This paper is an attempt to explain the role of erosion during the process of coal combustion in a circulating fluidized bed. Different kinds of carbon deposits found in Poland, both bituminous as well as lignite with the particle of 10 mm in diameter were the Subject of the research. According to many publications it is well known that erosion plays a significant role in coal combustion, by changing its mechanism as well as generating an additional mass loss of the mother particle. The purpose of this research was to determine the influence of an inert material on an erosive mass loss of a single coal particle burning in a two-phase flow. The determination of the influence of a coal type, the rate of flow of inert material and the temperature inside the furnace on the erosive mass loss of burning coal particle was also taken into consideration. The results obtained indicate that the velocity of the erosive mass loss depends on the chemical composition and petrographic structure of burning coal. The mechanical interaction of inert and burning coal particles leads to the shortening of the period of overall mass loss of the coal particle by even two times. The increase in the rate of flow of the inert material intensifies the generation of mass loss by up to 100%. The drop in temperature Which slows down the combustion process, decreases the mass loss of the coal particle as the result of mechanical interaction of the inert material. As was observed, the process of percolation plays a significant role by weakening the surface of the burning coal. (C) 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved.