Petrographic and geophysical assessment of coal quality as related to briquetting: the Miocene lignite of the Lower Rhine Basin, Germany

In the Lower Rhine Basin, Germany, Tertiary lignites are mined primarily for electrical power generation and briquetting purposes. Until 2000, when the mine was closed, coals from the Bergheim open pit mine were used for briquetting. After 2000, briquettes were produced from the Hambach open pit mine but did not show the same quality and hardness as those from the Bergheim pit. In this context, the macropetrographic and microlithotype composition of the Hambach lignites was studied in detail. Samples were taken from the three profiles, S1, S2 and S3, and a well, R1. All of the samples were macropetrographically described, analyzed in their microlithotype composition, and coals from profile S3 were analyzed for their briquetting compression strength. Three horizons of high gelite content were detected in the Main Seam, two of them with negligible thickness and one with a thickness of up to 1 m. Briquettes produced from these horizons are characterized by significantly reduced hardness. By careful interpretation of subtle changes in geophysical log data, it was possible to map the occurrence of these gelite horizons. As a consequence of these studies, an excavation plan was set up by the RWE Rheinbraun to avoiding mining of critical strata for briquetting purposes.