The possibility of underground gasification of lignite from Polish deposits

Abstract

The paper focuses on the possibility of underground gasification of lignite from Polish deposits. Lignite deposits in Poland are part of the European Lignite Formation. The profile of coal bearing sediments in Poland is several hundred meters (Paleocene–Pliocene), but it is fragmented vertically and is not complete at any point. It includes marine and brackish sediments, as well as Paleogene and Neogene land sediments. Lignite deposits originated both in platform areas and sedimentary basins in orogenic belts. The coals form extensive seams or lenses ranging from few meters to several dozen meters in thickness. There are 90 documented lignite deposits in Poland.Currently, geological resources of lignite are about 26,132Mt. On the Polish Lowland, ten lignite (eight major and two accompanying) seams have been distinguished within the Paleogene and Neogene stratigraphic columns. Only three of them (1st Mid-Polish, 2nd Lusatia, 3rd Ścinawa), and locally-five (additionally 2ndA Lubin and 4th Dąbrowa) are important from the economic point of view.The annual production of lignite in Polish open cast mines amounts to 65.0Mt per year, while it is primarily used by power plants. However, chemical processing of lignite is not yet developed. It is planned that pilot plants are to be developedfor underground lignite gasification in the near future. The geological structure of the Tertiary coal-bearing formation in the Polish Lowland was the basis for the development of guidelines and parameters for criteria verification of resource base (ortho-lignite) for underground coal gasification (UCG) in Poland. Lignites from the Polish coal deposits havethe characteristics of low rank coal (mean Rr 0.2–0.35), an average carbon content at around 62–65% C, high moisture content (>50%) and net calorific value (NCV) 6–20MJ/kg (mean 8.0MJ/kg).Petrographic composition of lignite (>80% humic components) makes it a preferred material for chemical processing. The available resources and lignite deposits have been verified on the basis of the assumed geological and technological criteria. Since the geologic and reservoir conditions are accompanied by the requirements of environmental protection, protection of groundwater reservoirs of drinking water and distance requirements between the gasification plants and residential buildings, roads and transmission lines, a significant reduction in coal resources suitable for underground gasification in Poland occurred. The aforementioned criteria were applied to the initial verification of lignite resources in the Polish deposits. The deposits useful for underground gasification are mainly located in the area from Głogów up to Ściniawa and Legnica. Some individual deposits are scattered in different locations (e.g. Węglewice, residual part of the Turów deposit).