Abstract: The present invention relates to a method of intensifying the washing of a fiber suspension. In particular, the present invention relates to decreasing the lignin content of a fiber suspension by extracting. Lignin removal is usually carried out at a consistency of less than 3% whereby heating consumes much energy. The method of the invention allows a considerable increase in the consistency of the suspension which results in that the energy consumption is decreased to a fraction of the one required by prior art methods. A characteristic feature of the method of the invention is that dry substance and chemicals contained in the fibers are extracted at a raised pressure and temperature.

Abstract: A method of controlling an alkaline pulping process, sulphate pulping in particular. The concentration of the dissolved components as well as the concentration of the recidual cooking chemical are measured. The measurements are carried out by means of an analyzer positioned outside of the cooking process in a separate liquid flow. The measuring devices are per se known detectors. The cooking process is observed and the necessary corrections are made on the basis of the measuring results.

Abstract: A method of controlling sulphite pulping or hydrolytic processes by means of a rapid furfural analyzer. Furfural and 5-hydroxymethylfurfural are separated from the other UV-absorbing compounds of a process liquor sample. The concentration measurements are carried out by menas of an UV-method. The obtained measuring results are utilized for on-line controlling of the process in question.

Abstract: A method for rapid determination of the contents of lignin, monosaccharides and organic acids in the process solutions of sulfite pulping. Accordingly, any non-ionized compounds that disturbs the measurement of these concentrations are separated from the lignin material by an ion-exclusion technique. The measurements of concentrations are carried out by means of the UV-method, refractive-index method, and/or by means of the polarimetric method. The method of the present invention is usable for the controlling of sulfite cooking or other pulping or by-product production processes as well as for the characterization of the spent liquor.

Abstract: An alkaline sulfite pulping process in which the lignocellulosic material is cooked in a solution containing sodium sulfite is provided. Sodium aluminate is used as a buffering agent. As a result of this, the stability of the pH of the cook and the properties of the pulp are improved. The amount of sodium aluminate as NaOH is from 2% to 8% based on the dry weight of the chips. The pulping process is carried out with the addition of a small dosage of anthraquinone, to produce chemically defibered pulps.