US3486516A - Method of uniformly discharging high consistency pulp from a flow chamber containing a constricted opening - Google Patents

Description

United States Patent 3,486,516 METHOD OF UNIFORMLY DISCHARGING HIGH CONSISTENCY PULP FROM A FLOW CHAMBER CONTAINING A CONSTRICTED OPENING Robert W. Stoertz, Charleston, S.C., assignor to Westvaco Corporation, New York, N.Y., a corporation of Delaware No Drawing. Filed Apr. 11, 1966, Ser. No. 541,523 Int. Cl. D21c 3/00; F17d 1/08 US. Cl. 137-8 3 Claims ABSTRACT OF THE DISCLOSURE A method for discharging high consistency cellulose fiber pulp by passing said pulp at 10-45% by .weight fibers through a flow chamber, i.e., a pipe, having a constricted opening therein; whereby said high consistency pulp is discharged at a uniform rate.

This invention relates to methods for uniformly feeding high consistency cellulose fiber pulps.

It has in the past been customary in papermakmg processes to refine the cellulose fiber pulps at consistencies of between about 2 and 5%. At these consistency levels there are about 50 to 20 parts of water present per each part of pulp and the resultant slurry behaves much like water itself so long as there is sufiicient agitation to keep the fibers in uniform suspension.

In recent years it has been found that substantial benefits can be obtained by refining fibers at much higher consistencies. At these high consistencies of from about to 45%, only 9 to 1 parts of water are present per part of cellulose fibers and the resultant slurry, which has little or no free water present, no longer exhibits the characteristics of water but those of a semi-plastic solid. As a result difficulties have been encountered in uniformly feeding high density pulps to the refiners through pipes, even though this plastic solid can be pumped through the pipes quite readily. Due to the nature of the high consistency pulp, instead of obtaining a uniform discharge from the end of the pipe into the refiners, the pulp is discharged in a series of intermittent slugs of pulp. This in turn creates severe fluctuations in the load applied to the refiners, seriously interfering with their efiicient operation.

It is the object of this invention to provide a method wherein high consistency cellulose fiber pulps may be discharged from a pipe or other fiow chamber at a uniform rate.

I have discovered that this object may be simply and easily accomplished by discharging the high consistency pulp through a very small orifice. Surprisingly the orifice instead of obstructing the flow of the semi-solid high consistency pulp results in a uniform stream of pulp being delivered. The reasons for these are still obscure; however, it appears that the high consistency pulp has certain thixotropic properties which under the shearing action of the orifice results in a change in the pulp from a semisolid to a fluid. Unfortunately, this action appears to be reversible, and the pulp after passing through the orifice quickly reverts to a semi-solid within several feet. For

this reason, the orifice should be located within about 3 feet from the discharge opening.

For proper functioning the orifice must have an opening no greater than about one-eighth of the cross-sectional area flow chamber leading to the orifice. Preferably the orifice opening should be about one-twentieth of the crosssectional area of the flow chamber.

The shape of the orifice opening does not appear to be very important as circular and slit shaped orifices have been employed with equally good results. Likewise, the orifice may be either of the plate type wherein the reduction of the diameter of the flow chamber is changed abruptly or of a type wherein the passage is gradually restricted until the orifice opening is reached, such as a venturi.

It has been found that in order for the orifice to function properly, it is necessary to provide a pressure drop of at least 3 p.s.i. across the orifice. For most conditions, it has been found that maintaining the pressure drop between about 5 and 15 p.s.i. produces the best results. Higher pressure drops, above 25 p.s.i., merely tend to Waste pumping power without providing any benefits.

A very satisfactory arrangement for supplying high consistency bleached kraft pine pulp to a refiner is obtained by the following arrangement: 60 feet of 16''. diameter pipe (approximately 200 square inches in cross section) is connected in sequence to two transistion sections of 100 and square inches in cross section. A circular orifice of 3 /2" diameter (approximately 9.6 inches square) is installed at the end of the last transition section. When pumping 600 gpm. of 14% consistency pulp through this system a very uniform flow of pulp is discharged through the orifice at a pressure drop of 5 p.s.i.

I claim:

1. A method of passing high consistency cellulose fiber pulp through a flow chamber having a discharge opening which comprises, passing said pulp at 10 to 45 percent by weight pulp fibers through said flow chamber containing therein a constricted opening, the cross sectional area of said constricted opening being not more than one-eighth of the cross sectional area of said flow chamber, maintaining a pressure drop across said constricted opening between 3 and 25 p.s.i. and locating said constricted opening in such position that substantially uniform fiow of said pulp is obtained from said discharge opening.

2. The method of claim 1 wherein said constricted opening is one-twentieth of the cross sectional area of said flow chamber.

3. The method of claim 1 or 2 wherein said constricted opening is not more than three feet from said discharge openmg.

References Cited UNITED STATES PATENTS 2,889,242 6/1959 Teichmann l622l XR 3,041,233 6/1962 Richter l62-52 XR 3,098,787 7/1963 Sieber 162343 XR FRANK W. MIGA, Primary Examiner R. H. TUSHIN, Assistant Examiner US. Cl. X.R.