LOW CONSISTENCY REFINING OF THERMOMECHANI CAL PULP

The effect of low consistency refining on pulp quality and energy cons umption were examined on an industrial scale. First, comparisons were made between a two stage high consistency refining (Primary [Pr] + Sec ondary [Sc]) sequence followed by a low consistency refining (LCR) seq uence, and a two stage conventional refining (Pr + Sc) sequence. Test results showed a 5% energy saving in favor of the three stage refining (Pr + Sc + LCR) sequence with pulp quality equal to conventional refi ning (Pr + Sc). The addition of LCR in the third stage increased refin ing productivity by 10%.Other refining tests were carried out with a h igh consistency (Pr) refining stage followed by a low consistency refi ning (LCR) stage (Sc). Results showed a specific energy reduction of 1 2% for the two stage (Pr + LCR) refining process as compared to the co ntentional high consistency refining process. However pulp quality was 10% lower than the conventional process. By optimizing primary refini ng plates pulp quality could be increased. Further tests for two stage refining (rejects + LCR) of pulp rejects were carried out and results compared with these obtained using conventional high consistency refi ning of rejects. The tests showed energy savings of 7 to 10% in compar ison with conventional refining of rejects. However these energy savin gs had a negative effect on pulp quality.