Reference Manual

15−2
Figure 15-2. Pulper
Drawing is from TAPPI’s Making Pulp and
Paper Series and is used with permission.
diluted to a slurry in order to break the fibers apart
before they are pumped toward the paper
machine.
Pulpers
Pulpers, also known as repulpers or slashers, help
to break down the bales into individual fibers
(figure 15-2). The bales of pulp or waste paper are
fed to the pulper, either by a forklift truck or by a
conveyor. In some mills, different fiber
components are re-pulped separately and blended
together later in stock prep. Water is added to the
pulper, the pulp bales are added, and the
remaining water is added to bring the pulp to the
right consistency; typically around 4 to 5% solids
for low consistency pulpers or up to 18% solids for
high-consistency pulpers.
Pulping can be done by one of two types of
pulpers:
D Batch pulper: Typically, this process is
completed in a single vessel.
D Continuous pulper: Supplemental in-line
treatment is commonly used following the pulper
to ensure complete dispersion.
The agitator in the bottom, or side, of the pulper
provides the repulping action. Steam is often
added along with sodium hydroxide or caustic to
raise the pH of the slurry. Dyes and fillers can also
be added at this point.
Figure 15-3. Pulper Dump
Drawing is from TAPPI’s Making Pulp and
Paper Series and is used with permission.
Depending on the type of pulp, a batch pulper
might take 30 minutes or more to break up the
fibers. Once all the fibers are individually broken
apart, the pulp slurry can be pumped into the
pulper dump or storage chest (figure 15-3). Once
the broken apart pulp is pumped away, a new
batch of bales is re-filled into the pulper.
A continuous pulper is similar to a batch pulper
except the bales of pulp are continually added and
the slurry is continually removed through an
extraction plate under the rotor. The extraction
plate has holes of 3/8 to 5/8-inch.
Refining
This process helps the individual pulp fibers to
bond together by employing both mechanical and
hydraulic forces to alter the fiber characteristics.
This is done by imposing shear stress on the
fibers through rolling, twisting, and other tensional
actions occurring in a refiner. This process can be
performed by two different types of continuous
refiners.
1. Disc refiner: The most common type of
refiner, this unit has a rotating disc and a set of
stationary plates, typically with a plate on each
side of the disc (figure 15-4). These discs are set
closely together so only a small passage between
the bars exists. Stock can flow in a parallel
arrangement (duo-flow) or a series arrangement
(mono-flow). Fibers pass between the moving
bars where they are mechanically abraded. The
water can then enter the walls of the fiber and
cause it to swell. This process also helps to break
off the extra small pieces of fiber, called fines.