The Effects on the Mined Lignite Quality Characteristics by the Intercalated Thin Layers of Carbonates in Ptolemais Mines, Northern Greece

The role of the thin intercalated carbonate sterile layers (marly limestones and carbonaceous marls) coexcavated with lignite in the Southern Field Mine, Ptolemais Basin, Northern Greece is investigated. For this purpose, laboratory mixtures of lignite-marly limestone and lignite-carbonaceous marl in different proportions are prepared and the quality characteristics of these mixtures are compared with those of the geological, the recoverable, and the mined lignite. The quality characteristics investigated are the ash content (db), the gross calorific value (db), and the CaO_(free) content of the ash. The addition of marly limestone and carbonaceous marl to lignite by 10% increases the ash content (db) up to 33.7% and 21.1%, respectively, and the CaO_(free) content of the ash up to 79% and 57.3%, respectively, while reducing the gross calorific value (db) by 12.9% and 8.4%, respectively. Marly limestones must be avoided as soon as possible in order to minimize the contamination impacts. Carbonaceous marls can be used up to a permissible limit, where benefits from their calorific value and the natural desulfurization are obtained.