SI9010827A - Procedure for elimination of nitrogen oxides - Google Patents

Abstract

In the procedure for deciding NO, we add v dissolved ammonia combustion chambers, at using gaseous or as a spray medium evaporated auxiliary into which we inject the reducer before entering the combustion chamber and thereby partially drying to form intermediates compounds, especially decomposition products. By this procedure can be maintained in stoichiometry 1 to 2 during the statutory emission limit without additional shows appeared, e.g. with NH, at the same time waste liquids with dissolved can be taken care of or emulsified organic matter.

Description

PROCEDURE FOR REMEDY OF NITROGEN OXIDES

Technical field of the invention

The present invention relates to the field of inorganic chemical technology and ecology, and more specifically to a process for the removal of nitrogen oxides from waste gases by means of ammonia or. ammonia compounds, in the form of aqueous solutions, which are injected into the waste gas stream in the temperature range 700 to 1200 ° C and distributed throughout the waste gas cross section and to provide aqueous waste solutions from industry and / or agriculture.

Definition of a technical problem

It is known that solid sorption agents are blown into the combustion chamber of the steam generating plant and thus partially bind harmful substances such as SO _x , chlorine, fluorine and also nitrogen oxides. These processes, however, have the disadvantage of creating or causing them. solid chemical compounds remain that increase the ash content of the waste gases and ultimately burden the landfill. A further drawback is that, according to these known methods, it is generally not possible to achieve the legally prescribed purity of the waste gas in the purification stage, so that further, absorptive purification steps are required which increase the need for space and therefore are not suitable for old installations but they also drastically impair operating results.

The state of the art

Blowing ammonia gas into hot waste gases is known, resulting in the reduction of nitrogen oxides, where it is a disadvantage that, especially with fluctuating nitrogen oxide content, ammonia leaks through the fireplace, so that further action is needed, especially through catalysts that the process becomes unnecessarily expensive. Furthermore, direct injection of urea is known. of urea solutions into the combustion chamber (US-PS 4,208,386 or 4,325,924), with the addition of an additive or a to move the temperature range in which nitrogen degradation is possible. This process is highly unstable against fluctuations in load and temperature changes, and since most of the organic compounds decompose at 1000 ° C, urea life is limited in time so that, with minor changes in temperature, the reduction of kcije _{χ is} reduced.

Description of solution to a technical problem with implementation examples

It is therefore an object of the invention to take action against existing defects in ammonia as well as the storage of ammonia as well as the decomposition of urea and, if possible, to remove nitrogen oxides from waste gas in one step or to reduce them to comply with legal requirements for maintaining air cleanliness.

A positive effect is that it is easier to store ammonia water than liquid ammonia.

The present invention is characterized in that ammonia or ammonia compounds and optionally one or more additives in aqueous solution and the gaseous or evaporated auxiliary medium is individually distributed in the waste gas stream, or that the ammonia or The ammonia compounds are pulverized into a stream of gaseous or evaporated auxiliary medium, and the mixture is distributed in the waste gas stream, using combustion air, water vapor, compressed air or inert gases as the auxiliary medium for blowing the reducing agent with the additive, and as an additive of the order of magnitude up to maximum 10% by weight, based on the amount of ammonia, use nitrogen and / or oxygen-containing organic compounds that are either added to the ammonia solution or mixed separately with the waste gas stream in dissolved form to decompose secondary emissions and / or improve reactivity ammonia or. ammonium compounds, especially in the direction of the lower temperature range.

Further essential features are set out below. Additive solutions contain N- and / or O-containing organic compounds, in particular glycerin, glycol and / or other solutions containing polyvalent alcohols or waste solutions, respectively. solutions from industry and / or agriculture.

Reducing agents are added to the waste gas, depending on the nitrogen oxide load to be removed, and in particular up to a 2.0 molar ratio.

The ammonia solution is blown into a dust-containing, hot waste gas from a steam boiler fired mainly by coal dust in a combustion chamber at or. by burner level, whereby the dust generated in the combustion waste gas acts as a catalyst in the high temperature range.

The ammonia solution is introduced into the combustion chamber at one or more levels, preferably with peak air, secondary or tertiary burner air.

The ammonia solution is dusted in the supply air of the peak air and previously dried, as well as evenly distributed in the atmosphere of the water vapor in the combustion chamber.

The additive is dissolved in alcohol or other organic liquid and used in particular with dilute or water-filled.

The introduction of the reducing agent takes place in a dissolved form in the waste stream through a system of nozzles, especially multi-threaded nozzles, with a small size of droplets that allow a fine and in particular even distribution throughout the cross-section of the waste gas. When performing the nitrogen removal experiments, we found that ammonia water, when blown into the combustion chamber, inhibits the formation of ΝΟ _χ or. decomposes the formed ΝΟ _χ . Particularly good results are obtained by dissolving the ammonia in water and dispersing it as a solution in hot air before blowing it through the nozzle into the combustion chamber, so as to produce supersaturated ammonia droplets in the hot air, which are blown into a particularly fine form by surrounding steam in the combustor. chamber at temperatures of 700 to 1200 ° C. The notion of water applies not only to pure water, but in particular to waste solutions of any kind, such as water. slurry, contaminated, inappropriate wine, and aqueous chemical wastes, to the extent that they do not contain solids.

The effective temperature range can be shifted by adding to the solution additives such as triazines, cyanamides, guanidines, and in particular their salts, in amounts up to 10% by volume of ammonia. However, it is not necessary to inject the additives dissolved together with ammonia, they can also be injected in some other place, so that the reactivity of the ammonia is prolonged. However, the effects of burned fuel are also reflected, so that the catalytic effects of the summer, especially with the increasing content of heavy metals, appear to be demonstrable. A further feature is that ammonia water is not injected with primary air but with peak air or. secondary or tertiary air in step combustion to reduce the formation of ΝΟ _χ in the combustion chamber, ie ammonia water causes a somewhat delayed and prolonged reduction. For this reason, it is also appropriate to reverse the suction of flue gases, especially for flue gas rich in oxygen, if the fuel has been burned with excess air. However, as mentioned earlier, it is essential that the water vapor generated by drying the solution catalyzes the reduction. Water vapor and oxygenated oxygen molecules excited by high temperatures, thus practically in the nascent state, produce intermediates of compounds that break down ΝΟ _χ or. prevent the formation of new ΝΟ _χ molecules. In any case, the ΝΟ _χ content in most cases dropped to and below the legally transferable value at the entrance to the fireplace or at a previously included second cleaning stage. Further positive effects occur when ammonia is dissolved in N- and / or O-containing hydrocarbons such as e.g. polyvalent alcohols, especially in aqueous mixtures or emulsions, with suitable waste chemicals, emulsions such as drilling oil, possibly with a lower alcohol content, not necessarily pure, with the use of additional additives which may be restricted or waived. In principle, however, it can be said that in some cases, the use of additional additives or waste solution may be waived.

The decomposition, respectively. preventing the formation of ΝΟ _χ in the high temperature range due to the decomposition of organic compounds has the advantage that the breakthrough of the reducing agent is insignificant, even though the highly variable formation of ΝΟ _{χ must be} accounted for on the fuel side, especially in the combustion process. Due to the high temperatures, the formation of secondary emissions or. breakdown of organic compounds maintained at extremely low levels. In addition, no additional depositing material is generated, even when the reducing agent is dosed to the protruding ΝΟ _χ in a superstoichiometric amount. Particularly good experimental results were shown in the dosage of a reducing agent of the order of 1 or 2. 2-fold stoichiometry against the expected formation of ΝΟ _χ . In the experiments we further found that the heating surfaces of the steam generator were not burdened with additional blowing of the ammoniacal solution, so that there was neither delay nor clogging nor additional corrosion. Unpleasant fuels can be used in this process, such as for example. brown coal with a variable ash content, without exceeding the emission limit values, even showed that ash-rich fuels would appear to be able to reduce the required reducing agent, which is also evident from the heavy metal content in summer or in the summer. its catalytic effects. In principle, the process is suitable for combustion plants for all fuels, as well as for process waste gases.

It is not necessary for the ammonia to be dissolved in pure water. All waste liquids are suitable for this, insofar as NH ₃ melts and does not increase the level of harmful substances in the waste gas, ie glycol-containing wine, oil-containing water, washing alcohol, etc., but may cause mineral solutions (saline solutions) again problems due to emerging solid constituents.

One of the ideas of the invention is also that the waste solutions, respectively. industrial and / or agricultural solutions containing ammonia or. ammonia compounds used instead of synthetically prepared ammonia solutions, such as e.g. of ammonia water. It is further an idea of the invention to add additional additives to the ammonia solutions which, on the one hand, can enhance the effect of the pure ammonia solution, prevent further secondary emissions or extend the specific temperature range to be used. Additional additives are generally O- and / or N-containing organic compounds which can only be added in a small amount to ammonia solution. Additional additives can also be added in the form of waste solutions, or. industrial and / or agricultural solutions containing the above additional additives. As an example, here we should mention glycerin or. glycol-containing solution or solutions containing glycerin and / or glycol derivatives, respectively. other multivalent alcohols.

It turns out that solutions of additional additives have only in some cases contributed to the improvement of the level of decision making. reductions in secondary emissions so that they are not strictly necessary in each case.

Claims (8)

PATENT APPLICATIONS 1. Process for the removal of nitrogen oxides from waste gases by means of ammonia or ammonia compounds, in the form of aqueous solutions, which are blown into the waste gas stream in the temperature range 700 ° C to 1200 ° C and distributed throughout the exhaust gas cross section, and to provide aqueous waste solutions from industry and / or agriculture, characterized by the fact that ammonia or. ammonia compounds and optionally one or more additives in aqueous solution and the gaseous or evaporated auxiliary medium is individually distributed in the waste gas stream, or that the ammonia or The ammonia compounds are pulverized into a stream of gaseous or evaporated auxiliary medium, and the mixture is distributed in the waste gas stream, using combustion air, water vapor, compressed air or inert gases as the auxiliary medium for blowing the reducing agent with the additive, and as an additive of the order of magnitude up to maximum 10% by weight, based on the amount of ammonia, use nitrogen and / or oxygen-containing organic compounds that are either added to the ammonia solution or mixed separately with the waste gas stream in dissolved form to decompose secondary emissions and / or improve reactivity ammonia or. ammonium compounds, especially in the direction of the lower temperature range. Process according to claim 1, characterized in that the additive solutions contain N- and / or O-containing organic compounds, in particular glycerin, glycol and / or other solutions containing multivalent alcohols or waste solutions or. solutions from industry and / or agriculture. Method according to claim 1, characterized in that the reducing agents are added to the waste gas, depending on the nitrogen oxide load to be removed, and in particular up to a 2.0 molar ratio. Process according to claim 1, characterized in that the ammonia solution is blown into the dust containing, hot waste gas from a steam boiler fired mainly by coal dust in a combustion chamber on or. by burner level, whereby the dust generated in the combustion waste gas acts as a catalyst in the high temperature range. Method according to claim 1, characterized in that the ammonia solution is introduced into the combustion chamber at one or more levels, preferably with peak air, secondary or tertiary burner air. 6. A process according to claim 1, characterized in that the ammonia solution is dusted in the supply air of the peak air and pre-dried thereafter and evenly distributed in the atmosphere of the water vapor in the combustion chamber. 7. A process according to claim 1, characterized in that the additive agent is dissolved in alcohol or other organic liquid and used in particular by diluting or flooding with water. Method according to claim 1, characterized in that the introduction of the reducing agent takes place in a dissolved form in the waste stream through a system of nozzles, in particular multi-threaded nozzles, with a small size of droplets allowing a fine and in particular even distribution throughout the cross-section of the waste gas.