Hollow fiber gas membrane-based removal and recovery of ammonia from water in three different scales and types of modules

Abstract

Ammonia present in many industrial process streams and effluent streams is beginning to be recovered by means of microporous hydrophobic hollow fiber-based membrane contactor devices with gas-filled pores; the process is often characterized as supported gas membrane (SGM) process. Ammonium sulfate is usually obtained in a sulfuric acid stream on the other side of the membrane. It is useful to develop a quantitative basis for the extent of ammonia removal in such devices. Unlike deoxygenation of aqueous streams in such devices, membrane resistance is quite important for ammonia transport. Ammonia transport modeling in such devices is hampered by the complexity of feed liquid flow in the shell side of commercially used devices and lack of information on membrane resistance where membrane tortuosity introduces considerable uncertainty. The approach adopted here involves studying ammonia transport with the feed solution flowing through the hollow fiber bore where the fluid mechanics is simpler than shell-side flows. Comparison of model-based predictions of overall mass transfer coefficient (ko) with experimentally observed values allows estimation of the membrane mass transfer coefficient (km). One can use such estimates of km to model the observed ammonia transport in small crossflow devices and develop an empirical guidance of the dependences of the shell side mass transfer correlations. Guided by such information and deoxygenation SGM literature, a model was developed for large modules used for ammonia recovery via SGM. Model predictions of performances of the large modules are likely to be useful for various process considerations including the effect of temperature and feed flow rate variations on ammonia removal.