Agitating – Having specified feed means – Liquid injector within mixing chamber
Reexamination Certificate
2000-08-17
2004-01-06
Cooley, Charles E. (Department: 1723)
Agitating
Having specified feed means
Liquid injector within mixing chamber
C366S174100, C366S178100, C366S181200, C366S181300
Reexamination Certificate
active
06672755
ABSTRACT:
The present invention relates to the mixing of a powder with a liquid, particularly for enabling a solid reagent to mix and react with a liquid reagent.
Various methods of mixing solids and liquids are known. Many involve the agitation of the components in a rotary mixer combined with their stirring by driven blades or other mixing equipment. Such equipment can be very expensive to operate and can require the components to remain in the equipment for a considerable length of time to ensure that mixing is thorough and any solid lumps that may be formed are broken down.
An object of the present invention is to provide a method for mixing a powdered solid with a liquid that is both efficient and can be put into practice relatively cheaply so that it is suitable for use even with relatively large quantities of the components.
Accordingly the invention provides a method of mixing a powder and a liquid comprising forming the liquid into a flowing film and dispersing the powder and directing it at the flowing liquid film so that it impinges thereon and mixes therewith. The film is preferably formed in adherence with a wall surface, the liquid preferably being supplied to an upper part of the surface so that it flows downwardly along the surface under gravity and the powder is dispersed and directed at the wall to mix with the liquid.
The invention further provides, in another aspect, equipment for mixing a powder with a liquid, comprising a mixing chamber, liquid inlet means in the upper part of the chamber for directing the liquid on to an upper part of a supporting surface in the chamber, the liquid inlet means and the supporting surface being so arranged that the liquid flows downwardly in adherence with the surface in use, and means for introducing the powder to the chamber at a position spaced from the liquid inlet flow, for dispersing the powder within the chamber and for directing it toward the said surface so that it impinges on the liquid flowing down it, in use, and mixes therewith.
The advantage of the mixing method of the invention is that the liquid, being formed into a film presents a large surface area to the powder while the latter, being dispersed before it hits the liquid, will be captured thereby with less tendency to form aggregates than when a powder and liquid are simply fed into a container and mixed. A uniform mixture can thus be obtained fairly readily without great expenditures of energy.
In preferred embodiments of the invention the film is formed in such a way that its surface area expands as it moves away from the point at which the film is formed; this may be achieved by suitable shaping, for example curving, of a surface on which it is formed. Moreover conditions are preferably such that the film is turbulent, which, together with its large surface area, enhances the capture of the particles and mixing thereof within the liquid flow.
Although it is conceivable that the mixing might be carried out in an open environment, it is preferably carried out in a closed chamber and, again, although the film might be formed at one side of the chamber with the powder being directed at that side, it is preferred to employ a circular-section chamber with the film formed so as to flow down substantially the entire peripheral wall with the powder being dispersed from the central region and directed at the entire circumference.
Rotary feed inlets could be arranged to supply both the liquid and solid into the chamber, the inlets rotating to cover the entire circumference and the powder possibly being blown into the chamber to disperse it. Much more preferably, however, the powder is fed through a central, axial inlet and is centrifuged to direct it at the circumferential wall while the liquid is supplied through an annular inlet or array of spaced inlets coaxially around the powder inlet. Centrifuge means provided in the chamber may disperse the powder as well as directing it at the wall but suitable gas jets may also assist the dispersal and/or direction of the powder.
Although the invention as defined above is applicable to the mixing of any powder and liquid, it has been developed with particular concern to the mixing of an hygroscopic powder with an aqueous liquid and, even more particularly, to the mixing of powder and liquid reagents which react together. In these circumstances it is important to keep the solid and liquid components separate until they are brought together in the flowing liquid film and, in particular, to keep the powder supply dry up to this point.
More particularly it is found, in practice, with the use of hygroscopic solids, that it is both difficult and important to keep surfaces adjacent the powder inlet to the mixing chamber dry as any moisture in this region can cause the powder to cake, the caking gradually building up with time. Eventually this provides a path for mixture to track back into the powder supply duct, causing caking within the duct which obstructs the supply itself and necessitates stoppage of the process for cleaning. At worst, in the case of hygroscopic materials which react exothermically with water, this can result in substantial and even dangerous overheating, particularly if the moisture reaches a supply container.
Accordingly, a further aspect of the invention comprises a method for mixing an hygroscopic powder with an aqueous liquid comprising supplying the liquid to a chamber so that it flows in adherence with a surface therein, supplying the powder to powder delivery and dispersal means which disperse the powder in the chamber and direct it at the said surface so that it impinges on the flowing liquid and mixes therewith while preventing liquid/solid contact on or adjacent the powder delivery means that could result in moisture tracking back to the powder supply, the supporting surface preferably comprising a wall of the chamber itself.
The chamber might be arranged with appropriate baffles to prevent liquid/powder contact near the powder inlet but it has been found preferable to provide a dynamic seal between the powder inlet and parts of the chamber that might be contaminated by the liquid, the seal being formed, for example, by a gaseous flow. In particular, in the preferred circular-section chamber described above, an annular gas inlet is provided coaxially around the powder inlet through which gas is supplied to sweep moisture away from this region. The gas may be air depending on the nature of the components to be mixed. This arrangement has the added advantage that the gas flow assists in the dispersal of the powder within the chamber.
In addition to the provision of the dynamic seal to prevent liquid/powder contact at the powder inlet, the above mixing method provides for the formation of the liquid into a film that adheres to a surface in the chamber, preferably the chamber wall. Indeed steps are preferably taken to ensure that the liquid does flow on the wall surface without any splashing within the container which could result in splashing back to the powder inlet. For this purpose the delivery of the liquid to the wall surface is controlled both in quantity and direction so as to avoid splashing. To this end, the liquid may be delivered to the surface in a direction substantially along the surface and concordant with the desired direction of flow.
In a particularly preferred embodiment, the chamber has a domed upper wall and the liquid is fed substantially tangentially onto it from an upper inlet. The domed shape, conveniently although not necessarily spherical, ensures the desired spreading of the film out from the inlet to increase the surface area available to the solid particles. The chamber wall may continue in a smooth curve from its maximum circumference to an axial outlet but a frusto-conical shape is preferred in the lower part of the chamber to speed the fluid flow and to enhance turbulence which improves the mixing of the solid and liquid components.
The conical taper also enhances vortical flow within the chamber which may be further promoted by the provision of swirler means within the lower
Piper Brian
Potter Clive
Cooley Charles E.
Darby & Darby
Klean Earth Environmental Company Inc.
Sorkin David
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