As part of its back water system, Paper Machine 2 at Maryvale Mill has a Sven Pedersen Floatation Saveall whose design was set up in the early 1930s. The Saveall makes use of compressed air, a high molecular weight long chain polymer (flocculant) and wooden paddles with a rubber coating to skim the fines which float to the to the top via a continuous scraping mechanism. It is currently at 85% of its operational capacity and produces clarified water which is reused all over the paper machine. Laboratory tests have been conducted to measure the saveall efficiency based on suspended solids removal and turbidity for different grades. For waste grades its efficiency has been significantly improved by reducing its throughput and with the help of a newly enhanced polymer dosing system. Trials have been conducted on unbleached grades where we put the recovered fibre (mainly fines) back into our machine in order to reduce fibre loss which resulted in slight improvement in strength properties of the paper such as TEA, tensile strength and tear. When the saveall is turned off or bypassed, water usage and effluent flow increases drastically causing additional expenses being incurred by the mill. Currently the paddle design in terms of material of construction to optimise the skimming process and quality of clarified water produced is being investigated.
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