Numerical Simulation of Heat and Mass Transfer in Sludge Low-Temperature Drying Process

Abstract

Based on the sludge mass transfer flux model, this paper conducts a simulation study on the drying characteristics of sludge under low-temperature environment and compares it with the previous experimental results. It is found that when the sludge moisture content is low, the change of its drying curve is basically consistent with the experimental results, but there is a large error when the sludge moisture content is 0.4–0.6. In order to better simulate sludge drying characteristics, a model of cracking and shrinkage coefficients based on sludge moisture content is proposed, and the effective diffusion coefficient and mass transfer coefficient are modified. The maximum error between simulation and experiment is reduced to 23.78%. Based on this model, the sludge drying mechanism was studied. It was found that heat transfer and diffusion played a major role in the initial stage of sludge drying, and diffusion played a major role in sludge drying 30 min later.

Physico-chemical characterization and possible uses of sludge processed from an urban sewage treatment plant

“…The two different temperatures of 50 ∘ C and 100 ∘ C were chosen in both ventilation cases, to highlight the direct relationship between temperature, the evaporation degree, and humidity of the analyzed samples. These two temperatures of 50 ∘ C and 100 ∘ C were chosen for different reasons: (i) after 150 ∘ C, a significant loss of the volatile solids is encountered (due to the thermal degradation of the sludge) [16] ; (ii) low-temperature drying technologies are more and more studied and used nowadays, to save energy, money, and contribute to a more friendly, less polluted or nonpolluted environment [17] .…”