Variation of lignite ash in vertical and horizontal sections of mining walls in the Konin Lignite Mine, central Poland

Abstract

This paper focuses on the variations of lignite ash along selected sections and mining walls from three lignite opencast mines in central Poland. They are owned by the Konin Lignite Mine, where the first Mid-Polish lignite seam is being mined to produce electricity. Ash content in lignite is important because ash lowers the calorific value of the lignite. The results obtained are based on 266 samples of lignite collected from the Drzewce, Tomisławice, and Jóźwin IIB opencasts. All samples were tested according to ISO 1171 standard procedures, that is, they were first burned at a temperature of 850°C, then the ash content was determined on a dry basis (A$^{d}$), before the basic statistical parameters were calculated. The studied lignite seam is characterised by a variable distribution pattern of ash both along selected vertical sections and lignite walls, as well as between the three opencasts. The ash content of individual samples ranged from 6.5 to 69.8 wt%, while the average content in opencast mines varied from 9.7 to 17.6 wt%. The coefficient of variation is large (80.23–96.33%) in the case of the Drzewce and Tomisławice, and low to average (14.53–37.75%) in the case of Jóźwin IIB. Significant ash enrichment of some beds is interpreted in this article as a consequence of floods occurring in a Mid-Miocene mire (backswamp), but also of chemical precipitation. When lignite is burned to generate electricity, a relatively large amount of ash is produced. Therefore, recognition of ash content in lignite, in addition to the chemical composition and phase of ash, is recommended to better protect the environment. At the first stage of protection, it can be best achieved by analysing field samples for ash content.