Compaction of lignite: a review of methods and results

Abstract

The published peat:coal compaction ratios range from 1.1:1 to 60:1 and from 1.1:1 to 11:1 for lignites. These probably represent realistic end-member values for the degree of compaction during the transformation of peat into lignite and then to coal. Hence, in many cases, the obtained values of the compaction ratio are under- or overestimated with reference to the entire coal seam.

This study focuses on the changes of thickness between a peat bed and the resulting lignite seam. The fundamental question is how many times the thickness of the peat bed, prior to covering the mire by the overburden, was greater than the present-day thickness of the lignite seam.

The majority of methods reported in this paper cannot be used directly to quantify the amount of compaction of the lignite seam. In this context, the only category of methods which allow a direct estimation of the peat:lignite compaction ratio are the so-called stratigraphic methods. Therefore, based on comparison of the initial peat bed thickness with lignite seam thickness, the most accurate peat:lignite compaction ratio ranges from 2:1 to 4:1.