Measurement of true specific heats of bituminous coals of different rank, and of a high-temperature coke, in the temperature range 30–350 °C

Abstract

The true specific heats of four bituminous coals from the Ruhr district with volatile matter ranging between 9 and 37 wt% and of a high-temperature coke were measured with an adiabatic metal calorimeter. The precision of the equipment was checked by measurements on pure nickel, with the result that the experimental values were found to differ by <1% from the adequately accurate average values given in the literature. The results of this study and the scrutiny of all obtainable systematic specific heat measurements of bituminous coals lead to the conclusion that, contrary to the opinion given in the literature, the specific heats do not increase rectilinearly with the volatile matter. The relation of the specific heats of the coals investigated to volatile matter and temperature can be explained by the chemical composition and structure of the coals. The specific heats calculated from the distribution of the elements carbon, hydrogen and oxygen in the structural groups of bituminous coals correspond well to the experimental values. The procedure is more promising than that using only the results of immediate analysis without taking into account chemical composition and structure. In the initial stage of pyrolysis, variations from a monotonic increase are observed and semiquantitative considerations on this are given. The effect of temperature on the specific heats of coals is compared with that on other physical quantities and explained.