Biomass can be used in a variety of forms. (For those who wish to know what biomass is, here is my post on what it is).
While some sectors use biomass in its natural form (stalks, saw dust, ground nut shells), many sectors prefer to use biomass in a more compact form, especially when biomass is used in specific heating appliances such as furnaces, boilers, hot air generators etc.
There are two main densified or compact forms into which biomass is processed currently. One is in the form of pellets and another is in the form of briquettes. While both are more compact and densified than loose biomass, there are some differences between them.
Let us consider pellets, which are the more compact of the two.
Pellets typically are about 6-10 mm thick and of varying lengths. Put another way, they are only slightly thicker than a typical pencil.
Briquettes, the less dense of the two, can be 60-90 mm in width (diameter), and in some select cases, even wider. Briquettes too, similar to pellets, can be of varying lengths.
Pellets have the following advantages over briquettes:
- They are more dense, and usually contain less moisture than briquettes. As a result, pellets have a significantly higher (about 20% higher) calorific value than briquettes.
- Pellets, owing to their more compact sizes, can be used in a wider variety of heating appliances than briquettes. If the heating appliances are smaller in size – cooking stoves, for instance – pellets are far more suitable than briquettes. (Larger heating appliances such as boilers may use either pellets or briquettes, depending on the specific boiler make and depending on other operational requirements).
- Pellets in many cases lead to a better efficiency than briquettes for the overall heating system – this is owing to a number of benefits that their compact sizes provide at different points along the heating operations cycle.
Thus, while pellets cost significantly higher than briquettes per kilogram (sometimes as much as twice), these also provide significant operational and logistical benefits over briquettes, and loose/raw biomass. As a result, many sectors prefer to use pellets, instead of briquettes, in their heating appliances.
From what I have seen, some countries in Europe appear to be using biomass pellets for their boilers even when these are costlier than biomass briquettes, and much more expensive than loose biomass (both on a per Kg basis). What could be the reason? It is quite possible that if one were to put a number to each additional benefit that pellets provides at various stages of the heat generation process, the cost per unit of useful heat from pellets might not be much higher than what it is for briquettes. This is my guess, anyway.