium form gaseous oxides As 2 O 3 and SeO 2, which pass into the roasting gas and become catalytic poisons for vanadium contact masses. Dust and sulfuric acid mist are removed from the roasting gas during general gas cleaning, which includes mechanical (coarse) and electrical (fine) cleaning operations. Mechanical gas cleaning is carried out by passing gas through centrifugal dust collectors (cyclones) and fibrous filters that reduce the dust content in the gas to 10 - 20 g / m 3. Electric gas cleaning in electrostatic precipitators reduces the content of dust and fog in the gas to 0.05 - 0.1 g / m 3. After general purification, the roasting gas obtained from pyrite is necessarily subjected to special purification to remove residual dust and fog and, mainly, arsenic and selenium compounds, which are utilized in this case. The special purification of gas includes the operation of cooling it to a temperature below the melting temperatures of arsenic oxide (315 0 C) and selenium (340 0 C) in towers, irrigated successively with 50% and 20% sulfuric acid, removing sulfuric acid mist in wet electrostatic precipitators and final gas drying in scrubbers irrigated with 95% sulfuric acid. The firing gas leaves the special cleaning system at a temperature of 140-50С. Selenium (IV) oxide, recovered from roasting gas, is reduced by sulfur (IV) oxide dissolved in sulfuric acid to metallic selenium:SeO 2 + 2SO 2 + 2H 2 O \u003d Se + 2H 2 SO 4,
which settles in sedimentation tanks. A new and progressive method for cleaning flue gas is the adsorption of impurities contained in it with solid absorbers, for example, silica gel or zeolites. With such dry cleaning, the firing gas is not cooled and enters contacting at a temperature of about 400 ° C, as a result of which it does not require intensive additional heating.
Contacting sulfur oxide (IV)
The oxidation reaction of sulfur (IV) oxide to sulfur (VI) oxide, underlying the process of contacting the firing gas, is a heterogeneous catalytic, reversible, exothermic reaction and is described by the equation:
SO 2 + 0.5 O 2 SO 3 - H.
The heat effect of the reaction depends on the temperature and is equal to 96.05 kJ at 25 0 С and about 93 kJ at the contacting temperature. The system "SO 2 - O 2 - SO 3" is characterized by the state of equilibrium in it and the rate of the oxidation of sulfur (IV) oxide, on which the overall result of the process depends. The degree of conversion of sulfur (IV) oxide to sulfur (VI) oxide or the degree of contact achieved on the catalyst depends on the activity of the catalyst, temperature, pressure, the composition of the gas to be contacted, and the contact time. The rate of oxidation of sulfur (IV) oxide depends on the amount of sulfur (IV) oxide oxidized per unit time, and, consequently, on the volume of the contact mass, dimensions of the reactor, and other characteristics of the process. The organization of this stage of production should ensure as much high speed oxidation at the maximum degree of contact achievable under these conditions. The activation energy of the oxidation reaction of sulfur (IV) oxide with oxygen to sulfur (VI) oxide is very high. Therefore, in the absence of a catalyst, the oxidation reaction practically does not proceed even at high temperatures. The use of a catalyst can reduce the activation energy of the reaction and increase the rate of oxidation. In the production of sulfuric acid, vanadium (V) oxide-based contact masses are used as a catalyst. The ignition temperature of contact vanadium masses is 380 - 420 0 С and depends on the composition of the contact gas, increasing with decreasing oxygen content in it. The contact masses must be in such a state that minimum hydraulic resistance to the gas flow and the possibility of diffusion of components through the catalyst bed are provided. For this, the contact masses for fixed bed reactors are formed in the form of granules, tablets or rings with an average diameter of about 5 mm, and for fluidized bed reactors, in the form of balls with a diameter of about 1 mm. Reactors or contact devices for the catalytic oxidation of sulfur (IV) oxide by their design are divided into devices with a fixed catalyst bed (shelf or filter), in which the contact mass is located in 4-5 layers, and fluidized bed devices. Heat removal after the gas passes through each catalyst bed is carried out by introducing cold gas or air into the apparatus, or by means of heat exchangers built into the apparatus or separately removed. The advantages of fluidized bed contact devices include: - a high coefficient of heat transfer from the catalyst in a fluidized bed state to the surface of the heat exchanger (10 times more than from gas), which allows contacting furnace gas with a high content of sulfur oxide (IV) without overheating and catalyst ignition temperature; - insensitivity to dust introduced together with the furnace gas.
Sulfur oxide absorption (VI)
The last stage in the production of sulfuric acid by the contact method is the absorption of sulfur oxide (VI) from the contacted gas and converting it into sulfuric acid or oleum. The absorption of sulfur oxide (VI) is a reversible exothermic reaction and is described by the equation:
n SO 3 + H 2 O H 2 SO 4 + ( n - 1) SO 3 - H.
The heat effect of the reaction depends on the value of n and for n \u003d 1 (the formation of sulfuric acid monohydrate) is 92 kJ. Depending on the quantitative ratio of sulfur (VI) oxide and water, a product of various concentrations can be obtained:
- at n 1 oleum, for n \u003d 1 monohydrate (100% sulfuric acid), at n 1 aqueous acid solution (dilute sulfuric acid).
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Commercial grades of sulfuric acid
Modern industry produces several grades of sulfuric acid and oleum, differing in concentration and purity (Table 2). To reduce the possibility of crystallization of products during transportation and storage, as well as in production itself, standards (GOST 2184-77) have been established for their commercial grades, the concentrations of which correspond to eutectic compositions with the lowest crystallization temperatures.4. Short description industrial methods for producing sulfuric acid
The production of sulfuric acid from sulfur-containing raw materials includes several chemical processes in which the oxidation state of raw materials and intermediate products changes. This can be represented as the following diagram:
where I is the stage of obtaining furnace gas (sulfur (IV) oxide),
II - stage of catalytic oxidation of sulfur oxide (IV) to sulfur oxide (VI) and its absorption (processing into sulfuric acid).
In real production, these chemical processes are supplemented by the processes of preparing raw materials, cleaning furnace gas and other mechanical and physicochemical operations.
In general, the production of sulfuric acid can be expressed as follows:
Raw materials raw material preparation combustion (roasting) of raw materials
furnace gas cleaning contacting absorption
contacted gas SULFURIC ACID
The specific technological scheme of production depends on the type of raw material, the features of the catalytic oxidation of sulfur (IV) oxide, the presence or absence of the stage of absorption of sulfur oxide (VI).
Depending on how the process of oxidation of SO 2 to SO 3 is carried out, there are two main methods for producing sulfuric acid.
In the contact method for producing sulfuric acid, the oxidation process of SO 2 to SO 3 is carried out on solid catalysts.
Sulfur trioxide is converted into sulfuric acid at the last stage of the process - the absorption of sulfur trioxide, which can be simplified by the reaction equation:
SO 3 + H 2 O H 2 SO 4
When carrying out the process according to the nitrous (tower) method, nitrogen oxides are used as an oxygen carrier.
Oxidation of sulfur dioxide is carried out in the liquid phase and the end product is sulfuric acid:
SO 3 + N 2 O 3 + H 2 O H 2 SO 4 + 2NO
At present, the industry mainly uses the contact method for producing sulfuric acid, which makes it possible to use devices with greater intensity.
1) The chemical scheme for producing sulfuric acid from pyrite includes three successive stages:
Oxidation of iron disulfide pyrite concentrate with atmospheric oxygen:
4FеS 2 + 11О 2 \u003d 2Fе 2 S 3 + 8SO 2,
Catalytic oxidation of sulfur (IV) oxide with an excess of oxygen in the furnace gas:
2SО 2 + О 2 2SО 3
Absorption of sulfur (VI) oxide with the formation of sulfuric acid:
SO 3 + H 2 O H 2 SO 4
In terms of technological design, the production of sulfuric acid from iron pyrite is the most complex and consists of several successive stages.
2) The technological process for the production of sulfuric acid from elemental sulfur by the contact method differs from the production process from pyrite in a number of features. These include:
Special design of furnaces for producing furnace gas;
Increased content of sulfur (IV) oxide in the furnace gas;
Absence of the stage of preliminary cleaning of furnace gas.
Subsequent operations of contacting sulfur (IV) oxide in terms of physicochemical principles and instrumentation do not differ from those for the pyrite-based process and are usually formalized according to the DKDA scheme. Gas thermostating in the contact apparatus in this method is usually carried out by introducing cold air between the catalyst beds
3) There is also a method for the production of sulfuric acid from hydrogen sulfide, called "wet" catalysis, consists in the fact that a mixture of sulfur (IV) oxide and water vapor obtained by burning hydrogen sulfide in a stream of air is fed without separation into contacting, where sulfur oxide ( IV) is oxidized on a solid vanadium catalyst to sulfur oxide (VI). Then the gas mixture is cooled in a condenser, where the vapors of the resulting sulfuric acid are converted into a liquid product.
Thus, in contrast to the methods for the production of sulfuric acid from pyrite and sulfur, in the process of wet catalysis there is no special stage for the absorption of sulfur oxide (VI) and the whole process includes only three successive stages:
1. Combustion of hydrogen sulfide:
H 2 S + 1.5O 2 \u003d SO 2 + H 2 O
with the formation of a mixture of sulfur oxide (IV) and water vapor of equimolecular composition (1: 1).
2. Oxidation of sulfur oxide (IV) to sulfur oxide (VI):
SO 2 + 0.5O 2<=> SO 3
while maintaining the equimolecular composition of the mixture of sulfur (IV) oxide and water vapor (1: 1).
3. Condensation of vapors and formation of sulfuric acid:
SO 3 + H 2 O<=> H 2 SO 4
thus, the process of wet catalysis is described by the general equation:
H 2 S + 2O 2 \u003d H 2 SO 4
There is a scheme for obtaining sulfuric acid at elevated pressure. The influence of pressure on the rate of the process can be estimated in the kinetic region, where there is practically no influence of physical factors. An increase in pressure affects both the speed of the process and the state of equilibrium. The reaction rate and product yield increase with increasing pressure due to an increase in the effective concentrations of SO 2 and O 2 and an increase in the driving force of the process. But as the pressure increases, the operating cost of compressing the inert nitrogen also increases. The temperature in the contact apparatus also increases, because at high pressure and low temperature, the value of the equilibrium constant is small in comparison with the scheme under atmospheric pressure.
The large scale of the production of sulfuric acid makes the problem of its improvement especially acute. The following main directions can be distinguished here:
1. Expansion of the resource base through the use of waste gases from boiler houses of combined heat and power plants and various industries.
2. Increasing the unit capacity of installations. The increase in capacity by two or three times reduces the cost of production by 25 - 30%.
3. Intensification of the raw material firing process by using oxygen or oxygen-enriched air. This reduces the volume of gas passing through the equipment and increases its performance.
4. Increase in pressure in the process, which contributes to an increase in the intensity of the main equipment.
5. Application of new catalysts with increased activity and low ignition temperature.
6. Increase in the concentration of sulfur oxide (IV) in the furnace gas supplied to the contact.
7. Introduction of fluidized bed reactors at the stages of raw material roasting and contacting.
8. Using thermal effects chemical reactions at all stages of production, including for generating steam.
The most important task in the production of sulfuric acid is to increase the degree of conversion of SO 2 to SO 3. In addition to increasing the productivity of sulfuric acid, the fulfillment of this task allows solving environmental problems - reducing emissions in environment harmful component SO 2.
To solve this problem, many different studies have been carried out in various fields: absorption of SO 2, adsorption, research in changing the design of the contact apparatus.
There are various designs of contact devices:
Single-contact contact apparatus: This apparatus is characterized by a low conversion of sulfur dioxide to trioxide. The disadvantage of this apparatus is that the gas leaving the contact apparatus has a high content of sulfur dioxide, which has a negative effect from an environmental point of view. Using this apparatus, the exhaust gases must be cleaned of SO 2. For the disposal of SO 2, there are many different ways: absorption, adsorption,…. This, of course, reduces the amount of SO 2 emissions into the atmosphere, but this, in turn, increases the number of devices in the technological process, the high content of SO 2 in the gas after the contact device shows a low degree of SO 2 utilization, therefore, these devices in the production of sulfuric acid I am using.
Contact device with double contact: DC allows you to achieve the same minimum SO 2 content in exhaust gases as after chemical cleaning. The method is based on the well-known Le Chatelier principle, according to which the removal of one of the components of the reaction mixture shifts the equilibrium towards the formation of this component. The essence of the method consists in carrying out the process of oxidation of sulfur dioxide with the release of sulfur trioxide in an additional absorber. The DC method allows you to process concentrated gases.
Contact apparatus with intermediate cooling. The essence of the method is that the gas entering the contact apparatus, passing through the catalyst bed, enters the heat exchanger, where the gas is cooled, then enters the next catalyst bed. This method also increases the utilization of SO 2 and its content in the exhaust gases.
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Sulfurous anhydride production in sulfuric acid production
Functional diagram of sulfuric acid production. The chemical scheme includes the following reactions: burning of sulfur pyrite 4FeS2 + 11O2 \u003d 2Fe2O3 + 8SO2 or sulfur S2 + 2O2 \u003d 2SO2; oxidation of sulfur dioxide SO2 + 1 / 2O2 \u003d SO3; absorption of sulfur trioxide SO3 + H2O \u003d H2SO4 ...
Low pressure polyethylene production
polymerization ethylene fire-fighting cyclohexane Polyethylene and polypropylene are obtained by polymerizing ethylene and propylene, respectively, by the low pressure method using a weak solution of triethylaluminum in ...
Sulfuric acid production
The raw material in the production of sulfuric acid can be elemental sulfur and various sulfur-containing compounds, from which sulfur or directly sulfur (IV) oxide can be obtained. Natural deposits of native sulfur are small, although its clarke is 0 ...
Sulfuric acid production
Sulfuric acid vapor condensation. In some cases, the gas used to produce sulfuric acid does not contain harmful impurities (arsenic, fluorine). Then it is economically expedient not to expose such a gas to flushing in special equipment ...
Sulfuric acid production
In technology, sulfuric acid is understood as a system consisting of sulfur oxide (VI) and water of various compositions: At \u003e\u003e 1, it is sulfuric acid monohydrate (100% acid), at< - водные растворы моногидрата...
Sulfuric acid production
Figure 6 shows a process flow diagram of sulfuric acid production by the contact method on pyrite. Figure 6 - Technological scheme of obtaining sulfuric acid by contact method on pyrite 19 1,2-washing towers; 3 ...
Sulfuric acid production
Back in the XIII century. sulfuric acid was obtained in insignificant quantities by thermal decomposition of ferrous sulfate FeSO4, therefore even now one of the varieties of sulfuric acid is called vitriol oil ...
Sulfuric acid production at elevated pressure
The raw material base for the production of sulfuric acid is sulfur-containing compounds, from which sulfur dioxide can be obtained by roasting. In industry, about 80% of sulfuric acid is obtained from natural sulfur and iron pyrite ...
Development of a process for the production of isopropyl benzene at JSC "Omsk rubber"
There are three main methods of producing isopropylbenzene that are of industrial importance: 1. Alkylation of benzene with propylene in the presence of anhydrous aluminum chloride (Friedel-Crafts alkylation). 2 ...
Development of a technology for producing sulfuric acid by burning pyrite
All industrial methods for the synthesis of sulfuric acid are based on the following stages: 1) the first stage of the process is the oxidation of raw materials to obtain a roasting gas containing sulfur oxide SO2 ...
Development of a technology for producing sulfuric acid by burning pyrite
In industry, two methods are used for producing sulfuric acid, which differ in the method of oxidation of SO2: -nitrous - using nitrogen oxides obtained from nitric acid, -contact - using solid catalysts (contacts) ...
Sulfuric acid alkylation of isobutane with butylene
Acid concentration. For C-alkylation of butane-butylene hydrocarbons, sulfuric acid is usually used, containing from 88 to 98% monohydrate ...
Description of the production scheme sulfuric acid
The sulfuric acid production process can be described as follows.
The first stage is the production of sulfur dioxide by oxidation (roasting) of sulfur-containing raw materials (the need for this stage disappears when using waste gases as raw materials, since in this case the roasting of sulfides is one of the stages of other technological processes).
Firing gas 350-400o C o C
Getting roasting gas. To stabilize the firing process in the fluidized bed, the following is automatically controlled: the concentration of SO2 in the gas, the amount of air entering the furnace, the height of the fluidized bed and the vacuum in the furnace. The constancy of the volume of sulfur dioxide and the concentration of SO2 in it at the outlet of the furnace is maintained by automatically regulating the supply of air and pyrite in the furnace, depending on the temperature of the exhaust gas. The amount of air supplied to the oven is regulated by a regulator acting on the position of the throttle valve in the blower branch pipe. The stability of the SO2 concentration in the gas in front of the electrostatic precipitator is ensured by an automatic regulator by changing the speed of the feeder feeding pyrite into the furnace. The height of the fluidized bed in the furnace is regulated by the cinder removal rate by changing the rotational speed regulator of the unloading auger or the degree of opening of the sector gate to the cinder unloading. A constant vacuum in the upper part of the furnace is maintained by a regulator, which accordingly changes the position of the throttle valve in front of the fan.
Firing gas 350-400o C enters the hollow wash tower where it is cooled to 80o C irrigation tower with 60-70% sulfuric acid.
From the hollow washing tower, the gas enters the second washing tower with a packing where it is irrigated with 30% sulfuric acid and cooled to 30about S.
In the washing towers, the gas is freed from dust residues in the droplets of sulfuric acid, the oxides of arsenic and selenium, which are present in the firing gas and are poisonous for the catalyst in the contact apparatus, are dissolved. Sulfuric acid mist with dissolved arsenic and sulfur oxides is deposited in wet electrostatic precipitators.
The final drying of the firing gas after the electrostatic precipitator is carried out in an absorption column with a packing
concentrated sulfuric acid (93-95%).
The cleaned dry SO2 gas is fed to the heat exchanger. where it is heated by hot gases from the contact apparatus.
The gas enters the contact apparatus and is oxidized to SO3. The catalyst is vanadium pentoxide.
Hot gas SO3 (450-480about C), leaving the contact device enters the heat exchanger, gives off heat to the fresh gas, then enters the refrigerator and then is sent for absorption.
SO3 absorption takes place in two towers in series. The tower is irrigated with oleum on the first trip. Containing 18-20% SO3 (free) The second tower is irrigated with concentrated sulfuric acid. Thus, during the production process, two products are formed: oleum and concentrated sulfuric acid.
Waste gases containing residual SO2 are passed through alkaline absorbers, which are sprayed with ammonia water and, as a result, ammonium sulfite.
1.3 Main main process equipment
In the process of sulfuric acid production, the following technological equipment is used:
1. Washing tower.
2. Washing tower with a nozzle.
3. Wet filter.
4. Drying tower.
5. Turbocharger.
6. Tubular heat exchanger.
7. Contact apparatus.
8. Tubular gas cooler.
9. Absorption tower.
10. Refrigerator acid.
11. Collection of acid.
12. Centrifugal pump.
13. Fluidized bed furnace.
14. Firebox.
The main phase of the sulfuric acid production process is the oxidation of sulfur dioxide in the contact apparatus.
Description of the design of the main units of the contact apparatus / 11 /.
Figure 1 - Diagram of a contact compartment with double contact
Figure 1 shows a schematic diagram of a double contact compartment. The gas passes through heat exchangers 1 and 2 and enters the first, and then the second and third layers of the contact mass of the apparatus 3. After the third layer, the gas is supplied to the intermediate absorber 8, from it to heat exchangers 5 and 4, and then to the fourth layer of the contact mass ... The gas cooled in the heat exchanger 5 passes through the absorber 6 and is discharged from it into the atmosphere. Figure 2 shows a modern contact apparatus in terms of H2 SO 4 depending on their size ranges from 50 to 1000 t / day H2 SO 4 ... The apparatus is loaded with 200-300 liters of contact mass per 1 ton of daily production. Tubular contact devices are used for the oxidation of SO2 less often than shelf units.
Figure 2 - Diagram of a contact apparatus with an external heat exchanger
For oxidation of sulfur dioxide of increased concentration, it is rational to use contact devices with fluidized beds of catalyst. To reduce the SO2 in the exhaust gases, the double contacting method is widely used, the essence of which is that the oxidation of SO2 on the catalyst is carried out in two stages. In the first stage, the conversion is about 0.90. Before the second stage of contacting, sulfur tri-oxide is separated from the gas; as a result, the ratio of O2: SO 2 , and this increases the equilibrium degree of conversion (xr ). As a result, in one or two layers of the contact mass of the second stage of contacting, the degree of conversion of the remaining sulfur dioxide is 0.995-0.997, and the SO2 in waste gases is reduced to 0.003%. Double contacting gas heats up from 50 to 420-440about With two times - before the first and before the second stage of contact, therefore, the concentration of sulfur dioxide begins to be higher than with a single contact in accordance with the adiabatic level.
1.4 Normal process parameters
In the technological process of sulfuric acid production, there are values \u200b\u200bthat characterize this process, the so-called process parameters.
The set of values \u200b\u200bof all process parameters is called / 12 / technological mode, and the set of parameter values \u200b\u200bthat ensure the solution of the target problem is called the normal technological mode.
The main technological parameters to be monitored have been determined with the justification of their influence on the quality of the manufactured product and the safety of the process.
The following parameters / 2 / are subject to control:
- The temperature of the firing gas supplied to the first wash tower. When the temperature deviates from the specified range: downward - the reaction of SO concentration2
- Temperature in 1, 2, 3, 4, 5 acid tank. When the temperature deviates from the specified range: downward - SO concentration2 will slow down, deviations in a large direction - will lead to an unjustified consumption of heat.
- The temperature of the firing gas at the outlet from the tubular heat exchanger. When the temperature deviates from the specified range: downward - SO concentration2 to SO 3 will slow down, deviations in a large direction - will lead to an unjustified consumption of heat.
- SO 3 temperature in fridge. After leaving the SO3 must be cooled to continue the reaction in the absorption tower.
- Gas pressure supplied to the KS furnace. Natural gas pressure control is essential for correct and efficient combustion. Pressure fluctuations in the gas network can make the combustion process unstable and lead to incomplete combustion of the fuel, and as a result, an unjustified overconsumption of gas fuel will occur. Complete combustion of the gas is important not only to achieve a high furnace efficiency, but also to obtain a harmless mixture of exhaust gases that does not affect human health.
- Air pressure supplied to the turbocharger. Air pressure control is essential for correct and effective work compressor. Air pressure deviation from the specified range will lead to low efficiency of its operation.
- The air pressure supplied to the refrigerator. Air pressure control is essential for maximum refrigerator performance.
- Air flow supplied to the furnace. Air flow control is essential for a correct and efficient combustion process. With small excess air in the combustion space, incomplete combustion of the fuel will occur, and as a result, an unjustified excessive consumption of gas fuel will occur. Complete combustion of the gas is important not only to achieve a high furnace efficiency, but also to obtain a harmless mixture of exhaust gases that does not affect human health.
- Consumption of roasting gas leaving the KS furnace. The amount of firing gas must be constant, as deviation from the norm can harm the production as a whole.
- Pyrite consumption in the furnace. If there is a lack of product, it will lead to unjustified consumption of heat
- Level 1, 2, 3, 4, 5 of the acid collector is needed to obtain the required amount of acid and its further concentration. With a lack or excess of acid, the required concentration will not be achieved.
- Concentration at the first wash tower. The acid supplied to the irrigation of the first washing tower must be of the correct concentration (75% sulfuric acid), otherwise the reaction as a whole will not proceed correctly.
- Concentration at the second wash tower. The acid supplied to the irrigation of the second washing tower must be of the required concentration (30% sulfuric acid), otherwise the reaction as a whole will not proceed correctly.
- Concentration in a drying tower. The acid supplied to the irrigation of the drying tower must be of the correct concentration (98% sulfuric acid), otherwise the reaction as a whole will not proceed correctly.
Table 1 - Technological parameters to be controlled
sulfuric acid production
2. Selection and basis of control and management parameters
2.1 Selection of both basic parameters and controls
2.1.1 Temperature control
It is necessary to control the temperature in the washing tower. In the contact apparatus, it is necessary to control the temperature at 450 ° C, since / 2 / only at this temperature does sulfur burn out from pyrite. Also, with an increase in this temperature, equipment and devices may fail.
2.1.2 Flow control
Control of the flue gas is necessary because its amount affects the combustion of sulfur in the KS furnace. In order for the process to proceed correctly, we put a flow control sensor into the pipeline before the firing gas enters the KS furnace, since it is he who controls the degree of sulfur burnout in the furnace.
2.1.3 Concentration control
Constant monitoring of the sulfur concentration in the acid reservoir is required.
The required level of sulfur concentration is equal to 30% of the total mass of the mixture.
A decrease or an increase in this parameter will lead to product rejects already at the initial stage of production.
It is also necessary to control the concentration of sulfuric acid in the washing tower with a packing equal to 75%, as well as the concentration of the drying tower equal to 92%.
2.1.4 Level control
Level control is necessary in a container for collecting acid, if there is a lot of acid, it can leak out and thereby harm equipment and people nearby.
2.2 Selection and justification of control parameters and exposure channels
2.2.1 Temperature control in the control center
It is necessary to regulate the temperature in the PKS, which should be equal to 450 ° C. An increase in this temperature leads to incomplete burnout of sulfuric acid, and due to insufficiently low temperature, products are defective. Temperature control in this section of the technological process is carried out by controlling the supply of flue gas to the PSC - using an actuator.
2.2.2 Controlling the concentration in the wash tower
It is necessary to constantly monitor the sulfur concentration in the acid collector, which should be equal to 92%. A decrease or increase in this parameter will lead to an incorrect reaction, which will disrupt the entire technological process. The concentration control in this section of the technological process is carried out by controlling the water supply to the acid collector - using the actuator.
2.2.3 Pressure control in the PKS
It is necessary to constantly monitor the pressure in the PKS, which should be equal to 250 kPa. A decrease or an increase in this parameter will lead to product rejects already at the initial stage of production. Pressure regulation in this section of the technological process is carried out by controlling the supply of atmospheric air - using an actuator.
2.2.4 Level control in the acid reservoir
It is necessary to constantly monitor the level in the acid collector, which should not exceed 75 cm. A decrease or increase in this parameter may not harm the technological process.
3. Description of ACP and technical means of automation, selection and justification of regulation laws
3.1 ACP of firing gas temperature after - PCS
The main parameters influencing the process in the PMS are: Fk - pyrite consumption, T - heat loss, Tp - heating steam temperature, Tk - pyrite temperature, TV - air temperature, Pp - heating steam pressure.
Figure 1 - Block diagram of a fluidized bed furnace as a control object
The firing gas temperature at the outlet of the PSC is the main controlled parameter. In order to reach the required temperature, the flue gas flow rate is regulated in accordance with normal operating conditions, using deviation control as the most efficient method in this case.
Figure 2 - Schematic diagram of firing gas temperature control
Figure 3 - Block diagram of firing gas temperature control
3.2 ACP concentration in the wash tower
The main parameters influencing the process in the washing tower:
Fb.g - firing gas consumption, Fк- acid consumption, Qк- acid concentration, Fв- water consumption, Q- impurity concentration, Q SO2- SO2 concentration
Figure 4 - Block diagram of the washing tower
The concentration of sulfuric acid supplied to the wash tower irrigation is the main control parameter. To achieve the required concentration, in accordance with the normal technological mode, the water supply to the acid collector is regulated.
Figure 5 - Schematic diagram of regulation of sulfuric acid concentration
Figure 6 - Block diagram of regulation of sulfuric acid concentration
3.3 ACP of pressure in the PKS
The main parameters affecting the process in the PMS are:
Fk is the pyrite consumption, T is the temperature in the PCC, Fw is the air temperature, Fk is the pyrite temperature.
Figure 7 - Block diagram of the PSC
The air flow supplied to the PKS is the main controlled parameter. In order to achieve the required pressure, in accordance with normal process conditions, the air flow is regulated, while deviation control is used as the most effective method in this case.
Figure 8 - Schematic diagram of pressure regulation
Figure 9 - Block diagram of pressure control in the control center
3.4 ACP level in acid collector
The main parameters affecting the process in the acid collector are: Fk - pyrite consumption, T - temperature in the PCC, Fw - air temperature, Fk - pyrite temperature.
Figure 10 - Block diagram of the level collection
The flow rate of water supplied to the acid collector is the main controlled parameter. In order to achieve the required level, in accordance with the normal technological mode, the water flow is regulated, in this case, deviation control is used, as the most effective method in this case.
Figure 11 - Schematic diagram of level control
Figure 12 - Block diagram of level control
“There is hardly another artificially produced substance that is so often used in technology as sulfuric acid.
Where there are no factories for its production, the profitable production of many other substances of great technical importance is inconceivable ”
DI. Mendeleev
Sulfuric acid is used in various chemical industries:
- mineral fertilizers, plastics, dyes, artificial fibers, mineral acids, detergents;
- in the oil and petrochemical industry:
- in nonferrous metallurgy:
- in ferrous metallurgy:
- in the pulp and paper, food and light industries (for starch, molasses, bleaching of fabrics), etc.
Sulfuric acid production
Sulfuric acid is produced in industry in two ways: contact and nitrous.
Contact method for the production of sulfuric acid
Sulfuric acid is produced by the contact method in large quantities at sulfuric acid plants.
At present, the main method for the production of sulfuric acid is contact, because this method has advantages over others:
Obtaining a product in the form of pure concentrated acid, acceptable to all consumers;
- reduction of emissions of harmful substances into the atmosphere with exhaust gasesI. Raw materials used for the production of sulfuric acid.
Main raw material
sulfur - S
pyrite (pyrite) -FeS 2
sulfides of non-ferrous metals -Cu 2 S, ZnS, PbS
hydrogen sulfide - H 2 S
Supporting material
Catalyst - vanadium oxide -V 2 O 5
II. Preparation of raw materials.
Let us analyze the production of sulfuric acid from pyrite FeS 2.
1) Grinding of pyrite. Large pieces of pyrite are crushed in crushers prior to use. You know that when a substance is ground, the reaction rate increases, because the area of \u200b\u200bthe contact surface of the reactants increases.
2) Purification of pyrite. After crushing the pyrite, it is purified from impurities (waste rock and earth) by flotation. To do this, crushed pyrite is dipped into huge vats of water, mixed, the waste rock floats up, then the waste rock is removed.
III... Basic chemical processes:
4 FeS 2 + 11 O 2 t \u003d 800 ° C→ 2 Fe 2 O 3 + 8 SO 2 + Q or burning sulfurS + O 2 t ° C→ SO 2
2SO 2 + O 2 400-500 ° FROM , V2O5 , p↔ 2SO 3 + Q
SO 3 + H 2 O → H 2 SO 4 + Q
IV ... Technological principles:
Continuity principle;
The principle of the integrated use of raw materials,use of waste from other production;
Waste-free production principle;
Heat transfer principle;
Counterflow principle (fluidized bed);
The principle of automation and mechanization of production processes.
V ... Technological processes:
Continuity principle: roasting of pyrite in a furnace → intake of sulfur oxide (IV ) and oxygen to the cleaning system → to the contact device → supply of sulfur oxide (VI ) into the absorption tower.
VI ... Environmental protection:
1) tightness of pipelines and equipment
2) gas cleaning filters
Vii... Production chemistry :
FIRST STAGE - firing pyrite in a fluidized bed kiln.
To obtain sulfuric acid, they mainly use flotation pyrite - production waste during the beneficiation of copper ores containing mixtures of sulfur compounds of copper and iron. The process of enrichment of these ores takes place at the Norilsk and Talnakh enrichment plants, which are the main suppliers of raw materials. This raw material is more profitable because Sulfur pyrite is mainly mined in the Urals, and, naturally, its delivery can be very expensive. Use is possible sulfur, which is also formed during the dressing of non-ferrous metal ores mined in mines.The Pacific and NOF are also suppliers of sulfur. (concentration factories).
First stage reaction equation
4FeS 2 + 11O 2 t \u003d 800 ° C →2Fe 2 O 3 + 8SO 2 + Q
The crushed purified wet (after flotation) pyrite is poured from above into a "fluidized bed" kiln. Oxygen-enriched air is passed from below (counterflow principle) for a more complete firing of pyrite. The kiln temperature reaches 800 ° C. The pyrite becomes red hot and is "suspended" due to the air blown from below. It all looks like a boiling red-hot liquid. Even the smallest particles of pyrite do not cake in the "fluidized bed". Therefore, the firing process is very fast. If earlier it took 5-6 hours to bake pyrite, now it takes only a few seconds. Moreover, in the "fluidized bed" you can maintain a temperature of 800 ° C.
Due to the heat released as a result of the reaction, the temperature in the furnace is maintained. The excess amount of heat is removed: pipes with water pass along the perimeter of the furnace, which heats up. Hot water is used further for central heating of adjacent premises.
The formed iron oxide Fe 2 O 3 (cinder) is not used in the production of sulfuric acid. But it is collected and sent to a metallurgical plant, where iron and its alloys with carbon are obtained from iron oxide - steel (2% carbon C in the alloy) and cast iron (4% carbon C in the alloy).
Thus, chemical production principle - waste-free production.
Comes out of the oven furnace gas , the composition of which: SO 2, O 2, water vapor (the pyrite was moist!) and the smallest particles of cinder (iron oxide).Such furnace gas must be cleaned from impurities of solid particles of cinder and water vapor.
Cleaning of furnace gas from solid cinder particles is carried out in two stages - in a cyclone (centrifugal force is used, solid cinder particles hit the walls of the cyclone and fall down). For removing small particles the mixture is sent to the electrostatic precipitators, where it is purified under the action of a high voltage current of ~ 60,000 V (electrostatic attraction is used, the cinder particles adhere to the electrified plates of the electrostatic precipitator, with sufficient accumulation under their own weight, they are poured down), to remove water vapor in the furnace gas (drying the furnace gas) use concentrated sulfuric acid, which is a very good desiccant because it absorbs water.
Drying of oven gas is carried out in a drying tower - oven gas rises from bottom to top, and concentrated sulfuric acid flows from top to bottom. To increase the contact surface of gas and liquid, the tower is filled with ceramic rings.
At the outlet of the drying tower, the furnace gas no longer contains any cinder particles or water vapor. The furnace gas is now a mixture of sulfur oxide SO 2 and oxygen O 2.
SECOND STAGE - catalytic oxidation of SO 2 to SO 3 with oxygen in the contact apparatus.
The reaction equation for this stage:
2 SO 2 + O 2 400-500 ° C, V 2 O 5 , p ↔ 2 SO 3 + Q
The complexity of the second stage lies in the fact that the process of oxidation of one oxide to another is reversible. Therefore, it is necessary to select the optimal conditions for the direct reaction (obtaining SO 3).
It follows from the equation that the reaction is reversible, which means that at this stage it is necessary to maintain such conditions so that the equilibrium shifts towards the exitSO 3 otherwise the whole process will be disrupted. Because the reaction proceeds with a decrease in volume (3V ↔2 V ), then increased pressure is required. The pressure is increased to 7-12 atmospheres. The reaction is exothermic, therefore, taking into account the Le Chatelier principle, this process cannot be carried out at high temperatures, because balance will move to the left. The reaction starts at a temperature of \u003d 420 degrees, but thanks to the multilayer catalyst (5 layers), we can increase it to 550 degrees, which significantly speeds up the process. The catalyst is vanadium (V 2 O 5). It is cheap, lasts a long time (5-6 years), the most resistant to the action of toxic impurities. In addition, it helps to shift the balance to the right.
The mixture (SO 2 and O 2) is heated in a heat exchanger and moves through pipes, between which a cold mixture passes in the opposite direction, which must be heated. The result is heat exchange: the starting materials are heated, and the reaction products are cooled to the desired temperatures.
THIRD STAGE - absorption of SO 3 by sulfuric acid in the absorption tower.
Why is sulfur oxide SO 3 do not absorb in water? After all, it would be possible to dissolve sulfur oxide in water: SO 3 + H 2 O → H 2 SO 4 ... But the fact is that if water is used to absorb sulfur oxide, sulfuric acid is formed in the form of a fog, consisting of tiny droplets of sulfuric acid (sulfur oxide dissolves in water, releasing a large amount of heat, sulfuric acid heats up so much that it boils and turns into steam ). In order to avoid the formation of sulfuric acid mist, use 98% concentrated sulfuric acid. Two percent water is so little that heating the liquid will be weak and harmless. Sulfur oxide dissolves very well in such an acid, forming oleum: H 2 SO 4 nSO 3.
The reaction equation of this process:
NSO 3 + H 2 SO 4 → H 2 SO 4 nSO 3
The resulting oleum is poured into metal tanks and sent to the warehouse. Then the tanks are filled with oleum, the trains are formed and sent to the consumer.