Minimum effluent process for pulp mill.

摘要

This work studied the possibility and effectiveness of concentrating pulp mill effluents through gas hydrates purification process. The pulp mill effluents were proven to be able to form gas hydrates under proper temperature and pressure conditions. The important parameters affecting the effectiveness of the gas hydrate concentration, such as the presence of fiber, operating temperature and pressure, mass transfer, and washing, were also studied in this research. This purification process was shown to be very effective in terms of the reduction of Total Dissolved Solids (TDS) and Total Suspended Solids (TSS) reductions. The Chemical Oxygen Demand (COD) reduction, however, only achieved 53% reduction in the batch reactor. With application of multistage recrystallization, the COD reduction improved to just over 80%, still lower than the industrial expected over 95% reduction. The unsatisfied COD reduction was mainly due to the inherent equipment limitation and possibly unknown chemical compositions of the pulp mill effluents. Layer crystallization model was used to predict the impurity concentration in the final recovered water. Over 95% COD reduction can be achieved with 2 crystallization stages. In addition, final product purity and process yield was found to strongly depend upon the yield of each gas hydrate concentration stage and growth rate of gas hydrates. Meanwhile, the relationship between final product purity and process yield implicated the necessary optimization between yield and purity.