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Recycled fibre RCF plants are comprised of different sequential unit operations including pulping deinking deinked pulp DIP bleaching fibre fractionation screening cleaning and refining before the fibre they process is finally made into paper. The productivity efficiency and manufacturing costs of these units are interdependent the output of a previous stage determines the operating characteristics of the next. If the fibre supply was uniform and predictable these operations could be optimised with relative ease. But variable and generally poor quality fibre supply plus higher costs for recycled fibre are industry wide problems. How can these variables be controlled so the process becomes more efficient and costs optimised InlIne meaSurement By Daniel wtzig Application Manager Central Europe BTG Instruments GmbH world pulppaper34 Inline measurements optimise recycling and deinking operations All too often processes are not well controlled the installed equipment is either old or not used in the right way. Nevertheless there are enough ways to improve the fibre recycling process to make up for this. The importance of controlling selected parameters as early as possible in the process is key to success. With the implementation of application-specific inline technology such as consistency and ash sensors brightness UV fluorescence and residual ink transmitters many of these unit operation issues can be solved and the downstream benefits can be realised. Control strategies can be established step by step with low investments. The key measurements in a typical RCF process are shown in figure 1. Several examples of how the measurements can be used to get better plant performance results are reviewed. StaBIlISIng InK removal effIcIencY Stabilising ink removal efficiency will produce a consistently bright furnish for papermaking. In one case a newsprint mill with a furnish of deinked pulp and TMP operated a 500 td capacity flotation deinking line with BT-55 series inline brightness and residual ink ERIC transmitters installed before and after the flotation line. Both transmitters were calibrated to measure brightness and ERIC. The inlet stock was measured at a consistency of 3.5 to 4.0 then diluted to normal operating consistency whereas the diluted outlet stock is measured at 1.25 to 1.5. The two transmitters are primarily used to measure the ink removal efficiency so that process operators can make timely adjustments to the soap and other chemical feeds to all too often processes are not well controlled the installed equipment is either old or not used in the right way figure 1. Important measurement points in a recycled fibre plant