Recovery of sulfur from sulfur-rich filter cakes in a rotary kiln: Process optimization. (1st May 2021)

• Record Type: Journal Article
• Authors: Masotta, Matteo; Rocchi, Irene; Pazzagli, Gabriele; D'Ambrosio, Roberto; Seggiani, Maurizia
• Is Part Of: Waste management. Volume 126(2021)
• Page Start: 567
• Page End: 577
• Publication Date: 2021-05-01
• Subjects: Sulfur waste -- Sulfur recovery -- Rotary kiln -- Refractory -- Filter cakes; Hazardous wastes -- Periodicals; Refuse and refuse disposal -- Periodicals; 363.728
• DOI: 10.1016/j.wasman.2021.04.009
• Languages: English
• ISSNs: 0956-053X

Abstract

Highlights: Sulfur recovery from sulfur-rich filter cakes was conducted in a rotary kiln. Recovery efficiencies of 85–90% were obtained operating at 1100–1200 °C. Operating temperatures above 1200 °C reduce plant operativity. Ca-Fe-Al-silicate slag forms at the kiln walls at temperature above 1200 °C. Fe- and Cr-free refractory materials for the internal lining of the kiln are recommended. Abstract: In this work, sulfur recovery from sulfur-rich wastes deriving from sulfur filtration was investigated through laboratory experiments and full-scale tests in an industrial combustion rotary kiln, where elemental sulfur is converted to SO2 in a sulfuric acid production plant. Phase equilibria experiments carried out in the temperature range 1100–1400 °C and industrial scale tests demonstrated that temperature is the most important operating parameter in determining the recovery efficiency and the plant operability. The full-scale tests performed on the rotary kiln showed that, at operating temperatures around 1200 °C, a continuous sulfur recovery from the filter cakes was obtained with an average efficiency of 87% and a consequent reduction of about 70% of the solid waste material to be disposed as inert in landfills or used in cement/glass industries. The efficiency of sulfur recovery increases with the increasing operating temperature but, above 1300 °C, the melting of the residual Ca-Fe-Al-silicate phase and the eventual recrystallization at the kiln refractory walls occurred, causing a forced plant shutdown. The chemical-physical interaction between the sulfur-rich filter cake and different refractory materials was further investigated in the temperature range 1100–1300 °C. At the recommended operation temperatures of 1100–1200 °C, the interaction between the refractory material and the combustion ashes is negligible for all tested materials. Nonetheless, the use of Fe- and Cr-free refractory materials for the internal lining of the kiln must be preferred to minimize the deposition/adhesion of Ca-Fe-Al-silicates derived from combustion over long-term operation.