Study On Characteristics Of Sewage Sludge With Hot Air Convection Drying

Sewage sludge has become a social problem that hinder the urbanization, treatment volume increased year by year, thermal drying is an effective way to achieve the goal of sludge reduction and harmless. Based on the review of the research status of sludge drying and the progress of sludge treatment and disposal, This paper were studied by the experimental method on drying characteristics, drying model and drying phenomenon, in order to help design the hot air dryer, optimization of process parameters to provide theoretical support and data accumulation.By using a self-made hot air convection dryer, the influence of temperature, wind speed, size and shape were investigated for drying characteristics. The results showed that:High efficiency did not increase as feature size becomes larger and larger, when the drying temperature was 60℃, wind speed was 5.1m/s,10mm and 30mm was appropriate thin thickness and spherical diameter. In the industry, we could use high temperature and large wind speed at first to make the drying rate rapidly increase, and the dry condition can be reduced after removing the partial moisture. In practice, we should not make the sludge be absolutely dry, when the moisture of sludge was Enough the drying Process would be over, it could save time and energy. Drying temperature and wind speed were similar effects on the apparent of drying before and after. After comparison, thin pancake is more suitable than spherical in hot air convection drying.After comparing five common drying models, Newton, Modified Page, Henderson and Pabis, Logarithmic, Two term, the drying process is predicted by the model, and the heat and mass transfer parameters is calculated under the condition that the drying temperature is 40℃,50℃,60℃, wind speed is 1.1m/s,3.1m/s,5.1m/s. The results showed that:Modified Page model is best for hot air drying process of sludge in Chenggong area.By using Fick diffusion model, it have obtained that the effective diffusion coefficient of thin pancake sludge is from 9.50×10-10m2/s～5.90×10-9m2/s, the effective diffusion coefficient of spherical sludge is 3.12×10-9m2/s～9.12×10-8m2/s. By arrhenius equation, activation energies of thin pancake and spherical sludge are 28.00kJ/mol and 30.21kJ/mol. Drying constant is the slope of the fitted line InMR-t take negative, with the drying temperature rise increases.