Air stripping of ammonia and methanol in a bubble-cap column

Abstract

A twenty-tray single bubble-cap column was used to air strip ammonia and methanol from a synthetic, as well as a plant wastewater stream. When feeding synthetic solutions containing ∼ 700 mg/kg ammonia, stripping efficiencies of more than 98% were achieved at gas to liquid mass ratios (G/L) ratios of 2.5-2.7. This produced stripper bottom solutions contains ∼10 mg/kg ammonia. Reducing the airflow by 25% increased the ammonia content in the stripper bottoms to ∼30 mg/kg. Using the graphical McCabe-Theile method, the overall column efficiency for the bubble cap column during ammonia stripping was between 9 and 26% because of the low contact efficiency of this column. When treating the "as received" plant wastewater, the ammonia removal efficiency was only 84% at the lower G/L ratio. This increased to 99% by raising the pH from 9.8 to 11.5 and increasing the G/L mass ratio. The ammonia volumetric mass transfer coefficient (KLa) for these tests was calculated to be between 0.38 and 0.58 h-1. Both stripping and absorption of methanol occurred in the column during stripping of ammonia. Based upon solution analyses, the methanol removal efficiency varied between 55 and 95%. ©2007 American Institute of Chemical Engineers.