Displacement washing of soda rapeseed pulp

Abstract

The paper deals with the displacement washing of unbleached pulp cooked from rapeseed straw by soda pulping under laboratory conditions. Pulp fibres were characterised by their average length, as well as by effective specific volume and surface. Using the step function input change method, the washing breakthrough curves measured for alkali lignin as a tracer were described by the dispersed plug flow model containing a dimensionless criterion, the Péclet number. Besides the wash yield, the dispersion coefficient as well as the mean residence time and space time were evaluated. Preliminary results obtained for soda rapeseed pulp were compared with those for kraft hardwood (beech) and softwood (spruce, pine) pulps published earlier. The wash yield measured for soda pulp was found to be lower than that for hardwood and softwood pulps which manifested lower hydraulic resistance. The presence of silique valves in rapeseed straw resulted in lower mean residence time of lignin removed from the pulp bed in comparison with pulp manufactured from stalks only.

Number of Ideal Stages as an Efficiency Parameter for Displacement Washing of Pulp

“…The cooking conditions were described earlier. 11,12,26 The degree of delignification, expressed in terms of kappa number determined as per the Tappi test method T 236 om-99 for the kraft beech, kraft spruce, and soda rapeseed pulps was equal to 51.6, 50.1 and 49.7, respectively. Using the Kajaani FS-100 instrument, the arithmetic average length, l A , and weighted average length, l W , along with fibre coarseness, FC, were measured for the wet state of pulp fibres.…”

“…Further properties of the black liquors, which were obtained from industrial mills, can be found in previous papers. 11,12,26 Displacement washing experiments simulated under laboratory conditions were performed in a cylindrical glass cell with the inside diameter of 35 mm. Pulp beds were formed from a dilute suspension of unbeaten pulp in black liquor.…”

“…Displacement washing experiments with pulp fibres, as well as the washing equipment, were described in detail in previous papers. 8,9,[11][12][13] After completing the washing run, the volumetric flow rate of the wash liquid was measured gravimetrically at the pressure drop of 7 kPa to determine the permeability and average porosity of the pulp bed. Analogous measurements at various consistencies of the bed were focused on the determination of the effective specific surface of pulp fibres, a V and a m , according to Ingmanson.…”

“…Since, for the same amount of wash water at constant discharge pulp consistency, displacement washing is more effective than washing based on dilution followed by thickening, the former has been investigated in several papers. [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] In order to decrease the amount of wash water, several pulp washers are arranged in a countercurrent manner. The performance of a set of staged washers can be quantified by the number of equivalent ideal stages of dilution and thickening, where the incoming streams are perfectly mixed and the effluent streams are in equilibrium.…”

Lignin from Annual Plants as Raw Material Source for Flavors and Basic Chemicals

“…For the alkaline soda pulping, a sodium hydroxide solution and the following parameters were used: ω (NaOH) = 3 wt %, T = 160 °C, H ‐factor = 320 with a liquid/solid ratio = 8.2 mL g −1 . The pulp was separated from the lignin‐rich black liquor and washed with sodium hydroxide solution ( ω (NaOH) = 0.3 wt %) at 80 °C.…”