U.S. patent application number 13/432546 was filed with the patent office on 2013-09-26 for method and arrangement for measuring and controlling chip and/or liquid level.
This patent application is currently assigned to SAVCOR FOREST OY. The applicant listed for this patent is Martti Pulliainen. Invention is credited to Martti Pulliainen.
Application Number | 20130248127 13/432546 |
Document ID | / |
Family ID | 49210677 |
Filed Date | 2013-09-26 |
United States Patent
Application |
20130248127 |
Kind Code |
A1 |
Pulliainen; Martti |
September 26, 2013 |
METHOD AND ARRANGEMENT FOR MEASURING AND CONTROLLING CHIP AND/OR
LIQUID LEVEL
Abstract
A method for measuring and controlling a chip level and/or a
chip-liquor combination level and/or liquor level height of a
liquid-steam phase digester or a hydraulic digester which digester
comprises a chip screw for feeding chips into a digesting volume.
The method comprises mounting electrode pairs in certain heights
and vertically at distances from each other in the digesting volume
of the digester, the electrode pairs being formed of electrodes;
connecting the electrode pairs to electric circuits; measuring in
each electric circuit a current or voltage value during operation
of the digester; determining, based on the measurement, type of
material layer (for example, steam, chips, combination of chips and
liquor, or liquor) located in a certain height, based on the
electrical conductivity of the materials in the digesting volume.
An arrangement for measuring and controlling a chip level and/or a
chip-liquor combination level and/or a liquor level height of a
liquid-steam phase digester or a hydraulic digester.
Inventors: |
Pulliainen; Martti;
(Mikkeli, FI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Pulliainen; Martti |
Mikkeli |
|
FI |
|
|
Assignee: |
SAVCOR FOREST OY
Mikkeli
FI
|
Family ID: |
49210677 |
Appl. No.: |
13/432546 |
Filed: |
March 28, 2012 |
Current U.S.
Class: |
162/49 ;
162/263 |
Current CPC
Class: |
D21C 7/06 20130101; D21C
3/22 20130101; D21C 7/12 20130101 |
Class at
Publication: |
162/49 ;
162/263 |
International
Class: |
D21C 3/22 20060101
D21C003/22 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 22, 2012 |
FI |
20125317 |
Claims
1. A method for measuring and controlling a chip level and/or a
chip-liquor combination level and/or a liquor level height of a
liquid-steam phase digester or a hydraulic digester which digester
comprises a chip screw for feeding chips into a digesting volume;
and the method comprising mounting electrode pairs in certain
heights and vertically at distances from each other in the
digesting volume of the digester, the electrode pairs being formed
of electrodes; connecting the electrode pairs to electric circuits;
measuring in each electric circuit a current or voltage value
during operation of the digester; determining, based on the
measurement, type of material layer located in a certain height,
based on the electrical conductivity of the materials in the
digesting volume.
2. The method according to claim 1 comprising arranging a potential
difference between the electrodes of the electrode pairs and
measuring the current in the electric circuit.
3. The method according to claim 1 comprising supplying a constant
current to the electric circuit of the electrode pairs and
measuring the voltage in the electric circuit.
4. The method according to claim 1 comprising using the determined
height information of the chip level and/or the chip-liquor
combination level and/or the liquor level as control for the
digesting process and repeating the measuring and control steps of
the method.
5. The method according to claim 1 comprising arranging a changing
potential difference between the electrodes of the electrode pairs
which is preventing generation of precipitation on electrode
surfaces.
6. An arrangement for measuring and controlling a chip level and/or
a chip-liquor combination level and/or a liquor level height of a
liquid-steam phase digester or a hydraulic digester which digester
comprises a chip screw for feeding chips into a digesting volume;
and the arrangement comprises electrode pairs which are formed of
electrodes and mounted in certain heights and vertically at
distances from each other in the digesting volume of the digester;
and the electrode pairs are connected to electric circuits such
that, during operation of the digester, a current or voltage value
measured in each electric circuit is determining the type of
material layer located in a certain height, based on the electrical
conductivity of the materials in the digesting volume.
7. The arrangement according to claim 6, wherein the arrangement
comprises a circuit measuring means which is during operation of
the digester arranged to measure current of the circuits when
potential differences are arranged between the electrode pairs.
8. The arrangement according to claim 6, wherein the arrangement
comprises a circuit measuring means which is during operation of
the digester arranged to measure voltage of the circuits when
current is supplied in the circuits.
9. The arrangement according to claim 6, wherein the arrangement
comprises an output for communicating the height information of the
chip level and/or the chip-liquor combination level and/or the
liquor level from the circuit measuring means for the control of
the digesting process.
10. The arrangement according to claim 6, wherein the electrode
pairs are arranged under the chip screw.
11. The arrangement according to claim 6, wherein the arrangement
comprises one or more measuring rods to which is/are mounted
electrodes for the electrode pairs.
Description
TECHNICAL FIELD
[0001] The invention relates to a method and an arrangement for
measuring and controlling a chip and/or liquor level. The invention
relates particularly, though not exclusively, to measuring of the
surface level of chips in a steam-liquid phase digester and a
hydraulic digester.
BACKGROUND ART
[0002] In a continuous pulp digester the chips are fed as a regular
flow to the digester together with the liquor while a corresponding
amount of pulp and liquor is blown out of the digester. There are
two types of continuous digesters, the liquid-steam phase digester
and the hydraulic digester.
[0003] In the liquid-steam phase digester the liquid surface is
lower than the chip surface wherein a steam phase is formed in an
upper portion of the digester. A steam supply is provided via a top
of the digester. The chips can be fed from outside the digesting
volume, in the level of the steam phase, to a chip screw which is
feeding the chips upwards to the top of the digester. The chips are
dropping outside the chip screw from the top of the digester to the
digesting volume.
[0004] The hydraulic digester is filled with a digesting liquid,
i.e., under hydraulic pressure. The chips are brought to the upper
portion of the digester by means of filling liquor and the upper
screw in a cylindrical screen presses the chips into the digesting
liquid to the actual digesting volume. Then the chips proceed
downwards in an impregnation zone and after that reach a cooking
zone. In the cooking zone the temperature is increased to a cooking
temperature.
[0005] The surface height of the chips is measured in the
liquid-steam phase digester and the hydraulic digester in order
that the cooking process can proceed undisturbed. The chip surface
of the digester can be influenced by blow flow, bottom scraper
rotation speed and chip screw rotation speed which is regulating
the chip feed. The blow flow is affecting the mass flow which is
exiting the digester and the rotation speed of the bottom scraper
is affecting the consistency of the mass in the bottom of the
digester. The described control quantities can be applied as
different combinations.
[0006] The liquor surface can rise above the chip surface in the
liquid-steam phase digester what is causing an abnormal situation.
The situation may arise for example due to disruption in the feed
of the chips what may be caused by a blockage of the input path of
the chips.
[0007] In the regulation of the chip surface the surface height is
in the prior art measured with mechanical or, in the liquid-steam
phase digester, with radiometrical sensors. A precipitation which
is accruing onto walls of the steam phase, and scum, are disturbing
the radiometrical measurement. The mechanical surface height
sensors are blades which are mounted inside the digester and
measuring torque. The chips on the blade are causing to the blade a
torque which is increasing when the load against the blade is
increasing. There are many measuring variations in the blade
measurements because the height of the chip pile is differing in
different locations of the digester. Further the precipitation is
accumulating on the blades which is increasing measuring
uncertainty in the course of time.
[0008] A mechanical chip surface meter is used in the prior art as
a prolongation of the upper screw of the hydraulic digester wherein
torque is measured by members which are lead through the upper
screw and sunken into the mass. Precipitation is accruing to the
mechanical parts wherein the measuring uncertainty is
increasing.
[0009] An object of the invention is to provide an alternative
method and arrangement for measuring the surface height of the
chips. An object of the invention is to eliminate or at least
minimize drawbacks in the prior art. Still an object of the
invention is to increase reliability of surface height measuring of
the chips, improve surface height regulation of the chips and
decrease service need of surface height measuring equipment.
SUMMARY
[0010] According to a first aspect of the invention there is
provided a method for measuring and controlling a chip level and/or
a liquor level height of a liquid-steam phase digester or a
hydraulic digester which digester comprises a chip screw for
feeding chips into a digesting volume, and the method comprising
mounting electrode pairs in certain heights and vertically at
distances from each other in the digesting volume of the digester,
the electrode pairs being formed of electrodes, connecting the
electrode pairs to electric circuits, measuring in each electric
circuit a current or voltage value during operation of the
digester, determining, based on the measurement, type of material
layer (for example, steam, chips, combination of chips and liquor,
or liquor) located in a certain height, based on the electrical
conductivity of the materials in the digesting volume.
[0011] Preferably the method comprises arranging a potential
difference (AC, DC) between the electrodes of the electrode pairs
and measuring the current in the electric circuit.
[0012] Preferably the method comprises supplying current to the
electric circuit of the electrode pairs and measuring the voltage
in the electric circuit.
[0013] Preferably the method comprises using the determined height
information of the chip level and/or the liquor level as control
for the digesting process and repeating the measuring and control
steps of the method.
[0014] Preferably the method comprises arranging a changing
potential difference (AC, DC) between the electrodes of the
electrode pairs which is preventing generation of precipitation on
electrode surfaces.
[0015] According to a second aspect of the invention there is
provided an arrangement for measuring and controlling a chip level
and/or a liquor level height of a liquid-steam phase digester or a
hydraulic digester which digester comprises a chip screw for
feeding chips into a digesting volume, and the arrangement
comprises electrode pairs which are formed of electrodes and
mounted in certain heights and vertically at distances from each
other in the digesting volume of the digester, and the electrode
pairs are connected to electric circuits such that, during
operation of the digester, a current or voltage value measured in
each electric circuit is determining the type of material layer
(for example, steam, chips, combination of chips and liquor, or
liquor) located in a certain height, based on the electrical
conductivity of the materials in the digesting volume.
[0016] When the electric circuits are in an electrified state, the
locations of the vertical chip and liquor zones can be determined
based on the electrical conductivities of the chips, the liquor and
the combination of chips and liquor which are at least
approximately known.
[0017] Preferably the arrangement comprises a circuit measuring
means which is during operation of the digester arranged to measure
current of the circuits when potential differences (AC, DC) are
arranged between the electrode pairs. Preferably the arrangement
comprises voltage supplying means for generating potential
difference (AC, DC) in the circuits of the electrode pairs.
Preferably the circuit measuring means comprises voltage supplying
means for generating potential difference (AC, DC) in the circuits
of the electrode pairs.
[0018] Preferably the arrangement comprises a circuit measuring
means which is during operation of the digester arranged to measure
voltage of the circuits when current is supplied in the circuits.
Preferably the circuit measuring means comprises current measuring
means for measuring current of the circuits.
[0019] Preferably the arrangement comprises an output for
communicating the height information of the chip level and/or the
liquor level from the circuit measuring means for the control of
the digesting process.
[0020] Preferably the electrode pairs, more preferably measuring
rods, are arranged under the chip screw. Preferably the electrode
pairs, more preferably the measuring rods, are arranged under a
chip basket.
[0021] Preferably the arrangement comprises one or more measuring
rods to which is/are mounted electrodes for the electrode pairs.
Preferably the measuring rod/rods is/are mounted under the chip
screw.
[0022] Preferably the electrode pair is formed in the same
measuring rod of electrodes which are mounted in two different
heights.
[0023] Preferably the electrode pair is formed in two or more
measuring rods of electrodes which are mounted in the same height
or different heights.
[0024] Preferably the electrode pair is formed in the same
measuring rod of electrodes which are mounted in the same height
and are at a horizontal distance from each other, preferably at
opposite sides of the rod.
[0025] Preferably the vertical distances of the electrode pairs
form the neighboring electrodes are in the upper end of the
measuring rod (in the gas phase) larger than in the bottom end of
the measuring rod.
[0026] With the method and the arrangement the chip surface height
measured in the liquid-steam phase digester or the hydraulic
digester can be exploited in improving the fluency of the cooking
process. The measured chip surface and/or liquor surface height can
be used as a control quantity when controlling the blow flow; the
bottom scraper rotation speed; the chip screw rotation speed and/or
material flows of the digester such as supply of liquor to the
digesting volume.
[0027] By the method and the arrangement the level height
measurement of masses in the digesting volume of the continuous
pulp digester can be improved, the reliability of the surface
height measurement can be increased and the reliable lifetime of
the measuring means in the digesting volume can be improved, the
surface height regulation of the masses in the digesting volume can
be improved and the service need of surface height measuring means
can be reduced. By the method and the arrangement the problem of
the so called floating chips can be recognized which can exist both
in the liquid-steam phase digester and in the hydraulic digester.
Then the chips don't sink under the liquor but are floating on the
liquor surface. A region is forming under a thin chip bed where
exist sole liquor what can also be detected in the surface height
measurement. Generally the chips are then too dry and the chips can
block quickly the chip feeding openings until the chip feeding
screw and the process is stopping. This failure can be detected
proactively by the surface height measurement and there may be time
left for making some improvements in order to prevent the
blockage.
[0028] Different embodiments of the present invention will be
illustrated or have been illustrated only in connection with some
aspects of the invention. A skilled person appreciates that any
embodiment of an aspect of the invention may apply to the same
aspect of the invention and other aspects alone or in combination
with other embodiments as well.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] The invention will be described, by way of example, with
reference to the accompanying drawings, in which:
[0030] FIG. 1 shows the method and the arrangement in connection
with a liquid-steam phase digester;
[0031] FIG. 2 shows the method and the arrangement in connection
with a hydraulic digester;
[0032] FIG. 3 shows a first alternative placement of the measuring
electrodes;
[0033] FIG. 4 shows a second alternative placement of the measuring
electrodes;
[0034] FIG. 5 shows the method and the arrangement in an abnormal
situation;
[0035] FIG. 6 shows details of a first measuring rod; and
[0036] FIG. 7 shows details of a second measuring rod.
DETAILED DESCRIPTION
[0037] In the following description, like numbers denote like
elements. It should be appreciated that the illustrated drawings
are not entirely in scale, and that the drawings mainly serve the
purpose of illustrating embodiments of the invention.
[0038] FIGS. 1 and 3 to 5 show a liquid-steam phase digester 100
which comprises a chip screw 102 in an upper portion 101 of the
digester. Feed of the chips into the digester 100 is illustrated
with dashed line arrows. The chips are fed from outside a digesting
volume through an input channel 103, in the height of a steam
phase, to a chip screw 102 which is feeding the chips upwards to a
top 104 of the digester. A motor 105 which is located in the top
104 of the digester is rotating the chip screw 102 which is located
in a screen basket 106. During lifting motion of the chip screw the
liquid which is separated from the chips is lead through the screen
basket 106 to a collecting channel 107 and further outside the
digester (arrow 108 in FIG. 1). The chips are dropping outside the
chip screw 102 from the top 104 of the digester to the digesting
volume.
[0039] The steam phase is extending around the chip screw 102 and
to a steam volume 109 below the chip screw. An upper surface of a
chip layer 111 is called chip surface 110. The boundary surface
between the chip layer 111 and a combined chip and liquor layer 113
is called liquor surface 112.
[0040] The arrangement comprises electrode pairs which are formed
of electrodes and mounted at certain heights and vertically at
distances from each other in the digesting volume of the digester
100, and the electrode pairs are connected to electric circuits 300
such that, during operation of the digester, a current or voltage
value measured in the electric circuit is determining the type of
material layer (for example, steam, chips, combination of chips and
liquor, or liquor) located at certain height, based on electrical
conductivity of the materials in the digesting volume. The electric
circuits 300 are measured by a circuit measuring means 301 to which
preferably the electric circuits of all electrode pairs are
connected.
[0041] Additionally the arrangement comprises an output 302 for
communicating the height information of the chip level 110 and/or
the combined chip and liquor level 113 and/or the liquor level 115
from the circuit measuring means 301 to be exploited in the control
of the digesting process such as when controlling the blow flow;
regulating the bottom scraper rotation speed; regulating the chip
screw rotation speed and/or regulating the material flows of the
digester such as supply of the liquor into the digesting
volume.
[0042] In the method and the arrangement a voltage (preferably a
constant voltage) is regulated between the electrodes of the
electrode pairs forming the measuring circuit which electrodes are
mounted in the digesting volume and the current in the measuring
circuit is measured. Alternatively a constant current can be
supplied to the measuring circuit and the voltage can be measured.
The voltage is preferably constant voltage DC but also pulsed DC or
alternating voltage AC can come into question wherein accruing of
precipitation on the electrodes can be decreased. In the method and
the arrangement the chip surface and the liquor surface height can
be measured by one or more measuring rods 2, 3, 4 based on
electrochemical measurement and mounted in the digester 100.
[0043] In FIGS. 1 and 6 the measuring rod 2 comprises electrodes E
of which two electrodes are connected in the measuring circuit and
placed in the same measuring rod in different heights, for example,
both electrodes E4-E5 in the steam volume 109; and E5-E6 at both
sides of the chip surface 110. Electric properties of a gas or a
mass or a liquid existing in each height of the digesting volume
can be determined with the voltage or current which is connected to
the electrodes E. The surface height of the chips or liquor can be
deduced from the measured properties such as electric conductivity
in a normal operation situation and an abnormal situation wherein
for example liquor can be accrued to a layer above the chips.
[0044] Electrodes E are preferably arranged in an upper part 2' of
the measuring rod 2 in a region of the steam phase of the digesting
volume with larger distances than in a lower part 2'' of the
measuring rod in an actual location region of the mass and the
liquid in a height of the chip layer 111 and the combined chip and
liquor layer 113 (liquid phase). The electrodes which are located
more sparsely, in a height of an unlikely location height of the
mass, are saving costs of the construction. The electrodes E placed
in different heights in the measuring rod 2 are denoted with an
indexing E(1+n), where n=1, which is continuing downwards from top.
For the sake of clarity only a part of the electrodes are named in
the figures.
[0045] The distance between the electrodes is preferably 30 to 40
cm in the upper end 2' of the measuring rod located in the steam
volume (particularly in the upper portion of the steam volume), and
lower than that the distance is smaller. Naturally, the distance
between the electrodes must not be constant in any region of the
measuring rod when the location of the electrodes is known in the
vertical direction of the digesting volume, in order to control the
cooking process based on the measuring results of the surface
heights.
[0046] FIG. 2 shows the method and the arrangement in connection
with the hydraulic digester 200. Feed of the chips into the
digester 200 is illustrated with dashed line arrows. The chips are
fed through an input channel 203 to a chip screw 202 which is
located in an upper portion 201 of the digester 200. The chip screw
202 is feeding the chips downwards from a top 204 of the digester.
A motor 205 which is located in the top 204 of the digester is
rotating the chip screw 202 which is located in a screen basket
206. During rotating motion of the chip screw the liquid which is
separated from the chips is lead through the screen basket 206 to a
collecting channel 207 and further outside the digester (arrow 208
in FIG. 2). The chips are dropping under the chip screw 202 to an
upper portion 209 the digesting volume which is filled with liquor.
An upper surface of a chip layer 111 is called chip surface 110. In
the hydraulic digester there can be found only the upper portion
filled with liquor and a lower portion which is covered with the
combined chip and liquor layer. The chip surface must not rise too
high wherein the digester starts to become blocked. On the other
side the chip surface must not drop too low wherein the capacity of
the cooking process collapses and the quality of the fiber suffers
from the excessive alkali dosage.
[0047] A space 220 through the rotation motor 205 and the chip
screw 202 is arranged in the digester 200 for placing the measuring
rod 2 in the digesting volume on the rotation axis 202' of the chip
screw. The space can exist for the known mechanical surface height
measuring apparatus wherein the digester is easy to rebuild
according to the arrangement of the invention.
[0048] In connection with FIG. 2 it is referred to FIG. 1 where a
corresponding measuring rod 2, electrodes E, electric circuits 300,
measuring means and output 302 are described. The digesting volume
209 in FIG. 2 is deviating from the digesting volume in FIG. 1
below the chip screw 202 in that the digesting volume 209 is filled
with liquid.
[0049] The electrical conductivity in different layers of the
digesting volume changes depending on the conductivity in the
material which is located between the electrodes of the electrode
pair. A closed electric circuit is substantially not generated in
the steam volume 109 (if at least one electrode is in the steam
volume), i.e., there flows no current. There flows current in the
chip layer 111 depending on the amount of liquor in the chips when
a potential difference is generated in the electric circuit. In an
abnormal situation (FIG. 5) the amount of current in the liquor
layer 115 above the chip layer 111 is larger related to the
combined chip and liquor layer 113 because the undiluted fresh
liquor is conducting electricity better than the combined
layer.
[0050] The potential difference to be connected between the
electrode pairs can be about 2V wherein the current in the electric
circuit can be more than 100 mA, maximally about 2 A. The current
is preferably at a mA level when current is supplied to the
electric circuit.
[0051] The examples of arranging one measuring rod and electrode
pairs described in connection with FIGS. 1, 3, 5, 6 and 7 can be
applied also with the hydraulic digester 200 in FIG. 2, preferably
when the measuring rod is placed on the rotation axis of the
feeding screw. Examples of arranging electrodes to pairs are
described in the following.
[0052] In FIG. 1, the electrodes E1 . . . E5 are located in the
steam volume 109, the electrodes E6 . . . E11 in the chip layer 111
below the steam volume and the electrodes E12 . . . E14 are located
in the liquor layer 113 below the chip layer 111. The electrodes
are connected in electric circuits such that there are formed
electrode pairs.
[0053] In FIG. 2, the electrodes E1 . . . E14 are arranged to
electrode pairs corresponding to FIG. 1, for example, E1-E2, in
certain heights vertically at distances from each other such that
the electrodes of the electrode pair connected in one electric
circuit 300 are placed in different heights in the same measuring
rod.
[0054] FIG. 3 shows an example of placing electrodes in two or more
measuring rods 2, 3. Two electrodes A, B which are connected in a
measuring circuit are placed in separate measuring rods 2, 3 in the
same height, for example, the electrodes A2-B2 in the steam volume
109; and A9-B9 in the chip layer 111. Naturally, electrodes located
in two or more measuring rods and connected to the same measuring
circuit can locate in different heights.
[0055] In FIG. 3, the electrodes placed in neighboring measuring
rods 2 and 3 are denoted in the same height in the following way:
in the first measuring rod 2 with an indexing A(1+n), where n=1
which is continuing from above downwards, and in the second
measuring rod 3 with an indexing B(1+n), where n=1 which is
continuing from above downwards.
[0056] In FIG. 3, the electrode pairs A1-B1 . . . A5-B5 are located
in the steam volume 109, the electrode pair A6-B6 in the height of
the chip surface 110, the electrode pairs A7-B7 . . . A11-B11 in
the chip layer 111 and the electrode pairs A12-B12 . . . A14-B14 in
the chip-liquor layer 113 below the chip layer 111.
[0057] FIGS. 4 and 7 show two electrodes which are connected in the
same measuring circuit and placed in the same height in the same
measuring rod, for example, both electrodes C1-D1 in the steam
volume 109.
[0058] In FIG. 4, the neighboring electrodes placed in the same
measuring rod 2 at opposite sides are denoted in the same height
with an indexing C(1+n) and D(1+n) where n=1 which is continuing
from above downwards.
[0059] In FIG. 4, the electrode pairs C1-D1 . . . C5-D5 are located
in the steam volume 109, the electrode pair C6-D6 in the height of
the chip surface 110, the electrode pairs C7-D7 . . . C11-D11 in
the chip layer 111 and the electrode pairs C12-D12 . . . C14-D14 in
the chip-liquor layer 113 below the chip layer 111.
[0060] FIG. 5 shows the method and the arrangement in an abnormal
operation situation of the liquid-steam phase digester 100.
[0061] The surface of the liquor in the digester is risen above the
chip surface wherein the liquor layer is above the chip layer when
the chip layer 111 is sunken abnormally deep inside the liquor. The
situation may arise for example due to disruption in the feed of
the chips what may be caused by a blockage of the input path of the
chips.
[0062] In FIG. 5, the electrodes E1 . . . E4 are located in the
steam volume 109, the electrodes E5 . . . E6 in the liquor layer
114 above the chip-liquor layer 113, the electrodes E7 . . . E14
are located below the chip surface 110.
[0063] Examples of arrangements in which a constant voltage is
regulated in electric circuits which are connected between an
electrode pair, and the current in the electric circuits is
measured is shown in Tables 1 to 4. The voltage can be connected to
all measuring circuits at the same time. It is preferable to
measure the current of the electrode pairs in the arrangement
alternately in suitable time intervals (to poll alternately the
electric circuits of the electrode pairs) for example in intervals
of some seconds. In the measurement can be determined a) if the
current flows or not, and if desired, additionally b) the amount of
the current.
[0064] Table 1 shows the relations of the voltage and the current
when the digester 100 is in the normal state which is shown in FIG.
1.
TABLE-US-00001 electrode pairs, constant voltage current E1-E2 . .
. E5-E6 0 E6-E7. . . E10-E11 small, increases downwards E11-E12
>small E12-E13 . . . largest
[0065] Table 2 shows the relations of the voltage and the current
when the digester 100 is in the normal state which is shown in FIG.
3.
TABLE-US-00002 electrode pairs, constant voltage current A1-B1 . .
. A5-B5 0 A6-B6 ~0 A7-B7 . . . A11-B11 small A12-A12 . . .
largest
[0066] Table 3 shows the relations of the voltage and the current
when the digester 100 is in the normal state which is shown in FIG.
4.
TABLE-US-00003 electrode pairs, constant voltage current C1-D1 . .
. C5-D5 0 C6-D6 ~0 C7-D7 . . . C11-D11 small C12-D12 . . .
largest
[0067] Table 4 shows the relations of the voltage and the current
when the digester 100 is in the abnormal state which is shown in
FIG. 5.
TABLE-US-00004 electrode pairs, constant voltage current E1-E2 . .
. E4-E5 0 E5-E6 . . . E6-E7 largest E7-E8 . . . E10-E11
<previous E11-E12 <previous E12-E13 . . . <previous
[0068] FIG. 6 shows a side view and a top view of a portion of the
measuring rod 2 in more detail. The measuring rod 2 comprises a
body 10, an isolation layer 11 which is surrounding the body and an
electrode E1 outside the isolation layer. Preferably the body is
metal, for example, stainless steel which is suitable in the
circumstances of the digester. The material of the isolation layer
11 can be isolating material polytetrafluoroethylene (PTFE, Teflon)
which is suitable in the circumstances of the digester without
softening too much. FIG. 6 shows a circular single electrode E1
which is preferably of stainless steel and fixed to the body by a
screw 12. An electric wire is leading from the electrode to the
electric circuit 300 inside the body 10.
[0069] FIG. 7 shows a side view and a top view of a portion of the
measuring rod 4 in more detail. The measuring rod 4 comprises the
body 10 and the isolation layer 11 corresponding to FIG. 6.
Additionally the measuring rod comprises in the same height two
electrodes C1 and D1 which are connected to the electric circuit
300 by wires which are lead inside the body. The electrodes shown
in FIG. 7 are designed rounded in their shapes such that they
resist flow marginally what is reducing the precipitation. If
desired, the electrodes comprise above and below chamfers 13.
[0070] The foregoing description provides non-limiting examples of
some embodiments of the invention. It is clear to a person skilled
in the art that the invention is not restricted to details
presented, but that the invention can be implemented in other
equivalent means. Some of the features of the above-disclosed
embodiments may be used to advantage without the use of other
features.
[0071] As such, the foregoing description shall be considered as
merely illustrative of the principles of the invention, and not in
limitation thereof. Hence, the scope of the invention is only
restricted by the appended patent claims.
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