Abstract:

Flue gas from coal-fired power plants contains profuse water vapor. The direct emission of wet flue gas may lead to visual pollution and a series of environmental problems. Herein, we report the use of hydrophobic Al₂O₃ ceramic membrane modified by n-octyltriethoxysilane to construct air-cooling condenser for flue gas dehumidification and water recovery. Compared with conventional impermeable hydrophobic steel tube, porous hydrophobic ceramic membrane can condense vapor more efficiently. With the same water contact angle of 120°, the flue gas temperature drop of the ceramic membrane is 1.3—2.5 times higher than that of the 304 steel tube. The parametric study of the hydrophobic ceramic membrane has been done. The water flux improves with the increase of flue gas flowrate, flue gas temperature and sweeping factor, but decreases with the increase of transmembrane pressure difference and sweeping gas temperature. The water recovery efficiency decreases with the increase of flue gas flowrate, transmembrane pressure difference and sweeping gas temperature, and improves with the increase of sweeping factor. The water recovery efficiency increases first, then tends to be stable, and lastly decreases with the increase of flue gas temperature. Under experimental conditions, the water flux of 0.6—5.2 kg·m^-2·h^-1 and water recovery of 7.6%—57.4% are achieved. At low cooling medium flowrate, the condensation performance of hydrophilic ceramic membrane using water cooling is better. With the increase of cooling medium flowrate, the condensation performance of the air-cooling hydrophobic ceramic membrane rapidly improves and is gradually close to the performance of the water-cooling hydrophilic ceramic membrane. Air cooling enhanced by hydrophobic ceramic membranes is promising to replace water cooling to reduce water consumption. Hydrophobic ceramic membrane condensers can efficiently recover water from flue gas to alleviate water-energy-environment collisions in industrial processes.

Key words: porous ceramic membranes, dehumidification, water recovery, hydrophobic modification, flue gas, condensation, heat transfer

摘要：

以环境空气为冷源，采用硅烷接枝的疏水Al₂O₃陶瓷膜构建膜冷凝器开展烟气脱湿实验。对比了疏水陶瓷膜与传统疏水钢管的冷凝性能；系统考察了烟气流量、烟气温度、吹扫因子、吹扫气温度、跨膜压差等过程参数对疏水陶瓷膜水回收性能的影响；比较了疏水陶瓷膜冷凝器(空冷)与亲水陶瓷膜冷凝器(水冷)的冷凝性能。结果表明，相同水接触角下(120°)，多孔陶瓷膜的烟气温降是致密304钢管的1.3~2.5倍，疏水陶瓷膜能有效强化冷凝传热。疏水陶瓷膜的过程水通量随烟气流量、烟气温度、吹扫因子的增加而上升，随跨膜压差、吹扫气温度的增加而降低。过程水回收率随烟气流量、跨膜压差、吹扫气温度的增加而降低，随吹扫因子的增加而增加，随烟气温度的增加先上升，然后趋于稳定，而后下降。实验工况下，疏水陶瓷膜实现了0.6~5.2 kg·m^-2·h^-1的水通量和7.6%~57.4%的水回收率。低冷却介质流量下，基于水冷的亲水陶瓷膜的烟气冷凝性能更优异；随着冷却介质流量的上升，疏水陶瓷膜的冷凝性能迅速提升，并达到亲水陶瓷膜的性能。疏水陶瓷膜冷凝器在气体脱湿和水分回收领域有广阔的应用前景，将为改善工业过程的“能源-水资源-环境”关系助力。

关键词: 多孔陶瓷膜, 脱湿, 水分回收, 疏水改性, 烟道气, 凝结, 传热