Insights into the kinetics, thermodynamics and evolved gases for the pyrolysis of freshly excreted and solid-liquid separated swine manures

Abstract

Swine manure (SM) is one of the dominant livestock wastes in China. Pyrolysis is increasingly needed in valorizing SM into diverse products. However, little is known about the pyrolysis characteristics for SM. The results showed that the common-used solid-liquid separation in the SM management chain changed its physicochemical properties and pyrolysis characteristics. Specifically, the average activation energies (Ea) calculated by Flynn-Wall-Ozawa, Kissenger-Akahira-Sunose and Starink models for SM collected in pigsty (SM-A) were 184.70, 181.34 and 181.73 kJ/mol (R2 > 0.9) at conversion rate (a) = 0.2–0.7, respectively, which were increased by > 30 kJ/mol for solid-liquid separated SM (SM-B). Top pre-exponential values (A) for SM-A were also lower than these for SM-B. The ΔG and ΔS were decreased with the progressing of SM-A pyrolysis, while these for SM-B pyrolysis showed increases. Furthermore, SM-A pyrolysis produced more gas species than SM-B, which was more reactive during pyrolysis. Finally, this study suggested that although SM could be a potential energy source through the conversion by pyrolysis, attention should be paid on the impacts of manure management chain on SM pyrolysis.