EP0955405A1 - Laveur de pâte à papier pressurisé et complètement submergé, et son procédé d'utilisation - Google Patents

Laveur de pâte à papier pressurisé et complètement submergé, et son procédé d'utilisation Download PDF

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Publication number
EP0955405A1
EP0955405A1 EP99630042A EP99630042A EP0955405A1 EP 0955405 A1 EP0955405 A1 EP 0955405A1 EP 99630042 A EP99630042 A EP 99630042A EP 99630042 A EP99630042 A EP 99630042A EP 0955405 A1 EP0955405 A1 EP 0955405A1
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EP
European Patent Office
Prior art keywords
wash liquid
reservoir
drum
primary
pulp
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP99630042A
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German (de)
English (en)
Inventor
Ian James Henry Clarke-Pounder
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Beloit Technologies Inc
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Beloit Technologies Inc
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Filing date
Publication date
Application filed by Beloit Technologies Inc filed Critical Beloit Technologies Inc
Publication of EP0955405A1 publication Critical patent/EP0955405A1/fr
Withdrawn legal-status Critical Current

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    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
    • D21C9/02—Washing ; Displacing cooking or pulp-treating liquors contained in the pulp by fluids, e.g. wash water or other pulp-treating agents
    • D21C9/06—Washing ; Displacing cooking or pulp-treating liquors contained in the pulp by fluids, e.g. wash water or other pulp-treating agents in filters ; Washing of concentrated pulp, e.g. pulp mats, on filtering surfaces

Definitions

  • the present invention relates generally to pulp washing technology. More specifically, the present invention is a new and improved liquid filled pressurized pulp washer and methods of operation thereof.
  • a pulp mat is formed from a pulp slurry by passing the slurry between a rotating permeable drum and a containing baffle.
  • the pressure on the outside of the drum is higher than the pressure on the inside of the drum and filtrate flows from the slurry into the drum to form the mat on the outside of the drum.
  • the mat is a liquid filled fibrous lattice structure that is permeable.
  • Maintaining the permeability of the mat structure is essential because the mat must be washed after formation so as to remove as much black liquor from the pulp as possible during the washing process. If the washer is operated at too high of a pressure differential across the mat, the mat can structurally collapse, compress, and become substantially impermeable. Collapsing and compressing of the mat substantially precludes the flow of wash liquid through the collapsed interstices of the fibrous mat and through the densified impermeable flat skin of collapsed fiber that is created on the surface of the drum when a mat collapses. As a result, the vat fills with incoming thickened slurry and the washing operation becomes inoperable.
  • Mat collapse is all too frequent an occurrence due to fluctuating resistance and the small pressure drop across the mat and due to the small difference between a satisfactory mat operating pressure differential and the critical pressure differential.
  • typical mat operating pressure differentials will be in the range from 1 to 5 inches of water (2.5 to 12.5 cm) while the operating pressure of the vat will be in the range of 3 psi or higher (210 cm water or higher).
  • the problem is compounded by liquid incompressibility and the way in which the washing liquid and pulp slurry are injected into the vat.
  • centrifugal pumps are used to inject both the washing liquid and pulp slurry.
  • These pumps are known to generate pressure pulsations and attendant surges which can have a significant influence on the pressure drop across the mat due to the incompressibility of liquid. Accordingly, a surge from either the pump that supplies the wash liquid or pulp slurry to the vat can cause the pressure drop across the mat to reach or exceed the critical ⁇ p resulting in mat collapse and subsequent washer plugging.
  • mat collapse occurs due to the inability of pressure and flow controls and sensors to adequately react to minuscule changes in the mat drainage resistance.
  • currently available equipment is unable to consistently maintain the pressure drop across the mat in a liquid filled pressurized washer below the critical ⁇ p at all times.
  • the present invention satisfies the aforenoted need by providing a method of forming and washing a pulp mat that comprises the steps of introducing a pulp slurry into a pulp washer at a first inlet, the pulp washer including a rotating permeable drum and forming a pulp mat on the drum.
  • Wash liquid is supplied and flows freely from a wash liquid reservoir which is partially filled with wash liquid.
  • the gas/wash liquid interface level in the primary wash liquid reservoir is hydraulically disposed above the drum or the top of the vat so that the drum is submerged and the vat remains filled with washing liquid during operation.
  • Gas from a filtrate reservoir may be used to pressurize the primary wash liquid reservoir and to create an additional positive differential pressure between the primary wash liquid reservoir and the pulp washer.
  • the method includes the step of introducing wash liquid under pressure from the primary wash liquid reservoir into the pulp washer at a second inlet disposed downstream of the first inlet.
  • the second inlet provides communication between the pulp washer vat and the primary wash liquid reservoir.
  • the method further includes the step of measuring the level of wash liquid in primary wash liquid reservoir and adjusting the rotational speed of the drum in response to the level of wash liquid. Specifically, at a constant preset wash liquid flow and tonnage, if the wash liquid level drops below a predetermined optimal level for the current speed of the drum, the speed of the drum is reduced to optimize mat drainage and increase washing efficiency. On the other hand, if the level of wash liquid rises above a predetermined optimal level for the speed of the drum, the current speed of the drum is increased to avoid mat collapse and optimize washing efficiency.
  • the primary wash liquid reservoir is integrally connected to the pulp washer.
  • the mat is removed from the pulp washer without exposing the mat to gas during the formation and washing processes.
  • the method further comprises the step of pumping wash liquid into the primary wash liquid reservoir from a make up wash liquid reservoir to replenish the wash liquid supply in the primary wash liquid reservoir.
  • the filtrate is drained from the drum into a filtrate reservoir.
  • the filtrate reservoir further includes a space for accommodating gas.
  • the space in the filtrate reservoir that accommodates the gas is in communication with the primary wash liquid reservoir and the method further includes the step of pumping gas from the filtrate reservoir to the primary wash liquid reservoir.
  • the step of pumping filtrate gas into the primary wash liquid reservoir further comprises the substeps of controlling the filtrate gas pressure in the primary wash liquid reservoir by monitoring the filtrate gas pressure in the primary wash liquid reservoir, comparing the measured filtrate gas pressure in the primary wash liquid reservoir with a predetermined value, and, in the event the measured pressure is greater than the predetermined value, recirculating filtrate gas back to the filtrate reservoir or, in the event the measured pressure is less than the predetermined value, pumping additional filtrate gas into the primary wash liquid reservoir.
  • the step of pumping filtrate gas from the filtrate reservoir to the primary wash liquid reservoir further comprises the sub-steps of controlling the filtrate gas pressure in the primary wash liquid reservoir by measuring the filtrate gas pressure in the primary wash liquid reservoir, comparing the measured filtrate gas pressure value in the primary wash liquid reservoir with a predetermined value, and, in the event the measured pressure is greater than the predetermined value, recirculating the filtrate gas to a gas handling system or, in the event the measured pressure is less than the predetermined value, pumping additional gas into the primary wash liquid reservoir.
  • the present invention provides an improved pulp washer that includes a primary wash liquid reservoir partially filled with wash liquid.
  • the surface of the wash liquid is disposed above the drum and the vat to provide a hydrostatic head between the primary wash liquid reservoir and the vat and to insure that the vat remains filled and the mat submerged during operation.
  • the pulp washer of the present invention includes a wash liquid level control for measuring the surface level of the wash liquid in the primary wash liquid reservoir and comparing that surface level to a predetermined surface level for the current operating conditions of the washer and rotational velocity of the rotating drum. If the surface level of the wash liquid is higher than a predetermined optimum level, the controller increases the speed of rotation of the drum to reduce mat basis weight, increase wash liquid use, decrease mat pressure resistance, avoid mat collapse and optimize washing efficiency. If the surface falls below a predetermined optimum level, the controller decreases the rotational velocity of the drum to optimize mat drainage and increase washing efficiency.
  • pressurized gas is used to pressurize the primary wash liquid reservoir and provide an additional positive differential pressure between the primary wash liquid reservoir and the vat.
  • a pump is also provided for pumping filtrate gas from the filtrate reservoir to the primary wash liquid reservoir.
  • the primary wash liquid reservoir further comprises a wash liquid level control system that includes at least one sensor for sensing the level of wash liquid in the primary wash liquid reservoir.
  • the sensor is in communication with a controller that controls the rotational velocity of the drum.
  • the wash liquid control system also includes a pressure sensor for sensing the filtrate gas pressure in the primary wash liquid reservoir.
  • the primary wash liquid reservoir further includes an outlet for releasing excess filtrate gas from the primary wash liquid reservoir.
  • the outlet includes an adjustable valve which is connected to an actuator that is in communication with a controller. In the event the filtrate gas pressure in the primary wash liquid reservoir becomes too high, the controller sends a signal to the actuator to open the valve at the outlet thereby enabling pressurized filtrate gas to be transmitted from the primary wash liquid reservoir back to the filtrate reservoir or other suitable gas handling system.
  • an improved pulp washer which includes multiple counter current washing zones.
  • the filtrate reservoir is divided into two parts -- a primary filtrate side and a secondary filtrate side.
  • the primary filtrate side receives pressate (or fluid that is initially pressed out of the pulp slurry) from the forming zone of the drum and twice-used wash liquid from a preliminary washing zone of the drum.
  • the secondary filtrate side receives once-used wash liquid from a primary washing zone of the drum.
  • the wash liquids reservoir is also divided into two parts -- a preliminary wash liquid side and a fresh wash liquid side.
  • the preliminary wash liquid side receives once-used wash liquid from the secondary filtrate side of the filtrate reservoir.
  • the fresh wash liquid side of the wash liquids reservoir receives fresh wash liquid from a fresh wash liquid make up source.
  • the speed of the drum is controlled in response to changes in the level of once-used wash liquid in the preliminary wash liquid side of the wash liquids reservoir or, altematively, by the level of fresh wash liquid in the fresh wash liquid side of the wash liquids reservoir
  • Another advantage of the present invention is that the speed of rotation of the permeable drum, and therefore the speed and efficiency of the washing process, is controlled by the level of wash liquid in the wash liquid reservoir.
  • Yet another advantage of the present invention is that the wash liquid is introduced into the vat under a hydrostatic head and is not pumped from the wash liquid reservoir to the vat. Accordingly, pulsations or flow disturbances caused by a pump are not transmitted to the vat by the washing liquid.
  • Another advantage of the present invention that the formed and washed pulp mat is not exposed to pressurized gas prior to removal from the pulp washer.
  • Another advantage of the present invention is that the speed of the formation and washing process is controlled by variations in the wash liquid level in the wash liquid reservoir.
  • a washer 10 includes a vat 11 that houses a rotating permeable drum 12.
  • the rotating permeable drum 12 rotates at a speed that may controlled by a controller such as that as shown at 13.
  • the drum 12 also rotates within a number of baffles, two of which are shown at 14 and 15.
  • a pulp slurry from a pulp slurry reservoir is pumped or injected into the inlet 17 through a conduit 18.
  • the slurry reservoir 16 is pressurized and the flow of slurry through the conduit 18 is controlled through an automated control valve 19.
  • a slurry is drawn towards the drum 12 because the pressure at the outside of the drum 12 is greater than the pressure inside the drum 12.
  • the slurry is drawn towards the drum 12 and a mat (not shown) is formed against the drum 12 in a section of the drum 12 shown at 21 is referred to as a forming section 21.
  • liquid which will hereinafter be referred to as pressate is drained off the mat through the perforate surface of drum 12 and is discharged out of the drum 12 through a filtrate outlet 21a.
  • Pressate is the liquid that is squeezed out of the mat in the forming zone 21.
  • the pressate consists mainly of black liquor.
  • the term filtrate is used for wash liquid that is removed from the mat or a combination of wash liquid removed from the mat and pressate downstream of the forming zone 21 in an area such as a washing zone 22.
  • the term filtrate is used for the combination of once and twice used wash liquid that is removed from the mat or once and twice used wash liquid in combination with pressate. Because the pressate and the used wash liquid are stored in a common reservoir after removal from the vat, such reservoirs will be referred to as filtrate reservoirs (see reference numeral 56 in Figure 2; 115 in Figures 3, 4 and 6; and 170 in Figure 7).
  • the drum 12 rotates towards the washing zone 22.
  • the mat is washed with wash liquid injected into the vat 11 through a wash inlet 23 and conduit 24.
  • the baffle 14 compacts the mat during the initial washing process.
  • Flow of wash liquid through the mat is controlled by an automated valve control system 25.
  • the wash liquid is pumped to the inlet 23 from a wash liquid reservoir 26 by a pump 27.
  • Gas pressure venting is provided to the top portion of the wash liquid reservoir 26 through a gas line shown at 31. In the event the gas pressure exceeds an acceptable value, air enters into reservoir 26 through vacuum pressure relief valve shown at 29 or out of reservoir 26 through conduit 34 to a gas/vapor recovery system shown schematically at 31.
  • a control system 32 includes a sensor 33 for monitoring the gas pressure inside the reservoir 26. In the event the gas pressure reaches an unacceptable level, the controller 32 opens a valve 34a to release gas through conduit 34 to the gas/vapor recovery system 31. Wash liquid is supplied to the wash liquid reservoir 26 from a make up wash liquid reservoir shown schematically at 35.
  • a level controller 36 is employed which includes a sensor 37 to indicate when the wash liquid level in the wash liquid reservoir tank 26 has reached an acceptable level. When such an acceptable level is reached, the controller 36 closes a valve 38.
  • the controller 13 shown in Figure 1 may be used to adjust the angular velocity of the drum 12 by measuring vat pressure or the flow of filtrate through the outlet 21a or the flow of wash liquid through the conduit 18.
  • the controller 13 has no way to measure or gauge the changes in permeability of the mat formed on the drum 12.
  • the controller 13 has no direct way to compensate for minuscule changes in the mat drainage characteristics and, as discussed above, minuscule changes in the system can mean the difference between the system operating below the critical ⁇ p or going above the critical ⁇ p and plugging the washer.
  • Figure 2 illustrates the use of a dual "series countercurrent" washer system employing washers 40 and 41.
  • the washer 40 includes a vat 42 into which a slurry is supplied through the inlet 43 by way of a conduit 44 and slurry reservoir or supply shown schematically at 45. The flow of slurry through the conduit 44 is controlled by an automatic valve system shown at 46.
  • the washer 40 operates in a manner similar to the washer 10 shown in Figure 1.
  • the wash liquid used in the washer 40 is provided from a primary filtrate reservoir 47 which collects pressate and the once used wash liquid through an outlet 48 of a vat 49 of the washer 41.
  • the primary filtrate is pumped to the vat 42 by way of a pump 51. While the flow of primary filtrate through a conduit 52 and into a wash liquid inlet 53 is controlled by an automatic valve 54, pulsations and/or surges caused by the centrifugal pump 51 will be directly communicated to the vat 42 by way of the liquid flowing through the conduit 52.
  • a pump 57 is used to recycle malodorous gas from reservoir 56 to the top of the reservoir 47.
  • Vacuum relief valves are shown at 58, 59.
  • the level control system 61 is used to control the level of liquid in the reservoir 56.
  • a controller 62 may be used to control the angular velocity of the drum (not shown) of the washer 40. After the pulp mat is dislodged from the drum, it exits the washer 40 through the pulp outlet 63. The pressure in and the rate of flow out of outlet 63 is controlled by the pressure control system 65.
  • Pulp is then discharged into a reservoir 66 where it is diluted with liquid pumped from the primary filtrate reservoir 47 by the pump 67.
  • the level of slurry in the reservoir 66 is controlled by the level control system 69, and the slurry pump out consistency is controlled by consistency control system 68.
  • the slurry is then pumped from the reservoir 66 to a slurry inlet 72 of the washer 41 by the pump 71.
  • the flow of slurry through a conduit 73 may be measured by the flow meter system 74.
  • Fresh wash liquid is provided to the washer 41 through an inlet 75 and from a fresh wash liquid reservoir 76.
  • the fresh wash liquid is pumped from the reservoir 76 by a pump 77.
  • the flow through a conduit 78 is controlled by an automatic valve 79.
  • Control systems 81, 82 operate in a manner similar to that discussed above with respect to control systems 32, 36 of Figure 1 respectively.
  • the pump 77 is in direct communication with the vat 49 and therefore any pulsations and/or surges created by the pump 77 will be directly communicated to the vat 49 by way of the wash liquid proceeding through the conduit 78.
  • pulsations generated by the pump 77, or the pump 51 for that matter can greatly contribute to the causation of mat collapse and the plugging of the washers 41, 40 respectively.
  • pump 71 which, as discussed above, pumps slurry from the reservoir 66 to the inlet 72 of the washer 41. Like the pump 77, the pump 71 can cause pulsations and/or surges thereby contributing to mat collapse and the plugging of the washer 41.
  • a washer 101 includes a vat 102 which includes a slurry inlet 103 that is in communication with a slurry supply means shown only schematically at 104.
  • the flow of slurry through the conduit 105 is controlled by a flow control system 106.
  • the mat After formation of a mat on a drum 107, and compaction of the mat on the drum 107 by a baffle 108, the mat is continuously flushed with wash liquid contained in a primary wash liquid reservoir 112.
  • the primary wash liquid reservoir 112 is connected directly to the vat 102.
  • the primary wash liquid reservoir 112 is only partially full and includes a space 113 for accommodating gas pumped into the wash liquid reservoir 112 by a pump 114 from a filtrate reservoir 115.
  • the filtrate reservoir 115 contains pressate and used wash liquid transmitted from the drum 107 by way of the outlet conduit 106a.
  • the gas pressure provided in the space 113 pressurizes the primary wash liquid reservoir 112 and, in addition to the hydrostatic head, it eliminates the need for any pump disposed between the feed wash liquid reservoir 112 and the washer vat 102.
  • Fresh wash liquid is supplied to the primary wash liquid reservoir 112 by a make-up secondary wash liquid reservoir 116.
  • a pump 117 is provided to pump wash liquid through the inlet 118.
  • the hydrostatic head between the wash liquid in the feed reservoir 112 and the washer vat 102 is indicated at "Y".
  • Control of make up wash liquid from the pump 117 through the conduit 119 is provided by a flow control system 121.
  • the make-up reservoir 116 is equipped with a pressure control system 122 for releasing gas pressure which, in tum is supplied through a gas conduit 123 from an outlet 123a of the primary wash liquid reservoir 112.
  • a pressure control system 125 releases gas pressure from the feed reservoir 112 through the conduit 123 as needed.
  • Fresh wash liquid is supplied to the make up reservoir 116 by a wash liquid supply shown only schematically at 126.
  • the flow of fresh make-up wash liquid to the make up reservoir 116 is controlled by a level control system 127.
  • the mixture of pressate and used wash liquid is discharged from the filtrate reservoir 115 on an as needed basis by way of the pump 128 and level control system 129.
  • the washing control system shown schematically at 124 maintains the level of wash liquid 111 in the reservoir 112 as follows. First, sensors 132, 133 monitor the level 131 of liquid 111 in the reservoir 112. An increase in the liquid height "Y" would result from a decrease in permeability of the mat formed on the drum 107. In order to avoid mat collapse, the drum speed must be increased. Accordingly, if the liquid height "Y" increases to a height above a predetermined preferred height for a particular angular velocity of the drum 107, the controller 124 will increase the angular velocity of the drum 107 in order to optimize washing efficiency, avoid mat skinning and avoid mat collapse and washer plugging.
  • the angular velocity of the drum 107 is controlled by the level controller 124 in response to permeability changes of the mat formed on the drum 107. These changes in permeability result in and are measured directly by the changes in liquid level height Y in the wash liquid reservoir 112.
  • the control system or controller shown at 124, 125 controls the angular velocity of the drum 107 as well as the pressure in the space 113.
  • the gas pressure in the space 113 of the reservoir 112 is also monitored by a sensor 133.
  • the pressure control system 125 which releases gas through the conduit 123 to the make up wash liquid reservoir 116.
  • a hydrostatic head represented by "X" is needed between the drum 107 and liquid 134 contained in the filtrate reservoir 115. This head "X" is maintained by the level control system 129.
  • a level controller 124 is used to maintain the hydrostatic head "Y" between free surface 131 of the wash liquid 111 in the primary feed wash liquid reservoir 112 and the top of the vat 102 in order to eliminate the need for a pump in a conduit 134 between the primary wash liquid reservoir 112 and the vat 102.
  • the level controller 124 monitors the height "Y" of the wash liquid 111 and, in the case of an increase in the height Y of the liquid due to a decrease in permeability of the mat formed on the drum 107, the controller 124 increases the angular velocity of the drum 107.
  • the controller 124 will decrease the angular velocity of the rotating drum 107.
  • the controller 124 controls the angular velocity of the drum 107 based upon changes in permeability of the mat during rotation of the drum 107 through the formation and washing zones.
  • the primary difference between the system 100 shown in Figure 3 and the system 100a shown in Figure 4 is that the gas pressure in the primary feed wash liquid reservoir 1 12 of Figure 4 may have to be greater than the gas pressure in the reservoir 1 12 of Figure 3 in order to compensate for added friction loss in the conduit 134 of Figure 4 and any change in the elevation of the liquid surface 131 of the reservoir 112 of Figure 4 relative to the top of the vat 102 of Figure 4.
  • FIGs 5A and 5B illustrate the pulp outlet shown at 135 in Figure 6 where the wash liquid feed 134 is disposed at the top of the vat 102 and adjacent to the pulp outlet 135.
  • a downstream end 136 of the baffle 109 is slidably attached to a vat section 137 by way of the sandwiching of a lip 138 of the baffle 109 between a seal 139 and a ledge 140.
  • the baffle 109 can slide in the direction of the arrows 141 and 142 as shown in Figure 5B.
  • a doctor blade is shown at 143 which peels the pulp mat 144 off of the drum 107. Continuous rotation of the drum 107 in the direction of the arrow 145 causes the pulp to exit through the outlet 135 as shown in Figure 5A.
  • a third system 100c is illustrated in Figure 6. Again, like reference numerals are used to define like or similar parts.
  • a hydrostatic head "Y" is maintained between the wash liquid 111 and the wash liquid reservoir 112 and the top of the vat 102.
  • the controller 124 controls the speed of the drum 107 in response to the changes in the height or hydrostatic head Y. Again, no pump is disposed between the primary wash liquid reservoir 112 and the vat 102. Instead, the conduit 134 directly connects the reservoir 112 to the vat 102 and includes a check valve 151.
  • a system 160 which includes multiple counter current wash zones is illustrated.
  • a vat 161 houses a permeable drum 162 and baffles 163, 164, 165.
  • a pulp inlet is shown at 166.
  • pressate is extracted from the slurry as the mat is formed on the drum 162 at a forming zone shown generally at 162a.
  • the pressate exits the permeable drum 162 through a conduit 168 and enters a primary filtrate side 169 of a filtrate liquids reservoir 170.
  • fresh wash liquid is passed through the mat and exits the permeable drum 162 through an outlet conduit 172 which is in communication with a secondary filtrate side 173 of the filtrate liquids reservoir 170.
  • the secondary filtrate is recirculated to a preliminary wash liquid side 173' of a washing liquids reservoir 175 by way of a pump 176 and conduit 177.
  • the wash liquid supplied to the vat 161 from the preliminary side 173' of the washing liquids reservoir 175 is recycled filtrate wash liquid and therefore is supplied through the conduit 178 and after passing through the mat combines with the pressate in a preliminary washing zone shown at 179 before it is routed to the primary filtrate side 169 of the reservoir 170.
  • the forming zone 162a is the area that includes the periphery of the drum 162 where the mat is initially formed as well as the area inside the drum where the pressate is collected.
  • washing zones such as 179 and 171, as discussed below, include the outer periphery of the drum 162 where the mat is washed as well as the areas inside the drum where used wash liquid is collected.
  • the washing zone 171 is a final or primary washing zone prior to the discharge of the washed pulp through the outlet 181.
  • the wash liquid provided to the final washing zone 171 is provided from a clean fresh wash liquid side 182 of the reservoir 175 through the conduit 183.
  • Fresh wash liquid make up is provided to the fresh wash liquid side 182 through a conduit 184 which is in communication with a fresh wash liquid make up supply shown schematically at 185.
  • the supply of fresh wash liquid make up to the fresh wash liquid side 182 of washing liquids reservoir 175 is controlled by an automatic valve 186.
  • the washing liquids reservoir 175 is pressurized by gas supplied from the filtrate liquids reservoir 170 through a conduit 187.
  • the pressure in the washing liquids reservoir 175 is controlled by a pressure control system 188.
  • Controller 189 monitors the level of secondary filtrate in the secondary filtrate wash liquid side 173' of the washing liquids reservoir 175. In the event the level in the secondary filtrate side 173' rises due to a decrease in permeability of the formed mat, the controller 189 will increase the angular velocity of the drum 162. In contrast, if the level in the secondary filtrate side 173' drops due to an increase in permeability of the formed mat, the controller 189 will reduce the angular velocity of the drum 162.
  • the controller 189 may also monitor the fresh wash liquid side 182 and adjust the angular velocity of the drum 162 in the same manner depending upon a rise or drop in the level of fresh wash liquid in the fresh side 182 of the washing liquids reservoir 175.

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  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Wood Science & Technology (AREA)
  • Paper (AREA)
EP99630042A 1998-05-05 1999-04-30 Laveur de pâte à papier pressurisé et complètement submergé, et son procédé d'utilisation Withdrawn EP0955405A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US72892 1987-07-14
US7289298A 1998-05-05 1998-05-05

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EP0955405A1 true EP0955405A1 (fr) 1999-11-10

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2805773A (en) * 1954-12-14 1957-09-10 Standard Oil Co Continuous rotary filtration
US4827741A (en) * 1988-03-21 1989-05-09 Ingersoll-Rand Company Pulp washer discharging a pulp slurry at a controlled consistency
WO1990010750A1 (fr) * 1989-03-14 1990-09-20 Green Bay Packaging, Inc. Procede et appareil de lavage de pate de cellulose
WO1993008518A1 (fr) * 1991-10-21 1993-04-29 Ingersoll-Rand Company Procede et appareil de regulation du niveau de liquide dans un egouttoir de separation de n×uds
DE4428515A1 (de) * 1994-08-11 1996-03-14 Siegfried Hirschmann Verfahren zur Steuerung und Regelung des Reinigungsvorgangs des Filtermediums von Tuchfilterapparaten, die der Abtrennung von Feststoffen aus Abwässern dienen, inbesondere in den Ausführungen auswärts durchströmter Drehtrommelfilter

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2805773A (en) * 1954-12-14 1957-09-10 Standard Oil Co Continuous rotary filtration
US4827741A (en) * 1988-03-21 1989-05-09 Ingersoll-Rand Company Pulp washer discharging a pulp slurry at a controlled consistency
WO1990010750A1 (fr) * 1989-03-14 1990-09-20 Green Bay Packaging, Inc. Procede et appareil de lavage de pate de cellulose
WO1993008518A1 (fr) * 1991-10-21 1993-04-29 Ingersoll-Rand Company Procede et appareil de regulation du niveau de liquide dans un egouttoir de separation de n×uds
DE4428515A1 (de) * 1994-08-11 1996-03-14 Siegfried Hirschmann Verfahren zur Steuerung und Regelung des Reinigungsvorgangs des Filtermediums von Tuchfilterapparaten, die der Abtrennung von Feststoffen aus Abwässern dienen, inbesondere in den Ausführungen auswärts durchströmter Drehtrommelfilter

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