• Solid bunkers
• Sacksilos
• Subterranean tanks
• Metal containers

Solid bunkers

In most cases pellets are stored in solid store-rooms with slants in cellar or loft. The fuel is transported by screw conveyor, suction or by chain according to demand.

It should be taken into account when constructing a bunker that considerable weight is pressing on slants and walls because of the relatively high density (1.1 kg/dm3; 650kg/m3) of pellets. If the bunker is wood-made, a solid timber-construction made of plywood or oriented strand boards should be chosen. The pressure of the weight of pellets on a wall is equivalent to about 1/3 of the hydrostatic pressure.

The slants should have an angle of at least 400 so that the bunker can be completely emptied. It is recommended to sweep off the slants after two fillings. Dust is removed and pellets will slide down more easily to the conveyor system.

Behind the small door of the bunker there should be a further construction that aooows to open the door, even when the bunker is filled.

Between bunker wall and outer wall air circulation protecting against humidity should take place.

To prevent penetration of dust into other parts of the house the bunker should be sealed or should be dustproofed; otherwise dust will penetrate other parts of the house during the process of blowing in pellets. In this context emphasis has to be laid on the stability of the bunker, because the blower sucking off the air (causes a low vacuum) inside the bunker, and by that wall pieces insufficiently fixed may be shifted a few millimetres to the inside.

Opposite the filler neck a bounding mat should be installed. Its function is the protection of the wall behind and prevention of a too high grade of abrasion of the pellets blown in.

If the storage room has a rectangular form, the filler neck should be situated at the narrow side. If this is not possible and if the bunker has a breadth of more than 5 m, two filler necks may have to be installed.

As the pellets are to be protected from too much abrasion the filler neck should be situated about 15-20 cm below the ceiling.
With bunkers that are longer than 5 m the pipe for blowing in pellets may have to project into the room for 1.5 m. However, the pipe should be open at the bottom for pellets to fly on the air stream to the opposite end of the bunker. When the room is filled, pellets drop down through the open pipe.

The suction neck may be situated right under the ceiling or in corners of the storage room, yet not close to the filler neck, because then pellets already blown in are in danger of being sucked out again.

Sometimes filler neck and suction neck are employed alternately for blowing in pellets. This method has the disadvantage that in front of the filler neck pellets are lying and therefore the suction mechanism cannot be connected because pellets would be sucked out.

As the hoses of the pellet lorries normally have a diameter of 100 mm necks and pipes of the bunker should not be narrower.

Any obstruction of the pellets blown in increases the number of abraded particles, i. e. the less bends and diameter variations, the less abrasion.

The optimal neck is provided with a coupling of 100 mm inner diameter (Storz A).

Near the suction neck a 220 V wall socket planned for 16 A should be installed.

The hoses of the lorries are relatively heavy and stiff and should be placed in wide loops. This has to be taken into account when positioning the necks.

About the capacity of pellet storage-rooms:

Sacksilos

Sacksilos are common in agriculture, yet they are suited for pellets, too. Some manufacturers have specialized on silos for this sector. Apart from standard sizes each sacksilo is produced according to the proportion of the respective storage room.

Here are some examples of sacksilos.

The “Hubsilo” (lifting silo) shown above represents a modification of conventional silos. If the silo is full to the brim its lower end rests on the floor. So the entire space inside the support is used. Due to its special lifting mechanism the silo rises again when pellets are taken out and thus forms the cone necessary for complete emptying.

If suitable material is used sacksilos may also be put up out of doors.

Visit the following addresses to find some manufacturers:
www.abs-products.de
www.silobau-steinecke.de

Subterranean silo

If no room is available inside the house a subterranean silo may be a good solution. It has to be planned for pellets though, because in ‘normal’ tanks water of condensation may occur and affect the quality of pellets.

Metal tanks

Metal storage tanks are another possibility of storing pellets. The capacity of these storage systems ranges from 0.3 m3 up to 20 m3.