Every recycled fiber line needs a proper water, sludge, and reject treatment system to operate economically. The first and obvious goal is to minimize costs for resources (water, energy) and disposal.
Example of an ANDRITZ reject treatment system with drum pulper
Every recycled fiber line needs a proper water, sludge handling, and reject system in order to operate economically. The goal is to minimize losses of process materials, recover and conserve resources (fiber, water, and energy), and minimize waste disposal.
In addition, many rejects can be valuable and even generate income for a mill: for example metals as raw materials and plastics as a source of energy. Rejects from recycled fiber processes are worthy of optimum and properly adapted treatment to extract their full value. The processes must be cost-efficient and simple, as well as fulfilling certain requirements to ensure that the rejects can become fuel (e.g. combusted), can be sold or re-used (e.g. pelletized), or can be disposed of at minimum cost and effort. This requires knowledgeable handling of the reject and a thorough knowledge of the individual process steps.
The reject material fed to the ANDRITZ Reject Compactor ReCo is conveyed by a rotating screw and compressed in a counter pressure unit by two hydraulically actuated pressure flaps.
Wear-resistant, heavyduty baskets retain the solids, while the filtrate flows through the holes in the baskets and is collected in a tray.
The final dryness depends on the type of reject material and its fiber content.
System based on conventional pulping
Shredders are typically fed coarse rejects from pulping and coarse screening. Coarse particles are reduced to the desired size by slowly rotating shafts fitted with wear-resistant cutting devices. A screen plate determines the particle size.
ANDRITZ ADuro shredders are easy to install and have good accessibility, their robust design ensures reliable operation with little maintenance.
Near infrared technology (NIR) can be used to detect and classify a wide range of various plastic materials (PP, PE, PVC, etc.). Depending on the end use of the raw material recovered (e.g. chloride from PVC is critical for corrosion in boilers), one or several detected components can be ejected by compressed air nozzles.
The separator requires a certain dryness and particle size distribution.
Low-consistency rejects with high heavy-particle content – typically coming from cleaning stages – need different treatment. The suspension is fed into a gravity sedimentation chamber. The heavy particles that settle are discharged by an inclined spiral screw conveyor. Sufficient retention time and optimal machine design ensure high filtrate quality and low maintenance.
Sludge is mixed with flocculants and pre-thickened gently on a gravity-based thickener. The final dry content is achieved with a screw press applying maximum shear forces. The high-quality filtrate from the system reduces the requirements in water clarification. Both units provide superior uptime and availability, as well as low maintenance for continuous and flexible operation.
A protection system is required ahead of sewage treatment plants, biofilters and similar plants; and for recovery of suspended solids. A revolving, endless filter belt with specially designed hooks is submerged into the sewage channel and collects contaminants. The mesh size of the high-strength filter elements determines the water quality. The units can be installed quickly into any type of channel. They are reliable to operate and easy to maintain due to their compact, robust design.
Key eqipment ANDRITZ Reject Compactor ReCo-C for optimal dryness levels
Reject Compactor ReCo-C – Dewatering of rejects from recycled fiber lines
