U.S. patent application number 09/815201 was filed with the patent office on 2001-09-27 for process and apparatus for the catalytic elimination of a pollutant from the exhaust gas from a combustion installation.
Invention is credited to Dolling, Winfried, Latsch, Reinhard, Mathes, Wieland, Neufert, Ronald, Tost, Rainer, Weisensel, Dietmar, Wenzlawski, Klaus, Zurbig, Jurgen.
Application Number | 20010023585 09/815201 |
Document ID | / |
Family ID | 7881830 |
Filed Date | 2001-09-27 |
United States Patent
Application |
20010023585 |
Kind Code |
A1 |
Dolling, Winfried ; et
al. |
September 27, 2001 |
Process and apparatus for the catalytic elimination of a pollutant
from the exhaust gas from a combustion installation
Abstract
A process for catalytic removal of a pollutant from a combustion
installation exhaust gas includes calculating, from operationally
relevant parameters of the installation, a pollutant concentration
using a predetermined characteristic diagram. A predetermined
quantity of a reagent is introduced into the exhaust per unit time
as a function of the calculated pollutant concentration, the
reagent reacting with the pollutant at a catalytic converter.
Operating states of the installation with substantially constant
pollutant emission levels are determined. The pollutant
concentration during an operating state of the installation with a
substantially constant pollutant emission level is determined with
a sensor and only a pollutant concentration from the installation
in a steady operating state is used to correct the diagram. The
pollutant concentration from the installation is calculated with
the diagram in a non-steady operating state. An apparatus for the
catalytic removal of the pollutant from the exhaust gas is also
provided.
Inventors: |
Dolling, Winfried;
(Weissenbrunn, DE) ; Latsch, Reinhard; (Sinsheim,
DE) ; Mathes, Wieland; (Michelau, DE) ;
Neufert, Ronald; (Michelau, DE) ; Tost, Rainer;
(Nurnberg, DE) ; Weisensel, Dietmar; (Sinzing,
DE) ; Wenzlawski, Klaus; (Nurnberg, DE) ;
Zurbig, Jurgen; (Burgkunstadt, DE) |
Correspondence
Address: |
LERNER AND GREENBERG, P.A.
Post Office Box 2480
Hollywood
FL
33022-2480
US
|
Family ID: |
7881830 |
Appl. No.: |
09/815201 |
Filed: |
March 22, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09815201 |
Mar 22, 2001 |
|
|
|
PCT/DE99/02857 |
Sep 9, 1999 |
|
|
|
Current U.S.
Class: |
60/286 ; 60/285;
60/295; 60/301 |
Current CPC
Class: |
Y02T 10/12 20130101;
F01N 2610/02 20130101; B01D 53/9431 20130101; F02B 3/06 20130101;
F01N 3/2066 20130101; B01D 53/9495 20130101 |
Class at
Publication: |
60/286 ; 60/285;
60/301; 60/295 |
International
Class: |
F01N 003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 22, 1998 |
DE |
198 43 423.5 |
Claims
We claim:
1. A process for the catalytic removal of a pollutant from an
exhaust gas from a combustion installation having operationally
relevant parameters, which comprises: calculating, from
operationally relevant parameters of a combustion installation, a
concentration of a pollutant in an exhaust gas with a predetermined
characteristic diagram; introducing a predetermined quantity of a
reagent into the exhaust gas per unit time as a function of the
calculated concentration of the pollutant, the reagent reacting
with the pollutant at a catalytic converter; determining operating
states of the combustion installation with substantially constant
pollutant emission levels; determining, with a sensor, the
concentration of the pollutant in the exhaust gas during an
operating state of the combustion installation with a substantially
constant pollutant emission level and using only a concentration of
the pollutant from a combustion installation in a steady operating
state to correct the characteristic diagram; and calculating the
concentration of the pollutant in the exhaust gas from a combustion
installation with the characteristic diagram in a non-steady
operating state.
2. The process according to claim 1, which further comprises
determining, with the sensor, the operating state with the
substantially constant pollutant emission level.
3. The process according to claim 2, which further comprises
determining an operating state of the combustion installation as an
operating state with a substantially constant pollutant emission
level when the sensor measures a constant value over a time period
longer than a response time of the sensor.
4. The process according to claim 1, which further comprises:
comparing a value for the concentration of the pollutant
predetermined in the characteristic diagram with the value for the
concentration of the pollutant determined by the sensor to correct
the characteristic diagram; and replacing the predetermined value
with the determined value in the event of a comparison deviation
lying outside a predetermined tolerance band.
5. The process according to claims 1, which further comprises
directly determining the concentration of the pollutant in the
exhaust gas with a pollutant-sensitive sensor.
6. The process according to claim 1, which further comprises:
determining the concentration of the pollutant as a result of
another sensor sensitive to a component of the exhaust gas;
measuring a concentration of the component with the other sensor;
and determining the concentration of the pollutant from the
concentration of the component.
7. The process according to claim 1, which further comprises:
adding one of ammonia and a substance releasing ammonia to the
exhaust gas as the reagent; and reacting the pollutant nitrogen
oxides with a denox catalytic converter in accordance with the
selective catalytic reduction process.
8. The process according to claim 1, wherein the substance
releasing ammonia is urea.
9. The process according to claim 9, which further comprises
determining a concentration of nitrogen oxides in the exhaust gas
with a sensor used to measure a concentration of at least one of
hydrocarbons and carbon monoxide in the exhaust gas; and drawing a
conclusion as to the concentration of nitrogen oxides from the
concentration measured by the sensor.
10. A process for the catalytic removal of a pollutant from an
exhaust gas from a diesel engine, which comprises: calculating,
from operationally relevant parameters of a combustion
installation, a concentration of a pollutant in an exhaust gas with
a predetermined characteristic diagram; introducing a predetermined
quantity of a reagent into the exhaust gas per unit time as a
function of the calculated concentration of the pollutant, the
reagent reacting with the pollutant at a catalytic converter;
determining operating states of the combustion installation with
substantially constant pollutant emission levels; determining, with
a sensor, the concentration of the pollutant in the exhaust gas
during an operating state of the combustion installation with a
substantially constant pollutant emission level and using only a
concentration of the pollutant from a combustion installation in a
steady operating state to correct the characteristic diagram; and
calculating the concentration of the pollutant in the exhaust gas
from a combustion installation with the characteristic diagram in a
non-steady operating state.
11. An apparatus for the catalytic removal of a pollutant from
exhaust gas of a combustion installation having operationally
relevant parameters, comprising: an exhaust-gas duct connected to a
combustion installation for directing flow of an exhaust gas
containing at least one pollutant; a sensor disposed in said
exhaust-gas duct for producing output values; a reagent; an
introduction apparatus for introducing said reagent into the
exhaust gas; a catalytic converter for reacting said reagent with
the at least one pollutant, said catalytic converter fluidically
connected to said exhaust-gas duct to conduct the exhaust gas flow;
a predetermined characteristic diagram; a control unit for
receiving operationally relevant parameters of the combustion
installation, said control unit connected to said sensor, to said
characteristic diagram, to the combustion installation, and to said
introduction apparatus; said control unit programmed to calculate a
concentration of the at least one pollutant from the operationally
relevant parameters based on said predetermined characteristic
diagram and to control a throughput of said reagent in said
introduction apparatus as a function of a calculated concentration;
and said control unit programmed: to determine the concentration of
the at least one pollutant based upon said output values from said
sensor; to detect an operating state of the combustion installation
with a substantially constant pollutant emission level; and to
correct said characteristic diagram only based on a value of the
concentration of the at least one pollutant from the combustion
installation in a steady operating state determined by said sensor
during such an operating state.
12. The apparatus according to claim 11, wherein said control unit
is programmed: to compare the value for the concentration of the at
least one pollutant predetermined in said characteristic diagram
with a value determined by said sensor during the operating state
with a substantially constant pollutant emission level; and to
correct said characteristic diagram by replacing the predetermined
value in said characteristic diagram with the value determined by
said sensor in the event of a deviation lying outside a
predetermined tolerance band.
13. The apparatus according to claim 11, wherein said sensor is a
pollutant-sensitive sensor.
14. The apparatus according to claim 11, wherein said sensor is
additionally sensitive to an exhaust-gas component different from
the at least one pollutant.
15. The apparatus according to claim 11, wherein said catalytic
converter is a deNox catalytic converter for removing nitrogen
oxides with a reducing agent, said deNOx catalytic converter has
one of a honeycomb and a plate configuration, and said deNOx
catalytic converter is made from 70 to 95% by weight of titanium
dioxide, 5 to 20% by weight of at least one of tungsten trioxide
and molybdenum trioxide, and less than 5% by weight of vanadium
pentoxide.
16. An apparatus for the catalytic removal of a pollutant from
exhaust gas of a diesel engine having operationally relevant
parameters, comprising: an exhaust-gas duct connected to a
combustion installation for directing flow of an exhaust gas
containing at least one pollutant; a sensor disposed in said
exhaust-gas duct for producing output values; a reagent; an
introduction apparatus for introducing said reagent into the
exhaust gas; a catalytic converter for reacting said reagent with
the at least one pollutant, said catalytic converter fluidically
connected to said exhaust-gas duct to conduct the exhaust gas flow;
a predetermined characteristic diagram; a control unit for
receiving operationally relevant parameters of the combustion
installation, said control unit connected to said sensor, to said
characteristic diagram, to the combustion installation, and to said
introduction apparatus; said control unit programmed to calculate a
concentration of the at least one pollutant from the operationally
relevant parameters based on said predetermined characteristic
diagram and to control a throughput of said reagent in said
introduction apparatus as a function of a calculated concentration;
and said control unit programmed: to determine the concentration of
the at least one pollutant based upon said output values from said
sensor; to detect an operating state of the combustion installation
with a substantially constant pollutant emission level; and to
correct said characteristic diagram only based on a value of the
concentration of the at least one pollutant from the combustion
installation in a steady operating state determined by said sensor
during such an operating state.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of copending
International Application No. PCT/DE99/02857, filed Sep. 9, 1999,
which designated the United States.
BACKGROUND OF THE INVENTION
[0002] Field of the Invention
[0003] 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.
[0004] 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.
[0005] 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.
[0006] 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.
[0007] 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.
[0008] 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.
[0009] 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.
[0010] 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.
[0011] 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.
[0012] 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.
[0013] 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.
[0014] 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.
[0015] As a solution to the problem, German Published,
Non-Prosecuted Patent Application DE 195 36 571 A1 discloses
checking the predetermined characteristic diagram while the
combustion installation is operating and adapting it to the current
state of the combustion installation. To carry out the check,
sensors record the current pollutant concentration and the
concentration is compared with the precalculated value. The
characteristic diagram is then adapted to the actually emitted
value by mathematical methods.
[0016] However, it is a drawback that the imperative need to
measure the concentration of the pollutant to correct the
characteristic diagram in practice entails high measurement errors
due to the inadequacy of the sensors. The above-mentioned concept
has only a limited suitability for a combustion installation in
which the quantity of exhaust gas varies very rapidly.
SUMMARY OF THE INVENTION
[0017] It is accordingly an object of the invention to provide a
process and apparatus for the catalytic elimination of a pollutant
from the exhaust gas from a combustion installation, in particular,
a diesel engine, by a reagent, that overcomes the
hereinafore-mentioned disadvantages of the heretofore-known devices
and methods of this general type and that controls the quantity of
reagent introduced based on a characteristic diagram, which leads
to a high conversion of the pollutant being achieved even in a
combustion installation that is operated with frequent and rapid
load changes. The high conversion is to be ensured equally well in
the event of aging or production spreads in the combustion
installation.
[0018] With the foregoing and other objects in view, there is
provided, in accordance with the invention, a process for the
catalytic removal of a pollutant from an exhaust gas from a
combustion installation having operationally relevant parameters
including the steps of calculating, from operationally relevant
parameters of a combustion installation, a concentration of a
pollutant in an exhaust gas with a predetermined characteristic
diagram, introducing a predetermined quantity of a reagent into the
exhaust gas per unit time as a function of the calculated
concentration of the pollutant, the reagent reacting with the
pollutant at a catalytic converter, determining operating states of
the combustion installation with substantially constant pollutant
emission levels, determining, with a sensor, the concentration of
the pollutant in the exhaust gas during an operating state of the
combustion installation with a substantially constant pollutant
emission level and using only a concentration of the pollutant from
a combustion installation in a steady operating state to correct
the characteristic diagram, and calculating the concentration of
the pollutant in the exhaust gas from a combustion installation
with the characteristic diagram in a non-steady operating
state.
[0019] With regard to the process, the objectives of the invention
are achieved by a process for the catalytic removal 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
operationally relevant parameters 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 a catalytic
converter, in which process, according to the invention, operating
states of the combustion installation with a substantially constant
pollutant emission levels are determined. During an operating state
of the combustion installation with a substantially constant
pollutant emission level, the concentration of the pollutant in the
exhaust gas is determined by a sensor and is used for a correction
of the characteristic diagram.
[0020] The invention is based on the consideration that sensors for
recording the concentration of the pollutant that have become known
to date and are inadequate due to their response time, in the event
of a temporarily constant emission level of the pollutant,
generally record the actual concentration value. Consequently, it
is possible to determine the concentration of the pollutant in the
exhaust gas from a combustion installation during an operating
state with a substantially constant pollutant emission level
without major measurement errors. Also, such a process allows a
dynamic equilibrium to prevail on the catalytic converter during an
operating state with regard to the adsorption of the reagent.
Therefore, adsorption processes do not influence the
measurement.
[0021] Furthermore, the invention is based on the consideration
that a constant pollutant emission level occurs in a large number
of operating states of the combustion installation that differ by
virtue of the other operationally relevant parameters. For example,
a diesel engine that is used to pull a truck, is distinguished by a
constant pollutant emission level both during an idling phase and,
equally when the truck is driving at a constant speed and with a
high load. However, the two operating states described differ, in
particular, with regard to the accelerator pedal position, the
torque, and the fuel consumption.
[0022] The invention is furthermore based on the consideration
that, over time, most of the families of parameters that are
covered by the characteristic diagram are covered by operating
states with a constant pollutant emission level. The effect allows
simple and reliable, gradual correction of the overall
characteristic diagram and, therefore, allows the characteristic
diagram to be adapted to the current state of the combustion
installation.
[0023] In accordance with another mode of the invention, a sensor
determines the operating states with a substantially constant
pollutant emission level. For such a purpose, the measured value
supplied by the sensor is monitored continuously during operation.
If the measured value remains constant for a predeterminable time
period, an operating state of such a type is recognized as an
operating state with a constant pollutant emission level. The
characteristic diagram is used to calculate the assumed value of
the concentration of the pollutant associated with the defined
operating state based on the other operationally relevant
parameters that are available, for example, through an interface
with the control unit of the combustion installation. The
calculated value is then used to correct the characteristic
diagram.
[0024] In accordance with a further mode of the invention, an
operating state of the combustion installation is determined as an
operating state with a substantially constant pollutant emission
level when the sensor measures a constant value over a time period
that is longer than its response time. The shorter the time that
can be predetermined for estimation of the constant emission level,
the greater the measurement errors become for the determined
concentration of the pollutant and, therefore, for the correction
of the characteristic diagram. However, the correction of the
overall characteristic diagram will take place more quickly.
[0025] In accordance with an added mode of the invention, to
correct the characteristic diagram, the value for the concentration
of the pollutant that is predetermined in the characteristic
diagram is compared with the value for the concentration of the
pollutant that has been determined by the sensor, and in that in
the event of a deviation that lies outside a predetermined
tolerance band the predetermined value is replaced by the
determined value. In a combustion installation with frequent load
changes or frequently differing operating states, point by point
correction rapidly leads to the overall characteristic diagram
being adapted to the current state of the combustion
installation.
[0026] In accordance with an additional mode of the invention, the
concentration of the pollutant in the exhaust gas is determined
directly by a pollutant-sensitive sensor. The measured value
supplied by such a sensor is proportional to the concentration of
the pollutant and can then be directly converted into the
concentration.
[0027] In accordance with yet another mode of the invention, for
such a purpose, the concentration of the pollutant is determined as
a result of a sensor that is sensitive to a further component of
the exhaust gas and is used to measure the concentration of the
further component, and in that the concentration of the pollutant
from the concentration of the further component is determined. Such
a procedure is recommended if no suitable sensors are available for
the pollutant to be measured. For conversion, it has to be assumed
that the composition of the exhaust gas emitted from the combustion
installation is subject to certain laws. If the concentration of
one component of the exhaust gas rises or falls, it is possible to
conclude that the other component is rising or falling. For
example, in the exhaust gas from a diesel engine, the concentration
of the nitrogen oxides can be worked out from the concentration of
the carbon monoxide and/or of the hydrocarbons.
[0028] In accordance with yet a further mode of the invention,
ammonia or a substance that releases ammonia, in particular, urea,
is added to the exhaust gas as reagent, and as the pollutant
nitrogen oxides are reacted, in accordance with the selective
catalytic reduction (SCR) process, on a deNOx catalytic
converter.
[0029] In such a case, it is advantageous if the concentration of
nitrogen oxides in the exhaust gas is determined by using a sensor
to measure the concentration of hydrocarbons or carbon monoxide in
the exhaust gas and drawing a conclusion as to the concentration of
nitrogen oxides from the concentration of hydrocarbons or carbon
monoxide.
[0030] With the objects of the invention in view, there is also
provided an apparatus for the catalytic removal of a pollutant from
exhaust gas of a combustion installation, in particular, a diesel
engine, having operationally relevant parameters, including an
exhaust-gas duct connected to a combustion installation for
directing flow of an exhaust gas containing at least one pollutant,
a sensor disposed in the exhaust-gas duct for producing output
values, an introduction apparatus for introducing a reagent into
the exhaust gas, a catalytic converter for reacting the reagent
with the at least one pollutant, the catalytic converter
fluidically connected to the exhaust-gas duct to conduct the
exhaust gas flow, a predetermined characteristic diagram, a control
unit for receiving operationally relevant parameters of the
combustion installation, the control unit connected to the sensor,
to the characteristic diagram, to the combustion installation, and
to the introduction apparatus, the control unit programmed to
calculate a concentration of the at least one pollutant from the
operationally relevant parameters based on the predetermined
characteristic diagram and to control a throughput of the reagent
in the introduction apparatus as a function of a calculated
concentration, and the control unit programmed to determine the
concentration of the at least one pollutant based upon the output
values from the sensor, to detect an operating state of the
combustion installation with a substantially constant pollutant
emission level, and to correct the characteristic diagram only
based on a value of the concentration of the at least one pollutant
from the combustion installation in a steady operating state
determined by the sensor during such an operating state.
[0031] With regard to the apparatus, the above-mentioned objectives
are achieved by an apparatus for the catalytic removal of a
pollutant from the exhaust gas of a combustion installation, in
particular, a diesel engine, having an exhaust-gas duct, an
introduction apparatus for introducing a reagent into the exhaust
gas, a catalytic converter through which the exhaust gas can flow
for reacting the reagent with the pollutant, and a control unit
that is connected to the combustion installation and the
introduction apparatus. Operationally relevant parameters of the
combustion installation are available to the control unit and the
control unit is configured to calculate the concentration of the
pollutant from the operationally relevant parameters based on the
predetermined characteristic diagram and to control the reagent
throughput in the introduction apparatus as a function of the
calculated concentration. In the apparatus according to the
invention, a sensor that is connected to the control unit is
disposed in the exhaust-gas duct. The control unit is additionally
configured to determine the concentration of the pollutant in the
exhaust gas by the values that are available through the sensor, to
detect an operating state of the combustion installation with a
substantially constant pollutant emission level, and to correct the
characteristic diagram based on the value of the concentration of
the pollutant that is determined by the sensor during such an
operating state.
[0032] The introduction apparatus may, in a conventional manner, be
constructed as an injection valve, an injection nozzle, or, in the
case of a large combustion installation, as an injection grid that
is distributed over the cross section of the exhaust-gas duct. The
reagent throughput can be controlled either by direct control of
the injection nozzle or the injection valve, or by a controllable
valve disposed in the feed line for the reagent.
[0033] To record the operationally relevant data of the combustion
installation, suitable sensor elements are assigned to the control
unit in the combustion installation. The measured values from the
sensors are available to the control unit through corresponding
data lines. Particularly in the case of an internal-combustion
engine with electronic engine management, the operationally
relevant parameters are particularly simple to record and transmit.
First, such an engine has the necessary sensors for recording the
operationally parameters. Second, such an engine management system
inherently has an electronic interface through which the
operationally relevant parameters, which the engine management
system monitors, are available. Through such an interface,
parameters of the internal-combustion engine, such as, for example
combustion temperature, fuel consumption, torque, rotational speed,
but also injection time and the like, can be picked up in a simple
manner.
[0034] The sensor, as seen in the direction of flow of the exhaust
gas, is usually disposed upstream of the catalytic converter. As
such, the pollutant emission level emitted from the combustion
installation can be measured directly. However, it is also
conceivable for the sensor to be disposed downstream of the
catalytic converter. As such, the functioning of the catalytic
converter can be monitored at the same time. However, it then
becomes relatively difficult to convert the values measured by the
sensor to the concentration of the emitted pollutant level.
[0035] In accordance with yet an added feature of the invention,
the control unit is configured to compare the value for the
concentration of the pollutant that is predetermined in the
characteristic diagram with the value that is determined by the
sensor during the operating state with a substantially constant
pollutant emission level, and to correct the characteristic diagram
by replacing the predetermined value in the characteristic diagram
with the determined value in the event of a deviation that lies
outside a predetermined tolerance band. As such, the overall
characteristic diagram is gradually adapted, in a simple and
effective manner, to the current state of the combustion
installation.
[0036] In accordance with yet an additional feature of the
invention, the sensor is preferably a pollutant-sensitive sensor.
The control unit can use the recorded measured values to calculate
directly back to the current concentration of the pollutant in the
exhaust gas.
[0037] In another advantageous configuration, the sensor is a
sensor that is sensitive to a further exhaust-gas component. The
alternative is recommended if there is no sensor available that is
suitable for the pollutant. The control unit can then use a
correspondingly predetermined relationship to calculate the
concentration of the pollutant.
[0038] In accordance with again another feature of the invention,
the sensor is additionally sensitive to an exhaust-gas component
different from the at least one pollutant.
[0039] In accordance with a concomitant feature of the invention,
the catalytic converter is a deNOx catalytic converter in honeycomb
or plate form for removing nitrogen oxides with a reducing agent.
For such a purpose, the catalytic converter includes the following
materials: titanium dioxide in a proportion of from 70 to 95% by
weight; tungsten trioxide and/or molybdenum trioxide in a
proportion of from 5 to 20% by weight; and vanadium pentoxide in a
proportion of less than 5% by weight. Such a catalytic converter is
particularly suitable for breaking down nitrogen oxides using the
SCR process.
[0040] If the invention is constructed as an apparatus for removing
nitrogen, it is advantageous, in particular, if there is no rapid
and sensitive nitrogen sensor, to use a sensor that is sensitive to
a further exhaust-gas component. As such, it is recommended to use
a hydrocarbon sensor or a carbon monoxide sensor.
[0041] Other features that are considered as characteristic for the
invention are set forth in the appended claims.
[0042] Although the invention is illustrated and described herein
as embodied in a process and apparatus for the catalytic
elimination of a pollutant from the exhaust gas from a combustion
installation, it is, nevertheless, not intended to be limited to
the details shown because various modifications and structural
changes may be made therein without departing from the spirit of
the invention and within the scope and range of equivalents of the
claims.
[0043] The construction and method of operation of the invention,
however, together with additional objects and advantages thereof,
will be best understood from the following description of specific
embodiments when read in connection with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWING
[0044] The FIGURE is a diagrammatic illustration of a diesel engine
with an apparatus for the catalytic removal of nitrogen oxides from
the exhaust gas connected to the engine according to the
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0045] Referring now to the single FIGURE of the drawing, a
combustion installation 1 is shown that is a diesel engine equipped
with an apparatus for the catalytic removal of the nitrogen oxides.
The diesel engine has an interface 3 at which the current values of
operationally relevant parameters can be tapped electronically.
Operationally relevant parameters are available, in particular, the
rotational speed, the torque, the operating temperature, the fuel
consumption, and the injection time. A fuel/air mixture for
combustion is made available to the diesel engine through a fuel
feedline 4 and an air connection 5. The exhaust gas 6 from the
diesel engine is passed into an exhaust-gas duct 7 through a
manifold and is guided to the outside through a catalytic converter
8. The catalytic converter 8 is configured as a deNOx catalytic
converter that uses the conventional SCR process to break down
nitrogen oxides, with the aid of the reagent ammonia, to form
molecular nitrogen and water. The quantity of ammonia required is
obtained in the exhaust gas 6 by hydrolysis and pyrolysis of urea,
which is metered in.
[0046] An introduction device 9, which includes a storage vessel 11
for the reagent 10 (urea), a feedline 12, a controllable metering
valve 13 with a control line 25, and an injection nozzle 14, is
provided for metering the urea.
[0047] The catalytic converter 8 is constructed as a honeycomb body
through which the exhaust gas can flow and that has a number of
parallel flow passages. The honeycomb body is constructed as a
unsupported extrudite including a ceramic material containing 80%
by weight of titanium dioxide, 8% by weight of tungsten trioxide,
less than 2% by weight of vanadium pentoxide, remainder inorganic
support, and film-forming agents. The configuration of the
catalytic converter 8 depends on the occurrence and pressure of the
exhaust gas from the diesel engine.
[0048] In addition, a sensor for recording the nitrogen oxide
concentration or nitrogen oxide sensor 15 in the exhaust gas 6 is
disposed between the combustion installation 1 and the catalytic
converter 8 in the exhaust-gas duct 7. The nitrogen oxide sensor 15
may, for example, be a capacitance sensor or conductivity
sensor.
[0049] To control the reagent throughput in the introduction
apparatus 9, a control unit 18 is provided. Through the outputs 19,
20, 21 of the interface 3 of the diesel engine, the current values
for rotational speed, torque, operating temperature, fuel
consumption, and injection time are available to the control unit
18 as operationally relevant parameters. Furthermore, a value that
is proportional to the nitrogen oxide concentration in the exhaust
gas can be accessed through the output 22 of the nitrogen oxide
sensor 15.
[0050] The control unit 18, starting from the current parameter
values, calculates the concentration of the nitrogen oxides in the
emitted exhaust gas 6 from the diesel engine which is to be
expected for a time section with a characteristic diagram that has
been defined on an engine test bed for the type of diesel engine in
question. The characteristic diagram is implemented in the control
unit 18 in the form of stored values. An associated quantity of
reagent is metered into the exhaust gas 6 per unit time according
to the precalculated concentration.
[0051] In addition, the control unit 18 continuously checks the
values supplied from the nitrogen oxide sensor 15. If the values do
not change within a predetermined time period, which is generally
selected to be slightly longer than the response time of the
sensor, the control unit 18 interprets the corresponding operating
state of the diesel engine as an operating state with a
substantially constant pollutant emission level.
[0052] The value of the concentration of the nitrogen oxides that
has been determined with the nitrogen oxide sensor 15 for an
operating state of such a nature is compared with the value
calculated in advance for the operating state of the diesel engine
with the characteristic diagram. During the comparison, the
operationally relevant parameters recorded in the last working
cycle of the control unit are used. If the difference between the
precalculated value and the value recorded with the nitrogen oxide
sensor 15 lies outside a predetermined tolerance, the value
associated with the present parameters for the concentration of the
nitrogen oxides in the emitted exhaust gas 6 is replaced in the
characteristic diagram by the recorded, i.e., measured, value. Over
time, such a procedure results in an adaptation of the overall
implemented characteristic diagram to the current state of the
diesel engine.
[0053] As such, aging phenomena or tolerances in the engines within
one type are taken into account in a simple manner. It is
ultimately possible to further reduce the safety margin between the
quantity of reagent metered in and the quantity required for
maximum conversion of the nitrogen oxides when compared to the
prior art. Therefore, by adapting the characteristic diagram, it is
possible to achieve a high level of conversion of the nitrogen
oxides combined with a low risk of ammonia slippage.
[0054] As an alternative, a hydrocarbon sensor or a carbon monoxide
sensor 16 can also be used as a sensor for recording the
concentration of the nitrogen oxides for an exhaust gas from a
diesel engine. Due to the combustion conditions in the diesel
engine, the concentration of the nitrogen oxides can be worked out
from the concentration of hydrocarbons or of carbon monoxide in the
exhaust gas from a diesel engine.
* * * * *