CA1123626A - On-line monitoring of specific surface of mechanical pulps - Google Patents
On-line monitoring of specific surface of mechanical pulpsInfo
- Publication number
- CA1123626A CA1123626A CA327,137A CA327137A CA1123626A CA 1123626 A CA1123626 A CA 1123626A CA 327137 A CA327137 A CA 327137A CA 1123626 A CA1123626 A CA 1123626A
- Authority
- CA
- Canada
- Prior art keywords
- pulp
- specific surface
- measuring
- consistency
- determining
- 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.)
- Expired
Links
Classifications
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
- D21F1/00—Wet end of machines for making continuous webs of paper
- D21F1/66—Pulp catching, de-watering, or recovering; Re-use of pulp-water
- D21F1/68—Pulp catching, de-watering, or recovering; Re-use of pulp-water using hydrocyclones
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
- D21F7/00—Other details of machines for making continuous webs of paper
- D21F7/06—Indicating or regulating the thickness of the layer; Signal devices
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume, or surface-area of porous materials
- G01N15/06—Investigating concentration of particle suspensions
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume, or surface-area of porous materials
- G01N15/08—Investigating permeability, pore-volume, or surface area of porous materials
Abstract
ON-LINE MONITORING OF SPECIFIC SURFACE
OF MECHANICAL PULPS
ABSTRACT OF DISCLOSURE
The specific surface distribution of a pulp may be obtained by fractionating the pulp in a hydrocyclone means into an overflow and an underflow fraction and measuring the specific surface of each of the fractions and the amount of each of the fractions and based on a cumulative normal distribution relationship of cumulative weight fraction as a percent of feed to specific surface, determining the specific surface distribution for said pulp.
Also disclosed is a method and apparatus for determining the specific surface of a pulp sample by measuring the light scattering characteristics to obtain a turbidity measurement of the pulp sample, measuring the consistency of the sample and determining the specific surface of said pulp based on the relationship of specific surface to the turbidity measurement for the measured consistency of the pulp.
OF MECHANICAL PULPS
ABSTRACT OF DISCLOSURE
The specific surface distribution of a pulp may be obtained by fractionating the pulp in a hydrocyclone means into an overflow and an underflow fraction and measuring the specific surface of each of the fractions and the amount of each of the fractions and based on a cumulative normal distribution relationship of cumulative weight fraction as a percent of feed to specific surface, determining the specific surface distribution for said pulp.
Also disclosed is a method and apparatus for determining the specific surface of a pulp sample by measuring the light scattering characteristics to obtain a turbidity measurement of the pulp sample, measuring the consistency of the sample and determining the specific surface of said pulp based on the relationship of specific surface to the turbidity measurement for the measured consistency of the pulp.
Description
z~
FIELD OF INVENTION
The present invention relates to a method and apparatus for on-line monitoring of specific surface of a mechanical pulp. More specifically, the present invention relates to a method and apparatus for determining the cumulative distribution by weight of specific surface of a pulp.
By the term "mechanical pulps" is understood pulps produced primarily by mechanical processing with or without auxillary steps of chemical or physical nature. Such pulps include conventional (stone) ground wood and refiner ground-wood and pulps produced by an array of chemi-mechanical or thermo-mechanical processes.
It has been shown in the art that the fibre properties for mechanical pulp that determine the strength, optical and printing characteristics include amon~st other things (a~ the average specific surface of ~he fibres which is important in determining the strength properties of mechanical pulp (i.e. tear, tensile, burst, wet web, etc) and some printing properties such as strike-through, ink absorptivity and which also influences significantly the opacity and brightness of the paper and (b) specific surface distribution of the fibres which affects printing characteristics such as linting.
It has been proposed to determine specific surface of a pulp, on-line using at least two measuring techniques which measure other characteristics of the pulp but wherein each measurement is influenced by specific surface and by solving simultaneous equations to obtain indication of the specific surface of the pulp. This procedure was further complicated by the fact that the technique for measuring consistency also was not a true measurement and further reflected the characteristics of specific surface so the . , .
~ 3~6 three simultaneous equations had to be solved in order to ~ termine ~he specific surface (average speci~ic surfao~ of the pulp, Such a technique is desoribed in the ~.S. patent 3,802,9~4 issued ~n April 9, 1974 to Forgacs and Karnis.
Nost measurements of specific surface utilize the permeability method, hcwever such methods are not well suited for on-line measurements.
BRIE~ DESCRIPTION OF TEE INVENTION
It is an object of the present invention to provide a method and apparatus for on-line determination o~ the average specific surface and~or the specific surface distribution of a pulp~
i It is yet another object of the present invention to provide an optical system for on~line determining the specific surface of a pulp.
Broadly the present invention also relates to a method and apparatus for determining the fibre specific surface distribution by weight of a pulp comprising:
hydrocyclone meens for separating pulp fed thereto into an over~low ~rec.ion and underflow Eraction, means for measuring the specific surface and means for measuring the amount of fibre flow of pulp of at least a selected t~ of said pulp feed and each of said fractions, d~termining the s~eci~ic surrace distribution of said pulp fed to said l~ hydrocyclone means based on said measured flow o~ pulp aQd speciLic sur4aces of said selected ~o of said feed, said underflow and said overflow fractions and a c~mulative normal distrihution relationship of cumulative weLght ~r-ction as a percent of eed to specific surf2ce~ -The present invention als~ broadly relates to a process for on-line determination of the specific surface of a Qulp suspension which comprises m~asuring the light scattering characteristics of the pulp suspension and .
. ~ .
~Z36;~6 thereby obtaining a measurement of the turbidity of said suspension, measuring the consistency of said suspension and determining the average specific surface of said pulp suspension based on the relationship of specific surface to the turbidity reading for the measured consistency.
BRIEF DESCRIPTION OF THE DRAWINGS
Further features, objects and advantages will be evident from the following detailed description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings and which:
Figure 1 is a schematic illustration of the monitoring system of the present invention.
Figure 2 is a plot of specific surface in meters squared per gram vs the turbidity meter reading in Jackson Turbidity Units (JTU) showing the effect of consistency change on the relationship of specific surface to the turbidity meter reading.
Figure 3 is a schematic diagram of a turbidity meter.
Figure 4 is plot of cumulative weight fraction as a percent o~ feed vs specific surface in meters square per gram on normal probability paper.
DETAILE~ DESCRIPTION OF THE PREFERRED EMBODIMENTS
As shown in Figure 1 a pulp sample bled from the mechanical pulping process enters the system by line 10 and depending on the point in the mechanical pulping arrangement from which the sample is taken, it passes through a latency removal device 12 and then enters the container 14 via the line 16.
A suitable principle for liberating the la~ent properties in mechanical pulp relatively quickly is used in a laboratory disintegrator sold under the name Domtar Disintegrator by Noram Quality Control and Research ~I~LZ3~6 Equipment Ltd This device releases the latent properties of a mechanical pulp by rapidly recirculating the pulp through a centrifugal pump (the pulp being at a temperature of about 90~-95C).
Pulp from the container 14 is pumped via pump 18 to consistency meter 20 and is returned to the containPr 14 via line 22.
The requirements of a consistency meter 20 for use in an on-line monitoring system are such ~hat it should measure consistency independent of other ~ibre properties (i.e. fibre length and specific surface) and should be capable of measuring absolute consistencies with an accuracy and reproducibility within + 5% of the absolute valueO Thus in consistency meters for use in the present invention the principle for consistency determination should be a direct one, namely it should be based on the definition of consistency. Most consistency meters measure consistency indirectly i.e. they measure other pulp properties, such as, resistance to flow, dielectric properties of the pulp suspension etc., which are related to consistency as well as other fibre properties.
Techniques have been proposed for determining consistency of a pulp free of other characteristics of the pulp by sensing directly the density of the pulp slurry.
For example, Thiessen and Dagg proposed sensing the vibrations resulting from an inbalanced rotor to determine the density of a liquid compared with a control liquid using a rotating sample container and determining the imbalance of the system (see Pulp & Paper Magazine of Canada, September 1959)-It is also proposed to use a Sperry Gravitymasterto determine consistency directly independent of other pulp properties. This device uses a gravity balance technique to ~` .
~ ~ ~2 determine the changing weigh~ o~ the given size sample~
~See Measurement and Control Vol. 1 Nov. 11, 1968 pages T179 to T186) Neither of the above two devices are believed to cùrrently be available on ~he market.
If one is to measure consistency directly using either of the above techniques or the one proposed hereinbelow it is essential that the sample be substantially free of or contain known quantities of extraneous matter, in particular there be no air in the sample and any extraneous material with the fibres (fillers etc.) be accurately known before the consistency can be determined. Also it is important that the temperature be accurately controlled or known since a change in temperature will change the accuracy of the instrument although the instrument can be calibrated for different temperatures.
It has now been found that an instrument known as a density cell such as that sold under -Dynatrol--Cl-lOHY (TM) manufactured by Automatic Products, Houston, Texas can provide a very accurate indication of consistency independent of other pulp properties. This device measures the change in frequency of a vibrating tube through which the pulp suspension is continuously passed and thereby a continuous indication of the consistency of the stock is obtainable for stock consistencies in the range.of about 0.1 to 1.5% which is the consistency range in which the present invention operates.
- The consistency meter 20 measures a consistency of the stock in the container 14 and preferably adjusts the water (essentially free of fibre and.other solids (input through line 24 via control valve 26 to maintain the coosistency of the stock in the container 14 substantially constant.
~L123~
The dash lines used in Figure 1 indicate control lines from the various instrumentalities to the various elements controlled and to the master control 28.
~ t will be noted that the consistency me~er 20 is connected to the valve 26 via control line 30 and to the master control 28 via line 32. In the event that the consistency in the tank 14 is always maintained constant, the control line 32 may be omitted since it will not be variable in the system.
Stock in the tank 14 is also circulated via a pump 34 through a specific surface meter 36 and returned to the tank 14 via line 38. The specific surface me~er 36 directs a signal to the master control 28 via the control line 40.
This provides the average specific surface of the pulp.
SPECIFIC SURFACE MEASUREMENT
Generally, specific surface meters use the perme-ability method to determine specific surface, however, such a method is not particulàrly suited for on-line measurementO
A more suitable means for measuring specific surface has been found utilizing an optical method that senses scattered light from a pulp sample i.e. a device known as a turbidity meter which is normally used to determine solids concentration in a slurry. The ligh~
scattered from an assembly of pulp fibres in the pulp ~ample may be considered to be proportional to the number of particles per unit volume of suspension and their area i.e.
T = KNA
Where T is the amount of scattered light (meter reading) K = a constant dependent on refractive index of the fibres and their size relative to the wavelength of the light used, N = number of particles, and A - average area of a particle. The consistency of the stock is C = Nm where m is the average mass of a particle, thus ; T = KC(A) m and the term A is the area per unit mass, i~e.
m the specific surface of the particle, therefore, ~ = RC (SS)g or (SS)g = T
(SS)g is the average speci~ic surface of the fibre network.
The subscript (g) is used to denote a geometric specific surface or light scattering area, in contrast to the hydrodynamic specific surface measured by the permeability method. However, these two specific surfaces, while they are not necessarily the same numerically have a definite correlation between them.
For 130 pulp samples which included~ stone groundwood, refiner and thermomechanical pulps, chemical pulps and mixturPs of ~hemical fibres with stone groundwood the experimental results were correlated with the following regression equation.
(SS) = 8.92 x 10 7 ~JTU)1.77 (Cg)-2~16 2 where (SS) is the average (hydrodynamic) specific surface in meters squared per gram, JTU is the turbidity meter reading in Jackson turbidity units and Cg is the consistency in ~
R2 - the Coefficient of Determination for equation 2 is 0~88 indicating that 88~ of the variations of specific surface is explained by variations in JTU and C~
Fi~ure 2 is a plo~ of equation 2 at different consistencies showing the relationship found between specific surface and the turbidity meter rPading. It will be apparent that the turbidity meter provides a good, easy and quickly operating technique for determining the specific surface of a pulp sample.
.~
3~2~ii The light scattering property of the pulp can be measured by a commercially available turbidity meter, th~
specific model used in the present.invention is a DRT-1000 on-line turbidity meter manufactured by HF Instruments, Bolton, Ontario. Turbidity meters generally pass a light beam through a suspension and measure the scattered light on opposite sides of the light beam (at an angle of 90 to the beam) as well as the light projected through the suspension (in line with the light beam).
Figure 3 has schematically illustrated a Turbidity Meter which is provided with a light source 200, passing light through a lens 202 and through a sample 204 continuously passing through the transparent pipe section or tube 206. Three detectors 208, 210 and 212 are arranged to detect the light reflected from and passing through the sample i.e. the detectors 208 and 210 detect the amount of reflected or scattered light on opposite sides of the sample and the detector 212 detects light trans~itted th~ough the sample. The light source 200, pipe 206 and detector 212 are on a straight line and the detectors 208 and 210 and pipe 206 are also positioned on a straight line with the two lines so formed being substantially mutually perpendicularO
The specific surface meters used in the present invention such as meter 36 are in fact turbidity meters which are operated in conjunction with a consistency meter (or a fixed consistency) to determine the specific surface of the pulp fraction or feed pulp based on the curves such as those shown in Figure 2~
The consistency meter 20 and specific surface meter 36 (turbidimeter), describe the consistency and specific surface of the feed pulp.
SPECIFIC SURFACE DISTRIBUTION
The pulp is pumped by pump 34 through line 40 to _ g _ ~s"~.
3~'~
the specific surface measuring instrumentalities generally indicated at 42 and which include a hydrocyclone 44 having an overflow (base) outlet line 46 and an underflow (apex) outlet line 48. Consistency meter 50, ~peci~ic surface meter 52, (turbidity meter)~ and flow meter 54 measure ; respectively the consistency, speci~ic sur~ace and rate of ~low of fib~e through the overflow outlet line 96. The outputs from these meters are fed via lines 56, 58 and 60 respectively to the master controller 28 and the stock in line 46 is re~urned to the system via line 62.
The consistency and specific surface of the underflow fraction in line 48 may also be measured by the consistency meter 64 and the specific surface meter 66 (turbidity meter)O The outputs ~rom these meters are fed via lines 68 and 70 respectively to the master controller 28 and the stock in line 48 is returned to the system via line 62.
Flow to the instrumentalities 42 and in particular to the hydrocyclone 44 is controlled via the control flow meter 72 which via line 74 controls the valve 76 and thus the flow through line 40.
The flow meter output may be connected to the master controller 28 via line 78 but obviously if flow to the hydrocyclone 44 is maintained substantially constant there needn't be a direct input from the flow meter 72 to the master con~rol 28.
The consistency in line 4a or 46 can be calculated since the consistency and flow of the stock entering the system is known and the consistency and flow stock in the line 46 or 48 is determined.
The instrumentalities 42 input the master controller 28 with the specific surface and weight fraction of the overflow and underflow fraction and the specif ic 362$
the range can be obtained as well as the low speci~ic surface fraction of the pulp which is important for determining lintingO
Alternatively or as a check the specific surface of the feed as measured by meters 36 and 20 and its flow (meter 72) and the specific surface of the overflow measured by meter 62 and 60 and its flow (meter 64) (or the underflow fraction line 48) may be used to obtain the required points on the curve. Any two of the underflow, overflow or feed may be measured to obtain the required two points from a material balance of the hydrocyclone.
It will be apparent that the specific surface distribution and average specific surface of the pulp is obtainable using the (or selected ones of the) instrumentalities 42 and that the pulp sample used to determine these parameters is returned to the system via lines 46 and 48 which connect with line 62.
Modification may be made without departing from the spirit of the invention as defined in the appended claims.
.
~ L~3~ 2~
surface of the feed pulp is provided via meter 36.
A laboratory method of determining specific surface distribution employs a hydrocyclone means in which the sample is cascaded and the weight fractions and specific surface of the various underflow and/or overflow fractions are measured, thereby to determine the distribution curve of the fibres specific surface. When such data for a mechanical pulp or chemi-mechanical pulp is plotted on cumulative normal probabili~y paper as cumulative specific surface fraction by weight as a percentage of feed vs specific surface it has been found that they approximate a straight line relationship over the significant range of the specific surfaces of the fibres in the pulp. In principle then, only two points are needed to determine the entire fibre specific surface distribution over the range.
Typical cumulative probability curves of specific surface are shown in figure 3~ These curves were developed from lab data and show the accurate linear relationship of cumulative specific surface fraction as a percent of feed vs specific surface plotted on the cumulative probability paper. The hollow and solid circles designate two different thermo-mechanical pulps and the hollow and solid triangles two different groundwood pulps.
In the specific on-line sensor of the present invention, the hydrocyclone 44 had a major diameter of 51 mm and was equipped with a 7.9 mm underflow opening. The flow, consistency and specific surface (turbidity) of the feed, underflow and overflow fractions are measured (or calculated) using the input to the master controller 28 from the consistency meter 20, flow meter 7~, consistency meter 50, specific surface meter 52, flow meter 54, consistency meter 64 and specific surface meter 66. Using the straight line relationship the distribution of specific surface over `~
`' `2~
FIELD OF INVENTION
The present invention relates to a method and apparatus for on-line monitoring of specific surface of a mechanical pulp. More specifically, the present invention relates to a method and apparatus for determining the cumulative distribution by weight of specific surface of a pulp.
By the term "mechanical pulps" is understood pulps produced primarily by mechanical processing with or without auxillary steps of chemical or physical nature. Such pulps include conventional (stone) ground wood and refiner ground-wood and pulps produced by an array of chemi-mechanical or thermo-mechanical processes.
It has been shown in the art that the fibre properties for mechanical pulp that determine the strength, optical and printing characteristics include amon~st other things (a~ the average specific surface of ~he fibres which is important in determining the strength properties of mechanical pulp (i.e. tear, tensile, burst, wet web, etc) and some printing properties such as strike-through, ink absorptivity and which also influences significantly the opacity and brightness of the paper and (b) specific surface distribution of the fibres which affects printing characteristics such as linting.
It has been proposed to determine specific surface of a pulp, on-line using at least two measuring techniques which measure other characteristics of the pulp but wherein each measurement is influenced by specific surface and by solving simultaneous equations to obtain indication of the specific surface of the pulp. This procedure was further complicated by the fact that the technique for measuring consistency also was not a true measurement and further reflected the characteristics of specific surface so the . , .
~ 3~6 three simultaneous equations had to be solved in order to ~ termine ~he specific surface (average speci~ic surfao~ of the pulp, Such a technique is desoribed in the ~.S. patent 3,802,9~4 issued ~n April 9, 1974 to Forgacs and Karnis.
Nost measurements of specific surface utilize the permeability method, hcwever such methods are not well suited for on-line measurements.
BRIE~ DESCRIPTION OF TEE INVENTION
It is an object of the present invention to provide a method and apparatus for on-line determination o~ the average specific surface and~or the specific surface distribution of a pulp~
i It is yet another object of the present invention to provide an optical system for on~line determining the specific surface of a pulp.
Broadly the present invention also relates to a method and apparatus for determining the fibre specific surface distribution by weight of a pulp comprising:
hydrocyclone meens for separating pulp fed thereto into an over~low ~rec.ion and underflow Eraction, means for measuring the specific surface and means for measuring the amount of fibre flow of pulp of at least a selected t~ of said pulp feed and each of said fractions, d~termining the s~eci~ic surrace distribution of said pulp fed to said l~ hydrocyclone means based on said measured flow o~ pulp aQd speciLic sur4aces of said selected ~o of said feed, said underflow and said overflow fractions and a c~mulative normal distrihution relationship of cumulative weLght ~r-ction as a percent of eed to specific surf2ce~ -The present invention als~ broadly relates to a process for on-line determination of the specific surface of a Qulp suspension which comprises m~asuring the light scattering characteristics of the pulp suspension and .
. ~ .
~Z36;~6 thereby obtaining a measurement of the turbidity of said suspension, measuring the consistency of said suspension and determining the average specific surface of said pulp suspension based on the relationship of specific surface to the turbidity reading for the measured consistency.
BRIEF DESCRIPTION OF THE DRAWINGS
Further features, objects and advantages will be evident from the following detailed description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings and which:
Figure 1 is a schematic illustration of the monitoring system of the present invention.
Figure 2 is a plot of specific surface in meters squared per gram vs the turbidity meter reading in Jackson Turbidity Units (JTU) showing the effect of consistency change on the relationship of specific surface to the turbidity meter reading.
Figure 3 is a schematic diagram of a turbidity meter.
Figure 4 is plot of cumulative weight fraction as a percent o~ feed vs specific surface in meters square per gram on normal probability paper.
DETAILE~ DESCRIPTION OF THE PREFERRED EMBODIMENTS
As shown in Figure 1 a pulp sample bled from the mechanical pulping process enters the system by line 10 and depending on the point in the mechanical pulping arrangement from which the sample is taken, it passes through a latency removal device 12 and then enters the container 14 via the line 16.
A suitable principle for liberating the la~ent properties in mechanical pulp relatively quickly is used in a laboratory disintegrator sold under the name Domtar Disintegrator by Noram Quality Control and Research ~I~LZ3~6 Equipment Ltd This device releases the latent properties of a mechanical pulp by rapidly recirculating the pulp through a centrifugal pump (the pulp being at a temperature of about 90~-95C).
Pulp from the container 14 is pumped via pump 18 to consistency meter 20 and is returned to the containPr 14 via line 22.
The requirements of a consistency meter 20 for use in an on-line monitoring system are such ~hat it should measure consistency independent of other ~ibre properties (i.e. fibre length and specific surface) and should be capable of measuring absolute consistencies with an accuracy and reproducibility within + 5% of the absolute valueO Thus in consistency meters for use in the present invention the principle for consistency determination should be a direct one, namely it should be based on the definition of consistency. Most consistency meters measure consistency indirectly i.e. they measure other pulp properties, such as, resistance to flow, dielectric properties of the pulp suspension etc., which are related to consistency as well as other fibre properties.
Techniques have been proposed for determining consistency of a pulp free of other characteristics of the pulp by sensing directly the density of the pulp slurry.
For example, Thiessen and Dagg proposed sensing the vibrations resulting from an inbalanced rotor to determine the density of a liquid compared with a control liquid using a rotating sample container and determining the imbalance of the system (see Pulp & Paper Magazine of Canada, September 1959)-It is also proposed to use a Sperry Gravitymasterto determine consistency directly independent of other pulp properties. This device uses a gravity balance technique to ~` .
~ ~ ~2 determine the changing weigh~ o~ the given size sample~
~See Measurement and Control Vol. 1 Nov. 11, 1968 pages T179 to T186) Neither of the above two devices are believed to cùrrently be available on ~he market.
If one is to measure consistency directly using either of the above techniques or the one proposed hereinbelow it is essential that the sample be substantially free of or contain known quantities of extraneous matter, in particular there be no air in the sample and any extraneous material with the fibres (fillers etc.) be accurately known before the consistency can be determined. Also it is important that the temperature be accurately controlled or known since a change in temperature will change the accuracy of the instrument although the instrument can be calibrated for different temperatures.
It has now been found that an instrument known as a density cell such as that sold under -Dynatrol--Cl-lOHY (TM) manufactured by Automatic Products, Houston, Texas can provide a very accurate indication of consistency independent of other pulp properties. This device measures the change in frequency of a vibrating tube through which the pulp suspension is continuously passed and thereby a continuous indication of the consistency of the stock is obtainable for stock consistencies in the range.of about 0.1 to 1.5% which is the consistency range in which the present invention operates.
- The consistency meter 20 measures a consistency of the stock in the container 14 and preferably adjusts the water (essentially free of fibre and.other solids (input through line 24 via control valve 26 to maintain the coosistency of the stock in the container 14 substantially constant.
~L123~
The dash lines used in Figure 1 indicate control lines from the various instrumentalities to the various elements controlled and to the master control 28.
~ t will be noted that the consistency me~er 20 is connected to the valve 26 via control line 30 and to the master control 28 via line 32. In the event that the consistency in the tank 14 is always maintained constant, the control line 32 may be omitted since it will not be variable in the system.
Stock in the tank 14 is also circulated via a pump 34 through a specific surface meter 36 and returned to the tank 14 via line 38. The specific surface me~er 36 directs a signal to the master control 28 via the control line 40.
This provides the average specific surface of the pulp.
SPECIFIC SURFACE MEASUREMENT
Generally, specific surface meters use the perme-ability method to determine specific surface, however, such a method is not particulàrly suited for on-line measurementO
A more suitable means for measuring specific surface has been found utilizing an optical method that senses scattered light from a pulp sample i.e. a device known as a turbidity meter which is normally used to determine solids concentration in a slurry. The ligh~
scattered from an assembly of pulp fibres in the pulp ~ample may be considered to be proportional to the number of particles per unit volume of suspension and their area i.e.
T = KNA
Where T is the amount of scattered light (meter reading) K = a constant dependent on refractive index of the fibres and their size relative to the wavelength of the light used, N = number of particles, and A - average area of a particle. The consistency of the stock is C = Nm where m is the average mass of a particle, thus ; T = KC(A) m and the term A is the area per unit mass, i~e.
m the specific surface of the particle, therefore, ~ = RC (SS)g or (SS)g = T
(SS)g is the average speci~ic surface of the fibre network.
The subscript (g) is used to denote a geometric specific surface or light scattering area, in contrast to the hydrodynamic specific surface measured by the permeability method. However, these two specific surfaces, while they are not necessarily the same numerically have a definite correlation between them.
For 130 pulp samples which included~ stone groundwood, refiner and thermomechanical pulps, chemical pulps and mixturPs of ~hemical fibres with stone groundwood the experimental results were correlated with the following regression equation.
(SS) = 8.92 x 10 7 ~JTU)1.77 (Cg)-2~16 2 where (SS) is the average (hydrodynamic) specific surface in meters squared per gram, JTU is the turbidity meter reading in Jackson turbidity units and Cg is the consistency in ~
R2 - the Coefficient of Determination for equation 2 is 0~88 indicating that 88~ of the variations of specific surface is explained by variations in JTU and C~
Fi~ure 2 is a plo~ of equation 2 at different consistencies showing the relationship found between specific surface and the turbidity meter rPading. It will be apparent that the turbidity meter provides a good, easy and quickly operating technique for determining the specific surface of a pulp sample.
.~
3~2~ii The light scattering property of the pulp can be measured by a commercially available turbidity meter, th~
specific model used in the present.invention is a DRT-1000 on-line turbidity meter manufactured by HF Instruments, Bolton, Ontario. Turbidity meters generally pass a light beam through a suspension and measure the scattered light on opposite sides of the light beam (at an angle of 90 to the beam) as well as the light projected through the suspension (in line with the light beam).
Figure 3 has schematically illustrated a Turbidity Meter which is provided with a light source 200, passing light through a lens 202 and through a sample 204 continuously passing through the transparent pipe section or tube 206. Three detectors 208, 210 and 212 are arranged to detect the light reflected from and passing through the sample i.e. the detectors 208 and 210 detect the amount of reflected or scattered light on opposite sides of the sample and the detector 212 detects light trans~itted th~ough the sample. The light source 200, pipe 206 and detector 212 are on a straight line and the detectors 208 and 210 and pipe 206 are also positioned on a straight line with the two lines so formed being substantially mutually perpendicularO
The specific surface meters used in the present invention such as meter 36 are in fact turbidity meters which are operated in conjunction with a consistency meter (or a fixed consistency) to determine the specific surface of the pulp fraction or feed pulp based on the curves such as those shown in Figure 2~
The consistency meter 20 and specific surface meter 36 (turbidimeter), describe the consistency and specific surface of the feed pulp.
SPECIFIC SURFACE DISTRIBUTION
The pulp is pumped by pump 34 through line 40 to _ g _ ~s"~.
3~'~
the specific surface measuring instrumentalities generally indicated at 42 and which include a hydrocyclone 44 having an overflow (base) outlet line 46 and an underflow (apex) outlet line 48. Consistency meter 50, ~peci~ic surface meter 52, (turbidity meter)~ and flow meter 54 measure ; respectively the consistency, speci~ic sur~ace and rate of ~low of fib~e through the overflow outlet line 96. The outputs from these meters are fed via lines 56, 58 and 60 respectively to the master controller 28 and the stock in line 46 is re~urned to the system via line 62.
The consistency and specific surface of the underflow fraction in line 48 may also be measured by the consistency meter 64 and the specific surface meter 66 (turbidity meter)O The outputs ~rom these meters are fed via lines 68 and 70 respectively to the master controller 28 and the stock in line 48 is returned to the system via line 62.
Flow to the instrumentalities 42 and in particular to the hydrocyclone 44 is controlled via the control flow meter 72 which via line 74 controls the valve 76 and thus the flow through line 40.
The flow meter output may be connected to the master controller 28 via line 78 but obviously if flow to the hydrocyclone 44 is maintained substantially constant there needn't be a direct input from the flow meter 72 to the master con~rol 28.
The consistency in line 4a or 46 can be calculated since the consistency and flow of the stock entering the system is known and the consistency and flow stock in the line 46 or 48 is determined.
The instrumentalities 42 input the master controller 28 with the specific surface and weight fraction of the overflow and underflow fraction and the specif ic 362$
the range can be obtained as well as the low speci~ic surface fraction of the pulp which is important for determining lintingO
Alternatively or as a check the specific surface of the feed as measured by meters 36 and 20 and its flow (meter 72) and the specific surface of the overflow measured by meter 62 and 60 and its flow (meter 64) (or the underflow fraction line 48) may be used to obtain the required points on the curve. Any two of the underflow, overflow or feed may be measured to obtain the required two points from a material balance of the hydrocyclone.
It will be apparent that the specific surface distribution and average specific surface of the pulp is obtainable using the (or selected ones of the) instrumentalities 42 and that the pulp sample used to determine these parameters is returned to the system via lines 46 and 48 which connect with line 62.
Modification may be made without departing from the spirit of the invention as defined in the appended claims.
.
~ L~3~ 2~
surface of the feed pulp is provided via meter 36.
A laboratory method of determining specific surface distribution employs a hydrocyclone means in which the sample is cascaded and the weight fractions and specific surface of the various underflow and/or overflow fractions are measured, thereby to determine the distribution curve of the fibres specific surface. When such data for a mechanical pulp or chemi-mechanical pulp is plotted on cumulative normal probabili~y paper as cumulative specific surface fraction by weight as a percentage of feed vs specific surface it has been found that they approximate a straight line relationship over the significant range of the specific surfaces of the fibres in the pulp. In principle then, only two points are needed to determine the entire fibre specific surface distribution over the range.
Typical cumulative probability curves of specific surface are shown in figure 3~ These curves were developed from lab data and show the accurate linear relationship of cumulative specific surface fraction as a percent of feed vs specific surface plotted on the cumulative probability paper. The hollow and solid circles designate two different thermo-mechanical pulps and the hollow and solid triangles two different groundwood pulps.
In the specific on-line sensor of the present invention, the hydrocyclone 44 had a major diameter of 51 mm and was equipped with a 7.9 mm underflow opening. The flow, consistency and specific surface (turbidity) of the feed, underflow and overflow fractions are measured (or calculated) using the input to the master controller 28 from the consistency meter 20, flow meter 7~, consistency meter 50, specific surface meter 52, flow meter 54, consistency meter 64 and specific surface meter 66. Using the straight line relationship the distribution of specific surface over `~
`' `2~
Claims (7)
1. A method for on-line determining the fibre specific surface distribution by weight of a pulp comprising, continu-ously separating a feed sample of said pulp in a hydrocyclone means into an overflow fraction and an underflow fraction measuring the parameters of at least two of said feed and each of said fractions required to determine their fibre mass flow rates and average specific surfaces, determining the said fibre mass flow rate and average specific surfaces, determin-ing the specific surface distribution by weight of said feed sample based on said mass flow rates and the specific surfaces of said at least two of said feed and said fractions and a substantially cumulative normal distribution relation-ship for said pulp of cumulative specific surface fraction as a % by weight of feed to specific surface.
2. An apparatus for determining the fibre specific surface distribution by weight of a pulp comprising, hydro-cyclone means having an overflow outlet and an underflow outlet, means for feeding said pulp to said hydrocyclone means thereby to fractionate said pulp into an underflow fraction and an overflow fraction, means for measuring the parameters of at least two of said feed, said overflow and said underflow fractions required to determine their fibre mass rates and average specific surfaces, means for determining said fibre mass flow rates and average specific surfaces, computing means for determining the fibre specific surface distribution of said pulp based on said fibre mass flow rates and specific surfaces and a cumulative normal distribution relationship for said pulp of cumulative specific surface fraction as a percent by weight of feed to specific surfaces.
3. An apparatus as defined in claim 2 wherein said means for measuring said parameters each comprises means for measuring the rate of flow and means for measuring the the consistency of the pulp being measured, said means for measuring consistency providing a measure of consistency substantially independent of other characteristics of the pulp.
4. An apparatus as defined in claim 2 wherein each of said means for measuring specific surface comprises means for measuring the consistency substantially independent of other characteristics of the pulp and means for measuring the turbidity of the pulp being measured.
5. An apparatus as defined in claim 4 wherein said means for measuring turbidity includes means for measuring scattered light reflected from the pulp being measured.
6. An apparatus as defined in claim 4 wherein said means for measuring specific surface further comprises means for determining said specific surface based on a predeter-mined relationship of measured turbidity and consistency to specific surface.
7. An apparatus as defined in claim 5 wherein each said means to measure said parameters include means to measure the rate of flow and means to measure the consistency of the pulp being measured, and said means for measuring consist-ency measures consistency substantially independent of other characteristics of the pulp.
Priority Applications (5)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA327,137A CA1123626A (en) | 1979-05-08 | 1979-05-08 | On-line monitoring of specific surface of mechanical pulps |
| AU57994/80A AU539306B2 (en) | 1979-05-08 | 1980-05-01 | Monitoring pulp surface characteristics |
| FI801476A FI71617C (en) | 1979-05-08 | 1980-05-07 | DIRECTIVE REQUIREMENTS SPECIFIC TO THE MECHANICAL MASSOR. |
| SE8003413A SE437043B (en) | 1979-05-08 | 1980-05-07 | SET FOR LINE DETERMINATION OF THE KEY DISTRIBUTION OF THE SPECIFIC SURFACE OF THE FIBERS IN A MASS AND DEVICE FOR IMPLEMENTATION OF THE SET |
| JP6119080A JPS55152440A (en) | 1979-05-08 | 1980-05-08 | Online measuring method of and apparatus for specific area of mechanically produced pulp |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA327,137A CA1123626A (en) | 1979-05-08 | 1979-05-08 | On-line monitoring of specific surface of mechanical pulps |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1123626A true CA1123626A (en) | 1982-05-18 |
Family
ID=4114157
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA327,137A Expired CA1123626A (en) | 1979-05-08 | 1979-05-08 | On-line monitoring of specific surface of mechanical pulps |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPS55152440A (en) |
| AU (1) | AU539306B2 (en) |
| CA (1) | CA1123626A (en) |
| FI (1) | FI71617C (en) |
| SE (1) | SE437043B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5500735A (en) * | 1994-07-18 | 1996-03-19 | Pulp And Paper Research Institute Of Canada | Method and apparatus for on-line measurement of pulp fiber surface development |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| SE442247B (en) * | 1984-02-14 | 1985-12-09 | Svenska Traeforskningsinst | DEVICE FOR IN A SUSPENSION WITH ATMINSTONE TWO TYPES OF SUSPENDED SUBSTANCES WERE FOR THE META CONTENT OF EACH SUBJECT TYPE |
| JPH0677013B2 (en) * | 1984-10-31 | 1994-09-28 | 大成建設株式会社 | Geological survey method |
| FI126688B (en) * | 2014-06-30 | 2017-03-31 | Upm Kymmene Corp | Method and apparatus for controlling the quality of nanofibrillar cellulose |
-
1979
- 1979-05-08 CA CA327,137A patent/CA1123626A/en not_active Expired
-
1980
- 1980-05-01 AU AU57994/80A patent/AU539306B2/en not_active Ceased
- 1980-05-07 FI FI801476A patent/FI71617C/en not_active IP Right Cessation
- 1980-05-07 SE SE8003413A patent/SE437043B/en not_active IP Right Cessation
- 1980-05-08 JP JP6119080A patent/JPS55152440A/en active Pending
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5500735A (en) * | 1994-07-18 | 1996-03-19 | Pulp And Paper Research Institute Of Canada | Method and apparatus for on-line measurement of pulp fiber surface development |
Also Published As
| Publication number | Publication date |
|---|---|
| AU539306B2 (en) | 1984-09-20 |
| FI801476A (en) | 1980-11-09 |
| AU5799480A (en) | 1980-11-13 |
| SE8003413L (en) | 1980-11-09 |
| SE437043B (en) | 1985-02-04 |
| FI71617C (en) | 1987-01-19 |
| JPS55152440A (en) | 1980-11-27 |
| FI71617B (en) | 1986-10-10 |
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