EP1367858B1 - Heating installation of products, particularly viscous - Google Patents

Description

The present invention relates to a product heating installation, including viscous, comprising at least one heating pipe for the flow of said products. This may be in particular food products that must be subjected to cooking, sterilization, pasteurization, thermization or any other essential treatment in food processing. It could also be the treatment of effluents for the valorization of certain by-products.

During these operations, the treatment must be carried out as efficiently as possible, and the quality of the products must remain excellent, a goal sought in all agri-food industries, where the regulations and vitamin content, texture, color of products etc.

In some known installations, the product is continuously heated, the product flowing continuously in a heat-conducting wall pipe heated from the outside. The velocity of the product however remains zero on the wall, and its laminar flow is the cause of a bad transmission of heat and a great heterogeneity in the heating of the product, which is substantially less important in the center of the flow than 'in the vicinity of the wall. This is all the more annoying that the wall temperature must be relatively high because of the low heat exchange coefficient. In addition, the heating time is also important, the transferable power per unit of power being low.

To remedy some of these drawbacks, it has already been proposed by FR A 2 741 228 a product heating system, in particular viscous, comprising at least one heating pipe intended to be traversed by a flow of said products, and in accordance with the preamble of claim 1.

In this known installation, the products flow continuously in the longitudinal direction of the pipe, and are heated continuously by conduction of electric current through the product between the electrodes which are transverse electrodes fixed inside the pipe. , and in the form of a star, or equivalently, each formed of a series of bars or a grid disposed transversely in the pipe. In fact, it suffices to have perforated electrodes fixed in planes transverse to the pipe to obtain obstacles to the flow of product and to mix it, the transverse arrangement of the electrodes along the pipe being essential according to FR A 2 741 228.

But such a known installation does not however remove all the aforementioned drawbacks.

The object of the present invention is to overcome these disadvantages of the prior art, and to homogenize much more heat treatment of the product, thus increasing the quality of the treated product, without having to increase the heating power involved for a given flow rate.

For this purpose, an installation according to the present invention is carried out according to the characterizing part of claim 1. Volumes of the product to be heated are sequentially fed between the electrodes to remain there for a determined ohmic heating time, the current passing between the electrodes through its entire section the volume of product introduced and immobilized together, then what volume of the treated product is removed from said pipe.

Ohmic and voluminal heating is thus carried out in the mass of the product and perfectly homogeneous, since the product does not flow into the pipe during its treatment, and there is no hot wall. The product only flows during the introduction or evacuation of the pipe. It will therefore be possible to use less heating energy than in known installations, while obtaining a better result, because of the reduction in losses. While the product is stopped in the pipe during its treatment, but by implementing several parallel-fed pipes operating with a certain offset, we can obtain a high flow, with a flow of the treated product virtually uninterrupted.

The installation may still be in accordance with claim 2.

It can also be provided that each electrode is mechanically connected to a motor adapted to rotate it between its open and closed positions, and second electrically to the power source via a connection terminal, these mechanical and electrical connections being provided by sealed passage passages through the wall of the pipe.

Advantageously, the pipe will consist of several tubular sections aligned so as to constitute a continuous and smooth passage, two adjacent sections being separated by a tubular connection section of electrically insulating material and constituting a housing for an intermediate electrode, which link section will be connected to the two adjacent tubular sections by fixing clamps, sections of the same type, constituting electrode housings, being provided at both ends of said pipe and being connected by flanges to pipes with metal fittings, respectively inlet and Release.

For example, it can be provided that each pipe will consist of two successive tubular sections and will consequently comprise three electrodes respectively disposed in three connecting sections. The intermediate electrode will then advantageously be connected to a phase of a single-phase alternating current source via an isolating transformer, the end electrodes being connected to the other phase as well as to the earth. It will also be possible to use, for large powers, a three-phase supply, with four electrodes defining three heating sections, the end electrodes being connected to the ground. In other words, the pipe is then constituted of three successive tubular sections and consequently comprises four electrodes respectively arranged in four connecting sections, the two intermediate electrodes being connected to the phases of a three-phase AC source via an isolation transformer, and both end electrodes are connected to the ground.

In order to increase the throughput of an installation according to the invention and to ensure that the treated product flows almost continuously, it will still be advantageous to provide that this installation will include several pipes supplied with product volumes. in parallel and with staggered heating cycles, so that a pipe is in phase of supply or discharge product while another pipe will be in the heating phase. The power supply may be common to the various pipes, by implementation of a power unit connecting in turn the power supply on the pipe to be put in heating phase.

An embodiment of the invention will now be described by way of non-limiting example with reference to the single figure of the accompanying drawing which schematically shows a three-electrode installation and two sections.

The heat treatment pipe of the plant comprises two tubular sections 1 with round cross section, aligned and separated from each other by an intermediate connecting section 2i of the same section and constituting a housing for a disk-shaped electrode circular thick and rounded edges, corresponding diameter, referenced in 3. The material constituting the sections and sections of the pipe is an electrically insulating material having good mechanical strength in temperature, such as for example polypropylene usable up to temperatures of the order of 100 ° C, or the PEEK usable up to 200 to 250 ° C. It is also possible to envisage using ceramics, glass or a resin composite impregnated with glass fibers. In 4 is schematized a cylinder or other engine adapted to pivot on command the electrode around its vertical diametral axis, to bring it to the open position shown in the figure, for which the electrode disc 3 is parallel to the axis of the pipe and allows the passage of products, either in a closed position for which the electrode 3 is brought into a position perpendicular to this axis and completely closes the pipe. In 5 is also shown schematically an electrical connection terminal for providing the electrical connection between the electrode 3 and an AC power source, not shown. Crossings of the wall of the pipe by these mechanical and electrical connections are provided by sealed passages 6m and 6e of any known type.

In contrast to the intermediate section 2i, the sections 1 are connected to two other sections exactly similar and serving as housing for similar electrodes and connected in the same way as in the intermediate section; it is an inlet section 2e and an outlet section 2s, themselves connected to short stainless steel pipes equipped with standard metal connectors 7. The connections between sections 1 and sections on the one hand between end sections 2e, 2i and connections 7, on the other hand, are provided by flanges 8.

From the point of view of the circuit diagram (not shown), the central terminal 5 is connected to a phase of the AC network. single phase through an isolating transformer to prevent current looping with the distributor network, and the end terminals are connected to the other phase and to the earth. A measuring toroid can be inserted in this connection in order to control the leakage current and to be able to cut the power supply if a predetermined threshold is exceeded, this for safety. The entire installation is fixed horizontally on a base of insulating material, and a cover (also not shown) covers the entire work area to avoid operator contact with the live parts during operation.

• commande de la rotation des électrodes 3 pour les amener dans une position d'ouverture parallèle à l'axe de la conduite de traitement;
• introduction, par l'extrémité d'entrée de la conduite, du produit à traiter grâce à un système de pompage et éventuellement à un gaveur en cas de produit extrêmement visqueux ;
• commande de la rotation des électrodes 3 pour les amener dans une position de fermeture perpendiculaire à l'axe de la conduite, déterminant ainsi deux sections de chauffage identiques ;
• mise en tension des électrodes pendant le temps nécessaire à la montée en température jusqu'à la valeur choisie, puis coupure de l'alimentation, éventuellement après un palier de maintien en température ;
• rotation en sens inverse des électrodes pour les ramener en position d'ouverture ; et
• remise en marche du système de pompage, le produit arrivant dans la conduite chassant le produit traité qui en est ainsi évacué.

This operation of the installation, the different phases of which can be managed by an automaton, is as follows

• controlling the rotation of the electrodes 3 to bring them into an open position parallel to the axis of the treatment pipe;
• introducing, through the inlet end of the pipe, the product to be treated by means of a pumping system and possibly a gaveur in case of extremely viscous product;
• controlling the rotation of the electrodes 3 to bring them into a closed position perpendicular to the axis of the pipe, thereby determining two identical heating sections;
• tensioning of the electrodes for the time necessary for the rise in temperature to the chosen value, and then disconnection of the supply, possibly after a maintenance stage in temperature;
• rotation in the opposite direction of the electrodes to return them to the open position; and
• restarting the pumping system, the product arriving in the pipe chasing the treated product which is thus evacuated.

A new cycle identical to the previous one can then be realized.

It is understood that the geometric and electrical characteristics of the installation will be determined from a specification specifying the initial and final temperatures of the product, its electrical conductivities at these temperatures and the hourly flow of the product, number of hourly operations. or heating time. Sizing shall be calculated taking into account, in particular, the maximum voltage applicable to the electrodes and the permissible current density at their surface which, with certain materials, may be of the order of 2500 A / m ² continuously, with a frequency of 50 Hz.

The material of the electrodes will be chosen according to the nature of the treated product, the current density and its frequency. In principle, there should be no corrosion or electrochemical reaction with the product. Such materials are proposed in French Patent No. 98 03 154 in the name of the Applicant.

The present invention has the advantage of allowing the heating of highly viscous and heat-sensitive products, and eliminating many of the disadvantages of conventional installations, regardless of the viscosity of the product. There is no risk of overheating, in the absence of a hot wall, and the heating of the product has excellent homogeneity and can be relatively fast, even with reduced electrical energy. It should be noted that the products should preferably have an electrical conductivity less than 20 S / m.

Finally and as already indicated above, it is possible to further increase the throughput of such an installation by implementing several pipes supplied, in product point of view, in parallel, with time lag of the different operating phases, a pipe being for example in the product introduction or discharge phase while another will be in the heating phase. These phases will preferably be controlled by an automaton or other control device, which may also automatically connect, via a power unit, the AC power supply to the electrodes of the single conduct which will be in phase of operation. heater. In this way it will be possible to make practically continuous production of treated product, without increasing the need for installed electrical power.

Claims (8)

1. Heating installation for products, particularly viscous, comprising at least one heating conduit, through which a flow of said products is to pass, said conduit comprising at least one tubular section (1) made of an electrically insulating material, at each of the two ends of which one of two respective electrodes (3) is permanently mounted which is connected (5) to an electrical power supply source adapted to pass between the electrodes (3) crossing in its whole cross-section a volume of product to be heated which is passed between said electrodes (3), characterised in that the two ends of said tubular section (1) can each be closed off by the corresponding electrode (3) which can be moved between two positions, of which a first is an opening position in which said electrode (3) allows free passage in said conduit for the introduction of a volume of product in said tubular section (1) before heating or the evacuation of a volume of product after heating, and of which the second position is a closing position of said conduit in order to close off said tubular section (1) by immobilising a volume of product between the two electrodes (3) during an ohmic heating operation.
2. Installation according to claim 1, characterised in that said tubular section (1) of the conduit has a round cross-section and each electrode (3), in the form of a circular disc with a diameter corresponding to the diameter of said round cross-section, can be moved in rotation around a diametral axis of said circular disc of the electrode (3) between said opening position in which said circular disc of the electrode (3) is parallel to the axis of the conduit and said closing position in which said circular disc of the electrode (3) is perpendicular to said axis of the conduit.
3. Installation according to claim 2, characterised in that each electrode (3) is connected on the one hand mechanically to a motor (4) which can cause it to pivot between its opening and closing positions and on the other hand electrically to the electrical supply source through a connection terminal (5), these mechanical and electrical connections been ensured by impermeable passages (6m, 6e) crossing the wall of the conduit.
4. Installation according to any one of the preceding claims, characterised in that the conduit is constituted by a plurality of aligned tubular sections (1) in such a way as to constitute a continuous and smooth passage, two neighbouring tubular sections being separated by a tubular connection section (2i) made of electrically insulating material and constituting a receiving area for an intermediate electrode (3), which connection section (2i) is connected to the two neighbouring tubular sections (1) by fixing flanges (8), sections (2e, 2s) of the same type constituting electrode receiving areas being provided at the two ends of said conduit and being connected by flanges (8) to pipework with metal inlet and outlet connections (7).
5. Installation according to claim 4, characterised in that the conduit is constituted by two successive tubular sections and comprises three electrodes (3) arranged respectively in three connection sections (2e, 2i, 2s) and of which the intermediate electrode (3) is connected to a phase of a single-phase alternating current source through an insulation transformer, the end electrodes (3) being connected to the other phase as well as to earth.
6. Installation according to claim 4, characterised in that the conduit is constituted by three successive tubular sections (1) and comprises four electrodes (3) arranged respectively in four connecting sections (2), the two intermediate electrodes (3) being connected to the phases of a three-phase alternating current source through an insulation transformer, and the two end electrodes (3) being connected to earth.
7. Installation according to any one of the preceding claims, characterised in that it comprises a plurality of conduits supplied with volumes of product in parallel and having heating cycles with time lags in such a way that a conduit is in the product supply or product evacuation phase while another conduit is in the heating phase.
8. Installation according to any one of the preceding claims, characterised in that said conduits are made of polypropylene, PEEK, ceramic, glass or a resin composite impregnated with glass or similar fibres.

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