RU2523204C1 - Method of obtaining elemental sulphur from sulphur dioxide-containing discharge gas - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method includes concentration of sulphur dioxide, partial high-temperature reduction of the concentrated sulphur dioxide with concentrated hydrogen to sulphur, hydrogen sulphide and water, condensation of the formed sulphur vapour with output of a liquid medium into a sulphur collector. Then, processing of discharged technological gas by catalytic Claus-conversion, and following purification of the tail gas, which contains residual quantities of H₂S, SO₂, N₂ and water vapours, is carried out. A part of flow of concentrated sulphur dioxide is diverted by a bypass line, skipping stages of high temperature reduction, condensation of sulphur and catalytic convention, and the discharged from a catalytic stage of Claus-conversion tail gas is introduced into a hydrogenation unit. Gas after hydrogenation, consisting of H₂S, H₂ and water vapours, is supplied into a condensation column for water separation. Dehydrated gas is mixed with a bypass flow of concentrated sulphur dioxide and a mixture is directed to an additional catalytic stage of Claus-conversion, residual gases after which are returned to the input of any catalytic stage, which precedes the hydrogenation unit.

EFFECT: increase of the outgoing gas utilisation efficiency.

8 cl, 2 dwg, 1 ex

Description

The invention relates to the field of chemistry and can be used to obtain elemental sulfur from exhaust gas containing sulfur dioxide at the enterprises of the chemical, petrochemical, gas processing and metallurgical industries.

A known method of producing elemental sulfur from an exhaust gas containing sulfur dioxide, according to French patent No. 2212290, IPC СВВ 17/04.

The known method includes cooling the off-gas sulfur dioxide, separating sulfur dioxide from it and reacting concentrated sulfur dioxide with a reducing gas in a thermal reactor, followed by cooling the combustion products, releasing the sulfur formed and further treating the gas in several catalytic steps. Hydrogen or hydrogen enriched gas is used as the reducing gas. The process gas leaving the last catalytic stage, according to the known invention, is sent to the afterburner, where all sulfur-containing components are oxidized to sulfur dioxide. Next, the stream is returned to the stage of separation of sulfur dioxide from the exhaust gas.

The main disadvantage of this technical solution is the burning of process gas leaving the last catalytic stage. This leads to an increase in the load at the stages of separation and concentration of sulfur dioxide from the exhaust gas and to an increased consumption of concentrated hydrogen.

The closest in technical essence and the achieved result is a method for producing elemental sulfur from exhaust gas containing sulfur dioxide, according to the patent for the invention of the Russian Federation No. 2474533, IPC СВВ 17/04.

The method includes concentration of sulfur dioxide extracted from the exhaust gas, partial high-temperature recovery of concentrated sulfur dioxide with concentrated hydrogen to sulfur, hydrogen sulfide and water, condensation of the generated sulfur vapor with the withdrawal of liquid sulfur to the sulfur collector, processing of the released process gas by sequential catalytic Claus conversion and subsequent purification of the process gas leaving the last catalytic stage containing residual amounts of H ₂ S, SO ₂ , H ₂ and vapors in odes. To do this, the process gas is sent to the reactor of the purification unit, in which H ₂ S interacts with SO ₂ in an aqueous solution to form a suspension of sulfur in water and in which a temperature gradient is maintained in the cold part of 20-60 ° C, and in the hot part of 70-100 ° C and create the oncoming movement of the gas and liquid phases.

Upon receipt of sulfur in accordance with the method, the bulk of the sulfur is produced in commercial, molten form by condensation of sulfur vapor from gas in condensers of thermal and catalytic stages.

However, up to 1.5% of all sulfur is produced in the column reactor in the form of an aqueous suspension (colloidal sulfur). Due to the lack of demand for suspended sulfur, a number of additional operations are required to bring this type of sulfur to marketable conditions. Such operations include filtering sulfuric pulp, compaction of sludge and removal of residual moisture, and melting of sulfur cake. Carrying out these operations requires additional capital and operating costs, it is necessary to allocate additional personnel and production facilities.

The technical problem that the present invention solves is to increase the efficiency of the process of utilization of waste gas containing sulfur dioxide by reducing operating costs and capital costs, which is associated with the ability to get all of the sulfur in marketable, molten form.

The technical problem is solved in that sulfur dioxide is extracted and concentrated from the exhaust gas containing sulfur dioxide, and it is subjected to partial high-temperature reduction to sulfur, hydrogen sulfide and water using concentrated hydrogen. Next, the formed sulfur vapor is condensed with liquid sulfur being withdrawn to a sulfur collector and the exhausted process gas is processed by catalytic Klaus conversion. Process gas is passed sequentially through 1-3, mainly one, Klaus stage. The gas before each stage of the catalytic conversion is heated so that the gas temperature at the outlet of the catalytic reactor is 5-30 ° C, mainly 8-15 ° C, higher than the temperature of the sulfur dew point in this gas using indirect heating, which ensures constant H ₂ S: SO ₂ ratio.

The tail gas leaving the catalytic step of the Klaus conversion, containing residual amounts of H ₂ S, SO ₂ , H ₂ and water vapor, is introduced into the hydrogenation unit. The gas, preheated to 200-240 ° C, enters a catalytic reactor in which the SO ₂ and sulfur vapor are reduced to H ₂ S on the hydrogenation catalyst due to interaction with the residual hydrogen contained in the gas.

The process gas that enters the hydrogenation unit must have a reducing medium, i.e. contain such an amount of hydrogen that at the outlet of the hydrogenation unit all sulfur-containing components react to hydrogen sulfide and, in addition, the excess hydrogen content in the output stream is 1-4 mol.%. This guarantees the absence of sulfur dioxide in the reaction products, which, in turn, prevents the formation of colloidal sulfur during subsequent condensation of water from the gas. These data were obtained as a result of the analysis of the operation of similar units in existing industrial plants.

To obtain a reducing medium in the gas in front of the hydrogenation unit, the concentration ratio of Н ₂ / (SO ₂ + S) at the inlet to the thermal reactor should be greater than 2. This is achieved by the fact that part of the concentrated sulfur dioxide input stream is diverted along the bypass line, bypassing the high-temperature reduction stages sulfur condensation and catalytic conversion. In this case, the concentration ratio of (H ₂ S + H ₂ ) / SO ₂ in the process gas to the hydrogenation unit will be more than 2.

The dehydrated gas leaving the hydrogenation unit is mixed with a bypass stream of concentrated sulfur dioxide, the proportion of which is 2-15%, mainly 5-7%, of the total amount of concentrated sulfur dioxide. In this case, the concentration ratio of (H ₂ S + H ₂ ) / SO ₂ in the gas will be equal to two.

The mixture of dried gas from the hydrogenation unit and part of the initial sulfur dioxide is fed to an additional catalytic stage for processing, where the Claus reaction is carried out on the catalyst. Gas processing is carried out in 1-3, mainly in two catalytic stages. The purpose and technological design of these catalytic stages are similar to those described above. A feature of their operation is a lower ratio of the concentrations of H ₂ S / SO ₂ components in the process gas compared with this indicator for Klaus steps to the hydrogenation unit. This is a consequence of bypassing part of the sulfur dioxide and is necessary to maintain a reducing atmosphere in the gas at the outlet of the hydrogenation unit, as shown above.

Gases leaving the last catalytic stage of the Klaus process, after condensation of sulfur, are returned to the inlet of any catalytic stage preceding the hydrogenation unit.

The justification of the found fraction of the initial sulfur dioxide, which is discharged along the bypass line, is shown in Fig. 1.

From Fig. 1 it follows that an increase in the fraction of bypass of sulfur dioxide leads to an increase in the hydrogen content in the gas leaving the hydrogenation unit, and at the same time leads to an increase in the recycle gas flow rate from the exit of the end catalytic stage to the plant head. An increase in recycle gas consumption leads to an increase in operating costs at the facility. With a decrease in bypass gas flow, a decrease in the concentration of hydrogen in the gas at the outlet of the hydrogenation unit occurs. The optimum hydrogen content in this gas is 2-4 mol.% Corresponds to bypassing 9-12% of the initial sulfur dioxide, which corresponds to the minimum possible gas recirculation in the installation at the level of 8-10.7% of the total consumption of processed gases.

The invention will be better understood when reading the description of the operation of the installation below, a diagram of which is shown in the attached Fig. 2.

The method is as follows.

Sulfur dioxide gas from the liquefied sulfur dioxide storage unit (not shown) and hydrogen gas from the hydrogen production unit (not shown) enter the thermal reactor 1.

The ratio of the total consumption of hydrogen to sulfur dioxide, which are fed for processing, is 2 moles of H ₂ per 1 mol of SO ₂ . This ratio is optimal for conducting the process, since it corresponds to the stoichiometry of the next reaction, which describes the process as a whole.

$$2H_2+\mathrm{<figure-callout\; id="2"\; label="S\; O"\; filenames="00000006.png"\; state="\{\{state\}\}">S\; </figure-callout>}{O}_{}{}_2\to S+2H_{2}O\left(\text{one}\right)$$

Based on the specifics of the operation of the hydrogenation unit 2, part of the sulfur dioxide - about 6% of the total required amount, is discharged along the bypass line 3, bypassing the thermal reactor, and mixed with the gas leaving the hydrogenation unit.

In the furnace of thermal reactor 1 at a temperature of 1200–1300 ° C, an exothermic reaction of reduction of sulfur dioxide to elemental sulfur by reaction (1) and to hydrogen sulfide by reaction (2) takes place.

$$3H_2+\mathrm{<figure-callout\; id="2"\; label="S\; O"\; filenames="00000006.png"\; state="\{\{state\}\}">S\; </figure-callout>}{O}_{}{}_2\to 3H_{2}S+2H_{2}O\left(\text{2}\right)$$

Sulfur vapor, water vapor, hydrogen sulfide and unreacted sulfur dioxide enter the waste heat boiler 4, in which saturated water vapor is produced by cooling the combustion products. For further cooling, the process gas is fed to the condenser 5, where at a temperature of about 135 ° C vaporous sulfur condenses and is removed from the apparatus in liquid form.

Further processing of the process gas takes place in the catalytic stage. The catalytic stage is shown in the drawing in the form of a unit 6, which includes a steam heater 7, a catalytic reactor 8 and a sulfur condenser 9. The number of catalytic stages can be from 1 to 3.

Before being fed to the catalytic reactor 8, the process gas is heated in a steam heater 7 to a temperature of 150-190 ° C and sent to the inlet of the first catalytic reactor 8. An exothermic Claus reaction (3) proceeds in the reactor on the catalyst, which leads to the formation of additional sulfur and an increase gas temperature at the outlet of the reactor 8.

, $$2H_{2}S+S{O}_2\to 3/n{S}_n+2H_{2}O\left(\text{3}\right)$$

,

where n is the number of sulfur atoms in the molecule at a given temperature.

The sulfur obtained is released in liquid form when the gas is cooled in the second sulfur condenser 9. Next, sulfur is removed outside the installation.

After passing through the catalytic stages, the gas is sent for further processing to the hydrogenation unit 2. This gas contains water vapor and residual amounts of H ₂ S, SO ₂ , H ₂ and sulfur vapor. The hydrogenation unit 2 includes a gas heater 10, a catalytic reactor 11, a gas cooler 12 and a condensation column 13.

The gas heated in the heater 10 to 200-240 ° C enters the catalytic reactor 11, in which the hydrogenation catalyst reduces SO ₂ and sulfur vapor to H ₂ S due to the interaction with the residual hydrogen contained in the gas according to the reactions (2 and four):

, $${\mathrm{<figure-callout\; id="2"\; label="H"\; filenames="00000006.png"\; state="\{\{state\}\}">H</figure-callout>}}_2\mathrm{one}/n{S}_n\to H_{2}S\left(\text{four}\right)$$

,

where n is the number of sulfur atoms in the molecule at a given temperature.

In this case, the gas is heated to 20-50 ° C or more, depending on the amount of additional hydrogen sulfide obtained in the reactor. Next, the gas mixture is cooled in a cooler 12 and a column 13 to a temperature of 35-40 ° C, while the water contained in it is condensed and removed from the process.

To obtain a reducing environment in the gas in front of the hydrogenation unit 2, the ratio of the flow rates H ₂ / (SO ₂ + S) at the inlet to the thermal reactor 1 should be more than two. For this, part of the initial sulfur dioxide, bypassing the thermal stage, is mixed with gas that has left the hydrogenation unit. In this case, the concentration ratio of (H ₂ S + H ₂ ) / SO ₂ in the process gas to the hydrogenation unit will be more than 2, and after it is equal to 2.

The optimal operating mode of the installation is such a mode in which the hydrogen content after the hydrogenation unit is 2-4 mol.%. This optimal operating mode of the installation in the general case depends on its structural scheme, and determines the minimum possible bypass of the initial sulfur dioxide and the minimum consumption of recirculation gases. So for the circuit in Fig. 2, this corresponds to a bypass of 9 to 12% of the initial sulfur dioxide. In the general case, the bypass value of the initial sulfur dioxide can vary from 2 to 50%.

The mixture of dried gas from the hydrogenation unit and the bypass stream of sulfur dioxide is fed to the processing in an additional catalytic stage, the purpose and technological design of which are similar to those described above. Gas processing is carried out in 1-3, mainly in two catalytic stages. A feature of their operation is the lower ratio of the concentrations of the H ₂ S / SO ₂ components in the process gas compared with the Klaus steps to the hydrogenation unit. This is a consequence of bypassing part of the sulfur dioxide and is necessary to maintain a reducing atmosphere in the gas at the outlet of the hydrogenation unit, as shown above.

The gas that leaves the last catalytic stage is sent to the "head" of the installation - to mix with the gas at the exit of the thermal stage.

To illustrate, below is an example implementation of the above method, not limiting the scope of the invention.

Example.

The waste metallurgical gas of the suspension smelting furnace is processed, containing (mol.%): SO ₂ - 30; O ₂ - 10; CO ₂ - 1; N ₂ - the rest. Gas consumption is 110 thousand nm ³ / h. Separated from the exhaust gas and concentrated SO ₂ with a flow rate of 150 kmol / h and gaseous H ₂ with a flow rate of 300 kmol / h are fed to the sulfur production unit for processing. 135 kmol / h of SO ₂ and 300 kmol / h of hydrogen gas are supplied to the burner of the thermal reactor. Part of the sulfur dioxide (15 kmol / h), bypassing the thermal reactor, is sent to mix with the process gas at the outlet of the hydrogenation unit.

As a result of the exothermic reaction of hydrogen oxidation, the temperature of the products rises to 1256 ° C. Moreover, the reaction products are present (mol.%): Sulfur vapor - 11.2, water vapor - 65.7, hydrogen sulfide - 10.5, sulfur dioxide - 4.9, hydrogen - 7.8.

This gas is then cooled to a temperature of 135 ° C in a 2-stage sulfur recovery boiler. In this case, up to 2.56 t / h of liquid sulfur is released, which is removed outside the installation. When the gas is cooled, heat is generated in the amount of 21.3 GJ / h, which is directed to the production of high pressure steam (44 atm). This steam is further used for indirectly heating the process gas in front of the catalytic steps.

Before the first catalytic stage, the process gas is heated to a temperature of 151 ° C and fed to the first catalytic stage. Due to the heat of the sulfur formation reaction, the gas is heated to 286 ° C, and the temperature of the sulfur dew point in it is 271 ° C, i.e. 15 ° C lower than gas temperature. This temperature regime is optimal for the Klaus reaction. When the gas is cooled in the condenser of the catalytic stage, heat is generated in the amount of 2.6 GJ / h, which is used to generate low pressure steam (5 kg / cm ² ). The resulting sulfur in the amount of 1.69 t / h output from the installation. The total degree of sulfur recovery after reaching this stage of the installation is 88.4% of the amount that, together with sulfur dioxide, was supplied to the installation.

Next, the gas is heated in a steam heater to a temperature of 190 ° C and fed to a catalytic hydrogenation reactor. The composition of this gas contains (mol.%): Water vapor - 83, hydrogen sulfide - 2.0, sulfur dioxide - 2.7, hydrogen - 12.2 and a trace amount of sulfur vapor.

This gas enters the reactor, where in the catalyst bed reactions of the interaction of hydrogen with sulfur dioxide and sulfur vapor occur. As a result, the gas at the outlet of the reactor contains (mol.%): Hydrogen sulfide - 4.9, hydrogen - 4.0 and water vapor - 90.9. This gas is cooled to 35 ° C in a column type apparatus, which leads to condensation of water and its removal from the gas. Then this gas is mixed with a part of the initial sulfur dioxide and fed to the processing in an additional catalytic reactor. The composition of the gas mixture (mol.%): Hydrogen sulfide - 35.0, sulfur dioxide - 32.4, hydrogen - 29.8 and water vapor - 2.8.

This gas is heated, it passes through two catalytic stages, where 0.56 t / h of liquid sulfur are released. Residual gas in the amount of 40.4 kmol / h is sent to the inlet of the first catalytic stage. Thus, the gas consumption for recirculation is 9% of the total capacity of the installation for feed gases. The total amount of liquid sulfur obtained in the thermal and catalytic steps is 115.43 tons / day. This corresponds exactly to the sulfur content of the sulfur dioxide that has been submitted for processing, i.e. 100% sulfur recovery.

Thus, the present invention ensures the achievement of almost complete extraction of sulfur from sulfur dioxide, the absence of gas emissions from the sulfur production department, the production of all sulfur in a salable form, the reduction of the prototype operating costs for the production of sulfur from sulfur dioxide.

Claims (8)

1. A method of producing elemental sulfur from an exhaust gas containing sulfur dioxide, comprising concentrating sulfur dioxide extracted from the exhaust gas, partial high-temperature recovery of concentrated sulfur dioxide with concentrated hydrogen to sulfur, hydrogen sulfide and water, condensation of the generated sulfur vapor with the withdrawal of liquid sulfur to the sulfur collector , processing of the released process gas by catalytic Klaus conversion and subsequent purification of the tail gas containing residual amounts of H ₂ S, SO ₂ , H ₂ and steam water, characterized in that part of the stream of concentrated sulfur dioxide is diverted along the bypass line, bypassing the stages of high-temperature recovery, sulfur condensation and catalytic conversion, and tail gas leaving the catalytic stage of Klaus conversion is introduced into the hydrogenation unit to convert all sulfur-containing components to hydrogen sulfide, the gas after hydrogenation, consisting of H ₂ S, H ₂ and water vapor, is fed into a condensation column, in which the water contained in it is separated and condensed, the dehydrated gas is mixed with passing stream of concentrated sulfur dioxide, then this mixture is sent to an additional catalytic stage Klaus-conversion, the residual gases after which are returned to the inlet of any catalytic stage preceding the hydrogenation unit. 2. The method according to claim 1, characterized in that the proportion of the bypass stream of sulfur dioxide is 2-50%, mainly 9-12%, of the total amount of concentrated sulfur dioxide. 3. The method according to claim 1, characterized in that concentrated hydrogen is used at a ratio of 2 moles of hydrogen per 1 mole of sulfur dioxide. 4. The method according to claim 1, characterized in that the number of catalytic stages to the hydrogenation reactor is 1 ÷ 3, mainly 1. 5. The method according to claim 1, characterized in that the number of catalytic stages after the hydrogenation reactor is 1 ÷ 3, mainly 2. 6. The method according to claim 1, characterized in that before hydrogenation, the gas is heated to a temperature of 205-240 ° C. 7. The method according to claim 1, characterized in that the gas in front of the catalytic steps of the Claus conversion is heated so that the gas temperature at the outlet of each catalytic reactor is 5-30 ° C, mainly 8-15 ° C, higher than the temperature sulfur dew points in this gas. 8. The method according to claim 6 or 7, characterized in that the gas is heated by indirect heat transfer due to the utilization of steam obtained at the stage of high-temperature reduction of sulfur dioxide.

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