SPOUTED BED DRYING OF SLUDGE FROM METALS FINISHING INDUSTRIES WASTEWATER TREATMENT PLANTS

A 0.15 m diameter half cylindrical spouted bed was used to dry a ferric hydroxide - zinc hydroxide sludge with a moisture content of 83.4 % wet basis. Heat for drying was provided by an electrical air preheater. The sludge was fed through an air cooled feeder into the spout and dried product was removed by elutriation; it was captured by a cyclone and baghouse. The mechanisms of drying and the performance of the drier were studied as a function of the operating variables. A glass front panel was used for visual observation of the system to elucidate the drying mechanisms, a stainless steel panel was used at other times.

The study showed that a spouted bed drier could produce a consistent fine powder product with a mechanically simple and reliable design. A cost comparison of a spouted bed with other driers for a typical metals finishing installation shows that the spouted bed is cost competitive with conventional technology.