Upgrading biomass pyrolysis gas from corn stalk by charcoal catalytic reforming

Biomass pyrolysis technology is a thermochemical conversion technique. Through the pyrolysis technology, straw recycling can be realized, and high value-added energy products such as biochar and pyrolysis gas can be obtained. However, the tar produced in the pyrolysis process contains heavy poisonous components, and the low temperature viscosity is high, which easily causes pipeline blockage. In order to study the effect of biochar as catalyst for reducing tar and improving pyrolysis gas quality, taking corn stalk as raw material, the tar conversion rate, pyrolysis gas yield and pyrolysis gas heat value were selected as index. The effects of reforming temperature (550, 600, 650, 700, 750, 800 ℃), residence time (0.2, 0.6, 1.0, 1.4, 1.8 s) and biochar characteristics (corn straw charcoal, rice husk, wood charcoal) on pyrolysis gas quality were studied. The changes of specific surface area of biochar catalysts before and after reforming were analyzed. The results showed that at high temperature cracking, the pyrolysis gas yield was 33.8%, and the pyrolysis gas heat value was 18.0 MJ/m3, biochar had better catalytic properties than quartz sand (high temperature cracking), and its catalytic properties were: rice husk charcoal > wood charcoal > corn straw charcoal, indicating that the catalytic properties of rice hull carbon were better. The pyrolysis gas yields of rice husk charcoal, wood charcoal and corn straw charcoal were 39.7%, 38.6%, and 37.9%, respectively, and the tar conversion rates were 79.8%, 78.6% and 72.6%, the calorific values were 17.8, 17.7 and 17.6 MJ/m3, respectively. When the reforming temperature was increased from 550 to 800 ℃, the pyrolysis gas yield increased from 21.0% to 37.9%, the tar conversion rate increased from 23.8% to 72.6%, and the pyrolysis gas calorific value increased from 13.0 to 17.6 MJ/m3, which was due to the increase of temperature to promote the cracking reaction of tar. The tar heavy components were partially converted into light components and non-condensable gases. As the residence time increased from 0.2 to 1.8 s, the pyrolysis gas yield increased from 37.9% to 54.3%, and the tar conversion rate increased from 72.6% to 79.8%. The pyrolysis gas heat value was reduced from 17.6 to 16.8 MJ/m3. It was due to the increase in residence time, which promoted the catalytic conversion of the tar component on the active site of the mineral component on the surface of the biochar, resulting in an increase in the yield of the pyrolysis gas. At 800 ℃, the specific surface area of biochar after catalytic cracking was 79.81 m2/g, which was higher than the specific surface area of pyrolysis biochar of 37.96 m2/g. In summary, as the reforming temperature and residence time increased, the pyrolysis gas yield and tar conversion rate increased, and the pyrolysis gas heat value increased only as the reforming temperature increased. Although biochar can increase pyrolysis gas yield and tar conversion rate, the calorific value was low. Biochar can not only improve the quality of pyrolysis gas, but also increase the specific surface area of biochar at 800 ℃, indicating that the interaction between biochar and pyrolysis gas can not only improve the quality of pyrolysis gas, but also increase the specific surface area of biochar.