Energy efficient refining of black spruce TMP by using acid hydrogen peroxide: Part 1. A pilot plant study

The potential of using acid hydrogen peroxide for lowering the electrical energy consumption during production of Black spruce (Picea mariana) thermomechanical pulp (TMP) was investigated. The chemical system, which consisted of ferrous sulphate, hydrogen peroxide and optionally an enhancer [ethylenediaminetetraacetic acid (sodium salt), 3,4-dimethoxybenzyl (veratryl) alcohol or oxalic acid/sodium oxalate], was evaluated as an inter-stage treatment where the primary refiner was used as a mixer. The approach has the advantage of minimising the capital investment needed for implementation, thus being directly applicable in a thermomechanical pulping process consisting of two or more refiners in series. The results obtained in a pilot plant trial revealed that is was possible to significantly reduce the specific energy consumption by approximately 20-and 35% to a freeness value of 100 ml CSF by using 1 and 2% hydrogen peroxide, respectively. The energy reduction could be obtained without any substantial change in fibre length, fractional composition of the pulp or tensile strength of the paper. The tear strength was slightly reduced however, as was the pulp yield. The major drawback with the acid hydrogen peroxide system was a reduction in brightness by at least 6 brightness units. The addition level of ferrous sulphate was too high and the possibility to reducing the discoloration should be considerable when the chemical system is optimized.