Flow Induced Venturi Cavitation to Improve Energy Efficiency in Pulp Production

Abstract

In order to lower the energy consumption of the fibrillation stage for the pulp and paper industry, a new technology need to be innovated and developed. This paper presents an innovative new design of a venturi nozzle as a concept for refining pulp using hydrodynamic cavitation. The conditions created by cavitation bubbles collapsing near paper fibres are similar to the conditions in conventional refiners used in the pulp and paper industry. The cavitation created in the venturi implodes on the surface of the cellulose fibres, increasing the fibrillation and processing the fibres further. Cavitation is hard to control and can cause high mechanical wear, therefore an optimization study of the venturi nozzle is performed using Computational Fluid Dynamics (CFD) and state-of-the-art optimization techniques. Finally, the optimal venturi shape is investigated in a series of detailed numerical simulations, using a Bingham fibre model to include the effect pulp fibres has on the flow. The investigation shows that cavitation bubbles start to form at an outlet pressure of 1.87 bar, for an inlet pressure of 3.00 bar. The intensity of the bubble collapse depends on the surrounding pressure and this outlet pressure therefore enables a powerful treatment of the pulp fibres. In conclusion, the venturi concept is plausible and seems promising at this stage. More research, in particular physical experiments, is however required before a conclusive verdict can be given.

Comparison of the beatability for fast-growing plants, softwood, and hardwood sources of fibers

“…To adapt the refiners to processing of primary and secondary fibers, it is necessary to change the operation principles. Conventional refining has been replaced by unconventional methods of fibre treatment such as ultrasound (Tatsumi et al 2000;Manfredi et al 2013), enzymes (Gil et al 2009;Cui et al 2015), steam explosion, pressure fluctuation, low temperature treatment (Young 1980;Bajpai 2005), and cavitation (Shankar et al 2018). Unfortunately, none of these methods have brought any crucial progress in this field (Przybysz and Przybysz 2013).…”