Handling of Fuel

The majority of operating problems experienced is no doubt caused by the plant system for transport of wood chips from storage to the feeding system. The entire transport system from storage to boiler should be viewed as a chain in which the reliability of operation of the individual
links is equally important. The entire district heating plant stops in case of a “missing link” in the transport chain, e.g. a defective crane wire.

Wheel Loader
At plants with outdoor storage, it is normal to use a wheel loader with a large shovel for the transport of wood chips to the indoor wood chip storage.

Crane Transport
Between the indoor wood chip storage and boiler feeding system, a crane is often used for the transport of wood chips. The crane is flexible, has a high capacity, and is also the transport equipment that best tolerates a poor wood chip quality. However, it is important for the crane shovel to be toothed. If not toothed, it is difficult to fill and it easily turns over on top of the pile. For relatively large plants, the crane is also relatively inexpensive,
while it is a too expensive solution for very small systems.

Hydraulic Push Conveyor
The hydraulic push conveyor is used for unloading rectangular silos with level floors. It is normally not as technically reliable
as the crane solution. The hydraulic push conveyor is relatively inexpensive and is therefore particularly suitable for small systems (0.1-1 MW boiler nominal
output).

Tower Silos
Tower silos with rotating screw conveyor should not be used for wood chips. The silo is time-consuming to fill due to the great tower height, and the mechanical parts in the silo bottom are not very accessible for the purposes of maintenance and repair work. Technical problems normally arise when the silo is full of wood chips.
Before starting any repair work, it must be emptied - manually or preferably with crane grab. For storage of wood pellets, the equipment used in animal feed
industry is normally suitable.

 

Screw Conveyors

Conveyors are inexpensive, but vulnerable to foreign matter and slivers. In general, screw conveyors with boltedon top are recommended instead of
conveyors enclosed in tubes. The recommendation is easily understood after just one experience of manually emptying of a tube conveyor blocked
by slivers or foreign matter. Similarly, it may be considered erroneous projecting if screw conveyors are embedded in concrete floors or otherwise located
so that repair work and replacement of parts for maintenance work.
Correctly dimensioned, screw conveyors are an acceptable solution at small plants (0.1-1 MW boiler nominal output). But unless hardened steel is
used, normal wear and tear will result in a relatively short life of the screw conveyor.
Screw conveyors are seldom used as transport equipment at large district heating plants.

 

Belt Conveyors

Belt conveyors are rather insensitive to foreign matter. At this point, they are better than screw conveyors, but unless equipped with barriers, the belt conveyor cannot manage as high inclinations as the screw conveyor. High price and dust emissions (which may necessitate covering) are the major drawbacks of the belt conveyor.

 

Pneumatic Conveyors

In general, wood chips are not suitablefor transport in pneumatic systems. If wood chips are available in a particularly uniform size, however, transport by
pneumatic conveyors may be a possibility, but the energy consumption of pneumatic conveyors is great.

 

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