Phosphorus recovery from sewage sludge ashes with the RecoPhos process | Phosphorrückgewinnung aus Klärschlammaschen mit dem RecoPhos-Prozess
2020
Windisch, Stefan | Ponak, Christoph | Mally, Valentin | Raupenstrauch, Harald
In order to continue utilising sewage sludge in currently applied co-incineration processes (e.g. waste incineration plants, cement works) in the future, a possibility to recover the contained phosphorus must be provided. The so-called InduRed reactor, which was developed at the Chair of Thermal Processing Technology at the Montanuniversitaet Leoben, is the crucial element of the RecoPhos process, aiming at the reduction of phosphorus compounds in sewage sludge ashes. Due to the challenging reaction behaviour of phosphorus in the presence of iron, such a process faces a number of challenges. In the RecoPhos process, a high-quality phosphoric acid, a low-phosphorus metal phase and a residual mineral fraction are produced from sewage sludge ash by means of carbo-thermal reduction in an inductively heated graphite bed with subsequent post-combustion and gas scrubbing. The ambitious goal of the process is the further development and improvement of the phosphorus recovery so that recovery rates over 75% can be achieved, and to moreover produce a valuable mineral fraction. The latter should be done by choosing suitable additives and rapidly cooling the residual slag after the reduction (e.g. by dry slag granulation). First experimental trials in the RecoPhos plant at the Chair of Thermal Processing Technology at the Montanuniversität Leoben have already been successful. For example, it was possible to reduce the residual phosphorus content in the slag to virtually zero and to limit the accumulation of phosphorus in the metal phase.
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