| A rectangular opposed-flow diffusion flame burner was used to study the evolution of sulfur and nitrogen species from two coals: low sulfur (0.61%) sub-bituminous and high sulfur (3.43% S) bituminous, the nitrogen content in both being about 0.8%. The conditions involved inert, reducing and oxidizing atmospheres with temperatures of up to 1500 K and residence times of up to 100 ms.; Sulfur dioxide, SO(,2), is the major sulfur species that appeared, followed by hydrogen sulfide, H(,2)S. Total sulfur release in Illinois coal (3.43% S) is kinetically controlled and can be approximated by a pseudo-first-order reaction in the sulfur remaining in the char. Total sulfur release exhibits two kinetic regions. The first is below 1000 K and has the following rate constant: k = 338 exp(-1913/T) sec('-1) and the second is above 1000 K and has the following rate constant: k = 2.46 x 10('6) exp(-11500/T) sec('-1). Total sulfur release from coal is a strong function of the amount of inorganic matter in coal. Centralia coal (0.61% S) released less than 10.0% of its sulfur, and Illinois coal released 33.0% of its sulfur in the first 100 ms.; Total nitrogen release from the two coals studied is similar in the first 40 ms and below 1000 K. It can be approximated by a pseudo-first order reaction in the nitrogen remaining in the char, with an activation energy of about 30 kJ/mol. However, the behavior after 1000 K is completely different, where Centralia coal appears to have a negative activation energy, and Illinois coal requires a higher activation energy of 76 kJ/mol with the following rate constant: k = 6.4 x 10('6) exp(-9120/T) sec('-1). While Hydrogen cyanide, HCN, is the major nitrogen species released from Illinois coal, this is not the case for Centralia coal. Nitrogen released from both is converted rapidly to nitric oxide, NO, and the conversion is a weak function of temperature. |
