VORTEX-TYPE SLURRY SEPARATOR WITH DILUTION MEANS

This invention relates to dilution in vortex-type slurry separators (hydxocyclones), such as are used, e.g., to remove specks, dirt, metal, and other impurities from paper and pulp slurries.

Dilution is commonly carried out in a vortex separator both to aid separation by reducing consistency in the outer vortex, and, by reducing the bleed rate (i.e., the fraction of solids in the original slurry appearing in the rejects flow), to decrease the amount of acceptable stock lost. In some devices diluent has been introduced through a nozzle-like opening in a con¬ verging outlet section of the separator body. In others, the diluent has been introduced downstream of such converging section, through an additional diverg¬ ing frustoconical wall of an elutriation chamber, e.g. as shown in U.S. Patent No. 3,612,276.

The invention makes possible excellent mixing of dilution liquid into the outer vortex, with simple controls (e.g., without an undesirable highly sensitive relationship between bleed rate and the dilution liquid flow rate, which,complicates bleed rate control), and with reliable, inexpensive apparatus.

Easy access to the rejects orifice is provided. Separation efficiency is high.

The dilution can be carried out sufficiently upstream of the rejects orifice to permit reconcentration of the rejects. The liquid can be effectively added over a wide range of dilution flow rates, in both large and small diameter separators.

According to the invention there is provided, in a vortex-type slurry separator having a tubular body for containing slurry flowing in a pattern in¬ cluding an outer vortex flowing generally toward an outlet and an inner vortex flowing generally toward another outlet, the improvement consisting of apparatus fox introducing dilution liquid into said outer vortex, said apparatus compris¬ ing a housing positioned adjacent said body and having an internal smooth wall extending about an axis to form an eddy chamber about said axis, said wall hav¬ ing an inlet for introduction of dilution liquid to cause said liquid to form an eddy in said chamber, and a transfer opening which extends through the wall of said body to allow said eddy to overlap said outer vortex, whereby said liquid will pass smoothly into said outer vortex by eddy current transfer.

XQZIZB3 the inside diameter of said body at said opening.

At least 10% of the axial extent of the tubular body preferably lies downstream of the transfer opening with respect to the outer vortex.

Preferably at least 40% of the axial extent of the tubular body lies upstream of the transfer opening with respect to the outer vortex. Preferably the tubular body has a converging section, and the transfer opening communic¬ ates with the converging section intermediate the maximum and minimum diameters of the converging section.

Other advantages and features of the invention will be apparent from the description arid drawings herein of a preferred embodiment thereof.

Figure 1 is an elevational view, partly sectioned, of a typical example of a vortex separator embodying the invention.

Figure 2 is an enlarged fragment of Figure 1, without the section¬ ing.

Figure 3 is a sectional view taken along line 3-3 of Figure 2.

Referring to the drawings, the separator has a tubular body 10 with a cylindrical section 12 and a downwardly converging generally frustoconical section 14 terminating in rejects orifice 16. At the upper end of portion 12 are tangential slurry inlet 18 and outlet 20 with vortex finder 22 aligned with the separator axis.

Toward the lower end of portion 14 the separator is laterally enlarged to provide a housing 30 having an internal cylindrical wall 32 which curves smoothly about axis 34 generally parallel to the main separator axis 36 to form an eddy chamber 38. The chamber has a tangential inlet 40 and a trans¬ fer opening 42 which opens into the adjacent portion of the separator proper which is formed by a second cylindrical wall 44 in housing 30. Thus, the separator wall 44 and wall 32, in cross-section transverse to axes 34 and 36, follow overlapping circles. Edges 46 and 48 are rounded slightly.

In operation, the slurry to be separated is supplied under pressure to inlet 18. Operation of separators of this type is described in the above identified patent. In general, however, the stock, as it flows about and along axis 36, separates into an outer, downwardly progressing vortex contain¬ ing a large percentage of the heavier material which is to be rejected through orifice 16, and an inner, upwardly progressing vortex containing primarily the acceptable material to be collected through outlet 20.

According to the invention, dilution water is supplied under pressure to inlet 40 and circulates in chamber 38 in a continuing eddy which, through transfer opening 42, overlaps the outer vortex in the separator proper, as suggested by the arrows in Figure 3. In the zone of overlap dilution - 2a - water enters the outer separator vortejc, mixing smoothly and uniformly in the slurry layer, with minimal loss of the water into the inner vortex. Some solids from the outer vortex pass into chamber 38 to flow in the eddy therein.

The dilution of the outer vortex reduces the loss of acceptable solids through orifice 16, increasing separator efficiency. Bleed rate reduction will increase with dilution rate, but the relationship is smooth and relatively insensitive, allowing accurate control over bleed rate without great precision in dilution rate.

In general, the inside diameter of chamber 38 is preferably being used if either the chamber or the separator taper at opening 42). Too small an eddy chamber would unduly limit dilution. Preferably, the eddy chamber should be located along the separator axis so that at least 10% of the axial extent of body 10 lies downstream of the transfer opening with respect to the outer vortex, and at least 40% lies upstream of the transfer opening; in this respect location of the transfer opening too close to orifice 16 causes an overly sensitive dilution rate-bleed rate relationship, and location too far from the orifice results in an excessively high dilution water requirement for a given reduction in bleed rate. Opening 42 should be at least as large as inlet 18, to avoid plugging, and should other¬ wise be dimensioned so as to preserve true eddy flow in chamber 38 without unduly limiting transfer through the opening. The extent of dilution inlet 40 along axis 34 should be close enough to the axial extent of chamber 38 itself to allow the eddy flow to cover the entire internal vertical wall of the chamber.