Experimental investigation of pulp dewatering by high vacuum suction boxes

Abstract Reducing energy consumption by industrial processes has become imperative because of rising energy costs and efforts toward decarbonisation. The continuous manufacturing of paper is energy intensive due in part to the water removal process required to convert pulp slurries to valuable paper products. This necessitates the development of energy conservation techniques, while simultaneously ensuring the quality of the product. A pilot-scale test unit was developed to quantify the effects of dwell time, vacuum pressure, and refining energy on the achievable pulp concentration or dryness level of three pulp types utilised in paper machines. Pulp dry matter was investigated as a means of gauging vacuum consumption and hence energy utilisation in paper machines, which could potentially reduce utility consumption of the overall drying process. A novel approach to simulate the pulsating high vacuum zone in the forming section of a paper machine was implemented, allowing the development of statistical correlations to explore vacuum dewatering conditions that may lead to energy efficiency. Bleached hardwood, mechanical/groundwood and recycled pulp were characterised to determine the effects of refining energy on fibre morphology and their drainage behaviour in pulp slurries. A dryness level of 21.8% at − 55 kPa gauge was achieved for bleached hardwood, whereas lower values of 19.8 and 18.3% were observed for recycled and mechanical pulps, respectively. This behaviour was attributed to the differences in drainability and morphology of the pulps due to their respective unique properties, further exaggerated by refining.