Co-pyrolysis of peanut shell with municipal sludge: reaction mechanism, product distribution, and synergy.

Abstract

Biomass/sludge co-pyrolysis contributes to the high-efficiency resource utilization, harmless treatment, and reduction in volume of sludge. Due to the complexity of co-pyrolysis reaction, it is essential to evaluate the thermodynamic behavior, synergy, and reaction mechanism of this process to make it commercially viable. In this work, the pyrolysis properties, thermodynamic analysis and product distribution of municipal sludge (MS), peanut shell (PS), and their blends with various sludge mass ratios (SMRs) were investigated by a thermogravimetric analyzer and a fixed bed reactor. There was a considerable synergy existing in the process of PS/MS co-pyrolysis, and the synergy occurred mainly at the devolatilization phase, accelerating the mixture pyrolysis. When the conversion rate α was less than 0.7, the apparent activation energy decreased continuously with SMR at the same α; however, it increased dramatically with SMR when α was greater than 0.7. Reactants and reaction stages greatly affected the kinetic mechanism of fuel pyrolysis, and this finding was beneficial for the numerical simulation of mixture pyrolysis. Based on the conclusions and precision of this work, the mass ratio of PS to MS was recommended to be 6:4, which had the strongest synergy, with a gas yield of 26.69 wt.% at 600°C and a lower heating value (LHV) of pyrolysis gas of 14.89 MJ/Nm3.