Technical Bulletin No. 0095: A Laboratory and Field Study of Factors Affecting the Soluble Sulfide Control of Lime Mud (AQTB)

The control of hydrogen sulfide emissions from lime kilns is dependent on (a) maintenance of the proper combustion conditions in the kiln, (b) use of a particulate scrubber solution essentially free of strippable reduced sulfur compounds and (c) residual soluble sulfide in the dewatered lime mud cake. Earlier field studies revealed that the soluble sulfide control of lime mud, which is responsible for the hydrogen sulfide contributed by dewatered lime mud, was effectively oxidized at some filters. This is not consistently observed to be the case, however. The investigative work consisted of a series of laboratory investigations designed to determine factors which might affect cake porosity, hence air passage through the cake, as a means of enhancing oxidation at the filter. A series of field investigations were then carried out to determine if the level of residual soluble sulfide in dewatered cake could be traced to design and operating conditions at various field installations. Finally, the design and limited performance data available on in-line mud oxidizers was assembled. The laboratory investigation indicated that (a) the initial sodium content of the mud, (b) particle size in the slurry, and (c) vacuum level at the filter all probably play a role in determining the extent to which residual soluble sulfide is effectively oxidized at the filter. The field studies tended to support the laboratory findings in that (a) air volume at the filter face, (b) vacuum level, (c) lower drum speeds, (d) sulfide level in the fed mud, and (e) maintenance of an empirical measurement of filterability (CST) of 10 or less all contribute to effective lime mud oxidation.