Effects of chip pretreatment and feeding segments on specific energy and pulp quality in TMP production

Abstract

Abstract Increased wood softening and refining intensity have earlier been utilized to improve refining efficiency in mechanical pulping. We have evaluated a combination of increased softening by low dose sulphite chip pretreatment and increased intensity by feeding segment design in a TMP line for production of high quality printing papers. Norway spruce wood chips were preheated, compressed in an Impressafiner and impregnated with water or sodium sulphite solutions (Na2SO3 charges 3.6 and 7.2 kg/t). Chips were refined in two parallel 68” double disc refiners using two different refining conditions: standard bidirectional segments at normal production rate (9 t/h) and feeding segments at increased production rate (11.1–12.1 t/h). The feeding segments enabled a 30 % increase in production rate. Refining with feeding segments at 12.1 t/h production rate combined with chip pretreatment with 3.6 kg/t sodium sulphite reduced the specific energy 360 kWh/t (19 %) compared to refining with standard segments and no pretreatment. Pulp properties were similar for the two configurations. The combination of feeding segments and chip pretreatment with water reduced the specific energy 180 kWh/t (9 %). Implementation of most of the technology presented has reduced the electrical energy use for the mill by approximately 80 GWh/year.