Effects of N2/CO2 atmosphere on the pyrolysis characteristics for municipal solid waste pellets

Abstract

The pyrolysis characteristics of cylindrical municipal solid waste (MSW) pellets were studied in N2/CO2 atmospheres with different proportion in fixed bed reactor. Gas release property, tar composition and char structure were analyzed and discussed. Results showed that the addition of CO2 in the pyrolysis atmosphere increased the yields of char and gas, and decreased the tar yield significantly. For the gas components, the CO yield increased noticeably as CO2 present, while the contents of light hydrocarbon and H2 decreased. The volume fraction of CO increased from 15% (100% N2) to 22% (10% CO2) and 34% (20% CO2) at 700 °C. The volume fraction of H2 decreased from 21% (100% N2) to 10% (10% CO2) and 7% (20% CO2) at 700 °C. In addition, the CH4 yield increased with the proportion of CO2. For the tar components, external CO2 contributed to eliminate asymmetric substitutions and dearomatization. In addition, the aromatic rings, polycyclic aromatic hydrocarbons, and asymmetric aliphatic hydrocarbon structures were reduced in the N2/CO2 atmosphere. At the temperature above 600 °C, CO2 was favorable to the cracking of the small ring structures, which led to collapse the micro-pores and resulted in the lower accumulative pore volume of the char. At 700 °C, the specific surface area of pyrolytic char was 14.32 m2/g in N2, when CO2 added, this value increased by 35%, which was further enlarged as the proportion of CO2 increasing.