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Study of Sulfite Pulp Washing Process under Industrial Conditions

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M.I. Kravchenko

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Instability of spent sulfite liquor extraction processes after the cooking at the stage of pulp washing in batch cooking digesters of 320 m3 capacity was analyzed. Displacement washing kinetics of sulfite pulp in cooking digesters was studied. Theoretical feasibility of washing constants determination at high temperature and pressure was found. For stabilizing high-
temperature washing of pulp and enhancing its efficiency it is recommended to install the
hydraulic distributors (hydromonitors) of washing liquor, to apply increased temperature of displacement liquor and excess pressure in the digesters that has to be higher than final relief pressure at cooking. The kinetics results enabled to make a conclusion about two-stage washing process, running in the out-diffusion area at the first stage and at the second –in internal (pore) diffusion zone. The hydraulic distributors of washing liquor are proposed to install to increase high-temperature pulp washing efficiency in industrial cooking digesters of 320 m3 capacity. It is also recommended to provide slow and regulated pumping of washing liquor into a higher-temperature digester. Hydraulic pressure in cooking digester during extraction of strong sulfite liquor out of digester at sulfite pulping for producing middle-hardness pulp should be remained within (4,5…6,0)105 Pa. For soft sulfite pulps hydraulic pressure should be decreased to (2,5…3,0)105 Pa. Pulp washing kinetics was studied
for cooking digesters equipped with washing liquor distributors and controlled pumping of washing liquor into digester at hydraulic pressure no more than 3*105 Pa. The liquor extraction in digesters under an elevated temperature and hydraulic pressure enabled improving considerably the washing efficiency in that process. Thus, concentration of evaporation dry solids increased by 1…3 %, which reduced energy consumption by 0.13 Gcal in the liquid lignosulfonate production. Sulfurous anhydride emissions dropped twice. COD and BOD in the effluents from the pulping-and-washing shop significantly improved.


M.I. Kravchenko, Candidate of Engineering Sciences, Associate Professor

Authors job

Saint Petersburg State Forest Technical University under name of S.M. Kirov, Institutskiy per., 5, Saint Petersburg, 194021, Russian Federation; e-mail:


pulp washing, cooking digester, washing liquor distributors (hydromonitors), spent liquors, hydraulic pressure, filtration, washing constants, out-diffusion, internal (pore) diffusion, lignosulfonate, effluents, energy consumption, pulp bleaching, pulp ha


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Study of Sulfite Pulp Washing Process under Industrial Conditions