Construction and simulation comparison of sectional combined evaporation system for sodium nitrate wastewater

Sodium nitrate wastewater is a high boiling point rise solution. This study compared and calculated the boiling point rise of sodium nitrate wastewater using three methods, including empirical chart-Gisinko formula, simulation, and Durin’s straight line rule. Combined with the ability of steam compressors to enhance the temperature of secondary steam, the sectional combined evaporation processes, namely “MVR+single-effect” and “MVR+double-effect”, were proposed. Using Aspen Plus software to simulate the process of “MVR+double-effect” system, the effect of feed temperature on the amount of steam replenished in the MVR system was quantitatively analyzed. The effects of MVR discharge concentration and compression ratio on the effective heat transfer temperature difference, heat transfer area, and compressor energy consumption of the evaporator were investigated. Economic analysis was conducted on traditional three effect evaporation, “MVR+single-effect” and “MVR+double-effect”. The results showed that the heating steam volume and supplementary steam volume of the MVR evaporator decreased linearly with the increase of feed temperature. When the feed temperature was greater than 81.5 ℃, the spray water volume of the compressor could provide the required supplementary steam volume for the MVR system. The optimal working condition for the MVR evaporation section was a compressor compression ratio of 1.9 and MVR discharge concentration of 45%. The “MVR+double-ffect” system had the lowest annual operating cost and annual total cost.