Identification of the Limiting Mechanism in Contact Drying of Agitated Sewage Sludge

Abstract

International audienceIn spite of a great number of industrial applications, the thermal design of contact dryers for sewage sludge remains empirical. To improve the understanding of drying mechanisms, the penetration theory developed by Schlünder and co-workers for mono and multi dispersed packing is used to represent the experimental results from a laboratory scale dryer. For granular packing, the only adjustment parameter of the model is the mixing number, which characterizes the dryer and its stirrer. For pasty-like materials, the pasty phase is assumed to be a saturated particulate phase. As the calculation of the effective properties calculation is cumbersome for a multi-granular packing, the particulate phase is considered as a mono-dispersed packing, whose dimension is unknown. To identify the two adjustment parameters, the mixing number was quantified from experiments performed on activated alumina balls, for which physical and thermal characteristics are known, and then the characteristic dimension of the sludge was determined by adjustment of experimental drying kinetics measured in a batch agitated dryer. According to this model, drying is exclusively controlled by the contact resistance between the wall and the biggest particles contained in the dewatered sludge. The model allows to find most of the tendencies experimentally observed for different operating conditions

Atomized sludges via spray-drying at low temperatures: An alternative to conventional wastewater treatment plants

“…Thus, sludge drying in general (flocculation, electroosmotic dewatering and then thermal drying, etc. ), and spraydrying of sludges in particular, are issues still under investigation, as evidenced by several recent works (Amos, 1998;Novak, 2006;Arlabosse and Chitu, 2007;Woo et al, 2007).…”

Modeling of a continuous sewage sludge paddle dryer by coupling Markov chains with penetration theory

“…It has been proven efficient in describing drying kinetics of SS in batch lab-scale installations under different operating conditions: partial air vacuum [26], atmospheric air pressure [25] or superheated steam atmosphere where there is no mass transfer resistance in the gaseous phase [24]. This work is concerned with the latter configuration, in which it has been shown that the limiting mechanism during SS drying is the contact resistance between the heated walls and the biggest particles.…”

“…It was then successfully adapted to the drying of pasty products such as bentonite [23] and SS in batch lab-scale installations [24][25][26]. This theory postulates that, in such systems, drying can be described by a series of static periods during which transient heat transfer and water evaporation occur, separated by instantaneous perfect macro-mixing of the bulk [21,22].…”

Forced Convective Drying of Wastewater Sludge with the Presentation of Exergy Analysis of the Dryer

“…Also drying wastewater sludge using solar energy is considered as time consuming process and highly depending on the weather conditions. Conductive drying of wastewater sludge was extensively explored by Ferasse, Arlabosse and Lecompte (2002), Deng et al (2009 a,b), Yan et al (2009), Arlabosse and Chitu (2007). They were able to study the fundamental behaviour and the variation of the drying kinetics of wastewater sludge during application of conductive drying.…”