| Popis: |
Detrimental substances that originate from deinked pulps and other raw materials tend to build up in paper machine circulation waters, hindering process efficiency and paper quality. The applicability of selective flotation to remove substances from circulation waters was investigated in a two-stage flotation process in which no chemical additives were used. The first stage of the process consisted of a flow channel for white water deaeration, including first-stage flotation. The overflow of the channel flow flotation was further treated in a separate second-stage flotation. The efficiency of the flow channel and a secondary flotation to remove bubbly gases, ink, stickies, and wood extractives were quantified in relation to the reject flow rates or solids yield. The total removal efficiency of a simulated two-stage flotation process was then analyzed for a specific case. The results showed that a considerable reduction of contaminant load can be obtained using a two-stage flotation process without affecting the deaerating function of the channel flow. Further optimization of the proposed internal white water purification scheme may provide substantial benefits to paper or board machine operations with reasonable solids recovery rate. |
