An Energy-Efficient Solution to Sludge Drying and Combustion Process Through Camellia Oleifera Shells Amended Foaming

Abstract

Foaming pretreatment has been proved to be effective in promoting sludge drying, however, the variation of sludge properties significantly influences the foaming efficiency. Inspired by foam stabilizer of solid particles, Camellia oleifera shells (COS) was screened out from various biomasses as its potential on promoting the sludge foaming. For the introduce of COS, this study analyzed the drying behaviors of foamed sludge, quantified the surface cracks information, characterized the combustion performance, and evaluated the energy consumption. The results indicated that about 50% of time could be saved in foaming the sludge to 0.70 g/mL by addition of 3.0 wt% COS. Compared with the original sludge (OS), the 0.70 g/mL foamed sludge saved 47.43% of time for sludge drying at 80 oC, and this value further increased to 53.14% with 3.0 wt% COS addition. Combining the multifractal spectra and drying kinetics analysis, the foaming promoted the formation of complex surface cracks in the warm-up period, while COS further improved the complexity of cracks in the constant rate period, and the shrinkage of isolated sludge blocks in the falling rate period, thus enhanced the moisture diffusion and heat transfer. Furthermore, the appropriate porous structure and additional volatile matters promoted the combustion performance. The 0.90 g/mL foamed sludge with COS presented the lowest activation energy of 180.362 kJ/mol in combustion. Overall, compared with OS, the 0.70 g/mL foamed sludge with COS saved 40.65% energy consumption in the foaming, drying and combustion process, which provided an energy-efficient solution for the sludge treatment and disposal.

Keywords: Sludge drying, Foaming pretreatment, Camellia oleifera shell, Multifractal analysis, Combustion characteristics, Energy consumption