Drying and gas or vapor contact with solids – Apparatus – Houses – kilns – and containers
Reexamination Certificate
2002-01-16
2004-08-31
Nguyen, Camtu Tran (Department: 3743)
Drying and gas or vapor contact with solids
Apparatus
Houses, kilns, and containers
C034S083000, C034S443000, C034S326000, C162S009000, C162S055000
Reexamination Certificate
active
06782637
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a system for making a dried singulated crosslinked cellulose pulp fiber product using a jet drier.
BACKGROUND OF THE INVENTION
Dried singulated cellulose pulp fibers are desirable for many products from absorbent personal articles to a reinforcer in concrete. Currently, in the most common process of making singulated fibers, a roll of conventional pulp fibers is hammermilled into singulated fibers. This process is energy and time intensive, requiring many steps and pieces of processing equipment. Each piece of processing equipment requires a significant capital expenditure and occupies valuable factory floor space. Further, the current hammermilling process often produces fibers with undesirable physical properties, such as low kink, curl, and twist.
This dry singulated pulp will also contain knots of fiber, sometimes referred to as nits or nodules. Knots are fiber clumps that remain strongly adhered to one another as can be seen by placing a small portion of pulp into a clear beaker of water and stirring the water to mix the fibers. Most of the fiber will mix into the water as singular fibers, however there will be fiber clumps that are readily visible. The fiber clumps or knots are undesirable by-products of the hammermilling process. The amount of knots in a pulp that has been hammermilled can be quantified by using a screening system with acoustical energy used as the means to classify the fiber into amounts of knots, accepts and fines. It is desirable to have low knots and fines and high accepts where the accepts are the singulated fibers.
Canadian Patent No. 993618 (Estes, 1976) describes a process for producing a low density fluff pad or batt from individual fibers that have significant kink and interlocking to provide improved batt strength and higher bulk. In accordance with the process, wet pulp is separated into individual fibers during the drying stage. The process uses fluid jet drying equipment that employs air-jets or steam-jets for separating the fibers. The fibers are laid on a perforated screen upon exiting from the jet drier. The process of the Canadian patent produces a mat of interlocked fibers.
Crosslinked fibers are conventionally produced by wetting an already dried roll of conventional pulp fibers with a solution containing a crosslinker prior to hammermilling. The hammermilled pulp containing a crosslinker is then run through a flash drier and further heated in an oven to complete the crosslinking process. This crosslinked pulp has a knot content that is greater than 15%. It is desirable to have a lower amount of knots in crosslinked pulp. Also this conventional process is energy intensive and therefore expensive because the pulp is dried before it is rolled, then hammermilled in wet form with crosslinker, then dried again.
Flash drier systems have been used to directly dry dewatered never dried pulp. The use of flash driers to directly dry dewatered never dried pulp, however, produces a dried pulp with a high amount of knots. Typical knot amounts for flash drying of never dried pulps are 30-40%. Crosslinker containing pulp dried in this manner also results in a knot content similar to or exceeding this level. An overview of a commercial flash drier, the Flakt Flash Drier, and typical flash drier equipment installation is provided by Larsson and Lindstrom, 1996 (“Recent Developments in Pulp Drying”, Larson, O; Lindstrom, B, The World of Pulp and Paper Week, 5
th
International Conference on New Available Techniques, Jun. 4-7, 1996, Stockholm, Sweden).
SUMMARY OF THE INVENTION
This invention provides a dried singulated crosslinked cellulose pulp fiber product as well as an apparatus and a method for forming singulated, crosslinked, and dried fibers that have a relatively low knot content. In accordance with the process, wet pulp containing a crosslinker and air are introduced into a jet drier. The pulp is dried in the jet drier to form singulated pulp fibers. The pulp is removed from the jet drier and separated from the air. The process may be used on several types of feed pulp and on further treated feed pulp. The product formed by the process has advantageous properties such as a low knot count, a low fines count, as well as improved kink, curl and twist. The apparatus for carrying out the process may include a pretreatment station for supplying a treatment substance, a pulp feed device designed only for pulp, a pulp feed device designed for suspensions of pulp in foam, and/or a fiber separation station having a vacuum conveyor.
In accordance with the process described above, the wet pulp containing a crosslinker treatment substance, may be further treated with a treatment substance before drying to reduce the knot content of the pulp fibers. The process also includes producing singulated pulp fibers by introducing wet pulp and air into a jet drier through a rotary airlock. The rotary airlock has vanes and a housing, with the end of the vanes being spaced from the housing by a distance sufficient to prevent wet fibers from clogging the airlock. The process includes producing singulated pulp fibers by withdrawing the fibers from said jet drier in an air stream at a velocity sufficient to prevent the fibers from interlocking and knotting. The process also includes producing singulated pulp fibers by withdrawing the pulp fibers from an outlet from said jet drier under a partial vacuum.
The pulp product includes singulated, crosslinked and jet dried fibers with a knot count equal to or less than preferably 15%, more preferably 10%, even more preferably 5%, and most preferably 2%. The product may be further treated with a treatment substance selected from the group consisting of a surfactant and a mineral particulate. The product of singulated, crosslinked, and jet dried fibers can be incorporated into concrete, an absorbent article, a plastic product, a paper product, or a filter product.
The drying system for the processing of pulp into singulated, crosslinked and dried fibers includes a jet drier, a pulp supply station, an air supply station, an outlet flow conduit and a fiber separation station. The jet drier has a jet conduit, a manifold for air intake into the jet conduit, a pulp intake for delivery of pulp into the jet conduit, and a fiber outlet for removal of singulated and dried fibers, outlet air and fines from the jet conduit. The pulp supply station is coupled to the pulp intake for supplying a feed pulp to the pulp intake. The pulp supply station includes a treatment supply source for delivering a treatment substance to the pulp. The air supply station is coupled to the manifold for delivering air to the manifold. The outlet flow conduit is coupled to the fiber outlet for the transport of the fibers, outlet air and fines from the jet conduit. The fiber separation station is coupled to the outlet flow conduit for separating the fibers from the outlet air.
The present invention thus provides a dried singulated crosslinked cellulose pulp fiber product as well as an apparatus and a method that enable forming singulated, crosslinked, and dried fibers. The process may take wet pulp directly from a pulp mill and produce a singulated product from the never-dried pulp by using a drying process that singulates the pulp directly. This process forms singulated crosslinked fibers with greater kink, curl, and individual twist than hammermilled fibers. A further advantage is the ability of the present invention to produce crosslinked fibers having a low fiber interlock, knot and fines content. Other advantages are the further treatments, in addition to crosslinking, that can be performed on the pulp that are difficult or impossible to perform on a roll of dried pulp. Treatments can be done on the never-dried pulp that reduce the amount of knots, increase production rate, and/or form fibers having desirable characteristics.
REFERENCES:
patent: 2991946 (1961-07-01), Croft
patent: 3268954 (1966-08-01), Joa
patent: 3415456 (1968-12-01), Bidwell
patent: 3440135 (1969-04-01), Chung
patent: 3491953 (1970-
Dezutter Ramon Charles
Vrbanac Michael David
Wester Brian
Yancey Michael J.
Christensen O'Connor Johnson & Kindness PLLC
Nguyen Camtu Tran
Weyerhaeuser Company
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