Evaluation and techno-economic analysis of packed bed scrubber for ammonia recovery from drying fumes produced during the thermal drying of sewage sludge

This study investigates the recovery of ammonia from drying fumes during thermal drying of sewage sludge with packed bed acid scrubbers to recover ammonia and to produce ammonium sulfate. The process is modelled for two concentrations, 75 and 100 ppm, and 1000m3/h inlet flowrate of drying fumes containing air and ammonia gas. It results in finding optimal parameters for scale-up of drying fumes during thermal drying of 7700t/a sewage sludge of Lappeenranta city. It is found that a single scrubber, with a 24000 m3/h of inlet gas and an ammonia concentration of 75 ppm, liquid to gas ratio of 1.5, temperature and pH of liquid acid as 100°C and 3 respectively, gives the efficiency of more than 99%, and reduces ammonia concentration in the outlet stream to 0.2 ppm. The capital cost is 290 k€, operating cost is 113k€/a, removal cost with and without revenue of ammonium sulfate is 20 €/t and 18 €/t of sludge. The packed bed acid scrubber would be suitable to remove ammonia in the drying fumes to recover ammonia from the drying fumes, but the initial economic analysis highlights that the production of commercial grade ammonium sulfate fertilizer would be an expensive option.