MINISTRY OF EDUCATION OF THE REPUBLIC OF BELARUS

BELARUSIAN STATE UNIVERSITY OF ECONOMY

Department of Technology

Individual work on the topic:

"Production of sulfuric acid by the contact method".

Completed by a student of the 1st year of FBD: Klimenok M.A.

Checked by the teacher: Tarasevich V.A.

Minsk 2002

· Abstract

Description of the contact method for the production of sulfuric acid

· Schematic diagram of the production of sulfuric acid by the contact method

The dynamics of labor costs in the development of the technological process

Calculation of the level of technology, those armament and productivity of living labor

· Conclusion

Literature and sources

This work consists of 12 pages.

Key words: Sulfuric acid, Contact method, Reaction, Production technology, Dynamics of labor costs, Technological process.

In this paper, the technology for the production of sulfuric acid by the contact method has been studied and described. Illustrations, diagrams, graphs, and tables reflecting the essence of the technological process are given. The most important trends in the development of sulfuric acid production by the contact method are highlighted.

An analysis of the dynamics of labor costs of living and past labor, as well as the dynamics of labor costs during the development of the technological process, was carried out. The level of technology, those armaments and the productivity of living labor are calculated. Appropriate conclusions and conclusions are drawn.

Description of the contact method for the production of sulfuric acid

A large number of grades of sulfuric acid are produced by the contact method, including oleum containing 20% ​​free SO3, vitriol (92.5% H 2 SO 4 and 7.5% H 2 O), battery acid, about the same concentration as and vitriol oil, but more pure.

The contact method for the production of sulfuric acid includes three stages: gas purification from impurities harmful to the catalyst; contact oxidation of sulfur dioxide to sulfuric anhydride; absorption of sulfuric anhydride by sulfuric acid. The main step is the contact oxidation of SO 2 to SO 3 ; the name of this operation is also called the whole method.

Contact oxidation of sulfur dioxide is a typical example of heterogeneous oxidative exothermic catalysis. This is one of the most studied catalytic syntheses.

Reversible reaction equilibrium
2SO 2 + O 2 >< 2 SO 3 + 2 x 96,7 кдж (500 оС) (а)
in accordance with the Le Chatelier principle, it shifts towards the formation of SO 3 with a decrease in temperature and an increase in pressure; accordingly, the equilibrium degree of conversion of SO 2 to SO 3 increases

It should be noted that an increase in pressure naturally increases the rate of reaction (a). However, it is irrational to use increased pressure in this process, since, in addition to the reacting gases, it would be necessary to compress ballast nitrogen, which usually makes up 80% of the entire mixture, and therefore catalysts are actively used in the production cycle.

The most active catalyst is platinum, but it has fallen into disuse due to high cost and easy poisoning by impurities in the roasting gas, especially arsenic. Iron oxide is cheap, but with the usual gas composition - 7% SO2 and 11% O2, it exhibits catalytic activity only at temperatures above 625 ° C, i.e. when xp 70%, and therefore used only for the initial oxidation of SO2 until reaching xp 50-60%. The vanadium catalyst is less active than the platinum one, but it is cheaper and is poisoned by arsenic compounds several thousand times less than platinum; it turned out to be the most rational and it is the only one used in the production of sulfuric acid. Vanadium contact mass contains on average 7% V2O5; activators are oxides of alkali metals, the K2O activator is usually used; the carrier is porous aluminosilicates. At the moment, the catalyst is used in the form of a compound SiO2, K and/or Cs, V in various proportions. Such a compound turned out to be the most resistant to acid and the most stable. All over the world, its more correct name is "vanadium-containing". Such a catalyst is designed specifically to operate at low temperatures, which results in lower emissions into the atmosphere. In addition, such catalysis is cheaper than potassium / vanadium. Conventional vanadium contact compounds are porous granules, tablets or rings (Fig. 1).

Under the conditions of catalysis, potassium oxide is converted into K2S2O7, and the contact mass is generally a porous carrier, the surface and pores of which are wetted with a film of a solution of vanadium pentoxide in liquid potassium pyrosulfate.
Vanadium contact mass is operated at temperatures from 400 to 600 °C. With an increase in temperature above 600 °C, an irreversible decrease in the activity of the catalyst begins due to the sintering of the components with the formation of inactive compounds that are insoluble in potassium pyrosulfate. As the temperature decreases, the activity of the catalyst sharply decreases due to the conversion of pentavalent vanadium into tetravalent vanadium with the formation of low-activity vanadyl VOSO4.

The catalysis process consists of the following stages: 1) diffusion of the reacting components from the cores of the gas flow to the granules, and then in the pores of the contact mass; 2) oxygen sorption by the catalyst (transfer of electrons from the catalyst to oxygen atoms); 3) sorption of SO2 molecules with the formation of the complex SO2 * O * catalyst; 4) rearrangement of electrons with the formation of the complex SO2 * catalyst; 5) desorption of SO3 from the pores of the contact mass and from the surface of the grains.

With large granules of the contact mass, the total rate of the process is determined by the diffusion of reagents (1st and 6th stages). Usually strive to get granules no more than 5 mm in diameter; in this case, the process proceeds at the first stages of oxidation in the diffusion region, and at the last (at x 80%) in the kinetic region.

Due to the destruction and caking of the granules, contamination of the layer, poisoning of the catalyst with arsenic compounds and its temperature damage in case of accidental violations of the regime, the vanadium contact mass is replaced on average after 4 years. If the gas purification obtained by roasting pyrites is disturbed, then the operation of the contact apparatus is disrupted due to poisoning of the first layer of the contact mass after a few days. To preserve the activity of the catalyst, fine gas cleaning is used by the wet method.

Schematic diagram of the production of sulfuric acid by the contact method

The best raw material for the production of sulfur dioxide is sulfur, which is smelted from natural rocks containing sulfur, and is also obtained as a by-product in the production of copper, gas purification, etc. Sulfur melts at a temperature of 113 degrees C, easily ignites and burns in simple furnaces (Fig. 2). It turns out a gas of high concentration, with a small content of harmful impurities.

Sulfur combustion occurs according to the reaction S + O 2 > SO 2 + 296 kJ. In fact, sulfur melts and evaporates before combustion (bp ~ 444 ° C) and burns in the gas phase. Thus, the combustion process itself is homogeneous.

Compressor and combustion chamber

Unburned sulfur
Air for combustion and afterburning of sulfur
liquid sulfur
Compressed air
Product - roasting gas

flow chart of sulfuric acid production

1 - 1st washing tower; 2 - 2nd washing tower with a nozzle; 3 - wet electrostatic precipitator; 4 - drying tower with a nozzle; 5 - turbocharger; 6 - tubular heat exchanger; 7 - contact device; 8 - tubular gas cooler; 9 and 10 - absorption towers with a nozzle; 11 - centrifugal pumps; 12 - acid collectors; 13 - acid refrigerators

Roasting gas after coarse cleaning from dust in cinder electrostatic precipitators at a temperature of about 300 ° C enters the hollow washing tower (Fig. 3: 1.2), where cold sulfuric acid (75% H 2 SO 4) is sprayed. When the gas is cooled, the sulfuric anhydride and water vapor present in it condense in the form of tiny droplets. Arsenic oxide dissolves in these droplets. An arsenic acid mist is formed, which is partially captured in the first tower and in the second tower with a ceramic nozzle. At the same time, dust residues, selenium and other impurities are captured. Dirty sulfuric acid is formed (up to 8% of the total output), which is issued as non-standard products. The final purification of the gas from the elusive arsenic acid mist is carried out in wet filters (Fig. 3: 3), which are installed in series (two or three). Wet filters work in the same way as dry filters. Fog droplets are deposited on tubular collecting electrodes made of lead or ATM plastic and flow down. Gas cleaning is completed by drying it from water vapor with vitriol oil in a tower with a packing (Fig. 3: 4). Usually two drying towers are installed. Towers, gas ducts and acid collectors in the treatment section are usually steel, lined with acid-resistant bricks or diabase tiles. Dry sulfur dioxide and sulfuric anhydride are not corrosive, so all subsequent equipment up to the monohydrate absorber can be mounted from ordinary carbon steel without corrosion protection.

A large number of equipment creates significant resistance to gas flow (up to 2 m w.c.), so a turbocharger is installed to transport gas (Fig. 3: 5). The compressor, sucking gas from the furnaces through all the equipment, pumps it into the contact assembly.

The contact assembly (Fig. 3: 6,7,8) consists of a contact apparatus, a shell-and-tube heat exchanger and not shown in the diagram (Fig. 4). fire starting gas heater. In the heat exchanger of the starting heater, the gas is heated before entering the apparatus during start-up or when the temperature in the apparatus drops below normal.
Shelf contact devices are usually used. Such an apparatus has a cylindrical body with a diameter of 3 to 10 m and a height of 10-20 m. Four or five gratings are installed inside the body with a layer of contact mass granules on each of them. Intermediate tubular or box-shaped heat exchangers are installed between the layers of the contact mass. The diagram shows a four-layer contact apparatus, although five-layer apparatuses are more often used, but the principle of their operation is completely similar, the difference is only in one more layer of the catalyst. Fresh gas is heated by the heat of the reacted hot gas, first in an external heat exchanger, then it partially or completely passes three or four internal heat exchangers for heating in succession, at 440-450 ° C it enters the first layer of the contact mass. This temperature is controlled by opening valves. The main purpose of the internal heat exchangers is to cool the partially oxidized and heated gas in the catalyst bed, so that the regime gradually approaches the optimum temperature curve.

Shelf contact devices - one of the most common types of contact devices. The principle of their operation is that the heating and cooling of the gas between the catalyst layers lying on the shelves is carried out in the contact apparatus itself using various heat carriers or cooling methods. In apparatuses of this type, the height of each underlying catalyst layer is higher than that located above it, i.e. .e. increases along the gas flow, and the height of the heat exchangers decreases, since as the total degree of conversion increases, the reaction rate decreases and, accordingly, the amount of heat released decreases. In the annular space of the heat exchangers, fresh gas passes sequentially from bottom to top, cooling the reaction products and heating up to the temperature of the beginning of the reaction

The productivity of contact devices in terms of H 2 SO 4, depending on their size, ranges from 50 to 500 tons per day of H 2 SO 4 . Designs of contact devices with a capacity of 1000 and 2000 tons per day have been developed. 200-300 liters of contact mass per 1 ton of daily output are loaded into the apparatus. Tubular contact apparatuses are used for SO 2 oxidation less frequently than shelf ones. For the oxidation of high concentration sulfur dioxide, it is rational to use contact apparatuses with fluidized catalyst beds.

The absorption of sulfuric anhydride according to the reaction SO 3 +H 2 O = H 2 SO 4 +9200 J is usually carried out in towers with a packing (Fig. 3: 9.10), since bubbling or foam absorbers with high work intensity have increased hydraulic resistance. If the partial pressure of water vapor over the absorbing acid is significant, then SO 3 combines with H 2 O in the gas phase and forms tiny droplets of an elusive sulfuric acid mist. Therefore, absorption is carried out with concentrated acids. The best in terms of absorption capacity is an acid containing 98.3% H 2 SO 4 and having a negligible elasticity of both water vapor and SO 3. However, in one cycle in the tower it is impossible to fix the acid from 98.3% to standard oleum containing 18.5-20% free sulfuric anhydride. Due to the large thermal effect of absorption during the adiabatic process in the tower, the acid is heated and absorption stops. Therefore, to obtain oleum, absorption is carried out in two successively installed towers with a nozzle: the first of them is irrigated with oleum, and the second with 98.3% sulfuric acid. To improve absorption, both the gas and the acid entering the absorber are cooled, thus increasing the driving force of the process.

In all contact production towers, including absorbers, the amount of reflux acid is many times greater than necessary to absorb gas components (H 2 O, SO 3) and is determined by the heat balance. To cool circulating acids, irrigation refrigerators are usually installed, in the pipes of which, irrigated from the outside with cold water, the cooled acid flows.

The production of sulfuric acid is greatly simplified by the processing of gas obtained by burning pre-melted and filtered natural sulfur, which contains almost no arsenic. In this case, pure sulfur is burned in air that has been previously dried with sulfuric acid in a packed tower. It turns out a gas of 9% SO2 and 12% O2 at a temperature of 1000 ° C, which is first directed under the steam boiler, and then without purification into the contact apparatus. The intensity of the apparatus is greater than on pyrite gas, due to the increased concentration of SO2 and O2. There are no heat exchangers in the apparatus, since the temperature of the gases is reduced by adding cold air between the layers. SO3 absorption is carried out in the same way as in the flow chart.

The most important trends in the development of sulfuric acid production by the contact method:

1) intensification of processes by carrying them out in a suspended layer, the use of oxygen, the production and processing of concentrated gas, the use of active catalysts;

2) simplification of gas purification methods from dust and contact poisons (shorter technological scheme);

3) increase in equipment power;

4) complex automation of production;

5) reduction of consumption coefficients for raw materials and the use of sulfur-containing wastes from various industries as raw materials;

6) neutralization of waste gases.

Dynamics of labor costs during the development of the technological process

In general terms, all of the above material can be depicted as follows:

It is known that this technological process and the dynamics of labor costs are characterized by the following formulas:

Tf = ---------------------- Tp = 0.004 * t 2 +0.3 Tc = Tf + Tp

The relationship between these formulas looks like this:

Tp \u003d 0.004 * - 75 +0.3 and Tf \u003d 21 * Tp-0.3 +1575

Based on the above formulas, we will carry out the calculations and summarize them in a general table (Table 1):

(Table 1): Dynamics of labor costs in the production of sulfuric acid for 15 years
t (Time, years)	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15
Living labor costs	0,78	0,75	0,71	0,654	0,595	0,54	0,48	0,43	0,38	0,34	0,3	0,27	0,24	0,22	0,198
Past labor costs	0,3	0,32	0,34	0,364	0,4	0,44	0,496	0,56	0,62	0,7	0,78	0,88	0,98	1,08	1,2
Total costs	1,09	1,07	1,04	1,018	0,995	0,98	0,976	0,98	1,01	1,04	1,09	1,15	1,22	1,3	1,398

Based on the table, we will plot the dependences of Tf, Tp, Ts on time (Fig. 7) and the dependences of Tf on Tp (Fig. 6) and Tp on Tl (Fig. 8).

From this graph it can be seen that this technological process is limited in its development.

The economic limit of the accumulation of past labor will come in seven years.

From graphs 7 and 8 it can be seen that the type of technological process is labor-saving.

Calculation of the level of technology, those armament and productivity of living labor.

The technology level is calculated using the formula:

Comfort \u003d 1 / Tzh * 1 / TP

Productivity of living labor:

L = Y those * B

Technical equipment is calculated:

B \u003d Tp / Tzh

Relative technology level:

Watnos = Comfort / L

Let's carry out the calculations using the above formulas and enter the data in the table (Table 2):

T Time (years)	1	2	3	4	5	6	7	8	9	10	11	12	13
Living labor costs	0,78	0,75	0,71	0,654	0,595	0,54	0,48	0,43	0,38	0,34	0,3	0,27	0,24
Past labor costs	0,3	0,32	0,34	0,364	0,4	0,44	0,496	0,56	0,62	0,7	0,78	0,88	0,98
Total costs	1,09	1,07	1,04	1,018	0,995	0,98	0,976	0,98	1,01	1,04	1,09	1,15	1,22
Technology level	4,2	4,2	4,2	4,2	4,2	4,2	4,2	4,2	4,2	4,2	4,2	4,2	4,2
Those. armament	0,39	0,42	0,47	0,556	0,672	0,83	1,033	1,3	1,64	2,058	2,58	3,22	4
Productivity Tzh	1,28	1,33	1,41	1,529	1,68	1,86	2,083	2,34	2,62	2,94	3,29	3,68	4,1
Relative technology level	3,29	3,16	2,98	2,747	2,5	2,25	2,016	1,8	1,6	1,429	1,28	1,14	1,02

From this table it can be seen that rationalistic development is expedient only for seven years, since during this period of time the relative level of technology is greater than the productivity of living labor.

Conclusion

In this paper, the technology for the production of sulfuric acid by the contact method is studied and described, an analysis is made of the dynamics of labor costs of living and past labor, as well as the dynamics of labor costs during the development of the technological process. Based on the work done, the following conclusions were obtained: The development of those processes is limited, the economic limit of the accumulation of past labor is seven years, this technological process is labor-saving and rationalistic development is expedient for seven years.

Literature and sources:

1. PRODUCTION OF SULFURIC ACID / Baranenko D. http://service.sch239.spb.ru:8101/infoteka/root/chemistry/room1/baran/chem.htm

2. Technology of the most important industries: Proc. For eq. Specialist. Universities / A.M. Ginberg, B.A. Khokhlov. - M .: Higher school, 1985.

Stages - preparation of raw materials and their burning or roasting. Their content and instrumentation significantly depend on the nature of the raw material, which to a large extent determines the complexity of the technological production of sulfuric acid. 1. Iron pyrites. Natural pyrite is a complex rock consisting of iron sulfide FeB2, sulfides of other metals (copper, zinc, lead, etc.), ...

Not always feasible yet. At the same time, exhaust gases are the cheapest raw material, wholesale prices for pyrites are also low, while sulfur is the most expensive raw material. Therefore, in order for the production of sulfuric acid from sulfur to be economically viable, a scheme must be developed in which the cost of its processing will be significantly lower than the cost of processing pyrite or waste ...

For automatic control, it is necessary to know as much as possible the requirements of various chemical-technological processes. 1.Main part 1.1 Technological process of obtaining sulfuric anhydride in the production of sulfuric acid. The production of sulfuric acid by the contact method consists of the following steps: 1. Unloading, storage and preparation of raw materials...

Nitric acid is formed: NO(HSO4) + H2O®H2SO4 + HNO2 It oxidizes SO2 according to the equation: SO2 + 2HNO2®H2SO4 + 2NO At the bottom of towers 1 and 2, 75% sulfuric acid accumulates, naturally, in a larger amount than it was spent on the preparation of nitrose (after all, “newborn” sulfuric acid is added). Nitric oxide NO is returned again for oxidation. Because some...

Contact sulfuric acid is reflected in the technological scheme, in which pyrites serve as the feedstock (classical scheme) (Fig. 34). This scheme includes four main stages: 1) obtaining sulfurous anhydride, 2) purification of gas containing sulfurous anhydride from impurities, 3) oxidation (on a catalyst) of sulfurous anhydride to sulfuric anhydride, 4) absorption of sulfuric anhydride.

The apparatuses of the first stage of the process include a kiln 2, in which sulfur dioxide is produced, and a dry electrostatic precipitator 5, in which the kiln gas is cleaned of dust. At the second stage of the process - purification of the roasting gas from impurities that are toxic to the catalyst, the gas enters at 300-400 ° C. The gas is cleaned by washing it with sulfuric acid that is colder than the gas itself. To do this, the gas is sequentially passed through the following apparatuses: washing towers 6 and 7, the first wet electrostatic precipitator 8, the humidifying tower 9 and the second wet electrostatic precipitator 8. In these apparatuses, the gas is purified from arsenic, sulfuric and selenium anhydrides, as well as from dust residues. Next, the gas is released from moisture in the drying tower 10 and splashes of sulfuric acid in

Sprinkler 11. Both washing 6 and 7, humidifying 9 and drying 10 towers are irrigated with circulating sulfuric acid. There are 20 collectors in the irrigation cycle, from which sulfuric acid is pumped to the irrigation towers. In this case, the acid is pre-cooled in refrigerators 18, where the physical heat of the roasting gas is mainly removed from the washing towers, and the heat of dilution of the drying sulfuric acid with water is removed from the drying tower.

Supercharger 12 in this scheme is placed approximately in the middle of the system; all devices located in front of him are under vacuum, after him - he sang under pressure. Thus, apparatuses operate under pressure to ensure the oxidation of sulfur dioxide to sulfur dioxide and the absorption of sulfur dioxide.

When sulfurous anhydride is oxidized to medium, a large amount of heat is released, which is used to heat the purified roasting gas entering the contact apparatus 14. Hot sulfuric anhydride through the walls of the pipes through which it passes in the heat exchanger 13 transfers heat to the colder sulfurous anhydride passing in the annulus the space of the heat exchanger 13 and entering the contact apparatus 14. Further cooling of sulfuric anhydride before absorption in the oleum 16 and monohydrate 17 absorbers occurs in the anhydride refrigerator (economizer) 15.

When sulfuric anhydride is absorbed in the absorption compartment, a large amount of hepl is released, which is transferred to the circulating acid, which irrigates the oleum 16 and monohydrate 17 absorbers, and is removed in refrigerators 19 and 18.

The concentration of oleum and monohydrate increases due to the absorption of more and more portions of sulfuric anhydride. Drying acid is diluted all the time due to the absorption of water vapor from the burning gas. Therefore, to maintain stable concentrations of these acids, there are cycles of dilution with olsumsі monohydrate, monohydrate with drying acid and a cycle of increasing the concentration of drying acid with monohydrate. Since the water entering the monohydrate absorber with drying acid is almost always insufficient to obtain the desired concentration of SOUR!, water is added to the monohydrate absorber collector.

In the first washing tower 6, the acid concentration increases due to the absorption of a small amount of sulfuric anhydride from the gas, which is formed during the roasting of pyrites in furnaces. To maintain a stable concentration of wash acid in the first wash tower, acid from the second wash tower is transferred to its collector. In order to maintain the required concentration of acid in the second washing tower, acid from the humidification tower is transferred to it. If at the same time there is not enough water to obtain a standard acid concentration in the first washing tower, then it is introduced into the collector of either the humidifier or the second washing tower.

Contact sulfuric acid plants usually produce three types of products: oleum, commercial sulfuric acid and dilute sulfuric acid from the first washing tower (after separation of selenium from acid).

In some plants, washing acid after cleaning from impurities is used to dilute the monohydrate or to prepare concentrated sulfuric acid by diluting oleum. Sometimes oleum is simply diluted with water.

According to the scheme shown in Fig. 34, a gas containing 4-7.5% SO2 is processed. autothermicity of the process.) At a higher concentration of SO2, the degree of contact decreases.

Currently, work is underway to improve the scheme for the production of contact sulfuric acid by redesigning the individual stages of this process and using more powerful devices that provide high system performance.

In many plants, drying towers and monohydrate absorbers use acid distributors, after which the gas contains a minimum amount of spatter. In addition, devices for separating mist droplets and splashes are provided directly in the towers or after them. At a number of plants, the humidification tower was excluded from the technological scheme; its absence is compensated by an increase in the power of wet electrostatic precipitators or some change in the operating mode of the washing towers for more intensive gas humidification in the second washing tower, which makes it possible to reduce the cost of electricity for wet cleaning.

In the sulfuric acid industry, intensive and more advanced devices are beginning to be widely used, replacing packed towers, irrigation coolers, centrifugal pumps, etc. sprayed with gas.

As a result of the use of oxygen blowing during the roasting of raw materials in non-ferrous metallurgy, the concentration of SO2 in the exhaust gases increases, which makes it possible to intensify sulfuric acid systems operating on these gases. The use of acid-resistant materials in the manufacture of equipment for the production of sulfuric acid by the contact method can significantly improve product quality and increase the production of reactive sulfuric acid.

The technological process for the production of sulfuric acid from elemental sulfur by the contact method differs from the production process from pyrites in a number of features:

special design of furnaces for production of furnace gas;

increased content of sulfur oxide (IV) in furnace gas;

no pre-treatment of furnace gas. The production of sulfuric acid from sulfur using the double contact and double absorption method (Fig. 1) consists of several stages:

The air after cleaning from dust is supplied by a gas blower to the drying tower, where it is dried with 93-98% sulfuric acid to a moisture content of 0.01% by volume; The dried air enters the sulfur furnace after preheating in one of the heat exchangers of the contact unit.

The combustion (combustion) of sulfur is a homogeneous exothermic reaction, which is preceded by the transition of solid sulfur to a liquid state and its subsequent evaporation:

S TV →S F →S STEAM

Thus, the combustion process takes place in the gas phase in a stream of pre-dried air and is described by the equation:

S + O 2 → SO 2 + 297.028 kJ;

For burning sulfur, burner and cyclone furnaces are used. In burner furnaces, molten sulfur is sprayed into the combustion chamber by compressed air through nozzles that cannot provide sufficient mixing of sulfur vapor with air and the required combustion rate. In cyclone furnaces, operating on the principle of centrifugal dust collectors (cyclones), a much better mixing of the components is achieved and a higher intensity of sulfur combustion is provided than in nozzle furnaces.

Then the gas containing 8.5-9.5% SO 3 at 200°C enters the first stage of absorption into the absorber irrigated with oleum and 98% sulfuric acid:

SO 3 + H 2 O→N 2 SO 4 +130.56 kJ;

Next, the gas is cleaned from splashes of sulfuric acid, heated to 420°C, and enters the second conversion stage, which takes place on two catalyst layers. Prior to the second absorption stage, the gas is cooled in an economizer and fed into the second stage absorber, sprayed with 98% sulfuric acid, and then, after being splashed, it is released into the atmosphere.

Furnace gas from sulfur combustion has a higher content of sulfur oxide (IV) and does not contain a large amount of dust. When burning native sulfur, it also completely lacks arsenic and selenium compounds, which are catalytic poisons.

This circuit is simple and is called the "short circuit" (Fig. 2).

Rice. 1. Scheme for the production of sulfuric acid from sulfur by the DK-DA method:

1 sulfur furnace; 2-heat recovery boiler; 3 - economizer; 4-starter firebox; 5, 6-heat exchangers of the starting furnace; 7-pin device; 8-heat exchangers; 9-oleum absorber; 10 drying tower; 11 and 12 respectively. first and second monohydrate absorbers; 13-collectors of acid.

Fig.2. Production of sulfuric acid from sulfur (short scheme):

1 - melting chamber for sulfur; 2 - liquid sulfur filter; 3 - furnace for burning sulfur; 4 - waste heat boiler; 5 - contact device; 6 - absorption system of sulfur oxide (VI); 7- sulfuric acid refrigerators

The existing plants for the production of sulfuric acid from sulfur, equipped with cyclone-type furnaces, have a capacity of 100 tons of sulfur or more per day. New designs are being developed with a capacity of up to 500 t/day.

Consumption per 1 ton of monohydrate: sulfur 0.34 tons, water 70 m 3, electricity 85 kWh.

Sulfuric acid is produced in large quantities in 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 pyrite FeS2.

1) Grinding of pyrite.

Before use, large pieces of pyrite are crushed in crushers. You know that when a substance is crushed, the reaction rate increases, because. the surface area of ​​contact of the reactants increases.

2) Purification of pyrite.

After crushing pyrite, it is purified from impurities (waste rock and earth) by flotation. To do this, crushed pyrite is lowered 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 - pyrite roasting in a "fluidized bed" kiln.

First stage reaction equation

4FeS2 + 11O2 2Fe2O3 + 8SO2 + Q

Crushed, cleaned, wet (after flotation) pyrite is poured from above into a furnace for firing in a "fluidized bed". From below (counterflow principle) air enriched with oxygen is passed through for a more complete firing of pyrite. The temperature in the kiln reaches 800°C. Pyrite is heated to red and is in a "suspended state" 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. Excess heat is removed: pipes with water run along the perimeter of the furnace, which is heated. Hot water is used further for central heating of adjacent premises.

The formed iron oxide Fe2O3 (calcine) is not used in the production of sulfuric acid. But it is collected and sent to a metallurgical plant, where iron metal 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 (pyrite was wet!) And the smallest particles of cinder (iron oxide). Such furnace gas must be cleaned from impurities of solid particles of cinder and water vapor.

Purification of furnace gas from solid particles of cinder is carried out in two stages - in a cyclone (centrifugal force is used, solid particles of cinder hit the walls of the cyclone and fall down) and in electrostatic precipitators (electrostatic attraction is used, particles of cinder stick to the electrified plates of the electrostatic precipitator, with sufficient accumulation of under they fall down with their own weight), to remove water vapor in the furnace gas (drying the furnace gas), concentrated sulfuric acid is used, which is a very good desiccant, since it absorbs water.

Drying of furnace gas is carried out in a drying tower - furnace 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 any cinder particles or water vapor. Furnace gas is now a mixture of sulfur oxide SO2 and oxygen O2.

SECOND STAGE - oxidation of SO2 to SO3 by oxygen.

It flows in the contact device.

The reaction equation for this stage is: 2SO2 + O2 2SO3 + Q

The complexity of the second stage lies in the fact that the process of oxidation of one oxide into another is reversible. Therefore, it is necessary to choose the optimal conditions for the direct reaction (obtaining SO3).

a) temperature:

The direct reaction is exothermic +Q, according to the rules for shifting chemical equilibrium, in order to shift the reaction equilibrium 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 the direct reaction to proceed with the maximum formation of SO3 is a temperature of 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:

The direct reaction proceeds with a decrease in the volumes 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 shifting 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 the heat exchanger, which is installed in front of the contact apparatus. The mixture passes between the tubes of the heat exchanger and is heated from these tubes. Inside the tubes, hot SO3 passes from the contact apparatus. Getting into the contact apparatus, the mixture of SO2 and O2 continues to heat up to the desired temperature, passing between the tubes in the contact apparatus.

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, sulfur oxide could be dissolved 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 mist consisting of tiny droplets of sulfuric acid (sulfur oxide dissolves in water with the release of a large amount of heat, sulfuric acid is so hot 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 small 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 for this process is nSO3 + H2SO4 H2SO4 nSO3

The resulting oleum is poured into metal tanks and sent to the warehouse. Then tanks are filled with oleum, 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.

Sulfuric acid is produced in three stages: SO2 is produced in the first stage, FeS2 is calcined, then SO3, after which sulfuric acid is obtained in the third stage.

The scientific and technological revolution and the intensive growth of chemical production associated with it cause significant negative changes in the environment. For example, poisoning of fresh water, pollution of the earth's atmosphere, extermination of animals and birds. As a result, the world is in the grip of an ecological crisis. Harmful emissions from sulfuric acid plants should be assessed not only by the effect of the sulfur oxide they contain on the areas located near the enterprise, but also other factors should be taken into account - an increase in the number of cases of respiratory diseases in humans and animals, the death of vegetation and the suppression of its growth, the destruction of structures made of limestone and marble, increase in corrosion 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 is dangerous, 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 snow melts, causes the death of eggs and juvenile fish. In addition to environmental damage, there is economic damage - huge amounts are lost every year due to soil deoxidation.

Let's take a look at chemical cleaning methods for 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. Also of interest are catalytic methods for the oxidation of sulfur oxide in the presence of vanadium oxide.

Of particular importance is the purification of gases from fluorine-containing impurities, which, even in small concentrations, adversely affect vegetation. If the gases contain hydrogen fluoride and fluorine, then they are passed through columns with countercurrent packing in relation to a 5-10% sodium hydroxide solution. The following reactions take place within one minute:

F2+2NaOH->O2+H2O+2NaF

HF+NaOH->NaF+H2O;

The resulting sodium fluoride is treated to regenerate sodium hydroxide.

The initial reagents for the production of sulfuric acid can be elemental sulfur and sulfur-containing compounds, from which either sulfur or sulfur dioxide can be obtained.

Traditionally, the main sources of raw materials are sulfur and iron (sulfur) pyrites. About half of sulfuric acid is obtained from sulfur, a third - from pyrites. A significant place in the raw material balance is occupied by off-gases from non-ferrous metallurgy, containing sulfur dioxide.

At the same time, exhaust gases are the cheapest raw material, wholesale prices for pyrite are also low, while sulfur is the most expensive raw material. Therefore, in order for the production of sulfuric acid from sulfur to be economically viable, a scheme must be developed in which the cost of its processing will be significantly lower than the cost of processing pyrite or off-gases.

Obtaining sulfuric acid from hydrogen sulfide

Sulfuric acid is produced from hydrogen sulfide by wet catalysis. Depending on the composition of combustible gases and the method of their purification, hydrogen sulfide gas can be concentrated (up to 90%) and weak (6-10%). This determines the scheme for processing it into sulfuric acid.

Figure 1.1 shows a scheme for the production of sulfuric acid from concentrated hydrogen sulfide gas. Hydrogen sulfide mixed with air purified in the filter 1 enters the furnace 3 for combustion. In the waste heat boiler 4, the temperature of the gas leaving the furnace decreases from 1000 to 450 °C, after which the gas enters the contact apparatus 5. The temperature of the gas leaving the layers of the contact mass is reduced by blowing in dry cold air. From the contact apparatus, the gas containing SO 3 enters the condenser tower 7, which is a scrubber with a nozzle irrigated with acid. The temperature of the irrigating acid at the entrance to the tower is 50-60°С, at the exit 80-90°С. In this mode, in the lower part of the tower, the gas containing H 2 O and SO 3 vapors is rapidly cooled, high supersaturation occurs and a fog of sulfuric acid is formed (up to 30-35% of all output goes into fog), which is then captured in the electrostatic precipitator 8. For For the best deposition of fog droplets in electrostatic precipitators (or filters of another type), it is desirable that these droplets be large. This is achieved by increasing the temperature of the spray acid, which leads to an increase in the temperature of the acid flowing out of the tower (an increase in the temperature of the condensation surface) and contributes to the coarsening of the fog droplets. The scheme for the production of sulfuric acid from weak hydrogen sulfide gas differs from the scheme shown in Figure 1.1 in that the air supplied to the furnace is preheated in heat exchangers by the gas leaving the catalyst layers, and the condensation process is carried out in a bubbling condenser of the Chemiko concentrator type.

The gas passes through the acid layer in succession in three chambers of the bubbling apparatus, the temperature of the acid in them is controlled by supplying water, the evaporation of which absorbs heat. Due to the high temperature of the acid in the first chamber (230-240°C), H 2 SO 4 vapors condense in it without fog formation.

1-filter, 2-fan, 3-furnace, 4-steam waste-heat boiler, 5-pin apparatus, 6-refrigerator, 7-tower-condenser, 8-electric filter, 9-circulation collector, 10-pump.

Figure 1.1 Scheme for the production of sulfuric acid from high concentration hydrogen sulfide gas:

In the two subsequent chambers (the temperature of the acid in them, respectively, is about 160 and 100 °C), fog is formed. However, due to the rather high temperature of the acid and the large amount of water vapor in the gas, corresponding to the pressure of saturated water vapor over the acid in the chambers, the mist is formed in the form of large droplets that are easily deposited in the electrostatic precipitator.

Productive acid flows out of the first (along the gas) chamber, is cooled in the refrigerator and fed to the warehouse. The surface of refrigerators in such an absorption compartment is 15 times smaller than in an absorption compartment with a condenser tower, due to the fact that the main amount of heat is removed by water evaporation. The concentration of acid in the first chamber (production acid) is about 93.5%, in the second and third chambers, respectively, 85 and 30%. .