Evaluation of Various Alternatives to Reduce TRS Emissions of the Lime KILN, 1998 International Chemical Recovery Conference Proceedings

During the last decade, substantial advances have been made in TRS (Total Reduced Sulfur) emission control technology. Due to the elimination of earlier major emission sources, those previously considered to be minor sources (e.g. lime kiln) account today for a relatively greater part of the overall TRS emission and furthermore, also significant portion of the foul odor in the area surrounding the mill. In this paper, formation mechanisms of the hydrogen sulfide (H2 S), which is a major TRS compound, in the lime kiln and the main principles for reducing H2 S emission from the lime kiln are presented. In addition, results from a 12 months field survey made at a modem Finnish pulp mill are presented. In this field survey, lime mud filtering and lime kiln operation were studied with the aim of finding out the influence of operational parameters on the TRS emission. During the field survey, process data both at the ten minute and the one hour average level were gathered by using plant automation and information systems. The large amount of the data collected was preprocessed and the influence of operational parameters on the lime kiln TRS emission were examined, based on statistical analysis of the data sets formed. Furthermore, this paper describes a neural network model developed for predicting TRS emission.

According to the field survey results, the H2 S emission of the lime kiln is directly related to the function of the lime mud washing and filtration operation (i.e. lime mud dry solids content). Furthermore, proper lime kiln burning conditions (i.e. excess oxygen content) are required to maintain an acceptable H2 S emission level.