What are Agri-pellets?
Agri-pellets are a range of sustainable and carbon neutral biomass fuels which are made by agricultural residues such as straws, husks, stalks and bagasse, etc. With wood pellets are widely used in many countries and areas, biomass pellets are popular all over the world. However, due to possible shortage of wood pellets production in areas like Southern European, the agricultural residues which can also be processed into pellets came into people’s eyes.
Characteristics of Agri-pellets Compared to Wood Pellets
Compared with wood pellets, agri-pellets which use rice straws, corn stalks, wheat straws, sunflower husks, cotton stalks as raw materials have their unique characteristics:
1. The raw materials are easy to get. As agricultural plants grow and harvest each year, and the life cycle of agricultural plants is shorter than wood. So the agricultural residues as raw materials of agri-pellets are much easier and cheaper to get.
2. Agricultural residues like straws, husks, stalks are with lower moisture content than forestry residues. Agricultural residues usually are delivered with lower moisture content than the wood, thus the drying process can be omitted.
3. Agri-pellets are carbon neutral fuel resources. Compared with wood pellets, the carbon emitted by agri-pellets burning cost less time to be resorbed than that of wood pellets.
4. The friability of agri-pellets is higher than wood pellets. Since the density of agri-pellets are lower than wood pellets, agri-pellets more inclined to break up.
5. The ash content of agri-pellets are higher than wood pellets. The ash content of agri-pellets is about 10 times higher than that of wood pellets.
6. The chemical composition of agri-pellets and wood pellets are different.
Problems Occurred During the Combustion of Agri-pellets
With the unique characteristics of agri-pellets, there are some problems occurred during combustion of agri-pellets. Currently, the burning equipments in the market are mainly designed for wood pellets, so it is inevitable to have some problems when burning agri-pellets in these equipments like wood pellet burner. The main problems are in the following:
Firstly, since the ash content of agri-pellets is high, the ash slagging problem of agri-pellets is serious.
Secondly, compared with wood pellets, agri-pellets contain more potassium(K), nitrogen(N), sulphur(S), which will lead to increased emission of NOx, SOx and HCL.
Thirdly, the content of chlorine(CL) of agri-pellets will cause corrosion of the boiler internals.
Solution of Problems Which Occur at Combustion of Agri-pellets
1. Use multi-fuel boilers which is more suitable for burning agri-pellets.
2. Co-firing with fossil fuel may solve this problems.
3. Clean the agricultural residues before pelletizing them into agri-pellets to make them with less ash content.
4. To add in specific anti-slagging agents or mix in some sawdust to change the fuel characteristic.
