Compaction of lignite: a review of methods and results

Abstract

ABSTRACT:Widera, M. 2015. Compation of lignite: a review of methods and results. Acta Geologica Polonica, 65 (3), 367-378. Warszawa.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.

What can be learned about the deposition and compaction of peat from the Miocene lignite seam exposed in the Chłapowo Cliff on the Polish coast of the Baltic Sea?

“…All of the compaction ratio values discussed herein were obtained by using stratigraphic methods. Furthermore, it is worth noting that only stratigraphic methods allow a direct quantification of the compaction ratio for the entire lignite seam (Widera 2015). The average peat-to-lignite compaction ratio for lignites from the Krzywiń and Złoczew grabens is equal to 2.2 (Kasiński 1984a(Kasiński , 1984b.…”

“…Thus, such an approach results in the reconstructed original peat thickness often being over or underestimated. This is best demonstrated by the very wide range of compaction ratio included in the geological literature, which is between 1.1 and 11.0 for lignite from around the world, as the author of this work previously compiled (Widera 2015).…”

“…According to the classification of Ryer & Langer (1980), the methods for calculating the peat-to-coal compaction ratio, including the peat-to-lignite one, can be grouped into the following categories: density, inclusions, petrographic and stratigraphic. For more information, the interested reader is directed to the paper where all these methods and the results of their application have been reviewed (Widera 2015). It should be stated here that the research method used in this study belongs to the inclusions method category, as distinguished by Ryer & Langer (1980).…”

Early stages of clastic deposition in the Most Basin (Ohře Rift, Czech Republic, Early Miocene): timing and possible controls

“…However, a detailed analysis of sediment bodies in the Most Basin showed that the extensive lacustrine clastic strata above the coal seam caused the compaction of the underlying peat to one-seventh of its former thickness, compaction of the fluvial clays to one-third of their former thickness, and negligible compaction of the fluvial sands (Hurník 1972, Mach 2003, Novotný & Mach 2016. Studies of fluvial and deltaic sediment bodies embedded in the local coal seam demonstrated that the compaction of the peat strata contributed to the formation of accommodation space for the fluvial clastics (Dvořák & Mach 1999, Rajchl & Uličný 2005, Rajchl et al 2008, Overviews of this peat compaction and examples from other basins are given by Van Asselen et al (2009), Van Asselen (2011), and Widera (20152016a, b).…”

Oligo-Miocene coal in a microtidal environment reworked under Quaternary periglacial conditions (Western Falkland Islands/Isla Gran Malvina) – Coal formation and natural sand processing

“…The lignite studied in the Falklands has been derived from peatland with possibly periodic flooding by brackish waters or seawater. Taking into account that the majority of the peat: lignite compaction ratios for various lignite range from 2:1 to 4:1 as reported by Widera (2015), it can be assumed that the peat thickness prior to burial was 2-4 times greater than today. The observed vascular tissues with sieve plates and fibers are considered here to represent primary vascular tissue, most possibly of herbaceous angiosperms.…”