FR2684021A1 - Process for concentrating a liquid fluid laden with suspended and/or dissolved solid matter and device for making use of this process - Google Patents

Abstract

The process consists in performing a fractionation of the fluid into separate drops of given size by means of centrifuging of this fluid and in then entraining the laden liquid phase into a flow of air or of entrainment gas which preferably has a high ability to oxidise the solid particles so that a fraction of the liquid which is then removed separates off and that the remaining fraction is collected without dispersion of the solid particles, and, if appropriate, in recycling this collected fraction until the intended concentration is reached. The invention also relates to a device comprising a centrifuge (1), preferably bowl-shaped, a nozzle (5) for feeding the laden liquid fluid so that this fluid spreads and flows against the inner wall of the bowl and is ejected outside the latter through calibrated orifices (14) in the form of liquid drops of given size, and a source of air or entrainment gas, the drops being subsequently collected and/or recycled according to the intended concentration.

Description

 The present invention relates to a process allowing the concentration of a liquid fluid charged with suspended or dissolved solid matter, with a view to obtaining a juice or the like, liquid or pasty, if necessary supersaturated, the solid enrichment can be adjusted on demand depending on the conditions of its use.

 Processes are already known which carry out a separation of the liquid and solid phases of a solution or of a dispersion, using techniques of instantaneous evaporation of a given fraction of the liquid phase. By way of example, mention may be made of the processes operated in concentration towers, using at their lower end a heat source and at their upper end exhaust nozzles from the vaporized part of the liquid phase, pressurized, the process being all the more efficient as the liquid is brought to a temperature close to its boiling point. The remaining fraction is in these conditions largely enriched in solid matter, dissolved or in suspension, and can be recovered in another place of the tower, generally by using gravity.

 However, these devices are heavy, of a poor flexibility of use and a delicate handling. Above all, they consume very great energy. In addition, an additional difficulty results from the fact that it is necessary to carry out a precise calculation of the spray nozzles, these being likely to be frequently obstructed, partly or totally, by the solid particles which come from the concentration of the product.

 Another method for separating matters in suspension or in solution in a liquid, consists in using an intense spraying technique of the charged liquid phase, in a flow of moving air, to ensure a fine division of the liquid phase entrained by air in motion, while solid particles, in suspension or suddenly crystallized if they are dissolved beforehand, are collected by gravity on a collection area, mounted at the bottom of an installation comprising, at its top, spray nozzles, possibly rotary, and laterally a source, of the fan or other type, which delivers the flow of drive air; if necessary, a simple natural or forced air flow can be used. Means are provided for controlling the flow rate of the charged liquid, the speed of the air flow and the spraying ratio of the nozzles, as a function of the nature of this liquid and of the solid particles which it contains, of the ambient humidity and of the temperature.

 However, if such a technique allows, to a certain extent at least, an improvement in the separation factor of the liquid and solid phases, it is quickly limited according to the ability of this liquid to be sprayed in a sufficiently fine and rapid manner to ensure effective separation, and also due to the risks of localization in the surrounding atmosphere of the aerosols produced and of the dust which result from the complete evaporation of the liquid phase, with, depending on the nature of this dust, pollution which is sometimes very troublesome.

 The present invention relates to a process which is based on an entirely different physical principle, by achieving within the liquid itself, a notable concentration of the solid phase which is not separated from the liquid but is concentrated in the latter, in a variable proportion. and adjustable according to the user's wishes and the applications of the concentrated liquid which he envisages, this concentration being carried out without dispersing in the ambient atmosphere the possibly polluting products which constitute all or part of this solid phase. The invention also relates to a device for the implementation of this process as well as all the products the concentration of which is carried out in accordance with it and preferably by means of this device.

 To this end, the method according to the invention, for the concentration of a liquid fluid charged with solid materials or particles in suspension and / or dissolved in the liquid phase of this fluid, having where appropriate a polluting character imposing that these particles are not dispersed in the atmosphere, is characterized in that it consists in carrying out a fractionation of the liquid fluid in separate but practically identical drops, of given dimensions, loaded with the solid particles, by means of a centrifugation of this fluid, then entraining the charged liquid phase thus fractionated in a flow of air or entraining gas preferably having a strong oxidizing power of the solid particles contained therein, so that it separates at l inside this flow, due to the gradual drying of the fluid produced by the air or gas flow, a fraction of the liquid which is then eliminated, and that the liq fraction uide remaining, enriched with the solid phase at least partly oxidized which remains trapped in the liquid phase, is collected without dispersion of the solid particles and if necessary to recycle this collected fraction until reaching the desired concentration with the solid particles.

 The invention also relates to a device for implementing this method, which comprises a centrifuge, preferably in the form of a bowl, of revolution about a vertical axis, having a substantially conical profile, the bowl being driven in rotation at speed adjustable around the axis and comprising an internal wall, flaring from the axis towards the periphery of the bowl, a supply nozzle along the axis of this bowl or in the immediate vicinity thereof with the liquid fluid charged with suspended solid particles and / or dissolved in the liquid phase of this fluid, delivering a given flow rate of the latter into the bowl, so that this fluid spreads and flows against the internal wall of the bowl and either ejected outside of it through orifices calibrated in the form of liquid drops of given dimensions, a source of air or entraining gas, preferably with strong oxidizing power, providing a entraining flux of these drops, subsequently collected and / or recycled according to the desired concentration of the liquid phase with the solid particles.

 Under the effect of the centrifugal force created by the rotation of the bowl at adjustable speed, the liquid fluid charged with solid particles introduced into the bowl through the axial feed nozzle, spreads and spreads out in the form of a film. liquid of substantially constant thickness against the surface of the wall of the bowl, before being ejected from it through the calibrated orifices provided in its wall, the drops meeting the flow of entraining air which partially dries them without going to the total elimination of the liquid phase, thereby increasing the concentration of solid particles without any dispersion of the latter in the atmosphere.

 Preferably, the feed nozzle has the shape of a cylindrical sleeve, surrounding the axis of the bowl and open at its lower end to deliver the liquid fluid into the bowl driven in rotation, the sleeve being connected to the outside of the bowl with a discharge pump, in particular a volumetric pump, capable of adjusting the flow rate of the fluid delivered.

 In a first embodiment of the invention, the bowl has a conical wall, the opening of which is directed towards the lower part of the bowl and which is connected to a transverse partition provided with recesses for passage of the liquid fluid coming from the nozzle. supply, the conical wall of the bowl extending beyond the transverse partition by a substantially cylindrical and coaxial skirt, in the side wall of which are formed the calibrated orifices through which the drops of charged liquid are formed.

 Advantageously, the calibrated orifices provided in the wall of the bowl and in particular in the cylindrical skirt, have a flared profile, from the inside to the outside of the bowl.

 In another embodiment, the opening of the conical wall of the bowl is directed towards the upper part of the bowl, which has at its lower end a bottom facing the end of the feed nozzle, and in its wall conical, inside the bowl, at least one scraping member for driving the solid particles possibly deposited in the bowl. Preferably, the scraping member is constituted by a helical fin winding around the axis of the bowl against its conical wall, from the bottom to its open upper end.

 Finally, the invention relates to an installation using at least one centrifuge bowl provided with the aforementioned characteristics, this installation comprising an open enclosure consisting of two side curtains, forming a windbreak, joined in the front part of the enclosure by a bottom wall, the two curtains and the wall being arranged vertically above a tank for collecting loaded liquid drops.

 Advantageously, the drop collection tank is filled with water or another similar liquid or the liquid to be treated.

 According to another characteristic, the enclosure and the tank are orientable in the direction of the drive air flow, the tank resting on wheels or skids capable of making it possible to modify its orientation on the ground.

Other characteristics of a process for the concentration of a charged liquid fluid, of a device for implementing this process and of an installation using this device, will become more apparent from the following description of various examples. of realization, given as an indication and without limitation, with reference to the appended drawings on which
- Figures 1 and 2 are views in axial section of a centrifuge bowl adapted to the implementation of the method according to the invention, according to two particular embodiments.

 - Figure 3 is a perspective view of a treatment installation, using a centrifuge bowl according to any one of these two variants.

 In FIG. 1, the reference 1 generally designates a centrifugation bowl comprising a conical wall 2 of vertical axis 3, terminated at its upper end by a flange 4 inside which engages a supply nozzle 5.

This is in the form of an annular, cylindrical and hollow sleeve 6, the axis of which coincides with that of the bowl, this sleeve being open at its lower end 7 and connected at its upper end to an inlet pipe 8, making it possible to deliver inside the bowl 1 an appropriate flow rate of a liquid fluid charged with solid particles, dissolved or in suspension. The pipe 8 is connected for this purpose to a delivery pump 9, in particular of the positive displacement type, which makes it possible to continuously adjust the flow rate of the fluid introduced into the bowl.

 At its end directed downwards, opposite the flange 4, the bowl 1 comprises a transverse partition 10, integral with the wall 2 and comprising, distributed around the vertical axis 3, a set of recesses 11, allowing the liquid fluid delivered to the bowl to flow downwards after the partition 10 has passed through the recesses 11. The partition 10 is integral with a centering shaft 12 whose axis coincides with the axis 3 of the bowl, this shaft making it possible to animate the bowl with an appropriate speed of rotation around this axis, this drive speed being created and made variable by means of a control gear motor (not shown).

 The conical wall 2 is extended, in the embodiment considered, by a cylindrical skirt 13, coaxial with the bowl and which extends downwards following the latter, as illustrated in the drawing. In its lateral surface, the skirt 13 has a plurality of orifices 14, the diameter of which is preferably calibrated, these orifices making it possible to create, in the flow of air outside the bowl, liquid drops of given dimensions, loaded with solid particles.

 At its lower end, the skirt 13 has a circular opening 15 to allow the natural evacuation of the solid particles separated from the liquid phase, the remainder of the latter being forced through the orifices 14 for the formation of drops of controlled diameter, enriched with these particles and able to be entrained in a suitable air or gas flow, coming either from a mechanical source of the fan or other type, or being in the form of a simple air stream. Advantageously, the orifices 14 formed in the cylindrical skirt 13 have a flared profile 16, extending from the inside of the bowl to the outside, so as not to disturb the formation of the drops as the latter are discharged from the bowl from the liquid film created on its internal wall under the effect of the rotation of this bowl.

 Figure 2 illustrates an alternative embodiment of the centrifuge bowl 1, in which the conical wall 2 this time has its opening directed upwards (and not downwards, as in the previous example).

 The lower end of the wall 2 is closed by a transverse bottom 17, axially secured to the shaft 12 for driving the bowl around the vertical axis 3 thereof. The orifices 14 are directly formed in the conical wall 2 and include, as in the previous example, a flared profile 16 with an increasing diameter as one moves away from the internal surface of the bowl to get closer of its outer surface.

The annular sleeve 5 has the same profile as in the case of Figure 1, surrounding the shaft 12 but extends over a greater height so that its lower end 7 is disposed substantially opposite and in the vicinity of the bottom 17 from the bowl.

 At least one scraper member, comprising at least one helical fin 18, is provided in the internal surface of the conical wall 2 and is wound against the latter around the vertical axis 3, from the bottom 17 to the open upper part 19 of the bowl 1, this fin allowing the solid matter falling into the bottom of the bowl to be taken up and easily evacuated from it.

 In operation and under the effect of the centrifugal force created by the rotation of the bowl at adjustable speed, the liquid fluid spreads and spreads over the walls of this bowl, in particular on the internal surface of the skirt 13 in the first variant described above or on the conical and inverted internal wall 2 in the second, the calibrated orifices 14 allowing in either case to fractionate the liquid phase and to produce drops outside the bowl of which the dimensions can be exactly determined.

 The solid particles contained in the liquid phase are then entrained by the flow of air or gas but remain trapped inside these drops as long as their own dimensions are not greater than those of the calibrated orifices 14, the particles the largest being directly discharged through the open part 15 of the skirt 13 in the first case or by the scraper in the form of a helical fin 18 which rises them during rotation and discharges them through the upper part 19 of the bowl in the second case.

 The drops produced through the calibrated orifices are very numerous and have a notable average diameter, of the order of 0.5 to 1 mm or even more, which totally differentiates the process envisaged from the known methods in which a real atomization of the liquid phase to vaporize it and separate it as completely as possible from the solid particles contained in the fluid supplied to the bowl. These drops are ejected outside the bowl in the air or gas stream, preferably with a strong oxidizing power, which on the one hand will cause these drops to dry out by eliminating a limited fraction of the liquid phase, the remainder enriched with the remaining solid phase then being recovered or recycled. In all cases, the drops of liquid which trap the solid particles do not release any aerosol in the surrounding atmosphere, the size of the drops remaining in any case sufficient to trap in all circumstances the solid particles which they contain.

 The flow rate of the liquid fluid treated inside the centrifuge bowl can be very large, provided that the size of the drops produced does not risk creating a complete vaporization of the liquid phase due to complete drying by air or external entrainment gas, which makes it possible to avoid any pollution by the solid phase, in particular when the latter contains harmful materials or dust.

 Of course, also involved in the drop formation process, in addition to the flow rate of the liquid fluid, the speed of rotation of the bowl and the ambient temperature and humidity conditions, these parameters can also intervene to modify the degree of oxidation of the solid particles and their concentration rate in the remaining liquid phase.

 Two examples are given below, among others, of use of a centrifuge bowl for the implementation of the method according to the invention, carrying out the concentration of a charged liquid fluid, these examples not having by themselves no limiting character.

 It is thus possible, using this process, to carry out a high concentration of a sugar cane extraction juice, containing 3 to 5% of dry and solid materials, with high nutritive power, in order to ensure its concentration up to 50 to 60% with such materials, to obtain a very rich syrup capable of serving as an adjuvant in small quantities for the manufacture of various foods.

 In another example, one can proceed to the concentration of a pig slurry, containing 5 to 7% of dry matter and approximately 2.5% of dissolved nitrogen, 4% of phosphates and 3% of potassium, in order to concentrate up to 20 to 40% of dry matter, 15% of nitrogen, 24% of phosphorous anhydride and 18% of potassium, the product obtained constituting a very rich organic fertilizer, capable of being easily packaged, transported and used replacing more conventional chemical amendments.

 In all cases, the passage of the liquid fluid inside the centrifuge bowl produces a thin film in continuous travel, which remains pressed against the wall under conditions such as at the exit of this bowl, through the calibrated orifices, it can be very widely dispersed in drops of selected dimensions, ensuring in part its fractionation into a gaseous phase which evaporates and is consequently eliminated, and a remaining liquid fraction which is enriched with the solid particles, partially or completely oxidized.

 FIG. 3 illustrates an installation using a set of centrifuge bowls 1, of the type described above with reference to FIGS. 1 or 2.

 This installation comprises an open enclosure 20, in particular consisting of two side walls 21 and 22 forming wind curtains, these curtains being joined in the front part of the enclosure by a bottom wall 23. In contrast, the enclosure is open at 24, so as to allow the outside atmosphere to communicate with the enclosure in the direction of the prevailing wind, this enclosure being able to be suitably oriented in the corresponding direction. For this purpose, the lower part of the enclosure is constituted by a tank 25 which has a bottom 26 and a lateral rim 27, the assembly resting on pads or wheels (not shown) allowing variations in position to be ensured. of the enclosure according to the changes occurring in the wind direction. The wind curtains 21 and 22 are plumb with the tray 25 so that their lower ends fall freely inside the latter, so that the liquid drops from the centrifuge bowls 1 which strike these curtains, run against it and are collected in the bin. This contains a suitable quantity of water or of a suitable liquid or of liquid to be treated 28, so that the solid particles trapped in the liquid drops discharged from the bowls 1, in accordance with the process of the invention, are completely recovered.

 The enclosure 20 comprises one or more transverse beams 29 to which the centrifugal bowl 1 are suspended, the number of which depends on the distance between the side wind curtains 21 and 22. Each of the bowls is also joined by means of an intake pipe 30 to a distribution pipe 31, the end of which is connected to an installation 32, itself supplied with the liquid phase to be treated by a pipe 33 and comprising in particular suitable pumping and filtering means.

 The centrifuge bowls 1 are used as already explained, so that, by combining the effect of the rotation of the bowls and of the entrainment by the air or the oxidizing gas at the periphery of these bowls, a separation of a fraction of the liquid phase and simultaneously, thanks to the partial drying of the drops produced, an enrichment of the latter with the oxidized solid phase. Under these conditions, by varying the supply pressure of the liquid phase in the bowls, the speed of rotation of the latter and the flow of air or gas, it is therefore possible, depending on the hygrometric degree and the temperature of the external atmosphere, act on the size of the liquid drops collected at the outlet of the rotating bowls.

Thus, the reference 34 in the drawing shows schematically a recovery zone in the tank 25 of large liquid drops and the reference 35 an area where the drops are much smaller in diameter, allowing further oxidation of the solid particles, while now the latter suitably trapped to avoid dispersion into the atmosphere of the enclosure of possibly polluting aerosols.

 This produces an installation allowing the concentration and oxidation of solid particles in suspension or dissolved in a highly efficient liquid fluid, in particular thanks to an easy action on the various adjustment parameters, provided at all appropriate points of the installation by sensors or probes measuring the values of these various parameters, so as to avoid the total passage of the liquid drops in the vapor state with dispersion of the solid products, while simultaneously controlling the size of these drops, in particular their reduction volume and their drying rate, until their final recovery in the bottom of the basin.

 Of course, as already follows from the above, it goes without saying that the invention is not limited to the examples more specifically described, with reference to the accompanying drawings; on the contrary, it embraces all its variants. In particular, provision can also be made to recycle the enriched phase inside the drops once they have been recovered, in particular in the lower tank of the installation, until the chosen final concentration is reached. Likewise, provision can be made to heat the air or the entrainment gas inside the enclosure to improve the efficiency, this heating possibly being obtained in an exchanger through which the vaporized fraction passes. In the case in particular where it comes from a leachate of compacted household waste, provision may be made for a device for recovering fermentation gases to heat the entrainment air.

 Once the size of the drops has been determined, the dimensions of which are defined in particular to avoid any production of aerosols or dust in the drive air, the installation can operate uninterrupted. In the diurnal phase, part of the liquid phase evaporates, causing the concentration of the remaining fraction of the liquid phase. On the other hand, if the atmospheric conditions are unfavorable, especially if the ambient humidity is very high, the installation only performs the oxidation of solid particles and elements in solution. The variation of the speed of rotation of the centrifugation bowls allows to play on the number and the size of the drops produced, which leads to increase or decrease the rate of oxidation of the treated liquid phase, by increasing or reducing the contact surface. and therefore exchange with the drive air, at constant flow.

 The method according to the invention allows the treatment of any type of charged liquid and in particular of those whose oxygen or carbon dioxide levels do not comply with the standards for discharge into the natural environment and also to carry out the concentration of any product. liquid of industrial origin.

Claims (11)

 1 - Process for the concentration of a liquid fluid charged with solid materials or particles in suspension ion and / or dissolved in the liquid phase of this fluid, having if necessary a polluting character imposing that these particles are not dispersed in the atmosphere, characterized in that it consists in carrying out a fractionation of the liquid fluid into separate but practically identical drops, of given dimensions, loaded with the solid particles, by means of a centrifugation of this fluid, then in entraining the liquid phase charged thus fractionated in a flow of air or entraining gas preferably having a strong oxidizing power of the solid particles contained therein, so that it separates inside this flow, due to the progressive drying of the fluid produced by the flow of air or gas, a fraction of the liquid which is then eliminated, and the remaining liquid fraction, enriched with p solid base at least partly oxidized which remains trapped in the liquid phase, collects without dispersion of the solid particles and if necessary to recycle this collected fraction until reaching the desired concentration with the solid particles.  2 - device for implementing the method according to claim 1, characterized in that it comprises a centrifuge (1), preferably in the form of a bowl, of revolution about a vertical axis (3), having a profile substantially conical, the bowl being entrained in rotation at an adjustable speed around the axis and comprising an internal wall (2), flaring from the axis towards the periphery of the bowl, a supply nozzle (5) according to the axis of this bowl or in its immediate vicinity with the liquid fluid charged with solid particles in suspension and / or dissolved in the liquid phase of this fluid, delivering a given flow rate of the latter in the bowl, so that this fluid spreads and flows against the internal wall of the bowl and is ejected outside of the latter through calibrated orifices (14) in the form of liquid drops of given dimensions, a source of air or entrainment gas, preferably with strong oxidizing power, providing t a flow of entrainment of these drops, subsequently collected and / or recycled according to the desired concentration of the liquid phase with the solid particles.  3 - Device according to claim 2, characterized in that the feed nozzle (5), has the shape of an annular sleeve (6), cylindrical and hollow, surrounding the axis of the bowl and open at its lower end ( 7) for delivering the liquid fluid into the bowl driven in rotation, the sleeve being connected outside the bowl to a delivery pump (9), in particular volumetric, suitable for adjusting the flow rate of the fluid delivered.  4 - Device according to one of claims 2 or 3, characterized in that the bowl (1) has a conical wall (2) whose opening is directed towards the lower part of the bowl and which is connected to a transverse partition ( 10) provided with recesses (11) for the passage of the liquid fluid coming from the supply nozzle (5), the conical wall of the bowl extending beyond the transverse partition by a skirt (13) substantially cylindrical and coaxial, in the side wall of which the calibrated orifices (14) are formed through which the drops of charged liquid are formed.  5 - Device according to claim 4, characterized in that the calibrated orifices (14) provided in the wall of the bowl and in particular in the cylindrical skirt (13), have a flared profile (16), from the inside to the outside from the bowl.  6 - Device according to one of claims 2 or 3, characterized in that the opening (19) of the conical wall of the bowl is directed towards the upper part of the bowl, which comprises at its lower end a bottom (17) in look at the end of the feed nozzle (5), and in its conical wall (2), inside the bowl, at least one scraper member (18) for entraining the solid particles possibly deposited in the bowl.  7 - Device according to claim 6, characterized in that the scraper member (18) consists of a helical fin winding around the axis (3) of the bowl against its conical wall (2), from the bottom (17) to its open upper end (19).  8 - Installation using at least one centrifuge bowl according to any one of claims 2 to 7, characterized in that it comprises an open enclosure (20) consisting of two side curtains (21, 22), forming a windbreaker, joined together in the front part of the enclosure by a bottom wall (23), the two curtains and the wall being arranged vertically above a container for collecting charged liquid drops (25).  9 - Installation according to claim 8, characterized in that the collecting tank (25) of the drops is filled with water or another similar liquid (28) or the liquid to be treated.  10 - Installation according to one of claims 8 or 9, characterized in that the enclosure (20) and the tray (25) can be oriented in the direction of the flow of drive air, the tray resting on wheels or skids suitable for changing its orientation on the ground.  11 - Installation according to any one of the preceding claims, characterized in that it is used to concentrate a liquid when the atmospheric conditions allow it, or to oxidize a liquid when the atmospheric conditions do not allow the reduction of the liquid phase.