Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – With classifying – separating or screening of pulp
Reexamination Certificate
2000-07-05
2001-09-04
Chin, Peter (Department: 1731)
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
With classifying, separating or screening of pulp
C162S380000, C209S731000
Reexamination Certificate
active
06284096
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. §119 of German Patent Application No. 199 31 166.8, filed on Jul. 6, 1999 and German Patent Application No. 200 04 255.6, filed on Mar. 7, 2000, the disclosure of which is expressly incorporated by reference herein in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for discharging impurities from a suspension containing paper fibers using a hydrocyclone in which diluting liquid is added into the suspension in the radially inner area of the hydrocyclone. The invention also relates to a hydrocyclone for carrying out the process.
2. Discussion of Background Information
As is known, hydrocyclones are well suited to concentrating the heavy parts and/or the light parts of a pulp suspension. Such devices typically utilize centrifugal forces in order to conduct such parts out of the hydrocyclone through a discharge aperture provided for this purpose. As a rule, hydrocyclones also serve to remove impurities such as small metal parts, glass slivers, sand, styropor, as well as light plastics. Moreover, it is important for such devices to achieve a high separating effect with increased operational reliability, e.g., freedom from clogging. In these known devices, clogs can occur when the impurities collect together and become concentrated in specific locations, e.g., in the area of the discharge aperture provided for them. These concentrations can accumulate over time in such a way that they result in a blockage. In many cases, a compromise must be found between the operational reliability of the device, e.g., the avoidance of clogs, and the highest possible efficiency of the machine, e.g., throughput and/or separating effect. One known method which attempts to address the problem of clogging utilizes the feeding in a diluting liquid in heavy-part hydrocyclones. Such a device utilizes a water feed line which opens in an edge area of the hydrocyclone, e.g., through slits in the cyclone wall in the peripheral direction. The diluting liquid acts to cause eddies at the edge layers. However, this design suffers from the fact that the diluted liquid must penetrate the heavy soil that is already concentrated therein, which can lead to a back washing of heavy parts into the accepted stock stream.
Other solutions utilize a central pipe having apertures facing radially outwards for adding the diluting liquid. For example, Canadian Patent Application No. 1 138 378 A describes a device wherein the diluting liquid quickly reaches the wall of the hydrocyclone with the detrimental effects already described. In such a design, undesired rebound effects can arise owing to the short distance and the flow of the diluting liquid directly onto the cyclone wall. Moreover, there is also an increased risk of clogging of the apertures, which are kept relatively small. In addition, the suggested swirl flow leads to further interfering eddies.
A known design is described in U.S. Pat. No. 3,785,489. This device utilizes an axial outflow. However, the design also produces a rotating flow at the central inflow of the diluting water by way of a number of vanes. Accordingly, this flow quickly drives the diluting water outwards. The effect of this flow is also an increased risk of clogging.
SUMMARY OF THE INVENTION
The invention is therefore directed to a process for discharging impurities from hydrocyclones which enables both an operationally more reliable removal of the impurities and a good separating effect.
According to the invention, the diluting liquid is introduced approximately centrally and in an axial direction rather than at the edge of the hydrocyclone, where clogging can be expected. Moreover, this design provides for the introduction of the diluting fluid predominantly into the core flow. Accordingly, if the rate of inflow is sufficiently high, the diluting liquid reaches the conical area of the separating chamber and gradually mixes with the surrounding pulp suspension owing to the effect of the shear flow prevailing there. This type of dilution leads to a gentle backwash of the fibers into the accepted stock, but without this happening to already concentrated heavy parts as well. The reason being that the latter are at the wall and are not affected by the addition of the diluting water. Without the measures of the invention, a portion of the already concentrated heavy parts could be stirred up and might reach the center of the hydrocyclone. From there, they would then disadvantageously be discharged with the accepted stock.
The invention provides for a process for discharging impurities from a suspension containing paper fibers using a hydrocyclone comprising a radially inner area, the process comprising adding a diluting liquid into the suspension in the radially inner area of the hydrocyclone, wherein the diluting liquid is added in a flow direction opposite to an axial discharge direction of the impurities. The hydrocyclone may comprise a separating cone having a narrowest point and an addition point wherein the diluting liquid is added. The addition point may be axially displaced from the narrowest point by a distance “a”. The distance “a” may comprise an axial length which is no greater than approximately 30% of an axial length of the hydrocyclone. The adding may comprise adding a flow of the diluting liquid without swirl. The adding may comprise adding a flow of the diluting liquid with only a swirl whose resulting flow rate vector is defined by a peripheral speed (Vu) and axial speed (Vax) at an edge of a jet, the resulting flow rate vector having an angle (&agr;) relative to an axial axis of no greater than approximately 30°. The adding may comprise adding the diluting liquid via a smooth jet. The adding may comprise adding the diluting liquid via a round jet. The adding may comprise adding the diluting liquid via a ring-shaped jet. The adding may comprise adding the diluting liquid into a center portion of the radially inner area with the aid of an injector, the injector drawing in liquid from a ring-shaped area around an addition point. The adding may comprise adding the diluting liquid at an axial speed of at least approximately 4 m/s.
The process may further comprise forming a light fraction from the suspension containing paper fibers, the light fraction comprising an accepted stock. The process may further comprise separating out a heavy fraction from the suspension, the heavy fraction comprising heavy parts.
The invention also provides for a hydrocyclone for discharging impurities from a suspension containing paper fibers, the hydrocyclone comprising an inflow for introducing the suspension to be purified, an accepted stock outflow for discharging the purified suspension, a separating part, a reject discharge device for discharging impurities of the suspension, at least one element for adding a diluting liquid at an addition point which is located in a radially inner area of the hydrocyclone, wherein the at least one element has at least one aperture opening axially and opposite to a discharge direction of the impurities. The reject discharge device may be directly attached to the separating part. The reject discharge device may be indirectly attached to the separating part. The addition point may be located away from the inflow at a point which is at least approximately 70% of an axial length of the hydrocyclone. The the separating part may comprise a separating cone. The addition point may be disposed on part of a flow insert which is located inside the hydrocyclone. The flow insert may be removable. The hydrocyclone may be adapted to accept different flow inserts having different flow actions. The at least one aperture may comprise an adjustable cross section. The position of the at least one aperture may be adjustable. The addition point may be arranged to be concentric with respect to a center of the hydrocyclone. The addition point may be arranged to be eccentric with respect to a center of the hydrocyclone. The addition point may be loc
Chin Peter
Greenblum & Bernstein P.L.C.
Hug Eric
Voith Sulzer Papiertechnik Patent GmbH
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