ADVANCED PLANT FOR THE PRODUCTION OF UREA IN AQUEOUS SOLUTION IN OPERATING UNITS OF LIMITED SIZE

FIELD OF APPLICATION

The present invention relates to an advanced plant for the production of urea in aqueous solution in operating units of limited size.

In particular, the present invention relates to an advanced plant for the production of urea in aqueous solution in operating units of limited size such as to enable an in-house production of said aqueous solution; in other words, the invention enables production within an operating unit and a local use in the operating unit or a use distributed to a limited degree with respect to the operating unit itself in a manner that does not require transport with heavy vehicles such as lorries, trains, ships, etc.

By way of example, the operating unit can be a company, a means of transport of varying nature, an incinerator, a plant for the production of energy by combustion, a cement factory or a tannery.

PRIOR ART

Urea solutions, the best known of which is AdBlue (also known as Diesel Exhaust Fluid (DEF)), are a mixture of urea and pure water, whose purpose is to limit atmospheric emissions of nitrogen oxides (NO _x ) deriving from the combustion processes that can take place in engines and motors, and hence in the transport sector, but also in incinerators and industrial plants. The different applications require a different concentration of urea in the solution. In the automotive industry, for example, a percentage concentration of urea of 32.5% by weight (corresponding to AdBlue) is required. The use of urea solutions allows NO _x , atmospheric pollutants, to be converted into a harmless mixture of nitrogen and water through a process called selective catalytic reduction (SCR), which takes place thanks to the high temperatures reached in combustion processes. Through this process NO _x interact with urea, leading to the formation of ammonia and carbon dioxide, and subsequently react with the ammonia that has formed and give rise to elementary nitrogen and water. AdBlue can also be used for a process of selective non-catalytic reduction (SNCR), which is associated with plants in which the combustion of biomasses, coal or waste takes place.

The production of urea solutions requires pure water, which can be obtained by filtering mains water, and urea, which can be found, for example, in granular form. It is important that the urea used is of good quality and that there are no traces of metals or chemical additives that could impact the effectiveness of the AdBlue or its quality (which is certified). The main defect of the process currently used for the production of urea solutions is that it is carried out on large volumes.

This is mainly due to the need to have equally large production volumes.

The main operational problem in the production of urea mixtures is the decrease in temperature due to the fact that the dissolution of urea in water is an endothermal process: the lower the temperature, the lower the capacity of the urea to dissolve in water; it is even possible that the solution will freeze, thus completely precluding dissolution.

In order to avoid this problem, the plants operating today bring the system to temperatures that are excessive for the process, around 90°C, and consequently add urea in large quantities in the certainty that the temperature will remain within optimal values.

The problems typical of large-sized plants are of varying nature: less control over operating precision, the need to use a large amount of personnel, operating costs due to the operation of large machinery and energy consumption (also caused by the need to reach higher temperatures than what is actually necessary).

Furthermore, in every large-sized plant, it is complicated to control the homogeneity of the product and emissions; in particular, an excessive production of ammonia vapours (correlated both to the large quantities of urea and the temperature used) is inevitable.

The currently known plants of reduced size, on the other hand, have lower production capacities compared to the present invention.

Summing up, the most serious problems tied to the production of urea in large-sized plants are a reduced capacity to control the process and high atmospheric emissions of ammonia (due mainly to the large quantities of urea treated), as well as difficulty in interrupting the production process as a result of the possible costs correlated to the heating of large volumes (typically by means of thermal oil at 200°C); lastly, a large use of personnel also represents a problem. Furthermore, the production in large volumes imposes a distribution of urea solutions over land by means of lorries that produce high levels of pollution and represent potential dangers in everyday traffic.

What is more, there are no known systems for producing urea solutions which, given a specific required final concentration, are capable of ensuring with precision the obtainment of the required concentration of urea.

In other words, a real-time qualitative control over the concentration of urea in aqueous solution is lacking today and this can cause serious repercussions on the final concentration of the solution produced, with grave consequences for and/or possible damage to engines and motors or plants - such as incinerators, plants for the production of energy by combustion, cement factories and tanneries - which exploit that solution, and it can also represent a health hazard for plant operators.

Effective technologies for a rapid, high-efficiency dissolution of urea are not used for the production of AdBlue; the system usually employed provides for simple rotating blades or systems for recirculating the solution. Interesting mixing technologies in this respect come from the food industry, especially from sectors dedicated to the production of beverages. For example, in the fruit juice sector use is made of machines that produce mixtures of different liquids and sugars with high flow capacities while occupying limited space. However, this type of technology deals with products where the temperature is kept low. This type of process is not applicable for the production of urea due to the cooling that ensues from its dissolution. Appropriate improvements are necessary in order for the technology to be applicable to this sector as well.

The object of the present invention is to overcome the drawbacks described in relation to the prior art.

A general object of the present invention is to ensure an efficient production of urea in aqueous solution in operating units of limited size.

A further object is to ensure an efficient production of urea in aqueous solution of guaranteed quality - i.e. with a guaranteed percentage of urea - in operating units of limited size.

A specific object of the present invention is to ensure a production of urea in aqueous solution that is in line with environmental requirements, in operating units of limited size. Another object is to ensure an efficient production of urea in aqueous solution in plants that are less complex to construct and control compared to the prior art.

Another object is to ensure a production of urea in aqueous solution with reduced production costs and consequently reduced costs for the end user. Another object is to enable a reconditioning, a surface treatment and an improvement in the performance of post combustion systems, SCR and SNCR systems, exhausts and other components coming into contact with combustion gases.

SUMMARY OF THE INVENTION

In a first aspect of the invention, these and other objects are achieved by a plant for the production of urea in aqueous solution, according to what is described in claim 1. Advantageous features are comprised in dependent claims 2 to 14.

In a second aspect of the invention, these and other objects are achieved by a method for the production of urea in aqueous solution, according to what is described in claim 15.

The proposed solution of the invention envisages that the production of urea in aqueous solution takes place in limited volumes in house, i.e. within an operating unit and for a local use in the operating unit or a use distributed to a limited degree. The invention as described achieves the following technical effects:

- efficient production of urea in aqueous solution in operating units of limited size.

-assurance of an efficient production of urea in aqueous solution of guaranteed quality, i.e. with a guaranteed percentage of urea;

- assurance of an efficient production of urea in aqueous solution that is in line with environmental requirements in operating units of limited size;

- production of urea in aqueous solution in a more efficient and safer manner than occurs in the large plants of the prior art;

- production of urea in aqueous solution in a more efficient and safer manner than occurs in the small plants of the prior art;

-production of urea in aqueous solution in operating units that are less complex to construct and control compared to the prior art;

-production of urea in aqueous solution with real-time control of the process parameters and uploading to a database correlated to the production batch to allow complete traceability; -possibility of completely remote management and control of production, thanks also to the use of a dedicated application;

-production of urea in aqueous solution in a transportable system;

-efficient production of urea in aqueous solution with reduced production costs and consequently reduced costs for the end user;

-production of urea in aqueous solution that enables a reconditioning, a surface treatment and an improvement in the performance of post-combustion systems, SCR and SNCR systems, exhausts and other components coming into contact with combustion gases.

The aforesaid technical effects/advantages of the invention will emerge in greater detail from the description, provided below, of examples of embodiments given by way of illustration, but not limitation, with reference to the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a conceptual block diagram of a plant for the production of urea in aqueous solution, according to the invention.

Figure 2 is a block diagram of a detail of figure 1 .

Figure 3 is a structural diagram of a plant for the production of urea in aqueous solution according to the invention.

Figures 4 and 5 represent a first example of regulation of the amount of heat exploited by the plant in fig. 3.

Figure 6 represents a second example of regulation of the amount of heat exploited by the plant in fig. 3. Figures 7, 8 and 9 show a user interface associated with the plant of the invention.

DETAILED DESCRIPTION

The term “pure water” means, for the purposes of the present invention, water which, following at least one treatment, preferably filtration, has a reduced or zero content of impurities such as, for example, microorganisms, mineral salts and/or gases dissolved therewithin. Preferably, for the purposes of the present invention, “pure water” means water selected in the group consisting of: ultrapure water, Milli-Q water, distilled water, deionised water and osmotized water.

For the purposes of the present invention, the terms “urea mixture”, “urea solution”, “aqueous solution of water and urea”, “aqueous solution comprising water and urea”, “urea dissolved in water”, AdBlue and DEF are used as perfectly interchangeable synonyms.

For the purposes of the present invention, the expression “concentration of urea” is used to indicate the concentration, expressed as % by weight, of the urea in the aqueous solution comprising urea and water obtained with the plant according to the present invention. Furthermore, the “concentration of urea” is directly linked to the degree of dissolution of the urea itself in water. Preferably, the urea solution comprises additives, preferably nanostructured additives.

The present invention relates to a high-tech plant capable of dissolving urea, preferably granular urea, in pure water in an extremely reduced time, with low energy consumption and with control of the dissolution of urea in water so as to obtain an aqueous solution comprising water and urea as a finished product by means of IOT system logics.

The plant is of reduced size and can be easily moved and placed on the ground or on means of transport of varying types, e.g. a lorry, train, or ship.

By virtue of its conception, the plant is capable of producing on demand urea solutions with a certified concentration, i.e. a certified degree of dissolution. The product obtained by using the innovative technology is urea in aqueous solution which is suitable for a variety of antipollution applications and in particular for reducing the emissions of nitrogen oxides from exhaust gases produced by vehicles equipped with a diesel engine or by various types of industrial plants.

The same product is used in an industrial setting, in transport by sea, in rail transport and in the agricultural sector.

The product can be produced at a different concentration of urea according to the required application.

The technology developed by the owner of the present patent application makes it possible to optimise the conditions of preparation of urea in aqueous solution in operating units of limited size, i.e. such as to allow in-house production of said solution.

In particular, the invention enables production within an operating unit and a local use in the operating unit or a use distributed to a limited degree with respect to the operating unit itself in a manner that does not require transport with heavy vehicles such as lorries, trains, ships, etc.

By way of example, the operating unit can be a company, a means of transport of varying nature, an incinerator, a plant for the production of energy by combustion, a cement factory or a tannery.

The dissolution of urea in water is an endothermal process, which leads to a decrease in the temperature of the solution obtained and consequently decreases the miscibility of the urea in water and may even lead to freezing of the urea mixture itself.

Given its limited dimensioning, the plant of the invention is capable of balancing the decrease in temperature by providing an equal amount of heat to the mixture so as to maintain a temperature that is as constant as possible over time and close to a pre-set value TSOL _TA RG, around a temperature of 20°C, and, at the same time, regulate in general the total amount of heat supplied to the plant.

To this end, the plant of the invention records and adjusts various reaction parameters: the volume (initial and over time) inside the hold-up tank (S2), the amount of incoming water (mH20 in), the amount of urea introduced into the solution (mCH4N20 in) and the temperature of the water and of the solution. Based on these parameters a calculation is made of how much heat will be absorbed by the dissolution (qia) of the incoming mass (mCH4N20 in); accordingly, the amount of heat to be supplied to maintain the temperature stable will be sent to the machinery.

In a first aspect, the invention describes a plant for the production of urea in aqueous solution; said solution will be indicated hereinafter as SOL. According to the invention, the plant comprises a housing having volumetric dimensions comprised between 25 and 80 m^, preferably between 28 (the maximum value has been based on the volume of a 12-metre container).

With particular reference to figures 1 and 3, the plant comprises a water treatment apparatus lmp_H20 for the production of pure water H20 and a storage and heating tank S1 for the pure water H20.

Preferably, said water treatment apparatus is a filtration apparatus. Even more preferably, said water treatment apparatus is a reverse osmosis filtration apparatus. Preferably, said pure water is water selected in the group consisting of: ultrapure water, Milli-Q water, distilled water, deionised water and osmotized water, more preferably said pure water is osmotized water. The plant comprises first heating means R1 , R2 coupled to the storage and heating tank S1 and configured to vary an adjustable water temperature T _H 2 _O in the storage and heating tank S1 .

Preferably, the first heating means R1 , R2 comprise electric heating elements; alternatively, or in addition, it is possible to use microwave generators, jacketed tubing, heat exchangers or residual heat coming from energy production plants or plants having an excess thereof. The storage and heating tank S1 is in fluid connection with the water treatment apparatus lmp_H20.

Preferably, the water that is treated is mains water. Alternatively, it is also possible to use water with higher saline concentrations, such as water coming from industrial waste or simply places where the salinity of the water is greater (seawater, in the case of maximum salinity). The tank comprises a first temperature probe TT01 configured to measure a temperature T1 of the pure, preferably osmotized, water H20 contained in the tank, a conductivity probe C01 configured to measure a degree of purity of the pure, preferably osmotized, water according to the indications given in ISO protocol 22241 , H20 contained in the tank and a first level probe LSL01 configured to measure a minimum level L1 _M IN of the pure, preferably osmotized, water H20 contained in the tank. The treatment apparatus, preferably a filtration apparatus, for treating the water lmp_H20 comprises a first adjustment means M H20, configured to adjust an adjustable volume of pure, preferably osmotized, water (V _H 2o) exiting from the treatment apparatus, preferably a filtration apparatus, for treating the water lmp_H20 and entering the storage and heating tank S1 , on the basis of one or more among: the data received from the first temperature probe TT01 , the data received from the first level probe LSL01 and the data received from the conductivity probe C01 . The same level probe LT01 further makes it possible to constantly monitor the level and to know the amount of pure water V_H20i inside the tank.

The entry of the pure, preferably osmotized, water into S1 is regulated on the basis of the level alone, whereas the exit of the pure, preferably osmotized, water heated by S1 is regulated on the basis of the level, the conductivity and the temperature.

Preferably, the first adjustment means M H20 comprises a first regulating valve EV1 , for example a butterfly valve (fig.3).

With particular reference to figure 1 , the plant comprises a hold-up tank (S2) which first permits the accumulation of the pure, preferably osmotized, water with a temperature value T H20 equal to the required value, with a conductivity value c_H20 lower than the maximum set threshold and in amounts V_H20m required by the process. Subsequently, the hold-up tank (S2) is used to accumulate the solution that will be produced and will develop a growing degree of urea concentration until reaching the desired concentration of urea (urea CONC) in the solution. The concentration CONC of urea in the solution is monitored by a refractometer placed in communication with the hold-up tank (S2).

With particular reference to figure 1 , the plant comprises a urea loading means LOAD urea for loading urea into the plant. The plant further comprises a nanoemulsion system 5 in fluid connection with the hold-up tank S2 and with the urea loading means LOAD urea.

The urea loading means LOAD urea can comprise a feed screw, preferably with a hollow shaft, for loading, to permit the transfer of urea from the hopper for loading the urea loading means to the hopper present in the nanoemulsion system.

The urea loading means further comprises one or more lump breakers LB1 and LB2 which impede the formation of lumps in the urea and enable an effective movement thereof.

The nanoemulsion system 5 is configured to mix the urea, loaded in a given adjustable mass M _urea , and the pure, preferably osmotized, water H20, loaded in a given adjustable volume of water VH20 _m and at the given adjustable water temperature T _H 2o-

In this manner, the nanoemulsion system gives rise to an aqueous solution comprising water and urea SOL that has an adjustable solution temperature T _S oi_ and a concentration CONC of urea.

According to the invention, the plant for the production of urea in aqueous solution is such as to enable in-house production of the aqueous solution SOL; in fact, the adjustable volume of pure, preferably osmotized, water V _H2 o is limited to a maximum threshold value V _H 2OMAX comprised between 1 and 60 m^, preferably between 5 and 40 m^.

The plant described by the invention can provide for filtration systems prior to storage, in order to retain any insoluble substances that may be present in the solution.

According to the invention, the plant for the production of urea in aqueous solution is such as to enable in-house production of urea in aqueous solution SOL; in fact, the adjustable mass volume of urea m _urea is limited to a maximum threshold value m _ureaMA x comprised between 0.5 t and 5.51, preferably between 1 t and 41.

The plant described by the invention provides for a cycle of the solution in production between the nanoemulsion system 5 and the hold-up tank S2.

The hold-up tank S2 comprises a second temperature probe TT02 configured to measure a temperature T2 of the solution SOL in the hold-up tank S2, a second conductivity probe C01 for measuring a value of conductivity c_H20 of the hold-up tank S2 at the beginning of the cycle (prior to dissolution), a second level probe LSL02 configured to measure a minimum level L2 _M IN of the solution SOL in the nanoemulsion system 5 and a third level probe LSH02 configured to measure a maximum level L2 _M AX of the solution SOL in the hold-up tank S2. As an alternative to the plant represented in figure 3, it is possible to envisage a plant in which the probes LSL01 , LSL02 and LSH02 are replaced by radar level probes that enable the level inside the tanks to be monitored without necessarily having minimum and maximum level thresholds.

The hold-up tank S2 preferably comprises a refractometer Q01 for determining the concentration DECT CONC during the dissolution process.

The urea loading means LOAD urea comprises second adjustment means M urea configured to adjust the adjustable mass of urea m _urea entering the nanoemulsion system 5 on the basis of one or more among: the data received from the second temperature probe TT2, the data received from the second and third level probes LSL02 and LSH02 and the urea concentration value CONC.

With reference to figures 1 and 3, the second adjustment means M urea comprises a screw C2 configured to regulate the urea, preferably granular urea, which, by means of a loading hopper C1 , is fed to the nanoemulsion system 5.

The first adjustment means M H20 and the second adjustment means M urea are configured to set a variation AT _S oi_ of the adjustable temperature of the aqueous solution comprising water and urea T _S oi_ such as to modify the measured urea concentration value CONC until arriving at a target concentration value CONCTARG at a target solution temperature TSOL _A R _G , such that 17 ^O C<TSOL _TA R _G <30 ^O C.

With particular reference to figures 1 and 3, in order to contribute to the variation AT _S oi_ of the adjustable temperature of the aqueous solution comprising water and urea T _S oi_, the plant comprises a second heating means 7 located between the nanoemulsion system 5 and the hold-up tank S2.

Preferably, said second heating means 7 is located in line between the nanoemulsion system and hold-up tank S2 and is configured to maintain the temperature of the urea in aqueous solution at optimal values for dissolution.

Preferably, said second heating means 7 comprises a cavitation system, the same one used as a dissolution means.

Cavitation is a phenomenon that develops when a liquid undergoes a decrease in pressure until the latter is lower than the vapour pressure; this results in a passage of the liquid into a gaseous phase, which is manifested with the formation of vapour bubbles. After this first phase, called the triggering of cavitation, the liquid pressure must exceed the vapour pressure in order for actual cavitation to occur. At this point the vapour bubbles that have formed will undergo a rapid collapse, which enables very high temperatures and pressures to be reached, also generating turbulence. This mechanism could be exploited at an industrial level to increase the dissolution of substances.

Alternatively said second heating means 7 comprises a system with heating elements, the use of jacketed tubing or a microwave emitter.

Preferably, the second heating means is provided at the storage and heating tank S1 .

The recirculation line connects in a feedback loop an outlet OUT _S oi_ of the nanoemulsion system 5 to an inlet FEED _S oi_ of the hold-up tank S2.

The recirculation line allows the aqueous solution comprising water and urea SOL, which has undergone a variation AT _S oi_ of the adjustable solution temperature T _S oi_, to re-enter the hold up tank S2.

The dissolution means comprises a pump that enables the solid urea, preferably in prilled form, to be drawn in and initially mixed with the pure water and subsequently with the solution being formed, both likewise drawn in by the pump.

The dissolution means also comprises a cavitation system CAV inside the nanoemulsion system 5.

The addition of a further solution stirrer M7 similar to the previous one located downstream thereof can also be provided to increase the dissolution speed.

According to the invention, the urea concentration value CONC can vary as a function of a degree of dissolution Deg_Diss of the urea itself in the solution SOL determined by the dissolution means CAV and M7.

The required degree of dissolution determines a corresponding cooling of the solution and, consequently, it determines a value of the increase in the temperature AT _S oi_ that is necessary to compensate for the decrease that has occurred in order to maintain the solution SOL in equilibrium, that is, in order to be able to continue the dissolution process.

The heat supplied to determine AT _S oi_ is defined as a function of the degree of dissolution; in particular, it is directly proportional thereto.

The degree of dissolution indicates how much urea can be dissolved in the solution SOL.

In other words, it indicates the percentage of the mass of incoming urea that dissolves in water thanks to the heat supplied.

The supplied heat balances the dissolution heat (negative) lost in order to achieve the dissolution.

As the amount of heat absorbed by one kilogram of urea in order to dissolve, k _u , is known, it will be necessary to supply the plant with an amount of heat equal to k _u for every kg of urea added if it is desired to maintain a constant temperature. Accordingly, a calculation is made of the “instantaneous heat to be supplied” (q _if ) - which determines the variation AT _S oi_ - calculated as equal to the “instantaneous heat absorbed” (q _ia ), which in turn is equal to the incoming mass of added urea multiplied by k _u kcal/kg, i.e.:

Pi _t (kcal) = q _ia (kcal) = m _C 4N02in(kg) k _u (kcal/kg)

The plant of the invention envisages measuring the supplied heat in kcal because 1 kcal is the amount of heat to be supplied in order to increase 1 kg of water by 1°C; this allows the calculations to be simplified considerably (in some formulas the conversion factor 1 kcal/°C kg will appear).

It is important to note that both q^and qi _a are indicated as positive, but in reality they should be of the opposite sign, since in one case it is a matter of heat absorbed by the plant and in the other of heat supplied to the plant. For the sake of simplicity, the positive sign has been maintained in both cases.

It may be understood that the invention, given how it is structured, allows urea in aqueous solution SOL at different urea concentration values CONC as a function of the set degree of dissolution Deg_Diss.

With particular reference to figure 1 , the plant of the invention comprises a detection means DECT conc configured to detect the urea concentration value CONC and coupled to the nanoemulsion system 5.

According to the invention, the detection means DECT conc for detecting the urea concentration value CONC is configured to detect said concentration CONC of urea in real time.

Preferably, the detection means DECT conc comprises a refractometer RT.

The plant of the invention comprises a control unit 100 configured to control the dissolution process.

The control unit 100, in general terms, is configured for a plurality of controls to be executed in succession. Primarily, the control unit 100 is configured to control the starting conditions of the plant, such as the level of filling of the various tanks and the temperature of the contents thereof; this is useful in order to know, for example, the amount of pure, preferably osmotized, water already present in the tank for heating the pure, preferably osmotized, water.

Subsequently, with reference to figure 1 , the control unit 100 is configured first to control a preparation of pure water, by enabling the start-up of the process of purification of mains water by means of a pure water treatment apparatus lmp_H20.

According to a preferred embodiment of the invention, the control unit 100 is configured to control a preparation of osmotized water by enabling the start-up of the purification process that permits the entry of mains water into the water treatment apparatus lmp_H20, which carries out a treatment by reverse osmosis filtration.

The control unit 100 further enables the opening of the intake valve EV1 so that the pure, preferably osmotized, water produced is pushed into the storage and heating tank S1.

The storage and heating tank S1 is monitored by the aforesaid first temperature probes TT01 , first level probe LSL01 and conductivity probe C01.

The control unit 100 regulates the treatment process, preferably filtration, even more preferably reverse osmosis filtration, according to the amount of pure, preferably osmotized, water present in the storage and heating tank S1 , so as to begin when a level SL _M IN defined as minimum is present inside the tank and instead stop when a level SL _M AX defined as maximum has been reached.

Alternatively, the control unit 100 regulates the treatment process, preferably filtration, even more preferably reverse osmosis filtration, according to the amount of pure, preferably osmotized, water present in the storage and heating tank S1 , so as to begin even upon only reaching a level lower than SL _M AX (independently of the operating mode) and instead stop when a level SL _M AX defined as maximum has been reached. Subsequently, the control unit 100 provides for the determination, based on the information obtained from the aforesaid first temperature probe TT01 , first level probe LSL1 and conductivity probe C01 , of an amount of heat to be supplied to the pure, preferably osmotized, water in the storage and heating tank S1 , in order to reach a set temperature TSOL _TA RG or the setting of a water pumping command until arriving at pre-established volumes for the start-up of the dissolution process. Subsequently, the control unit 100 will permit the transfer of the pure, preferably osmotized, water heated in the hold-up tank S2 by enabling the opening of the valves EV2 and EV4.

The aforesaid second temperature probe TT02, second conductivity probe C02 and second level probe LSL02 are present in the hold-up tank S2, while a first refractometer Q01 is present.

Subsequently, the control unit 100 will allow the process of urea dissolution in water to take place by enabling the opening of the valves EV5 and EV6 to permit the entry of the pure water into the nanoemulsion system 5 and at the same time the control unit will regulate the entry of urea, preferably granular urea.

Preferably, the urea is placed in a loading hopper C1 , and the control unit 100 regulates the entry of urea by means of an adjustment screw C2, enabling the opening of the valve EV7 located at the base of a small hopper dedicated to accumulating part of the urea, preferably granular urea.

Alternatively, the control unit will regulate other apparatus suitable for loading a solid component with the characteristics of urea.

Mixing in the reactor is regulated by the parameters that arrive from these systems to the control unit 100, which is configured to ensure that the process takes place under optimal conditions such that:

At the start, in the point of junction between the inlet tubing for the pure, preferably osmotized, water and the inlet tubing for the urea, preferably granular urea, mixing of pre- established amounts of these solid and liquid components takes place thanks to the pump P3/M6 of the nanoemulsion system 5.

The entry of these two components is established and monitored both by a pump that regulates the access thereof and by a load cell.

Therefore, a first solution with a concentration of urea differing from the target one exits from the nanoemulsion system 5. This first solution is reintroduced into the hold-up tank S2 where it will be mixed with further pure, preferably osmotized, water.

The presence of the above-mentioned heating systems is provided for between the nanoemulsion system 5 and the hold-up tank S2.

The insertion, between the nanoemulsion system 5 and the hold-up tank S2, of an additional solution stirrer M7 similar to the previous one may also be provided for.

During the dissolution process the temperature is monitored and, consequently, heat is supplied to maintain the mixture within a predefined temperature range;

The process continues iteratively with the addition of pure water and urea in such a way as to maintain the optimal conditions. Maintaining the optimal conditions means having a balance between the temperature of the mixture, the heat to be supplied to the mixture and stirring.

It should be taken into consideration that, since the entry of urea and pure water is pre- established, it is possible to predict the temperature conditions and concentration of urea in the solution over time. This means that the machinery can proceed in an almost identical manner in the various operating batches provided that the previously defined parameters are maintained (for example the temperature of the pure water in the heating tank or the type of urea solution produced).

During the recirculation of the solution there will thus be an increase in the concentration of urea in the solution until the target concentration is reached and the loading of urea is interrupted.

The dissolution process ends when the complete dissolution of the urea has been reached and the correct concentration thereof in the aqueous solution comprising water and urea has been obtained; it will then be possible to define this amount as certified.

A preferred embodiment of the plant for the production of urea in aqueous solution of the present invention will now be described.

In a preferred embodiment of the invention, the control unit 100 is configured to receive the measured concentration value CONC and to set 100_1 the variation AT _S oi_ of the adjustable solution temperature T _S oi_ so as to modify the measured concentration value CONC until arriving at the target concentration value CONCTARG at a target solution temperature TSOL _A R _G , such that 17°C<TSOL _JA R _G <30°C.

Preferably, the first adjustment means M H20 and the second adjustment means M urea are controlled by the control unit 100 (fig. 1 and 2). Preferably, the control unit 100 is contained in the housing provided to contain the plant of the invention.

Alternatively, the control unit 100 is located remotely from the plant of the invention.

In the course of the present description and in the subsequent claims, the control unit 100 is logically divided into distinct functional modules (memory modules or operating modules) which perform the functions described, in particular with reference to figure 2.

The control unit 100 can consist of a single electronic device, suitably programmed to perform the functions described, and the different modules can correspond to hardware entities and/or routine software forming part of the programmed device.

Alternatively, or in addition, said functions can be carried out by a plurality of electronic devices over which the aforesaid functional modules can be distributed.

The control unit 100 can further rely on one or more processors to execute the instructions contained in the memory modules.

The aforesaid functional modules can also be distributed over various local or remote computers based on the architecture of the network they reside in.

With particular reference to figures 1 and 2, the control unit 100 is configured to 100_1 determine the variation AT _S oi_ of the adjustable solution temperature T _S oi_ _.

The control unit 100 determines the variation AT _S oi_ by setting the heat to be supplied to the nanoemulsion system (5), such that

Pi _t (kcal) = q _ia (kcal) = m _C 4N02in(kg) k _u (kcal/kg)

In other words, with particular reference to figure 2, the control unit 100 comprises a temperature setting module 100_1 configured to 100_1 determine the variation AT _S oi_ of the adjustable solution temperature T _S oi_ by setting the heat supplied to the nanoemulsion system (5), such that q _if (kcal) = q _ia (kcal) = m _C 4N02in(kg) k _u (kcal/kg). The control unit 100 is further configured to 100_2 control the water treatment apparatus lmp_H20 for the production of pure water, lmp_H20, said treatment apparatus preferably being a reverse osmosis filtration apparatus and said pure water preferably being osmotized water, by setting a variation DT _H 2o of the adjustable temperature of pure water T _H 2o, starting from a predefined initial value T _PRED .

The control unit 100 is thus configured to 100_2 activate the first heating means R1 , R2 so as to set the variation DT _H2 o which determines the variation DT ₃ oi_ of the adjustable solution temperature T _S oi_ in order to reach the target adjustable solution temperature TSOL _A R _G ·

In other words, with particular reference to figure 2, the control unit 100 comprises a pure water temperature variation module 100_2 configured to set a variation DT _H 2o of the adjustable water temperature T _H 2o, starting from a predefined initial value T _PRED , SO as to determine the variation DT ₃ oi_ of the adjustable solution temperature T _SOi _ in order to reach the target adjustable solution temperature TSOL _A R _G ·

The pure water temperature variation module 100_2 determines the variation DT ₃₀ i_ of the adjustable solution temperature T _SOi _by setting a value of the amount of heat to be supplied to the plant for the production of osmotized water (lmp_H20) q _h (kcal/min)=(m _H 20i _n (kg)-( TSOL _TARG -T _H 20i _n )( ^o C)-1kcal/ ^o C-kg-min)+q _p0th ^* (kcal/min)

In other words, the invention, by means of the control unit 100, calculates the heat to be supplied to heat the pure water (q _h ) with the aim of maintaining the temperature constant at the set value.

In one embodiment of the invention, it is envisaged that the pure water necessary is introduced into the nanoemulsion system all at once.

In an alternative embodiment, it is envisaged that an initial amount of water is introduced into the nanoemulsion system and water is added over time until arriving at the desired amount necessary for the dissolution process.

In one embodiment, it can be necessary to heat the water before adding the urea.

In an alternative embodiment, urea can be introduced right from the start and the cooling can be compensated for by heating the mixture.

If the water is not made to enter all at once but rather has an entry that is prolonged over time, it should be considered that it will be necessary to supply heat in order to also enable the water to reach the set temperature, preferably in a range of between 17° and 30°, more preferably in a range of between 19° and 25°, the optimal value substantially being 20°. q _h (kcal/min)=(m _H 20i _n (kg)-( TSOL _A RG -T _H 20i _n )(°C)-1kcal/°C-kg-min) +q _poth ^* (kcal/min)

^* The heat capacity is added only if T< TSOL _A RG

The heat capacity q _h (q _poth ) represents the amount of heat that can be exchanged by the selected heating system, established specifically for q _h (it thus does not represent the maximum potential heating of the plant).

If there is no incoming water, q _h will consist solely of the heat capacity of the plant and only until the temperature is reached, after which q _h will be equal to 0.

The control unit 100 can set the amount of incoming pure water at a value of zero in several cases:

- in the case where the entry of water is not constant, but is rather defined by an operator or

- in the case where it is desired to have the water present in the reactor reach the target temperature before adding urea.

The control unit also calculates the excess heat (q _c ) that has been supplied to the plant and leads to excessive heating.

If excess heat has been supplied, and thus the temperature is higher than the target temperature (TSOL _TARG ), in the subsequent period no heat will be supplied or a smaller amount of heat will be supplied until an equilibrium is reached. q _c (kcal/min)=m _t0t (kg)-(T- TS0L _TARG )( ^o C)-1 kcal/ ^o C-kg-min)

The control unit 100 separately calculates the amount of heat to be supplied to the nanoemulsion system and then determines the sum thereof as q _tot : q _t ot=qf+qh - (k _d ^c) where K _d represents a decrease coefficient, i.e. a value, expressed in percentage, that is used in the event that it is desired to decrease the contribution of q _c (in some cases preventing q _ot from becoming negative).

The control unit 100 is further configured to 100_3 adjust the concentration CONC in the nanoemulsion system 5 as a function of the degree of dissolution Deg_Diss.

In particular, the adjustment of the concentration CONC in the nanoemulsion system 5 is performed in real time.

The adjustment comprises a variation in the volume 100_3A of urea in the given adjustable volume V _urea and a variation in the volume 100_3B of the osmotized water H20 in the given adjustable volume of pure, preferably osmotized, water V _H 2o, so as to determine the variation AT _SO L of the adjustable solution temperature T _S oi_-

In other words, with particular reference to figure 2, the control unit 100 comprises a volume variation module 100_3 comprising in turn a urea volume variation sub-module 100_3A and a water volume variation sub-module 100_3B.

The plant of the invention thus supplies heat whenever urea is added, but it can also be developed so as to give constant heat if the addition also takes place in a constant manner. As the flow rate of the feed screw or of other analogous systems is known (rhCH4N20, measured in kg/min), the software calculates the amount of heat to be supplied constantly to the plant (q _f , measured in kcal/min) in order to maintain a constant temperature and avoid supplying excess heat. For example: q _f (kcal/min) = q _a (kcal/min) = mCH4N20(kg/min)-(k _u (kcal/kg)

Finally, the parameters in terms of the concentration of urea (CONC _TA R _G ) and mass (m _targ ) it is desired to reach are also provided to the control unit 100.

If the mass in the reactor has reached the desired value, the process is interrupted. Otherwise, the concentration is adjusted over time so as to enable the mixture to reach and maintain the pre-set value; to this end a calculation is made of the concentration over time and if the latter reaches the pre-set value, the entry of water and urea will start to be balanced (and consequently the heat supplied will vary).

In particular, the software for regulating the concentration of urea balances the entry of water while the loading of urea is interrupted at the same time.

The formula that regulates the entry of water into the reactor at every minute is in fact the following:

If CONC CONC _A R _G m _H 20i _n (kg)=rhFI20(kg/min)-1 min

If CONC>CONC _A R _G m _H 20in(kg)=(m _C H4N2o(kg)-k _r ) — m^o (kg) where K _r represents the coefficient of the ratio between urea and water, which is dependent on the concentration of urea it is desired to reach in the mixture: According to the invention, the control unit 100 is further configured to 100_4 actuate a second heating means (7), previously described, in order to determine the variation ATSOL of the adjustable solution temperature TSOL.

In other words, with particular reference to figure 2, the control unit 100 comprises an actuation module 100_4 configured to actuate a second heating means (7) in order to determine the variation ATSOL of the adjustable solution temperature TSOL.

EXAMPLE EMBODIMENTS

One example of how the control unit is capable of acting and regulating the amount of heat supplied is represented in the graphs below (figures 4, 5 and 6).

The most important parameters have been indicated in the graphs: the mass of water present in the nanoemulsion system (5) (m _H 2o tot), the mass of urea present in the nanoemulsion system (5) (m _C H4N2o tot), the concentration of urea (CONCCH4N2O), the temperature inside the reactor (Temperature), the heat absorbed by the urea introduced (q, _a ) and the total heat supplied (q _tot ).

The first example in figures 4 and 5 represents the case with a fixed initial volume of water, to which granular urea was added over time.

In the first example case (Fig 4) a fixed volume of water of 67.5 kg was set, to which granular urea was added over time with a flow rate of 1 kg/min, a reaction temperature (TSOLTARG) of 20°C, a heat capacity of 50 kcal/min, a target concentration of 32.5% by weight and a target mass of 101 kg and, finally, T _H 2o i _n was set at 10°C (the entry of water taking place only to balance the concentration of urea).

In the graph it is possible to see that for the first 20 minutes, heating of the pure water present in the tank S1 takes place.

The initial temperature is equal to 5°C; 50 kcal (the heat capacity) are supplied every minute until a temperature of 20.5°C is reached at the 21st minute.

At this point, given that the threshold temperature TSOL _ARG has been exceeded, the entry of urea begins, and it is possible to see a decrease in the heat supplied in order to slightly lower the temperature, which is just above TSOL _targ .

In this case K _d is equal to 100%.

In fig. 5, by contrast, k _d is equal to 25% to show the difference; in this case, K _d causes only the total heat to vary.

Up until around 55 minutes it is possible to see the increase in mass and in the concentration of urea until the desired concentration of 32.5% by weight is reached.

Until this occurs, the heat supplied is equal to that absorbed by the urea, after which both decrease. In the last minutes it is possible to see an increase in the mass of water; this is due to the compensation that took place to ensure that the concentration was exactly 32.5% by weight.

Considering, in fact, that the initial mass of water is 67.5 kg and that the urea flow rate is 1 kg/min, it is predictable that, with the passage of the total urea from 32 to 33 kg (out of a total of 100.5 kg), the concentration will exceed the set threshold (32.8%); the software calculates how much water needs to enter in order to compensate and enables the entry thereof.

With the entry of new water, which is at a temperature below TSOL _TA RG, heat is supplied (on the basis of the temperature of the incoming water, T _H 20 _m )· The incoming water is equal to 1.038 kg and the final concentration of urea will have reached the desired value.

The second example shown in fig. 6 represents the case in which the volume of water increases over time.

In this case an initial volume of water of 67.5 kg, a water flow rate of 1 kg/min, a urea flow rate of 2 kg/min and a target mass of 185 kg were set.

All of the other values remained the same, and in particular: a reaction temperature (TSOL _ARG ) of 20°C, a heat capacity of 50 kcal/min and a target concentration of 32.5% by weight, whereas T _H 2o i _n was set at 10°C.

As may be seen, the main difference lies in the fact that more heat is supplied; for example, in the initial phase of heating of the starting amount of water, 60 kcal a minute are supplied, that is, 50 kcal of heat capacity and 10 kcal needed to bring the incoming water to the reaction temperature (in fact, 10 kcal are needed to bring 1 litre from 10°C to 20°C). At around 50 minutes it is possible to see that the concentration has reached the pre- established values and at this point the entry of urea and water is balanced, as is, consequently, the amount of heat supplied.

Going back to the description of the control of the plant of the invention, according to the invention the control unit 100 is coupled to a user interface 101 (fig.2) configured for the entry of control parameters INPIITJ for the plant of the invention.

The user interface 101 is configured to select, in a simple and clear manner, among the different types of urea solution. The software is integrated in an Internet Of Things framework.

Preferably, the graphic interface 101 is provided with a touchscreen. When a control device connected to the control unit 100 is switched on, on the user interface 101 the operator will be shown a screen, defined “Home”, in which the main and secondary selections are available. With specific reference to figures 7 and 8, the main selections appear in a larger size than the secondary selections.

Among the main selections it is possible to choose the final concentration of urea desired CONC ARG-

Two selection modes are possible: a “graphic” version (Figure 7), in which it is possible to select from among the different predefined types of AdBlue (for example for transport by ship) and a “minimal” version (Figure 8), in which it is possible to choose on the basis of the percentage by weight of urea (32.5%, 40% or 45%).

In general, every concentration of urea is selectable by means of the plant of the invention.

In the “graphic” version, in order to make the interface immediately understandable, the end users are represented in a stylised fashion (for example an icon of a stylised train for the option of AdBlue for rail transport).

It is possible to change the selection mode by means of the Options menu.

Various options are provided among the secondary selections: parameters, options, alarms and stop.

The secondary options have been developed for the purpose of entering into the details of the process and enabling the monitoring and, should it be necessary, the editing of some process parameters.

The control unit 100 is configured to execute the steps of the dissolution process automatically and eliminate the need for the constant presence of personnel dedicated to controlling the operation of the plant.

It is sufficient to have an operator who takes care of switching on the system and selecting the type of product it is desired to obtain; the control unit 100 is capable of reading, monitoring, managing and reporting the parameters in real time.

Once the operator has selected the type of AdBlue to be produced, the control unit 100 establishes the actions to be undertaken, leaving only the secondary options displayed on the interface 101 (Figure 9).

In particular, with specific reference to figure 9, the possible secondary options are:

- Parameters: it allows the operator to monitor the parameters measured by the probes in real time. These parameters include the temperature, weight, volume, pressure, purity of the pure, preferably osmotized, water and concentration of urea in the mixture (percentage concentration by weight).

The parameters are divided by plant section (tank of pure, preferably osmotized, heated water, dissolution reactor and every other further section provided for).

The parameters are displayable as real-time data or also by means of graphs which enable an assessment of the variation thereof over time.

In “Parameters” it is also possible to understand the step currently being performed by the machines (for example, it is signalled that the step of heating the pure, preferably osmotized, water has been reached).

It is further possible to display the “history”, i.e. the trends in the previous processes memorised.

- Options: it allows the operator to edit some parameters or modify the display mode of the interface. It will be possible to edit some operating parameters so as to render them better suited to the process underway according to the operator’s wishes; for example, it will be possible to change the temperature value of the pure, preferably osmotized, water inside the heating tank.

Furthermore, the interface can be modified in order to adapt it to the personnel who will have to interact with it.

The options make it possible to select the selection mode for the primary options, either the “graphic” mode or the “minimal” mode.

It is also possible to choose the concentration of urea in the solution finale (aqueous solution comprising water and urea) on the basis of one’s wishes, without following the pre- established recipes (the control unit is capable of adjusting all the process settings accordingly).

It is also possible to modify the display so that it can be used by persons with different disabilities, for example visual disabilities such as low vision or colour-blindness.

- Alarms: this option gives a clear signal of when a parameter is outside a range considered reliable by the software.

It represents an indication for whoever is in charge of managing the plant, as the control unit is capable of acting autonomously. It is normally opaque, whereas when it is activated it warns the operator by changing colour, flashing and emitting an audible signal.

- Stop: this option allows the process to be brought to an immediate halt. At this point the machine will interrupt every process. This represents an emergency option.

Once the operator has made the main selection, the control unit 100 will be capable of regulating the dissolution process in the various steps thereof in reference to the previously described plant for the production of urea in aqueous solution.

An inventive plant for the production of urea in aqueous solution, according to the invention, has been described.

In a second aspect, the invention further describes a method for producing urea in aqueous solution SOL, comprising the steps of

- producing pure water H20 in a given adjustable volume of water V _H 2o;

- providing a storage and heating tank S1 for the pure water H20;

- providing a nanoemulsion system 5 in fluid connection with the storage and heating tank S1 ;

- loading urea into the nanoemulsion system 5 in a given adjustable mass mJJREA;

- loading the pure water H20 in a given adjustable volume of water V _H2 o,

- in said nanoemulsion system 5, mixing the urea and the pure water H20 at a given adjustable water temperature T _H2 o, thereby determining urea in aqueous solution SOL at an adjustable solution temperature T _S oi_ and at a concentration CONC of urea;

- bringing about a dissolution of the urea in aqueous solution SOL;

- measuring a concentration CONC of urea in the solution SOL, wherein said concentration CONC of urea varies as a function of a degree of dissolution Deg_Diss of the urea in the solution SOL;

- setting a variation DT _d oi_ of the adjustable solution temperature T _S oi_ such as to modify the measured concentration value CONC until arriving at a target concentration value CONCTARG at a target solution temperature TSOLTARG, such that 17°<TSOLTARG<30°.

Further steps of the method of the second aspect of the invention coincide with the described corresponding functions of the components of the plant for the production of urea in aqueous solution according to the first aspect of the invention. The invention, as described, achieves the following technical effects:

-efficient production of urea in aqueous solution in operating units of limited size.

-assurance of an efficient production of urea in aqueous solution of guaranteed quality, i.e. with a guaranteed percentage of urea;

-assurance of an efficient production of urea in aqueous solution in line with environmental requirements, in operating units of limited size;

-production of urea in aqueous solution in a more efficient and safer manner than occurs in the large plants of the prior art;

- production of urea in aqueous solution in a more efficient and safer manner than occurs in the small plants of the prior art;

-production of urea in aqueous solution in plants that are less complex to construct and control compared to the prior art;

-production of urea in aqueous solution with real-time control of the process parameters and uploading to a database correlated to the production batch to allow complete traceability; -possibility of completely remote management and control of production, also through the use of a dedicated application;

-production of urea in aqueous solution in a transportable system;

-efficient production of urea in aqueous solution with reduced production costs and consequently reduced costs for the end user; -production of urea in aqueous solution to enable a reconditioning, a surface treatment and an improvement in the performance of post-combustion systems, SCR and SNCR systems, exhausts and other components coming into contact with combustion gases.