The biomass briquetting technology is a technique for compressing various loose biomass raw materials into a certain shape, big strength and density fuel briquette by heating and pressing techniques.
Common biomass waste includes sawdust, wood shavings, wood flour, crop straw, rice husk, etc.
The high moisture, irregular shape and size, and low bulk density of biomass feedstocks make it difficult to process, transport, store and utilize.
But when these biomass materials are processed into briquettes, the density is greatly improved, and the cost of transportation and storage is reduced.
Their uniform shape and size make these solid fuel briquettes can be easily stored using standard facilities.
Everyone knows the importance of pressure for biomass briquetting, but apart from this, there are also many other factors that affect the process of biomass briquetting.
These factors mainly include raw material moisture, particle size and various parameters of the biomass briquetting equipment.
Among them, the moisture of raw materials is an important factor in the process of biomass briquetting. The proper moisture content can make the briquetting effect on the best condition. A moisture too high or too low will adversely affect the briquetting process.
Effect of moisture on biomass briquetting process
Moisture acts as a binder and lubricant during briquetting.
As a kind of indispensable free radical, the water in the biomass flows between the biomass particles, and under the action of pressure, it is mixed with pectin or sugar to form a colloid, which acts as a binder.
The appropriate amount of bound water and free water make the internal friction between the particles becomes smaller, the fluidity is enhanced. Thereby promoting the particles to slide under the action of pressure and fitting, with the role of lubricant.
Raw bio waste with low moisture
When the moisture content of the biomass material is too low, the particles are not sufficiently extended, and the surrounding particles are not tightly bound and cannot be formed.
For example, if the moisture is too low, the trace moisture is vaporized at a high temperature, which will facilitate the rapid conduction and uniform distribution of the heat flow, thereby lowering the softening point of the lignin, resulting in difficulty in briquetting.
Studies have shown that biomass like corn stalks and reeds are suitable with moisture around 12% to 18% during briquetting, and the optimum moisture is 15%.
The density of the biofuel briquette is in proportion to the moisture of the raw biomass. The density of the biofuel briquette is maximized and remains relatively stable over a suitable moisture range;
When the moisture is increased to a certain extent, the density of the briquette fuel begins to decrease, eventually leading to the failure to make briquette.
The biofuel briquette produced by the lower moisture raw material having the tendency to absorb moisture in the air, causing the biofuel briquette to burst and deform, as well as reducing the briquette density.
Raw bio waste with high moisture
If the moisture of the raw material is too high, the particles can be sufficiently extended in the direction perpendicular to the maximum principal stress. Although the particles can be meshed with each other, since more water in the raw material is extruded, it is distributed between the particle layers, so that the particles are dispersed. The layers do not fit snugly and therefore cannot make the briquette to be formed.
Moreover, too much water vapor increases the distance between molecules, affects heat conduction, lowers the briquetting temperature, makes the lignin in the raw biomass difficult to melt, and the crude fiber is not easy to soften, resulting in a decrease in the bonding force.
Therefore, when the moisture content of the raw material is too high, the heating temperature required in the briquetting process is increased.
During the biomass briquetting process, as the shaped fuel in the forming cone and the retaining cylinder is subjected to the radial forces exerted by the tapered sleeve and the retaining cylinder, this will generate friction and consume a certain amount of energy.
Excessive moisture increases the radial force experienced by the forming briquette, which also increases power consumption.
At the same time, a part of the heat of the preheating material of the biomass briquetting machine is consumed on the excess water, the evaporated water is quickly vaporized, but the steam cannot be discharged from the molding cylinder in time, resulting in volume expansion, occupying an increase in space, easily forming a gas blockage, and forming large steam pressure in the longitudinal direction of the cylinder.
When the steam pressure is slight, the biofuel briquette fuel will be cracked and the surface is rough;
But when its big, it will cause the material to be quickly ejected out of the forming cylinder, causing the phenomenon of shooting, briquette cannot be made then. It will also cause damage to the surrounding environment and may even affect personal safety.
After the biofuel briquette is extruded from the forming sleeve, the expansion and disintegration due to the high-pressure water vapor inside the biofuel briquette may affect the subsequent packaging and transportation and the briquetting characteristics of the briquette.
The effect of biofuel briquette is the result of a combination of multiple factors, but moisture is an important factor in the formation.
The moisture of the raw material is related to whether the biomass can be compressed into briquette, which has a significant effect on the relaxation density of briquette. Whether the moisture content is too high or too low, the briquette with better relaxation density cannot be obtained.
Studies have shown that the optimum moisture of cereal raw materials should be between 11% and 12%, while the optimum moisture content of forestry raw materials is about 8%.
There is a large difference in the moisture range of various raw materials because of the large differences in raw material characteristics and processing methods.