Energy and exergy analysis for fast drying of ribbed smoked sheets in a novel forced-convection rubber smoking room

Abstract

Rubber sheet smoking rooms are widely used by small farmers in rubber growing regions: sheets of raw rubber latex are ‘smoked’ in them to remove moisture, preserve and prepare the rubber for transport. Energy and exergy for a novel forced-convection rubber sheet smoking room were analyzed. Inlet hot air velocity varied between 12 and 14 m/s and the fuel-wood moisture content was between 24–55 % dry basis. Thermal efficiency for drying ribbed smoked sheet (RSS) rubber was 13.4–16.7 %. The specific energy consumption (SEC) was between 13.5–16.9 MJ/kg of water evaporated. The highest thermal efficiency or lowest specific energy consumption was achieved when using the dry fuel-wood (inlet velocity 14 m/s, 53 % db fuel-wood), while the RSS quality was maximum (100 %). The overall second law (exergy) efficiency was from 2.2-5.8 %. The highest exergy efficiency was obtained for air at 12 m/s and 24 % db fuel-wood. However, in this condition, only 55 % of sheets showed good quality. The exergy efficiency for the most suitable condition (100 % high quality sheets) was 2.6 %. Compared to an earlier forced-convection smoking room, the new room reduced the drying time from 48 h to 36 h, while thermal efficiency increased from 14.3 % to 16.5 %. When compared to the original smoking room, 65 % fuel-wood and 50 % drying time were saved and the rubber sheet quality increased from ∼90 % to 100 %. Overall, our forced-convection room was more efficient, dried faster and produced better quality than all previous types.