Abstract
Abstract The bleaching sector of the wood pulp industry is its largest effluent generator. The aim of this study was to reuse the bleaching filtrate in order to reduce water consumption. The experiment was conducted by simulating the D0(EP)D1 bleaching sequence and recirculating different amounts of filtrate from the oxidation stage to control the pulp consistency of the delignification stage (pre-O). Physical, mechanical, chemical and optical properties of the pulp were studied. The accumulation of the non-process elements (NPE) and their effects were evaluated with the Aspen-Plus® computer simulator. The results of the computational modeling were satisfactory. The recirculation of filtrates increased the saturation index of the system by 19 %, but remained at sub-saturation levels. The pulp viscosity and elongation remained statistically stable. Recirculation of up to 50 % of the filtrate did not produce differences in pulp brightness; however, there were slight losses in the pulp resistances. In order to maintain 84 % ISO brightness, there was a higher consumption of the bleaching reagents. Up to 50 % of recirculation of the filtrates was accomplished without jeopardizing the system and the pulp quality and resulted in a savings of 55 m3 h−1 of water – 7 % of the consumption of the entire mill.
Highlights
Competition and mitigation of environmental impacts in the pulp and paper industry have led to more efficient production processes (Mahmood and Elliott 2006, Kamali et al 2016)
Closing the water circuit is an option for accomplishing this goal; it should be carried out in a cautious way to avoid the accumulation of non-process elements (NPE) that can generate incrustation and corrosion in pipes and equipment (Amaral et al 2012, 2014), besides reducing the quality of the pulp (Santos et al 2015)
The reduction of differences in pulp quality between each recirculation level is due to the ability of the bleaching process to absorb chemicals and organic loads throughout each stage (Sixta 2006)
Summary
Competition and mitigation of environmental impacts in the pulp and paper industry have led to more efficient production processes (Mahmood and Elliott 2006, Kamali et al 2016). These processes include genetic improvement of plants for wood production, reduction of resource uses and production of materials with higher quality (Hung et al 2015, Frigieri et al 2015, Chen et al 2016). Many mills are looking for solutions to reduce their environmental impacts, such as water conservation and effluents with lower organic loads. Closing the water circuit is an option for accomplishing this goal; it should be carried out in a cautious way to avoid the accumulation of non-process elements (NPE) that can generate incrustation and corrosion in pipes and equipment (Amaral et al 2012, 2014), besides reducing the quality of the pulp (Santos et al 2015)
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