EP4311992A1

EP4311992A1 - Rotary type dryer for drying wet melamine

Info

Publication number: EP4311992A1
Application number: EP23187650.9A
Authority: EP
Inventors: Alberto De Amicis; Giuseppe DI RUOCCO; Roberto Santucci
Original assignee: Proman Ag
Current assignee: Proman Ag
Priority date: 2022-07-26
Filing date: 2023-07-25
Publication date: 2024-01-31
Also published as: IT202200015684A1; CN117450758A

Abstract

A rotary type dryer for the production of melamine comprising a rotating container comprising a cylindrical side wall and two end tube plates defining a cavity for containing the wet melamine, rotation means for rotating the container, insertion means for inserting the wet melamine into the cavity at a first end of the container, extraction means for extracting the dried melamine from the cavity at a second end of the container, and heating means in the form of tubes extending axially inside the cavity for heating the wet melamine contained in the cavity so as to dry it. The two tube plates comprise a first side facing inside the container, in particular towards the cavity, and a second side facing outside the container, in particular towards an external environment. The heating means comprise a first tube conducting water vapour from the second end to the first end and one or more second tubes conducting at least partly condensed water vapour and which are fluidly coupled outside the container to the first tube at the first end.

Description

FIELD OF THE INVENTION

The present invention relates to a rotary type dryer for drying wet melamine.

STATE OF THE ART

There are currently many types of dryers on the market in the melamine production field. These include contact dryers, typically of the rotary type, in which wet melamine is fed at a first end and the melamine dried by means of heating is collected at a second end.
A dryer typically comprises a cylindrical container, which essentially constitutes the drying chamber, which rotates around its axis and contains the melamine during drying, and a series of tubes through which a hot fluid flows, providing heat necessary for the evaporation of the water contained in the melamine by means of contact between the wall of the tube and the wet melamine advancing inside the drying chamber from a first end to a second end of the chamber. Furthermore, the introduction of an air flow into the chamber is envisaged for removing the water vapour which develops while the melamine dries. The configuration of the current dryers typically provides that the hot fluid, usually steam, is fed and distributed through a system of bayonet tubes situated inside the drying chamber and having a first end fixed to a tube plate from which the steam is fed. Such a configuration is characterised by the presence of a first inner tube surrounded by a second outer return tube fluidically connected to the first inner tube at a second end. The inner tube ('steam tube') receives the steam through the tube plate and feeds the steam to the second end of the outer tube ('condensation tube' or 'heat exchange tube'), which is closed at its second end by a bottom, so that the steam can flow from the second end of the outer tube into the drying chamber, exchange heat with the melamine contained in the drying chamber (and thus at least partly condense) and finally be collected at the tube plate. It should be noted that according to this configuration, the ratio of the number of steam tubes to the number of condensation tubes is 1: 1. Typically, the supply of steam to the inner tubes and the collection of condensate from the outer tubes, respectively occurs by means of distribution and collection chambers located at the second end of the drying chamber and delimited, towards the outside, by a closing wall and, towards the drying chamber, by the tube plate to which the bayonet tubes are connected and fixed. However, in the event of a steam leak in a conventional rotary type dryer as just described, the steam could enter the drying chamber (the drying chamber is typically at a lower pressure than that of the steam and sometimes slightly under vacuum with respect to ambient pressure).
In fact, in general, it is known that the weakest points in a fluid distribution system are the points where two elements of the system join, typically made by means of welding or sealing; for example, leakage may occur at a weld of the outer tube bottoms or at a seal fixing the tubes to the tube plate. It should be highlighted that in the known drying systems, the dryer provides two chambers, in particular a steam distribution chamber and a condensate collection chamber, and two tube plates, a first tube plate which supports the steam distribution tubes and fluidly couples the steam distribution tubes and the steam distribution chamber, and a second tube plate which supports the condensation tubes (i.e., the heat exchange tubes in which the condensate forms) and which fluidly couples the condensation tubes and the condensate collection chamber. It should further be noted that the fluids contained in the two chambers are pressurised, e.g., at a relative pressure of 8 bar, while the drying chamber in which the tubes pass through which the fluids flow is at a lower pressure or even under vacuum, e.g., at -20 mmH₂O (water column millimetres). Consequently, the wall thickness of the chambers and tube plates must be such as to withstand such pressure differences.
The loss of steam inside the drying chamber causes an increase in the relative humidity (=HR) of the air at the exit of the drying chamber with a consequent increase in the condensation temperature (=Tcond) of the wet air at the exit of the drying chamber, which could result in the dew point of the wet air being reached with the consequent danger of condensation in the systems downstream of the dryer (e.g., wet air treatment and filtering systems).
A further problem may be the continual increase in capacity demanded by the market for melamine production plants. As a result, the dryer must be designed with ever larger dimensions and with steam distribution and condensate recovery chambers with ever larger diameters; as a consequence, there is a considerable increase in the weight of the dryer due, on the one hand, to the increase in diameter and length (of both the chamber and the tubes) and, on the other hand, due to the increase in wall thickness of the steam distribution chambers at the same steam pressure. It should be noted that the portion of the dryer's weight due to the presence of the distribution chambers and tube plates, as well as the number of tubes through which the fluids flow, can amount to up to 16 tonnes, for example.

SUMMARY

The general object of the present invention is to provide a dryer which overcomes the drawbacks of the prior art.
A more specific object is to provide a dryer which has little or even no risk of water vapour leaking into the drying chamber.
A second, more specific object is to provide a dryer with a reduced weight for the same dryer capacity, in particular by eliminating the weight due to the distribution chambers and tube plates and reducing the number of steam distribution tubes.
This general object and other more specific objects are reached thanks to what is expressed in the appended claims that form an integral part of the present description.

LIST OF FIGURES

The present invention shall become more readily apparent from the detailed description that follows to be considered together with the accompanying drawings in which:

Fig. 1 shows a schematic side view of an example of a dryer for drying wet melamine according to the present invention,
Fig. 2 shows a more detailed (partial) side view of an example of a fluid connection at the first end of the dryer of Fig. 1,
Fig. 3 shows a more detailed (partial) side view of a first alternative embodiment of a fluid connection at the second end of the dryer of Fig. 1,
Fig. 4 shows a more detailed (partial) side view of a second alternative embodiment of a fluid connection at the second end of the dryer of Fig. 1,
Fig. 5 shows a schematic cross-sectional view of the first end of the dryer of Fig. 2, and
Fig. 6 shows a schematic cross-sectional view of the second end of the dryer of Fig. 4

As it can be easily understood, there are various ways of practically implementing the present invention which is defined in its main advantageous aspects in the appended claims and is not limited either to the following detailed description or to the appended drawings.

DETAILED DESCRIPTION

For the illustration of the drawings, use is made in the following description of identical numerals to indicate construction elements with the same function. Further, for illustration clarity, some numerical references may not be repeated in all the figures.
Indications such as "vertical" and "horizontal", "upper" and "lower" (in the absence of other indications) are to be read with reference to the assembly (or operating) conditions and with reference to the normal terminology used in everyday language, where "vertical" indicates a substantially parallel direction to that of the gravitational force vector "g" and horizontal to a direction perpendicular thereto, coinciding with the "direction of the horizon".
With general reference to the various figures, a preferred, but not limiting, embodiment of a machine for drying wet melamine according to the present invention is shown, referred to as a whole by the numerical reference 100. It will be hereinafter referred to by the abbreviated notation 'dryer 100'.
The dryer 100 is a rotary type dryer adapted to be integrated in a melamine production plant, in particular in a section of the plant dedicated to drying the melamine produced, typically in the form of pasty material ('cake').
Figure 1 shows a schematic side view of an example of a dryer 100 for drying wet melamine according to the present invention in which the flows of substances into and out of the dryer 100 are highlighted, as will be further explained below (see the large black arrows in the figure).
In particular, the dryer 100 is configured to receive wet melamine MU, typically a wet melamine paste, at a first end thereof and to extract dried melamine ME, typically dried melamine crystals, at a second end thereof. The wet melamine MU which advances along the dryer, in particular in a container of the dryer, from the first end to the second end is dried by means of heat transfer from a hot fluid to the wet melamine MU, so that (all or most) of the water contained in the wet melamine MU is evaporated and dried melamine ME is generated. In more detail, a flow of water vapour V is fed from the second end of the dryer into first tubes which cross the dryer from the second end to the first end and is returned at least partly (advantageously totally) condensed C in second tubes which cross the dryer from the first end to the second end and which are adapted to exchange heat with the wet melamine MU; the condensed water vapour C is then collected and discharged at the second end of the dryer, as is the dried melamine ME. Lastly, an air flow A, advantageously an air flow with a low humidity percentage, is fed to the dryer at the second end of the dryer, in particular in a counterflow configuration with respect to the feed direction of the wet melamine MU; the air flow A is adapted to collect (in particular entrain) the evaporated water from the wet melamine MU, so that a wet air flow AU is discharged at the first end of the dryer. It should be noted that the discharged wet air AU could contain further melamine crystals which have been entrained by the air flow itself (typically crystals which are smaller in size and thus lighter in weight, known as 'fine', are entrained).
In more detail, the dryer 100 comprises a container 10 comprising a cylindrical side wall 16 and two end tube plates 13 and 14, in particular a first tube plate 13 at a first end 11 and a second tube plate 14 at a second end 12 opposite the first end. As will be described in more detail below, the two tube plates 13 and 14 are adapted to close the ends of container 10, making heating means in the form of tubes exit therefrom. The container 10, in particular the cylindrical side wall 16 and the two tube plates 13 and 14, defines a cylindrical cavity 15 adapted to contain the wet melamine MU. Furthermore, the container 10 is adapted to rotate about the rotational axis R thereof, so as to move the wet melamine MU contained in cavity 15. Typically, the pressure P1 inside the cavity 15 is slightly lower than the pressure Pamb of the environment outside the cavity 15; in particular, the dryer 100 provides means adapted to keep the pressure P1 slightly lower than the pressure Pamb, e.g., P1 is substantially equal to -20 mmH₂O (water column millimetres) and Pamb is substantially equal to 1 bar. For example, the dryer 100 can provide fans adapted to keep the pressure P1 slightly lower than the pressure Pamb; in particular, the dryer 100 can provide a first fan upstream of the inlet of the air flow A, in particular a fan adapted to push the air flow A inside the cavity 15, and a second fan downstream of the discharge of the wet air flow AU, in particular a fan adapted to suck the wet air flow AU outside the cavity 15. It should be noted that by appropriately adjusting the flow rates of the air flow A and the wet air flow AU, it is possible to keep the cavity 15 slightly under vacuum (i.e., at a pressure slightly lower than the pressure Pamb of the environment outside the cavity 15). The wet melamine MU is fed into the cavity 15 at the first end 11 of the container 10 by feeding means 30; typically, the melamine feeding means 30 comprise an auger which acts as a basically continuous feeder of wet melamine into the cavity 15 at the first end 11.
According to the example in the figures, both the container and the cavity are cylindrical in shape.
The container 10 is rotated (and kept in rotation) by rotation means 20, typically comprising a crown and pinion system, adapted to rotate the container 10 about the axis R thereof at least while it contains the wet melamine MU. It should be noted that in the schematic view of Fig. 1, the rotation axis R of the container 10 is shown horizontal, i.e., the first end 11 and the second end 12 of the container 10 are shown at the same height. However, advantageously, the dryer 100 is typically installed so that the rotation axis R of the container 10 forms an angle greater than 0° with the horizon line (coincident with the horizontal direction), advantageously by about 4° or 5°. In other words, the first end 11 and the second end 12 of the container 10 are placed at different heights; in particular, the first end 11 is placed at a higher height with respect to the second end 12, so that the feeding of the wet melamine MU inside the cavity 15 from the first end 11 to the second end 12 is facilitated. The dryer 100 further comprises extraction means 40 at the second end 12, typically in the form of openings in the side wall of the container 10, associated for example with a hopper, for extracting dried melamine ME from the cavity 15.
As already mentioned, dryer 100 is adapted to dry the wet melamine MU fed into the container 10. The container 10 therefore comprises heating means 50 adapted to heat the wet melamine MU which is contained in the cavity 15 of the container 10. The heating means 50 are generally in the form of tubes which extend axially at least partly inside the cavity 15 and which are adapted to conduct hot fluids, as will be further explained below.
According to the example in the figures, all the tubes of the heating means extend axially.
In particular, the heating means 50 extend inside the cavity 15 and exit therefrom at the two ends 11 and 12, and in particular exit from the tube plates 13 and 14 located at the ends of the container 10. Advantageously, and as will be described below, the heating means 50 are adapted to circulate fluids and such fluids are fed and collected outside the container 10, so that the fluid couplings between the heating means 50 and other elements of the drying machine, in particular manifolds and/or fluid distributors, are at an external environment, in particular an external environment at atmospheric pressure. In other words, the container 10 does not provide any fluid distribution or collection chambers located at the ends 11 and 12 of the container 10, in particular located at the tube plates 13 and 14, to which the heating means are coupled; each tube plate 13 and 14 therefore has a first side (see references 13B and 14B in Figures 2, 3 and 4) facing towards the inside of the container 10, in particular facing the cavity 15, and a second side (see references 13A and 14A in Figures 2, 3 and 4) - opposite the first - facing outside the container 10, in particular facing an external environment. Advantageously, the first side 13B and 14B of each tube plate 13 and 14 is therefore subject to the pressure of the cavity 15 (typically being at a slightly lower pressure with respect to the pressure of the environment outside the cavity 15) and the second side 13A and 14A of each tube plate 13 and 14 is subject to the pressure of the external environment, in particular atmospheric pressure.
The heating means 50 comprise:

at least one first tube 51, advantageously a plurality of first tubes 51, extending from at least the second end 12 of the container 10 to at least the first end 11 of the container 10, and which is adapted to conduct water vapour V from the second end 12 to the first end 11, and
one or more second tubes 52, advantageously a plurality of second tubes 52, extending from at least the first end 11 of the container 10 to at least the second end 12 of the container 10 at least in part inside the cavity 15, and adapted to conduct at least partly condensed water vapour C (advantageously totally condensed) from the first end 11 to the second end 12.

It is important to note that the one or more second tube(s) 52 are fluidly coupled outside the cavity 15 to the first tube(s) 51 at the first end 11, in particular at the external environment outside the tube plate 13, (see for example Fig. 2). In other words, the second tube(s) 52 are fluidly coupled to the first tube(s) 51 at the pressure Pamb of the environment outside the cavity 15, so that any fluid leakage due to for example, failure, malfunction or wear, in particular at the couplings between the first tube(s) 51 and the second tube(s) 52, occurs outside the cavity 15, in particular at the pressure Pamb of the environment outside the cavity 15.
Advantageously, the at least one first tube 51 extends at least in part inside the cavity 15; in particular, the first tube(s) 51 can have a first portion extending along the entire cavity 15 and two second portions, typically of much shorter length with respect to the first portion, which exit from the cavity 15 at the first end 11 and the second end 12 of the container 10, respectively (note that the two second portions can have different lengths from each other). Alternatively, the at least a first tube 51 could be outside the cavity 15 (according to this alternative, however, the rotation of the container 10 actuated by the rotation means 20 could be more difficult).
Advantageously, the at least a first tube 51 is surrounded by one or more layers of thermal insulating material between the second end 12 and the first end 11 so as to prevent heat transfer from the water vapour V transported inside the at least one first tube(s) 51 to the wet melamine MU contained in the cavity 15 (if the at least one first tube 51 is located inside the cavity 15) or to an environment outside the cavity 15 (if the at least a first tube 51 is located outside the cavity 15).
With non-limiting reference to Fig. 1, the heating means 50 of the dryer 100 comprise, for example, two first tubes 51-1 and 51-2 for conducting water vapour V and six second tubes 52-1, 52-2, 52-3, 52-4, 52-5 and 52-6 for conducting at least partly condensed water vapour C.
More in general, the dryer 100 according to the present invention comprises one or more first tubes 51 and a plurality of second tubes 52, in particular a minimum of two and a maximum of fifty second tubes 52 are provided for each first tube 51; for example, the dryer 100 of Fig. 1 provides two first tubes 51 and six second tubes 52: a first first tube 51-1 for the transport of water vapour V to which three second tubes 52-1, 52-2 and 52-3 are associated (in particular fluidly coupled so that the water vapour V transported by the first tube 51-1 can pass to the three second tubes 52-1, 52-2 and 52-3) for the transport of at least partly condensed water vapour C and a second first tube 51-2 for the transport of water vapour V with which three second tubes 52-4, 52-5 and 52-6 are associated (in particular fluidly coupled, so that the water vapour V transported by the first tube 51-2 can pass to the three second tubes 52-4, 52-5 and 52-6) for the transport of at least partly condensed water vapour C. Preferably, a minimum of ten to a maximum of twenty-five second tubes 52 are provided for each first tube 51.
As already mentioned and as will be better described below, the first tube(s) 51 and the second tube(s) 52 are fluidly coupled together. Advantageously, therefore, in the dryer 100 according to the present invention there is a self-distribution of the fluids transported inside the second tubes 52 (in particular of the at least partly condensed water vapour C): when the water vapour condenses, there is a decrease in the volume of the fluid and thus a creation of a vacuum which, as a result, naturally draws more fluid inside the tube.
With non-limiting reference to Fig. 2 and Fig. 5, a side view and a (simplified) cross-sectional view of examples of fluid coupling between first tubes 51 and second tubes 52 at the first end 11 are shown, respectively, at the external environment outside the tube plate 13. In particular, the heating means 50 of the dryer 100 can further comprise one or more third tubes 53, preferably in the form of flexible tubes, adapted to fluidly couple outside the cavity 15 the at least one first tube 51 and the second tubes 52.
Figure 2 shows, by way of example, two first tubes 51-1 and 51-2 in which each of the first tubes 51-1 and 51-2 has a portion which extends outside of the cavity 15 and is fluidly coupled to the second tubes 52-1, 52-2 and 52-3 and the second tubes 52-4, 52-5 and 52-6, respectively. In particular, the fluid coupling between the first tubes 51-1 and 51-2 and the second tubes 52-1, 52-2, 52-3, 52-4, 52-5 and 52-6 is made outside the cavity 15 by means of third tubes 53. In particular, a first end of the third tube 53 is fluidly coupled to a first tube 51-1 or 51-2 and a second end of the third tube 53 is fluidly coupled to a second tube 52-1 or 52-2 or 52-3 or 52-4 or 52-5 or 52-6. Advantageously, the dryer 100 provides a third tube 53 for each of the second tubes 52-1, 52-2, 52-3, 52-4, 52-5 and 52-6 (for the sake of clarity, not all the references for each third tube 53 have been shown in Figure 2). Even more advantageously, the dryer 100 provides a first manifold 61 at the first end 11 outside the cavity 15. Fig. 5 shows an example of a first manifold 61 in the form of a circular crown extending around the rotation axis R. Alternatively, the first manifold 61 can have a different configuration. In particular, the first manifold 61 is fluidly connected to the first tubes 51-1 and 51-2, so as to receive water vapour V from the first tubes 51-1 and 51-2, and to the third tubes 53, in particular to a first end of the third tube 53, so as to distribute the water vapour V to the third tubes 53; in other words, the first manifold 61 acts as a distribution chamber of the water vapour V between the first tubes 51-1 and 51-2 and the third tubes 53 (advantageously, in fact, the number of second tubes 52 - and consequently of third tubes 53 - is much greater with respect to the number of first tubes 51 and the presence of the first manifold 61 favours the homogeneous distribution of the water vapour V in the third tubes 53).
According to a first possibility, the dryer 100 comprises a first valve 71 upstream of each second tube 52 and a third valve 73 downstream of each second tube 52 in relation to a flow direction of at least partly condensed water vapour C. Preferably, the first valve 71 and the third valve 73 are shut-off valves.
In particular, each of the third tubes 53 comprises a first valve 71 at the first end of the third tube 53, i.e., at the fluid coupling between the manifold 61 and the third tube 53. In particular, the first valve 71 is adapted to decouple the manifold 61 and the third tube 53, i.e., to prevent the passage of water vapour V from the manifold 61 to the third tube 53. Advantageously, during the normal operation of the dryer 100, the first valve 71 is in an open configuration, so that the water vapour V can flow from the manifold 61 to the third tube 53; in case of need, for example in case of wear of the third tube 53, the first valve 71 passes to a closed configuration (preferably, the third valve 73 also passes to a closed configuration, as will be better explained below), so that the flow of water vapour V from the manifold 61 to the third tube 53 is prevented and the maintenance of only the third tube 53 associated with the closed first valve 71 is facilitated without having to interrupt the flow of fluids in the entire dryer 100. According to a second possibility, each of the third tubes 53 further comprises a second valve 72 at the second end of the third tube 53, i.e., at the fluid coupling between the third tube 53 and the second tube 52. Preferably, the second valve 72 is a shut-off valve adapted to decouple the third tube 53 and the second tube 52, i.e., to prevent the passage of water vapour V from the third tube 53 to the second tube 52. Advantageously, during the normal operation of the dryer 100, the second valve 72 is in an open configuration, so that the water vapour V can flow from the third tube 53 to the second tube 52; with non-limiting reference to the embodiment example shown in Fig. 2, in case of need, e.g., in the event of wear of the third tube 53, both the first valve 71 and the second valve 72 pass to a closed configuration, so that the third tube 53 is fluidly isolated and maintenance, in particular replacement, of only the third tube 53 is facilitated.
With non-limiting reference to Fig. 3, Fig. 4 and Fig. 6, two side views and a (simplified) cross-sectional view, respectively, are shown of examples of fluid coupling between first tubes 51 and second tubes 52 at the second end 12, as well as the supply of water vapour V and the extraction of at least partly condensed water vapour C to/from the heating means 50, as will be further explained below.
As mentioned, during the operation of the dryer 100, i.e., when the container 10 contains the wet melamine MU to be dried, the container 10 is rotated about the rotation axis R thereof. Advantageously, the dryer 100 further comprises a rotary joint 70 mechanically coupled to the container 10 at the second end 12 thereof, in particular at the rotation axis R thereof. In general, the rotary joint 70 is adapted to connect a rotating part, in particular the container 10 and the heating means 50, and a fixed part, in particular feed pipes for the water vapour V (not shown in the figures but schematized by the black arrow of water vapour V supply shown for example in Fig. 1, Fig. 3 and Fig. 4). In particular, the rotary joint 70 is designed to manage several fluids simultaneously: the rotary joint 70 is adapted to feed water vapour V to the first tube(s) 51 outside the cavity 15 and to receive at least partly condensed water vapour C from the second tube(s) 52 outside the cavity 15. Advantageously, the dryer 100 further comprises a second manifold 62 fluidly coupled to the second tube(s) 52 at the second end 12, so as to receive at least partly condensed water vapour C from the second tube(s) 52 outside the cavity 15, in particular at the external environment outside the tube plate 14. The second manifold 62 is further coupled to the rotary joint 70 so as to feed the at least partly condensed water vapour C to the rotary joint 70. With non-limiting reference to Fig. 3, Fig. 4 and Fig. 6, the second manifold 62 can be in the form of tubes extending radially from the rotary joint 70 to the second tube(s) 52 (it should be noted that the second tube(s) 52 can be coupled directly - see Fig. 4 - or indirectly - see Fig. 4 and Fig. 5 - to the second manifold 62, as will be further explained below). Alternatively, the second manifold 62 can have a different configuration.
Advantageously, the dryer 100 further comprises a distributor 63 fluidly coupled to the rotary joint 70 at the second end 12, so as to feed water vapour V to at least the first tube 51, advantageously to a plurality of first tubes 51, outside the cavity 15, in particular at the external environment outside the tube plate 14 (see for example Fig. 3 and Fig. 4). As shown for example in Fig. 6, the distributor 63 can be in the form of tubes extending radially from the rotary joint 70 to the first tubes 51. Alternatively, the distributor 63 can have a different configuration.
As mentioned, the one or more second tubes 52 can be coupled directly or indirectly to the second manifold 62 at the second end 12: according to a first example shown in Fig. 3, the one or more second tubes 52 are fluidly coupled outside the cavity 15, in particular at the external environment outside the tube plate 14, directly to the second manifold 62; according to a second example shown in Fig. 4, the heating means 50 of the dryer 100 further comprise one or more fourth tubes 54 at the second end 12. With non-limiting reference to Fig. 4, the dryer 100 provides a fourth tube 54 for each second tube 52. Even more advantageously, each of the fourth tubes 54 is fluidly coupled to a respective second tube 52 at a first end of the fourth tube 54 and to the second manifold 62 at a second end of the fourth tube 54, so that each of the second tubes 52 and the second manifold 62 are fluidly coupled outside the cavity 15, in particular at the external environment outside the tube plate 14, by means of the fourth tubes 54. In other words, the first end of each fourth tube 54 is fluidly coupled to a second tube 52 and the second end of each fourth tube 54 is coupled to the second manifold 62. Preferably, the fourth tubes 54 are in the form of flexible tubes.
According to a first possibility, each of the fourth tubes 54 further comprises a third valve 73 at the second end of the fourth tube 54, i.e., at the fluid coupling between the fourth tube 54 and the second manifold 62. Preferably, the third valve 73 is a shut-off valve adapted to decouple the fourth tube 54 and the second manifold 62, i.e., to prevent the passage of at least partly condensed water vapour C from the fourth tube 54 to the second manifold 62 and vice versa (there may be a return of at least partly condensed water vapour C from the manifold 62 to the fourth tube 54). Advantageously, during the normal operation of the dryer 100, the third valve 73 is in an open configuration, so that the at least partly condensed water vapour C can flow from the fourth tube 54 to the second manifold 62; if necessary, for example in the event of wear of the fourth tube 54, the third valve 73 passes to a closed configuration. Advantageously, at least one of the two valves 71 or 72 (associated with the same second tube 52 with which the fourth tube 54 requiring maintenance is associated) also passes to a closed configuration, so that the flow of the at least partly condensed water vapour C into the fourth tube 54 is prevented and the maintenance of only the fourth tube 54 associated with the third closed valve 73 is facilitated without having to interrupt the flow of fluids in the entire dryer 100. It should be noted that in the event of the presence of the third valve 73 for each fourth tube 54, the second valve 72 could advantageously not be present; in other words, in the event of use of third tubes 53 and fourth tubes 54 to make the fluid coupling between first tubes 51 (or first manifold 61) and second tubes 52 and between second tubes 52 and rotary joint 70 (or second manifold 62), only a first valve 71 at the first end of the third tube 53 and a third valve 73 at the second end of the fourth tube 54 can be present. For example, if maintenance is required on the third tube 53 (or similarly on the fourth tube 54), the first valve 71 and the third valve 73 pass into a closed configuration. Thereby, both the third tube 53 and the fourth tube 54 can be advantageously fluidly isolated, so that maintenance can be carried out thereon, e.g., carrying out a tube replacement.
According to a second possibility, each of the fourth tubes 54 further comprises a fourth valve 74 at the first end of the fourth tube 54, i.e., at the fluid coupling between the second tube 52 and the fourth tube 54. Preferably, the fourth valve 74 is a shut-off valve adapted to decouple the second tube 52 and the fourth tube 54, i.e., to prevent the passage of at least partly condensed water vapour C from the second tube 52 to the fourth tube 54. Advantageously, during the normal operation of the dryer 100, the fourth valve 74 is in an open configuration, so that the at least partly condensed water vapour C can flow from the second tube 52 to the fourth tube 54; in case of need, for example in the event of wear of the fourth tube 54, both the third valve 73 and the fourth valve 74 pass to a closed configuration, so that the fourth tube 54 is fluidly isolated and maintenance, in particular replacement, of only the fourth tube 54 is facilitated.

Claims

Machine (100) for drying wet melamine, comprising:
- a container (10) comprising a cylindrical side wall (16) and two end tube plates (13, 14), said container (10) rotating about the axis (R) thereof and defining a cavity (15) adapted to contain said wet melamine (MU),

- rotation means (20) adapted to rotate said container (10) about the axis (R) thereof at least while it contains said wet melamine (MU),

- feeding means (30) adapted to feed said wet melamine (MU) in said cavity (15) at a first end (11) of the container (10),

- extraction means (40) adapted to extract dried melamine (ME) from said cavity (15) at a second end (12) of the container (10);

wherein said container (10) comprises heating means (50) adapted to heat said wet melamine (MU) contained in said cavity (15) so as to dry it, said heating means (50) being in the form of tubes extending axially, said tubes being adapted to conduct hot fluids;

wherein said heating means (50) comprise:
- at least one first tube (51) extending from at least said second end (12) to at least said first end (11), and adapted to conduct water vapour (V) from said second end (12) to said first end (11), and

- one or more second tubes (52) extending from at least said first end (11) to at least said second end (12) at least in part inside said cavity (15), fluidly coupled outside said cavity (15) to said first tube (51) at said first end (11), and adapted to conduct at least partly condensed water vapour (C) from said first end (11) to said second end (12); and
and wherein said two tube plates (13, 14) comprise a first side (13B, 14B) facing towards the inside of the container (10), in particular towards the cavity (15), and a second side (13A, 14A) facing towards the outside of the container (10), in particular towards an external environment.
Machine (100) according to claim 1, wherein said first side (13B, 14B) is subjected to the pressure of the cavity (15) and said second side (13A, 14A) is subjected to the pressure of the external environment.
Machine (100) according to claim 1 or 2, wherein said heating means (50) comprise one or more first tubes (51) and a plurality of second tubes (52), said one or more first tubes (51) being fewer in number with respect to said plurality of second tubes (52), in particular from a minimum of 2 to a maximum of 50 second tubes (52) for each first tube (51), preferably from 10 to 25 second tubes (52) for each first tube (51) are provided.
Machine (100) according to claim 1 or 2 or 3, wherein said at least a first tube (51) extends at least partly inside said cavity (15).
Machine (100) according to any one of the preceding claims, wherein said at least one first tube (51) is surrounded by one or more layers of thermal insulating material at least between said second end (12) and said first end (11) so as to prevent heat transfer from said water vapour (V) to said wet melamine (MU) contained in said cavity (15) or to an environment outside said cavity (15).
Machine (100) according to any one of the preceding claims, wherein said heating means (50) further comprise one or more third tubes (53), said one or more third tubes (53) being adapted to fluidly couple outside said cavity (15) said at least one first tube (51) and said one or more second tubes (52) at said first end (11), said third tubes (53) preferably being flexible tubes.
Machine (100) according to claim 6, wherein each of said one or more third tubes (53) is fluidly coupled to a first tube (51) at a first end of said third tube (53) and to one of said one or more second tubes (52) at a second end of said third tube (53).
Machine (100) according to any one of the preceding claims, further comprising a first manifold (61) at said first end (11) outside said cavity (15), said first manifold (61) being fluidly coupled to said at least one first tube (51), so as to receive water vapour (V) from said at least one first tube (51).
Machine (100) according to claim 6 and 8, wherein each of said one or more third tubes (53) is fluidly coupled to said first manifold (61) at a first end of said third tube (53) and to one of said one or more second tubes (52) at a second end of said third tube (53), respectively.
Machine (100) according to any one of the preceding claims, further comprising at least a first valve (71) upstream of said one or more second tubes (52) and at least a third valve (73) downstream of said one or more second tubes (52) in relation to a flow direction of at least partly condensed water vapour (C), said first valve (71) and said third valve (73) preferably being shut-off valves.
Machine (100) according to claim 10, wherein each of said one or more third tubes (53) comprises said first valve (71) at said first end of said third tube (53).
Machine (100) according to claim 10 or 11, wherein each of said one or more third tubes (53) further comprises a second valve (72) at said second end of said third tube (53), said second valve (72) preferably being a shut-off valve.
Machine (100) according to any one of the preceding claims, further comprising a rotary joint (70) mechanically coupled to said container (10) at said second end (12), in particular at the axis (R) thereof, said rotary joint being adapted to feed water vapour (V) to said at least a first tube (51) outside said cavity (15) and to receive at least partly condensed water vapour (C) from said one or more second tubes (52) outside said cavity (15).
Machine (100) according to any one of the preceding claims, further comprising a second manifold (62) at said second end (12) outside said cavity (15), said second manifold (62) being fluidly coupled to said one or more second tubes (52), so as to receive at least partly condensed water vapour (C) from said one or more second tubes (52).
Machine (100) according to claim 14, wherein said second manifold (62) is further adapted to feed at least partly condensed water vapour (C) to said rotary joint (70).
Machine (100) according to claim 13, further comprising a distributor (63) at said second end (12), said distributor (63) being fluidly coupled to said rotary joint (70) and adapted to feed water vapour (V) to said at least a first tube (51) outside said cavity (15).
Machine (100) according to claim 14 or 15, wherein said heating means (50) further comprise one or more fourth tubes (54), said one or more fourth tubes (54) being adapted to fluidly couple said one or more second tubes (52) to said second manifold (62) at said second end (12) outside said cavity (15), said one or more fourth tubes (54) preferably being flexible tubes,
wherein each of said one or more fourth tubes (54) is fluidly coupled to a second tube (52) at a first end of the fourth tube (54) and to said second manifold (62) at a second end of said fourth tube (54).
Machine (100) according to claims 10 and 17, wherein each of said one or more fourth tubes (54) comprises said third valve (73) at said second end of the fourth tube (54).
Machine (100) according to claim 17 or 18, wherein each of said one or more fourth tubes (54) further comprises a fourth valve (74) at said first end of the fourth tube (54), said fourth valve (74) preferably being a shut-off valve.
Machine (100) according to any one of the preceding claims, comprising means for maintaining a pressure (P1) inside said cavity (15) slightly lower than a pressure (Pamb) of the environment outside said cavity (15).