DE202011110564U1 - Ammonia precursor storage system including a semi-permeable membrane - Google Patents

Abstract

A system for storing an ammonia precursor, comprising: a tank designed to receive the ammonia precursor, a filling opening which is closed by a cap, said cap being removable for refilling the tank; and a semi-permeable membrane positioned in said cap, the semi-permeable membrane designed to block liquid from the ammonia precursor and designed to allow air and vapors from the ammonia precursor to pass therethrough happen when the cap closes the fill opening and, when the cap closes the fill opening, a path is provided which allows a substantial amount of vapors to escape from the tank into the atmosphere so that the entire internal volume of the reservoir 1 is divided due to the flow rate through the membrane at 10mbar (l / h) is less than 20h.

Description

Background of the invention

Field of the invention

The present invention relates to a storage system for an ammonia precursor comprising a semi-permeable membrane.

Description of the related art

Laws that regulate passenger and commercial vehicle emissions sometimes require a reduction in the amount of nitrogen oxides (NOx) released into the atmosphere. This goal can be achieved by the SCR (Selective Catalytic Reduction) method which serves to reduce the nitrogen oxides by injecting a reducing agent, generally ammonia, into the exhaust gas line. This ammonia can be generated by thermolytic decomposition of a solution of an ammonia precursor, of which the concentration may be eutectic. Such an ammonia precursor may be, for example, a urea solution.

The SCR process treats the high NOx releases produced in the engine during combustion with optimum efficiency at the engine exit in a catalytic converter. This treatment requires the use of a reducing agent in a precise concentration and in an extreme quality. The solution is therefore precisely metered and injected into the exhaust stream where it is hydrolyzed before the nitrogen oxides (NOx) are converted to nitrogen (N2) and water (H2O).

For this purpose, vehicles may be equipped with a tank containing an aqueous urea solution and with a device for metering and injecting the desired amount of additive into the exhaust pipe.

In addition to the possibility of filling urea tanks must generally be vented when they reach a certain limit of pressure and / or vacuum. Accordingly, urea tanks can be equipped with pressure relief valves, such as a dual valve system (for example, a system comprising 2 valve elements: one suitable for overpressure and one suitable for dealing with vacuum (vacuum) situations) to ventilate to enable. The use of a dual-valve system limits the overpressure in the tank, which may be caused by a rise in temperature, a freezing of the urea solution, or a drop in atmospheric pressure. The use of a dual-valve system also limits excessive waste in the tank caused by a decrease in temperature, thawing of the urea solution, an increase in atmospheric pressure, or a consumption of urea solution.

The Applicant has found that a vent valve including a moving part can be blocked by the crystallization of the urea solution after the sealing area has become wet by the manure solution. Thus, the valve may be difficult to open or close, resulting in poor pressure control.

The Applicant therefore had the idea of replacing such a valve with a semi-permeable membrane designed to block liquid from the ammonia precursor and designed to allow air and vapors from the ammonia precursor to pass therethrough , Preferably, a specific membrane is selected which is not impaired in performance by the urea crystallization.

Nevertheless, when such a membrane is used as a venting device, it is advantageously combined with an OFP (overfill protection) device (since generally the pressure build-up will be severely limited, typically: of only about 10 mbar, so that the filler nozzle does not automatically shut off at the end of refilling), which increases the cost and the technical complexity (crystallization resistance, process, packaging).

In order to avoid the use of such a device, the Applicant had the idea to incorporate said membrane in a cap of the filling tube, so that during filling of the tank is not vented and can build up pressure. In addition, in this way, the ventilation function is maintainable (easy to replace if damaged), which is highly appreciated by car manufacturers, since not the entire tank in the event of a fault of the ventilation component must be replaced.

The use of such venting membranes is known for fuel tanks (see for example US 2006/0096258 and US 2007/0175514 ), but so far it has never been used in SCR tanks (or has been proposed for use), because urea-compatible membranes are not common in the marketplace.

It is worth noting that the latter ( US 2007/0175514 ) proposes to receive the membrane in the stuffing tube cap, but since said cap is provided only with a cover with a small vent hole which provides only a limited connection between the inside and the outside of the tank, a substantial amount of pressure build-up in operation occurs mechanical reinforcing means (oversizing of wall thickness, specific shapes and reinforcements, etc.) which in turn add cost (and weight) to the system.

Summary of the invention

The present invention aims to provide a system for storing an ammonia precursor which allows for aeration in operation while still having a reduced weight, being robust and cheap and easy to maintain.

• – einen Tank, ausgelegt zum Aufnehmen des Ammoniakvorprodukts,
• – eine Füllöffnung, die durch eine Kappe verschlossen ist, wobei die besagte Kappe zum Wiederbefüllen des Tanks entfernbar ist; und
• – eine semi-permeable Membran, die in der besagten Kappe positioniert ist,

wobei die semi-permeable Membran dazu ausgelegt ist, Flüssigkeit von dem Ammoniakvorprodukt zu blockieren und dazu ausgelegt ist, Luft und Dämpfe aus dem Ammoniakvorprodukt zu erlauben, durch diese hindurch zu passieren, wenn die Kappe die Füllöffnung verschließt, und wobei, wenn die Kappe die Füllöffnung verschließt, ein Pfad bereitgestellt ist, der einer wesentlichen Menge von Dämpfen erlaubt, von dem Tank in die Atmosphere zu entweichen, so dass das gesamte innere Volumen des Reservoirs (1) geteilt durch die Flussrate durch die Membran bei 10 mbar (l/h) geringer ist als 20h. Therefore, the present invention relates to a system for storing an ammonia precursor, comprising:

• A tank designed to receive the ammonia precursor,
• A filling opening closed by a cap, said cap being removable for refilling the tank; and
• A semi-permeable membrane positioned in said cap,

wherein the semi-permeable membrane is adapted to block liquid from the ammonia precursor and is adapted to allow air and vapors from the ammonia precursor to pass therethrough when the cap closes the fill opening, and wherein when the cap is closed Filling port closes, a path is provided which allows a substantial amount of vapors to escape from the tank into the atmosphere, so that the total internal volume of the reservoir (1) divided by the flow rate through the membrane at 10 mbar (l / h ) is less than 20h.

 The system according to the invention comprises a tank (storage volume bounded by a wall), preferably made of a plastic material (for example polyethylene), and which comprises a filling opening provided with a cap which integrates the semi-permeable membrane.

The filling opening may be a mere opening in the wall of the tank, for example a mere passageway (which is the usual case in practice). In general, the cap suitable for closing said opening comprises a device enabling it to be fixed on the opening. A relief section which cooperates with a relief section of the filling tube offers good results. In practice, corresponding threaded portions on the cap and on the filling tube are suitable, since generally the filling tube and cap are molded from a plastic material.

Therefore, according to a preferred embodiment of the invention, the tank is made of a plastic material and comprises a filling tube comprising the filling opening, wherein the filling tube and the cap are formed of plastic material and comprise corresponding threaded portions.

According to the invention, the semi-permeable membrane is designed to block liquids, but to allow ammonia vapors to pass through them without any substantial pressure build-up. This means that preferably the semi-permeable membrane is designed to allow not more than 100 mbar overpressure, more preferably not more than 50 mbar overpressure, and most preferably not more than 10 mbar overpressure to occur during operation.

For this purpose, a path must generally be provided to allow escape of a substantial amount of the vapor from the tank into the atmosphere. In practice, the path is dimensioned according to the following rule: The total internal volume of the reservoir (1) divided by the flow rate through the membrane at 10 mbar (l / h) is less than 20h, preferably less than 15h, and more preferably less than 10h ,

The semi-permeable membrane may comprise a suitable tissue or a known porous material. For example, the semi-permeable membrane may comprise a polytetrafluoroethylene (PTFE) based material (or may comprise a sintered PTFE) or another perfluorinated polymer. However, alternative materials that are hydrophobic or water repellent may also be suitable, such as membranes or fabrics available under the trade name GORE-TEX.

The semi-permeable membrane preferably has openings with size in the range of 0.05 μm to 10 μm. Further, a thickness of 50 μm to 250 μm of the semi-permeable membrane is preferred. In particular, GORE's trade-type AM1XX membrane (with an opening diameter of approximately 0.07 μm and a thickness of approximately 200 μm) gives good results in practice.

In a preferred embodiment, the semi-permeable membrane is free of any non-hydrophobic material. In a preferred embodiment, the membrane is free of any material moistened by water or polar liquid, metal mesh, polyamide membranes, glass fibers or glass fiber membranes.

In general, according to the invention, the cap is a part comprising a body which is preferably made by injection molding and which preferably comprises a threaded portion (see above). This body is generally a hollow part comprising a bore which has a generally cylindrical passage passing through the membrane. " is closed, if the membrane is fixed substantially perpendicular to its axis, so that the entire cross section of the same is occupied).

The semi-permeable membrane can be attached to the cap by welding, for example by thermal or (ultra) sonic welding. The weld width should be large enough to ensure proper anchoring of the diaphragm in the cap to prevent leakage even after aging on the vehicle. It is strongly recommended to use a profile (i.e., a sort of grid to support the membrane) to prevent membrane elongation over time, especially for membranes with a diameter greater than 15mm. For very large membranes, these are preferably supported every 15 mm and fixed on the support (for example by welding).

In a preferred embodiment of the invention, the cap comprises a membrane holder or a type of hollow ring (the membrane will generally be circular, although other shapes may be used), possibly reinforced by ribs or spokes to which the membrane is peripherally welded, said membrane holder is in turn fixed in the body of the cap, preferably also by welding. Preferably, said membrane holder includes the above-mentioned membrane support for large membranes, as needed.

Preferably, the cap includes a seal to provide a tight attachment of the cap to the fill port. Although this seal may have the (classic) shape of an O-ring or the like, the seal according to a preferred embodiment of the invention is a flat, circular seal comprising small openings. This embodiment prevents access to the membrane by a user, and thus prevents the membrane from being damaged.

To allow the seal to function as such and not to be compressed when the cap is mounted on the fill port, the cap preferably includes an undercut on which the seal may be compressed. In particular, in the event that the body of the cap is injection-molded, this undercut may have a horizontal surface and thus provide a stagnation zone for liquids under the membrane. To prevent this, an inner conical surface may be used which provides an inclined conical surface between the membrane and the distinction so as to prevent the stagnation zone. This inner conical surface can be fixed on a ring as a separate part inside the cap. Alternatively, the cap may be molded in one piece with such an inner conical surface. This solution is generally preferred on an industrial scale.

Finally, in order to protect the (membrane) of the cap during transport and during assembly on the fill port (where the torsion may deform and damage the cap), it may be advantageous to use a cover mechanically attached to the top of the cap but in a non-sealing way, so that the required steam path can be obtained. For this purpose, the cover preferably comprises at least one opening, and more preferably said opening is in the form of a slot. Advantageously, said opening in the side wall of the cover, so that no dust or dirt can pollute the membrane.

In practice, good results are achieved with the present invention when the pressure drop through the path downstream of the membrane is at least 20 (preferably 15 and more preferably 10) times less than the pressure drop across the membrane.

• – Polyethylen (und vorzugsweise HDPE von hoch-dichtem Polyethylen) für die Wand des Tanks,
• – Polyamid (PA, wie PA6 zum Beispiel), oder Polyacetal und vorzugsweise POM (oder Poly-Oxy-Methylen) für die Kappe (und die Abdeckung, im Fall des vorhandenseins), wobei ersteres ökonomisch gesprochen von größerem Interesse ist während letzteres möglicherweise besser für seine chemische Beständigkeit ist (nicht nur gerichtet auf Harnstoff/Ammoniak-Korrosion, sonder auch auf Korrosion von Substanzen die aus der Korrosion anderer Teile des Systems austreten, zum Beispiel PCV-Teile, die HCl freisetzen können).

Regarding the materials used for the parts of the system according to the invention, these are preferably:

• Polyethylene (and preferably HDPE of high-density polyethylene) for the wall of the tank,
• Polyamide (PA, such as PA6 for example), or polyacetal and preferably POM (or poly-oxy-methylene) for the cap (and the cap, in the case of presence), the former being of greater interest economically speaking, while the latter may be better for its chemical resistance is (not only directed to urea / ammonia corrosion, but also to corrosion of substances that escape from the corrosion of other parts of the system, for example PCV parts that can release HCl).

The ammonia precursor is advantageously an aqueous solution. The invention gives good results with an aqueous solution of hull and in particular eutectic solutions of urea and water, such as AdBlue, whose urea content is between 31.8% by weight and 33.2% by weight and which contains about 18% ammonia. This can also be applied to urea / ammonium formate mixtures in aqueous solution sold under the trade name Denoxium and containing about 13% ammonia. The latter has the advantage, relative to urea, of a freezing of -35 ° C forward (as opposed to -11 ° C), but has the disadvantage of corrosion problems associated with the release of formic acid.

Brief description of the figures

A more complete appreciation of the invention and many of the attendant advantages will be readily obtained as the same becomes better understood by reference to the following detailed description taken in conjunction with the accompanying drawings, in which:

1 shows a schematic view of a section through the cap of a system according to the invention by a plane comprising the axis of said cap; and

2 shows a three-dimensional (or CAD) view of said cap (halved).

Detailed description of preferred embodiments

• 1. eine Kappe mit einem Gewindeabschnitt, vorgesehen um auf einen korrespondierenden Gewindeabschnitt eines Füllrohrs eines Tanks (nicht gezeigt) geschraubt zu werden
• 2. eine Abdeckung, mechanisch befestigt (in jeder bekannten Art und Weise, wie Quick Connect oder dergleichen) oben auf der Kappe und ihr genug mechanische Stärke gebend, um Torsion während ihres Aufschraubens auf das Füllrohr zu widerstehen
• 3. ein Membranhalter mit einem Rahmen in der Form eines Kreuzes, der als Träger für den inneren (nicht angeschweißten) Teil der Membran wirkt
• 4. eine Membran mit ausreichender Atmungseigenschaft und Ammoniakbeständigkeit
• 5. eine kreisförmige, flachte Dichtung mit kreisförmigen Öffnungen
• 6. eine Unterschneidung gegen die die besagte Dichtung komprimiert werden kann, wenn die Kappe auf dem Füllrohr montiert ist
• 7. ein Ring, der eine innere konische Oberfläche im Inneren der Kappe zwischen der Membran und der Unterschneidung bereitstellt

Offensichtlich sind zahlreiche Modifikationen und Variationen der vorliegenden Erfindung im Lichte der obigen Lehre möglich. Es versteht sich daher, dass innerhalb des Umfangs der beigefügten Ansprüche die Erfindung anders ausgeführt werden kann als spezifisch. In the figures, like reference numerals designate identical or corresponding parts, namely:

• 1 , a cap having a threaded portion provided to be screwed onto a corresponding threaded portion of a stuffing tube of a tank (not shown)
• 2 , a cover, mechanically fastened (in any known manner, such as Quick Connect or the like) on top of the cap and giving it enough mechanical strength to withstand torsion while being screwed onto the fill tube
• 3 , a membrane holder having a frame in the shape of a cross, which acts as a support for the inner (not welded) part of the membrane
• 4 , a membrane with sufficient respiration and ammonia resistance
• 5 , a circular, flat seal with circular openings
• 6 , an undercut against which said seal can be compressed when the cap is mounted on the fill tube
• 7 , a ring that provides an internal conical surface inside the cap between the diaphragm and the undercut

Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 2006/0096258 [0010]
• US 2007/0175514 [0010, 0011]

Claims (15)

 A system for storing an ammonia precursor, comprising: A tank designed to receive the ammonia precursor, A filling opening closed by a cap, said cap being removable for refilling the tank; and A semi-permeable membrane positioned in said cap, wherein the semi-permeable membrane is adapted to block liquid from the ammonia precursor and is adapted to allow air and vapors from the ammonia precursor to pass therethrough when the cap closes the fill opening, and wherein when the cap is closed Closing fill port, a path is provided which allows a substantial amount of vapors to escape from the tank to the atmosphere such that the total internal volume of the reservoir 1 divided by the flow rate through the membrane is less than 10mbar (l / h) 20h. The system of claim 1, wherein the tank is made of a plastic material and includes a fill tube including the fill opening, the fill tube and the cap being molded from plastic material and having corresponding threaded portions. The system of any one of the preceding claims, wherein the semi-permeable membrane is configured to allow no more than 100 mbar overpressure. The system of any one of the preceding claims, wherein the semi-permeable membrane comprises a fabric available under the trade name Gore-Tex. The system of any one of the preceding claims, wherein the semi-permeable membrane has apertures sized in the range of 0.05 μm to 10 μm and having a thickness of 50 μm to 250 μm.  The system of any one of the preceding claims, wherein the semi-permeable membrane is fixed to the cap by welding. The system of any one of the preceding claims, wherein the cap comprises a body having a hollow portion with a bore defining a generally cylindrical passage, the membrane being fixed substantially perpendicular to its axis such that the entire cross section thereof is occupied. The system according to the preceding claim, wherein the cap comprises a membrane holder to which the membrane is peripherally welded, said membrane holder is in turn fixed in the body of the cap, preferably also by welding. The system of any one of the preceding claims, wherein the cap includes a planar, circular seal having small openings. The system of the preceding claim, wherein the cap includes an undercut on which a gasket can be compressed and an interior conical surface that provides an inclined conical surface between the membrane and the distinction. The system according to any one of the preceding claims, comprising a cover which is mechanically fixed to the upper portion of the cap. The system according to the preceding claim, wherein the cover comprises at least one opening in the form of a slot. The system of the preceding claim, wherein the opening is in the sidewall of the cover.  The system of any one of the preceding claims, wherein the pressure drop through the vapor path downstream of the membrane is at least 20, preferably 15 and more preferably 10 times less than the pressure drop across the membrane. The system of any of the preceding claims, wherein the tank has a wall made of polyethylene, preferably HDPE of high density polyethylene, and wherein the cap and the cover, the housing of polyamide PA, such as PA6 for example, or polyacetal, and preferably POM, poly-oxy-methylene is produced.

Images