THE EFFECT OF INTEGRATING POLYSULFIDE PULPING AND BLACK LIQUOR GASIFICATION ON PULP YIELD AND DELIGNIFICATION

摘要

Kraft recovery based around black liquor gasification would present several opportunities and benefits with regard to process operation and economics. Gasification of black liquor would split sodium and sulfur into two separate fractions. The separation of these chemicals would enable the application of modified pulping technologies to increase the pulp yield or extend delignification. The experimental objective of this work was to explore and compare MCC and polysulfide-anthraquinone cooks with different alkali profiles, to illustrate the potential effects of polysulfide and anthraquinone addition on delignification and total pulp yield. Laboratory pulps were prepared using 20.5% active alkali at sulfidity levels of 25 and 40%. When comparing the polysulfide-anthraquinone cooks to cooks using MCC with anthraquinone, yield benefits in the range of 1-2% were obtained at 25% sulfidity using a polysulfide charge of 2% on OD wood and 3-3.5% at 40% sulfidity using a 3% polysulfide charge on OD wood. By controlling active alkali profiles under the fixed pulping protocol used throughout the project, it was possible to achieve comparable or improved delignification rates using polysulfide, while maintaining higher pulp yield. Generated residual effective alkali profiles illustrate the difference between MCC and polysulfide pulping, and indicate the importance of alkali control and its effects on delignification and pulp yield. A greater benefit from PSAQ pulping can be realized at higher levels of sulfidity, where it is possible to charge a higher concentration of PS and the effects of alkali profiling can be used to optimize both delignification rate and resulting pulp yield. The most advantageous results, as compared to the MCC reference, were obtained using the PSAQ procedure at 40% sulfidity with 3% PS on wood and an alkali profile of (45/31/24). These values represent the percentages of the total available alkali charged to (stage 1/ stage 2 / stage 3) in the cook.