Recovery of high-purity NO2 and SO2 products from iron-ore sintering flue gas by distillation: process design, optimization and analysis

Abstract High-purity NO2 and SO2 have significant economic values and are widely used in many fields. The large amounts of NO2 and SO2 in industrial flue gases are worthy of recovery for environmental protection and economic benefits. In this work, a dual-column distillation separation process was proposed to further separate and upgrade NO2 and SO2 following a flue gas adsorption capture process. The feasibility of distillation separation of NO2/SO2 from the desorbed gas, and the advantage of liquid-phase feeding way over gas-phase counterpart in terms of lower energy consumption (1286.39 kW) were demonstrated. Key process parameters such as the number of total stages, the feed stage number, the mole flow rate at bottom of column, the reflux ratio and operating pressure for the two columns (15, 6, 16.66 kmol/h, 0.16, 4 bar; 21, 10, 4.43 kmol/h, 0.50, 1 bar) were determined. Heat and mass transfers along the column height as well as the process robustness against feed composition fluctuation indicate its applicability for practical operation and adaptation to industrial needs. An economic analysis shows a significant annual revenue of 14,333.52 thousand USD based on high-purity (>99.5%) SO2 and NO2 products recovered from a typical scale (~1000,000 m3/h) of iron-ore sintering flue gas, not only offsetting the total operating cost of the entire adsorption capture-distillation recovery process but also generating net profit.