RU2474533C1 - Method of producing elementary sulphur from sulphur dioxide-containing exhaust gas - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to chemistry and can be used to produce elementary sulphur from exhaust gas which contains sulphur dioxide at chemical, petrochemical, gas processing and metallurgical companies. The method involves concentrating sulphur dioxide extracted from exhaust gas; partial high-temperature reduction of the concentrated sulphur dioxide with a gaseous reducing agent to sulphur, hydrogen sulphide and water; condensation of the formed sulphur vapour with removal of liquid sulphur into a sulphur collecting tank; processing the exhaust process gas by successive catalytic Claus conversion and subsequent cleaning of the process gas from the last catalytic stage, which contains residual amounts of H₂S, SO₂, H₂ and water vapour. To this end, the process gas is fed into the reactor of a cleaning unit in which H₂S reacts with SO₂ in aqueous solution to form a suspension of sulphur in water and in which temperature gradient of 20-60°C is maintained in the cold part and 70-100°C in the hot part, and counter flow of the gaseous and liquid phases is formed. Gas which consists of unreacted hydrogen, traces of hydrogen sulphide and sulphur dioxide is separated from the suspension and returned to the high-temperature reduction step.

EFFECT: high efficiency of the method.

4 cl, 1 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 exhaust gas by thermal reduction of sulfur dioxide in which hydrocarbon fuel, gaseous or liquid, is partially oxidized in a reaction furnace to produce H ₂  and CO. SO ₂  add to the thermal reaction zone for the purpose of interaction H ₂  and to some extent with CO. The degree of combustion is regulated in a molar ratio of 2: 1 to obtain a mixture of H ₂ S and SO ₂ . The competing reactions in this technology are the formation of COS and CS ₂  in the interaction of CO and free carbon with SO ₂  and gray. Potential soot is washed out of the system by the introduction of liquid sulfur, which is recycled to allow the use of extracted carbon. The resulting process gas is rapidly cooled to a temperature of 425 ° C or lower in order to further suppress the formation of undesirable organic sulfur by-products. Elemental sulfur can be regenerated and returned to the reactor for gasification of the extracted carbon solid products and resins. Subsequently, the process gas passes through a series of standard Klaus catalytic stages (US Pat. No. 4,207,304, IPC C01B 17/04).

The disadvantage of this method is the fact that the resulting sulfur is contaminated with carbon, and additional technological operations are required to clean it, which leads to additional capital and operating costs.

A known method of producing elemental sulfur from an exhaust gas containing sulfur dioxide, according to the patent of the Russian Federation No. 2221742, IPC C01B 17/04.

The known method includes cooling the waste metallurgical gas containing sulfur dioxide, concentrating SO ₂  by its complete or partial liquefaction followed by evaporation by heating, enrichment with oxygen to a predetermined concentration, reduction with hydrocarbon gas at an elevated temperature with cooling of the products and condensation of the obtained elemental sulfur. This is followed by the catalytic processing of the reduced gas, at least at two stages of catalytic conversion with condensation of the obtained sulfur and afterburning of toxic and combustible sulfur compounds in the tail gas to SO ₂ . Before the first catalytic stage, the reduced gas is heated by mixing with the products of the combustion of hydrocarbon fuel in oxygen-containing gas supplied in a ratio of 0.5-1.0 from the stoichiometric one, which ensures the ratio of the concentrations of the sum of carbon monoxide and hydrogen in the gas mixture at the inlet of the first catalytic conversion stage to SO ₂  over two.

However, in accordance with this method, the equilibrium content of the target product — sulfur vapor — does not exceed a value that corresponds to 40-60% of the degree of sulfur extraction from its initial content in SO ₂ , and further processing in the catalytic stages is associated with difficulties that are associated with the presence in the process gas of a whole spectrum of organosulfur impurities.

The closest in technical essence and the achieved result to the claimed method is a method for producing elemental sulfur from exhaust gas containing sulfur dioxide, according to UK patent No. 1452970, IPC C01B 17/04, B01D 53/34.

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 a post-combustion furnace, where all sulfur-containing components are oxidized to sulfur dioxide. Further, the stream is returned to the step of separating 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 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 the need for supplying hydrogen to the gas processing and reducing the volume of gas processed at the SO concentration stage ₂ .

The technical problem is achieved by the fact that SO is contained and concentrated from the exhaust gas ₂ , they are subjected to partial high-temperature reduction to sulfur, hydrogen sulfide and water using a reducing gas, the formed sulfur vapor is condensed and liquid sulfur is discharged to the sulfur collector, and the released process gas is fed to the Klaus catalytic stages. At the same time, concentrated hydrogen is used as a reducing gas in a ratio of 2 ÷ 2.3 and preferably 2.1 mol per 1 mol of SO ₂ . This ratio was obtained by calculation and provides the optimal mode of operation of the catalytic stages. The ratio of the input costs of sulfur dioxide and hydrogen is maintained by measuring their concentrations at the outlet of the last catalytic stage and is regulated based on the ratio H ₂ S: SO ₂ = 2: 1.

The process gas is passed sequentially through 1-4 and mainly 2-3 Klaus stages, each of which includes an indirect heating apparatus, a catalytic reactor and a sulfur condenser, and indirect heating of the process gases is carried out so that the gas temperature at the outlet of each catalytic reactor is at 5 ÷ 30 ° C and mainly 8-15 ° C above the temperature of the sulfur dew point in this gas. Indirect heating ensures constant ratio H ₂ S: SO ₂ and the temperature of the catalytic reactor is selected from the conditions of optimal operation of the catalyst. The water contained in the process gas is condensed at the outlet of the last Klaus catalytic stage.

After exiting the last catalytic stage, a process gas containing residual amounts of H ₂ S, SO ₂ , H ₂  and water vapor is sent to a purification unit including a reactor in which H ₂ S interacts with SO ₂  in an aqueous solution with the formation of 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 - 70 ÷ 100 ° C. These conditions are selected from the point of view of the residual water content in the process gas and the completeness of its condensation, and are also determined by the boiling point of water at atmospheric pressure. Due to the temperature difference in the reactor of the purification unit, an oncoming phase movement is formed: combined-cycle - up, liquid - down. This creates favorable conditions for condensation of water vapor, dissolution in it of unreacted sulfur dioxide and hydrogen sulfide with the simultaneous interaction of these substances with each other with the formation of colloidal sulfur. The reaction is almost complete. The process gas that exits the purification unit reactor and consists mainly of hydrogen and traces of unreacted hydrogen sulfide and sulfur dioxide is cooled and returned to the high-temperature reduction stage. Condensed water is partially directed to the top of the reactor of the purification unit, which is a necessary condition for its normal operation, and the rest is removed. Water containing a suspension of sulfur removed from the bottom of the reactor of the purification unit is filtered, sulfur is squeezed out, melted and sent to a heated sulfur collector, and the filtrate is partially heated and returned to the bottom of the reactor of the purification unit, and partially removed.

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

The method is as follows.

Sulfur dioxide gas from a liquefied sulfur dioxide storage unit (not shown) and hydrogen gas from a hydrogen production unit (not shown) enter the thermal reactor 1 with a burner 2. In the furnace of the thermal reactor 1, an exothermic dioxide reduction reaction occurs at a temperature of 1200–1300 ° C sulfur to elemental sulfur. Vapors of sulfur, water, hydrogen sulfide and unreacted sulfur dioxide enter the waste heat boiler 3, in which saturated water vapor is produced by cooling the combustion products. For further cooling, the process gas is supplied to the condenser 4, where at a temperature of about 135 ° C vaporous sulfur condenses and is removed from the apparatus in liquid form through the pipe 5.

Further processing of the process gas takes place in the catalytic stage. For this, the process gas is heated in a steam heater 6 to a temperature of 150-190 ° C and sent to the inlet of the first catalytic reactor 7. Due to the heat of the Klaus exothermic reaction, additional sulfur is formed on the catalyst, and the gas temperature at the outlet of reactor 7 rises to 270 -300 ° C. The resulting sulfur is released in liquid form when the gas is cooled in the second sulfur condenser 8. Next, the sulfur is removed outside the installation through the pipe 5. The catalytic stage is shown in the drawing in the form of a block 9.

Similar operations (heating - chemical reaction - cooling and condensation of sulfur) are carried out with process gas at subsequent catalytic stages, which are not shown in the attached drawing. An automatic in-line gas analyzer 10 is located on the gas exit line from the last catalytic stage. After passing the last catalytic stage, the process gas enters the reactor of the purification unit 11, which maintains a temperature gradient: above 20-60 ° C, below 70-110 ° C. This is achieved due to the continuous supply of heat to the heater 12 and the removal of heat in the condenser 13. Due to the temperature difference in the reactor 11, a counter phase motion is formed: combined-cycle - up, liquid - down. This creates favorable conditions for condensation of water vapor, dissolution in it of unreacted sulfur dioxide and hydrogen sulfide with the simultaneous interaction of these substances with each other with the formation of colloidal sulfur.

Unreacted hydrogen is removed from the top of the reactor 11, cooled in the refrigerator 13, separated from the water in the separator 14 and returned to the process head in the thermal reactor 1. Water from the separator 14 is returned to the top of the reactor 11 and partially removed from the unit through the regulator 15. A suspension of sulfur from the bottom of the reactor 11 enters the separating device 16, where the separation of colloidal sulfur from water. Sulfur enters the smelter 17, from where it is withdrawn from the plant in molten form. Water from the separating device 16 with the help of the regulator 18 is partially removed from the installation, and partially sent to the heater 12 and returned to the bottom of the reactor 11.

Colloidal sulfur has an independent commercial value and can be used as a final product or can be melted in a smelter 17 and directed into the general stream of liquid sulfur produced at the plant.

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

Example.

The waste metallurgical gas of a suspension smelting furnace is processed, containing,%: SO ₂  - thirty; O ₂  - 10; CO ₂  - one; N ₂  - the rest. Gas consumption is 110 thousand nm ³ / h Isolated from flue gas and concentrated SO ₂  with a consumption of 33 thousand nm ³ / h and gaseous H ₂  with a flow rate of 72.5 thousand nm ³ / h served in the burner. As a result of the exothermic reaction of hydrogen oxidation, the temperature of the products rises to 1253 ° C. At the same time, only sulfur vapor in the amount of 19.6 mol.% (In terms of S _one ), water vapor, hydrogen sulfide and unreacted sulfur dioxide, and the concentration ratio H ₂ S to SO ₂  in this gas is 2, i.e. is optimal for further gas treatment in Klaus catalytic reactors.

It should be noted that this optimal ratio does not change as the reaction proceeds in subsequent catalytic reactors, since there are no reagents in the system that can initiate side reactions.

This gas is then cooled in a 2-stage sulfur recovery boiler to a temperature of 135 ° C. In this case, up to 27.9 t / h of liquid sulfur is released, which is removed outside the installation. When the gas is cooled, heat is generated in an amount of 231 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 158 ° C and fed to the first catalytic stage. Due to the heat of the sulfur formation reaction, the gas is heated to 283 ° C, and the temperature of the sulfur dew point in it is 268 ° 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 24 GJ / h, which is used to generate low pressure steam (5 kg / cm ² ) The resulting sulfur in an amount of 15 t / h is removed from the installation. Similarly, the processing of gas is carried out in the 2nd and 3rd catalytic stages. At the same time, 2.7 and 0.8 t / h of sulfur are produced in the 2nd and 3rd stages, respectively. The total degree of sulfur recovery after reaching this stage of the installation is 98% of the amount that, together with sulfur dioxide, was supplied to the installation.

The gas that is discharged from the top of the purification unit reactor is combustible and contains,%: sulfur compounds - 0.9; H ₂  - 94; water - the rest (based on the degree of conversion in the column reactor, equal to 90%). Its consumption is 7 thousand nm ³ / h

In normal operation, this gas is sent to a thermal reactor, with no gaseous emissions from the installation. The degree of sulfur recovery is 100%. By recirculating part of the tail gas to the thermal reactor, the total demand for concentrated hydrogen is reduced by the amount of recycle, i.e. at 7 thousand nm ³ / h and is approximately 65.5 thousand nm ³ / h

Colloidal sulfur has an independent commercial value and can be used as a final product or it can be melted and directed into the general stream of liquid sulfur produced at the plant. The amount of sulfur obtained from the smelter is 0.64 ÷ 0.78 t / h.

Thus, the claimed technical solution allows to increase the efficiency of the process of utilization of the exhaust gas containing sulfur dioxide by reducing the need for supplying hydrogen and reducing the volume of gas processed at the stage of concentration of SO ₂ .

Reducing the load on the installation of concentrating SO ₂ In addition, it has a positive environmental effect.

Claims (4)

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 a reducing gas to sulfur, hydrogen sulfide and water, condensation of the generated sulfur vapor with the withdrawal of liquid sulfur to the collection sulfur, the subsequent processing of the released process gas by sequential catalytic Klaus conversion, characterized in that it emerged from the last catalytic step or a process gas containing residual amounts of H ₂ S, SO _2, H ₂ and water vapor is fed to a purification unit comprising a reactor in which the H ₂ S reacts with the SO ₂ in aqueous solution to form a suspension of sulfur in water, and wherein the support the temperature gradient in the cold part is 20 ÷ 60 ° C, and in the hot part it is 70 ÷ 100 ° C and they create the oncoming movement of the gas and liquid phases, then the gas consisting of unreacted hydrogen, traces of hydrogen sulfide and sulfur dioxide is separated from the suspension and returned to stage of high-temperature recovery, and suspension Zia is divided into sulfur and water are withdrawn. 2. The method according to claim 1, characterized in that as the reducing gas using concentrated hydrogen in a ratio of 2 ÷ 2.3 and, preferably, 2.1 mol of hydrogen per 1 mol of sulfur dioxide, and the ratio of input costs of sulfur dioxide and hydrogen support by measuring their concentrations at the outlet of the last catalytic stage and adjust based on the ratio of H ₂ S: SO ₂ = 2: 1. 3. The method according to claim 1, characterized in that the process gas in each Klaus catalytic stage passes through an indirect heating apparatus, a catalytic reactor and a sulfur condenser sequentially, while indirect heating is carried out so that the gas temperature at the outlet of each catalytic reactor is at 5 ÷ 30 ° C and, mainly, 8-15 ° C above the temperature of the sulfur dew point in this gas. 4. The method according to claim 1, characterized in that the number of Klaus catalytic stages is 1 ÷ 4 and, preferably, 2 ÷ 3.

Images