DE10228643A1 - Process for cleaning exhaust gas from an incinerator - Google Patents

Abstract

The invention relates to a method for cleaning exhaust gas (A) from a combustion system (2) from particles (3) contained in the exhaust gas. In the method, the particle size distribution (f) of the particles (3) contained in the exhaust gas (A) is specifically adjusted in order to achieve the best possible cleaning result. The method is particularly suitable for cleaning an exhaust gas (A) from an internal combustion engine, such as, for example, a stationary or mobile diesel engine. In a preferred embodiment, the method can be combined with the denitrification of the exhaust gas (A) in an SCR process with injection of a reducing agent (R) into the exhaust gas duct (7) of the incineration plant (1).

Description

The invention relates to a method for cleaning exhaust gas from an incinerator contained in the exhaust gas Particles.

Under an incinerator both internal combustion engines, i.e. stationary and transient internal combustion engines, as well as plants containing combustion chambers for the production of electrical Energy or district heating be understood from a combustion process. In particular, should an internal combustion engine of a motor vehicle under an incineration plant, for example a diesel passenger car or truck, or even a stationary one Diesel engine to be understood. The application is also intended for gasoline engines be extended with particle emission.

When a fuel or a fuel is burned in a combustion system in a stationary or mobile application, in particular in a vehicle engine, an exhaust gas is produced which contains, inter alia, nitrogen oxides and soot particles. These exhaust gas components are particularly noticeable when diesel is burned in a stationary or mobile diesel engine. Both the nitrogen oxides and the soot particles are environmentally harmful substances and should therefore be largely removed from the exhaust gas. For example, in today's diesel engines in the automotive sector, extremely fine soot particles occur in the exhaust gas, which can be carcinogenic. In the conventional way, the arrangement of a particle filter, such as that from the DE 100 20 170 C1 can be seen.

With regard to reducing the nitrogen oxides contained in the exhaust gas, the so-called SCR process (Selective Catalytic Reduction) has proven itself. In this method, a reducing agent is added to the exhaust gas before it enters the SCR catalytic converter. The nitrogen oxides are then reduced to water and nitrogen in the SCR catalytic converter. Such a method is described for example in the WO 99/55445 , It is then provided that an aqueous urea solution is injected into the exhaust gas. This must then be converted into ammonia, which acts as the actual reducing agent in the catalytic process.

The arrangement of a particle filter together with an SCR catalytic converter is, for example, in FIG CH 689 687 A5 described. The two systems of particle filtering and nitrogen oxide reduction are arranged one after the other in the flow direction of the exhaust gas and are operated independently of one another. This requires a relatively large installation space.

From the EP 1 096 116 A2 discloses a method and an apparatus for the combined catalytic NO _x reduction and sound attenuation of exhaust gas in the exhaust line of an internal combustion engine. In the process, urea in solid or dissolved form is first injected into the exhaust gas coming from the internal combustion engine, which may already have passed through a pre-oxidation catalyst, then this exhaust gas, which is doped in this way, is injected through an urea that acts as an evaporator, flow mixer, hydrolysis and NO _x reduction catalyst. Passed decomposition catalyst and then fed to the silencer. This is channeled in the muffler by means of an exhaust gas inlet pipe through a front inflow chamber - and introduced into a rear inflow chamber and calmed there in terms of sound absorption and flow. The exhaust gas is then distributed to a plurality of NO _x reduction catalytic converter modules through them - and returned to the front outflow chamber, where it is again calmed in terms of sound absorption and flow. Particle emissions from the internal combustion engine are not taken into account in this cleaning process of the exhaust gas from the internal combustion engine.

The invention has for its object a enable effective exhaust gas purification of exhaust gas from an incineration plant, with the particles contained in the exhaust gas particularly efficiently from the Exhaust gas to be removed.

The object is achieved according to the invention solved by a method for cleaning an exhaust gas of an incinerator of particles contained in the exhaust gas, in which the particle size distribution is targeted is set.

With the invention a completely new one Pioneered the particle emission from exhaust gases from incineration plants to reduce highly efficiently. The particle emission is indeed today's diesel engines are relatively small, but they are mutagenicity of diesel particles that is always under discussion, whether from deposited hydrocarbons or maybe from Particles of certain size directly is caused by the legally specified particle emission limit for the diesel engine let it sink even further. An effective particle reduction is therefore within the expected limit values for active and efficient exhaust gas cleaning of essential importance.

The invention now takes into account for the first time the targeted setting of the particle size distribution of the particles emitted from the exhaust gas with a view to adapting and increasing the cleaning efficiency. Surprisingly, there was a connection between the particle size distribution in the exhaust gas emitted by the incineration plant and the cleaning efficiency of the particles contained in the exhaust gas can be found. The exhaust gas can be cleaned by cleaning devices which are usually connected downstream of the combustion system on the exhaust gas side. Through the targeted adjustment of the particle size distribution, an adaptation to a respective essentially conventional cleaning device connected downstream on the exhaust gas side, for example a filter system or a catalytically operating system, is possible.

On the choice of cleaning equipment it’s not fixed.

Advantageously, by this tailoring of the particle size distribution far higher degrees of cleaning compared to common cleaning methods can be achieved, as this has the qualitative influence of the particle size distribution have not yet taken into account the degradation efficiency. It can the particle size distribution advantageously be set so that maximum reduction the number of particles from the exhaust gas is reached.

In a particularly preferred embodiment According to the invention, the particles are in one of the incinerators downstream catalyst unit oxidized.

In addition to conventional filter devices especially the catalytically supported oxidation of the particles in the exhaust is an effective way to remove the particles in the exhaust dismantle from the incinerator. For this, the catalyst unit with one for the particles, e.g. soot from a diesel engine, oxidizing catalytic converter fitted. This can be a honeycomb-shaped catalyst, for example in the form of a full ceramic catalytic extrudate or inert honeycomb coated with active ceramic, or for example also a plate catalyst with an active ceramic or with an active ceramic coated metallic support structure. The catalytically supported oxidation process for removing particles is particularly advantageous in the concept applicable to the invention, since it could be demonstrated that the targeted setting of a favorable Particle size distribution in combination with the oxidation process at one of the incinerators Exhaust gas-connected catalyst unit to particularly high Degrees of purification in the exhaust gas.

Here it was surprisingly found that for example the average diameter of the particles as one possible Characteristic of the particle size distribution have a significant impact on the degradation efficiency in the catalyst unit Has. With a targeted pre-setting and appropriate adaptation the particle size distribution can thus reduce the efficiency of cleaning with the lowest possible Particle emission can be optimized.

The particles from the combustion process of a Diesel or petrol engines are, for example, agglomerates with one Number of direct soot kernels, those with soluble organic compounds (hydrocarbons) are coated. The Oxidation process in the product channel should, if possible, only to form Lead water and carbon dioxide from the oxidation of the particle. To size Agglomerates have an unfavorable surfaces to volume ratio and can usually not completely be implemented in the catalyst unit. Agglomerates with too small Diameters are unfavorable in terms of degradation in an oxidation process if they are Deteriorate mass transfer to the catalyst surface. thats why optimally always an average particle diameter of the particles to be expected in the raw exhaust gas and also to be found at the maximum reduction the number of particles is reached.

In a preferred embodiment a the particle size distribution influencing parameters of the incineration system that a cheap Reduction in the number of particles from the exhaust gas is achieved.

For example, in the case of a Diesel engine related to the time of fuel injection the position of the piston (crank angle) as such a parameter be used. A change the angular position thus defines the position of the piston and hence the time of injection for the fuel. Here has it has been shown that plant-side measures, i.e. motor side Adaption alone is unable to achieve the desired reduction in the number of particles bring about. However, it has been shown that the advantageous combination the system-side adjustable and appropriately assembled Particle size distribution with a downstream cleaning device, e.g. an oxidation catalyst, a potential of about 70% to 80% reduction in total particle emissions across from can also exhaust the raw exhaust gas of the EURO 3 emissions standard.

Depending on the incineration plant, therefore, too others the particle size distribution influencing parameters specified in a simple manner and their Influence be examined quantitatively. There may also be one Set of parameters to take into account to take into account when setting the particle size distribution and are to be optimized in their entirety.

The setting can preferably be adapted accordingly for a particular operating state of the incineration plant. In the case of a diesel engine, for example, an operating state of the combustion system can be characterized by the engine speed, the injection quantity, the boost pressure or the charge air temperature. For a particular operating state, a particle size distribution which is advantageous with regard to the removal of the particles from the raw exhaust gas can be found, which is to be carried out by appropriate adaptation on the motor side, ie setting one or more parameters of the motor influencing the particle size distribution. This information can be used for a certain type of engine in an all in one In practice, the expected operating conditions comprehensive map are stored. When changing an operating state, the particle size distribution can be assembled on the motor side by adapting the critical parameters in order to achieve the desired cleaning result across all operating states.

In addition to particle reduction, preference is given to Exhaust gas additionally a sound absorption carried out. For this purpose, a sound absorption device is in flow direction of the exhaust gas of the incinerator. In advantageous The catalyst unit in the noise damping device is configured here housed so that a combined catalytic particle reduction from the exhaust and a soundproofing for the Incinerator is reached.

In a particularly preferred embodiment The invention contains nitrogen oxides contained in the exhaust gas in a denitrification catalyst reduced by the selective catalytic reduction process, wherein a reducing agent is introduced into the exhaust gas.

In addition to particularly effective particle reduction from the exhaust gas, the combination with the SCR process also enables nitrogen oxides to be removed from the exhaust gas. If necessary, the catalyst device is constructed from two different types of catalyst, the hydrolysis and the SCR catalyst. The hydrolysis catalytic converter has the task of producing ammonia from the urea metered in aqueous solution. In the actual NO _x reduction section, the SCR catalytic converter, the nitrogen oxide is then converted into nitrogen and water with the help of ammonia. In addition, the SCR catalyst also acts as an oxidation catalyst for hydrocarbons. This has the particular advantage that, in order to reduce, among other things, the hydrocarbon content (SOF: Soluble Organic Fraction) in the exhaust gas, the catalyst unit does not specifically need an oxidation catalyst, since the SCR catalyst already catalytically supports the oxidation of the particles.

The packaging of the particle size distribution in combination with an SCR device for removing nitrogen oxides while injecting a reducing agent into the exhaust gas duct can advantageously take advantage of the particularly favorable use of the NO _x and particle reduction potential.

As already stated, the NO _x reduction can also be achieved with exhaust gas recirculation.

As already explained above, the method is preferred for a diesel engine Incinerator can be used. Acting in a diesel engine it is a drive source e.g. in a motor vehicle like a car, or utility vehicle like a truck, one Omnibus, forklift or off-road vehicle, or rail vehicle, or watercraft, or agricultural vehicle like tractor, combine harvester, or military Vehicle such as a chain or wheel armor, or an emergency generator, a combined heat and power plant or another power plant. The procedure can be the same also for Gasoline engines with particle emissions are used.

The start of injection of the Fuel over the crank angle as influencing the particle size distribution Diesel engine parameters set.

The process and its advantages are explained below with reference to a drawing. Show:

1 an incinerator with a downstream exhaust system

2 1 shows a diagram with particle size distributions obtained in the exhaust gas of an incineration plant under different plant-side settings,

3 in a diagram, a comparison of the total particle emissions in the exhaust gas of an incineration plant with and without a downstream catalytic converter unit according to the different particle size distributions 1 ,

1 shows a schematic, highly simplified illustration of a combustion system 1 designed as a diesel engine 1, in the exhaust gas line of which has an exhaust pipe 7 and a catalytic converter unit 9 connected into the exhaust pipe 7. A measuring device 11 is provided downstream of the exhaust gas A of the catalyst unit 5. In operation of the diesel engine 1, particles 3 are also emitted in addition to nitrogen oxides. The particle size distribution f of the particles 3 contained in the exhaust gas A from the combustion system 1 can be determined using the measuring device 11. The catalyst unit 5 comprises a denitrification catalyst 9, which works according to the selective catalytic reduction method. For this purpose, an injection device 10 for a reducing agent R is connected upstream of the denitrification catalytic converter 9 in the flow direction of the exhaust gas. The denitrification catalyst 9 is constructed as a full extrudate on a ceramic basis and has honeycomb-shaped channels through which the exhaust gas A flows and which consist of a catalytically active material. In the optional operation of the SCR catalytic converter, the nitrogen oxides contained in the exhaust gas A are reduced by the selective catalytic reduction method. The reducing agent R is required for this. As such, ammonia is used. Since this can only be stored in a motor vehicle at great expense, the ammonia is obtained from a urea solution during operation. This urea solution is injected into the exhaust gas A via an injection device 10, namely in front of the catalytic converter 9 as seen in the direction of flow.

An essential aspect of the in 1 The arrangement shown is that the catalytic converter 9 is also designed as an oxidation catalytic converter and is suitable for converting, ie oxidizing, the particles 3 in the exhaust gas. To clean the exhaust gas A of the diesel engine 1 from the particles 3 contained in the exhaust gas, these are oxidized in the catalyst unit 5 connected downstream of the diesel engine 1. In addition, the injection device 10 can optionally be activated and the nitrogen oxides can thus be removed from the exhaust gas A via the SCR process described above.

According to the concept of the invention, for cleaning the exhaust gas A of the diesel engine 1 from the particles 3 contained in the exhaust gas A, the particle size distribution f is set in a targeted manner in order to achieve the best possible cleaning result. It has been shown that the particle size distribution f depends significantly on parameters P that can be set on the motor side. In the case of a diesel engine 1, the injection point in time (crank angle α _kw ), for example, is a possible parameter P that influences the particle size distribution f. This is specifically set so that a favorable reduction in the number of particles from the exhaust gas A is achieved. The setting or presetting of the parameter P (s) of the diesel engine 1 influencing the particle size distribution f takes place for a respective operating state of the engine. This means that the motor can be optimally adapted for each operating state with regard to a particle size distribution f that is favorable for the downstream cleaning process. In particular, an adaptation to a respective cleaning device for the particles, which is usually connected downstream of the diesel engine 1, is possible. In the present case, this “preparation” of the particle size distribution f takes place beforehand with a view to the most efficient possible degradation of the particles 3 by the oxidation processes in the catalyst unit 5.

In 2 The measurement results of the particle size distribution f for various settings of the injection point in time (crank angle α _kw ) and with and without connection of the catalyst unit 5 in the exhaust system of the diesel engine 1 are shown as examples. The operating state B25 of a diesel engine 1 known in engine construction has been examined as an example. On the x axis of the in 2 The diagram shown shows the particle size of the particles 3 emitted from the diesel engine 1 in units of nanometers in logarithmic plots. The particle number concentration (number of particles per cm ³ ) assigned to a specific particle size is plotted on the y-axis. The measurement curves f ₁ , f ₂ and f ₃ shown as a solid line in the diagram correspond to particle size distributions f at different injection times (crank angle α _kw ), wherein no catalyst unit 5 for activating the particles 3 was activated or installed in the exhaust pipe 7. In contrast, the measurement curves f ₁ ', f ₂ ' and f ₃ 'shown as dashed lines show the corresponding results when the catalyst unit 5 is switched on. Under these measurement conditions, the exhaust gas A was cleaned of particles 3 as a result of the oxidation of the particles 3 on the catalyst unit 5. This can be seen from the fact that the corresponding measurement curves f ₁ ', f ₂ ' and f ₃ 'show a significantly reduced particle number concentration. A surprising finding of this investigation was, however, that the cleaning efficiency depends on the particle size distribution f which can be set in each case via the injection timing (crank angle α _kw ). In the present case, the best result is achieved at an injection point in time (crank angle α _kw ) of 18 °. As a look at the measurement curves f ₃ and f ₃ 'in comparison to the measurement curves at one of the other settings of the injection timing (crank angle α _kw ) shows, the decrease in the number of particles when the catalytic converter unit 5 is switched on is on the one hand the greatest and on the other hand also a minimal number remaining undegraded particle 3 in exhaust gas A is reached.

Therefore, among the measurement curves f ₁ , f ₂ and f _{3 shown,} the particle size distribution f _{3 is} set most favorably with regard to a maximum cleaning effect, at least for the operating state B25 under consideration. Other operating states of the diesel engine 1 can be very easily optimized in this way with a view to a favorable reduction in the number of particles from the exhaust gas A by specifically setting a parameter P of the engine 1 which influences the particle size distribution f.

In 3 is a diagram showing the total particle emission in mg / kWh for each in the 2 shown measurement curves f ₁ , f ₂ , f ₃ without catalyst unit 5, and the corresponding measurement results f ₁ ', f ₂ ', f ₃ 'when the catalyst unit 5 is switched on for the oxidative degradation of the particles 3 in the exhaust gas A (see also 1 ). As already out 2 there is evidently a dependence of the cleaning result on the particle size distribution f that is set in each case. The most favorable setting is achieved at an injection point in time (crank angle α _kw ) of 18 °. This leads to a particle size distribution f ₃ in the raw exhaust gas with the lowest total particle emission in mg / kWh compared to the other settings. With the particle size distribution f ₃ , however, the best cleaning efficiency is also achieved. In activation of the catalyst unit 5 for the oxidation of the particles 3 in the exhaust gas A, this leads to a decrease Δ _PM by about 70%, at the same time is achieved with this setting, the lowest total particulate emissions of ca. 50 mg / kWh.

With the invention, the particle size distribution f is taken into account for the first time for cleaning an exhaust gas A from particles 3 contained in the exhaust gas A and is specifically adjusted with a view to a favorable cleaning result. The setting is preferably carried out on the system side on the combustion system 1, for example on the engine side in the case of a diesel engine. This proves to be particularly advantageous In accordance with the invention, the particle size distribution is proposed for the first time in a combination with an SCR device for removing nitrogen oxides while injecting a reducing agent into the exhaust duct of the incineration plant 1.

In detail, it could be shown that particles 3 with a suitably assembled, ie preset particle size are particularly advantageously suitable in connection with a catalyst unit 5 in order to be reduced with a catalytically supportive oxidative process. The use of the catalyst unit 5, for example, brings about a 70% reduction in the total particle emission in operating state B25 of a diesel engine compared to the raw exhaust gas emission of the EURO 3 exhaust gas standard. The number of particles is even reduced by more than 85% by the catalyst unit 5. In addition, the engine-side measures to influence the particle size distribution f can reduce fuel consumption. Any NO _x development that may have to be accepted must be adapted by means of alternative measures to the SCR process, such as exhaust gas recirculation (EGR) etc., which should not have a decisive influence on the particle size distribution f.

Claims (8)

Process for cleaning an exhaust gas (A) from an incinerator (1) of particles (3) contained in the exhaust gas (A), in which the particle size distribution (f) is set specifically. The method of claim 1, wherein the particles (3) in one of the Incinerator (1) downstream catalyst unit (5) oxidized become. Method according to one of claims 1 or 2, wherein a die Particle size distribution (f) influencing parameters (P) of the incinerator (1) specifically is set to be a cheap one Reduction in the number of particles from the exhaust gas (A) is achieved. Method according to one of claims 1, 2 or 3, wherein for one the respective operating state of the incinerator (1) the setting is adjusted. Method according to one of claims 2 to 4, wherein the catalyst unit (5) in a flow direction of the exhaust gas (A) of the incinerator (1) downstream sound attenuation device is housed. Method according to one of the preceding claims, wherein nitrogen oxides contained in the exhaust gas (A) in a denitrification catalyst (5) reduced by the selective catalytic reduction method are, wherein a reducing agent (R) is introduced into the exhaust gas (A) becomes. Method according to one of the preceding claims, wherein this in a combustion system designed as a diesel engine (1) is used. Method according to Claim 6, the injection time being set via the crank angle (α _kw ) as a parameter (P) influencing the particle size distribution (f).