CHIP WASHERS

The washing of chips was developed by demand in the semi-chemical and groundwood
industries. The main effect of this development was to extend the plate life of the refiners
used in the production of this type of pulp.

Due to the moisture pick-up in the chip washing system, this procedure is limited to pulp
production using refiners as the source of production.

A Lundberg Chip Washer serves the essential task of removing non-wood debris from
wood chips prior to the refiners in the CTMP, TMP and RGW pulping systems. The
Lundberg Chip Washer consists of five major components used to separate rocks, sand,
grit and extraneous materials from the chips. These components are (1) scrap separator,
(2) scrap discharger, (3) screw drainer, (4) cyclone separator, and (5) recirculation pump.

The scrap separator is a paddle drum rotor which submerges the incoming chips into a
water bath and transports the chips through the washing water for discharge over a fixed
weir. Heavy foreign material, loosened from the chips by the agitation of the paddles falls
to the bottom of the scrap separator. All wetted parts are normally constructed of T-304
stainless steel.

The scrap discharger provides a means for discharging the foreign materials separated
from the chips in a scrap separator. A discharge chamber located between the two
valves is alternately filled and emptied by automatically actuating the valves.

Washed chips are discharged into the screw drainer where excess wash water is
removed. The inclined drainer is equipped with conveyor screw(s) operating in a
perforated bottom conveyor trough. Either single or double screws are utilized, depending
upon the design capacity of the chipwasher. As the washed chips rise in the conveyor,
discharge water is drained away. Additional washing is obtained by fresh water showers
located along the conveyor. The drained water is collected in a small pump head tank.

The recirculation pump delivers the collected water from the drainer and feeds the
cyclone separator. As the water passes through the cyclone separator, sand, dirt and
debris from the wash water are collected at the bottom of the cyclone and discharged.
Cleaned water is discharged from the top of the cyclone separator and is delivered to the
scrap separator for re-use in the system.

Caution should be exercised in installing any chip washer. If it is intended to
pneumatically transport the chips, this should be done prior to washing them. This may
impact where you wish to locate the chip washer. As stated previously, the chip washer
will cause about a 10% moisture pick-up (by weight). This moisture pick-up will increase
the horsepower required to transport "washed chips".

300 T/D Chip Washer General Arrangement
88-531-D-1