Low-temperature drying of industrial biosludge with simulated secondary heat

Drying is an energy-intensive unit operation and future sludge dryers should be able to take advantage of the secondary energy of industrial environments. This work reports the use of a pilot cyclone for drying biosludge at low temperatures and simulating the use of secondary waste heat. The pilot-scale experiments were performed according to an experimental design and the results interpreted using principal components and multiple linear regression. The dry solids content of processed sludge increased from 9 to 19–68% during the experiments with a predicted energy consumption of <1.7 kWh kg⁻¹H₂O. However, the combined energy consumption was 80–230% higher indicating that the efficiency of sludge drying was governed by the availability of secondary heat. Drying sludge to solid contents sustainable for fossil fuel replacement at pulp and paper mills could be performed with secondary heat at a temperature of 70 °C, a pilot-scale feeding capacity of 170 kg h⁻¹and a corresponding energy consumption of 1.0 kWh kg⁻¹H₂O. The results suggest that the use cyclones could be an efficient option for future sludge drying at pulp and paper mills.