Experimental study of the characteristics of solid fuel from fry-dried swine excreta

► We investigated the swine excreta were dried by evaporative drying by immersion in hot oil. ► The low heating values of the dried swine excreta were 14,393–28,169kJ/kg. ► TGA showed the characteristic of dried swine excreta was similar to bituminous coal. ► Combustion of the dried product could be possible by adjusting the coal combustor. Swine excreta were dried by boiling via immersion in hot oil. In this method, moisture in the excreta is replaced with oil or evaporated by turbulent heat transfer in high-temperature oil. The dried excreta can be used in an incinerator like low-rank coal or solid fuel. Refined waste oil and B–C heavy oil were used for drying. Drying for 8min at 150°C reduced the water content of raw excreta from 78.90wt.% to 1.56wt.% (refined waste oil) or 1.62wt.% (B–C heavy oil) and that of digested excreta from 79.58wt.% to 3.40wt.% (refined waste oil) or 3.48wt.% (B–C heavy oil). The low heating values of the raw and digested excreta were 422kJ/kg and −2,713kJ/kg, respectively, before drying and 27,842–28,169kJ/kg and 14,394–14,905kJ/kg, respectively, after drying. A heavy metal analysis did not detect Hg, Pb, Cd, As, and Cr in the dried excreta, but Al, Cu, and Zn, which occur in the feed formula, were detected. Thermogravimetric analysis before and after drying revealed that emission of volatiles and combustion of volatiles and fixed carbon occurred at temperatures of 250–500°C when air was used as the transfer gas.