U.S. patent application number 12/921617 was filed with the patent office on 2011-02-03 for method for heating a scr system.
This patent application is currently assigned to INERGY AUTOMOTIVE SYSTEMS RESEARCH (societe Anonym. Invention is credited to Jae Sik Choi, Nicolas Duret, Stephane Leonard, Frederic Peucat.
Application Number | 20110027740 12/921617 |
Document ID | / |
Family ID | 40193500 |
Filed Date | 2011-02-03 |
United States Patent
Application |
20110027740 |
Kind Code |
A1 |
Peucat; Frederic ; et
al. |
February 3, 2011 |
Method for Heating a SCR System
Abstract
Process for heating a urea component of a SCR system comprising
besides said component, a temperature sensor, a heating device in
the component, according to which: 1. the temperature (Tcpt) of the
liquid in the component is determined and compared to a 1.sup.st
setpoint (T0); 2. if the temperature (Tcpt) is greater than the
1.sup.st setpoint (T0), step 1 is repeated; 3. if the temperature
(Tcpt) is less than or equal to the 1.sup.st setpoint (T0), the
heating device is actuated, 4. the time during which the heating
device is actuated is measured and the heating device is stopped if
this time is greater than a time t1; 5. the temperature (Tcpt) is
determined after a time t2 and compared to a 2.sup.nd setpoint (T1
with T1>T0); if the temperature (Tcpt) is less than or equal to
the 2.sup.nd setpoint (T1) the heating device is actuated and step
4 is repeated; 6. if the temperature (Tcpt) is greater than the
2.sup.nd septoint (T1), the heating device is stopped and step 1 is
repeated.
Inventors: |
Peucat; Frederic; (Brussels,
BE) ; Leonard; Stephane; (Brussels, BE) ;
Choi; Jae Sik; (Woluwe-St-Pierre, BE) ; Duret;
Nicolas; (Nancy, FR) |
Correspondence
Address: |
Solvay;c/o B. Ortego - IAM-NAFTA
3333 Richmond Avenue
Houston
TX
77098-3099
US
|
Assignee: |
INERGY AUTOMOTIVE SYSTEMS RESEARCH
(societe Anonym
Brussels
BE
|
Family ID: |
40193500 |
Appl. No.: |
12/921617 |
Filed: |
March 11, 2009 |
PCT Filed: |
March 11, 2009 |
PCT NO: |
PCT/EP2009/052848 |
371 Date: |
October 15, 2010 |
Current U.S.
Class: |
432/1 |
Current CPC
Class: |
F01N 2610/1486 20130101;
F01N 3/2066 20130101; Y02T 10/12 20130101; F01N 9/00 20130101; F01N
3/208 20130101; F01N 2610/02 20130101; F01N 2900/0422 20130101;
F01N 2610/10 20130101; Y02T 10/24 20130101; Y02T 10/40 20130101;
Y02T 10/47 20130101; F01N 2900/1811 20130101 |
Class at
Publication: |
432/1 |
International
Class: |
F01N 3/10 20060101
F01N003/10 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 11, 2008 |
FR |
0851583 |
Claims
1. A process for heating a urea component of a Selective Catalytic
Reduction (SCR) system comprising besides said component, a
temperature sensor, and a heating device in the component, said
process comprising the following steps: step 1: the temperature
(Tcpt) of the liquid in the component is determined and compared to
a first setpoint (T0); step 2: if the temperature (Tcpt) is greater
than the first setpoint (T0), step 1 is repeated; step 3: if the
temperature (Tcpt) is less than or equal to the first setpoint
(T0), the heating device is actuated, step 4: the time during which
the heating device is actuated is measured and the heating device
is stopped if this time is greater than a time t1; step 5: the
temperature (Tcpt) is determined after a time t2 and compared to a
second setpoint (T1 with T1>T0); if the temperature (Tcpt) is
less than or equal to the second setpoint (T1), the heating device
is actuated and step 4 is repeated; and step 6: if the temperature
(Tcpt) is greater than the second septoint (T1), the heating device
is stopped and step 1 is repeated.
2. The process according to claim 1, wherein the liquid in the
component is urea.
3. The process according to claim 1, wherein the component is a
tank.
4. The process according to claim 1, wherein the heating device is
a flexible heater.
5. The process according to claim 2, wherein the first setpoint
(T0) is greater than or equal to a freezing temperature of the
urea.
6. The process according to the preceding claim, wherein the first
setpoint (T0) is greater than or equal to a freezing temperature
that corresponds to the concentration of the urea after ageing of
the urea.
7. The process according to claim 1 wherein the time t1 corresponds
to the time necessary for the temperature (Tcpt) to exceed a
safeguard temperature (Tsaf) with Tsaf<Tover where Tover is an
overheating temperature.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a U.S. national stage application under
35 U.S.C. .sctn.371 of International Application No.
PCT/EP2009/052848 filed Mar. 11, 2009, which claims priority to
French Patent Application No. 08.51583 filed Mar. 11, 2008, this
application being incorporated herein by reference in its entirety
for all purposes.
TECHNICAL FIELD OF THE INVENTION
[0002] The present application relates to a method for heating a
SCR system using resistive heating elements and also to an SCR
system suitable for the application of this method.
BACKGROUND OF THE INVENTION
[0003] Legislation on vehicle and heavy goods vehicle emissions
stipulates, amongst other things, a reduction in the release of
nitrogen oxides NO into the atmosphere. One known way to achieve
this objective is to use the SCR (Selective Catalytic Reduction)
process which enables the reduction of nitrogen oxides by injection
of a reducing agent, generally ammonia, into the exhaust line. This
ammonia may derive from the pyrolytic decomposition of an ammonia
precursor solution, whose concentration may be that of the
eutectic. Such an ammonia precursor is generally a urea
solution.
[0004] With the SCR process, the high levels of NO produced in the
engine during combustion at optimized efficiency are treated in a
catalyst on exiting the engine. This treatment requires the use of
the reducing agent of extreme quality at a precise concentration.
The solution is thus accurately metered and injected into the
exhaust gas stream where it is hydrolysed before converting the
nitrogen oxide (NO.sub.x) to nitrogen (N.sub.2) and water
(H.sub.2O).
[0005] In order to do this, it is necessary to equip the vehicles
with a tank containing an additive (generally urea) solution and
also a device for metering the desired amount of additive and
injecting it into the exhaust line. In general, the SCR device
comprises, besides the additive tank, an injector, a pump, and a
urea feed line.
[0006] In order to be able to correctly meter the additive solution
into the exhaust gases, it is known practice to incorporate, into
the additive tank, elements such as a level gauge, a temperature
sensor, a quality sensor, a resistive heating element, etc. U.S.
Pat. No. 6,063,350 proposes, for example, to group these various
components together on the mounting plate of the pump, positioned
on the upper wall of the tank.
[0007] During the start-up of the SCR process, the plate may be
subjected to a temperature rise capable of causing a deterioration
of the components grouped together on the mounting plate of the
additive tank.
SUMMARY OF THE INVENTION
[0008] The present invention aims to solve this problem and is
based on the idea of taking into account the values of the
temperature of the surroundings of the SCR device and of the
temperature in the tank to decide whether or not to activate a
device for heating the feed lines of the SCR system, and/or for
heating the urea tank and/or to decide when to start the pump.
[0009] Hence, the present application relates to a method for
heating a urea SCR system comprising at least one line for
circulating the urea and a device for heating said lines, the
method using a temperature probe capable of measuring the ambient
temperature, the method comprising the following steps: [0010] 1.
the ambient temperature Tamb is measured; [0011] 2. Tamb is
compared to a setpoint value T1; [0012] 3. if Tamb<T1 then the
heating device is activated and Tamb is measured again; Tamb is
compared to a second setpoint value T2>T1; if Tamb<T2, the
heating device is kept active; [0013] 4. if Tamb>T2, the heating
device is deactivated and the first step of the method is returned
to.
[0014] The application also relates to a method for starting a pump
of a urea SCR system comprising a urea tank, a temperature probe in
the tank and a urea injector, the method comprising the following
steps: [0015] 1. the temperature Tres in the tank is measured;
[0016] 2. the EPA time is determined; a timer is started: [0017] 3.
Tres is measured again; [0018] 4. Tres is compared to a setpoint
temperature T3 and the counter value is compared to EPA; [0019] 5.
if Tres<T3 and if the counter value is <EPA, the method
proceeds to the preceding step; [0020] 6. the pump is started and
the pressure level at the pump outlet is measured; [0021] 7. if the
pressure level is stabilized and corresponds to a setpoint level P,
the injector is activated; [0022] 8. if the pressure level is not
stabilized or does not correspond to the setpoint level P after a
time t0, the pump is stopped for a waiting time t1; the method goes
back to step 6.
[0023] The application additionally relates to a method for heating
a urea tank in a urea SCR system comprising at least said tank, a
temperature probe in the tank and a device for heating the tank,
the method comprising the following steps: [0024] 1. the
temperature Tres in the tank is measured; [0025] 2. Tres is
compared to a setpoint value T4; [0026] 3. if Tres>T4 the method
proceeds to step 2; [0027] 4. if Tres<T4, the heating device is
activated, a timer is started and the timer value is measured; if
the timer value is less than a value t3, the method goes back to
step 4; [0028] 5. the heating device is deactivated and the
temperature Tres in the tank is measured after a time t4; if Tres
is below a setpoint temperature T5, the method goes back to step 4;
[0029] 6. the method goes back to step 1.
[0030] The expression "SCR system" is understood to mean a system
for the catalytic reduction of the NO from the exhaust gases of an
internal combustion engine, preferably of a vehicle, using urea as
a liquid ammonia precursor.
[0031] The term "urea" is understood to mean any, generally
aqueous, solution containing urea. The invention gives good results
with eutectic water/urea solutions for which there is a quality
standard: for example, according to the standard DIN 70070, in the
case of the AdBlue.RTM. solution (commercial solution of urea), the
urea content is between 31.8% and 33.2% (by weight) (i.e.
32.5+/-0.7 wt %), hence an available amount of ammonia between
18.0% and 18.8%. The invention may also be applied to the
urea/ammonium formate mixtures, also in aqueous solution, sold
under the trade name Denoxium.TM. and of which one of the
compositions (Denoxium-30) contains an equivalent amount of ammonia
to that of the AdBlue.RTM. solution. The latter have the advantage
of only freezing from -30.degree. C. onwards (as opposed to
-11.degree. C.), but have the disadvantages of corrosion problems
linked to the possible release of formic acid. The present
invention is particularly advantageous in the context of eutectic
water/urea solutions.
[0032] As mentioned previously, SCR systems generally comprise at
least one tank for storing the urea solution and also a system for
feeding this to the exhaust gases, which generally comprises active
components such as a pump, filter, valve(s), conduits (feed and/or
return conduits).
[0033] The idea behind the present invention may be generalized to
any component of a SCR system. It may also be combined with the
invention of co-pending application EP2008/062183 in the name of
the Applicant, which also deals with the problem of overheating in
urea components and proposes therefore to use at least two
resistive heating elements (R1, R2), one of which (R1) is intended
for heating one or some (part(s) of) component(s) always in contact
with a substantial amount of urea and the other (R2) is intended
for heating one or some (part(s) of) component(s) which are
sometimes not in contact with a substantial amount of urea, and
according to which, when starting the system in freezing
conditions, the resistive element R1 is activated but the resistive
element R2 is activated only when its component is actually in
contact with a substantial amount of urea. The problem of
overheating may still be present at the upper part of R1.
[0034] Alternatively to this solution, some car manufacturers
specify a given duration for which the tank must be heated, which
duration has been determined experimentally in order to provide a
minimum liquid quantity so as to be able to start the pump. As an
example, the following table gives experimental data for a urea
tank of 7.5 L equipped with a flexible heater extending inside the
tank and with a temperature sensor located in the upper part of the
heater corresponding to a zone of the tank that may be more easily
emerged (i.e. not in contact with urea) and accordingly where
overheating may occur more regularly. The tank is placed in a cold
chamber where the temperature is maintained at a constant value of
-9.degree. C. The flexible heater is actuated with a constant
heating power, continuously, during a period fixed by a given
specification (20 min. in this case). During the experiments, the
time needed for a temperature (Tcpt) in the tank to reach a
safeguard temperature (Tsaf) of 100.degree. C. in the upper area of
the heater was measured. The maximum temperature (Tmax) that was
reached in the upper area of the heater after 20 minutes was also
measured and the table shows that this maximum temperature (Tmax)
may exceed an overheating temperature (Tover) of 120.degree. C. for
low volumes of urea in the tank (i.e., 2 first sets of data). When
the volume of urea corresponds almost to the full capacity of the
tank (i.e., last set of data with a volume of 6.5 L), there is no
overheating because the heater is almost immerged in urea.
TABLE-US-00001 Cold chamber Volume Time to reach 100.degree. C. in
the Tmax in the upper area Overheating temperature of urea upper
area of the heater of the heater (Tmax > 120.degree. C.)
-9.degree. C. 2 L 0:05:57 127.82.degree. C. Yes -9.degree. C. 3 L
0:05:54 121.01.degree. C. Yes -9.degree. C. 6.5 L.sup. 100.degree.
C. not reached after 21.30.degree. C. No 1:10:00
[0035] Hence, such a strategy leads to overheating of the tank and
may lead to some damage to it and/or to components inside of
it.
[0036] The present invention aims at solving these problems of the
prior art heating strategies.
[0037] For this purpose the invention relates to a process for
heating a urea component of a SCR system comprising besides said
component, a temperature sensor and a heating device in the
component, according to whidh: [0038] 1. the temperature (Tcpt) of
the liquid in the component is determined and compared to a first
setpoint (T0); [0039] 2. if the temperature (Tcpt) is greater than
the first setpoint (T0), step 1 is repeated; [0040] 3. if the
temperature (Tcpt) is less than or equal to the first setpoint
(T0), the heating device is actuated; [0041] 4. the time during
which the heating device is actuated is measured and the heating
device is stopped if this time is greater than a time t1; [0042] 5.
the temperature (Tcpt) is determined after a time t2 and compared
to a second setpoint (T1 with T1>T0); if the temperature (Tcpt)
is less than or equal to the second setpoint (T1) the heating
device is actuated and step 4 is repeated; [0043] 6. if the
temperature (Tcpt) is greater than the second setpoint (T1), the
heating device is stopped and step 1 is repeated.
[0044] The present invention is advantageously applied to diesel
engines, and in particular to the diesel engines of heavy goods
vehicles.
BRIEF DESCRIPTION OF THE DRAWINGS
[0045] For a detailed description of the preferred embodiments of
the invention, reference will now be made to the accompanying
drawing in which:
[0046] FIG. 1 consists of a block diagram of one preferred variant
of the process according to the invention applied to a system for
the injection of urea into the exhaust gases of an internal
combustion engine (or SCR system).
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0047] The component that can be heated by the process of the
invention generally is a hollow component like a tank, a line, a
connector . . . . For sake of simplicity, the component will be
referred hereafter as "tank", this term being hence not
limitative.
[0048] As explained previously, the liquid for which the invention
is intended is a liquid capable of freezing or solidifying (setting
solid) when the temperature reaches a low temperature threshold.
This may, for example, be an aqueous solution. One liquid to which
the present invention applies particularly well is urea or another
reducing agent that can be used in the SCR system of an engine.
[0049] Preferably, the device heating the component is also a
flexible heater.
[0050] According to the invention the heating device is actuated if
the temperature (Tcpt) in the tank is less than the first setpoint
(T0). The first setpoint (T0) is chosen firstly so as to prevent
freezing of the liquid in the tank. As described above, the liquid
in the tank may be a urea solution that freezes at a freezing
temperature of -11.degree. C. (eutectic 32.5 wt % urea solution).
Therefore the first setpoint (T0) is chosen so as to be greater
than or equal to the freezing temperature of the liquid, and in
particular to a temperature where the liquid begins to
solidify.
[0051] But the freezing temperature of the solution may increase
with regard to ageing of the solution, i.e., with a change of the
concentration of the solution. Therefore, in a preferred variant of
the process, the first setpoint (T0) is chosen so as to be greater
than or equal to a freezing temperature that corresponds to the
concentration of the urea solution after ageing of the
solution.
[0052] In the process according to the invention, the temperature
(Tcpt) in the tank is compared with the second setpoint (T1) with
T1>T0. The second setpoint (T1) is chosen so that when the
temperature (Tcpt) in the tank is greater than the second setpoint
(T1), the solution in the tank is defrost.
[0053] The temperature (Tcpt) in the tank is measured by a
temperature sensor that is located at a specific location in the
tank (e.g., a feeding zone in the tank) and is therefore not always
representative of the temperature of the solution elsewhere in the
tank. Therefore the second setpoint (T1) is preferably chosen so as
to be sure that the solution is defrost almost everywhere in the
tank.
[0054] More preferably, the second setpoint (T1) is also chosen so
as to limit the energy consumption and to be sure that a minimum
volume of urea is defrosted for the injection in the SCR
system.
[0055] In a particular embodiment of the process, the second
setpoint (T1) may be determined so as to take account of the volume
of the solution present in the tank.
[0056] In the process according to the invention, the heating
device is actuated for the time t1.
[0057] As described above, the process aims to prevent overheating
in the tank. Overheating can be characterized by an overheating
temperature (Tover) above which part of the SCR system, and in
particular components, may be deteriorated. The overheating
temperature can be determined experimentally.
[0058] In the context of the invention, the time t1 corresponds in
general to the time necessary for the temperature (Tcpt) to exceed
the overheating temperature (Tover) when the heating device is
actuated. One possible way to determine the time t1 is to heat with
a specific power and in a continuous way a determined volume of a
urea solution in a tank and to measure the time after which the
temperature (Tcpt) in the tank exceeds the overheating temperature
(Tover).
[0059] Preferably, the time t1 corresponds to the time necessary
for the temperature (Tcpt) to exceed a safeguard temperature (Tsaf)
with Tsaf<Tover.
[0060] In the process according to the invention, the temperature
(Tcpt) is determined after the time t2 has elapsed from the moment
when the heating device is stopped. The time t2 corresponds to the
time estimated for the temperature (Tcpt) to reach a stabilized
value after the heating is switched off.
[0061] In the method according to the invention, the heating of the
SCR system is preferably also adjusted during the operation of the
system (when the vehicle is being driven) in case of freezing.
Preferably, this adjustment is carried out using simple switches
controlled as a function of the reading of the temperature sensors.
Preferably the heating device is actuated by means of a simple
switch ON/OFF, i.e., when the switch is triggered on, the heating
device is actuated, and when the switch is triggered off, the
heating device is stopped.
[0062] Commercial sensors have an accuracy of around one .degree.
C. Therefore it is advantageous to adjust over a wider range (e.g.,
of at least 2.degree. C.) to prevent the untimely activation of the
relays (MOSFET relays) and therefore to limit the wear thereof. In
particular, it is advantageous for the tank to be equipped with a
temperature sensor; for the heating of the SCR system to be
adjusted duting normal operation of the system using switches
controlled by the temperature sensor; for the switches to activate
the heating device for a time t1 when the temperature read by the
sensor drops below the first setpoint (T0), for the temperature
given by the sensor to be read after a time t2 and for the switches
to deactivate the heating device when the temperature read by the
sensor reaches/exceeds the second setpoint (T1).
[0063] The following table gives experimental data for the urea
tank described in the experiments above (referring to the prior art
strategy) where a process according to the invention is applied.
According to this process, the heater is powered under a constant
voltage of 14V when it is actuated; times t1 and t2 correspond
respectively to 6 minutes and 1 minute (based on the data in the
previous table) while the first setpoint (T0) corresponds to
-8.degree. C. (i.e. temperature where an eutectic solution of urea
begins to solidify) and the second setpoint (T1) corresponds to
-3.degree. C.
TABLE-US-00002 Time needed to Time needed to make 5 bars Cold Time
to reach Overheating Urea available make 5 bars available for
chamber Volume 100.degree. C. in the upper (Tmax > through the
available for dosing temperature of urea area of the heater
120.degree. C.) injector (150 mL/h) dosing (Specs.) (experiments)
-9.degree. C. 1 L 100.degree. C. not reached No No pressure 0:20:00
0:02:47 after 1:08:00 drop after 1:08:00 -25.degree. C. 6.5 L
100.degree. C. not reached No No pressure 0:45:00 0:38:13 after
2:43:13 drop after 2:43:13 -17.degree. C. 1 L Peak of temp. at No
No pressure 0:26:30 0:24:13 100.degree. C. during 2 * 30 s drop
after 2:34:58
[0064] In this table, experiments show that no overheating (i.e.,
Tcpt does not exceed Tover, i.e., 120.degree. C. in this case) is
observed whatever the volume of urea in the tank and the
temperature of the cold chamber. Furthermore no pressure drop is
observed in the SCR system and the time needed to make 5 bars
available for dosing urea in the SCR system is lower than
specifications.
[0065] The present invention is illustrated, in a non-limiting
manner, by appended FIG. 1.
[0066] FIG. 1 consists of a block diagram of one preferred variant
of the process according to the invention applied to a system for
the injection of urea into the exhaust gases of an internal
combustion engine (or SCR system).
[0067] At the beginning of the process (step 1), a heating device
is OFF.
[0068] A system controller measures the temperature (Tcpt) in a
tank (step 2) and verifies (step 3) whether the temperature (Tcpt)
of the liquid in the tank is less than or equal to a first setpoint
(T0).
[0069] If this is not the case (N or NO), the controller keeps
verifying whether the temperature (Tcpt) is less than or equal to
the first setpoint (T0) (loop between steps 3 and 2).
[0070] If this is the case (Y or YES), the heating device is
actuated (step 4) for a time t1 during which the tank is heated.
The time elapsed from the actuation of the heating device is
measured at step 5 and the process checks at step 6 if the time
elapsed is greater than t1. If it is not the case the process
continues at step 5 and a loop between steps 5 and 6 starts. If it
is the case the heating device is stopped (step 7). The time
elapsed from the stop of the heating device is measured at step 8
and the process checks at step 9 if the time elapsed is greater
than t2. If it is not the case the process continues at step 8 and
a loop between steps 8 and 9 starts. If it is the case the process
verifies (step 10) whether the temperature (Tcpt) is greater than a
second setpoint (T1).
[0071] The time t1 and t2 may be chosen experimentally so as to
avoid overheating of components in the SCR system and in particular
to avoid that the temperature (Tcpt) in the tank exceeds a
safeguard temperature (e.g., 100.degree. C.) or an overheating
temperature (e.g., 120.degree. C.) whatever the volume of urea
contained in the tank.
[0072] If the temperature (Tcpt) is less than or equal to the
second setpoint (T1 with T1>T0), the process continues at step 4
and the heating device is actuated.
[0073] If the temperature (Tcpt) is greater than the second
setpoint (T1), the heating device is stopped (step 11) and the
process continues with step 2.
* * * * *