Antracite

The volatile matter increases from less than 8% in antracite to more than 27 wt% in lignite. In addition, the content of water may vary from less than 5 wt% in antracite to about 60% in German brown coal. Nitrogen (0.5-2%) will be converted into ammonia. The sulphur content may typically vary from 0.5-5 wt%. Sulphur will be converted to COS and H2S. Sulphur will poison downstream synthesis catalysts and must be removed. Chlorine is normally below 1 wt%. Chlorine may cause corrosion problems in downstream equipment. Chlorine will react with ammonia from the nitrogen and deposition of ammonia chloride may foul waste heat boilers and limit their operating temperature [230]. 

The main aim of calcination is to remove the volatile resin, such as organic compounds (10-15 %). Not all antracites may be used after calcination for the production of carbon cathode blocks, and not all antracites may be calcined in a similar manner. 

Fig. 2.36 Pore size distributions in carbon cathode antracitic graphitic (30 % graphite) blocks of different producers, having open porosity below 20 %...

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