EP0770428A1

EP0770428A1 - Flotation plant with cyclic liquid volume variation

Info

Publication number: EP0770428A1
Application number: EP96111906A
Authority: EP
Inventors: Antonio Caravaggio; Giuliano Saltarella; Mancini Carmine
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-10-27
Filing date: 1996-07-24
Publication date: 1997-05-02
Also published as: IT1275810B1; ITMI952212A1; ITMI952212A0

Abstract

A flotation plant that includes at least one tank (1, 2, n) suitable to be fed with a must and is characterized in that the volume of the must contained in the at least one tank varies cyclically.

Description

The present invention relates to a flotation plant with cyclic liquid volume variation.
Flotation processes are known and used in chemical, agricultural, food, and mining industries, to separate components suspended in a liquid by making them float on the liquid. In particular, in the food industry, the flotation process tends to separate unwanted organic substances, generally aggregated in chains or groups of cells (for example pectins and the like), from fruit juices (hereinafter generally termed musts). Separation by flotation is allowed and accelerated by using gas (often air) and/or agents to aggregate the parts to be eliminated into flocks whose density is significantly lower than that of the surrounding liquid.
Conventional plants are generally of the continuous type: the liquid to be clarified enters one end of the tank and exits, once it has been clarified, from another end. A system of partitions induces extraction of the clarified liquid from a lower part of the tank and keeps a constant total level of the liquid (that is to say, the level reached by the sum of the layers of the actual liquid and of the separated substances). Systems of various kinds (mechanical or suction) continuously extract the substances to be eliminated. There are also plants of the discontinuous type, in which the liquid is fed into a tank (whose size depends on the production capacity of the plant) and, after separation of the two fractions (cleared fraction and waste fraction) by flotation, the two fractions are extracted from below in succession.
Both tupes of plants have the drawback of disturbing the flotation process due to the motions of the liquid that lies below the layer of the substances that have been separated or are being separated. These motions are essentially a translatory motion, in the case of continuous plants, and turbulence motions, in the case of discontinuous processes, and these turbulent motions are due to the considerable dimensions of the tank in which the process occurs. In turn, these dimensions are linked to productive potential requirements; turbulent motions arise because the liquid that is introduced is lighter than the clarified liquid and tends to send the clarified liquid downward again. The extent of these motions increases as the tank size increases. Discontinuous flotation in a tank also entails the drawback of having to accurately wash the tank after each cycle, in order to eliminate the unextracted waste residues. Both types of plant also have the drawback of restricting their operation to the presence of a single type of must to be processed, whereas it may be necessary to simultaneously process more or less large volumes of different musts with a single plant.
The aim of the present invention is to solve the above drawbacks of the prior art.
Within the scope of this aim, an object of the invention is to provide a plant in which notions of the liquid that lies below the parts that have been separated or are being separated are minimized.
Another object of the invention is to provide a plant that allows to separately subject multiple different musts to the flotation process.
This aim, these objects, and others which will become apparent hereinafter are achieved by a flotation plant that includes at least one tank suitable to be fed with a must, characterized in that the volume of the must contained in the at least one tank varies cyclically.
Further characteristics and advantages will become apparent from the description of a preferred but not exclusive embodiment of the invention, illustrated only by way of non-limitative example in the accompanying drawings, wherein the only figure is a diagram of a plant according to the invention.
With reference to the above figure, the plant according to the invention includes a plurality of tanks 1,2... n, fed by an agent dosage device 3 and by a device 4 for enriching with air or another gas; these devices are connected to the tanks by a duct 5 and respective valves 101, 102, 100n.
The tanks are advantageously located within a hopper 7 that is provided with a drain 8 so that the material that overflows out of the tanks is collected by the hopper and discharged through drain 8.
Each tank 1, 2, n is provided with a gate valve 201, 202, 200n connected to manifolds 9 and 10.
The operation of the plant according to the invention is as follows. The liquid to be subjected to the process, which has been termed "must" merely for the sake of brevity and in a non-limitative sense, passes through the optional agent dosage device 3, through the optional enriching device 4, and then, through the valve 101, 102, 100n, enters the respective tank 1, 2, n, filling it up to a preset level.
An adapted level control, not shown in the figure, opens valve 102 to fill tank 2, simultaneously closing the valve 101, and so forth up to tank n. In this step (pre-feeding), the tanks are filled to a level that is lower than the upper tank rim. In all subsequent cycles, instead, the volume of liquid that is fed into each tank is such as to make part of the volume occupied by the separated unwanted substances overflow out of the tank. The overflow of the separated substances can be assisted by various kinds of mechanical systems.
This additional volume can be adjusted by per se known systems, which are based for example either on the presetting of infeed times or on optical turbidity detections or on other conventional systems. The overflowed floated substances are conveyed from hopper 7 toward drain 8.
In each tank, after a settling step, each step for the expulsion of the separated substances is followed by a step for drawing the clarified liquid, which is collected through valves 201, 202, 200n by manifolds 9 and 10 (if there are one or more musts to be treated in the same plant). The duration of the settling step may be adjusted by per se known systems. During settling (or even during infeed), separation between the clarified liquid and the floated substances can be accelerated by using one or more vibrating agitators, which subject the content to small shock waves. Each liquid drawing step is followed by a step for further feeding each tank and for the consequent expulsion of the separated substances.
The dimensions of each tank are such that the infeed time of the liquid to be treated is slightly shorter than the time required for separation, so that the motions produced by infeed do not disturb, except perhaps very slightly, the upward motion of the particles that are being separated. Since this entails restrictions to the size of the tanks, the necessary production capacity is provided by introducing in a single plant a sufficient number of tanks, each of which can be fed with different kinds of must, so as to divide the production capacity among the various kinds.
The advantages of the plant according to the invention are considerable. First of all, the total volume of the two fractions is no longer practically fixed, as in conventional plants, but varies during the various steps of the process, and in particular its increase beyond the volume contained in the tank causes the overflow of the waste to be eliminated.
Furthermore, whereas in conventional continuous plants the volume V of the tank (and therefore its size), the time t for which the liquid remains in the tank, and the capacity Q of the plant are linked by the relation $V = Qt$
, in the plant according to the present invention this relation is no longer binding. The total capacity Q of the plant is in fact affected by the introduction of two new parameters; the number of tanks and the volume V of liquid introduced in each cycle. For example, for an equal time available for flotation and for an equal tank volume, the capacity Q depends on the increases in the volume V. This allows to make the size of each tank independent, allowing its optimization in order to minimize the motions of the liquid during flotation.
In addition to controlling the dosage of agents and gas enrichment, the optional presence of a programmable controller (PLC) can optimize the times of the various above described steps, for example so as to allow continuous infeed of the must to be processed, providing in practice a continuous method by the coordination of as many per se discontinuous processes as there are tanks.
In practice it has been observed that the invention achieves the intended aim and objects, a plant having been provided in which the size of the tank or tanks is determined by the optimization of the process for separation by flotation instead of by the production capacity of the plant.
The introduction of liquid to be processed causes the overflow ( which may or may not be assisted by mechanical devices) of the separated waste, and the total volume of liquid contained in the tank decreases during the drawing of the clarified liquid.
Every time clarified liquid is drawn, this is followed in each tank by the infeed of such a volume of liquid to be clarified as to cause the overflow of part of the separated substances.
An adapted system of valves and manifolds allows to simultaneously subject various kinds of must to flotation, keeping them separated.
The process does not occur continuously in a single tank, but in multiple mutually connected tanks, so that the clarified liquid drawing step and the step for expelling the separated substances occur in succession in the various tanks.
The plant is controlled by an adjustment system which, by optimizing for each tank the times and volumes related to each step, allows continuous infeed of the liquid to be processed.
The plant according to the invention is susceptible of numerous modifications and variations, all of which are within the scope of the inventive concept; all the details may furthermore be replaced with technically equivalent elements.
The materials employed, as well as the dimensions, may of course be any according to the requirements and the state of the art.
Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the scope of each element identified by way of example by such reference signs.

Claims

Flotation plant comprising at least one tank (1, 2, n) suitable to be fed with a must, characterized in that the volume of said must contained in said at least one tank varies cyclically.
Plant according to claim 1, characterized in that said must is fed into said tank in a lower region of said tank.
Plant according to claim 1 or 2, characterized in that the separated waste overflows out of said tank from the upper rim when said must is introduced.
Plant according to one or more of the preceding claims, characterized in that said waste is collected in a hopper (7) that comprises said at least one tank.
Plant according to one or more of the preceding claims, characterized in that the clarified liquid is extracted from a lower region of said at least one tank.
Plant according to one or more of the preceding claims, characterized in that it comprises a plurality of tanks.
Method for the flotation of a must to be clarified, comprising the steps of: feeding said must into the lower region of a tank, filling said tank up to a preset level; feeding further must into said tank, causing the generated waste to overflow above the upper rim of said tank; drawing the clarified liquid from a lower region of said tank.
Method according to claim 7, characterized in that said drawing step is preceded by a settling step.
Method according to claim 7, characterized in that it is performed in multiple tanks that are mutually connected so that the steps for drawing the clarified liquid and for expelling the separated substances occur in succession in the various tanks.
Method according to claim 7, characterized in that said separation of the clarified liquid from the substances to be separated is assisted by subjecting the liquid to be clarified to vibrations, either directly or by said tank.