Note: Descriptions are shown in the official language in which they were submitted.
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MONITORING AND ADJUSTMENT SYSTEM AND METHOD FOR A
HIGH PRESSURE FEEDER IN A CELLULOSE CHIP FEEDING
SYSTEM FOR A CONTINUOUS DIGESTER
RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional Patent
Application Serial No. 60/984,699 filed November 1, 2007, the entirety
of which is incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] This invention relates to a method and system for feeding
comminuted cellulosic fibrous material ("chips") to a treatment vessel,
such as a continuous digester which produces cellulosic pulp. This
invention particularly relates to monitoring and adjusting a high pressure
feeder.
[0003] High pressure feeders (HPFs) transfer chips from a low
pressure chip supply system to a high pressure system, such as a
continuous digester system for chemical pulping of wood chips or other
cellulosic material. HPFs are well-known and are described in, for
example, U.S. Patent No. 6,669,410. HPFs are a critical component of a
continuous digester system in that they provide a high pressure slurry of
wood chips and liquor to be fed to the digester vessel. Without the high
pressure chip slurry provided by the HPF, the digester system is
disabled. When a HPF is shut-down for repair or maintenance, the
digesting process and the resultant production of pulp ceases until the
HPF is restarted. There is a long felt need to prolong the operational
periods of HPF and minimize the shut-downs of HPFs for maintenance.
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[0004] High pressure feeders are conventionally mechanical rotary
valve devices adjusted with manual controls. A common control
adjustment is to manually adjust the clearance between a rotating
pocket rotor and a cylindrical chamber of the housing for a HPF. The
clearance is a gap between an outer cylindrical surface of the rotor and
an inner cylindrical surface of the chamber. The clearance allows a
small amount of liquid to serve as a lubricant between the pocket rotor
and chamber. If the clearance is too wide, a pressure loss can occur in
the high pressure fluid flow through the HPF, excessive liquid and fines
may flow through the gap and accumulate in the housing, e.g., in end
bells of the housing, and excessive liquid may leak through to a low
pressure outlet of the HPF. If the clearance is too narrow, metal to metal
contact may occur between the rotor and chamber and debris caught in
the gap may etch grooves in the rotor or chamber. Accordingly, the
clearance between the pocket rotor and chamber should be maintained
in an acceptable range.
[0005] The clearance between the pocket rotor and chamber of the
housing is adjusted by moving the rotor axially with respect to the
housing. The pocket rotor and chamber each are slightly tapered.
Because of the taper, the clearance between the rotor and housing can
be adjusted by axial movement of the rotor. Conventionally, axial
movement of the rotor was by means of a manual turning wheel at the
end of a high pressure feeder.
[0006] Maintaining an optimal clearance between the pocket rotor
and chamber is helpful to extend the operational life of the HPF,
particularly the pocket rotor and surface of the chamber; avoid damage
to the rotor and chamber; minimize the power load of the HPF, and
minimize the fluid pressure loss due to fluid leakage through the
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clearance between the pocket rotor and the chamber of the housing.
There is a long felt need for extending the operational period of high
pressure feeders between maintenance or repair shut-downs of the
HPFs. When a HPF is shut-down, the digesting operation may be
temporarily interrupted for a period of, for example, eight (8) hours of no
pulp production. Extending the operational period between maintenance
and repair of HPFs can reduce the interruptions that occur in pulp
production and allow for greater pulp production of the digester system.
SUMMARY OF THE INVENTION
[0007] A method has been developed to control fluid leakage in a
high pressure feeder and a stationary housing with a chamber in which
rotates a pocket rotor, the method comprising: monitoring the fluid
leakage from the high pressure feeder, wherein the fluid leakage is
discharged from a low pressure outlet of the high pressure feeder;
determining whether the fluid leakage is within a predefined range of
acceptable fluid leakage, and moving the pocket rotor in the chamber to
adjust the fluid leakage.
[0008] The fluid leakage may be determined as a difference
between a flow through a high pressure outlet from the high pressure
feeder and a sum of flows into the feeder. The pocket rotor may be
coaxial with the chamber, and moving the pocket rotor includes moving
the pocket rotor axially with respect to the chamber. The method may
further comprise receiving vibration or acoustical signals from a
vibration or acoustical sensor monitoring vibrations in or sounds
emanating from the high pressure feeder, determining whether the
vibration or acoustical signals indicate metal-to-metal contact between
the pocket rotor and chamber, and if inetal-to-metal contact is
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determined, moving the pocket rotor increase a gap between the pocket
rotor and chamber.
[0009] A method has been developed to control a gap between a
pocket rotor and a chamber of a high pressure feeder comprising:
collecting data from at least one sensor monitoring at least one
condition of the high pressure feeder; analyzing the collected data using
a computer controller to generate a desired value of the gap, and
adjusting an axial position of the pocket rotor in the chamber to achieve
the desired value for the gap.
[0010] A method has been developed to control a rotational speed
of a pocket rotor in a chamber of a high pressure feeder comprising:
rotating the pocket rotor; determining an actual flow rate of a high
pressure slurry discharged by the high pressure feeder, wherein the
high pressure slurry passes through the rotating pocket rotor; comparing
the determined actual flow rate to a desired flow rate of the high
pressure slurry discharged by the high pressure feeder; adjusting a
rotational speed of the rotating pocket rotor until the comparison of the
determined actual flow rate and the desired flow rate are within a
predefined range.
[0011] A high pressure feeder for a slurry has been developed
comprising: a housing having a low pressure inlet for the slurry, a high
pressure outlet for the slurry, a low pressure outlet for low pressure fluid
removed from the slurry in the feeder, a high pressure fluid inlet, and a
chamber in fluid communication with each of the inlets and outlets; a
pocketed rotor rotatably positioned in the chamber, wherein said
pocketed rotor is movable in the chamber and the movement
determines a gap between the pocketed rotor and the chamber; an
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actuator moving the pocketed rotor to adjust the gap, and a computer
controller generating commands to the actuator to determine an
adjustment to the gap, wherein the controller includes a control
algorithm which generates the commands based on an input sensor of
an operating condition of the high pressure feeder.
[0012] In the high pressure feeder, the pocketed rotor may be a
tapered cylindrical rotor and is movable axially in the chamber which
includes a tapered cylindrical surface facing the rotor, and the actuator
includes a shaft coaxial with the pocketed rotor and the shaft is moved
axially based on the generated commands. The actuator may further
comprise a gear motor which axially moves the shaft and said gear
motor is actuated based on the generated commands. In addition, a
remote computer may be coupled via the internet to the computer
controller, wherein the remote computer communicates information
regarding a desired gap to the computer controller which applies the
desired gap information to generated the commands. The input sensor
may include at least one of a vibration sensor monitoring a vibration of
the feeder, an acoustical sensor monitoring sounds emanating from the
feeder, a fluid pressure sensor monitoring a fluid pressure in the gap, a
power meter monitoring power applied to rotate the pocket rotor, and
flow meters measuring a high pressure slurry flow from the high
pressure outlet, a high pressure liquid flow into the high pressure inlet,
and a low pressure slurry flow into the low pressure inlet.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIGURE 1 is a schematic diagram of a conventional chip
feed system for feeding a slurry of comminuted cellulosic fibrous
material to a continuous digester or other high pressure vessel.
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[0014] FIGURE 2 is a perspective view a high pressure feeder
having a remotely controllable rotor clearance adjustment mechanism
and shows a cut-away view of the interior of the housing for the feeder
and a pocket rotor in the housing.
[0015] FIGURE 3 is an exploded view of a conventional pocket
rotor, cylindrical chamber of the feeder housing and a screen plate.
[0016] FIGURE 4 is side view of a housing for the rotor clearance
adjustment mechanism with a portion of the housing cut away to show
the axial movement of the control shaft for the mechanism.
[0017] FIGURE 5 is an end view of the housing for the rotor
clearance adjustment mechanism.
DETAILED DESCRIPTION OF THE INVENTION
[0018] FIGURE 1 is a schematic diagram of a conventional feed
system 10 for providing a slurry of comminuted cellulosic material, e.g.,
wood chips, to a high pressure feeder (HPF) 12 and to a high pressure
output conduit 14 leading to an inlet, e.g., a top separator 16, of a
continuous digesting vessel 17. The HPF receives a low-pressure
slurry or lo-level feed, via a chip chute 18, of comminuted cellulosic
fibrous material ("chip slurry") and outputs a high-pressure chip slurry.
The high pressure slurry is suitable for introduction into a continuous
digester, chip steaming vessel and other high pressure chip processing
systems. A flow meter 15 may measure the rate of slurry flow through
the output conduit 14 and to the inlet 16 of the digester 17.
[0019] The low pressure slurry is fed to the chip chute 18 through a
chip flow meter 20 from a chip bin 22 or other chip supply system, such
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as shown in U.S. Patent 5,622,598. Additional liquor may be added to
the chip flow in the chip chute 18 through conduit 23.
[0020] The HPF has a low pressure outlet 24 for liquor which flows
through the HPF but does not exit to the high pressure stream in conduit
14. The liquor from the low pressure outlet 24 flows through conduit 26
to a liquor recovery system 28 that may circulate the liquor to, for
example, the low pressure side of the chip feed system. Liquor is
pressurized by pump 32 and flows at high pressure through conduit 30
to the high pressure inlet 33 of the HPF. The high pressure liquor in the
HPF pressurizes the chip slurry from the chip chute such that the chip
slurry exits the HPF at high pressure into conduit 14.
[0021] FIGURE 2 shows a high pressure feeder 12 comprising a
stationary housing 34 with a pocketed cylindrical rotor 35 mounted for
rotation in a tapered cylindrical chamber 48 of the housing. The housing
includes four ports: a high-pressure inlet port 33 (in rear of housing and
show in Fig. 1); a high-pressure outlet port 38; a low-pressure inlet port
40 and a low-pressure outlet port 24 (in bottom of housing and shown in
Fig. 1). The low-pressure inlet port 40 is opposite on the housing 34 the
low-pressure outlet port 24. The high-pressure inlet port 33 is opposite
on the housing the high-pressure outlet port 38.
[0022] The pocket rotor 35 is driven by a variable speed motor and
gear reducer 37 coupled to a drive shaft 42. The pocket rotor is driven
to rotate in the housing chamber 48, such that the through-going
pockets 36 of the rotor sequentially communicate with the four ports of
the housing.
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[0023] As shown in Figure 3, the pocket rotor 35 contains two or
more through-going pockets 36 such that different pockets
communicate with different high and low-pressure ports as the rotor
rotates. Each pocket in the rotor defines a passage through the rotor
with openings on opposite sides of the passage. The rotor typically
rotates at a speed of between about 5 to 15 revolutions per minute
(rpm), preferably, between about 7 to 10 rpm, depending upon the
capacity of the HPF and the production rate of the pulping system it is
used to feed.
[0024] The low-pressure outlet port of the HPF is typically provided
with a screen element 54, for example, a cast horizontal bar type screen
element such as the screen element 29 in U.S. Pat. No. 5,443,162. The
screen element retains the chips in the slurry within the feeder and
allows some of the liquid in the slurry to pass out of the second end of
the pocket, through the screen and out through the low pressure outlet
port.
[0025] (if we go into too much detail about the grid do we give up
protection on Metso compact feed systems where the HPF has no grid?
Answer: It is OK to give detail in the description portion of the patent
application. The detail will not limit the scope of the claims of the
application. The claims (at the end of the application) define the scope
of the patent. The claims are not limited to a screen and seem not to
exclude the Metso compact feed system.)
[0026] Chips flow into a pocket(s) 36 of the rotor 35 when the
openings of the pocket align with the low pressure inlet 40 and low
pressure outlet 24 of the HPF, e.g., the pocket is vertical. The chips flow
into the pocket from the chip chute 18 and mix with any remaining chips
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retained in the pocket by the screen element 54. The screen element
prevents chips flowing through the pocket and out the low pressure
outlet 24. As the pocket rotates 90 degrees, e.g., a quarter turn, the
chips in the pocket are transported from a low pressure flow to a high
pressure flow as the openings in the pocket align with the high pressure
inlet 33 and high pressure outlet 38 of the HPF. After this one-quarter
revolution of the rotor, the first end of the pocket that was once in
communication with the low-pressure inlet 40 is placed in
communication with the high pressure outlet 38. The high-pressure
outlet typically communicates with the inlet of a digester, either a
continuous or batch digester, via one or more conduits. At the same
time, this quarter-turn rotation of the rotor also places the second end of
the through-going pocket, which was just in communication with the low-
pressure outlet, in communication with the high-pressure inlet 33. The
high pressure inlet typically receives a flow of high-pressure liquid from
a high-pressure hydraulic pump 32. The pressure of this liquid typically
ranges from about 5 to 15 bar gauge, and is typically about 7 to 10 bar
gauge. This high-pressure liquid displaces the slurry of chips and liquid
from the through-going pocket and out of the high-pressure outlet and
ultimately to the inlet of the digester.
[0027] As the pocket rotor continues to rotate, the second end of
the pocket which received the high-pressure fluid is placed in
communication with the low-pressure inlet and receives another supply
of slurry from the conduit connected to the low-pressure inlet. Similarly,
the first end of the pocket is rotated into communication with the low-
pressure outlet of the housing, having the screen element. The process
described above repeats such that during one complete revolution of
the rotor each through-going pocket receives and discharges two
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charges of chips and liquid. The rotor typically contains at least two,
typically four, through-going pockets such that the rotor is repeatedly
receiving slurry from the low-pressure inlet and discharging slurry out
the high-pressure outlet. The ends of the these pockets act as both an
inlet for slurry and an outlet depending upon the orientation of the rotor.
[0028] FIGURE 3 shows the pocket rotor 35 having a cylindrical
shape with a slight taper extending from one end 44 of the rotor to the
opposite end 46 of the rotor. The first end 44 of the rotor may a smaller
diameter than the opposite end of the rotor. The rotor 35 fits in a
tapered cylindrical chamber 48 (Fig. 2) fixed to the housing. The
chamber has a taper similar to the taper of the rotor. A first end 50 of
the chamber has a smaller diameter than an opposite end 52 of the
chamber. The chamber has openings 49 that are aligned with the inlets
and outlets of the housing of the HPF. The chip slurry flows through
openings 49 in the chamber to enter the pockets 36 of the rotor and exit
the pocket through openings in the chamber to the high pressure outlet
of the HPF. Similar, high pressure liquid pass through the openings 49
in the chamber to enter the pockets of the rotor and discharge through
openings in the chamber to exit through the low pressure discharge of
the HPF.
[0029] A small tapered annular gap 51 is formed between the rotor
and the chamber, when the rotor is inserted into the chamber. The gap
51 allows the rotor to rotate within the chamber. The width of the gap is
determined by the axial position of the pocket rotor 35 with respect to
the chamber 48. Due to the complementary conical shapes of the rotor
pocket and chamber, the gap may be narrowed by moving the pocket
rotor axially towards the small diameter end of the chamber. Similarly,
the gap 51 may be expanded by moving the rotor pocket axially towards
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the large diameter end of the chamber. During its axial movement, the
rotor remains within the chamber.
[0030] The width of the gap 51 may be changed by automatically or
manually adjusting the axial position of the rotor pocket. In contrast to
the conventional practice of manually adjusting the axial position of the
rotor pocket in the chamber, the high pressure feeder disclosed herein
includes a motor driven shaft 58 that is coupled to an end of the pocket
rotor. The shaft 58 is axially aligned with the pocket rotor. A controller
assembly 68 adjusts the axial position of the shaft and, thus, the axial
position of the pocket rotor in the chamber of the housing.
[0031] A small amount of liquid flows through the gap 51, such as
from outlets in the pocket rotor 35. The liquid serves as a lubricant
between the rotor 35 and cylindrical chamber 48. The liquid drains
through the screen 54 below the chamber and adjacent the low
pressure outlet of the housing. The liquid from the low pressure outlet
may be reused in, for example, the feed system 10.
[0032] In addition, liquid may collect in end bell chambers 56 of the
housing that are adjacent opposite ends of the pocket rotor 35 and
chamber 48. The liquid in the bell chambers 56 is preferably maintained
under pressure to prevent additional flow, which may include fines, into
the bell chambers. A conduit 57 for additional white liquor is connected
to an inlet port to each of the bell chambers 56 at opposite ends of the
housing for the HPF. The white liquor is provided under pressure from
the conduit 57 to pressurize the liquid in the bell chambers and to
prevent a flow of liquor and fines from the pocket rotor into the bell
chambers.
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[0033] If the gap 51 is too large, excessive liquids and small
particles, such as fiber fines, sand and other small debris, especially
metal, rock and sand, in the gap may cause grooves to form in the outer
surface of the pocket rotor 35 and the inner surface of the chamber 48.
If the gap 51 between the pocket rotor 35 and the cylindrical chamber
48 is too large, excess liquid, fines and other small debris may enter the
gap through openings in the pocket rotor. The fines and debris may flow
through the gap and collect in interior bell chambers 56 and adjacent
the axial ends of the rotor pocket. If excessive fines and debris collect in
the bell chambers, the fines may resist the rotation of the rotor, cause
the rotor components to wear and increase the power consumption of
the high pressure feeder.
[0034] FIGURE 4 shows a controller assembly 62 for a controller
68, gear motor 64, gear box 65, and a shaft 58 that is coupled to and
adjusts the axial position of the pocket rotor. The shaft 58 is contained
within housing 60. The controller housing has an end 65 that couples to
an end bell housing 56 of the HPF. The controller assembly 62 supports
an actuator for axially moving the shaft 58 and pocket rotor. The
actuator includes a gear motor 64 and gearbox 65 that controls the axial
position (indicated by the arrows) of the shaft 58 and hence the axial
position of the pocket rotor. The gearbox engages spiral threads on the
shaft 58 to rotate the shaft. The rotation of the shaft by the gearbox
causes axial movement of the shaft and pocket rotor. The gear motor 64
receives commands from the computer controller 68 to turn the gearbox
65 by a prescribed angular amount. By commanding the gear motor and
gear box, the computer controller adjusts the axial position of the shaft
and pocket rotor. The gear motor 64 tracks the rotation of the shaft by
the gearbox and provides signals of the rotation that enable the
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computer controller to determine the axial position of the shaft. In
addition, the axial position of the shaft is monitored or measured by a
position sensor, such as by a laser position sensor 72.
[0035] FIGURE 5 shows an end view of the controller assembly 62
and HPF. The controller assembly is attached to the HPF by a pair of
brackets 78 that form cantilevered beams attached at one end to the
housing of the HPF and support a track 80 for the rollers 66 of the
controller assembly 62. The beams of the brackets may be hollow
rectangular beams that extend horizontally. The controller assembly 62
may fit between the brackets. The roller wheels 66 of the controller
assembly 62 rest on the tracks 80 and enable the controller assembly
62 to move laterally along the tracks as the shaft 58 moves laterally with
respect to the HPF. A pair of roller wheels 66 on each side of the
controller assembly are mounted on a frame 82 that is fixed to the
controller assembly. The roller wheels may include an annular groove
that rides on a ridge of the track 80. A lower frame 84 is also fixed to
each side of the controller. The lower frame 84 includes a bolt 86, pin
or other positioning device prevents the roller wheels 66 from jumping
upward and unintentionally coming off the track. The bolt 86 may be
retracted to allow the controller assembly 62 to be installed on or
removed from the HPF. A generally horizontal frame 88 supports the
gear motor 64, gear box 65 and other components of the controller
assembly. The horizontal frame is arranged between the brackets 78.
A protective guard 90 may cover the rollers 66 and the tracks 80.
[0036] The computer controller 68 receives input signals indicative
of the operating condition of the HPF and chip feed system. The input
signals may be generated by sensors that may include vibration or
acoustical sensors 70 (Fig. 2), e.g., three to four, mounted on the
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housing of the HPF; a chip flow meter 20 measuring the chip flow from
the low pressure side of the chip feed system; a flow meter 15
measuring the high pressure flow through conduit 14 leading to the
digester; a power meter in the motor drive 37 for the HPF (where the
meter measures the electrical load of the HPF); pressure sensors 74 in
the interior of the HPF such as in the bell chambers 56; a sensor 72
measuring the rotation and position of the drive shaft 58, and a sensor
76 measuring a fluid pressure in the gap 51. The computer controller
68 monitors the output signals from the sensors, meters and other
devices monitoring various operating conditions of the HPF and chip
feed system. Based on the output signals, the computer controller 68
may determine an appropriate clearance gap 51 between the pocket
rotor and the chamber in the HPF. The controller uses the appropriate
gap clearance to determine a desired axial position of the shaft 58.
[0037] The computer controller 68 may include a display and user
input device 69 that presents information to a human operator regarding
the current operating condition of the HPF, and prompts for suggested
changes to the axial position of the pocket rotor. For example, the
dispiayed prompt may indicate that the pocket rotor should be advanced
inward or outward a suggested distance, e.g., 2 mm, or one
predetermined step.
[0038] The computer controller 68 may have a manual mode in
which no automatic adjustments are made by the controller to the axial
position of the pocket rotor. In manual mode, the controller may only
display suggested actions by generating prompts to be presented on the
display and for the benefit of human operators reading the display. The
manual mode may allow an operator to enter commands in the user
interface device 69 to cause the drive gears to advance or retract the
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shaft and pocket rotor by a distance specified by the operator. The
commands may include, for example, commands to advance the pocket
rotor by one millimeter or position pocket rotor at a specified axial
position.
[0039] The computer controller 68 may have an automatic mode
that includes the features of the manual mode and an additional feature
that allows the human operator to authorize the controller 68 to
automatically execute certain operations, such as a "flush operation"
during which the position the axial position of the pocket rotor is moved
slightly in and out in a cyclical operation to flush fines out of the end bell
of the HPF housing. Fines are small fibrous particles from wood chips.
In automatic mode, the display 69 prompts the operator to authorize the
flush operation when the controller detects that an excessive amount of
fines may be in the end bells.
[0040] The computer controller 68 may have a remote mode in
which it automatically adjusts the axial position of the shaft and pocket
rotor based on analysis performed by the controller of sensor signal
inputs regarding the condition of the HPF. In remote mode (but equally
applicable to automatic and manual modes), the controller 68 may
report the operation condition of the HPF to a remote computer 75 via
the internet. In remote mode, the axial position of the pocket rotor may
be adjusted based on commands entered by an operator at the remote
computer 75.
[0041] In at least the remote mode, the computer controller 68
automatically turns the gears of the gear box 65 to move the shaft and
pocket rotor and thereby adjust the clearance gap 51. The controller 68
may adjust the clearance based on the sensor signals that provide data
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regarding the operation of the HPF and algorithms stored in electronic
memory of the controller. The algorithms convert the input signals from
the sensors and commands from the operator into command signals for
the gear motor 64 and gear box 65.
[0042] For example, the clearance gap 51 is preferably maintained
such that the pressure of the liquor in the gap is below the pressure
level of the white liquor injected into the end bell chambers 56 by the
conduits 57. Maintaining the pressure in the gap to be below the
pressure in the bell chambers assists in preventing fines from flowing
into the bell chambers. In addition, the gap is preferably maintained to
minimize wear between the rotor and cylindrical chamber 48 of the
housing. Monitoring the vibration in or sounds emanating from the HPF
provides an indication of whether metal-to-metal contact is occurring
between the pocket rotor and chamber. The signals from the vibration
or acoustical sensors provide data used by the controller to determine if
the clearance gap should be adjusted. Further, the gap should
preferably be varied periodically by shifting the pocket rotor axially with
respect to the cylindrical chamber to avoid forming a groove in the
housing or pocket rotor due to metal, sand or other hard debris caught
in the gap.
[0043] If the clearance of gap 51 remains constant, the rate of
leakage of liquid through the gap should be substantially constant. A
change in the rate of leakage while the gap 51 is constant, suggests
that the gap should be adjusted. An approach to determining when the
gap should be adjusted is to monitor the leakage of liquor through the
low pressure outlet of the HPF and reduce the clearance if the leakage
becomes excessive. The leakage may be determined as the rate of flow
through the high pressure conduit (as measured by flow meter 15)
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minus the input flows to the HPF including the chip flow as measured by
flow meter 20, liquid flow, e.g., cold blow flow, through conduit 23, and
the high pressure liquid entering the HPF feeder through input 33). The
ratio of the leakage to the makeup liquor flow through conduit 57 to the
HPF housing minus the ratio of make-up liquor to the flow of chips from
the chip supply. An increase in the ratio of makeup liquor to chip flow
indicates the amount of leakage through the gap is increasing.
[0044] The computer controller 68 may perform various analysis of
the condition of the HPF and, specifically, the gap between the pocket
rotor 35 and the cylindrical chamber 48 of the HPF housing. A first
exemplary analysis is to monitor the electrical load placed by the HPF
on the drive motor 37. This electrical load is measured by a power
meter and reported to the computer controller 68. The electrical load is
indicative of the width of the gap between the pocket rotor and the
cylindrical chamber. A relatively low electrical load indicates that the gap
is wide because relatively little friction is induced by the cylindrical
chamber on the rotating rotor. A narrow gap increases the friction
induced by the cylindrical chamber on the rotor and thus increases the
electrical load of the HPF on the motor.
[0045] The computer controller 68 may store a predetermined
maximum electrical load level and a predetermined preferred range of
electrical loads, which may be a range of 95% to 85% of the maximum
electrical load level. By comparing the actual electrical load to the
predetermined maximum electrical load level and a preferred range of
electrical loads, the controller may issue prompts on the display of
suggested adjustments to be made to the axial position of the pocket
rotor and displays warnings that, for example, the current electrical load
level exceeds the maximum load level. Further, the controller may
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automatically retract the pocket rotor by a predetermined distance, e.g.,
0.5 to 3mm. If the actual electrical load exceeds the maximum load level
for a predetermined period of time, the controller may command an
automatic retraction of the pocket rotor. The controller may issue a
warning on the display if the actual electrical load is outside of the
preferred range of electrical loads.
[0046] A build up of fines in the bell chambers 56 tends to increase
the rotational friction between the pocket rotor and chamber and thereby
increases the power load on the motor driving the HPF. The build up of
fines in the bell chambers will press fines against the ends of the pocket
rotor. The movement of the rotating ends of the rotor against the fines in
the bell ends results in friction that acts against the rotation of the
pocket rotor. The data output signals from the sensors monitoring the
motor power load typically detect an increase in the motor power load
when the fines build up in the end bells. An increase in the power load
while the gap clearance is held constant suggests that friction in the
HPF is increasing and an assumption may be made that the friction
increase is due to a build of fines in the bell ends 56.
[0047] It is preferable to confirm the presence of fines in the end
bell because an increase in the motor power load of an HPF may be
caused by conditions other than the presence of fines in the end bells.
For example, the motor power load may increase due to the gap
clearance being too small such that the pocket rotor is too close to the
cylindrical chamber of the housing.
[0048] The sensors may be monitored by the controller 68 to
confirm that the increase in motor power load corresponds to an
unacceptable build up of fines in the end bell. For example, a vibration
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or acoustical sensor 70 attached to one or both of the end bells may
sense a vibration or acoustic signal indicative of fines build up in the end
bell. In addition, the vibration or acoustical sensors may generate output
signals indicating that metal-to-metal contact is occurring in the gap or
that debris is caught in the gap. The controller 68 may interpret these
signals indicative of metal-to-metal contact or debris in the gap as
indicating that the gap is too narrow and generate a prompt or
command to retract the pocket rotor by for example, 0.5mm to 2mm,
increase the gap between the rotor and chamber. Further, a sensor,
e.g., a light source and photo-detector sensor to detect reflections by
fines, may be internal to the end bells to monitor the composition of the
liquid in the end bell and, particularly, detect fines in the liquid.
[0049] Another potential approach to determining whether a power
load increase is due to fines build up is to monitor the rate of increase in
the power load. A slow increase rate may indicate that fines are building
up in the end bells. A rapid rate of increase may indicate that the
clearance gap is too narrow and/or that debris has become lodged in
the gap.
[0050] To purge a build up of fines in the bell ends, the pocketed
rotor is moved axially inward and outward in small incremental steps to
agitate the fines in the ends and flush out the fines as liquor in the ends
flows out through the gap and into the pocket rotor. The agitated fines
flow with the liquor through the gap, into the pocket rotor and out the
high pressure outlet of the HPF.
[0051] To purge fines, the controller for the motor drive advances
the pocket rotor axially further into the cylindrical chamber 48, such by a
small step of, for example, 0.25 to 4 millimeters (mm) and preferably
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0.5mm to 1 mm. An encoder 72, e.g. a laser position measurement
instrument, measures the axial movement of the shaft and hence the
axial movement of the rotor pocket with respect to the cylindrical
chamber. Signals from the encoder to the controller 68 allow the
controller to accurately determine the axial position of the pocket rotor
with respect to the cylindrical chamber.
[0052] The controller may monitor the rotational speed of the HPF
feeder and control the HPF speed or issue prompts as to suggested
HPF speeds. For example, the controller may determine the HPF speed
based on the chip flow meter 20, such that the flow rate determined by
the flow meter is proportional to the HPF speed. Further, the HPF speed
may be based on an average of the chip flow rate as determined by flow
meter 20 over a period of time, such as 10 minutes to two hours. If the
controller automatically adjusts the speed of the HPF, the controller may
make adjustments in small speed steps, e.g., less than 5% of the
rotational speed of the HPF. After each speed step adjustment, the
controller waits for the chip level in the chip chute 18 to maintain a
steady state and thereafter determines if the HPF speed is within a
predetermined range, e.g., a standard deviation, of the prescribed
proportion of the chip flow rate. Another speed step adjustment may be
made if the HPF speed is outside of the predetermined range.
[0053] The "Plug Position" is the axial position of the pocketed rotor.
The shaft encoder sensor 72 provides an indication of the axial position
of the pocketed rotor. Other signal indicators of the plug position
include whether the gear motor is one or off, and the HPF rotor drive
motor load as measured by power sensor 37. The positioner motor
receives commands from the computer controller 68 that indicate the
rotation to be applied to turn the gears and hence axially move the shaft
CA 02642312 2008-10-29
56 and the pocket rotor. For example, the computer controller 68 may
command the positioned motor to turn the gears in the gear box 65
clock-wise and counter-clockwise a certain rotational amount over a
predefined period to move the pocket rotor in and out axially to flush
fines from the bell chamber.
[0054] Manual mode: The operator moves the axial position of the
pocket rotor by inputting commands to the user interface 69 or by a
remote computer 75. If the operator moves the pocket rotor in too far in
an axial direction and the controller detects that the power load exceeds
a predefined maximum load, the controller automatically overrides the
human operator and retracts the pocket rotor to increase the gap 51. In
this situation, the controller issues an alarm and informs the operator
that the maximum motor power load had been exceeded.
[0055] Reciprocating Movement of Pocket Rotor: If the computer
controller detects a power load increases and determines that the
vibration or acoustic sensors do not indicate metal on metal contact
between the rotor and casing, the controller determines that a potential
fines build up has occurred in the bell chambers. The controller may
automatically act to move the pocket rotor in and out axially or issue an
advisory notice to the operator to recommend such in and out
movement to flush the fines from the bell chamber.
[0056] Storage of Pocket Rotor Axial Position. The computer
controller stores data regarding the operational history of the HPF,
including data indicating historical axial positions of the rotor pocket and
whether the axial positions had associated excessive liquid leakage or
metal-to-metal contact. Prior acceptable rotor pocket axial positions
may be used to reset the rotor pocket after HPF maintenance
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procedures or other operations in which the rotor pocket is retracted
partially from the chamber. Preferably, the rotor pocket is advanced
axially to the last known acceptable axial position in the chamber. If
further axial movements of the pocket rotor are made, such further
movements may be at a slower axial speed than the speed at which the
rotor was advanced to its last known acceptable position.
[0057] Auto Mode: The controller automatically determines a
desired axial rotor position. The desired axial rotor position may be
determined to achieve a optimal amount of fluid leakage through the low
pressure outlet of the HPF. In auto mode, the controller may periodically
move the pocketed rotor in and out (axial reciprocal movement) to flush
fines from the bell end chambers. The positioner motor may relatively
rapidly turn the gears box 65 to move the reciprocally to flush the fines
and then returns the pocket rotor to the last known acceptable axial
position. After the pocket rotor has returned to its last known acceptable
position, the positioner motor may more slowly turn the gears as the
controller determines the axial position of the pocket rotor that provides
the best leakage flow from the HPF or the controller applies some other
criteria to optimize the HPF.
[0058] Flush Indications: The leakage flow exceeds a predefined
flow limit, and the power load sensor detects a high or increasing power
being applied to rotate the pocket rotor.
[0059] A flush should preferably move the pocket rotor reciprocally
axially about 2 mm, as an example. After two or three reciprocal cycles
the pocket rotor may be moved to its last acceptable axial position. The
controller thereafter determines if the power load has been reduced
which indicates that the fines were successfully flushed from the bell
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chambers. In addition, flush schedules may be performed pursuant to a
schedule, such as every 10 hours. The controller stores data indicating
when flush operations occurred.
[0060] During a flush operation, the controller may apply a relatively
high pressure purge flow to the conduit 57 to provide high pressure
liquor to the end bell chambers 56. This purge flow may only be used for
the fines flush operation and assists in flushing fines from the bell
chambers and maintain adequate pressure and liquor flow at and
through the end bell chambers. This flow will have a high flow limit
except for the fines flush procedure.
[0061] Pocket Position Adjustment: The controller may applied a
position adjustment that measures the amount of liquor leakage from
the HPF and, based on this measurement, determines whether to adjust
the axial position of the pocket rotor. For example, when leakage
exceeds a predetermined rate, the controller may advance the pocket
rotor into the chamber until the power load increases to a predetermined
limit. Thereafter, the controller may retract the pocket rotor by a
prescribed distance, such as 2 mm.
[0062] Leakage Test: If Leakage is greater than a predefined value,
the controller may perform a leakage adjustment operation. During this
operation, the controller calculates leakage as the amount of make-up
liquor flow added to the low pressure chip feed minus the white liquor
added initially to the chips from which sum is subtracted the cold blow to
feed (CbtoFeed) (DEFINE THIS). Alternatively, the leakage may be
determined based on a Leakage RPM (revolutions per minute) which is
the makeup liquor flow RPM divided by the chip meter RPM. An
exemplary equation defining leakage is:
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[0063] HPF LeakageRPM/ChipmeterRPM =
MakeupLiquorFlowMeterRPM/chipmeterRPM.
[0064] Baseline Data: When the HPF is started, the controller may
apply baseline data as acceptable liquor leakage values and as power
loads indicating fines buildup. Baseline Data: Current Life expectancy
Weekly runin (slope)% Ace Uptime (hpf control is off) After the HPF has
operated and data has been acquired regarding its operation, the
controller may thereafter use historical data collected from HPF
operation to provide better leakage values and power load values
indicating a fine buildup.
[0065] While the invention has been described in connection with
what is presently considered to be the most practical and preferred
embodiment, it is to be understood that the invention is not to be limited
to the disclosed embodiment, but on the contrary, is intended to cover
various modifications and equivalent arrangements included within the
spirit and scope of the appended claims.
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