Wood Storage. Wood chips can be stored outdoors in piles and
reclaimed as usage demands. For recommended practices for outdoor storage of
wood chips see NFPA 46, Storage of Forest Products. Storage of wood chips
generally should not exceed 1 year. In areas of deep snows and extreme cold,
covered or indoor storage is desirable. Sawdust and bark should be stored
indoors because they absorb moisture when stored outdoors. In large
installations, 3 to 4 days storage in a prefabricated storage building with a
traveling transverse reclaim screw should be considered. Maximum duration of
chip storage with under-pile reclaim screw should not exceed 15 days. If
reclaim is with mobile equipment, more storage of chips can be provided.
Solid Waste Handling. Unprepared refuse in quantities greater than
150 tons (136 050 kg)/day is handled most conveniently with a pit and crane
system. The refuse is dumped from the refuse trucks into a storage pit where
wet and dry material can be mixed by the crane operator. Crane speed and
bucket (or grapple) size should be sufficient to permit the operator to mix
the refuse in addition to feeding it to the incinerator hopper. Handling of
prepared refuse is one of the key problem areas requiring further development.
Because of the difficulty of removing all the abrasives from refuse, pneumatic
handling systems deteriorate rapidly. Delivery of RDF to the incinerator-
boiler on a full-scale, reliable basis is essential. Dual processing and
conveying trains have not completely eliminated fuel bottlenecks in existing
Ash Handling. The disposal of bottom-ash collected below the
furnace and fly-ash collected from back-pass hoppers must be considered in
plant design. Pneumatic, hydraulic, and mechanical conveying systems are used
to transport ash from hoppers to a silo where it is collected for disposal.
Dust control equipment must be provided to limit ash dust levels in occupied
areas. Clinker grinders may be necessary to reduce the size of bottom ash in
some cases. Special considerations such as smoldering embers or char, which
may be present in ash from wood and solid waste fuels, must also be
incorporated in design.
Pneumatic Systems. For plants over 50,000 pounds of steam per hour
(6.30 kg/s), a negative pressure pneumatic handling system is usually used.
This type of system will also include; a clinker grinder, a receiver-
separator, an ash silo with vent filter, and an ash conditioner for dustless
dumping of ash. Mechanical exhausters (blowers) or steam exhausters may be
used to produce the vacuum which pulls ash from the dry ash hoppers. The
steam exhauster requires approximately 2500 lbs of steam per hour (at 80 psig
(552 kPa)) for a 6-inch (152.4 mm) piping system (8-inch (203.2 mm) systems
require 3500 pounds).