The potential of sulfur dioxide treatment to lower radiata pine TMP energy demand

摘要

Pretreating radiata pine chips with sulfur dioxide (SO_2) gas was found to reduce the energy required to produce refiner mechanical pulp of a given freeness provided relatively high application rates in the range 2-4% (w/w) were used. This reduction in refining energy was achieved without any adverse effects on the pulp strength and optical properties. Lower application rates in the range 0.5-1.0% (w/w) were not effective in reducing the energy demand.rnThe chip preheating temperature was found to have a major influence on the effectiveness of the SO_2 treatment. Energy reductions of 8-9% were obtained when 2-4% SO_2 application rates were used to pretreat chips in a PRMP pulping system that involved atmospheric chip presteaming (90℃) prior to pressurised refining. In this system most of the applied SO_2 gas did not appear to react with the fibre until the chips entered the refining operation. In contrast, when the SO_2 gas was applied ahead of the pressurised chip preheating operation (125℃) in a conventional TMP system, all the SO_2 gas was consumed during chip preheating and only a marginal reduction in refining energy was obtained with a high, 4% SO_2 application rate.rnThese findings indicate that it may be more effective to use SO_2 as an in-refiner treatment than as a chip pretreatment. However, based on the current costs of electricity and SO_2 gas, application rates in the range 2-4% would not be cost effective for a commercial PRMP pulping operation.