The Viscosity Reduction Technology Of Black Liquor From Wheat Straw Soda Pulping

In order to reduce the viscosity of black liquor, a four-factor and three-level orthogonalexperiment was employed to study the effects of alkali charge, maximum temperature, holdingtime, and nitrogen pressure on the viscosity of black liquor from wheat straw soda pulping by annitrogen enhanced heat treatment. While a four-factor and three-level orthogonal experiment wasdesigned to study the effects of alkali charge, maximum temperature, holding time, and oxygenpressure on the viscosity reduction of black liquor from wheat straw soda pulping by an oxygenenhanced heat treatment. The article analyzed the rheological properties of the black liquor andtemperature of viscous flow. The influence of several compounds of silicide to the viscosity ofblack liquor was discussed. The main results were as follows:1. The viscosity reduction result of the oxygen enhanced heat treatment was much betterthan the simple heat treatment and nitrogen enhanced heat treatment. The optimal conditionsof the heat treatment which pressurized by oxygen were determined as follows: alkali chargeon total solids content was1.0%(based on NaOH), with maximum temperature of170℃,oxygen pressure of0.7MPa, and holding time at the maximum temperature was45min.. Thetemperature has the most remarkable influence on the viscosity of the black liquor. And thealkali charge has the least influence on the viscosity of the black liquor.2. The heat treatment with oxygen can improve the critical concentrations of the wheatstraw soda pulping black liquor from35%to45%. At the concentration of45%, the viscosityof the black liquor was reduced by81.1%after heat treatment with oxygen than the blackliquor without any heat treatment at the same concentration.3. The rheological properties of black liquor showed that the consistency coefficient ofuntreated,heat treatment with nitrogen and heat treatment with oxygen were1855.7,1202.6and317.2Pa·sn. Heat treatment with oxygen was much efficient than those treated by simpleheat treatment due to the heat treatment with oxygen can decompose hemicelluloses and ligninmacromolecules in black liquor. The shear thinning phenomenon of black liquor by oxygenenhanced was more obvious. The oxygen enhanced heat treatment will also contribute toimprove the transmission efficiency of pipeline.4. Having been analyzed the temperature of viscous flow, the temperature dependence ofblack liquor with oxygen enhanced heat treatment was decreasing. And oxygen enhanced heattreatment was helpful to improve the transportation at lower temperature of black liquor,5. Compared with the ash of wheat straw and the silica, the sodium silicate was evenmore effective to improve the viscosity of black liquor. The effect of the sodium silicate ondifferent concentration of black liquor was: high consistency black liquor≥medium consistency black liquor>low consistency black liquor. When the percentage of silicon fortotal solid content was greater than15%(based on SiO₂), the sodium silicate has a significantimpact on low consistency black liquor. When the percentage of silicon for total solid contentwas between13-15%(based on SiO₂), the sodium silicate has a significant impact on mediumconsistency black liquor. When the percentage of silicon for total solid content was between11-13%(based on SiO₂), the sodium silicate has a significant impact on high consistency blackliquor.