The chemical versus energy cost tug of war: A pulp mill perspective

As the cost of energy and processing chemicals changes, the optimal, lowest cost operating conditions within a pulp mill also change. Additionally, the optimal cost operating point within one area of the mill may not result in a total mill low cost operation. Three practical pulp mill examples have been analyzed under varying cost constraints for energy and chemicals to determine the impact of energy and chemical cost changes on the low cost operating point. These examples include changing the digester kappa number target, changing the brownstock washing dilution factor, and the conversion of a continuous digester from one type of cooking process to a lower energy cooking process. Selected mill operating results and laboratory data were employed to tune various process simulation models to obtain cost predictions over a wide range of operating conditions.