The limits of mechanical sludge drying sometimes create the need for thermal drying by water evaporation. SUEZ has developed a number of sludge drying processes that allow the sludge to be recovered for a multitude of uses as fertilisers, co-products for composting or as fuel for incineration plants.
This fully automated drying process uses the principle of continuous drying by the convection of hot air in a closed tunnel. Greenhouse gas emissions are limited and olfactory nuisances are kept under control. The recovery of the low calories (heating and cooling networks, residual energy, etc.) also reduces energy consumption.
Evaporis LE (Low Energy): mixed drying that combines a thin-film dryer and a hot air belt dryer
This sludge drying process features the recovery of thermal energy. The sludge goes through three treatment steps:
- indirect drying by a thin-film evaporator: the dried sludge is pre-dried to dry content levels of 40% to 50%
- mechanical extrusion: the sludge is forced through a perforated grid to form pellets
- direct drying by the belt dryer: the final dry content of the pellets is between 65% and 90%
Heliantis: solar drying
With this process, SUEZ is promoting the use of clean and renewable energy sources to dry sludge. It uses the same principle as horticultural greenhouses, completed by a ventilation system and a sludge stirrer.