SULFUR AND NITROGEN EVOLUTION IN THE ARGONNE COALS - EXPERIMENT AND MODELING

Sulfur and nitrogen evolution from the Argonne Premium coals has been studied using thermogravimetric analysis with measurement of evolved products by Fourier transform infrared spectroscopy (TG-FTIR). The method combines temperature-programmed pyrolysis and combustion. H2S and tar sulfur were monitored by measuring SO2 after oxidation of volatile products. The SO2 evolution curves produced with volatile oxidation exhibit two main evolution peaks and one smaller high-temperature evolution peak. For each peak, the temperature of the maximum evolution rate (T(max)) increases with increasing rank. The individual evolution curves of the organic and pyritic sulfur were identified, and their evolution kinetics were derived. The overall SO2 evolution curves were modeled by using the FG-DVC coal pyrolysis model. The evolution curves for both NH3 and HCN show an increase in T(max) with increasing rank. NH3 is the dominant product at low heating rate. Results from previous high heating rate experiments show that HCN is the dominant product. The heating rate dependence of the conversion of coal nitrogen to HCN and NH3 is believed to be due to the secondary reaction of HCN and coal hydrogen in the char pores to produce NH3. This reaction can be completed with enough gas residence time within the char pores. At high heating rate, the residence time is reduced and HCN conversion does not occur. Such a reaction sequence was added to the FG-DVC model and the kinetics were derived.