Pellet fines - small troublemakers
Fines refer to fragments of broken pellets that fall through a sieve with holes of 3.15 mm diameter.
A partly high amount of fines may cause problems with the boiler or the pellet retrieval system.Fines in the pellet store are caused mainly by mechanical stress during pellet delivery. Bends in the pipework, inadequate impact mats, obstacles in the route of the pellets, a high pellet velocity and a low solids loading factor during delivery, all increase the amount of fines.
High fines at the boiler may also be due to damage from the extract system taking pellets from the store to the boiler. Through particle segregation processes in the store, fines will concentrate over time on the bottom of the pellet store. To ensure a smooth operation of the boiler, the storage should be emptied and cleaned completely at least once in the previous two years. This is best done in the summer.
ENplus-certified suppliers accept complaints of more than 4 percent fines in the store under the following conditions:
- The amount of fines in a delivery will only be < 4% w-% when the total length to be blown between the end user storage and delivery vehicle is less than 30 metres. (30 metre blows are only possible in the right circumstances - see next point)
- ENplus certified companies in the UK may provide further restrictions on the blown length to allow for any bends, gradients or other impediments to smooth delivery.
- The end-user’s store must have been cleaned periodically. The frequency of cleaning is based on the number of deliveries but a minimum of once every two years. The store must have been completely cleaned after every 5 deliveries.
- Compliance with ENplus storage guideline
- Residual amount of pellets before delivery was less than ten percent of storage capacity
- Maximum of twenty percent of the new delivery has been used