Thermal evolution of gas-liquid-solid products and migration regulation of C/H/O elements during biomass pyrolysis

摘要

Pyrolysis is a fundamental part of the biomass thermal conversion and utilization. A one-stage fluidized bed reactor was used to study the characteristics of gas-liquid-solid products and the migration regulation of C/H/O elements during biomass pyrolysis. The specific conclusions are as follows: the char yield decreases from 24.3 %-14.9 % during pyrolysis from 500 degrees C to 800 degrees C. The tar yield decreases from 16.9 % to less than 5 %, while the gas yield increases from 24 % to 71.3 %. The graphitization of biochar decreases and its aromaticity increases during pyrolysis. The form of hydrogen existing in biochar is converted from aliphatic hydrogen to aromatic hydrogen during pyrolysis. The content of weaken-bound oxygen such as carboxyl and aldehyde decreases significantly while the content of strong-bound oxygen such as C-O and C-O-C is essentially unchanged. The peak emission of CO during the instantaneous combustion of biochar increases from 0.0013 L/(g min to 0.0032 L/(g min at 500 degrees C to 800 degrees C. The tar starts its aromatization at 700 degrees C. The aliphatic component disappears from 33 % at 500 degrees C-600 degrees C. The double bond equivalent parameter of tar increases significantly, while its H/C ratio and O/C ratio both decrease. The yields of CO/CO2/CH4 increase significantly from 500 degrees C to 700 degrees C. H-2 starts to appear at 700 degrees C. A noticeable CH4 steam reforming reaction starts when raising to 800 degrees C, leading to a decrease in CH4 yield and an increase in CO yield and H-2 yield. C/H/O elements in biochar and tar are gradually lost during pyrolysis. The gas phase becomes the main existing form of C/H/O elements after raising to 700 degrees C.