FI122631B - Sulfur recovery process - Google Patents

Description

Method for sulfur recovery

Field of the Invention 5

The invention relates to a process for removing sulfur from a sulfur dioxide-containing gas in a metallurgical furnace.

State of the art

In the manufacture of metals, ores and concentrates are produced in large quantities, the treatment and purification of which have a significant impact on the functionality, costs and environment of the entire production process. The composition of the various production methods, the raw materials used and the resulting gas mixture (in particular sulfur compounds, dust, metallic impurities) will influence the choice of technology to achieve a cost-effective and environmentally acceptable package.

A major problem in the production of metals from sulfur-containing ores is the high amount of sulfur compounds, particularly sulfur dioxide, formed in the process gas, the proportion of which in the exhaust gases may vary from about 3 to about 80%.

The techniques used to limit sulfur dioxide emissions are based on sulfur recovery in a form where they can be used in the manufacture of other products. Most commonly, sulfur is recovered from the exhaust gases of metal-making furnaces as sulfuric acid, liquid sulfur dioxide or gypsum, which are used e.g. built the pulp, pulp, sugar and fertilizer industries. Methods in which elemental sulfur was prepared from sulfur dioxide, e.g. coal and natural gas were in use in the 1970s (Fl 44588, Fl 45037), when their use was supported by the high world market price of sulfur> 30 and low energy costs. The tightening of environmental regulations will further increase the supply of sulfur products resulting from the treatment of exhaust gases and continuously reduce the cost factors of the various processes through technical solutions.

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o ^ 35 The sulfur contained in the flue gas or roasting furnace exhaust gas must be almost completely eliminated from the gases discharged into the environment. In a market situation where there is no demand for sulfuric acid or where storage and transportation of sulfuric acid is difficult, it is an alternative to produce sulfur dioxide in the waste gas containing 2 elements. Storing elemental sulfur is much simpler than sulfuric acid. However, the production of elemental sulfur presents considerable problems, but current solutions are not satisfactory, both in terms of emission standards and cost factors.

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The traditional elemental sulfur manufacturing process aims to complete the reduction of gases. However, the achievable sulfur content of the exhaust gas remains too high from an environmental point of view. In order to achieve a satisfactory level of sulfur emissions, the sulfur still present in the gas has been further reduced by succession through the following hot and cold catalytic steps. The process requires several heating and cooling steps, which makes the process unsuitable for the thermally economical efficiency concept. Technically, accurate temperature control in a catalytic bed is extremely difficult and difficult to maintain the desired equilibrium. The sulfur dioxide content of the exhaust gases affects not only the controllability of the processes but also their economic efficiency as investment and operating costs. The following is a brief description of the principles by which the treatment of sulfur dioxide in the gas produced by the use of a sulphide concentrate proceeds when the sulfur is recovered as sulfuric acid or when the aim is to recover the elemental sulfur.

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The recovery of sulfur dioxide as sulfuric acid has traditionally been accomplished by the process of initially purifying the gas to remove dust, for example, by means of electrical filters at the rear of the furnace, which, however, must first be cooled to maintain functionality. After removing the metal vapors, halides and sulfur trioxide remaining in the gas, the gas is led to a so-called sulfuric acid plant. 300-350 ° C. In the contact part, the gas is brought into contact with a dilute £! with sulfuric acid, followed by cooling before the c3 SO2 contained in the gas passes into reactors containing the catalytic material, which may be of the contact type, double contact type or other suitable reactors.

g> 30 In these catalyst layers containing an oxidizing material such as aluminum or vanadium pentoxide (V203) catalyze the exothermic reaction.

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The reaction is reversible and the equilibrium state is shifted towards the formation of sulfur dioxide by the heat released in the catalysis reaction if the gas mixture is not effectively cooled between the catalytic steps. The SO3 formed is then absorbed into the sulfuric acid in one or two steps. The end product is 3 spring sulfuric acid, which has special requirements for storage, storage and transportation. container materials.

In some cases, sulfur recovery in elemental form is applied with the aim of reducing the sulfur contained in SO 2 to elemental sulfur by binding oxygen to a suitable material such as carbon and hydrogen. Various solutions have followed the principle of first reacting a sulfur dioxide gas, with or without additional oxygen, with a hydrocarbon-containing compound at high temperature, whereby the sulfur is partially reduced to elemental sulfur and other sulfur components such as H2S and COS. The cooled, particulate impurity-free gas is then subjected to one or more catalytic steps in which typically a metal oxide-containing catalyst catalyzes the reactions 2 H 2 S + SO 2 → 3 S + 2 H 2 O (so-called Claus process) and 2 H 2 S 2 O 2 S + also binds a significant proportion of the elemental sulfur. The composition of the remaining gas 20 is substantially dependent on the thermodynamic equilibrium under the reaction conditions. The conversion rate is lowered by the reversible Claus reaction and the reaction of the sulfur with oxygen back to sulfur dioxide according to the reaction equations below: 25 S + 02 SO 2 and w 3 S + 2 H 2 O - 2 H 2 S + SO 2 δ

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g As a starting point, sulfur recovery solutions have focused on eliminating or reducing g> 30 the effect of preventing or rendering economically feasible the elimination of sulfur dioxide x in the gas as completely as possible. Platonov et al. (Proc.of EMC 2005, pp. 1293-1299; Optimal δ Technology of Sulfur Recovery Out of Autogenous Smelting Off-Gas) have developed § models to influence the formation of intermediates (hydrogen sulfide)

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The kinetic and thermodynamic properties of the process so that the consumption of the necessary reducing agents would be lower than before and the solution would also be economically viable. One approach has been to find alternative, more cost-effective sources of the considerable amount of 4 H2S required for the Claus reaction (Okura et al., Advanced Processing of Metals and Materials May 8 - International Symposium on Sulphide Smelting 2006, pp. 425-431). Furthermore, research has focused on the catalytic steps necessary to complete the reduction (and also the costs). Better catalyst materials and their structures are described, e.g. WO 97/32813) and US 5,762,899.

DESCRIPTION OF THE INVENTION It is an object of the present invention to provide a process which provides a sufficient low sulfur content in a purified gas and, on the other hand, reduces the proportion of sulfuric acid products that are difficult to store and transport. The invention is characterized in that part of the sulfur dioxide of the gas is reduced to elemental sulfur and some is converted to sulfuric acid or sulfate, and that the elemental sulfur and sulfuric acid or sulfate are recovered. The term 'sulfate' refers to both sulfate and thiosulfate.

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The process of the invention can completely bypass the catalytic step required by the prior art elemental sulfur process, thereby reducing the required investment and operating costs. Compared to previous gas treatment processes, the essential advantage of the process is the removal of sulfur as an elemental sulfur and sulfuric acid or sulphate 20 in appropriate proportions, whereby the cost of final disposal of final products is lower than in solutions based on single alternatives such as sulfuric acid. In addition, the various alternatives for treating the off-gas according to the invention reduce sulfur emissions and the quality problems caused by the cracking of the sulfur that arise when the sulfur contained in the off-gases is sought to be recovered exclusively as elemental sulfur.

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The method according to the invention is illustrated by the following figures, in which g 1 x 30 1 shows a flow chart of a first embodiment of the invention,

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Fig. 2 shows a flow diagram of a first modification of the second embodiment of the invention wherein the reduced and cooled gases are introduced into the scrubbing liquid, the elemental sulfur is foamed and the solution is treated to form additional sulfuric acid, sulfuric acid and sulfuric acid. shows a flow diagram of a second variant of another embodiment of the invention wherein the reduced and cooled gases are introduced into the scrubbing liquid, and after filtration the solution and the precipitate are separately treated to form the elemental sulfur and sulfates, and Figure 4 is a flow chart of a third variant of the second is led to pressure leaching to recover elemental sulfur and sulfates.

DETAILED DESCRIPTION OF THE INVENTION 10

In the process according to the invention, the sulfur dioxide gas preferably coming from the metallurgical furnace, most preferably from the flame smelting furnace or roasting furnace, is desulphurized.

The sulfur dioxide content of the sulfur dioxide gas coming from the melting furnace is preferably 10-70% by volume, more preferably 30-60% by volume. Preferably, the sulfur dioxide contained in the gas is reduced to 50 to 95%, more preferably 60 to 85%, as the elemental sulfur. The reduction occurs when the gas is kept at a high temperature, typically 1000-1300 ° C, and is mixed with a reducing carbonaceous substance such as a hydrocarbon. In the reduction, not all sulfur dioxide is reduced to sulfur, but other sulfur compounds such as sulfur carbon and / or hydrogen sulfide remain in the gas. It is typical of the process that the gas to be reduced is taken hot from the metal-making furnace. In the embodiment according to the invention, the reduction is preferably carried out in connection with a metal-making furnace, and most preferably in its riser shaft. The concentration of sulfur dioxide gas coming from the roasting furnace 25 is of the above-mentioned class and is similarly reduced at the top of the roasting furnace.

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c3 In a first embodiment of the invention, at least a portion of the initial sulfur sulfur formed in the reduction is removed from the gas. The sulfur dioxide trapped in the gas is converted to sulfuric acid or sulfate.

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Said removal of elemental sulfur after reduction is preferably effected by cooling the gas containing the gaseous elemental sulfur and dust.

S Cooling is typically carried out in a waste heat boiler at 300-450 QC. After this

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The gas is fed to an electric filter to remove dust from the gas. Still in this embodiment, it is advantageous to continue cooling by introducing the gas into a low pressure boiler having a temperature of 100-200 ° C, whereby the element is condensed and can be further removed from the gas.

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Preferably, after removing at least some of the elemental sulfur from the gas, the remaining elemental sulfur and / or sulfur and / or hydrogen sulfide in the gas is oxidized to the second sulfur dioxide such that the total sulfur dioxide content of the gas 5 is preferably 3-30% by volume. more preferably 5 to 15% by volume. The sulfur dioxide remaining in the gas is converted into sulfuric acid or sulfate by oxidation and contacting the sulfur trioxide formed with water or a neutralizing base. See. the above sulfuric acid process.

In another embodiment of the invention, the reduced and cooled gas is introduced into an aqueous scrubbing solution wherein the elemental sulfur solidifies and the sulfur dioxide reacts with the sulfide to form the second elemental sulfur and sulfate, whereby both elemental sulfur and sulfate are recovered. As in the first embodiment, the gas is cooled to 300-450 ° C, preferably 15 in a waste heat boiler, to recover heat. The sulfide may be derived from gas and / or added to the wash solution. The sulfide to be added is typically an alkaline earth metal or alkali metal sulfide, preferably sodium sulfide, and the sulfide present in the gas in the presence of dust is typically copper, nickel or zinc sulfide. The solidified elemental sulfur is typically separated from the wash solution and other solid therein by foaming or draining after filtration and thawing. The precipitate thiosulfate and other sulfur compounds in the washing solution are reacted by pressure leaching to a third elemental sulfur and sulfate which is also recovered.

Examples 25

The following are four variants of the invention in which, in the first embodiment, partial reduction to elemental sulfur is carried out, followed by conversion of sulfur dioxide to sulfuric acid.

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g> 30 In the first, second and third variants of the second embodiment, said partial reduction (first sulfur) is carried out, whereupon the gas is introduced into a scrubbing solution in which sulfur dioxide is reacted with sulfide to produce additional elemental sulfur (second sulfur). In addition to sulfur, other sulfur § compounds, mainly thiosulfate, are formed which react in the autoclave to elemental sulfur (co-

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£ 3 35 mas sulfur) and sulphates.

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The following concentrate is melted in a copper flame smelter at 93 t / h:

Cu 31.2%

Fe 23.3% 5 S 32.4%

SiO2 5%

Zn 0.7%.

About 70% is used for oxygen enrichment. The melt is made of 66% stone 10 (Cu content 66%). The flame smelting furnace produces 25000 Nm3 / h of gas at a temperature of 1350 to 1400 ° C having the following composition: S02 58.1% H20 1.5% 02 1.8% 15 N2 38.6%

Oxide dust 168 g / Nm3

Natural gas is fed from the back wall of the furnace and / or the manhole cover at high speed with a special nozzle (s) for efficient mixing of the gases, 3.6 t / h. This reduces some of the gas, lowers the temperature and produces the following gas: ^ N2 15% o ™ H20 13%

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^ SO2 10%

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x C02 5.5% and

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_ 25 S2 4.3% 00 o H2S 0.7% o CO 1.9% H2 1.3% COS 0.2% 8

In addition, the gas contains 5.2 t / h dust.

The following reduction reactions occur in the mixture: 2SO2 + CH4 = 2H2O + CO2 + S2 SO2 + CH4 = H2S + CO + h2o5 2H20 + 1 / 2S2 = 2H2 + SO2 2H20 + 11 / 2S2 = 2H2S + SO2

CO + 1 / 2S2 = COS

2C0S = C02 + CS2 10 1. An embodiment for treating a partially reduced gas

The method according to the first embodiment is illustrated in Figure 1. As described above, the sulfur dioxide-containing gas has been partially reduced in the melting furnace riser. The gas is led to a waste heat boiler where the gas is cooled to about 450-300 ° C and part of the sulfide dust is recovered. After the boiler, the gas is led to an electric filter, where the residual dust is recovered. Dusts are recycled to the reaction shaft. After the electric filter, the temperature of the sulfur-containing gas is about 400 ° C. The gas from the electric filter is led to a low pressure boiler at about 100-200 ° C, where it is cooled and some of the sulfur drips. Elemental sulfur is recovered from the droplet separator following a low pressure boiler at about 8 20 t / h. After the recovery of elemental sulfur, the gas is introduced into the combustion chamber, where the reducing components contained in the gas and the elemental sulfur droplets 5 still contained therein are oxidized using an oxyfuel burner as ignition and support burner. After the post-combustion, the C \ 1 gas is cooled and then all the sulfur contained in the gas is SC on 2 and the gas is led to a sulfuric acid plant where the remaining sulfur is recovered as sulfuric acid.

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x 25 2. Embodiment for Treatment of Partially Reduced Gas Q_ ^ In another alternative, the sulfur dioxide-containing gas is also subjected to partial reduction in the melting furnace riser. The partially reduced dust-containing gas is cooled in a waste heat boiler to about 450-300 ° C. Unlike the first application,

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An alternative of the embodiment is that the dust-containing cooled gas 30 is subjected to gas scrubbing, whereby the gas is led to scrubbers, for example venturi scrubbers. In these scrubbers, the elemental sulfur condenses and the gas components are washed in solution by the addition of sodium sulfide (SULFRED process) or sulfides in dust such as ferric and / or zinc sulfides to form elemental sulfur, metal thiosulfates and sulfates, and possibly other sulfur compounds. The dust also contains copper sulphide and inert slags.

To treat the wash solution, there are the following treatment options, which are illustrated in Figures 2, 3, and 4. Each figure illustrates the entire gas treatment process, whereby the gas is first subjected to partial reduction and cooling, and then the gases are led to the scrubber. After the scrubbing step, the purified gases can be discharged into the environment.

10 1) According to Figure 2, the first modification, the reduced gases are absorbed into the washing solution, to which sulfide is also introduced. Elemental sulfur (first and second sulfur) (about 8 t / h) is then foamed from the wash solution. The residual sludge is filtered with the Cu2S precipitate and inert material (about 2 t / h) that came with the dusts and recycled to the flame smelting furnace. The solution is subjected to pressure leaching, for example in an autoclave, whereupon the thiosulphates and other sulfur compounds formed in the solution are reacted to form the elemental sulfur and sulfates. The elemental sulfur formed (third sulfur) (about 11 t / h) is counted in an autoclave and the sulfate solution is crystallized, dried and recycled to the reaction pit (about 1 t / h).

2) Also, according to Figure 3, the second modification, the reduced gases are absorbed into the washing solution, to which sulfide is also introduced. Thereafter, a precipitate consisting of an insoluble sulfide precipitate, inert slags and elemental sulfur (first and second sulfur) (about 10 t / h) is filtered from the wash solution. The precipitate is heated so that its temperature is raised above the sulfur melting point and the elemental sulfur (about 6 t / h) is filtered off from the precipitate. The remaining precipitate is predominantly alpha 25 sulfur-containing cuprous sulphide, Cu 2 S (4 t / h), which is returned to the reaction pit.

The solution separated by filtration of the wash solution is subjected to pressure leaching, whereupon it is treated in an autoclave to react the thiosulphates and other sulfur compounds to form the elemental sulfur and the sulphates. Fashion | the elemental sulfur (third sulfur) precipitated (about 11 t / h) is drained from the autoclave and the sulfate solution is crystallized, dried and recycled to the reaction pit (about 1 t / h).

00 en S 3) As in the previous embodiments, the reduced gases according to Fig. 4, third variant, are absorbed into the washing solution, which is also fed with sulfide. Elemental sulfur (first and second sulfur) is not separated from the wash solution, but the solution and the elemental sulfur are led to pressure leaching in an autoclave in which thiosulfates and other sulfur compounds react to form elemental sulfur 10 (third sulfur) and sulfates. The sulfur formed during the reduction, washing and pressure leaching is calculated from the autoclave as elemental sulfur (about 27 t / h). The solution containing copper sulfide, inert materials and metal sulfates is passed to evaporation, for example in a vacuum evaporator, and then to the crystallizer, drying and further to the reaction shaft (about 7.5 t / h of crystalline sulfate).

Although the above example describes the reduction and post-treatment of gas in a smelting furnace, the various treatment methods for the reduced gases described above are also applicable to the treatment of the roasting gas in the roasting furnace. This is, for example, the roasting of a zinc concentrate, whereby the sulfide supplied with the gas 10 can act as a reactive sulfide in the washing. The zinc sulphate produced by scrubbing the gases can be directly led to the dissolution of the zinc pellet or the solution purification of the zinc sulphate solution.

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Claims (13)

A process for removing sulfur from a sulfur dioxide-containing gas in a metallurgical furnace, comprising the following stages: i) the gas is poured into reducing ratios, so that a portion of its sulfur dioxide is reduced to elemental sulfur, ii) a separation of the gas is performed; such that at least a portion of the elemental sulfur is removed from the gas, and (iii) the gas is poured into oxidizing conditions, such that the sulfur dioxide it contains is oxidized to sulfur trioxide, which is converted to sulfuric acid or sulfate and is added to iv) separation stage ii) and before the oxidation stage iii) the gas is poured into oxidizing conditions, such that in the gas residual non-separated element sulfur, the sulfur coal and / or the hydrogen sulphide remaining in the gas is oxidized to sulfur dioxide and the sulfur dioxide content of the sulfur dioxide gas in the gas the oven is 30-60% by volume. 2. A process according to claim 1, characterized in that the sulfur dioxide-containing gas in the metallurgical furnace is an outlet gas from a furnace for the manufacture of metal using sulphidic raw materials. 20 3. A method according to claim 2, characterized in that the exhaust gas from a furnace for the manufacture of metal is an outlet gas from a flame melting furnace. 4. A process according to claim 2, characterized in that the exhaust gas from a metal furnace is an exhaust gas from a roasting oven. £! Process according to any one of the preceding claims, characterized in that 50- c3 95%, preferably 60-85% of the sulfur dioxide of the gas is reduced to elemental fluid. S 30 1 Process according to any of the preceding claims, characterized in that a portion of the sulfur dioxide of the gas is reduced to elemental sulfur by keeping the gas ro at a temperature in the range 1000-1300 ° C and by mixing a reducing carbonaceous substance such as hydrocarbon in the gas. . o 35 ° C Process according to claim 6, characterized in that the gas is taken in hot state from a metallurgical furnace. Process according to any of claims 2-7, characterized in that the reduction is carried out in connection with a furnace for the manufacture of metal, preferably in the ladder of a flame-melting furnace or in the upper part of a roasting furnace. 5 Process according to any of the preceding claims, characterized in that after the reduction the elemental sulfur is removed from the gas and the sulfur dioxide remaining in the gas is converted to sulfuric acid or sulphate. Process according to claim 9, characterized in that said reduction and possible oxidation are carried out such that the total sulfur dioxide content of the gas is 3-30% by volume, preferably 5-15% by volume. 11. A process according to claim 9 or 10, characterized in that, after the reduction, the gaseous elemental sulfur and the gas containing dust are first cooled, preferably to a temperature of 300-450 ° C in a waste heat boiler to take the heat of the gas. 12. A process according to claim 11, characterized in that, after cooling, the gas containing elemental sulfur and dust is fed to an electrofilter to separate dust from the gas, and then to a low pressure boiler to condense the elemental sulfur and remove it from the gas. Process according to any one of claims 9-12, characterized in that the sulfur dioxide is converted to sulfuric acid by oxidizing it and by bringing the sulfur trioxide which has come into contact with water or a neutralizing base. C \ J δ (M (M o σ> (M X and CL δ σ> o CD o o (M