Cleaner removes particles from suspension, which affect paper quality or cause excessive wear in subsequent processing machinery.
These contaminants may include heavy weight particles such as sand, metal pieces, cement, glass, bark or light weight particles including plastic material. The purpose of a cleaner is also to remove shives and undeveloped fibers, which are returned to the process for further treatment. For efficient removal particles must differ in density from water and in size and shape from other suspension components
The physical properties of particles have a strong effect on whether they will end up in accept or reject flow, see table I
Table I Physical properties that influence whether particles are accepted or rejected in a cleaner.
Cleaners such as fig. 1 shows are used for separation. The centrifugal field generated in the equipment force the heavy particles outward while the light particles move to the center. The flow streams containing primarily heavy or light particles are separated from the main flow.
There are several factors that affect the cleaning performance and efficiency:
Pressure drop (pfeed-paccept)
– Feed consistency
– Reject rate
The pressure difference affects capacity, flow velocity, rotation speed and therefore cleaning efficiency. Increasing the pressure drop will increase the cleaning efficiency to a certain point at which the flow motion in the cleaner becomes turbulent.
At higher consistencies the fiber network becomes more dense and restrict the particle motion ie. the lower the consistency the better the cleaning efficiency. As a downside to small consistency is a larger cleaner plant size, pump, piping and instrumentation sizes.
The higher the reject rate the higher the cleaning efficiency. As a downside to high reject rates is increased size of cleaner plant and latter stages.
Generally the process itself determines the temperature of the pulp. The temperature has been proven to have a slight effect on the cleaning efficiency. As a general rule, the higher the temperature the higher the efficiency. Higher temperature increases the reject thickening and therefore reject rates.
2. High Density cleaners
The Ahlcleaners RB200HD and RB300HD are designed for high, up to 4.5%, consistency cleaning. RB200HD and RB300HD are equipped with a junk trap for collecting impurities. Junk trap dumping is fully automatic (intermittent reject removal). Impurities such as sand, stones, dirt, metal, glass, other heavy reject material and also high percentage of small impurities are removed with a minimum fiber loss. Fiber loss is kept low by adding water to the junk trap for washing good fibers back from the rejects. Note that the separation of coarse contaminants into rejects decreases when consistency increases. Figure 14. shows the construction of a RB300 HD cleaner.
3. Ahlcleaner RB45
The Ahlcleaner RB45 is mainly used in recycled fiber lines. RB45 is also an efficient cleaner for removal of fillers. Picture 16 shows a RB45 plant in Mexpapel – Mexicana De Papel Periodico, Mexico, DIP-line.
4 The Ahlcleaner RB150
The main application is cleaning of mechanical pulp with low CSF level. In some cases the RB150 can be used in board machine approach system. Figure 19 shows a RB150 unit in Abitibi Consolidated Donohue Lufkin, Texas, U.S.A , mechanical pulp line (GW)
5 The Ahlcleaner RB200
The Ahlcleaner RB200 is the most appropriate cleaner for classifying mechanical pulp. It is also very suited for cleaning unbleached pulp and It can also be used in recycled fiber lines. In PM approach systems where Flying Wing Deculators are used RB200PI’s are installed to Deculator wings and RB200 to the machine floor (ie. latter stages). RB200PI’s construction is similar to RB200 but it is equipped with a long accept pipe. Figure 20 shows a RB200 unit in Metsä Botnia Joutseno mill, Finland, mechanical pulp line (BCTMP).
6 The Ahlcleaner RB300
The Ahlcleaner RB300 is suited for board machine approach systems and also with the Flying Wing Deculator (RB300PI) if the cleaning efficiency is not the most important factor. RB300PI’s construction is similar to RB300 but it is equipped with a long accept pipe. In addition these cleaners are suited for mechanical pulps for cleaning of rejects and for unbleached sulphate pulp.
4.7 The Ahlcleaner RB200HD and RB300HD
The Ahlcleaners RB200HD and RB300HD are mainly installed before last stage coarse and/or fine screening to protect last stage screen baskets. HD –cleaners are also installed after pulpers and are used for broke cleaning. Picture 21 shows a RB300HD unit.