Effect of Gas Composition on Fume Sintering Rates, 2004 International Chemical Recovery Conference

Sintering of fume deposits in recovery boilers can contribute to the long term growth of deposits, resulting in decreasing boiler efficiency and lower liquor throughput rates. In our earlier work an experimental reactor was constructed to measure the sintering rates of uncompacted ESP dust samples. The reduction of the specific surface area of the particles was used as a measure of the degree of sintering. In the present work, a series of tests was designed to determine which of the major gas components present in the recovery boiler has a significant impact on the rate of sintering. Sulfur dioxide (SO2) at 1.0% by volume (10,000 ppmv) in the gas was found to greatly accelerate the rate of sintering. However, when the SO2 level was reduced to 0.1% by volume (1000 ppmv) there was little or no effect on the sintering rate. Sulfur dioxide at 1.0% by volume in the gas phase also resulted in the conversion of sodium carbonate to sodium sulfate and some decrease in the chloride level of the fume.

None of the other gases tested (O2 at 3% by volume, H2O at 18% by volume, and CO2 at 14% by volume) had a significant effect on the rate of sintering. In general the sintering trends with time and temperature are similar to the results found during earlier studies. Since levels of SO2 over 1000 ppm are rarely found in recovery boilers in the superheater section or downstream of it, these results suggest that SO2 is not usually a major factor in sintering of deposits. However, the impact of SO2 may be important during upset conditions when the char bed is cold and higher levels of SO2 are generated for a short period of time.