Sulfur combustion in dry air and heat recovery to produce power steam. Characteristics of sulfur, its interaction with metals, halogens and oxygen

Dependence of the degree of dissociation of sulfur vapor on temperature.

The combustion of sulfur is a complex process due to the fact that sulfur has molecules with a different number of atoms in different allotropic states and a large dependence of its physicochemical properties on temperature. The reaction mechanism and the yield of products change both with temperature and oxygen pressure.

An example of the dependence of the dew point on the content of CO2 in combustion products.

The combustion of sulfur at 80°C is possible for various reasons. There is as yet no firmly established theory of this process. It is assumed that part of this occurs in the furnace itself at high temperature and with a sufficient excess of air. Studies in this direction (Fig. 6b) show that at small excesses of air (on the order of cst 105 and below), the formation of 80 s in gases is sharply reduced.

The combustion of sulfur in oxygen proceeds at 280 C, and in air at 360 C.

Sulfur combustion occurs throughout the entire volume of the furnace. In this case, gases are obtained more concentrated and their processing is carried out in apparatuses of smaller dimensions, and gas purification is almost eliminated. Sulfur dioxide obtained by burning sulfur, in addition to the production of sulfuric acid, is used in a number of industries for cleaning oil cuts as a refrigerant, in the production of sugar, etc. SCb is transported in steel cylinders and tanks in a liquid state. Liquefaction of SO2 is carried out by compressing pre-dried and cooled gas.

The burning of sulfur occurs throughout the volume of the furnace and ends in the chambers formed by partitions 4, where additional air is supplied. Hot furnace gas containing sulfur dioxide is discharged from these chambers.

Sulfur burning is very easy to observe in mechanical furnaces. On the upper floors of the furnaces, where there is a lot of FeS2 in the burning material, the entire flame is colored blue - this is the characteristic flame of sulfur combustion.

The process of burning sulfur is described by the equation.

The burning of sulfur is observed through a sight glass in the wall of the furnace. The temperature of the molten sulfur should be maintained within 145 - 155 C. If you continue to increase the temperature, the viscosity of sulfur gradually increases and at 190 C it turns into a thick dark brown mass, which makes it extremely difficult to pump and spray.

When sulfur burns, there is one oxygen molecule per atom of sulfur.

Scheme of a combined contact-tower system using natural tower acid as a raw material.

During the combustion of sulfur in the furnace, roasting sulfur dioxide is obtained with a content of about 14% S02 and a temperature at the outlet of the furnace of about 1000 C. With this temperature, the gas enters the waste heat boiler 7, where steam is obtained by lowering its temperature to 450 C. Sulfur dioxide with a content of about 8% SO2 must be sent to contact apparatus 8, therefore, after the waste heat boiler, part of the gas or all of the combustion gas is diluted to 8% SO2 with air heated in heat exchanger 9. In the contact apparatus, 50 - 70% of sulfurous anhydride is oxidized to sulfuric anhydride.

From Wikipedia.

Fire properties of sulfur.
Finely ground sulfur is prone to chemical spontaneous combustion in the presence of moisture, in contact with oxidizing agents, and also in mixtures with coal, fats, and oils. Sulfur forms explosive mixtures with nitrates, chlorates and perchlorates. It ignites spontaneously on contact with bleach.

Extinguishing media: water spray, air-mechanical foam.

According to W. Marshall, sulfur dust is classified as explosive, but an explosion requires a sufficiently high concentration of dust - about 20 g / m³ (20,000 mg / m³), this concentration is many times higher than the maximum permissible concentration for a person in the air of the working area - 6 mg/m³.

Vapors form an explosive mixture with air.

The combustion of sulfur proceeds only in the molten state, similar to the combustion of liquids. The upper layer of burning sulfur boils, creating vapors that form a faint flame up to 5 cm high. The temperature of the flame when burning sulfur is 1820 ° C.

Since air by volume consists of approximately 21% oxygen and 79% nitrogen, and when sulfur is burned, one volume of SO2 is obtained from one volume of oxygen, the maximum theoretically possible content of SO2 in the gas mixture is 21%. In practice, combustion occurs with a certain excess of air, and the volume content of SO2 in the gas mixture is less than theoretically possible, usually 14 ... 15%.

Detection of sulfur combustion by fire automatics is a difficult problem. The flame is difficult to detect with the human eye or a video camera, the spectrum of blue flame lies mainly in the ultraviolet range. The heat generated in a fire results in temperatures lower than fires of other common flammable substances. To detect combustion with a heat detector, it is necessary to place it directly close to sulfur. The sulfur flame does not radiate in the infrared range. Thus, it will not be detected by common infrared detectors. They will only detect secondary fires. A sulfur flame does not emit water vapor. Therefore, ultraviolet flame detectors using nickel compounds will not work.

To comply with fire safety requirements in sulfur warehouses, it is necessary to:

Structures and process equipment should be regularly cleaned of dust;
the storage room must be constantly ventilated by natural ventilation with the doors open;
crushing of sulfur lumps on the grate of the bunker should be carried out with wooden sledgehammers or a tool made of non-sparking material;
conveyors for supplying sulfur to production facilities must be equipped with metal detectors;
in places of storage and use of sulfur, it is necessary to provide devices (sides, thresholds with a ramp, etc.) that ensure in an emergency that the sulfur melt does not spread outside the room or open area;
in the sulfur warehouse it is prohibited:
performance of all types of work with the use of open fire;
store and store oiled rags and rags;
when repairing, use a tool made of sparking material.

Pure sulfur is supplied through a heated pipeline from the overpass to the collector. The source of liquid sulfur in the roasting compartment can be both the unit for melting and filtering lump sulfur, and the unit for draining and storing liquid sulfur from railway tanks. From the collector through an intermediate collector with a capacity of 32 m3, sulfur is pumped through a ring sulfur pipeline to the boiler unit for combustion in a stream of dried air.

When sulfur is burned, sulfur dioxide is formed by the reaction:

S(liquid) + O2(gas) = SO2(gas) + 362.4 kJ.

This reaction proceeds with the release of heat.

The combustion process of liquid sulfur in an air atmosphere depends on the firing conditions (temperature, gas flow rate), on the physical and chemical properties (presence of ash and bituminous impurities in it, etc.) and consists of separate successive stages:

mixing drops of liquid sulfur with air;

heating and evaporation of drops;

formation of a gas phase and ignition of gaseous sulfur;

combustion of vapors in the gas phase.

These stages are inseparable from each other and proceed simultaneously and in parallel. There is a process of diffusion combustion of sulfur with the formation of sulfur dioxide, a small amount of sulfur dioxide is oxidized to trioxide. During the combustion of sulfur, with an increase in the temperature of the gas, the concentration of SO2 increases in proportion to the temperature. When sulfur is burned, nitrogen oxides are also formed, which pollute the production acid and are polluting harmful emissions. The amount of nitrogen oxides formed depends on the mode of sulfur combustion, excess air and process temperature. As the temperature rises, the amount of nitrogen oxides formed increases. With an increase in the excess air coefficient, the amount of nitrogen oxides formed increases, reaching a maximum at an excess air coefficient from 1.20 to 1.25, then drops.

The sulfur combustion process is carried out at a design temperature of not more than 1200ºC with excess air supply to the cyclone furnaces.

When liquid sulfur is burned, a small amount of SO3 is formed. The total volume fraction of sulfur dioxide and trioxide in the process gas after the boiler is up to 12.8%.

By blowing cold dried air into the gas duct in front of the contact apparatus, the process gas is additionally cooled and diluted to operating standards (the total volume fraction of sulfur dioxide and trioxide is not more than 11.0%, temperature is from 390 ° C to 420 ° C).

Liquid sulfur is supplied to the nozzles of the cyclone furnaces of the combustion unit by two submersible pumps, one of which is standby.

The air dried in the drying tower by a blower (one - working, one - reserve) is supplied to the unit for burning sulfur and diluting the gas to operating standards.

Combustion of liquid sulfur in the amount of 5 to 15 m 3 /h (9 to 27 t/h) is carried out in 2 cyclone furnaces located relative to each other at an angle of 110 degrees. and connected to the boiler by a connecting chamber.

Liquid filtered sulfur with a temperature of 135 o C to 145 o C is supplied for combustion. Each furnace has 4 nozzles for sulfur with a steam jacket and one starting gas burner.

The gas temperature at the outlet of the energy technological boiler is controlled by a throttle valve on the hot bypass, which passes gas from the afterburning chamber of cyclone furnaces, as well as a cold bypass, which passes part of the air past the boiler unit into the flue after the boiler.

Water-tube energy technology unit with natural circulation, single-pass for gas is designed for cooling sulfurous gases when burning liquid sulfur and generating superheated steam with a temperature of 420 ° C to 440 ° C at a pressure of 3.5 to 3.9 MPa.

The energy technological unit consists of the following main units: a drum with an intra-drum device, an evaporator device with a convective beam, a tubular cooled frame, a furnace consisting of two cyclones and a transition chamber, a portal, a frame for the drum. The 1st stage superheater and the 1st stage economizer are combined into one remote unit, the 2nd stage superheater and the 2nd stage economizer are located in separate remote units.

The temperature of the gas after the furnaces in front of the evaporation unit rises to 1170 ° C. In the evaporation part of the boiler, the process gas is cooled from 450 ° C to 480 ° C, after the cold bypass, the gas temperature decreases from 390 ° C to 420 ° C. The cooled process gas is sent to the subsequent stage of sulfuric acid production - the oxidation of sulfur dioxide to sulfur trioxide in a contact apparatus.

Sulfur (S)
atomic number	16
Appearance of a simple substance	light yellow brittle solid, odorless in pure form
Atom properties
Atomic mass (molar mass)	32.066 a. e.m. (g/mol)
Atom radius	127 pm
Ionization energy (first electron)	999.0 (10.35) kJ/mol (eV)
Electronic configuration	3s 2 3p 4
Chemical properties
covalent radius	102 pm
Ion radius	30 (+6e) 184 (-2e) pm
Electronegativity (according to Pauling)	2,58
Electrode potential	0
Oxidation states	6, 4, 2, -2
Thermodynamic properties of a simple substance
Density	2.070 g/cm³
Molar heat capacity	22.61 J/(K mol)
Thermal conductivity	0.27 W/(m K)
Melting temperature	386K
Melting heat	1.23 kJ/mol
Boiling temperature	717.824K
Heat of evaporation	10.5 kJ/mol
Molar volume	15.5 cm³/mol
The crystal lattice of a simple substance
Lattice structure	orthorhombic
Lattice parameters	a=10.437 b=12.845 c=24.369 Å
c/a ratio	—
Debye temperature	n/a K

S	16
32,066
3s 2 3p 4
Sulfur

Sulfur (Sulfur- designation "S" in the periodic table) - a highly electronegative element, exhibits non-metallic properties. In hydrogen and oxygen compounds, it is part of various ions, forms many acids and salts. Many sulfur-containing salts are sparingly soluble in water.

Natural sulfur minerals

Sulfur is the sixteenth most abundant element in the earth's crust. It occurs in the free (native) state and bound form. The most important natural sulfur compounds FeS2 are iron pyrite or pyrite, ZnS is zinc blende or sphalerite (wurtzite), PbS is lead gloss or galena, HgS is cinnabar, Sb2S3 is antimonite. In addition, sulfur is present in oil, natural coal, natural gases and shale. Sulfur is the sixth element in natural waters, occurs mainly in the form of sulfate ion and causes the "permanent" hardness of fresh water. A vital element for higher organisms, an integral part of many proteins, is concentrated in the hair.

History of discovery and origin of the name

Sulfur (Sulfur, French Sufre, German Schwefel) in its native state, as well as in the form of sulfur compounds, has been known since ancient times. With the smell of burning sulfur, the suffocating effect of sulfur dioxide and the disgusting smell of hydrogen sulfide, people probably met in prehistoric times. It is because of these properties that sulfur was used by priests as part of sacred incense during religious rites. Sulfur was considered the product of superhuman beings from the world of spirits or underground gods. A very long time ago, sulfur began to be used as part of various combustible mixtures for military purposes. Homer already describes "sulphurous fumes", the deadly effect of the secretions of burning sulfur. Sulfur was probably part of the "Greek fire", which terrified opponents.

Around the 8th century the Chinese began to use it in pyrotechnic mixtures, in particular, in mixtures such as gunpowder. The combustibility of sulfur, the ease with which it combines with metals to form sulfides (for example, on the surface of pieces of metal), explains why it was considered the "principle of combustibility" and an indispensable component of metal ores. Presbyter Theophilus (XII century) describes a method of oxidative roasting of sulfide copper ore, probably known in ancient Egypt.

During the period of Arabic alchemy, the mercury-sulfur theory of the composition of metals arose, according to which sulfur was considered an obligatory constituent (father) of all metals. Later it became one of the three principles of alchemists, and later the "principle of combustibility" was the basis of the theory of phlogiston. The elementary nature of sulfur was established by Lavoisier in his combustion experiments. With the introduction of gunpowder in Europe, the development of the extraction of natural sulfur began, as well as the development of a method for obtaining it from pyrites; the latter was common in ancient Russia. For the first time in the literature, it is described by Agricola. Thus, the exact origin of sulfur has not been established, but as mentioned above, this element was used before the birth of Christ, which means it has been familiar to people since ancient times.

origin of name

Origin of Latin sulfur unknown. The Russian name of the element is usually derived from the Sanskrit "sire" - light yellow. Perhaps the relationship of "sulphur" with the Hebrew "seraph" - the plural of "seraph" - letters. burning, and sulfur burns well. In Old Russian and Old Slavonic, “sulfur” is generally a combustible substance, including fat.

Origin of sulfur

Large accumulations of native sulfur are not so common. More often it is present in some ores. Native sulfur ore is a rock interspersed with pure sulfur.

When did these inclusions form - simultaneously with accompanying rocks or later? The direction of prospecting and exploration works depends on the answer to this question. But, despite the millennia of communication with sulfur, humanity still does not have a clear answer. There are several theories, the authors of which hold opposing views.

The theory of syngenesis (that is, the simultaneous formation of sulfur and host rocks) suggests that the formation of native sulfur occurred in shallow water basins. Special bacteria reduced sulfates dissolved in water to hydrogen sulfide, which rose up, entered the oxidizing zone, and here it was oxidized chemically or with the participation of other bacteria to elemental sulfur. The sulfur settled to the bottom, and subsequently the sulfur-bearing sludge formed the ore.

The theory of epigenesis (sulfur inclusions formed later than the main rocks) has several options. The most common of them suggests that groundwater, penetrating through the rock masses, is enriched with sulfates. If such waters come into contact with oil or natural gas deposits, then sulfate ions are reduced by hydrocarbons to hydrogen sulfide. Hydrogen sulfide rises to the surface and, oxidizing, releases pure sulfur in voids and cracks in rocks.

In recent decades, one of the varieties of the theory of epigenesis, the theory of metasomatosis (in Greek, “metasomatosis” means replacement), has been finding more and more confirmation. According to it, the transformation of gypsum CaSO4-H2O and anhydrite CaSO4 into sulfur and calcite CaCO3 is constantly taking place in the depths.

This theory was created in 1935 by Soviet scientists L. M. Miropolsky and B. P. Krotov. In its favor speaks, in particular, such a fact.

In 1961, the Mishrak field was discovered in Iraq. Sulfur here is enclosed in carbonate rocks, which form a vault supported by outgoing supports (in geology they are called wings). These wings are composed mainly of anhydrite and gypsum. The same picture was observed at the domestic Shor-Su field.

The geological originality of these deposits can only be explained from the standpoint of the theory of metasomatism: primary gypsum and anhydrite have turned into secondary carbonate ores interspersed with native sulfur. Not only the proximity of minerals is important - the average sulfur content in the ore of these deposits is equal to the content of chemically bound sulfur in anhydrite. And studies of the isotopic composition of sulfur and carbon in the ore of these deposits gave additional arguments to supporters of the theory of metasomatism.

But there is one “but”: the chemistry of the process of converting gypsum into sulfur and calcite is not yet clear, and therefore there is no reason to consider the theory of metasomatism the only correct one. There are lakes on the earth even now (in particular, Sulfur Lake near Sernovodsk), where syngenetic deposition of sulfur occurs and sulfur-bearing sludge does not contain either gypsum or anhydrite.

The variety of theories and hypotheses about the origin of native sulfur is the result not only and not so much of the incompleteness of our knowledge, but of the complexity of the phenomena occurring in the depths. Even from elementary school mathematics, we all know that different paths can lead to the same result. This law also applies to geochemistry.

Receipt

Sulfur is obtained mainly by smelting native sulfur directly in places where it occurs underground. Sulfur ores are mined in different ways - depending on the conditions of occurrence. Sulfur deposits are almost always accompanied by accumulations of poisonous gases - sulfur compounds. In addition, we must not forget about the possibility of its spontaneous combustion.

Ore mining in an open way is as follows. Walking excavators remove layers of rocks under which ore lies. The ore layer is crushed by explosions, after which the ore blocks are sent to a sulfur smelter, where sulfur is extracted from the concentrate.

In 1890, Hermann Frasch proposed to melt sulfur underground and pump it to the surface through wells similar to oil wells. The relatively low (113°C) melting point of sulfur confirmed the reality of Frasch's idea. In 1890, tests began that led to success.

There are several methods for obtaining sulfur from sulfur ores: steam-water, filtration, thermal, centrifugal and extraction.

Sulfur is also found in large quantities in natural gas in the gaseous state (in the form of hydrogen sulfide, sulfur dioxide). During extraction, it is deposited on the walls of pipes and equipment, disabling them. Therefore, it is captured from the gas as soon as possible after extraction. The resulting chemically pure fine sulfur is an ideal raw material for the chemical and rubber industries.

The largest deposit of native sulfur of volcanic origin is located on the island of Iturup with reserves of category A + B + C1 - 4227 thousand tons and category C2 - 895 thousand tons, which is enough to build an enterprise with a capacity of 200 thousand tons of granulated sulfur per year.

Manufacturers

The main sulfur producers in Russia are the enterprises of OAO Gazprom: OOO Gazprom dobycha Astrakhan and OOO Gazprom dobycha Orenburg, which receive it as a by-product during gas purification.

Physical properties

Natural intergrowth of crystals of native sulfur

Sulfur differs significantly from oxygen the ability to form stable chains and cycles of sulfur atoms. The most stable are cyclic molecules S 8 having the shape of a crown, forming rhombic and monoclinic sulfur. This is crystalline sulfur - a brittle yellow substance. In addition, molecules with closed (S4, S6) chains and open chains are possible. Such a composition has plastic sulfur, a brown substance. The formula for plastic sulfur is most often written simply as S, since, although it has a molecular structure, it is a mixture of simple substances with different molecules. Sulfur is insoluble in water, some of its modifications dissolve in organic solvents, such as carbon disulfide. Sulfur is used for the production of sulfuric acid, rubber vulcanization, as a fungicide in agriculture, and as colloidal sulfur - a drug. Also, sulfur in the composition of sulfur-bitumen compositions is used to obtain sulfur asphalt, and as a substitute for Portland cement - to obtain sulfur concrete. S + O 2 \u003d SO 2

Using spectral analysis, it was found that in fact the process of oxidation of sulfur to dioxide is a chain reaction and occurs with the formation of a number of intermediate products: sulfur monoxide S 2 O 2 , molecular sulfur S 2 , free sulfur atoms S and free radicals of sulfur monoxide SO.

When interacting with metals, it forms sulfides. 2Na + S = Na 2 S

When sulfur is added to these sulfides, polysulfides are formed: Na 2 S + S = Na 2 S 2

When heated, sulfur reacts with carbon, silicon, phosphorus, hydrogen:
C + 2S = CS 2 (carbon disulfide)

Sulfur dissolves in alkalis when heated - disproportionation reaction
3S + 6KOH = K 2 SO 3 + 2K 2 S + 3H 2 O

Fire properties of sulfur

Finely ground sulfur is prone to chemical spontaneous combustion in the presence of moisture, in contact with oxidizing agents, and also in a mixture with coal, fats, oils. Sulfur forms explosive mixtures with nitrates, chlorates and perchlorates. It ignites spontaneously on contact with bleach.

Extinguishing media: water spray, air-mechanical foam.

The detection of sulfur combustion is a difficult problem. The flame is difficult to detect with the human eye or a video camera, the spectrum of blue flame lies mainly in the ultraviolet range. Combustion occurs at a low temperature. To detect combustion with a heat detector, it is necessary to place it directly close to sulfur. The sulfur flame does not radiate in the infrared range. Thus, it will not be detected by common infrared detectors. They will only detect secondary fires. A sulfur flame does not emit water vapor. Therefore, ultraviolet flame detectors using nickel compounds will not work.

Since air by volume consists of approximately 21% oxygen and 79% nitrogen, and when sulfur is burned, one volume of SO2 is obtained from one volume of oxygen, the maximum theoretically possible content of SO2 in the gas mixture is 21%. In practice, combustion occurs with a certain excess of air and the volume content of SO2 in the gas mixture is less than theoretically possible, usually 14 ... 15%.

Fires in sulfur warehouses

In December 1995, a major fire broke out in an open-air sulfur storage facility located in the city of Somerset West, Western Cape, South Africa, killing two people.

On January 16, 2006, at about five in the evening, a warehouse with sulfur caught fire at the Cherepovets plant "Ammophos". The total fire area is about 250 square meters. It was possible to completely eliminate it only at the beginning of the second night. There are no victims or injured.

On March 15, 2007, early in the morning, a fire broke out in a closed sulfur warehouse at Balakovo Fiber Materials Plant LLC. The fire area was 20 sq.m. 4 fire brigades with a staff of 13 people worked on the fire. The fire was extinguished in about half an hour. No harm done.

On March 4 and 9, 2008, a sulfur fire occurred in the Atyrau region in TCO's sulfur storage facility at the Tengiz field. In the first case, the fire was extinguished quickly, in the second case, the sulfur burned for 4 hours. The volume of burning oil refining wastes, which, according to Kazakh laws, includes sulfur, amounted to more than 9 thousand kilograms.

In April 2008, a warehouse caught fire near the village of Kryazh, Samara Region, where 70 tons of sulfur were stored. The fire was assigned the second category of complexity. To the scene left 11 fire brigades and rescuers. At that moment, when the firefighters were near the warehouse, not all the sulfur was still burning, but only a small part of it - about 300 kilograms. The area of ignition, together with areas of dry grass adjacent to the warehouse, amounted to 80 square meters. Firefighters managed to quickly bring down the flames and localize the fire: the fires were covered with earth and flooded with water.

In July 2009 sulfur burned in Dneprodzerzhinsk. The fire occurred at one of the coke enterprises in the Bagleysky district of the city. The fire engulfed more than eight tons of sulfur. None of the employees of the plant was injured.

Physical and chemical bases of the sulfur combustion process.

The combustion of S occurs with the release of a large amount of heat: 0.5S 2g + O 2g \u003d SO 2g, ΔH \u003d -362.43 kJ

Combustion is a complex of chemical and physical phenomena. In an incinerator, one has to deal with complex fields of velocities, concentrations, and temperatures that are difficult to describe mathematically.

The combustion of molten S depends on the conditions of interaction and combustion of individual droplets. The efficiency of the combustion process is determined by the time of complete combustion of each particle of sulfur. The combustion of sulfur, which occurs only in the gas phase, is preceded by the evaporation of S, the mixing of its vapors with air, and the heating of the mixture to t, which provides the necessary reaction rate. Since evaporation from the surface of the drop begins more intensively only at a certain t, each drop of liquid sulfur must be heated to this t. The higher t, the longer it takes to heat the drop. When a combustible mixture of vapors S and air of maximum concentration and t is formed above the surface of the drop, ignition occurs. The combustion process of a drop S depends on the combustion conditions: t and the relative velocity of the gas flow, and the physicochemical properties of liquid S (for example, the presence of solid ash impurities in S), and consists of the following stages: 1-mixing drops of liquid S with air; 2-heating of these drops and evaporation; 3-thermal vapor splitting S; 4-formation of the gas phase and its ignition; 5-combustion of the gas phase.

These stages occur almost simultaneously.

As a result of heating, a drop of liquid S begins to evaporate, vapors of S diffuse to the combustion zone, where at high t they begin to actively react with O 2 of the air, the process of diffusion combustion of S occurs with the formation of SO 2.

At high t, the rate of the oxidation reaction S is greater than the rate of physical processes, so the overall rate of the combustion process is determined by the processes of mass and heat transfer.

Molecular diffusion determines a calm, relatively slow combustion process, while turbulent diffusion accelerates it. As the droplet size decreases, the evaporation time decreases. Fine atomization of sulfur particles and their uniform distribution in the air flow increases the contact surface, facilitates heating and evaporation of the particles. During the combustion of each single drop S in the composition of the torch, 3 periods should be distinguished: I- incubation; II- intense burning; III- burnout period.

When a drop burns, flames erupt from its surface, resembling solar flares. In contrast to conventional diffusion combustion with the ejection of flames from the surface of a burning drop, it was called "explosive combustion".

The combustion of the S drop in the diffusion mode is carried out by the evaporation of molecules from the surface of the drop. The evaporation rate depends on the physical properties of the liquid and the t of the environment, and is determined by the characteristic of the evaporation rate. In differential mode, S lights up in periods I and III. Explosive combustion of a drop is observed only in the period of intense combustion in period II. The duration of the intense burning period is proportional to the cube of the initial droplet diameter. This is due to the fact that explosive combustion is a consequence of the processes occurring in the volume of the drop. Burning rate characteristic calc. by f-le: To= /τ sg;

d n is the initial droplet diameter, mm; τ is the time of complete combustion of the drop, s.

The characteristic of the burning rate of a drop is equal to the sum of the characteristics of diffusion and explosive combustion: To= K vz + K diff; kvz= 0.78∙exp(-(1.59∙p) 2.58); K diff= 1.21∙p +0.23; K T2\u003d K T1 ∙ exp (E a / R ∙ (1 / T 1 - 1 / T 2)); K T1 - burning rate constant at t 1 \u003d 1073 K. K T2 - const. heating rate at t different from t 1 . Еа is the activation energy (7850 kJ/mol).

THEN. The main conditions for efficient combustion of liquid S are: the supply of all the necessary amount of air to the mouth of the torch, fine and uniform spraying of liquid S, flow turbulence and high t.

The general dependence of the intensity of evaporation of liquid S on the gas velocity and t: K 1= a∙V/(b+V); a, b are constants depending on t. V - speed gas, m/s. At higher t, the dependence of the evaporation intensity S on the gas velocity is given by: K 1= K o ∙ V n ;

t, o C	lgK about	n
	4,975	0,58
	5,610	0,545
	6,332	0,8

With an increase in t from 120 to 180 o C, the intensity of evaporation of S increases by 5-10 times, and t 180 to 440 o C by 300-500 times.

The evaporation rate at a gas velocity of 0.104 m/s is determined by: = 8.745 - 2600/T (at 120-140 o C); = 7.346 -2025/T (at 140-200 o C); = 10.415 - 3480 / T (at 200-440 ° C).

To determine the evaporation rate S at any t from 140 to 440 ° C and gas velocity in the range of 0.026-0.26 m / s, it is first found for a gas velocity of 0.104 m / s and recalculated to another speed: lg = lg + n ∙ lgV `` /V ` ; Comparison of the value of the intensity of evaporation of liquid sulfur and the rate of combustion suggests that the intensity of combustion cannot exceed the intensity of evaporation at the boiling point of sulfur. This confirms the correctness of the combustion mechanism, according to which sulfur burns only in the vapor state. The rate constant of sulfur vapor oxidation (the reaction proceeds according to the second-order equation) is determined by the kinetic equation: -dС S /d = К∙С S ∙С О2 ; C S is the vapor concentration S; C O2 - conc-I vapors O 2; K is the reaction rate constant. The total concentration of vapors S and O 2 op-yut: C S= a(1-x); With O2= b - 2ax; a is the initial vapor concentration S; b - initial concentration of O 2 vapors; х is the degree of vapor oxidation S. Then:

K∙τ= (2,3 /(b – 2a)) ∙ (lg(b – ax/b(1 - x)));

The rate constant of the oxidation reaction S to SO 2: lgK\u003d B - A / T;

about C	650 - 850	850 - 1100
AT	3,49	2,92
BUT

Drops of sulfur d< 100мкм сгорают в диффузионном режиме; d>100 µm in explosive, in the area of 100-160 µm, the burning time of drops does not increase.

That. to intensify the combustion process, it is advisable to spray sulfur into droplets d = 130-200 µm, which requires additional energy. When burning the same number of S received. SO 2 is the more concentrated, the smaller the volume of furnace gas and the higher its t.

1 - C O2; 2 - With SO2

The figure shows an approximate relationship between t and the SO 2 concentration in the furnace gas produced by the adiabatic combustion of sulfur in air. In practice, highly concentrated SO 2 is obtained, limited by the fact that at t > 1300, the lining of the furnace and gas ducts is quickly destroyed. In addition, under these conditions, side reactions between O 2 and N 2 of air can occur with the formation of nitrogen oxides, which is an undesirable impurity in SO 2, therefore, t = 1000-1200 is usually maintained in sulfur furnaces. And furnace gases contain 12-14 vol% SO 2 . From one volume of O 2 one volume of SO 2 is formed, therefore the maximum theoretical content of SO 2 in the combustion gas when burning S in air is 21%. When burning S in air, firing. O 2 The content of SO 2 in the gas mixture may increase depending on the concentration of O 2 . The theoretical content of SO 2 when burning S in pure O 2 can reach 100%. The possible composition of the roasting gas obtained by burning S in air and in various oxygen-nitrogen mixtures is shown in the figure:

Furnaces for burning sulfur.

Combustion of S in sulfuric acid production is carried out in furnaces in atomized or TV state. For burning the melted S, use nozzle, cyclone and vibration furnaces. The most widely used are cyclone and injector. These furnaces are classified according to the signs:- according to the type of installed nozzles (mechanical, pneumatic, hydraulic) and their location in the furnace (radial, tangential); - by the presence of screens inside the combustion chambers; - by execution (horizons, verticals); - according to the location of the inlet holes for air supply; - for devices for mixing air flows with S vapors; - for equipment for using the heat of combustion S; - by number of cameras.

Nozzle oven (rice)

1 - steel cylinder, 2 - lining. 3 - asbestos, 4 - partitions. 5 - nozzle for spraying fuel, 6 nozzles for spraying sulfur,

7 - a box for supplying air to the furnace.

It has a fairly simple design, easy to maintain, it has an image of gas, a constant concentration of SO 2. To serious shortcomings include: gradual destruction of partitions due to high t; low heat stress of the combustion chamber; difficulty in obtaining high concentration gas, tk. use a large excess of air; dependence of the percentage of combustion on the quality of spraying S; significant fuel consumption during start-up and heating of the furnace; comparatively large dimensions and weight, and as a result, significant capital investments, production areas, operating costs and large heat losses in the environment.

More perfect cyclone ovens.

1 - prechamber, 2 - air box, 3, 5 - afterburning chambers, 4. 6 pinch rings, 7, 9 - nozzles for air supply, 8, 10 - nozzles for sulfur supply.

Delivery: tangential air input and S; ensures uniform combustion of S in the furnace due to better flow turbulence; the possibility of obtaining the final process gas up to 18% SO 2; high thermal stress of the furnace space (4.6 10 6 W / m 3); the volume of the apparatus is reduced by a factor of 30-40 compared to the volume of a nozzle furnace of the same capacity; permanent concentration SO 2; simple regulation of the combustion process S and its automation; low time and combustible material for heating and starting the furnace after a long stop; lower content of nitrogen oxides after the furnace. Basic weeks associated with high t in the combustion process; possible cracking of the lining and welds; Unsatisfactory spraying of S leads to a breakthrough of its vapors in the t / exchange equipment after the furnace, and consequently to corrosion of the equipment and inconstancy of t at the inlet to the t / exchange equipment.

Molten S can enter the furnace through tangential or axial nozzles. With the axial location of the nozzles, the combustion zone is closer to the periphery. At tangent - closer to the center, due to which the effect of high t on the lining is reduced. (rice) The gas flow rate is 100-120m / s - this creates a favorable condition for mass and heat transfer, and the burning rate increases S.

Vibrating oven (rice).

1 – burner furnace head; 2 - return valves; 3 - vibration channel.

During vibrating combustion, all the parameters of the process periodically change (pressure in the chamber, speed and composition of the gas mixture, t). Device for vibrats. combustion S is called a furnace-burner. Before the furnace, S and air are mixed, and they flow through check valves (2) into the head of the furnace-burner, where the mixture is burned. The supply of raw materials is carried out in portions (processes are cyclic). In this version of the furnace, the heat stress and burning rate increase significantly, but before igniting the mixture, a good mixing of the sprayed S with air is necessary so that the process goes instantly. In this case, the combustion products mix well, the SO 2 gas film surrounding the S particles is destroyed and facilitates the access of new portions of O 2 in the combustion zone. In such a furnace, the resulting SO 2 does not contain unburned particles, its concentration is high at the top.

For a cyclone furnace, in comparison with a nozzle furnace, it is characterized by 40-65 times greater thermal stress, the possibility of obtaining more concentrated gas and greater steam production.

The most important equipment for furnaces for burning liquid S is the nozzle, which must ensure a thin and uniform spray of liquid S, good mixing of it with air in the nozzle itself and behind it, quick adjustment of the flow rate of liquid S while maintaining the necessary its ratio with air, the stability of a certain shape, the length of the torch, and also have a solid design, reliable and easy to use. For the smooth operation of the nozzles, it is important that the S is well cleaned of ash and bitumen. Nozzles are mechanical (yield under its own pressure) and pneumatic (air is still involved in spraying) action.

Utilization of the heat of combustion of sulfur.

The reaction is highly exothermic, as a result, a large amount of heat is released and the gas temperature at the outlet of the furnaces is 1100-1300 0 C. For contact oxidation of SO 2, the gas temperature at the entrance to the 1st layer of the cat-ra should not exceed 420 - 450 0 C. Therefore, before the SO 2 oxidation stage, it is necessary to cool the gas flow and utilize excess heat. In sulfuric acid systems operating on sulfur for heat recovery, water-tube heat recovery boilers with natural heat circulation are most widely used. SETA - C (25 - 24); RKS 95 / 4.0 - 440.

Energy-technological boiler RKS 95/4.0 - 440 is a water-tube, natural circulation, gas-tight boiler, designed to work with pressurization. The boiler consists of 1st and 2nd stage evaporators, stage 1.2 remote economizers, stage 1.2 remote superheaters, drum, sulfur combustion furnaces. The furnace is designed for burning up to 650 tons of liquid. Sulfur per day. The furnace consists of two cyclones connected relative to each other at an angle of 110 0 and a transition chamber.

Inner body with a diameter of 2.6 m, rests freely on supports. The outer casing is 3 m in diameter. The annular space formed by the inner and outer casings is filled with air, which then enters the combustion chamber through nozzles. Sulfur is supplied to the furnace by 8 sulfur nozzles, 4 on each cyclone. Sulfur combustion occurs in a swirling gas-air flow. The swirling of the flow is achieved by tangentially introducing air into the combustion cyclone through air nozzles, 3 in each cyclone. The amount of air is controlled by motorized flaps on each air nozzle. The transition chamber is designed to direct the gas flow from the horizontal cyclones to the vertical gas duct of the evaporator. The inner surface of the firebox is lined with mulite-corundum brick of the MKS-72 brand, 250 mm thick.

1 - cyclones

2 - transition chamber

3 - evaporation devices