OA21029A - Device and method for measuring a liquid level in an apparatus. - Google Patents

Abstract

A device (3) for measuring a process liquid level in a pressurized apparatus (1), in particular an apparatus of a urea plant, comprises a radar instrument (18); a waveguide probe (19) for transmitting microwaves, defined by a solid rod body (26); and a confinement cover (20) arranged around at least a measurement portion (28) of the probe (19) immersed at least partially in use in the process liquid; the cover (20) is arranged above the probe (19) and along the measurement portion (28) of the probe (19) so as to surround the probe (19) externally and be radially spaced from a lateral surface (31) of the probe (19)

Description

DETAILED DESCRIPTION OF THE INVENTION

F igure 1 shows a pressurized apparatus 1, in particular a high-pressure stripper of a urea plant, of which only a lower part 2 is illustrated.

The apparatus 1 is provided with a measuring device 3 for measuring the level of a process liquid that collects in the lower part 2 of the apparatus 1, where the liquid attains a free surface H (which is assumed, here and hereafter, to be substantially horizontal in the absence of turbulence).

Although in the example described and illustrated herein the apparatus 1 is a stripper, the measuring device 3 of the invention also finds application in other apparatuses, for example (but not necessarily) in other apparatuses of the high-pressure section of a urea plant, such as in particular a urea synthesis reactor, a carbamate separator, or a carbamate condenser. It is also understood that the measuring device 3 of the invention may be used not only in apparatuses of the high-pressure section, but also in apparatuses in other sections of a urea plant.

In general, the measuring device 3 of the invention may be used in various apparatuses, even outside the urea production industry.

The apparatus 1 extends along a longitudinal axis A (generally vertical in use) and comprises a casing 4 having a side wall 5, arranged around the axis A, and delimiting an internai process chamber 6.

The casing 4 comprises, beginning at a lower end 7 of the apparatus 1: a substantially cylindrical end portion 8, enclosed by a bottom wall 9, located at the end 7; an intermediate domed (for example, substantially hemispherical) 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 casing 4 contains, in particular in the lower end part 2, a certain 15 quantity of a process liquid, which in the présent case (high-pressure stripper of a urea plant) flows from the top to the bottom of the apparatus 1 and collects in the process chamber 6 reaching a level defined by the free surface H; the level of the process liquid in the apparatus 1 is 20 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 conduit 12, arranged for example through the side wall 5 of the casing 4 and elbow-bent towards the bottom wall 9.

The measuring device 3 comprises: a radar instrument having a microwave emitter and a microwave receiver, in particular capable of emitting/receiving microwaves with a frequency between 100 MHz and 1.5 GHz; a waveguide probe 19 for transmitting microwaves; and a confinement cover 20 5 associated with the probe 19 and serving to protect the probe from falling process liquid in the apparatus 1 and to minimize dispersion of the signal from the probe 19.

The radar instrument 18 is arranged outside the casing and faces and is connected to a nozzle 21 that pénétrâtes 10 the casing 4 through the side wall 5 and is attached to the casing 4, for example, by means of a flange coupling (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 related nozzle 21 may 15 be located at different levels on the apparatus 1.

In general, the radar instrument 18 is positioned on the apparatus 1 at a level, measured parallel to the axis A, above the maximum level of the process liquid to be measured in the apparatus 1.

In the example shown in Figure 1, the radar instrument and the nozzle 21 are arranged on the main (cylindrical) portion 11. Alternatively, also depending on the effective size of the apparatus 1, the radar instrument 18 and the nozzle 21 are arranged on the intermediate (domed) portion

10.

The nozzle 21 is arranged substantially transversely to the axis A through the side wall 5. In the embodiment of Figure 1, but not necessarily, the nozzle 21 is substantially perpendicular to the axis A and substantially horizontal.

Beneficially, the radar instrument 18 intégrâtes both an emitter and a receiver, located in the radar instrument 18 itself.

The probe 19 enters laterally into the apparatus 1 and in particular inside 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, positioned inside the process chamber 6 near the bottom wall 9 so as to be immersed in use in the process liquid.

The proximal end 24 of the probe 19 is coupled to the radar instrument 18 by means of the connecter 22, which also acts as a sealing element around the probe 19.

The probe 19 has a solid rod body 26, made, entirely or at least for ail its part intended, in use, to be submerged 20 in the process liquid, of a conductive material, in particular a metallic material, capable of transmitting along the 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 exemplative case described herein, the rod body 26 is made of a material suîtable to withstand the conditions typical of a urea environment, for example (316L urea-grade type) stainless Steel, titanium, zirconium, or duplex or super duplex Steel, preferably having a 25Cr/22Ni/2Mo composition.

The rod body 26 extends along a longitudinal profile that may hâve various shapes and different lengths, also depending on the size and type of the apparatus 1.

In general, the probe 19 (i.e. its rod body 26) comprises an upper connection portion 27, which extends from the proximal end 24 (connected to the radar instrument 18) and pénétrâtes the apparatus 1 through the nozzle 21; and a lower measurement portion 28, which in use is at least partially immersed in the process liquid and terminâtes at the distal end 25.

The connection portion 27 and the measurement portion 28 may be variously oriented or arranged relative to one another.

For example, in the embodiment of Figure 1, the rod body 26 of the probe 19 follows an L-shaped longitudinal profile: the connection portion 27 and the measurement portion 28 are straight and substantially orthogonal to each other and joined by a curved joint portion 29; the connection portion 27 extends radially into the apparatus 1 substantially orthogonally to the axis A, and the measurement portion 28 extends parallel to the axis A.

In this configuration, the measurement portion 28 (defining the part of the probe 19 immersed in the process liquid) is immersed into the process liquid in an axial direction, that is, it extends parallel to the (vertical) axis A of the apparatus 1 and perpendicular to the free surface H of the process liquid (understood, as already indicated above, to be in the absence of turbulence) ..

The rod body 26 may hâve a different cross-sectional shape, for example circular (as shown in Figure 4) or in the shape of a regular polygon (square, hexagon, etc.).

Preferably, the rod body 26 has a constant crosssection along the entire length of the rod body 26.

For example, the rod body 26 has a circular cross section and a diameter of between 5 mm and 30 mm (preferably approximately 20 mm) .

The probe 19 is mechanically supported by the connecter 22 and/or support éléments (known and not shown), for example positioned 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 around the rod body 26 of the probe 19 and extends along the probe 19 following its longitudinal profile, whose shape it replicates.

The cover 20 surrounds the probe 19 externally and is radially spaced from a latéral surface 31 of the rod body 5 26.

The cover 20 has a longitudinally open cross-section so that it only partially surrounds the probe 19 angularly. 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 10 longitudinal opening 32 facing the latéral surface 31 of the rod body 26.

In this way, the formation of liquid stagnation zones is avoided, and it is possible for the gas phase présent in the apparatus 1 to pass through.

The opening 32 is delimited laterally by a pair of opposing longitudinal edges 33 of the cover 20, fac:.ng and parallel to each other (Figure 4).

The cover 20 has a concave inner latéral surface 34 facing the latéral surface 31 of the rod body 26 of the probe 20 19, and a convex outer latéral surface 35 opposite the concave inner latéral surface 34.

Preferably, the cover 20 extends around the probe 19 for an angular extent 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 an arc of a circle or an arc of an ellipse, parabola, or other conic.

In the embodiment shown in Figure 1, the cover 20 extends from the proximal end 24 of the probe 19, where the cover 20 is connected to the nozzle 21, to the distal end 25, where the probe 19 optionally protrudes out of the cover 20 with a short end section.

It is understood that the cover 20 may extend over a different length of the probe 19.

The cover 20 is positioned so that the inner latéral surface 34 faces the latéral surface 31 of the probe 19.

The cover 20 is positioned above the probe 19 so as to fully cover the vertical projection of the probe 19, meaning the projection of the probe 19 on a horizontal plane parallel to the free surface H of the process liquid and perpendicular to the axis A.

In particular, the cover 20 is located above the connection portion 27 and the joint portion 29, so as to protect the probe 19 from the process liquid flowing in the apparatus 1 from top to bottom; and is arranged alongside the measurement 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 métal material, preferably a material of the same type, or the same material, as the probe 19.

The cover 20 is mechanically and electrically connected to the probe 19 by means of tie rods 37 extending, 5 for example, radially between the inner latéral surface 34 of the cover 20 and the latéral surface 31 of the probe.

The tie rods 37 are arranged, for example, at the ends 24, 25 and/or spaced along the cover 20.

The tie rods 37, in addition to mechanically supporting 10 the cover 20 by holding it in position with respect to the probe 19, also make the electrical connection between the cover 20 and the probe 19.

Appropriately, the tie rods 37 are made of the same material (or a material of the same type), in particular a 15 métal material, as the cover 20 (and/or the probe 19).

In use, the measuring device 3 opérâtes by implementing the measuring method of the invention as follows.

The emitter of the radar instrument 18 emits microwave puises that travel along the probe 19 through the rod body 20 26 to the process liquid contained in the apparatus 1. The microwave puise is reflected when it reaches the interface between the liquid phase and the gas phase (i.e. the free surface H), which hâve different dielectric constants. The reflected puise is in turn transmitted from the probe 19 to 25 the receiver of the radar instrument 18.

The level of liquid contained in the apparatus 1 is calculated by converting the time différence of the transmitted and reflected waves into distance, in particular by TDR (Time Domain Reflectometry). The calculation is 5 carried out, for example, by a processing unit which is either integrated into the radar instrument or connected to i t.

In the embodiment of Figure 2, in which details similar to or the same as those already described are indicated by 10 the same numbers, the probe 19 again enters the apparatus 1 laterally, in particular through the nozzle 21. The probe 19 again comprises an upper connection portion 27 and si lower measurement portion 28, which are straight and joined by a curved joint portion 29.

The connection portion 27 extends radially in the apparatus 1 and substantially orthogonally to the axis A; while the measurement portion 28 is inclined with respect to the axis A and the free surface H of the process liquid (and not parallel to the axis A and perpendicular to the free 20 surface H, as described above with reference to Figure 1).

The measurement portion 28 and the connection portion 27 are inclined relative to each other by an angle greater than 90°, preferably between 120° and 180°.

In this configuration, therefore, the measurement portion 28 is immersed in the process liquid at an inclination: the portion of the probe 19 immersed in the process liquid extends obliquely with respect to the axis Ά of the apparatus 1 and the free surface H of the process liquid.

In this embodiment, as already described with reference to Figure 1, the probe 19 is also associated with a cover 20 covering the probe 19.

Again in this case, the cover 20 is arranged above the probe 19 so as to cover the vertical projection of the probe 10 19.

In particular, the cover 20 is positioned above the connection portion 27, the joint portion 29, and also the inclined measurement portion 28, so as to protect the entire probe 19 from the process liquid flowing in the apparatus 1 15 from top to bottom. The entire outer latéral surface 35 of the cover 20 faces upward (albeit partially inclined) and the entire opening 32 faces downward (partially inclined).

In the further embodiment of Figure 3, in which details similar to or the same as those already described are 20 indicated by the same numbers, the nozzle 21 is again arranged through the side wall 5 of the casing 4, but instead of being perpendicular to the axis A it is inclined with respect to the axis A and the side wall 5.

In this case, the probe 19 is completely straight,

i.e. it has an entirely straight rod body 26, and it is

aligned with the nozzle 21. The probe 19 thus extends along a straight axis inclined with respect to the axis A.

The connection portion 27 and the measurement portion 28 are aligned with each other along a common straight axis 5 inclined with respect to the axis A and the free surface H of the process liquid.

Accordingly, the cover 20 also extends parallel to the probe 19 and straight, with the outer latéral surface 35 inclined parallel to the probe 19 and facing upwards.

For example, the probe 19 is inclined at an angle of between 30° and 60° with respect to the axis A.

In the embodiment of Figure 5, in which details similar to or the same as those already described are indicated by the same numbers, the probe 19 is inserted into the apparatus 15 1 through the bottom wall 9.

The nozzle 21 is thus arranged through the bottom 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 20 18, to which it is connected by means of the proximal end 24 .

In this case, the probe 19 has a profile which is bent by 180° and the rod body 26 of the probe 19 has a U-shaped longitudinal profile.

In particular, the probe 19 comprises a connection

portion 27, which extends from the proximal end 24 connected to the radar instrument 18 and pénétrâtes the apparatus 1 through the nozzle 21, and a measurement portion 28, which in use is at least partially immersed in the process liquid 5 and terminâtes at the distal end 25.

The connection portion 27 and the measurement portion 28 are straight and substantially paralîel to each other and to the axis A, and are joined by a U-shaped joint portion 29.

In this configuration, the measurement portion 28 (which is immersed in the process liquid) also extends paralîel to the (vertical) axis A of the apparatus 1 and perpendicular to the free surface H of the process liquid.

With reference also to Figures 6-7, the probe 19 is 15 partially covered by a covering sheath 40, arranged around the rod body 26 of the probe 19 on the latéral surface 31 of the probe 19.

The sheath 40, optionally made from several pièces joined together, has a closed cross-section around the rod 20 body 26 and covers the latéral surface 31 of the probe 19, being in contact therewith.

The sheath 40 extends to cover in particular the connection portion 27 and the U-shaped joint portion 29. In contrast, the sheath 40 leaves at least part of the 25 measurement portion 28 uncovered so that it is exposed to the process liquid.

The purpose of the sheath 40 is to isolate t.he rod body 26 of the probe 19 from the process environment at the connection portion 27, and it is therefore made of 5 electrically insulating material capable of withstanding process conditions (particularly the conditions of a urea environment), such as ceramic materials or polymeric materials such as PTFE or PEEK.

Similarly to the description above, the probe 19 is 10 again associated, at least in the part exposed to the process liquid, with the cover 20.

In particular, the cover 20 extends along the measurement portion 28, to which it is flanked lateraLly and faces as described above. Optionally, the cover 20 extends 15 above the joint portion 29.

Again in this case, the cover 20 is connected to the probe 19 by tie rods 37 which support the cover 20 and provide electrical continuity with the probe 19.

Finally, it is understood that further modifications 20 and variations may be made to the device and the measurement method described and illustrated herein without thereby departing from the scope of the attached claims.

For example, according to further embodiments not shown, the probe 19 is inserted into the apparatus 1 from 25 above, through an upper wall of the casing 4. The nozzle 21

is therefore arranged at the top of the apparatus 1 and is, appropriately, parallel to the axis A.

In this case, similarly to the description above with reference to Figure 3, the probe 19 may be completely 5 straight, i.e. hâve an entirely straight rod body 26. The probe 19 thus extends along a straight axis and the cover 20 accordingly also extends straight and parallel to the probe 19.

The probe 19 may be substantially vertical and parallel 10 to the axis A, with the cover 20 arranged laterally beside the probe 19 and the inner latéral surface 34 facing the latéral 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 latéral surface 34 facing and above the 15 latéral surface 31 of the probe 19.

Claims (17)

1. A device (3) for measuring a level of a process liquid in a pressurized apparatus, for example an apparatus of a urea plant, comprising a radar instrument (18) positioned in use outside the apparatus (1) and having a microwave emitter and a microwave receiver; a waveguide probe (19) for transmitting microwaves, defined by a solid rod body (26) and extending in use inside the apparatus (1) between a proximal end (24), joined to the radar instrument (18), and a distal end (25), immersed in use in the process liquid below a free surface (H) of the process liquid; and a confinement cover (20), arranged about at least a measurement portion (28) of the probe (19) at least partly immersed in use in the process liquid; the cover (20) being positioned above the probe (19) and along said measurement portion (28) of the probe (19) so as to surround the probe (19) externally, and being radially spaced from a latéral surface (31) of the probe (19); the measuring device (3) being 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) facing the latéral surface (31) of the probe (19); the cover (20) extending about the probe (19) with an angular extent between 150° and 250°.

2. The measuring device according to claim 1, wherein the cover (20) has a concave inner latéral surface (34) facing the latéral surface (31) of the probe (19), and a convex outer latéral surface (35), opposite to the concave inner latéral surface (34).

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

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

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

6. The measuring device according to one of the preceding claims, wherein the probe (19) comprises said measurement portion (28), that in use is at least partly immersed in the process liquid and ends with the distal end

(25), and a connection portion (27), connected to the radar instrument (18) at the proximal end (24) of the probe (19).

7. The measuring device according to claim 6, wherein the connection portion (27) and the measurement portion (28)

5 are rectilinear and substantially perpendicular to each other and joined by a curved joint portion (29); and wherein the connection portion (27) extends radially in the apparatus (1) substantially perpendicular to a longitudinal axis (A), vertical in use, of the apparatus (1), and the measurement

10 portion (28) extends parallel to said axis (A); and wherein the cover (20) is positioned above the connection portion (27) and the joint portion (29) and laterally beside the measurement portion (28).

8. The measuring device according to claim 6, wherein

15 the connection portion (27) and the measurement portion (28) are rectilinear and inclined with respect to each other and are joined by a curved joint portion (29); and wherein the connection portion (27) extends radially in the apparatus (1) substantially perpendicular to a longitudinal axis (A),

20 vertical in use, of the apparatus (1), and the measurement portion (28) is inclined with respect to said axis (A); and wherein the cover (20) is positioned above the connection portion (27), the joint portion (29), and also the inclined measurement portion (28).

25

9. The measuring device according to claim 6, wherein the connection portion (27) and the measurement portion (28) are aligned with each other along a common rectilinear axis and the probe (19) is entirely straight; the probe (19) being inclined with respect to a longitudinal axis (A) , vertical 5 in use, of the apparatus (1) ; and wherein the cover (20) extends parallel to the probe (19) and rectilinearly and above the probe (19) .

10. The measuring device according to claim 6, wherein the probe (19) is to be inserted in the apparatus (1) from 10 the top, through a top wall of the apparatus (1), and the connection portion (27) and the measurement portion (28) are aligned with each other along a common rectilinear axis; the probe (19) being inclined with respect to a longitudinal axis (A), vertical in use, of the apparatus (1), with the

15 cover (20) positioned parallel to the probe (19) and above the probe (19).

11. The measuring device according to claim 6, wherein the probe (19) is to be inserted in the apparatus (1) from the bottom, through a bottom wall (9) of the apparatus (1);

20 and the connection portion (27) and the measurement portion (28) are rectilinear and substantially parallel to each other and to a longitudinal axis (A) , vertical in use, of the apparatus (1) and are joined by a U-shaped joint portion (29); and wherein the probe (19) is partially covered by a

25 covering sheath (40) made of an electrically insulting material and having a closed cross section; the sheath (40) being positioned about the connection portion (27) and the joint portion (29), and leaving uncovered at least a part of the measurement portion (28) that remains exposed, in use, 5 to the process liquid; and wherein the cover (20) is positioned laterally beside and facing the measurement portion (28) and above the joint portion (29).

12. A pressurized apparatus (1), for example an apparatus of a urea plant, provided with a measuring device 10 (3) for measuring a level 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, 15 in particular of a high-pressure section of a urea plant, for example a stripper, a urea synthesis reactor, a carbamate separator, or a carbamate condenser.

14. A method for measuring a level of a process liquid in a pressurized apparatus, for example an apparatus of a 20 urea plant, comprising the steps of:

- sending microwave puises along a waveguide probe (19), defined by a solid rod body (26) and extending inside the apparatus (1) below a free surface (H) of the process liquid;

- protecting the probe (19) from process liquid flowing from

25 the top downwards in the apparatus (1) and minimizing signal dispersions from the probe (19) by means of a confinement cover (20) associated with the probe and arranged about at least a measurement portion (28) of the probe (19) iinmersed at least partly in the process liquid; the cover (20) being positioned above the probe (19) and along said measurement portion (28) of the probe (19) so as to surround the probe (19) externally, and being radially spaced from a latéral surface (31) of the probe (19);

- detecting puises reflected by the interface between a liquid phase and a gas phase contained in the apparatus (1), and re-transmitted along the probe (19);

- calculating the level of the process liquid contained in the apparatus (1) from the différence between the travel times of the reflected and transmitted microwaves;

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) facing the latéral surface (31) of the probe (19) so as to avoid stagnation of the process liquid between the cover (20) and the probe (19); the cover (20) extending about the probe (19) with an angular extent between 150° and 250° .

15. The measuring method according to claim 14, wherein the cover (20) is positioned above the probe (19) so as to cover entirely a vertical projection of the probe (19),

in order to protect the probe (19) from process liquid flowing in the apparatus (1) from the top downwards.

16. The measuring method according to claim 14 or 15, wherein the cover (20) is made of a conductive material, in 5 particular a métal material, preferably a material of the same type, or the same material, of the probe (19).

17. The measuring method according to one of claims 14 to 16, wherein the cover (20) is connected mechanically and electrically to the probe (19) by tie rods (37) extending 10 between the cover (20) and the probe (19).