DE4117477A1 - Oxidative post-treatment of incinerator waste gas - includes injecting oxidant into waste gas region at elevated temp., to avoid dioxin and furan formation - Google Patents

Abstract

In the oxidative post-treatment in which an oxidant is injected into the gases prior to dust removal, the improvement is that the oxidant is injected into a waste gas region at above 400 (pref. 400-600) deg. C. The oxidant may be O3 or pref. H2O2, esp. a 6-40 (pref. 30-35)% aq. H2O2 soln. Pref., the oxidant is injected in a stoichiometric ratio such that at least the organic pollutants, carbon and carbon cpds. are converted into CO2. Injection is carried out pref. by nozzles uniformly distributed over the cross-section of the waste gas stream. ADVANTAGE - Noxious substances (esp. polychlorinates dibenzodioxins and furans) are reduced to levels of 0.1ng/cu.m. toxicity equiv. or less in a relatively simple manner.

Description

The invention relates to a method for oxidative After-treatment of the incineration of waste and waste derived from exhaust gases, in accordance with the Concept of claim 1.

In the case of incineration of industrial and municipal waste, garbage and hazardous waste very frequently chlorinated dibenzodioxins and furans (PCDD / PCDF) are produced as pollutants in the trace range, which can be released into the environment with the exhaust gases (flue gases, raw gases) or with separated dusts. By maintaining ideal combustion conditions, the PCDD / PCDF concentration in the combustion exhaust gases can be reduced to as low as 1 ng / m ³ TE (TE = toxicity equivalents). However, the legally prescribed new emission standards only allow a PCDD / PCDF concentration in such combustion exhaust gases of a maximum of 0.1 ng / m ³ TE. In order to comply with this new emission standard, additional measures are required to at least accordingly reduce the content of dioxins and furans in the combustion exhaust gases accordingly.

From the practice as well as from the relevant Fachlitera tur, it is already known, behind the actual Incinerators for waste, garbage and Special waste other than conventional filtering equipment, such as z. As cyclones, electrostatic precipitators or the like., In addition Downstream activated carbon or Aktivkoksfilter too use, in which the pollutants of the gas at the Activated carbon or the activated coke to be adsorbed, where also additional, oxidative catalytic Measures can be taken. In these  Filtering measures, the pollutants but not prevented, but only collected. In addition, the forms Adsorption of the pollutants on activated carbon / activated coke certain potential for danger insofar as it occasionally to dangerous fires this Activated carbon / activated coke filter can come, with the collected pollutants directly into the environment reach.

Further, in the book by Karl J. Thom'-Kozmiensky, waste incineration and environment 3, EF-Verlag for energy and environmental technology, Berlin 1989, pp. 15 to 32 (or p. 1 to 18) in a "contribution to the solution of the dioxin-problem in the case of waste incineration "also already a Ver drive approximately as proposed in the preamble of claim 1. After this proposal, for example, hydrogen peroxide (H ₂ O ₂ ) just before a separation device (multicyclone and wet flue gas cleaning) as an additive in the smoke or raw gases at 200 to 250 ° C are injected. These measures are intended to destroy gaseous dioxins and furans in particular. Again, there is the problem that the condensed on the dusts, especially flue dusts chlorinated hydrocarbons can not be completely destroyed by the H ₂ O ₂ and thus reach the environment.

The invention is therefore based on the object Method predicted in the preamble of claim 1 set way to create that by relative measures reduce the pollutant content, in particular the Content of chlorinated dibenzodioxins and furans (PCDD / PCDF) at least to a minimum value zen who is responsible for compliance with the preamble  new emission standards for waste and waste combustion systems is necessary.

This object is achieved by the in Kenn Sign of claim 1 specified procedure ge solves. Advantageous embodiments and developments This invention is the subject of the dependent claims.

In contrast to the last described state of Technology (in Karl J. Thom'-Kozmiensky, waste incineration and environment 3) is the process of the invention the oxidizing agent in a range in the exhaust gases injected, in which these exhaust gases are still a temperature of at least about 400 ° C, d. H. the injection of the oxidizing agent follows in a range of from preferably above 400 ° C. The invention is there taking advantage of the fact that the mentioned PCDD / PCDF Compounds generally in a temperature range of be formed about 200 ° C to 400 ° C. According to the invention Thus, the oxidizing agent is in the of the owner waste and waste incinerator the exhaust gases already injected in an area in which these exhaust gases still have a temperature above is half the temperature range in which the ge called PCDD / PCDF connections form this connection So are still not available in the exhaust gases.

For this oxidative aftertreatment of the still over 400 ° C hot exhaust gases is mainly a strong oxidizing agent in question, and indeed - as will be explained in more detail later - preferably hydrogen peroxide (H ₂ O ₂ ), but also ozone (O ₃ ) can cause similarly good after-treatment results.

With particular advantage, this strong oxidizing agent, preferably so hydrogen peroxide (H ₂ O ₂ ) is injected liquid in a liquid or gasför mig in the exhaust gases in an approximately stoichiometric with respect to the oxidation conversion ratio. In this case, it is assumed that this injection of H ₂ O _{2 is} preferably carried out in the stoichiometric ratio (which will be explained later on the basis of a numerical example); but it is not excluded that the herbeizu leading oxidation or combustion in case of need (especially depending on the operation or of the completeness / incompleteness of Oxida tion / combustion) can also be influenced in such a way that a slight stoichiometric or even slightly overstoichiometric amount ratio when introducing H ₂ O _{2 is} brought about.

It is also particularly advantageous if the Oxidati onsmittel, so preferably H ₂ O ₂ , in such a stoichiometric ratio in the exhaust gases is scored that at least in the exhaust gases contained (carbonaceous) organic pollutants, carbon (C) and carbon compounds in inert Koh dioxide (CO ₂ ) are transferred.

In this method according to the invention, therefore, all, or at least all significant organic pollutants can be oxidized to carbon dioxide (CO ₂ ). In this oxidative aftertreatment of the above-mentioned combustion Ver gases especially the carbon (C), which is present in the form of organic trace pollutants, and the carbon monoxide (CO) converted into the inert Koh dioxide. It is here, so to speak, brought about a stoichiometric post-oxidation of pollutants contained in these gases or pollutant traces at a time in which these gases were still warmer than 400 ° C and in which thus no toxic dioxins and furans may have formed, so that primarily inerting the carbonaceous organic pollutants to carbon dioxide. Accordingly need in this inventions to the invention process these pollutants, such as dioxins and furans not to be destroyed (since they are not even available), but it is very reluctant casual prevents that these pollutants can form or can form in a proportion which exceeds the initially mentioned new emission standards.

In the injection of H ₂ O ₂ in the exhaust gases, for example, a waste or hazardous waste incineration in Be rich above an exhaust gas temperature of 400 ° C in addition to the mentioned inerting of carbon and carbon compounds in the exhaust gas available sulfur dioxide (SO ₂ ) to sulfur trioxide (SO ₃ ) are oxidized, which can be used to separate the wet scrubbing in a particularly good for dust removal. Namely, reduces the SO ₂ concentration, then more nitrogen dioxide is formed, which is otherwise re-formed in the presence of SO ₂ again in the insoluble nitrogen oxide. Added to this is the destructive effect of this oxidizing agent on all aromatic compounds, so that all "precursor" forms of PCDD / PCDF and possibly existing dioxins and furans are destroyed.

Hydrogen peroxide (H ₂ O ₂ ) is due to its high Re activity in the temperature range above 400 ° C as Oxi dationsmittel for this inventive oxidative aftertreatment of said combustion gases at the most suitable. H ₂ O ₂ is converted into the said combustion conditions and the presence of particulate metal oxides in OH radicals, whereby the strongest oxidant is ever formed.

As regards the handling and transport of the hydrogen peroxide (H ₂ O ₂ ) used as the oxidant, H ₂ O _{2 should be used} in the form of at least 6% aqueous solution, preferably in 6 to 40% aqueous solution Solution. Here, taking into account the required H ₂ O ₂ amount for the stoichiometric conversion in the oxidative after-treatment of the exhaust gases, a lower solution than a 6% aqueous H ₂ O ₂ solution because of an unnecessarily high amount of water makes little sense, while at a higher than 40% H ₂ O ₂ solution may cause safety or transportation problems. For the practice of this method, an about 30 to 35% aqueous H ₂ O ₂ solution can be particularly preferred, which is due to the fact that on the one hand a 30% aqueous H ₂ O ₂ solution and possibly also a 35 % aqueous H ₂ O ₂ solution without difficulty on the market are Lich and that on the other hand present a particularly favorable solution amount for a uniformly ver divided injection into an exhaust gas stream.

As has already been mentioned above, when using ozone (O ₃ ) as the oxidizing agent just in case a relatively good oxidative post-treatment result of the combustion exhaust gases can be achieved. Compared to hydrogen peroxide (H ₂ O ₂ ), however, the handling of ozone is much more difficult, and it is manoeuvrable to produce ozone.

The oxidative aftertreatment process according to the underlying invention will be described below with reference to a Embodiment explained in more detail that in an An Scheme illustrated in the attached drawing light is.

The only very simplified and schematically illustrated in the drawing system for carrying out the oxidi tive aftertreatment of combustion gases containing a industrial or municipal waste, with garbage or hazardous waste according to the arrows 1 chargeable combustion furnace 2 , for example in the form of a rotary kiln, but also can be implemented in any other suitable furnace construction. This combustion furnace 2 is at its outlet end 2 a, a post-combustion chamber 3 immediately downstream, from which the originating from the combustion exhaust gases (dashed arrows 4 ) are passed through a waste heat boiler 5 . After this waste heat boiler 5 , the exhaust gases (arrows 4 ) are fed to a conventional and therefore unspecified veran illustrated exhaust or flue gas cleaning, in particular a dust separation or dedusting and possibly additionally a catalytic purifying Rei this exhaust can take place.

In a temperature range which is approximately between the After combustion chamber 3 and the mentioned exhaust or flue gas cleaning and in which the flue gases (arrows 4 ) still have a temperature of about 400 ° C, should in this combustion gases hydrogen peroxide (H ₂ O ₂ ) as an oxidizing agent for an oxidative aftertreatment. In the example of an installation according to the drawing, it is assumed that said temperature range TB is located in the rear section as viewed in the exhaust gas flow direction and in the region of an upper exhaust gas deflection point 5 a of the waste heat boiler 5 . In this temperature range TB or in the region of this exhaust gas to steering point 5 a within the waste heat boiler 5, a nozzle device 6 for injecting the hydrogen peroxide (H ₂ O ₂ ) is arranged. This nozzle device 6 is connected via a supply line 7 arranged therein feed pump 8 , optionally in the form of a metering pump, with a sufficient from large storage tank 9 for hydrogen peroxide, in particular in the form of an aqueous hydrogen peroxide solution.

The nozzle device 6 is suitably the cross section of the associated exhaust gas flow space, so the deflection point 5 a, adapted. Accordingly, it may already be sufficient in small plants, if this nozzle device contains only a single nozzle. but lm all common, and in particular for larger and large to lay, it is advantageous and therefore vorzuzie his hen, more evenly distributed over the entire cross-section of he mentioned exhaust flow space Dü sen in the nozzle device 6 provided (in the veran illustrated Plant schematic are four such nozzles interpreted to) to inject the hydrogen peroxide in the exhaust stream (arrows 4 ) finely divided over the entire flow cross-section can.

As has been mentioned above, the tempera TB, in which the oxidizing agent is injected will be above 400 ° C. Although for this temperature area TB generally no upper limit In many cases, it can be particularly advantageous this temperature range TB between 400 and 600 ° C from for practical reasons, and in particular  even if some tendency to re-reactions could exist in the range above 600 ° C.

In the described and illustrated in the drawing clear embodiments of a suitable for carrying out the process of the invention system can work in operation in general with a kontinuierli chen injection (without special regulation) tion medium for the Oxida. In this case, of course, there is also the possibility to provide additional dosage and Men genregulier facilities for the injection of Oxida tion medium, for example, fluctuate in the pollutant concentrations in the Verbrennungsabga sen, ie it can then made a function of the jewei time pollutant concentrations, a volume control of einzudüsenden oxidizing agent become. The feed pump 8 in the supply line 7 should preferably be designed so that flow rate and För derdruck can be kept constant, the specific delivery pressure depends on the size and interpretation of the nozzles.

The amount of H ₂ O _{2 to} be injected is explained below on the basis of a calculation example.

calculation example To determine the einzudüsenden amount of H₂O₂ for stoichiometric post-oxidation of the combustion exhaust gases

The calculation is approximately based on the above The drawing described embodiment. In order to the following data result:

60 000 m³ / h of exhaust gas (conservative assumption) CO: 50 mg / m³ C _tot : 100 mg / m³ (mainly dustbound) SO₂: 1000 mg / m³

Calculation of freights

To calculate the stoichiometry you need the molecular weight (from literature):

CO: 28 g / mol C: 12 g / mol SO₂: 60 g / mol H₂O₂: 34 g / mol CO₂: 44 g / mol H₂O: 18 g / mol SO₃: 76 g / mol

example

In a 30% aqueous H₂O solution results a total of 250 l / h.

In a 35% aqueous H₂O₂ solution results a total of 215 l / h.  

From the preceding calculation example, he can see that when using a 30% or 35% aqueous H ₂ O ₂ solution (as an oxidizing agent) be particularly easy to handle liquid amount results, which is also particularly favorable for storage and In addition, with regard to safety technical aspects proves. If, in connection with this calculation example, an average value for the CO concentration of 50 mg / Nm ³ (standard cubic meter), for particulate (dust-bound) carbon of 100 mg / Nm ³ and for sulfur dioxide of 1000 mg / Nm ^{3 is used} , then one needs for oxidative aftertreatment of the mentioned combustion exhaust gases - rounded up - about 75 l / h of pure H ₂ O ₂ . This corresponds in the case of a 30% strength aqueous H ₂ O ₂ solution to an hourly amount of liquid to be injected per hour of 250 l (for a 35% strength aqueous H ₂ O ₂ solution of 215 l / h). It should be noted that the energy is supplied for heating and evaporation of this eingedü most liquid from the exhaust gas and the exothermic exiting reactions. The cooling of the exhaust gases resulting in this calculation example is about 5 K and is thus insignificant or negligible. In the case of a lower-percentage aqueous H ₂ O ₂ solution, on the other hand, a considerably higher cooling of the exhaust gases is to be expected due to the larger amount of water to be evaporated. Due to the 30% and 35% aqueous H ₂ O ₂ solutions used in the calculation example thus the exhaust gas temperatures are practically hardly affected. It can therefore be adhered to the necessary temperatures of <250 ° C for conventional dedusting, example, electrostatic precipitator, usually for safety reasons.

In addition, there is no danger to the environment by possibly unconsumed hydrogen peroxide in this type of H ₂ O ₂ -Eindü solution in the combustion gases. Unused hydrogen peroxide breaks down to water and oxygen.

By the oxidative aftertreatment according to the invention This combustion exhaust gas also becomes a deposit of heavy metal oxides or salts, in particular also Traces of any volatile heavy metals present (especially mercury) favors, if this spu oxidized and in a subsequent scrubbing ab be divorced.

As can be seen from the above relationships further is, by this inventive oxidative after treatment of said combustion gases the Ausbil tion of the conventional, downstream Reinigungsstu fen, in particular the dust separation and katalyti cleaning, not affected. This can be done here proposed method also particularly advantageous already existing exhaust gas cleaning systems nachträg Lich and be installed with relatively little effort.

Claims (8)

1. A method for the oxidative after-treatment of waste gases from the incineration of waste and waste, wherein the exhaust gases before their dedusting a means for the oxidation of ent in these exhaust gases held pollutants is injected, characterized in that the oxidizing agent in an area in the From gases is injected, in which these exhaust gases still have a temperature of more than about 400 ° C. 2. The method according to claim 1, characterized that the oxidizing agent is in one with regard to the oxidation conversion approximately stoichiometric Amount ratio liquid or gaseous in the Ab is injected gas. 3. The method according to claim 2, characterized in that hydrogen peroxide (H ₂ O ₂ ) is used as the oxidizing agent. 4. The method according to claim 3, characterized in that H ₂ O ₂ in the form of an at least 6% aqueous solution, preferably a 6- to 40% aqueous solution, in particular an approximately 30- to 35% wäs serige solution used becomes. 5. The method according to claim 2, characterized in that is used as the oxidant ozone (O ₃ ). 6. The method according to claim 1, characterized in that the oxidizing agent is injected in such a stoichiometric cal ratio in the exhaust gases that contained at least in the exhaust gases orgasmic African pollutants, carbon (C) and carbon compounds in inert carbon dioxide (CO ₂ ) are transferred. 7. The method according to claim 1, characterized that the oxidizing agent in a temperature range from about 400 ° C to about 600 ° C in the exhaust stream is injected. 8. The method according to claim 1, characterized that the oxidizing agent with the aid of several, over the cross section of an exhaust gas flow space Evenly distributed nozzles in the exhaust stream feinver is shared.