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From a biosolids management perspective, heat drying has gained acceptance as a means of producing a marketable granular product from wastewater residuals called sludge. The heat dried granular product meets Class A requirements under EPA 503 regulations as well as displaying good material handling characteristics, which permit extended storage and transportation prior to marketing. Numerous large waste water treatment plants (WWTP) in USA, Asia and Europe, over the last ten years, have implemented Andritz Drum Drying (DDS) and Fluid Bed (FDS) technologies to convert their sludge to a granular product. Many small and mid-size WWTP plants, due to growing restrictions in their disposal of sludge as Class B product, are choosing heat drying technology for achieving Class A status. This paper discusses Andritz' newly introduced convective low temperature drying technology that dries different sludge types on a belt conveyor via hot air. The belt dryer was developed with an aim of offering a simple and safe solution for these small and mid-size WWTP plants. Three different operating modes are offered in supplying the heat to the process air. A novel feature of the new technology is that it can use a variety of “free” selectable heat energy sources such as waste steam or waste heat from engine exhaust gases. In this case, heat from these sources is transferred indirectly to process air via heat exchangers. More importantly, the belt dryer, similar to DDS and FDS dryers, produces a granular product with a relatively small fraction of fines and is arguably comparable in safety to the DDS and FDS drying systems. A case study of this technology is the new regional drying facility in Frohnleiten, Austria, which is located on a landfill site and utilizes waste heat energy from gas engines for drying. The features of this dryer facility, its performance, and the project economics are summarized. A brief discussion on the application of this drying technology to U.S.A. market conditions is presented.

Document Type: Research Article


Publication date: 2006-01-01

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