Patent Application
20090078382
The present invention relates to a washing arrangement for washing and dewatering cellulose pulp of the type comprising a compartmented drum.
All fiber lines comprise some type of washing equipment to separate the digestion liquor from the pulp. Later on in the process washing equipment is provided to separate bleaching liquors, after bleaching stages. There are a number of different types of washing equipment operating according to different principles.
A well-known type of washing arrangement is the drum washer, where the pulp is dewatered on a rotating filter drum after addition of washing liquid, which displaces the liquor remaining on the pulp web after the preceding process stage, for example a digestion stage or a bleaching stage. An underpressure inside the drum causes the displaced liquid to pass through a perforated metal sheet arranged on the rotatable drum. A further development of the original drum washer is the pressurized displacement washer, where the filtrate, at an overpressure, is brought to pass through the metal sheet. The increase in pressure difference leads to a more efficient filtrate displacement.
According to a known design of a pressurized displacement washer, the drum is provided with compartments, extending in the axial direction of the drum, and intended to be filled with pulp. The compartments are defined by walls in the form of bars arranged axially along the entire drum shaft, as well as a bottom formed by the perforated metal sheet. The compartmentalization of the drum ensures that the pulp cake does not break up and get transported away, but instead maintains the shape which is produced upon application of the pulp. The perforated metal sheet, on which the pulp is deposited, is located at a distance from the main surface of the drum, so that filtrate channels are formed in the space between the drum and the metal sheet. Along the circumference of the drum there are at least as many filtrate channels as pulp compartments.
In a drum washer, a plurality of different washing stages can be carried out, with separate addition of washing liquid to the different stages, as well as re-cycling of filtrate from one stage for use as washing liquid in another stage. In order to achieve maximum washing efficiency, it is desirable that washing liquid intended for a particular washing stage is not transferred to a later washing stage. (Due to pressure differences between the stages, the supplied washing liquid tends to be transported towards the lower pressure.) In order to be able to separate different washing stages, which are carried out in one or more washing zones of the drum, and forming stages, which are carried out in the forming zone of the drum, and discharge stages, which are carried out in a discharge zone of the drum (a zone for enhanced pulp concentration constitutes a first part of the discharge zone), the respective zones are sealed by longitudinal (i.e. axially extending) seals. These longitudinal seals are arranged between the rotary drum and the surrounding casing. The filtrates from the respective zones are separated by seals in a peripheral end valve arranged at one or both of the end walls of the drum.
A problem associated with drum washers of the type that has zones separated by means of longitudinal seals is that these seals are exposed for abrasion, wear and other stresses. The seals change over time, which affects the general wash performance in a negative manner and also leads to risks of leakage and production interruptions.
According to the prior art, it is possible that the working staff can make manual adjustments of the longitudinal seals. The principle is to wheel the seal in the direction towards the drum until the staff perceives a sound which serves to indicate that the seal lies in close contact with the drum, and thereafter back the seal off by an arbitrary distance. This procedure is circumstantial, irregular and completely dependent on personal qualities of the working staff.
Accordingly, there is a need for an improved solution to the problem with seals that are worn and change over time.
One object of the present invention is to provide an improved washing apparatus of the kind with a compartmented rotatable drum. In particular, the present invention aims at accomplishing a more secure and more effective seal mechanism of the washing apparatus.
In accordance with the present invention, these and other objects have now been realized by the invention of a controller for use in a washer for washing and dewatering cellulosic pulp material comprising a rotary drum including a plurality of axial compartment walls extending along the rotary drum so as to create a plurality of external axial compartments for washing the cellulosic pulp material, a stationary cylindrical casing enclosing the rotary drum thereby defining a ring-shaped space between the rotary drum and the stationary cylindrical casing, a plurality of axially extending seals disposed along the rotary drum thereby dividing the ring-shaped space into a plurality of zones for feeding, washing and discharging the cellulosic pulp material, the controller comprising a force sensor for sensing a force acting on at least one of the plurality of axially extending seals in a direction outwardly from the rotary drum and a seal positioning member for moving the at least one of the plurality of axially extending seals in the radial direction with respect to the rotary drum in a predetermined pattern based upon the force measured by the force sensor. Preferably, the seal positioning member is adapted to reverse the direction of movement of the at least one of the plurality of axially extending seals a predetermined distance if the force measured by the force sensor exceeds a contact threshold force. In a preferred embodiment, the seal positioning member is adapted to move the at least one of the plurality of axially extending seals in a direction towards the rotary drum based on a comparison of the force measured by the force sensor and a first contact threshold force and reverse the at least one of the plurality of axially extending seals a first predetermined distance when the first contact threshold force has been exceeded in a first mode of operation, and to reverse the at least one of the plurality of axially extending seals a second predetermined distance when the force measured by the force sensor exceeds a second contact threshold force. Preferably, the seal positioning member is adapted to reverse the at least one of the plurality of axially extending seals when the force measured by the force sensor exceeds at least one of the first and second contact threshold forces for a predetermined period of time.
In accordance with one embodiment of the controller of the present invention, the controller comprises at least two of the force sensors associated with the at least one of the plurality of axially extending seals, and at least two corresponding seal positioning members associated therewith, and includes a pivoted connection between each of the seal positioning members and the at least one of the plurality of axially extending seals, whereby different portions of the at least one of the plurality of axially extending seals can be moved independently with respect to the other of the plurality of axially extending seals.
In accordance with one embodiment of the controller of the present invention the force sensor comprises a load cell.
In accordance with another embodiment of the controller of the present invention, the seal positioning member comprises a holder for holding the at least one of the plurality of axially extending seals in a radial position with respect to the rotary drum and a drive member for driving the at least one of the plurality of axially extending seals by driving the holder. Preferably, the seal positioning member further comprises a spring force member in cooperative association with the driving member, whereby the spring force member becomes active when the driving member has reached a predetermined maximum capacity.
In accordance with another embodiment of the controller of the present invention, the seal positioning member is adapted to move the at least one of the plurality of axially extending seals based on at least one pressure associated with the at least one of the plurality of axially extending seals.
In accordance with another embodiment of the controller of the present invention, the controller includes a control member for collecting the force measured by the force sensor and transmitting a control signal based thereon to the seal positioning member.
In accordance with the present invention, a washer has also been provided for washing and dewatering cellulosic pulp material comprising a rotary drum including a plurality of axial compartment walls extending along the rotary drum so as to create a plurality of external axial compartments for washing the cellulosic pulp material, a stationary cylindrical casing enclosing the rotary drum thereby defining a ring-shaped space between the rotary drum and the stationary cylindrical casing, a plurality of axially extending seals disposed along the rotary drum thereby dividing the ring-shaped space into a plurality of zones for forming, washing and discharging the cellulosic pulp material, and a controller comprising a force sensor for sensing a force acting on at least one of the plurality of axially extending seals in a direction outwardly from the rotary drum and a seal positioning member for moving the at least one of the plurality of axially extending seals in the radial direction with respect to the rotary drum in a predetermined pattern based on the force measured by the force sensor.
In accordance with the present invention, a method is also provided for controlling a washer for washing and dewatering cellulosic pulp material comprising a rotary drum including a plurality of axial compartment walls extending along the rotary drum so as to create a plurality of external axial compartments for washing the cellulosic pulp material, a stationary cylindrical casing enclosing the rotary drum thereby defining a ring-shaped space between the rotary drum and the stationary cylindrical casing, a plurality of axially extending seals disposed along the rotary drum thereby dividing the ring-shaped space into a plurality of zones for forming, washing and discharging the cellulosic pulp material, the method comprising measuring a force acting on at least one of the plurality of axially extending seals in a direction outwardly from the rotary drum and moving the at least one of the plurality of axially extending seals in a radial direction with respect to the rotary drum in a predetermined pattern based on the force measured by the force sensor. Preferably, the moving of the at least one of the plurality of axially extending seals comprises reversing the direction of movement of the at least one of the plurality of axially extending seals a predetermined distance when the measured force exceeds a contact threshold.
In accordance with the present invention, there is provided a compartmented washing apparatus with adjustment of at least one longitudinal (i.e. axially extending) seal based on the force that acts on the seal in a direction radially outwardly from the drum. The force is measured, for example with a load cell or the like, and based thereon the seal is moved when necessary, for example when the seal gets too close to the drum due to wear or deformation of the drum or when there is an unfamiliar object between the seal and the drum. Preferably, this is achieved by comparing the measured force with a contact threshold value, whereby exceeding the threshold is interpreted as an indication that the seal lies in contact with the drum (i.e. is too close to the drum). The movement of the seal is accomplished by means of a motor, hydraulics or another drive means, normally connected to the seal over one or more intermediary members and/or positioning means.
The proposed seal adjustment enables washing apparatuses with “self sensing” seal arrangements where the seal is automatically moved back (reversed) upon contact with the drum. The seal adjustments can thus be performed independent of the personal qualities and perceptional abilities of the working staff. Among other things, the present invention enables compensation for changes in the position of the longitudinal seals in relation to the drum as a result of deformations of the drum washer upon changed operational conditions. A more secure sealing function is obtained, the risk of leakage is considerably reduced, and operation of the washer drum can be optimized such that the washing process provides better results.
Thus, according to the present invention there is provided a washing arrangement for washing and dewatering of cellulose pulp, which washing arrangement comprises a rotatable drum with a plurality of outer compartments on the drum for the pulp to be washed, which compartments are defined by axial compartment walls distributed along the circumference of the drum, a stationary cylindrical casing which encloses the drum, whereby an annular space is defined between the casing and the drum, and where the annular space, by means of longitudinal seals in the axial direction of the drum, is divided into zones for forming, washing and discharge of the pulp, the washing arrangement comprising a unit for seal adjustment with measuring means for measuring a force acting towards one of the longitudinal seals in a direction from the drum and moving means for moving the longitudinal seal substantially in the radial direction of the drum according to a predetermined pattern based on the force measured by the measuring means.
The moving means is preferably adapted to reverse the longitudinal seal in a predetermined manner, for example a predetermined distance, if the measured force exceeds a contact threshold. According to a preferred embodiment, the moving means is in this respect adapted to, in a first mode of operation, bring the seal in a direction towards the drum while comparing the measured force against a first contact threshold, whereby the seal is reversed a predetermined distance after the first contact threshold has been exceeded, and, in a second mode of operation, reverse the longitudinal seal a predetermined distance if the measured force exceeds a second contact threshold.
Furthermore, there may be at least two measuring means arranged in connection with the longitudinal seal together with a respective individually controlled moving means. By means of a pivoted (articulated) connection between the moving means and the seal, different parts of the seal may be moved independent of each other.
According to a particular embodiment of the present invention, the moving means comprises a positioning means that holds the seal in the radial direction of the drum, as well as drive means that drives the movement of the seal by, directly or indirectly, affecting the positioning means. The moving means may further comprise a spring force-based means, which is adapted to co-operate with the drive means such that the spring force-based means comes into force when the maximum capacity of the drive means is reached. Moreover, there is a control unit which is arranged to collect a force signal from the measuring means and transmit a control signal to the moving means based on the force signal.
According to other aspects of the present invention, a unit for seal adjustment is provided, and also a method for seal adjustment.
The present invention, as well as further objects and advantages thereof, is best understood by reference to the following detailed description, which in turn refers to the attached drawings, wherein:
Throughout the drawings, the same reference numbers are used for similar or corresponding elements, referring to
Each seal 40 has a width which is somewhat larger than the distance between two adjacent compartment walls 12b. Consequently, the compartment walls 12b will pass the seal 40 one by one as the drum 10 rotates and the position of the seal is such that at each point in time it “covers” either one or two compartment walls 12b. Further, the seal may, for example, extend in principle in the axial direction along the entire drum. Alternatively, the drum may present two (or more) separate seals in the axial direction, such as when the drum is provided with an annular structure that divides every compartment into two sub-compartments in the axial direction, whereby the filtrate can be conducted away from both of the end walls of the drum.
The rotatable drum 10, including the compartment walls 12b thereof, is normally made of steel. The longitudinal seals 40 may also be made of a metal material, but can with advantage be made in a polymer material, intended to be replaced by means of particular opening parts 22 in the casing 20.
A drum washer 100 of the above described design is run with continuously rotating drum 10 according to the following principle. Pulp to be washed is fed into the forming zone F (the inlet is not shown), whereby the pulp is placed in the compartments 12 of the drum 10 forming, in the axial direction of the drum, long and narrow rectangles on the perforated metal sheet which constitutes the bottom of the compartments 12a. The compartmentalization of the drum makes sure that the formed pulp cake structure is maintained. Washing liquid is supplied to the annular space 30 and filtrate is squeezed out of the pulp and thereby passes through the perforated metal sheet. Preferably, this occurs under an overpressure in order to obtain an improved dewatering of the pulp. The perforated metal sheet is placed at a distance from the drum 10 such that filtrate channels 14 are formed in the space between the drum 10 and the perforated metal sheet. The washing may, as in
As mentioned in the background section, the longitudinal seals of the drum wash are exposed to abrasion, wear and other stresses. The seals change over time, which affects the general washing performance in a negative way and also leads to risks of leakage and operational interruptions. Occasionally, various objects, such as chips or metal sheet parts, may also enter between a seal and the drum, whereby the function of the seal is considerably impaired and leakage may arise. As mentioned in the background section, in such cases the prior art suggests manual adjustments of a more or less arbitrary nature.
In particular, it has been observed that the position of the longitudinal seals of the drum washer is altered and displaced in response to varying conditions of operation. Varying conditions of operation may imply considerable differences in pressure and/or temperature in the washing apparatus, whereby the drum washer presents deformations. Thereby, the respective seal positions change in relation to the drum and the sealing function is affected in a negative way. The aforementioned manual adjustments are particularly unreliable in respect of adjustments for these kinds of changes, which sometimes appear comparatively fast and in an unpredictable way.
According to the present invention, a mechanism for seal adjustment is proposed, which mechanism enables a more sophisticated handling of the longitudinal seals of the washing drum.
The proposed seal adjustment is preferably “self sensing” and automatic in the sense that the seal is automatically reversed, for instance upon contact with the drum. The seal settings do not depend on the working staff's personal qualities and apprehension. The present invention enables compensation for changes in the position of the longitudinal seals in relation to the drum due to varying conditions of operation and deformations of the drum washer. Such compensation, as well as compensation for wear and other seal changes, may thus be carried out automatically.
It should be emphasized that expressions used in this description, such that the seal is in contact with or lies in (close) contact with or bears against the compartment walls/drum and the like, refers to direct as well as indirect contact between seals and compartment walls. Thus, there does not necessarily have to be any physical contact directly between the seal and the compartment walls/drum for these conditions to be fulfilled. For example, the seals may be arranged at a certain distance from the drum and its compartment walls, whereby the contact arising from the meeting with the compartment walls occurs by means of the pulp compressed in the compartments. It can also be the case that there is an object, such as a chip or a metal sheet part, between the seal and the compartment walls.
A preferred embodiment of the unit 60 for seal adjustment will now be described with reference to
A support structure 69, such as a shelf, encloses the load cell 61, the spring package 68 and also a part of the cylinder 67. The cylinder 67 works as a positioning means and holds the longitudinal seal 40 in the radial direction as seen from the drum. Movement of the seal 40 in a substantially radial direction is driven by the electrical motor 65, the rotational movement of which is translated to linear movement by means of the jackscrew 66. The jackscrew 66 is connected to the cylinder 67 and in this way the driving power of the motor 65 is transferred to the seal 40. (The function of the spring package 68 is described below.) The task of the load cell 61 is to measure the force acting on the seal 40 in a direction substantially radially out from the drum 10. In order to achieve this, it is suitably arranged between the cylinder 67 and the jackscrew 66, as in the example.
An advantage of the force-based seal adjustment according to the present invention is that it may be implemented by essentially mechanical measuring equipment, at least in respect of the parts that are arranged within the casing of the washing apparatus. The adjustment unit is therefore suitable for use in the demanding environment in the washing apparatus, where pulp suspension may be present between the seal and the drum.
The load cell 61 as well as the motor 65 are preferably connected to a control unit/function (63 in
The seal adjustment according to the present invention may with advantage be provided with a positioning function for positioning the seal at the correct distance from the drum at selected points of time as well as with a function that reacts by moving the seal at the occasions when it comes too close to the drum during “normal operation”.
The first-mentioned function, the positioning function, may for example be adapted to adjust the seal in the following way. Starting from the start/zero position of the system, the seal is moved in a direction towards the drum until a force greater than a contact threshold F1 is recorded by the measuring means. F1 is chosen such that it serves as an indication of the fact that the seal has come into contact with (bears against) the drum. This means that the value F1 should be different from the force range which the force on the seal lies within when there is no contact with the drum, but at the same time not be unnecessarily large in order to avoid undesired contact between the seal and the drum. This is illustrated in
The described positioning procedure is suitably repeated at certain intervals and may also according to some embodiments be initiated, by the working staff in between these points of time. It has been observed that the warming up of the washing drum leads to considerable geometrical deformations, whereby the distance between the drum and the longitudinal seal can vary by as much as several millimeters. This results in problems in the form of an impaired sealing function with less good washing results as well as an enhanced risk of leakage and production interruptions during the period of heating. According to an advantageous embodiment of the present invention, it is therefore proposed to adapt the system for seal adjustment, upon start-up with a cold machine, during a certain period of time performing positioning at more frequent points of time (e.g. at time intervals in the magnitude of hours), and thereafter switch to the same mode of operation with regard to positioning as upon start-up with a warm machine (e.g. with time intervals in the magnitude of days). Variants with two positioning modes are possible and so are variants with a successive increase of the positioning intervals. In this way, a well-functioning and safe seal between the zones of the drum is also achieved during the initial phase of the washing process, e.g. after a comparatively long interruption in the operation.
The second function mentioned above, which reacts upon contact, may for example be arranged to adjust the seal in the following way. The measuring means registers the force acting on the longitudinal seal in a direction away from the drum, more or less continuously. When the force exceeds a contact threshold F2, the system responds by backing the seal off. The threshold F2 is selected as a clear indication of the fact that the seal lies in contact with the drum, directly or by means of some object between the seal and the drum. Generally, F2 is chosen such that F2>F1, as illustrated in the diagram in
The input parameters to an algorithm for seal adjustment used in accordance with the present invention in order to perform the above-described functions, typically include the measured force against the seal as well as the position of the seal in relation to the start/zero position. Also, the distance of movement from the position where the seal touches the drum can be used. However, it should be noted that in these cases it is a question of relative positions and distances. With the force measurement according to the present invention, there is no need for a direct distance determination (distance sensor), whereby a seal adjustment that is sophisticated and at the same time comparatively easy to implement is possible. Yet another advantage of the proposed force-based seal adjustment is that it has a built-in correction for the wear on the seal. In other words, there will be an automatic adaptation to the degree of wear on the seal without the need for additional measurements or adjustments.
According to one embodiment of the present invention, the mechanism for seal adjustment comprises more than one unit for seal adjustment per seal. This is illustrated in
As mentioned, the longitudinal seal 40 is, according to a preferred embodiment, made of a polymer material. Hereby, a supporting meal sheet or the like (not shown) of a more rigid material may be arranged in connection with the seal in order to prevent unwanted bending thereof. Embodiments where there are intermediate parts between the seal and the casing 20 thus lie within the scope of the present invention.
Again referring to
According to a preferred embodiment, one or more pressures in the washer drum are used as additional input parameters based on which the position and movement of the seal is controlled. In particular, those of the longitudinal seals of the drum that seal between air (atmospheric pressure) on one side and pulp/liquid on the other side can be affected by a pressure difference which will influence the measured force towards the inner side of the seal (i.e. the side closest to the drum). Disturbances on the force signal due to pressure changes are illustrated in
Yet another embodiment of the present invention provides a more safe sealing function of the washing drum in cases where there are a plurality of units 60 for seal adjustment. The units 60 may be arranged in association with the same (
There may also be embodiments where some longitudinal seals of the washing apparatus are provided with units for seal adjustment while others lack this functionality. Of course, such embodiments also lie within the scope of the present invention. In general, it is most important to optimize the function of the seals which are adjacent to a forming zone and discharge zone, respectively, of the drum. Consequently, according to an embodiment of the present invention, as illustrated in
As mentioned above, the moving means 64 can also comprise a spring force-based means 68, which, by means of the positioning means 67, moves the seal when the upper capacity of the drive means 65 is reached. The spring force-based means 68 may often be excluded, which in
A system where positioning is not required or, alternatively, already has been performed, enters a second mode of operation, which in
It is to be understood that the above-described method for seal adjustment can be varied within the scope of the present invention. The measures taken when the contact thresholds are exceeded can, for example, be different. According to a preferred embodiment it is only when the contact threshold has been exceeded for a certain predetermined period of time that the system reacts. This can be true for one or both thresholds, F1 and F2, on the condition that the force must be exceeded during a certain period of time in one or more of the comparing steps (S4, S7, S9 or the corresponding).
Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/SE2006/050175 | 5/31/2006 | WO | 00 | 12/3/2007 |
