THE EFFECT OF SHOE PRESS ANGLE ON BULK, DRYNESS AND PAPER PROPERTIES, 23TAPPICon



Efficient water removal in the press section has long been a key objective in paper production. A common rule of thumb is that a 1% increase in the dry content after pressing can result in a 4-6% reduction of the dryer demand. Increasing the web dryness after pressing is therefore extremely important for production efficiency. At the same time, pressing densifies the wet web which affects nearly every important paper property. The objective of this study was to investigate the effect of different press profiles on web density, dryness and paper properties under industrially relevant conditions and with two different stock compositions. A series of pilot production trials were performed on the pilot paper machine, FEX, where the shoe press tilt angle was varied to produce a range of different press profiles isolating key press profile parameters, namely the rate of compress in the press nip, the peak load and the location of the peak load in the press profile. It was shown that by increasing the shoe tilt angle and thereby producing a press profile with low initial rate of compression followed by a high peak pressure at the end of the press profile, dryness could be increased by several percentile units without sacrificing density and paper properties. Trials were repeated for stocks composed of 100% unbleached softwood kraft (UBSK), and for a mixture of 50/50 CTMP/UBSK, where both similarities and differences were observed for the two different stocks. Efficient water removal in the press section has long been a key objective in paper production. A common rule of thumb is that a 1% increase in the dry content after pressing can result in a 4-6% reduction of the dryer demand. Increasing the web dryness after pressing is therefore extremely important for production efficiency. At the same time, pressing densifies the wet web which affects nearly every important paper property. The objective of this study was to investigate the effect of different press profiles on web density, dryness and paper properties under industrially relevant conditions and with two different stock compositions. A series of pilot production trials were performed on the pilot paper machine, FEX, where the shoe press tilt angle was varied to produce a range of different press profiles isolating key press profile parameters, namely the rate of compress in the press nip, the peak load and the location of the peak load in the press profile. It was shown that by increasing the shoe tilt angle and thereby producing a press profile with low initial rate of compression followed by a high peak pressure at the end of the press profile, dryness could be increased by several percentile units without sacrificing density and paper properties. Trials were repeated for stocks composed of 100% unbleached softwood kraft (UBSK), and for a mixture of 50/50 CTMP/UBSK, where both similarities and differences were observed for the two different stocks.

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Author: Paul Krochak; Catherine Östlund; and Lennart Hermansson
THE EFFECT OF SHOE PRESS ANGLE ON BULK, DRYNESS AND PAPER PR
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