Usage of Additives in Wood Pellet Mill Equipment Opertation
Wood pellet mill equipment is an example of biofuel machine, which is a cost effective way of producing biomass fuel that is environmentally friendly, eliminating the use of fossil fuels like oil and gas. Quite frankly, biofuel machines produce the oldest source of renewable energy. However, new technology makes it practical for today.
Wood pellet mill transforms biomass materials, (organic) into wood pellets for heating, but the wood pellets, which replace logs, must be durable, and have a moisture content that is below 10%. Most are much lower. The processes that are implemented by wood pellet mill equipments are more complicated than placing logs in one end, to pop out pellets on the other side. There are a number of steps and principles involved to producing quality, wood pellets.
Function of Additives in Pellet Production
Biomass pellets must have certain bonding characteristics. During biomass production binders are added. These additives are for bonding purposes and produce a quality pellet that is highly durable.
The additives increase the strength of the pellet. These bonding agents produce better bonding, increase lubrication, and also decrease problems that are associated with combustion. The additives also eliminate another problem that is sometimes associated with handling and transportation, as dust can be an issue. However, additives help to eliminate dust particles. Additionally, the pellet die is lubricated. This increases pellet production.
Factors Influences Bonding Effect
The bonding process is fairly complex, and there are a number of factors that will affect the wood pellets durability.
- Feedstock composition: Lignin is an organic polymer present in many plants. lt’s what makes the plant woody and rigid. It also affects composition of biomass material. Higher lignin content produces a composition that is easier molded into pellets. Additives are necessary in lower lignin composition.
- Particle size: The size of the particles fed into the wood pellet mill affects bonding. Decreasing the particle size increases attractive intermolecular force. Another factor that affects pelletization is temperature.
- Temperatures: A high temperature assists particle molecular diffusion, by melting the biomass constituents. Bridges form as cooling goes into effect.
- Moisture: We touched on moisture above. The proper amount of moisture is essential to the bonding process. It increases the pellets bond, as it spreads lignin within the pellets. The result is an increase the die holes compression. An excess of moisture could lower the strength of the pellets bond, because it may block pellet die holes.
- Pelletizing pressure: Wood pellet mill equipment delivers just the right pressure to produce the correct pellet bond. It is a major factor to the bonding process. High pressure results in better bonding, and ensures pellet quality.
Common binders in biomass pellet production
Biomass pellet production requires the following for binding: lignin, starch, lime, fiber, etc.
- Lignin: a natural organic polymer
- Starch: derived from corn or rice, and common in Austria, which is a leading producer of biomass pellets.
- Lime: CaSO4 is a chemical compound that has a higher melting temperature, and is a result from limestone.
- Fiber is water-soluble and increases thickness for a pellet with more positive and structural integrity.
Potential additives also include hydrated lime and pea starch. Each of these will improve pellet quality. There are a number few binders that aren't allowed in European markets, so wood pellet making equipment workers, and plant operators should be well aware. Starch content is allowed in Austria, however only by 2% weight. Emission control legislation in Germany only allows molasses as a residue, including natural paraffin, starch and from sugar production.