Evaluation of effect of evaporation on supercritical water gasification of black liquor by energy and exergy analysis. (26th July 2018)

• Record Type: Journal Article
• Authors: Cao, Changqing; He, Youyou; Chen, Jia; Cao, Wen; Jin, Hui
• Is Part Of: International journal of hydrogen energy. Volume 43:Number 30(2018)
• Page Start: 13788
• Page End: 13797
• Publication Date: 2018-07-26
• Subjects: Black liquor -- SCWG -- Evaporation -- Exergy efficiency -- System modelling; Hydrogen as fuel -- Periodicals; Hydrogène (Combustible) -- Périodiques; Hydrogen as fuel; Periodicals; 665.81
• DOI: 10.1016/j.ijhydene.2017.11.158
• Languages: English
• ISSNs: 0360-3199

Abstract

Abstract: Supercritical water gasification (SCWG) is a promising innovative black liquor handling method. The low concentration of black liquor is a burden for the system scale and investment cost. In this study, we introduced black liquor evaporator to increase the concentration using self-generated steam and power, and studied its influence on the energy and exergy efficiency. The results showed that increasing black liquor concentration from 10 wt% to 20 wt% reduced the energy efficiency but increased the exergy efficiency of the system without evaporator. With the evaporator, an optimal target concentration existed for the exergy efficiency owing to the influence of the target concentration on the balance between the energy consumption and saving brought by the evaporator. With black liquor condensed from 15 wt% to 21.82 wt%, maximum exergy efficiency of the system (41.95%) was obtained. For lower-concentration black liquor, more water needs to be evaporated to get the optimal concentration and evaporator was more desired because it brought greater improvement on the exergy efficiency. The increasing effect number of multi-effect evaporator shifted the optimal concentration to higher values, which increased from 19.93 wt% to 23.13 wt% when the effect number increased from 4 to 7. The exergy efficiency of the system was also improved, and the improvement was more significant at higher target concentration. Highlights: An integrated system of SCWG with black liquor evaporator was constructed and modelled. An optimal target concentration existed to get the highest exergy efficiency of the system. The evaporation had more effect on SCWG of black liquor with lower initial concentration. The optimal concentration was higher when using more energy-efficient evaporator.