Process flow diagrams of sulfur production units

Properties, application, raw material base and methods for the production of sulfuric acid. Wet gas sulfuric acid technology WSA and SNOX-control of sulfur and nitrogen oxides emissions. Development and optimization of technology. Sulfur production by the Claus method.

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MINISTRY OF EDUCATION OF THE REPUBLIC OF BELARUS

INSTITUTION OF EDUCATION

"POLOTSK STATE UNIVERSITY"

Department of Chemistry and TPNG

Test

In the discipline "Industrial ecology"

Efficient methods of hydrogen sulfide processing at refineries (production of sulfuric acid, elemental sulfur, etc.)

Novopolotsk

• 1. Properties of sulfuric acid
• 2. Application of sulfuric acid
• 3. Raw material base for the production of sulfuric acid
• 5.1 Firing sulfur-containing raw materials
• 5.2 Gas purging after firing
• 5.3 Oxidation of sulfur dioxide
• 5.4 Absorption of sulfur trioxide
• 5.5 Double contacting and double absorption system (DK / DA)
• 6. Technology for the production of sulfuric acid from wet gas WSA and SNOX ™ - control of emissions of sulfur and nitrogen oxides
• 6.1 Basic research
• 6.2 Development and optimization of technology
• 6.3 SNOX ™ Technology
• 7 Claus sulfur production

sulfuric acid emission oxide

1. Properties of sulfuric acid

Anhydrous sulfuric acid (monohydrate) is a heavy oily liquid that mixes with water in all proportions, releasing a large amount of heat. The density at 0 ° C is 1.85 g / cm 3. It boils at 296 ° C and freezes at -10 ° C. Sulfuric acid is called not only monohydrate, but also its aqueous solutions (), as well as solutions of sulfur trioxide in monohydrate (), called oleum. Oleum "smokes" in air due to desorption from it. Pure sulfuric acid is colorless, technical is colored by impurities in a dark color.

The physical properties of sulfuric acid, such as density, crystallization temperature, boiling point, depend on its composition. In fig. 1 shows a diagram of the crystallization of the system. The maxima in it correspond to the composition of the compounds or, the presence of minima is explained by the fact that the crystallization temperature of mixtures of two substances is lower than the crystallization temperature of each of them.

Rice. 1 Crystallization temperature of sulfuric acid

Anhydrous 100% sulfuric acid has a relatively high crystallization temperature of 10.7 ° C. To reduce the possibility of freezing of a commercial product during transportation and storage, the concentration of technical sulfuric acid is chosen such that it has a sufficiently low crystallization temperature. The industry produces three types of commercial sulfuric acid.

Sulfuric acid is very active. It dissolves metal oxides and most pure metals; at elevated temperatures it displaces all other acids from salts. Especially eagerly sulfuric acid combines with water due to its ability to give hydrates. It takes water away from other acids, from crystalline salts of salts and even oxygen derivatives of hydrocarbons, which do not contain water, but hydrogen and oxygen in a combination of H: O = 2.wood and other plant and animal tissues containing cellulose, starch and sugar are destroyed in concentrated sulfuric acid; water binds to acid and only finely dispersed carbon remains from the fabric. In dilute acid, cellulose and starch break down to form sugars. Concentrated sulfuric acid causes burns if it comes into contact with human skin.

2. Application of sulfuric acid

The high activity of sulfuric acid in combination with the relatively low cost of production predetermined the enormous scale and extraordinary variety of its application (Fig. 2). It is difficult to find an industry in which sulfuric acid or products made from it have not been consumed in certain quantities.

Rice. 2 Application of sulfuric acid

The largest consumer of sulfuric acid is the production of mineral fertilizers: superphosphate, ammonium sulfate, etc. Many acids (for example, phosphoric, acetic, hydrochloric) and salts are produced in large part with the help of sulfuric acid. Sulfuric acid is widely used in the production of non-ferrous and rare metals. In the metalworking industry, sulfuric acid or its salts are used for pickling steel products before painting, tinning, nickel plating, chrome plating, etc. significant amounts of sulfuric acid are spent on refining petroleum products. The production of a number of dyes (for fabrics), varnishes and paints (for buildings and machines), medicinal substances and some plastics is also associated with the use of sulfuric acid. With the help of sulfuric acid, ethyl and other alcohols, some esters, synthetic detergents, and a number of pesticides are produced to combat agricultural pests and weeds. Diluted solutions of sulfuric acid and its salts are used in the production of artificial silk, in the textile industry for processing fibers or fabrics before dyeing them, as well as in other branches of light industry. In the food industry, sulfuric acid is used in the production of starch, molasses and a number of other products. Transport uses lead sulfuric acid batteries. Sulfuric acid is used to dry gases and to concentrate acids. Finally, sulfuric acid is used in nitration processes and in the manufacture of most explosives.

3. Raw material base for the production of sulfuric acid

The raw material base for the production of sulfuric acid is sulfur-containing compounds, from which sulfur dioxide can be obtained. In industry, about 80% of sulfuric acid is obtained from natural sulfur and iron (sulfuric) pyrite. Sulfur pyrite consists of the mineral pyrite and impurities. Pure pyrite () contains 53.5% sulfur and 46.5% iron. The sulfur content in sulfur pyrite can range from 35 to 50%. A significant place is occupied by waste gases of non-ferrous metallurgy, obtained during the roasting of non-ferrous metal sulfides and containing sulfur dioxide. Some industries use hydrogen sulfide as a raw material, which is formed during the purification of oil products from sulfur.

4. Methods for the production of sulfuric acid

Currently, sulfuric acid is produced in two ways: nitrous, which has existed for more than 20 years, and contact, mastered in industry at the end of the 19th and beginning of the 20th centuries. The contact method displaces the nitrous (tower) method. The first stage of sulfuric acid production by any method is the production of sulfur dioxide by burning sulfurous raw materials. After purification of sulfur dioxide (especially in the contact method), it is oxidized to sulfur trioxide, which combines with water to produce sulfuric acid. Oxidation under normal conditions is extremely slow. To speed up the process, catalysts are used.

In the contact method for the production of sulfuric acid, the oxidation of sulfur dioxide to trioxide is carried out on solid contact masses. Thanks to the improvement of the contact method of production, the cost of the purer and highly concentrated contact sulfuric acid is only slightly higher than that of the tower acid. Therefore, only contact shops are being built. Currently, over 80% of all acid is produced by the contact method.

In the nitrous method, nitrogen oxides serve as a catalyst. Oxidation occurs mainly in the liquid phase and is carried out in packed towers. Therefore, the nitrous method on the basis of the apparatus is called tower. The essence of the tower method lies in the fact that the sulfur dioxide obtained during the combustion of sulphurous raw materials, containing about 9% and 9-10%, is cleaned of pyrite cinder particles and enters the tower system, consisting of several (four to seven) towers with packing. Packed towers work according to the principle of perfect displacement in polythermal mode. The gas temperature at the entrance to the first tower is about 350 ° C. A number of absorption and desorption processes, complicated by chemical transformations, take place in the towers. In the first two or three towers, the packing is sprayed with nitrose, in which dissolved nitrogen oxides are chemically bound in the form of nitrosylsulfuric acid. At high temperatures, nitrosylsulfuric acid hydrolyzes according to the equation:

the latter reacts with nitrogen oxides in the liquid phase:

absorbed by water also gives sulfuric acid:

Nitrogen oxides are absorbed by sulfuric acid in the next three to four towers according to the reaction inverse to equation 15.1. For this purpose, cooled sulfuric acid with a low nitrose content, flowing from the first towers, is fed into the towers. When oxides are absorbed, nitrosylsulfuric acid is obtained, which takes part in the process. Thus, nitrogen oxides are circulating and theoretically should not be consumed. In practice, due to incomplete absorption, there are losses of nitrogen oxides. the consumption of nitrogen oxides in terms of is 12-20 kg per ton of monohydrate. The nitrous method is used to obtain contaminated with impurities and diluted 75-77% sulfuric acid, which is used mainly for the production of mineral fertilizers.

5. Functional diagram of sulfuric acid production

The chemical scheme includes reactions:

If the initial substances (raw materials) contain impurities, then the functional diagram (Fig. 15.4) includes the stage of gas purification after firing. The first stage - roasting (combustion) - is specific for each type of raw material, and further it will be considered for pyrite and sulfur as the most common starting materials. The stages of oxidation and absorption are basically the same in different processes for the production of sulfuric acid. We will carry out a sequential consideration of the indicated stages (subsystems of chemical engineering systems for the production of sulfuric acid) from the standpoint of their fundamental technological, instrumental and operational solutions.

Rice. 4 Functional schemes for the production of sulfuric acid from sulfur (a) and sulfur pyrite (b) 1 - roasting of sulfur-containing raw materials; 2 - cleaning and flushing the firing gas; 3 - oxidation; 4 - absorption

5.1 Firing sulfur-containing raw materials

Roasting of pyrite (pyrite) is a complex physicochemical process and includes a number of sequentially or simultaneously occurring reactions:

Overall response:

With a slight excess or lack of oxygen, mixed iron oxide is formed:

.

Chemical reactions are practically irreversible and highly exothermic.

If (oil refining) is used as a raw material, then gas-phase combustion has the form of a chemical reaction:

,

those. practically irreversible, exothermic and decreases in volume.

Thermal decomposition of pyrite begins already at a temperature of about 200 ° C and sulfur ignites at the same time. At temperatures above 680 ° C, all three reactions are intense. In industry, firing is carried out at 850-900 ° C. The limiting stage of the process is the mass transfer of decomposition products into the gas phase and the oxidant to the site of the reaction. At the same temperatures, the solid component softens, which contributes to the adhesion of particles. These factors determine the way the process is carried out and the type of reactor.

Initially, a shelf reactor (chamber furnace) was used (Fig. 5, a). Pyrite is continuously fed from above to the shelves, while air from below passes through the fixed layers. Naturally, pyrite is lumpy (finely ground would create significant hydraulic resistance and could easily stick together, which would create non-uniform combustion). Firing is a continuous process, solid material is moved by special strokes rotating on a shaft located along the axis of the apparatus. The paddles of the strokes move the pieces of pyrite along the plates from top to bottom, alternately from the axis of the apparatus to its walls and back, as shown in the figure by the arrows. This mixing prevents the particles from sticking together. The cinder is continuously removed from the bottom of the reactor. The reactor provides the intensity of the process, measured by the amount of pyrite passing through the unit of the reactor cross-section, not more than 200 kg / (m 2 · h). In such a reactor, moving scrapers in the high-temperature zone complicate its design, an unequal temperature regime is created along the shelves, and it is difficult to organize heat removal from the reaction zone. Difficulties in heat removal do not allow obtaining firing gas with a concentration of more than 8-9%. The main limitation is the impossibility of using small particles, while for a heterogeneous process, the main way to accelerate the conversion rate is particle crushing.

Rice. 5 Pyrite roasting reactors

a - shelf (1 - housing, 2 - shelves for pyrite, 3 - rotating scrapers, 4 - scrapers drive axis); b - fluidized bed furnace (1 - housing, 2 - heat exchanger). Arrows inside the apparatus - the movement of solid pyrite in the reactors.

Fine particles can be processed in a boiling (fluidized) bed, which is implemented in KS furnaces - a fluidized bed (Fig. 15.5, b). Powdered pyrite is fed through a feeder to the reactor. Oxidant (air) is fed from below through the distribution grid at a speed sufficient to weigh the solids. Their hovering in the layer prevents sticking and contributes to their good contact with the gas, equalizes the temperature field throughout the layer, ensures the mobility of the solid material and its overflow into the outlet pipe for removing the product from the reactor. In such a layer of movable particles, heat exchange elements can be arranged. the coefficient of heat transfer from the fluidized bed is comparable to the coefficient of heat transfer from a boiling liquid, and thus efficient heat removal from the reaction zone, control of its temperature regime and the use of reaction heat are provided. The intensity of the process increases to 1000 kg / (m 2 · h), and the concentration in the roasting gas - up to 13-15%. The main disadvantage of KS furnaces is the increased dustiness of the firing gas due to mechanical erosion of mobile solid particles. This requires a more thorough cleaning of the gas from dust - in a cyclone and an electrostatic precipitator. The pyrite roasting subsystem is represented by the flow diagram shown in Fig. 6.

Rice. 6 Technological scheme of pyrite firing

1 - disc feeder; 2 - fluidized bed furnace (reactor); 3 - waste heat boiler; 4 - cyclone; 5 - electrostatic precipitator

As mentioned earlier, sulfur can be used as a raw material (native sulfur was mentioned earlier, sulfur can be used as a raw material () and in Fig. 15.6 .. return from a boiling liquid, and thereby provide). Sulfur is a low-melting substance: its melting point is 113 ° C. Before burning, it is melted using steam obtained by utilizing the heat of its combustion. The molten sulfur is settled and filtered to remove the impurities present in natural raw materials and is pumped into the combustion furnace. Sulfur burns mainly in a vapor phase state. To ensure its rapid evaporation, it must be dispersed in the air stream. For this, nozzle and cyclone furnaces are used.

Rice. 8 Technological scheme of sulfur combustion

1 - sulfur filter; 2 - collection of liquid sulfur; 3 - combustion furnace; 4 - waste heat boiler

During the combustion of sulfur, according to the reaction, part of the oxygen is equimolarly converted into sulfur dioxide, and therefore the total concentration and is constant and equal to the concentration of oxygen in the source gas (), so that when sulfur is burned in air.

Gas from burning sulfur is richer in oxygen than from burning pyrite.

5.2 Gas purging after firing

Pyrite roasting gases contain in the form of impurities compounds of fluorine, selenium, tellurium, arsenic and some others, formed from impurities in the raw material. The natural moisture of the raw material also turns into gas. Combustion produces some and possibly nitrogen oxides. These impurities either lead to corrosion of the apparatus, or to catalyst poisoning, and also affect the quality of the product - sulfuric acid. They are removed in the washing compartment, a simplified diagram of which is shown in Fig. nine.

Rice. 9 Scheme of the washing section of the sulfuric acid production

1, 2 - washing towers; 3 - wet filter; 4 - drying tower

5.3 Oxidation of sulfur dioxide

Reaction

According to the law of mass action, in equilibrium

The expression shows the relative change (decrease) in the volume of the reaction mixture. Equation 15.11 is implicitly defined and solved by fit. The required degrees of conversion (about 99%) are achieved at temperatures of 400-420 ° C. The pressure does not greatly affect, therefore, in the industry, the process is carried out at a pressure close to atmospheric.

Oxidation catalysts are prepared on the basis of vanadium oxide () with the addition of alkali metals supported on silicon oxide. The reaction rate is described by the Boreskov-Ivanov equation:

where is the reaction rate constant;

= 0.8 is a constant;

, - partial pressures of the corresponding components, atm.

The temperature limits and the value in them for different catalysts may differ. For catalysts IK-1-6 and SVD kJ / mol at K., these are low-temperature catalysts. The activity of industrial catalysts at temperatures below 680 K is very low, and above 880 K they are thermally deactivated. Therefore, the operating temperature range for the operation of most catalysts is 580-880 K, and the degree of conversion in the reactor, determined by the lower limit of this range, is 98%.

,

Rice. 11 Oxidation reactor circuit

1 - catalyst layer; 2 - intermediate heat exchangers; 3 - mixer; 4 - external heat exchanger; X g - cold gas inlet

The initial concentration of the processed gas is chosen so that the process mode is within the operating temperatures of the catalyst. A large value at K leads to a sharp decrease in the reaction rate with decreasing temperature. In order for the adiabatic process in the first layer to develop intensively, the initial temperature must be at least 713 K. It is called the "ignition temperature" (for low-temperature catalysts it is lower). In the diagram "" the adiabatic process is represented by a straight line. Its slope is determined by the value of adiabatic heating. For oxidation, approximately 1% hail. The more (or the initial concentration -), the more warming up. The process can develop to equilibrium, and the maximum (equilibrium) temperature should not exceed the allowable one. In fig. 10 this corresponds to an initial concentration of 7-8%. The low-temperature catalyst allows the concentration to be increased up to 9-10%. The temperatures in the remaining layers are determined from the optimization of the reactor mode.

5.4 Absorption of sulfur trioxide

The absorption of sulfur trioxide is the last stage of the process in which sulfuric acid is formed. Interaction

proceeds quite intensively in both liquid and gaseous (vapor) phases. In addition, it can dissolve in itself, forming oleum. This product is convenient for transportation as it does not corrode even common steels. Sulfuric acid solutions are extremely corrosive. Oleum is the main product of sulfuric acid production.

The gas - liquid equilibrium for the "" system is shown in Fig. 3. A feature of this system is that in a wide range of solution concentrations in the vapor phase there are almost pure water vapor (left side of the graph), and over oleum (solution c) in the gas phase prevails (right side of the graph). the same composition of the liquid and vapor phases (azeotropic point) will be at a sulfuric acid concentration of 98.3%. If you absorb with a solution with a lower concentration, then reaction 5 will also proceed in the vapor phase - a mist of sulfuric acid will be formed, which will leave the absorber with the gas phase. And this is the loss of a product, and corrosion of equipment, and emissions into the atmosphere. If absorbed with oleum, then absorption will be incomplete.

A two-stage (two-tower) absorption scheme follows from these properties (Fig. 12). The gas containing, after the reactor, passes sequentially oleum 1 and monohydrate 2 absorbers. The other component of the reaction () is fed in countercurrent to the monohydrate absorber. Due to the intensity of circulation of the liquid (absorbent) in it, it is possible to maintain a concentration close to the optimal - 98.3% (the increase in concentration per passage of the liquid is no more than 1-1.5%). The technical name of such an acid is monohydrate, hence the name of the absorber. Absorption concentration conditions ensure complete absorption and minimal formation of sulfuric acid mist. The acid from the monohydrate absorber enters the oleum one. A 20% solution circulates in it, which is partially taken as the final product - oleum. The acid from the previous absorber - the monohydrate - can also be a product.

The formation of sulfuric acid and the absorption of sulfur trioxide are exothermic processes. Their heat is removed in the irrigation heat exchangers 3 on the liquid circulation line in the absorbers. At temperatures below 100 ° C, it is absorbed by almost 100%. Sulfur dioxide is practically not absorbed.

Rice. 12 Diagram of absorption separation in sulfuric acid production

1 - oleum absorber; 2 - monohydrate absorber; 3 - refrigerators; 4 - acid collectors; 5 - spray separators

5.5 Double contacting and double absorption system (DK / DA)

Despite the rather high degree of conversion - 98%, powerful sulfuric acid systems, producing up to 540 tons of product per day, emit more than 300 kg of sulfur dioxide into the atmosphere every hour. Based on the data on the equilibrium of the oxidation reaction, the degree of conversion can be increased by lowering the temperature in the last layers below 610 K or by increasing the pressure above 1.2 MPa. The possibility of lowering the temperature is limited by the activity of the available catalysts, increasing the pressure complicates the engineering design of the process, and therefore these methods have not yet received industrial application.

An effective way to increase the conversion in a reversible reaction is to remove its product. The technological scheme of this method is shown in Fig. 13. In the first stage of oxidation, a three-layer reactor 1 was used. The concentration in the incoming gas is 9.5-10.5%. The degree of conversion at the outlet of the reactor is 90-95%. Intermediate absorption includes oleum 2 and monohydrate 3 absorbers. After them, the gas contains only 0.6-1%. To heat it up to the reaction temperature (690-695 K), a heat exchanger is used after the second layer of reactor 1. The reactors of the first and second stages of oxidation are structurally combined in one housing. The conversion of the remainder is about 95%, the overall conversion is 99.6-99.8%. Let's compare: if there was no intermediate absorption, then the degree of conversion of the remaining 1-0.6% in the presence would not exceed 50%. A small amount of the formed is completely absorbed in the second monohydrate absorber 3.

As you can see, the amount of unconverted (and, therefore, emissions into the atmosphere) in the DC / DA system is reduced by almost 10 times in comparison with the single contact system. But for this it is necessary to increase the surface of the heat exchangers by 1.5-1.7 times.

Rice. 13 Flow chart of contacting and absorption stages in the "double contacting - double absorption" system

I, III - the first and second stages of oxidation; II, IV - the first and second water absorption systems; 1 - reactor (the first and second stages of oxidation, located in the same housing, are shown separately); 2 - oleum absorber; 3 - monohydrate absorber; 4 - remote heat exchangers of the reactor; 5 - acid refrigerators

6. Technology for the production of sulfuric acid from wet gas WSA and SNOX ™ - control of emissions of sulfur and nitrogen oxides

The development of Topsoe's WSA technology for the removal of sulfur compounds from flue gases with sulfuric acid production began in the late 1970s. WSA technology builds on Topsoe's vast experience in the sulfuric acid industry and a continued determination to move further and further in catalyst and process development. The main areas of research are the oxidation of SO2 on sulfuric acid catalysts and the process of acid condensation.

6.1 Basic research

The ability to condense sulfuric acid vapors to produce concentrated sulfuric acid without the release of acid mist is a unique feature of the WSA technology, which was achieved on the basis of fundamental experimental and theoretical work carried out at Topsoe.

During the cooling of the sulfuric acid vapor contained in the gas phase, spontaneous homogeneous formation of condensation centers, heterogeneous condensation and condensation on the walls occur simultaneously. For the development and improvement of the WSA condenser, Topsoe laboratories conduct fundamental research into these critical condensation mechanisms.

Fig. 4. Topsoe glass tube technology is used at WSA to condense sulfuric acid vapors

6.2 Development and optimization of technology

Pilot and plant-level tests, along with detailed simulations of the WSA condenser, are used to study the effect of condenser design and mode of operation on its performance in order to establish design criteria and process control.

Another priority area of ​​our technical development is the improvement of WSA glass tube technology and the continuous improvement of the quality of construction materials. The latter challenge calls for our expertise in material testing for the harsh operating conditions of sulfuric acid plants.

In order to fully exploit the potential of WSA technology, we use innovative methods in the creation of technological schemes while introducing Topsoe's own calculation tools to optimally solve various industrial problems. One of the drivers of this development is the growing focus on energy consumption and CO2 emissions worldwide, which requires maximum heat recovery.

6.3 SNOX ™ Technology

To remove sulfur and nitrogen oxides from flue gases, Topsøe has developed SNOX ™ technology, combining WSA technology with SCR nitrogen oxide removal to provide optimal integration for the power industry.

7. Sulfur production by the Claus method

LLC "Premium Engineering" can offer four main methods of the Claus process for the production of elemental sulfur from the acidic components of natural gas and refinery gases:

Direct-flow (fiery)

Branched

Branched with heated sour gas and air

Direct oxidation

1. The direct-flow Claus process (flame method) is used when the volume fraction of hydrogen sulfide in acid gases is above 50% and hydrocarbons are less than 2%. In this case, all the sour gas is fed for combustion to the thermal stage reactor-furnace of the Claus installation, made in the same building with the waste heat boiler. In the furnace of the reactor furnace, the temperature reaches 1100-1300 ° C and the sulfur yield is up to 70%. Further conversion of hydrogen sulfide to sulfur is carried out in two or three stages on catalysts at a temperature of 220-260 ° C. After each stage, the vapors of the formed sulfur are condensed in surface condensers. The heat released during the combustion of hydrogen sulfide and the condensation of sulfur vapor is used to produce high and low pressure steam. The sulfur yield in this process reaches 96-97%.

2. With a low volume fraction of hydrogen sulfide in acid gases (30-50%) and a volume fraction of hydrocarbons up to 2%, a branched scheme of the Claus process (one third or two thirds) is used. In this scheme, one third of the acid gas is incinerated to produce sulfur dioxide, and two thirds of the acid gas stream enters the catalytic stage, bypassing the reactor furnace. Sulfur is obtained in the catalytic stages of the process by the interaction of sulfur dioxide with hydrogen sulfide contained in the rest (2/3) of the original acid gas. The sulfur yield is 94-95%.

3. With a volume fraction of hydrogen sulfide in acid gas of 15-30%, when using the scheme one third to two thirds of the minimum allowable temperature in the furnace of the reactor furnace (930 ° C) is not reached, use a scheme with preheating of acid gas or air.

4. With a volume fraction of hydrogen sulfide in acid gas of 10-15%, a direct oxidation scheme is used, in which there is no high-temperature stage of gas oxidation (combustion). The acidic gas is mixed with a stoichiometric amount of air and is fed directly to the catalytic conversion stage. The sulfur yield reaches 86%.

To achieve the degree of sulfur recovery of 99.0-99.7%, three groups of methods for post-treatment of exhaust gases from the Claus process are used:

· Processes based on the continuation of the Claus reaction, i.e. on the conversion of H2S and SO2 to sulfur on a solid or liquid catalyst.

· Processes based on the reduction of all sulfur compounds into hydrogen sulfide with its subsequent extraction.

· Processes based on the oxidation of all sulfur compounds to SO2 or to elemental sulfur with their subsequent extraction.

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One who always smells good smells bad.

Decimus Magnus Avsonius. "Epigrams"

Various types of impurities can be found in crude oil. During the movement of petroleum fractions through refinery installations, these contaminants can adversely affect equipment, catalysts and the quality of end products. In addition, the content of many impurities in petroleum products is officially or unofficially limited.

Hydrotreating has an important function in removing many impurities from a variety of petroleum products. Hydrogen is a vital component in the hydrotreating process.

Hydrotreating

Petroleum fractions containing hydrocarbons C ^ and heavier, very likely contain organic sulfur compounds. Sulfur atoms can be attached to carbon atoms in different positions of the molecules and, therefore, from a chemical point of view, sulfur is included in the fraction. Hydrotreating removes sulfur atoms from hydrocarbon molecules.

At present, light distillates of direct distillation, boiling at temperatures below 350 ° C, are hydrotreated, including distillates sent to platforming, similar to distillates from secondary raw materials (catalytic cracking and coking gas oils), heavy gas oils supplied to catalytic cracking, as well as other products. - Approx. ed.

The stream of oil is mixed with a stream of hydrogen and heated to 260-425 ° C (500-800 ° F). Then the mixture of oil and hydrogen is sent to a reactor filled with a catalyst in the form of tablets (see Fig. 15.1). For the hydrotreating of petroleum products from sulfur compounds, a cobalt-molybdenum or nickel-molybdenum catalyst on an alumina support is usually used. - Approx. ed. Several chemical reactions take place in the presence of a catalyst:

Hydrogen combines with sulfur to form hydrogen sulfide (H2S).

Some nitrogen compounds are converted to ammonia.

Any metals in the oil are deposited on the catalyst.

Some olefins and aromatics are saturated with hydrogen; in addition, naphthenes are hydrocracked to some extent and some methane, ethane, propane and butanes are formed.

The stream leaving the reactor is directed to an evaporator, where gaseous hydrocarbons, as well as a small amount of ammonia, immediately rise upward. In order to completely separate all these light products, a small distillation column is installed at the outlet of the reactor.

The importance of the hydrotreating process is constantly increasing due to two main reasons:

Removal of sulfur and metals from fractions sent for further processing is an important protection for catalysts for reforming, cracking and hydrocracking processes.

Pursuant to clean air laws, the permissible sulfur content in petroleum products is constantly decreasing, which requires desulfurization of distillates and jet fuels.

Hydrotreating of residual oil products. As with other products, residual fuels must comply with environmental regulations. So-

Mu, albeit with some delay, installations were created for their desulfurization. Although the process flow diagrams of these units are similar to those of light ends hydrotreaters, the equipment required as well as the products obtained are different. Residual petroleum products are characterized by low hydrogen / carbon ratios, therefore, despite the presence of excess hydrogen, a high pressure must be maintained in the reactor to prevent coke formation. It turns out that the residue hydrotreating unit must be as robust as the hydrocracking unit, which is very expensive.

The product leaving the residue hydrotreater contains a higher amount of low boiling water. The fact is that from these large molecules of the "trimethyl-honeycomb" type, you cannot simply remove sulfur, nitrogen and metals without destroying literally the entire molecule. This is why smaller molecules are obtained.

Hydrotreating jet fuel. Hydrotreating is used to improve the combustion performance of distillate fuels, especially jet fuels. The kerosene fraction can contain many aromatic hydrocarbons, which are characterized by a high carbon / hydrogen ratio. When these compounds are burned, a large amount of smoke can be produced due to the lack of hydrogen. By the way, one of the standardized indicators of jet fuel is the maximum height of a non-smoking flame.

The device for measuring this indicator resembles a kerosene lamp. The fuel is placed in a vessel equipped with a wick, the length of which can be varied and thereby the magnitude of the flame is regulated. The height of a non-smoking flame is measured as the maximum wick length (in mm) at which a non-smoking flame is produced.

Hydrotreating improves kerosene with a low non-smoking flame height. During this process, the benzene rings in the molecules of aromatic hydrocarbons are saturated with hydrogen and thus turn into naphthenes, which are no longer smoked when burning.

Hydrotreating pyrolysis gasoline. With ethylene, pyrolysis gasoline is also obtained from naphtha or gas oil (see Chapter XVIII). This product contains large amounts of dienes - these are unsaturated hydrocarbons, in molecules of which two pairs of carbon atoms are linked by double bonds. Pyrolysis gasoline only in small doses is suitable for the preparation of motor gasoline. It smells bad, is peculiarly colored and forms gum in the carburetor.

During hydrotreating, the double bonds are saturated and most of the undesirable properties are lost. However, as a result of saturation of aromatic rings, the octane number may slightly decrease.

Hydrogen production

Since a modern oil refinery has a large number of hydrocracking and hydrotreating units, it is important to supply them with hydrogen. - Approx. ed.

The source of hydrogen in a refinery is usually a catalytic reformer. The light boiling fraction from this unit is characterized by a high hydrogen / methane ratio; it is usually deethanized and depropanized to increase the hydrogen concentration.

Sometimes the hydrogen from the reformer is insufficient to meet all the needs of the refinery, for example, if a hydrocracker is in operation. Hydrogen is then produced in a steam methane reformer shown in Figure 15.2.

In the search for hydrogen synthesis opportunities, various compounds with high hydrogen content were considered as potential feedstocks so that as little waste as possible and as little energy as possible wasted. The two compounds we ultimately chose seem obvious enough — methane (CH4) and water (H20).

The task of the steam methane conversion process is to extract as much hydrogen from these compounds as possible, while spending as much

Rice. 15.2. Conversion of methane with steam.

Less energy (fuel). This process is carried out in four stages with the help of some useful catalysts.

Conversion. Methane and steam (H20) are mixed and passed over the catalyst at 800 ° C (1500 ° F), resulting in the formation of carbon monoxide and water

Additional conversion. Not satisfied with the hydrogen that has already formed, the installation squeezes out everything it can from carbon monoxide. Additional steam is added to the mixture and passed over another catalyst at 340 ° C.

The result is carbon dioxide and

Separation of gases. To obtain a stream with a high hydrogen content, it is separated from carbon dioxide using a diethanolamine (DEA) extraction process.

Methanation. Since the presence of even small amounts of carbon oxides in a hydrogen stream can be detrimental to some applications, in the next stage of the process these impurities are converted to methane. The process runs on a catalyst at 420 ° C (800 ° F).

In some cases, refiners do not have sulfur-free methane (natural gas) at their disposal. In this case, instead of methane, you can use heavier hydrocarbons, such as propane or naphtha. This process requires different equipment and different catalysts. Also, it is less energy efficient, but still works.

Sulfur production

Hydrotreating creates a stream of hydrogen sulphide (H2S), a deadly gas that must be disposed of somehow. The usual process for its conversion involves two stages: first you need to separate hydrogen sulfide from other gases, and then turn it into elemental sulfur, which is harmless.

Isolation of H2S. Until about 1970, hydrogen sulphide from refinery plants, along with other gaseous fractions, was mainly used as fuel in the same refinery. When hydrogen sulphide is burned in a furnace, sulfur dioxide B is formed

Currently, laws regulating air purity limit the emissions of this substance to such an extent that it prevents the main amount of hydrogen sulfide from entering the fuel system.

Hydrogen sulfide can be separated by several chemical methods. The most commonly used is DEA extraction. A mixture of DEA and water is pumped from top to bottom through a vessel filled with plates or a nozzle. The gas mixture containing hydrogen sulfide comes from

Zu. During the passage of the flow, DEA selectively absorbs H2S. After that DEA, saturated with hydrogen sulfide, is fractionated to separate H2S, which is then sent to the sulfur recovery unit, and DEA is returned to the process. This scheme is analogous to the circulation of lean oil and fatty oil in the demethanization process described in chapter VII on gas fractionation plants, with the difference that DEA selectively absorbs hydrogen sulphide and does not absorb hydrocarbons.

Obtaining sulfur. The process for converting H2S to ordinary sulfur was developed by a German by the last name as early as 1885. Various versions of this method have now been created for different ratios of H2S to hydrocarbons, but the classic two-stage split-flow process is mainly used.

Burning. A portion of the H2S stream is burned in a furnace, resulting in the formation of sulfur dioxide, water and sulfur. Sulfur is obtained due to the fact that the oxygen supplied to the furnace is not enough to burn all the hydrogen sulphide to S02, but only enough to burn one third.

Reaction. The remaining hydrogen sulfide is mixed with combustion products and passed over the catalyst. H2S reacts with the formation of sulfur:

Sulfur is removed from the reaction vessel in the form of a melt. In most cases, it is stored and shipped molten, although some companies pour the sulfur into molds and allow it to solidify. In this form, sulfur can be stored for as long as you like.

In the Clauss process, approximately 90-93% of the hydrogen sulfide is converted to sulfur. Depending on the local environment, the remaining hydrogen sulphide, called tail gas, can sometimes be burned in the plant's fuel system. except

In addition, the tail gas can be processed to remove most of the H2S using more modern methods such as the Sulfreen process, the Stretford process, or SCOT (Shell's Clauss process).

EXERCISES

1. Determine which of the following streams are feed, product, or internal streams for hydrotreating, DEA extraction, Clauss sulfur production, and steam methane reforming.

The basic process flow diagrams of Claus plants include, as a rule, three different stages: thermal, catalytic and afterburner. The catalytic stage, in turn, can also be divided into several stages, differing in temperature. The afterburner stage can be either thermal or catalytic. Each of the similar stages of the Claus installations, although they have common technological functions, differ from each other both in the design of the apparatus and in the piping of communications. The main indicator that determines the layout and mode of Claus units is the composition of acid gases supplied for processing. The sour gas entering the Claus furnaces should contain as little hydrocarbons as possible. During combustion, hydrocarbons form resins and soot, which, when mixed with elemental sulfur, reduce its quality. In addition, these substances, being deposited on the catalyst surface, reduce their activity. The efficiency of the Claus process is particularly negatively affected by aromatic hydrocarbons.

The water content in acid gases depends on the condensation mode of the overhead product of the regenerator of the gas treatment plant. Acid gases, in addition to equilibrium moisture corresponding to the pressure and temperature in the condensation unit, may also contain methanol vapors and droplet moisture. To prevent the ingress of droplet liquid into the reactors of sulfur production units, sour gases undergo preliminary separation.

The cost of sulfur produced at the Claus plants primarily depends on the concentration of H 2 S in the acid gas.

The specific capital investment in the Claus plant increases in proportion to the decrease in the H 2 S content in the sour gas. The cost of treating an acid gas containing 50% H 2 S is 25% higher than the cost of treating a gas containing 90% H 2 S.

Before being fed into the combustion chamber of the thermal stage, the gas passes through the inlet separator C-1, where it is separated from the dropping liquid. To control the concentration of H 2 S in sour gas, an in-line gas analyzer is installed at the outlet of the C-1 separator.

To ensure the combustion of acid gas, atmospheric air is blown into the combustion chamber by means of a blower, which passes through the filter and the heater beforehand. Air heating is performed to eliminate the impulsive combustion of acid gas and prevent pipeline corrosion, since during the combustion of H 2 S the formation of SO 3 is possible, which at low temperatures in the presence of water vapor can form sulfuric acid.

The air flow is regulated depending on the amount of acid gas and the H 2 S: SO 2 ratio in the gas at the outlet of the KU waste heat boiler.

The combustion gases of the reaction furnace (CR) pass through the tube bundle of the waste heat boiler, where they are cooled to 500 ° C. In this case, there is a partial condensation of sulfur. The resulting sulfur is discharged from the apparatus through the serum trap. Due to the partial removal of the reaction heat by water, high-pressure steam is obtained in the boiler (P = 2.1 MPa).

After the boiler, the reaction gases enter the R-1 catalytic converter-reactor, where carbon disulfide and carbon sulphide are hydrolyzed.

Due to the exothermicity of the reactions taking place in the converter, the temperature on the catalyst surface rises by about 30-60 ° C. This prevents the formation of a liquid sulfur precipitate, which, falling on the surface of the catalyst, would reduce its activity. Such a temperature regime in the converter simultaneously ensures the decomposition of the products of side reactions - COS and CS 2.

The main part of the gas (about 90%) from the reactor enters the tube space of the X-1 condenser for cooling, and then goes to the R-2 reactor. Heat removal in the X-1 condenser is carried out due to the evaporation of water in its annular space to obtain low pressure steam (P = 0.4 MPa). When gases are cooled in X-1, sulfur condensation occurs. Liquid sulfur is discharged through the gray-gate to the degassing unit.

Some of the reaction gases (about 10%), bypassing the X-1 condenser, are mixed with colder gases coming out of the same condenser. The temperature of the mixture before entering the reactor R-1 is about 225 ° C.

To regulate the temperature in reactors R-1, R-2, R-3 (during the start-up period and in the event of sulfur ignition), low pressure steam and nitrogen are supplied to them.

During normal operation, the temperature of gases at the outlet of X-2 and P-1 is 191 and 312 ° C, respectively.

The removal of heat in the X-2 apparatus is carried out due to the evaporation of water in its annular space to obtain low pressure steam.

Waste gases from the R-2 reactor are fed to the third condenser X-3 for cooling, from where they are fed to post-treatment at a temperature of 130 ° C.

To control the concentration of H 2 S and SO 2 in the exhaust gases, in-line gas analyzers are installed at the outlet of the X-3.

To prevent the carryover of liquid sulfur with exhaust gases, a coalescer is installed in their lines.

To prevent the solidification of sulfur in the coalescer, a periodic supply of water vapor is provided.

The streams of liquid sulfur withdrawn from the condensers contain 0.02-0.03% (mass) of hydrogen sulfide. After degassing sulfur, the concentration of H 2 S in it decreases to 0.0001%.

Sulfur degassing is carried out in a special unit - a sulfur pit. This ensures normal conditions for storage, loading and storage of gas sulfur.

The main amount (~ 98%) of the acid gas is fed to the reactor-generator, which is a gas-tube steam boiler. Process gas - combustion products - successively passes through the pipe part of the boiler and the condenser-generator, where it is cooled to 350 and 185 ° C, respectively.

At the same time, due to the heat released in these devices, water vapor is formed with a pressure of 2.2 and 0.48 MPa, respectively.

The degree of conversion of H2S to sulfur in the reactor-generator is 58-63%. Further conversion of sulfur compounds into elemental sulfur is carried out in catalytic converters.

Table 1.1 - Compositions of the streams of the Claus plant,% (vol.):

Table 1.2 - Duration of residence (f S) of the process gas in the apparatuses at various flow rates of the acid gas G:

Table 1.1 and 1.2 show the results of a survey of the installation.

The degree of conversion of H2S to sulfur in the furnace of the reactor-generator is 58-63.8, in the first and second converters 64-74 and 43%, respectively. After the last stage of sulfur condensation, the process gases enter the afterburner.

With a gas flow rate of 43-61 thousand m3 / h, the afterburner provided almost complete oxidation of H 2 S to SO 2. With a long residence time of the gas in the furnace, the complete conversion of H 2 S to SO 2 is not ensured: at the outlet of the furnace, the concentration of H 2 S in the gas was 0.018-0.033%.

The main indicators of gas sulfur must meet the requirements of GOST 126-76.

At present, dozens of modified versions of the Claus installations have been developed. The field of application of these schemes depends both on the content of hydrogen sulfide in acid gases and on the presence of various impurities in them, which have a negative effect on the operation of sulfur production plants.

For gases with low sulfur content (from 5 to 20%), four variants of improved Claus plants were analyzed.

The first option provides for the supply of oxygen to the combustion chamber (CC) of the furnace instead of air according to the standard scheme. To obtain stable flares as the H2S content in the feed gas decreases, an acid gas stream is introduced into the combustion chamber bypassing the burners. The jets of streams ensure good mixing of the combustion gases with the gas supplied to the system, bypassing the burners. Furnace sizes and flow rates are selected to provide sufficient contact time for interaction between the components of both gas streams. After the combustion chamber, the further course of the process is similar to the conventional Claus process.

In the second variant, the feed gas is heated before being fed for combustion due to partial heat recovery from the gas stream leaving the combustion chamber. If the preheating is insufficient to achieve the required temperature in the combustion chamber, fuel gas is fed into the combustion chamber.

The third option involves the combustion of sulfur. Part of the feed gas stream is fed into the combustion chamber, pre-mixing with air. The remainder of the acid gas is introduced into the combustion chamber in separate jets through the bypass lines. To maintain the required temperature and stabilize the process in the combustion chamber, the resulting liquid sulfur is additionally burned in a special burner mounted in the combustion chamber.

In case of insufficient heat in the system, the required amount of fuel gas is supplied to the compressor station.

In the fourth version, unlike the previous versions, the process does not require a combustion chamber: the acid gas is heated in the furnace, then fed to the converter. The sulfur dioxide required for the catalytic conversion is produced in a sulfur combustor, where air is fed to support the combustion process. Sulfur dioxide from the combustor passes through the waste heat boiler, then mixes with the heated acid gas and enters the catalytic converter.

Analysis of these tables leads to the following conclusions:

• - the use of a process with preheating of the feed gas is preferable when the cost of oxygen is high;
• - the use of the oxygen process is beneficial when the price of oxygen is less than 0.1 grades 1 m 3.

At the same time, relatively low concentrations of H2S in sour gas also favorably affect the cost of sulfur;

• - in terms of the cost of sulfur, the best performance is achieved by the catalytic process with the production of sulfur dioxide from sulfur;
• - the most expensive is the process with the combustion of sulfur. This process can be applied in the absence of hydrocarbons in the feed gas, since the presence of hydrocarbons in the gas causes the formation and deposition of carbon and tar on the catalyst, and reduces the quality of sulfur.

Figure 1.4 - Influence of the price of oxygen y on the cost of sulfur CS at various concentrations of H2S in the gas:

Table 1.3 - Average indicators of options for processing low-sulfur gas at the Claus unit:

There is a possibility of improving the Claus process due to the two-stage conversion of H 2 S into elemental sulfur: part of the gas is fed into the reactor according to the usual scheme, and the other part, bypassing the reaction furnace, is fed to the second conversion stage.

According to this scheme, it is possible to process acid gases with a hydrogen sulfide concentration of less than 50% (vol.). The lower the content of H 2 S in the feed, the greater part of it, bypassing the reaction chamber, is fed to the converter stage.

However, one should not get carried away with bypassing large volumes of gas. The larger the amount of bypass gas, the higher the temperature in the converter, which leads to an increase in the amount of nitrogen oxides and three - sulfur oxide in the combustion products. The latter, upon hydrolysis, forms sulfuric acid, which reduces the activity of the catalyst due to its sulfation. The amount of nitrogen oxide and SO3 in gases increases especially at temperatures above 1350 ° C. VNIIGAZ has also developed a technology for producing polymer sulfur. Polymer sulfur differs from conventional sulfur modifications by its high molecular weight. In addition, unlike ordinary sulfur, it does not dissolve in carbon disulfide. The latter property serves as the basis for determining the composition of polymer sulfur, the quality requirements for which are given in Table 1.4. Polymer sulfur is mainly used in the tire industry.

It is known from the official registers of the Ministry of Energy of the Russian Federation that today several oil refineries are being built in our country. A huge number of refineries are still at the stage of official design according to the data Department of Energy registry.

Total will be covered by the order 18 regions of Russia, and in some regions, even several refineries.
The main number of new refineries will be located in the Kemerovo Region:

• LLC "Itatsky Oil Refinery"
• LLC "Oil refinery" Severny Kuzbass "
• LLC "Anzherskaya oil and gas company"

Rosneft builds a plant called Eastern petrochemical complex by 30 million tons capacity.

Refineries under construction and projected at various stages of readiness

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Sulfur is an unavoidable by-product of hydrocarbon processing, which can bring both profit and problems due to its environmental insecurity. At the Moscow Oil Refinery, these problems were solved by modernizing the sulfur production unit, which had a positive effect on the economic component of the process.

Sulfur is a common chemical element and is found in many minerals, including oil and natural gas. When processing hydrocarbons, sulfur becomes a by-product that must be somehow disposed of, and ideally made a source of additional profit. A complicating factor is the non-ecological nature of this substance, which requires special conditions for its storage and transportation.

On a global market scale, the volumes of sulfur produced during oil and gas processing are approximately equal and in total make up about 65%. Almost 30% more comes from non-ferrous metallurgy waste gases. The small remaining share is the direct development of sulfur deposits and the extraction of pyrites *. In 2014, the world produced 56 million tons of sulfur, while experts predict an increase in this indicator by 2017-2018 due to the commissioning of new large gas fields in Central Asia and the Middle East.

The Russian sulfur market can be considered significantly monopolized: approximately 85% of raw materials are supplied by Gazprom's gas processing enterprises. The remaining share is divided between Norilsk Nickel and oil refining. According to Rosstat, in 2015, Russia produced about 6 million tons of sulfur, which allows the country to occupy a tenth of the world market. The domestic market is in surplus: Russian consumers (and these are mainly fertilizer producers) annually buy about 2-3 million tons of sulfur, the rest is exported. At the same time, the consumer market can also be considered a monopoly: about 80% of all liquid sulfur produced in Russia is purchased by enterprises of the PhosAgro group, another 13% is sent to another producer of mineral fertilizers - EuroChem. Only granulated and lumpy sulfur is exported (see section on types of sulfur).

Types of commercial sulfur

Simple sulfur is a light yellow powdery substance. In nature, sulfur can occur both in its native crystalline form and in various compounds, including it can be present in natural gas and oil. Currently, three forms of sulfur are mainly produced - lumpy, liquid and granular. When sulfur is separated from gases, liquid (or molten) sulfur is obtained. It is stored and transported in heated tanks. For the consumer, the transport of liquid sulfur is more profitable than smelting it on site. The advantages of liquid sulfur are the absence of losses during transportation and storage and high purity. Disadvantages - danger of fire, waste on heating tanks.

When liquid sulfur is cooled, lump sulfur is obtained. It was her that, until the early 1970s, was mainly produced in the USSR. Among the disadvantages of lump sulfur: low quality, losses for dust and chips during loosening and loading, fire hazard, low environmental friendliness.

Granular sulfur is obtained directly from liquid sulfur. Various methods of granulation are reduced to breaking the liquid into separate droplets, followed by their cooling and encapsulation.

Obviously, large consumers are interested in a supplier that can fully meet their demand. “In this situation, small producers, as a rule, are looking for buyers among neighboring enterprises - this allows them to save on logistics and thereby increase interest in the product,” explained Zakhar Bondarenko, head of the petrochemistry and LPG department of Gazprom Neft. “Sometimes sulfur, being a by-product of production, is sold for next to nothing, just to get rid of raw materials that are unsafe for storage.”

Choosing its strategy for the utilization of hydrogen sulfide, the Moscow Oil Refinery relied on ecology, but was able to take into account financial interests as well.

No smell and dust

Reconstruction of the sulfur production unit at the Moscow Refinery became part of a comprehensive production modernization project aimed at improving the plant's environmental performance. In 2014, the Moscow Refinery switched to the production of granular sulfur, a modern product that meets the most stringent environmental requirements. As part of the reconstruction, the equipment of the plant was renewed, a granulation block and a block for post-treatment of off-gases were built.

Significant volumes of hydrogen sulfide (sour) gases at refineries are obtained as a result of the catalytic cracking process, as well as the hydrotreatment of gasoline and diesel fuel from sulfur initially contained in oil. Today this problem is especially urgent: oil is becoming more and more sulfurous, and environmental standards for fuels severely limit the content of this element. The ecological class "Euro-5", which corresponds to all gasoline produced at the Moscow Refinery, implies a fivefold decrease in the sulfur content in the fuel compared to "Euro-4", from 50 to 10 mg / kg.

Yuri Erokhin,
Head of the Department of Labor Protection, Industrial Safety and Environmental Protection of the Moscow Oil Refinery

For the oil refining industry, a sulfur production unit is primarily an air-shielding facility that allows hydrogen sulfide to be utilized without harming the environment. After the introduction of modern technologies at the Moscow Refinery, we were able to completely eliminate emissions of hydrogen sulfide into the atmosphere. This is not an unfounded statement. Zero emissions are also confirmed by instrumental control, which we regularly carry out in accordance with the legislation by an independent accredited laboratory. In fact, the reconstruction of the sulfur recovery unit has reduced the volume of emissions at the Moscow Refinery by 50%. This is a significant achievement not only for the plant, but for the ecology of the entire region. At the same time, by switching to the production of granular sulfur and moving away from the production of lump sulfur, we were able to improve the environmental situation directly on the territory of the plant.

At the sulfur production unit, hydrogen sulfide is first oxidized to sulfur dioxide, which then, when reacted with the same hydrogen sulfide in the presence of a catalyst, turns into elemental sulfur (Clauss process). However, in order to completely utilize hydrogen sulfide, it is necessary not only to drive acid gases through the unit, but also to carry out subsequent additional purification. “During the modernization of the unit, we changed 90% of the equipment,” said Vladimir Suvorkin, supervisor of the sulfur recovery unit. “But one of the main stages of the project was the construction of an off-gas post-treatment unit. The new post-treatment unit allows minimizing sulfur dioxide emissions, and returning all hydrogen sulfide to the technological process. Thus, we managed to increase the sulfur recovery by more than 20% - now it reaches 90%. At the same time, hydrogen sulfide emissions are completely excluded. "

Another important environmental aspect is disposal of lump sulfur, a bulk material, the storage of which is inevitably associated with the formation of a large amount of harmful dust. Initially, the plant produces liquid sulfur, which can either be sold in liquid form, or cooled and turned into lumps, or granulated. “The old plant had two sulfur pits with a volume of 50 tons each for storing liquid sulfur,” said Vladimir Suvorkin. - When there was no shipment of liquid sulfur, it was necessary to pump sulfur into a warehouse and store it in a crystallized lump form in railway or tank trucks. With the commissioning of a new unit (sulfur pit) with a volume of 950 tons, we got rid of this problem ”. Part of the liquid sulfur is now sold to one of the enterprises located in the Moscow region, the rest is sent to the granulation plant.

Sulfur consumption structure in the RF

Commodity structure of sulfur production in the Russian Federation
in 2009-2015,%

Source: "Infomine"

Sulfur market structure in the Russian Federation,
million tons

Unlike the production of lump sulfur, during granulation, dust and odor are practically not formed. Each granule is a hemisphere with a size of 2 to 5 mm and is in a polymer shell, which prevents its dissolution. At the exit from the conveyor, finished products are packed in modern packaging - sealed big bags. Such packaging completely excludes contact of sulfur with the environment.

Transport node

Of course, sulfur granulation is a rather complicated and costly process, which significantly increases the cost of the product. Gazprom Neft could have avoided commissioning costs for additional equipment provided that all liquid sulfur produced was sold on the market. However, this cannot be counted on. The main problem of the Russian market for this product today is the shortage of tanks associated with the new technical regulations, which oblige the owners of rolling stock to either modernize the outdated rolling stock or take it out of service. Tank owners prefer the second option, while no one is in a hurry to invest in the production of new tanks. “On the scale of the domestic sulfur market, the MNPZ is a small producer, so the company does not make sense to spend money on expanding its own tank fleet,” said Zakhar Bondarenko. “It turned out to be much more profitable to pelletize unrealized liquid sulfur residues and sell to foreign markets, where you can always find a buyer, even for small volumes.”

Sulfur recovery unit

The modernized sulfur production unit at the Moscow Refinery includes two sulfur recovery units, each of which has been reconstructed. The depth of sulfur extraction in these blocks reaches 96.6%. The unit is also equipped with an off-gas post-treatment unit, which ultimately makes it possible to recover 99.9% of sulfur. The new sulfur offloading unit can simultaneously store up to 950 tons of liquid sulfur, which completely eliminates the need for the production and storage of lump sulfur. In addition, a sulfur granulation unit was put into operation. The design capacity of the unit for liquid degassed sulfur, taking into account the operation of the off-gas cleaning unit, is 94 thousand tons per year, and the design capacity of the liquid sulfur granulation unit is 84 thousand tons per year, which fully covers the existing needs of the enterprise for the utilization of hydrogen sulfide-containing gases.

If for Russian consumers granular sulfur turns out to be too expensive a product, which also requires additional equipment to process, then on foreign markets the demand for granular sulfur is steadily high. Today granulated sulfur from the Moscow Refinery is supplied to more than a dozen countries, including Latin America, Africa and Southeast Asia. “At present, granulated sulfur in the world market is gradually replacing its other commercial forms due to its higher quality (absence of impurities and contaminants) and ease of transportation,” explained Olga Voloshina, head of the chemical products markets department of the Infomine research group. “At the same time, the domestic market traditionally uses mainly liquid sulfur. In the near future, this situation is unlikely to change, since in order to switch production to the use of granular sulfur instead of liquid sulfur, it is necessary to re-equip them, including the creation of sulfur-smelting capacities. This will require additional costs, which few people will spend in the conditions of the economic crisis ”.

Prospects and opportunities

Despite the current demand for sulfur in foreign markets, experts are very cautious in forecasting the development of this area. The world market is highly dependent on the largest importers, primarily China, which imported about 10 million tons of sulfur in 2015. However, the development of its own production is gradually reducing the interest of the Chinese in imports. The situation with other significant players is also unstable. In this regard, for several years in a row, Gazprom, as the largest exporter, has been talking about the need to look for alternative markets for sulfur sales within the country. Such a market could be the sphere of road construction, provided that new materials are actively introduced - sulfur asphalt and sulfur concrete. Comparative studies of these materials show a number of their advantages, in particular, environmental safety, wear resistance, heat resistance, crack resistance, and rutting resistance. “Despite the creation of pilot batches of paving slabs from sulfur concrete, as well as the coverage of road sections with gray asphalt, mass industrial production of these building materials has not yet been established,” stated Olga Voloshina. - The developers explain this by the lack of a regulatory and technical base that regulates the requirements for this type of materials, as well as for road surface construction technologies.

So far, Gazprom is working on a long-term target program for the creation and development of a sub-sector of the industry of construction and road-building materials based on sulfur binder in the Russian Federation. At one time, the company spoke about the advisability of locating the production of such materials in regions with a high level of road construction and the availability of raw materials. Then the Moscow Refinery was named as a potential raw material and production base. True, there are no such projects in Gazprom Neft yet.