Pellet binders and lubricants is a complicated area of pellet production, and one that many people find confusing. Whether a binder or lubricant is required depends on several factors, and is something which is gained through experience.

Pellet binders are additives to the pellet production process, which help to increase pellet quality, productivity and reduce fines loses. All biomass is cellulosic material, and contains a certain percentage of natural binder lignin. Most cellulosic material can be pelletized without using additional binders, however some materials do require an additional binder.

For lignin to work as a binder, sufficient heat needs to be generated in the pellet mill, to essentially melt the lignin. Now to obtain the heat required in the pellet mill, the correct pressure must be reached. Several factors are needed to reach the correct pressure; two of the most important factors are roller height and moisture percentage. If the roller height is too low or too high, or the moisture percentage is too low or too high, the critical pressure point required to melt lignin cannot be reached. In large-scale pellet production they use high temperature steam to begin the melting process. So many materials can be pelletized without binders, however it does require good process control to obtain the correct pressure.

Binders can be used to make the process easier, removing the need for precise pressure control. Pellet binders can also increase the efficiency and productivity of the pellet mill, reducing energy demands. The lubricating factor of the binder increases productivity and reduces the chances of die blockages. The decision that arises is, does increased pellet quality and productivity justify the additional cost of the pellet binder. Again the answer to this question is gained through experience with the raw material.

There are many different types of commercially available pellet binders on market, however there are waste resources from other industries which can also be used, for example dried distiller’s grain and rape cake.

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The aim in pellet production is always to produce the best quality pellets, with the highest productivity possible. A quality pellet will be dense, shiny and break cleanly. Will every pellet out of the pellet mill look exactly the same, with the same density and surface shine, the answer, probably not.

The reasons for differences in pellet quality through the batch are to do with raw material consistency. Simply, to produce a consistent batch of every pellet being of the highest quality, the raw material going into the pellet mill must also be of the same consistent quality. Therefore raw material consistency with regards to the correct moisture content and binding qualities are directly related to the consistency of the pellet batch.

The question then is how important is pellet quality consistency, and this depends on the end use. For this example if we look at fuel pellets instead of other biomass pellet uses, it depends what type of burner the pellets are used in. For example the smaller the pellet burner, for example a small stove compared to a larger boiler, pellet quality consistency is of greater importance. Also the type of burn pot used affects how important pellet quality is. Use the search on the blog to find entries on different stoves, boiler and burn pots.

So sufficient pellet quality is judged on the end use requirements, but how can pellet quality be judged? Well the target quality pellet is dense, smooth, shiny and breaks cleanly with a sharp edge. So if a pellet does not have all of these features, what are the core requirements? A lower quality pellet still needs to serve a purpose; therefore it should hold its shape and take small forces without breaking. Lower quality pellets will not break as cleanly, however if the pellet under breaking completely crumbles this is not acceptable. Surface shine is an instant indication of a quality pellet, and lower quality pellets may not shine, however they may still be of sufficient quality.

Every batch of pellets will have a percentage of lower quality pellets. The question is, is the percentage of lower quality pellets acceptable or not, and this answer will be gained through experience. Generally though, the highest pellet quality should always be the target, as this gives lower maintenance and higher thermal efficiency.

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