Benchmarking Laboratory Fiber Yield Assessment Methods for EcoModulation Fee Calculation
Laboratory fiber yield metrics depend on screen slot geometry and ash corrections, directly determining EPR eco-modulation fee surcharges on packaging.
Fine Rejects
Particulate Waste
Small fibre fragments and non-fibrous debris are removed from the pulp stream during the screening process to ensure the purity of the final paper sheet. These rejects consist of short fibres, mineral fillers, wood shives, and minute contaminants that pass through primary filters but are trapped by secondary separation equipment. These material fragments are typically too small to contribute to the strength of the paper web and can cause dusting or surface imperfections if left in the stock.
Process Efficiency
Centrifugal cleaners and fine-slotted screens isolate these particles based on their density or size relative to the desired long fibres. While some fine rejects are recirculated to recover usable material, the bulk of the stream is diverted to the wastewater treatment system or pressed for disposal. Excessive accumulation of these fines in the white water system increases the demand for retention aids and can slow down the drainage on the wire.
Monitoring the volume of this waste helps mill operators assess the health of the refining process and the quality of the incoming raw material.
Surface Quality
Surface quality improves when the concentration of small debris is strictly controlled. If fine rejects are not effectively removed, the resulting paper may suffer from lower opacity or reduced pick resistance during printing. High levels of these fragments also interfere with the bonding between larger fibres.