The Effect of Water Reduction in Kraft Pulp Washing in Ecf Bleaching

Abstract

-The main objective of this work was to study the technical viability of using the cellulose bleaching effluent, at several stages of the process, seeking fresh water reduction in pulp washing, and evaluating its effect on pulp quality. Eucalyptus spp. industrial cellulosic pulp with oxygen was used in this experiment. The same bleaching sequence D(E+P)DP was performed ten times, under the same conditions (temperature, consistency and time). Counter current washing was used in the bleaching stages, and each sequence was carried out with different washing factors: 9, 6, 3, 0 m³ of distilled water/ton of pulp, trying to reach brightness of 92 ± 0,5% ISO. The ten sequences sought to achieve the stability of the effluent organic load, measured by the chemical oxygen demand (COD). Then, the COD results were compared to the brightness ones from the bleached pulp. The evaluated results from the ten sequences and four different washings showed an increasing in COD due to the organic load accumulation, resulting from the reuse of effluent from previous sequences. This COD increasing provided the lower brightness results during the cycles, besides the water reduction, evidencing the necessity of washing between bleaching stages. In this study, the obtained result for the pulp washing up to 3m³/t was tolerable and even recommended. On the other hand, the pulp without any washing (0m³/t), due to the lack of enough brightness, it is commercially unviable.Keywords: Pulp; Bleaching; Eucalyptus.O EFEITO DA REDUÇÃO DE ÁGUA NA LAVAGEM DA POLPA KRAFT NO BRANQUEAMENTO ECF RESUMO -O objetivo principal do presente trabalho foi estudar a viabilidade técnica de se usar o efluente da lavagem do branqueamento da celulose, nas diversas etapas do processo, visando uma redução no consumo de água fresca na lavagem da polpa avaliando seu efeito na qualidade da polpa. Foi utilizada polpa celulósica industrial de Eucalyptus spp. deslignificada com oxigênio. Foi feita a mesma sequência de branqueamento D(E+P)DP dez vezes, nas mesmas condições (temperatura, consistência e tempo). Utilizou-se a lavagem em contra-corrente nos estágios de branqueamento, cada sequência foi feita com um diferente fator de lavagem: 9, 6, 3 e 0 m³ de água destilada por tonelada de polpa, buscando atingir a alvura de 92 ± 0,5% ISO. As dez sequências realizadas foram uma busca da estabilidade da carga orgânica do efluente medida pela DQO e então comparados os resultados da DQO com os resultados da alvura da polpa já branqueada. Os resultados avaliados das dez sequências e nas quatro diferentes lavagens mostrou o aumento da DQO por causa do acúmulo da matéria orgânica decorrente da reutilização dos efluentes das sequências anteriores. Este aumento da DQO fez com que os resultados da alvura baixassem durante os ciclos e também na redução da água de lavagem, provando a necessidade de que haja lavagem entre os estágios de branqueamento. Neste trabalho o resultado da lavagem até 3m³/t de polpa foi tolerável e ainda recomendável, já para a polpa sem lavagem (0m³/t de p...

The Effects of Alkaline Filtrate Recirculation Towards the Properties of Long Fiber Pulps With Od(epo)ded Bleaching Sequence

“…The ions and salt concentrations varied depending on carryover use after (EPO) stage (Table 8). Calcium and magnesium content was lower and sodium content increased 21% in the filtrate from the (EPO) stage due to the increase in NaOH consumption by 19% in the extraction alkaline stage (Frigieri et al, 2016). Partial circuit closure of the alkaline filtrate did not change the calcium or carbonate concentrations in the filtrate (EPO).…”

“…odt -1 of the filtrate (EPO) recirculation ( Table 7). The increase of calcium and sodium ions concentrations generated precipitated salts, causing incrustation and increasing the carbonate, oxalate and sulfate concentrations (Frigieri et al, 2016).…”

“…Circuit closure can recycle water and chemical reagents, reducing pollutant loads (Frigieriet et al, 2015;Frigieri et al, 2016). Bleaching is the industrial stage with the highest water consumption and reversing this scenario would result in economic and environmental gains (Kansalet al, 2008;Kamali and Khodaparast, 2015).…”

Post-O2 Eucalyptus Pulp in a/D(ep)dp Bleaching Sequence Washed With Recirculation of the Alkaline Filtrate

“…The optimisation of water use in pulp mills should be prioritised on bleaching, as this stage generates 50% of the factories effluents (Kansal et al 2008, Kamali & Khodaparast 2015. Circuit closure reduces water use; however, the effect of this operation on reagent consumption, equipment wear and final product quality should be evaluated (Frigieri et al 2015, Frigieri et al 2016, Masrol et al 2018.…”

The effects of temperature, alkali charge and additives in the oxygen delignification in high kappa number eucalyptus pulp kraft

“…Condições típicas da deslignificação com oxigênio no meio industrial (MCDONOUGH, 1996). The oxygen delignification with high kappa number pulps allows removing large amounts of residual lignin present in pulp (VENSON et al, 2015); however, its implementation requires planning, since its effectiveness is limited: approximately 50% of delignification (FRIGIERI, 2016;SILVA, 2010). If the delignification is higher, there is a serious degradation of the carbohydrate fraction DOI: dx.doi.org/10.18671/scifor.v46n118.08 of pulp, resulting in the deterioration of the pulp viscosity and mechanical strength properties (MCDONOUGH, 1996, GIACOMIN, 2015.…”