AU599914B2 - Method at the manufacture of mechanical pulp - Google Patents

Description

AU-AT 561B6 3:2 8 6 WORLD INTELLECML FlaiPE ORANIZATION' n..01 au INTERNATIONAL APPLICATION PUBLISHED UNDE5 HE4TEN1CoO4RAT1O N TREATY (PCT) (51) International Patent Classification 4: (11) International Publication Number: WO 86/ 06770 0~21D 1/30 B02C 7114 Al (43) International Publicatiop Date, N.)vember 1986 (20.1 1.86) (21) International Application Nvmber: PCT/SE86/00160 (74) Agent: ILLUM, Leif-Otto,; Svenska Cellulosa Aktiebo- (222) International Filing Date: 8 April 1986 (08.04.86) aeSCKnstn3,S-1 (81) Designated States: AT (European patent), AU, DE (Eu- (31) Priority Application Number: 8502211-9 ropean patent), Fl, FR (European patent), GB (Euro- (32)PrirityElae: May198 (0605,51) pean patent), JP, NO, SE (European patent), US.

(33) Priority Country: SE Published With international search report.

(71) Applicant (for all designated States except SUNDS DEFIBRATOR AKTIEBOLAG [SE/SE]; S-851 94 Sundsvall (SE).

(72) Inventors; and Inventors/Applicants (for US onh') HARTLER, Nils, I.,A OJ 5 AN 98 Chi. fSE/SE];, Blib~rsvtigeei 16, S-181 64 Lidingb 15JN18 STR AND, William, Caristad 401 Pondgrosa CT 202, Moscow, ID 83843 (US).

tlAUSTRALIAN This document conas ther amendm nts ade u nder Sctn 49 aends M coret for 4 DEC 1986 rinting. PATENT OFFICE (54) Title: METHOD AT TH-E MANUFACTURE OF MECHANICAL PULP~ 17.6-25 kc/s ri-i

AMPLITUDE

11. 2-17 kc/s ri-i (57) Abstract 10 20 30 kc/s The refiner process and the properties of the pulp produced are controlled~ by means of an accelerometer positioned on a refiner disc, which accelerometer measures high-frequency vibrations. The signal from the accelerometer is converted to vibration energy, which is utilized together with one or several other process ,ariables for controlling and adjusting the process, WO 86/06770 PCT/SE86/00160 Method at the manufacture of mechanical pulp This invention relates to a method of controlling the manufacture of mechanical pulp in a refining process where cellulose-containing material in lumps, such as wood chips', is refined. The chips prior to the refining can be treated with heat and/or chemicals for manufecturing TMP (thermomechanical pulp) or CTMP (chemi-thermomechanical pulp). The refining is carried out in one or several steps by single- or double-disc refiners. These refiners are provided with opposed refiner discs rotating relative one another. The discs are provided with disc segments comprising bars and intermediate grooves.

Opposed disc segments form a gap where the material is refined during its passage outward.

The properties of the manufactured pulp are influenced, besides by the quality of the wood chips, by a great number of system parameters. Among them can be mentioned the distance between the disc segments (gap), the load of the motor driving a rotary refiner disc, the pressure by which the refiner discs are pressed in the direction toward each other, the pressure at the feed-in of the chips, the pressure in the housing enclosing the discs, the supply of diluting water, the material flow through the refiner (the production), the material concentration. Some of these parameters are depending on each other while other are substantially independent. For example, the motor load increases and so does the pressure by which the discs are pressed toward each other when the gap decreases.

It is impossible in practice to check and control all parameters influencing the properties of the pulp. It was found, however, that a desired pulp quality can be achieved with pretty high precision by controlling some especially important parameters, viz. the gap size, the matriai concentration and the production.

i: -2 A great problem is that the measuring of the system parameters does not yield a direct measure of the pulp properties. For being able to determine the properties of the pulp, such as tensile strength, tearing resistance, dewatering capacity, shives content, fibre length etc., it is, of course, necessary to analyze the pulp and the paper made thereof. In a mill it takes normally several hours to obtain the results of such analysis, and sampling usually is carried out not more than times per day. It is, therefore, impossible to rapidly discover and compen.sa-e for such va'.iations in the pulp properties which are due to system parameters, which have not been determined, or where there is no simple relation between the system parameter and the pulp properties.

One factor causing the relation between the measured system parameters and pulp properties to change in operation is the wear of the refiner disc segments.

This implies that certain pulp properties can deteriorate 20 although the measured system parameters remain unchanged.

This implies in practice, that the system parameters must be adjusted on the basis of analysis results of a pulp, which had been manufactured several hours earlier. This is, of course, a great disadvantage.

The delay in obtaining the analysis results involves substantial disadvantages also in connection with the testing of an comparison between different refiner disc segments. It is desired, therefore, to be able during the refining process to measure sue. system i parameters, which render it possible to predict the pulp properties with greater accuraciy than it has been ~heretofore possible.

The present invention offers a solution of this problenm.

U1 2a According to the present invention there is provided a method of controlling the manufacture of mechanical pulp in a refiner process where cellulose-containing materiaJ in lumps is refined during the passage through a gap between two opposed refiner discs rotating relative to each other, characterized in, that the vibrations of at least one refiner disc are measured by means of an accelerometer attaclied to the disc and are converted to vibration energy, which together with one or more of the process variables production, gap size and material concentration are ,,itilized for controlling and adjusting the properties of the manufactured pulp.

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I O 1 1 ecoj Iq i WO 86/06770 PCT/SE86/0016) The invention is described in greater detail in the following, with reference to embodiments and test results shown in the accompanying drawing, in which Fig. 1 shows a frequency analysis of the measured vibrations, Figs.2 show the agreement between measured and calculated and 3 tensile strength without and, respectively, with utilization of the vibrations in the refiner discs.

One property important for the quality of pulp is the tensile strength. This applies especially to mechanical pulp intended for papermaking.

By controlling and adjusting the three system parameters gap size, .naterial concentration and production, it is possible with pretty good precision to maintain a desired pulp quality. Experiments carried out on mill scale, however, have shown that the pulp quality deteriorates with the time due to wear of the refiner discs, without the possibility of predicting this by control of the aforesaid system parameters.

By measuring the high-frequency vibrations arising in the refiner discs due to their relative rotation and their segment design, it is possible to calculate the vibration energy over the refiner disc segment. The frecquency depending on the rotation speed of the discs and the design of the disc segments can amount to several thousands c.p.s. The measuring is carried out by means of an accelerometer attached to the disc, preferably to the rear side of a segment.

In a single-disc refiner the accelerometer is attached on the stationary disc. It is also imaginable to attach accelerometers to both discs in a single- or double-disc refiner, in order to obtain additional information on the vibrations of the discs.

By including the vibration energy thus measured in the calculation of the pulp properties, it was found by surprise, that these propierties can be predicted with much higher WO 86/06770 PCT/SE86/00160 precision. This applies especially to the strength properties of the pulp (tensile strength). It was found possible, thus, to predict the reduction in tensile strength caused by wear of the disc segments.

This implies simultaneously that the vibracion energy also can be utilized for determining the condition of the processing surfaces of the segments. The vibration energy, furthermore, can be utilized for comparing the efficiency of disc segments of different types.

Example In a single-disc refiner an accelerometer was mounted in J a hole drilled in the rear side of a disc segment in the stationary disc. The segments were designed with three zones comprising bars and grooves of different size.

The refining was carried out with pre-heated chips for the manufacture of TMP. The system parameters and pulp properties at two test runs were as follows: Test I Test II Production (ton bone-dry pulp/24 h) 70 Material concentration 48 48 Gap size (mm) 0.46 0.38 Tensile index (Nm/g) 33 33 CSF (ml) 184 150 Tear index (mN m 8.5 Specific energy (kWh/ton pulp) 2150 2075 The signal from the accelerometer was simultaneously measured and analysed. The frequency range in question was 5 25 kc/s. In Fig. 1 a frequency analysis of this signal is shown. The signal can be divided into three different areas corresponding to the three zones of the segments.

In the inner zone comprising the qoarsest bars the frequencies 5.6-11.2 kc/s were noted. In the central zone 11.2-17.6 kc/s, and in the outer zone comprising the finest bars 17.6kc/s were noted. The vibration energy is represented by the surface beneath the frequency curve in Pig. 1.

After 800 operation hours new measurements of the system parameters and pulp properties were carried out. It was then found, that most of the measured pulp properties agreed well with the pulp properties, which were calculated by means of measured system parameters and results from previous tests. One exemption was the tensile strength, of which the measured values were lower than the calculated ones. In Fig. 2 the measured tensile index is shown as a function of the tensile index, which was calculated by ineans of measured values *of production, gap size and material concentration. It shows that there is a heavy systematic error. The fully .drawn line designates full agreement, and the dashed lines designate an acceptable error range.

By including in the calculation of the pulp properties the vibration energy obtained from the accelerometer oooo co•* signal, all measured pulp properties could be predicted Swith high precision. In Fig. 3 the measured tensile index is shown as a function of the calculated tensile index where the vibration energy has been utilized together with the adjusted production, gap size and material concentration. Specifically, the calculated tensile index was calculated by multiplying the •calculated tensile index of Fig. 2 by the vibration energy obtained from the accelerometer signal. Th agreement between the calculated tensile index and the measured tensile index lies within the error range. No systematic errors could be stated.

The deterioration in the tensile strength of the pulp can bc explained by the wear of the disc segments.

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1 Heretofore it has not been possible to find a controllable relation between the tensile strength and the wear of the segments. The present invention, thus, offers such a control possibility. By measuring the vibration energy according to the invention, thus, the condition of the disc segments can be determined, which also can be utilized for determining the time when the segments have to be exchanged. The invention can also be used for comparing different segment patterns and materials.

The invention, of course, is not restricted to the embodiments described, but can be varied within the scope of the invention idea.

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Claims (4)

1. A method of controlling the manufacture of mechanical pulp in a refiner process where cellulose-containing material in lumps is refined during the passage through a gap between two opposed refiner discs rotating relative to each other, characterized in, that the vibrations of at least one refiner disc are measured by means of an accelerometer attached to the disc and are converted to vibration energy, which together with one or more of the process variables production, gap size and material concentration are utilized for controlling and adjusting the properties of the manufactured pulp.

2. A method as defined in Claim 1 where the refiner process is carried out in a single-disc refiner, characterized in, that the vibrations are measured in a disc segment located on the stationary disc in the refiner. S.

3. A method as defined in Claim 1 or 2, characterized in, that the control is based on the vibration energy in combination with the production, gap size and material concentratin.

4. A method as defined in any one of the preceding claims, characterized in, that the vibration energy also is utilized for determining the condition of the beating surfaces of the disc segments. DATED THIS 13TH DAY OF JUNE 1989 SUNDS DEFIBRATOR AB By its Patent Attorneys: GRIFFITH HACK O. Fellows Institute of Patent Attorneys of Australia. Li 1 if 9 r c 0