THERMOPLASTIC PROPERTIES OF COAL PYROLYZED AT ELEVATED PRESSURES: ROLE OF EXPERIMENTAL VARIABLES, INORGANIC ADDITIVES AND PREOXIDATION (COAL, PRESSURE, COKING, OXIDATION, INORGANICS)

The primary objective of this investigation is to provide a basis for interpretation of the thermoplastic properties of coals pyrolyzed at gasification conditions (elevated pressure, reducing atmosphere), by utilizing a high-pressure microdilatometer as the primary research tool.; It is shown the behavior of coal, regardless of its rank, is significantly different at elevated pressures when compared to that observed at atmospheric pressure. The maximum swelling parameter (Vs%) may increase, decrease or pass through a maximum with the increase in pressure. Other observed effects of increased pressure, regardless of rank, are (i) to increase the contraction parameter (Vc%) and (ii) to increase the temperature range over which the coal is plastic. It is also shown that the effects of heating rate, particle size distribution and gas atmosphere on the thermoplastic properties of coal are dependent on the particular experimental conditions utilized. It is possible to correlate the maximum swelling parameter (Vs%) of the coal with the degree of hydrogenation of the coal.; It is demonstrated that the Vs parameter of mildly preoxidized coals is significantly restored when pyrolyzed at elevated pressure. At elevated pressures of H(,2), Vs is further restored suggesting that high pressure H(,2) removes some of the oxygen introduced during preoxidation.; Addition of K, Ca or Fe additives, depending on the nature and quantity of the additives, significantly reduces the thermoplastic parameters at most conditions. The effeciveness of the additives in reducing Vs increases with the increase in the concentration of the additives. While K(,2)CO(,3) and KOH show significant effectiveness, KCl serves as a poor decaking additive (at 0.1 MPa). Similarly, CaO and Ca(Ac)(,2) are more effective decaking additives when compared to CaCO(,3) (at 0.1 MPa H(,2) or He). Both Fe(,2)O(,3) and Fe(,3)O(,4) destroyed the thermoplastic parameters at 0.1 MPa (H(,2) or He). It is proposed that the additives that affect the thermoplastic properties of coal promoted the char-forming reactions during coal pyrolysis. For nearly all additives, pyrolysis at elevated pressures (>2.0 MPa) of H(,2), restores the Vs parameter. This phenomenon is explained by invoking that reactive H(,2) reduces the extent of char-forming reactions and increases the fluidity of the system.