Anti-Corrosion Treatment and Performance of Air Gap Membrane Distillation Condensing Tubes AITranslate

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Basic Information:

DOI：10.13373/j.cnki.cjrm.XY20060038

Chinese Library Classification Number:X758

Citation Information:

In the production process of the smelting industry，flue gas scrubbing generated a large amount of waste acid. Direct discharge of such waste acid not only caused severe environmental pollution but also wasted the recyclable resources contained therein. Therefore，achieving concentration and volume reduction of waste acid as well as resource recovery had become one of the key issues in environmental governance and resource recycling in the smelting industry. Among numerous treatment technologies，membrane distillation technology was regarded by many literature studies as an effective means to realize concentration and volume reduction of waste acid from smelting flue gas scrubbing，thanks to its advantages such as mild operating conditions，high separation efficiency，and strong adaptability to pollutants. As an important application form of membrane distillation technology，the air gap membrane distillation system had been used in continuous concentration treatment of contaminated acid waste liquid in literature studies. However，it had been found that the use of stainless steel condensation walls led to severe corrosion. Corrosion not only caused damage to the material of the condensation wall and a significant reduction in its service life，but also made corrosion products mix into the treatment system，affecting the waste acid concentration effect and the purity of subsequent resource recovery. Furthermore，it undermined the continuity and stability of the membrane distillation process，greatly restricting the industrial application of air gap membrane distillation technology in the field of waste acid treatment. To address this problem，this paper applied an organic anti-corrosion material to the surface of the stainless steel condensation wall and conducted a systematic study on its corrosion resistance and membrane distillation application characteristics. In the corrosion resistance test，the stainless steel samples coated with the organic anti-corrosion coating and the uncoated stainless steel samples were immersed together in the waste acid from smelting flue gas scrubbing for an immersion duration of 140 hours. The experimental results showed that the surface of the uncoated stainless steel samples had suffered severe corrosion，with a large amount of loose corrosion products formed. These corrosion products easily fell off under slight external force，and the exposed substrate surface was covered with obvious corrosion pits，resulting in significant damage to the material structure. In contrast，the surface of the stainless steel samples coated with the organic anti-corrosion coating remained intact，with no obvious corrosion traces observed. The coating was tightly attached to the substrate surface，effectively isolating the direct contact between the waste acid and the stainless steel substrate，thus demonstrating excellent corrosion protection effects. In the study on membrane distillation application characteristics，a condensation tube with a diameter of 18 mm was used to construct an air gap membrane distillation system for concentrating the waste acid from smelting flue gas scrubbing，with a focus on investigating the impact of the organic anti-corrosion coating on the membrane flux of the system. When the inlet water temperature on the hot side was controlled at 60 ℃，comparative experimental data showed that compared with the uncoated condensation wall，the membrane flux of the membrane distillation system corresponding to the condensation wall coated with the organic anti-corrosion coating on its surface increased by 23.33%，significantly improving the mass transfer efficiency of the system；To explore the internal reason for the increase in membrane flux，an in-depth analysis was further conducted on the condensation mechanism on the surface of the condensation wall. The results indicated that the organic anti-corrosion coating possesses good chemical stability and surface modification function. The contact angle on the surface of the coated condensation tube increased to 58.98°. This change in surface characteristics was conducive to the transition of the condensation process from film condensation to dropwise condensation. Under the dropwise condensation state，the condensate was not easy to form a continuous liquid film on the wall surface，which reduced the thermal resistance during heat transfer，thereby significantly enhancing the heat transfer efficiency of the system. The improvement in heat transfer efficiency further accelerated the condensation rate of water vapor on the surface of the condensation wall，providing more favorable conditions for mass transfer in the membrane distillation process，and ultimately achieving an increase in the membrane flux of the system.