DD265388A5 - PROCESS FOR OBTAINING ELEMENTARY SWEEP - Google Patents

Abstract

The invention relates to a method for recovering elemental sulfur from laundry obtained by washing obtained from a combustion resulting SO2-containing gases SO2 Reichgas described. In order to provide a simple method which can be incorporated inexpensively with little outlay on equipment in a total exhaust gas purification process, it is proposed that the SO2 Reichgas in the presence of a reducing gas after heating is incompletely reduced to sulfur and H2S, the sulfur is condensed by cooling and separated, burned during the reduction of H2S-containing gas and thereby formed SO2 and unreduced SO2 are returned to the laundry. Fig. 1

Description

For this 2 pages drawings

Field of application of the invention

The invention relates to a process for recovering elemental sulfur by means of heat. of SO generated in a combustion; containing gases containing SOj-Fteichgas.

Characteristics of the known prior art

There are a number of 'Experienced to convert SO; to elemental sulfur. They are essentially based on two basic offenses:

Reduction of SO; by passing over glowing coke;

Reduction of SO ₂ by adding a H ₂ -, CO- and / or hydrocarbon-containing gas as a reducing agent and reaction in the gas phase over a catalyst.

However, the known processes have the following significant disadvantages for use in flue gas desulphurisation plants:

Reduction via glowing coke produces many by-products which must be decomposed by incineration (eg COS, CS ₂ ) and therefore either burned in the combustion chamber for the steam boilers or in a separate furnace and returned for flue gas desulphurisation ,

Reduction by the addition of a reducing agent (eg Hydrocarbon-Processing, April 1984, page 83) results in the problem that, even if simplified Claus plant is required, from the H ₂ S formed by reduction by reaction with SO ₂ generate elemental sulfur ai. The equipment required for this is considerable.

Object of the invention

The aim of the invention is to provide an improved method of recovering elemental sulfur! from S0 ₂ -Roichgas obtained by washing of accumulating in a combustion SO ₂ -containing gases S0.

Presentation of the Invention The invention is therefore based din task to provide a simple method of the type mentioned,

which can be integrated in a cost-effective manner with little equipment expense in a Abgasreinigungs- ^ allamtverfahren

This object is achieved according to the invention in that SO ₂ -rich gas in the presence of a reducing gas after heating

is reduced incompletely to sulfur and H ₂ S, the sulfur is condensed from both reactions by cooling and separated, burns the bj of the reduction resulting HjS-containing gas and thereby formed SO ₂ and unreduced

SO _{2 be returned} to the laundry. The orfordungsgemäße method makes use of the fact that iisbesondere in a SO ₂ -selective physical - Washing process both the investment and energy expenditure for SO ₂ separation almost independent of the SO ₂ concentration in the gas stream to be purified. Thus, the S0 ₂ -reduction to elemental sulfur in a relative

simple reactor to be carried out with very incomplete implementation, that is, in the one-time Durchmuß not as much SO ₂ must be converted to elemental sulfur. The remaining or after combustion of H ₂ S, COS,

CS ₂ , etc., still to be depleted SO ₂ is used as a relatively concentrated fraction to the raw gas for physical washing

recycled.

The resulting sulfur in the reduction is in vapor form. For the separation of the sulfur, the reduction product

cooled, for example, against high-pressure steam. The cooling is carried out to a temperature below the sulfur dew point, preferably about 12O ⁰ C. In this case, the elemental sulfur condenses with high purity and can be withdrawn.

It is essential in the process according to the invention that is dispensed with a Claus plant and no reactors for Production of reducing gas, in particular H ₂ or CO are required. As a reducing gas is in the

Process according to the invention advantageously uses a hydrocarbon gas, such as natural gas. However, it is also possible to use H ₂ or CO as the reducing gas should it be available from another process step.

The process of the invention provides a relatively simple, good in the physical washing process and

economically einfügenden process for obtaining the separated from a gas stream to be purified Schv / efel problem-to be stored, transportable and environmentally friendly form.

The resulting after the SO ₂ reduction gas still has a significant fuel word. According to a particularly preferred Embodiment of the inventive concept, therefore, this gas is returned to the combustion and burned there. at

This procedure increases or increases the sulfur content of the combustion exhaust gas. However, this has practically no influence on this subsequent physical washing when using an organic laundry, since there essentially the

Total amount of gas is of importance - but the S0 ₂ amount of some 1000 ppm. If a return to the combustion, from which the So ₂ -containing gas comes, exceptionally not be desired, a Afterburning be provided and the gas are then passed to So ₂ scrubbing. According to a further extremely advantageous embodiment of the method according to the invention, the reduction of the So ₂ -Relchgases fuel in the presence of an oxygen-containing gas unteröchlometrisch burned, in which at the Combustion gas, which is used as a reducing gas, a ratio of hydrocarbon calculated as Cl Joe set fuel to SO ₂ of about 1: 2 based on the hydrocarbon of the fuel before combustion, the

hot reducing gas is brought into contact with the SO; -rich gas to SOjReduktlon and in the gas after dev SO? -reductlon oin

Ratio of Eiemontarschwefel to SO ₂ to H ₂ S of about 3: 1: 2 «set. A plant for the reduction of SO ₂ to elemental sulfur thus substantially entoches from a reactor, such as a Claus burner with enlarged reaction chamber, a waste heat boiler and sulfur condenser. In Clausbrenner is with Fuel, such as natural gas, fuel oil, set a temperature of 700 to 1000 ° C. The combustion becomes hypochlorometric

carried out so that after combustion still, for example, CH ₄ , H ₂ , CO is present, in the ratio of CH ₄ / SO ₂ of about 1/2 based on the CH ₄ before combustion, ie without decomposition of CH ₄ to H ₂ and CO. The reducing one

Gas mixture is brought in the hot zone with the SOrFraktion from the laundry in contact. The mixture reacts too

a mixture in which sulfur, SO ₂ and H ₂ S are typically represented in the ratio 3/1/2. This mixture is then after

Sulfur separation recycled for combustion. If 60% of the sulfur contained in the fuel for combustion is recovered in the sulfur separation,

increases by the return of the gas mixture from the Schwofelabtrennung for combustion, the SOj fraction to

Flue gas scrubbery on double. As a result, the fuel consumption in the Claus burner is also doubled. Therefore

but is also produced in the waste heat boiler twice the amount of steam.

According to another advantageous embodiment of the process according to the invention, a maximum of 80% by weight,

preferably reduced to a maximum of 67 wt .-% of SO ₂ . The unreacted portion of the SO ₂ is called the enriched fraction of

Laundry supplied. There, the SO _{2 is taken up} again by the particular physically acting solvent and

in a usual regeneration (relaxation, stripping and / or heating) released as SOj-Reichgae.

Suitable solvents are all chemically and physically active detergents in question, which in particular a high Have absorption capacity for SO ₂ .

In the event that the high-pressure steam produced during the cooling can not be removed, it has proven to be expedient if, after the Schwjtelkondensation and separation, a conversion of SO ₂ and H ₂ S to elemental sulfur is carried out according to the Claus reaction, the resulting sulfur is separated and the residual gas is returned to the combustion. By downstream of a Claus application of any kind behind the Schwefelabt / tion is a recovery of more than 90% of the sulfur in the SO ₂ fraction possible. This reduces the consumption meters! for fuel in the Claus burner, which in turn results in reduced steam production. However, the investment costs increase due to the additional Claus reactors.

As a further alternative procedure, the remaining gas after sulfur separation can be increased to elevated pressure and at least 50% by volume recycled to S0 ₂ reduction. For this purpose, a hot sucking blower must be arranged after the sulfur separation. Most of the gas is conveniently recycled to the stoichiometric combustion in the Claus burner. In this case, the reducing components contained in the gas mixture, predominantly H / and CO, are used for the reduction of SO ₂ . However, a partial flow of the gas must be recycled in each case for combustion, since inert gases such as N ₂ and CO ₂ must be discharged, which happens bosttn in the flue gas scrubbing.

In addition, in order to pre-precipitate Clementarschwafel in the piping from the sulfur condiner to incineration, it is envisaged to heat the remaining gas after combustion and after recirculation. This can be achieved by external heat sources, eg. B. steam from the combustion take place. Suitably, a small partial flow of the hot reducing gas can be derived from the burner and mixed with the cool gas from the sulfur separation. A heating of the pipeline is conceivable. It is also possible to heat this cool gas in the heat exchange, in particular using regenerators, to product gas.

In addition to the combustion of fuel, the heating of the (> O ₂ gas and the reducing gas is also subject to the possibility of using external heat sources, in particular in heat exchange with hot combustion gases Instead of this, CH _{4 is} mixed as a reducing agent with the SO ₂ -rich gas after external heating, and accordingly the consumption of fuel, such as CH _{4, is} reduced according to

CH ₄ + 2So ₂ - CO ₂ + 2H ₂ O + S ₂

4CH ₄ + 6SO ₂ - »4CO ₂ + 4H ₂ O + 4H ₂ S + S ₂

To speed up the reduction of SO ₂ to elemental sulfur and H ₂ S, this may be conveniently carried out over a catalyst. The catalyst can be used in or behind the hot zone of the burner. The highly exothermic reaction of SO ₂ takes place at very high temperatures of z. B 850 to 1 20O ⁰ C usually over a catalyst based on Al ₂ O ₃ .

It is particularly expedient in this case if the SO ₂ -rich gas is passed for reduction via a quasi-isothermally operated catalyst bed and the catalyst bed is cooled by means of a cooling medium inside. This embodiment offers the advantage that an approximately constant temperature is maintained above the catalyst and that the heat released during exothermic reduction can be dissipated immediately. Advantageously ka / in this case in isothermal reactor for Anwandung reach, which is designed in the manner of a wound tube bundle heat exchanger with winding core tube. The wound tubes then serve as cooling coils for the cooling medium and the catalyst bed is arranged in the outer space of the core tube. The ancestor according to the invention can be used with particular advantage as a process step in an exhaust gas, in particular flue gas cleaning system.

Ausführungsbelepiel "

The invention is explained in more detail below with reference to some examples. In the attached drawing show:

Fig. 1: Basisvario do3 inventive method with several alternative process guides; Fig. 2: special embodiment with external heating of the SO ₂ -riching gas.

According to Fig. 1, a power plant 1 via line 2 air and fed via line 3 sulfur and hydrocarbon-containing fuel. Via line 4, 4483 kmol / h of flue gas at a temperature of 147 ° C. flow from the power plant 1 under a pressure of 1.05 bar. The flue gas has the following composition:

N ₂ 77.8 mol%

O ₂ 4.9 mol%

CO ₂ 10.0mcl-%

SO ₂ 0.1 mol%

H ₂ O 7.2 mol%.

The gas is supplied to a flue gas scrubber 5 indicated only schematically. In the laundry 5, the SO ₂ -containing gas is washed with a physically acting solvent which becomes soluble with SO ₂ . Purified gas passes via line 6 with a temperature of 120 ⁰ C and a pressure of 1.01 bar in an amount of 4475kmol / h to Kan in. This gas has the following composition:

N ₂ 78.0 mol%

O ₂ 4.8 mol%

CO ₂ 10.0 mol%

H, 0 7.2 mol%

SO ₂ tracks.

The loaded solvent is regenerated by heating, stripping and / or pressure reduction and reused in the laundry. During regeneration, an SO ₂ -rich gas fraction (7 kmol / h) with a temperature of 30 ° C. and a pressure of 0.7 bar is produced in line 7. This SO ₂ -riching gas has the following composition:

N, 4.5mol%

CO, 12.0 mol%

SO, 78.5 mol%

H, 0 5.0 mol%.

The SO, -rich gas in line 7 is brought in a compressor 8 a-jf a pressure of 1.6 bar and fed at a temperature of 101 ⁰ C of the reaction chamber of a quasi-Claus burner 9. .

Via line 10, moreover, 4.68 kmol / h of natural gas are fed under a pressure of 5.5 bar, a temperature of 35 ° C and the following composition:

N, 1.7 mol%

CH ₄ 94.0 mol%

C, H _e 3.5 mol%

C ₃ H ₈ 0.1 mol%

H, 0 0.7 mol%.

The natural gas is burned in Gegenwml supplied via line 11, in a blower 12 to 1.6bar / 72.5 ⁱ C compressed air (9kmol / h). During the combustion in the Zono 13 a gas mixture (1,55bar, 649 ⁰ C) of the following composition is produced:

H, 29.2 mol% N ₂ 40.7 mol% CO 13.5 mol% CO, 2.8 mol% CH ₄ 10.9 mol% H ₂ O 2.9 mol% C ₂ H ₆ , NH ₃ traces

This gas mixture is brought into contact with the SO, regichus. To accelerate the reduction reaction, a catalyst 14 is arranged in the reaction chamber. After the catalyst 14 25 kmol / h unreacted gas skins having a temperature of 1079 ⁰ C and a pressure of 1,45bar the following composition:

H ₂ 2.3 mol% N, 29.8 mol% CO 3.0 mol% CO ₂ 19.4 mol% H ₂ S 8.5 mol% SO, 1.3 mol% COS + CS, 0.3 mol% Elemental sulfur 7.1 mol% (calculated ils S?) hjo 28.3 mol%

This gas mixture is fed to a waste heat boiler 15 by producing high pressure steam (20 to 100 bar) Boiler feed water is cooled to 300 ⁰ C. When cooling already condenses about 1 kg / h of element sulfur, the

is deducted via line 16.

The gas from the waste heat boiler 1D is sodunn in a heat exchanger 17 against boiler feed water to produce Low-pressure steam (2 to 5 bar) below the sulfur dew point cooled to 120 ° C rb. Dobel condenses elemental sulfur

from which is separated from a separator 18 via line 19 in an amount of 113kg / n as a product.

The remaining after the sulfur separation gas (23kmol / h, 120 ⁰ C, 1.2 bar) has the following composition:

H, 2.5 mol% N, 32.1 mol% CO 3.2 mol% CO, 20.9 mol% H ₂ S 9.1 mol% SO, 1.6 mol% CCS + CS ₂ 0.3 mol% H ₂ O 30.4 mol%

The remaining gas is returned via line 20 to the power plant 1 and burned there unteretöchiomotrisch together with the fuel.

As shown by dashed lines in Figure 1, the remaining gas can also be a schematically drawn Claus plant 21st

be supplied from the dor via line 22 further sulfur separated and recovered as a product. The residual gas of the Claus plant is then passed via line 20 back to the power plant 1.

As a further method option, according to FIG. 1, a hot-sucking blower 23 in line 20 is also engraved

arranged, with which the gas is brought to a, ι pressure of 1, B boron. Under this pressure, a majority of the remaining gas can then be returned directly to the Claus burner via the dashed line 24 with valve 25. Only a smaller partial flow, for example 20%, is returned in this case via line 20 to the power plant.

Finally, according to a likewise dashed line variant, the possibility of hot reducing gas (649 ⁰ C) over Line 26 to admix the cooler (120 ° C) gas in line 20 to make losses due to precipitating sulfur in the lines To prevent pipes. The heating of the cool gas in line 20 can also be represented schematically by means of an external heat source

through the dashed heat exchanger 27, done, or by heating the pipeline, z. B. with steam.

FIG. 2 shows a special process procedure in which the heating of the SO ₂ refining gas and reducing gases? Not

done in his own Brenne '. The same system components as in FIG. 1 are provided with the same numbers.

Via line 4 is flue gas from a power plant 1, in the fuel from line 3 in the presence of line 2

supplied air is burned, in an amount of 500000 NmVh with a temperature of 41 ⁰ C and oinom pressure of about 1.1 bar a wash column 6, respectively. The flue gas has the following composition:

N, / 4Vol.% O ₂ 6Vol .-%

COj 13% by volume SO ₂ 0.1% by volume

H ₂ O 6.9 vol.%.

In the lower column section, an unillustrated water scrubbing may take place, removing solids and water-soluble compounds from the gas. In addition, part of the water vapor introduced is condensed out and discharged and no longer pollutes the subsequent process steps.

In the upper part wild, the wash column 5 with 800t / h chenerteiertem, physically acting solvent via line 30 acted upon. The solvent increases in the countercurrent to ascending gas from diosem SO ₂ and leaves the column in the lower part via line 28 via line 6 is from the head of Waschkolonno E SO ₂ -freius gas with a temperature of 16 ° C and a pressure of 0 , Deducted 97 bar. For solvent recovery, a water wash, not shown, can take place in the head of the wash column 5. The clean gas has the following composition:

N ₂ 76.7% by volume

O ₂ 6.3% by volume

CO ₂ H 0 vol.%

SO ₂ 50 ppm

H ₂ O 3.0 vol.%.

The loaded solvent is fed by means of a line 28 arranged in pump 29 after heating in a heat exchanger 31 against regenerated solvent a regenerating column 32. In the regeneration column 32, the loaded solvent via a Sutnpfheizung 33 with steam of z. B. 2 bar and the SO ₂ expelled from the solvent. The expelled SO ₂ is cooled in a head cooler 34 to vermeneiden solvent losses. The regenerated Iccungsmittel is withdrawn from the bottom of the regenerating column 33 and after cooling in the heat exchanger 31 via line 30 is again applied to the wash column.

Via line 7, SO ₂ - Reichgai is withdrawn from the top of the: regeneration column. The SO ₂ -rich gas contains \ lOONiivVh SO ₂ . After compaction in a grain; 8 to 1.5bnr and heating in a heat exchanger 35 to about 400 ⁰ C is added to the SO ₂ Reichga8 via line 36 Mv.t! tan in an amount of 400 Nm ³ / h and the mixture fed to a reactor 37. In the reactor 37 takes place over a catalyst on Al ₂ O ₃ -based at 1000 ⁰ C dio reduction of SO ₂ to elemental sulfur instead. Via line 38, the product gas is withdrawn from the reactor 37 and cooled in a cooler 39 by generating 0.3 t / h of high pressure steam to 400 ° C. In the heat exchanger 35, the product gas is further at a below the sulfur dew point) temperature, for. B. 118 ° C cooled. In a separator 18, the product sulfur is separated. Via line 19 then 0.71 t / h elemental sulfur can be deducted with a purity of 93%. Since this reaction is not complete, the product gas contains other sulfur compounds besides SO ₂ , especially H ₂ S, but also COS and CS. available. Via line 20, a gas stream is withdrawn from the separator 18, which consists of about 20% of these sulfur compounds. This gas stream is passed back to the power plant 1 for combustion.

Claims (12)

Anspruch [en] A process for recovering elemental sulfur from SO ₂ -riched gas obtained by scrubbing SO ₂ -containing gases obtained by combustion, characterized in that the SO ₂ -riching gas is incompletely reduced to sulfur and H ₂ S in the presence of a reducing gas after heating , The auskonaensiert sulfur by cooling and separated, burned in the reduction resulting H ₂ S-containing gas and thereby formed SO ₂ and nichtreduziertos SO _{2 are returned} to the laundry. 2. The method according to claim 1, characterized in that the resulting in the reduction of H ₂ S-containing gas is returned to the combustion and burned there. 3. The method according to Ansprucn 1 or 1, characterized in that for the reduction of SO ₂ rich gas fuel is stoichiometrically burned in the presence of an oxygen-containing gas, that in the gas produced during the combustion, which is used as a reducing gas, a ratio of hydrocarbon calculated as Cl of the fuel to SO ₂ of about 1: 2, drawn on the hydrocarbon of the fuel before combustion, the hot reducing gas is brought into contact with the SO ₂ -rich gas for SO ₂ reduction, and in the gas after the SO ₂ reduction, a ratio of elemental sulfur to SO ₂ to H ₂ S of about 3 : 1: 2 is set. 4. The method according to any one of claims 1 to 3, characterized in that a maximum of 80Gew .-%, preferably at most 67Gew .-% of SO _{2 are} reduced. 5. The method according to any one of claims 1 to 4, characterized in that carried out after the sulfur condensation and separation, a reaction of SO ₂ and H ₂ S to elemental sulfur according to the Claus reaction, the resulting sulfur separated and the residual gas is returned to the combustion , 6. The method according to any one of claims 1 to 5, characterized in that the remaining Ha-. brought to elevated pressure after the sulfur separation and at least 50 vol .-% for SO ₂ reduction are recycled. 7. The method according to claim 6, characterized in that the brought to increased pressure remaining gas is returned to the substoichiometric combustion. 8. The method according to any one of claims 1 to 7, characterized in that the remaining gas is warmed after the sulfur separation before recycling the combustion. 9. The method according to claim 8, characterized in that the heating of the remaining gas is carried out by diverting a partial stream of the hot reducing gas. 10. The method according to claim 1 or 2, characterized in that the heating of the SO ₂ refining gas and the reducing gas is carried out in heat exchange to hot Verbronnungsgasen. 11. The method according to any one of claims 1 to 10, characterized in that the reduction of SO ₂ to sulfur and H ₂ S is carried out over a catalyst. 12. The method according to claim 11, characterized in that the SO ₂ -riching gas passed for reduction via a quasiisothermally operated catalyst bed and the catalyst bed is cooled by means of a cooling medium inside.