Boiler feed water deoxygenation using hollow fiber membrane contactor

A pilot plant scale hollow fiber membrane system was developed for the removal of dissolved oxygen from boiler feed water via vacuum degassing process. Feed water was introduced to the shell side; a vacuum was applied to the lumen side of the hollow fiber. The effects of water flow rate, vacuum level, and water temperature on removal efficiency of dissolved oxygen and mass transfer coefficient were investigated. The membrane fouling issue was further addressed on the membrane used on the full-scale system. The foulants were identified by SEM, ATR/FTIR, EDX and water analysis to be the organic matter with the combination of aluminum silicate. Mass transfer resistances of the fouled membrane were also theoretically calculated. Finally, two membrane cleaning methods were investigated and the air backwash method was found to be effective to clean the fouled membrane and was recommended as the regular cleaning method.

A pilot plant scale hollow fiber membrane deoxygenation system was developed and found to be efficient in removing the dissolved oxygen from boiler feed water at the appropriate operating conditions. The shell-side liquid phase mass transfer coefficients of the oxygen in the hollow fiber membrane module used was found to vary with 0.71 power of the liquid flow rate. This indicates that the membrane module used in this study was a highly efficient mass transfer device. The oxygen removal efficiency and mass transport coefficient decreased dramatically after long time ran using surface water as source boiler feed water. Water sample characteristics, combining with SEM, ATR/FTIR and EDX analysis indicated that the membrane fouling was accounted for the oxygen removal efficiency decrease. The organic matter and aluminum silicate in the feed water together caused the membrane fouling problem.