DEVICE AND METHOD FOR MEASURING THE LIQUID LEVEL IN AN APPARATUS.

Abstract

Device (3) for measuring the level of process liquid in a pressurized apparatus (1), in particular, an apparatus of a urea plant, comprising a radar instrument (18); a waveguide probe (19) for transmitting microwaves, defined by a solid rod body (26); and a confinement cover (20) disposed around at least a measuring portion (28) of the probe (19) submerged at least partially during use in the process liquid; the cover (20) is disposed above the probe (19) and along the measuring portion (28) of the probe (19) to surround the probe (19) on the outside and be radially separated from a lateral surface (31) of the probe (19).

Description

DEVICE AND METHOD FOR MEASURING THE LIQUID LEVEL IN A APPARATUS A / C / ZUZO / UUO 130 CROSS-REFERENCE WITH RELATED APPLICATIONS This patent application claims priority over Italian patent application no. 102020000017122 filed on July 15, 2020, the full description of which is incorporated herein by reference. FIELD OF INVENTION The present invention relates to a device and a method for measuring a liquid level in an apparatus, in particular a pressure apparatus and more precisely an apparatus of a urea plant. The invention finds a preferred application, in particular, in apparatus that forms part of a high-pressure section of a urea production plant (urea plant), such as a urea synthesis reactor, a high-pressure stripper, a high-pressure carbamate separator, etc. BACKGROUND OF THE INVENTION Measuring the level of a fluid in high-pressure urea production equipment is normally It is carried out using nucleonic (radioactive) or radar instruments. The operating principle of nucleonic instruments is based on the measurement of radiation emitted by a nuclear source that is not absorbed by the fluid whose level is measured in the devices. Typically, a nucleonic instrument has a emitting unit (source), installed inside a special container (called a dry spot) housed inside the apparatus whose level is to be measured and consists of a wire or a series of point sources distributed longitudinally so that they emit radiation along the measuring field, and a receiving unit (detector) installed outside the apparatus and generally consisting of one or more receivers. Radioactive instruments, in general, provide satisfactory performance in terms of reliability and resolution (i.e., the least appreciable variation with respect to the quantity under review over the entire measurement interval). However, given the position of the source and the receivers, the measurements made with such instruments are greatly influenced by the thickness of the walls of the apparatus (in the specific application of the 25 high-pressure apparatus of a urea plant, as is, in general, the case of apparatus that operate at high pressure, relatively large wall thicknesses are required) and by the geometry of the apparatus. Therefore, when the apparatus has thick walls and / or complex geometry, measurements with low resolution are obtained. This is the case, for example, of the stripper in the high-pressure section of a urea plant (i.e., the apparatus in the high-pressure section of a urea plant located downstream of the urea synthesis reactor where the carbamate is decomposed), which typically has a complex shape (in particular, a lower cylindrical portion that protrudes internally from a hemispherical dome) right at the bottom of the apparatus, where the 1í qu idoa medir. Due to the geometric complexity and in particular the variations in diameter at the bottom of the apparatus and also the large thickness of the steel walls of the apparatus, the measurement resolution is very poor 20 precisely in the low level zone, i.e., where the liquid level is normally maintained while the system is running and which needs to be measured. Other problems and technical disadvantages of radioactive meters stem from: - the need for sources of high radioactivity A / C / ZUZO / UUO 130 due to the great thickness of the devices and the complexity of their geometry; - the need to confine the radioactive sources to ensure an adequate level of safety for the 5 operators; - the user's need to comply with applicable legal requirements for the introduction, handling and disposal of radioactive materials. As an alternative to measurement with nucleonic (radioactive) instruments, it is known that level gauges based on radar technology are used. This type of measurement is carried out by sending microwave pulses, generated by a transmitter, to the liquids whose level is to be determined. When a microwave pulse reaches the liquid phase, which has a different dielectric constant than the gas phase, part of the pulse is reflected back to a receiver. The time difference between the transmitted and reflected pulses is converted into distance, from which the liquid level is then calculated. The intensity of the reflection depends on the dielectric constant of the liquid whose level is being measured: the higher the value of the dielectric constant, the more intense the reflection. Typically, the solution developed for high-pressure urea apparatus involves the use of a tube (called a riser tube) connected at one end to a microwave transmitter and at the other end submerged in the liquid whose level is to be measured. The liquid penetrates the tube. The function of this tube is to guide the microwaves emitted by the transmitter (guided wave radar) into the process fluid. Such a solution is shown, for example, in document WO2013 / 036108A1. However, configurations of the type described (with a waveguide defined by a vertical tube, i.e., a hollow tube) present additional problems, in particular: difficulty in detecting the reflected pulse that determines the measurement of the process fluid level within the confined volume of the vertical tube, especially when the process conditions are supercritical, i.e., when the fluids have properties intermediate between those of gas and liquid (as, for example, in the case of a urea reactor) and, therefore, little differentiation between the dielectric constants of the phases; - difficulty in detecting the free liquid surface within the confined volume of the vertical tube, accentuated by turbulent conditions, for example, during the chemical reaction of urea synthesis; A / E / ZUZO / UUO 130 - the appearance, inside the vertical tube, of crystallization and corrosion phenomena in the liquid phase typical of a high-pressure urea environment; delay and discrepancy in measurement when the volume change is abrupt due to the reduction of the communication area between the inside and outside of the vertical tube; - complexity of the design and construction of the sealing system because the 10 microwave transmission antenna is in direct contact with a process environment characterized by high temperatures and pressures and high chemical aggressiveness. To overcome these problems, at least in part, there are commercially available systems in which the radar signal is transmitted through a waveguide in the form of an elongated solid rod (and not an internally hollow tube), with the lower end submerged in the liquid. An example is described in document WO2019 / 096623A1. However, using a solid rod as a waveguide has some drawbacks. First, since the level measurement is carried out under dynamic conditions, i.e., a certain amount of liquid flows continuously into and out of the device, the measurement is affected by 52 / 1810 / 23 A / C / ZUZO / UUO 130 fact that the liquid flowing from the top to the bottom of the apparatus (cone, for example, in the case of the high-pressure scrubber of the urea plant) falls on the waveguide, altering the signal in transit along the waveguide and therefore the accuracy of the measurement. Furthermore, the use of solid waveguides immersed in process liquid results in some dispersion of the measurement signal and the signal reflected in the surrounding environment. SUMMARY OF THE INVENTION An objective of the present invention is to provide a device and method for measuring a liquid level in a pressurized apparatus, in particular, an apparatus of a urea plant, which is practically free from the drawbacks evidenced in this document with respect to the known art; in particular, an objective of the invention is to provide a measuring device and method that allow the use of a radar instrument (thus avoiding the use of radioactive materials) and at the same time provide high resolution and accuracy in the level measurement. Thus, the present invention relates to a device and a method for measuring a liquid level in a pressurized apparatus, in particular a pressurized apparatus of a urea plant, as defined respectively in essential terms in appended claims 1 and 16. The invention also relates to a pressurized apparatus, in particular, an apparatus of a urea plant, as defined in claim 14. Other preferred features of the invention are indicated in the dependent claims. The measuring device of the invention makes it possible to solve the technical problems of traditional solutions, allowing reliable and accurate measurements of the level of process fluids in high-pressure urea apparatus. The device of the invention employs a radar-type instrument and a probe that functions as a waveguide to guide microwaves into the process liquid: the probe is in the form of a solid rod (and not a hollow rod as in vertical tube systems) and is associated with a special confinement cover that covers and protects the probe from the process liquid. In this way, the measurement is always accurate and reliable, even under dynamic conditions (i.e., even if a certain amount of liquid continuously enters and exits the device, directly impacting the measuring probe): in fact, the cover, made of a material suitable for the process conditions, protects the probe (the waveguide that transmits the microwaves) from the liquid flowing from top to bottom, preventing contact with the falling liquid from altering the measurement. The cover, also made of conductive material (like the probe) and electrically connected to the probe, also serves to minimize the dispersion of the measurement signal and the signal reflected in the surrounding environment, ensuring a significant improvement in the measurement. 0 At the same time, the device of the invention is not affected by any rapid change in the level of the liquid to be measured or turbulence due to vapor generation, since the measurement is carried out in an open environment and not in a confined space as in application 15 of a vertical tube. The device and the measuring method according to the invention thus make it possible to perform a level measurement that: - It is direct and does not require compensation for 20 variable process conditions (i.e., density, conductivity, temperature, and pressure); - it is independent of the geometry of the device; - occurs in the absence of radioactive materials and therefore without all the problems associated with the use of radioactive materials; 52 / 1819 / 23 A / C / ZUZO / UUO I DO - It has a simple and reliable sealing system; - It is reliable even under turbulent conditions, in supercritical phases, and with an aggressive process fluid that tends to crystallize. BRIEF DESCRIPTION OF THE DRAWINGS Other features and benefits of the present invention will become apparent from the following description of a non-limiting example of one embodiment thereof, with reference to the figures in the accompanying drawings, in which: - Figure 1 is a schematic view of a longitudinal section of a portion of the lower end of a pressurized apparatus, in particular a high-pressure stripper of a urea plant, provided with a measuring device for measuring a liquid level according to the invention; - Figure 2 shows a variation of the measuring device shown in Figure 1; - Figure 3 shows another variant of the measuring device shown in Figure 1; - Figure 4 shows a cross-section detail, according to the plan of strakes IV-IV of Figures 1, 2 and 3, of the device of the invention; - Figure 5 shows another mode of the device 52 / 1812 / 23 of the measuring invention; - Figure 6 shows a cross-section detail according to the VI-VI trace plane of Figure 5; - Figure 7 shows an enlarged detail of the measurement of the device in Figure 5. DETAILED DESCRIPTION OF THE INVENTION Figure 1 shows a pressurized apparatus (1), in particular a high-pressure scrubber (stripper) of a urea plant, of which only a lower part is illustrated (2). The apparatus (1) is provided with a measuring device (3) for measuring the level of a process liquid that is collected at the bottom (2) of the apparatus (1), 15 where the liquid reaches a free surface H (which, it is assumed, here and henceforth, to be substantially horizontal in the absence of turbulence). Although in the example described and illustrated herein the apparatus (1) is a scrubber, the measuring device (3) of the invention is also applicable in other apparatus, for example (though not necessarily) in other apparatus of the high-pressure section of a urea plant, in particular, such as a urea synthesis reactor, a carbamate separator, or a carbamate condenser. It is also understood that the measuring device (3) of the invention can be used not only in apparatus of the high-pressure section but also in apparatus of other sections of a urea plant. In general, the measuring device (3) of the invention can be used in various apparatuses, even outside the urea production industry. The apparatus (1) extends along a longitudinal axis A (usually vertical during use) and comprises a housing (4) having a side wall (5), arranged around axis A and delimiting an internal process chamber (6). The housing (4), starting from a lower end (7) of the apparatus (1), comprises: a substantially cylindrical end portion (8), enclosed by a lower wall (9), located at the end (7); a dome-shaped (e.g., substantially hemispherical) intermediate portion (10), located above the end portion (8); and a substantially cylindrical main portion (11), positioned above the intermediate portion (10) and having a diameter ID1 greater than the diameter ID2 of the end portion (8). During normal operation of the apparatus (1), the housing (4) contains, in particular in the lower end part (2), a certain amount of a process liquid, 52 / 1810 / 23 which in the present case (high pressure scrubber of a urea plant) flows from the top to the bottom of the apparatus (1) and is collected in the process chamber (6) reaching a level defined by free surface H; the level of the process liquid in the apparatus (1) is variable during the operation of the apparatus (1), hence the need to measure this level and monitor its changes over time. The end portion (8) is provided with an outlet duct (12), arranged, for example, through the side wall (5) of the housing (4) and bent into an elbow shape towards the bottom wall (9). The measuring device (3) comprises: a radar instrument (18) having a microwave emitter 15 and a microwave receiver, in particular, capable of emitting and / or receiving microwaves with a frequency between 100 MH and 1.5 GHo; a waveguide probe (19) for transmitting microwaves; and a confinement cover (20) associated with the probe (19) serving to protect the probe (19) from the process liquid falling into the apparatus (1) and to minimize the dispersion of the probe (19) signal. The radar instrument (18) is arranged outside the housing (4) and oriented towards a nozzle (21), to which it is connected. The nozzle penetrates the housing (4) through the side wall (5) and is joined to the housing (4), for example, by means of a flange coupling (already known and not illustrated). The radar instrument (18) is connected and secured to the nozzle (21) by means of a connector (22). The radar instrument (18) and its associated nozzle (21) 5 may be located at different levels of the apparatus (1 ). In general, the radar instrument (18) is located in the apparatus (1) at a level, measured parallel to axis A, above the maximum level of the process liquid to be measured 10 in the apparatus (1). In the example shown in Figure 1, the radar instrument (18) and the nozzle (21) are arranged in the main (cylindrical) portion (11). Alternatively, and also depending on the effective size of the apparatus (1), the radar instrument (18) and the nozzle (21) are arranged in the intermediate (dome-shaped) portion (10). The nozzle (21) is arranged substantially transverse to axis A, through the side wall (5). In the second embodiment of Figure 1, although not necessarily, the nozzle (21) is substantially perpendicular to axis A and substantially horizontal. Beneficially, the radar instrument (18) integrates a transmitter and a receiver, located within the radar instrument (18) itself. 52 / 1819 / 23 The probe (19) enters laterally into the apparatus (1) and in particular into the interior of the process chamber (6) through the nozzle (21) and extends between two opposite ends (24), (25) and in detail: a proximal end (24) connected to the radar instrument (18) and a distal end (25) placed inside the process chamber (6) near the lower wall (9) to be immersed during use in the process liquid. The proximal end (24) of the probe (19) is coupled to the radar instrument (18) by means of the connector (22), which also functions as a sealing element around the probe (19). The probe (19) has a solid rod body (26), made entirely or at least in the portion that is intended to be immersed in the process liquid during use, of a conductive material, in particular a metallic material, capable of transmitting throughout the A / C / ZUZO / UUO IUO rod body (26) the microwaves generated by the radar instrument (18) and reflected towards the radar instrument (18). The rod body (26) of the probe (19) is made of a material suitable for use in the process conditions in which the measuring device (3) is used, i.e., depending on the apparatus (1) in which the measuring device (3) is mounted. For example, in the illustrative case described in this document, the rod body (26) is made of a material suitable to withstand the typical conditions of a urea environment, for example, stainless steel (urea grade 316L), titanium, zirconium, or duplex or super duplex steel, preferably with a composition of 25Cr / 22Ni / 2Mo. The rod body (26) extends along a longitudinal profile that can have various shapes and different lengths, also depending on the size and type of apparatus (1). In general, the probe (19) (i.e. its rod body (26)) comprises an upper connecting portion (27), which extends from the proximal end (24) (connected to the radar instrument (18)) and penetrates the apparatus (1) through the nozzle (21); and a lower measuring portion (28), which during use is submerged, at least partially, in the process fluid and terminates at the distal end (25). The connection portion (27) and the measuring portion 20 (28) can be oriented or arranged in various ways. For example, in the modality of Figure 1, the rod body (26) of the probe (19) follows a longitudinal L-shaped profile: the connecting portion (27) and the measuring portion (28) are straight and substantially orthogonal to each other and joined by a curved assembly portion (29); the connecting portion (27) extends radially into the apparatus (1) substantially orthogonal to axis A, and the measuring portion (28) extends parallel to axis A. In this configuration, the measuring portion (28) (which defines the part of the probe (19) submerged in the process liquid) is submerged in the process liquid in an axial direction, i.e., it extends parallel to the axis A 10 (vertical) of the apparatus (1) and perpendicular to the free surface H of the process liquid (it is understood, as already stated above, that it is in the absence of turbulence). The rod body (26) can have a different cross-sectional shape, for example, circular (as shown in Figure 4) or in the shape of a regular polygon (square, hexagonal, etc.). Preferably, the rod body (26) has a constant cross-section along the entire length of the rod body (26). For example, the rod body (26) has a circular cross-section and a diameter between 5 and 30 mm (preferably about 20 mm). The probe (19) is mechanically supported by the connector (22) and / or support elements (known, not shown), for example, placed in the nozzle (21) and / or on the wall (5). With reference to Figures 1 and 4, the cover (20) is arranged around the probe (19) and in particular, 5 around the rod body (26) of the probe (19) and extends along the probe (19) following its longitudinal profile, the shape of which it replicates. The cover (20) surrounds the probe (19) on the outside and is radially separated from a lateral surface (31) of the rod body (26). The cover (20) has a longitudinally open cross-section so that it only partially surrounds the probe (19) at an angle. In other words, the cover (20) is open around the probe (19) and is not closed in a ring around the probe (19), leaving a longitudinal opening (32) facing the lateral surface (31) of the rod body (26). In this way, the formation of liquid stagnation zones is avoided and it is possible for the gaseous phase 20 present in the apparatus (1) to pass through it. The opening (32) is laterally delimited by a pair of opposing longitudinal edges (33) of the cover (20), opposite and parallel to each other (Figure 4). The cover (20) has a concave internal lateral surface (34) oriented towards the lateral surface (31) of the A / C / ZUZO / UUO 130 rod body (26) of the probe (19) and a convex inner lateral surface (35) opposite the concave inner lateral surface (34). Preferably, the cover (20) extends around the probe (19) in an angular dimension of at least 120° and less than 360°, between approximately 150° and 250°. For example, the cover (20) has a cross-section in the shape of the arc of a circle or the arc of an ellipse, parabola or other conical shape. In the modality shown in Figure 1, the cover (20) extends from the proximal end (24) of the probe (19), where the cover (20) connects to the nozzle (21), to the distal end (25), where the probe (19) optionally protrudes from the cover (20) with a short end section. It is understood that the cover (20) can be extended further to a different length than the probe (19). The cover (20) is positioned so that the inner side surface (34) faces the side surface (31) of the probe (19). The cover (20) is positioned above the probe (19) so that it completely covers the vertical projection of the probe (19), i.e., the projection of the probe (19) onto a horizontal plane parallel to the free surface H of the process liquid and perpendicular to axis A. A / E / ZUZO / UUO 130 In particular, the cover (20) is located above the connection portion (27) and the assembly portion (29), to protect the probe (19) from the process liquid flowing in the apparatus (1) from top to bottom; and is arranged next to the measuring portion (28). The cover (20) is also made of a material suitable for use in the process conditions of the apparatus (1). In particular, the cover (20) is made of a conductive material, in particular a metallic material, preferably a material of the same type as that of the probe (19) or of the same material. The cover (20) is mechanically and electrically connected to the probe (19) by means of tie rods (37) 15 that extend, for example, radially between the inner lateral surface (34) of the cover (20) and the lateral surface (31) of the probe. The braces (37) are arranged, for example, at the ends (24), (25) and / or spaced apart along the 0 cover (20 ) . The braces (37), in addition to mechanically supporting the cover (20) and keeping it in position with respect to the probe (19), also make the electrical connection between the cover (20) and the probe (19). Appropriately, the suspenders (37) are made A / C / ZUZO / UUO 130 of the same material (or a material of the same type), in particular, a metallic material, than the cover (20) (and / or 2 to probe (19)). During use, when implementing the measurement method of the invention, the measuring device (3) works in the following manner. The radar instrument emitter (18) emits microwave pulses that travel along the probe (19) through the rod body (26) to the process liquid contained in the apparatus (1). The microwave pulse is reflected when it reaches the interface between the liquid and gas phases (i.e., the free surface H), which has different dielectric constants. The reflected pulse is then transmitted from the probe (19) to the radar instrument receiver (18). The liquid level contained in the apparatus (1) is calculated by converting the time difference of the transmitted and reflected waves into distance, in particular, by DDR (time domain reflectometry). The calculation is carried out, for example, by a processing unit integrated into or connected to the radar instrument. In the embodiment of Figure 2, where details similar or identical to those already described are indicated by the same numbers, again, the probe (19) enters the apparatus 52 / 1819 / 23 (1) in a lateral position, in particular, through the nozzle (21). The probe (19) again comprises an upper connecting portion (27) and a lower measuring portion (28), which are straight and are joined by a curved assembly portion (29). The connecting portion (27) extends radially into the apparatus (1) and is substantially orthogonal to axis A; whereas the measuring portion (28) is inclined with respect to axis A and the free surface H of the process liquid (and not parallel to axis A and perpendicular to the free surface H, as described above with reference to Figure 1). The measuring portion (28) and the connecting portion (27) are inclined to each other at an angle greater than 90°, preferably between 120° and 180°. In this configuration, therefore, the measuring portion (28) is submerged in the process liquid at a certain inclination: the portion of the probe (19) submerged in the process liquid extends obliquely with respect to the axis e A of the apparatus (1) and the free surface H 20 of the process liquid. In this mode, as already described with reference to Figure 1, the probe (19) is also associated with a cover (20) that covers the probe (19). Again, in this case, the cover (20) is 25 arranged above the probe (19) to cover the vertical projection of the probe (19). In particular, the cover (20) is positioned above the connection portion (27), the assembly portion (29), and also the inclined measuring portion (28), to protect the entire probe (19) from the process fluid flowing in the apparatus (1) from top to bottom. The entire outer side surface (35) of the cover (20) faces upwards (although partially inclined), and the entire opening (32) faces downwards (partially inclined). In another embodiment of Figure 3, where details similar or identical to those already described are indicated by the same numbers, the nozzle (21) is again arranged through the side wall (5) of the housing (4), but instead of being perpendicular to axis A, it is inclined with respect to axis A and the side wall (5). In this case, the probe (19) is completely straight, that is, it has a perfectly straight rod body (26), and is aligned with the nozzle (21). The probe (19) thus extends along a straight axis inclined with respect to axis A. The connecting portion (27) and the measuring portion (28) are aligned with each other along a common straight axis inclined with respect to axis A and the free surface H of the process liquid. Therefore, the cover (20) also extends parallel to the probe (19) and straight, with the outer side surface (35) inclined and parallel to the probe (19) and oriented upwards. For example, the probe (19) is inclined at an angle between 30° and 60° with respect to axis A. In the modality of Figure 5, where details similar or identical to those already described are indicated with the same numbers, the probe (19) is inserted into the apparatus (1) 10 through the lower wall (9). The nozzle (21) is thus arranged through the lower wall (9) and the radar instrument (18) is arranged below the nozzle (21) and the apparatus (1). The probe (19), again, extends from the radar instrument (18), to which it is connected by means of the proximal end (24). In this case, the probe (19) has a profile that is bent at 180° and the rod body (26) of the probe (19) has a longitudinal U-shaped profile. In particular, the probe (19) comprises a connecting portion (27), which extends from the proximal end (24) connected to the radar instrument (18) and penetrates the apparatus (1) through the nozzle (21), and a measuring portion (28), which during use is at least partially immersed in the process fluid and terminates in the A / C / ZUZO / UUO 130 distal end (25). The connecting portion (27) and the measuring portion (28) are straight and substantially parallel to each other and with respect to the axis. They are joined by a U-shaped assembly portion (29). In this configuration, the measuring portion (28) (which is submerged in the process liquid) also extends parallel to the axis A (vertical) of the apparatus (1) and perpendicular to the free surface H of the process liquid. Also, with reference to Figures 6-7, the probe (19) is partially covered by a cover sleeve (40), arranged around the rod body (26) of the probe (19) on the lateral surface (31) of the probe (19). The sheath (40), as an option, is made of several pieces joined together, has a closed transverse section around the rod body (26) and covers the lateral surface (31) of the probe (19), being in contact with it. The sleeve (40) extends to cover mostly the connection portion (27) and the U-shaped assembly portion (29). In contrast, the sleeve (40) leaves at least part of the measuring portion (28) uncovered, so that it is exposed to the process liquid. The purpose of the sheath (40) is to isolate the rod body (26) of the probe (19) from the process environment at the connection portion (27) and is therefore made of an electrically insulating material capable of withstanding the 5 process conditions (in particular, the conditions of a urea environment), such as ceramic or polymeric materials, e.g. PTFE (polytetrafluoroethylene) or PEEK (polyether ketone). As in the previous description, the probe (19), 10 again, is associated, at least in the part exposed to the process liquid, with the cover (20). In particular, the cover (20) extends along the measuring portion (28), which it flanks laterally and is oriented as described above. 15 As an option, the cover (20) extends above the assembly portion (29). Again, in this case, the cover (20) is connected to the probe (19) by means of ties (37) that support the cover (20) and provide electrical continuity with the probe (19). Finally, it is understood that other modifications and variations may be made to the device and the measuring method described and illustrated herein, without deviating from the scope of the attached 25 claims. For example, according to other embodiments not shown, the probe (19) is inserted into the apparatus (1) from above, through an upper wall of the housing (4). Therefore, the nozzle (21) is arranged in the upper part 5 of the apparatus (1) and is appropriately parallel to axis A. In this case, as in the previous description referring to Figure 3, the probe (19) can be completely straight, that is, have a perfectly straight rod body 10 (26). The probe (19) thus extends along a straight axis and, consequently, the cover (20) also extends straight and parallel to the probe (19). The probe (19) can be substantially vertical and parallel to the axis Ά, with the cover (20) arranged in a lateral position next to the probe (19) and the inner lateral surface (34) oriented towards the lateral surface (31) of the probe (19); or inclined with respect to the axis A, with the cover (20) arranged above the probe (19), with the inner lateral surface (34) oriented towards and above the lateral surface (31) of the probe (19).

Claims

1. A device (3) for measuring a level of a process liquid in a pressurized apparatus, for example, 5 an apparatus of a urea plant, comprising a radar instrument (18) positioned during use outside the apparatus (1), having a microwave emitter and a microwave receiver; a waveguide probe (19) for transmitting microwaves, defined by a solid rod body (26) extending during use inside the apparatus (1) between a proximal end (24) attached to the radar instrument (18) and a distal end (25) immersed during use in the process liquid, below a free surface (H) of the process liquid; 15 and a confinement cover (20) disposed around at least a measuring portion (28) of the probe (19) immersed at least partially during use in the process liquid;The cover (20) is positioned above the probe (19) and along said measuring portion 20 (28) of the probe (19), so that it surrounds the probe (19) on the outside and is radially separated from a lateral surface (31) of the probe (19); the measuring device (3) is characterized in that the cover (20) has a longitudinally open cross-section, so that the cover (20) only partially surrounds the probe (19) angularly, leaving a longitudinal opening (32) oriented towards the lateral surface (31) of the probe (19); the cover (20) extends around the probe (19) with an angular dimension between 150° and 250°. 5; 2. The measuring device according to claim 1, wherein the cover (20) has a concave inner lateral surface (34) oriented towards the lateral surface (31) of the probe (19), and a convex outer lateral surface (35), opposite the concave inner lateral surface (34).

3. The measuring device according to one of the preceding claims, wherein the cover (20) is positioned above the probe (19) to completely cover a vertical projection of the probe (19), defined as the projection of the probe (19) onto a horizontal plane parallel to the free surface (H) of the process liquid, and thereby protect the probe (19) from the process liquid flowing in the apparatus (1) from top to bottom.

4. The measuring device according to one of the 20 preceding claims, wherein the cover (20) is made of a conductive material, in particular a metallic material, preferably a material of the same type or of the same material as the probe (19).

5. The measuring device according to one of the 25 preceding claims, wherein the cover (20) is mechanically and electrically connected to the probe (19) by means of tie rods (37) extending between the cover (20) and the probe (19).

6. The measuring device according to any one of the preceding claims, wherein the probe (19) comprises said measuring portion (28), which during use is submerged, at least partially, in the process liquid and terminates with the distal end (25), and a connection portion (27) connected to the radar instrument 10 (18) at the proximal end (24) of the probe (19).

7. The measuring device according to claim 6, wherein the connecting portion (27) and the measuring portion (28) are straight and substantially perpendicular to each other and are joined by a curved assembly portion (29); and wherein the connecting portion (27) extends radially in the apparatus (1) substantially perpendicular to a longitudinal axis (A), vertical during use, of the apparatus (1), the measuring portion (28) extends parallel to said axis (A); and wherein the cover (20) is positioned above the connecting portion (27) and the assembly portion (29) and laterally to the side of the measuring portion (28).

8. The measuring device according to claim 6, wherein the connecting portion (27) and the measuring portion (28) are straight and inclined to each other and are joined by a curved assembly portion (29); and wherein the connecting portion (27) extends radially in the apparatus (1) substantially perpendicular to a longitudinal axis (A), vertical during use, of the apparatus (1), the measuring portion (28) is inclined with respect to said axis (A); and wherein the cover (20) is positioned above the connecting portion (27), the assembly portion (29), and also the inclined measuring portion.

9. The measuring device according to claim 6, wherein the connecting portion (27) and the measuring portion (28) are aligned with each other along a common straight axis and the probe (19) is perfectly straight; the probe (19) is inclined with respect to a longitudinal axis (A), vertical during use, of the apparatus (1); and wherein the cover (20) extends parallel to the probe (19) in a straight line and above the probe (19).

10. The measuring device according to claim 6, wherein the probe (19) is inserted into the apparatus (1) from above through an upper wall of the apparatus (1) and the connecting portion (27) and the measuring portion (28) are aligned with each other along a common straight axis; the probe (19) is inclined with respect to a longitudinal axis (A), vertical during use, of the apparatus (1), with the cover (20) positioned parallel to and above the probe (19).

11. The measuring device according to claim 6, wherein the probe (19) is inserted into the apparatus (1) from below, through a lower wall (9) of the apparatus (1); and the connecting portion (27) and the measuring portion (28) are straight and substantially parallel to each other and to a longitudinal axis (A), vertical during use, of the apparatus (1) and are joined by means of a U-shaped assembly portion (29); and wherein the probe (19) is partially covered by a cover sleeve (40) made of an electrically insulating material and having a closed cross-section; the sleeve (40) is positioned around the connecting portion (27) and the assembly portion (29) and leaves at least a portion of the measuring portion (28) uncovered, which remains exposed, during use, to the process liquid; and wherein the cover (20) is positioned laterally next to the measuring portion (28) and in front of it and above the assembly portion (29).

12. A pressurized apparatus (1), for example, an apparatus of a urea plant, provided with a measuring device (3) for measuring the niz^el of a process liquid in the apparatus; characterized in that the measuring device (3) is a measuring device according to one of the preceding claims.

13. The apparatus according to claim 12, wherein the apparatus (1) is an apparatus that is part of a urea plant, in particular, of a high-pressure section of a urea plant, for example, a scrubber, a urea synthesis reactor, a carbamate separator or a carbamate condenser.

14. A method for measuring the level of a process liquid in a pressurized apparatus, for example, an apparatus in a urea plant, comprising the steps of: 10 - sending microwave pulses through a waveguide probe (19), defined by a solid rod body (26) extending within the apparatus (1) below a surface (H) of the process liquid; - shielding the probe (19) from the process liquid flowing from top to bottom in the apparatus (1) and minimizing signal scattering from the probe (19) by means of a confinement cover (20) associated with the probe and disposed around at least a measuring portion (28) of the probe (19) submerged, at least partially, in the process liquid; The cover (20) is positioned above the probe (19) and along said measuring portion (28) of the probe (19) so that it surrounds the probe (19) on the outside and is radially separated from a lateral surface (31) of the probe (19);25 - detecting pulses reflected by the interface between a liquid phase and a gas phase contained in the apparatus (1) and retransmitted by the probe (19); - calculating the level of the process liquid contained in the apparatus (1) from the difference between the travel times of the reflected and transmitted microwaves; characterized in that the cover (20) has a longitudinally open cross-section such that the cover (20) only partially surrounds the probe (19) at an angle, leaving a longitudinal opening (32) facing the lateral surface (31) of the probe (19) to prevent the process liquid from stagnating between the cover (20) and the probe (19); the cover (20) extends around the probe (19) with an angular dimension between 150° and 250°.

15. The measuring method according to claim 14, wherein the cover (20) is positioned above the probe (19) to completely cover a vertical projection of the probe (19) in order to protect the probe (19) from the process liquid flowing in the apparatus (1) from top to bottom.

16. The measuring method according to claim 14 or 15, wherein the cover (20) is made of a conductive material, in particular a metallic material, preferably a material of the same type or of the same material as the probe (19).

17. The measuring method according to any one of claims 14 to 16, wherein the cover (20) is mechanically and electrically connected to the probe (19) by means of tie rods (37) extending between the cover (20) and the probe (19).

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