What are wood pellets?
Wood pellets are small pellets of compressed saw dust. Simply put saw dust is a by product of other more lucrative wood processing. This saw dust is dried to a specified moisture content, and compressed by a very high pressure machine. Generally no glue or binding agent is required other than the sap from the timber itself.
The benefits of wood pellets are
- Its easy to transport
- It is clean
- It complies to standards. Things which have standard sizes, shaped and moisture content can easily be designed for
So these pellets, how do they get to the boiler?
No, a shovel is not required. The pellets are blown from a delivery truck up to 20m to a storage unit. In the past there has been a lot of hassle with dust, but this was largely down to the use of agricultural feed trucks being used to deliver the pellets. As dust is not really an issue for agriculture, they did not have dust minimisation technology, and it was a mess. If you use one of the large suppliers these days, there is little problem.
So the pellets are in the storage unit… what now? Well the next stage is getting it to the boiler. The simplest solution here is to use a screw system. These systems turn very slowly and draw the pellets from the storage unit to the boiler.
Wood pellet boilers are fed into the “burner” where they are burned. The burner in all boilers does much the same job. It’s a place where the fuel is mixed with air to provide the optimal conditions for combustion, and lit. Before you know it the combustion gases are travelling through the heat exchanger where it heats up the water.
The flame from the burner, and the resultant combustion gases escape into the boiler, transferring their heat to the water circulating through the heat exchanger within the boiler. The heat is then distributed the house using a wet system. In most cases water flows through the heat exchanger in the boiler, absorbing heat from the flam and the combustion gases. This hot water is then circulated around the house to radiators, underfloor heaters and hot water cylinders.
For more infor See my boilers post
for the pix!