WO1994024541A1

WO1994024541A1 - Procedure and apparatus for determining the resin substance content of a pulp stock sample

Info

Publication number: WO1994024541A1
Application number: PCT/FI1994/000150
Authority: WO
Inventors: Pentti NIEMELÄ; Jouni Tornberg; Eero Hietala; Timo Korpi
Original assignee: Valtion Teknillinen Tutkimuskeskus
Priority date: 1993-04-20
Filing date: 1994-04-20
Publication date: 1994-10-27
Also published as: FI93902C; FI931779A; FI93902B; FI931779A0

Abstract

The present invention concerns a procedure for determining the pitch substance content of a pulp slurry sample, wherein (a) from part of the pulp slurry sample are separated, with the aid of a separator means based on specific gravity, the wood fibres and other solids, if any, except for the pitch substances, in order to obtain a sample proper; (b) from part of the pulp slurry sample are separated, with the aid of a separator means based on particle size, the pitch substances and wood fibres which may be present, and other solids, in order to obtain a reference sample; and (c) the pitch matter content of the sample is determined by measurement on the sample proper thus obtained, using the reference sample for reference. The invention further concerns apparatus for implementing the procedure, said apparatus comprising (a) a separating means based on specific gravity for preparing a sample proper, said separating means separating from part of the pulp slurry sample the wood fibres and solids, if any, excepting pitch substances; (b) a separating means based on particle size for preparing a reference sample, said separating means separating from part of the pulp slurry sample the pitch substances and wood fibres and solids which may be present; (c) a measuring means for measuring the sample proper and the reference sample in order to determine the pitch matter content of the sample.

Description

PROCEDURE AND APPARATUS FOR DETERMINING THE

RESIN SUBSTANCE CONTENT OF A PULP STOCK SAMPLE.

The present invention concerns a procedure for determining the pitch matter content of a pulp slurry sample. The invention further concerns apparatus for determining the pitch matter content of a pulp slurry sample.

The work done in order to develop paper and pulp processes to become better in economy and more friendly to the environment has introduced new prob¬ lems. For instance, increasing the degree of closedness of a paper machine's wet part and, among others, in¬ creasingly general use of recirculated fibre have had the effect that objectionable substances which become enriched in the recycled water present a problem of increasing magnitude. The chemistry of the wet part is generally incompletely known as yet, and its control is therefore difficult. This causes problems of quality and of productivity which are quite remarkable. Insuf¬ ficient information gained concerning the variables in the wet part has resulted in abundant, uneconomical use of additive chemicals, and has detrimentally affected the quality of the ultimate product. Selective measu- ring methods describing the state of the pulp slurry process are thus required. What is particularly needed is selective on-line measuring methods by which the continuous variations of different variables could be followed in the pulp slurry process. Among the objects which should be monitored in the case of recycled waters, dissolved and colloidal organic compounds, and pitch substances in particular, have been found to be highly important objects needing to be monitored. - Pitch substances are in this context understood in general to be various resinous extractive substances derived from coniferous or deciduous wood. - Pitch matter can be problematic in connection with paper-making, e.g. producing holes and spots in the paper, losses of finished paper, and it may plug the felts of the paper machine, thus lengthening its shut¬ down time. Heretofore, some of the greatest problems in determining the pitch matter quantity have been due to the relatively small quantity of such matter in the re¬ cycling water, and by the water treatment. Laboratory measuring processes have been elaborated for deter- mining the pitch substances present in the form of pitch globules.

A common method applied in measuring the quantity of pitch globules in a sample drawn from a process is manual counting performed with a microscope, so-called pitch globule counting. However, nothing but the largest pitch globules are detectable by this met¬ hod owing to the microscope's limit of resolution, which happens to coincide with the maximum range of the pitch globule distribution. Furthermore, the results of measurement are dependent on the person making the count. The procedure is also laborious, and adequate statistical accuracy is hard to attain by counting.

The quantity of pitch globules has also been indirectly estimated in laboratory conditions by the aid of previously known turbidity measurement after centrifuging or settling the whole sample. Settling has been applied in order to separate the pitch globules from the process sample. Turbidity measurement involves uncertainty factors, however. It is for instance diffi- cult to implement pretreatment because the particle size distribution of the sample should remain stable independent of process conditions. The size distributi¬ on (density function) graph of the pitch globules is exceedingly steep in the sensitive range of turbidity measurement (0.3 to 0.6 μm) , and turbidity measurement is therefore sensitive to changes of globule size; such changes occur all the time in the process. Applicabili- ty of the measurement as an on-line procedure has not been demonstrated.

One has furthermore employed, towards pitch globule counting, the hemacytometer, which was origi- nally developed to serve medical applications. This procedure is likewise difficult to adapt for on-line measurement.

In a procedure of prior art, the sample is first centrifuged, the sample thus obtained is ex- tracted with MTBE (methyl-tert.butylester) solvent, and the quantity of pitch substances is measured by means of gas chromatography in laboratory conditions. How¬ ever, gas chromatography is difficult to use in process conditions and does not easily lend itself to use as an on-line measuring instrument.

In a new laboratory procedure, the pitch globules are stained with a fluorescent dye substance and the stained globules are determined using optical measurement based on use of laser light (Lorenzak P., Krδhl T. and Horn D., Determination of the Effective¬ ness of Pitch Control Agents by Means of a New Laser- Optical Particle Counting Method; Proceedings of the 4th International Conference: New Available Techniques and Current Trends, SPCI, p. 334-347). This procedure, too, is unsuitable for on-line use.

As set forth in the foregoing, direct contin¬ uous on-line measurement for determining pitch matter content in a sample has not been feasible heretofore. The object of the present invention is to eliminate the drawbacks pointed out in the foregoing. Specifically, the object of the invention is to disclose a procedure by the aid of which the state of a pulp slurry process can be monitored better than heretofore. Regarding the circumstances characterizing the invention, reference is made to the claims.

In the procedure of the present invention for determining the pitch matter content of a pulp slurry sample, said sample containing wood fibre, pitch mat¬ ter, other potential solids, dissolved organic and inorganic substances and water: (a) from part of the pulp slurry sample by means of a separating apparatus based on specific gravity are separated the wood fibres and other potential solids, except pitch substances, in order to obtain the sample proper; (b) from part of the pulp slurry sample by means of a separating apparatus based on particle size are sepa¬ rated the pitch substances, and wood fibres which may be present, and other potential solids in order to obtain a reference sample; and (c) .the pitch matter content of the sample is deter¬ mined by measurement from the sample proper, using the reference sample for reference.

In preparing the sample proper, one may use for separating apparatus based on specific gravity, a centrifuge or a separator. This operation involves separation from the pulp slurry sample of wood fibres, other potential solids such as fines originating from wood, fillers and pigments, while leaving unseparated the pitch substances, lighter in specific gravity than the solids just mentioned and water, and which are present in the form of pitch globules, and the dis¬ solved substances, which may be organic dissolved sub¬ stances or inorganic dissolved substances.

In preparing the reference sample one may use for separating apparatus based on particle size, a filter, e.g. a mechanical filter, such as a ceramic or paper filter. The hole size of the filter is selected in conformity with the pitch globule size distribution. The size distribution of the pitch globules lies for its greater part in the range from 0.2 to 2 μm (Allen, L.H., Pitch in Wood Pulps, Pulp and Paper Canada, May 1975, p. 70-77), and therefore the hole size of the filter is advantageously chosen to be about 0.1 to 0.2 μm. The operation involves separation from the pulp slurry sample, in addition to the aforementioned solid components possibly present therein, of colloidal pitch globules, whereby the organic and inorganic dissolved substances are left in the reference sample.

In the determination of the sample's pitch matter content, measurement is made using the sample proper and the reference sample. The reference sample serves to eliminate the interfering effect, if any, exerted on the results of measurement by dissolved or¬ ganic substances present in the pulp slurry sample, such as carbohydrates and lignins. It is then possible to use for determination of pitch content a measuring apparatus utilizing the structure of organic substan¬ ces, e.g. an instrument measuring absorption, emission or scattering of electromagnetic radiation. Further¬ more, RAMAN spectroscopy may be used in the determina¬ tion. Advantageously, an IR spectrophotometer is used, with which the pitch matter content can be quan¬ titatively determined on the basis of the absorption spectrum typical of the pitch substances present. On the basis of the absorption spectrum of pitch substan- ces a favourable wave number range is selected, or al¬ ternatively a fixed wavelength. About 2400 to 3000 cm^"1 is an advantageous wave number range. When a reference sample prepared as taught by the invention is used in the measurement, specific pitch matter content meas- urement can be implemented. Moreover, the measurement can be carried out swiftly and in continuous operation. The procedure of the invention is eminently suited to serve as a continuous on-line method in con¬ nection with any pulp slurry process, such as a process in which groundwood, cellulose or paper is being made. Papermaking is in this context understood to be the producing of actual paper or cardboard or any other web-formed non-woven product made of lignocellulose fibre.

According to a continuously operating embodi¬ ment of the procedure, preparation of the sample proper and that of the reference sample are arranged to take place in parallel, the pulp slurry sample coming from the process being divided into two parts so that

(a) one part is centrifuged, or separated, with a con¬ tinuous action centrifuge or separator for preparing the sample proper; and

(b) the other part is filtered through a continuous action filter for preparing a reference sample.

According to another continuously operating embodiment of the procedure, preparation of the sample proper and that of the reference sample are arranged to take place consecutively, in that

(a) the pulp slurry sample is centrifuged, or separat¬ ed, with a continuous action centrifuge or separator for obtaining the sample proper; (b) part of the solution sample obtained in step (a) is filtered through a continuous action filter for ob¬ taining a reference sample.

It is thus understood that the present inven¬ tion discloses a procedure enabling the total quantity of pitch matter contained in the sample to be specif¬ ically determined and which can be fitted in conjunc¬ tion with pulp slurry processes to serve as an on-line measuring method. Furthermore, the present invention discloses apparatus for implementing this procedure. Thanks to the invention, the pitch matter content of a pulp slurry process can now, for the first time ever, be continuously followed in connection with a pulp slurry process.

Moreover, the reference sample prepared by the procedure of the invention enables continuous action, fast measuring instruments such as IR analyzers to be used in pitch matter content determination, on line, in connection with any paper or cellulose process what¬ soever.

The invention is described more in detail in the following with the aid of embodiment examples fol¬ lowing hereinbelow, with reference to attached draw¬ ings, wherein

Fig. 1 presents schematically an apparatus according to the invention, in which the separating means have been disposed in parallel.

Fig. 2 presents schematically another apparatus ac¬ cording to the invention, in which the separating means have been disposed consecutively one after the other. Fig. 3 displays absorption spectra obtained with an IR spectrophotometer, these spectra having been obtained using a reference sample prepared as taught by the in¬ vention, and pure water for reference sample, and Fig. 4 shows the correlation of IR measurement with pitch globule determinations made in the laboratory.

Example 1:

In Fig. 1 is depicted a continuous action ap¬ paratus according to the invention in which the sepa¬ rating means have been disposed in parallel. The appa- ratus comprises a continuous action centrifuge 1, a continuous action filter 2, and a continuous action IR spectrophotometer 3. The apparatus is connected to serve as on-line measuring apparatus in conjunction with the wet part of a paper machine 4. In this embodiment the pulp slurry sample flow

5 drawn from the paper machine 4, e.g. from its head- box, is divided into two parts 6,7. The centrifuge 1 is disposed to receive one part 6, and the ceramic filter 2 is disposed to receive the divided other part 7. The pulp slurry sample arriving at the cen¬ trifuge 1, in the present case a continuous action decanter centrifuge, need not be prefiltered, although prefiltering may be used if desired. The speed of ro¬ tation of the centrifuge has been so adapted that it will separate the solids present in the sample, all but the light pitch substances. In the present example the speed of 6000 rpm was selected, corresponding to cen¬ trifugal force acceleration about 3000g. From the cen¬ trifuge a continuous liquid flow 8 is obtained, and pulp balls 9 of rather high viscosity (viscosity on the order of about 30 to 40%), which may be returned to the process.

The liquid flow 8 from the centrifuge is con¬ ducted as sample proper to the IR spectrophotometer 3. The hole size of the continuous action ceramic filter 2 has been selected to be about 0.1 to 0.2 μm, whereby the filter 2 will separate the wood fibres, and other solid matter, present in the pulp slurry sample, and virtually all pitch globules. In the filtrate 10 that is obtained will only be left the dissolved or¬ ganic and inorganic substances which the sample con- tains. The filtrate is conducted to the continuous action spectrophotometer 3 to serve as reference sam¬ ple. The separated solid matter 11 may be returned to the process.

In determination with the aid of a reference sample the effect of the absorption peaks of dissolved substances present in the sample in abundance, such as carbohydrates and lignins, is eliminated in a selected wavelength range advantageous in view of pitch sub¬ stances, thereby achieving specific measurement of pitch substances.

The procedure of the invention was put in operation in a paper machine environment. The pitch matter quantity contained in the liquid flow from the centrifuge was first examined, and it was found to be of the same order of magnitude as that of a sample settled and analyzed in the laboratory.

The IR analyzer employed was a commercial Bomem MB 155 FTIR analyzer. The wavelength range about 2400 to 3000 cm^"1 was selected for analysis of pitch substance content. Calibration was effected by the PLS method. Reference compensation was accomplished with a reference sample.

Example 2:

In Fig. 2 is depicted a continuous action ap¬ paratus otherwise like that of Example 1, but in which the separating means have been disposed one after the other.

In this embodiment a continuous action cen¬ trifuge 1 has been arranged to receive the pulp slurry sample flow 5 from the paper machine 4. The centrifuge 1 and its mode of operation are as described in Example 1. Of the liquid flow 8 obtained from the centrifuge 1, which contains pitch substances as residual solids, and dissolved organic and inorganic compounds, a part 12 is conducted to a ceramic filter 2, and the remainder 13 is conducted, as sample proper, to an IR spectrophoto¬ meter 3. The solids 9 separated by the centrifuge 1 may be returned to the process 4.

The continuous action ceramic filter 2, which is as described in Example 1, substantially separates from the sample 12 entering the filter the solids still present therein, i.e., the pitch substances. The filt¬ rate 14 thus obtained will carry only the dissolved organic and inorganic substances contained in the samp¬ le. The filtrate is conducted to the spectrophotometer 3 to serve as background sample.

The pitch matter content is determined as in Example 1.

In Fig. 3, absorption spectra are compared which were obtained by the procedure of the invention, using in the procedure for reference sample a reference sample (A) prepared as taught by the invention, and with a reference sample in which pure water (B) was used for reference sample.

Fig. 4 shows a comparison between pitch matter quantities determined by the procedure of the invention and pitch globule determinations made in the laboratory by counting from pulp slurry samples drawn at the same time*. The IR measurement results are relative.

On the basis of the foregoing, the procedure of the invention is eminently applicable in continuous operation pitch matter determinations on pulp slurry sample processes.

The purpose with the examples is merely to illustrate the invention, without confining it.

Claims

1. A procedure for determining the pitch matter content of a pulp slurry sample containing wood fibre, pitch matter, potentially other solids, dis¬ solved organic and inorganic substances, and water, characterized in that

(a) from part of the pulp slurry sample are separated, with the aid of a separator means based on specific gravity, the wood fibres and other solids, if any, except for the pitch substances, in order to obtain a sample proper;

(b) from part of the pulp slurry sample are separated, with the aid of a separator means based on particle size, the pitch substances and wood fibres which may be present, and other solids, in order to obtain a ref¬ erence sample; and

(c) the pitch matter content of the sample is deter¬ mined by measurement on the sample proper thus obtain- ed, using the reference sample for reference.

2. Procedure according to claim 1, charac¬ terized in that the procedure is implemented in con¬ tinuous action mode in connection with a pulp slurry process.

3. Procedure according to claim 2, charac¬ terized in that from the pulp slurry sample

(a) a part is centrifuged or separated with a centri¬ fuge or separator for obtaining the sample proper; and

(b) part is filtered with a filter in order to obtain a reference sample.

4. Procedure according to claim 2, charac¬ terized in that

(a) the pulp slurry sample is centrifuged or separated with a centrifuge or separator in order to obtain the sample proper; and

(b) part of the sample obtained in step (a) is filtered with a filter in order to obtain a reference sample.

5. Procedure according to any one of claims 1-4, characterized in that in the filtering operation a filter is used which has hole size 0.1 to 0.2 μm.

6. Procedure according to any one of claims 1-5, characterized in that for determination of pitch matter content is used a method of measurement based on the structure of organic substances.

7. Procedure according to any one of claims 1-6, characterized in that determination of pitch mat- ter content is accomplished with a measuring instrument measuring absorption, emission, scattering or RAMAN spectroscopy of electromagnetic radiation that has been produced, caused by the samples, advantageously an IR spectrophotometer.

8. Apparatus for determination of the pitch matter content of a pulp slurry sample containing wood fibre, pitch matter, potential other solids, dissolved organic and inorganic substances and water, character¬ ized in that the apparatus comprises: (a) a separating means based on specific gravity for preparing a sample proper, said separating means sepa¬ rating from part of the pulp slurry sample the wood fibres and solids, if any, excepting pitch substances;

(b) a separating means based on particle size for pre- paring a reference sample, said separating means sepa¬ rating from part of the pulp slurry sample the pitch substances and wood fibres and solids which may be present;

(c) a measuring means for measuring the sample proper and the reference sample in order to determine the pitch matter content of the sample.

9. Apparatus according to claim 8, charac¬ terized in that the apparatus has been disposed to determine pitch matter content in continuous mode from the pulp sample.

10. Apparatus according to claim 9, charac¬ terized in that the apparatus comprises: (a) a continuous action centrifuge or separator for preparing the sample proper, a centrifuge which is disposed to receive the sample flow from the pulp slurry process; (b) a continuous action filter for preparing a refer¬ ence sample, said filter being disposed to receive a sample flow from the pulp slurry process; and (c) a continuous action measuring means for measuring the sample and the reference sample, said measuring means being disposed to measure the sample proper com¬ ing from the centrifuge or separator and the reference sample coming from the filter.

11. Apparatus according to claim 9, charac¬ terized in that the apparatus comprises: (a) a continuous action centrifuge or separator for preparing the sample proper, disposed to receive the sample flow from the pulp slurry process;

(b) a continuous action filter for preparing a refer¬ ence sample, disposed to receive a part of the sample flow coming from the centrifuge or separator; and

(c) a continuous action measuring means, disposed to measure the sample proper coming from the centrifuge or separator and the reference sample coming from the filter.

12. Apparatus according to any one of claims

8-11, characterized in that the hole size of the filter is about 0.1 to 0.2 μm.

13. Apparatus according to any one of claims 8-12, characterized in that the continuous action measuring means is a measuring instrument based on absorption, emission or scattering of electromagnetic radiation, advantageously an IR spectrophotometer.