DE102007020281A1 - System for finishing treatment of exhaust gases, for reduction of nitrogen oxides in exhaust gases of internal combustion engine, has solution, water, urea and reaction chamber - Google Patents

Abstract

The system has a solution, water, urea and a reaction chamber. The units are provided to inject the solution into the reaction chamber. The solution has a tenside. The tenside has a hydrophilic functional group, which form a hydrogen bridge. The hydrophilic group is selected from carboxyl, carboxylate, hydroxyl, sulfone, sulfate, sulfonate, ammonium, amino, amide, polyether alcohols and betaines. The tenside has a lipophilic part made from hydrocarbon chains, dimethyl silicone catenae or fluorocarbon chains. An independent claim is also included for a method for reduction of nitrogen oxides in exhaust gases of internal combustion engine.

Description

State of the art

The The invention relates to a system for the aftertreatment of exhaust gases Internal combustion engines according to the preamble of claim 1.

For the reduction of nitrogen oxides in exhaust gases of internal combustion engines, in particular self-igniting internal combustion engines, NO _x reduction catalysts are generally used. In these, a reducing agent for reducing the nitrogen oxides is injected. The injection of the reducing agent is generally via injection valves, which atomize the solution via spray holes. The atomization takes place due to the pressure of the solution.

Around to achieve a sufficient reduction effect, it is necessary that the solution is sufficiently finely atomized. In the currently used injectors, the solution over However, spraying spray holes is the spray generated generally not sufficiently finely atomized.

Disclosure of the invention

One Inventively designed system for aftertreatment of exhaust gases from internal combustion engines comprises a solution containing hydrogen and urea, and a reaction space. Means are provided for the solution in the reaction space inject. Contains according to the invention the solution still contains at least one surfactant.

The reaction space is generally a NO _x reduction catalyst, as already used in exhaust gas aftertreatment. In the reaction space, the nitrogen oxides contained in the exhaust gas of the internal combustion engine are reduced in the presence of urea as a reducing agent to nitrogen, water and carbon dioxide. The reaction is preferably carried out in the presence of a catalyst. Suitable catalysts for playing are conventional catalysts, such as those used in nitrogen reduction and are known in the art.

The proportion of water in the solution is preferably in the range of 40 to 90 wt .-%, particularly preferably in the range of 65 to 75 wt .-%. The proportion of urea is preferably in the range of 10 to 60 wt .-%, particularly preferably in the range of 25 to 35 wt .-%. Usually, a solution according to DIN 70070 AUS 32 used with a urea content in the range of 31.8 to 33.2 wt .-%.

Of the Proportion of the surfactant in the solution is dependent on the type of surfactant, but is preferably less than 0.1 g / l.

When Surfactant are, for example, nonionic surfactants, anionic Surfactants, cationic surfactants or amphoteric surfactants. Also mixtures The aforementioned surfactant classes can be used.

If the solution contains a nonionic surfactant, so this can for example be selected from the group, consisting of alcohol alkoxylates, alkylphenol alkoxylates, alkylpolyglucosides, N-alkylpolyglucosides, N-alkylglucamides, fatty acid alkoxylates, fatty acid polyglucol esters, Fatty acid amine alkoxylates, fatty acid amide alkoxylates, Fatty acid alkanolamide alkoxylates, N-alkoxyl polyhydroxy fatty acid amides, N-Aryloxipolyhydroxifettsäureamiden, block copolymers Ethylene oxide, propylene oxide and / or butylene oxide, polyisobutene alkoxylates, Polyisobutene-maleic anhydride derivatives, fatty acid glycerides, Sorbitan esters, polyhydroxy fatty acid derivatives, polyalkoxy fatty acid derivatives and bisglycerides.

If the solution contains an anionic surfactant, so For example, this can be selected from the group, consisting of fatty alcohol sulphates, sulphated alkoxylated alcohols, Alkanesulfonates, N-alkyl sarcosinates, alkylbenzenesulfonates, olefin sulfonates and disulfonates, alkyl ester sulfonates, sulfonated polycarboxylic acids, Alkyl glycerol sulfonates, fatty acid glycerine ester sulfonates, Alkylphenol polyglucol ether sulfates, paraffin sulfonates, alkyl phosphates, Acylisothianates, acyltaurates, acylmethyltaurates, alkylsuccinic acids, Alkenylsuccinic acids or their half-esters or half-amides, Alkylsulfonbernsteinsäuren or their amides, mono- and diesters of sulfosuccinic acids, sulfated alkyl polyglycosides, alkyl polyglycol carboxylates and Hydroxyalkylsarkosinaten.

The Surfactant may further be a cationic surfactant, the cationic Surfactant, for example, is selected from the group consisting from tetraalkylammonium salts, imidazolinium salts and amine oxides.

Finally, the surfactant may be a surfactant of the group of amphoteric surfactants, wherein the amphoteric surfactant is, for example, selected from the group consisting of surfactants containing carboxylic acids and furthermore at least one ethylenically unsaturated monomer unit of the general formula (I) R ¹ (R ² ) = C (R ³ ) R ⁴ (I); in the R ¹ to R ⁴ independently of one another are -H-CH ₃ , a straight-chain or branched saturated Al kylrest having 2 to 12 carbon atoms, a straight-chain or branched, mono- or polyunsaturated alkyl radical having 2 to 12 carbon atoms, with -NH ₂ , -OH or -COOH substituted alkyl or alkylene radicals as defined above, a heteroatomic group having at least one positive charged group, a quaternized nitrogen atom or at least one amine group having a positive charge in the pH range between 2 and 11 or -COOH or -COOR ⁵ , wherein R ^{5 is} a saturated or unsaturated, straight-chain or branched hydrocarbon radical having 1 to 12 carbon atoms ,

In a preferred embodiment contains the Surfactant is a hydrophilic functional group that is a hydrogen bridge can form. Preferably, the hydrophilic group is selected from carboxyl, carboxylate, hydroxil, sulfone, sulfonate, sulfate, ammonium, Amino, amide, polyether alcohols and betaines.

The Surfactant preferably further contains a lipophilic Part selected from hydrocarbon chains, dimethylsilicone chains and / or (per) fluorohydrocarbon chains.

The Means for injecting the solution into the reaction space are preferably injectors. Suitable as injectors all the injection valves known to the person skilled in the art, by which the injected solution is atomized. Preferably Injectors are used, in which the atomization by Printing done. This is a pressurized liquid through an opening in a room with lower pressure injected. The pressure difference relaxes the liquid and it is atomized. The bigger the Pressure difference is, the finer is the atomization the liquid.

Particularly preferred for injecting the solution, a multi-fan jet atomizing nozzle is used, as for example in WO-A 2006/072487 is described. Unlike atomizing systems with turbulent jet disintegration, liquid lamellae are created here, which disintegrate into droplets. With a low surface tension smaller drops are achieved.

A finer atomization can also be achieved by that the surface tension of the solution is lowered becomes. According to the invention, this is done by the addition of the surfactant. By the decrease of the surface tension due to the addition of the surfactant is injected into the reaction space Solution better atomized. The efficiency of the System for aftertreatment of exhaust gases with regard to nitrogen oxide reduction in the exhaust system is improved.

The The invention further relates to a process for the reduction of nitrogen oxides in exhaust gases of internal combustion engines in which a solution containing hydrogen and urea, injected into a reaction space becomes. The reaction space is traversed by the exhaust gas of the internal combustion engine. According to the invention, the solution contains Surfactant.

When Surfactant are those already specified above Surfactants.

Around to achieve a sufficiently fine atomization and thus a sufficient reduction of nitrogen oxides in the exhaust gas of the internal combustion engine the solution is preferably dependent on a pressure from the atomizer system in the range of 3 to 30 bar in the Reaction space injected. Injecting the solution takes place generally via an injection valve, as is known to the person skilled in the art.

In a preferred embodiment of the invention System for the reduction of nitrogen oxides in exhaust gases of internal combustion engines used. The internal combustion engine is in particular a self-igniting Internal combustion engine. In general, the internal combustion engine used in a passenger car or truck. however The system according to the invention can also be found at each other, known in the art self-igniting internal combustion engine be used.

Brief description of the drawings

embodiments The invention are illustrated in the drawing and in the following description explained in more detail.

The single figure shows a schematic representation of an emission control system.

embodiments the invention

An internal combustion engine 10 is with an exhaust system 12 connected. About the exhaust system 12 become exhaust gases of the internal combustion engine 10 delivered to the environment. The exhaust gases are produced by combustion of fuel in the individual cylinders of the internal combustion engine 10 ,

The internal combustion engine 10 is generally a self-igniting internal combustion engine, as used for example for driving medium or heavy trucks. The exhaust system 12 However, it can also be used with any other internal combustion engine, preferably a self-igniting internal combustion engine. Such self For example, igniting internal combustion engines are also used in passenger cars. But even ships or construction vehicles are powered by self-igniting internal combustion engines. These too can be equipped with an exhaust system 12 , as shown in the figure, be connected.

The exhaust system 12 includes an exhaust pipe 14 in which an oxidation catalyst 16 is included. In the oxidation catalyst 16 Nitrogen monoxide is first emitted from the exhaust gas of the internal combustion engine 10 converted with oxygen to nitrogen dioxide. Furthermore, in the oxidation catalyst 16 a part of the carbon contained in the exhaust, as carbon black carbon present in carbon dioxide.

To the oxidation catalyst 16 can connect to a particle filter, not shown here. In the particulate filter soot particles from the exhaust gas of the internal combustion engine 10 separated. For this purpose, the particulate filter generally has a ceramic honeycomb structure with a plurality of channels that are mutually sealed so that channels that are the oxidation catalyst 16 are open, on the oxidation of the catalyst 16 pioneering side are closed and vice versa. As a result, the particulate-laden exhaust gas flows through porous walls of the honeycomb body. In the process, the particles, which essentially consist of carbon, deposit in the pores of the walls. As a result, the pores of the particulate filter in the course of operation to set. For this reason, the particle filter must be regenerated from time to time. For this purpose, the particle filter is heated, so that the particles deposited in the honeycomb structure burn to carbon dioxide. This is discharged together with the exhaust gas from the particulate filter.

In the further course closes in the exhaust system 12 to the oxidation catalyst 16 and optionally to the particulate filter, an SCR catalyst 18 at. In the SCR catalyst, nitrogen oxides contained in the exhaust gas, ie, nitrogen monoxide and nitrogen dioxide, are reduced to molecular nitrogen and water with ammonia as a reducing agent. The ammonia is generally produced by a hydrolysis reaction in the SCR catalyst 18 obtained from a reducing agent. The reducing agent becomes the SCR catalyst 18 from a reducing agent dosing system 20 added.

The reducing agent dosing system 20 includes a reducing agent tank 22 in which the reducing agent is stored. The reducing agent tank 22 is via a dosing line 24 with a nozzle 26 connected. About the nozzle 26 the reducing agent is added to the exhaust gas before flowing into the SCR catalyst. The amount of reducing agent added is via a metering valve 28 controlled. The control takes place with the help of a control unit 30 in which, for example, from operating data of the internal combustion engine 10 the required amount of the reducing agent is determined.

To the reducing agent from the reducing agent tank 22 via the dosing line 24 and the nozzle 26 into the exhaust gas is in the dosing line 24 a pump 32 intended. With the pump 32 the reducing agent is removed from the reducing agent tank 22 under pressure into the dosing line 24 promoted. Due to the pressure, the reducing agent as it flows out of the nozzle 26 atomized.

The reducing agent used is usually a solution containing water and urea. When injecting through the nozzle 26 to achieve a sufficient atomization, according to the invention, a surfactant is added to the reducing agent. The proportion of surfactant in the reducing agent depends on the surfactant used and is for example about 0.04 g / l for polydocanol.

Of the Proportion of urea in the reducing agent is preferably in the range from 10 to 60% by volume, in particular in the range from 25 to 35% by volume.

The Fine atomization of the reducing agent is achieved by that by the surfactant, the surface tension of the reducing agent is lowered. Due to the lower surface tension can the resulting droplets during injection easier from each other be torn and thus lead to a finer atomization. The finer atomization distributes the reducing agent more uniformly in the exhaust. This results in an improved reduction of nitrogen oxides achieved in the exhaust.

Also, due to the finer atomization, the reducing agent can be injected into the exhaust pipe at a lower pressure 14 dosing, as even at a lower pressure already sufficient atomization takes place. This causes the pump 32 can be made smaller, since with this no longer so high pressures must be generated. This results in both a savings in the acquisition costs and in the operating costs, since less energy must be expended to the pump 32 to operate.

The effect of the reduced surface tension of the reducing agent is such that a pressure reduced by the same factor is sufficient for the same atomizing effect as the factor by which the surface tension has been reduced. This further means that when the surface tension is reduced by a predetermined factor, the effect is the same as the atomizer pressure has been increased by just this factor. For example, with a surface tension reduced by a factor of 2, the effect is the same as if the double atomization pressure were available.

in the In general, in applications for the reduction of nitrogen oxides in Exhaust gases from internal combustion engines a pressure of 5 bar for the reducing agent available. If by the addition of the surfactant, the surface tension of the reducing agent halved for example, thus the same effect is achieved which would be achieved if the atomization pressure would be doubled, d. h., as if a sputtering pressure of 10 bar would be available. The so improved Atomization causes the average drop size in the spray would decrease by about a factor of √2.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - WO 2006/072487 A [0016]

Cited non-patent literature

• - DIN 70070 AUS 32 [0006]

Claims (12)

System for aftertreatment of exhaust gases from internal combustion engines ( 10 ), a solution containing water and urea, and a reaction space ( 18 ), where means ( 26 ) are provided to the solution in the reaction space ( 18 ), characterized in that the solution further contains at least one surfactant. System according to claim 1, characterized in that the proportion of the surfactant in the solution at less than 0.1 g / l lies. System according to claim 1, characterized in that the proportion of water in the solution in the range of 40 to 90 wt .-% and the proportion of urea in the range of 10 to 60 wt .-% lies. System according to one of claims 1 to 4, characterized in that the surfactant is a hydrophilic functional Contains group that form a hydrogen bridge can. System claim 4, characterized in that the hydrophilic group is selected from carboxyl, carboxylate, Hydroxyl, sulfone, sulfate, sulfonate, ammonium, amino, amide, polyether alcohols and betaine. System according to one of claims 1 to 5, characterized in that the surfactant is a lipophilic part Hydrocarbon chains, dimethylsilicone chains and / or (per) fluorohydrocarbon chains includes. System according to one of claims 1 to 6, characterized in that the means for injecting the solution into the reaction space at least one injection valve ( 26 ). System according to claim 7, characterized in that the injection valve ( 26 ) Has openings through which the solution is injected into the reaction space. System according to one of claims 1 to 6, characterized in that the means for injecting the solution in the reaction space at least one multi-jet atomizing nozzle include. Process for the reduction of nitrogen oxides in Exhaust gases from internal combustion engines, in which a solution Containing water and urea, injected into a reaction space is, wherein the reaction space from the exhaust gas of the internal combustion engine is flowed through, characterized in that the solution furthermore contains a surfactant. Method according to claim 10, characterized in that that the solution with a pressure in the range of 3 to 30 bar is injected into the reaction space. Use of the system according to one of the claims 1 to 9 for the reduction of nitrogen oxides in exhaust gases of internal combustion engines.