Oral · Pages 258–265
Abstract
Research summary supplied by the authors
The sludge drying system envisages treating the wastewater from tanning water treatment plants, downstream of mechanical dewatering. The sludge has a dry matter of 20÷25%, so it is mainly composed of water. This wastewater is taken to landfi lls located far away, with consequent landfi lls overloading and trucks movement. Water evaporation from the sludge allows to: - Reduce sludge quantities (78% weight reduction, from 80% down to 10% moisture) - Reduce transports - Stabilise the sludge with subsequent energy recovery (dried sludge has a PCI of 2.800 kcal/kg). The process consists of two phases: product extrusion (to increase heat exchange surface and limit the dust) and extruded product drying (by passing it over modules with air at low temperature - 80°C). The system is supplied with hot water (85- 90°C) from thermal waste or cogeneration processes. The effi ciency of the heat exchange is guaranteed by special conveyor systems that shoot the air over the sludge at high speed (10m/s). The plant works in closed circuit, the evaporated water is condensed through an integrated condenser, the safety of the opera- tion is guaranteed by a continuous renewal of air (about 1% of total process air) that is cleaned through a two-stage scrubber, acid and basic oxidative, with continuous monitoring of the concentrations of potentially dangerous substances through PID (ammonia and related compounds) and IR (hydrocarbons) sensors. This process allows the reduction of sludge in closed cycle, with zero emissions and low consumption, aimed at creating a by-product (fuel for energy plants) from waste