Ease of extraction
The design and siting of a biomass store must also take account of ease of extraction of the content and supply to its next destination, whether this is a boiler, combustion unit, conversion plant or another site altogether. Use may be made of gravity, if this is convenient, thus reducing energy requirements.
The 'take off' point
It is important to design the store such that if the content is in a form that can flow, such as slurry, wood pellets or chips, this naturally brings the fuel to the take off point from the store. This take off point should not leave regions where the biomass can build up or get stuck, forming dead areas where it can stay indefinitely and potentially allow moulds to form.
For many stores the take off point will be at the bottom, feeding into an auger feed or an agitator, and it is important that this cannot become jammed with sawdust or other detritus.
Transferring biomass from the store
There are many different methods for transferring biomass, depending upon its form. Possible methods include:Handling biomass
- Simply gravity feed or chute
- Screw type auger feed
- Conveyor belt
- Pneumatic blower
- Pumped flow
- Bucket conveyor
- Front loader
- Bucket grab.
Different methods will suit different materials, situations and throughput.
With some fuels such as wood pellets it can be important to ensure that they are not handled too roughly as they can disintegrate into sawdust which may cause difficulties for subsequent handling, processing or combustion. This may or may not be of concern, depending upon application, but if it is it must be considered at all points of handling and storage from production to usage.
It is generally considered best practice to minimise the number of handling steps with wood pellets. Resistance to mechanical handling will depend upon the quality of the pellet, pressure used in manufacture and any binders added.