The Effect of the Countercurrent Washing Process for KP Brown Pulp Stock Line

摘要

The washing process of KP (Kraft pulp) brown pulp stocks, following to KP cooking continuous digester, is consist of a series of washing equipment. This multi stage washing process is not only to wash the brown pulp stocks effectively but also to recover KP cooking chemicals (expensive sodium compounds) and some wood lignin components that dissolved in the filtrated dilute black liquors. And the filtrated and extracted black liquors are send to the following KP causticizing process, and the chemicals are recovered finally. In this KP washing process, "Countercurrent flow washing" strategy has been utilized in general, and expected to the washing process to achieve better washing states for the pulp stocks not to remain much chemicals in it. And, furthermore, they are required to be washed effectively with lesser amount of fresh water usage, and, at once expected to decrease the energy loads of the following black liquor evaporation process. In this paper, a washing calculation model for this KP multi stage washing process that can simulate and estimate the chemical material balance was proposed. Next, utilizing the simulated results by this model and another "Cross flow washing strategy", that used simple fresh washing water flow lines were compared. As the result, the effect of the "Countercurrent flow washing" was confirmed from the superiorities of the simulated results of the recovered chemical amounts in each washing filtrate line, lost chemical amounts to be carried away attached to the brown pulp stocks and the variance of the recovered chemical consistencies etc.