Anthracite is the most highly metamorphic humic coal. It features a high fixed carbon content, low volatile matter, high density, high hardness, smokeless combustion, and a strong metallic luster. Anthracite is widely used as a fuel for household purposes, power generation, and steelmaking, as well as a raw material for gasification and synthetic ammonia production. In carbon production, it is used to produce various carbon materials, including carbon blocks and electrode paste.
When used in carbon production, anthracite should possess the following properties:
1. Low ash content.
During the carbon production process, all of the anthracite's ash is incorporated into the carbon material. Excessive ash content will reduce product quality. For example, in carbon block production, the anthracite ash content (mass fraction) should not exceed 8%, and the presence of gangue should be minimized. This is because some gangue forms lime after calcination. Particles of lime mixed with the carbon blocks expand upon contact with water, causing surface cracking. For anthracite used in electrode paste production, the ash content (mass fraction) should also be less than 10%-12%.
2. High mechanical strength.
The mechanical strength of anthracite is closely related to the mechanical strength of the carbon materials produced from it. The mechanical strength of anthracite includes mechanical properties such as resistance to crushing, wear, and compression. The carbon industry often uses the drum test (also known as the anti-wear test). This involves tumbling a certain amount of anthracite lumps larger than 40 mm in a drum. The percentage of lumps remaining larger than 40 mm is used to characterize the mechanical strength of the lumps. The general requirement is that the percentage of lumps larger than 40 mm remaining after the drum test should be no less than 35%.
3. Good thermal stability.
The thermal stability of anthracite refers to the ability of lumps to retain their original size under high temperatures. Anthracite with good thermal stability exhibits minimal change in size and strength after calcination. Coal with poor thermal stability tends to break into small pieces after calcination. Thermal stability can be measured according to the national standard GB/T1573-2001. Low sulfur content. Carbon production requires anthracite to have a sulfur content (mass fraction) no greater than 1% to 2%.