Biomass Molding Fuel (BMF) is biomass particles forming fuel. This passage will focus on the combustion characteristic and various factors affecting the combustion of BMF.
1. Combustion Characteristics of Biomass Molding Fuel
BMF mainly includes two types: pellet and briquette. Firstly, the collected biomass raw materials are crushed, dried, and sent into biomass molding machine. Under certain pressure, the crushed biomass is compressed into molded fuel with regular shape by mechanical compression. Particle fuel is small cylindrical size with diameter of 4~6mm, length of 6~8mm, and density of 1.0~1.21t/m3. Briquette fuel is large cuboid size, with side length of 20x20mm, 30x30mm, 40x40mm, etc. The briquette length is 20~60mm, density is 0.8-1.3t/m3, and raw material requirement is low. It can make full use of crop straws, municipal solid waste, sludge, etc.
Volatile content of biomass fuel is high as 60%~70%, while fixed carbon is relatively small as about 20%. The combustion of biomass molding fuel is mainly early-stage combustion, which belongs to static infiltration diffusion combustion. Ash content of different biomass fuel is different, straw is the highest 12.20%, while peanut shell is the lowest 1.60%. The biomass ash contains relatively high alkali metal element potassium, which will form KCI in the process of combustion. It will result in a series of problems, such as deposition, slagging and high-temperature corrosion. Efficient ash-cleaning and slag-removing devices are necessary.
2. Influence of moisture content on combustion of Biomass Molding Fuel
Biomass raw materials mainly include agricultural wastes, forestry wastes, wood processing wastes, municipal wastes and sewage sludge. Agricultural wastes mainly include wheat straw, corn straw, rice straw, etc., and moisture content of newly harvested reaches 30%. Forestry wastes mainly include pruning branches, the roots and bark of trees, etc. Wood processing waste is mainly wood chip and shavings in wood processing plant. These two types have high calorific value, and the water content is more than 40%. The water content of municipal waste and sewage sludge is high as 70%. Too high moisture content will not only affect the ignition of biomass molding fuel, but also increase the vapor share in flue gas, increase the heat loss, and reduce the calorific value of fuel. Moreover, the higher the moisture content, the easier the biomass briquette will crack.
3. Influence of bulk density on combustion of Biomass Molding Fuel
Bulk density is an important index to measure biomass energy density, which depends on the particle density, size and shape. Increasing the bulk density of biomass can effectively improve the quality and energy density of biomass, improve the storage and transportation conditions, and reduce the fly ash amount.
4. Impact of breakage rate on combustion of Biomass Molding Fuel
The higher the breakage rate, the worse the quality of formed fuel. A large amount of floating dust arises during the combustion process, which will increase the emission concentration of solid particle. In order to ensure the quality of biomass molding fuel, the breakage rate shall be within 10%.
