DE2736488C3 - Process for removing sulfur oxides from flue gases - Google Patents

Description

The invention relates to a method for removing sulfur oxides from flue gases, in which the Flue gas is contacted in a scrubbing tower with dilute sulfuric acid as scrubbing liquid and that in sulfur dioxide enriched in sulfuric acid using an iron compound as a catalyst is oxidized.

Such methods are used to remove the flue gases that are in particular leaving power plants from the ones that are carried along To free sulfur oxides. Due to the continuously tightened environmental protection regulations increasingly higher demands are placed on such processes.

In a known method, the flue gases freed from the fly ash are cooled down ^{to 50 to 80 ° C. in a washer by injecting fresh water and recycled washing liquid.} Then they are treated in a washing tower with dilute sulfuric acid in countercurrent. The flue gas, which has been cleaned of the sulfur oxides, must then be heated to over 100 ° C to regain a sufficiently large buoyancy. It is then released into the atmosphere through a chimney. The scrubbing liquid enriched with sulfur oxides (SO2 and SO3) is pressed into an oxidation column via an injector through which air is added to the scrubbing liquid. A dissolved catalyst in the form of an iron compound is added to the washing liquid to accelerate the oxidation. Sulfuric acid is formed. The exhaust air from the oxidation column is fed to the washing tower. Part of the sulfuric acid produced is returned to the washing tower and the other part - used to extract gypsum in a crystallizer.

In other known methods, the sulfur oxides contained in the flue gas at temperatures of about 450 ⁰ C to sulfur trioxide are converted by the flue gas is passed over a V2O5-contact. The sulfur trioxide produced in this way is then dissolved in the countercurrent sulfuric acid. Here, too, the end product is sulfuric acid. If the flue gases are at temperatures of 100 to 150 ^° C., they must be heated ^{to the corresponding reaction temperature of 450 ° C.} This is e.g. B. necessary for the flue gases that leave the power plant.

The invention is based on the object of a method operated with dilute sulfuric acid for Remove sulfur oxides from flue gases in such a way that the flue gases cool down superfluous and to find a catalyst that allows easy handling.

The object is achieved according to the invention in that iron (II) sulfate is used as the catalyst and the catalyst is already added to the washing liquid and that in a partial stream from the Sulfuric acid drawn off from the washing tower is deposited electrolytically and metallic iron this metallic iron is returned to the washing liquid via a release device. With the Procedure according to the invention, it is possible to remove all of the pollutants still present in the flue gases to capture and separate from the smoke gases. This is a significant reduction in environmental pollution, especially of coal-fired power plants. In particular, there are no the wastewater polluting substances are separated. The generated Products are further processed into marketable or landfillable end products.

The dust load of the flue gas is reduced according to the invention or a return to the The washing tower is prevented by the fact that the partial flow to remove the fly ash is prevented by a filter system to be led.

For a better understanding of the invention, an embodiment based on a for Implementation of the process suitable system, which is shown in the single drawing, explained.

At 1, the flue gases are introduced into the scrubbing tower 2, which contain numerous pollutants and also fly dust. In the washing tower 2, the already washed flue gases are cleaned with the aid of the fully demineralized water fed in via line 3. At the same time, the fully demineralized water is used to compensate for water losses. A mixture of dilute sulfuric acid and iron (II) sulfate is fed into the washing tower 2 via the line labeled 4. At 5, the washed flue gases leave the washing tower 2 and are released into the atmosphere via the chimney. The washing liquid consisting of dilute sulfuric acid and iron (II) sulfate is drawn off at 6 and fed to the filter system 8 in a partial flow. The washing liquid contains, in aqueous solution, H ₂ SO ₄ , H (NO) SO ₄ , Fe (NO) SO ₄ as well as iron-II-sulfates and Fe-1! -Chlorides and dust.

A partial flow of the washing liquid withdrawn at 6 flows into the filter system 8 via line 7 which the airborne dust is released via line 9a after appropriate separation. The filter system 8 is supplied with washing water via line 10. In

W) of the filter system 8, two filters are preferably provided in parallel. When cleaning one Filter, the inlet in line 7 is closed, the acid adhering to the filter cake drips off and becomes pumped into the circulation line 13. Then the filter cake is poured with fresh water from the pipe 10 washed until the process 9 is neutral. The washing water is collected in the template 11.

The partial flow of the withdrawn via line 7

Washing liquid is fed to the electrolysis system 15 behind the filter system 8 via line 14. ^{Metallic E:} sen is produced at the cathode 16 and, after redissolving as Fe (II) sulfate, is fed via the line 17 into the line 4 and thus back into the washing tower. The iron concentration in the substream in line 14 is approx. 250 to 500 mg Fe / l. The partial flow rate (l / h) in line 14 is directly dependent on the SC> 2 entry in the washing solution. The amount of Fe to be deposited at the cathode every hour is therefore 250 to 500 mg Fe / h.

The amount of Fe to be separated results from the multiplication of the iron concentration in the partial flow and the Partial flow rate in l / h

15th

/ mgFe 1 _ mgFe ^x

The C12 produced at the anode is transferred to the Line 19 is fed to a washing template 20. In these, the CI2 reacts with the one from line 21 coming water to a hypochlorite solution, which via line 22 to the not shown Cooling tower make-up water treatment system arrives.

From the electrolysis plant 15 sulfuric acid exits, which is free of iron and heated above the vaporizer 23 to about 130 to 140 ⁰ C, while sodium to approximately 70% H is concentrated ₂ SO _4, as a salable end product via line 24 can be deducted. During this constriction, hydrochloric acid, traces of HF and the NO released from the nitrosyl compound at this temperature are driven off in gaseous form, in addition to water vapor. These substances reach a cooler 26 via lines 25, hydrochloric acid with small amounts of HF being formed, which is drawn off via line 27. The remaining NO, together with the remaining water vapor, is passed through a coal bed 28 and converted to N2 and CO2, which can be drawn off via line 29. The small amount of HF-containing hydrochloric acid flowing out of the cooler can be used as a regeneration column in the desalination plant (not shown) or for decarbonization in the additional water treatment for cooling tower (not shown), where it is discharged via line 30.

Tests that were carried out in the plant described have shown that the above Almost one hundred percent of the pollutants are separated from the flue gases. In addition, there are no input raw materials, such as lime. Sulfuric acid, coke, Sand or other expensive additives required. Technical sulfuric acid in particular falls as the end product from 70 to 76%. which is readily salable. Only on the entrance side of the washing tower is fully demineralized water is supplied.

1 sheet of drawings

Claims (2)

Patent claims: 1. Process for removing sulfur oxides from flue gases, in which the flue gas in one Washing tower is contacted with dilute sulfuric acid as washing liquid and that in the Sulfuric acid enriched sulfur dioxide using an iron compound as a catalyst is oxidized, characterized in that iron (II) sulfate is used as the catalyst and the catalyst is already added to the washing liquid and that in a partial stream of the The sulfuric acid withdrawn from the washing tower electrolytically deposited metallic iron and this metallic iron is returned to the washing liquid via a dissolving device will. 2. The method according to claim 1, characterized in that the partial flow for the removal of Airborne dust is passed through a filter system.