Abstract:

A novel method based on oxidative pyrolysis in combination with microwave irradiation was proposed, which could overcome the poor microwave absorption ability and the tar production from microwave-assisted pyrolysis of biomass. The heating behavior, products output behavior and characteristics of the product of microwave-assisted oxidative pyrolysis of larch were studied. The results showed that heating rate of the microwave irradiation increased with the addition of oxygen, and it was close to linear when the molar ratio of oxygen to carbon was 0.44. The oxygen promoted the microwave irradiation pyrolysis and when the molar ratio of oxygen to carbon was 0.22, the yields of gaseous, liquid and solid products were 75.55%, 15.61%, and 8.84%, respectively, which were much better than the results of microwave irradiation pyrolysis without oxygen(the yields of gaseous, liquid and solid products were 19.37%, 48.78%, and 31.85%, respectively). The addition of oxygen led to the increase of the carbon conversion rate, gas yield, and gasification efficiency from 7.4%, 0.16 m³/kg, and 14% to 52%, 0.82 m³/kg, and 37.5%, respectively and the decrease of power consumption by 80% with increasing the molar ratio of oxygen to carbon from 0 to 0.22. However, when the molar ratio of oxygen to carbon was beyond 0.055, the heat value of gas declined. The addition of oxygen also reduced the amounts of by-products such as tar and char, and achieved liquid composed of polycyclic aromatic hydrocarbons and the low acid char. In addition, the appropriate amount of oxygen could significantly benefit the formation of micro- and mesoporous structure and improve the specific surface properties of the obtained char. When the molar ratio of oxygen to carbon was 0.22, the specific surface area and average micropore size of char were 489 m²/g and 4.13 nm.

Key words: oxygen-assisted pyrolysis, microwave irradiation, gasification, tar removal