Effect of Hydrothermal Pretreatment on Convective Drying Characteristics of Paper Sludge

Abstract

This work concerns the influence of hydrothermal (HT) pretreatment on sludge drying performance. Sludge was dried in an air duct dryer at a temperature of 30.4 ± 0.4 °C with a constant air velocity of 1.34 ± 0.04 m/s and a relative humidity of about 56%. Drying rate curves, defined as the mass flux (kg/(m2 h)) versus the dry basis moisture content (kg/kg), showed that the drying process mainly took place in the falling rate period. HT pretreatment can improve drying speed and shorten drying time. Six classical semi-theoretical drying models, including Lewis, Page, Logarithmic, Henderson and Pabis, Wang and Singh, and Approximation of Diffusion, were evaluated to represent the experimental results in terms of the coefficient of determination (R 2), reduced chi-square (χ2), and root means square error (E RMS). The Approximation of Diffusion model was the best one to reproduce the experimental data with R 2 close to 1, χ2 around 0.00001–0.00005, and E RMS of 0.00371–0.00686. The HT pretreatment changed the model constants. The expression was M R = 0.4868 exp(−0.0036τ) + 0.5132 exp(−0.0014τ) for the untreated sludge and M R = −0.8945 exp(−0.0071τ) + 1.8945 exp(−0.0045τ) for the HT pretreated sludge. The increase in the effective diffusivity accounted for the improvement in the drying performance.

Clean solid biofuel production from high moisture content waste biomass employing hydrothermal treatment

“…It is also visible that the thermal drying performance has also been improved by the HT. Zhao et al [179,180] investigated the dying performance of the HT pretreated and untreated paper sludge with an air duct dryer at an air temperature of 30.4±0.4 °C and velocity of 1.34±0.04 m/s. The results show that the drying process mainly took place in the falling rate period and was mainly controlled by the diffusion properties of the inner structure of the product.…”

Hydrothermal carbonization of lignocellulosic biomass: Effect of process conditions on hydrochar properties

“…As HTC is ideally operated under saturated steam pressure, the energy required for evaporation can be avoided making the theoretical energy requirement for heating the reaction medium significantly lower compared to active drying [7,13]. Energy is still required for post-treatment separation of the solid and liquid phases, but can be significantly lower compared to conventional sludge drying due to potential sludge cell breakage and enhanced drying characteristics [14].…”

Utilization of Sewage-Sludge-Derived Hydrochars toward Efficient Cocombustion with Different-Rank Coals: Effects of Subcritical Water Conversion and Blending Scenarios

“…10 Moreover, the quality of emissions from combustion of SSderived hydrochars (SHCs) can be further improved. Parshetti et al 7 reported that emissions of CO and CH 4 were mitigated through cocombustion of SHC and low-rank coal. During the combustion of hydrothermally pretreated sludge, as a result of the transformation of protein structure via hydrothermal treatment, interactions between NO and NH 3 were facilitated, allowing NO emissions to be reduced.…”