EP0168453A1 - Process for stripping nitrogen oxides and sulphur oxides as well as optionally other noxious elements of flue gas from combustion plants - Google Patents

Abstract

Process for the extraction of nitrogen oxides and sulfur oxides, as well as, where appropriate, other harmful elements from flue gases from combustion plants, preferably from boilers of electric plants supplied with fossil fuels , the nitrogen oxides being reduced to elemental nitrogen and the sulfur oxides, as well as the other harmful elements being extracted by means of a washing process. In order to improve this process of the type mentioned above with regard to the simplicity of the implementation and the possible results, the present invention proposes a series of measures, such as the addition of a monobasic and / or multibasic carbonic acid to EDTA with limestone or the like, the addition of phosphoric acid or its salt to the washing liquid up to an electrochemical process according to which salts forming with the desulfurization plant are added to the washing liquid nitric oxide complexes which are reduced to elemental nitrogen and water if mixed with formic acid to prevent precipitation of the hollow iron hydroxide III at a potentiostatic mounting cathode.

Description

"Process for the separation of nitrogen oxides and sulfur oxides and possibly other pollutants from the flue gases of incineration plants"

The invention relates to a process for the separation of nitrogen oxides and sulfur oxides and possibly other pollutants from the flue gases of combustion plants, preferably from power boilers fed with fossil fuels, the nitrogen oxides being reduced to elemental nitrogen and the sulfur oxides and possibly other pollutants by means of a washing process be eliminated.

When fossil fuels are burned, nitrogen oxides (NO and NO ₂ ) are generated by the thermal reaction of atmospheric nitrogen and atmospheric oxygen (thermal NO _x ), by the reaction of nitrogen a the fuel with atmospheric oxygen (fuel - NO _x ) and the reaction of nitrogenous compounds (radicals) with the combustion air (prompt NO _x ).

The nitrogen oxide content varies depending on the fuel used and the combustion conditions. After being released into the atmosphere, the nitrogen oxides are subject to further chemical, in particular photochemical conversions, which can eventually lead to organic peroxide compounds with hydrocarbons, which in turn are held responsible for plant damage that can be largely determined.

Together with the sulfur oxides (SO ₂ and SO ₃ ) resulting from the sulfur compounds of the fuels as well as the resulting acids, the nitrogen oxides and their secondary products formed in the atmosphere are regarded as the main cause of air pollution and the resulting damage.

The hewn mechanisms of action of the various types of damage are currently insufficiently known.

To reduce the emission of sulfur and nitrogen oxides, legal regulations, requirements and guidelines have already been issued in various industrialized countries.

For the separation of nitrogen oxides, catalytic processes are known in which NO and NO ₂ are reduced to elemental nitrogen by reducing agents. In the combustion plants of power plants, for example, ammonia is mainly used as a reducing agent for nitrogen oxides and on different catalysts such as transition metal oxides, zeolites, activated carbon or Activated coke converted to elemental nitrogen and water.

The removal of sulfur oxides from the flue gases is often carried out by contact with washing solutions which contain calcium ions and which separate sulfur oxides oxidized to sulfalt as gypsum.

Starting from this prior art, the object of the invention is to further improve the method of the type mentioned at the outset with regard to the fact that it is carried out as well as the achievable results.

According to the invention this is achieved in that the washing liquid of a desulfurization plant ethylene-diamine-tetra-acetic acid (EDTA) C ₁₀ H ₁₆ O ₈ N ₂ and a mono- and / or polybasic carboxylic acid, preferably formic acid, together with limestone, white fine lime or their derivatives is added. It was found that the reduction of the SO ₂ and NO _x components by the EDTA in the combined action of the two additives was achieved more cheaply, ie with a higher efficiency and more economically, ie with a lower concentration density than the total additive. It is known to simultaneously NO _x . to separate the flue gas behind incineration plants by adding EDTA and iron-II-sulfate to the desulfurization wash cycle, whereby a special ratio between SO ₂ and NO _x (min. 2: 1) and the oxygen content of the flue gas must be observed.

It has been found that the simultaneous NO _x separation can be significantly increased, the previously known interfering influences thereby being reduced, and even avoided, that the simultaneous NO _x separation together with the chloride or. Hydrogen chloride washing is carried out in front of a desulfurization plant or between the HCl prewash and the desulfurization as a separate wash.

The advantages are that the NO _x separation can be carried out in a controllable acidic washing solution (pH 2.5-4.5), since a) the complex-bound iron-II is difficult to oxidize in this acidic medium and b) the NO - Binding is maintained without significant hindrance to iron oxidation.

Another advantage is that the full amount of SO _{2 in} the flue gas, since the amount of lime is only added to the desulfurization plant, for which NO reduction is available and the binding value of the EDTA cannot be used for calcium ions and is only available for the iron (II) ion.

The wash cycle can be controlled via the pH adjustment and wash water evaporation so that a max. EDTA can be achieved and can be recovered as a precipitate by lowering the pH in the wash solution to pH 2 of the EDTA.

It was also found that the potassium salt of N- (2-caboxy-ethyl) -1-amino-ethane-1,1-diphosphonic acid and the potassium salt of N, N-bis (caboxymethylene) -1-amino-ethane instead of EDTA -1,1-diphosphonic acid can preferably be used, since the phosphonic acid found can bind significantly more iron-II complex than EDTA.

It is known for the simultaneous washing of NO _{x in} addition to SO ₂ , SO ₃ , HF and HCl from the flue gas to use polycarboxylic acids or phosphonic acids in conjunction with iron (II) sulfate.

This washing can take place in a prewash together with the hydrogen halides before the SO ₂ wash, at a pH value the wash solution from pH 2.5 - 4.5 or after the hydrogen halide prewash, but before the SO ₂ wash as a separate wash at a pH value of the wash solution from pH 2.5 - 4.5.

It is also possible to carry out the simultaneous NO _x wash together with the SO ₂ wash or after the SO ₂ wash with its own wash water circuit at pH values of pH 2.5 -> 8.0.

It has been found that, according to the invention, the simultaneous NO _x wash can be considerably increased and forced if the polycarboxylic acid (including EDTA) or phosphonic acid used is complexed with the iron (II) sulfate beforehand, ie before being added to the wash water circuit. According to the invention, this takes place depending on the pH of the polycarbonate solution, preferably using sulfuric acid or other mineral acids at pH values above pH 5 and by means of alkalis or alkaline earths at pH values less than pH 5. The pH in the wash water solution can then be changed as desired without affecting the stability of the iron (II) complex.

The complexation of the iron (II) complex of phosphonic acid takes place according to the invention by adding alkali or alkaline earths to a pH of 8-10 Iron complex stable against any pH change.

The polycarboxylic acid solutions or phosphonic acid solutions prepared in this way can be added to the wash water with the desired pH value of the wash water.

With simultaneous SO ₂ and NO _x washing, the results obtained are generally unsatisfactory.

In many cases, the ratio of SO ₂ to NO _{x is} not designed so that there is a good reaction in the direction of NO _x separation.

In order to carry out the NO _x separation regardless of the SO ₂ content in the raw gas, it is proposed according to the invention that alkali metal or alkaline earth metal bisulphite, for example calcium or sodium bisulphite, is produced in a first washing stage, preferably using a weakly acidic short-term washing process it etc., this being educated

Bisulfite is added to the NO _x wash alone or to the simultaneous washing stage, which simultaneously washes SO ₂ and NO _x , with polycarboxylic acid (including EDTA) and / or phosphonic acid being added to this washing stage.

Instead of self-generation of alkaline earth or alkali bisulfite, solid sulfite salts or waste sulfite liquors are used simultaneously SO ₂ - and NO _x or single NO _x washing as external supplies application.

The above-mentioned components of the second washing stage are optionally used, or the second washing stage is used as a pure SO ₂ washing stage, the bisulfite from the first washing stage being fed to the third washing stage after the SO ₂ washing and polycarboxylic acid and / or phosphonic acid in the third washing stage (Including EDTA) NO _x wash is used.

With the simultaneous washing out of SO ₂ and NO _x from the flue gases of incineration plants, the washing out of SO ₂ with an efficiency greater than 90% is not a problem, but the washing out of NO _x of greater than 70% is generally not feasible, but only below very specific conditions, ie the molar ratio of SO ₂ to NO _x must be greater than 2: 1.

In order to achieve especially in flue gases which have a low SO ₂ value, still very high NO _x -Auswaschgrade, the invention proposes to operate a two-stage washing process as follows:

In the first stage, SO _{2 is} preferred with polycarboxylic acid and Lime additive washed, e.g. lime in the form of limestone or fine white lime or dolomite.

In the second washing stage, the exhaust gas, which is greatly reduced by SO ₂ , is washed with an alkali metal hydroxide solution, preferably sodium hydroxide solution, this alkali metal hydroxide solution or sodium hydroxide solution being mixed with polycarboxylic acid (including EDTA). Here, the NO is converted to nitrogen, that is to say elementally with the clean gas, and the remainder SO ₂ , and in order to simultaneously obtain the iron as divalent iron in the complex, since there are too few SO ₂ molecules a reducing agent, such as ascorbic acid, is also added.

In order to prevent an accumulation of sodium sulfate or sodium sulfite fractions, a partial amount of the washing solution of the second washing circuit is transferred to the first washing circuit in order to convert the alkali sulfates or sulfites into gigs here.

In order to achieve a high NO _x separation, particularly in the case of exhaust gases behind combustion plants which have a smaller SO ₂ / NO _x molar ratio of 2: 1, a two-stage process is proposed according to the invention, the first Washing stage has the task of SO ₂ separation and does not include the main feature of simultaneous No _x separation, and that in the second washing step the main feature is NO _x removal, in which SO ₂ is inevitably washed out to a certain extent, whereby Both washing stages work with separate washing liquid circuits and the first washing liquid circuit is operated with carboxylic acid without polycarboxylic acid (EDTA) and in the second washing stage polycarboxylic acid (EDTA) or diphosphonic acids containing divalent iron complex are added, with the simultaneous addition of oxygen-binding substances such as salts the sulfurous acid and / or reducing agents, such as ascorbic acid.

The washing liquid circuit of the second washing stage has a washing liquid circulation tank and a settling tank, an amount of washing liquid enriched with polycarboxylic acids (EDTA) and iron (II) salts or diphosphonic acids and reducing agents, such as ascorbic acid, being added to the washing liquid circulation tank and a portion of the washing liquid circulation tank being fed to the settling tank. in which additional calcium hydroxide or calcium oxide is added and the CaSO ₃ thus precipitated or CaSO _{4 is transported} to a dewatering station and from here the filtrate is fed to the washing liquid circulation container and the solid in the washing liquid container to the first washing stage. The temperature for washing stage 2 is preferably 50 ° C.

It is known that EDTA solutions for NO _x reduction which contain iron-II complexes are not stable.

It cannot be prevented that iron-II oxidizes to iron-III and consequently the NO _x absorption in the washing process is greatly reduced.

It has been found that the used solution can be activated and stabilized by adding alkali sulfite and / or another reducing agent, preferably ascorbic acid.

Sodium dithionite is also added to the reducing agent for stabilization and reactivation.

It is known to wash SO ₂ using limestone, hydrated lime or NaOH It is also known to add sodium sulfite in a two-stage system and additional reducing agents to release the N ₂ .

This process is only stable and functional if the iron in the polycarboxylic acid-chelate complex is retained as divalent iron.

It was found that not only sodium sulfite plus another reducing agent is required to keep the divalent iron stable in the washing solution, but instead only sodium dithionite instead of this additive combination.

It is further proposed according to the invention to use lotrieslacetic acid (NTA) and its salts instead of EDTA nitrite, which is biodegradable and thus the amounts of water to be released can be passed on to the receiving water in a simple manner and without harm.

It is known to separate SO ₂ and NO _x in a washing solution in a single scrubber or in multi-stage washers in which the washing solution is enriched with limestone, fine white lime, EDTA and / or polycarboxylic acid. It is desirable that in the simultaneous SO ₂ and NO _x separation stage the end product is a usable or depositable product.

The best known product is end product CaSO ₄ .

The difficulty in separating SO ₂ and NO _x in one stage is due to the fact that CaSO ₄ has to be produced due to the SO ₂ washing and the necessary oxidation, but on the other hand a reducing property would have to be present in the same washing device in order to achieve this Reduce iron chelates via the deposited NO and maintain the iron II.

Since this does not run harmoniously with one another, there are high oxidation rates of iron-II to iron-III and thus inactivation of the complex. In order to reactivate the complex fraction, it is proposed according to the invention to treat a partial flow from the washing solution, preferably the filtrate from the dewatering of the solids in a special container with reducing substances such as ascorbic acid, sodium, pyrosulfite, sodium dithionite, etc., in order to treat a specific one The residence time then feed the reactivated additives to the washing process. According to the invention it is further proposed that a liquid, which is used for washing with additives such as limestone or hydrated lime and EDTA or NTA and / or polycarboxylic acids and CaSO ₄ or CaSO ₃ , as a partial amount via a solid-liquid separation stage with release of the inactive liquid in a reaction container in which reducing additives and / or metallic iron such as iron powder, iron filings and other forms of formation of metallic iron are added, the reducing additives being added in the acid phase, preferably pH value less than 6, is activated by means of a pump and the washing water supply is returned via an inlet level and / or is made available again for the washing process directly via pairs of nozzles.

Sodium bisulfite, ascorbic acid, sodium dithionite and metallic iron and similar reducing agents are preferably used as reducing agents.

A portion of the filtrate water is transferred to the boiler's firing chamber for environmentally friendly destruction before it is activated. A portion of the water in the filtrate water is used as a fuel for coal Sprayed into the boiler.

In order to obtain the highest possible efficiency for SO ₂ and NO _x separation in a multi-stage washing device, it is proposed according to the invention that in the first washing stage the washing liquid is circulated with a pH value between pH 3 and pH 4 via an iron reactor and in the subsequent one , second scrubber part, the circulating liquid has a pH greater than pH 5 and sodium dithionite is added as an inoculant to the washing circuit of the washing stage in order to obtain the iron (II) chelate via the redox potential formed in both washing stages.

It is known that the redox potential in the simultaneous SO ₂ and NO _x deposition depending on the molar ratio between SO ₂ and NO _x by adding reducing agents such as

Pyrosulfite or sodium dithionite, ascorbic acid, i.e. can be produced chemically by reducing agents.

According to the invention, it was found that, in addition to the chemical route, an electrochemical route and / or is to be used for the expedient design of the redox potential, in order thus to the electrolysis to save the chemical reducing agents in whole or in part.

It is known to wash out SO ₂ and NO _x simultaneously with single-stage washers »However, the success is not satisfactory.

According to the invention, it is therefore proposed that the single-stage scrubber, regardless of whether it is designed as a countercurrent or cocurrent scrubber, acidically divide the zone that is contacted first with the SO ₂ so that the molar ratio of SO ₂ to No in the NO _x - Driving as high as possible in favor of the SO ₂ .

In the part connected afterwards, the washing water is expediently added to a higher pH, for example greater than pH 5, in order to wash out the SO ₂ and traces of NO _x to the prescribed value.

It is known that for simultaneous SO ₂ and NO _x removal, the SO ₂ molecular weight must predominate over the NO _x molecular weight.

Often, especially in melting chamber boilers this need not exist in the prior art.

According to the teaching of the invention, a method is proposed with which SO ₂ and NO _x can be washed simultaneously in one washing stage in such a way that the SO _{2 is converted} to CaSO ₄ and the NO _{x is} reduced to N ₂ and the released oxygen accumulates SO ₂ accumulates.

According to the invention this is achieved in that the flue gas is fed to a single-stage countercurrent washer and in one or more nozzle levels the flue gas is first pressed against a washing liquid with a positive redox potential, this washing water being mixed with additives such as limestone or hydrated lime and preferably for better solubility Carboxylic acid, with which additive is added to the washing liquid and the last nozzle level consists of one and / or several nozzles or nozzle levels, and behind the first nozzle level arrangement in the last nozzle level a washing liquid with negative redox potential is dispensed, which is obtained by adding dithionite and / or other reducing agents or. via a reduction vessel, which is filled with iron plates, for example. In addition, dithionite can additionally be added as a reducing agent by electrochemical reduction (electrolysis), so that SO ₂ and NO _{x are} simultaneously deposited and oxidized in the laundry sump via the oxidation device and nitrogen N _{2 is transferred} to the chimney and / or cooling tower via the droplet separator arrangement according to the invention and calcium sulfate dihydrate is deposited.

The reducing wet processes for the separation of NO require the use of reducing chemicals, e.g. metallic iron, hydrogen sulfite or sodium dithionite. These chemicals introduce fiber into the laundry cycle, which has to be removed again. Chloride from the fuels is introduced through the flue gas, which must also be removed.

Since the discharged solutions contain complexing agents such as ethylenediamininotetraacetate (EDTA) or nitrilotriacetate (NTA) as well as a number of transition metals, a wastewater treatment facility must be used to treat the wastewater to the limits prescribed by the authorities. In the case of catalytic nitrogen oxy reduction (with hydrocarbons or ammonia), valuable feedstocks such as catalysts and hydrocarbons or ammonia are required.

The catalysts only work effectively in a narrow temperature range of approx. 320 to 380 ° C. They are subject to wear from dust. They can be poisoned by metals like lead. In catalysts behind power plant furnaces, sticky caking can arise from SO ₂ , H ₂ O and NH ₃ and fly ash, which mainly consist of NH ₄ H _S O ₄ . This caking can stick internals in the flue gas flow, such as air preheaters, catalysts and electrostatic precipitators, and lead to malfunctions. The catalytic converters are additional systems with not a small pressure drop, the installation of which, particularly when retrofitting existing power plants, leads to major technical, spatial and economic disadvantages. Eliminating spent transition metal catalysts and fly ash containing ammonium salts will pose further difficulties. If ammonia gets into the washing solution of flue gas desulphurization plants with gypsum as the end product, cleaning the gypsum and waste water from ammonium may be necessary Make connections because ammonium ions have a toxic effect on fish, for example, and ammonia can escape from gypsum products and can be perceived as a nuisance. Last but not least, ammonia is a dangerous substance that can only be transported, loaded and stored with great effort in terms of safety precautions.

The purpose of the present invention is to electrochemically reduce nitrogen monoxide, which makes up the majority of the nitrogen oxides in exhaust gases, by means of a potentiostatic process. This reduction takes place in the aqueous phase, the solubility of the nitrogen monoxide being decisively improved in a known manner by complexing, for example with divalent iron. By setting the redox potential required for the reduction with electrical current instead of reducing chemicals, the washing cycle required for exhaust gas treatment is kept low and not provided with ballast ions, such as sodium or sulfur compounds, which would have to be removed from the cycle and through then a necessary wastewater treatment or off Divorce as plaster can cause additional costs. Due to the advantage according to the invention of carrying out the reduction of nitrogen monoxide in the same plants as are already operated or intended predominantly for flue gas desulphurization with, for example, gypsum as the end product, plants for separate nitrogen oxide reduction are largely eliminated. There is no new pressure loss and no hazardous substances are required.

The invention follows the guiding principle of using existing or planned flue gas treatment devices for reducing sulfur oxides in the purification of the exhaust gases from combustion plants from nitrogen monoxide, so that no further apparatuses which cause additional pressure loss on the exhaust side are required. Furthermore, the washing cycle should be closed as far as possible, in any case no further fiber should be added as a chemical reducing agent, which in turn would pose further problems as a result. In addition to nitrogen monoxide, other flue gas constituents such as chlorides and soluble transition elements are to be reduced.

According to the invention, the redox potential required for the reduction from nitrogen monoxide to elemental nitrogen with a potentiometric device. At the cathode made of carbon, for example, the two electrons required to reduce NO are made available. Hydrogen sulfite formed from the SO _{2 of} the exhaust gases can serve as a reducing substance, which becomes dithionite, which transfers electrons to NO complexly bound to, for example, divalent iron and is itself oxidized to sulfate and finally removed as gypsum.

On the unassailable anode, e.g. consists of titanium, the chloride from the flue gas is oxidized to elemental chlorine in the solution, which is thus removed from the washing cycle and e.g. can be left to the chemical industry for use.

Dissolved transition metal ions contained in the washing solution are reduced at the cathode and can thus also be removed from the washing solution. If necessary, the deposited metals can be processed.

The setting of the redox potential can be in the sump of the washer or advantageously in a special flow vessel from which the reducing, regenerated washing solution is fed to the usual spray nozzles.

To separate the reducing and oxidizing areas around the cathodes and anodes, they must be separated by membranes to prevent accidental mixing, which can be semi-permeable or only anion or cation permeable.

The technical and technical-economic effects of the solution according to the invention lie in the extensive avoidance of additional apparatus, the non-use of dangerous or expensive feedstocks such as hydrocarbons, ammonia and catalysts, the avoidance of a further pressure loss on the exhaust gas side and the short-term retrofitting and commissioning at power plants. The additives required by the electrochemical reduction are based on iron salts and complexing agents such as EDTA, NTA and / or formic acid, a potentiostatic circuit with cathode and anode cells separated by membranes, a collecting device for elemental chlorine and possibly a processing device for cathodically deposited metals. The catalytic reduction processes that are mainly discussed today lead to high ones Investment costs, malfunctions due to sticky caking, restrictions on the exhaust gas temperature and high operating costs due to additional pressure loss, catalyst wear and reducing agent consumption.

As previously stated, the raw gas can first be fed to a direct current scrubbing stage, the scrubbing liquid from the course of the first scrubbing stage being adjusted via an iron reactor with a minus redox potential and first being contacted with the raw gas.

The second wash nozzle level is fed with a pump with a redox potential that is weaker than the top nozzle level. The counterflow washer, which is operated more alkaline, runs with the pump in its own circuit with the addition of sodium dithionite and other reducing agents from a container.

According to the invention, the simultaneous SO ₂ and NO _x separator process is improved by further process steps in that the DC scrubber, into which the raw gas is first introduced, is washed with a washing liquid in the first nozzle level is operated, which is first contacted to the gas stream via an iron reactor charged with negative redox potential, and then in the downstream nozzle levels the bound NO - NO _{2 is} split off from the area of the nozzles to form elemental nitrogen.

A washing liquid is supplied to the iron reactor, which is set to a negative redox potential by reducing agents from the container.

The nozzle level, which is used last in the washing process, is acted upon by a washing liquid which has a negative redox potential, which is preferably controlled by reducing agents from the container and / or from the electrolysis station.

The nozzle levels in the counterflow washer and the nozzles in the cocurrent washer have a smaller minus redox potential than the upper nozzle levels in the countercurrent washer and in the cocurrent washer.

The redox potential is set via the iron reactor and optional use of reducing agents such as sodium dithionite and / or electrolysis.

A method has already been described above in which, in order to adjust the redox potential and to stabilize the iron chelate solution, in addition to the additives added, electrolysis is switched on in the process instead of sodium dithionite.

According to the invention, this process is controlled such that if the SO ₂ content is not high enough in relation to the NO _x content, pyrosulfite for the difference between SO ₂ and NO _{x is} metered into the washing process with simultaneous addition of limestone and / or hydrated lime and addition of NTA or EDTA, and to control the redox potential, an iron reactor is switched on in the washing liquid circuit, with an acid, preferably formic acid, being added to stabilize the redox potential while improving the solubility of limestone and / or hydrated lime and simultaneously stabilizing the iron chelate, and for faster control of the redox potential in the amount of liquid, a corresponding amount of liquid is passed through electrolysis. With this measure, the process can be adapted very quickly to the task.

Exemplary embodiments of the invention are explained in more detail with reference to the drawings, which show:

1 shows the deposition process of a first embodiment in a schematic representation, FIG. 2 shows a variant of the process sequence according to FIG. 1, FIG. 3 shows the deposition process of a second embodiment in a schematic representation, FIG. 4 shows the deposition process of a third embodiment in a schematic representation, FIG. 5 shows the deposition process in a schematic representation a fourth embodiment, FIG. 6 shows a schematic illustration of the deposition process of a fifth embodiment, FIG. 7 shows a schematic illustration of the deposition process of a sixth embodiment, FIG. 8 shows a schematic illustration of the deposition process of a seventh embodiment, FIG. 9 shows a schematic illustration of the deposition process of an eighth embodiment, FIG. 10 shows a schematic representation of the deposition process of a ninth embodiment,

11 shows a schematic representation of a modification of the method according to FIGS. 10 and

Figure 12 is a schematic representation of the deposition process of a tenth embodiment.

In FIG. 1, 1 denotes the raw gas inlet, 2 the NO _x -HCl wash, 3 the wash water reservoir with the additives EDTA or phosphonic acid, 4 the wash water cycle NO _x or NO _x + HCl wash, 5 the SO ₂ -Laundry.

In FIG. 2, 1 denotes the raw gas inlet, 2 the HCl wash, 3 the wash water reservoir, 4 the wash water circuit for prewashing, for example HCl wash, 5 the NO _x wash, 6 the wash water reservoir with the EDTA additives and / or phosphonic acid, with 7 the wash water circuit, with 8 the SO ₂ wash.

Furthermore, according to the invention, instead of EDTA in the main wash circuit, the phosphonic acid can also be used without prewashing in a flue gas desulfurization, in particular when a coal with a low chloride content is to be burned.

In FIG. 3, 11 denotes the raw gas, 12 denotes the so-called sulfite scrubber, which is preferably run slightly acidic and produces with a relatively short scrubbing section (Ca (HSO ₃ ) ₂ ).

This is followed by the SO ₂ washer at 13.

The bisulfite formed is used in a subsequent washing stage for preferably simultaneous washing of SO ₂ or NO _x or only for washing out NO _x ; with 14 the NO _x scrubber, with 15 the sulfite basin, which is connected downstream of the sulfite separator 12 and transfers the sulfite formed to the NO _x wash water reservoir 16, from where it is fed to the NO _x scrubber 14 by means of pumps, to be used afterwards - oxidized to CaSO ₄ -; the SO ₂ scrubber sump 13.

The bisulfite formed from the washing stage 12 can also be used for simultaneous SO ₂ and NO _x washing in the scrubber 13 and additionally in the scrubber 14. Nevertheless, the inventive idea of self-bisulfite production for the scrubbing of NO _{x is} retained, and the further inventive idea of NO _x leaching by means of polycarboxylic acids with the use of bisulfite by in-house production or external purchases is also retained.

In FIG. 4, the washing stage 1 is designated with 21, the washing stage 2 with 22, with 23 the washing liquid circulation container, with 24 the so-called gypsum station for dewatering the discharged SaSO ₄ .2H ₂ O; with 25 of the washing liquid circulation container for washing stage 2, the washing liquid being prepared with limestone or hydrated lime or sodium hydroxide solution + iron (II) salt + Polycarboxylic acid (EDTA) or diphosphonic acid and reducing agents such as ascorbic acid; the gravity separator for precipitating CaSO ₃ · ½ H ₂ O and CaSO ₄ · 2 H ₂ O, the CaSO ₃ / CaSO ₄ dewatering station, the filtrate being transferred to the container 25 and the solids content 8 in the washing liquid circulation container 23, and by this is where the not yet oxidized CaSO ₃ becomes. ½ H ₂ O with the gypsum crystals CaSO ₄ · 2 H ₂ O inevitably introduced into the washing process of washing stage 1 and totally converted to CaSO ₄ · 2 H ₂ O via the downstream oxidizer. Carbon and polycarboxylic acid and lime in the form of limestone, hydrated lime or dolomite, preferably fine white lime, are added to the first washing cycle stage and SO _{2 is} washed out primarily. The SO ₂ leaching can be operated more or less intensively with regard to the second NO _x washing stage.

In the second scrubbing stage, the exhaust gas reduced by SO ₂ or less is used according to the invention at 30 using a wash water solution, the sodium hydroxide solution or calcium hydroxide or limestone or magnesium hydroxide or dolomite as well as polycarboxylic acid (EDTA), diphosphonic acids + iron (II) salt and reducing agents such as salts of sulfurous acid or ascorbic acid are added NO _x largely exempted.

Portions from the container 25 are fed to the container 26, and here at 31 with additional addition of hydrated lime or calcium oxide (CaO) calcium sulfite (CaSO ₃ ) or calcium sulfate (CaSO ₄ ) is precipitated and thickened.

This applies in particular when using sodium hydroxide solution and magnesium hydroxide in container 25.

The concentrated solids are washed from the container 26 via centrifuges or drum vacuum filters and dewatered to a few percent water.

The filtrate is fed to the container 25 and the solid from 28 to the container 23 and actively participates in the SO ₂ washing of washing stage 1 and is in the laundry sump of the laundry schers 21 oxidized and discharged via the gypsum drainage 24 to usable gypsum.

According to the invention, the EDTA of the simultaneous SO ₂ and NO _x washing stage 2 is not passed to washing stage 1, where SO _{2 is} washed and converted into gypsum at the same time, since here the EDTA a) with the amount of residual gypsum and with the amount of water to be dispensed b ) from washing stage 1 to prevent the CaCl ₂ concentration.

With a 600 MW block, up to 30 m ³

Wash water are discharged from the wash water circuit of wash stage 1 in order to obtain a calcium chloride enrichment which is not too high in wash stage 1.

No water is preferably released from the second washing stage. The solid is washed and with a residual moisture of e.g. less than 10% from the gypsum dewatering station 27 introduced into the washing circuit 23.

The container 25 contains polycarboxylic acids according to the invention (EDTA) or diphosphonic acids, which contain divalent iron, complex-bound, and the NO _x scrubbing is carried out at a temperature, preferably less than 50 ° C., and a pH of preferably 3.5 to 10.5.

Since the SO ₂ / NO _x molar ratio in the exhaust gas from the second scrubbing stage is too low to obtain the iron-II complex, oxygen-binding substances, such as salts of the sulfurous acid or reducing agents such as ascorbic acid, are additionally added to the scrubbing solution.

In FIG. 5, the raw gas containing SO ₂ and NO _x is designated with 41, with 42 the scrubber device, with 43 the wash water sump, with 44 the circulation pump to the nozzle levels 45, and with 46 the outlet from the circulation water tank 43

Drainage station 47. A portion of the water is transferred from the drainage station 47 to the regeneration tank 48.

The reducing agents 49 for activating the washing liquid are added in this.

The pump 50 supplies the activated washing liquid to the washing liquid container 53 via an inlet 51; at 52 a pump, at 53 the hot gas area.

The invention is not restricted to the embodiments described and illustrated in detail above, but numerous modifications are possible without, however, deviating from the basic idea that the washing liquid after contact with SO ₂ and NO _x via the outlet of the washing liquid container 43 of a solid liquid Separation stage 47, which supplies the separated liquid washing liquid, which is inactive, to the activator container 48, in which, by adding reducing agents at 49, preferably ascorbic acid, sodium bisulfite, sodium dithionite or similar reducing agents by means of a pump 50, then activates the washing liquid container 43 or 51 again is transferred, and / or at 45 can also be sprayed directly into a nozzle level again, and a part of the filtrate water, which is led from 47 to 48, is transferred via a pump 52 into the hot gas area 53 of the boiler system for thermal destruction is hrt or the starting material is sprayed coal.

In FIG. 6, the raw gas containing SO ₂ and NO _x is designated by 61, with 62 the washer device, with 63 the wash water sump, with 64 the circulation pump to the nozzle levels 65, with 66 the outlet from the circulation water tank 63 to the dewatering station 67. A part of the water quantity is transferred from the dewatering station 67 to the regeneration tank 68. This is where 69 the reducing agent for activating the washing liquid is added, the pump 70 feeds the activated washing liquid to the washing liquid container 63 via an inlet 71, with 72 a pump, with 73 the hot gas area.

The invention is not limited to the embodiments described and illustrated in detail above, but numerous modifications are possible without, however, deviating from the basic idea that the washing liquid after contact with SO ₂ and NO _x via the outlet of the washing liquid container 63 of a solid-liquid separation stage 67, which feeds the separated liquid washing liquid, which is inactive, to the activator container 68, in the ascorbic acid, preferably by adding reducing agents at 69, Sodium sulfite, sodium dithionite and / or metallic iron in the form of iron powder, iron shavings or a similar form of training - and similar reducing agents are then activated again by means of a pump 70 and passed back to the washing liquid container 63 or 71 and / or at 65 can additionally be sprayed directly into a nozzle level, and a subset of the filtrate water, which is conducted from 67 to 68, is transferred via a pump 72 into the hot gas area 73 of the boiler system for thermal destruction or the coal is sprayed on.

In FIG. 7, 81 is the so-called pre-scrubber, which is used for chlorine separation in chlorine-rich coal, 82 is the washing stage, which is acidic, preferably in the range between pH 3 and pH 4, and 83 is an iron reactor via which the liquid is discharged the acidic washing cycle is promoted, with 84 the alkaline washing tank in which the washing liquid with a pH value of greater than pH 5 is circulated, with 85 a droplet separator behind the second washing stage 84, with 86 a decanter which contains part of the washing liquid out the second washing circuit stage 84 cleans to the

Add droplet separators for rinsing, with 87 the washing liquid dispenser for gypsum dewatering (centrifuge or belt filter), with 88 a circulation pump for the washing circuit 82, with 89 the washing liquid pump for the washer 84, second washing stage for the circuit with a pH value greater than pH 5, whereby a partial amount is passed over the decanter 86 in order to discharge the solid (gypsum), with 90 the limestone or hydrated lime mixing container, with 91 the container for sodium dithionite, ascorbic acid or an equivalent reducing agent.

This process technology ensures that the necessary redox potential is generated in the first washing stage via the iron reactor 83 in order to obtain the iron (II) chelate in the washing solution at a low pH value 3-4. In the second washing stage, the addition of sodium dithionite in the washing liquid according to the invention at a pH greater than 5 compared to the first washing stage of less than 4 also produces a redox potential, so that the iron (II) chelate is retained and thus a correspondingly high simultaneous SO ₂ and NO _x separation is guaranteed.

In FIG. 8, 101 denotes a washer with three nozzle inserts A, B, C, which are fed by the container 102 in the upper region and three further nozzles D, E, F in the region 103, which are fed with a washing liquid from the container 104 become. The swamp is designated 105.

Lime hydrate or limestone is preferably added to the container for the upper nozzle level as well as for the lower nozzle level for different pH adjustment. However, the pH is kept above preferably less than pH 4 and the subsequent nozzles are preferably kept above pH 5.

It is further proposed according to the invention to make the dwell time in the downstream laundry sump so long that it is at least 10 minutes as a minimum in order to set the redox potential to greater than minus 100 millivolts.

In FIG. 9, 111 denotes the flue gas inlet, 112 and

113 the nozzle levels I and II, with 114 the nozzle level III, with 115 the CaCO ₃ dosing and mixing device for the washing water feed for the nozzle levels I and II with dissolved calcium carbonate or lime hydrate. Instead of CaCO ₃ or hydrated lime, alkali metal such as sodium hydroxide solution can also be used in the container 115.

The scrubber sump is shown at 116, and an air injection at 117, which is generated by a rotary blower e.g. is conveyed into the laundry sump.

With 118 the air blower is shown, with 119 a container with the addition of reducing agents, such as dithionite, is shown, with 120 the addition of formic acid, with 121 a reduction vessel with, for example, iron plates and the like or electrochemical reduction device (electrolysis), with 122 one Pump for supplying the washing liquid with reducing agents and a negative reduction potential into the nozzle plane 114, which lastly counteracts the raw gas flow, with 123 the pump, which supplies the washing water with a positive redox potential from the washing sump to the reducing vessel 121, 124 shows a pump which operates the nozzle levels II and III, which promotes the washing liquid enriched with positive redox potential and limestone and / or calhydrate in the circuit.

At 125 a nebulizer device is shown by droplet separation behind the washer and at 126 the gypsum discharge is shown.

This arrangement according to the invention ensures that SO ₂ and nitrogen oxide are simultaneously separated from the flue gas with the formation of calcium sulfate and released nitrogen.

The invention is not limited to the above-described in detail, but only a few modifications are possible without, however, deviating from the basic idea that the first nozzles are loaded with a washing liquid in a counterflow washer Limestone or dissolved hydrated lime and water, preferably carboxylic acid is used for better dissolution of the additive, with a washing liquid which has a minus redox potential, which is preferably obtained by adding reducing agents such as dithionite, being injected in the last nozzle level opposite to the first nozzle levels. or via a reduction vessel conducts, which is equipped with iron plates, is set. In addition, the desired redox potential can be set by electrochemical reduction (electrolysis), so that the washing liquid is fed into the scrubber flow area of the scrubber via a pump 122 at the nozzle level 114, ie the latter nozzle level.

At the same time, air is added in the scrubber sump, so that oxidation of CaSO ₃ to CaSO4 takes place in the lower part of the scrubber sump and a portion of the wash water with a positive reduction potential is pumped into the reduction device 121 by means of a pump 123 for setting the negative reduction potential.

The gypsum discharge is provided at 126 via centrifuges and the like.

In FIG. 10, the raw gas is denoted by 131, the scrubber by 132, the washing suspension by 133, the scrubber sump by 134, the cathode by 135, at 136 the anode with electrochemical cell and

Membranes 140, with 137 the nozzles, with 138 the chlorine gas outlet, with 139 a pump, with 140 the membranes, with 141 the sulfate separation, with 142 the clean gas.

In FIG. 11, the raw gas is denoted by 151, the clean gas by 152, the scrubber by 153, the pump by 154, the cathode by 155, the anode by 156, the nozzles by 157, the chlorine gas by 158, the scrubber sump by 159, with 160 the membranes, with 161 the gypsum for filtration, with 162 the fresh limestone suspension.

10 and 11, the raw gas 131, 151, which contains NO, NO ₂ , SO ₂ , SO ₃ , H ₂ O, N ₂ , O ₃ , CO, CO ₂ , as well as dusts, a washer, 132, 153, which is used in cocurrent or countercurrent treated with a washing solution 153. The examples are shown as countercurrent washing in FIGS. 10 and 11. The washing solution 153 contains divalent iron, which is present as a hydrated ion, as a sulfate complex, as a chloride complex and, depending on the complexing agent, for example as an EDTA or NTA complex. The divalent iron is used in a known manner to complexly bind the sparingly water-soluble NO molecule and to convert it into the aqueous phase.

The trivalent iron, which is also present in equilibrium, is complexed according to the invention by formic acid and is thus prevented from precipitating out as iron III hydroxide; only then does the electrochemical process run stably.

At pH ranges from 3 to 6 and redox potentials from

- 150 m V to 250 m V compared to the normal hydrogen electrode, less than 20% of the total iron is present as trivalent iron. To separate the sulfates formed by oxidation, cations, predominantly calcium ions, are added to the wash suspension in a known manner.

Washing suspension 133 is drawn off from the laundry sump 134 by a pump 139 and fed to the gypsum filtration (sulfate separation 136, 156).

A partial stream enters an electrochemical cell in which complex-bound NO is converted to nitrogen and water at the cathode 135, 155. Furthermore, the

Cathode 135, 155 trivalent iron reduced to divalent, dissolved transition metals such as Cu ⁺⁺ and Cd ²⁺

deposited cathodically and hydrogen sulfite converted to dithionate.

Chlorine gas is produced at the anode 136, 156, which is drawn off, dried and compressed in a known manner from the anode space, which is provided with semipermeable membranes 140, 160.

Waste water can be removed by suitable process control achieve a free driving style, since the chloride ions that are usually required to be discharged are discharged as chlorine gas.

In the flue gas scrubbing, nitrite ions and nitrate ions formed from NO ₂ can preferably be discharged from the main stream via anion exchange membranes. Nitrite can easily be oxidized to nitrate and extracted, for example, as nitric acid.

The use is not limited to the power plant sector, but the reduction of exhaust gas constituents can also be achieved in thermal power plants, various industrial lighting systems as well as mobile systems such as portable power generators, ships, diesel locomotives and motor vehicles.

In FIG. 12, the so-called pre-scrubber, which is used for chlorine separation in chlorine-rich coal, is denoted by 171, the washing stage, which is operated acidically, preferably in the range between pH 3 and pH 4, and 172, an iron reactor via which the liquid from the acidic Washing cycle is promoted, the second washing stage, which is preferably operated more alkaline, ie with a slightly higher pH value greater than 5, than the washing stage one, which is designated 172, a droplet separator behind the second washing stage 174, a decanter which removes part of the washing liquid from the second Wash circuit stage 174 cleans it in order to feed it to the droplet separator for rinsing, dispensing the washing liquid for gypsum dewatering (centrifuge or belt filter), a circulation pump for the washing circuit 172, the washing liquid pump for the washer 174, second washing stage for the circuit with a pH greater than pH 5, where a partial amount is passed over the decanter 176 to discharge the solid (gypsum), the limestone or hydrated lime mixing container, the container for sodium dithionite, ascorbic acid or an equivalent reducing agent, the addition of sodium dithionite or

Ascorbic acid or an equivalent reducing agent which is added to the washing liquid upstream of the iron reactor 173, this addition preferably only taking place for the start-up phase until the reactor 173 maintains the predetermined redox potential without reducing agent. Furthermore, a partial amount of the pump 179 is added to the area of the pump 184.

With 185 the amount of washing liquid is designated.

A portion of the washing liquid from the limestone mixing container 180 is added to an electrolysis station 183.

From the electrolysis station 183, a washing liquid 186 processed with a corresponding negative redox potential is fed into the area of the iron reactor 173 - line 187 - and / or into the area of the counterflow washer 174 - designated 188.

It is entirely possible that partial quantities can also be transferred from the container 181, which is filled with reducing agents, to the electrolysis station 183, so that a very rapid reaction for setting the reduction potential can be achieved by reducing agent and electrolysis and via a further pump 189 the concentrated negative redox potential in the washing liquid is supplied to the nozzle plane 190. This nozzle level is the last one in the washing system in order to add the not yet separated NO _x and SO ₂ to the washing liquid in order to feed it to the underlying nozzle level 191 and release elemental nitrogen N ₂ here.

The above-described arrangements according to the invention ensure the greatest possible simultaneous excretion of SO ₂ and NO _x .

The nozzle level in the DC scrubber is shown at 192. At 193 the downstream nozzle levels.

Claims

PATENT CLAIMS:

1.Procedure for the separation of nitrogen oxides and sulfur oxides and possibly other pollutants from the flue gases from irrigation plants, preferably from power plant boilers fed with fossil fuels, the nitrogen oxides being reduced to elemental nitrogen and the sulfur oxides and possibly other pollutants being eliminated by means of a washing process that the washing liquid of a desulfurization plant ethylene diamine tetra acetic acid (EDTA) C ₁₀ H ₁₆ O ₈ N ₂ and a mono- and / or polybasic carboxylic acid, preferably formic acid, is added together with limestone, white fine lime or their derivatives.

2.Procedure for the separation of nitrogen oxides and sulfur oxides and possibly other pollutants from the flue gases of combustion plants, preferably from power plant boilers fed with fossil fuels, the nitrogen oxides being reduced to elemental nitrogen and the sulfur oxides and possibly other pollutants being eliminated by means of a washing process, in particular after Claim 1, characterized in that phosphonic acid or salts of phosphonic acid are added to the washing liquid.

3. The method according to claim 2, characterized in that EDTA plus phosphonic acid or salts of the phosphonic acid are added to the washing liquid.

4. The method according to claim 2 or 3, characterized in that the additions of EDTA and / or phosphonic acid or salts of phosphonic acid and iron-II-sulfate for NO _x separation in a separate washing stage with separate washing water circuit, but together before desulfurization with the hydrogen chloride chloride wash in an acidic range (pH 2.5 - 4.5).

5. The method according to claim 2 or one of the preceding, characterized in that the NO _x wash after the hydrogen chloride chloride wash, but before the sulfur oxide wash is carried out as a separate wash with its own acidic wash water circuit (pH 2.5 4.5) .

6. The method according to claim 2 or one of the preceding, characterized in that the NO _x separation in pH-controllable acidic wash solution (pH 2.5 - 4.5) to maintain the full amount of sulfur dioxide for the NO _x separation without binding Sulfur oxides on alkalis or alkaline earths Can be performed, which is enriched with phosphonic acid, its salts and / or EDTA.

7. The method according to claim 2 or one of the preceding, characterized in that by the separate NO _x wash without the addition of alkali or alkaline earth additives the binding value of EDTA or the phosphonic acid or its salts for the calcium ion is minimal, but fully for the complex binding of the iron II ion is available.

8. The method according to claim 2 or one of the preceding, characterized in that the washing circuit of the NO _x wash can be controlled via the pH and the evaporation so that at a max. Wash water evaporation and adjustment of a pH to pH 2.0, the EDTA or phosphonic acid or its salts can be recovered by precipitation.

9.Procedure for the separation of nitrogen oxides and sulfur oxides and possibly other pollutants as well as from the flue gases from combustion plants, preferably from power plant boilers fed with fossil fuels, the nitrogen oxides being reduced to elemental nitrogen and the sulfur oxides and possibly other pollutants being eliminated by means of a washing process, in particular according to claim 1, characterized in that polycarboxylic acids, (EDTA included) and phosphonic acids, preferably di-phosphonic acids, are complexed with iron (II) sulfate before being added to the wash water.

10. The method according to claim 9, characterized in that the polycarboxylic acid solutions (EDTA included) depending on the pH using mineral acids, preferably sulfuric acid, when using polycarboxylic acids with an alkaline character, the solutions of which are in the alkaline range, are acidified to the extent that at the same time in this mixing process iron chelate, preferably iron (II) sulfate, is added.

11. The method according to claim 9 or 10, characterized in that when using polycarboxylic acids (including EDTA) with an acidic character, the solutions of which are in the acidic range, these are then alkalized by means of the alkalis or alkaline earths, iron chelate being simultaneously present in this mixing process, preferably iron (II) sulfate is added.

12. The method according to claim 9 or one or preceding, characterized in that as an additive to the washing water, washing water with or without carboxylic acid being used, phosphonic acid mixed with iron (II) salts or complexing is used, the phosphonic acid and the iron being added from alkaline or alkaline earths to strongly alkaline, whereby the iron-II is bound in the phosphonic acid complex before it is added to the wash water.

13.Procedure for the separation of nitrogen oxides and sulfur oxides and possibly other pollutants from the flue gases of combustion plants, preferably from power plant boilers fed with fossil fuels, the nitrogen oxides being reduced to elemental nitrogen and the sulfur oxides and possibly other pollutants being eliminated by means of a washing process, in particular after Claim 1, characterized in that in a first washing stage (2), preferably using weakly acidic short-term washing processes, alkali or alkaline earth bisulfite is produced, for example calcium or sodium bisulfite, etc., the bisulfite formed in the NO _x wash ( 4) alone or also to the simultaneous washing stage (3), which washes SO ₂ and NO _x at the same time, polycarboxylic acid (EDTA included) and or phosphonic acid being added to this washing stage.

14. The method according to claim 13, characterized in that instead of self-generation of alkaline earth or alkali bisulfite solid sulfite salts or waste sulfite liquors for simultaneous SO ₂ - and NO _x or single NO _x washing are used as external supplies application .

15. The method according to claim 13 or 14, characterized in that optionally the second washing stage according to claim 14 is added or the second washing stage is used as a pure SO ₂ washing stage and the bisulfite from the first washing stage is fed to the third washing stage after the SO ₂ washing, with polycarboxylic acid and or phosphonic acid (EDTA included) for NO _x in the third washing stage Wash application.

16.Process for the separation of nitrogen oxides and sulfur oxides and possibly other pollutants from the flue gases of combustion plants, preferably from power plant boilers fed with fossil fuels, the nitrogen oxides being reduced to elemental nitrogen and the sulfur oxides and possibly other pollutants being eliminated by means of a washing process, in particular after Claim 1, characterized in that in the first washing stage SO _{2 is} washed with a washing liquid which has been mixed with limestone or white fine lime or dolomite and at the same time contains polycarboxylic acid, and thus the exhaust gas pre-cleaned of SO ₂ with a simultaneous low SO ₂ reduction of a second one Wash stage is passed, in which the exhaust gas is washed with alkali, preferably sodium hydroxide solution, which is mixed with polycarboxylic acid (EDTA included), for NO _x and residual SO ₂ reduction, while maintaining the Fe ₂ from the EDTA or Polycarbonate acid reducing agents, such as ascorbic acid, are added.

17. The method according to claim 16, characterized in that to prevent sodium sulfate and sulfite accumulations in the second washing stage, a subset of the washing water is transferred to the first washing stage in order to convert the amounts of sodium sulfate and sulfite into calcium sulfates or gypsum.

18.Procedure for the separation of nitrogen oxides and sulfur oxides and possibly other pollutants from the flue gases of combustion plants, preferably from power plant boilers fed with fossil fuels, the nitrogen oxides being reduced to elemental nitrogen and the sulfur oxides and possibly other pollutants being eliminated by means of a washing process, in particular after Claim 1, characterized in that the first washing stage has the function of SOp separation and does not contain the main feature of the simultaneous NO separation, and that in the second washing step the main feature is the NO _x separation, in which to a certain extent Part inevitably washed out SO ₂ , with both washing stages working with separate washing liquid circuits and the first washing liquid circuit with carboxylic acid without Polycarboxylic acid (EDTA) is operated and in the second washing stage polycarboxylic acid (EDTA) or diphosphonic acids, which contain divalent iron complex, are added, with the simultaneous addition of oxygen-binding substances, such as salts of the sulfurous acid and or reducing agents, such as, for example, ascorbic acid.

19. The method according to claim 18, characterized in that the washing liquid circuit of the second washing stage has a container (25) and a container (26), wherein in the container (25) an amount of washing liquid, enriched with polycarboxylic acids (EDTA) and iron-II salts or diphosphonic acids and reducing agents such as ascorbic acid, and a portion of the container (25) is fed to the settling container (26) by additionally adding calcium hydroxide or calcium oxide and transporting the precipitated CaSO ₃ or CaSO ₄ to the dewatering station (27) and from here the filtrate is fed to the container (25) and the solid to the container (23).

20. The method according to claim 18 or 19, characterized in that the temperature for the washing stage (2) is preferably less than 50 °.

21.Procedure for the separation of nitrogen oxides and sulfur oxides and possibly other pollutants from the flue gases of combustion plants, preferably from power plant boilers fed with fossil fuels, the nitrogen oxides being reduced to elemental nitrogen and the sulfur oxides and possibly other pollutants being eliminated by means of a washing process, in particular after Claim 1, characterized in that alkali bisulfite is added to the solution.

22. The method according to claim 21, characterized in that in addition to alkali bisulfite, a further reducing agent is added to the method.

23. The method according to claim 21 or 22, characterized in that ascorbic acid is used as the reducing agent.

24. The method according to claim 21 or one of the preceding, characterized in that the liquid alkali bisulfite plus a reducing agent, preferably ascorbic acid and / or sodium dithionite is added for stabilization and reactivation according to the task.

25. Process for the separation of nitrogen oxides and sulfur oxides and possibly other pollutants from the Flue gases from combustion plants, preferably from power plant boilers fed with fossil fuels, the nitrogen oxides being reduced to elemental nitrogen and the sulfur oxides and possibly other pollutants being eliminated by means of a washing process, in particular according to claim 1, characterized in that sodium dithionite is added to the washing liquid.

26. The method according to claim 25, characterized in that NTA and sodium dithionite is added to the washing liquid.

27.Procedure for the separation of nitrogen oxides and sulfur oxides and possibly other pollutants from the flue gases of combustion plants, preferably from power plant boilers fed with fossil fuels, the nitrogen oxides being reduced to elemental nitrogen and the sulfur oxides and possibly other pollutants being eliminated by means of a washing process, in particular after Claim 1, characterized in that a liquid which is used for washing with additives such as limestone or hydrated lime and EDTA or NTA and / or polycarboxylic acids and CaSO ₄ or CaSO ₃ , as a partial amount via a solid-liquid separation stage (47) Dispensing the inactive liquid (48) into a reaction container in which reducing additives are added are activated, is returned by means of a pump (50) and the washing water reservoir (43) is returned via an inlet level (51) and / or is made available again for the washing process via pairs of nozzles (45).

28. The method according to claim 27, characterized in that sodium bisulfite, ascorbic acid, sodium dithionite and similar reducing agents are preferably used as reducing agents.

29. The method according to claim 27 or 28, characterized in that a subset of the filtrate water, before it is activated, is transferred with the salt load into the furnace of the boiler for environmentally friendly destruction.

30. The method according to claim 27 or one of the preceding, characterized in that a portion of the filtrate water (52) is sprayed onto the fuel coal (53) before use in the boiler.

31. Process for the separation of nitrogen oxides and sulfur oxides and possibly other pollutants from the flue gases of combustion plants, preferably from power plant boilers fed with fossil fuels, the nitrogen oxides being reduced to elemental nitrogen and the sulfur oxides and any other pollutants are eliminated by means of a washing process, in particular according to claim 1, characterized in that a liquid containing the additives such as limestone or hydrated lime and EDTA or NTA and / or polycarboxylic acids and CaSO ₄ or CaSO ₃ Washing is used as a partial amount via a solid-liquid separation stage (67) with the inactive liquid (68) being released into a reaction container (69) in which reducing additives and / or metallic iron such as iron powder, iron filings and other forms of formation of metallic iron are added , the reducing additives being added in the acid phase, preferably pH value less than 6, is activated by means of a pump (70) and the washing water reservoir (63) is returned via an inlet level (71) and / or via pairs of nozzles (65) is made available again directly for the washing process.

32. The method according to claim 31, characterized in that sodium bisulfite, ascorbic acid, sodium dithionite and metallic iron and similar reducing agents are preferably used as reducing agents.

33. The method according to claim 31 or 32, characterized in that a portion of the filtrate water before it is activated, with the salt load in the furnace of the boiler environmentally friendly destruction.

34. The method according to claim 31 or one of the preceding, characterized in that a portion of the filtrate water (72) is sprayed onto the fuel coal (73) before use in the boiler.

35. Process for the separation of nitrogen oxides and sulfur oxides and possibly other pollutants from the flue gases from combustion plants, preferably from power plant boilers charged with fossil fuels, the nitrogen oxides being reduced to elemental nitrogen and the sulfur oxides and possibly other pollutants being eliminated by means of a washing process, in particular after Claim 1, characterized in that in the first washing stage (82) the washing liquid is circulated with a pH value between pH 3 and pH 4 via an iron reactor (83) and in the subsequent, second scrubber part the circulating liquid has a pH value greater Has pH 5 and sodium dithionite is added as an inoculant to the washing circuit of washing stage (84) in order to maintain the iron (II) chelate via the redox potential formed in both washing stages (83) and (84).

36. Process for the separation of nitrogen oxides and Sulfur oxides and possibly other pollutants from the flue gases of combustion plants, preferably from power plant boilers fed with fossil fuels, the nitrogen oxides being reduced to elemental nitrogen and the sulfur oxides and possibly other pollutants being eliminated by means of a washing process, in particular according to claim 1, characterized in that the Redox potential in a purely chemical way by adding reducing agents such as sodium dithionite and the like. Reducing substances and / or additionally or alone is adjusted electrochemically.

37.Process for the separation of nitrogen oxides and sulfur oxides and possibly other pollutants from the flue gases of combustion plants, preferably from power plant boilers fed with fossil fuels, the nitrogen oxides being reduced to elemental nitrogen and the sulfur oxides and possibly other pollutants being eliminated by means of a washing process, in particular after Claim 1, characterized in that the scrubber is designed as a cocurrent or countercurrent scrubber with the nozzle levels A, B, C, which first oppose the raw gas stream and preferably with a pH value smaller pH 4 are applied, and the nozzle levels then contacted after, for example, three further nozzle levels D, E, F are subjected to a pH value preferably greater than pH 5 - and the washing liquid sump is so large that the residence time of the washing liquid in it is more than Is 10 minutes.

38.Procedure for the separation of nitrogen oxides and sulfur oxides and possibly other pollutants from the flue gases from combustion plants, preferably from power plant boilers fed with fossil fuels, the nitrogen oxides being reduced to elemental nitrogen and the sulfur oxides and possibly other pollutants being eliminated by means of a washing process, in particular after Claim 1, characterized in that the flue gas is fed to a single-stage countercurrent washer, and in one or more nozzle levels the flue gas is first pressed against a washing liquid with a positive redox potential, this washing water being mixed with additives, such as limestone or hydrated lime, and for better solubility, preferably Carboxylic acid with which additive is added to the washing liquid and the last nozzle level consists of one and / or more nozzles or nozzle levels and behind the first nozzle level arrangement (112) and (113) in the A washing liquid with a negative redox potential is added to the nozzle plane (114), which is adjusted by adding dithionite and / or other reducing agents or via a reduction vessel which is filled, for example, with iron plates. In addition, dithionite can additionally be added as a reducing agent by electrochemical reduction (electrolysis), so that SO ₂ and NO _{x are} simultaneously deposited and oxidized in the laundry sump (116) via the oxidation device (117) and nitrogen (N ₂ ) via the droplet separator arrangement via the nozzle arrangement according to the invention (125) is transferred to the chimney and / or cooling tower and calcium sulfate dihydrate is separated off.

39.Process for the separation of nitrogen oxides and sulfur oxides and possibly other pollutants from the flue gases of combustion plants, preferably from power plant boilers fed with fossil fuels, the nitrogen oxides being reduced to elemental nitrogen and the sulfur oxides and possibly other pollutants being eliminated by means of a washing process, in particular after Claim 1, characterized in that the washing liquid is fed to a conventional desulfurization plant salts be, which form complexes such as iron nitrosyl complex with nitrogen monoxide, which are reduced to elemental nitrogen and water by admixing formic acid to prevent precipitation of iron III hydroxide on a potentiostatically switched cathode.

40. The method according to claim 39, characterized in that chlorine gas is formed and discharged at an anode.

41. The method according to claim 39 or 40, characterized in that metal deposits occur on a cathode through which the metals can be removed.

42. The method according to claim 39 or one of the preceding, characterized in that in an anode cell separated by membranes an accumulation of nitrate ions occurs, which is treated separately.

43. The method according to claim 39 or one of the preceding, characterized in that the membranes consist of Anionausausaschermasse.

44. The method according to claim 39 or one of the preceding, characterized in that the methods can be operated in cocurrent and in countercurrent.

45. The method according to claim 39 or one of the preceding, characterized in that the anode consists of an unassailable material, preferably titanium.

46. The method according to claim 39 or one of the preceding, characterized in that the cathode consists of a suitable material, preferably carbon.

47. The method according to claim 39 or one of the preceding, characterized in that it is a waste water-free method in the electrochemical method.

48. The method according to claim 39 or one of the preceding, characterized in that the electrochemical reactions take place in a divided area of the laundry sump.

49. The method according to claim 39 or one of the preceding, characterized in that the electrochemical reactions take place in a separate apparatus which contains cathodes and anodes which are separated from one another by membranes and which transports the washing liquid through the apparatus with an already existing pump, preferably on the way to the existing nozzle levels.

50. The method according to claim 39 or one of the preceding, characterized in that it is stationary facilities such as power plants, heating plants, industrial firing and other nitrogen oxide-emitting systems.

51. The method according to claim 39 or one of the preceding, characterized in that it is mobile systems such as ships, trains, diesel-powered electricity generators or motor vehicles.

52. The method according to claim 39 or one of the preceding, characterized in that the oxidizing gases formed on the anode specifically for the oxidation of Sulfite to sulfate can be used.

53. The method according to claim 39 or one of the preceding, characterized in that the laundry sump is separated into different compartments, in whose oxidation and reduction processes take place separately from each other.

54.Process for the separation of nitrogen oxides and sulfur oxides and possibly other pollutants from the flue gases of combustion plants, preferably from power plant boilers fed with fossil fuels, the nitrogen oxides being reduced to elemental nitrogen and the sulfur oxides and possibly other pollutants being eliminated by means of a washing process, in particular after Claim 1, characterized in that the direct current scrubber, into which the raw gas is first introduced, is operated in the first nozzle plane (192) with a washing liquid which is charged to the gas stream first via an iron reactor charged with negative redox potential, and then in the downstream one Nozzle planes (193) split off the bound NO - NO ₂ from the area of the nozzles (192) to form elemental nitrogen.

55. The method according to claim 54, characterized in that the iron reactor (173) is supplied with a washing liquid which is set to a negative redox potential by reducing agent from the container (181).

56. Procedure according to. Claim 54 or 55, characterized in that the nozzle level, which is used last in the washing process, is acted upon with a washing liquid which has a negative redox potential, which is preferably obtained from the container (181) and / or from the electrolysis station (183) using reducing agents ) is controlled.

57. The method according to claim 54 or one of the preceding, characterized in that the nozzle planes (191) in the countercurrent washer and the nozzles (193) in the cocurrent washer have a smaller minus redox potential than the nozzle planes (190) and (192).

58. The method according to claim 54 or one of the preceding, characterized in that the setting of the redox potential via the iron reactor (173) and optional use of reducing agents (181) such as sodium dithionite and / or electrolysis (183).

59.Process for the separation of nitrogen oxides and sulfur oxides and possibly other pollutants from the flue gases of combustion plants, preferably from power plant boilers fed with fossil fuels, the nitrogen oxides being reduced to elemental nitrogen and the sulfur oxides and possibly other pollutants being eliminated by means of a washing process, in particular after Claim 1, characterized in that the washing liquid with limestone and / or hydrated lime with the addition of NTA and / or EDTA mixed with sodium dithionite is passed over an iron reactor, and with a negative balance between SO ₂ and NO _x the washing liquid is added pyrosulfite and to stabilize the Sequence - especially of the iron chelate - acids are supplied, preferably formic acid, and an electrolysis in the washing liquid circuit is interposed in order to quickly adjust the washing liquid in the range of the desired redox potential.