UBC Theses and Dissertations

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UBC Theses and Dissertations

Energy saving during pulp screening through addition of A-PAM Chowdhury, Ayesha


Pulp screening is an important operation in the manufacture of pulp and paper industry. Through the pulp screening process, low quality pulp and other contaminates are removed to form high quality pulp stream. However, this process consumes a significant amount of electrical energy. Turbulent fluid exerts frictional drag on all solid bodies present in the flow. Drag can be reduced in various ways that will consequently diminish the pumping and pulp processing cost. The frictional drag of turbulent flow can be dramatically reduced by dissolving a minute amount of long-chained polymer in water. Unfortunately, the mechanism of Drag reduction by polymer additives with pulp is poorly understood. In this work, the effect of polymer additives and surface contour modification on turbulent drag reduction in a pressure screen was studied with 0%, 1% and 2% pulp concentration. Drag reduction was measured for Northern Bleached Kraft Pulp in presence of APAM with a rotational speed of up to 1600rpm. Three different rotor power capacities were studied in presence of pulp, polymer additives and pulp with polymer additives for three different feed flow rates. Four different polymer concentrations were used during the experiment. 1% consistency pulp with 100 ppm polymer in EP rotor shows effective drag reduction of than 1% pulp consistency alone. At highest tip speed 15.43m/s drag reduction of EP rotor for 455 l/min flow rates of 1% consistency pulp with 100 ppm polymer is 38%±0.9%. Additionally, a rotor having longitudinal ribs in the stream wise direction is studied. Literature shows that up to a 40% drag reduction [1] can occur by riblets along the stream wise direction in a turbulent flow regime with polymer additives. In this study, a ribs rotor having s⁺=30 , the spacing between two ribs is 2.3mm, height of the ribs is 1.15mm and thickness is 0.5mm was studied. Hydraulically smooth rotor takes less power than rib rotor for water and pulp solution. Riblet geometry increases drag reduction at tip speed 10m/s to 90%±3.4% for 455l/min flow rate in presence of 100ppm A-PAM with 2% consistency pulp.

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