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Membrane Dehumidifi cation Technology for Removing Water Vapor from Exhaust Gas in Sludge Drying Process: Full-Scale Application and Membrane Autopsy
Abstract
Manufacturing solid fuels by drying sewage sludge is an eff ective method for increasing the production of renewable energy
sources; however, the existing technology presents considerable economic challenges owing to high energy consumptions of
the drying process. Here, an innovative sludge drying process that combines microwave drying and membrane dehumidifi cation
technologies, using a gas-separation membrane, was developed and applied for the fi rst time. Additionally, a membrane
autopsy study was conducted on the dehumidifi cation membranes. The 10 t/day system was continuously operated, and
after the stabilization period, a highly effi cient sludge drying process was observed; the consumed energy for drying was
maintained at ≤ 650 kcal/kg water. Mean water vapor removal ratio in the membrane dehumidifi er and dry air circulation
rate was 82.2% and 85.2%, respectively. After 80 days of continuous operation, membrane autopsy was done to compare the
performances of the contaminated and virgin membrane modules. We observed that long-term operation did not induce any
signifi cant change in membrane performance except for slight organic and inorganic (Al) contamination. Thus, we showed
and verifi ed that even under specifi c adverse conditions during the sludge drying process, the combined membrane drying
process was eff ective during long-term operation.
