The pyrolysis process of a lower rank coal as a fresh coal (FC) and a long-term stored coal (LTSC) was analyzed in a laboratory coking unit using X-raying and thermobalance. The changes in temperature of the charge of coals were determined along with the changes in volume of their carbonized charges, the mass loss of coals, and the mass loss rate. It was stated that LTSC has a lower thermal diffusivity at the stage of coal grain swelling and shows an almost twofold growth in charge volume at this stage. The samples of carbonized coals that correspond to the plasticity stage were investigated using the FT-IR and SEM methods. The pyrolysis products of coals were analyzed by the TG/FT-IR method. It is suggested that the formation of nano-size films and spherical objects in the pores of the plastic mass of LTSC results from an increase in content of non-saturated hydrocarbons, aldehydes, phenols, and alcohols in volatile products of pyrolysis of this coal. (C) 2016 Elsevier Ltd. All rights reserved.