FR2459967A1 - Determn. of turbidity in liq. by loss of luminous intensity - between opposed ends of two optical fibres cleaned by circulating liq., used in water purificn. plants etc. - Google Patents

Abstract

A measurement is taken of the loss of luminous intensity of light passed through a measuring zone of the liq.. The measurement is taken between (coaxially) opposed ends of two fibre optics, one used as emitter and the other as receiver. The liq. is circulated continuously between the ends of the fibres in order to clean them automatically pref. the immersed ends of the fibres are protected with transparent covers. The process is used to check the concn. of sludge in an aeration tank for the purificn. of waste water, to check the clarity of wash water passed through process pipework in milk factories, fruit juice bottling factories, sugar refineries etc. Readings remain reliable since the fibre ends in the measuring zone are continually claned. The immersed measuring zone assembly is of simple construction and easily fitted to a wide variety of installations.

Description

 The present invention relates to a method and a device for the quantitative evaluation of disorders and suspended matter in a fluid.

 In a manner known per se, the method calls for the measurement of a loss of light intensity through the fluid, in a measurement zone.

 Materials are known, for example intended for the study of fermentations and microbial cultures, comprising a transparent glass tube in which a piston allows at will the admission of the fluid to be studied, in practice a liquid, ensuring by its back and forth movement against the wall of the tube cleaning of any deposits formed thereon; in diametrically opposite positions are arranged, in the immediate vicinity of the outer face of the tube, respectively a lamp and a photo-receiver delivering a signal depending on the light intensity which it receives from the lamp, through the medium in the tube .

 The assembly formed by the tube, the piston, the lamp and the photoreceptor element is immersed in the fluid, which has a drawback in that in particular the photoreceptor element is thus exposed to the temperature, generally low, of this fluid and to variations in this temperature, whereas it is generally an element, such as a photo-diode, a photo-transistor, a photo-resistance, particularly sensitive to temperature.

 Another drawback of this system lies in the need to practice reference measurements to take account of possible variations in the light intensity emitted over time, for example due to the aging of the lamp.

 Finally, this system intended to take measurements spaced in time, discontinuously, does not lend itself to continuous use, for long periods of time, in particular due to the presence of the piston, on the one hand for reasons mechanical and on the other hand that a repeated friction of the piston against the glass wall of the tube causes on the latter the appearance of scratches which frost it and facilitate its fouling, which leads to the impossibility of practicing measurements significant.

 The object of the present invention is to propose a device which, by remedying these drawbacks, can be used in particular, but not exclusively, for the quantitative evaluation of disorders and suspended matter in a generally liquid medium, in particular when the we wish to make this evaluation continuously; among the possible applications of equipment offering these possibilities, we can for example cite the continuous measurement of the concentration of sludge in the aeration basins of water treatment plants, in order to use this parameter to control the purifying activity of the process by acting for example on the rate of recycling of sludge leaving the settling tank and on the purging of excess sludge, or even the quantification of residual pollution, in the form of suspended matter, of water leaving the sewage treatment plant in particular to verify the proper functioning of the decanter; we can also cite the control of the rinsing and cleaning operations of circuits in which a charged and / or fouling fluid is circulated, such as, for example, installations for treating milk and its derivatives, fruit juices, sugar solutions. , etc .....

 To this end, the invention provides a device in which the light emitter and receiver are placed far from the measurement zone, outside the fluid, and connected to this measurement zone by optical fibers whose ends are made face in this zone, chosen such that a circulation of fluid is established between these ends; thus, the light emitting and receiving means respectively are placed away from the thermal influence of the fluid and can operate under optimal conditions, even if this fluid is at low temperature or experiences significant temperature variations as is the case in many installations; on the other hand, the non-fouling of the respective ends of the optical fibers located in the measurement zone naturally results from the circulation of the fluid, without piston or other more or less delicate mechanical cleaning device and inevitably causing a loss of transparency surfaces with which it is in contact; it should be noted that the part of the device located in the measurement zone does not trap and immobilize fluid like the piston devices currently known, and therefore undergoes much less fouling, entirely compatible with self-cleaning due to the mere fact of the circulation of the fluid.

 The invention further proposes, in preferred embodiments, several arrangements tending to reduce the influence of various external factors on the measurements used; for example, the loss of light through the measurement area, that is to say between the corresponding ends of the optical fibers, is carried out by comparing the output signals of two photo-sensitive cells, one of which receives directly the radiation from the lamp and the other of which receives this radiation after passing through the optical fibers and through the measurement zone, that is to say output signals from analogous elements advantageously placed in the same place, in the same conditions, in particular of temperature, which considerably reduces the influence of temperature on the measurements; in addition, such an arrangement compensates for the influence of the aging of the lamp.

 According to another preferred arrangement, a lamp, or more generally a light source, emitting polychromatic light is used, which makes it possible to considerably reduce the influence on the measurements of any coloration of the fluid studied.

 The method according to the invention, for the quantitative evaluation of the disorders and suspended matter in a fluid, by measuring a loss of luminous intensity through the fluid in a measurement area, is characterized in that performs this measurement between the ends, immersed in said zone, of two optical fibers respectively emitting and receiving, and in that one causes self-cleaning of the immersed ends of the fibers by continuous circulation of the fluid disturbed therebetween.

 The invention will be better understood if reference is made to the description below, relating to a non-limiting mode of implementation, as well as to the appended drawings which form an integral part of this description.

 FIG. 1 shows an exemplary embodiment of a device according to the invention, and the mode of installation of such a device for example in an aeration tank of a water purification station.

 FIG. 2 shows a view of the measurement cell in this case, in section through a horizontal plane including the optical measurement axis.

 FIG. 3 shows an example of integration of the measurement cell at the wall of a pipe to evaluate the haze and / or the suspended matter in a fluid circulating inside this pipe.

 If we refer more particularly to the example of implementation illustrated in FIGS. 1 and 2, we have designated by 1 an aeration basin, inside which the waters to be purified 2 are caused to circulate from an entrance situated behind the plane of the figure towards an exit situated in front of this plane; by traversing the basin, the waters are brought into contact with activated and aerated sludge by means of surface aerators (turbines-4b- or brushes) or submerged aeration ramps (4a).

 The device according to the invention is in this case used for continuously measuring the concentration of sludge in water in order to use this parameter to control the purifying activity of the process by acting, for example, on the rate of recycling of sludge at the outlet of the settling tank and on the draining of excess sludge.

 In this case, the device according to the invention comprises a measuring cell 5 immersed in the waters 2, connected by optical fibers 6 and 7 to a transmitter-receiver assembly 8, meanwhile placed at a distance, outside the basin 1, and connected to an electronic drawer 9 for processing the information supplied by the transceiver 8.

 At the level of the measurement cell 5, the fibers 6 and 7 have one of their ends, respectively 10 and 11, and are held in the immediate vicinity of this end by a common device such as a stirrup 12 which provides them with a relative positioning such that the two extremities 10 and 11, in practice materialized by a transverse face with respect to the axis of the fiber at this level, are placed opposite one another, parallel to one another, in a position such that the respective axes of the two fibers 6 and 7 in the immediate vicinity of these two ends 10 and 11 coincide to define an optical measurement axis 13 oriented perpendicular to the direction 14 of displacement of the water to be purified in the basin 1, and for example horizontally.

 To this end, in the example illustrated, a zone of each of the fibers 6 and 7 situated in the immediate vicinity respectively of the end 10 and of the end 11 is immobilized, by any means not shown, in a vertical wing of the stirrup 12, respectively 15 and 16, the two wings 15 and 16 being connected under the optical axis 13 by a horizontal core 17 which maintains in fixed relative position the wings 15 and 16 and consequently the ends 10 and 11 of the fibers 6 and 7 they wear. The stirrup 12 is immobilized by any means in the basin 1.

 Preferably, as illustrated, the two end faces 10 and 11 are protected by a disc of a transparent material such as glass, respectively 18 and 19, preferably chosen such that it has non-stick properties. limiting its fouling; this glass disc is for example glued by its periphery to the edge of the end of a sheath, respectively 20 and 21, protecting the corresponding fiber, respectively 6 and 7, over its entire length and being interrupted at the end faces of this fiber; the distance d separating the faces of the discs 10 and 11 in contact with the water to be purified 2 defines the optical path, in the medium to be studied here consisting of water 2, of a light emitted by the assembly 8 via the fiber 6 and received by this assembly 8 via fiber 7.

 Between the measurement cell 5 and the transmitter-receiver assembly 8, the optical fibers 6 and 7 can undergo various detours which make it possible to place the measurement cell 5 and the transmitter-receiver assembly 8 respectively in any relative positions, this which allows each of these elements to be placed independently of the other in the most appropriate position.

 At the level of the transceiver 8, each of the fibers 6 and 7 has a second end, respectively 22 and 23, analogous respectively to the end 10 and to the end 11 and defined by a transverse face with respect to the 'axis of the fiber at this level; as shown schematically in FIG. 1, the transmitter-receiver assembly 8 comprises, facing the end 22 of the fiber 6, a light source such as a lamp 24 including a photosensitive cell 25, such as a photo-diode, a photo-transistor or a photo-resistance, placed in the immediate vicinity, translates the light intensity by an electrical output signal representative of this intensity; preferably, the lamp 24 emits polychromatic light, with wavelengths of, for example, between 300 n and 1,500 nm, in order to considerably reduce the influence of the possible coloring of the water 2 supporting the materials in suspension on measures.

 Facing the end 23 of the fiber 7, the transmitter-receiver assembly 8 also comprises a photo-sensitive cell 26 of the same type as cell 25, that is to say for example a photo-diode, a photo-transistor or a photoresistor, which translates by an electrical output signal the light intensity which it receives from the lamp 24 via the system constituted by the fiber 6, the water 2 over the distance d, and the fiber 7, that is to say a light intensity the variations of which reflect a variation in the disturbance created by the suspended matter placed on the optical path, that is to say between the discs 18 and 19 for protecting the ends 10 and 11 of fibers 6 and 7 with light intensity delivered by constant lamp 24.

 The effect of a possible variation in the light intensity emitted by the lamp 24 is eliminated from the fact that the instantaneous respective output signals of the cells 25 and 26, introduced into a measurement circuit Cm of the electronic drawer 9, which establishes the ratio of the signals supplied respectively by each of cells 25 and 26 and provides a signal which decreases logarithmically as the concentration of suspended matter increases; this output signal is linearized, that is to say translated by a signal directly proportional to the concentration of suspended matter, and therefore better visualizing the phenomenon, by a linearization module C1 essentially consisting of logarithmic amplifiers, the output signal is recorded or displayed by an IE indicator-recorder module, the assembly formed by the modules Cm, Cl and IE constituting the electronic drawer 9.

 This measurement mode, in principle, very strongly compensates for variations in the ambient temperature to which the detector photos are particularly sensitive.

 It will be noted that this device has no moving mechanical part, and can therefore be used for continuous, permanent measurements.

 Naturally, the optical path d, that is to say the path made by light within the medium to be analyzed, can be adapted to the conditions of use and in particular to the content of suspended matter to be measured in order to low grades, this path can be significantly longer than for high grades.

 In the example of the continuous measurement of the concentration of sludge, good results have been obtained with an immersed cell 5 whose optical path was 1.5 cm; it was found that the problem of fouling was resolved if the circulation speed of the medium remained sufficiently high, for example of the order of 0 * 3 m / sec. at least, what was naturally achieved by the various aeration systems of the basins and implied a judicious implantation of the cell in them; because of the choice of protective discs 10 and 11 made of glass having non-stick properties limiting fouling, periodic cleaning, every eight days in the most unfavorable cases, was sufficient for the maintenance of the cell. measured.

 However, a deflector is necessary to protect the cell from large particles, when the treatment plant does not have a primary settling tank, and from air bubbles when the basin is aerated from below.

 In general, the mechanical design of the measuring cell allows either its immersion in a stirred, homogeneous medium, as in the example illustrated in Figures 1 and 2, or the circulation of the product to be analyzed.

 In the case of implantation in an aeration tank, tests have shown the satisfactory functioning of a circulation model, using an immersed pump, protected by a plaster that is not cleaned every week for example, to transport the analyzed medium. in a direction perpendicular to the optical measurement axis.

 Good results have been obtained in these two cases for concentrations of suspension materials varying from 0 to 10 g / liter, these figures being given by way of nonlimiting example, which allows application to the vast majority of stations of 'purification; an electronic adjustment of the linearisation parameters on the one hand, zero and gain on the other hand, allow the adaptation ad hoc to each station with a range of measurements adapted to the maximum foreseeable sludge concentration.

 Good results have also been obtained by installing a measuring cell such as 5 on the outlet channel for the purified water from basin 1, to quantify the residual pollution, in the form of suspended matter, of the water leaving the treatment plant. in particular to check the proper functioning of the decanter; an immersed cell was used for this purpose, the optical path d of which was 2.5 cm, with a measurement range of 0 to 0.5 g of suspended matter per liter of water, these figures being given as 'nonlimiting example.

 FIG. 3 shows a variant of a measurement cell more particularly adapted to the study of a medium circulating in a tube, this cell being able to be connected in replacement of cell 5 illustrated in FIGS. 1 and 2 to the assembly transceiver 8 itself connected to the electronic drawer 9.

 27 has designated a tubular pipe, for example conveying milk in a processing installation, such as for example a pasteurization installation, ultra-high temperature treatment, sterilization, evaporation, ultra-filtration, packaging, etc.

 It is known that such installations are rinsed with water before carrying out the cleaning and disinfection.

 The device according to the invention is, for example, used here to measure the progressive dilution of milk by water during rinsing or, conversely, that of water by milk when the process is started.

 The medium studied is designated by 28, that is to say the liquid circulating in the pipe 27, in practice consisting of milk, or water, or a mixture of water and milk.

 In this case, the optical fibers 6a and 7a, analogous respectively to the optical fibers 6 and 7, emerge in the wall of the tube 27 in diametrically opposite positions thereof, such that the optical measurement axis 13a defined as previously coincides with a diameter of the tube; in addition, the ends of the fibers 6a and 7a are isolated from the medium to be studied 28 either by a glass tube 29 introduced into the measurement chamber, or by discs 18a and 19a, similar to the discs 18 and 19 respectively, so that that the distance separating their opposite faces is equal or approximately equal to the diameter of the tube here cylindrical, or for example of the order of 2.5 cm in the case of a milk processing installation.

 Under these conditions, a measurement was obtained on a liquid 28 ranging from whole milk to a dilution of 10 4, with better sensitivity up to dilutions of 10 3, with however the possibility of considering two adjustments corresponding to each of the extreme zones, namely very little diluted milk and very diluted milk, with automatic switching according to the phase of the process considered.

 Naturally, a measurement cell of the type illustrated in FIG. 3, integrated into the wall of a pipe in which a fouling liquid circulates either by its nature or by the nature of the treatment which it undergoes when passing through this pipe, can be applied to other technical fields.

 For example, it is known that certain treatments, such as heat or separation treatments, applied to fouling products such as milk and its derivatives, fruit juices, sugar solutions, etc., cause the formation of large deposits on all or part of the exchange surfaces, whether it is heat or material exchange; the resulting disturbances and bacteriological imperatives require users to regularly clean the installations with detergents.

 A measurement cell similar to that which is illustrated in FIG. 3 has been developed in order to monitor the removal of deposits by the detergents, which results in the appearance of a more or less significant clouding of the solution of cleaning according to the initial quantity of deposit and the conditions of this cleaning, that is to say the conditions of temperature, flow rate, concentration of detergents, etc.

 The sensor then constitutes an indicator of end of cleaning, by determining the moment when the haze disappeared during cleanings in open loop, or the instant when the haze is stable at its maximum value during a cleaning in closed loop, most common in the food industry; subject to adequate calibration, the sensor can indicate the speed of cleaning.

 Naturally, the field of application of the device according to the invention is not limited to the examples described above, because very numerous applications are possible, in particular to the separation process (filtration, continuous centrifugation, ultra-filtration, evaporation, etc ...), quality controls in the beverage industry and various cleaning and rinsing operations; in fact, all the processes using suspended materials can give rise to an application.

 The device can then be the subject, with respect to the embodiments described and shown, of numerous variants not departing from the spirit of the invention; thanks to high-performance electronics, it allows measurement of suspended matter under very different conditions, and the mechanical solutions retained at the level of the measurement cell, in particular the mode of circulation of the fluid studied and the optical path, can be '' adapt to the specific conditions of each problem to achieve the desired objective.

Claims (6)

 1) Method for quantitative evaluation of the disorders and suspended matter in a fluid, by measuring a loss of light intensity through the fluid, in a measurement area, characterized in that this measurement is carried out between the ends, immersed in said zone, of two optical fibers respectively emitting and receiving, and in that one provoquelauto-cleaning of the immersed ends of the fibers by continuous circulation of the fluid disturbed between them.  2) Device for implementing the method according to claim 1, characterized in that it comprises  - light emitting and receiving means respectively, placed at a distance from the measurement zone, outside the fluid,  - two optical fibers, each of which has a first end opposite the emitting means and the receiving means respectively, outside the fluid, and a second end located in the measurement zone, inside the fluid, facing the second end of the other fiber and at a predetermined distance therefrom,  means for establishing a circulation of fluid between said second ends, in the measurement zone,  - Means for comparing the light intensity emitted with the light intensity received through the system consisting of the two fibers and the fluid in the measurement area.  3) Device according to claim 2, characterized in that it comprises a transparent protective wall for the second end of each fiber with respect to the fluid.  4) Device according to any one of claims 2 and 3, charac terized in that the means for establishing a circulation of fluid between the respective second ends of the fibers, in the measurement zone, comprise means for creating this circulation perpendicular to the optical measurement axis defined by the common direction of the fibers in the immediate vicinity of said second ends.  5) Device according to any one of claims 2 to 4, the fluid flowing in a tube, characterized in that the distance separating the respective second ends of the two fibers is close to the diameter of circulation of the fluid in the tube.  6) Device according to any one of claims 2 to 4, for  the study of a fluid in an aeration tank, characterized in that it includes deflector means housing the area for measuring air bubbles and large particles.