Process consideration of fry-drying combined with steam compression for efficient fuel production from sewage sludge

The fry-drying and steam compression of wet sewage sludge were studied as part of efforts to enable the efficient production of fuel from wet sludge, the applicability of which requires energy-efficient drying. Fry-drying sludge in hot oil is fast and effective, while steam compressed to several bar enables the recovery of the latent heat of the steam evaporated from the sludge. The circulation of oil from the fry-drying bath to a steam condenser was examined as a medium of heat transfer for the absorption of the latent heat. The mass and energy flows through the process components were analyzed in order to evaluate the effects of important design parameters. Optimal ranges of steam pressure and oil circulation rate were identified to maximize heat recovery while maintaining an appropriate oil temperature.