FR3002784A1 - Reducing gas storage tank i.e. ammonia storage cartridge, for selective catalytic reduction of nitrogen oxides in exhaust gas of internal combustion engine of car, has heating bars heating storage areas in cartridge in differentiated manner - Google Patents

Abstract

The tank has a solid storage material of a reducing gas i.e. ammonia, and heating bars (a1-a3, 9') heating two separate storage areas in the tank in a differentiated manner for the selective catalytic reduction of nitrogen oxides, where the differentiated heating is heating at different temperatures and/or according to different durations. The heating bars are placed along a longitudinal axis (X), and a filling orifice (5) for the ammonia is provided at a longitudinal end of the tank. An electronic control unit controls the filling of the cartridge by controlling the differentiated heating of the storage areas. Independent claims are also included for the following: (1) a method for filling a reducing gas in a reducing gas storage cartridge (2) a method for releasing a reducing gas from a reducing gas storage cartridge.

Description

The invention relates to the depollution of the exhaust gases of a combustion engine. More specifically, it relates to the reduction of nitrogen oxides contained in the exhaust gas of an internal combustion engine by selective catalytic reduction (or SCR, according to the acronym of "Selective Catalytic Reduction"). The invention is more particularly concerned with the depollution of exhaust gases from vehicle engines, particularly motor vehicles. The nitrogen oxide reduction technology by selective catalytic reduction is to reduce the nitrogen oxides before they exit the exhaust system of a combustion engine, using a reducing agent (or a reducing agent precursor) introduced into the exhaust line. In the remainder of the present text, the term "reducing agent" will be used indifferently to designate the reducing agent or a precursor of the reducing agent. [0004] Two types of SCR technology are known. There is the so-called liquid SCR technology, which uses a reducing agent precursor in liquid form, such as an aqueous solution of urea, which can be converted into ammonia when it is injected into the exhaust line. There is also the so-called solid SCR technology, where the ammonia is stored in a solid material capable of absorbing / adsorbing it and then releasing it in a controlled manner, in particular by thermal activation. The invention is concerned with solid SCR technology, and more particularly with the absorbent / adsorbent solid material tanks of the reducer, a material which will be designated hereinafter by the term "storage material" for the sake of Conciseness. [0006] It is thus known, in particular from FR-2 957 630, SCR-type depollution devices which use storage material tanks in the form of one or more cartridges, each provided with heating means in the form of heating resistors whose power supply is controlled by computer / electronic control means to control the desorption of the reducing agent at the appropriate time and in appropriate quantities. These resistors may be either of the plunging type, for example in the form of a "bar" which is inserted into the cartridge and which directly heats the storage material, or in the form of an external resistor which surrounds a part at least the outer shell of the tank, and which comes to heat the storage material through the conductive wall of the tank. Hereinafter understood by "conductor" the fact that the material in question is a good thermal conductor in the usual sense of the term. The simplest example of this type of conductive material is a metallic or substantially metallic material (which, in fact, is also a good electrical conductor). The cartridges associated with their heating means are generally mounted on modules, themselves mounted on vehicles, and which may also include control boxes for controlling, by electronic or computer means the activation of heating means. It is for example known to associate in the same module a large cartridge called main cartridge, and a much smaller cartridge, said starter cartridge, the latter for initiating the release of gas reducer quickly, especially during startup of the vehicle, the main cartridge taking over, out of engine start phase, to provide the exhaust line of gaseous reductant and reload reducer starter cartridge. By way of example, the document WO 2011/119735 describes such a reservoir, in the form of a cartridge in which one comes to insert disks all identical to each other and stacked on each other, each disk consisting of the storage material, based on strontium chloride in the form of pressed powder, which is covered on at least one surface of the disc with a conductive coating. There is also a means for heating the cartridge, the heat being transmitted within the storage material at least in part via these conductive coatings, so that it desorbs ammonia gas. This cartridge design remains susceptible of improvements. Indeed, the heat propagates from the external source of heat to the conductive coatings, but it turns out that the time of release of a given quantity of reducing agent is not constant over time as and when the depletion of the storage material (it is understood by exhaustion that the storage material is becoming poorer in reducing gear). Indeed, when the cartridge is new, and the storage material loaded at its maximum rate of reducing agent, it is first of all the layers of the storage material closest to the heat source and / or the layers in direct contact with each other. with the conducting coatings of the discs which release the reducing agent. Then, progressively, the heat must travel a greater distance to reach the strata further and further away from storage material, knowing that the heat propagates poorly in the thickness of the storage material, this salt-type material being weakly thermal conductor. However, this increasing inertia in the release of reducing agent from the cartridge, as and when it wears, given thermal input, is not easy to compensate, and can lead to drifts in the injection process of reducing agent at the appropriate time in appropriate quantities in the exhaust line. Filling gaseous reducing cartridges is not always optimal either. Indeed, the cartridges are refilled once they no longer contain reducer, once disassembled, and it has been observed that a "plug" could randomly form in the vicinity of the opening of the opening of the cartridge by which the gaseous reductant is injected. The term "plug" is understood to mean that the solid storage material is saturated with gas over a small thickness, preventing or slowing the flow of the gaseous reductant towards strata of solid material further away from the opening. The invention therefore aims to develop a new type of storage tank that overcomes these disadvantages. It thus aims at a storage tank from which it is easier to control the release of gaseous reductant and / or the filling gaseous reducer, and which can, in particular, to simplify the management of storage cartridges. The invention firstly relates to a gaseous reducing storage tank for the selective catalytic reduction of nitrogen oxides, containing a solid storage material of said gaseous reductant, such that said reservoir is provided with a plurality of heating means adapted to differentially heat at least two storage areas in the tank. The gaseous reductant is preferably ammonia. The solid storage material is preferably a metal salt such as strontium or barium chloride. The invention, by operating a differentiated heating of the storage material, exploits the ability of the material to desorb / release a reducing gas such as ammonia as a function of its desorption temperature. The desorption temperature is understood to mean the temperature that the material must reach to desorb the first molecule of gaseous reductant. It should be noted that this property of desorption temperature is correlated with the desorption activation energy of the gaseous reductant, which property is measured in joule and which corresponds to the energy to be supplied to the storage material to release the gaseous reductant. And as for the adsorption temperature, this activation energy is considered as that necessary for the desorption of the first mole of ammonia. Consequently, the more the storage material is heated beyond its activation temperature, the more easily it will release ammonia. And, on the other hand, the cooler the storage material, the more easily it will pick up ammonia. Having a differentiated heating allows better management of the ammonia stock in the tank (throughout the present text, ammonia is given as an example and for the sake of brevity, but it is necessary to understand more general any reducing gaseous compound): when the tank is active and must release a given amount of ammonia so that it is injected into an exhaust line of a vehicle engine, we can choose to selectively heat a or several zones in the tank, to ensure a rate of release consistent over time according to the given instruction, and also allow to empty completely and efficiently the ammonia tank. And when the tank is disassembled to be charged with ammonia, it is also possible to play this differential heating to promote the recharge first of the areas farthest from the filling opening, and to avoid the phenomenon of plugs in the vicinity openings. Thus, one can choose to heat (or heat more and / or longer) the area near the filling opening of the front tank and / or at the beginning of filling, which has the effect of promoting the circulation of the ammonia throughout the storage material of the tank without an accumulation in the vicinity of the opening creating the plug phenomenon mentioned above. The zones furthest from the filler opening can be prevented from heating, heating or even cooling, to promote capture of ammonia in these zones and allow progressive ammonia filling, from the farthest areas closest to the filling opening. Preferably, it is understood by heating differentiated heating at different temperatures and / or different durations of the above mentioned areas and / or the fact that some areas are heated and others not. Advantageously, the reservoir has a longitudinal axis and the heating means are disposed along this axis and / or around this axis by defining superimposed areas to each other along the longitudinal axis of said reservoir. The further a zone will be longitudinally away from the filling opening, the more it will be advantageous to keep it at a lower temperature than the others during filling, to promote optimum filling of the tank starting with "the bottom" of the tank . It is then possible to define a temperature profile of the storage material according to its position in the reservoir, and therefore a corresponding heating profile, accordingly. More a zone will be remote from the release opening (which may be different from the filling opening, and in particular be arranged at the opposite longitudinal end), and more it may be advantageous to keep it at a temperature superior to those of the other zones, to favor the progressive emptying of the cartridge. Again, we can define a temperature profile, so a heating profile, accordingly. Preferably, the tank is provided with at least one gaseous reductant filling orifice provided at one of its longitudinal ends, one of the heating means being adapted to locally heat the tank in its vicinity. According to a first variant, the dedicated heating means are peripheral means at least partially surrounding the tank, and in particular mechanically associated with each other. According to another variant, which may be cumulative with the previous, the dedicated heating means are a heating means at least partially inserted into the tank, in particular in the form of heating bars aligned and possibly mechanically associated. Advantageously, the reservoir is associated with electronic or computer means which control the release of the gaseous reductant by controlling the differentiated activation of the heating means of the separate storage areas. Advantageously, the reservoir is associated with electronic or computer means that control the filling of the gaseous reductant tank by controlling the differentiated activation of the heating means of the separate storage areas. The invention also relates to a gaseous reductant filling method of a gaseous reducing storage tank for the selective catalytic reduction of nitrogen oxides, containing a solid storage material of said gaseous reductant provided with at least one gaseous reductant filling orifice provided at one of its ends, such that different zones of temperature are established in the reservoir for effective filling of the reservoir with the gaseous reductant. It may well be to heat one or more areas, and not to heat the other. It may also be to create a kind of temperature gradient or zones with different temperature levels, with a temperature profile that decreases - stepwise or gradually - from the proximity with the filling opening to the part tank that is farthest away. Preferably, the filling orifice is disposed at a longitudinal end of the reservoir and the different temperature zones are distributed in the reservoir along its longitudinal axis. Preferably, the temperature of the area closest to the filling orifice, during filling, is higher than in the other areas of the tank. Advantageously, a decreasing temperature gradient is established in the reservoir from the longitudinal end provided with the filling orifice to the opposite longitudinal end of the reservoir during its filling. The invention also relates to a gaseous reductant release method of a gaseous reducing storage tank for the selective catalytic reduction of nitrogen oxides, containing a solid storage material of said gaseous reductant provided with minus one exit orifice of the gaseous reductant provided at one of its longitudinal ends, such that different zones of temperature are established in the tank for the controlled release of gaseous reductant from the tank. In this case, one can establish in the tank a temperature profile, so a heating profile, such that the temperature is even higher than the storage material zone is away from the opening of at least for a given period of time during the life of the tank from its assembly (saturated ammonia tank) until it is dismounted once discharged into ammonia (empty ammonia tank or with a residual amount of weak ammonia). The invention also relates to the storage module intended to be mounted on a vehicle, in particular a motor vehicle, and on which are mounted at least one tank as described above and possibly also the electronic / computer means mentioned above. , and preferably at least one means for controlling the tank heating means. The invention also relates to any vehicle including automotive equipped with a module or a tank as described above. Other features and advantages of the invention will appear on reading the following detailed description of a non-limiting embodiment of the invention, given by way of example only, with reference to the following schematic figures. - Figure 1: a tank - hereinafter called the cartridge - ammonia storage in solid form according to the prior art, in the fully charged ammonia state, in longitudinal section; - Figure 2: the cartridge of Figure 1 in the completely discharged ammonia, at the start of its filling ammonia to recharge, still in longitudinal section; - Figure 3: the modified cartridge according to the invention, being filled with ammonia, in longitudinal section also. These figures are extremely schematic, and the various components shown do not necessarily respect the scale to facilitate reading. Only components that are important in the context of the invention are furthermore represented. The same components keep the same references from one figure to another. Figure 1 shows a comparative example of a cartridge 1 (cartridge and reservoir have the same meaning in the present text), with a metal outer shell 2 defining a substantially cylindrical volume (circular or oval section). Inside this envelope, pellets 3 of storage material are arranged. Cartridge 1 has a longitudinal axis X. By way of example, this storage material is strontium chloride (also commonly known as Adammine salt), of formula SrCl 2 (NH 3) 8 when it is saturated with ammonia , or barium chloride, of formula BaCl2 (NH3) 8 when it is saturated with ammonia. The pellets contain compressed salt and are optionally covered on at least their main faces with a conductive film, for example aluminum. In the center of the cartridge, is present a heating bar 4, provided with an extension in the form of tip out of the cartridge once inserted, tip that allows its grip on the one hand and its power supply of other (not shown). This bar is metallic and heated by Joule effect in a manner known per se. The cartridge, in known manner, is connected by a pipe system to a metering unit, which just inject ammonia in appropriate amounts into the exhaust line of a motor vehicle engine. The injection is controlled by a control unit. The unit also controls the heating of salt by the bar so that the cartridge desorbs the desired quantity of ammonia under the effect of heat. Figure 1 shows the cartridge 1 according to the prior art when it is full, that is to say when the salt pellets are saturated with ammonia. Figure 2 is a representation of the same cartridge once almost emptied ammonia, at the start of its filling once disassembled. Two observations can be made. On the one hand we see that the pellets 3, when the majority of the ammonia has been desorbed, occupy a smaller volume, are "worn". On the other hand, it can be seen that the start of the filling can create a "plug" 3 'formed by the pellet closest to the filling orifice 5 of the cartridge which is saturated with ammonia and slow the passage of gaseous ammonia to the more distant pellets. Figure 3 shows the modified cartridge 1 'according to the invention, in its discharged state of ammonia, at the beginning of its filling. According to the invention, the heating bar 9 'in fact comprises a plurality of independent portions a1, a2, a3, a4, etc., which are supplied separately with electricity, and which are held together mechanically. This bar can be provided with an extension in the form of tip out of the cartridge once inserted, tip that allows its grip on the one hand and its power supply on the other hand (not shown). This bar may optionally be inserted into a sheath itself metal which may or may not remain permanently in the cartridge 1 '. In this embodiment, each bar portion is able to directly heat a pellet 3, a pellet then correspondingly to a "zone" of differentiated heating as stated above. Naturally, it is possible for a portion of a bar to be able to heat not a pellet but a plurality of pellets, for example from 2 to 10 pellets: each pellet group then being a "zone" of differentiated heating within the meaning of the invention . The invention applies in the same way to a storage material compressed in the tank in a form other than in the form of pellets. The differentiated control of the different portions of the bar is done by the control unit in the following manner for filling the empty cartridge: it comes to supply electricity to the bar portions closest to the filling port 5 , which has the effect of heating the "front" of the cartridge, (part A of the cartridge), in the vicinity of the orifice 5, which has the effect of maintaining a lower temperature in the "bottom" of the cartridge (part B of the cartridge), and then gradually stops the heating at the front of the cartridge, which amounts to causing a gradual cooling of the salt from the front A to the bottom B of the cartridge 1 '. The ammonia cartridge is then filled, by coming, by this temperature difference before / bottom, optimize the ammonia loading of all the pellets 3 of the cartridge 1 ', and without formation of a plug as mentioned above. Once reassembled in its module on the motor vehicle, it can also make a differentiated heating of the cartridge by controlling the control unit of the electricity supply portions al, a2, a3 etc ... of the bar 9 '. It is thus possible to locate the heating on certain pellets according to the demand for ammonia to be injected.

It is also possible to heat the pellets one after the other, and, as and when the pellets wear, to heat only those still containing ammonia, which allows to consider gains in power consumption, and longer life of the cartridges between two fillings. To do this, one can couple this localized / differentiated heating function with a gauging strategy to precisely define the pellets or pellets to be heated depending on the amount of ammonia remaining. The invention thus makes it possible to fulfill three objectives: to improve the rate of reloading of the cartridges so that they have a longer life, to ensure a smooth operation of the filling process by avoiding the formation of plugs, and finally to improve the heating function when the cartridge is active to reduce the energy consumption for the same ammonia release efficiency, and / or to maximize the life of the cartridge. Alternatively or in addition to the heating bar 9 may be provided to equip each compartment with a heating element independent heater, disposed against the outer casing of the cartridge. Each resistor can be mechanically connected to others to manipulate and position them more easily. In known manner, the cartridge can also further integrate at least one of: a filter that prevents the passage of storage material to the outside of the cartridge, a metering device of the reducer, a check valve , a connection tip, a connection sealing device.

Claims (10)

REVENDICATIONS1. Storage tank (1 ') of gaseous reductant for the selective catalytic reduction of nitrogen oxides, containing a solid storage material of said gaseous reductant, characterized in that said tank is provided with a plurality of heating means (9' a1, a2, a3 ...) adapted to differentially heat at least two storage areas in the tank. 2. Tank (1 ') according to the preceding claim, characterized in that the differential heating is heating at different temperatures and / or different durations of said zones. 3. Tank (1 ') according to one of the preceding claims, characterized in that it has a longitudinal axis (X) and in that the heating means (9'; a1, a2, a3 ...) are disposed along this axis and / or around this axis by defining distinct zones superimposed on each other along the longitudinal axis of said reservoir. 4. Tank (1 ') according to the preceding claim, characterized in that it is provided with at least one filling orifice (5) in gaseous reducer provided at one of its longitudinal ends, at least one of the means of heating (9 '; a1, a2, a3 ...) being able to locally heat the reservoir in its vicinity. 5. Tank (1 ') according to one of the preceding claims, characterized in that the dedicated heating means are peripheral means at least partially surrounding the tank, and in particular mechanically associated with each other. 6. Tank (1 ') according to one of the preceding claims, characterized in that the dedicated heating means are a heating means at least partially inserted into the tank, in particular in the form of aligned heating bars (9'; a2, a3 ...) and possibly mechanically associated. 7. Tank (1 ') according to one of the preceding claims, characterized in that it is associated with electronic or computer means that drive the release of the gaseous reductant by controlling the differentiated activation of the heating means (9'; al, a2, a3 ...) separate storage areas. 8. Tank (1 ') according to one of the preceding claims, characterized in that it is associated with electronic or computer means that control the filling of the gaseous reductant tank by controlling the differentiated activation of the heating means (9). a1, a2, a3 ...) separate storage areas. 9. A gaseous reductant filling process of a gaseous reducing gas storage tank (1 ') for the selective catalytic reduction of nitrogen oxides, containing a solid storage material of said gaseous reductant provided with at least one filling orifice (5) Gaseous reducer arranged at one of its ends, characterized in that different zones of temperature in the tank for the actual filling of the tank by the gaseous reductant. 10. A process for the release of gaseous reductant from a reservoir (1 ') for the storage of gaseous reductant for the selective catalytic reduction of nitrogen oxides, containing a solid storage material of said gaseous reductant provided with at least one release orifice a gaseous reductant provided at one of its longitudinal ends, characterized in that different zones of temperature are set in the tank for the controlled release of gaseous reductant from the tank.