The elasticity of coal refers to the deformation of coal produced by external force, and the degree of recovery of deformation after external force is removed.
The elasticity of coal is generally expressed by the relative expansion ratio after the demolding of the briquettes. The greater the elasticity of the coal, the looser the coal after press forming and the lower the strength.
The elasticity of coal is related to the following factors:
1, the degree of coalification
According to the degree of coalification, coal is divided into peat, lignite, bituminous coal and anthracite. As the degree of coalification increases, the elasticity of coal increases. The elasticity of anthracite.
2, the level of granularity
In the same coal, the finer the particles, the more elastic and the poorer the formability.
3, the moisture of coal
The same coal type, generally the greater the external moisture, the greater its elasticity.
In addition, the minerals in the coal also have a certain influence on the elasticity. The coal with large elasticity is difficult to form, and the strength after molding is also low. When the mold is released, it is often cracked and swelled due to elastic expansion, so for the coal with large elasticity Try to reduce the elasticity and then reshape.
The main raw material of clean briquette is anthracite. The anthracite has large elasticity and poor plasticity. To pay attention to this feature, pay attention to the following matters in production：
1, the crushing process
After crushing, the particle size of the coal should be controlled below 3 mm, of which more than 70% is more than 1 mm. The upper limit of the specified particle size is to prevent the secondary crushing of the coal in the forming process and affect the strength of the briquette. The specified lower limit is advantageous for reducing the elasticity between the particles while reducing the amount of binder added and improving the burning performance of the briquette.
By the way, the coal moisture into the crusher is generally controlled below 15%, otherwise it will affect the crushing effect.
2, kneading process
The kneading process is a general term for mixing and kneading. The mixing is to mix several materials and water uniformly by mechanical agitation.
Kneading is to uniformly distribute water and binder on the surface of the coal particles so that it is closely adsorbed on the surface of the coal particles to form a hydrated film. In addition, the bulk density of the coal material can be increased, the elasticity between the coal particles can be eliminated, and the molding is facilitated.
Commonly used kneading equipments include twin-shaft mixers, wheel mills, vertical kneaders, etc.
3, purification process
The deuteration process is to infiltrate the binder into the interior of the coal particles, and at the same time increase the bulk density of the coal, eliminate the elasticity between the coal particles, and increase the strength of the briquette.
Some clean coal production lines do not have a deuteration process. If you increase the density of coal and eliminate the elasticity between coal particles, Xiao Bian recommends that you look at the coal for a period of time before the molding process.
The simmering time is generally 24 hours and is adjusted as the temperature changes.
4, molding process
When the coal particles are pressed, they will be elastically deformed, and the mechanical energy input from the power will be stored in the briquette. When the forming pressure is eliminated, this part of energy will be released, and the volume of the briquette will expand. Anthracite has large elasticity and high expansion ratio, so it adopts low pressure molding, and the molding pressure generally does not exceed 25 MPa. The pressure excessively generates cracks on the surface of the briquette, reducing strength and water resistance.