OCC Pulp Quality Improvement at Simpson-Tacoma Kraft Company, 2005 Engineering, Pulping & Environmental Conference

Simpson Tacoma Kraft Company, an integrated producer of bleached and unbleached linerboard, has found significant paper machine benefits from an operational change in its Old Corrugated Containers (OCC) repulping system. By increasing rotor speeds in the OCC system fine screens, and using high open area screen cylinders, the strength properties of the OCC increased dramatically. On average, the Canadian Standard Freeness (CSF) of the screened OCC going to the paper machines increased by 50 ml. Having a higher freeness enabled the paper machine to run faster due to better drainage while also improving the strength characteristics of the sheet. The higher strength OCC has permitted a reduction in the concentration of virgin softwood kraft pulp required in the linerboard, enabling the use of the virgin kraft pulp elsewhere in the mill.

An additional feature of the higher screen rotor speed is increased screen capacity, and lower fiber loss. The throughput of the OCC system has increased by over 20% since the speed up of the screen rotors, and the amount of fiber rejected by the tertiary stage screen has decreased by over 50%.