Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Particular raw cellulosic materials
Reexamination Certificate
2000-10-09
2002-04-16
Nguyen, Dean T. (Department: 1731)
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
Particular raw cellulosic materials
C162S091000, C162S056000, C162S057000, C162S060000
Reexamination Certificate
active
06372086
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to processes and apparatus for sugar extraction from cane, and more particularly to an efficient diffusion extraction process.
BACKGROUND OF THE INVENTION
In present day sugar diffusion processes, the entire cane is usually subjected first to a cutting or shredding process by which the cane sugar cells in the pith and rind are ruptured open, or at least in which a substantial number of such cells are ruptured. The finely divided cane is then subjected to diffusion, where the refined pulp material is applied to one of a number of different diffusers at a relatively high consistency, such as about 8%-12% solids or higher. Heated water or steam is applied and juices and liquids are extracted in a tank or on a conveyor belt. In some instances, the extracted material flows in a countercurrent manner against the direction of travel of the refined cane material. Extraction in such diffusers is by gravity combined, in some cases, with mechanical pressing.
The term “diffusion” has been applied to various apparatus and methods by which a shredded, sliced, ground or refined cane or, in some instances, bagasse, is subjected to extraction by contact with heated fluid. In a true diffusion process, the plant cell is not ruptured and advantage is taken of the property of the dissolved crystals passing through the cell wall when water or other solution is more dilute than that in the cell. Following such diffusion, all solutions in contact with cells tend to achieve equal concentrations with the fluid in the cell.
Current refining practice has been to treat the cane in such a manner that, to a large extent, the cells are ruptured, and the sugar removal more nearly resembles a washing process called lixiviation. Apparently, both diffusion and lixiviation occur at the same time, but the term “diffusion” has become generically applied to such extraction processes and equipment quite apart from the fact that limited actual diffusion may be taking place.
While a great deal of attention has been paid to the construction and operation of diffusion equipment, this equipment still operates principally upon through-flow arrangements which depend upon gravitational drainage, at relatively high consistency, and therefore the efficiency and production rates are accordingly limited.
Although the diffusion process has been used, it is not believed to be practiced currently to a considerable extent, having been replaced in deference to the “tandem” process of running the cane between sets of high pressure rolls, such as six such sets, to crush the cane under the extreme pressure of the rolls, which may exert forces of 1,000 to 4,000 pounds per square inch. The roller crushers or “tandems” as they are known in the trade require a substantial power to drive, typically with the equivalent of approximately 1,500 horsepower each, and are known to present high maintenance problems.
SUMMARY OF THE INVENTION
Substantially improved production rates and efficiency can be obtained by adapting certain processing equipment that has already been developed and used in the preparation of papermakers' pulp. The cane is “refined” or macerated in a tub type pulper known in the industry as a hydrapulper. In a hydrapulper, material to be pulped is placed in a tub in which a specially designed impeller or rotor is mounted at the tub bottom above a perforated bedplate. Heated dilution water is added as necessary to achieve a desired consistency, and the pulped material is extracted through the bedplate after a sufficient period of residence time has elapsed. The pulper, or pulpers may be made according to U.S. Pat. Nos. 4,725,007 and 4,109,872, incorporated herein by reference. The impeller or rotor is preferably a “MidCon” rotor of Thermo Black Clawson, Inc. according to U.S. Pat. No. 4,725,007 incorporated herein by reference. The hydrapulper is highly efficient in reducing the fibrous content of the cane and breaking open the cell structure, permitting release of the sugar juices into the slurry.
The pulping takes place at relatively high consistencies (approximately 8%-10%) and uses recycled filtrate from the countercurrent washer's formation and first stage wash zones. The pulping will continue until a major portion of the sugar content is dissolved in the liquid content, such as up to 30 minutes or more to each pulper preferably at an elevated temperature, such as about 50-75° C., so that about 70%-99% and preferably up to 98% or more of the sugar content has been extracted into the liquid phase.
When the pulping is completed, the slurry is extracted through the perforated pulper bedplate of the final pulping stage diluted to a lower consistency, and it is applied through a headbox onto the top side of the continuously moving belt of a flat bed fordrinier type countercurrent displacement type extractor. Such an extractor employs an endless foraminous belt, (often called a “wire”), a headbox which delivers the suspension to the on-running or upstream end of the horizontally traveling upper run of the belt while at the relatively low consistency of about 2%-4% solids at an elevated temperature. The pulped material is thus deposited on the upstream end of the run of the belt where a mat is formed as the sugar-rich liquid drains through the belt and is withdrawn for further processing.
The belt runs downstream from the formation zone and is divided into a series of displacement zones to which liquid is supplied as from showers from above for drainage through the mat and through the belt and into receptacles below the belt. Fresh washing liquid or heated water is applied at the last of these zones at the downstream end of the belt run, and the liquid drained from the last zone is collected and delivered to the zone immediately upstream from the last zone, and these steps are repeated for each of the other zones to affect countercurrent extraction from the pulp.
The entire apparatus is enclosed in a hood. A series of receptacles are positioned below the upper run of the belt in sealed relation with the hood. Suction or vacuum is applied to these receptacles. The vacuum from below and the air pressure above augment the action of gravity in forcing the liquor to flow through the pulped mass on the wire. A particular feature of the apparatus is that of recycling the gases and vapors drawn through the belt back to the hood to increase the pressure differential across the belt. The above-described apparatus is more fully described in the patents of Ericsson, U.S. Pat. No. 4,154,644, issued May 15, 1979 and Parks et al., U.S. Pat. No. 5,367,894, issued Nov. 29, 1994, which patents are incorporated herein by reference.
Preferably, immediately downstream of the final extraction stage, the pulp mass is subjected to pressure extraction by pressing one or more rolls above the belt against rolls within the belt loop, such as shown in U.S. Pat. No. 5,367,894. This provides mechanical extraction of liquid from the mat on the belt so that the pulp or bagasse remainder exits the apparatus having given up most of its liquid content, to the range of about 40% consistency. Thus, in the pressing stage, more than 70% of the liquid remaining in the pulp is expressed therefrom and captured. If desired, lime or other agents may be added to the pulp and liquid within the countercurrent extraction equipment.
A principal advantage of the use of the combination of the hydrapulper and countercurrent extraction washer resides in the fact that the hydrapulper releases 70% or more of the sugar content of the cane into the liquid content within the hydrapulper. When this is extracted through the hydrapulper bedplate with the pulped cane and applied to the headbox of the belt type extractor, the suspension is at about 2%-4% solids. On the belt, it increases from 2%-4% up to about 15% solids before final pressing. This extraction is of high efficiency by reason of the fact that it is accomplished with a pressure differential including a negative pressure head or vacuum below the belt. This translates into a hi
Haywood Steven T.
King Kirk A.
Sieron Michael A.
Biebel & French
Kadant Black Clawson Inc.
Nguyen Dean T.
LandOfFree
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