The basic design of the white-water system of the FEX paper machine is demonstrated below. The system is closed material-wise, by recovering material from the excess white water using a disc filter and mixing it into the thick stock. This is still unique for a pilot paper machine. All volumes involved are minimised, to reduce the time to equilibrium, which after start-up of a water filled system is within the range 60-90 minutes.
The cleaned excess white-water flow is used to dilute the web in the press broke chest. This broke is not recirculated; instead, fresh furnish is fed during the entire trial period.
The two short circulations (designed for maximum flow rates of 5000 and 10000 l/min) each include wire pit, thick stock addition, mix pump, trash separator and deaerator. The flow from the two deaerators can be distributed to three headbox pumps.
Extensive measurements of white-water flow rates at different positions, combined with off-line analysis of the concentration of different material components, make it possible to evaluate material flow balances in some detail.
Schematic of the white-water system of the FEX paper machine (click on the image for a high resolution version).