FI71960B - FOERFARANDE FOER STYRNING AV ALKALISK CELLULOSAKOKNING MEDELSTEN SNABB ANALYSATOR VILKEN MAETER ORGANISKA OCH ORGANISK A OKVAETSKEKOMPONENTER - Google Patents

Description

1 71960

The invention relates to a method for controlling alkaline cellulose soups, in particular sulphate cooking, in which process components are used to measure dissolved substances in wood and the remaining inorganic cooking chemical by means of a rapid analyzer.

The object of the invention was to provide a method for obtaining measurement information on the cooking chemistry of alkali cellulose soups from the concentrations of li and reaction products at short intervals for controlling the cooking on the basis of the actual progress of the cooking.

The object of the invention is achieved in that a small sample taken from the process is fed into the analyzer's own liquid flow, precisely conditioned under conditions, where, after dilution, it flows as a near-normally distributed peak-shaped zone with various flow-through measuring devices. Dissolved lignin from wood 20 is measured based on the absorption of ultraviolet radiation at one of the wavelengths of the UV spectrum of the lignin (e.g., 205 or 280 nm); the total dissolved solids content of the wood is measured based on the refractive index difference with respect to the pure, flowing medium at a differential refractometer of 25 meters; the remaining active alkali is measured by conductivity measurement. In addition, the liquid flow can be passed through any measurement carried out on the flow-through principle to obtain further measurements. The data from the above measurements are then utilized on the main principle that based on the alkali content measured in the cooking vessel and as it progresses, a target for the end point of the cooking is set and measurements of the reaction products monitor and correct if necessary. It is thus a matter of controlling the cellulose soup both with a forward feed control 35 and with a situation-based reverse feed control. Both control methods have been proposed to be performed with different direct measurements from process tubes or with automated titrators. What is new is that the arrangement according to the present invention combines all the control methods by producing the necessary data for it with a single device and from the same sample. What makes the present measurement technique particularly advantageous is that the measurements are not dependent on changes in the zero point, because between the measurements they always return to zero and only the differences caused by 10 samples in the measured quantity over time are measured. In addition, since the sample is dilute and a clean measuring medium flows between the samples, the contamination of the measuring devices is very small.

The control 15 of alkaline soups, in particular sulphate soups, is now based on the fact that a mathematical model of the dissolution of lignin in cooking has been developed, the so-called Factor H, which takes into account the cooking chemical dose, cooking temperature and cooking time, as described in Rekunen, S., Jutila, E., Lähteenmäki, E., Lönnberg, B., Virkola, NE., 20 Examination of reaction Kinetics in kraft cooking. Paper and

Tree 62 (1980): 2, 80-90. A model like this works quite satisfactorily if the cooking conditions and the quality and moisture of the chips are known. However, this is not usually the case at any mill, but conditions vary occasionally, and 25 variables such as moisture, quality and particle size distribution, which are particularly important for the control of cooking, are outside the scope of current measurement technology. Attempts have been made to remedy the situation by making various measurements of the digester's solutions. The amount of cooking chemical, i.e. active-30 alkali, has been measured either by conductivity measurement directly from the process piping in Lundqvist, G., Alkali analysis by conductivity measurements. Svensk Papperstid. 76 (1972): 9, 524-527, or U.S. Patents 4,104,028 and 4,012,197 and Wallin, G., Noreus, p., 35 Computer control of batch digesters. Svensk Papperstid.

3,71960 76 (1973): 9, 329-334 by known automatic microprocessor-controlled titration of a broth sample. However, direct conductivity measurement is hampered by heavy soiling in the process tubes and the consequent zero point slip and its difficulty in compensating. The titrators provide fairly reliable information on the effective alkali, but they are slow and only one point per soup in its initial stages does not yet tell the alkali wear profile and thus the residual alkali, which is perhaps the most important basis for forward control.

Attempts have also been made to measure wood-soluble lignin and to evaluate the end point of cooking on this basis. In particular, the absorption of ultraviolet radiation has been used by Kleinert, T.N., Joyce, C. S., Short wawel length ultraviolet absorption of 15 various lignins and related substances. IV ligning determination in sulphate Pulping liquor. Pulp and pap.mag.of Can. 58 (1957): 11, 147-152; Williams, D. J., The application of ultraviolet absorption characteristic of lignin to the control of pulp uniformity. Appita 22 (1968): 2, 45-52; Capart, R., 20 Obese -Decty, K-, Le Cardinal, G., Gelus, M., Contribution to on-line kraft Pulping control. IFAC PRP 4 Automation, Ghent, Belgium 1980, pp. 121-128. A major weakness of these methods has been their continuous performance, which results in difficult-to-control fouling and even more difficult-to-control continuous-dilution high dilution. Due to technical difficulties, lignin measurements have not been introduced continuously for cooking control. In addition, it can be estimated that lignin content alone without knowledge of alkali content and wood chip filling properties cannot be a reliable endpoint determination basis. 30 No mention has been made in the literature of the combined use of the above measurements, nor of the performance of measurements on a single apparatus on the same sample.

The present invention combines the individual assays mentioned above in the literature with a new technique, eliminating 35 previously existing issues affecting the reliability of measurement results and at the same time enabling in principle an unlimited number of different flow measurements from one and the same sample.

The following figures illustrate the invention: Figure 1 is an analyzer apparatus for monitoring and controlling alkaline cooking, Figure 2 is the progress of industrial scale sulphate batch cooking as a function of cooking time, Figure 3 is the leachate as a function of alkali titration performed in the laboratory, Fig. 5 is the relative dry matter content measured by the analyzer from the industrial sulfate batch soup as a function of the dry matter determination performed in the laboratory, Fig. 6 monitoring of continuous sulfate cooking.

According to Fig. 1, a small sample is taken from the process pipe, e.g. from the pressure side 1 of a pump 20 (batch circulator, recirculation pump), cooled by a condenser 3 and filtered in a sinter filter 4 and passed to the washing valve 5 in the normal position When the required amount of sample 25 (1/8 "approx. 50 ml) has passed through the loop, the injection valve 6 turns 60 degrees and the analyzer's own fluid flow 8 (pump or pressurized fluid reservoir) is directed through the loop to a constant volume (loop). In the liquid flow of the Ana-30 lysator (usually pure water but also dilute alkali or alkaline buffer solution) the sample is diluted in a long capillary tube 9 (5-6 m 0 0.8 mm Teflon capillary) by diffusion without any artificial dilution steps and diluted overnight flows through different-35 types of mit equipment: ultraviolet or UV detector 10 5 71960 measures the lignin content of the sample based on the absorption of ultraviolet radiation (205 or 280 nm), the refractive index or RI detector measures the dry matter content of the sample based on the difference in refractive index, the conductivity or residual JK detector based on the conductivity of the hydroxyl ions of the active alkali content. In addition, the flow can be derived from other flow-through measurements xx 13, such as ion-selective electrodes, pH electrodes, and the addition of a neutralizing chemical, whereby effective alkali and sulfidity can be measured by reaction heat and conductivity changes.

The measurement signals of the various detectors from the diluted sample zone are integrated as a function of time, i.e. the areas of the concentration peaks, which are directly the relative concentrations of the sample when running the analyzer liquid flow at a constant rate, are calculated. If desired, the relative concentrations can be converted to real, e.g., g / l, by running the samples analyzed in the laboratory and generating a calibration curve.

Once the sample zone has entered the dilution-20 capillary in the analyzer, wash the sample line immediately. Valve 5 directs the water countercurrently through the filter 4 and the condenser 3 and the washing water leaves the valve 14.

The advantages of the analyzer arrangement according to the invention are: - the amount of sample required is small (50 ml). It is advantageous because a small amount of sample is low in solids and thus the filter is easy to keep clean with a simple countercurrent wash. During factory test runs 0 30 mm sinter has remained completely clean in several thousand analyzes.

- the complex dilution devices required by the ultraviolet devices 30 mentioned in the literature are not needed at all.

Dilution occurs spontaneously in a long capillary tube due to diffusion.

- the measurements do not depend at all on the displacement of the zero points of the measuring devices, because only the difference caused by the sample zone is measured and between 6 71960 zero points between the measurements, whatever it is.

- contamination of the measuring equipment is non-existent because the sample is very dilute and a clean measuring medium flows between the samples.

5 - all measuring conditions are precisely standardized by keeping the temperature of the measuring equipment and the flowing measuring medium constant.

- due to the principle of integration, small variations in the operation of the device or in the form of the dilution zone do not cause interference.

Example 1

Use of analyzer equipment according to the invention for monitoring factory-scale sulphate batch cooking.

The analyzer equipment of Figure 1 was used to monitor the industrial sulfate batch digester at sampling intervals of 15 minutes by sampling the pressure side of the digester's calorizer pump.

3

The volume of the digester was 180 cm, the wood species was pine, the alkali dose was 21% based on the amount of wood, the sulfidity was 30% and the cooking temperature was 170 ° C. The apparatus of Figure 1 used pure water as the flowing liquid of 20 analyzers, 8 hose pumps as the liquid flow source, at a flow rate of 4 ml / min, the volume of the sample loop 7 was 25 μm, the length of the diffusion dilution capillary 9 was 5 μm0.8 mm. The ultraviolet detector 10 was a Knauer UV / VIS Photometer, the wavelength was 280 nm, the refractive index detector 25 was a Knauer Differential Pefractometer and the conductivity detector was a Vydac Conductivity Detector. The electrical signals of the detectors were integrated with an 8-bit SELMA microcomputer and a self-made integrator program. Measured in this way, the analysis time of one sample was about four minutes.

30 Example 2

Use of analyzer equipment according to the invention for monitoring factory-scale continuous sulphate cooking

The procedure was as in Example 1, except that various cycles of the continuous sulfate digester were monitored, which were a smoothing cycle, an effluent black liquor, a cutting cycle, and a 7,71960 wash cycle. With the analyzer, a sample was taken every about 5 minutes, moving from one cycle to another, with an analysis interval of one minute of 20 minutes. The results are shown in Figure 6.

Claims (5)

8 71960 A method for controlling alkaline cellulose soups, in particular sulphate cooking, characterized in that a sample is taken from the digester's process tube and fed to the capillary tube by means of the analyzer liquid medium, the analyzer being out of the cooking process, after which the sample zone is transferred to self-diluted The cooking chemical, in particular the concentration of active alkali at the beginning of cooking and how the active alkali is consumed during cooking, as well as the concentrations of reaction products, ie lignin and dry matter, are measured continuously and zero, and that the cooking is controlled by adjusting the active cooking time and temperature. the amount of alkali. Process according to Claim 1, characterized in that the sulphate batch soup is controlled. Process according to Claim 1, characterized in that a continuous sulphate cooking is controlled. Method according to one of Claims 1 to 3, characterized in that the liquid medium of the analyzer is water. Method according to one of Claims 1 to 3, characterized in that the measuring devices are an ultraviolet detector, a refractive index detector and a conductivity detector.