WO1987002269A1

WO1987002269A1 - Process for simultaneous extraction of so2 and nox contained in waste gases

Info

Publication number: WO1987002269A1
Application number: PCT/EP1986/000572
Authority: WO
Inventors: Heinz HÖLTER; Heinrich IGELBÜSCHER; Heinrich Gresch; Heribert Dewert
Original assignee: Hoelter Heinz
Priority date: 1985-10-11
Filing date: 1986-10-08
Publication date: 1987-04-23
Also published as: EP0241496A1

Abstract

Process for simultaneous extraction of SO2 and NOx contained in waste gases in one or several stages by a wet method. The purpose of the invention is to improve such a process so that it can be performed at a relatively small cost, obtaining in addition values which are much lower than the maximum values specified by the authorities. For this purpose, the SO2 absorbed during the process, which is precipitated by lime in the form of solid CaSO3/CaSO4 x 2H2O is no longer oxidized by an oxidizer to become CaSO4 x 2H2O but is added in the solid state to the flow of washing liquid of a prewashing stage for the purpose of oxidizing the quantity of CaSO3 by the oxygen of the waste gas supply, the washing solution having a pH of between 2 and 2.5. The solid matter is transferred to the washer or to the washing basin of the prewashing stage and maintained in contact with the washing liquid at a corresponding pH value (pH 1 to 1.5) until the release of the appropriate quantity of SO2 required for the simultaneous washing reaction of SO2/NOx in the washer.

Description

"Process for simultaneous SO2 and NOx separation from flue gases"

The invention relates to a method for single or multi-stage simultaneous SO2 and NOx separation from flue gases in a wet process.

The object of the invention is to improve such a method in such a way that it can be carried out with comparatively little effort, the maximum value prescribed by the authorities still being significantly below.

It is known to simultaneously separate SO2 / NOx from the flue gas, preferably behind power plants, in one-stage or multi-stage washing. There must be a certain quantitative ratio between SO2 and NOx (e.g. 2.0 - 2.4 g SO2: 1 g NOx per Nm3 flue gas). In the case of melting chamber boilers in particular, the above-mentioned ratio between the SO2 load and the NOx load in the flue gas is not available for the hatching process. SO2 is in most cases less than stoichiometric compared to NOx and the SO2 deficiency can be replaced by adding liquid sulfur dioxide, sodium pyrosulfite or by a gypsum cracking system become. These SO2 additions are very expensive.

According to the invention, it is proposed that SO2 absorbed in the process, which is precipitated as lime as CaSO3 / CaSO4 x 2H2O solid, no longer to be oxidized to CaSO4 x 2H2O via an oxidizer, but rather to the washing liquid stream of a prewash stage for the oxidation of the CaSO3 amount by means of Add oxygen to the amount of flue gas at a pH in the wash solution of pH 2 - 2.5. The solid is passed to the scrubber or laundry sump of the prewash stage and contacted with the washing liquid at a corresponding pH value (pH 1-1.5) until the corresponding amount of SO2 is released, which is used to react the Siraultan washing of SO2 / NOx in which washer is needed.

According to a further feature of the invention, for the production of rich gas and sodium sulfate as the end product, it is proposed that SO2 and NOx be fed from the raw gas to a first scrubber that the SO2 is washed out by sodium sulfite (in the washing water) with the formation of sodium bisulfite (NaI-ISO3) and the gas freed from SO2, but loaded with NOx, is fed to a second scrubber, that in the second scrubber an iron EDTA washing solution, which is enriched with SO2 rich gas, is used for NOx scrubbing and pure gas is produced, which is released, the washing liquid from the first scrubber being transferred to a crystallizer from which sodium sulfate is released. The SO2 rich gas generated in the process is handed over to its use, with partial quantities being introduced into the second scrubber to reduce the NOx compounds and the iron chelate complex compound.

A portion of the wash solution is passed from the second scrubber to thermal decomposition at about 650 degrees C to destroy U.S. compounds, with the amounts of SO2 released being sent to the scrubber and sodium sulfate being rejected from the process.

According to the invention, in particular with flue gases with high SO2 contamination, it is further proposed that the raw gas, which is enriched in particular with HCl and KF, is freed of HCl and / or HF in a pre-washer and SO2 and NOx in a first washer simultaneously with a specific washing solution , which is provided with an iron-EDTA complex, is washed. Part of the amount of washing liquid in the circuit is transferred to a circulation container into which reducing agents are added as required.

The washing liquid treated reducing in the circulation container quantity is transferred to the quantity of washing liquid for simultaneous SO2 and NOx washing. The SO2, which has been freed of NOx and partially required to reduce NOx, and which was extracted from the raw gas, passes into a second scrubber as SO2-contaminated gas. It is washed with sodium sulfite SO2 and a part of it is discharged into the circulation tank.

The gas freed from SO2 and NOx leaves the process as clean gas. A part of the first scrubber is fed as a washing liquid to a crystallization evaporator, from which SO2 rich gas is released. Sodium sulfate is released from the crystallization evaporator. The evaporation residue of the crystallization evaporator is transferred to thermal decomposition as a partial quantity and the SO2 released in the process is fed to the first scrubber or added to the SO2 rich gas. Sodium sulfate is removed from the thermal decomposition. A portion of the crystallization evaporator, which is not fed to the thermal decomposition, is returned to the first scrubber.

It is known that sulfur nitrogen compounds as well as sulfite and sulfate compounds formed with lime from the washing liquid are formed in the washing liquid Calcium sulfite and sulfate are precipitated as a solid. For the recovery of valuable materials, it is proposed according to the invention that sulfur dioxide, after simultaneous washing in a scrubber and precipitated solid with lime as calcium sulfite-calcium sulfate, is fed to a gravity separator and, after the solids have settled, a portion of the clarifying liquid is fed to an evaporation. From the evaporation, the evaporation residue, consisting of Na2SO4, Na2SO3 and NS compounds at approx. 750 degrees together with the dewatered solids CaSO3 / CaSO4 from the gravity separator, is subjected to thermal decomposition, so that SO2 is released and returned to the raw gas process.

In the thermal decomposition, an anhydrite-shaped solid product is obtained, which is used as an economic good, preferably in underground mining as a dam building material.

A portion of the filtrate is supplied to an evaporation from a dewatering station downstream of the gravity separator. After evaporation, the NS salts are decomposed separately at approx. 650 degrees and fed to the simultaneous washer. The solids calcium sulfate and sulfite are thermally decomposed separately at approx. 750 degrees Celsius. After the decomposition, an anhydrite-like building material without alkali falls salt on.

It is known, when there are high HCl loads in the raw gas, to precede the actual simultaneous scrubber, which is operated with iron chelate complexes, with an acidic HCl scrub. The chloride loads that occur in the acidic stage generally have to be evaporated, since they cannot be passed on to a receiving river. However, this is very expensive and also creates a landfill problem.

In order to avoid the pre-washer and the evaporation at the same time, it is proposed according to the practice to control a single washing stage which is operated simultaneously with the washing of SO2 and NOx with iron chelate complexes, so that the entire washing liquid is pumped via the electrolysis, so that the Alkaline chlorides present in the solution are decomposed and chlorine gas is formed at the anode and the alkali metals remain as residual material in the solution to form alkali metal hydroxide, thus forming an alkali cycle for the simultaneous washing of SO2 and NOx for SO2 washing and no waste water has to be released. Salting is therefore excluded. The chlorine gases are collected and recycled. There is thus a washing liquid with an iron chelate compound without the addition of a chloride wash in used a single scrubber, the washing liquid is fed in portions to an electrolysis, in which the iron III is reduced to iron II and at the same time the current is driven so that the alkali metal chloride is practically split and decomposed to chlorine gas, the chlorine gas being collected and one Recycling can be supplied and the alkali hydroxide is used for washing SO2 from the flue gas.

It is known that in the case of combustion products with a very high chlorine content, this interferes with the actual washing process for SO2 and NOx scrubbing, so that a so-called “pre-scrubber” is added to the actual SO2 and NOx scrubbing to remove the acidic components HCl, HF etc. to wash out beforehand.

The salt load that is inevitably generated in the pre-washer must not usually be handed over to a river or an outflow, but must be evaporated and used for other purposes or sent to a landfill. The gypsum, which is processed into mining building materials or other building materials, for example, often has to be provided with an additional chloride addition in order to have the appropriate properties. Often the gypsum also has to be put into interim storage, in order to then correspond to the Chlorine levels are subjected to further processing.

To add the gypsum to the salt load at the same time without disturbing the SO2 and NOx washing process, which above 10% calcium chloride in the washing solution, especially in the limestone washing process, no longer with a max. Leaching out of SO2 and NOx works and in order not to have to additionally oxidize the gypsum in the SO2 and NOx washing stage at a pH value above pH 5, where the oxidation is not complete, it is proposed according to the invention that the raw gas scrubbing in one Prewashing takes place, which is operated with an acidic pH, in which chlorides are washed out of the raw gas stream and in a postwashing unit downstream of the prewashing unit, into which SO2 and / or NOx is washed, the absorbents for washing SO2 and NOx being fed to the postwashing unit and the product obtained from the post-scrubber, consisting of not fully oxidized CaSO3 / CaSO4, is pumped into the pre-scrubber and a good oxidation and good mixture of the chlorides with the raw gypsum produced is generated here using an excess of oxygen in the raw gas.

It is known that gypsum can only be marketed with minor traces of calcium. On the other hand, it is also known that Chloride can be used as a dust binder in mining, for example.

In order to obtain a wastewater-free process, it is proposed according to the invention to wash the gypsum in a centrifuge or on a vacuum filter in such a way that it meets the specification of the low chloride-containing constituents and this washing water is fed to a spray dryer quencher stage upstream of the flue gas desulfurization system, in which an acidic pH the flue gas of e.g. 140 degrees C is pressed down to 100 degrees C, while the chloride-containing gases from the gypsum washing station, which are also enriched with chloride, are used to wash out the chloride-containing constituents in the gas with simultaneous cooling of the flue gas.

It has been found that with additives such as lime and iron-II-sulfate for the production of a washing solution for simultaneous SO2 / NOx processes with small amounts of manganese, the iron-II resistance in the Fe-EDTA complex is considerably more stable. It is therefore proposed according to the invention that the amount of manganese in the iron (II) salts should be kept at 0.05%, calculated on a dry basis, and the usual 0.14% dry basis. Wash-out degrees of better than 10% at 0.05% in the iron II salt over 0.14% in the iron II salt, measured dry, were achieved.

It is known that behind flue gas desulfurization plants there is a gypsum-like mass and ash behind power plants. Ash and gypsum and other additives often form the raw material basis for a finished product that is to be used for the cement industry, mining and tunneling.

However, there are river waters or industrial waters that are used for flue gas cleaning that are contaminated with ammonium compounds. It is necessary that the genic, consisting of raw gypsum and the other additives, has to be subjected to a thermal process. Here, the water with the ammonium compounds is evaporated and there is an environmental impact. Up until now, these vapors have been returned to the flue gas desulfurization systems and thus cleaned in an environmentally friendly manner. However, ammonium compounds gradually enrich the wash water egg and finally a portion of the wash water must then be removed again and sent to a wastewater treatment. In order to eliminate this disadvantage, it is proposed according to the invention to supply the vapors of the thermal process to the flange area of the boiler, in which the gaseous compounds such as ammonia are thermally decomposed.

It is also proposed to supply the water used for flue gas cleaning and which is loaded with ammonium salt to a container in which strong aeration and hydrated lime or alkali lye are added in order to drive off ammonia from the ammonium salts and the water is usable without To make ammonia pollution usable for the flue gas desulfurization and at the same time transfer the expelled ammonia according to the invention to the combustion area of the boiler and use it thermally.

It is known to use electrolysis for SO2 and NOx removal. An essential requirement for the economical operation of electrolysis is the conductivity of the washing solution. It has been found that it is expedient that a process for simultaneous SO2 and NOx separation based on complexed iron-II solution is operated with a washing liquid whose conductivity is greater than 70 mS / cm, preferably between 70 and 100 is mS / cm. In order to maintain or intensify the conductivity in the washing process, it is proposed according to the invention that the washing liquid is preferably adjusted to a pH between 4.5 and 6.5. The washing liquid is enriched with an Fe concentration of 5 - 6.5 g / l, in which case the Fe-II content must be greater than 90% with a washing-out degree of more than 2 g / l washing solution and with a washing-out degree of 80% approximately with less than 2 g / l washing solution, whereby the total content of Fe-II and Fe-III must be kept at 5 - 6.5 g / l.

It has also been found that carboxylic acids, preferably formic acid, citric acid and tartaric acid, contribute to the substantial improvement of the conductivity.

It is known that reducing agents are added to the iron chelation process in order to convert iron III back into iron II. Here, a reducing agent is often used, which is in powder form or in glycolized paste. The powder form is usually difficult to handle and convey. The pumpable mass of glycol interferes with the water treatment process. For this reason, it is proposed according to the invention to use a reducing agent which is easily pumpable and is provided with an oily mass, the oil with its specific gravity being so it is set that it floats in the washing liquid on the surface after use and, before the water treatment is carried out, this oil layer can simply be tapped off.

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

FIG. 1 shows a method with gypsum production and SO2 release,

FIG. 2 shows a process with the end product sodium sulfate,

FIG. 3 shows a method for cleaning flue gases with high SO2 loads,

FIG. 4 shows a method with recovery of valuable materials,

Figure 5 shows a process for combustion products with a very high chlorine content and

Figure 6 shows a process with gypsum discharge and calcium chloride extraction.

In FIG. 1, 1 denotes the pre-washer, which is operated acidic, preferably with a pH between 1-2, for washing HCl and HF. SO2 / NOx is washed out simultaneously in the main scrubber 2. The value Fabric recovery with a gypsum precipitation stage is denoted by 3. The precipitated mixture, consisting of CaSOS, CaSO4 and traces of pure CaO, is fed to the pre-scrubber I via the outlet 4.

Due to the acidic pH value, pre-washer 1 and in the subsequent sump the mixture of CaSO4 and CaSO3 is oxidized to CaSO4 x 2H2O by the excess oxygen additionally contained in the raw gas.

This saves the previously used oxidizer.

The missing amount of SO2, which is required for the reaction of the SO2 / NOx-Sinultan wash, is so far acidified in the prewash for HCl / HF by lowering the pH value and the residence time of the mixture of CaSO3 / CaSO4 in the laundry sump so increased that by decomposing CaSO3 enough SO2 is released to allow the reactions in the simultaneous washer 2 to proceed safely.

In FIG. 2, 11 denotes the first scrubber for the SO2 and NOx raw gas intake. In the first scrubber 11, only SO2 is separated off over a sodium sulfite solution, with the formation of sodium bisulfite (NaHSO3). The gas, cleaned of SO2, is washed in the second scrubber 12 with an EDTA solution which is mixed with sulfite and / or additional formate solutions.

The SO2 and NOx-cleaned gas leaves the washing zone via outlet 13.

In the crystallizer 15, SO2 pure gas is expelled from the sodium bisulfite wash solution from the first scrubber 11 at the temperature mentioned, which leaves the process via the outlet 16 as rich gas. Sodium sulfate (Na2SO4) is discharged from the crystallizer 15 via the outlet 20. A portion of the SO2 rich gas is introduced into the second scrubber 12 via outlet 14 to reduce Fe-III to Fe-II and reduce NOx to nitrogen from Sul uat.

In a thermal decomposition 17, the N / S salts formed are burned at about 650 ° C. and the residue sodium sulfate is released via the outlet 18. The released SO2 is transferred to the first scrubber 11 via the outlet 19.

In the course of the process according to FIG. 3, the raw gas 21, which is enriched in particular with HCl and HF, is freed of HCl and / or HF in a pre-scrubber 22. In the first washer 23, SO2 and NOx are washed simultaneously with a specific washing solution which is provided with an iron-EDTA complex.

Part of the amount of washing liquid 24 in circulation is transferred to a circulation container 25, into which reducing agents 26 are added as required.

The amount of washing liquid treated in a reducing manner in the circulation tank 25 is transferred via a line 27 to the washing liquid amount for the simultaneous washing SO2 and NOx. The SO2 that has been freed from NOx and partially required to reduce NOx and that was extracted from the raw gas goes into the second scrubber 29 as SO2-contaminated gas 28. Here, SO2 is washed with sodium sulfite and a portion is discharged into the circulation container 25.

The gas, freed from SO2 and NOx, leaves the process via the outlet 30 as clean gas. A portion 31 is fed from the first washer 23 to the crystallization evaporator 32 as washing liquid. SO2 rich gas is released from these via outlet 33.

Via the outlet 34, sodium sulfate from the crystals sationseindferfer 32 released.

The evaporation residue 35 is a subset of a thermal decomposition 36 and the released SO2 is fed to the first scrubber 23 or the SO2 rich gas outlet 33.

36 sodium sulfate is also removed from the thermal decomposition. A portion of the crystallization evaporator 32, which is not fed to the thermal decomposition process, is returned to the first scrubber 23 via the line 37.

In the method according to FIG. 4, 41 denotes the incoming raw gas which is introduced into the scrubber 42 of the simultaneous washing. 43 is the EDTA addition, which opens into the washer 42. The scrubber 42 is followed by a lime precipitate 45, into which the addition 44 of lime hydrate and reducing agents is also carried out.

The sulfur dioxide is supplied to the lime precipitate 45 after the simultaneous washing. From this, the solid precipitated with lime as calcium sulfite-calcium sulfate enters the gravity separator 46 as a suspension, which can be designed as a double-jacket sink separator. The Separator 46 is followed by a dewatering station 47 and this in turn is followed by a thermal decomposition 50. A partial amount of the filtrate from the dewatering station 47 enters an evaporation 49.

In the thermal decomposition 50 calcium sulfite and / or calcium sulfate are decomposed at approximately 750 degrees C. The SO2-containing raw gas 51 released in the process is fed back to the washing process. An anhydrite-shaped solid product 52 is obtained as a residual product, which is used as an economic material, preferably underground in mining, as a dam building material.

In the course of the process according to FIG. 5, the raw gas which is introduced into the pre-scrubber 62 is denoted 61. In the pre-scrubber 62, the raw gas is washed with an acidic pH, preferably below pH 5. The SO2 and / or SO2 and NOx scrubber 63 is preferably operated above pH 5. The clean gas leaves the scrubber 63 via the chimney 64. The mixture removed from the scrubber 63, which originates from the lime suspension used in the scrubber 63, is designated by 65. This consists of CaSO3 / CaSO4 that is not completely oxidized. This is pumped into the pre-washer 62 via the line 66. Due to the high excess of atmospheric oxygen in the raw gas in the acid phase in the washing liquid, a well-oxidized product is formed CaSO4 product 67 with the corresponding calcium chloride content. This mode of operation enables the optimal washing out of SO2 and NOx in the scrubber 63 and, moreover, an optimal oxidation with enrichment of chlorides in the raw gypsum, which for further use is produced well oxidized in the pre-scrubber 62 via the oxygen excess of the acidic pH value.

In the process representation according to FIG. 6, 71 denotes the upstream chloride spray tower, which is followed by the actual flue gas scrubber 72. With 73 a drum vacuum filter with gypsum washing station is designated and with 74 the return of the gypsum washing water into the spray and quench absorber 71. The salts 75 obtained are drawn off below the spray and quench absorber 71. The discharged, washed raw gypsum is designated 76.

Claims

PATENT CLAIMS:

1. A method for single-stage or multi-stage simultaneous SO2 and NOx separation from flue gases in a wet process, characterized in that the solid precipitated from a simultaneous scrubber from a resource recovery stage or from a washing liquid preparation stage, consisting of CaSO3 / CaSO4, the washing liquid stream Prewash stage (1) for oxidizing the amount of CaSO3 by means of oxygen to the flue gas at a pH value of the wash solution of pH 2 - 2.5.

2. The method according to claim 1, characterized in that the solid is passed to the scrubber (2) or laundry sump of the prewash stage (1) and is contacted with the washing liquid at a corresponding pH value (pH 1-1.5), until the corresponding amount of SO2 is released, which is required for the reaction of the simultaneous washing of SO2 / NOx in the scrubber (2).

3. The method according to claim 1, characterized in that a first scrubber (11) SO2 and NOx from the raw gas is supplied so that the SO2 is washed out by sodium sulfite (in the washing water) with formation of sodium sulfite (NaHSO3) and the gas freed from SO2, but loaded with NOx, is fed to a second scrubber (12), that in the second scrubber (12) an iron EDTA washing solution, which is enriched with SO2 rich gas, is used for NOx washing and clean gas is produced, which is discharged from the outlet (13), the washing liquid from the first scrubber (11) being a crystallizer (15) is transferred, from which sodium sulfate is released via the outlet (20).

4. The method according to claim 3, characterized in that the SO2 rich gas generated is transferred to the outlet (16) for use, partial quantities (14) for reducing the NOx compounds and the iron chelate complex compound in the second scrubber ( 12) can be initiated.

5. The method according to claim 3 or 4, characterized in that a part of the washing solution from the second scrubber (12) thermal decomposition (17) is passed at about 650 degrees C for the destruction of NS compounds, the released amounts of SO2 are transferred to the first scrubber (11) via the outlet (19) and sodium sulfate is discharged from the process via the outlet (18).

6. The method according to claim 1 or one of the preceding, in particular from flue gases with a high SO2 load, characterized in that the raw gas (21), which is enriched in particular with HCl and HF, in a pre-washer (22) of HCl and / or HF is freed and SO2 and NOx are simultaneously washed in a first scrubber (23) with a specific washing solution which is provided with an iron-EDTA complex.

7. The method according to claim 6, characterized in that a part of the amount of washing liquid in the circuit (24) is transferred to a Umiauf Containers (25), in which reducing agents (26) are added as required.

8. The method according to claim 6 or 7, characterized in that the amount of washing liquid treated in a reducing manner in the circulation container (25) is transferred via a line (27) to the washing liquid amount for the simultaneous washing SO2 and NOx.

9. The method according to claim 6 or one of the preceding, characterized in that the SO2 freed and partially required to reduce NOx SO2, which was extracted from the raw gas, as SO2-contaminated gas (28) in one second washer (29) is transferred and in this means

Washed sodium sulfite SO2 and a portion is discharged into the Umiauf containers (25).

10. The method according to claim 6 or one of the preceding, characterized in that the exempt from SO2 and NOx

Gas exits the second scrubber (29) via the outlet (30).

11. The method according to claim 6 or one of the preceding, characterized in that a subset as the clean gas

(31) from the first scrubber (23) is fed as a washing liquid to a crystallization evaporator (32), from which SO2 rich gas is released via the outlet (33).

12. The method according to claim 6 or one of the preceding, characterized in that from the crystallization evaporator (32) via the outlet (34) sodium sulfate is released.

13. The method according to claim 6 or one of the preceding, characterized in that the evaporation residue (35) of the crystallization evaporator (32) is passed as a subset of a thermal decomposition (36) and the SO2 released thereby to the first scrubber (23) or the SO2 Reichgas outlet (33) is supplied.

14. The method according to claim 6 or one of the preceding, characterized in that sodium sulfate is discharged from the thermal decomposition (36).

15. The method according to claim 6 or one of the preceding, characterized in that from the crystallization evaporator (32) a portion that is not supplied to the thermal decomposition (36) is returned to the first scrubber (23) via the line (37) .

16. The method according to claim 1 or one of the preceding, in particular with recovery of valuable material, characterized in that sulfur dioxide after the simultaneous washing in a scrubber (42) and with lime as calcium sulfite - calcium sulfate solid suspension is fed to a gravity separator (46) and after Sedimentation of the solids, a portion of the clarifying liquid is placed in an evaporation (49).

17. The method according to claim 16, characterized in that from the evaporation (49) the evaporation residue, consisting of Na2SO4, Na2SO3 and NS compounds, at about 750 degrees C together with the dewatered solids CaSO3 / CaSO4 is fed from the gravity separator (46) to thermal decomposition (50), and the released SO2 is returned to the raw gas process via the outlet (51).

18. The method according to claim 16 or 17, characterized in that in the thermal decomposition (50) an anhydrite-shaped solid product (52) is obtained, which is used as an economic asset, preferably in mining as a dam building material.

19. The method according to claim 16 or one of the preceding, characterized in that a portion of the filtrate from a downstream of the gravity separator (46) downstream drainage station (47) is fed to a dispensing (49).

20. The method according to claim 16 or one of the preceding, characterized in that the NS salts after evaporation (49) decomposed separately at about 650 degrees C and fed to the washer (42).

21. The method according to claim 16 or one of the preceding, characterized in that the solids calcium sulfate and sulfite decomposes separately at about 750 degrees C. become and after the 750 degrees C decomposition an anhydrite

Building material without alkali salts.

22. The method according to claim 1 or one of the preceding, characterized in that the flue gases are washed with iron chelate complex salts which are in the wash solution, and the wash solution is passed through an electrolysis cell and part of the iron chelate complex salt from iron-III to iron- II is reduced and at the same time the alkali chlorides in the wash solution are decomposed by driving the stron starch accordingly, chlorine gas forms at the anode and alkali hydroxide (e.g. NaOH) forms in the wash cycle, which is cycled to absorb SO2 / NOx and HCl Rauch¬

23. The method according to claim 1 or one of the preceding claims, characterized in that the raw gas scrubbing takes place in a pre-scrubber (62) which is operated at an acidic pH, in which chlorides are washed from the raw gas stream and in one of the pre-scrubbers (62) downstream post-scrubber (63), into which SO2 and / or NOx is washed, the absorption agents for washing SO2 and NOx being fed to the post-scrubber (63) and the product obtained from the post-scrubber (63), consisting of not completely oxidized CaSO3 / CaSO4, to which the pre-scrubber (62) is pumped, and here a good oxidation and good mixing of the chlorides with the raw gypsum produced is produced by means of an excess of oxygen in the raw gas.

24. The method according to claim 1 or one of the preceding, in particular with gypsum discharge and calcium chloride extraction, characterized in that the washing water, which is used for gypsum washing, is collected and the spray and quench absorber stage (71) is supplied to the flue gas desulfurization washing system (72) .

25. The method according to claim 1 or one of the preceding, characterized in that the iron (II) salts used for the preparation of the washing solution, preferably iron (II) sulfate and calcium oxide, in particular hydrated lime, have a manganese content of less than 0.05-0.07%. on a dry basis.

26. The method according to claim 1 or one of the preceding, in particular for the production of recovery products, characterized in that the released ammonia-containing vapors are fed from the process water into the flame area of the fossil fuel boiler

27. The method according to claim 26, in particular for releasing ammonia-containing loads on the wash water, characterized in that the wash water is inoculated with alkali or alkaline earth metal solutions, aerated and the ammonia-containing vapors formed are expelled and transferred to the flame area of the boiler.

28. The method according to claim 1 or one of the preceding, characterized in that the conductivity of the washing solution is kept between 70 to 100 mS / cm.

29. The method according to claim 28, characterized in that the washing liquid based on complex EisenII solution has a conductivity greater than 70 mS / cm, preferably between 70 and 100 mS / cm.

30. The method according to claim 28 or 29, characterized in that the washing liquid is adjusted to a pH, preferably between 4.5 to 6.5.

31. The method according to claim 28 or one of the preceding, characterized in that the washing liquid is enriched with an Fe concentration of 5 to 6.5 g / l, the Fe-II content at a washout degree of greater

90% is greater than 2 g / l washing solution and when it is off degree of washing of 80% with less than 2 g / l washing solution, the total content of Fe-II and Fe-III being kept at 5 to 6.5 g / l.

32. The method according to claim 28 or one of the preceding, characterized in that in order to improve and maintain the conductivity in the washing liquid in addition to EDTA compounds carboxylic acids, preferably formic acid, citric acid or tartaric acid are added.

33. The method according to claim 28 or one of the preceding, characterized in that in the washing liquid the Fe complex is greater than 6 g / l and the iron-II portion in the inlet of the electrolysis is approximately greater than 2 g / l, so that the lowest power consumption is given with optimal NOx cleavage.

34. The method according to claim 1 or one of the preceding, in particular for dosing reducing agents, characterized in that the reducing agent is stored in an oily mass and made pumpable and is sucked off after the use of the reduction on the surface of the washing liquid, and the oil has a specific weight that is less than that of the wash water.