Within the past two years the Berlin Centre of Competence for Water (KWB) operated a vacuum degasification pilot plant. This technology degasifies ammonia from agricultural digestate and recovers ammonia as mineral nitrogen fertiliser. During the past year we tested different fillings in the columns, stripping and scrubbing strategies. Besides operational difficulties with column flooding our results indicated different potentials to reduce the consumables of the process. Thereby associated environmental impacts as the carbon footprint and the economic costs of the process can be reduced.
Due to our knowledge gained in the Circular Agronomics project, we optimised the design of the process and reconstructed our pilot unit (see GIF). We ended up with a larger cross-sectional area of the column to avoid column flooding and problems with foaming. Preceding CO2 stripping prior NH3 stripping will reduce the caustic soda consumption by around 90 %. Preceding heat recovery from forming steam will reduce the heat consumption of the process by also around 90 %. These are essential steps to make the process environmentally and economically viable.
In the meantime, we will recommission stripping and scrubbing unit to test our optimised design. We will furthermore investigate potential optimisations of the scrubbing unit e.g. using cheap by-product gypsum instead of “expensive” sulfuric acid. Thereby we will recover the stripped NH3 as ammonium sulfate and utilise the stripped non-fossil CO2 with the calcium from gypsum to recover non-fossil limestone (calcium carbonate) instead of releasing CO2 to the atmosphere.