Economics of Integrating Black Liquor Gasification with Pulping: Part I Effect of Sulfur Profiling, 2002 Fall Technical Conference

Using black liquor gasification (BLG) the recovered sodium and sulfur can be split into two separate fractions with varying degrees of separation dependent on the operating conditions and the technology used. This separation creates some opportunities in the pulping process, due to its potential to increase the yield or to extend delignification. There may be an increase in the causticizing load. Of the various pulping options with black liquor gasification, sulfur profiling would be the lowest capital cost process to implement especially for mills with a modified continuous or batch process. In this paper, the process changes that are necessary to implement sulfur profiling are examined along with the economics. The results show that BLG increases the pulp production cost from $140.23/ODtP to $143.31/ODtP at H₂S/CO₂ co-absorption ratio of 10:1. Most of the cost increase is due to the increase in the lime kiln fuel and the lime makeup. An increase in yield of 1% changes the pulp production cost from $140.23/ODtP to $140.45/ODtP for the Tomlinson vs. BLG with split sulfidity pulping. If the yield increase is 2%, the cost decreases to $138.91. It may also possible to use the NaHS and Na<>CO₃ stream in the impregnation phase without affecting the overall alkali usage, since sulfur absorption is more effective at the lower pH. At the same EA charge of 19%, the cost increased from $140.23/ODtP for the Tomlinson case versus $141.15/OdtP for the BLG case with Na₂CO₃ pretreatment. But at the same TTA usage the %EA is 15% and the cost is decreased to $136.09/ODtP.