How Pellets For Stoves Are Produced

With the rising costs of heating solutions based on fossil fuels, wood pellet stoves have been growing more and more popular. Not only do they allow a cheaper alternative to gas or oil-based heating solutions, but they also allow a means for sawdust and other leftover wood products to be put to a good use. Though the pellets which these stoves use may be made of a number of different materials, in most cases they still are made from some form of wood that has been tightly compressed in order to keep them compact while still letting them burn easily.

The process by which wood pellets are made is relatively simple, regardless of the type of materials that are used to make them. There are some basic standards to which the pellets should conform when the manufacturing process is finished, of course, though these standards are generally easy to meet regardless of the material used to make them. Some materials are unsuitable for use in stove pellets, largely because they could present a danger to pellet stove users when burned.

Preparing the Wood

Before sawdust and other scrap wood can be made into pellets, it must first be processed and pulped. This is generally done by putting the wood through a hammer mill, a device which spins the wood material at high speeds while it is impacted repeatedly with pivoting hammers. This repeated pounding will pulverize the wood in the mill, reducing it to a dough-like mass with a uniform consistency. It's only when the wood has been pulped to this degree that it can be formed into pellets for use in pellet stoves.

Forming the Pellets

Once the wood "dough" has been made in the hammer mill, it's time to form the wood into pellets for use in stoves. The wood pulp is placed into a press which injects it under high pressure through a die that has holes from 6mm to 8mm or larger in it (depending on the size of the pellet that the manufacturer is wanting to make.) The wood pulp is under a high enough pressure that it is instantly compressed as it moves through the holes in the die; the process also causes the wood pulp to heat up significantly. This heat is vital to the pellet-making process, as it not only helps to remove any excess water that might have been in the wood pulp but it also causes the lignin contained within the cell walls of the wood to be released and form into a natural plastic-like glue that holds the pellet together without the need for any additives or additional materials.

Standards to Which Pellets Conform

Though there may be some very slight differences between pellets formed from one type of wood when compared to those from another wood, there are still some basic standards to which most if not all stove pellets will conform. The standards most commonly used require pellets to have less than 10% of their total mass as water, to have a density larger than 1 ton per cubic meter (which is dense enough that they won't float when placed in water), and that they are structurally sound enough that they won't easily crush or fall apart. Additionally the pellets should contain a low dust and ash content so that they will burn cleanly. These standards are generally easy to meet regardless of the type of wood used, since the hammer mill pulps the wood to the point that it is just broken down wood fiber (which generally has the same qualities for all types of wood.)

Materials Which Can't Be Used

Because of health and safety concerns, there are some materials which cannot be used in the manufacture of pellets. Any wood products which have been coated with melamine, painted, or otherwise treated can't be used because they can release harmful fumes when they are burned. Likewise, recycled materials such as particle board are unsuitable because of the chemicals which are generally used in the recycling and reforming process. The wood must also be free of contaminants or any artificial additives, since these additives and impurities can also cause the release of dangerous chemicals while burning.