VASA PROTOTYPE DEVELOPMENT

Post bench-scale models, the earliest pilot-scale ammonia recovery VaSA system was operated in a batch mode with anaerobic digestate at the optimum boiling point temperature and vacuum combination. It had a vacuum stripper connected by a vacuum pump to a gas absorption column. The stripper consisted of a reboiler and a demister, employing single-stage stripping. The kettle reboiler was built with a 40-L stainless-steel vacuum vessel and electric immersion heaters. Feed temperature was regulated and recorded by a temperature controller via a J-type thermocouple. A vacuum regulator was installed between the stripper and absorption column to control vacuum in the stripper and mixing intensity in the absorption column. A glass conical flask was used to trap water vapor and prevent dilution of the sulfuric acid solution. The demister was a stainless-steel pipe packed with poly-propylene mesh. The absorption column was built with a cylindrical PVC pipe and a drain valve. 

This upgraded version of VaSA system mainly composed of a vacuum stripper and a gas absorption column, which were connected through a demister and driven by a vacuum pump. All the vessels and fittings were stainless-steel triclamp sanitary products. The vacuum stripper was custom fabricated by a US Equipment Manufacturer. It had two flat-bottom tanks mounted vertically inside a 473-L vessel. Each tank had outer diameter of 743 mm and the bottom head with inner diameter of 762 mm of the large vacuum vessel with screw plug immersion heaters and thermocouple for temperature regulation and power control. The demister was built with concentric reducers and spools having diameters from 203 mm to 38 mm in a total length of 1.1 m and loosely packed with stainless-steel scrubbing pads. The demister was designed to separate water vapor from NH3 gas by surface air cooling and reflux water droplets and condensate, targeting a temperature drop from the stripper’s head to the demister top since ammonia solubility in water is nearly zero at temperatures 9 ◦C below the vacuum boiling point. Water reflux relies on gravity settling of water droplets against upward vapor flow. Demister height determines vapor residence time for condensation. Water reflux rate, hence, varies with its diameter and height. The demister was installed with gasket screens and stainless-steel scrubbers to improve water reflux and minimize water vapor flux. The demister was assembled with concentric reducers to match the gradual decrease in vapor flux and temperature. The gas absorption column was built on a cylindrical sanitary spool with ball valves and secondary chambers to add sulfuric acid and discharge absorption solutions. A water/air-cooled water trap was installed before the vacuum pump to further capture the escaped water vapor by condensation.

Information coming soon!!!