CHLORINE RELEASE FROM BURNING BLACK LIQUOR DROPLETS – EXPERIMENTAL AND CFD MODELING RESULTS

In this work, we look at the release of Cl from burning black liquor droplets as a function of temperature and droplet size. Single droplets, 10 or 50 mg, were burned at temperatures between 900 and 1150 °C in a single particle reactor in a gas atmosphere containing 1% O2, 11% CO2, 17% H2O and 71% N2. The black liquor used was a Nordic softwood black liquor with and without the addition of KCl. Interrupted runs were made to separate out the different stages of black liquor combustion: devolatilization, char burning and smelt oxidation. The release of Cl was determined by dissolving the salts in ultrapure water and analyzed by ion chromatography. The results indicate that there is little to no Cl release during devolatilization and char burning when water vapor is present and that Cl release occurs predominantly from the smelt bead. Experiments were carried out with 50 mg droplets at 1000 °C with either 11% CO2 + 1% O2 or just 1% O2 to study the effect of gas composition and Cl release was seen during char burning in these gases. The rate of Cl release from the smelt is dependent upon temperature, Cl concentration and surface area of the smelt bead. A single particle modeling approach is presented and the modeled Cl release corresponded well with the experimentally determined release.