Analysis and optimization of ammonia stripping using multi-fluid model

摘要

Ammonia recovery from anaerobic digestion (AD) is a notably beneficial process for removingnexcess nitrogen, producing low cost fertilizer and enhancing odor abatement. A process wasndeveloped for nutrients recovery by integrating a simple and effective stripping process with ADnsystem. To design, optimize and scale up this system, multi-fluid model was developed tonsimulate flow, mass transfer and reactions in the ammonia stripping tower. The mass and heatntransfer and dissociation reactions were introduced into the CFD framework. The air/liquid rationin each cell of the domain was considered in heterogeneous mass transfer rate. Good agreementnbetween CFD modeling and experiments employing a packed bed was obtained on the effect ofnpH and temperature upon ammonia removal. It was found that the liquid to gas mass transfernrate became slower at the lower part of the packed bed with high air/liquid ratio and short liquidnresident time, decreasing ammonia removal efficiency. The predicted contours at the lower partnalso showed decreases in liquid volume fraction and liquid temperature. These results suggestna great potential compensation to use the multi-section feed-in and recirculation for improvingnreactor performance.