System for ammonia removal from anaerobic digestion and associated ammonium sulfate production: Simulation and design considerations

A side-stream ammonia stripping system coupled with a full-scale anaerobic digestion plant is considered. The system is based on an ammonia stripping unit (thin film evaporator, TFE), a Venturi scrubber and a reactive absorption column. A portion of the sludge treated in the digesters is continuously withdrawn and transferred to the TFE, where ammonia is stripped through a biogas stream. The ammonia rich biogas is then treated with a sulfuric acid/water solution in the Venturi scrubber and in the absorption column, with production of an ammonium sulfate solution, which is stored in a tank until utilization as a fertilizer. The aim of this paper is to provide a comprehensive engineering framework supporting the design of a full-scale ammonia stripping system with associated ammonium sulfate production, to be coupled with pre-existing anaerobic digestion plants. On the one hand, an analytical equation is proposed for the simulation of ammonia desorption and the design of the ammonia stripping unit as a function of the selected operating conditions of flowrate, temperature and pH. On the other hand, corrosion issues affecting the storage tank are studied. Corrosion tests, carried out on a selected paint system, demonstrate no development of coating degradation or disbonding, even if local damage occurs in the film. Thus, guidelines to avoid corrosion are given. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.