U.S. patent application number 14/777646 was filed with the patent office on 2016-10-06 for selective catalytic reduction pollution-control system.
This patent application is currently assigned to Plastic Omnium Advanced Innovation and Research. The applicant listed for this patent is PLASTIC OMNIUM ADVANCED INNOVATION AND RESEARCH. Invention is credited to Francois DOUGNIER, Dominique MADOUX, Jules-Joseph VAN SCHAFTINGEN.
Application Number | 20160290203 14/777646 |
Document ID | / |
Family ID | 48741338 |
Filed Date | 2016-10-06 |
United States Patent
Application |
20160290203 |
Kind Code |
A1 |
DOUGNIER; Francois ; et
al. |
October 6, 2016 |
SELECTIVE CATALYTIC REDUCTION POLLUTION-CONTROL SYSTEM
Abstract
A housing for an ammonia-sensitive component in a selective
catalytic reduction pollution-control system. This housing includes
a wall and a trap configured to capture gaseous ammonia emanating
from the wall or which, if it were not trapped, would emanate from
the wall.
Inventors: |
DOUGNIER; Francois;
(Boortmeerbeek, BE) ; MADOUX; Dominique; (Rumes,
BE) ; VAN SCHAFTINGEN; Jules-Joseph; (Wavre,
BE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
PLASTIC OMNIUM ADVANCED INNOVATION AND RESEARCH |
Brussels |
|
BE |
|
|
Assignee: |
Plastic Omnium Advanced Innovation
and Research
Brussels
BE
|
Family ID: |
48741338 |
Appl. No.: |
14/777646 |
Filed: |
March 18, 2014 |
PCT Filed: |
March 18, 2014 |
PCT NO: |
PCT/FR14/50626 |
371 Date: |
September 16, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F01N 2610/02 20130101;
F01N 3/0828 20130101; Y02A 50/2325 20180101; Y02T 10/12 20130101;
Y02T 10/24 20130101; F01N 3/2066 20130101; F01N 2610/1433 20130101;
F01N 2610/1406 20130101 |
International
Class: |
F01N 3/20 20060101
F01N003/20; F01N 3/08 20060101 F01N003/08 |
Claims
1-10. (canceled)
11. A housing for an ammonia-sensitive component, the housing
configured to be placed in a selective catalytic reduction
pollution-control system configured to reduce an amount of nitrogen
oxides in exhaust gases of a motor vehicle, the housing comprising:
at least one wall and a trap configured to capture gaseous ammonia
emanating from the at least one wall or which, if it was not
trapped, would emanate from this at least one wall.
12. The housing as claimed in claim 11, wherein the trap is
integrated into the wall.
13. The housing as claimed in claim 11, wherein the trap is firmly
mounted to the wall in a fixed or removable manner.
14. The housing as claimed in claim 11, wherein the ammonia trap
comprises at least one of the following elements: a material on
which ammonia may be stored by sorption, or a salt or an
alkaline-earth metal chloride or magnesium chloride; or a
superabsorbent polymer.
15. The housing as claimed in claim 14, wherein the superabsorbent
polymer is in a form of a gel resulting from absorption of water by
the polymer.
16. The housing as claimed in claim 11, further comprising an
ammonia-sensitive device.
17. The housing as claimed in claim 11, further comprising a
caulking agent in the wall to seal possible cracks and reduce or
eliminate leaks of ammonia.
18. The housing as claimed in claim 11, wherein the
ammonia-sensitive component includes a winding of a motor of a urea
pump.
19. The housing as claimed in claim 11, placed in a urea storage
tank of the selective catalytic reduction pollution-control
system.
20. The housing as claimed in claim 11, is placed in a urea
injection line of the selective catalytic reduction
pollution-control system.
Description
[0001] The present invention relates to the trapping of ammonia in
a pollution-control system intended to reduce the amount of
nitrogen oxides in the exhaust gases of a motor vehicle.
[0002] The nitrogen oxides present in the exhaust gases of
vehicles, in particular diesel vehicles, can be eliminated by a
pollution-control system using a technique of selective catalytic
reduction (generally referred to as SCR). According to this
technique, doses of ammonia (NH.sub.3) are injected into the
exhaust line upstream of a catalyst on which the reduction
reactions take place.
[0003] Currently, the ammonia is produced by thermal decomposition
of a precursor, generally an aqueous solution of urea. In the
on-board systems for storing urea, the urea solution undergoes,
over time, a decomposition reaction to give gaseous ammonia, which
reaction increases when the temperature rises. In certain cases,
the gaseous ammonia resulting from this decomposition and which is
present inside the tank, may pass through the wall of the urea
storage tank. Thus, there is a risk of this gaseous ammonia
spreading outside of the tank, i.e. into the air surrounding the
tank. This is particularly inconvenient.
[0004] Indeed, gaseous ammonia is a source of a very acrid odor and
is toxic, in particular for man, but also for the environment.
Furthermore, it is corrosive for certain metals.
[0005] It is therefore necessary to trap the ammonia vapors
generated deliberately or accidentally and which are capable of
being released from the tank.
[0006] From document EP 1 911 508, a device intended to trap the
ammonia generated inside a urea storage tank of an SCR
pollution-control system is already known. The solution described
in that document consists in transporting the gaseous ammonia
present inside the urea storage tank to a trap external to the urea
storage tank, through a transport pipe. However, the drawback of
that solution lies in the fact that there is a risk that a portion
of the gaseous ammonia present in the tank is not transported to
the trap. This portion of gaseous ammonia may therefore pass
through the wall of the tank.
[0007] Furthermore, there is also a risk of leakage of ammonia at
the transport pipe. However, the aforementioned solution is not
suitable for solving this problem. More generally, the solution
from the prior art described above does not make it possible to
trap ammonia which could escape from components of the SCR system
other than the tank, such as for example a urea injection line. The
solution from the prior art does not make it possible either to
protect components of the SCR system placed in housings, the walls
of which may be made of materials that are permeable to ammonia,
such as for example a copper coil, more commonly referred to as a
winding, of a motor of a urea pump.
[0008] The invention aims to trap all or some of the gaseous
ammonia generated within an SCR pollution-control system everywhere
where it may be inconvenient.
[0009] For this purpose, one subject of the invention is a
subsystem of a selective catalytic reduction pollution-control
system, intended to reduce the amount of nitrogen oxides in the
exhaust gases of a motor vehicle, characterized in that said
subsystem comprises: [0010] at least one chamber comprising at
least one wall and [0011] a trap configured to capture gaseous
ammonia emanating from this at least one wall or which, if it was
not trapped, would emanate from this at least one wall.
[0012] A subsystem of a pollution-control system is understood to
mean a subassembly of the assembly constituted by all the
constituent elements of a pollution-control system that are
intended to be built into the vehicle.
[0013] A chamber is understood to mean a volume delimited by at
least one wall. Thus, in the case where, inside a first volume
delimited by a first wall, a second wall delimits a second volume,
two chambers are delimited. A chamber corresponds to the space
between the two walls. A second chamber corresponds to the second
volume delimited by the second wall.
[0014] A wall is understood to mean a structure which obstructs (at
least partially or completely) the ammonia. More specifically, this
structure has an ammonia permeability of less than 3 g/m.sup.2 per
day, for a thickness of 1 mm.
[0015] Optionally, the trap is integrated into the wall.
[0016] In the invention, the subsystem forms a single block which
makes it possible to optimize the overall volume occupied by the
chamber and the trap. The assembly of the chamber and of the trap
in the pollution-control system is also facilitated by this block
configuration.
[0017] As a first variant, the chamber contains the trap configured
to capture gaseous ammonia and contains an ammonia-sensitive
component.
[0018] Preferably, the ammonia-sensitive component is made of
copper or an alloy thereof, and preferably constitutes a coil of a
motor of a urea pump.
[0019] Ammonia attacks copper and all the alloys thereof by
corrosion. Yet, the on-board systems for storing, dispensing and
dosing urea of the SCR pollution-control systems may contain
ammonia resulting from the decomposition of the urea and comprise
copper-containing components. These components are placed in a
housing in order not to be in contact with the urea to which they
may also be sensitive. However, the wall of the protective housing
is not completely impermeable to ammonia. This configuration of the
invention makes it possible to increase the service life of these
components, which makes it possible to prevent the occurrence of
functional defects in the pollution-control system and confers an
economic advantage.
[0020] In a second variant, the trap is firmly mounted to the wall
in a fixed or removable manner.
[0021] The removable nature of the attachment of the trap to the
wall makes it possible to replace the trap, for example when it is
saturated with ammonia.
[0022] The trap may be attached according to various methods such
as adhesive bonding, welding, screwing, or other methods.
[0023] Advantageously, the subsystem comprises two chambers, a
first chamber of which contains an ammonia trap, said two chambers
being separated from one another by at least one wall of a second
chamber, so that ammonia contained in the second chamber, escaping
via permeability or via rupture of said at least one wall, can have
no other destination than the first chamber.
[0024] Advantageously, the ammonia trap comprises at least one of
the following elements: [0025] a material on which ammonia may be
stored by sorption, more particularly a salt and more particularly
still an alkaline-earth metal chloride such as magnesium chloride,
and [0026] a superabsorbent polymer.
[0027] These elements have a high absorption capacity if they are
compared to other absorbent elements such as for example activated
carbons. The use of these elements therefore makes it possible to
obtain traps of smaller volume.
[0028] They also have the advantage of not being dangerous for the
environment.
[0029] Finally, these elements are characterized by a capacity for
trapping ammonia over a relatively long term.
[0030] Advantageously, the superabsorbent polymer is in the form of
a gel resulting from the absorption of water by said polymer (the
ammonia being trapped by this water).
[0031] As a variant, the wall of the second chamber, which
separates the two chambers, is a wall common to the two
chambers.
[0032] Optionally, the ammonia trap is in contact with the wall
common to the two chambers.
[0033] This configuration makes it possible to improve the
capturing of the ammonia which is, as soon as it passes the wall
separating the two chambers, brought into contact with the
trap.
[0034] Optionally, the two chambers have two contiguous walls.
[0035] Contiguous is understood to mean walls which are
side-by-side, separated by a specified distance.
[0036] As a variant, the second chamber is suitable for containing
an ammonia precursor.
[0037] Preferably, the second chamber is suitable for containing
urea.
[0038] Optionally, the second chamber consists of a urea injection
line.
[0039] Optionally, the second chamber consists of a urea storage
tank.
[0040] Advantageously, one wall of at least one of the chambers is
made from a thermoplastic material.
[0041] As a variant, the first chamber contains an
ammonia-sensitive component.
[0042] Preferably, the ammonia-sensitive component is made of
copper or an alloy thereof, and preferably constitutes a coil or
winding of a motor of a urea pump.
[0043] Preferably, the second chamber is suitable for containing a
compound on which ammonia may be stored by sorption.
[0044] Indeed, an alternative technique for provision of ammonia in
SCR pollution-control systems consists in storing the ammonia by
sorption on a salt, usually an alkaline-earth metal chloride.
Generally, in this case, the storage system comprises a tank
designed to contain the salt and a heating device configured to
heat the salt. Thus, by heating the salt the ammonia is released.
The invention also makes it possible to make safe the SCR
pollution-control systems having such an ammonia storage device.
Indeed, this configuration makes it possible to trap the ammonia
which could be released suddenly from the chamber containing
gaseous ammonia in the event of an accidental situation such as a
defect or a rupture in the wall of this chamber, thus improving the
safety of the SCR pollution-control system.
[0045] European patent application EP 2 574 599 in the name of the
applicant describes an example of a tank intended to store ammonia
by sorption on a salt. Said tank comprises a plurality of storage
cells that communicate with one another and with at least one
orifice that communicates with a dispensing duct. The cells are
cavities capable of containing the compound on which the ammonia is
stored by sorption.
[0046] As a variant, the subsystem comprises a cell, at least one
portion of which defines the second chamber.
[0047] Optionally, at least one other portion of the cell defines
the first chamber.
[0048] This embodiment of the invention makes it possible to
simplify and accelerate the assembly since the two chambers are
provided in the form of a single part. Such a configuration also
makes it possible to provide a more compact subsystem.
[0049] Advantageously, the two chambers together comprise means for
establishing fluid communication which, in the event of
overpressure in the second chamber or in the event of desorption
operation of the storage means, send the ammonia to the first
chamber.
[0050] An overpressure in the second chamber may be generated by an
excessive heating of the storage means.
[0051] Thus, at least one portion of the means for establishing
fluid communication, including the connection between the means for
establishing fluid communication and the second chamber, is located
in the first chamber. This portion consequently also benefits from
the safety system formed by the trap.
[0052] The means for establishing fluid communication may also be
used to discharge the ammonia stored by sorption on the trap, in
order to regenerate the latter.
[0053] In this configuration, the trap therefore performs three
functions.
[0054] Advantageously, the trap consists of a matrix which occupies
the entire free space of the first chamber.
[0055] The space occupied by the matrix increases with the
absorption of ammonia. The matrix is then compressed within the
volume of the first chamber, thus limiting the flow of ammonia
through the wall.
[0056] The matrix makes it possible to improve the capturing of
ammonia which is, as soon as it passes the wall separating the two
chambers, brought into contact with the trap.
[0057] The matrix fulfils a thermal insulation role, which makes it
possible to prevent the urea solution from reaching too high a
temperature in order to limit the release of ammonia due to its
decomposition. The thermal insulation also makes it easier to
maintain the urea solution at a temperature above its
crystallization temperature. Finally, in the event of storage of
ammonia by sorption on a salt, the matrix makes it possible to
maintain the salt at a stable temperature in order to optimize the
control of the release of ammonia by heating.
[0058] Another subject of the invention is a selective catalytic
reduction pollution-control system comprising a subsystem as
described above.
[0059] Finally, another subject of the invention is a housing for
an ammonia-sensitive component, said housing being intended to be
placed in a selective catalytic reduction pollution-control system
intended to reduce the amount of nitrogen oxides in the exhaust
gases of a motor vehicle, said housing being characterized in that
it comprises at least one wall and a trap configured in order to
capture gaseous ammonia emanating from this at least one wall or
which, if it was not trapped, would emanate from this at least one
wall.
[0060] All the variants envisaged for the subsystem apply to the
housing.
[0061] An optional feature of the housing is that it contains an
ammonia-sensitive device (for example pH paper), so as to reveal
that the trap has been used, which may be one way of easily
verifying that the component is still protected at the time of a
maintenance operation.
[0062] Another optional advantageous feature is the presence of a
caulking agent in the wall in order to seal the possible cracks and
thus reduce, or even eliminate, leaks of ammonia.
[0063] The invention will be better understood on reading the
appended figures, which are provided by way of examples and have no
limiting nature, in which:
[0064] FIG. 1 is a schematic representation of an SCR
pollution-control system comprising a urea storage tank.
[0065] FIG. 2 is a view of a urea storage tank of an SCR
pollution-control system according to a first embodiment of the
invention.
[0066] FIG. 3 is a view of a urea storage tank of an SCR
pollution-control system according to a second embodiment of the
invention.
[0067] FIG. 4 is a view of a urea storage tank of an SCR
pollution-control system according to a third embodiment of the
invention.
[0068] FIG. 5 is a view of a portion of a urea injection line of an
SCR pollution-control system according to a fourth embodiment of
the invention.
[0069] FIGS. 6 and 7 are views of a urea injection line according
to a fifth embodiment of the invention. FIG. 6 is a cross section
along IV-IV of FIG. 7 and FIG. 7 is a cross section along V-V of
FIG. 6.
[0070] FIG. 8 is a cross section of a urea storage tank according
to a sixth embodiment.
[0071] FIG. 9 is a schematic representation of an SCR
pollution-control system comprising a system for storing gaseous
ammonia.
[0072] FIG. 10 is a view of a system for storing gaseous ammonia
according to a seventh embodiment of the invention.
[0073] FIG. 11 is a view of a system for storing gaseous ammonia
according to an eighth embodiment of the invention.
[0074] FIG. 12 is a view of a system for storing gaseous ammonia
according to a ninth embodiment of the invention.
[0075] In FIGS. 1 to 8, the components which are identical are
denoted by the same reference numbers.
[0076] Reference is now made to FIG. 1, in which a system is
represented for treating nitrogen oxides present in the exhaust
line 2 of a vehicle engine 1. The nitrogen oxides are sent to a
catalyst 8 in which the selective catalytic reduction (SCR) is
carried out. The selective catalytic reduction is obtained by
addition of ammonia to the exhaust gases. In the example from FIG.
1, the ammonia needed for the reduction originates from a urea
solution 4 which is stored in a urea storage tank 3. The urea
storage tank 3 is connected to the exhaust line 2 by a urea
injection line 5. The urea present in the tank 3 is transported to
the urea injection line 5 owing to the action of a urea pump 6
present inside the urea storage tank 3. Under the action of a urea
injector 7, the urea is injected into the exhaust line 2. With time
and temperature variations, a portion of the urea contained in the
tank 3 is decomposed to give gaseous ammonia. The gaseous ammonia
of the tank is capable of coming into contact with
ammonia-sensitive components present in the urea storage tank
3.
[0077] A first embodiment of the invention has been represented in
FIG. 2. A urea storage tank 3 contains an ammonia-sensitive
component 9. This component is placed in a housing 10 delimited by
a wall 17 and a cover 11. Since the wall 17 of the housing and the
cover 11 are porous to ammonia, an ammonia trap 12 was placed in
the wall 17 of the housing and that of the cover 11 in order to
keep, in the housing, the concentration of ammonia below a
threshold value capable of leading to the corrosion of the
component. This threshold value may be determined as a function of
the nature of the component, of the temperature or of the exposure
time. This threshold value or these threshold values may be
obtained following experiments. In this example, the subsystem
consists of the assembly of the housing 10 which corresponds to the
chamber comprising two walls, namely the wall 17 of the housing and
the cover 11. The trap 12 is configured in order to capture gaseous
ammonia emanating from the wall 17 or from the cover 11.
Alternatively, the trap may be placed in one or other of the walls
of the housing and of the cover. In this embodiment, the trap 12 is
in the form of magnesium chloride particles integrated into the
polymer wall 17 of the housing and of the cover 11. In one
particular embodiment, the wall 17 of the housing has, for example,
a thickness of around 2 mm and has a permeability equal to around
1.25 g/m.sup.2/day at 80.degree. C. In this particular embodiment,
the housing 10 has, for example, a total surface area of around 300
cm.sup.2. In this embodiment, the protection of the component is
ensured by 3 to 6 g of magnesium chloride.
[0078] A second embodiment of the invention has been represented in
FIG. 3. An ammonia-sensitive component 9' is placed in a housing
10' equipped with a cover 11' and placed in the vicinity of a urea
storage tank 3 delimited by a wall 18. The walls 17' of the housing
and 18 of the urea storage tank 3 may be a single wall common to
the two chambers. Since these two walls are porous to ammonia, an
ammonia trap 12' was placed inside the tank 3, in the vicinity of
the location of the housing 10' in order to keep, in the housing,
the concentration of ammonia below a threshold value capable of
leading to the corrosion of the component. This threshold value may
be determined as a function of the nature of the component, of the
temperature or of the exposure time. This threshold value or these
threshold values may be obtained following experiments. In this
example, the subsystem consists of the assembly of the urea storage
tank 3 which corresponds to the chamber comprising the wall 18. The
trap 12' is configured to capture gaseous ammonia which, if it was
not trapped, would emanate from the wall 18. The trap is provided
with a protection 19 that limits direct contact between the ammonia
trap and the liquid phase of the ammonia precursor. In this
embodiment, the trap 12' is firmly mounted to the wall 18. In this
embodiment, the protection of the component is ensured, for
example, by 1 to 2 g of magnesium chloride. In one particular
embodiment, the walls 17' of the housing 10' and 18 of the urea
storage tank 3, have a total thickness of 2 mm and a permeability
equal to 1.25 g/m.sup.2/day at 80.degree. C. This common wall has,
for example, a surface area of 100 cm.sup.2, or in the case of two
superposed walls, these may be superposed over a surface area of
100 cm.sup.2.
[0079] A third embodiment of the invention has been represented in
FIG. 4. A urea storage tank 3 contains an ammonia-sensitive
component 9''. This component is placed in a housing 10'' having a
wall 17'' and equipped with a cover 11''. Since the wall 17'' of
the housing and the cover 11'' are porous to ammonia, an ammonia
trap 12'' was placed in the cover 11'' of the housing in order to
keep, in the housing, the concentration of ammonia below a
threshold value capable of leading to the corrosion of the
component. This threshold value may be determined as a function of
the nature of the component, of the temperature or of the exposure
time. This threshold value or these threshold values may be
obtained following experiments. In this example, the subsystem
consists of the assembly of the housing 10'' which corresponds to
the first chamber and of the urea storage tank 3 which corresponds
to the second chamber. The two chambers are separated from one
another by the wall 17'' of the housing 10'' which corresponds to a
wall of the second chamber. In this embodiment, the trap 12'' is in
the form of a pad composed of an open-cell foam made for example of
polyethylene, impregnated with magnesium chloride. In one
particular embodiment, the wall of the housing 10'' has, for
example, a thickness of around 1 mm and has a permeability equal to
around 2.5 g/m.sup.2/day at 80.degree. C. In this particular
embodiment, the housing 10'' has, for example, a total surface area
of around 300 cm.sup.2. In this embodiment, the protection of the
component is ensured by 6 to 12 g of magnesium chloride.
[0080] A fourth embodiment of the invention has been represented in
FIG. 5. A urea injection line 5 contains an ammonia-sensitive
component 9''. As in the preceding embodiment, the component 9'''
is placed in a housing 10''' having a wall 17''', equipped with a
cover 11'''. An ammonia trap 12''' was placed in the cover of the
housing. In this example, the subsystem consists of the assembly of
the housing 10''' which corresponds to the first chamber and of the
urea injection line 5 which corresponds to the second chamber. The
two chambers are separated from one another by the wall 17''' of
the housing 10''' which corresponds to a wall of the second
chamber. The trap 12''' is in the form of a pad composed of an
open-cell foam made for example of polyethylene, impregnated with
magnesium chloride. In one particular embodiment, the wall 17''' of
the housing 10''' consists of polyphthalamide (PPA), has, for
example, a thickness of around 1 mm and has an ammonia permeability
at 80.degree. C. of around 1 to 2.5 g/m.sup.2/day. In this
particular embodiment, the housing 10''' has, for example, a total
surface area of around 300 cm.sup.2. In this embodiment, the
protection of the component over 40 days (around 1000 hours) is
ensured by 2 to 6 g of magnesium chloride.
[0081] A fifth embodiment of the invention has been represented in
FIGS. 6 and 7. A urea injection line 5 is surrounded over one
portion of its length by a sleeve 13 containing an ammonia trap 14.
In this example, the subsystem consists of the assembly of the
sleeve 13 which corresponds to the first chamber and of the urea
injection line 5 which corresponds to the second chamber. The two
chambers are separated from one another by the wall of the urea
injection line 5 which corresponds to the wall of the second
chamber. In this embodiment, the trap consists of magnesium
chloride crystals. In one particular embodiment, the wall consists
of polyamide 66 (PA 66) and has, for example, an ammonia
permeability of around 0.5 g/m.sup.2/day at 40.degree. C. for a
thickness of around 1 mm. In this particular embodiment, for a urea
injection line of around 4 mm in diameter and of around 1 m in
length, the surface area covered is around 125 cm.sup.2. In this
embodiment, around 0.25 g of ammonia is emitted in 40 days (around
1000 hours) through the wall of the urea injection line. Around
0.25 g of magnesium chloride may ensure the trapping of this amount
of ammonia. In this particular embodiment, the amount of magnesium
chloride forming the trap in such an embodiment is around 0.5 to 2
g.
[0082] A sixth embodiment has been represented in FIG. 8. A urea
storage tank 3 is surrounded by a shell 15 containing an ammonia
trap 16. In this example, the subsystem consists of the assembly of
the shell 15 which corresponds to the first chamber and of the urea
storage tank 3 which corresponds to the second chamber. The two
chambers are separated from one another by the wall of the urea
storage tank 3 which corresponds to the wall of the second chamber.
In this embodiment, the trap consists of a magnesium chloride
matrix. In one particular embodiment, the wall consists of
high-density polyethylene (hdPE) and has, for example, an ammonia
permeability at 80.degree. C. of around 1.5 g/m.sup.2/day for a
thickness of around 1 mm. In one particular embodiment, for a
thickness of around 4 mm and a tank surface area of around 1
m.sup.2, the protection over 40 days (around 1000 hours) may be
ensured, for example, by 14 g of magnesium chloride. In practice,
in this embodiment, the trap contains, for example, 15 to 25 g of
magnesium chloride.
[0083] In FIGS. 9 to 12, the components which are identical are
denoted by the same reference numbers.
[0084] Represented schematically in FIG. 9 is an example of a
selective catalytic reduction (SCR) pollution-control system
comprising a system for storing gaseous ammonia. The invention is
not limited to such an example of an SCR system with gaseous
storage. The engine 21 of the vehicle is controlled by an
electronic control unit 22. The engine 21 cooperates with an SCR
system 23. On leaving the engine, the exhaust gases 41 are sent to
an ammonia injection module 31, in which the ammonia 72 is mixed
with the exhaust gases 41. The ammonia/exhaust gas mixture 43 then
passes through an SCR catalyst 32 which enables the reduction of
the nitrogen oxides (NOx) by the ammonia. The decontaminated
exhaust gases 44 are then sent to the exhaust outlet.
[0085] The SCR system 23 comprises an ammonia storage system 25.
The storage system 25 comprises a cell 54 in which a compound 52,
for example a solid (preferably a salt), is stored. The ammonia is
stored by sorption on the solid 52. The storage system 25 also
comprises a control device 24 in charge of controlling a heating
device 53 for heating the solid 52 so as to release the ammonia.
The cell 54 is connected to a dosing module 51, via a dispensing
duct 27. The dosing module 51 is controlled by the control device
24. The control device 24 is capable of estimating the pressure of
ammonia in the storage system 25. If a difference is observed
between the estimated pressure and a setpoint pressure provided by
the electronic control unit 22, the control device 24 may adjust
the heating power of the heating device 53 in order to compensate
for this difference. The tank 54 is equipped with a
temperature-measuring device 26.
[0086] Represented in FIG. 10 is a seventh embodiment of the
invention in a selective catalytic reduction (SCR)
pollution-control system comprising a system for storing gaseous
ammonia. A cell 54, which contains a compound 52 on which the
ammonia is stored by sorption, is surrounded by a shell 63 which
delimits a chamber according to the invention that contains an
ammonia trap 62. A dispensing duct 27 connected to the cell 54
leads to a three-way valve 60. In the event of overpressure in the
cell 54 and of no request by the control device 24 for a discharge
of ammonia to the component located downstream of the cell 54,
namely, in this example, the temperature-measuring device 26, the
excess ammonia is rerouted to a duct 61 which is connected to the
shell 63 that contains the trap 62. In this example, the subsystem
consists of the assembly of the shell 63 which corresponds to the
first chamber and of the cell 54 which corresponds to the second
chamber. The shell 63 and the cell 54 are separated from one
another by the wall of the cell 54 which corresponds to the wall of
the second chamber. The dispensing duct 27, the three-way valve 60
and the duct 61 constitute means for establishing fluid
communication within the meaning of the invention. The three
functions already mentioned for the trap are found: making safe the
second chamber and a portion of the means for establishing fluid
communication, and also the control of the overpressure and of the
desorption. In this embodiment, the cell 54 has a volume of 500 ml.
The trap 62 consists of a magnesium chloride matrix.
[0087] In one particular embodiment, the thermal activation of the
desorption results in an emission of around 1 g of ammonia, which
translates into an overpressure of around 4 bar in the cell 54.
When the system is closed, all of the desorbed ammonia is sent to
the trap. For example, 0.93 g of magnesium chloride is needed for
trapping around 1 g of ammonia. Nevertheless, it is for example
advantageous to provide the trap with 5 g of magnesium chloride in
order to effectively absorb all of the ammonia suddenly
discharged.
[0088] In the event of an accidental situation such as a defect or
a rupture in the wall of the cell 54, at a temperature of
40.degree. C., the desorption of the ammonia takes place with a
flow rate of around 3.5 mg/s, i.e. around 12.6 g of ammonia in 1
hour. In this particular embodiment, around 11.9 g of magnesium
chloride are needed to absorb this amount of ammonia. For example,
a trap containing 12 g of magnesium chloride makes it possible to
ensure the protection with respect to such an accidental situation
for around 1 hour.
[0089] Finally, if it is intended to trap the ammonia resulting
from a desorption over a long duration, that is to say all the
ammonia contained in the cell 54, a trap containing for example 300
g of magnesium chloride is needed.
[0090] Represented in FIG. 11 is an eighth embodiment of the
invention in a selective catalytic reduction (SCR)
pollution-control system comprising a system for storing gaseous
ammonia. Three identical cells 54a, 54b and 54c, of 500 ml each,
are all three surrounded by a same shall 59 which contains an
ammonia trap 58. In this example, three subsystems are considered.
The first consists of the assembly of the shell 59 which
corresponds to the first chamber and of the cell 54a which
corresponds to the second chamber. The second consists of the
assembly of the shell 59 which corresponds to the first chamber and
of the cell 54b which corresponds to the second chamber. The third
consists of the assembly of the shell 59 which corresponds to the
first chamber and of the cell 54c which corresponds to the second
chamber. The shell 59 is separated from the cells 54a, 54b and 54c
by the walls of the latter which correspond, for each subsystem, to
the wall of the second chamber. A dispensing duct 27 connected to
the cells 54a, 54b and 54c is equipped with a pressure relief valve
56. In the event of overpressure in the cells 54a, 54b and 54c and
of no request by the control device 24 for a discharge of ammonia
to the component located downstream of the cells 54a, 54b and 54c,
namely, in this example, the temperature-measuring device 26, the
excess ammonia is rerouted to a duct 57 which is connected to the
shell 59 that contains the trap 58. The dispensing duct 27, the
pressure relief valve 56 and the duct 57 constitute means for
establishing fluid communication within the meaning of the
invention. As for the preceding figure, the three functions of the
trap are found. The trap 58 consists of a magnesium chloride
matrix.
[0091] In one particular embodiment, the thermal activation of the
desorption results in an emission of around 1 g of ammonia in each
cell 54a, 54b and 54c, which translates into an overpressure of
around 4000 hPa in each cell. When the system is closed, all of the
desorbed ammonia is sent to the trap. Around 2.79 g of magnesium
chloride are needed for trapping around 3 g of ammonia resulting
from the three cells. Nevertheless, it is advantageous to provide
the trap for example with 15 g of magnesium chloride in order to
effectively absorb all of the ammonia suddenly discharged.
[0092] In the event of an accidental situation such as a defect or
a rupture in the wall of one of the cells, at a temperature of
40.degree. C., the desorption of the ammonia takes place with a
flow rate of around 3.5 mg/s, i.e. around 12.6 g of ammonia in 1
hour. For example, around 11.9 g of magnesium chloride are needed
to absorb this amount of ammonia. A trap containing around 12 g of
magnesium chloride makes it possible for example to ensure the
protection with respect to such an accidental situation for around
1 hour.
[0093] Finally, if it is intended to trap the ammonia resulting
from a desorption over a long duration, that is to say all the
ammonia contained in the cells 54a, 54b and 54c, a trap containing
for example 900 g of magnesium chloride is needed.
[0094] Represented in FIG. 12 is a ninth embodiment of the
invention in a selective catalytic reduction (SCR)
pollution-control system comprising a system for storing gaseous
ammonia. A cell 70 contains two compartments 74 and 73 separated
from one another by a partition 71. The compartment 74 contains a
compound 52 on which the ammonia is stored by sorption. A
dispensing duct 27 connected to the compartment 74 leads to a
three-way valve 60. In the event of overpressure in the compartment
74 and of no request by the control device for a discharge of
ammonia to the component located downstream of the container 70, in
this example, the temperature-measuring device 26, the excess
ammonia is rerouted to a duct 61 which is connected to the
compartment 73 that contains a trap 62. In this example, the
subsystem consists of the assembly of the compartment 73 which
corresponds to the first chamber and of the compartment 74 which
corresponds to the second chamber. As for the preceding two figures
the three functions of the trap are found, although, in this
example, the wall separating the two chambers does not entirely
surround the other chamber. In this embodiment, the compartment 74
has a volume of 500 ml. The trap 62 consists of a magnesium
chloride matrix.
[0095] In one particular embodiment, the thermal activation of the
desorption results in an emission of around 1 g of ammonia, which
translates into an overpressure of around 4000 hPa in the
compartment 74. When the system is closed, all of the desorbed
ammonia is sent to the trap. For example, 0.93 g of magnesium
chloride is needed for trapping around 1 g of ammonia.
Nevertheless, it is advantageous to provide the trap for example
with 5 g of magnesium chloride in order to effectively absorb all
of the ammonia suddenly discharged.
[0096] In the event of an accidental situation such as a defect or
a rupture in the partition 71, at a temperature of 40.degree. C.,
the desorption of the ammonia takes place with a flow rate of
around 3.5 mg/s, i.e. around 12.6 g of ammonia in 1 hour. For
example, 11.9 g of magnesium chloride are needed to absorb this
amount of ammonia. A trap containing around 12 g of magnesium
chloride makes it possible to ensure the protection with respect to
such an accidental situation for around 1 hour.
[0097] Finally, if it is intended to trap the ammonia resulting
from a desorption over a long duration, that is to say all the
ammonia contained in the compartment 74, a trap containing around
300 g of magnesium chloride is needed.
[0098] The invention is not limited to the embodiments presented
and other embodiments will appear clearly to a person skilled in
the art. In particular it is possible to modify the first two
embodiments represented in FIGS. 2 and 3 in order to add at least a
second trap to a portion of the housing located opposite the first
trap.
[0099] The embodiments may also be modified in the form of the trap
(matrix, salt in crystalline form, etc.). The trap may contain
another salt such as, for example, strontium chloride or calcium
chloride. It may alternatively consist of water-saturated
superabsorbent polymers.
* * * * *