Patent ID: 12239997

Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate at least one embodiment of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

First, a screen sorting device1according to the present invention is described with reference toFIG.1. A fibrous stock suspension is fed tangentially into first sorting stage3through an inlet9above a first screen designed as a disc screen43. Contaminants are retained at disc screen43. The portion of the suspension already cleaned here passes through disc screen43into first accepts chamber13and exits sorting device1via first accepts discharge23. A control valve can be provided in the accepts discharge to limit the discharge volume, thereby increasing the portion of fibrous suspension into the second sorting stage.

Heavy dirt discharge33is located above disc screen43. The heavy dirt is discharged either via a conical centrifuge or via a periodically operating pneumatic gate valve. In this way, heavy dirt accumulation and thus extreme wear on screen sorting device1is prevented. Disc screen43is kept free by the disc rotor as the first rotor53of first sorting stage3. Said disc rotor, together with the webs welded onto disc screen43, provides a deflaking effect in the suspension. Inlet chamber31is limited at the top by an orifice plate7, which has an opening in the center. Due to the tangential inflow and rotor rotation a vortex flow is created. Specifically lighter components than the suspension pass through orifice7in the center of the vortex into the washout and dewatering zone of second sorting stage5.

The operating principle of this screen sorting device with the at least two sorting stages—sorting stages herein refer to screen sorting stages—is based on the utilization of the radial pressure gradient in the vortex flow: Screen sorting device1operates in the disk part of first sorting stage3with overpressure and thus achieves a relatively high throughput. In the cylindrical part in second sorting stage5, the transport and dewatering elements of second rotor55in the embodiment of a cylindrical rotor carry out a pressureless, continuous washing out of the fibrous stock suspension entering this sorting stage. At the same time, dewatering of the contaminants, referred to as reject material takes place. This second sorting stage, also referred to as the washout and dewatering zone, consists of a cylindrical screen basket45and a cylindrical rotor53. Dilution water, also referred to as rinsing water, is introduced below screen basket43via rinsing water inlet17. Dilution water and any fibers still present exit through screen basket45and leave screen sorting device1via second accepts discharge25. Any contaminants still present are retained by screen basket45and conveyed upwards by cylindrical rotor55. They leave the screen sorting device as a discharge with a high dry content via reject overflow35.

The following applies to the setting of accumulation height21, which is set above orifice plate7on upper screen basket45:If it is too low, the contaminants will not reach the upper part of screen sorting device1and no rejects—also referred to as contaminants—will be discharged. In particular, a pulverization of contaminants can occur in the first sorting stage. These pulverized contaminants then enter the first accepts chamber and represent a deterioration of the fibrous stock suspension obtained as accepts.If it is too high, fiber losses increase, and overflow can occur.An accumulation height in a central area of the screen basket45is ideal. Accumulation height21can also be viewed and adjusted via the installed inspection window, which is not shown. An accumulation height up to half the height of the inspection window has proven to be effective. The area between the screen basket and the housing should not be flooded by the accepts. Filling this gap between the screen basket and the housing to above the upper edge of the accepts discharge is considered to be flooding.

The inspection window provides a partial view of upper screen basket45, where accumulation height21can be determined via the outflowing accepts. This is usually adjusted by adjusting the inlet pressure in 0.05 bar increments until the screen sorting device discharges accepts with the smallest possible contaminant content and contaminants as “fiber-free” as possible during reject overflow. Rejects discharged at the reject overflow have a fiber contents of only 10 to 15% weight percent maximum.

The pressure drop across the disc screen and the dynamic pressure required for contaminant discharge depend on the stock consistency and contaminant load. If the stock consistency and/or the contaminant content changes, the throughput of screen sorting device1changes and so does the required dynamic pressure for contaminant discharge. Therefore, screen sorting device1is highly dependent on external influences and must be regularly monitored and readjusted.

If operation settles below low fill level77in order not to “lose” fibers, wear in screen sorting device1itself increases as a result. Downstream systems are subjected to increased contaminant contents due to the accepts being discharged from the screen sorting device. This leads to problems, especially in the final stages of fine screening. In general, an increased sticky and contaminant load can also occur, since the contaminants, especially in first sorting stage3, are ground small and fed forward as accepts.

Therefore, use of a fill level detection system11is provided. Fill level detection11makes it possible to permanently detect the fill level in sorting stage5and to readjust it if necessary. This ensures that a predetermined level stored in control system61is permanently maintained in the second sorting stage, in particular at upper screen basket45. Desired fill levels75which depend on additional parameters, such as the stock consistency of the supplied fibrous stock suspension, can also be stored in control unit61(FIG.2). Since the quality of the fibrous stock suspension supplied via the inlet will fluctuate to a small extent, a fluctuation of the fill level will occur. A fill level between maximum permissible height79, referred to as high fill level, and minimum height77, referred to as low fill level, is permissible. Maximum height79is at the level of the top edge of the inspection window. Minimum fill level77is at the height of the lower edge of the inspection window. A fill level that is considered too low is below low fill level77, and a fill level that is considered too high is above high fill level79, shown as an example inFIG.1.

A fill level detection11can be realized in different ways. The following three possibilities are explained in more detail below:1. Pressure measurement above the orifice plate, direct detection;2. Heat detection of the housing, indirect detection;3. Capacitive detection of the splash water, indirect detection.
Pressure Measurement:

The simple possibility is a pressure measurement above orifice plate7. This measurement is then purged of influences from inlet chamber31. A measurement in feed line9of the fibrous stock suspension or in inlet chamber31has proven to be unsuitable due to the high dynamics within screen sorting device1.

Since deposits can form above orifice plate7and these deposits can make pressure measurement difficult, the pressure can be recorded, i.e. at the rinsing water nozzle and in the supply line by way of a pressure sensor63without the risk of the measured values being dissipated by deposits. At this point, water is added permanently during operation, thus flushing the nozzle. However, care must be taken here to ensure that the dynamic pressure is accounted for. The dynamic component can be compensated via the height equation (Bernulli) and the existing value of the FIC (Flow Indication Control) reference27.

Depending on detected accumulation height21, control unit61can regulate the pressure during infeed of the fibrous stock suspension. Pump19which is controlled by control unit61is provided for feeding the fibrous stock suspension. Pressure sensor69is provided in the infeed to inlet9of the fibrous stock suspension, so that the infeed of the fibrous stock suspension can be adjusted, in this case pressure-controlled, as a function of the respectively detected accumulation height.

Temperature Detection:

Another possibility for fill level detection is by way of temperature detection. It has been shown that the accumulation height, also referred to as fill level, can be inferred by “hand contact”. The temperature of housing29in the area of second sorting stage5can be used as an indirect detection of the accumulation height. The rotor pushes the accepts through the second screen, the accepts then splash against the wall of housing29, run down the wall and are discharged via second accepts discharge25. For determination of the accumulation height by way of temperature detection, it is also necessary to detect the temperature of the fibrous stock suspension in order to use the temperature of the fibrous stock suspension as a reference temperature.

If the ambient temperature is close to the reference temperature, and if for example, the temperature difference between the reference temperature and the ambient temperature is less than 5° C., external cooling is required to be able to reliably detect the accumulation height. For example, one of the fins of the housing wall can be cooled using cool service water as cooling.

The temperature profile of the housing in the region of second sorting stage5is the basis for the determination of the accumulation height by way of temperature acquisition. An IR-sensor may for example be utilized as temperature sensor71for this purpose.

Capacitive Detection:

Similarly, material splashing against the wall can be detected using a capacitive or comparable method. For this purpose, a portion of housing29is replaced with non-magnetic material, such as an acrylic inspection window. This method is particularly suitable in the case of aqueous accepts, wherein the accepts run off the inner wall of the housing due to their consistency.

COMPONENT IDENTIFICATION LISTING

1Screen sorting device31st sorting stage52nd sorting stage7Orifice plate9Fibrous stock suspension inlet11Fill level detection131st accepts chamber152nd accepts chamber17Rinsing water inlet19Pump for fibrous suspension21Accumulation height231st accepts discharge252nd accepts discharge27Rinsing water control29Housing31Inlet chamber33Heavy material discharge35Reject overflow37Lower support431st screen/disc screen452nd screen/screen basket531st rotor552nd rotor57Rotor drive59Belt drive61Control system63Pressure sensor for rinsing water inlet65Rinsing water flow rate sensor67Capacitive sensor69Pressure sensor suspension inlet71Temperature sensor73Cooling75Target fill level77Low fill level79High fill level

While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.