Pellet storage
  • Pellet storage

Pellet storage

 

Small-scale pellet storage at residential end user sites

Ensuring pellet quality during storage, standards and guidelines such as ÖNORM M 7137 and VDI 3464 dealing with construction requirements of pellets storage facilities and storages in basements already exist. According to ÖNORM M 7137 pellets storages have to fulfil different requirements such as safety, fire protection and maintenance of pellet quality. Moreover, a brochure of the German Wood Fuel and Pellet-Association (DEPV) is providing information on static requirements, equipment used in pellet storages, examples of equipment and ready-built storage systems. Furthermore, it is necessary to avoid contamination with other substances and protect pellets from moisture.

Wood pellets should be stored in pellet storage rooms, storage tanks and underground pellet storages. All those pellet storage types should meet the following general requirements. Since the pellets are delivered by silo truck the access road to the pellet storage should be about 3 m wide and 4°m high. During the filling of the pellet storage the piping must not exceed 30 metres. Not only the accessibility of storages but also the proximity of storages to furnaces are essential. Pellet storages for home use should include the fuel amount at least for one year. At the planning and design of the pellet storage room the amount and weight of needed pellets should be considered. Therefore, the fuel demand and the depending volume has to be calculated. It is recommended to empty the storages at least every three years and to eliminate the fines and dust completely, which should be taken into account during planning the storage room.

Pellet storage rooms
Pellet storage rooms for residential heating are located in the cellar just beside the combustion system. Storage rooms must be erected dustproof as separated rooms. The doors to adjoining rooms must be completely sealed. These homemade pellet storages are erected conically and should consist of a plastic baffle plate, a fire door, a filling and a return pipe.

Storage tanks
Storage tanks or storage containers can be erected in the cellar, next to cellar in unused rooms and in the heating room itself. A typical storage tank is the synthetic fibre tank carried by a metal frame. Additionally, tanks made of plastic and metals are also available. The storage tanks can be set up indoor and outdoor depending on the design. Outside erected storage tanks nevertheless should be protected against direct sunlight and rain.

Underground pellet storage tanks
Underground pellet storage tanks are made of plastic or concrete and are used if storages cannot be set up in the cellar of a house e.g. lack of space in the cellar or no cellar is available. Those underground tanks can be established in gardens as well as under car parking spaces. Different systems of such underground tanks such as conical, spherical or vertically cylindrical tanks are available. The pellets are discharged pneumatically either from the top or the bottom of the storage.

Medium- and large-scale pellet storage

Intermediaries, pellet producers and large consumers such as district heating plants or combined heat and power plants, are storing pellets in medium- or large-scale pellet storages. Different storage types are used in pellets industry like silos and flat storages. All mentioned storage types are considering that pellets have to be protected against moisturising. It is recommended to keep the outside of the storage in bright colours, allowing low temperature in the tank.

Hopper bottom silos
Hopper or cone bottom silos are vertical silos with a cone bottom and are often used in agricultural sector. That silos can be made of concrete or galvanised steel structures. Metal silos are built of rings and segments which are put on top of each other and possible gaps are sealed tightly. Vertical silos with tapered bottom are common in the agriculture sector and are available in range from 50 to 10,000 m³. The silos are filled from an overhead conveyor and are falling down. In order to reduce dust during the filling process the height of fall can be minimized by using bean ladders. The pellets in discharge tunnel are discharged with a conveyor. Using hopper bottom silos complete discharge is possible.

Flat bottom silos
They are vertical silos with flat bottoms and are made for example of concrete or steel. Flat bottom silos are very often used in the agricultural sector. The pellets are moved via circulating auger to discharge tunnel and the pellets are discharged with conveyor.

A-frame flat storages
A-frame storages are built economically and are used for storing bulk pellets. They are used for large scale storages and exist in size from 15,000 to 100,000 m³. The storage is filled by telescoping conveyor system at the top of the storage. The pellets fall down to given areas on the bottom. Depending on the distance between the storage and the feeding system of the heating and/or power plant, the pellets are transported via front loaders, trucks, railcars, respectively.

General purpose flat storage
That storages are used for storing pellets as well as other bulk and commodities. They are often located at ports and can be filled with about 10,000 to 100,000 m³ pellets. Pellets are brought in by trucks and front loaders and are discharged by front loaders. To form a pile in the storage movable conveyors are used.