WO2018041754A1

WO2018041754A1 - System and method for increasing the urea concentration of an aqueous solution on-board a vehicle

Info

Publication number: WO2018041754A1
Application number: PCT/EP2017/071496
Authority: WO
Inventors: François Dougnier; Beatriz MONGE-BONINI; Pierre De Man; Julien SCHWEICHER; Jules-Joseph Van Schaftingen
Original assignee: Plastic Omnium Advanced Innovation And Research
Priority date: 2016-08-30
Filing date: 2017-08-28
Publication date: 2018-03-08
Also published as: CN109641743A

Abstract

The invention relates to a vehicle system for increasing the urea concentration of an aqueous urea solution on-board a vehicle. The vehicle system comprises: a tank (1) storing an aqueous urea solution having a first urea weight percentage; a dissolving system (1000) comprising a dissolving flow zone (3) with a solid urea bed, said dissolving system being configured for generating a flow of aqueous urea solution coming from the tank through the dissolving flow zone; said dissolving flow zone being arranged for guiding the flow of aqueous urea solution through the solid urea bed out of the dissolving flow zone; and a control device (2000) configured for controlling at least one parameter influencing the dissolving in the dissolving flow zone such that the aqueous urea solution leaving the dissolving flow zone has a second urea weight percentage which is higher than the first urea weight percentage.

Description

System and method for increasing the urea concentration of an aqueous solution on-board a vehicle

Field of Invention

The invention relates to a system and method for increasing the urea concentration of a urea solution on-board a vehicle.

Background

There exist prior art systems for supplying ammonia or ammonia precursor to an exhaust line of a vehicle in order to reduce the NOx emissions. A SCR (Selective Catalytic Reduction) process is used for converting nitrogen oxides of an exhaust gas coming from a vehicle engine into diatomic nitrogen and water. The SCR process enables the reduction of nitrogen oxides by injection of a reducing agent, generally ammonia, into the exhaust line. This ammonia may be obtained by using different techniques.

One known technique is based on the use of an ammonia precursor, for example an aqueous urea solution. Generally, such urea solution is stored in a tank mounted on the vehicle. The urea solution is injected into the exhaust line, and the gaseous ammonia is derived from the pyrolytic (thermal) decomposition of the injected urea solution. A problem with the known technique is that the urea concentration in the solution is relatively low, and that it cannot be increased without causing the freezing temperature of the urea solution to increase significantly.

Known SCR systems are injecting ammonia precursor such as Adblue® into the vehicle exhaust pipe. Adblue® is an Aqueous Urea Solution made with 32.5% by weight high-purity urea and 67.5% deionized water. The concentration of urea is limited to that level because it corresponds to a eutectic solution with a freezing point of -11°C. The AdBlue® remains liquid above this temperature but heating systems are required whenever temperatures are lower. Higher urea concentrations that would allow more compact storage and weight savings are not used today on vehicles, because freezing would start at even higher temperatures.

European patent application EP 2 975 233 Al in the name of the applicant, which is included herein by reference, proposes an ammonia precursor generating system which is capable of producing an ammonia precursor solution having a higher ammonia precursor concentration compared to prior art solutions whilst maintaining an acceptable handling, and in particular an ammonia precursor boosting system for increasing the ammonia precursor concentration in an ammonia precursor liquid. The ammonia precursor generating system comprises a storage compartment storing at least ammonia precursor granules; a dissolving compartment adapted for storing an ammonia precursor solution, and for dissolving ammonia precursor granules in the ammonia precursor solution; and a transfer means configured for transferring ammonia precursor granules from said storage compartment to said dissolving compartment. By adding granules from the storage compartment, the concentration of ammonia precursor in the ammonia precursor liquid in the dissolving compartment can be increased when needed. The granules can be stored safely in the storage compartment without increasing the freezing point of the ammonia precursor solution and it is only when the ammonia precursor is needed and when the temperature in the dissolving unit is sufficiently high that granules will be added. The advantage of such a system is that the ammonia precursor concentration can be increased on-board as needed, which reduces necessary volumes and weights of storage, whilst at the same time keeping low temperature freezing points.

Summary

It is an object of embodiments of the invention to provide a vehicle system and method for increasing the urea concentration of an aqueous solution on-board a vehicle which can be used as an alternative for the system described in EP 2 975 233 Al, and which is simple and robust and allows for a good controlling of the urea concentration.

According to a first aspect of the invention there is provided a vehicle system for increasing the urea concentration of an aqueous solution on-board a vehicle. The vehicle system comprises a tank, a dissolving system, and a control device. The tank is configured for storing an aqueous solution having a first urea weight percentage. The dissolving system comprises a dissolving flow zone with a solid urea bed. The dissolving system is configured for generating a flow of aqueous solution coming from the tank through the dissolving flow zone. The dissolving flow zone is arranged for guiding the flow of aqueous solution through the solid urea bed out of the dissolving flow zone. The control device is configured for controlling at least one parameter influencing the dissolving in the dissolving flow zone such that the aqueous solution leaving the dissolving flow zone has a second urea weight percentage which is higher than the first urea weight percentage. By sending a flow of aqueous solution having a first urea weight percentage (which may be zero, i.e. the aqueous solution may be water) through a solid urea bed and by controlling a parameter, e.g. the temperature, influencing the dissolving in the solid urea bed, the urea concentration of the resulting aqueous solution, i.e. the second urea weight percentage, can be controlled in a simple and accurate manner. Compared to EP 2 975 233 Al where granules are added to a dissolving compartment, the dissolving system of the present invention uses a fixed solid urea bed and generates a flow through said solid urea bed. In that way dosing devices of granules can be avoided. Because the dissolving of solid urea in aqueous solution is an endothermic reaction, heat will be consumed in the dissolving flow zone, decreasing the temperature of the aqueous solution and increasing the urea concentration. Depending on the temperature of the aqueous solution in the tank, the appropriate controlling may be performed to obtain the desired concentration of the aqueous solution flowing out of the dissolving flow zone.

In the context of the present invention the term "aqueous solution having a first urea weight percentage" has to be understood as an aqueous solution which may or may not contain urea. For example, the aqueous solution having a first urea weight percentage can consist in water (without urea and without urea decomposition products) or in an ammonia water solution. The aqueous solution having a first urea weight percentage may contain other products like carbon monoxide (CO), carbon dioxide (C02), and methane (CH4), and traces of metals and metal oxides.

In the context of the present invention the term "aqueous solution having a second urea weight percentage" has to be understood as an aqueous solution containing urea or as a solution containing products coming from the partial or total decomposition (hydrolysis) of urea, even if part of these decomposition products are released as gases in the process of urea hydrolysis. For example, the resulting aqueous solution having a second urea weight percentage can consist in an ammonia water solution. The aqueous solution having a second urea weight percentage may contain other products like carbon monoxide (CO), carbon dioxide (C02), and methane (CH4), and traces of metals and metal oxides.

In an exemplary embodiment the control device is configured to control any one or more of the following: a temperature of the flow of aqueous solution upstream of the dissolving flow zone, a temperature of the flow of aqueous solution in the dissolving flow zone, a temperature of the flow of aqueous solution downstream of the dissolving flow zone; the flow rate of the flow of aqueous solution in the dissolving flow zone; a dimension of the solid urea bed through which the flow of aqueous solution flows. By controlling any one or more of those parameters it is possible to influence the dissolving and hence to control the urea concentration of the aqueous solution flowing out of the tank.

In an exemplary embodiment the control device comprises a temperature control means configured for controlling the temperature of the aqueous solution upstream of the dissolving flow zone and/or in the dissolving flow zone such that the aqueous solution leaving the dissolving flow zone has a second urea weight percentage which is higher than the first urea weight percentage. For example when the aqueous solution in the tank is at a too high temperature the aqueous solution may be cooled before allowing it to flow into the dissolving flow zone. Also, the temperature of the solid urea bed in the dissolving flow zone may be controlled.

In an exemplary embodiment the control device is configured to control at least one parameter influencing the dissolving in the dissolving flow zone such that, when the first urea weight percent is between 28 and 37 wt , the second urea weight percent is between 40 and 80 wt , preferably between 40 and 70 wt , more preferably between 50 and 60 wt , most preferably between 54 and 56 wt . More preferably the first urea weight percent is between 32 and 33 wt , e.g. 32.5 wt . In an exemplary embodiment the control device is configured to control at least one parameter influencing the dissolving in the dissolving flow zone such that the temperature of the aqueous solution leaving the dissolving flow zone is between 10 and 45 degrees Celsius, preferably between 15 and 40 degrees Celsius, more preferably between 20 and 34 degrees Celsius.

Preferably, the control device is configured to control at least one parameter influencing the dissolving in the dissolving flow zone such that the temperature and concentration of the aqueous solution leaving the dissolving flow zone corresponds with the solubility limit of urea in water for that temperature. In that manner for a certain temperature the maximum concentration is obtained for which urea is entirely solubilized in water.

In an exemplary embodiment the control device comprises a temperature control means configured for controlling the temperature of the aqueous solution in the tank. The temperature control means may control a device configured for heating and/or cooling depending on the needs. The control device may comprise e.g. any one of the following: a temperature control means configured for controlling the temperature of aqueous solution flowing from the tank to the dissolving flow zone; a temperature control means configured for controlling the temperature in the solid urea bed of the dissolving flow zone.

In an exemplary embodiment the dissolving flow zone has a top end for receiving the aqueous solution from the tank, and a bottom end where the aqueous solution flows out of the dissolving flow zone, such that the aqueous solution can flow through the dissolving flow zone by gravity. The dissolving flow zone can for instance be realized by a vertical column or replaceable cartridge in which the aqueous solution flows essentially vertically from a top end to a bottom end.

In an exemplary embodiment the dissolving system comprises a heat exchanger for heating the dissolving flow zone, said heat exchanger being connected for receiving aqueous solution from the tank before it enters the dissolving flow zone. In that way, since the dissolving action is endothermic, the aqueous solution from the tank may be cooled before it is sent into the dissolving flow zone for being enriched.

In an exemplary embodiment the dissolving system comprises a heat exchanger configured for cooling aqueous solution flowing from the tank to the dissolving flow zone, said heat exchanger being connected for receiving aqueous solution flowing out of the dissolving flow zone. In that way, since the dissolving action is endothermic and hence the aqueous solution flowing out of the dissolving flow zone has a lower temperature than the solution in the tank, the aqueous solution from the tank may be cooled by such a heat exchanger before it is sent into the dissolving flow zone for being enriched.

In an exemplary embodiment the dissolving system comprises a heat exchanger for cooling the dissolving flow zone, said heat exchanger being connected for receiving aqueous solution from the dissolving flow zone. In that way, since the aqueous solution flowing out of the dissolving flow zone has a lower temperature than the aqueous solution flowing in the dissolving flow zone, the dissolving flow zone may be cooled by such a heat exchanger.

In an exemplary embodiment the dissolving flow zone comprises a first heater and a second heater downstream of the first heater, wherein the control device is configured for controlling said first heater such that the temperature of a first part of the dissolving flow zone is within a first temperature range and that the temperature of a second part of the dissolving flow zone, downstream of said first part, is within a second temperature range which is lower than said first temperature range. The first temperature range may be adapted to solubilize the urea and increase the concentration in the urea solution, e.g. between 30°C and 40 °C, and the second temperature range may be adapted to saturate the urea solution, e.g. at 27°C when the desired concentration of the urea solution after flowing through this layer is 55 wt .

In an exemplary embodiment the dissolving system comprises a temperature-controlled urea buffer connected for receiving aqueous solution from the dissolving flow zone. Such a temperature - controlled buffer will allow adjusting and fine-tuning the weight percentage and/or temperature of the aqueous solution from the dissolving flow zone. The temperature-controlled urea buffer may have an inlet for receiving aqueous solution from the dissolving flow zone and an outlet for connection to an injector and to a solubilizing loop including the dissolving flow zone. The temperature-controlled urea buffer may be configured for generating and/or stabilizing an enriched urea solution and may be controlled by the control device. In an exemplary embodiment the vehicle system further comprises a heater exchanger controlled by the control device between the outlet of the temperature-controlled urea buffer and an inlet of the dissolving flow zone. In an exemplary embodiment the temperature-controlled urea buffer and the heater exchanger may be included in a module which is mounted in the tank.

In an exemplary embodiment the dissolving system comprises a pump configured for pumping aqueous solution from the tank through the dissolving flow zone at a controlled flow rate, e.g. a more or less constant flow rate or a flow rate within a predetermined range. The flow rate may also be controlled by the control device in order to influence the temperature and/or the second urea weight percentage of the aqueous solution leaving the dissolving flow zone. Optionally the pump may be included in the module comprising the temperature-controlled urea buffer and the heater exchanger of the previous paragraph. Further one or more valves controlled by the control device may be included in this module in order to regulate the flow to the dissolving flow zone. The ammonia solution with increased or "boosted" concentration flowing out of the dissolving flow zone is ready to be sent a downstream tank, to an exhaust pipe or to any additional system storing or consuming aqueous solution.

According to another aspect, there is provided an SCR system comprising a vehicle system according to any one of the previous embodiments. The SCR system preferably comprises an injector configured and arranged for injecting the aqueous solution having the second urea weight percentage in the exhaust pipe.

According to yet another aspect, there is provided a fuel cell system comprising a vehicle system according to any one of the previous embodiments. Such a system may comprise a separate decomposition compartment provided with a decomposition activator device configured to convert aqueous solution to an ammonia solution in the decomposition compartment, and a transfer means configured for transferring ammonia precursor solution from the dissolving compartment to the decomposition compartment. The decomposition activator device may comprise an enzyme storage unit configured to store an enzyme, an enzyme transfer means configured for transferring enzyme to the decomposition compartment, said enzyme being adapted to convert aqueous solution to ammonia, and a heater. In an exemplary embodiment with a decomposition activator device, the system may further comprise a buffer compartment for storing the ammonia solution. The buffer compartment may be integrated in the same module as the flow dissolving zone. The system may further comprise a conversion unit for converting ammonia into hydrogen. The ammonia-hydrogen conversion unit may subsequently communicate with a hydrogen fuel cell where the hydrogen is converted into a power source. The ammonia solution could also be used in a direct ammonia fuel cell.

The dissolving flow zone may be arranged in the tank or outside the tank. In preferred

embodiments a portion of the dissolving system (e.g. a pump and a heater) may be arranged in the tank, and the dissolving flow zone with the solid urea bed (e.g. in the form of a replaceable cartridge) may be arranged outside of the tank. The tank may be storing an ammonia precursor solution, such as a eutectic 32.5 wt urea in water solution. According to yet another aspect, there is provided a method according to any one of the following clauses:

1. A method for increasing the urea concentration of an aqueous solution on-board a vehicle, said method comprising:

storing an aqueous solution having a first urea weight percentage;

generating a flow of aqueous solution having the first urea weight percentage through a solid urea bed in a dissolving flow zone;

controlling at least one parameter influencing the dissolving in the solid urea bed such that the aqueous solution leaving the dissolving flow zone has a second urea weight percentage which is higher than the first urea weight percentage.

2. The method of clause 1 , wherein the controlling comprises controlling any one or more of the following: a temperature of the flow of aqueous solution upstream of the dissolving flow zone, a temperature of the flow of aqueous solution in the dissolving flow zone, a temperature of the flow of aqueous solution downstream of the dissolving flow zone; the flow rate of the flow of aqueous solution in the dissolving flow zone; a dimension of the solid urea bed through which the flow of aqueous solution flows.

3. The method of clause 1 or 2, wherein the controlling comprises controlling the temperature of the aqueous solution upstream of the dissolving flow zone and/or in the dissolving flow zone such that the aqueous solution leaving the dissolving flow zone has a second urea weight percentage which is higher than the first urea weight percentage.

4. The method of any preceding clause, wherein the controlling of at least one parameter influencing the dissolving in the dissolving flow zone is such that, when the first urea weight percent is between 28 and 37 wt , the second urea weight percent is between 40 and 80 wt , preferably between 40 and 70 wt , more preferably between 50 and 60 wt , most preferably between 54 and 56 wt .

5. The method of any preceding clause, wherein the controlling of at least one parameter influencing the dissolving in the dissolving flow zone is such that the temperature (T3) of the aqueous solution leaving the dissolving flow zone is between 10 and 45 degrees Celsius, preferably between 15 and 40 degrees Celsius, more preferably between 20 and 34 degrees Celsius.

6. The method of any preceding clause, wherein the controlling of at least one parameter influencing the dissolving in the dissolving flow zone is such that the temperature and

concentration of the aqueous solution leaving the dissolving flow zone corresponds with the solubility limit of urea in water for that temperature.

7. The method of any preceding clause, wherein the controlling comprises controlling the temperature of the stored aqueous solution having the first urea weight percentage.

8. The method of any preceding clause, wherein the controlling comprises any one of the following: controlling the temperature of aqueous solution flowing from the tank to the dissolving flow zone; controlling the temperature in the solid urea bed of the dissolving flow zone.

9. The method of any preceding clause, wherein the aqueous solution flows through the dissolving flow zone by gravity.

10. The method of any preceding clause, wherein the dissolving flow zone is heated with a heat exchanger connected for receiving aqueous solution from the tank before it enters the dissolving flow zone.

11. The method of any preceding clause, wherein aqueous solution flowing from the tank to the dissolving flow zone is cooled using a heat exchanger connected for receiving aqueous solution flowing out of the dissolving flow zone.

12. The method of any preceding clause, wherein the dissolving flow zone is cooled using a heat exchanger connected for receiving aqueous solution from the dissolving flow zone.

13. The method of any preceding clause, wherein the controlling comprises controlling the temperature of a first part of the dissolving flow zone to be within a first temperature range and controlling the temperature of a second part of the dissolving flow zone, downstream of said first part, to be within a second temperature range which is lower than said first temperature range.

14. The method of any preceding clause, wherein aqueous solution having the second urea weight percentage is stored in a temperature-controlled urea buffer.

15. The method of any preceding clause, wherein the aqueous solution is pumped through the dissolving flow zone at a controlled flow rate.

16. The method of any preceding clause, wherein the method comprises receiving aqueous solution from the dissolving flow zone in a temperature-controlled urea buffer having an outlet for connection to an injector and to a solubilizing loop including the dissolving flow zone.

17. The method of the preceding clause, further comprising controlling the temperature of an aqueous solution flowing from the temperature-controlled urea buffer to the dissolving flow zone.

Brief description of the figures The accompanying drawings are used to illustrate presently preferred non-limiting exemplary embodiments of devices of the present invention. The above and other advantages of the features and objects of the invention will become more apparent and the invention will be better understood from the following detailed description when read in conjunction with the accompanying drawings, in which:

Figure 1 illustrates schematically an exemplary embodiment of a vehicle system;

Figures 2A, 2B and 2C illustrate three variants of vehicle systems with a heat exchanger;

Figure 3 illustrates schematically another exemplary embodiment of a vehicle system with a heat exchanger;

Figure 4 illustrates schematically an exemplary embodiment of a vehicle system with two dissolving flow zones;

Figure 5 illustrates schematically another exemplary embodiment of a vehicle system with two dissolving flow zones;

Figure 6 illustrates schematically an exemplary embodiment of a vehicle system with various fluid transfer devices controlled by a control device;

Figure 7A and 7B illustrate schematically an exemplary embodiment of a dissolving zone;

Figure 8A illustrates schematically an exemplary embodiment of an SCR system;

Figure 8B illustrates schematically an exemplary embodiment of a temperature controlled buffer for use in an SCR system;

Figure 9 illustrates schematically another exemplary embodiment of a vehicle system; and

Figure 10 shows a water-urea binary phase diagram.

Description of embodiments

Figure 10 shows a water-urea binary phase diagram plotting temperature against the relative concentrations of urea and water in a binary mixture. Four different zones can be observed, namely zones I to IV. In zone I urea is entirely solubilized in water, providing a colourless urea solution. Zone III is related to the case of a saturated urea solution, i.e. a urea solution co-existing with solid urea. Zone I is separated from zone III by curve 1. The line indicated as curve 1 determines the solubility limit. On curve 1 , each temperature value is associated with a unique urea weight fraction of the urea solution (for a concentration above the one of the eutectic), corresponding to the limit of solubility of urea in water at this temperature. For example, a urea solution with a 0.55 urea weight fraction is associated to a temperature of 27°C, according to curve 1.

Solubilizing of urea in water proceeds through an endothermic reaction, meaning that adding urea to water induces a drop of the temperature of the resulting solution. It has been observed that the desired concentration of a urea solution is settled through a set of temperature conditions. This metering process is especially well adapted for preparing urea-enriched solutions, meaning solutions with a urea concentration higher than 32.5 wt .

Figure 1 illustrates an exemplary embodiment of a system for generating a urea solution. The system comprises a tank 1, a dissolving system 1000 and a control device 2000. The dissolving system 1000 comprises an injector 2, and a dissolving flow zone 3 in the form of a column with solid urea. A quantity of urea solution, e.g. an Adblue® fluid (32.5 weight % urea in water) is available at the temperature Tl in tank 1. Dissolving flow zone 3 is filled with solid urea. The solid urea in the dissolving flow zone 3 may be in granules, flakes, prilled or powdered form. Compressed urea blocks can also be used. T2 is the temperature of the bed of solid urea in the dissolving flow zone 3 when no urea solution goes through it. The urea solution coming from tank 1 is uniformly dispersed at an upper end of the dissolving flow zone 3. This can be achieved e.g. by injection with a spray nozzle, or by dropping the liquid on a lattice or any porous media located on the top of dissolving flow zone 3 of solid urea. T3 is the temperature of the solution at the bottom end 5 of dissolving flow zone 3. Dissolving flow zone 3 may have e.g. a 24 mm section diameter. Dissolving flow zone 3 is filled with solid urea, e.g. 100 g of solid urea. The urea solution is sent through dissolving flow zone 3 with a certain flow rate, e.g. a 100 ml/hour Adblue® flow rate. The flow rate may be for example a more or less constant flow rate. The temperature of the fluid in the tank 1, i.e. upstream of dissolving flow zone 3, and/or of the solid urea in dissolving flow zone 3 may be controlled using a temperature control means. In the illustrated embodiment the fluid in tank 1 is heated using a temperature control means in the form of a heater 6a, and the solid urea in dissolving flow zone 3 is heated using a temperature control means in the form of a heater 6b. Control device 2000 is configured to control heaters 6a and 6b such that the Adblue® fluid in tank 1 is at a temperature Tl which is a function of the desired weight percentage of the urea solution and the solid urea bed in dissolving flow zone 3 is at a temperature T2. In that way a urea solution with an increased urea weight percentage at a temperature T3 is obtained at the bottom end 5 of dissolving flow zone 3.

For example, for obtaining a 55 wt urea solution, the Adblue® fluid may be heated at a temperature Tl = 50°C, and the solid urea bed may be maintained at a temperature T2 = 27°C, resulting in a target temperature T3 at the bottom end of the dissolving flow zone 3 being 27°C.

According to another example, the target temperature T3 (27°C) at the bottom end of the dissolving flow zone 3 may be obtained when the temperature Tl of the Adblue® fluid in tank 1 and the temperature T2 of the column environment are the same and equal to 37°C. According to yet another example, the target temperature T3 (27°C) at the bottom end of the dissolving flow zone 3 may be obtained when the temperature Tl of the Adblue® fluid in tank 1 is 27°C and the temperature T2 of the column environment is 30°C. In other words T2 may also be higher than Tl.

It is noted that T2 is the temperature at which the solid bed is brought before sending urea solution through the solid bed. Obviously, once urea solution is flowing through the solid bed, the temperature in the solid bed will gradually vary from Tl ' (here equal to Tl if it is assumed that no heat is lost between the tank 1 and the top end of dissolving flow zone 3) to T3.

The enriched urea solution with increased concentration at temperature T3 may be sent to a downstream buffer, to the exhaust pipe or to any additional system to store or consume enriched urea solution (not illustrated). The outlet 5 may be connected e.g. to a conversion unit for converting the enriched urea solution into an ammonia solution, and the resulting ammonia may then be sent to an ammonia-hydrogen conversion unit that subsequently communicates with a hydrogen fuel cell where the hydrogen is converted into a power source. The ammonia solution could also be used in a direct ammonia fuel cell.

Figure 2A illustrates an exemplary embodiment in which the same or similar components have been indicated with the same reference numerals as for the exemplary embodiment of figure 1. It may happen that the temperature Tl of the urea solution in tank 1 is too high to obtain the desired temperature T3 at the bottom of the dissolving flow zone 3 for the target urea concentration at the bottom end of dissolving flow zone 3, e.g. T3 = 27°C for a 55 wt urea solution. In such a situation, the concentrated urea solution leaving the bottom end of dissolving flow zone 3 can be used as a heat-exchange fluid to cool down the urea solution in a heat exchanger 4 inserted in a line 20 between the tank 1 and the injector 2. The heat exchanger 4 receives concentrated urea solution at temperature T3 through a line 31 between bottom end of dissolving flow zone 3 and heat exchanger 4. The concentrated urea solution leaves heat exchanger 4 though a further line 32 to obtain concentrated urea solution at an outlet 5' at a temperature T3' which is higher than T3. However, the effect of decreasing the temperature from Tl to Tl ' will have impact on the dissolving in dissolving flow zone 3, which in turn influences the concentration at the bottom end of dissolving flow zone 3.

As in the embodiment of figure 1 , there may be provided a heater 6a and/or 6b (not shown in figure 2A), and the control device 2000 may be configured to control heaters 6a and/or 6b to control a temperature of the flow of aqueous solution upstream of the dissolving flow zone and/or a temperature of the flow of aqueous solution in the dissolving flow zone. In addition or alternatively the flow rate of the flow of aqueous solution in the dissolving flow zone and/or a dimension, e.g. a length 1, of the solid urea bed through which the flow of aqueous solution flows, may be controlled by control device 2000. Controlling the length 1 may e.g. be achieved by having outlet openings at different heights of the dissolving flow zone and opening or closing said outlets in function of e.g. Tl.

Figure 2B illustrates a variant of the exemplary embodiment of figure 2A, wherein the same or similar components have been indicated with the same reference numerals. In this embodiment dissolving flow zone 3 is used as a heat exchanger 4 to cool down the urea solution leaving the tank 1. The urea solution leaving the tank 1 is used as a heat-exchange fluid in a heat exchanger 4 inserted in dissolving flow zone 3. The heat exchanger 4 receives urea solution at temperature Tl through a line 21 between tank 1 and heat exchanger 4. The cooled down urea solution leaves heat exchanger 4 through a further line 22 between heat exchanger 4 and injector 2. In that manner the injected urea solution will have a temperature Τ which is lower than Tl. The control device 2000 may control one or more parameters influencing the dissolving as in the embodiment of figure 2A or figure 1.

Figure 2C illustrates a variant of the exemplary embodiment of figure 2A, wherein the same or similar components have been indicated with the same reference numerals. In this embodiment dissolving flow zone 3 and the solution coming out of dissolving flow zone 3 are used for heat exchange in order to cool the fluid flowing from the tank 1. The concentrated urea solution leaving the bottom end of dissolving flow zone 3 is used as a heat-exchange fluid to cool down the urea solution in a heat exchanger 4a inserted in a line 21 between the tank 1 and a further heat exchanger 4b in dissolving flow zone 3. The heat exchanger 4a receives concentrated urea solution at temperature T3 through a line 31 between bottom end of dissolving flow zone 3 and heat exchanger 4a. The concentrated urea solution leaves heat exchanger 4a through a further line 32 to obtain concentrated urea solution at an outlet 5' at a temperature T3' which is higher than T3. The cooled urea solution at a temperature Tl" that has passed through heat exchanger 4a is used as a heat-exchange fluid in a heat exchanger 4b inserted in dissolving flow zone 3. The heat exchanger 4b receives urea solution at temperature Tl" through line 21. The further cooled down urea solution leaves heat exchanger 4b through a further line 22 between heat exchanger 4b and injector 2. In that manner the injected urea solution will have a temperature Τ < Tl" < Tl. The control device 2000 may control one or more parameters influencing the dissolving as in the embodiment of figure 2 A or figure 1. Figure 3 illustrates a further exemplary embodiment, wherein the same or similar components have been indicated with the same reference numerals. In this embodiment the solid urea bed is cooled, in order to get the right concentration of the urea solution at the bottom of dissolving flow zone 3. As in the exemplary embodiments of figures 2A-2C, if the temperature Tl of the urea solution in tank 1 or the temperature T2 (defined as the temperature of the solid urea inside dissolving flow zone 3 when there is no feed of urea solution) is too high to reach the target temperature T3 at the bottom of dissolving flow zone 3, the bed of solid urea in dissolving flow zone 3 can be cooled down by a heat exchanger 4 using the concentrated solution as available at the bottom 5 of dissolving flow zone 3. In that manner temperature T3' at outlet 5' (downstream of the heat exchanger 4) will be higher than the temperature T3 at the bottom of dissolving flow zone 3, and because of the lower temperature in the solid urea bed, the concentration of the urea solution at the bottom of dissolving flow zone 3 will be lower than in an embodiment where no heat exchanger 4 is present. The control device 2000 may control one or more parameters influencing the dissolving as in the embodiment of figure 2A or figure 1.

Figure 4 illustrates a further exemplary embodiment, wherein the same or similar components have been indicated with the same reference numerals. In this example the dissolving system 1000 comprises an upstream column 7 for cooling a buffer tank 16 with aqueous solution from tank 1, and a downstream dissolving flow zone 3 receiving cooled urea solution from buffer tank 16. The enriched aqueous solution leaving column 7 is collected in a tank 8 and may be mixed with cooled urea from buffer tank 16. A temperature control means 6b is provided to control the temperature in the solid urea bed in dissolving flow zone 3. The control device 2000 may control one or more parameters influencing the dissolving in dissolving flow zone 3 as in the embodiment of figure 2A or figure 1.

When the temperature Tl of the urea solution in tank 1 and the temperature T2 of the solid urea bed are too high (e.g. 65 °C) to get the target urea concentration, the buffer tank 16 may be used. The buffer tank 16 may be located in the line 21, 22 between tank 1 and injector 2. Column 7 is filled with solid urea and also connected to tank 1. A flow of urea solution goes through column 7, and becomes colder because of urea dissolution, i.e. Tl" at the outlet 7a of column 7 is lower than Tl. At the outlet 7a of column 7 the urea-enriched solution is used to cool down the content of the buffer tank 16 using a heat-exchanger 4. The urea-enriched solution at the outlet of the heat- exchanger 4 is stored in a tank 8. At the outlet of buffer tank 16 the temperature Τ of the urea solution is now suitable for spraying on the solid urea bed to reach the target temperature at the outlet 5, resulting in a solution with the desired urea concentration. The urea-enriched solution from tank 8 may also be used to produce a solution having a desired urea concentration. According to this embodiment, there exists a temperature T4 in tank 8 for which the content of the tank 8 can be fed to the dissolving flow zone 3, so that the temperature T3 at the bottom of the dissolving flow zone 3 is the one related to the desired saturation rate (for example: T3 = 27°C for a 55 wt urea solution). Part of the urea in solution in the tank 8 may be re -crystallized in the urea bed 3.

In the embodiment of figure 4, either the solution from tank 8 or the solution from buffer tank 16 may be used to feed the urea bed. Mixing the solutions of tank 8 and buffer tank 16 is also a possibility. Thereto one or more further devices, e.g. one or more flow meters (not shown) to control the flows from tanks 16 and 8, and/or a more complex control system may be provided.

Figure 5 illustrates a further exemplary embodiment similar to the embodiment of figure 4, wherein the same or similar components have been indicated with the same reference numerals. A difference is that a heat-exchanger 10 is added in line 22, 23 between the outlet of buffer 16 and the inlet of injector 2, using the urea-enriched solution coming from the outlet of the solid urea bed 3 as a heat transfer fluid, for further cooling of the urea solution in buffer 16 at temperature ΤΓ" , before spraying it on the urea solid bed 3 at a temperature Τ < ΤΓ". Figure 6 shows another exemplary embodiment, wherein the same or similar components have been indicated with the same reference numerals. The system includes a tank 1 which is filled with a urea-containing solution, a dissolving flow zone 3 in the form of a container which is filled with solid urea, a heat-exchanger 4 surrounding the dissolving flow zone 3, and three-way valves 2, 10, and 11. The outlet of the heat exchanger 4 is connected to a line 22 used as a fluid communication between valve 2 and dissolving flow zone 3. A line 33 connects tank 1 to valve 10.

Three operating modes are possible, depending on the temperature Tl of the fluid inside the tank 1 and the temperature T2 of the solid urea in the dissolving flow zone 3, when no urea solution goes through the urea bed:

1. The urea solution in tank 1 at T= Tl can compensate for the heat used for the dissolution in dissolving flow zone 3 so that the temperature T3 of the enriched urea solution at the outlet of dissolving flow zone 3 corresponds to the temperature of the saturation limit of the desired solution. The urea solution in tank 1 goes directly to dissolving flow zone 3. At the bottom end of dissolving flow zone 3, no further mixing between the urea-enriched solution and the initial solution is realized. In this operating mode valves 2, 11 and 10 are positioned such that the flow goes through lines 21, 22, 31, and 32 to outlet 5', and Tl = T1' . 2. The temperature Tl of the urea solution in tank 1 is too high, so that the heat used for the dissolution in the dissolving flow zone 3 is not sufficient to cool down the solution to get the target temperature T3 at the outlet of the dissolving flow zone 3. However, the heat used for the dissolution is sufficient to cool down, through heat exchanger 4, the urea solution from a temperature Tl to a temperature Τ < Tl. Τ is the fluid temperature at the inlet of dissolving flow zone 3 which is suitable for obtaining the desired target temperature T3 (related to the saturation limit of the desired solution) at the outlet of dissolving flow zone 3. In this operating mode a first volume VI of the fluid directly flows from tank 1, through lines 21, 22, to dissolving flow zone 3 where a cooling effect is provided due to the heat used for the dissolution of urea. When the front of the fluid flow reaches the outlet of dissolving flow zone 3, the fluid from tank 1 is directed through line 23 to heat exchanger 4 so that the fluid is conditioned at Τ (< Tl) at the inlet of dissolving flow zone 3, and pushing the volume VI of liquid already present in it. The liquid volume VI may be recycled in dissolving flow zone 3 through valve 11 and lines 24, 23. As dissolution proceeds in dissolving flow zone 3, the urea-enriched solution is further evacuated through the lines 31, 32 to outlet 5'.

3. The temperature Τ of the urea solution entering dissolving flow zone 3 is too high to reach the target temperature T3 at the outlet of dissolving flow zone 3, in the functioning mode as exemplified in point 2. In this case, as the concentration of the urea-enriched solution at the outlet of the dissolving flow zone 3 is higher than the desired one, this flow may be diluted with the fluid coming from tank 1 through the line 33 and the mixing valve 10.

In this embodiment control device 2000 is configured to control the valves 2, 10, 11 according to the above described modes. As in the embodiment of figure 1, in addition there may be provided heaters similar to heaters 6a and/or 6b in figure 1 (not shown in figure 6), and the control device 2000 may be configured to control those heaters to control a temperature of the flow of aqueous solution upstream of the dissolving flow zone 3 and/or a temperature of the flow of aqueous solution in the dissolving flow zone 3.

Figure 7A is an illustration of another exemplary embodiment in which a tank 1 is filled with a urea solution, and the urea solution is distributed from the bottom of tank 1 through an injection rail 2 into a solid urea bed SU in dissolving flow zone 3. The urea bed SU may be covered with a liquid spreading material on the top, so that the entire top surface of the urea bed is in contact with the urea solution. Dissolving flow zone 3 has two heated zones: a first heated zone 36 in an upstream part, which is used to solubilize the urea and increase the concentration in the urea solution, and a second heated zone 37 in a downstream part which is used to saturate the urea solution. For example, urea solution in tank 1 is first injected on the solid urea in dissolving flow zone 3, through rail 35. The first heated zone 36 in dissolving flow zone 3 is heated at 35°C for dissolution purposes. The urea-enriched solution further flows (e.g. under gravity) to a second heated zone 37 which is used for saturation. This means that the temperature of second heated zone 37 corresponds to the saturation temperature of the urea solution having the desired concentration. For example, this second layer is heated at 27°C when the desired concentration of the urea solution after flowing through this layer is 55 wt .

Figure 7B shows a further schematic view of a possible implementation of the embodiment of figure 7A. In this embodiment the injector 2 takes the form of a plurality of rails with nozzles 25 such that the entire top surface of the solid urea bed can be sprayed. In a possible variant thereof the nozzles can be controlled to be open or closed, and the number of nozzles that are open can be controlled to vary the flow rate through the solid urea bed. The first and second heated zone 36, 37 may be provided by arranging a wire grid forming an electrical heater in the solid urea bed. Figure 8 A shows another exemplary embodiment, wherein the same or similar components have been indicated with the same reference numerals. The system of figure 8A is for the generation and the injection of a urea-enriched solution. In figure 8A a tank 1 contains a diesel exhaust fluid (DEF), e.g. Adblue® being a 32.5 wt % urea solution. The urea solution is sucked at a suction point 102, using a pump 103, and introduced inside a urea enrichment control module 104. The urea flow (or part of it) warms up in heater 6, and is further sent to a dissolving flow zone 3 in the form of a cartridge which is filled with solid urea SU. Inside the dissolving flow zone 3 the urea concentration of the initial solution increases because of the solubilizing of the solid urea. The dissolving flow zone 3 may be equipped with a liquid spreading material 108 in order to enhance liquid/solid contact. A heat exchanger 109 using the heat of the aqueous solution flowing through the dissolving flow zone 3can limit the urea concentration when the ambient temperature is above the temperature corresponding to the saturation limit of the desired solution. In that case, the heater 6 is off. Dissolving flow zone 3 may further be provided with a moving spreader panel 110 to keep the urea solution in contact with the solid urea front during the solubilizing process. The position of the moving spreader panel 110 can be used as a way of gauging the solid urea content inside the dissolving flow zone 3. The moving spreader panel 110 can move thanks to a guiding system, possibly completed with springs. Flexible tubes 118a, 118b are connected to the top and the bottom of the spreader panel 110, respectively, to form the inlet and the outlet of the dissolving flow zone 3. The enriched-urea solution may be collected with a liquid collecting material 111, and sent to the inlet of the pump 103 through line 118b and a multi-port valve 122. This valve 122 allows the mixing of the urea-enriched solution with the fluid which is stored in tank 1. The dilution of the urea-enriched solution is controlled by the adjustment of the flow rates of both solutions (urea- enriched and the urea solution coming from tank 1. The urea content of the solution is further stabilized in a temperature-controlled urea buffer 112. At the outlet of buffer 112, the urea solution has reached the desired concentration and is injected in exhaust pipe 113 upstream an SCR catalyst 114, through line 115 and the injector 116. A check valve 117 may be used to set the necessary pressure for injection.

By reversing the rotation of pump 103, it is possible to purge injector 116 and line 115, as well as the loop including the urea enrichment control module 104 and the dissolving flow zone 3. The purging of injector 116 occurs when this component is maintained in an open position. Gas from the exhaust pipe is sucked through injector 116 and the liquid present in line 115 and in buffer 112 is rejected in the tank 1 through the outlet 102. For purging the enrichment control module 104 and the dissolving flow zone 3, the injector 116 is in the closed position. Air is sucked from the vapour dome of tank 1 through a check valve 120. The multi-port valve 122 is in a position ensuring a fluid communication between an air intake line 123 and line 118b, and a check valve 119 of a bypass line 121 is open due to the pressure drop. As air is further sucked, the dissolving flow zone 3 and the enrichment control module 104 are purged. The liquid returns in tank 1, as the multi-port valve 122 allows fluid communication between an outlet of pump 103 and suction point 102.

A control device 2000 may be configured to control heater 6 and/or heat exchanger 109 to control a temperature of the flow of aqueous solution upstream of the dissolving flow zone and/or a temperature of the flow of aqueous solution in the dissolving flow zone in dissolving flow zone 3. In addition to the temperature control, the required concentration can be further regulated to some extent using multi-port valve 122, by controlling the mixing of the urea solution of tank 1 with urea-enriched solution coming from the dissolution loop. However, the main controlling is preferably done by controlling the temperature in temperature-controlled urea buffer 112 which may also be done by control device 2000. Figure 8B illustrates an exemplary embodiment of a temperature-controlled urea buffer 112 for use in an embodiment of a system for generating enriched urea solution, e.g. the embodiment of figure 8A. An inlet 12a of the buffer 112 is intended to be connected to a pump, e.g. pump 103 as shown in figure 8 A. The flow at an outlet 12b of buffer 112 may be further divided into a flow to the injector 116 and a flow to the solubilizing loop, through a check valve 117, as shown in figure 8A. The buffer 112 is divided in two zones 12c and 12d, each one being equipped with an open cell foam material 12e and 12f, and heat exchangers 12g and 12h. Liquid spreading materials 12i and 12j cover the top of the foam parts, in order to get the suitable liquid distribution for an optimized flow of the fluid through the foam. Temperature sensors 12k and 121 are located at the inlet of each foam part, and a third sensor 12m measures the temperature at the outlet of the bottom foam. The role of the buffer 112 is to end up with a urea solution at a temperature T3 corresponding to the desired urea concentration.

Control device 2000 uses the measured temperatures by sensors 12k, 121, 12m to perform the controlling of heat exchangers 12g, 12f. If the urea solution temperature measured by sensor 12k is higher than the temperature T3 which is the target for sensor 12m, the foam part 12e is to be cooled down. This can induce an accumulation of solid urea in the cells of the foam. The fluid temperature can be further stabilized by heating/cooling the bottom zone 12d of the buffer 112. If the temperature measured by the sensor 12k is lower than the target temperature T3 at the outlet 12b of the buffer 112, the foam part 12e is heated up in order to saturate the urea solution at the desired concentration. In this step, part of the solid urea which is accumulated in the foam is dissolved. The temperature and the urea concentration are further controlled and stabilized in the bottom foam 12f, taking into account the temperatures measured by sensors 121 and 12m. More generally the heating or cooling of top foam part 12e and bottom foam part 12f may be controlled in function of the measured temperatures by sensors 12k, 121, 12m. Figure 9 shows another exemplary embodiment, wherein the same or similar components have been indicated with the same reference numerals. The system of figure 9 is for the generation and the injection of a urea-enriched solution. The system comprises a tank 1 to store a urea solution, a pump 103, a suction point 101 connected to a venturi device 125. The outlet of the venturi device 125 is connected to a heater 6 through the valve 126, and further supplies the dissolving flow zone 3 with urea solution. This zone integrates a solid urea cartridge and any elements promoting the dissolution, e.g. a spreading panel and material and a collecting material. The enriched solution is further sent to a temperature-controlled buffer 112, which may be similar to the buffer 112 of figure 8B. At the outlet of buffer 112, the correctly urea-enriched solution is ready to be injected through the injector 116.

The lines of the system can be purged by reversing the pump rotation:

• Line 115 connecting pump 103 to injector 116 is purged by sucking gas from the exhaust pipe while the injector is maintained in an open position.

• Line 118b, the dissolving flow zone 3, and heater 6 are purged when the injector 116 is in a closed position, and gas from the vapour dome of tank 1 is sucked through a check valve 120. The fluidic communication between heater 6 and pump 103 occurs through a bypass 121 which is connected to the line from heater 6 through the valve 126. Depending on the position of valve 127, the flow can be rejected either in tank 1 or in temperature-controlled buffer 112.

After purging, the normal mode function is realized either by pumping fluid from buffer 112 or urea solution from tank 1 at suction point 102. The position of valve 126 is such that the fluidic communication between venturi tube 125 and heater 6 exists.

In this embodiment control device 2000 is configured to control the valves 126, 127 according to the above described modes as well as heater 6 and temperature controlled buffer 112. As in the embodiment of figure 1, in addition there may be provided a heater 6b (not shown in figure 9), and the control device 2000 may be configured to control heater 6b to control a temperature of the flow of aqueous solution in the dissolving flow zone.

In the exemplary embodiments illustrated above, when using AdBlue® as the aqueous solution in tank 1, the total urea concentration in the resulting solution may be increased to 55% by weight. In other words, 1 kg of solution contains 450 g of water and 550 g of urea, from which 217 g (32.5% of (450 g + 217 g)) originate from the eutectic AdBlue® and 333 g have been added by sending the eutectic AdBlue® solution through the dissolving flow zone. While a conventional SCR system would require 45 litre useful volume to reach a driving range of 30000 km (corresponding for instance to the maintenance interval) with a consumption of 0.15 litre of AdBlue® per 100 km, embodiments of a system where the concentration is increased using a dissolving flow zone (e.g. provided in the form of a replaceable cartridge) would require only about 27 litre of useful volume for the same driving range. Accordingly, the weight of the full system would be reduced by about 20 kg. In the example of a fuel cell feeding system, a vehicle equipped with a prior art system of 70 litre useful volume based on AdBlue® and consuming 28 litre/100 km has a driving range of 250 km, while a system of the same useful volume in accordance with embodiments of the invention and having an urea concentration increased at 55% in weight as set out above, will reach a driving range of about 420 km.

Whilst the principles of the invention have been set out above in connection with specific embodiments, it is to be understood that this description is merely made by way of example and not as a limitation of the scope of protection which is determined by the appended claims.

Claims

A vehicle system for increasing the urea concentration of an aqueous solution on-board a vehicle, said vehicle system comprising:

- a tank (1) storing an aqueous solution having a first urea weight percentage;

- a dissolving system (1000) comprising a dissolving flow zone (3) with a solid urea bed, said dissolving system being configured for generating a flow of aqueous solution coming from the tank through the dissolving flow zone; said dissolving flow zone being arranged for guiding the flow of aqueous solution through the solid urea bed out of the dissolving flow zone;

- a control device (2000) configured for controlling at least one parameter influencing the dissolving in the dissolving flow zone such that the aqueous solution leaving the dissolving flow zone has a second urea weight percentage which is higher than the first urea weight percentage.

The vehicle system of claim 1 , wherein the control device (2000) is configured to control any one or more of the following: a temperature of the flow of aqueous solution upstream of the dissolving flow zone, a temperature of the flow of aqueous solution in the dissolving flow zone, a temperature of the flow of aqueous solution downstream of the dissolving flow zone; the flow rate of the flow of aqueous solution in the dissolving flow zone; a dimension of the solid urea bed through which the flow of aqueous solution flows.

The vehicle system of claim 1 or 2, wherein the control device (2000) comprises a temperature control means configured for controlling the temperature of the aqueous solution upstream of the dissolving flow zone and/or in the dissolving flow zone such that the aqueous solution leaving the dissolving flow zone has a second urea weight percentage which is higher than the first urea weight percentage.

The vehicle system of any preceding claim, wherein the control device (2000) is configured to control at least one parameter influencing the dissolving in the dissolving flow zone such that, when the first urea weight percent is between 28 and 37 wt , the second urea weight percent is between 40 and 80 wt , preferably between 40 and 70 wt , more preferably between 50 and 60 wt , most preferably between 54 and 56 wt .

The vehicle system of any preceding claim, wherein the control device (2000) is configured to control at least one parameter influencing the dissolving in the dissolving flow zone such that the temperature (T3) of the aqueous solution leaving the dissolving flow zone is between 10 and 45 degrees Celsius, preferably between 15 and 40 degrees Celsius, more preferably between 20 and 34 degrees Celsius.

The vehicle system of any preceding claim, wherein the control device (2000) is configured to control at least one parameter influencing the dissolving in the dissolving flow zone such that the temperature and concentration of the aqueous solution leaving the dissolving flow zone corresponds with the solubility limit of urea in water for that temperature.

The vehicle system of any preceding claim, wherein the control device (2000) comprises any one or more of the following:

- a temperature control means configured for controlling the temperature of the aqueous solution in the tank;

- a temperature control means configured for controlling the temperature of aqueous solution flowing from the tank to the dissolving flow zone;

- a temperature control means configured for controlling the temperature in the solid urea bed of the dissolving flow zone.

The vehicle system of any preceding claim, wherein the dissolving flow zone (3) has a top end for receiving the aqueous solution from the tank, and a bottom end where the aqueous solution flows out of the dissolving flow zone, such that the aqueous solution can flow through the dissolving flow zone by gravity.

The vehicle system of any preceding claim, wherein the dissolving system (1000) comprises any one or more of the following:

- a heat exchanger (6b) for heating the dissolving flow zone, said heat exchanger being connected for receiving aqueous solution from the tank before it enters the dissolving flow zone;

- a heat exchanger (4) configured for cooling aqueous solution flowing from the tank to the dissolving flow zone, said heat exchanger being connected for receiving aqueous solution flowing out of the dissolving flow zone;

- a heat exchanger (4) for cooling the dissolving flow zone, said heat exchanger being connected for receiving aqueous solution from the dissolving flow zone.

10. The vehicle system of any preceding claim, wherein the dissolving flow zone comprises a first heater and a second heater downstream of the first heater, wherein the control device is configured for controlling said first heater such that the temperature of a first heated zone (36) of the dissolving flow zone is within a first temperature range and that the temperature of a second heated zone (37) of the dissolving flow zone, downstream of said first part, is within a second temperature range which is lower than said first temperature range.

11. The vehicle system of any preceding claim, wherein the dissolving system comprises a temperature-controlled urea buffer (112) having an inlet for receiving aqueous solution from the dissolving flow zone and having an outlet for connection to an injector and to a solubilizing loop including the dissolving flow zone (3); said temperature-controlled urea buffer being configured for generating and/or stabilizing an enriched urea solution and being controlled by the control device (2000).

12. The vehicle system of the preceding claim, further comprising a heater exchanger (6) controlled by the control device (2000) between the outlet of the temperature-controlled urea buffer (112) and an inlet of the dissolving flow zone (3).

13. The vehicle system of claim 11 and 12, wherein the temperature-controlled urea buffer (112) and the heater exchanger (6) are included in a module which is mounted in the tank.

14. The vehicle system of any preceding claim, wherein the dissolving system comprises a pump (103) configured for pumping aqueous solution from the tank through the dissolving flow zone at a controlled flow rate.

15. SCR system comprising a vehicle system according to any one of the previous claims.

16. Fuel cell system comprising a vehicle system according to any one of the claims 1-14.

17. A method for increasing the urea concentration of an aqueous solution on-board a vehicle, said method comprising:

- storing an aqueous solution having a first urea weight percentage;

- generating a flow of aqueous solution having the first urea weight percentage through a solid urea bed in a dissolving flow zone; - controlling at least one parameter influencing the dissolving in the solid urea bed such that the aqueous solution leaving the dissolving flow zone has a second urea weight percentage which is higher than the first urea weight percentage.