Drying of municipal sewage sludge: from a laboratory scale batch indirect dryer to the paddle dryer

Among available technologies, disk and paddle dryers are often encountered in France to process municipal sewage sludge but their thermal design is still a question of know how rather than scientific knowledge. From experiments performed on an industrial Naratherm® paddle dryer and the literature, a simple model has been developed. The dryer is divided into two parts depending on the sludge consistency. A constant evaporating flow rate is assumed in the pasty zone whereas its linear decrease with the moisture content is taken into account in the granular zone. To compute this model, some of the sludge properties have to be characterized with a set of laboratory scale experimental techniques. The agreement with the experimental data is good