Stock water circuits

The system consists of three water loops, two in stock preparation (because of the combination of flotation - dispersion - flotation) and one in the paper machine. The water circuit design follows the previously mentioned principles of counter current flow and thereby allows the fresh water to be used to the maximum effect. In addition the save-all is followed by an additional DAF unit DAF 1 is used as a kidney for removal of detrimental substances, treating the make-up water from the paper machine (clear filtrate) together with part of the clear filtrate from the disc filter in loop II. DAF 2 treats the filtrates from reject and sludge dewatering. The clarified water is partly recycled back into loop I, the rest being sent to the effluent treatment... 

Fig. 10.4 Scheme of a closed water circuit [6]. (a) Paper machine, (b) stock preparation plant, (c) storage, (d) save-all, (e) fresh water,... 

Treatment of short circuit of the machine. This is a key application in paper making 100 to 300 cubic meters of water are recirculating very fast in the wet end part to form the paper web. The diluted stock enters the headbox between 0.5 and 1% consistency to form the paper web that will drain on a wire to remove free water make a paper sheet with a dry content around 20 to 25%. This sheet will then be pressed between press rolls and felts to remove the water bound to the fibers and reach around 50% dry content. 

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