Power plants – Internal combustion engine with treatment or handling of... – By means producing a chemical reaction of a component of the...
Reexamination Certificate
2001-03-22
2002-07-23
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, C060S303000, C060S297000
Reexamination Certificate
active
06422005
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention lies in the field of catalytic converters. The invention relates to a process for the catalytic elimination of a pollutant from the exhaust gas from a combustion installation, in particular, a diesel engine. The concentration of the pollutant in the exhaust gas is calculated by a predetermined characteristic diagram from an operationally relevant parameter of the combustion installation. A predetermined quantity of a reagent is introduced into the exhaust gas per unit time as a function of the calculated concentration of the pollutant and is reacted with the pollutant at the catalytic converter. The invention also relates to an apparatus for carrying out the above-mentioned process.
During the combustion of a fossil fuel or refuse in a combustion installation, a considerable amount of pollutants, such as nitrogen oxides, hydrocarbons, carbon monoxide, sulfur oxides, and, in particular, dioxins and furans, are formed and can pass into the environment through the exhaust gas from the combustion installation. Examples of a combustion installation that emits pollutants include a boiler plant, a coal-fired, oil-fired, or gas-fired power plant, a gas turbine, or an internal-combustion engine, in particular, a diesel engine. A refuse incineration plant also emits the above-mentioned pollutants.
Due to stringent statutory provisions that limit the amount of the above-mentioned pollutants that can be released, an additional treatment of the exhaust gases is required for the combustion installations to reduce the levels of pollutants contained therein. For such a purpose, a wide range of catalytic converters has been developed in the past that convert the pollutants into non-hazardous compounds.
In the event of an unsuitable exhaust-gas composition, it is from time to time necessary for a reagent to be added to the exhaust gas as well, which reacts, at a suitable catalytic converter, with the pollutant that is to be eliminated, to form non-hazardous compounds. For example, to break nitrogen oxides in an oxygen-containing exhaust gas, a suitable reducing agent must be added as a reagent, and, in the presence of oxygen, the reducing agent also reduces the nitrogen oxides contained in the exhaust gas to form non-hazardous nitrogen. The reaction can be catalyzed by a deNOx catalytic converter that is based on titanium dioxide with additions of vanadium pentoxide, molybdenum trioxide, and/or tungsten trioxide. At the deNOx catalytic converter, the nitrogen oxides are reacted with the reducing agent, usually ammonia, to form nitrogen and water in accordance with the selective catalytic reduction (SCR) process.
To completely break down the pollutant in the exhaust gas, the reagent, which is added separately, has to be added in a stoichiometric quantity with respect to the concentration of the pollutant. Therefore, the addition of the reagent is demand-dependent, in other words, is dependent on the quantity of pollutant emitted from the combustion installation per unit time.
Particularly in the case of a combustion installation that operates with frequent load changes, such as, for example, a diesel engine that is used to drive a vehicle, it is difficult to determine the quantity of reagent that is to be introduced per unit time. It is necessary for the quantity of reagent metered in to be varied quickly and to be adjusted accurately because the emission level of pollutants varies considerably within short time intervals according to the frequent load changes.
For demand-dependent, exact metering of the reagent, accurate knowledge of the quantity of pollutant that is actually emitted from the combustion installation is required. In the case of a combustion installation that is operated under steady-state conditions, knowledge of the quantity of pollutant that is actually emitted can be achieved by measuring the concentration of the pollutant in the exhaust gas. To make such measurements, a pollutant-sensitive sensor is placed in the exhaust gas and the measured values from the sensor are used to control the quantity of reagent introduced.
However, if the quantity of pollutant emitted varies rapidly, it is no longer possible to directly measure the concentration of the pollutant in the exhaust gas. Pollutant sensors that would be sufficiently quick for real-time measurement are as yet unknown. Sensors for determining pollutant concentrations in gaseous media are generally constructed as conductivity or capacitance sensors, in other words, as sensors that are based on a material whose conductivity or capacitance reacts sensitively to the pollutant. Because the pollutant has to penetrate into the material, such sensors have a relatively long response time, making direct measurement of the concentration of the pollutant impossible if the concentration varies very rapidly.
Even if sensors existed with a sufficiently rapid response time, in a combustion installation that is operated with frequent and rapid load changes, a measured-value oriented control of the quantity of reagent introduced does not result in the maximum possible conversion of the pollutant. The reason for this is that an adsorption of the reagent on the catalytic converter is required to catalytically break down the pollutant. Such an adsorption process proceeds relatively slowly in kinetic terms. Therefore, in the event of rapid load changes, a quantity of reagent that is tailored to the currently measured concentration of the pollutant does not lead to the maximum possible conversion.
To solve the problem, German Published, Non-Prosecuted Patent Application D 43 15 278 A1, corresponding to U.S. Pat. No. 5,628,186, discloses using operationally relevant parameters of the combustion installation to calculate, in advance, the quantity of pollutant emitted in the corresponding operating state or a value for the current concentration of the pollutant. The quantity of reagent introduced is controlled according to the precalculated value. Operationally relevant parameters specified for a diesel engine are air mass flow rate, control rod travel, charge air pressure, torque, and rotational speed. The advance calculation of the current concentration of the pollutant in the exhaust gas takes place based on a characteristic diagram that is implemented in a control unit and in which each family of parameters corresponding to a defined operating state of the combustion installation is assigned a concentration value for the pollutant. Such a characteristic diagram is determined, for example, by test runs on an engine test bed.
However, a drawback of such a characteristic-diagram-oriented control method is that the quantity of reagent that is actually introduced has to be selected to be smaller than the quantity that should he introduced stoichiometrically according to the precalculated concentration. Such a selection is required because a certain safety margin has to be maintained, so that slippage of the reagent, which for example in the case of ammonia has a toxic action, is reliably avoided. The reason for the procedure is, first, an inevitable production spread in the combustion installations and, second, an aging of the combustion installation or its components during operation. Both of these factors lead to the rigidly implemented characteristic diagram no longer correctly reproducing the actual relationships between the current operating state of the combustion installation and the quantity of pollutant emitted. Therefore, the characteristic diagram is used to precalculate a quantity of pollutant that does not correspond to the quantity of pollutant actually emitted. The process leads to incorrect metering of the reagent.
Accordingly, if the quantity of reaction quantity introduced is controlled based on a rigid characteristic diagram, it is, accordingly, not possible to achieve a maximum conversion of the pollutant if, at the same time, slippage of the reagent in the environment is to be reliably avoided.
As a solution to the problem, German Published, Non-Prosecuted Paten
Dölling Winfried
Latsch Reinhard
Mathes Wieland
Neufert Ronald
Tost Rainer
Denion Thomas
Greenberg Laurence A.
Locher Ralph E.
Stemer Werner H.
Tran Binh
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