EP0130110A1 - Heat exchanger for continuous crystallisation - Google Patents

Abstract

Heat exchanger for continuous crystallisation with a view to the production of crystals by evaporation of a solution, especially of sugar juice, heated by steam. To simplify the manufacture and the use of the exchanger, its exchange bundle (2) consists of hairpin tubes (13) distributed in groups (G) and vertical rows (R), the plane of each tube being inclined so that the steam entry branch is at a level higher than that of the condensed water exit branch, the said branches being substantially horizontal and the ends of the said tubes being fixed in a tube plate (3). <IMAGE>

Description

The present invention relates to an exchanger for continuous crystallization, for the production of crystals by evaporation of a solution, in particular of sweet juice, heated with steam.

Up to now, we have mainly used tube bundle exchangers whose rectilinear tubes were mounted at their ends in two tubular plates. These tubes pass through numerous partitions which hinder their free expansion.

This technique has serious drawbacks. It is necessary to provide for the mounting of the tubes with extremely precise bores each receiving a metal ring or any other material resistant to the medium, provided at least with an O-ring on the plate side and an O-ring on the tube side. The generally considerable number of rings and seals makes manufacturing particularly complicated and expensive. Furthermore, the presence of sugar residues in the grooves of current sealing rings can cause corrosion phenomena. Not only are the tubes no longer free to expand, but their extraction also becomes difficult and sealing problems can arise.

The main object of the invention is to eliminate the above-mentioned drawbacks.

It essentially consists of using hairpin tubes, the ends of which are fixed to a tubular plate by simple expansion, for example, and which do not pose any problem from the dilation point of view.

A more specific subject of the invention is a heat exchanger for continuous crystallization, for the production of tion of crystals by evaporation of a solution, in particular of sweet juice, heated with steam, characterized in that it comprises a bundle of hairpin tubes divided into groups, each group being constituted by at least one tube, the plane of the or each tube being inclined so that the inlet branch of the steam is at a level higher than that of the outlet branch of the condensed water, said branches being substantially horizontal, in that the groups are superimposed so as to form, along the length of the exchanger, parallel vertical rows, two adjacent rows being separated by a certain interval, and in that the ends of the tubes are fixed in a support plate on the outside of which is provided a vertical partition alternately separating the inlet ports and the outlet ports of the tubes.

Said partitioning defines vertically elongated boxes, all the boxes relating to the orifices of the same function communicating with each other.

A cover closes all of the boxes, a steam inlet pipe being integral with said cover.

Partitions supporting the tubes longitudinally divide the exchanger into a plurality of compartments supplied individually in solution, the compartment containing the elbows of the tubes being further supplied with seed magma, and the compartment contiguous to the tube plate being the outlet compartment of a mixture of crystals and mother liquor.

Each group advantageously consists of a plurality of tubes, three for example, whose elbows have different bending radii so that they can be arranged one inside the other.

The tubes are advantageously fixed to the tube plate by expansion.

• La figure 1 représente de façon schématique l'ensemble de l'échangeur de chaleur.
• La figure 2 est une vue en bout du faisceau d'échange, côté coudes des tubes, son couvercle étant supposé enlevé sur la partie droite de la figure.
• La figure 3 en est une vue partielle en plan.
• La figure 4 en est une vue en bout, côté extrémité des tubes, son couvercle étant supposé enlevé.
• La figure 5 est une vue de face du couvercle.
• La figure 6 est une coupe axiale dudit couvercle.
• La figure 7 est une vue en coupe axiale du caisson de sortie d'eau condensée et du gaz incondensable.

The invention will be better understood by referring to the description which follows, given with reference to the appended drawings, concerning a particular embodiment given by way of non-limiting example.

• Figure 1 shows schematically the entire heat exchanger.
• Figure 2 is an end view of the exchange bundle, elbow side of the tubes, its cover being assumed removed on the right side of the figure.
• Figure 3 is a partial plan view.
• Figure 4 is an end view, end side of the tubes, its cover being assumed removed.
• Figure 5 is a front view of the cover.
• Figure 6 is an axial section of said cover.
• Figure 7 is an axial sectional view of the condensed water outlet box and the noncondensable gas.

In Figure 1, we see the entire exchanger contained in a ferrule 1 horizontally elongated. The reference 2 designates the heat exchange bundle placed in the lower half of the shell 1 where it is covered by the solution (sweet juice, for example) which reaches level N. This bundle consists of tubes with pins at hair whose ends are fixed in a tubular plate 3. The arrangement of the tubes of bundle 2 will be described more explicitly below. Transversal partitions, such as 4, which support the tubes, divide the heat exchanger longitudinally into a plurality of compartments, such as 5, supplied individually with concentrated sweet juice by the pipes, such as 6, 7 and 9. The compartment end containing the bends of the tubes is further supplied, by the pipe 8, with a seed magma essentially constituted by small crystals suspended in supersaturated juice.

The reference 10 designates a deflecting plate which obstructs the liquid droplets, while the steam escapes through the outlet 11 connected to a dome 12.

The heating steam is introduced along V into the bundle 2 while the condensed steam is discharged along C. The introduced liquid circulates through the bundle 2 by means of a usual baffle system not shown. At the outlet, a mixture of crystals and mother liquor is collected at M, at the base of the end compartment opposite to that containing the elbows of the tubes, which it is easy to separate by centrifugation.

In Figures 2 to 7, there is shown in detail, on a larger scale, the structure of the exchange beam 2 and its associated members.

This bundle consists of a set of hairpin tubes divided into groups. As seen more particularly in FIG. 2, each group G taken as an example, comprises three tubes 13, 13 ′ and 13 ". These tubes have different bending radii so that they can be arranged one inside the As shown on the right of FIG. 3, the tube 13 has a bending radius greater than that of the tube 13 'and the latter has a bending radius greater than that of the tube 13 ". All these tubes have their horizontal branches, but their planes are inclined so that the inlet branch of the steam is at a level higher than that of the outlet branch of the condensates. This arrangement has the advantage of promoting flow and preventing condensate from stagnating in the loops of the tubes. Indeed these loops ensure the unevenness of the branches and consequently, the inclination of the plane of each tube.

The groups such as group G which we have just defined are superimposed so as to form a vertical row RI which extends along the length of the exchanger. According to the width of the latter are arranged rows R identical; two adjacent rows such as RI and R2 are separated by a certain interval d. In a row R, the height spacings between the branches of the tubes 13, 13 'or 13 "must be determined to leave sufficient space between each of the tubes with the same reference. In principle the inclination of the tubes 13, 13 'and 13 "would preferably be identical. The fact of accommodating a maximum of tubes in the available volume leads to adopt for the 13 "tube the shortest possible bending radius compatible with the diameter and the thickness of this tube. In this case it may be wise to give to these tubes 13 "have a greater inclination than for tubes 13 and 13 '. In the example chosen, the tubes 13 and 13 ′ have the same inclination, the tube 13 ′ being surrounded by the tube 13 with the near offset in height. The 13 "tube is much more inclined than the preceding ones which surround it. The 13" tube cannot however be contained in a vertical plane.

The ends of the tubes 13, 13 'and 13 "are fixed in the tubular plate 3, as is more particularly visible in FIGS. 3 and 4. This fixing is advantageously ensured by expansion.

At the end of the bundle 2, on the elbow side, a cover 14 provided with stiffeners, such as 15, closes the exchanger. This cover allows mounting and possible dismantling in case of tube replacement.

At the opposite end is provided a steam box 100 compartmentalized by vertical partitions such as 16, alternately separating the inlet ports and the outlet ports of the tubes. These partitions define alternate steam and condensate chambers, said chambers being vertically elongated. Partitions 16 have the same height as the belt 107 of the steam box 100.

On the right-hand side of FIG. 4 a distinction is made between the steam chambers 101, 103 and 105 as well as the condensate chambers 102, 104 and 106. On the left-hand side of the figure are symmetrical chambers. The only box 106 is a double box common to the two half-widths of the beam. As shown in detail in FIGS. 5 and 6, the steam box 100 is closed by a cover 17, the bottom wall 19 of which is fitted with a seal 108 bearing both on the belt 107 and on the edges of the partitions 16. The boxes 101 to 106 are thus isolated from each other. The cover 17 ensures the arrival of steam to the boxes such as 101, 103 and 105 and the exit of the light noncondensables from the boxes such as 102, 104 and 106. The condensate outlet, on the other hand, is directly ensured by the pipe 21 provided at the lower part of the belt 107 of the box 100 (see fig. 4 and 7). The cover 17 is provided with a steam inlet pipe 18. Between the inner end of the tube 18 and the bottom wall 19 of the cover which closes the aforementioned boxes, a transverse channel 20 is provided which brings steam to the boxes such as 101, 103 and 105 through orifices, respectively 51, 53, 55 made in said bottom wall 19. This same cover 17 is also provided with the pipes 23 opening at the top point of the boxes such as 102, 104 and 106 and counterparts boxes of the left part of FIG. 4 for the exit of the light noncondensable.

With the exception of the central box 106, the base of which is flat, the other boxes are delimited at their lower part by an inclined plane. The condensates and the heavy incondensables of the caissons 102 and 104 and of their counterparts on the left of FIG. 4 are brought to the central caisson 106 along this slope via passages 33 and 35 passing through respectively. the boxes 103 and 105 along said inclined plane. The heavy incondensables from all the boxes 102, 104, 106 and their counterparts from the left-hand side of FIG. 4 are finally extracted by the tube 22 provided on the wall 19 of the cover 17.

Although the invention has been described with reference to a particular embodiment, it goes without saying that it is in no way limited to it and that modifications can be made to it without departing from its field. In particular, there is nothing to prevent a row R from being made up of groups composed of only 2 tubes 13 "and 13 'and even at the limit of the single tube 13".

We can in particular replace any of the means described by a technically equivalent means. The invention therefore covers, in addition to the example shown, its different possible variants within the limits defined by the claims.

Claims (7)

1. Heat exchanger for continuous crystallization, for the production of crystals by evaporation of a solution, in particular of sweet juice, heated with steam, characterized in that it comprises a bundle (2) of tubes in hairpins divided into groups (G), each group consisting of at least one tube (13), the plane of the or each tube being inclined so that the inlet branch of the steam is at a higher level to that of the outlet branch of the condensed water, said branches being substantially horizontal, in that the groups (G) are superimposed so as to form, along the length of the exchanger, vertical and parallel rows (R) , two adjacent rows (Rl, R2) being separated by a certain interval (d), and in that the ends of the tubes (13) are fixed in a tubular plate (3) on the outside of which a vertical partition is provided (16) alternately separating the inlet orifices and the orifices es outlet tubes (13). 2. Heat exchanger according to claim 1, characterized in that said partitioning defines vertically elongated boxes (101, 102, 103, 104, 105, 106), all the boxes pertaining to the orifices of the same function communicating with each other . 3. Heat exchanger according to claim 2, characterized by a cover (17) closing all of said boxes, a steam inlet pipe (18) being integral with said cover. 4. Heat exchanger according to claim 1, characterized in that partitions (4) supporting the tubes (13) divide said exchanger longitudinally into a plurality of compartments (5) supplied individually with solution, the compartment containing the bends of the tubes (13) being additionally supplied with seeding magma, and the compartment (5) contiguous to the tubular plate (3) being the outlet compartment for a mixture of crystals and mother liquor . 5. Heat exchanger according to claim 1, characterized in that each group (G) consists of a plurality of tubes (13, 13 ', 13 ") whose elbows have different bending radii so that they can be arranged one inside the other. 6. Heat exchanger according to claim 5, characterized in that in each group (G) the tube (13 ") whose elbow has the smallest bending radius has a greater inclination than that of the other tube (s) (13 , 13 '). 7. Heat exchanger according to claim 1, characterized in that the tubes (13) are fixed to the tubular plate (3) by expansion.

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