Power plants – Internal combustion engine with treatment or handling of... – By means producing a chemical reaction of a component of the...
Reexamination Certificate
1999-08-06
2002-02-05
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
By means producing a chemical reaction of a component of the...
C060S274000, C060S285000, C060S303000
Reexamination Certificate
active
06343468
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to a method and a device for controlling a combustion system and for catalytic removal from exhaust gas of a noxious substance generated by the combustion system, in which the noxious substance reacts chemically with a fluid that is added to the exhaust gas in a metered manner. Such a reaction is, for example, the reaction of nitrogen oxides with a reducing agent such as ammonia to form nitrogen and water, which occurs in so-called deNOx catalytic converters. The invention also relates to a combustion system, in particular an internal combustion engine, which is equipped with such a device.
During the combustion of a fossil fuel in a combustion system, noxious substances such as nitrogen oxides, hydrocarbons, carbon monoxide and sulfur oxides are produced and, at appropriate combustion temperatures, dioxines and furanes as well, which can pass into the environment through the exhaust gas of the combustion system. Such a combustion system can, for example, be a boiler system, a fossil-fuel power plant or an internal combustion engine.
Due to strict legal requirements which limit the exhaust gas quantity of the above-mentioned noxious substances, additional treatment of the exhaust gases is necessary for the above-mentioned combustion systems in order to reduce the noxious substances contained in the exhaust gases. In the past, a number of catalytic converters have been developed for that purpose. For example, the deNOx catalytic converters already mentioned are known for reducing nitrogen oxides. The catalytic converters convert the nitrogen oxides contained in the exhaust gas by using a suitable reducing agent, usually ammonia, according to the method of selective catalytic reduction (SCR), to form environmentally friendly nitrogen and water. The reducing agent or a precursor of the reducing agent, for example urea as a precursor of ammonia, is introduced into the exhaust gas upstream of the catalytic converter, in flow direction of the exhaust gas, and then enters the catalytic converter in a preferably homogeneous mixture with the nitrogen oxides contained in the exhaust gas.
In order to reduce the noxious substances in the exhaust gas of an Otto or spark-ignition engine, noble metal-containing catalytic converters, for example, are known, in which hydrocarbons and carbon monoxide are converted by using nitrogen oxides to form carbon dioxide, nitrogen and/or water.
Furthermore, work is currently under way at many locations on the development of a regulated diesel catalytic converter with which it is to be possible to considerably reduce the nitrogen oxide content in the exhaust gas of a diesel engine. However, due to the high residual content of atmospheric oxygen in the exhaust gas, that is not possible with the noble metal-containing catalytic converter known for the Otto or spark-ignition engine. Instead, the already mentioned deNOx catalytic converter can be used to remove nitrogen oxide from the exhaust gas of a diesel engine. However, since a diesel engine is usually operated with variable load and variable rotational speed, in particular when it is used to provide traction, the quantity of nitrogen oxide generated per unit time is subject to fluctuation within wide limits. The same also applies, of course, to any other combustion system which is used with changing operating conditions.
On one hand, in order to achieve a high rate of precipitation of the nitrogen oxides and, on the other hand, to prevent a slip of the introduced reducing agent, the reducing agent must be metered precisely to the generated quantity of nitrogen oxides through the use of suitable measures in accordance with the stoichiometry of the reaction. An aggravating factor is that the ammonia which is used as a reducing agent is poisonous and even a small concentration constitutes a considerable olfactory nuisance for humans. Precise metering is also necessary with other catalytic cleaning methods in which a noxious substance reacts as a first reactant, with a fluid which has been additionally introduced into the exhaust gas as a second reactant.
Such precise metering of the fluid is associated with a considerable technical outlay since, in addition to monitoring the generated quantity of noxious substance, it is also necessary to additionally take parameters which relate to the operation of the combustion system into account. Those parameters are, for example, temperature and load, parameters which relate to the operation of the catalytic converter, for example catalytic converter temperature and storage capacity, and exhaust-gas parameters, for example pressure and temperature. A method for the controlled introduction of a fluid into a nitrogen oxide-containing exhaust gas, which takes the afore said parameters into account, is known from European Patent EP 0 697 062 B1, corresponding to U.S. Pat. No. 5,628,186. It is disadvantageous that the metering system which is necessary for the introduction of the fluid must be configured for a wide throughput range of the fluid and must have a highly dynamic configuration in order to function satisfactorily in every operating state of the combustion system. Such a metering system entails high costs, since it has to be adapted to the respective system.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method and a device for controlling a combustion system and for catalytic cleaning of exhaust gases, as well as a combustion system, which overcome the hereinafore-mentioned disadvantages of the heretofore-known methods and devices of this general type, which are technically simpler and more cost-effective than the prior art, in which a fluid is added to the exhaust gas in a metered manner and which thus achieve a high precipitation rate of a noxious substance without an appreciable slip of a fluid or of a product of the fluid.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for controlling a combustion system and for catalytic removal from exhaust gas of a noxious substance generated in the combustion system, which comprises controlling combustion in the combustion system to adjust a constant desired value for a mass flow of the noxious substance or a desired value for the mass flow of the noxious substance linearly dependent on at least one variable characterizing an operational state; and metering an addition of a fluid to the exhaust gas to correspond to the desired value for the mass flow of the noxious substance.
The invention is based in this case on the concept that the mass flow rate of the noxious substance produced during the combustion is dependent to a high degree on the conditions, such as pressure and temperature, for example, prevailing during the combustion. The mass flow rate of the noxious substance is defined in this case as the throughflow rate of the noxious substance per time unit, measured in kg/sec. The combustion can accordingly be controlled in accordance with a prescribed desired value for the mass flow rate of the noxious substance. Of course, controlling the combustion in such a way also makes it possible to regulate the mass flow rate, i.e. to set the value of the mass flow rate within a certain tolerance range about a prescribed desired value. Since, in this way, the mass flow rate no longer changes within wide limits, particularly under changing operating conditions of the combustion system, the metering of the fluid which is necessary for the catalytic removal of the noxious substance from the exhaust gas can be substantially simplified. It is specifically configured only for a very small throughput range of the fluid in accordance with the desired value of the mass flow rate of noxious substance and optimized for this range. The highly dynamic configuration of the metering device is eliminated.
In accordance with another mode of the invention, the combustion can be controlled by influencing the air quantity fed to the combustion and/or the fuel quantity fed to t
Doelling Winfried
Hofmann Lothar
Mathes Wieland
Denion Thomas
Greenberg Laurence A.
Lerner Herbert L.
Siemens Aktiengesellschaft
Stemer Werner H.
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