Measurement and Importance of Volatile Matter in Coals and Biofuels

Volatile matter values for solid fuels are used to assess their burning rates and, thus, provide a basis for the buying and selling of these fuels. The major factors that affect volatile matter yields are the type of fuel, moisture contents, and the heating rates used in the tests. This paper reports the results of experiments designed to improve the reliability and application of test methods for the determination of volatile matter in various solid fuels. The macro thermogravimetric analysis studies described herein include the rapid drying of analysis samples of coal and the effect on volatile matter yields, the heating of various chars at high temperatures to reach a state of constancy, the measuring of decomposition moisture, an "elusive" constituent in coal, and the cocombustion of coals and other solid fuels. The presence of residual moisture and decomposition moisture in the coal during the volatile matter tests increases the measured volatile matter yields even though the residual moisture has been factored out. The rates of heating solid fuels during volatile matter tests affect the volatile matter yields because of the presence of different types of moisture in the fuel that are released at different temperatures. The heating rates used in volatile matter tests affect the type of compounds released and the total volatile matter yields of coals and biofuels. The experiments reported in this paper were instrumental in the decision of ASTM Committee D05 on Coal and Coke to recently revise the classic volatile matter standard test method D3175 to change the temperature for drying sparking coals from 600 degrees C to 107 degrees C. The role volatile matter plays in the combustion of fuel blends is discussed in this article.