Microwave assisted pyrolysis of lignite with microwave absorbers

Microwave (MW) heating technology has the characteristics of high efficiency, cleanness, green and safety, which provides a new development direction for coal pyrolysis. The characteristics of MW pyrolysis of Ulanqab lignite were studied, and the effects of different MW absorbers on the MW pyrolysis of lignite were investigated, and the mechanism of MW pyrolysis of lignite was also discussed in this paper. The results indicate that under the condition of microwave frequency 2 450 MHz and normal temperature, the dielectric properties of activated carbon are best, SiC and CuO are followed, and Fe2O3 and Ulanqab lignite are the worst. Ulanqab lignite shows relatively low MW absorption, and under the action of microwave absorber, the MW heating rate of lignite is increased by nearly 2 to 3 times. Furthermore, activated carbon has the best dielectric properties that could be used as a better absorber for lignite MW pyrolysis. Under the action of activated carbon, the MW pyrolysis efficiency is improved remarkably. When the microwave radiation time is 12 min, the yields of H2, CH4 and CO are 0.144, 0.062 and 0.045 L/g, respectively. In pyrolysis process, the delayed pyrolysis of some functional groups on the surface of lignite results from a large increase in heating rate. The cracking temperature of most of carboxyl, carbonyl and hydroxyl groups begin at about 250, 450, 1 000℃, which is higher than that of conventional pyrolysis. © 2017, Editorial Office of Journal of China Coal Society. All right reserved.