WO1997032078A1

WO1997032078A1 - Process and apparatus for controlling the purification and yield of fibers from a fiber suspension

Info

Publication number: WO1997032078A1
Application number: PCT/SE1997/000335
Authority: WO
Inventors: Ryan M. Smith; Charles Moss; Roland FJÄLLSTRÖM
Original assignee: Alfa Laval Ab
Priority date: 1996-02-29
Filing date: 1997-02-27
Publication date: 1997-09-04
Also published as: NO983962D0; NO983962L; BR9707765A; KR19990087326A; EP0958429A1; CA2247101A1

Abstract

A process and apparatus for controlling separators used to separate suspensions of fibers is disclosed. In a system in which at least one separator is used to separate a fiber suspension into fractions containing components of the feed suspension, sensors are used to generate information relating to a characteristic of at least one of the formed fractions. The information so generated is then used to control the operational parameters of the separators. In further embodiments of the invention, sensors provide information to controllers, which in turn control the separators.

Description

PROCESS AND APPARATUS FOR CONTROLLING THE PURIFICATION AND YIELD OF FIBERS FROM A FIBER SUSPENSION

Field of the Invention

This invention relates to the separation of fibers suspensions into fractions and, in particular, to the monitoring of the fractions to determine characteristics thereof and controlling the separation based upon the monitored characteristics.

Background of the Invention

During processing of pulp slurries to separate fibers from contaminants, it is possible to operate a separator to either maximize fiber recovery, to maximize contaminant removal or to balance the two. For example, if a separator is operated to maximize the removal of contaminants, a relatively large amount of fine fibers will pass into the contaminant fraction and the yield will be reduced. However, if the separator is operated in a manner to maximize the recovery of fiber, more contaminants will be retained in the fiber fraction, resulting in a less pure recovered fiber fraction. Thus, the operation of a separator, such as a screw press, roll press, Fluidized Drum Washer™ (a trademark of Alfa Laval Celleco Inc.), belt washer, disc filter or other washing, filtering or dewatering device, is a compromise between acceptable fiber yield and purification efficiency. In operation of the separator, a variety of variables may be altered to select yield and purification parameters. Initial conditions which may be controlled are items such as the type of separation device and filter material utilized, the manner in which the feed suspension is applied to the filter device, the number and type of spray nozzles and the number and nature of any secondary separation devices used. In addition, a number of process variables may be controlled during operation. For example, the outlet pressure of nozzles applying the feed suspension or washing nozzles may be varied, as can other variables such as processing speed, the pressure applied by press-type separators, rotation speed of the filter medium in drum or disc type filters or washers, or any other known operational parameter of the separator. An additional complication, particularly in the case of the processing of waste paper to recover fiber, is the fact that the pulp comprising the feed suspension can vary over time. For example, initially the feed suspension may contain a lot of contaminants such as ink or stickies and the separator may be operated to maximize contaminant removal. However, as new waste paper is processed, the contaminant level in the feed suspension might be lower and thus, it might be more desirable to operate the separator in a manner which maximizes fiber yield.

Thus, there exists a need for methods and devices to allow for the monitoring of fiber suspensions and the operation of separators to maintain acceptable balances of fiber yield versus purification efficiency. It is therefore an object of the present invention to provide a method for the monitoring of fiber suspensions to allow proper selection of process or initial variables.

It is yet a further object of the present invention to provide a method for the separation of fibers from suspensions while maintaining a selected yield to purification balance.

It is still a further object of the present invention to provide a system for the separation of fibers from a feed suspension while optimizing the balance between yield and purification.

Summary of the Invention

In a preferred embodiment of the present invention, a number of separators are used to separate fiber suspensions in a number of fractions. Sensors are placed so as to sense a characteristic of one or more of the fractions and provide an output corresponding to the sensed characteristic. The output of the sensors is then used to control one or more of the separators. In a further preferred embodiment of the present invention, a system including first and second separators is provided. The first separator separates a feed suspension into first and second fractions. The second separator separates the first fraction into third and fourth fractions. At least one sensor is employed to sense a characteristic of at least one of the fractions and provide an output corresponding to the sensed characteristic. The output is then used to control either the first or second separator.

In yet a further embodiment, a third separator is provided which separates the second fraction into fifth and sixth fractions. In this embodiment, at least one sensor senses a characteristic of one of the fractions and generates an output corresponding to the sensed characteristic. This output is then used to control at least one of the three separators.

In an additional embodiment of the present invention, multiple sensors are used to sense characteristics of a number of the fractions generated by the separators. An output corresponding to the sensed characteristic is used to control one or more of the separators.

In still another embodiment of the present invention, at least one sensor generates data corresponding to a characteristic of at least one of the fractions. This data is then provided to a controller which controls the operation of at least one of the separators.

In a further embodiment of the present invention, at least one sensor generates data relating to a characteristic of at least one of the fractions. This data is supplied to a computer, which generates digital control signals. These control signals are then provided to a controller which controls at least one of the separators.

Brief Description of the Drawings Figs. 1 - 10 are block diagrams showing the components of a system embodying the present invention in various embodiments;

Fig. 11 is a diagram showing the construction of a Fluidized Drum Washer™ (a trademark of Alfa Laval Celleco Inc.);

Fig. 12 is a diagram showing the construction of a disc filter; and

Fig. 13 is a block diagram showing a preferred system embodying the present invention and the flow control components therefore.

Detailed Description of the Preferred Embodiments

Referring now to the Figures in which like reference numerals indicate like or corresponding features, the preferred embodiments of the present invention will be described.

Initially, reference will be made throughout the drawings to "separation devices." Typically, the separation device may be any type of device used to separate a fiber suspension into components. Primarily these "separation devices" serve to separate fiber from other components of the suspension such as contaminants and fluid. A separation device could include a screw press, roll press, Fluidized Drum Washer™ (a trademark of Alfa Laval Celleco Inc.), belt washer, disc filter or any other type of filter, dewaterer, washer or thickener. in particular embodiments of the present invention, a preferred "separation device" would be a Fluidized Drum Washer™ (a trademark of Alfa Laval Celleco Inc.) such as that made by Alfa Laval Celleco Inc., of Lawrenceville, Georgia, U.S.A. Similarly, the SPRAYDISC™ filter, also made by Alfa Laval Celleco Inc., is a suitable separation device. Various other types of suitable separation devices are known in the fiber recovery and paper making arts. Referring now to Fig. 1, a block diagram of the preferred embodiment of the present invention is described. A feed suspension, comprising coarse fibers, fine fibers and contaminants dispersed in a liquid carrier is provided to a first separator 100 on line 102. In the first separator 100, the feed suspension from line 102 is separated into first and second fractions. Typically, the first fraction consists of fine fibers, and contaminants dispersed in the liquid carrier, and will exit the first separator 100 on line 104. The second fraction typically consists of a thickened mixture of coarse fibers and fine fibers dispersed in a liquid carrier and exits the first separator 100 on line 106. The first fraction is carried on line 104 to a second separator 108 which separates the first fraction into third and fourth fractions. The third fraction consists of fine fibers dispersed in the liquid carrier, and the fourth fraction consists of contaminants dispersed in the liquid carrier. The third fraction then exits the second separator 108 on line 110 which joins line 106. Thus, the third fraction is added to the second fraction at the junction of lines 106 and 110. This combination of second and third fractions then proceeds on line 114 to sensor 116. Sensor 116 senses a characteristic of the combined fractions provided on line 114 and outputs the sensed characteristic as a data output 118. After sensing, the combined fractions on line 114 are provided for further processing or use. The fourth fraction exits the second separator 108 on line 112 and constitutes a waste stream for appropriate disposal.

The sensor 116 may be any of a wide variety of sensors which sense a pertinent characteristic of a fiber suspension. For example, pertinent characteristics could be consistency of the suspension, the amount of fibers present per volume of the suspension, the amount of contaminants present per unit volume of the suspension, fiber yield as a function of time, or other measurements of quality or quantity related to the fiber suspension present on line 114. The data output 118 may be any of a variety of types of data output such as a connection to a computer, connection to a human readable display, or connection to a control system. The data output 118 may then be used to control the processing parameters of the first separator 100 or second separator 108. For example, based upon the value of the characteristic sensed by sensor 116 and the data output 118, the processing speed, type of filter medium employed, outlet pressure of suspension spray nozzles, number and outlet pressure of washing nozzles, rotational speed of filter medium, or other variables related to the operation of the first separator 100, the second separator 108, or both, may be varied to achieve a desired value of the sensed characteristic. Fig. 2 is a block diagram which shows a slightly different configuration for the first separator 100 and second separator 108. As was the case with respect with Fig. 1, a feed suspension is provided on line 102. However, the output line 110 of the third fraction is re-routed to the first separator to be input by a first header 103 (shown in Fig. 11) . Thus, the third fraction output from the second separator 108 is provided again to the first separator 100 so that fibers recovered by the second separator 108 may be added to the second fraction in the first separator 100. As was previously the case, the first separator 100 separates the input suspension into first and second fractions. The first fraction is output from separator 100 on line 104 and the second suspension is output from the first separator 100 on line 106 and is provided to the second separator 108. There, the first fraction is separated into third and fourth fractions. The third fraction is provided for output on line 110 which subsequently is provided through a header 103 (shown in Fig. 11) . The fourth fraction, which consists of contaminants dispersed in liquid carrier, exits the second separator 108 on line 112 for appropriate disposal or further processing.

In the embodiment of Fig. 2, the sensor 116 is placed in the path of line 106 to sense a characteristic of the second fraction, to which the third fraction has been added. Once again, the data output 118 is used to provide information about the sensed characteristic for operation of either the first separator 100 or second separator 108.

Fig. 3 shows a further embodiment of the present invention in which a dewaterer 122 is included with first separator 100 and second separator 108. This embodiment operates substantially as was described with respect to Fig. l, except that the combined second and third suspensions on line 114 are provided to a dewaterer 122 which serves to separate the input into fifth and sixth fractions. The dewaterer 122 primarily exerts pressure on the input suspension to squeeze out the liquid carrier. In the process of removing liquid carrier from the fiber suspension, some fine fibers are typically lost with the liquid carrier. The thickened or dewatered fiber suspension constitutes the fifth fraction and is output on line 124 for further processing or use. The sixth suspension, comprising fine fibers in a liquid carrier is provided as output on line 126. Line 126 is then routed for disposal or, as shown by the dotted line in Fig. 3, is combined with the first fraction on line 104 for processing by the second separator 108, to recover the fine fibers present in the sixth fraction.

Fig. 4 shows a further embodiment of a system previously described with respect to Fig. l, in which the data output 118 from the sensor 116 is provided to a control module 128. The control module 128 utilizes the data output 118 to generate control signals which are provided on control bus 130 to the second separator 108. As was previously described, the characteristics sensed by the sensor 116 and provided as data output 118 can be used to determine processing parameters for control of the separators 100 and 108. In the embodiment of Fig. 4, the data output 118 is utilized by controller 128 to calculate processing parameters, such as rotational speed of the filter, nozzle pressure or flow rate of the first fraction into separator 108, the number of spray nozzles utilized for washing in separator 108 or the rotational speed of the filter medium within separator 108. Once the control signals are generated by the controller 128, they are provided on control bus 130 to the second separator 108 and control the operational parameters of the second separator 108. Alternatively, the control signals generated by controller 128, may be provided on control bus 132 to the first separator 100, for controlling the operation of the first separator 100. As a final alternative, control signals may be provided on both control buses 130 and 132 to control the operation of both the first and second separators 100 and 108.

Fig. 5 shows an alternative embodiment of the present invention in which multiple sensors are used to generate data relating to the various suspensions present on the various lines. The first through fourth fractions are generated as was previously described in the embodiment of Fig. 4, a first sensor 134 senses a characteristic of the feed suspension 102 and provides information relating to that characteristic as a data output 136. A second sensor 138 monitors a characteristic of the first fraction provided on line 104 and provides information relating to that characteristic as a data output 140. A third sensor 142, senses a characteristic of the second fraction provided on line 106 and information relating to the characteristic of the second fraction is provided as a data output 144. Finally, a fourth sensor 146 monitors a characteristic of the third fraction on line 110 and provides information relating to that characteristic as a data output 148. With the described position of the sensors 134, 138, 142 and 146, all of the inputs and outputs to the two separators 100 and 108 may be monitored and data relating to the characteristics of the various suspensions generated. This data may then be used as was previously described to control either the first separator 100 or the second separator 108, or both. For example, the data output 136 of the first sensor 134 and the data output 144 of the third sensor 142 might be used to control the processing variables of the first separator 100. Likewise, the data output 140 of the second sensor 138 and the data output 148 of the fourth sensor 146 could be used to control the processing variables of the second separator 108. As a specific example, sensor 134 could sense the consistency of the feed suspension provided on line 102 and generate information regarding the consistency of the feed suspension as data output 136. In response to variations in the consistency of the feed suspension on line 102, the data output 136 from the first sensor 134 could be used to vary the rotational speed of a filter body located within separator 100. Similarly, sensor 142 could sense the amount of contaminants present in the second fraction provided on line 106. Information relating to the amount of contamination of the second fraction on line 106, could then be provided as the data output 144, and used to adjust the amount washing the second fraction is subjected to in the first separator 100. Similarly, the second sensor 138 could sense the fine fiber content of the first fraction provided on line 104 and generate a data output 140 for use in controlling the second separator 108, while the fourth sensor 146 could sense the amount of contamination present in the third fraction on line 100 and provide a data output 148 for use in controlling the washing of the third fraction within the second separator 108.

Fig. 6 shows an embodiment in which a multiple sensor arrangement similar to that described in Fig. 5 is applied in the environment containing first and second separators 100 and 108 and a dewaterer 122 as was described with respect to Fig. 3. As was described with respect to Fig. 3, separator 100 generates a first fraction output on line 104 and a second fraction output on line 106. A second separator 108 generates a third fraction output on line 110 and a fourth fraction output in line 112. Finally, a dewaterer 122 generates a fifth fraction output on line 124 and a sixth fraction output on line 126. These fractions consist of the components previously described with respect to Figs. 3 and 5. As was the case with Fig. 5, a first sensor 134 is placed in the path of the feed suspension on line 102, a second sensor 138 is placed in the path of the first fraction on line 104, a third sensor 142, is placed in the path of the second fraction on line 106 and a fourth sensor 146 is placed in the path of the third fraction on line 110. As was described with respect to Fig. 5, these sensors generate data outputs 136, 140, 144 and 148 which may be used in the control of the first separator 100, the second separator 108, or both. In addition, a fifth sensor 150 is provided to monitor a characteristic of the fifth fraction on line 124. This sensor 150 generates a data output 152 providing information relating to the sensing characteristic for use in control of the dewaterer 122, or the first and second separators 100 and 108. For example, if the dewaterer 122 is press-type dewaterer in which a force is exerted on the suspension to squeeze out the liquid carrier, the fifth sensor 150 may detect the consistency of the fifth fraction and generate data corresponding thereto as the data output 152. This data output 152 could then be used to control the force applied to the input suspension in the dewaterer 122 or the rate at which the input suspension is processed by dewaterer 122.

Fig. 7 shows a multiple sensor arrangement in which the sensors are placed as was previously described with respect to Fig. 5. However, Fig. 7 shows an arrangement in which a first controller 158 controls the operation of the first separator 100 and a second controller 154 controls the operation of the second separator 108. As was previously described, sensors 134 and 142 sense characteristics of the fiber suspensions flowing on lines 102 and 106, respectively. The information relating to the sensed characteristics is provided as output on lines 136 and 1₄₄ for input to controller 158. Similarly, information from sensors 138 and 146 is provided as output on lines 140 and 148 for input to controller 154. The first controller 158 interprets the data 5 provided on lines 136 and 144 and calculates process control parameters for the first separator 100. The first controller 158 then generates control signals which are provided on a control bus 160 to the first separator 100. Similarly, the second controller 154 interprets the data provided on data lines 140 and

\0 148 and calculates control parameters for the second separator 108. The second controller 154 then generates control signals which are provided on a control bus 156 to the second separator 108 for controlling the processing conducted by the second separator 108.

15 Fig. 8 shows a system containing a dewaterer 122 and multiple sensors as was described with reference to Fig. 6, with the addition of controllers controlling the first separator 100, the second separator 108 and the dewaterer 122. As was described with reference to Fig. 6, multiple sensors 134, 138, 142, 146 and

20 150 monitor characteristics of the various fiber suspensions generated by the first and second separators 100, 108 and the dewaterer 122. As was described with reference to Fig. 7, signals from the first and third sensors 134 and 142 are provided to controller 158 which generates control signals on control bus

25 160 for control of the first separator 100. Likewise, the second and fourth sensors 138 and 146 generate data provided to controller 154, which then generates control signals provided on control bus 156 to the second separator 108. Fig. 8 shows the addition of a third controller 162 which receives the data output 152 generated by the fifth sensor 150. The third controller 162 generates control signals based upon the data provided on data output 152 and then provides these control signals to the dewaterer 122 via control bus 164. For example, the fifth sensor 150 could monitor the consistency or water content of the sixth fraction created by the dewaterer 122 on line 124. Based upon the value of the consistency or water content measured by the fifth sensor 150 and provided as data output 152, the third controller 162 could calculate a set of control parameters for use in varying the operational parameters of the dewaterer 122 and provide these control signals via the control bus 164 to the dewaterer 122. Alternatively, the fifth sensor 150 could sense any other characteristic of the fifth fraction on line 124, such as contaminant content, fiber content or output volume over a given period of time, and generate control signals based thereon. Fig. 9 shows a block diagram similar to that described above with respect to Fig. 5. In particular, the first, second, third, and fourth sensors 134, 138, 142 and 144, generate the data outputs 136, 140, 144 and 148 as was described with respect to Fig. 5. Additionally, the embodiment shown in Fig. 9 includes the first and second controllers 154 and 158 which were previously described with respect to Fig. 7. However, outputs

136, 140, 144 and 148 as shown in Fig. 9 are routed as input to a general purpose computer 166. The general purpose computer utilizes the data outputs 136, 140, 144 and 148 to determine the operational status of the system. The computer 166 then determines if changes to the control of either the first separator 100 or the second separator 108, or both, are necessary and generates control data on lines 168 and 170. This control data is provided to the first and second controllers 154 and 158 which generate appropriate control signals. Thus, the controller 158 would receive control data from line 168 and generate control signals that are output on control bus 160. The control signals on control bus 160 are then provided to the separator 100 to vary the control parameters of the separator 100. Similarly, the controller 154 associated with the second separator 108 receives control data on line 170 from the computer 166. The controller 154 then generates control signals which are output on the control bus 156 to the second separator 108 to vary the control parameters of the second separator 108.

Fig. 10 shows a system including a dewaterer 122, as was previously described with respect to Fig. 6, including the computer control previously described with Fig. 9. In Fig. 10, in addition to the data outputs 136, 140, 144 and 148, the general purpose computer 166 is also provided with the data output 152 from the fifth sensor 150. Also, the computer 166 generates control data on line 172 for provision to the controller 162 associated with the dewaterer 122. The controller 162, in response to the data provided on line 172, generates control signals which are provided via a control bus 164 to the dewaterer 122 which controls the operational parameters of the dewaterer 122. For example, the data output 152 generated by sensor 150 may indicate that the consistency of the fifth fraction on line 124 is too low. Thus, the computer 166 could determine that greater pressure needs to be exerted by the dewaterer 122 on the input suspension from line 114 and would generate control data on line 172 for the controller 162. Thus, the controller 162 could generate control signals on bus 164 which adjust the pressure exerted by the dewaterer 122 on the input suspension from line 114.

Obviously, any of the previously described embodiments could be modified by adding, removing, or changing the location of the sensors. Furthermore, multi-functional sensors could be utilized which could sense more than one characteristics of the fiber suspension and, thereby, generate more output information.

Figs. 11 and 12 show separation devices which could be used as the first separator 100 or the second separator 108. A description of these devices is provided to describe some of the types of operational parameters which may be adjusted on the separation devices 100 and 108 based upon the data output generated by the sensors. Furthermore, in addition to the illustrative embodiments shown in Figs. 11 and 12, a variety of drum and belt-type washers are described in co-pending application serial No. , filed on , and entitled "Improved Recovery of Fine Fibers from Suspensions Containing Fibers and Contaminants," the entire disclosure of which is incorporated herein by reference thereto. Also, in addition to the illustrative embodiments of Figs. 11 and 12, any type of separation device, dewaterer, filter, press or spray- screen, a multitude of which are well known in the fiber recovery and paper processing arts, may be used for the first and second separators 100 or 108 or the dewaterer 122.

Fig. 11 shows a Fluidized Drum Washer™ (a trademark of Alfa Laval Celleco Inc.) 101 which may be utilized as the first separator 100 and is shown with the connections corresponding to the block diagram of Fig. l. Alternatively, the Fluidized Drum Washer™ (a trademark of Alfa Laval Celleco Inc.) shown in Fig. 11 can be used as the second separator 108, as well. A feed suspension 174 is supplied through line 102 to nozzle 176 and inlet conduit 178. The feed suspension 174 forms a pool of suspension in a vat 180. Also disposed within the vat 180, is a hollow drum 182, the outer surface 184 of which is comprised of an appropriate filter material such as a wire mesh. The drum 182 is caused to rotate in direction 186 by operation of a toothed gear 190 attached to a motor 188 which engages a toothed wheel 192 attached to the drum 182. By the action of gravity and hydrostatic pressure, the feed suspension is drawn to the outer surface 184 of the drum 182 and contaminants and liquid carrier pass into the interior of the drum 182 and form a first fraction 194 therein. Fibers which are too large to pass through the filter material of the outer surface 184 of the drum 182, form a mat of second fraction 196 on the surface of the drum 182. The first fraction 194 exits the interior of the drum 182 through a take up or drain 198 and is provided as output on line 104. The rotation of the drum 182 in direction of arrow 186 forces the second fraction 196 up and out of the vat into a discharge chute 200 which provides the second fraction 196 as output on line 106.

As was previously described, the first fraction 194 is comprised of contaminants, liquid carrier and fine fibers which were able to pass through the mesh of filter material on the outer surface 184 of the drum 182. The second fraction 196 is comprised of coarse fibers, fine fibers and liquid carrier. Additionally, a return header 103 may provide an input to the Fluidized Drum Washer™ (a trademark of Alfa Laval Celleco Inc.)

101 for a fraction provided on line 105. For example, fibers recovered in a separator downstream of the washer 101 may be returned on line 105 and input into washer 101 through header 103. This type of system was described diagrammatically in Fig. 2 and is also shown in Fig. 13.

As can be seen from the configuration of the Fluidized Drum Washer™ (a trademark of Alfa Laval Celleco Inc.) 101 of Fig. 11, a variety of processing parameters may be varied. For example, the volume of feed suspension 174 flowing into the Fluidized Drum Washer™ (a trademark of Alfa Laval Celleco Inc.) 101 from line

102 may be controlled at the nozzle 176 or the inlet conduit 178. By varying the volume of feed suspension 174 flowing through nozzle 176, or the pressure of the feed suspension 174 sprayed by nozzle 176, the likelihood of fine fibers passing into the interior of drum 182 may be varied. For example, with a higher volume of feed suspension 174 flowing through nozzle 176, or if the material ejected from nozzle 176 is ejected with a higher force, more fine fibers are likely to pass through the mess on the outer surface 184 of the drum 182 and into the first fraction 194. Similarly, if the level of feed suspension 174 in vat 180 is increased, as by an increase flow through conduit 178, the hydrostatic pressure acting on the material in the vat 180 will be greater, which will increase the likelihood of fine fibers passing into the first fraction 194. Also, the rotational speed in the direction of arrow 186 may be varied by changing the speed of the motor 188 or using a different gearing ratio between gears 190 and 192. Thus, by variation of the controllable parameters of the Fluidized Drum Washer™ (a trademark of Alfa Laval Celleco Inc.) of Fig. 11, the operation of the Fluidized Drum Washer™ (a trademark of Alfa Laval Celleco Inc.) may be controlled to either increase the yield of second fraction 196 and minimize the number of fine fibers present in the first fraction 194 or, conversely, the washer may be operated to lessen the amount of contaminants present in the second fraction 196, which will result in an increased amount of fine fibers present in the first fraction 194.

The sensor(s) described with respect to the previous Figures could monitor the amount of contaminants in the second fraction 196 which is provided as output on line 106, and, if the amount of contaminants per unit volume of the second fraction 196 exceeded a predetermined level, the operational parameters of the washer 173 could be changed to reduce the amount of contaminants present in the second fraction 196. Similarly, a sensor could be placed to monitor the first fraction 194 on line 104 to determine the number of fine fibers present therein. If the number of fine fibers present in the first fraction 194 exceeded a predetermined level, the operational parameters of the washer 173 could be varied so that more of the fine fibers were retained in the second fraction 196. Another operational parameter of the

Fluidized Drum Washer™ (a trademark of Alfa Laval Celleco Inc.) 173 which may be varied is the pore size of the filter material disposed on the outer surface 184 of the drum 182. For example, if the amount of contaminants present in the second fraction 196 was unacceptably high, a filter material of larger pore size could be placed on the drum 182. Conversely, if it was determined if the amount of fine fibers passing into the first fraction 194 was unacceptably high, a finer mesh could be placed on the drum 182. Fig. 12 shows a preferred second separator 108 in a form of a disc washer 201. In a preferred embodiment, the second separator 108 may comprise a filter which is sold by Alfa Laval Celleco Inc., of Lawrenceville, Georgia, U.S.A., under the trademark SPRAYDISC™. Fig. 12 shows the components of this type of filter device in cross-section. Support members 202 support a rotatable axle 204. Attached to the axle 204 are filter discs 206. These discs are made of a metal support frame 206 which supports filter material 208. A motor 205, with any appropriate gearing, drives the axle 204 which rotates as indicated by the arrow. Nozzle support members are stationary so that the filtered discs 206 move relative to the nozzle support 209.

Nozzle supports 209 support a number of spray nozzles 210 which are directed towards the filter material 208 of the filter discs 206. When provided as the second separator 108 of the present invention, the first fraction is input on line 104 to the nozzles 210. The first fraction is sprayed on to the filtered discs 206 through the nozzles 210. Fibers and fine fibers present in the first fraction are retained on the filter material 208 and either falls or are washed, into collection sumps 212 to form the third fraction. The fine contaminants and a portion of liquid carrier pass through the filter material 208 and collect in the interior of the filter discs 206 to form a fourth fraction. The third fraction is drawn from the sumps 212 and is output on line 110. The fourth fraction is drawn from the interior of the discs 206 and provided as output on line 112.

As will be understood by reference to Fig. 12, several operational parameters may be varied during operation of the disc washer 201. For example, the rotational velocity of the discs 206 may be varied by varying the output speed of motor 205. In this manner, the discs 206 rotate more quickly relative to the spray nozzles 210, which will result in a given area of filter material 208 being exposed to the spray from the nozzles 210 for a less time. Thus, it is less likely that contaminants would be captured by a mat of fibers formed on the filter material 208, since a less thick mat would form. Also, the outlet pressure of the nozzles 210 may be varied. For example, a higher outlet pressure, resulting in the passage of a greater volume of first fraction through the nozzles 210 in a given period of time, will result in the formation of a thicker mat on the filter material 208. Thus, a higher production rate could be achieved, but the increased pressure could force a greater amount of fine fibers to pass through the filter material 208 and into the fourth fraction, lowering the yield while enhancing the filtration efficiency. Thus, by either monitoring the characteristics of the third fraction output on line 110 or the fourth fraction output on line 112, or both, one may determine that the operational parameters such as the rotational speed of the disc 206 or the outlet pressure of the nozzles 210 should be varied to achieve a desired result. In addition to the embodiment of specific separation devices shown in Figs. 11 and 12, a variety of separation, filtration or dewatering devices may be used in place of the first separator 100, the second separator 108 or the dewaterer 122 of the above- described embodiments. For example, dewaterers are typically of the press design in which a pressure is exerted on a fiber suspension supported by some type of mesh screen. Typically, the pressure exerted on the fiber suspension may be varied as may be the mesh size of the screen. In a situation where a fiber suspension of high consistency is desired, a greater pressure may be exerted on the suspension or a larger mesh size may be used for the support. However, in achieving a high level of consistency, a larger percentage of fine fibers present in the suspension will be forced out of the suspension due to the increased pressure or larger pore size. Thus, one could monitor the consistency of the dewatered fraction exiting a dewaterer or could measure the fiber content of the liquid fraction exiting the dewaterer to determine if the pressure exerted on the input fiber suspension should be varied or the mesh size should be changed in order to achieve a desired output fraction.

Screen type washers typically consist of a mesh upon which a fiber suspension is either sprayed or poured. Additionally, spray nozzles spraying clean water are typically used to wash contaminants present in the fiber suspension through the mesh. With screen type washers, one may vary the mesh size of the screen, the number of washing nozzles, or the pressure with which the washing fluid is expelled from the nozzles. For example, to obtain a high purification level, a large mesh size may be used, more washing nozzles may be employed or the washing nozzles may spray the washing fluid at a higher pressure. However, under such circumstances, a greater amount of fine fiber will typically pass through the screen washer and into the waste stream. Thus, to achieve a desired balance between purification efficiency and yield, the operational parameters such as the mesh size, the number of washing nozzles, or the pressure of washing fluid may be varied. Other types of filtration and separation devices are known in the art and may be utilized as well. All of these devices have some variable parameters with which one may determine the purification efficiency and yield of the device. It is these operational parameters that may be controlled in accordance with the previously described embodiments of the present invention. Fig. 13 is a block diagram which shows the flow control components and separation devices of a preferred embodiment of the present invention. In the embodiment of Fig. 13, the first separator 100 is a Fluidized Drum Washer™ (a trademark of Alfa Laval Celleco Inc.) as was described with respect to Fig. 12. The second separator 108 is a disc washer 201 which was described with respect to Fig. 13. The dewaterer 122 is preferably a screw type dewaterer as known in the art. In the embodiment of Fig. 13, a feed suspension comprised of fibers, contaminants and liquid carrier is provided as input on line 102 to a holding tank 214. At the lower portion of the tank 214, a pump 216 pumps the feed suspension to the first separator 100 on line 218. Preferably, the feed suspension enters the first separator 100 through a conduit 220. Also, the feed suspension is sprayed onto a filter body through nozzles supplied by conduits 222. Also, rinsing showers are provided within the first separator 100 by the input of clean water from line 224 into conduit 226. As was described previously, the first separator 100 separates the feed suspension into first and second fractions. The first fraction, consisting of fine fibers, contaminants and liquid carrier exits the first separator 100 on line 104 and is provided to a holding tank 228. The second fraction exits the first separator through chute 208 and is provided as output on line 106.

The first fraction is then pumped from tank 228 by pump 230 up line 232 to the inlet of the second separator 108. As was described previously, the second separator 108 separates the first fraction into a third fraction consisting of fibers and liquid carrier and a fourth fraction consisting of contaminants and liquid carrier. The third fraction exits the second separator 108 on line 110 and is provided to a holding tank 234. The fourth fraction exits the second separator 108 on line 112 and constitutes a waste stream for appropriate disposal.

As was previously described, the second fraction on line 106 may be further processed for use or may be provided to a dewaterer 122, such as a screw press, for additional thickening. If a dewaterer 122 is utilized, the dewaterer separates the second fraction into fifth and sixth fractions as was previously described. Preferably, the fifth fraction, constituting a thickened suspension of fibers, exits the dewaterer 122 on line 124. The liquid stream from the dewaterer 122, typically consisting of fine fibers and liquid carrier, exits the dewaterer 122 on line 126. In a preferred embodiment, line 126 is returned to tank 228 where the sixth fraction is added to the first fraction prior to provision to the second separator 108.

From tank 234, the third fraction is pumped by pump 236 on line 238. Line 238 preferably returns the third fraction on line 105 to header 103 and first separator 100, but line 238 may also return the third fraction to holding tank 214 for mixing of the third fraction with the feed stock, or, alternatively, line 238 may return the third fraction to line 106 to be mixed with the second fraction provided as output on line 114. In the embodiment shown in Fig. 13, which corresponds to the embodiment in Fig. 1, a sensor 116 is placed in the path of line 114 to generate data corresponding to a characteristic of the fiber suspension provided on line 114 as a data output 118. However, as was described in the various block diagrams of Figs. 1-10, multiple sensors could be placed throughout the system shown in

Fig. 13 to provide feedback control which has been described with respect to each of those figures. The embodiment shown in Fig. 13 serves merely for the purpose of illustrating the one implementation of the present invention in a functional fiber recovery system.

While the previous embodiments have described the present invention in terms of its application to fiber recovery/separation systems utilizing two or three separation devices, the present invention may be employed in other configurations utilizing any number of separation devices.

Furthermore, a number of permutations of the treatment of the various fractions exiting the separation devices is possible beyond the limited number demonstrated herein. The teachings of the present invention may be implemented in such permutations by one skilled in the art without departing from the scope of the claims. Finally, the foregoing detailed description of the preferred embodiments is for the purposes of illustration and not limitation. One skilled in the art may make numerous substitutions, modifications, additions or deletions without departing from the scope of the present invention as set forth in the following claims.

Claims

Claims :

1. In a fiber processing system for separating a feed suspension comprising fibers and liquid carrier into multiple fractions, a method for controlling processing of the feed suspension comprising the following steps: separating the feed suspension into a plurality of fractions; sensing a characteristic of one of the plurality of fractions; and controlling said separation of the feed suspension in response to the sensed characteristic.

2. The method of claim l wherein the feed suspension comprises fibers, contaminants and wherein: said step of separating the feed suspension further comprises, separating the feed suspension into first and second fractions, the first fraction comprising contaminants and the second fraction comprising fibers; said step of sensing a characteristic further comprises, sensing a first characteristic of said second fraction.

3. The method of claim 1 wherein the feed suspension comprises coarse fibers, fine fibers, contaminants and a liquid carrier and wherein said separating of the feed suspension into a plurality of fractions further comprises: separating the feed suspension into first and second fractions, the first fraction comprising contaminants and a first portion of the fine fibers and the second fraction comprising coarse fibers and a second portion of the fine fibers; and separating the first fraction into third and fourth fractions, said third fraction comprising fibers and said fourth 5 fraction comprising contaminants.

4. The method of claim 3 further comprising the following steps: adding said third fraction to said second fraction to create a fifth fraction; and '.0 wherein said step of sensing a characteristic further comprises, sensing a first characteristic of the fifth fraction.

5. The method of claim 3 further comprising the following steps: adding said third fraction to said feed suspension to create 5 a modified feed suspension; separating said modified feed suspension into the first and second fractions; and wherein said step of sensing a characteristic further comprises, sensing a first characteristic of said modified feed 0 suspension.

6. A method for the recovery of fibers from a feed suspension comprising coarse fibers, fine fibers and contaminants comprising the steps of: separating the feed suspension into first and second 5 fractions, the first fraction comprising contaminants and a portion of the fine fibers and the second fraction comprising coarse fibers and a portion of the fine fibers; separating the first fraction into third and fourth fractions, the third fraction comprising fine fibers and the fourth fraction comprising contaminants; separating the second fraction to form fifth and sixth fractions, the fifth fraction comprising coarse fibers and a portion of the fine fibers and the sixth fraction comprising fine fibers; sensing a characteristic of at least one of the first, second, third, fourth, fifth and sixth fractions; and controlling the separation of at least one of the feed suspension, first fraction and second fraction using the sensed characteristic.

7. A system for the recovery of fibers from a feed suspension comprising coarse fibers, fine fibers contaminants and liquid carrier comprising; a first separator having as input the feed suspension, wherein said first separator separates the feed suspension into a first fraction and a second fraction; a second separator having as input said first fraction, wherein said second separator separates said first fraction into third and fourth fractions; sensor means for sensing a characteristic of said one of first, second, third and fourth fractions; and control means for controlling one of said first and second separators based upon said sensed characteristic.

8. The system of claim 7 further comprising: combiner means for combining said second and third fractions to form a fifth fraction; and wherein said sensor means senses a characteristic of said fifth fraction and wherein said control means controls said second separator.

9. The system of Claim 7 further comprising: combiner means for combining said third fraction with said feed suspension to provide a modified feed suspension; and wherein said sensor means senses a characteristic of said modified feed suspension, said modified feed suspension is provided as input to said first separator, and said control means controls said first separator.

10. The system of Claim 7 further comprising a third separator having said second fraction as input and generating fifth and sixth fractions.

11. The system of claim 7 wherein said first separator is a fiber washer;

12. The system of claim 7 wherein said first separator is a press.

13. The system of claim 7 wherein said first separator is a filter.

14. The system of claim 7 wherein said first separator is a thickener.

15. The system of claim 7 wherein said second separator is a fiber washer.

16. The system of claim 7 wherein said second separator is a press.

17. The system of claim 7 wherein said second separator is a filter.

18. The system of claim 7 wherein said second separator is a thickener.

19. A system for the recovery of fibers from a feed suspension comprising coarse fibers, fine fibers, contaminants and liquid carrier comprising: a first separator having the feed suspension as input and generating first and second fractions as output, wherein said first fraction comprises contaminants and a portion of the fine fibers and said second fraction comprises coarse fibers and a portion of the fine fibers; a second separator having the first fraction as input and generating third and fourth fractions as output, wherein said third fraction comprises fine fibers and said fourth fraction comprises contaminants; first sensor means for sensing a characteristic of said second fraction and generating an output corresponding to the sensed characteristic; and first control means for controlling one of said first and second separators in response to the output of said first sensor means.

20. The system of claim 19 wherein said first control means controls said first separator.

21. The system of claim 19 wherein said first control means controls said second separator.

22. The system of 19 further comprising: second sensor means for sensing a characteristic of said third fraction and generating an output corresponding to said sensed characteristic; and second control means for controlling one of said first and second separators in response to the output of said second sensor means.

23. The system of claim 22 wherein said second control means controls said first separator.

24. The system of claim 19 wherein said second control means controls said second separator.