Impact of Deadload Reduction in the Kraft Chemical Recovery System

We developed a steady state Excel®-based model to study the effect of white liquor dead-load reduction on recovery process performance. The process equipment affected includes the evaporators, concentrator, recovery boiler, smelt dissolving tank, green liquor clarifier, dregs filter, slaker, causticizers, white liquor clarifier, lime mud washer, and lime kiln. The model was developed using fundamental engineering principles and a set of assumed process parameters that were in turn based upon literature references and operating experience. The interactive model allows for specific base case parameters and can calculate liquor cycle mass balances. A subsequent change in white liquor composition will result in a new set of balances that can be compared with the base case. A reduction in white liquor deadload will also reduce the inorganic solids content of green liquor and black liquor, along with the water that carries the deadload. The energy performance and production capacity of the process equipment will improve, most notably the evaporators, concentrator, and recovery boiler. Reducing outages due to scaling, corrosion, and plugging will increase recovery boiler productivity. Increased productivity in evaporator performance should also increase because of improved heat transfer due to less scaling and a lower rise in liquor boiling point.