Energetic-environmental-economic assessment of utilizing weak black liquor to produce syngas for replacing evaporation based on coal water slurry gasification

Abstract

As the main pollutant of paper mills, black liquor has brought great pressure to the wastewater treatment process of paper mills. Based on the coal-water slurry gasification (GS-CWS) technology, this paper designed the gasification system of black liquid coal-water slurry (GS-BLCWS) by utilizing weak black liquor of pulp mills, investigated and modeled the energy requirements of the GS-BLCWS. Feasibility assessment of the GS-BLCWS and the traditional alkali recovery systems (TARS) were carried out, including energy efficiency, economic feasibility and environmental impacts. The comparison results showed that the steam demands of two technologies can be self-sufficient. But the total energy efficiency of GS-BLCWS (69.78%) is higher than that of the TARS integrating GS-CWS (63.07%), and the energy output ratio of black liquor increased from 9.9% to 69.78%. From an economic point of view, GS-BLCWS can generate syngas, which can be used for drying in the papermaking workshop and shows better economic efficiency. Meanwhile, GS-BLCWS has lower environmental impacts that there is no emission of sulfur oxides and particulate matter. Considering the short payback period (5.81 years) of GS-BLCWS, the small environmental impact, and the self-sufficiency of steam and electricity, it has broad application prospects.