EP1773502B1 - Spray nozzle - Google Patents

Description

The invention relates to a watering nozzle, in particular a watering nozzle for multi-effect distillation seawater desalination plants.

Multi-effect distillation (MED) is, alongside successive distillation, one of the two main industrial methods of desalination of sea water imitating the natural cycle of water (evaporation- condensation-rain).

This method takes advantage of the heat of condensation, released during the condensation of a first quantity of water vapor, to vaporize sea water and thus again generate water vapor that can be condensed. , etc. This succession of evaporations and condensations is possible only if the vaporization pressure decreases sufficiently at each stage to allow a corresponding lowering of the vaporization temperature.

A multi-effect distillation seawater desalination plant thus comprises a multitude of juxtaposed chambers or distillation cells, called "effects", which operate at decreasing pressure and temperature from first to last effect. The first effect, which is also the hottest, is fed by steam condensing at a temperature generally between about 60 and 70 ° C (heating vapor). The condensation of this hot vapor in the heat exchanger of the first effect releases condensation heat. This heat of condensation provides the vaporization energy (latent heat of evaporation) necessary to transform into vapor some of the seawater flowing in thin film on the other side of the heat exchanger. The water vapor thus formed can be used to supply the heat exchanger with a second effect of similar design to the first but operating at a lower temperature and pressure.

In order for such a multi-effect system to operate with good efficiency and without disturbances, it is essential to ensure a steady flow of the thin film supply seawater over the largest possible outer surface of the heat exchanger tubes. , generally gathered in bundles, that is to say a homogeneous spraying of these tubes. However, the spraying of a liquid medium into fines droplets generally assume the passage of this liquid under pressure through small orifices or through turbulence chambers containing internal deflector elements forming an obstacle to the flow of fluid. It will be readily understood that such a spraying mechanism is problematic for natural liquid media such as seawater, containing a large number of insoluble impurities (algae, plankton, sand) likely to plug these orifices. Preliminary filtration of the withdrawn liquid medium implies a significant pressure loss detrimental to the good performance of the installation and also creates a cost of operation related to the need to regularly clean the filter elements. DE 199 48 939 describes a watering nozzle according to the preamble of claim 1.

Another approach for finely and homogeneously dispersing a natural liquid such as seawater without passing through obstacles or small openings is described in the French application of the Applicant, published under the number FR 2,811,916 . The watering nozzle described in this application comprises a cylindrical turbulence chamber in which the coolant is rotated according to a main swirling flow. The particular stepped conformation of the upper face of the turbulence chamber creates a series of secondary vortices carried by the main vortex, the vortex assembly filling the turbulence chamber such that the sprinkler cone formed by the diffuser is a solid cone. The risk of clogging such a nozzle, free of obstacles or small openings, can be completely eliminated by a simple coarse filtration involving virtually no pressure loss or cleaning cost.

Although this nozzle allows in principle a homogeneous dispersion of the seawater without risk of clogging or loss of pressure, this device, under the actual operating conditions with injection of the fluid under pressure in a partial vacuum chamber, has proved partly unsatisfactory because it provides an unstable watering rate with more or less regular pulsations impossible to correct.

The Applicant has therefore continued his research to improve the hydrodynamics of the nozzle of the type described above. This research resulted in a watering nozzle which, as a mechanical means to create secondary vortices, did not steps as described in FR 2,811,916 , but radial grooves arranged in a particular way, without symmetry of rotation with respect to the central axis of the turbulence chamber.

The subject of the present invention is therefore a watering nozzle comprising a substantially cylindrical turbulence chamber with an upper wall and a lower wall, an inlet duct for the cooling liquid discharging into the turbulence chamber in a direction causing a turbulence. tangential flow of the liquid in the turbulence chamber, and a diffuser, in the form of a trumpet horn widening downwards, coaxial with the turbulence chamber, characterized in that the upper wall of the turbulence chamber comprises , on its inner face, a central depression and a number of grooves radially arranged in a first sector corresponding to the beginning of the tangential flow path of the cooling liquid in the turbulence chamber, the other sector, complementary to the sector, being free of train paths.

Although particularly useful in multi-effect distillation seawater desalination plants, the nozzle of the present invention can be used in all applications where it is necessary to disperse finely, without risk of clogging, a liquid medium. slightly viscous according to a solid dispersion cone.

In the following description, we will repeatedly use the adjectives "horizontal" and "vertical" which make sense only to the extent that the watering nozzle to be described has a specific orientation in the 'space. For the purposes of the description, this spatial orientation is such that the central axis of the turbulence chamber and the diffuser is a vertical axis and the lower and upper walls of the cylindrical turbulence chamber are each in a horizontal plane, perpendicular to this central vertical axis. In this position, the flow direction of the liquid in the arrival duct is also located in a substantially horizontal plane.

The turbulence chamber of the watering nozzle according to the invention preferably has the shape of a relatively flat cylinder, that is to say a cylinder having a height less than the diameter of the base. The ratio of the height of the turbulence chamber to the diameter of the The lower or upper wall is preferably between 0.6 and 0.8 and in particular between 0.65 and 0.75.

In the nozzle of the present invention, the coolant is injected into the turbulence chamber in a substantially horizontal tangential direction. The liquid thus injected under pressure flows tangentially to the casing of the cylinder (turbulence chamber) and forms a main vortex. The centrifugal force of this main vortex, in the absence of central depression and grooves in the upper wall of the nozzle, would result in a dispersion of the liquid in a hollow cone, only watering the edges of a circular area. The grooves and the central depression provided in the upper wall of the nozzle according to the invention have the function of creating secondary turbulence and decreasing the relative importance of the main vortex, by bringing part of the liquid towards the central zone of the chamber turbulence. The Applicant, in the context of the numerous hydrodynamic tests carried out to arrive at the present invention, noted with surprise that a disposition of the grooves in a symmetry of revolution did not allow a perfectly regular dispersion of the liquid and systematically gave rise to a defect. watering in an eccentric zone. On the other hand, when the grooves are provided only in a given sector of the upper wall of the turbulence chamber, a solid watering cone is obtained allowing the whole of the circular watering zone to be moistened regularly. This sector having radial grooves must cover at least half of the surface of the upper wall and must correspond to the beginning of the tangential flow path of the coolant in the turbulence chamber. A second sector free of grooves, complementary to the first sector, corresponds to the end of the tangential flow path of the cooling liquid in the turbulence chamber. This second groove-free sector preferably covers an angle α of between 180 ° and 90 °, preferably between 150 ° and 120 °.

The number and the dimensions of the radial grooves located in the first sector have a great influence on the hydrodynamic behavior of the watering nozzle according to the invention. In fact, an insufficient or excessive number of grooves respectively results in an excess or a lack of watering in the periphery of the watering zone. The Applicant has found that a number of grooves equal to 3, 4, 5, 6 or 7, preferably 4, 5 or 6 and in particular 5, gave the best results in terms of homogeneity of watering.

In a preferred embodiment of the watering nozzle according to the invention, the inlet pipe has a substantially rectangular cross section at least in the part where it opens into the turbulence chamber. Upstream of this zone with a rectangular section, the inlet duct advantageously has a circular cross-section and a thread enabling the nozzle to be fixed on the supply of cooling liquid.

In the region of rectangular section, a vertical face of the inlet duct is preferably located in a plane tangent to the casing of the cylinder of the turbulence chamber. The height of this vertical face and the face opposite to it is approximately equal to half the total height of the turbulence chamber, ie the ratio of the height (vertical dimension) of the cross section of the duct to reach the height of the cylindrical turbulence chamber is preferably between 0.7 and 0.3, preferably between 0.4 and 0.6. The horizontal dimension (width) of the inlet duct is preferably close to the radius of the cylindrical chamber, ie the ratio of the width of the cross section of the inlet duct to the radius (r) of the turbulence chamber is included between 0.8 and 1.1, preferably between 0.9 and 1.

The cooling liquid is thus injected into the turbulence chamber over a width approximately equal to the radius of the turbulence chamber. As indicated above, in this first flow zone, the upper wall of the turbulence chamber comprises a number of grooves radially arranged and joining at the center of the wall. The first of these grooves is preferably substantially parallel to the axis of the arrival duct or forms with it an acute angle (β) less than or equal to 20 °, preferably less than or equal to 10 °. The other grooves are arranged radially at the same angular distance from each other in the image of the petals of a flower corolla, except that they do not cover the entire disc formed by the upper wall but only a first sector of it. The visual effect is comparable to that of a flower corolla to which the petals were torn out over part of its circumference.

The furrows, to be effective, must have a certain depth relative to the overall height of the turbulence chamber. In fact, too flat grooves do not effectively disturb the main vortex of the cooling liquid and oppose the centrifugal force thereof. Too deep furrows, on the contrary, would lead to excessive "centralization" of the watering liquid resulting in an excess of liquid in the center of the watering cone. The Applicant has found that one generally obtained a full watering cone of a satisfactory regularity for a ratio of the depth of the grooves to the total height of the turbulence chamber (= depth of the grooves + free height) between 0 , 2 and 0.5, preferably between 0.25 and 0.35. The term "groove depth" here means the maximum depth of the grooves at their peripheral end. This depth decreases towards the center of the "corolla" of grooves because of the central depression which affects the entire surface of the upper wall, that is to say both the sector with grooves that the sector without furrows. The depth of the grooves can thus be reduced by more than half between their peripheral end and the place where the furrows meet in a central hollow zone.

The width of the grooves is preferably similar to the maximum depth thereof. More precisely, a preferred ratio of the width to the maximum depth of between 0.8 and 1.2, and in particular between 0.9 and 1.1, can be defined.

The irrigation water leaves the turbulence chamber through the diffuser provided in the lower wall of the turbulence chamber. This diffuser is coaxial with the turbulence chamber. The ratio of the internal diameter of this diffuser to the internal diameter of the turbulence chamber is preferably between 0.2 and 0.4, in particular between 0.25 and 0.35. The diffuser includes a substantially cylindrical portion located between the turbulence chamber and the trumpet horn portion of the diffuser. The ratio of the height of the substantially cylindrical portion to the height of the trumpet horn shaped portion is preferably in the range of from 0.1 to 0.5, in particular from 0.2 to 0.4.

The invention further relates to a desalination plant of seawater by distillation comprising at least one watering nozzle as described above. This desalination plant is preferably a multi-effect installation as described in the introduction. In such an installation each effect comprises at least one watering nozzle according to the invention disposed above the heat exchange tubes in which the condensation of water vapor takes place, which will supply the energy necessary for the evaporation of the sea water sprayed by the spray nozzles.

The watering nozzle according to the invention can, however, also be used in other industrial processes such as processes for cleaning up fumes or treating water.

• la figure 1 est une vue en perspective de la buse d'arrosage selon l'invention,
• la figure 2 est une vue schématique en section transversale de la buse de la figure 1 selon le plan horizontal comprenant l'axe A-A' montrant la face intérieure de la paroi supérieure de la chambre de turbulence,
• la figure 3 est une vue en section transversale de la buse de la figure 1 selon le plan vertical perpendiculaire à l'axe A-A', et
• la figure 4 est une vue en perspective par le dessous de la surface interne de la paroi supérieure de la chambre de turbulence d'une buse d'arrosage selon l'invention.

The invention is now described with reference to the appended non-limiting drawings, in which:

• FIG. 1 is a perspective view of the watering nozzle according to the invention,
• FIG. 2 is a diagrammatic cross-sectional view of the nozzle of FIG. 1 along the horizontal plane including the axis AA 'showing the inside face of the upper wall of the turbulence chamber;
• FIG. 3 is a cross-sectional view of the nozzle of FIG. 1 along the vertical plane perpendicular to the axis A-A ', and
• Figure 4 is a perspective view from below of the inner surface of the upper wall of the turbulence chamber of a watering nozzle according to the invention.

Figure 1 shows a nozzle according to the invention with a turbulence chamber 1 having a substantially cylindrical shape, more particularly the shape of a flat cylinder whose height is slightly less than the diameter of its base. In this turbulence chamber 1 opens an inlet pipe of the cooling liquid 3 disposed along a substantially horizontal axis AA '. In the part immediately preceding the mouth in the turbulence chamber, the inlet pipe of the cooling liquid has a rectangular section. One of the four faces of this portion of the inlet duct 3 is located in the plane tangent to the casing of the cylinder of the turbulence chamber, a feature that is best seen in Figure 2 described in detail below. At its distal end, the inlet pipe of the cooling liquid has a circular section and has an external thread. to fix it by screwing into the sprinkler system.
The turbulence chamber comprises a second, circular opening located in the center of the bottom wall 2b of the turbulence chamber, where the diffuser 5 of the cooling liquid originates. This diffuser 5 is perfectly coaxial with respect to the turbulence chamber. It consists of a first portion, upper, substantially cylindrical and a second part in the form of a trumpet horn. In this Figure 1 the outer surface of the upper wall 2a is perfectly flat and does not reflect the particular geometry of its inner surface explained in detail with reference to Figures 2, 3 and 4 below. The Applicant, however, also intends to protect nozzles where the shape of the outer surface of the upper wall 2a at least partially reflects the geometry of the inner face, with the recessed portions corresponding to the protruding portions on the opposite face and vice versa.

Figure 2 shows the particular arrangement of the grooves in the inner surface of the upper wall 2a of the nozzle according to the invention. This surface comprises a total of five grooves 6 rounded at their ends. These five grooves define a first sector 4a of an angle complementary to the angle α. This first sector 4a corresponds to the beginning of the flow path of the cooling liquid arriving via the conduit 3. The second sector 4b is free of grooves and here has an angle α equal to 155 °. The first groove 6a here forms an acute angle β of 12 ° with the axis of the arrival duct but may possibly be parallel to this axis (β = 0).

The grooved sector 4b and the four triangular surfaces separating the grooves are not horizontal surfaces but slopes towards the center of the wall 2a. This slope, invisible in this figure 2 because of the perspective from below, appears clearly in Figures 3 and 4 below.

Figure 3 is a cross-sectional view from point A 'of the turbulence chamber. This figure clearly shows the cross section of the inlet duct of the cooling liquid 3.

For the sake of clarity of the representation, the grooves present on a portion of the upper wall 2a have been omitted from this figure. The wall 2a has a central depression 7 which here covers the all of its surface. However, the present invention also encompasses embodiments or a peripheral zone of the inner surface of the upper wall 2a is perfectly horizontal and comprises a central depression of a relatively more limited size than in this FIG. 3. The depression 7 corresponds here to a concavity of the inner surface of the upper wall 2a but may equally well be a cone-shaped hollow, truncated or not, with a constant slope along the entire length of the grooves.

Figure 4 is a synthesis of Figures 2 and 3 showing both the arrangement of the five grooves and the central depression in the inner surface of the upper wall. In this figure, the slope of the central depression is a straight slope of a value such that the depth of the grooves decreases approximately by half between their peripheral end and the point where each groove joins the neighboring groove (s) .

Claims (12)

1. A spray nozzle comprising an essentially cylindrical turbulence chamber (1) with an upper wall (2a) and a lower wall (2b), an inlet duct (3) for spraying liquid, which discharges into the turbulence chamber in a direction inducing a tangential flow of the liquid in the turbulence chamber, and a diffuser (5) which is in the form of a downwardly widening mouth of a trumpet and which is coaxial in relation to the turbulence chamber, characterised in that the upper wall (2a) of the turbulence chamber comprises, on its inner surface, a central depression (7) and also a number of slots (6) arranged radially in a first sector (4a) corresponding to the start of a tangential flow path of the liquid to be sprayed into the turbulence chamber, the other sector (4b), which is complementary to the sector (4a), being without slots.
2. A spray nozzle according to claim 1, characterised in that the ratio of the height of the turbulence chamber to the diameter of the inner or upper walls is between 0.6 and 0.8, preferably between 0.65 and 0.75.
3. A spray nozzle according to one of the preceding claims, characterised in that the angle (V) of the sector (4b) without slots is between 180° and 90°, preferably between 150° and 120°.
4. A spray nozzle according to claim 1 or 2, characterised in that the number of slots (6) is equal to 3,4,5,6 or 7, preferably equal to 4,5 or 6 and, in particular, equal to 5.
5. A spray nozzle according to any one of claims 1 to 3, characterised in that the cross-section of the inlet duct (3) is substantially rectangular in the portion in which it discharges into the turbulence chamber, one surface of the inlet duct being situated in a plane tangential to the envelope of the cylinder of the turbulence chamber.
6. A spray nozzle according to claim 4, characterised in that the ratio of the length (horizontal dimension) of the cross-section of the inlet duct to the radius (r) of the turbulence chamber is between 0.8 and 1,1, preferably between 0.9 and 1.
7. A spray nozzle according to claim 4 or 5, characterised in that the ratio of the height (vertical dimension) of the cross-section of the inlet duct to the height of the cylindrical turbulence chamber is between 0.7 and 0.3, preferably between 0.4 and 0.6.
8. A spray nozzle according to any one of the preceding claims, characterised in that the first slot (6a) forms with the axis of the inlet duct an acute angle (3) which is less than or equal to 20°, preferably less than or equal to 10°
9. A spray nozzle according to any one of the preceding claims, characterised in that the ratio of the depth of the slots (6) to the total height of the turbulence chamber (1) is between 0.2 and 0.5, preferably between 0.25 and 0.35.
10. A spray nozzle according to any one of the preceding claims, characterised in that the diffuser (5) comprises an essentially cylindrical first portion (5a) and a second portion (5b) in the form of the mouth of a trumpet.
11. An installation for desalinating sea water by distillation, comprising at least one spray nozzle according to any one of the preceding claims.
12. An installation for desalinating sea water according to claim 11, characterised in that it comprises a multiple action installation, and that each action comprises at least one spray nozzle disposed above and spraying heat-exchanger tubes in which the condensation of water vapour takes place to supply the energy required to evaporate the sea water atomised by the spray nozzles.

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