Predicting the drying properties of sludge based on hydrothermal treatment under subcritical conditions

WATER RESEARCH

卷:91

Article

Makela, Mikko^1,4  Fraikin, Laurent²  Leonard, Angelique²  Benavente, Veronica³  Fullana, Andres³ 

[1] Swedish Univ Agr Sci, Dept Forest Biomat & Technol, S-90183 Umea, Sweden

[2] Univ Liege, Dept Chem Engn, Agora B6c,Allee 6 Aout, B-4000 Liege, Belgium

[3] Univ Alicante, Dept Chem Engn, POB 99, E-03080 Alicante, Spain

[4] Tokyo Inst Technol, Dept Environm Sci & Technol, Midori Ku, G5-8,4259 Nagatsuta Cho, Yokohama, Kanagawa 2268502, Japan

关键词: Biosolids;    Moisture diffusivity;    Hydrochar;    Hydrothermal carbonization;    Shrinkage;    X-ray microtomography;   

DOI  :  10.1016/j.watres.2015.12.043

来源: Elsevier

【 摘 要 】

The effects of hydrothermal treatment on the drying properties of sludge were determined. Sludge was hydrothermally treated at 180-260 degrees C for 0.5-5 h using NaOH and HCl as additives to influence reaction conditions. Untreated sludge and attained hydrochar samples were then dried under identical conditions with a laboratory microdryer and an X-ray microtomograph was used to follow changes in sample dimensions. The effective moisture diffusivities of sludge and hydrochar samples were determined and the effect of process conditions on respective mean diffusivities evaluated using multiple linear regression. Based on the results the drying time of untreated sludge decreased from approximately 80 min to 37 -59 min for sludge hydrochar. Drying of untreated sludge was governed by the falling rate period where drying flux decreased continuously as a function of sludge moisture content due to heat and mass transfer limitations and sample shrinkage. Hydrothermal treatment increased the drying flux of sludge hydrochar and decreased the effect of internal heat and mass transfer limitations and sample shrinkage especially at higher treatment temperatures. The determined effective moisture diffusivities of sludge and hydrochar increased as a function of decreasing moisture content and the mean diffusivity of untreated sludge (8.56.10(-9) m(2) s(-1)) and sludge hydrochar (12.7-27.5.10(-9) m(2) s(-1)) were found statistically different. The attained regression model indicated that treatment temperature governed the mean diffusivity of hydrochar, as the effects of NaOH and HCl were statistically insignificant. The attained results enabled prediction of sludge drying properties through mean moisture diffusivity based on hydrothermal treatment conditions. (C) 2015 Elsevier Ltd. All rights reserved.

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