Name a few binder additives used in pelletizing of torrefied biomass. When is it necessary to use them?

Pelletizing is a process of compressing biomass materials into small, dense pellets. This is particularly useful in torrefied biomass, as it has been subjected to a mild thermal treatment that alters its properties to improve energy content and grindability. Pelletizing can improve handling, storage, and transportation properties, making torrefied biomass more attractive as a renewable energy source.

Binder additives, also known as binding agents, are substances that help to hold the biomass particles together, increasing the durability and stability of the resulting pellets. They have an essential role in the pelletizing process as they prevent the pellets from disintegrating and falling apart, especially during storage, transportation, and combustion.

Some common binder additives used in pelletizing torrefied biomass include: 1. Lignin: Lignin is a natural component found in plant cell walls, which can be used as a binder due to its adhesive properties. It can be liberated from the biomass during the torrefaction process, or added as an external agent. 2. Starch: Starch, a carbohydrate found in many plant sources, can be used as a binder additive due to its capability to form stable gels by heating and cooling. 3. Molasses: A byproduct of sugar refining, molasses, can be used as a binder agent due to its sticky nature and high sugar content, which can provide adhesion in torrefied biomass pellets. 4. Glycerol: Glycerol, a byproduct of biodiesel production, can be used because of its moisture-retaining capability and ability to form strong intermolecular bonds within the torrefied biomass.

The use of binder additives in pelletizing torrefied biomass is necessary when: 1. The natural binding properties of the biomass material are not sufficient to hold the particles together in a stable pellet form. 2. The pellet strength needs to be increased to enhance durability during storage, transportation, and combustion. 3. There is a need to reduce the risk of pellet disintegration that may lead to increased fines or dust generation, creating handling difficulties and potential safety hazards (e.g., dust explosions, respiratory issues). 4. There is a need to optimize the combustion properties of the pellets, such as ensuring consistent burn rates and minimal emissions.