Online Recovery Boiler Reduction Degree Data Review

摘要

Reduction degree is an important metric for recovery boiler performance. Reduction degree is a measure of how well sodium sulfate is converted to sodium sulfide in the recovery boiler. Stable and consistent sodium sulfide concentration is critical in the Kraft pulping process for protecting fiber properties in the digester and has implications in how well the causticizing and lime kiln areas perform. If the recovery boiler is not creating the proper reducing environment to optimize the conversion to sodium sulfide, both pulp quality and the liquor cycle can suffer and expensive sulfur make up chemicals may need to be added to maintain the proper sodium to sulfur ratio in the liquor cycle. As important as knowing what the reduction degree is in the recovery boiler, the Mill testing frequency for it varies dramatically in the industry. Mills typically test reduction anywhere from once per day to once per month and some do not test it all. Some of the reasons for this variation in testing frequency may be related to personnel safety if the Mill is collecting a smelt sample for reduction analysis, for other Mills depending on what laboratory procedure is used to analyze reduction, find the test time consuming and the results inaccurate. The bottom line is reduction degree measurements have not been available with a frequency and a high degree of accuracy to have value to the recovery boiler manager and operator...until now. This paper will review recovery boiler operational data collected from two Scandinavian mills utilizing an online chemical titrator performing standard ABC testing on dissolving tank green liquor samples followed by an optical measurement for sodium sulfate following the addition of excess barium chloride. The titrator is connected to the Mills DCS system so the analysis results are available to the operator as rate changes, air distribution adjustments and process upsets happen and provides valuable information on the reducing environment in the boiler. Because the online titrator is collecting and preparing the samples automatically in the field, personnel safety is improved. Also, the frequency with which the reduction analysis is performed adds value to the operation. Since the standard ABC test must be performed to know the sodium sulfide component in reduction, dissolving tank TTA measurements are also available and can be utilized in lieu of operator or laboratory run tests for managing dissolver density. Now that accurate and frequent reduction degree and TTA measurements are available automatically and online, the recovery boiler operator now has the tools to manage the boiler consistently in all operating conditions.