Integrating black liquor gasification with pulping - Process simulation, economics and potential benefits

LINDSTRÖM, ERIK VILHELM MATHIAS. Integrating Black Liquor Gasification with Pulping – Process Simulation, Economics and Potential Benefits. (Under the direction of Dr. Hasan Jameel and Dr. Adrianna G. Kirkman.) Gasification of black liquor could drastically increase the flexibility and improve the profit potential of a mature industry. The continuous efforts made in the area of black liquor gasification (BLG) are bringing this technology closer to commercial realization and potential wide-spread implementation. Research exploring the integration of BLG into the kraft process and the potential of BLG enabled modified pulping technologies on modern pulping operations is important to support this effort. The following effort is focused on such research, utilizing laboratory pulping experiments and process simulation. The separation of sodium and sulfur achieved through gasification of recovered black liquor can be utilized in processes like modified continuous cooking, split sulfidity and green liquor pretreatment pulping, and polysulfide-anthraquinone pulping to improve pulp yield and properties. Laboratory pulping protocols have been developed for these modified pulping technologies and different process options evaluated. The process simulation work around BLG has led to the development of a WinGEMS module for the low temperature MTCI steam reforming process, and case studies comparing a simulated conventional kraft process to different process options built around the implementation of a BLG unit operation into the kraft recovery cycle. The implementation of gasification, functioning as the core of wood pulping recovery operations in a biorefinery, would enable the application of modified pulping technologies while creating a synthetic product gas that could be utilized in the production of value added products in addition to wood pulp. The evaluated modified pulping technologies have indicated the potential of yield increases of 1-3% points with improved product quality, and the potential for capital and operating cost savings relative to the conventional kraft process. Process simulation work has shown that the net variable operating cost for a pulping process using BLGCC is highly dependent on the cost of lime kiln fuel and the selling price of green power to the grid. Under the initial assumptions taken in the performed case study, the BLGCC process combined with split sulfidity or PSAQ pulping operations had net variable operating cost 2-4% greater than the kraft reference. When comparing the BLG cases to the MCC reference, the net variable operating cost break even point based on lime kiln fuel cost is about $47/barrel for the split sulfidity and lower charge polysulfide processes, and about $38/barrel for the higher polysulfide charge process. This is significantly lower than assumed kiln fuel price of $60/barrel used in this work. If the sales price for power to the grid could be increased through green power credits from 3.5 to 6 ¢/KWh cost savings of about $40/ODtP could be realized in the investigated BLG processes. Other alternatives to improve the process economics around BLG would be to modify or eliminate the lime kiln unit operations, utilizing high sulfidity green liquor pretreatment, PSAQ with auto-causticization, or converting the process to mini-sulfide sulfite-AQ. INTEGRATING BLACK LIQUOR GASIFICATION WITH PULPING – PROCESS SIMULATION, ECONOMICS AND POTENTIAL BENEFITS by ERIK VILHELM MATHIAS LINDSTRÖM A dissertation submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the Degree of Doctor of Philosophy WOOD AND PAPER SCIENCE Raleigh, North Carolina 2007