DE2025353A1 - Sulphur recovery from flue gas - economically using microorganisms - in reduction stage - Google Patents

Abstract

S Is recovered from flue gases contg. S oxides by binding these with lime or alkali salts of weak acids, e.g. H2CO3, H3PO4 etc., in the form of solid or aqs. soln. or suspension and processing S cpds., opt. after dissolving or suspending in H2O. Soln. or suspension is treated at 20-60 degrees C with liquid, dissolved or suspended oxidizable organic material, with exclusion of air and in presence of sulphate- and sulphite-reducing microorganisms. H2S Is then expelled from resultant soln. contg. sulphide by treatment with O2-free gas contg. CO2 and converted to S in Claus plant. Process is economical, since pure S is readily saleable, and does not give rise to noxious solid residues or waste liquors.

Description

Process for obtaining sulfur from flue gases and flue gases from the Combustion of solid or liquid fuels, e.g. B. in power plants included Due to the sulfur content of the fuels, always sulfur oxides, especially SO2. Because of the harmful effects on human health and the flora as well as because of the corrosion on buildings and industrial plants one has been since long endeavors to find economical processes for removing the sulfur oxides from such To find flue gases before they escape into the atmosphere. Numerous procedures were developed, but could not prevail, either because they were because of the chemicals used were only of local importance or because they were in continuous operation caused too high costs. Furthermore, today it is required that no methods be used that turn an exhaust air problem into a sedimentation or sewage problem, by creating malodorous or harmful solid residues or sewage. For the economy, it is very important that from the sulfur oxides A well-salable product is created that is not only of local interest. A such a sellable product is pure elemental sulfur.

It has now been found that all of these requirements are met, if you remove the sulfur oxides contained in flue gases by treating them with solid or alkaline dissolved or suspended in water Fabrics, z. B. lime or alkali salts of weak acids such as carbonic acid, phosphoric acid or like. Binds and the sulfur-containing compounds obtained, if necessary after Dissolve or suspend in water at 20 to 60 ° C with exclusion of atmospheric oxygen in the presence of anaerobic sulfate- and sulfite-reducing microorganisms and optionally with the addition of nutrients with liquid, dissolved or suspended oxidizable, Treated organic substances, hydrogen sulphide from the sulphide-containing solutions obtained in this way expelled by a carbon dioxide-containing, oxygen-free gas and in a Claus plant converts in a known manner to elemental sulfur.

In this way, sulfur that is easily sold is obtained, and the sewage sludge is also removed Much easier to settle without increasing the volume than without the #treatment with sulphite and sulphate-containing aqueous solution. The flue gas is so largely desulphurized that it is practically harmless in the atmosphere. The leftover one Separated from the sludge aqueous solution can again for the formation of sulfite and Sulphate can be used to scrub the flue gas.

The method according to the invention is shown in the figure for example explained. The system shown schematically consists of the flue gas desulphurisation 1, the biological sulphite / sulphate reduction 2 and the Claus plant 3. The flue gas is fed to the desulfurization system 1 through line 4 and leaves it through line 5 to the atmosphere. Through line 6, the desulphurizing agent is abandoned in aqueous solution. It forms sulphite with the SO2 and SO3 of the flue gas and sulfate. Part of the running sulfite and sulfate-containing solution is used for the purpose better utilization through line 8 for further flue gas desulphurisation, while another part through line 7 into plant 2 for biological sulfite / sulfate reduction got. This plant is fed from line 9 sewage sludge, the organic, oxidizable substances in which hydrogen and / or nitrogen Carbon bound, as well as sulfate- and sulfite-reducing bacteria, e.g. Desulphovibrio desulphuricans.

Due to the action of the bacteria arises in the sludge-containing solution at temperatures between 20 and GOOC. Hydrogen sulfide, which is caused by CO2-containing> oxygen-free gas flowing in from line 10, expelled and through the line 11 is passed to Claus plant 3 The treated sludge is passed through the line 12 discharged again. The sludge-free solution from the biological plant 2 is The flue gas desulfurization system 1 is fed back via line 6.

The oxygen-free gas in line 10 can, for. B. from the desulphurized Flue gas from line 5 can be obtained.

In Claus position 3, the hydrogen sulfide is mixed with atmospheric oxygen converted from line 13 to elemental sulfur, which is withdrawn from line 14 will. The heat released during the reaction is converted into steam, which is generated by the Line 15 can be filled for use - the exhaust gas from the Claus plant is passed through line 16 to the flue gas before it enters the desulfurization system or mixed in in the desulphurisation plant itself.

In the manner described, the flue gas is desulphurized and more salable Sulfur obtained without creating a new exhaust air problem like that is otherwise the case with Claus systems.

The Claus plant is even relieved because you are there with a lower yield of e.g. B. 90 °; »o can satisfy; because the rest 10 Jo are recovered as SO2 in the flue gas desulphurisation system, without polluting the atmosphere. That is why the Claus system only needs one to be equipped with a catalytic reactor and an afterburning stage, while otherwise 2 or even 3 reactors and an afterburning are required, to achieve a yield of 96 to 98 Qo.

The advantages of the method according to the invention are even clearer from the following numerical example.

A power station burns coal with 2% 5 content. With one achievement of 300 MW with a capacity utilization of 75%, the fuel consumption is 85 t / h with 1700 kg S / h. This produces 1.2 million Nm³ / h of flue gas, for removal the sulfur oxides, the flue gas is cooled and at about 400C in an Enischulflungsanlage 1 washed with 100m3 / h of a P clay solution of ammonium carbonate in water.

The scrubbed flue gas only contains 0.0058 vol.% SO2, accordingly a leaching of over 94% of the sulfur originally contained in the flue gas.

The ammonium sulfite solution that runs off enters the biological reduction plant 2, where their sewage sludge with a solids content of 6% by weight is added. Due to the so-called sulphate-reducing bacteria contained in it, which also contain sulphites The sulfur oxides washed out of the flue gas can break down into H2S corresponding amount of sulfur converted into sulfide and sulfide ions.

As will be seen below, this amount of sulfur is greater than the amount of sulfur introduced by the fuel. and amounts to 1870 kg S / h. By gassing with 11.600 Nm3 / h CO2 -containing> but practically oxygen-free Gas is released and discharged, so that the Claus plant 3 with the CO2 -containing gas 1290Nm3 H2S / h, i.e. a gas with an H2S content of 10 Vol. Olo, After fumigation, the digested sludge and ammonium carbonate remain Solution left They are separated from each other in a known manner.

The sludge treated in this way has good settling properties of use. The sludge is drained while the ammonium carbonate solution again is used for flue gas desulphurisation. In the one with a Claus boiler and A Claus plant equipped with a single-stage reactor converts 90% of the H2S with air converted into elemental sulfur in a known manner and obtained. The remaining 10 % = 170 kg S / h are post-burned and leave together with the exhaust gas as sulfur oxides the Claus plant. They are discharged through line 16 and the flue gas admixed with the entry into the desulphurisation system 1. That way will be out of the Claus plant, despite its simple design, no harmful exhaust gases are released into the atmosphere discharged and the amount of sulfur from the fuel completely as pure, easily salable elemental sulfur obtained.

Instead of the ammonium carbonate solution used in the previous example can also use another weakly alkaline carbonate solution for flue gas desulphurisation be used, e.g. B. sodium carbonate solution or mixtures of carbonates and / or Bicarbonates and / or phosphates.

You can also use a sulfite-containing solution from the sulfur oxides of the Flue gas win by the fact that the flue gas, for. B. in a fluidized bed, treated with a carbonate solid mass at temperatures above 900 C, which which absorbs sulfur oxides and forms sulfites or sulfates. Then the sulfite and / or sulphate-containing mass extracted with aqueous carbonate solution, with sulphites and sulfates go into solution and the mass is regenerated. The mass can be separated, dried and used again for flue gas desulphurisation, while the sulphite and sulfate-containing solution in the manner described above for bacterial production of hydrogen sulfide is used.

After all, if the composition is favorable, it is communal and / or industrial wastewater, especially with sufficient alkalinity (PI-I> 7) possible, the wastewater, optionally after separation of troublesome solids, z. B. by letting it sit down, to use it directly to scrub the sulfur oxides from the flue gas, then the solution, if necessary after adding other organic substances, e.g.

of petroleum hydrocarbons to feed a digester where below With the help of sulfite- and sulfate-reducing microorganisms, sulfides are formed, which by treatment with a gas containing C502 with the formation of hydrogen sulfide be decomposed. The gas containing hydrogen sulphide becomes elemental sulfur in a known manner processed.

PATENT CLAIMS

Claims (8)

PATENTANSPRÜCJ-IE 1) Process for the production of sulfur from Scllvefeloxide containing flue gases by binding the sulfur oxides to. solid or in water dissolved or suspended alkaline substances, e.g. B. lime or alkali salts weaker Acids, such as carbonic acid, phosphoric acid or the like. And processing of the sellweielhaltigen Compounds, optionally after dissolving or suspending in water, characterized thereby, that the solutions or suspensions at 20 to G () ° C with the exclusion of atmospheric oxygen in the presence of sulfate- and sulfite-reducing microorganisms and optionally with the addition of nutrients with liquid, dissolved or suspended oxidizable, organic substances are treated and that from the sulfide solutions thus obtained by treatment with a carbon dioxide-containing, oxygen-free gas hydrogen sulfide driven out and in a Claus plant in a known manner to elemental sulfur is implemented. 9) Method according to claim 1, characterized in that as oxidizable Substances from municipal and / or industrial wastewater or from this wastewater Sewage sludge can be used 3) Method according to claim 1, characterized in that that as oxidizable substances petroleum hydrocarbons alone or together with waste water or sewage sludge can be used. 4) Method according to one of claims 1 to 3, characterized in that that the sulfide-containing solution after fumigation with carbon dioxide-containing gas of solid residues are separated and used again for flue gas desulphurisation 5) Method according to one of Claims 1 to 4, characterized in that the exhaust gas the Claus plant is mixed with the flue gas before desulfurization. 6) Method according to one of claims 1 to 5, characterized in that that the flue gas is desulphurized with an aqueous solution of 1 to 15% by weight Na2 CO3 will. 7) Method according to one of claims 1 to 5, characterized in that that an aqueous solution of sodium phosphate is advantageous for washing the flue gas a 5 to 50 elo aqueous solution of primary and / or secondary sodium phosphate is used. 8) Process for obtaining sulfur from sulfur oxides containing Flue gases, characterized in that the flue gases with alkaline communal or industrial wastewater can be washed and from the solutions obtained in this way hydrogen sulfide is formed in a septic tank according to one of claims 1 to 5 and cleared, whereupon the solution freed from hydrogen sulfide is discharged or is used again to scrub flue gases while the hydrogen sulfide is released is processed in the Claus furnace on elemental sulfur.