Removal Of NO_x From Flue Gas With Co²⁺ Complex Absorbent

With the fast develpment of national economy and the increasement of energy consumption, NOx emission has been racing up. At present, the principal processes for NOx control in China are low-NOx combustion technology, selective catalytic reduction(SCR) and selective non-catalytic reduction(SNCR). However, there are still some problems about these technologies. Because of the mild reaction conditions and efficient removal of NO, the metel-complexes process are attracting many researchers’ attention.Three cobalt complexes, Co2+-Cy SH, Co2+-Met, Co2+-MPA, were chosen as absorbents to compare their efficiency to remove NO with simple homemade absorption device. The optimized conditions of Co2+-Cy SH for the treatment of NO: absorbent concentration was 0.03 mol/L, molar ratio was 1:3, temperature was 30 oC,p H=9,NO inlet concentration was 759 mg/m3, NO removal efficiency was 87%. The optimized conditions of Co2+-Met for the treatment of NO: absorbent concentration was 0.05 mol/L, molar ratio was 1:2, temperature was 30 oC,p H=8,NO inlet concentration was 759 mg/m3, NO removal efficiency was 80%. The optimized conditions of Co2+-MPA for the treatment of NO: absorbent concentration was 0.02 mol/L, molar ratio was 1:4, temperature was 30 oC,p H=9, NO inlet concentration was 759 mg/m3, NO removal efficiency was 88%.Under the above optimal absorption conditions, the absorption capacity of Co2+-Cy SH, Co2+-Met and Co2+-MPA for NO removing were 0.83 mmol/L, 0.73 mmol/L and 0.90 mmol/L, respectively.Two kind of cobalt complexes above were used as absorbent to treat NO with hollow fiber memebrane contactor. The optimal membrane absorption parameters of Co2+-MPA: molar ratio of Co2+ and MPA was 1:4, NO inlet concentration was 612.47 mg/m3, flow rates was 0.027 m/s, absorbent concentration was 0.02 mol/L, the flue of absorbent was 2.97×10-6 m3/s, p H=9, temperature was 50 oC, the NO removal efficiency was 99.16% and the total mass transfer coefficient was 2.24×10-5 m/s.The optimal membrane absorption parameters of Co2+-Met: molar ratio of Co2+ and Met was 1:2, NO inlet concentration was 612.47 mg/m3, flow rates was 0.027 m/s, absorbent concentration was 0.05 mol/L, the flue of absorbent was 4.28×10-6 m3/s, p H=8, temperature was 50 oC, the NO removal efficiency was 98.85%and the total mass transfer coefficient was 2.23×10-5 m/s. In addition, the absorption mechanism of the cobalt complexes were investigated.Some reductants, Na2SO3, L-ascorbic acid and activated carbon, were used to regenerate of cobalt complexes(II). The result indicated that the regeneration capacity of these reductants was in the sequence of activated carbon>L-ascorbic acid> Na2SO3. Many methods can be used to enhance the regeneration efficiency of activated carbon, such as the increase of specific surface area, amount, reaction temperature, stirring speed and the decrease of p H. The optimized regeneration conditions of Co2+-MPA: the amount of power activated carbon was 6 g/L, reaction temperature was 80 oC, p H=3, stirring speed was 200 r/min, the regeneration rate was 94.35%; The optimized regeneration conditions of Co2+-Met: the amount of power activated carbon was 8 g/L, reaction temperature was 80 oC, p H=3, stirring speed was 300 r/min, the regeneration rate was 91.11%;...