CN100439908C - Method and device for measuring fiber concentration - Google Patents

Abstract

The invention relates to a method for measuring the fiber concentration in pulp in a machine (1) comprising a stator (5) and an opposing rotor (3), in particular in a pulp refiner , which form the grinding gap (6) for the pulp. The stator (5) is provided with at least one sensor device (7) designed to interact with the rotor surface and comprises an impedance meter body (10) with a sensor surface (18) with It is installed in the stator (5) in a manner capable of axial movement. The method is characterized in that the impedance between the rotor surface and the sensor surface (18) is measured during the axial movement of the impedance meter body (10), and the measured impedance difference is used together with the magnitude of the stroke to determine the dielectric constant of the pulp, from which the fiber concentration in the pulp is deduced. The invention also relates to a sensor device (7) arranged to carry out the method according to the above.

Description

Method and device for measuring fiber concentration

technical field

The present invention relates to a method and a device for measuring the fiber concentration in pulp in a machine, especially in a refiner for the manufacture of pulp.

Background technique

In the manufacture of pulp it is important to know the fiber concentration in the pulp as this determines the properties of the final product. Therefore, for this purpose, in refiners designed for the manufacture of pulp, optical densitometers arranged in the spray line coming out of the refiner are generally used.

This method is described in WO 86/07458, where at least two optical densitometers are used, which shine infrared light and polarized light through the final pulp respectively, after which the absorption and reflection of this light and the depolarization effect are measured respectively . These measurements are then used to calculate the fiber concentration in the pulp.

US 4,171,916 also describes a method in which the polarization, absorption and reflection of transmitted light is used to determine the fiber concentration in the pulp.

These methods work relatively well at not too high fiber concentrations, preferably below about 5% by volume, but are less suitable for pulps with higher fiber concentrations. Since fiber concentrations exceeding 30% by volume are desired in some cases, it would be desirable to propose methods and apparatus that would produce reliable results even at such high fiber concentrations.

Contents of the invention

It is an object of the present invention to provide methods and devices for measuring the fiber concentration in pulp which give reliable results even at high values for said fiber concentration.

This object is achieved by a method and a sensor arrangement according to the first and fifth aspects of the invention, respectively.

A first aspect of the invention relates to a method for measuring the fiber concentration in pulp in a machine, especially in a pulp-making refiner, the machine comprising a stator and an opposing rotor forming a grinding gap for the pulp . The stator is provided with at least one sensor device designed to interact with the rotor surface and comprising an impedance meter body with a sensor surface mounted axially movable in the stator. The method is characterized in that the impedance between the rotor surface and the sensor surface is measured during the axial movement of the impedance meter body and the measured impedance difference is used together with the magnitude of the stroke to determine the dielectric strength of the pulp. constant, from which the fiber concentration in the pulp is derived.

By using the impedance to calculate the fiber concentration instead of the optical method, a method whose degree of reliability is independent of the value of the fiber concentration is realized.

Advantageously, the measuring device communicated with the main body of the impedance meter is used to measure the size of the stroke, which makes it possible to adjust the size of the stroke according to the size of the grinding gap.

In addition, it is also advantageous to measure the size of the grinding gap and use this value in determining the dielectric constant of the pulp, whereby a higher reliability can be achieved.

A fifth aspect of the present invention relates to a sensor device for measuring the fiber concentration in pulp in a machine, in particular in a pulp refiner, comprising a stator and an opposing rotor forming a grinding process for the pulp gap. The sensor device is designed to be mounted in the stator to interact with the rotor surface and includes an impedance meter body having a sensor surface movable in an axial direction and connected to an operating mechanism for axial movement relative to the housing. The sensor device is characterized in that the impedance meter body is arranged to measure the impedance between the sensor surface and the rotor surface during its axial movement.

By using the impedance to calculate the fiber concentration, a sensor device is obtained whose reliability is independent of the value of the fiber concentration.

It is preferred that substantially the entire body of the impedance meter is clad with insulating material, since in this way leakage flows which could affect the results are reduced and the reliability of the sensor arrangement is thus improved.

As mentioned above, it is preferred that the sensor means comprise measuring means in communication with the impedance meter body for measuring axial movement of the impedance meter body.

It is also preferable that the impedance meter body is also arranged to measure the size of the grinding gap, because taking this into consideration can improve the reliability of the sensor device, and by having the impedance sensor body perform this measurement, a small sensor device is realized.

Finally it is also preferred that the sensor device comprises a separate distance meter body which is separate from the impedance meter body and which is arranged to measure the size of the grinding gap, since this enables the existing distance meter body to be used for this function, thereby enabling The impedance meter body is simpler and thus less expensive to manufacture.

Description of drawings

The invention will now be described with reference to the accompanying drawings, in which:

Figure 1 shows a side view of a refiner with a sensor arrangement according to a preferred embodiment of the invention; and

FIG. 2 shows a detailed view of the sensor arrangement according to FIG. 1 .

Detailed ways

Figure 1 shows schematically a refiner-like machine 1 designed for the manufacture of pulp. The refiner 1 comprises a rotor 3 mounted in a frame 2 in such a manner that it can move, is grounded via a grounding conductor 33 (see FIG. The orientation of the stator 5 is moved axially in order to adjust the size of the grinding gap 6 between the rotor 3 and the stator 5 in which grinding of the pulp takes place. The refiner 1 is also provided with two sensor devices 7 according to the invention for measuring the fiber concentration in the pulp as well as inlets (not shown) and spray ducts (not shown) for feeding and removing pulp.

As shown in more detail in Figure 2, both the rotor 3 and the stator 5 are provided with grinding sections 20 having suitable surfaces for grinding pulp and arranged in suitable numbers in a ring between the stator 5 and the rotor 3 on. These abrasive parts 20 are subject to wear in use and are therefore suitably arranged to be replaceable. As shown in FIG. 2 , each sensor device 7 comprises a housing 11 permanently mounted in the stator 5 (for example screwed into a hole in the stator), the impedance meter body 10 being arranged in such a way that it can move axially. in. The case 11 is grounded via a ground wire 12 . The axial movement of the impedance meter body 10 is achieved by the operation of the operating mechanism 13 (here in the form of a roller screw). The roller screw 13 has a suitably fine pitch and is connected to the rear end of the impedance meter body 10 in such a way that rotation of the roller screw 13 causes its movement in the axial direction. The operation of the roller screw 13 can take place, for example, by means of wheels 14 , but other operating means can also be used, including for example stepper motors or servo motors, by means of which the operation can be carried out at a distance from the stator 5 . Impedance meter body 10 is connected to a power supply 15 via lines 16 and is preferably coated on the outside with a heat insulating material 19 on substantially all of its surfaces except for the sensor surface 18 located in front. This insulating material 19 can consist, for example, of a paint layer, a Teflon hose, a plastic pipe, etc., and its effect is to reduce the leakage flow, thereby minimizing its influence on the impedance measurement.

Before the sensor device 7 in FIG. 2 is put into use, a calibration measurement is made in which a correlation is established between the dielectric constant of the pulp and the fiber concentration in said pulp, possibly because the dielectric constant depends on The moisture content in the pulp, which is related to the fiber concentration. Thereafter, while moving the impedance meter main body 10 in an axial direction toward and away from the rotor 3, the rotor surface (here, the grinding part surface) and The impedance between the sensor surfaces 18 is measured. The magnitude of the stroke is measured here by a measuring device 21 communicated with the impedance meter main body 10, but a predetermined value may be assumed or calculated from the number of revolutions of the roller screw that have been performed. By knowing the size of the stroke of the impedance sensor main body 10 and the impedance change on the stroke, the value of the dielectric constant of the pulp can be determined, and then the above-mentioned correlation between the dielectric constant and the fiber concentration is used to determine the value of the pulp. of the fiber concentration. The fiber concentration has been calculated here by means of a calculation device 31 connected to the sensor device, but it can also be done manually.

In some cases the distance d between the grinding part 20 located on the rotor 3 and the stator 5 may affect the measured value, because this distance d determines the fineness of the pulp, i.e. the size of the fibers (the reduction of the distance results in the fiber smaller size). It is thus possible to measure this distance d by having a distance meter body 9 which is arranged separately with respect to the impedance meter body 10 and which is preferably of the AGS type according to e.g. Swedish patent SE 520322 or Swedish patent application No. 0300794-5, And connected to the computing device 31, or optionally, the impedance meter body and the aforementioned rangefinder body can form an integrated unit that performs both impedance and distance measurements.

Finally, it is preferred that the sensor means comprise a flow meter (here schematically indicated by 30 ) located in the inlet or shotcrete duct and also connected to the computing means 31 , for measuring the flow of pulp.

With the apparatus and method as described above, the fiber concentration of the pulp in the grinding gap can be measured even when the fiber concentration of the pulp is assumed to be about 30% by volume because the method is independent of the transparency of the pulp.

It is obvious to a person skilled in the art that the invention described above can be modified within the framework of the scope of the patent claims. For example, a refiner may be provided with one sensor device or more than two sensor devices comprising any number of impedance meter bodies or distance meter bodies which can be located anywhere in the stator. In addition, the roller screw 13 can be replaced by a different mechanism, such as a hydraulic mechanism or a pneumatic mechanism.

Claims (10)

1. method that is used in machine (1) measuring the fibre concentration of paper pulp, this machine (1) comprises stator (5) and relative rotor (3), they are formed for the grinding gap (6) of paper pulp, and stator (5) is provided with at least one sensor device (7), described sensor device is designed to interact with rotor surface and comprises the have sensor surface impedometer main body (10) of (18), this impedometer main body (10) is installed in the stator (5) in mode that can axially-movable, it is characterized in that, during the axially-movable of impedometer main body (10) impedance between rotor surface and sensor surface (18) is being measured, and measured impedance contrast is used for determining the specific inductive capacity of paper pulp with the size of traverse, therefrom derives the fibre concentration of paper pulp.

2. the method that is used to measure fibre concentration as claimed in claim 1 is characterized in that, adopts the measurement mechanism (21) that is communicated with impedometer main body (10) to measure the size of traverse.

3. the method that is used to measure fibre concentration as claimed in claim 1 or 2 is characterized in that, also measures the size of grinding gap (6), and this numerical value is used for determining the specific inductive capacity of paper pulp.

4. the method that is used to measure fibre concentration as claimed in claim 1 is characterized in that, it is used for the fibre concentration in making the fiberizer measurement paper pulp of paper pulp.

5. sensor device (7) that is used in machine (1) measuring the fibre concentration of paper pulp, this machine (1) comprises stator (5) and relative rotor (3), they are formed for the grinding gap (6) of paper pulp, this sensor device (7) is designed to be installed in the stator (5) to interact with rotor surface, and comprise the have sensor surface impedometer main body (10) of (18), this impedometer main body (10) can be moved along axial direction, and being connected to operating mechanism (13) goes up so that with respect to shell (11) axially-movable, it is characterized in that, impedometer main body (10) is arranged the impedance be used for measuring between sensor surface (18) and rotor surface during its axially-movable, and measured impedance contrast is used for determining fibre concentration in paper pulp with the size of the traverse of impedometer main body (10).

6. sensor device as claimed in claim 5 (7) is characterized in that, whole impedometer main body (10) is coating thermal insulation material (19).

7. as claim 5 or 6 described sensor devices (7), it is characterized in that measurement mechanism (21) is communicated with impedometer main body (10), is used for measuring its axially-movable.

8. as claim 6 or 7 described sensor devices (7), it is characterized in that described impedometer main body (10) is also arranged and is used for measuring the size of grinding gap (6).

9. as claim 6 or 7 described sensor devices (7), it is characterized in that described sensor device (7) also comprises range-viewfinder main body (9), it separates with impedometer main body (10), and arranges the size that is used for measuring grinding gap (6).

10. sensor device as claimed in claim 5 (7) is characterized in that, it is used for the fibre concentration in making the fiberizer measurement paper pulp of paper pulp.

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