Liquid purification or separation – Filter – Movable medium
Reexamination Certificate
1999-11-24
2001-11-06
Chin, Peter (Department: 1731)
Liquid purification or separation
Filter
Movable medium
C162S251000
Reexamination Certificate
active
06311849
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a device for dewatering and washing fibre stock suspensions by two counter-rotating rolls, a stock feed and a stock discharge, where the headbox is separate at the two rolls and a discharge screw (
6
) is arranged for filter mat discharge below the gap between the two rolls.
Such systems are known which have a lateral stock feed and a downward-running formation zone, where a fibre mat is formed. This may be followed by a displacement wash zone and a subsequent press nip. Here, the stock discharge takes place above the two rolls into a repulper screw. This type of device shows a number of disadvantages, especially the stock discharge is complicated and susceptible to failure because the repulper vat must be sealed off against the rolls. Furthermore, approximately only half of the circumference is utilized for dewatering and washing. Additionally, this type of device has a tendency toward clogging because the force of gravity attempts to separate the fibre mat from the rolls. Operation without wash water is, therefore, not possible. Devices for fibre stock dewatering are also known from WO 96/06221 A and WO 96/18495, which work in counter-rotation of the rolls versus the devices mentioned. This type of equipment cannot, however, be used for washing. WO 96/06221 A furthermore shows a two-roll press with a stock feed arranged approximately in the area of the horizontal diameter. Thus the maximum range of circumference cannot be used. FR 2 006 772 A also shows the dewatering of a fibre stock suspension on a roll, with two superimposed rolls being represented in FIG.
3
. Here, two identical units are placed on top of each other. As a result of the difference in the geodetic height and the joint mat take-off on the lower roll, widely different conditions for the two fibre mats are created before pressing them together in gap
59
. The fibre mat therefore has widely different characteristics on the upper and lower sides especially with regard to the dewatering and washing degree. Additionally, in such an arrangement, the stock discharge is not foreseen in the lower section of the rolls but essentially between the 3 o'clock and the 4 o'clock positions.
BRIEF SUMMARY OF THE INVENTION
The aim of the present invention is therefore to avoid the disadvantages mentioned and to create a device for fibre stock dewatering and washing which safeguards a high dewatering performance with washing and advantageously shows low rewetting of the fibre mat.
As per the invention, this is achieved by the headbox being foreseen separately in the lower roll section, the axes of the rolls being placed on a horizontal plane, the rolls having channels for filtrate discharge and the channels having inlets arranged against the sense of rotation. This makes it possible to achieve an essentially much simpler stock take-off (take-off of the fibre mat) and utilization of a large part of the circumference of the two rolls and a high efficiency of the device. With the channels for filtrate discharge, which are arranged in the rolls, large quantities of filtrate and wash water can be discharged without any problem. Therefore, an especially favourable displacement washing can also be achieved. With the channels having inlets arranged against the sense of rotation, rewetting of the fibre mat is prevented as far as possible. The efficiency of the device can thus be further increased.
A favourable design of the invention is characterized by a guide plate, whose distance to the roll surface decreases continually, joining the headbox. With this guide plate a continuously increasing pressure on the fibre stock suspension can be created and thus especially favourable dewatering can be performed. A favourable design of the invention is characterized in that a wash zone is arranged in the upper part of the two rolls. This makes it possible to achieve good dewatering as well as, subsequently, good washing.
A favourable advancement of the invention is characterized by the wash zones being separated on both sides by a separative plate, or alternatively in that the wash water feed can be designed as a joint wash pool jointly for both sides. With these designs an optimum adaptation of the washing section and optimum utilization of the roll surface for dewatering and washing can be achieved.
A favourable design of the invention is characterized by the rolls having channels for filtrate discharge, where the channels may have inlets arranged against the sense of rotation. A favourable advancement of the invention is characterized by the channels having additional openings which are connected with the previous channel viewed in the sense of rotation. With such a design an even better filtrate and wash water discharge is possible, whereby rewetting can be further reduced.
A favourable design of the invention is characterized by the roll surface being designed as a perforated plate having large holes, these holes in the perforated plate having a diameter in the range of 10 to 25 mm. With this constructional design cost can be reduced because substantially fewer holes are required and also manufacture is simple and cheaper. The risk of incrustation is also substantially lower and cleaning of the holes is possible even during operation.
A favourable advancement of the invention is characterized by the rolls being individually clothed with wires. With these wires especially favourable dewatering is achievable. Especially the combination of these wires, which are supported by the perforated plates, brings about special advantages versus previously existing variants with small holes (1 to 1.5 mm diameter) drilled into the steel shell of the rolls, which especially constitutes a reduction of the risk of incrustation and more favourable cleaning options. Also it is easily possible to change the wires, and the rolls may be of the cantileverable design.
A favourable advancement of the invention is characterized by both rolls being suitable for being pressed against each other. To control the pressure and thus to increase the final dryness of the fibre mat, the rolls can be pressed against each other, for instance with hydraulic cylinders or other suitable equipment.
An advantageous design of the invention is characterized by the upper parts being suitable for folding down. This makes it possible to dismantle the rolls easily without major disassembling.
REFERENCES:
patent: 3980518 (1976-09-01), Ljung et al.
patent: 4589923 (1986-05-01), Gruenewald
patent: 4750340 (1988-06-01), Anderson
patent: 5667642 (1997-09-01), Luthi
Kappel Johannes
Mausser Wilhelm
Petschauer Franz
Sbaschnigg Johann
Alix Yale & Ristas, LLP
Andritz-Patentverwaltungs-Gesselschaft m.b.H.
Chin Peter
Hug Eric
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