A feasibility study on a new chemimechanical pulping process including a new chemical recovery process from waste liquor was conducted. A new type of high-yield chemimechanical pulp was produced from raw cellulosic materials which were lightly heated in aqueous solution of sodium sulphate and sulphur dioxide (as Na2O, 1060 g/l, SO2 1073 g/l) and then mechanically treated with a single disk refiner. It was found that a plain sodium sulphate solution has no cooking potential.
Wood SOX pulp of high yield (4585%) and of high grade was produced from softwood, hardwood, and tropical wood. Yezo spruce SOX pulp (yield 68%) gave 29.7% brightness, by Hunter 0.608g/cm3 bulk density, 7.81 km breaking length, 4.77 JIS burst factor, and 43.9 tear factor.
Nonwood SOX pulp of high yield (4863%) and high grade was produced from bamboo, rice straw, and bagasse. Rice straw SOX pulp (yield 63.2%) gave 84.1 Kappa no., 12.7% pentosan, 20.9% ash, 39.6% brightness, 0.479g/cm3 bulk density, 3.02 km breaking strength, and 1.61 JIS burst factor.
Water soluble, crude sodium sulphate;KP fly ash from precipitator in recovery unit (Na2SO4 97.3%, Na2CO3 1.2%) and ash from NSSC waste liquor (Na2SO4 64.7%, Na2CO3 30.0%) were also used for SOX cooking.
Recovery of SOX cooking chemicals was proven to be quite easy. Upon incinerating concentrated waste liquor, sodium sulphate was recovered from ash, while sulphur dioxide was recovered from relief gas and gas produced during incineration of waste liquor.