Fractional pulping of packaging board in high consistency drum pulping

A wide variety of packaging materials with different wetting rates and wet strength properties are used in old corrugated container (OCC) processing. The disintegration rates of the different grades also vary and enable the use of the fractional pulping concept where easily disintegrated material is removed at the early stages. In the present study, fractional drum pulping was studied by pulping (Pilot drum pulping) and fractionating (Tampella oscillating screen) a mixture of strong-grade kraftliner and weak-grade fluting at high consistency to determine if energy consumption could be reduced. The results showed that a 25% energy saving could be realized through fractional pulping and an even higher potential might be possible if pulping conditions are optimized. Average fiber length, fines content, and ash content in the separated fractions were analyzed. The separated short fiber fractions and long fiber fractions could be individually processed, thus decreasing the volumes in the unit processes on the OCC line.