OA16844A

OA16844A - Urea reactor tray, reactor, and production process

Info

Publication number: OA16844A
Application number: OA1201400015
Authority: OA
Inventors: Ugo AVAGLIANO; Lino Carlessi
Original assignee: Saipem S.P.A.
Priority date: 2011-07-12
Filing date: 2012-07-04
Publication date: 2016-01-07

Abstract

A urea reactor tray (4) having a base plate (10); and a number of hollow cup-shaped members (11, 11A), which project vertically from the base plate (10) along respective substantially parallel axes (A) perpendicular to the base plate (10), and have respective substantially concave inner cavities (17, 37) communicating with respective openings (15) formed in the base plate (10); the tray (4) having a number of first cupshaped members (11), each of which extends axially between an open top end (21) having the opening (15), and a closed bottom end (22), and has a lateral wall (23) with through holes (25) substantially crosswise to the axis (A), and a bottom wall (24) which closes the closed bottom end (22) and has no holes.

Description

UREA REACTOR TRAY, REACTOR, AND PRODUCTION PROCESS

TECHNICAL FIELD

The présent invention relates to a urea reactor tray, reactor, and production process.

BACKGROUND ART

As is known, urea is produced industrially using processes whereby carbon dioxide reacts with ammonia to form ammonium carbamate, which décomposés into urea and typical reactor therefore contains a gaseous and a liquid phase flowing in co-current flows a pressurized reaction chamber.

Conversion of ammonia and carbon dioxide to ammonium carbonate and ultimately urea is enhanced, i.e. to increase urea output, using tray reactors.

c, Ux^_ea tray reactors substantially comprise a normally cylindrical shell, which extends substantially along a normally vertical axis, and is fitted inside with éléments, i.e. trays, defined by respective métal sections shaped and/or perforated to divide the reaction chamber into compartments and form spécifie paths for the substances inside the reactor.

The trays are normally perpendicular to the vertical axis of the reactor, and equally spaced along the axis to the full height of the reactor.

0RTG^TNAL

The trays are very often perforated, i.e: hâve holes variously arranged and possibly of different shapes and/or sizes.

The trays are preferably designed for insertion through the manhole reactors are normally provided with, so they can also be fitted to existing reactors and/or removed and replaced. For which reason, the trays are normally made in a number of parts that fit together.

The trays	hâve various	functions,	and in
particular:
- maximize	the hold time	of the light	(faster)
phase ;
- distribute	the reactants	as evenly as	possible

along the reactor section, to prevent 'back-mixing';

- enhance mixing of the gaseous- and liquid phases; and

- reduce 'bubble size' to improve diffusion of the ammonia in the carbon dioxide.

Nuraerous urea reactor tray designs and configurations are known.

ürea reactors with perforated trays are described, for example, in EP495418, EP781164, US6444180 and

US6165315.

Other tray designs for other applications are described in US3070360 and US3222040.

Known configurations - particularly those in

ORTGTNAL above documents specifically designed for producing urea

- indeed provide mixing and load for increasing output by reducing back losses, by ensuring substantially even distribution of the light (gaseous) and heavy (liquid) phases by providing preferential paths for each of the two phases, and by enabling non-intrusive (non-impact) mixing between one tray and another.

Known solutions, however, still leave room for improvement.

•10

- Generally speaking, known solutions fail to provide for thorough mixing of the light and heavy phases (both consisting of supercritical fluids), which, because of the différence in density, tend to flow along separate preferential paths defined by the design and arrangement of the trays, and in particular by the shape, location, and size of the holes in the trays.

This drawback also impairs final conversion of the reactants, thus reducing urea output.

DISCLOSURE OF INVENTION

It is therefore an object of the présent invention to provide a urea reactor tray, reactor, and production process designed to eliminate the above drawbacks of the known art, and which, in particular, provide for thorough mixing of the gaseous and liquid phases, and high urea output.

The présent invention therefore relates to a

ORTGtnàL reactor tray substantially as defined in Claim 1.

The présent invention also relates to a urea reactor and urea production process substantially as defined in Claims 16 and 19 respectively.

Further preferential characteristics of the invention are indicated in the dépendent Claims.

The geometry of the reactor tray according to the présent invention provides for thoroughly mixing the gaseous and liquid phases in a urea reactor and urea production process, and so greatly increasing urea output.

The reactor tray according to the présent invention and the reactor as a whole are also extremely easy to produce and install.

BRIEF DESCRIPTION OF THE DRAWINGS

A non-limiting embodiment of the présent invention will be described by way of example with reference to the accompanying drawings, in which ;

Figure shows a partial schematic of a urea reactor in accordance with a first embodiment of the invention;

Figure shows a larger-scale detail of the Figure reactor;

Figure shows a top plan view of the Figure 2 detail;

Figures 4 and 5 show schematic plan views of two

ORtgtNAL trays usable in the Figure 1 reactor;

Figure 6 shows a partial schematic of a urea reactor in accordance with a second embodiment of the invention;

Figure 7 shows a larger-scale detail of the Figure 6 reactor.

BEST MODE FOR CARRYING OUT THE INVENTION

Figure 1 shows an inner portion of a urea reactor

1, in particular a tray reactor.

Reactor 1 comprises a shell 2 extending substantially along a vertical axis X and defining a reaction chamber 3 inside reactor 1; and a number of trays 4 (only one shown in Figure 1) housed inside shell

2.

For the sake of simplicity, other known component parts of reactor 1 not relating to the présent invention, such as reactant and product loading and unloading Systems, heating and pressurizing Systems, etc., are not shown.

Shell 2 has a latéral, e.g. substantially cylindrical, wall 5; and two end portions (not shown) at respective opposite axial ends of latéral wall 5.

Trays 4 are fitted to latéral wall 5, e.g. by means of brackets 6 or other supports.

Though Figure 1 shows only one tray 4, reactor 1 houses a number of trays 4 substantially perpendicular ortgtnal to and spaced along axis X to divide reaction chamber 3 into compartments 7 and define paths for the substances inside reaction chamber 3.

Each tray 4 advantageously, though not necessarily, comprises a number of removable modular sections 8 connected to one another by appropriate fastening devices 9.

With reference also to Figures 2 and 3, each tray 4

	comprises	a base plate 10,	e.g. in the	form of	a
40	circuler	disk; and a number	of cup-shaped	members	11
	projecting downwards from base	plate 10.
	More	specifically, base plate 10 has a	top face	13

and a bottom face 14 opposite each other and which, for example, are substantially fiat and parallel.

Top face 13 has a number of openings 15 bounded by respective edges 16 preferably flush with top face 13.

Cup-shaped members 11 project downwards from bottom face 14 of base plate 10.

Each cup-shaped member 11 is hollow, extends vertically along an axis A substantially parallel to axis X, defines a substantially concave inner cavity 17 communicating with a respective opening 15, and extends axially between an open top end 21 with opening 15, and a closed bottom end 22.

More specifically, each cup-shaped member 11 comprises a latéral wall 23, and a bottom wall 24.

OR^G^NAL

In the non-limiting example in Figures 1	to	3,
though not	necessarily,	cup-shaped member	11	is
substantially	cylindrical : latéral wall	23	is
substantially	cylindrical	and extends about axis	A,	and
bottom , wall	24 is	substantially circular	and
perpendicular	to axis A.

Cup-shaped members 11 may, however, be shaped differently from those described and illustrated by way of example. More specifically, they may hâve latéral Ί0 walls 23 sloping with respect to axis A and/or other than circular cross sections (perpendicular to axis A) . In other embodiments not shown, cup-shaped members 11 may be substantially truncated-cône-shaped, prismatic, truncated-pyramid-shaped, etc. and/or hâve cross sections of various shapes, e.g. substantially circular or polygonal, and either constant or varying along axis

A. As opposed to being centrally symmetrical, as in the example shown, cup-shaped members 11 may even be elongated longitudinally along a horizontal axis 0 (perpendicular to axis A). They may, for example, hâve a shape in plant view that is substantially rectangular or oval or basically elongated; and latéral walls 23 may be substantially parallel to axis A, or slope variously with respect to axis A to define, for example, a number 25 of parallel or variously arranged projections beneath bottom face 14 of base plate 10

0R^TG^TNAL

Generally speaking, however, each cup-shaped member 11 has an open top end 21 with opening 15; and a bottom end 22 closed by bottom wall 24 with substantially no holes, as explained below.

The position of cup-shaped members 11, and more specifically of open end 21 and closed end 22, is determined by the normal flow direction of the process fluids inside reaction chamber 3. As in most reactors for producing urea.from ammonia and carbon dioxide, the Ί0 process fluids circulating in reactor 1 „substantially comprise a gaseous or so-called light phase, and a liquid or so-called heavy phase. Both phases substantially flow upwards.

In the substantially axial direction (parallel to axes A and X) substantially corresponding to the flow direction of the process

3, closed end 22 of each fluids inside reaction chamber cup-shaped member 11 therefore précédés open end 21.

Regardless of its shape, latéral wall has through circulation holes 25 designed to permit preferential throughflow of the liquid and/or gaseous phase.

Each cup-shaped member 11 therefore has circulation holes 25 substantially crosswise to axis A, and which, in the example shown, are substantially radial with respect to axis A.

0RTG^TNAL

Each cup-shaped member 11 has holes 25 of different sizes, and more specifically, has smaller holes 25A for throughflow of the gaseous (light) phase in a top area close to open top end 21; and larger holes 25B for throughflow of the liquid (heavy) phase in a bottom area close to closed bottom end 22.

Holes 25 may be any shape, not necessarily circular. For example, they may be circular, polygonal, oval, substantially rectangular, in the form of slots or slits, etc.

In the Figure 2 example (which shows a more detailed view of holes 25 than in the Figure 1 schematic) , holes 25 are circular, and cup-shaped member comprises a first group of holes 25A of diameter DI in top area 26, and a second group of holes 25B of diameter D2, larger than diameter Dl, in bottom area 27.

Holes 25 in both groups are preferably equally spaced on latéral wall 23, and are arranged, for example, in a number of successive rows equally spaced 20 axiaïly. The holes 25 in adjacent rows may be aligned (as shown by the larger holes 25B) or staggered (as shown by the smaller holes 2SA).

By way of example, the holes 25A in the first group (smaller) hâve a diameter Dl of roughly 2-20 mm and 25 preferably of about 2-4 mm,- and holes 25A in the top row in the group (i.e. the row closest to open top end 21 of or^qtnal

cup-shaped member 11 and face 14 of base plate 10)	are
located at a distance of roughly 1 mm or more,	and
preferably of about 15-30 mm, from bottom face 14	of
base plate 10.

The above measurements are purely indicative and, in the case of other than circular holes 25, may refer, as opposed to the diameter of the holes, to the équivalent or hydraulic diameter, i.e. the diameter a circular section of the same area would hâve.

₍ Holes 25A in the first group slope optionally with respect to latéral wall 23 and, more specifically, about 30° inwards and preferably downwards with respect to the perpendicular to latéral wall 23. This slope is in no way binding, and holes 25A may even slope upwards with η- respect to the perpendicular to latéral wall 23. The slope of holes 25A . also dépends on the thickness of latéral wall 23, and serves to ensure substantially and prédominant ly only gaseous phase flow through holes 25A, and thorough mixing of the phases inside cup-shaped 20 member 11.

The holes 25B in the second group (larger) hâve a diameter D2 of roughly 4-30 mm and preferably of about 4-8 mm; and the row of holes 25B closest to bottom end is located at a distance of 0 mm or more from bottom wall 24 to ensure throughflow of the liquid phase.

The distance from the base plate 10 of the top row

ORTGtnal t* of gaseous phase holes 25A (i.e. the row closes to bottom face 14 of base plate 10) is important to ensure even distribution of the gaseous phase beneath tray 4, i.e. beneath bottom face 14 of base plate 10, by forming a uniform gaseous phase 'hood'.

In other words, in each compartment 7, both the gaseous and liquid phases of the process fluids flow upwards in a substantially axial direction (parallel to axis X) , and the gaseous (light) phase accumulâtes against bottom face 14 of tray 4 to form a head equal in height to the distance between bottom face 14 of base plate 10 and the top row of holes 25A. The gaseous phase therefore flows mainly through holes 2 SA in a substantially radial direction with respect to axes A of cup-shaped members 11, or at any rate substantially crosswise to vertical axis X of reactor 1. On reaching a sufficient head, the heavier liquid phase also flows through holes 25B, lower than holes 2SA, in a direction substantially crosswise to vertical axis X of reactor 1; and both the liquid and gaseous phases flow up along cavity 17, where they are mixed locally and flow through opening 15 to the next compartment 7.

By virtue of the geometry of the présent invention, the process fluids are therefore forced, by the compulsory paths defined by holes 25, to flow radially into each cup-shaped member 11, which therefore acts a

0RTGTNAL a local mixer to ensure thorough mixing of the two phases.

In the non-limiting examples in Figures 4 and 5, cup-shaped members 11 (and openings 15) are arranged on 5 base plate 10 in a regular pattern, e.g. equally spaced in a grid pattern. More specifically, cup-shaped members are spaced apart by a spacing L of roughly 1.5D or more, and preferably of about 2D to 5/2D (where D is the diameter of cup-shaped members 11) to simplify manufacture of sections 8. In other embodiments not shown, cup-shaped members 11 are arranged on base plate 10 in other, even irregular, patterns and/or with spacings other than the one shown.

By way of example, diameter D of cup-shaped members η5 11 is roughly 20 mm or more, and preferably of about

100-160 mm.

Cup-shaped members 11 preferably number fewer than 36 per square métré, and more preferably range between and 18 per square métré, depending on the number of 20 holes 25.

The number of holes 25 in the two groups (i.e. for the two phases) is selected according to the number of cup-shaped members 11 on tray 4, which in turn is selected according to the diameter and location of tray 25 4 inside reactor 1. Generally speaking, the geometry of tray 4 (in particular, the size and number of holes 25 ortgtnal and the number of cup-shaped members 11) is selected so that the total gaseous phase flow section (i.e. the total area of holes 25A) is roughly 0-20%, and preferably about 0-4%, of the total area of tray 4, and the total liquid phase flow section (i.e. the total area of holes 25B) is roughly 1-20%, and preferably about 15%, of the total area of tray 4, again depending on the location of tray 4 inside reactor 1.

Generally speaking, the total gaseous and liquid phase flow sections (i.e. the total areas of holes 25A and 25B) vary depending on the location of tray 4 inside reactor 1 : trays 4 at different heights inside reactor 1 may, and preferably do, hâve different total gaseous and liquid phase flow sections. More specifically, working upwards from one tray 4 to the next, the total gaseous phase flow section decreases (even to practically zéro at the top tray 4) , while the total liquid phase flow section increases or remains substantially constant.

To avoid creating preferential paths for the two phases, there are no circulation holes, i.e. allowing direct fluid flow from one compartment 7 to another, in the surface of tray 4 (i.e. of base plate 10) or in bottom walls 24 of cup-shaped members 11.

The surface of tray 4 and/or bottom walls 24 of cup-shaped members 11 may hâve stagnation holes 28 toi ortgtnal prevent the formation of stagnant gas pockets which may resuit in corrosion. Stagnation holes 28 (only some of which are shown schematically in Figure 1) are smaller in diameter than both diameters DI and D2 of gaseous and liquid phase flow holes 25, are preferably about 2-3 mm in diameter, and are also fewer in number than holes 25, roughly by at least one order of magnitude, again to avoid creating preferential flow paths.

Bottom wall 24 therefore has substantially no holes, in the sense of having no circulation holes 25 (through which the process fluids preferably circulate), and only has optional stagnation holes 28. The term 'stagnation hole' is intended to mean a hole which, in size and/or location, does not form a preferential liquid or gaseous phase path with respect to the circulation holes.

To implement the urea production process according to the présent invention, a reaction between ammonia and carbon dioxide is produced inside reactor 1 in appropriate pressure and température conditions. More specifically, the ammonia-containing liquid phase and the carbon-dioxide-containing gaseous phase are circulated upwards in the same direction inside reaction chamber 3 and through successive compartments 7 separated by trays 4.

As stated, in each compartiment 7, both the liqui

OR^TG^TNAL and gaseous phases flow upwards in a substantially axial direction (parallel to axis X) and accumulate against bottom face 14 of. tray 4; the gaseous phase flows into cavities 17 of cup-shaped members 11 mainly through holes 25A, and the liquid phase into cavities 17 mainly through holes 25B; and the two phases are mixed locally inside cavities 17 and flow on to the next compartment 7.

In the Figure 6 and 7 embodiment, in which any details similar or identical to those already described are indicated using the same reference numbers, each tray 4 comprises base plate 10; a number of bottom first cup-shaped members 11 as described with reference to Figures 1 to 3, and which project vertically downwards from base plate 10 (i.e. from bottom face 14 of base plate’ 10) ; ancL a number of top second cup-shaped members 11A, which project upwards from base plate 10 (i.e. from top face 13 of base plate 10), and are aligned with and superimposed on respective first cup-shaped members 11.

Cup-shaped members 11A are also hollow, and extend vertically along respective axes A substantially parallel to axis X. More specifically, each cup-shaped member 11A extends, along axis A, between a closed top end 31 located over base plate 10, and an open bottom 25 end 32 communicating with opening 15, and comprises a latéral wall 33, which extends about axis A and ha

ORTGTNAL through circulation holes 25C substantially crosswise to axis A and. located over base plate 10; and a top end wall 34 substantially perpendicular to axis A, and which closes closed top end 31 and has substantially no holes, i.e. no circulation holes.

In other words, pairs of opposite cup-shaped members 11, 11A, superimposed vertically along axes A, project from base plate 10; and each bottom cup-shaped member 11 and the respective superimposed top cup-shaped member 11A define respective portions 35 - projecting below and above base plate 10 respectively - of a tubular body 3 6 fitted through one of openings 15 in base plate 10.

Each cup-shaped member 11A has a substantially concave inner cavity 37, which communicates with opening 15 and with one cavity 17 of cup-shaped member 11 underneath.

Holes 25C in latéral wall 33 of each top cup-shaped member 11A are, for example, similar or identical in 2q shape and arrangement to the prédominantly liquid phase circulation holes 25B of respective bottom cup-shaped member 11. More specifically, holes 25C of each top cupshaped member 11A hâve a total area (defining the total flow section for both phases through cup-shaped member 25 LIA) substantially equal to the total area of holes 25B of the corresponding bottom cup-shaped member 11.W

ORtqtnaL

For example, the size of holes 25C and the number of holes 25C and cup-shaped members 11A are selected so that the total flow section for both phases (i.e. the total area of holes 25C) is roughly 1-20%, and preferably about 1-5%, of the total area of tray 4, depending on the location of tray 4 inside reactor 1.

In this variation, too, a reaction between ammonia and carbon dioxide is produced inside reactor 1 in appropriate pressure and température conditions. More specifically, the ammonia-containing liquid phase and the carbon-dioxide-containing gaseous phase are circulated upwards in the same direction inside reaction chamber 3 and through successive compartments 7 separated by trays 4.

As stated, in each compartiment 7, both the liquid and gaseous phases flow upwards in a substantially axial direction (parallel to axis X) and accumulate against bottom face 14 of tray 4; the gaseous phase flows into cavities 17 of cup-shaped members 11 mainly through holes 25A, and the liquid phase into cavities 17 mainly through holes 25B; and the two phases are mixed locally inside cavities 17.

Both phases flow upwards in a substantially axial (vertical) direction inside cup-shaped members 11, and into cup-shaped members 11A aligned with and superimposed on respective cup-shaped members 11, and_f

ORTGtnàL flow out of cup-shaped members 11A through holes 25C,

i.e. exclusively crosswise to axes A, and on to the next compartment 7.

In this variation, too, there are no circulation holes, i.e. allowing direct flow from one compartment 7 to another, in the surface of tray 4 (i.e. of base plate

10) or in end walls 24, of cup-shaped members 11,

11A, to avoid creating preferential paths for the gaseous and/or liquid phase.

'10

The surface of tray 4 and/or bottom walls 24 and/or end walls 34 hâve optional stagnation holes as described above.

The additional characteristics referred to above with reference to

Figures 1-5, and relating, for example, to the size and arrangement of the circulation holes and cup-shaped members, also apply to the Figure 6 and 7 variation.

Clearly, changes may be made to the reactor tray, reactor, and process as described and illustrated herein 20 without, however, departing from the scope of the accompanying Claims.o

ORTGTNAL

Claims

1) A urea reactor tray (4) comprising at least one base plate (10); and a number of hollow cup-shaped members (11, 11A), which project vertically from the base plate (10) along respective substantially parallel axes (A) perpendicular to the base plate (10) , and hâve respective substantially concave inner cavities (17, 37) communicating with respective openings (15) formed in the base plate (10); the tray (4) being characterized by comprising a number of first cup-shaped members (11),

10 each of which extends axially between an open top end (21) having the opening (15) , and a closed bottom end (22) ; and in that each first cup-shaped member (11)

comprises a latéral wall (23) with through circulation holes (25) substantially crosswise to the axis (A) and Ί 5 for preferential throughflow of a gaseous phase and/or liquid phase; and a bottom wall (24) which closes the closed bottom end (22) and has no circulation holes.

2) A reactor tray as claimed in Claim 1, wherein the latéral wall (23) of each first cup-shaped member 0 (11) has first circulation holes (25A) predominantly for throughflow of a gaseous phase, and second circulation holes (25B) predominantly for throughflow of a liquid phase, ail substantially crosswise to the axis (A) ; the first holes (25A) being located doser to the

ORTG^NAL end (21) than the second holes (25B).

3) A reactor tray as claimed in Claim 2, wherein the first holes (25A) differ in size from the second holes (25B).

4) A reactor tray as claimed in Claim 2 or 3, >

wherein the first holes (25A) are smaller than the second holes (25B).

5) A reactor tray as claimed in one of Claims 2 to

4, wherein the first holes (25A) are located in a top l area (26) of the cup-shaped member (11) , close to the open top end (21); and the second holes (25B) are located in a bottom area (27) of the cup-shaped member (11), close to the closed bottom end (22).

6) A reactor tray as claimed in one of Claims 2 to η 5, wherein the first holes (2SA) hâve a diameter (Dl) .of roughly 2-20 mm and preferably of about 2-4 mm; and the second holes (25B) hâve a diameter (D2) of roughly 4-30 mm and preferably of about 4-8 mm.

7) A reactor tray as claimed in one of Claims 2 to

20 wherein the first holes (25A) are arranged in one or more axially successive rows; and the row closest to the open top end (21) is located at a distance of roughly 1 mm or more, and preferably about 15-20 mm, from a bottom face (14) of the base plate (10).

8) A reactor tray as claimed in one of Claims 2 to

7, wherein the first holes (25A)

ORTGTNAL the latéral wall (23) .

9) A reactor tray as claimed in one of Claims 2 to

8, wherein the second holes (25B) are arranged in one or more axially successive rows; and the row closes to the closed bottom end (22) is located at a distance of 0 mm or more from the bottom wall (24).

10) A reactor tray as claimed in one of Claims 2 to

9, wherein the size and number of the first and second holes (25A, 25B) and the number of first cup-shaped

Ί0 members (11) are such that the total area of the first holes (25A) ranges between roughly 0% and 20%, and preferably between roughly 0% and 4%, of the total area of the tray (4) , and the total area of the second holes (25B) ranges between roughly 1% and 20%, and preferably between roughly 1% and 5%, of the total area of the tray (4) .

11) A reactor tray as claimed in one of the foregoing Claims, and comprising a number of second cupshaped members (11A) aligned with and superimposed on respective first cup-shaped members (11), and which Project upwards from the base plate (10) between respective closed top ends (31) over the base plate (10) , and respective open bottom ends (32) communicating with respective openings (15) ; each of the second cupshaped members (11A) comprising a latéral wall (33) with third through circulation holes (25C) substantially

ORtqthal crosswise to the axis (A) and located over the base plate (10); and a top end wall (34) substantially perpendicular to the axis (A) , and which closes the closed top end (31) and has no circulation holes.

12) A reactor tray as claimed in Claim 11, wherein each first cup-shaped member (11) and the respective superimposed second cup-shaped member (11A) define respective portions (35), projecting beneath and above the base plate (10) respectively, of a tubular body (36) fitted through one of the openings (15) in the base plate (10).

13) A reactor tray as claimed in Claim 11 or 12, wherein the third holes (25C) in the latéral wall (33) of each second cup-shaped member (11A) are similar or identical in shape and arrangement to the second holes (25B), for prédominantly throughflow of a liquid phase, in the first cup-shaped members (11).

14) A reactor tray as claimed in one of the foregoing Claims, wherein the cup-shaped members (11,

11A) are substantially cylindrical.

15) A reactor tray as claimed in one of the foregoing Claims, wherein the first and second cupshaped members (11, 11A) are arranged on the base plate (10) in a grid pattern, with a spacing ranging between roughly 2D and 5/2D, where D is the diameter of the first ànd second cup-shaped members (11, 11A).

ORtgtnàL

16) A urea reactoi' (1) comprising a shell (2) extending substantially along a vertical axis (X) and defining a reaction chamber (3); and a number of reactor trays (4) housed in a mutual spatial relationship inside the shell (2) ; the reactor (1) being characterized in that the trays (4) are as claimed in one of the foregoing Ciaims.

17) A reactor as claimed in Claim 16, wherein each tray (4) is positioned with the base plate (10) substantially perpendicular to the axis (X), and so that each first cup-shaped member (11) projects downwards from the base plate (10) , with the closed bottom end (22) preceding the open top end (21) in the vertical axial upward direction substantially corresponding to the normal flow direction of the process fluids inside the reaction chamber (3).

18) A reactor as claimed in Claim 16 or 17, wherein trays (4) at different heights along the axis (X) hâve respective first holes (25Ά) and second holes (25B), predominantly for throughflow of a gaseous phase and liquid phase respectively, whose total areas, defining respective total flow sections for the gaseous phase and liquid phase, differ according to the location of the tray (4) inside the reactor (1) ; and wherein the total area of the first holes (25A) decreases upwards from one tray (4) to another, and the total area of the second.

0R^TG^TNAL holes (25B) increases upwards from one tray (4) to another.

19) A urea production process comprising the step of : producing a reaction between ammonia and carbon c, dioxide inside a reactor (1) by feeding an ammoniacontaining liquid phase and a carbon-dioxide-containing gaseous phase in the same upward direction inside the reactor and through compartments (7) separated by trays (4); the process being characterized in that the gaseous Ί0 phase and liquid phase flow from one compartment (7) to the ‘ next through transverse holes (25) formed through latéral walls (23) of a number of hollow first cupshaped members (11) projecting downwards from each tray (4) along respective axes (A) and between respective open top ends (21) and respective closed bottom ends (22); said first cup-shaped members (11) having respective bottom ends (22) closed by bottom walls (24) with no holes, so said phases flow through said 20 transverse holes (25) into each first cup-shaped member (11) exclusively in a direction crosswise to the axes (A) .

20) A process as claimed in Claim 19, and comprising the steps of :

__ - feeding the gaseous phase prédominantly through first holes (25A) formed through the latéral walls (23) of the first cup-shaped members (11) qrtgtual feeding the liquid phase predominantly through second holes (25B) also formed through the latéral walls (23) of the first cup-shaped members (11) and located lower down than the first holes (25A) through the latéral walls (23).

21) A process as claimed in Claim 20, wherein the first holes (25A) differ in size from the second holes (25B).

22) A process as claimed in Claim 20 or 21, wherein the first holes (25A) are smaller than the second holes (25B).

23) A process as claimed in one of Claims 20 to 22, wherein the first holes (25A) hâve a diameter (Dl) of roughly 2-20 mm and preferably of about 2-4 mm; and the second holes (25B) hâve a diameter (D2) of roughly 4-30 mm and preferably of about 4-8 mm.

24) A process as claimed in one of Claims 20 to 23, wherein the first holes (25A) are arranged in one or more axially successive rows; and the row closest to the open top end (21) is located at a distance of roughly 1 mm or more, and preferably about 15-20 mm, from a bottom face (14) of the base plate (10).

25) A process as claimed in one of Claims 20 to 24, wherein the first holes (25A) slope with respect to the latéral wall (23).

26) A process as claimed in one of Claims 20 to 25, ortgtnal wherein the second holes (25B) are arranged in one or more axially successive rows; and the row closes to the closed bottom end (22) is located at a distance of 0 mm or more from the bottom wall (24).

27)

A process as claimed in one of Claims 20 to 26,

wherein the size and number ’ of the first and second holes (25A, 25B) and the number of first cup-shaped members (11) are such that the total area of the first holes (25A) ranges between roughly 0% and 20%, and

preferably between roughly 0% and 4%, of the total area of the tray (4), and the total area of the second holes (25B) ranges between roughly

1% and 20%, and preferably between roughly 1% the total area of the tray '»5

28) A process as claimed in Claim 27, wherein trays (4) at different heights along the axis (X) hâve different total areas of the first holes (25A) and second holes (25B), and therefore different total flow sections for the gaseous phase and the liquid phase ; and wherein the total area of the first holes (25A) decreases upwards from one tray (4) to another, and the total area of the second holes (25B) increàses upwards from one tray (4) to another.

29)

A process as claimed in one of Claims 19 to 28, wherein,