WO2001075228A1

WO2001075228A1 - Apparatus and method for measuring pulp quality

Info

Publication number: WO2001075228A1
Application number: PCT/NZ2001/000049
Authority: WO
Inventors: Geoffrey Graeme Duffy
Original assignee: Auckland Uniservices Limited
Priority date: 2000-04-03
Filing date: 2001-04-03
Publication date: 2001-10-11
Also published as: AU2001252783A1

Abstract

An apparatus for measuring and controlling characteristics of pulp within a pulp slurry is provided. The apparatus includes a detector (6) to detect a mechanistic characteristic of the pulp slurry, for example the heat transfer coefficient. A pumping means (3) is provided to maintain a pulp slurry flow past the detector (6). The flow rate may be measured by a flow meter (5). The flow rate and/or concentration of the slurry may be maintained at a substantially constant predetermined level.

Description

APPARATUS AND METHOD FOR MEASURING PULP QUALITY

Technical Field

This invention relates to apparatus and method(s) for measuring the quality of pulp and in particular but not exclusively to apparatus and method(s) for obtaining a measurement of fibre properties within a pulp slurry from measurements of characteristics of the slurry.

The invention also relates to a control system for controlling pulp characteristics.

Background and Prior Art

In a typical pulp and paper mill, between 1 and 7% of the paper produced may be of defective quality and therefore is typically recycled or discarded. Although the loss in materials due to defective quality output may be relatively small, the losses are compounded by the associated energy losses, operating costs and resulting loss in production/rate. Combined, the losses typically become significant.

The final quality of paper manufactured from wood pulp fibre suspensions (abbreviated to pulp in the text hereafter) is known to be directly dependent on a number of characteristics of the fibres comprising the pulp as well as the processing conditions. Two particularly important characteristics of a pulp slurry which influence paper quality are the fibre length and fibre stiffness. However, fibre coarseness, surface topography and the amount of fibrillar fines on the fibres may also have a direct effect on the final quality of paper produced from the pulp slurry. In order to monitor the pulp quality, samples of a pulp slurry may be taken, which are then measured in separate testing apparatus to monitor any substantial changes in fibre characteristics and suspension conditions. Changes to the operating parameters of the processing system may then be made to counteract any adverse trends in pulp quality. For example, the beating time may be increased or decreased in order to influence the average fibre length, fibre stiffness and fibre conformability. Or a screen may be adjusted to alter the various fibre fractions. A problem with this approach is that the measured pulp sample has characteristics of pulp which has already progressed through the processing line and has been transformed to what may be defective or out-of-specification paper. The characteristics of the pulp slurry currently in the processing line when the changes are made in response to the sample may have different characteristics. This may be caused by the fibres in the pulp slurry coming from different parts of the tree, from a varying wood supply, or from various in the pulp manufacturing process. Furthermore, fibre characteristics between species of trees largely influence the fibre characteristics, requiring predetermined parameters in the processing line to accommodate for these differences.

The separate testing system is typically slow and expensive to operate as the characteristics of the fibres within the slurry need to be determined. Monitoring the characteristics of pulp slurry, is easily achieved, but currently there is no effective way of reliably and efficiently monitoring the characteristics of the fibres within the pulp in order to provide a real-time monitoring and control system.

In order to obtain meaningful measurements of the characteristics of fibres within a pulp slurry, without having to directly examine individual fibres by separating them from the slurry, a relationship between the characteristics of the slurry and fibre characteristics is required. This requires an understanding of the flow of a pulp slurry and a knowledge of fibre-liquid interactions.

Thus, it is an object of the present invention to overcome or at least alleviate problems in monitoring pulp quality at present, or at least provide the public with a useful choice.

Further objects of the present invention may become apparent from the following description.

Summary of the Invention

According to one aspect of the present invention, there is provided apparatus for measuring characteristics of pulp within a pulp slurry, the measuring apparatus including:

• a detector adapted to detect at least one mechanistic characteristic (as herein defined) of a pulp slurry flow and produce a measurement output dependent on the mechanistic characteristic or characteristics; and • pumping means to create the pulp slurry flow past the detector, within a suitable conduit or channel, or,

• a vessel in which a quantity of pulp slurry may be agitated by a transporting means to flow or move passed a detector

Preferably, the detector may detect a change in momentum of the pulp slurry flow between two predetermined points of the conduit or channel.

Preferably, the detector may detect a pressure differential between two predetermined points.

Preferably, the detector may detect mass transfer of the pulp slurry. According to another aspect of the present invention, there is provided apparatus for measuring characteristics of fibre within a pulp slurry including:

• a detector adapted to detect a value indicative of the heat transfer coefficient of a flow of pulp slurry and produce a measurement output dependent on the detected value; and

• pumping or transport means to create a pulp slurry flow within a suitable vessel, conduit or channel past the detector.

Preferably, the pumping or transporting means may be adapted to maintain the pulp slurry flow at a predetermined and substantially constant flow rate or velocity.

Preferably, the apparatus may be adapted to maintain the pulp slurry at a predetermined and substantially constant concentration.

Preferably, the pumping or transporting means may be adapted to maintain a flow rate between 0.2 - 3.0 meters per second.

Preferably, the apparatus may be adapted to maintain a pulp slurry concentration substantially equal to or below about 0.8%.

Preferably, the apparatus may be adapted to maintain a pulp slurry concentration substantially equal to 0.4%.

According to another aspect of the present invention, there is provided a method of measuring pulp characteristics, the method including:

• providing a flow of pulp slurry within a suitable conduit or channel;

• detecting at least one mechanistic characteristic (as herein defined) of the pulp slurry flow; and • generating a measurement output dependent on the mechanistic characteristic or characteristics.

Preferably, a mechanistic characteristic may include a change in momentum between two predetermined points.

Preferably, the method may include measuring a mechanistic characteristic by detecting a pressure differential between two predetermined points.

Preferably, a mechanistic characteristic may include mass transfer of the pulp slurry by contact, collision, concentration differential between the two predetermined points.

Preferably, the method may include maintaining the pulp slurry flow rate at a predetermined and substantially constant flow rate or velocity, wherein the predetermined flow rate is determined by:

• measuring a mechanistic characteristic (as herein defined) for two or more control pulp slurries having different characteristics that require measurement;

• determining a flow rate that results in a suitably large difference in the measured mechanistic characteristic.

Preferably, the method may include maintaining the pulp slurry concentration at a predetermined and substantially constant concentration, wherein the predetermined concentration is determined by:

• determining a concentration that results in a suitably large difference in the measured mechanistic characteristic. According to another aspect of the present invention, there is provided a method of measuring pulp characteristics, the method including:

• providing a flow of pulp slurry within a suitable conduit or channel;

• detecting at a value indicative of the heat transfer coefficient of the pulp slurry flow; and

• generating measurement output dependent on the detected value indicative of heat transfer coefficient.

Preferably, the pulp slurry may be maintained substantially at a constant predetermined flow rate or velocity.

In an alternate form, the method may include taking measurements two or more different flow rates and averaging the measurements.

Preferably, the method may include maintaining a substantially constant pulp slurry flow rate substantially between 0.2 - 3.0 metres per second.

Preferably, the method may include maintaining the pulp slurry substantially at a predetermined fibre concentration.

Preferably, the fibre concentration may be equal to or below

0.8%.

Preferably, the concentration may be substantially 0.4%.

Preferably, the method may include determining the predetermined flow rate by: • measuring a mechanistic characteristic (as herein defined) for two or more control pulp slurries having different fibre properties that require measurement;

Preferably, the method may include determining the predetermined concentration by:

• measuring a mechanistic characteristic (as herein defined) for two or more control pulp slurries having different fibre properties that require measurement;

• determining a concentration that results in a suitably large difference in the measured mechanistic characteristic.

Preferably, an optimum concentration and/or flow rate may be determined for fibres from each species of tree to be measured.

According to another aspect of the present invention, there is provided a control system for controlling pulp characteristics, the control system including:

• a detector adapted to detect at least one mechanistic characteristic (as herein defined) of a pulp slurry flow and produce a measurement output dependent on the mechanistic characteristic or characteristics; • pumping means to create the pulp slurry flow past the detector within a suitable conduit or channel; and

• control means adapted to control one or more processing parameters dependent on the measurement output from the detector.

Preferably, the control means may control at least one processing parameter for a process yet to be performed on the pulp slurry flow. Preferably, a mechanistic characteristic detected by the detector may include a value indicative of the heat transfer coefficient of the pulp slurry.

Preferably, the value indicative of the heat transfer coefficient may be the only mechanistic property detected.

Further aspects of the present invention may become apparent from the following description, given by way of example only and in which reference is made to the accompanying drawings.

Brief Description of the Drawings

Figure 1 : shows a schematic representation of apparatus for controlling the quality of pulp according to one aspect of the present invention.

Figure 2: shows a plotted relationship between heat transfer coefficient and flow velocity for varying pulp slurries.

Figure 3: shows a plotted relationship between heat transfer coefficient and flow velocity for TMP pulp.

Figure 4: shows a plotted relationship between fibre length and heat transfer coefficient for varying mass per unit length pulp fibres.

Figure 5: shows a plotted relationship between median fibre flexibility and heat transfer coefficient for varying pulp slurries. Figure 6: shows a plotted relationship between heat transfer coefficient and Ambertec Formation Index for varying pulp slurries.

Figures 7A, B: shows a plotted relationship between pressure difference and flow velocity for varying pulp slurries.

Figure 8: shows a plotted relationship between fibre length and pressure difference for varying mass per unit length pulp fibres.

Figure 9: shows a plotted relationship between fibre coarseness and pressure difference for varying mass per unit length pulp fibres.

Figure 10: shows a plotted relationship between fibre wall area and pressure difference for varying mass per unit length pulp fibres.

Figure 1 1 : shows a plotted relationship between relative fibre number and pressure difference for varying mass per unit length pulp fibres.

Figure 1 2: shows a plotted relationship between tensile index, tear index and pressure difference for varying mass per unit length pulp fibres.

Figure 1 3: shows a plotted relationship between burst index and pressure difference for varying mass per unit length pulp fibres. Figure 14: shows a plotted relationship between relative flexibility and pressure difference for varying mass per unit length pulp fibres.

Figure 1 5: shows a graphical representation of a control strategy for controlling a quality parameter of pulp.

Description of Preferred Embodiments of the Invention

Traditionally, models relating to pulp flow have been based on non-Newtonian laminar flow models. These have been developed for homogeneous systems and adapted in an attempt to better reflect the inhomogeneous slurry systems. The adaptations however are typically somewhat limited, leading to anomalies between the models and the actual characteristics of slurry systems. These anomalies prevent accurate determination of the characteristics of the particles that make up the slurry system, particularly when the suspensions are structured such as fibre entanglement in wood pulp slurries.

In conventional solid-liquid slurry systems, the particles are discrete bodies in the slurry and hence are easily analysed, characterised and modelled. However, for pulp slurries, the fibre particles exist as individual discrete bodies only at very low fibre concentrations. At higher concentrations the large length-to-width ratio and flexibility of fibres causes entanglement of the fibres. This results in the formation of much larger particles or floes within the slurry flow, with each particle or floe consisting of numerous fibres. These larger particles have their own characteristics which must be identified and related to the characteristics of the individual fibres in order to determine the fibre characteristics based on the slurry characteristics. At still higher concentrations, the floes tend to coalesce into a single large particle moving along the flow path. This single large particle or plug, has different properties again from the floes and the individual fibres.

The floes and fibres interact with the turbulent flow within a pulp slurry depending on the characteristics of each floe and the fibres comprising the floe. These have a direct influence on the mechanistic characteristics of the flow of pulp slurry. For example, longer and flexible fibre 'particles' may interact and damp turbulence of several eddies of several eddy sizes within the flow whereas shorter fibre particles may influence smaller scale eddies and eddies of different intensity. Also, the flexibility of the particles influences the extent of damping and the response of the system to that damping. Observations have shown that the action of particles to influence the mechanistic characteristics of slurries can be related to the properties of the fibres within the flow.

The mechanistic characteristics of a flow of pulp slurry may be determined in numerous ways. In general, the mechanistic characteristics of the slurry provide a useful means for measuring the fibre characteristics and subsequent paper properties. These characteristics include measurable properties of the flow directly relating to the kinetic motion and interaction of the floes including temperature differentials and heat transfer coefficient, pressure differences, point pressure, pressure change over a predetermined distance, local force or any other momentum, mass or thermal-based measurements. For the purposes of this specification, the term "mechanistic characteristics" refers to any or all these variables and should be so interpreted. Referring first to Figure 1 , a schematic representation of apparatus for monitoring the quality of pulp is generally indicated by arrow 1 . A supply of pulp slurry is provided to the measuring apparatus 1 , for example from a holding tank 2. A sample of the pulp slurry is taken from the tank 2 by a pump 3 or other suitable pulp transport means and circulated at a substantially constant flow rate around a flow loop 4. A flow meter 5 may be included to measure the flow rate and provide feedback to pump 3 in order to maintain a constant flow rate at a predetermined level. A detector 6 is provided to measure one or more mechanistic characteristics of the pulp slurry. In the example shown in Figure 1 , a difference in one or more mechanistic characteristics between predetermined points 7 and 8 in the flow loop 4 is used, although for at least some mechanistic characteristics, a single measurement point may be sufficient. The pulp slurry is then returned to the tank 2.

The flow loop 4 may contain the pulp slurry within a pipe or other conduit or channel. In an alternative embodiment, the detection process may be conducted within a cell or tank with a stirrer to create a flow past a suitable detector.

It will be appreciated by those skilled in the art that the system shown in Figure 1 is only representative of a very simplified processing system. In practice, the invention may be used in much more complex systems at any point where a slurry having a suitable concentration and flow rate is available to a detector and does not necessarily involve a flow loop.

The detector 6 may measure any parameter, or parameters related to the mechanistic characteristics of the pulp slurry. The heat transfer coefficient may be measured using techniques well known in the art. For example, the pulp slurry flow may be subjected to a constant suspension-to-pipe or temperature differential. This may be provided by external, electric band-heaters supplying a controlled amount of heat energy to the external surface of a metal pipe section. The heaters may be provided just prior to point 7 in the flow loop 4 and the temperature may be measured at point 8 in the flow loop 4 to obtain a wall temperature and a bulk temperature. A temperature difference can therefore be calculated which is indicative of the heat transfer coefficient of the pulp slurry. Of course, calculations to find the exact heat transfer coefficient are not required, the change in temperature between points 7 and 8 is sufficient for the purposes of this invention.

In an alternative embodiment, the detector 6 may measure a pressure difference between points 7 and 8 of the flow loop 4. The pressure within the flow loop 4 is indicative of the momentum of the pulp slurry and therefore indicative of the nature of the pulp particles within the slurry. Measuring changes in pressure has the advantage of allowing the use of simpler detectors, which also tends to be more reliable than detectors used to measure the heat transfer coefficient. Furthermore, by measuring the pressure differential, the need for electric band heaters or the like is removed, and the risk of damage to the monitoring apparatus 1 is reduced due, for example, to the risk of inadvertent operation of the heaters without a supply of pulp slurry through the flow loop 4.

In a further alternative embodiment, the detector 6 may measure a mass transfer rate, which may be measured by a suitable sensitive impact or absolute pressure detector or other probe known in the art. In this embodiment a dispersive additive may be introduced to the pulp slurry and the extent of mass transfer from that additive measured to indicate mechanistic characteristics of the pulp slurry flow. For example, chemical or polymer dispersion additives may be used for this purpose. Alternatively, the mass transfer of the fibres within the pulp slurry may be measured. Although the remainder of this description is given in reference to the use of heat transfer coefficient and pressure difference, similar principles also apply to measurements of mass transfer rate and may also be applied to other measurements of mechanistic characteristics of the pulp slurry. Although some characteristics of the pulp slurry may be measurable by heat transfer coefficient and not pressure differential and vice versa, overall both have been found to be indicators of pulp slurry mechanistic characteristics.

Referring to Figure 2 of the accompanying drawings, a plot of the heat transfer coefficient as a function of velocity for four wood fibres and water is shown. The wood fibres are characterised as having a high (Hi), medium (Med), low (Lo) or ultra-low (ULo) mass per unit length characteristic (coarseness). Each fibre type is plotted on the graph as indicated by the legend. The concentration of fibres within the pulp slurry was maintained at a constant level, in this case 0.4%.

Figure 2 shows that the heat transfer coefficient varies as a function of the mass per unit length of the fibres within the pulp slurry. The maximum variation in transfer coefficient occurs around a flow rate of approximately one metre per second. Therefore, in monitoring pulp quality, a flow rate of approximately one metre per second should be maintained for the species of pulp fibre measured in Figure 2, in this case Kraft pine pulp to obtain the most reliable and accurate measurements.

The concentration of 0.4% was selected as an optimum concentration to maximise the measurable difference in at least one mechanistic characteristic, in this case heat transfer coefficient for the fibre characteristic, in this case mass per unit length. Lower concentrations have been found to be generally less accurate and less reliable due to limitations in the detector and higher concentrations generally gave less variation in the measurable characteristics of the fibres in the flow. It will be appreciated that lower concentrations may be preferred as detector technology advances.

Figure 3 shows a graph of heat transfer coefficient as a function of flow velocity for a Thermomechanical pulp (TMP) . Again, it is noted that the greatest difference in heat transfer coefficient between the primary (500 CSF) and a secondary (200 CSF) TMP pine pulp is at approximately a flow rate of one metre per second.

It will be appreciated that measurements may be taken of heat transfer coefficient as a function of flow velocity in relation to many pulp fibre characteristics. For example, fibre length, fibre perimeter, fibre coarseness, fibre flexibility, fibre surface topography, a fibre geometry ratio or the amount of fibrillar fines may be used. These may be prioritised in order of importance due to their effect on paper quality and the optimum flow rate chosen to maximise the change in heat transfer coefficient for a variation in those variables. The optimum flow rate and concentration of the slurry may be determined experimentally for a set of fibres having a known variation in one or more important characteristic, for example fibre conformability and length, which may be influenced by the amount of beating performed on the pulp.

Now referring to Figure 4, a graph of the fibre length as a function of heat transfer coefficient for varying fibre types is shown. The graph shows results for fibres having a high (Hi), medium (Med), low (Lo) and ultra-low (ULo) mass per unit length (coarseness) and for spruce (Sp) and unbleached eucalypt (UEu) pulps. Figure 4 shows that there is a clear relationship between the fibre length and heat transfer coefficient to the mass per unit length of radiata pine. The measurements for spruce and unbleached eucalypt pulps are substantially different for radiata pine, suggesting that other relationships such as length/diameter ratio, length/fibre wall thickness, or say longitudinal fibre flexibility, or other separate measurements will be required depending on the species of the wood fibre used in the pulp slurry.

The fibre length, for example is known as one of the contributing factors to the characteristics of paper produced from a pulp slurry. Therefore, by monitoring the heat transfer coefficient, the length of the fibres in the pulp slurry can be monitored. If the fibre length varies outside a predetermined acceptable range, this will be indicated by a change in the heat transfer coefficient of the pulp slurry, which would be detected and measured by the monitoring apparatus 1 . The measurement output provided by the monitoring apparatus 1 may then be used as a feedback mechanism to, for example, increase or decrease the beating to be applied to a pulp in order to decrease or increase the fibre length.

It will be appreciated by those skilled in the art that the relationships among heat transfer coefficient and other mechanistic characteristics are dependent on more than one characteristic of the fibres and that the overall interaction is complex. However, relationships have been obtained among heat transfer coefficient and:

• Fibre properties such as fibre length to fibre perimeter, fibre length to fibre cell wall thickness, fibre perimeter to fibre cell wall thickness, fibre wall area, fibre coarseness (mass/unit length), relative fibre number, and relative flexibility.

• Paper sheet properties (which are related to the fibre properties) such as paper tensile index, paper tear index, paper burst index, tensile energy absorption, and paper sheet formation or uniformity of mass. Similar relationships have been obtained among pressure differentials and the host of both fibre and paper properties as outlined above.

Similar but limited relationships have been obtained among absolute point pressure and the host of both fibre and paper properties as outlined above.

It will also be appreciated that by modifying a single processing parameter, for example the beating time, several characteristics of the fibres may be affected, which combined result in a known influence on mechanistic characteristics. For example, increased beating reduces average fibre length, and increases flexibility and the amount of fibrillar fines, thereby resulting in different fibre agglomerates, generally smaller floes and hence different mechanistic characteristics. With this prior knowledge, an effective control system can be designed.

Figures 5 and 6 show two more examples of fibre characteristics that have a direct relationship with the heat transfer coefficient of a pulp slurry. The graph shows results for fibres having a high (Hi), medium (Med), low (Lo) and ultra-low (ULo) mass per unit length and for spruce pulp (Sp). Thus, having identified this relationship, an appropriate measurement and control system can be designed.

Figures 8 - 1 4 illustrate examples of relationships between fibre properties and pressure difference for fibres having varying mass per unit length. After identification of these relationships, appropriate control mechanisms may be designed to control the fibre properties. Other relationships between a fibre property and pressure drop may be used, for example a dimensional ratio, light scattering coefficient may be related to pressure drop. Whether the relationship is sufficiently certain and measurable may be determined experimentally. Figure 7A shows a plot of pressure drop against pulp velocity for different fibres having known mass per unit length. This plot may be used to identify an appropriate velocity to take measurements of pressure drop in order to control the mass per unit length. A flow velocity of 1 .2 m/s was chosen for the purposes of Figures 8-14. Figure 7B shows the pressure and velocity relationship for primary (500 CSF) and a secondary (200 CSF) TMP pulp, confirming that 1 .2 m/s is an appropriate velocity. A measurement concentration may be determined using the same method.

Figure 7 illustrates the general control principle of the present invention, with a quality parameter being plotted as a function of heat transfer coefficient. The acceptable thresholds of the quality parameter, which may be fibre length, fibre coarseness, or any other characteristic or combination of characteristics, are identified and matched to acceptable limits of heat transfer coefficient. The measured value of heat transfer coefficient, or other mechanistic characteristic as previously described, is then related to an operating parameter within the processing line in order adjust the processing to bring the quality parameter within the acceptable limits. Therefore, a level of fibre quality is maintained in the pulp slurry, which will be translated into a level of quality in paper manufactured from the pulp slurry.

Although, in the above description, measurements were taken to optimise the flow rate of the pulp slurry it will be immediately apparent to those skilled in the art that measurements will also be taken for any other variables of the pulp slurry in order to optimise their properties for measurement purposes. For example and in particular, an optimum concentration may be found using a similar method. Where in the foregoing description, reference has been made to specific components or integers of the invention having known equivalents then such equivalents are herein incorporated as if individually set forth.

Although this invention has been described by way of example and with reference to possible embodiments thereof, it is to be understood that modifications or improvements may be made thereto without departing from the scope spirit of the invention as defined in the appended claims.

Claims

Claims:

1 . Apparatus for measuring characteristics of fibre within a pulp slurry, the measuring apparatus including: • a detector adapted to detect at least one mechanistic characteristic (as herein defined) of a pulp slurry flow and produce a measurement output dependent on the mechanistic characteristic or characteristics; and • pumping or transporting means to create the pulp slurry flow past the detector, within a suitable conduit, channel or vessel.

2. Apparatus for measuring characteristics of fibre as claimed in claim 1 , wherein the detector detects a change in momentum of the pulp slurry flow between two predetermined points of the conduit.

3. Apparatus for measuring characteristics of fibre as claimed in either claim 1 or claim 2, wherein the detector detects a pressure differential between two predetermined points.

4. Apparatus for measuring characteristics of fibre as claimed in any one of claims 1 to 3, wherein the detector detects mass transfer within the pulp slurry.

5. Apparatus for measuring characteristics of fibre within a pulp slurry including:

• pumping or transporting means to create a pulp slurry flow within a suitable conduit or channel past the detector.

6. Apparatus for measuring characteristics of fibre as claimed in any one of the preceding claims, wherein the pumping or transporting means is adapted to maintain the pulp slurry flow at a predetermined and substantially constant flow rate.

7. Apparatus for measuring characteristics of fibre as claimed in any one of the preceding claims, wherein the apparatus is adapted to maintain the pulp slurry at a predetermined and substantially constant concentration.

8. Apparatus for measuring characteristics of fibre as claimed in claim 6, wherein the pumping means is adapted to maintain a flow rate between 0.2 - 3.0 meters per second.

9. Apparatus for measuring characteristics of fibre as claimed in claim 7, wherein the apparatus is adapted to maintain a pulp slurry concentration substantially equal to or below 0.8% .

10. Apparatus for measuring characteristics of fibre as claimed in claim 7, wherein the apparatus is adapted to maintain a pulp slurry concentration substantially equal to 0.4%.

1 1 . A method of measuring fibre characteristics, the method including: • providing a flow of pulp slurry within a suitable conduit, channel or vessel;

• detecting at least one mechanistic characteristic (as herein defined) of the pulp slurry flow; and

• generating a measurement output dependent on the mechanistic characteristic or characteristics.

1 2. A method of measuring fibre characteristics as claimed in claim 1 1 , wherein a mechanistic characteristic includes a change in momentum between two predetermined points.

1 3. A method of measuring fibre characteristics as claimed in either claim 1 1 or claim 1 2, including measuring a mechanistic characteristic by detecting a pressure differential between two predetermined points.

14. A method of measuring fibre characteristics as claimed in any one of claims 1 1 to 1 3, wherein a mechanistic characteristic includes mass transfer of the pulp slurry.

1 5. A method of measuring fibre characteristics as claimed in any one of claims 1 1 to 14, further including maintaining the pulp slurry flow rate at a predetermined and substantially constant flow rate, wherein the predetermined flow rate is determined by:

• measuring a mechanistic characteristic (as herein defined) for two or more control pulp slurries having different characteristics that require measurement; and

1 6. Preferably, the method may include maintaining the pulp slurry concentration at a predetermined and substantially constant concentration, wherein the predetermined concentration is determined by:

• measuring a mechanistic characteristic (as herein defined) for two or more control pulp slurries having different fibre characteristics that require measurement; and

1 7. A method of measuring fibre characteristics, the method including:

• providing a flow of pulp slurry within a suitable conduit , channel or vessel; • detecting at a value indicative of the heat transfer coefficient of the pulp slurry flow; and

1 8. A method of measuring fibre characteristics as claimed in claim 1 7, wherein the pulp slurry is maintained substantially at a constant predetermined flow rate.

1 9. A method of measuring fibre characteristics as claimed in claim 1 7, wherein the method includes taking measurements at two or more different flow rates and averaging the measurements.

20. A method of measuring fibre characteristics as claimed in any one of claims 1 1 to 1 9, wherein the method includes maintaining a substantially constant pulp slurry flow rate substantially between 0.2 - 3.0 metres per second.

21 . A method of measuring fibre characteristics as claimed in any one of claims 1 7 to 20, wherein the method includes maintaining the pulp slurry substantially at a predetermined fibre concentration.

22. A method of measuring fibre characteristics as claimed in any one of claims 1 1 to 21 , wherein the fibre concentration in the pulp slurry is equal to or below 0.8 %.

23. A method of measuring fibre characteristics as claimed in any one of claims 1 1 to 21 , wherein the fibre concentration in the pulp slurry is substantially 0.4%.

24. A method of measuring fibre characteristics as claimed in any one of claims 1 7 to 23, wherein the method includes determining the predetermined flow rate by:

• determining a flow rate that results in a suitably large difference in the measured mechanistic characteristic .

25. A method of measuring fibre characteristics as claimed in any one of claims 1 7 to 24, further including determining the predetermined concentration by:

• measuring a mechanistic characteristic (as herein defined) for two or more control pulp slurries having different fibre properties that require measurement; • determining a concentration that results in a suitably large difference in the measured mechanistic characteristic.

26. A method of measuring fibre characteristics as claimed in claim

24, wherein a predetermined flow rate is determined for fibres from each species of tree to be measured.

27. A method of measuring fibre characteristics as claimed in claim

25, wherein a predetermined concentration is determined for fibres from each species of tree to be measured.

28. A control system for controlling fibre characteristics, the control system including: • a detector adapted to detect at least one mechanistic characteristic (as herein defined) of a pulp slurry flow and produce a measurement output dependent on the mechanistic characteristic or characteristics; • pumping means to create the pulp slurry flow past the detector within a suitable conduit or channel; and

29. A control system as claimed in claim 28, the control means controls at least one processing parameter for a process yet to be performed on the pulp slurry flow.

30. A control system as claimed in either claim 28 or claim 29, wherein a mechanistic characteristic detected by the detector includes a value indicative of the heat transfer coefficient of the pulp slurry.

31 . A control system as claimed in claim 30, wherein the value indicative of the heat transfer coefficient may be the only mechanistic property detected.

32. A control system as claimed in either claim 28 or claim 29, wherein a mechanistic characteristic detected by the detector includes a value indicative of the pressure difference of the pulp slurry between two points.

33. Apparatus for measuring characteristics of fibre substantially as herein described and with reference to the accompanying drawings.

34. A method of measuring pulp characteristics substantially as herein described and with reference to the accompanying drawings.

35. A control system substantially as herein described and with reference to the accompanying drawings.