Repulper (hydropulper) operations

Influence of circulation rate or agitation:
1. The speed of developing a slurry (defibering) is roughly proportional to the intensity of the mechanical action.
2. This agitation or turbulence requirement is fundamental to repulping.
— pulper operating with poor circulation is usually unsatisfactory for anything.
3. If broke or wastepaper is to be slurried, the stock must repeatedly pass over the device creating the turbulence or causing the mass to move in the vat.
4. Broke flakes and fiber bundles moving with the stock are reduced in size only when the rapidly rotating impellers hit them.
5. Essentially no fiber separation occurs once stock leaves the tip of the rotating elements and slows to the circulating velocity of the mass of the stock.

Influence of rotational speed:
1. Increasing rotor speed improves defibering and circulation but power requirements go up exponentially.
2. As the impeller speed increases, the hits on the fiber bundles become increasingly harder.
3. At lower rotor speeds (» 3000 fpm), initial break-up of pulp or broke proceeds readily providing there is good circulation.
— this still may not be sufficient for complete fiber separation.
4. At higher rotational speeds (» 5000 fpm), defibering time is reduced by 1/3rd but horsepower hours per ton can increase by 2/3rds.
5. Must have relatively high rotor speed for good mechanical attrition of fiber bundles and broke flakes.

Action of impellers:
1. Increments of pulp or fiber bundles caught on the impeller surface are hit harder as rotor speed increases.
2. The force of the blow (hits) varies as the square of the impeller velocity.

Temperature effects:
1. For a given degree of defiberization, the power required for the high-speed rotor falls off at higher temperatures.
2. With increasing temperature, there is a large drop in both the time required and the power used for repulping.
— for example, at 150 F degree versus 90 F degree , the time will be reduced from 30 to 12 min. and power from 200 to 120 horsepower-hours per ton for complete defibering.
3. Mills should provide adequate hot water so repulping system is not overloaded and defibering is more effectively completed.

Influence of consistency:
1. Consistency in range of 3 – 8 %, at fixed temperature, has little effect on time for complete defibering.
2. The horsepower-hours per ton for complete defibering are greatly reduced at higher consistencies.
— it is desirable to keep stock consistency as high as possible.
— good circulation must be the determining factor to maximize consistency and minimize repulping costs.
3. Repulpers are designed to operate in 5 – 8 % consistency range; good average in practice is about 6 – 6.5 %.