关键词: 可逆气态膜, 多效膜蒸馏, 氨, 蒸馏, 膜, 吸收, 再生, 节能

Abstract:

The integrated process of reversible gas membrane process (RGM)-multiple effect membrane distillation (MEMD)-distillation can be used to remove ammonia from aqueous solution and to get highly purified and concentrated aqueous ammonia as by-product. The performance of ammonium dihydrogen phosphate as reversible absorbent in the RGM process and the performance of regeneration process of the used absorption solution by using MEMD- distillation were studied. The experimental results showed that the mass transfer coefficient and ammonia removal rate of RGM process could be up to 13.9 μm·s^-1 and 97.5% respectively when polytetrafluoroethylene (PTFE) hollow fiber membrane contactor was used, ammonia content in the aqueous feed could be reduced to < 5 mg·L^-1. By using MEMD-distillation coupled system, the used absorption solution could be regenerated and a concentrated aqueous ammonia solution of 5%-18% was produced as by-product. The integrated process has extremely low energy consumption. While the power consumption is very low, the thermal consumption is steam of 28-40 kg·m^-3 aqueous solution, which is less than 1/5 of the traditional distillation (steam stripping) process. Furthermore, this integrated process effectively avoids the pollution from the volatile components from the aqueous feed. The process has harsh requirement in the stability of microporous hydrophobic membrane modules used in the RGM and MEMD process, and the long-term operation stability test demonstrates that microporous hydrophobic PTFE membrane could satisfy this requirement.

Key words: reversible gas membrane, multiple effect membrane distillation, ammonia, distillation, membrane, absorption, regeneration, energy saving