Fire hazardous properties of sulfur.
Finely ground sulfur is prone to chemical spontaneous combustion in the presence of moisture, upon contact with oxidizing agents, and also in a mixture with coal, fats, and oils. Sulfur forms explosive mixtures with nitrates, chlorates and perchlorates. Spontaneously ignites on contact with bleach.
Extinguishing agents: sprayed water, air-mechanical foam.
According to V. Marshall, sulfur dust is classified as explosive, but for an explosion a sufficiently high concentration of dust is required - about 20 g/m³ (20,000 mg/m³), this concentration is many times higher than the maximum permissible concentration for humans in the air of the working area - 6 mg/m³.
Vapors form an explosive mixture with air.
The combustion of sulfur occurs only in a molten state, similar to the combustion of liquids. The top layer of burning sulfur boils, creating vapors that form a dimly luminous flame up to 5 cm high. The flame temperature when burning sulfur is 1820 °C.
Since air by volume consists of approximately 21% oxygen and 79% nitrogen, and when sulfur burns, one volume of oxygen produces one volume of SO2, the maximum theoretically possible SO2 content in the gas mixture is 21%. In practice, combustion occurs with some excess air, and the volumetric SO2 content in the gas mixture is less than theoretically possible, usually amounting to 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. Heat release from a fire results in temperatures lower than fires of other common fire hazards. To detect combustion with a heat detector, it must be placed directly close to the sulfur. Sulfur flame does not emit infrared radiation. Thus, it will not be detected by common infrared detectors. They will only detect secondary fires. A sulfur flame does not release water vapor. Therefore, UV flame detectors that use nickel compounds will not work.
To comply with fire safety requirements at sulfur warehouses, it is necessary:
Structures and technological equipment must be regularly cleaned of dust;
the warehouse premises must be constantly ventilated with natural ventilation with the doors open;
crushing lumps of sulfur on the bunker grate should be done with wooden sledgehammers or tools made of non-sparking material;
conveyors for supplying sulfur to production premises must be equipped with metal detectors;
in places where sulfur is stored and used, it is necessary to provide devices (boards, thresholds with a ramp, etc.) that ensure in an emergency the prevention of the spreading of molten sulfur outside the room or open area;
At the sulfur warehouse it is prohibited:
carrying out all types of work using open fire;
store and store oily rags and rags;
When making repairs, use tools made of non-sparking material.
Sulfur is a chemical element that is found in the sixth group and third period of the periodic table. In this article we will take a detailed look at its chemical properties, production, use, and so on. The physical characteristic includes such characteristics as color, level of electrical conductivity, boiling point of sulfur, etc. Chemical characteristics describe its interaction with other substances.
Sulfur from a physics point of view
This is a fragile substance. Under normal conditions, it remains in a solid state of aggregation. Sulfur has a lemon-yellow color.
And for the most part, all its compounds have yellow tints. Does not dissolve in water. It has low thermal and electrical conductivity. These features characterize it as a typical non-metal. Despite the fact that the chemical composition of sulfur is not at all complicated, this substance can have several variations. It all depends on the structure of the crystal lattice, with the help of which atoms are connected, but they do not form molecules.
So, the first option is rhombic sulfur. It is the most stable. The boiling point of this type of sulfur is four hundred and forty-five degrees Celsius. But in order for a given substance to pass into a gaseous state of aggregation, it first needs to pass through the liquid state. So, the melting of sulfur occurs at a temperature of one hundred and thirteen degrees Celsius.
The second option is monoclinic sulfur. It is a needle-shaped crystal with a dark yellow color. Melting the first type of sulfur and then slowly cooling it leads to the formation of this type. This variety has almost the same physical characteristics. For example, the boiling point of this type of sulfur is the same four hundred and forty-five degrees. In addition, there is such a variety of this substance as plastic. It is obtained by pouring rhombic water heated almost to boiling into cold water. The boiling point of this type of sulfur is the same. But the substance has the property of stretching like rubber.
Another component of the physical characteristics that I would like to talk about is the ignition temperature of sulfur.
This indicator may vary depending on the type of material and its origin. For example, the ignition temperature of technical sulfur is one hundred and ninety degrees. This is a fairly low figure. In other cases, the flash point of sulfur can be two hundred forty-eight degrees and even two hundred fifty-six. It all depends on what material it was extracted from and what its density is. But we can conclude that the combustion temperature of sulfur is quite low, compared to other chemical elements; it is a flammable substance. In addition, sometimes sulfur can combine into molecules consisting of eight, six, four or two atoms. Now, having considered sulfur from a physics point of view, let's move on to the next section.
Chemical characteristics of sulfur
This element has a relatively low atomic mass, equal to thirty-two grams per mole. The characteristics of the element sulfur include such a feature of this substance as the ability to have different degrees of oxidation. This differs from, say, hydrogen or oxygen. When considering the question of what the chemical characteristics of the element sulfur are, it is impossible not to mention that, depending on the conditions, it exhibits both reducing and oxidizing properties. So, let’s look at the interaction of this substance with various chemical compounds in order.
Sulfur and simple substances
Simple substances are substances that contain only one chemical element. Its atoms may combine into molecules, as, for example, in the case of oxygen, or they may not combine, as is the case with metals. Thus, sulfur can react with metals, other non-metals and halogens.
Interaction with metals
To carry out this kind of process, high temperature is required. Under these conditions, an addition reaction occurs. That is, metal atoms combine with sulfur atoms, forming complex substances sulfides. For example, if you heat two moles of potassium and mix them with one mole of sulfur, you get one mole of sulfide of this metal. The equation can be written as follows: 2K + S = K 2 S.
Reaction with oxygen
This is the burning of sulfur. As a result of this process, its oxide is formed. The latter can be of two types. Therefore, sulfur combustion can occur in two stages. The first is when one mole of sulfur dioxide is formed from one mole of sulfur and one mole of oxygen. The equation for this chemical reaction can be written as follows: S + O 2 = SO 2. The second stage is the addition of another oxygen atom to the dioxide. This happens if you add one mole of oxygen to two moles at high temperatures. The result is two moles of sulfur trioxide. The equation for this chemical interaction looks like this: 2SO 2 + O 2 = 2SO 3 . As a result of this reaction, sulfuric acid is formed. So, having carried out the two processes described, you can pass the resulting trioxide through a stream of water vapor. And we get The equation for such a reaction is written as follows: SO 3 + H 2 O = H 2 SO 4.
Interaction with halogens
Chemicals, like other non-metals, allow it to react with a given group of substances. It includes compounds such as fluorine, bromine, chlorine, iodine. Sulfur reacts with any of them except the last one. As an example, we can cite the process of fluoridation of the element of the periodic table we are considering. By heating the mentioned non-metal with a halogen, two variations of fluoride can be obtained. The first case: if we take one mole of sulfur and three moles of fluorine, we get one mole of fluoride, the formula of which is SF 6. The equation looks like this: S + 3F 2 = SF 6. In addition, there is a second option: if we take one mole of sulfur and two moles of fluorine, we get one mole of fluoride with the chemical formula SF 4. The equation is written as follows: S + 2F 2 = SF 4. As you can see, it all depends on the proportions in which the components are mixed. In exactly the same way, the process of sulfur chlorination (two different substances can also be formed) or bromination can be carried out.
Interaction with other simple substances
The characteristics of the element sulfur do not end there. The substance can also react chemically with hydrogen, phosphorus and carbon. Due to interaction with hydrogen, sulfide acid is formed. As a result of its reaction with metals, their sulfides can be obtained, which, in turn, are also obtained directly by reacting sulfur with the same metal. The addition of hydrogen atoms to sulfur atoms occurs only under very high temperature conditions. When sulfur reacts with phosphorus, its phosphide is formed. It has the following formula: P 2 S 3. In order to get one mole of this substance, you need to take two moles of phosphorus and three moles of sulfur. When sulfur interacts with carbon, a carbide of the nonmetal in question is formed. Its chemical formula looks like this: CS 2. In order to get one mole of a given substance, you need to take one mole of carbon and two moles of sulfur. All the addition reactions described above occur only when the reagents are heated to high temperatures. We have looked at the interaction of sulfur with simple substances, now let's move on to the next point.
Sulfur and complex compounds
Complex substances are those substances whose molecules consist of two (or more) different elements. The chemical properties of sulfur allow it to react with compounds such as alkalis, as well as concentrated sulfate acid. Its reactions with these substances are quite peculiar. First, let's look at what happens when the nonmetal in question is mixed with alkali. For example, if you take six moles and add three moles of sulfur, you get two moles of potassium sulfide, one mole of potassium sulfite and three moles of water. This kind of reaction can be expressed by the following equation: 6KOH + 3S = 2K 2 S + K2SO 3 + 3H 2 O. The same principle of interaction occurs if you add Next, consider the behavior of sulfur when a concentrated solution of sulfate acid is added to it. If we take one mole of the first and two moles of the second substance, we obtain the following products: sulfur trioxide in an amount of three moles, as well as water - two moles. This chemical reaction can only occur when the reactants are heated to a high temperature.
Obtaining the non-metal in question
There are several main ways in which sulfur can be extracted from a variety of substances. The first method is to isolate it from pyrite. The chemical formula of the latter is FeS 2. When this substance is heated to a high temperature without access to oxygen, another iron sulfide - FeS - and sulfur can be obtained. The reaction equation is written as follows: FeS 2 = FeS + S. The second method of producing sulfur, which is often used in industry, is the combustion of sulfur sulfide under the condition of a small amount of oxygen. In this case, the nonmetal in question and water can be obtained. To carry out the reaction, you need to take the components in a molar ratio of two to one. As a result, we obtain the final products in proportions of two to two. The equation for this chemical reaction can be written as follows: 2H 2 S + O 2 = 2S + 2H 2 O. In addition, sulfur can be obtained through a variety of metallurgical processes, for example, in the production of metals such as nickel, copper and others.
Industrial use
The nonmetal we are considering has found its widest application in the chemical industry. As mentioned above, here it is used to produce sulfate acid from it. In addition, sulfur is used as a component for making matches, due to the fact that it is a flammable material. It is also indispensable in the production of explosives, gunpowder, sparklers, etc. In addition, sulfur is used as one of the ingredients in pest control products. In medicine, it is used as a component in the manufacture of medicines for skin diseases. The substance in question is also used in the production of various dyes. In addition, it is used in the manufacture of phosphors.
Electronic structure of sulfur
As you know, all atoms consist of a nucleus in which there are protons - positively charged particles - and neutrons, i.e. particles with zero charge. Electrons with a negative charge rotate around the nucleus. For an atom to be neutral, it must have the same number of protons and electrons in its structure. If there are more of the latter, it is already a negative ion - an anion. If, on the contrary, the number of protons is greater than electrons, it is a positive ion, or cation. The sulfur anion can act as an acid residue. It is part of the molecules of substances such as sulfide acid (hydrogen sulfide) and metal sulfides. The anion is formed during electrolytic dissociation, which occurs when a substance is dissolved in water. In this case, the molecule breaks down into a cation, which can be presented in the form of a metal or hydrogen ion, as well as a cation - an ion of an acidic residue or a hydroxyl group (OH-).
Since the serial number of sulfur in the periodic table is sixteen, we can conclude that its nucleus contains exactly this number of protons. Based on this, we can say that there are also sixteen electrons rotating around. The number of neutrons can be found by subtracting the serial number of the chemical element from the molar mass: 32 - 16 = 16. Each electron does not rotate chaotically, but in a specific orbit. Since sulfur is a chemical element that belongs to the third period of the periodic table, there are three orbits around the nucleus. The first of them has two electrons, the second has eight, and the third has six. The electronic formula of the sulfur atom is written as follows: 1s2 2s2 2p6 3s2 3p4.
Prevalence in nature
Basically, the chemical element in question is found in minerals, which are sulfides of various metals. First of all, it is pyrite - an iron salt; It is also lead, silver, copper luster, zinc blende, cinnabar - mercury sulfide. In addition, sulfur can also be part of minerals, the structure of which is represented by three or more chemical elements.
For example, chalcopyrite, mirabilite, kieserite, gypsum. You can consider each of them in more detail. Pyrite is ferrum sulfide, or FeS 2 . It has a light yellow color with a golden sheen. This mineral can often be found as an impurity in lapis lazuli, which is widely used for making jewelry. This is due to the fact that these two minerals often have a common deposit. Copper luster - chalcocite, or chalcocite - is a bluish-gray substance similar to metal. and silver luster (argentite) have similar properties: they both resemble metals in appearance and have a gray color. Cinnabar is a dull brownish-red mineral with gray flecks. Chalcopyrite, the chemical formula of which is CuFeS 2, is golden yellow, it is also called gold blende. Zinc blende (sphalerite) can range in color from amber to fiery orange. Mirabilite - Na 2 SO 4 x10H 2 O - transparent or white crystals. It is also called used in medicine. The chemical formula of kieserite is MgSO 4 xH 2 O. It looks like a white or colorless powder. The chemical formula of gypsum is CaSO 4 x2H 2 O. In addition, this chemical element is part of the cells of living organisms and is an important trace element.
Physico-chemical basis of the sulfur combustion process.
The combustion of S occurs with the release of a large amount of heat: 0.5S 2g + O 2g = SO 2g, ΔH = -362.43 kJ
Combustion is a complex of chemical and physical phenomena. In a combustion device 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, mixing of its vapors with air and heating of the mixture to t, which ensures the required reaction rate. Since more intense evaporation from the surface of a drop begins only at a certain t, each drop of liquid sulfur must be heated to this t. The higher t, the more time it will take to warm up the drop. When a flammable mixture of vapor S and air of maximum concentration and t is formed above the surface of the drop, ignition occurs. The combustion process of a drop of S depends on the combustion conditions: t and the relative speed of the gas flow, and the physical and chemical properties of liquid S (for example, the presence of solid ash impurities in S), and consists of stages: 1-mixing drops of liquid S with air; 2-heating of these drops and evaporation; 3-thermal splitting of S vapors; 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, S vapors diffuse to the combustion zone, where at high t they begin to actively react with O 2 in the air, and 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, therefore 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 spraying of sulfur particles and their uniform distribution in the air flow increases the contact surface, facilitating heating and evaporation of particles. When burning each single drop S in the torch composition, 3 periods should be distinguished: I-incubation; II- intense combustion; III- the period of afterburning.
When a drop burns, flames emit from its surface, reminiscent of solar flares. In contrast to ordinary diffusion combustion with the emission of flames from the surface of a burning drop, it is called “explosive combustion”.
Combustion of a droplet S in the diffusion mode occurs through the evaporation of molecules from the surface of the droplet. The rate of evaporation depends on the physical properties of the liquid and 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 during the period of intense combustion in period II. The duration of the period of intense combustion is proportional to the cube of the initial diameter of the drop. This is due to the fact that explosive combustion is a consequence of processes occurring in the volume of the drop. Characteristics of burning rate calc. by f-le: TO= /τ сг;
d n – initial diameter of the drop, mm; τ – time of complete combustion of the drop, s.
The characteristic of the droplet burning rate is equal to the sum of the characteristics of diffusion and explosive combustion: TO= K in + K diff; Kvz= 0.78∙exp(-(1.59∙р) 2.58); K diff= 1.21∙r +0.23; K T2= K T1 ∙exp(E a /R∙(1/T 1 – 1/T 2)); K T1 – combustion rate constant at t 1 = 1073 K. K T2 – constant. heating rate at t different from t 1. E a – activation energy (7850 kJ/mol).
THAT. The main conditions for effective combustion of liquid S are: supply of the entire required amount of air to the mouth of the torch, fine and uniform spraying of liquid S, turbulence of the flow and high t.
The general dependence of the intensity of evaporation of liquid S on 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: 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 evaporation intensity S increases by 5-10 times, and from 180 to 440 o C by 300-500 times.
The evaporation rate at a gas speed of 0.104 m/s is determined: = 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 o C).
To determine the evaporation rate S at any t from 140 to 440 o C and gas speed in the range of 0.026-0.26 m/s, it is first found for a gas speed of 0.104 m/s and recalculated to another speed: lg = lg + n ∙ lgV `` /V ` ; A comparison of the intensity of evaporation of liquid sulfur and the combustion rate 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 for the oxidation of sulfur vapor (the reaction proceeds according to a second-order equation) is determined by the kinetic equation: -dС S /d = К∙С S ∙С О2 ; С S – vapor concentration S; C O2 – concentration of O 2 vapor; K is the reaction rate constant. The total concentration of S and O 2 vapors is: With S= a(1-x); With O2= b – 2ax; a is the initial vapor concentration S; b – initial concentration of O 2 vapor; x is the oxidation state of vapor S. Then:
K∙τ= (2.3 /(b – 2a)) ∙ (log(b – ax/b(1 - x)));
Rate constant for the oxidation of S to SO 2: lgK= B – A/T;
| o C | 650 - 850 | 850 - 1100 |
| IN | 3,49 | 2,92 |
| A |
Sulfur drops d< 100мкм сгорают в диффузионном режиме; d>100 µm in the explosion, in the area of 100-160 µm the burning time of the droplets 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 quantity, S is obtained. SO 2 is more concentrated, the smaller the volume of furnace gas and the higher its t.
1 – C O2; 2 – С SO2
The figure shows the approximate relationship between t and the concentration of SO 2 in the furnace gas formed during 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 quickly collapses. In addition, under these conditions, side reactions can occur between O 2 and N 2 of the air 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 calcining gas when burning S in air is 21%. When burning S in air, it burns. O 2 SO 2 content in a gas mixture can increase depending on the O 2 concentration. 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.
The combustion of S in sulfuric acid production is carried out in furnaces in atomized or solid state. For burning molten S, nozzle, cyclone and vibration furnaces are used. The most widely used are cyclone and nozzle. These furnaces are classified according to the following criteria:- by the type of installed nozzles (mechanical, pneumatic, hydraulic) and their location in the furnace (radial, tangential); - the presence of screens inside the combustion chambers; - according to execution (horizontal, vertical); - according to the location of the inlet holes for air supply; - on devices for mixing air flows with vapors S; - on equipment for using combustion heat S; - by the number of cameras.
Nozzle furnace (rice)
1 - steel cylinder, 2 - lining. 3 - asbestos, 4 - partitions. 5 - nozzle for spraying fuel, 6 - nozzle for spraying sulfur,
7 - box for supplying air to the furnace.
It has a fairly simple design, easy to maintain, it produces gas with a constant concentration of SO 2. To serious deficiencies include: gradual destruction of partitions due to high t; low heat stress of the combustion chamber; difficulty in obtaining high concentration gas, because use up a large excess of air; dependence of the percentage of combustion on the quality of atomization S; means fuel consumption when starting and warming up the furnace; comparatively large dimensions and weight, and as a result, significant capital investment, derived areas, operating costs and large heat losses to 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.
Access: tangential air and S input; ensures uniform combustion of S in the furnace due to better turbulization of flows; possibility of obtaining concentrated process gas up to 18 vol% SO 2; high thermal voltage of the combustion space (4.6 10 6 W/m 3); the volume of the apparatus will be reduced by 30-40 times compared to the volume of a nozzle furnace of the same productivity; constant concentration of SO 2; simple regulation of combustion percentage S and its automation; low consumption of time and combustible material for heating and starting the furnace after a long stop; lower content of nitrogen oxides after the furnace. Main weeks associated with high t in the combustion percentage; cracking of the lining and welds is possible; unsatisfactory atomization of S leads to the breakthrough of its vapors into the exchange equipment after the furnace, and consequently to corrosion of the equipment and instability of t at the entrance to the exchange equipment.
Molten S can enter the furnace through nozzles with a tangential or axial arrangement. With the axial arrangement of the nozzles, the combustion zone is closer to the periphery. With tangen - closer to the center, due to which the effect of high t on the lining is reduced. (fig) The gas flow speed is 100-120 m/s - this creates favorable conditions for mass and heat transfer, and increases the combustion rate S.
Vibrating oven (rice).
1 – burner furnace head; 2 – return valves; 3 – vibration channel.
During vibration combustion, all parameters of the process periodically change (pressure in the chamber, speed and composition of the gas mixture, t). Device for vibration combustion S is called a burner stove. 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 (cyclic). In this version of the furnace, the heat stress and combustion rate will increase significantly, but before igniting the mixture, a good mixing of the sprayed S with air is necessary so that the process occurs instantly. In this case, the combustion products are well mixed, 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 SO 2 formed does not remove unburned particles; its concentration is high.
A cyclone furnace, compared to a nozzle furnace, 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 combustion furnaces is liquid S nozzles, which must ensure a fine and uniform spraying 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 relationship with the air, the stability of a certain shape, the length of the torch, and also have a robust design, reliable and easy to use. For uninterrupted operation of the injectors, it is important that S is well cleaned of ash and bitumen. Nozzles can be mechanical (liquid under its own pressure) or pneumatic (air also participates in the spraying).
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 furnace 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 waste heat boilers with natural heat circulation are most widely used. SETA – C (25 - 24); RKS 95/4.0 – 440.
The energy-technological boiler RKS 95/4.0 – 440 is a water-tube, natural circulation, gas-tight boiler, designed to operate with pressurization. The boiler consists of evaporation devices of the 1st and 2nd stages, remote economizers of the 1st and 2nd stages, remote superheaters of the 1st and 2nd stages, a drum, and furnaces for burning sulfur. The firebox is designed to burn 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.
The inner casing has a diameter of 2.6 m and rests freely on supports. The outer casing has a diameter of 3 m. An annular space formed by the inner and outer casings introduces air, which then enters the combustion chamber through nozzles. Sulfur is supplied to the furnace using 8 sulfur nozzles, 4 on each cyclone. Sulfur combustion occurs in a swirling gas-air flow. Flow swirl is achieved by tangentially introducing air into the combustion cyclone through air nozzles, 3 in each cyclone. The amount of air is regulated by electrically driven flaps on each air nozzle. The transition chamber is designed to direct the gas flow from horizontal cyclones into the vertical gas duct of the evaporation device. The internal surface of the firebox is lined with mulite-corundum brick, grade MKS-72, 250 mm thick.
1 – cyclones
2 - transition chamber
3 – evaporation devices
The combustion of sulfur is a complex process due to the fact that sulfur has molecules with different numbers of atoms in different allotropic states and the large dependence of its physicochemical properties on temperature. The reaction mechanism and product yield vary with both temperature and oxygen pressure.
| An example of the dependence of the dew point on the CO2 content in combustion products. |
Combustion of sulfur at 80 degrees is possible for various reasons. There is no firmly established theory of this process yet. It is assumed that part of this occurs in the firebox itself at high temperatures and with sufficient excess air. Research in this direction (Fig. 66) shows that with small excess air (of the order of cst 1 05 and below), the formation of 80 s in gases is sharply reduced.
The combustion of sulfur in oxygen occurs at 280 C, and in air - at 360 C.
Sulfur combustion occurs throughout the entire volume of the furnace. In this case, the gases are more concentrated and their processing is carried out in devices 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 the purification of oil runs as a refrigerant, in the production of sugar, etc. SCb is transported in steel cylinders and tanks in a liquid state. SO2 liquefaction is carried out by compressing pre-dried and cooled gas.
Sulfur combustion occurs throughout the entire volume of the furnace and ends in chambers formed by partitions 4, where additional air is supplied. Hot furnace gas containing sulfur dioxide is removed from these chambers.
The combustion of sulfur is very easy to observe in mechanical furnaces. On the upper floors of furnaces, where there is a lot of FeS2 in the burning material, the entire flame is colored blue - this is a characteristic flame of sulfur combustion.
The combustion process of sulfur is described by the equation.
The combustion of sulfur is observed through a sight glass in the furnace wall. The temperature of the molten sulfur should be maintained within 145 - 155 C. If you continue to increase the temperature, the viscosity of the 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 sulfur atom.
| Scheme of a combined contact-tower system using natural tower acid as a raw material. |
When sulfur is burned in a furnace, calcined sulfur dioxide is produced with a content of about 14% S02 and a temperature at the outlet of the furnace of about 1000 C. At this temperature, the gas enters waste heat boiler 7, where steam is produced by reducing its temperature to 450 C. It is necessary to send sulfur dioxide containing about 8% SO2 to contact apparatus 8, therefore, after the recovery boiler, part of the gas or all of the roasting gas is diluted to 8% SO2 with air heated in heat exchanger 9. In the contact apparatus, 50 - 70% of sulfur dioxide is oxidized to sulfuric anhydride.
| Sulfur/Sulfur (S) | |
|---|---|
| Atomic number | 16 |
| Appearance of a simple substance | light yellow brittle solid, odorless in pure form |
| Properties of the atom | |
| Atomic mass (molar mass) |
32,066 a. e.m. (g/mol) |
| Atomic 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 | 386 K |
| Heat of Melting | 1.23 kJ/mol |
| Boiling temperature | 717.824K |
| Heat of vaporization | 10.5 kJ/mol |
| Molar volume | 15.5 cm³/mol |
| 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- symbol “S” in the periodic table) is a highly electronegative element that exhibits non-metallic properties. In hydrogen and oxygen compounds it is found in various ions and forms many acids and salts. Many sulfur-containing salts are slightly soluble in water
Natural Sulfur Minerals
Sulfur is the sixteenth most abundant element in the earth's crust. It is found in a 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 luster or galena, HgS is cinnabar, Sb2S3 is stibnite. In addition, sulfur is present in petroleum, natural coal, natural gases and shale. Sulfur is the sixth most abundant element in natural waters; it is found mainly in the form of sulfate ions and causes the “constant” 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. Man probably became familiar with the smell of burning sulfur, the suffocating effect of sulfur dioxide and the disgusting smell of hydrogen sulfide back in prehistoric times. It was because of these properties that sulfur was used by priests as part of sacred incense during religious rites. Sulfur was considered the work 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 flammable mixtures for military purposes. Homer already described “sulphurous fumes,” the deadly effect of burning sulfur emissions. Sulfur was probably part of the “Greek fire” that terrified opponents.
Around the 8th century The Chinese began to use it in pyrotechnic mixtures, in particular, in mixtures such as gunpowder. The flammability 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 flammability” and an essential component of metal ores. Presbyter Theophilus (12th century) describes a method of oxidative roasting of sulfide copper ore, probably known in ancient Egypt.
During the period of Arab alchemy, the mercury-sulfur theory of the composition of metals arose, according to which sulfur was revered as an essential component (father) of all metals. Later it became one of the three principles of alchemists, and later the “principle of flammability” became the basis of the theory of phlogiston. The elemental nature of sulfur was established by Lavoisier in his combustion experiments. With the introduction of gunpowder in Europe, the development of natural sulfur mining began, as well as the development of a method for producing it from pyrites; the latter was common in ancient Rus'. It was first described in literature by Agricola. Thus, the exact origin of sulfur has not been established, but as stated above, this element was used before the birth of Christ, and therefore 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 “sira” - light yellow. It is possible that “sulphur” is related to the Hebrew “seraphim” - the plural of “seraph” - lit. burning, and sulfur burns well. In Old Russian and Old Church Slavonic, “sulfur” is generally a flammable substance, including fat.
Origin of sulfur
Large accumulations of native sulfur are not very common. It is more often present in some ores. Native sulfur ore is a rock interspersed with pure sulfur.
When were these inclusions formed - simultaneously with the accompanying rocks or later? The direction of prospecting and exploration work depends on the answer to this question. But, despite thousands of years of communication with sulfur, humanity still does not have a clear answer. There are several theories whose authors 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 basins. Special bacteria reduced sulfates dissolved in water to hydrogen sulfide, which rose upward, entered the oxidation zone, and here, chemically or with the participation of other bacteria, was oxidized to elemental sulfur. The sulfur settled to the bottom, and subsequently the sulfur-containing silt formed ore.
The theory of epigenesis (sulfur inclusions formed later than the main rocks) has several options. The most common of them assumes that groundwater, penetrating through rock strata, 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, when oxidized, releases pure sulfur in the voids and cracks of rocks.
In recent decades, one of the varieties of the theory of epigenesis has found more and more confirmation - the theory of metasomatosis (translated from Greek “metasomatosis” means replacement). According to it, the transformation of gypsum CaSO4-H2O and anhydrite CaSO4 into sulfur and calcite CaCO3 constantly occurs in the depths.
This theory was created in 1935 by Soviet scientists L. M. Miropolsky and B. P. Krotov. In particular, this fact speaks in its favor.
In 1961, the Mishrak field was discovered in Iraq. The sulfur here is contained in carbonate rocks, which form an arch supported by pillars going deep (in geology they are called wings). These wings consist mainly of anhydrite and gypsum. The same picture was observed at the domestic Shor-Su field.
The geological uniqueness of these deposits can only be explained from the standpoint of the theory of metasomatism: primary gypsum and anhydrites 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 supporters of the theory of metasomatism additional arguments.
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 still lakes on earth (in particular, Sernoye Lake near Sernovodsk), where syngenetic deposition of sulfur occurs and the sulfur-bearing silt contains neither gypsum nor 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 as of the complexity of the phenomena occurring in the depths. We all know from elementary school mathematics 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 spontaneous combustion.
Open pit mining of ore occurs like this. Walking excavators remove layers of rock 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 melting sulfur underground and pumping it to the surface through 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 known methods for obtaining sulfur from sulfur ores: steam-water, filtration, thermal, centrifugal and extraction.
Sulfur is also contained in large quantities in natural gas in a gaseous state (in the form of hydrogen sulfide, sulfur dioxide). During mining, it is deposited on the walls of pipes and equipment, rendering them inoperable. Therefore, it is recovered from the gas as quickly as possible after production. 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 producers of sulfur in Russia are the enterprises of OJSC Gazprom: LLC Gazprom Dobycha Astrakhan and LLC Gazprom Dobycha Orenburg, which receive it as a by-product during gas purification.
Physical properties
Natural intergrowth of native sulfur crystals
Sulfur is significantly different from oxygen the ability to form stable chains and cycles of sulfur atoms. The most stable are cyclic S8 molecules, having the shape of a crown, forming orthorhombic and monoclinic sulfur. This crystalline sulfur is a brittle yellow substance. In addition, molecules with closed (S4, S6) chains and open chains are possible. This composition has plastic sulfur, a brown substance. The formula of plastic sulfur is most often written simply 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 medicinal product. Also, sulfur in sulfur bitumen compositions is used to produce sulfur asphalt, and as a substitute for Portland cement to produce sulfur concrete. S + O 2 = SO 2
Using spectral analysis, it was established that in fact the process of sulfur oxidation into 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)
When heated, sulfur dissolves in alkalis - a disproportionation reaction
3S + 6KOH = K 2 SO 3 + 2K 2 S + 3H 2 O
Fire hazardous properties of sulfur
Finely ground sulfur is prone to chemical spontaneous combustion in the presence of moisture, upon contact with oxidizing agents, and also in a mixture with coal, fats, and oils. Sulfur forms explosive mixtures with nitrates, chlorates and perchlorates. Spontaneously ignites on contact with bleach.
Extinguishing agents: sprayed water, air-mechanical foam.
Detecting 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 low temperature. To detect combustion with a heat detector, it must be placed directly close to the sulfur. Sulfur flame does not emit infrared radiation. This way it will not be detected by common infrared detectors. They will only detect secondary fires. A sulfur flame does not release water vapor. Therefore, UV flame detectors that use nickel compounds will not work.
Since air by volume consists of approximately 21% oxygen and 79% nitrogen, and when sulfur burns, one volume of oxygen produces one volume of SO2, the maximum theoretically possible SO2 content in the gas mixture is 21%. In practice, combustion occurs with some excess air and the volumetric content of SO2 in the gas mixture is less than theoretically possible, usually amounting to 14...15%.
The combustion of sulfur occurs only in a molten state, similar to the combustion of liquids. The top layer of burning sulfur boils, creating vapors that form a dimly luminous flame up to 5 cm high. The flame temperature when burning sulfur is 1820 °C
Fires in sulfur warehouses
In December 1995, a major fire occurred in an open-air sulfur warehouse at a company located in 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 enterprise “Ammofos”. The total area of the fire is about 250 square meters. It was possible to completely eliminate it only at the beginning of the second night. There are no casualties or injuries.
On March 15, 2007, early in the morning at Balakovo Fiber Materials Plant LLC, a fire occurred in a closed sulfur warehouse. The fire area was 20 sq.m. There were 4 fire crews with 13 personnel working on the fire. After about half an hour, the fire was extinguished. No harm done.
On March 4 and 9, 2008, a sulfur fire occurred in the Atyrau region in the TCO 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 waste, which according to Kazakh laws includes sulfur, amounted to more than 9 thousand kilograms.
In April 2008, not far from the village of Kryazh, Samara region, a warehouse in which 70 tons of sulfur was stored caught fire. The fire was assigned the second category of complexity. 11 fire brigades and rescuers went to the scene of the incident. At that moment, when firefighters found themselves near the warehouse, not all of the sulfur was burning, but only a small part of it - about 300 kilograms. The area of the fire, including areas of dry grass adjacent to the warehouse, amounted to 80 square meters. Firefighters managed to quickly put out the flames and localize the fire: the fires were covered with earth and filled with water.
In July 2009, sulfur burned in Dneprodzerzhinsk. A fire occurred at one of the coke-chemical plants in the Bagleysky district of the city. The fire consumed more than eight tons of sulfur. None of the plant employees were injured.