The issue of wood pellet storages has become very important with the development of renewable energy consumption and biomass energy production. Thus, there are various instructions to provide necessary service for wood pellet storages and provide sustainability in the process of wood pellet preservation.
Wood pellet storage facilities: guidelines
Storage facilities for wood pellets require safe utilization and that is why safety rules should be followed. Before filling the storage room pellet boilers should be switched off. All the instructions of wood pellet boiler manufacturer should be taken into account. In general, the experts advise the boiler should be switched off at least for one hour before filling the storage installations. The only time when people can be present in pellet boiler storages is when some kind of shortcomings are found out and necessary corrections are vital for the further wood pellet boiler functioning. Before entering storage space sufficient ventilation is required. In contrast, purpose-built storage installations do not need additional ventilation in case they are made of fabrics which can guarantee an exchange of air.
In case the system is closed, special ventilation caps on the both inblow and exhaust pipes are recommended. These caps will allow the exchange of air between inside and outside sections of wood pellet storage. Moreover, the prevent emissions and unpleasant smells of pellets blown into the silo. These caps should be changed in due time and are as a rule ordered from the suppliers of heating installations.
Wood pellets are as a rule delivered by a silo truck and blown into the silo. It is recommended that silo track parks to the connectors as close as possible. If the transport is equipped with a long hose, it can cause mechanical wear of the pellets and lead to additional expenditures. In case the inblow distance and height between pellet truck and silo is very high, special care must be taken in the process of inblow.
Wood pellet storage facilities: German experience
As far as the designing of a wood pellet storage facility is concerned, there are certain recommendations and guidelines as to how it should be done properly. First of all, the determining factor of the efficiency of a pellet boiler is the quality of the fuel, that is, wood pellets. Thus, it is strongly advisable that one should buy wood pellets only from certified suppliers. Secondly, the boiler must be turned off before the storage room for pellets is filled. In order to locate the pellet storage room, wood pellets must be delivered by a silo truck so that they could later be blown into the storage room. It is important to get the silo truck as close to the connection as possible. This is bound to reduce damage during the process of pellets' off-loading. For the transporting of pellets, 30-meter pumping hoses attached to silo trucks are usually used, thus, the distance between the silo truck and the storage room must be no more than 30 meters. The storage room should also be adjacent to the outer wall so that the filling connectors could have access from the outside. All in all, the storage room must be available for cleaning and maintaining.
As far as the construction of the pellet storage room is concerned, it is best to use a storage room in the rectangular or oblong shape. It is the most appropriate to locate filling connectors in the narrow part of the storage room, and they must be easily accessible.
As to the size of the storage room, it varies depending on the so called heat load of the building but obviously the storage room should be rather large so that it could contain the total annual required amount of wood pellets.
Purpose-built storage facilities
The most widespread and frequently used purpose-built storage facilities are considered to be those of the above-ground type. Such systems have a cladding of flexible polyester fabric, plastic or metal sheeting. Purpose-built pellet silos are also recommended to be built into earth.
On the German market purpose-built systems are available in those shapes and sizes that match the storage room. The market of Germany offers round, square, rectangular silos as well as silos in different heights. The type of the system also defines the movement of the pellets to the exit hole. There are two approaches of pellets moving: by funnel (common when the pellets are removed from the bottom by a screw conveyor) or through a moving withdrawal system from above (suction devices).
Industry recommendations for wood pellet storage facilities
It should be taken into account that wood pellets are quite vulnerable to water and moist as in contact with liquid and damp surfaces they absorb water and fall apart losing their useful properties. If wood pellets are wet they can also clot the mechanism of infeed. That is why the storage room for wood pellets must stay dry throughout the whole year. If the house is newly built, it is better to completely dry out the storage room before filling it.
As to the ceiling and walls around the storage room, they should be designed and built in a way so as to prevent wood pellets from contamination through crumbling or abrasion. The thickness of walls should be as follows: 10 cm for concrete; 17.5 cm for brick; standard thickness for timber, plastered on the inside.
As far as electrical equipment is concerned, there should be no such installations as connectors, lights, switches in the pellet storage room. The filling connector and the filling system should be connected to earth so that no electrostatic charges occur during the process of filling. All pipes and bends in the filling system should be smooth on the inside so that pellets were not damaged during the process of filling. For that reason one should also avoid using such items as e.g. screws. As to the length of the filling pipes, they should be rather short(less than 10 meters) and end in a straight 50 cm pipe rather than a bend so that pellets could settle. The size of the filling connector and the exhaust air pipe should be exactly the same as the one of the filling pipe. The connectors should also have a lid so that they could be closed after the filling.
There are also some special contraptions which it is appropriate to install along with the storage room. One of them is a so called "house connection box", which should be located nearby the filling connector. This box should have a 230 V power outlet for the exhaust ventilator and a door switch to disconnect the boiler so that the exhaust ventilator could not draw smoke from it.
There are different ways to apply silo systems in the wood pellet storage facilities. German Biomass Portal biomassa.de analyzed German experience and market in using silo systems and states that there different types of silo systems on the market of Germany. In order to be able to use them properly and efficiently one should stick to the security utilization and recommendations as to the building and designing of the wood pellet storage facilities using silo systems.