New developments of the highly efficient sludge drying process Innodry 2E®
Buechler, M., Knoer, P., Poisson, A., and Paolini, B., Degrémont Technologies, Switzerland
(free)
The rapid increase of energy costs is driving to study alternative processes for sewage sludge drying. Therefore a new design of the INNODRY 2E® was performed, focussed on the reduction of the energy consumption, achieved by the optimization of the values key-parameters, like air flow, air temperature and heat transfer of the evaporation-condensation process.
The INNODRY 2E® system can be divided in two process steps. During the first step the sludge is distributed on a horizontal thin film evaporator. The transported sludge undergoes primarily trough a heat transfer operation, for which the dewatered sludge is heated up and water is evaporate. At the end of the thin film evaporator the sludge paste, containing 45% of dry substance, is pressed through a screen to produce sludge strings.
In the second process step, being primarily a mass transfer operation, the strings are dried with a belt dryer, for which the used air is heated up through the condensation heat arising from the first process step. This drying process, through the string formation at 45% of dry substance, guarantees a safe operation, since no explosive dust is produced.
In this paper we show the development of the new INNODRY 2E® with a higher evaporation capacity, achieved by the optimization of the recovered vapour energy generated during the first process step and by the optimization of the air flow in the belt dyer. The new design of the belt dryer, which increases the efficiency of the whole drying process, was performed by means of Computational Fluid Dynamics (CFD). Through CFD modeling the air flow and the geometry of the belt dryer was analyzed. Modeling results show an increase of the evaporation rate of 30%. In order to lower capital costs and increase overall efficiency, also the use of different materials was taken into account and will be presented with the general benefits as energy savings, evaporation capacity, plant safety and the odor abatement.
Keywords:
Energy efficiency, fluid dynamics, operating safety, sewage sludge, thermal sewage, sludge drying
