US2723194A - Process of separating bagasse pith and fiber - Google Patents

Description

Nov. 8, 1955 c. BIRDSEYE PROCESS OF SEPARATING BAGASSE PITH AND FIBER Filed May 6, 1952 IN V EN TOR.

;III IIIIIIIIII United States Patent PROCESS OF SEPARATING BAGASSE PITH AND FIBER Clarence Birdseye, Gloucester, Mass., assiguor to Eleanor G. Birdseye, Gloucester, Mass.

Application May 6, 1952, Serial No. 286,237 1 Claim. (Cl. 92-1) This invention relates to the manufacture of paper pulp from bagasse or other stalks of the Grammae type. It comprises a novel process of separating the pith from the fiber of such vegetable material preparatory to converting the pith-free fiber into paper pulp.

It is essential for the economical production of pulp from bagasse that the pith cells, which are more delicate and have dilferent charatceristics from the fiber cells, should be separated so that the fiber may be treated in a substantially pith-free condition and not while contaminated or diluted with an extraneous substance.

As the bagasse leaves the last grinding mill in the sugar factory it resembles crushed corn stalks and is composed of about 40% pith and 60% bast fibers on a dry basis. The pieces of bagasse may be of any size or length up to 6 or 8". Some of the pith cells are completely free of the fiber bundles and vice versa but in most cases pith is found clinging to the fibers.

The process of the present invention comprises an optional dry sifting step, a step in which the broken bagasse fibers are subjected to fluid pressure, a step of fractionating by pressure and friction, and an explosive expansion of the compressed fiber mass. If desired the liquid ingredients of the fiber mass may be removed in hot condition during the fractionating step and their latent energy recovered and utilized, and if desired the explosive expansion step may be followed by wet beating of the fibers.

Going more into detail, the dry sifted pieces of bagasse are passed into and through a confined space, such as a tube, wherein they are saturated with hot water or an aqueous solution and subjected to substantial fluid pressure. The hot saturated fiber mass is then compressed into a compact body or plug and thus subjected to mechanical frictional fractionation which tends to separate pith from fiber and fiber from fiber. Subsequently, the compact body of the fiber mas-s is discharged at atmospheric pressure, whereupon the compressed vapor expands explosively causing further and adequate separation of the pith and fibers.

These and other features and characteristics of my novel process will be best understood and appreciated from the following description of a preferred manner of carrymg it out with the assistance of apparatus shown in the ac companying drawings, in which the figure is a diagrammatic view of the apparatus with its various elements shown in flow sheet relation. 7

The dry sifting step may be carried out by feeding the broken bagasse to a rotary drum 10 having cylindrical perforated or mesh walls and equipped at its delivery end with vanes or lifts 11 which pick up the material and drop it upon a discharge chute 12. In this step the loose pith cells will pass through the walls of the drum while the fiber with some adherent cells will be advanced for the next step of the process.

The dry-sifted bagasse fiber is directed by the chute 12 to a hopper 13 having a pipe connection 14 by which hot water or any desired solution may be suplied to and mixed with the fiber as it passes downwardly in the hopper to a screw conveyor 15. The conveyor has a power driven helical screw 16 which forcesv the fiber into a tube 17 through a constricted section wherein the fiber is contacted mto a dense plug that is effective to prevent flow back to a screw press 19. During 2,723,194 Patented Nov. 8, 1955 into the hopper. A steam connection 18 leads to the tube at a point beyond the constricted section and through this steam at a pressure of 75 to 150 p. s. i. is admitted to the tube 17 thereby saturating and subjecting the fiber to heat and substantial fluid pressure.

The saturated bagasse fiber is conveyed through the tube 17, which may be of any convenient length and shape, this step the fiber bundles are softened and the bond of the pith cells to the fiber is weakened.

The screw press 19 is conical in shape and has a perforated inner wall 20 enclosing a power driven helical screw 21. The bagasse fiber, still under the full tube pressure, is delivered to the upper end of the press and forced downwardly again into a compressed plug at the discharge nozzle 22 of the press. In this compressing operation the fiber is mechanically kneaded and worked causing a partial separation of fiber from fiber as well as pith from fiber by friction between the moving fibers and between the fibers and the walls of the press.

During the pressing step the hot liquor that has permeated the fibers is forced out through the perforated wall 20 of the press, collected within the outer wall and drawn off by an outlet connection 23. The hot liquor may be utilized as a substantial source of energy at any convenient point in the system and if desired a limited amount may be led back through the pipe 14 to the hopper 13.

The screw 21 operates to force the compressed fiber plug progressively out through the nozzle 22 and in this step the fiber is suddenly relieved of pressure with the result that the contained vapor expands with explosive force separating the fiber bundles into component individual fibers and substantially freeing them of pith cells.

The pith and fiber may now be segregated in any desired manner, as for example, by that shown in my copending application Ser. No. 285,844 filed May 3, 1952.

In the drawings a wet-beating step is suggested and for carrying out such a step a tank 24 is arranged to receive the fibers and pith cells discharged from the screw press. The tank is equipped with rotary heaters 25 and with an overflow end fiber conveyor, not shown. The pith cells are carried off in the overflowing liquid and the now pith-free fibers are removed by the conveyor in condition for immediate use in the preparation of paper pulp.

Having thus disclosed my invention and described in detail a preferred manner of practicing it, I claim as new and desire to secure by Letters Patent:

The process of separating pith from the fibers of bagasse which comprises the steps of first dry-sifting the broken bagasse and thereby removing loose pith cells from the fiber, advancing the sifted bagasse fiber with adherent pith cells through a circuitous path while subjected to steam pressure of to p. s. i., compressing the hot moist fiber into a dense plug by mechanical pressure and thereby frictionally working the fibers upon each other and causing partial separation of those pith cells from the fibers that have been carried over from the dry sifting step, explosively expanding the plug, wet beating the expanded product and removing the now freed pith cells by floatation.

References Cited in the file of this patent UNITED STATES PATENTS

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