Selective grindability of lignites and their application for producing an advanced fuel

This paper presents the experimental results on the Hardgrove and Bond grindabilities of the Hungarian lignite and its isolated textural components. It is shown that for such heterogeneous materials as lignites, the Hardgrove grindability index can be used only as a quantitative feature. Nevertheless the Bond-work index is the genuine grindability parameter. A Smith formula for re-calculating the Bond-work index from the Hardgrove grindability is also analysed. A new self-developing algorithm for the simulation of Bond grindability is introduced: this algorithm fits the experimental data better than the ones proposed earlier and, at the same time, has shorter testing times. It was proved experimentally that selective grinding was a very effective technique for producing an advanced solid fuel or other products with low ash and high humic acid contents from lignites having a high tendency for size degradation. The paper also deals with the theoretical and experimental possibilities of the further improvement of the advanced lignite product by steam dehydration.