Classifying – separating – and assorting solids – Sifting – Feeding and discharging
Reexamination Certificate
1999-11-12
2001-11-13
Nguyen, Tuan N. (Department: 3653)
Classifying, separating, and assorting solids
Sifting
Feeding and discharging
C209S913000, C162S052000, C162S245000, C162S246000
Reexamination Certificate
active
06315128
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
In the art of chemical pulping, natural cellulose material, for example, softwood chips, is treated to produce cellulose pulp from which paper products are made. As a prerequisite to this treatment, the cellulose material is typically introduced and conditioned prior to being formally “cooked” in pressurized vessels, that is digesters, by what is known in the art as a “feed system”. Since their introduction in the 1940s and 1950s, feed systems for continuous digesters have been essentially unchanged. However, U.S. Pat. No. 5,476,572 introduced the first significant development to the means of feeding a chip slurry to a digester, either continuous or batch, since the initial development of chip feeding systems. The system disclosed in the U.S. Pat. No. 5,476,572 and marketed under the name LO-LEVEL® Feed System by Ahlstrom Machinery Inc. of Glens Falls, N.Y., first introduced the concept of pumping a slurry of chips and liquor into a high-pressure transfer device instead of using a downstream pump to draw the slurry into the transfer device. As described in the '572 patent (the disclosure of which is incorporated by reference herein) this system dramatically reduces the complexity of the overall feed system by permitting, among other things, the high pressure transfer device to be positioned at, for example, ground level instead of elevated as was required by the prior art. Further improvements to the system initially disclosed in the '572 patent are described in U.S. Pat. Nos. 5,622,598 and 5,635,025 (the disclosures of which are also incorporated by reference herein).
As disclosed in co-pending application Ser. No. 08/744,857, filed on Nov. 4, 1996 and Ser. No. 08/738,239, filed on Oct. 25, 1996, the ability to pump a slurry of chips provides numerous opportunities to improve the efficiency by which comminuted cellulosic material can be introduced to a cooking system. The present invention provides further improvements to the feeding system for the chemical treatment of wood, particularly wood chips. For example, one embodiment of the present invention comprises a refinement of the invention disclosed in application Ser. No. 08/744,857 (the disclosure of which is incorporated by reference herein). Specifically, one embodiment of this invention comprising the refinement of the system illustrated in FIG. 2 of application Ser. No. 08/744,857, wherein instead of splitting the flow path into two or more paths to distinct digesters, two or more flow paths are used to feed a single digester. This is particularly advantageous when the capacity of one component of the feed system is exceeded by the desired capacity of the entire pulping system, or if the cost of manufacturing a larger capacity device is either technically or economically unfeasible.
The present invention also addresses the problem of isolating and removing undesirable material from the fiberline to avoid interference with the process or damage to the equipment. The comminuted cellulosic fibrous material, for example, softwood chips, that are treated in conventional pulping systems typically contains non-cellulose debris, for example, sand, dirt, stones, miscellaneous metal parts (for example, nails, pieces of wire, nuts and bolts) or metal fragments, or other heavy cellulose (e.g. knots) or non-cellulose material. This material is collectively referred to as “tramp material”, and typically has a density at least about 10% greater than the cellulose material being processed (e.g. at least 50% greater). Much of this material is separated during chip preparation, but some still passes to the digester feed system and to the digester itself. Conventionally, this material can be separated from the chips in the feed system by some form of separator. for example, a Tramp Material Separator marketed by Ahlstrom Machinery Inc., of Glens Falls, N.Y. One such Separator is shown schematically as item 12 in U.S. Pat. No. 4,743,338. This Separator is described in the brochure entitle “Digester Update”, 4
th
Edition, published in September 1981 by Kamyr, Inc. (now Ahlstrom Machinery Inc.) Tramp material may also be separated from the fiberline downstream of the digester, after the chips have been converted to a slurry of fibers and liquid. For example, the MC® Tramp Material Separator described in a 1986 pamphlet published by Kamyr, Inc., marketed by Ahlstrom Machinery Inc., and illustrated in U.S. Pat. No. 4,737,274, may be located in the blowline of a digester wherever convenient. Tramp material may also be separated from a liquid stream. U.S. Pat. No. 4,280,902 illustrates a cyclone-type separating device for removing undesirable material, in particular sand and the like, from a liquid stream in the feed system. This device is marketed under the name Sand Separator by Ahlstrom Machinery Inc. Though these devices have proven to be effective in removing tramp material from the feed systems of digesters, the introduction of the Lo-Level® feed system provides additional novel methods for isolating and removing such undesirable material.
According to one aspect of the present invention a tramp material separator for use in a comminuted cellulosic fibrous slurry feed system, e.g. for a digester, is provided. The separator comprising the following components: A first conduit having a top portion including an inlet and a bottom portion below the top portion, and an outlet. Means for providing centrifugal force on a slurry flowing in the first conduit to cause less dense solids in the slurry to move in a first flow path, and more dense, tramp material, solids in the slurry to separate from the first flow path and move in a second flow path under the influence of centrifugal force; the means for providing centrifugal force consisting essentially of a radiused section of the first conduit adjacent the bottom portion thereof, so that no moving or powered elements are provided for effecting separation. And a cavity defined adjacent and below the radiused section of the first conduit for receipt of more dense solids flowing in the second flow path.
This system may be used to feed comminuted cellulosic fibrous material to a digester, continuous or batch, or it may be used in any system that transfers comminuted cellulosic fibrous material that contains tramp material that is preferably separated and removed. For example, this system may be used in a chip transport system as disclosed in copending application Ser. No. 08/738,239 filed on Oct. 25, 1997 (the disclosure of which is included here by reference).
The separator may further comprise a baffle adjacent a portion of the cavity most downstream of the cavity in the first flow path, the baffle extending into the first flow path to aid in directing more dense, tramp material, solids into the cavity and retaining the tramp material in the cavity. Also the tramp metal separator preferably further comprises a nozzle for introducing liquid into the top portion of the first conduit at high speed so as to maximize the flow rate of slurry in the first flow path, and thereby enhance the centrifugal force moving more dense, tramp material, solids in the second path.
The separator may further comprise means for intermittently removing tramp material from the cavity, or for continuously removing it. The intermittent removal means may comprise any conventional device for removing trapped material. Preferably the means for intermittently removing tramp material from the cavity comprises a first valve closest to the cavity, a second valve remote from the cavity, and a chamber between the first and second valves, the first and second valves independently operable (although a conventional system/interlock is used to see that they are not both open at the same time) to allow tramp material to collect in the chamber when the first valve is open and the second valve is closed, and to allow discharge of tramp material from the chamber when the second valve is at least partially opened and the first valve is at least partially closed.
The separator also preferably
Andritz-Ahlstrom Inc.
Nguyen Tuan N.
Nixon & Vanderhye P.C.
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