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

摘要：

可逆气态膜-多效膜蒸馏-精馏耦合工艺可用于脱除料液或废水中的氨氮并得到高纯浓氨水。考察了磷酸二氢铵为可逆吸收剂时气态膜法脱氨效果和多效膜蒸馏-精馏法吸收完成液再生效果。实验结果表明:可逆气态膜总传质系数K和单程氨氮脱除率η分别可达13.9 μm·s^-1和97.5%,废水氨氮值可降至5 mg·L^-1以下;吸收完成液经多效膜蒸馏预浓缩后再经精馏再生可同时得到浓度为5%～18%的氨水。该耦合过程电耗极小的同时蒸汽耗量为28~40 kg·m^-3废水,约为单纯精馏过程的1/5。此外气态膜脱氨和多效膜蒸馏预浓缩过程有效地阻止了废水中挥发性杂质进入浓氨水产品。该过程对气态膜和膜蒸馏用微孔疏水膜组件的稳定性要求苛刻,长期操作试验显示聚四氟乙烯膜能够满足此要求。

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