DE3429999A1 - Process for separating out SO2 and NOx - Google Patents

Abstract

A process for separating out SO2 and NOx, in particular from flue gases, the majority of the SO2 and a smaller part of the NOx being separated out from the flue gas in a wet scrubber and the majority of the NOx being catalytically separated off from the flue gas on activated charcoal/activated coke with the addition of ammonia and the residual SO2 being separated off by reaction with the ammonia. The activated charcoal/activated coke is delivered to a moving bed reactor, the loaded adsorbent is withdrawn from the moving bed reactor and conducted over a screen, ammonium sulphate is separated off and the purified adsorbent is returned for re-use to the moving bed reactor. A part-stream of the screened adsorbent can be fed to a wet scrubber, then dried and returned to the moving bed reactor. Ammonia can be expelled from the scrubber water and also from the screened ammonium sulphate and returned to the process cycle. <IMAGE>

Description

The invention relates to a method for the deposition of

SO and N0, especially from smoke gases, the main 2 amount of SO, and a smaller proportion of the NO from the x flue gas deposited in a wet scrubber and the main amount of NO from the flue gas in activated carbon / activated coke with x ammonia addition catalytically and the residual SO2 is separated off by reaction with the ammonia.

So far, so-called Flue gas scrubbing used. These are usually between the electrostatic precipitator and arranged by the chimney. The flue gas in this area has a temperature of about 120-1500C.

The washing process cools down to 50 - 70 ° C.

So that the flue gases do not lose their thermal buoyancy they are reheated, for example in a heat exchanger. The laundry Inflowing smoke gases give heat to the smoke gases coming out of the laundry from, so that the flue gases before entering the chimney again a temperature of have about 90 0c.

Flue gas scrubbing can according to the prior art with different aqueous solutions in T, laschern of various types can be carried out. As the most common Washing liquids are used as aqueous solutions of hydrated lime or limestone. In these Washing solutions are made by chemical reactions of the S02 with calcium in the solution Calcium sulphite / calcium sulphate formed from which in downstream processing stages tradable gypsum can be obtained.

(T4. Kaminsky, Chem.-Ing.-Technik 55 (1983), p. 673 ff) It is today It is desirable that, in addition to the SO2, the nitrogen oxides also largely separated from the exhaust gases will. The invention is therefore based on the object of the known wet washing process to be further developed for the separation of 502 so that an additional NO separation is made possible.

A method of the generic type is in the generic, unpublished patent application P 34 23 744.5. With this one Proposal it is disadvantageous that the entire adsorbent in a wet wash must be regenerated with connected, energy-consuming drying.

Also is in another unpublished patent application P 34 23 761.5 proposed thermal regeneration of the adsorbent been. This regeneration process requires a particularly high amount of energy necessary.

The invention is based on the object of a method of the above mentioned genus to the effect that regeneration by wet washing can be wholly or partially omitted.

This object is achieved according to the invention by the characterizing features of claim 1 solved.

Further developments are listed in the subclaims.

It was surprisingly found that the catalytic properties of activated charcoal / activated coke through the side reactions of the 902 with ammonia and the partial deposition of the resulting reaction products in the pore system in the With regard to the NO-x decomposition are not influenced. By sieving the Ammonium sulfate formed in the void volume is avoided in the technical Implementation through the deposits increases the pressure loss in the bed too much and denitrification is thereby hindered. The adsorbent can immediately reused and recycled back into the reactor. With this one The adsorbent needs a process for the simultaneous separation of SOL and NOx not consuming wet or thermally regenerated. Should be in certain In cases where residual loads caused by ammonium sulphate can be disruptive, according to the dependent claims part of the adsorbent of a wet wash be subjected to which compared to a complete wet wash still considerable savings in facilities and causes energy. The process can be carried out in cocurrent or in countercurrent, preferably but can be used in the cross-flow, flowed moving bed reactor. The sieved Ammonium sulfate can be processed into fertilizers. But it can also - According to a further development - be fed to a # 1H 3 recovery. The same applies when a partial flow is wet washed for the wash water that is produced. In this way, an environmentally friendly disposal of everyone involved in the process Substances ensured.

The invention is explained below with reference to the drawing and an example described in more detail.

The drawing shows in Figure 1 a schematic representation of the process management of the combined desulfurization and denitrification process and in FIG. 2 one schematic representation of a further development of the mode of operation according to FIG. 1, in which a partial flow of the screened adsorbent is fed to a wet scrubber will.

From Fig. 1 it can be seen that the flue gas from the flue gas scrubber through a line 1 is led into an activated coke / activated carbon reactor 2 (AK reactor). Ammonia is added to the flue gas stream by means of a line 6. In the AK reactor 2 the simultaneous separation of NO and SO2 takes place. 2The one leaving AK reactor 2, cleaned flue gas stream 5 is partially freed from the SOL. The MO reduction can between 20 and over 90%, depending on the addition of ammonia and the design of the AK reactor 2.

The activated carbon / activated coke in the AK reactor 2 is increasingly containing ammonium hydrogen sulfate and ammonium sulfate. The adsorbent is continuously in circulation out, with the ammonium sulfate separated from the adsorbent with the help of sieve 3 and the adsorbent for reuse the moving bed reactor is fed back with a line 4. The sieved ammonium sulfate can be appropriate use.

According to FIG. 2, the reference numerals 1 to 6 have the same meaning as in the mode of operation described in FIG. 1 Partial stream 10 of the screened adsorbent regenerated in a wet scrubber. This regeneration takes place by washing out with water in an AK wash 7 Activated coke / activated charcoal must be stored in a separate one before being used again in the AK reactor 2 AK drying 8 can be freed from water. The washing solution from the AK laundry 7 contains in addition to ammonium sulfate, also ammonium hydrogen sulfate and sulfuric acid.

Ammonium sulfate can be obtained from this solution by adding additional ammonia form. The further processing of the ammonium sulfate solution by evaporation to solid But ammonium sulfate is known to be very expensive. The disadvantages of this design are avoided by the fact that the AK-; Jasche 7 through a line 11 leaves Solution, as described in the unpublished patent application P 34 23 744.5, in a Ca precipitation 9 Ca (OH) 2 or CaCO3 are added (both substances are also used in flue gas scrubbing for SO 2 removal).

The sieved ammonium sulfate can also be poured into this solution via a Line 12 are performed. The addition of the Ca compounds has the effect that Calcium sulfate (gypsum) is formed from ammonium sulfate, releasing ammonia is removed by stripping from the solution and the flue gas before AK reactor 2 is fed through a line 13 again. There has to be for them anyway catalytic NO reduction and the 502 x bond NH 3 are added so that through Return of the NE3 the use of fresh NH3 is reduced. The Ca-containing wastewater from the Ca precipitation is shared with the aid of a line 14 with the waste water from the flue gas scrubbing in further processing 15 preferably further processed to the end product gypsum. Thus becomes a separate Further processing of the sulfur compounds from the regeneration of activated coke / activated carbon avoided.

Example 1: Flue gas from a coal furnace leaves a flue gas scrubber with aqueous calcium carbonate solution (end product from the laundry after further processing the washing solution: plaster of paris) in the following condition (after heating up): Flue gas volume flow: 100,000 m3 / h (i.N.) Temperature: 90 ° C Oxygen content: 6.2% by volume Sulfur dioxide content: 400 mg S02 / m3 (normal) Nitrogen oxide content: 800 mg NO2 / m3 (normal) (5% NO2 in NOx) Dem Flue gas is 37.0 kg NH3 / h in front of a moving bed reactor with a layer depth of 2.0 m and a cross-sectional area (inflow area) of 155 m. The moving bed reactor is filled with activated coke, which in the delivery condition has a bulk density of 580 kg / m³ and a specific surface area of 450 m²: g according to Brunauer, Emmett and Teller (DIN 66131). 4.7 m # activated coke are withdrawn at the lower end of the reactor per hour, sieved (and in the process of dust and ammonium sulfate adhering to the outer surface freed) and fed back to the top of the reactor. Fall when straining 53.6 kg / h of ammonium sulfate.

After the reactor, the cleaned flue gas contains nitrogen oxides, calculated as NO2, 190 mg NO2 / m3 (i.N.) (NO2 proportion in NOx less than 1 t) and 140 mg SO2 / m3 (in.).

Example 2 (comparative example) The flue gas leaves the flue gas scrubber under the same conditions as in Example 1. The moving bed reactor has as in Example 1 has an inflow area of 155 m and a layer depth of 2.0 m charged from above with a regenerated activated coke, which is a Bulk density of 580 kg / m3 2 and a specific surface of 450 m / g according to Brunauer, Emmett and Teller (DIN 66131). The flue gas is in front of the moving bed reactor 42.3 kg of NH3 / h metered in. 3.4 m3 of activated coke per hour are fed into the lower end of the The reactor is withdrawn and transferred again to the regeneration stage. It will adsorbed ammonium sulfate removed.

A flue gas leaves the reactor which contains 190 mg NO2 / m³ (n.d.) (NO2 proportion at NOX less than 1%) and less than 40 mg 3 SO2 / m (in the normal range).

The examples show that when the activated coke is circulated without costly regeneration (example 1) also the amount of NH3 to be added is less than in example 2 (with regeneration), the NOx separation being the same good is. In example 2, more favorable SO2 values are achieved, but the SO2 separation in example 1 is still far below the values required by law.

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Claims (4)

Process for the separation of SO and NO x Patent claims: 1. Process for the separation of SO2 and NOx, in particular from flue gases, the majority of which of the SO and a smaller proportion of the NO from the flue gas in a Naßx scrub separated and the main amount of NO from the x flue gas of activated carbon / activated coke with the addition of ammonia catalytically and the remaining S02 is separated by reaction with the ammonia, thereby characterized in that the activated carbon / activated coke is given to a moving bed reactor and the loaded adsorbent removed from the moving bed reactor and over a Sieve passed and thereby ammonium sulfate is separated and the purified adsorbent is fed back to the moving bed reactor for reuse. 2. The method according to claim 1, characterized in that a partial flow the sieved adsorbent is fed to a wet wash, then dried and also fed back to the moving bed reactor. 3. The method according to claim 1 and 2, characterized in that the sieved ammonium sulfate brought into solution and the ammonia driven off and in the course of the proceedings is returned. 4. The method according to claim 2, characterized in that from the Ammonium sulfate of the wash water removed ammonia and returned to the process cycle will.