Patent Description:
In particular, the flotation and dewatering treatments to which this sludge is subjected require that it be first added to and intimately mixed with specific chemical agents that change its chemical and physical characteristics, making it suitable for subsequent treatment. These chemical agents are usually polyelectrolytes, initially in the form of powders and/or emulsions.

In industry, the preparation of an aqueous solution of these polyelectrolytes in advance, with a concentration varying between <NUM> and <NUM> per thousand depending on the characteristics of the sludge to be treated, and then adding this solution to the sludge and mixing the mixture obtained, is known. The solution is usually prepared in special mixing tanks into which the appropriate quantities of water and polyelectrolytes are placed, where the mixing action is carried out by means of motor-driven propellers. The solution thus prepared is stored in the mixing tank until it is added to the sludge to be treated. The water used to make this solution can be mains water or reclaimed water, depending on availability.

This procedure has the important advantage of using an aqueous solution having chemical and physical characteristics that are quite similar to those of the aqueous sludge to be treated, making it relatively easy to mix the solution with the sludge itself, so that no special mixing equipment is needed to mix the two substances intimately together. Nevertheless the procedure described above also has significant disadvantages. A first disadvantage relates to the use of mains water to prepare the aqueous solution: the occurrence of sudden pressure changes in the water supply system can compromise correct proportioning of the water and polyelectrolytes needed for the subsequent flotation or dewatering treatment. In addition, mains water is particularly expensive and represents a significant cost item in plants using the process described above: an average-sized plant may use up to <NUM> cubic metres of water per day. If, on the other hand, waste water is used to make the aqueous solution, a different problem arises: waste water is usually very rich in chloride ions, which interfere with the added polyelectrolytes and significantly reduce their effectiveness in sludge treatment.

Another disadvantage of the above procedure is that, in the most common case where the aqueous solution is not completely used immediately, at least some of it is kept in the mixing tank until the next use: if stored too long, the solution may deteriorate and its effectiveness may be reduced.

In addition, stirring by means of motor-driven propellers subjects the polyelectrolytes to considerable mechanical stresses caused by the high rotation speed of the blades, and these stresses can eventually cause the molecules of the polyelectrolytes and the lattices they form to break down when added to the water, consequently reducing the effectiveness of the solution in sludge treatment.

Examples of kneading apparatuses according to the prior art are known from each of <CIT>, <CIT>, <CIT> and <CIT>. Particularly, <CIT> "[. ] relates to a continuous kneading apparatus capable of effectively kneading a variety of viscous material and having a small construction and, particularly to a continuous kneading apparatus in which material being kneaded is unlikely to remain. " The problem is solved by mounting screw flights 10a on an outer surface of each rotatable shaft used to knead the material fed to the apparatus, where each screw flight 10a is "formed with a notch at a downstream end thereof. <CIT> is relative to a method for producing a uniform silicone rubber through a screw extruder whose structure is very similar to the one of <CIT>.

<CIT> discloses an extruder designed for improving the degree of kneading of raw materials. According to <CIT> "The invention relates to a device for the production of polymers, preferably for the processing and polycondensation of polyesters, with a reactor which has an inlet opening on the one hand and an outlet opening on the other hand, as well as an outlet for discharging gases.

To overcome the above-mentioned disadvantages, a number of devices have been developed which allow the sludge to be treated to be mixed directly with the polyelectrolytes, thus avoiding preparation of the aqueous solution in advance. These devices are intended to effect particularly thorough mixing of the polyelectrolytes with the sludge, achieving a level of mixing between the two substances in just one step that would otherwise be achieved in two steps, that is by first making the aqueous polyelectrolyte solution and then adding this solution to the sludge. These devices comprise powerful motor-driven propellers to mix the two substances, and special compulsory paths along which the sludge is run to force it to pass through the propellers several times. It is clear that, while solving the problems associated with the use of an aqueous solution, these devices possibly worsen the disadvantages associated with the mechanical stresses to which the polyelectrolyte molecules are subjected. In fact, as well as forcing the polyelectrolytes to pass through the rotating blades of the propellers several times, these propellers are made to rotate at higher speeds than those used to mix the aqueous solution, because of the greater viscosity of the sludge compared to the aqueous solution itself, and therefore because of the greater energy required for the mixing operation.

The problem of providing a mixing device capable of ensuring thorough mixing of industrial sludge with polyelectrolytes, while preserving the effectiveness of the polyelectrolytes themselves, has not been solved at the present time, and constitutes an interesting challenge for the applicant.

In view of the situation described above, it would be desirable to have a mixing device that would make it possible to limit, and possibly overcome, the typical disadvantages in the state of the art.

The present invention relates to a mixing device according to claim <NUM>.

The above disadvantages are overcome by the present invention in accordance with at least one of the following claims.

According to the present invention there is provided a device for mixing a first fluid substance and a second fluid substance in order to obtain a mixture, said device comprising a hollow vessel extending along a first axis and having a first extremity and a second extremity opposite to said first extremity along said first axis, said vessel having a loading opening located at said first extremity to allow entry of said first substance and/or said second substance into said vessel, and a discharge opening located at said second extremity to allow said mixture to exit from said vessel; said device further comprising mixing means located within said container and able to rotate selectively about said first axis to mix said first substance and said second substance and to move said first substance and/or said second substance and/or said mixture along said first axis towards said second extremity, said mixing means further comprising a first screw extending along said first axis.

According to the invention, said mixing means comprise a second separating device located between said first screw and said second extremity to separate off a first portion, in which said first screw is located, and a second portion in said vessel; said second separating device having second fluid-dynamic communication elements arranged to allow fluid to pass between said first portion and said second portion.

According to one embodiment as described above, said mixing means comprise a first separating device located between said first extremity and said first screw conveyor to divide said first portion into a loading chamber, in which said loading opening is provided, and a first mixing chamber, in which said first screw conveyor is located; said first separating device having first fluid-dynamic communication elements arranged to allow fluid to pass between said loading chamber and said first chamber.

According to one embodiment as described above, said mixing means comprise a second screw extending along said first axis, said second screw being located in said second portion.

According to one embodiment as described above, said mixing means comprise a third separating device located between said second screw and said second extremity to divide said second portion into a second mixing chamber, in which said second screw is located, and a third portion; said third separating device having third fluid-dynamic communication elements arranged to allow fluid to pass between said second chamber and said third portion.

According to one embodiment as described above, said mixing means comprise a third screw extending along said first axis, said third screw being located in said third portion.

According to one embodiment as described above, said mixing means include a fourth separating device located between said third screw and said second extremity to divide said third portion into a third mixing chamber in which said third screw is located and a fourth portion; said fourth separating device having fourth fluid-dynamic communication elements arranged to allow fluid to pass between said third chamber and said fourth portion.

According to one embodiment as described above, said mixing means comprise a fourth screw extending along said first axis, said fourth screw being located in said fourth portion.

According to one embodiment as described above, said discharge opening is made in said fourth portion.

According to one embodiment as described above, said mixing means comprise a regulating device arranged to regulate the amount of fluid capable of passing between said first portion and said second portion via said second fluid-dynamic communication elements.

According to one embodiment as described above, said regulating device is selectively coupled to said second separating device.

According to one embodiment as described above, said mixing means comprise a mixing device located in said loading chamber, said mixing device being arranged to impart a rotational movement to said first substance and/or said second substance present in said loading chamber.

According to one embodiment as described above, said vessel is substantially cylindrical in shape and has an axis of symmetry coinciding with said first axis. According to one embodiment as described above, said device comprises drive means configured to drive said mixing means in rotation about said first axis. According to the invention, said device comprises a loading conduit located outside said vessel and connected to said loading opening, said loading conduit being arranged to feed said first substance and/or said second substance to said loading opening.

According to one embodiment as described above, said device comprises regulating means connected to said loading conduit, said regulating means being arranged to regulate the amount of said first substance and/or said second substance being fed to said loading opening.

Further features and advantages of the mixing device according to the present invention will become more clear from the following description, provided with reference to the appended figures illustrating at least one non-limiting embodiment thereof. In particular:.

In <FIG> denotes a device for mixing a first fluid substance with a second fluid substance to obtain a proportioned mixture. The term "fluid substance", here and hereafter, means any non-solid substance, that is one not having an intrinsic shape: this therefore includes liquids, gases, vapours, powders and emulsions, as well as any combination of one or more substances which, by their nature, take on the shape of the vessel containing them. In detail, but not in any limiting way, device <NUM> is particularly suitable for mixing liquids and/or emulsions: more particularly, the first substance may consist of an industrial sludge requiring purification treatment, while the second substance may consist of an emulsion of polyelectrolytes.

Device <NUM> comprises a hollow vessel <NUM>, extending along a first axis A and having a substantially cylindrical shape: vessel <NUM> comprises a hollow cylindrical body <NUM> having an axis of symmetry coinciding with first axis A and is bounded along axis A by a first extremity <NUM> and a second opposite extremity <NUM>, which are closed off by a first flange <NUM> and a second flange <NUM> respectively.

Body <NUM> has a loading opening <NUM> made in first extremity <NUM>, that is close to first flange <NUM>, and arranged to allow the first substance and the second substance to enter vessel <NUM>; body <NUM> also has a discharge opening <NUM>, made in second extremity <NUM>, that is close to second flange <NUM>, and arranged to allow the mixture to leave vessel <NUM>, the mixture being obtained by mixing the first substance and the second substance within vessel <NUM>.

Device <NUM> further comprises a loading conduit <NUM> located outside vessel <NUM> and connected to loading opening <NUM> to feed the first substance and the second substance to loading opening <NUM>, and consequently to vessel <NUM>; device <NUM> further comprises a discharge conduit <NUM> located outside vessel <NUM> and connected to discharge opening <NUM> to allow the mixture to be extracted from vessel <NUM> through discharge opening <NUM>. Additionally, with reference to <FIG>, the loading conduit <NUM> and the discharge conduit <NUM> are connected to the vessel <NUM> through respective connecting portions each one transversal to the first axis A. Device <NUM> further comprises a regulating device, which is known and not illustrated, connected to loading conduit <NUM> to regulate the quantities of the first substance and the second substance which travel through loading conduit <NUM> to be fed towards loading opening <NUM>, thereby entering vessel <NUM>. Said regulating device comprises a volumetric flow meter for the first substance, which is connected to a special pump arranged to feed the first substance along loading conduit <NUM> towards the container <NUM> at a constant flow rate, and a dosing device arranged to introduce a quantity of the second substance determined according to the flow rate of the first substance detected by the flow meter into loading conduit <NUM>, via an inlet opening <NUM>.

Loading conduit <NUM> may further comprise a further connection to a source of a scrubbing fluid, which is known and not illustrated, arranged to selectively feed a specified amount of the scrubbing fluid into loading conduit <NUM> to clean loading conduit <NUM>, vessel <NUM> and discharge conduit <NUM>.

Vessel <NUM> is supported, with first axis A horizontal, by means of supporting means <NUM>, which comprise a substantially rectangular base <NUM> provided with a plurality of supporting feet <NUM>, <NUM>, <NUM>, <NUM>, and a vertically positioned first bracket <NUM> and second bracket <NUM> connected to base <NUM> through their respective lower extremities, and connected to first flange <NUM> and second flange <NUM> respectively through their respective upper extremities.

With reference to <FIG>, device <NUM> comprises a cylindrical shaft <NUM> having a smaller diameter than the diameter of body <NUM> and a length greater than the length of vessel <NUM>: said shaft <NUM> is located along first axis A, partly inside vessel <NUM>, in such a way that its front end <NUM> projects from vessel <NUM> through a first support hole <NUM> provided centrally in first flange <NUM>, and its rear end <NUM> projects from vessel <NUM> through a second support hole <NUM> provided centrally in second flange <NUM>. At first support hole <NUM> and second support hole <NUM> respectively, there are first sealing elements <NUM> and second sealing elements <NUM> arranged to immobilise shaft <NUM> axially and radially, but to allow it to rotate about first axis A and at the same time prevent any leakage of the fluid substances present within vessel <NUM> through first support hole <NUM> and second support hole <NUM>. Rear end <NUM> of shaft <NUM> is connected to drive members <NUM>, configured to selectively drive shaft <NUM> in rotation about first axis A: such drive members <NUM> may, for example, comprise a motor and gearbox, or any electromechanical, pneumatic, hydraulic, thermal, chemical or similar drive device.

Shaft <NUM> carries a first disc <NUM>, a second disc <NUM>, a third disc <NUM> and a fourth disc <NUM> coaxially keyed and spaced between first extremity <NUM> and second extremity <NUM> within vessel <NUM>. These discs <NUM>, <NUM>, <NUM>, <NUM> have a diameter which is approximately smaller than the internal diameter of body <NUM> and, as described above, are able to rotate rigidly with shaft <NUM>; furthermore, within vessel <NUM>, disks <NUM>, <NUM>, <NUM>, <NUM> demarcate a loading chamber <NUM> between first flange <NUM> and first disk <NUM>, a first mixing chamber <NUM> between first disk <NUM> and second disk <NUM>, a second mixing chamber <NUM> between second disk <NUM> and third disk <NUM>, a third mixing chamber <NUM> between third disk <NUM> and fourth disk <NUM>, and a discharge chamber <NUM> between fourth disk <NUM> and second flange <NUM>. Chambers <NUM>, <NUM>, <NUM>, <NUM>, <NUM> are demarcated by discs <NUM>, <NUM>, <NUM>, <NUM> in such a way that fluid-tight access is gained to loading chamber <NUM> through loading opening <NUM>, and in such a way that fluid-tight access to discharge chamber <NUM> is gained through discharge opening <NUM>.

In the embodiment illustrated, chambers <NUM>, <NUM>, <NUM>, <NUM>, <NUM> can be abstractly grouped into a plurality of portions of vessel <NUM>. In particular, loading chamber <NUM> and first chamber <NUM> form a first portion, while second chamber <NUM>, third chamber <NUM> and discharge chamber <NUM> form a second portion. Moreover, more particularly, third chamber <NUM> and discharge chamber <NUM> in turn form a third portion, which thus consists of a subset of the second portion; finally, discharge chamber <NUM> alone coincides with a fourth portion, which thus consists of a subset of the third portion.

As may better be seen in <FIG>, each disc <NUM>, <NUM>, <NUM>, <NUM> respectively has fluid-dynamic communication elements <NUM>, <NUM>, <NUM>, <NUM> arranged to allow fluid to pass between the two chambers that the relative discs <NUM>, <NUM>, <NUM>, <NUM> separate: for example, first fluid-dynamic communication elements <NUM> are provided in first disc <NUM> and comprise a first service hole <NUM> and a second service hole <NUM> arranged symmetrically with respect to first axis A to allow fluid to pass between loading chamber <NUM> and first mixing chamber <NUM>. Similarly, second fluid-dynamic communication elements <NUM> on second disc <NUM> comprise a third service hole <NUM> and a fourth service hole <NUM>, third fluid-dynamic communication elements <NUM> on third disc <NUM> comprise a fifth service hole <NUM> and a sixth service hole <NUM>, fourth fluid-dynamic communication elements <NUM> on fourth disc <NUM> comprise a seventh service hole <NUM> and an eighth service hole <NUM>. One or more adjustment rings <NUM> may be coupled to each disc <NUM>, <NUM>, <NUM>, <NUM>, arranged to adjust the amount of fluid capable of passing through the relevant fluid dynamic communication elements <NUM>, <NUM>, <NUM>, <NUM>, and thus the amount of fluid capable of passing from one chamber to the adjacent chamber: said adjustment rings <NUM> are selectively coupled to relative discs <NUM>, <NUM>, <NUM>, <NUM> at service holes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> in such a way as to decrease the useful bore through which fluid is allowed to pass from one chamber to the adjacent one. Accordingly, by varying the inner diameter of said adjustment rings <NUM>, it is possible to vary the pressure that the fluid can reach inside the respective chamber.

With reference to <FIG>, first disc <NUM> supports a mixing device <NUM> located in loading chamber <NUM> and able to rotate together with first disc <NUM> to impart a rotational movement to the fluid substances present in loading chamber <NUM>: in particular, mixing device <NUM> comprises a first blade <NUM> and a second blade <NUM> integral with first disc <NUM>, extending parallel to the direction of first axis A and symmetrical with respect to first axis A.

Moreover, between them, first disc <NUM> and second disc <NUM> support a first screw conveyor <NUM> extending along first axis A within first chamber <NUM>, said first screw conveyor <NUM> being integral with first disc <NUM> and second disc <NUM>; first screw conveyor <NUM> has an external diameter substantially equal to the diameter of discs <NUM>, <NUM>, <NUM>, <NUM>, and an internal diameter substantially equal to the diameter of shaft <NUM>, to which first screw conveyor <NUM> can also be directly connected. Similarly, second disc <NUM> and third disc <NUM> support a second screw <NUM> in second chamber <NUM>, while third disc <NUM> and fourth disc <NUM> support a third screw <NUM> in third chamber <NUM>. Finally, fourth disc <NUM> supports a fourth screw <NUM> in discharge chamber <NUM>.

The operation of device <NUM> is easily understood from the above and requires no special explanation.

However, it may be useful to specify that, when device <NUM> is in use, the first substance and the second substance are fed into loading chamber <NUM> by means of loading conduit <NUM> connected to loading opening <NUM>. When motor <NUM> is switched on, shaft <NUM> starts to rotate about first axis A, causing all the elements integral with it, which as a whole are referred to as mixing means <NUM> and include discs <NUM>, <NUM>, <NUM>, <NUM>, mixing device <NUM>, and screws <NUM>, <NUM>, <NUM>, <NUM>, to rotate about first axis A. The two substances introduced into loading chamber <NUM> are caused to rotate by first blade <NUM> and second blade <NUM>: this first step has the sole purpose of imparting rotary motion to the substances, and therefore can be performed at low speed, avoiding the risk of breaking up the molecules of the polyelectrolytes with high intensity mechanical stress. As the two substances continue to be introduced into loading chamber <NUM>, a portion of them passes into first chamber <NUM> through first fluid-dynamic communication elements <NUM> provided on first disc <NUM>. In first chamber <NUM>, first screw <NUM> begins to mix the first substance and the second substance, and moves them towards second disc <NUM>, against which they are pressed by the rotation of same first screw <NUM>, thus favouring mixing. Under the effect of this pressure, a portion of the substances passes into second chamber <NUM> through second fluid-dynamic communication elements <NUM> provided on second disc <NUM>. Similarly, second screw <NUM> further mixes the two substances in second chamber <NUM> and presses them against third disc <NUM>, causing a portion of them to pass into third chamber <NUM> where third screw <NUM> further mixes the two substances and presses them against fourth disc <NUM>, causing a portion of them to pass into discharge chamber <NUM>. Finally, fourth screw <NUM> completes mixing of the two substances, obtaining the desired mixture and moving it towards discharge opening <NUM> to leave vessel <NUM>.

Mixing device <NUM> described above makes it possible to obtain homogeneous mixing of the first substance and the second substance by means of pressure applied to the two substances within chambers <NUM>, <NUM>, <NUM>, <NUM>, <NUM> through the rotation of screws <NUM>, <NUM>, <NUM>, <NUM>, and not through mechanical mixing: consequently shaft <NUM>, and consequently also screws <NUM>, <NUM>, <NUM>, <NUM>, can rotate at a moderate speed which safeguards the full effectiveness of the polyelectrolytes. The pressure within chambers <NUM>, <NUM>, <NUM>, <NUM>, <NUM> can be adjusted in advance, depending on the characteristics of the substances that are to be mixed, by means of regulating rings <NUM>, which limit the ability of the substances to pass into the next chamber via fluid-dynamic communication elements <NUM>, <NUM>, <NUM>, <NUM>.

On the basis of what has been described above, it is easy to see that device <NUM> is perfectly capable of overcoming the disadvantages in the state of the art described above.

Finally, it is clear that modifications and variations may be made to device <NUM> as described and illustrated herein without departing from the scope of protection of the present invention as it is defined by the claims.

For example, the number of chambers into which vessel <NUM> is divided may differ depending on the characteristics of the substances to be mixed.

In an alternative embodiment, not illustrated, the fourth portion of the vessel is in turn subdivided by a fifth disc into a fourth mixing chamber (in which a fifth screw is present) and a fifth portion (in which the discharge opening is located), which may in turn be subdivided into a fifth mixing chamber and a sixth portion by a sixth disc. It is evident that there is no limit to the number of mixing chambers that can be provided between the loading chamber and the discharge chamber, starting from a minimum of one mixing chamber.

Claim 1:
Device (<NUM>) suitable for mixing a first fluid substance and a second fluid substance to obtain a mixture, said device (<NUM>) comprising a hollow vessel (<NUM>) extending along a first axis (A) and having a first extremity (<NUM>) and a second extremity (<NUM>) opposite said first extremity (<NUM>) along said first axis (A), said vessel having a loading opening (<NUM>) obtained in said first extremity (<NUM>) to allow the entry of said first substance and/or said second substance into said vessel (<NUM>), and a discharge opening (<NUM>) obtained in said second extremity (<NUM>) to allow said mixture to leave said vessel (<NUM>); said device further comprising mixing means (<NUM>) located within said vessel (<NUM>) and able to selectively rotate about said first axis (A) to mix said first substance and said second substance and to move said first substance and/or said second substance and/or said mixture along said first axis (A) towards said second extremity (<NUM>), said mixing means (<NUM>) comprise a first screw (<NUM>) extending along said first axis (A); said mixing means (<NUM>) comprising a second separating device (<NUM>) located between said first screw (<NUM>) and said second extremity (<NUM>) so as to separate a first portion in which said first screw (<NUM>) is located and a second portion adjacent to said first portion within said vessel (<NUM>); said second separating device (<NUM>) embodies second fluid-dynamic communication elements (<NUM>) to allow said first substance and second fluid substance to pass between said first portion and said second portion;
wherein
it comprises a loading conduit (<NUM>) located outside the vessel (<NUM>) and connected to said loading opening (<NUM>) to feed the first substance and the second substance to said loading opening (<NUM>) and consequently to the vessel (<NUM>); it further comprises a discharge conduit (<NUM>) located outside the vessel (<NUM>) and connected to said discharge opening (<NUM>) to allow the mixture to be extracted from the vessel (<NUM>) through said discharge opening (<NUM>);
wherein
said loading conduit (<NUM>) and said discharge conduit (<NUM>) are connected to said vessel through respective connecting portions each one being transversal to said first axis (A),
said connecting portions being parallel to each other and being provided at the top of the vessel (<NUM>).