COAL DEVOLATILIZATION DURING RAPID TRANSIENT HEATING .1. PRIMARY DEVOLATILIZATION

Our new flow experiment heats entrained coal suspensions by radiation from a near-blackbody enclosure, not by a preheated stream. Since the entrainment stream is transparent to radiation, it can be made to remain much cooler than the suspension. Pristine products which have been quenched as soon as they were expelled can be recovered or, alternatively, the extent of secondary chemistry can be regulated at will. The furnace system also includes rapid quenching to resolve reaction times on a scale of several milliseconds, aerodynamic segregation of particulate, aerosol, and gaseous products, and analyses for C1-C4 hydrocarbons, oils, CO, CO2, H2O, NO, and HCN. Balances on mass, carbon, and nitrogen are usually closed to within 5% in individual runs. Product distributions for transient devolatilization at nominal heating rates of 10(4) K/s are reported for four coals of ranks from subbituminous to low-volatile bituminous. They show that during the initial stage of primary devolatilization, coals of lower rank expel significant amounts of noncondensibles with their tar, but predominant tar evolution is a distinctive feature of ranks of hvA bituminous and higher. Tars from this experiment have the highest H/C ratios ever reported, as well as the lowest proton aromaticities. Throughout primary devolatilization, their proton distributions shift from substantial fractions of beta- and gamma-protons to mostly alpha-protons. Yields of all gaseous hydrocarbons, carbon oxides, and water increase in proportion to the tar yields with no distinctive surges or lapses. The major C1-C3 hydrocarbons are CH4, C2H2, and C2H4 but oils are the major gaseous hydrocarbon product from bituminous coals. Aromatic hydrocarbons, especially tars, are the only shuttles for fuel nitrogen during the initial stage. During the later stage of primary devolatilization, no tars are expelled but additional C1-C2 hydrocarbons are generated, and distinct surges in the evolution of CO and H2O from coals of lower rank actually increase the rates of weight loss. Also, HCN appears for the first time during the later stage. H/C ratios for char from 0.3 to 0.4 and little residual oxygen signal the end of primary devolatilization.