Optimizing the Other Half of the Log (Using on line measurement to understand the properties of black liquor)

摘要

Wood is usually the largest cost of any pulp mill. A great deal of effort has been put into the optimization and improvement of the properties of pulp which is the principal product of the log that enters a pulp mill. However, depending on wood species, approximately one half of the log goes to the recovery boiler. In comparison to pulp very little research has gone into the understanding of black liquor properties. The majority of mills operate with an uncertain picture of the black liquor that they burn in their boilers. The lignin content, the inorganic content, the REA (residual effective alkali) and the viscosity of the liquor are not tested for on a regular basis and for the most part are not considered by operators as '"needed" information to burn the liquor in their boilers. Yet operators routinely face operational problems that they do not fully understand. Usually their response to problems of this type is "the liquor has changed". This presentation will use on line information from the FT-NIR and from viscometers to help explain operational changes that occur in the boiler and the evaporators. Liquor spray, boiler and evaporator fouling, quantity of smelt, and the impact of dead load including chlorides will be looked at using liquor parameters that are not traditionally measured on an ongoing basis. The potential use of these new measurements for the new lignin precipitation technologies will also be examined. As Lord Kelvin once stated "If you cannot measure it you cannot improve it". If we wish to improve on the economics associated with the half of the log that goes to the recovery boiler we need to measure and eventually control the properties of black liquor.