The effect of temperature and residence time on the distribution of carbon, sulfur and nitrogen between gaseous and condensed phase products from low temperature pyrolysis of kraft black liquor

The effect of temperature and residence time on the distribution of carbon, su(fur and nitrogen between gaseous and condensed phase products from pyrolysis of kraft black liquor were investigated using a laminar entrained flow reactor (LEFR). The measurements were, made with dry 88-125 micron, black liquor particles at temperatures between 400 degreesC-600 degreesC and particle residence times from 0.3 to 2.0 seconds. The char residue and the finer particles generated were collected and analyzed for carbon, sulfur and nitrogen content. The product gases were oxidized, and the total carbon content of the gases was measured In these experiments, the carbon converted to gases increased as both residence time and reactor temperature increased. The carbon recovered as gases after 2 seconds particle residence time increased only slightly with temperature, from 20% at 400 degreesC to 23% at 600 degreesC. Nearly all of the rest of the carbon was recovered as char residue. The nitrogen and sulfur retained in the char residue decreased as residence time increased. More sulfur and less nitrogen remained in the char at higher temperatures. Rare constants for a Kobayarhi-type model for devolatilization of kraft black liquor were extracted from the data obtained for each of the three elements.