Pulp and Paper Research Institute of Canada

Denys F LeClerc

Robert M Hogikyan

A rapid method is provided for the on-line determination of sodium sulfide concentration and/or percent sulfidity in green liquors or smelt solutions used for the production of either kraft or sulfite pulp. The method eliminates manual sampling, and the need for frequent equipment maintenance. The method includes the steps of withdrawing samples of a smelt solution or green liquor from the kraft or sulfite manufacturing process, subjecting the samples to near-infrared spectrophotometry over a predetermined range of wave numbers so as to produce absorbance measurements relative to a reference spectrum of either water or a caustic soda-sodium carbonate solution, determining the absorbance shown by different combinations of sodium sulfide, sodium hydroxide, sodium carbonate and sodium chloride concentrations, correlating by multivariate calibration the relationships between the absorbance measurements of unknown samples and the absorbance shown by different combinations of sodium sulfide, sodium hydroxide, sodium carbonate and sodium chloride so that the amount of sodium sulfide and/or the percent sulfidity can be accurately determined for any levels of TTA or chloride present in the liquor.

Determination of sodium sulfide and sulfidity in green liquors and smelt

A direct monitoring and control method is provided for on-line measurement of effective alkali, carbonate, sulfate and thiosulfate concentrations in process liquors for the production of kraft pulp. The control method eliminates frequent sampling, and the need for frequent equipment maintenance. The method includes the steps of withdrawing samples of a liquor from the kraft manufacturing process, subjecting the samples to infrared spectrophotometry at predetermined wave numbers to produce peak-absorbance measurements relative to a background spectrum of water, determining peak absorbance for different alkali concentrations, correlating relationships between the peak-absorbance measurements of samples with the peak absorbance for different alkali concentrations to determine optimum effective alkali in the samples, and controlling at least one process parameter to obtain effective alkali of the liquor.

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Surrey, Canada

Denys F LeClerc