Effect of steam on coke deposition during the tar reforming from corn straw pyrolysis over biochar

Coke deposition is a critical issue for catalysts in tar reforming. Steam is conducive to tar removal and hydrogen production in biomass pyrolysis, while its effect on coke formation is not well known. Thus, a two-stage fluidized bed/fixed bed reactor was used to study the effect of steam addition on coke deposition. The primary conclusions are as follows: combining steam and biochar, the tar removal efficiency is more than 90% within 20 min of time on stream (TOS). After the TOS reaches 30 min, the biochar surface is saturated with coke deposition and the specific surface area of the biochar stops decreasing. The addition of steam leads to a reduction in the combustion reactivity of the biochar. Besides, the aromatization of the biochar increase and the number of O-containing structures decreases. For the tar, the addition of steam reduces the aliphatics content and increases the O-containing aromatics content. For the gas composition, the addition of steam results in the decrease of CH4 yield while the H-2 yield increases to 0.12 L/g. The H/C atomic ratio of the gas composition decreases while the O/C atomic ratio increases. The active coke is consumed and decomposed after the introduction of steam. The remaining coke is dominated by inert coke. This contributes to the relatively developed pore structure but a weakened combustion reactivity of biochar.

Automated summary

The combination of steam and biochar can effectively remove tar in a short period of time, but the addition of steam reduces the combustion reactivity of biochar, increases aromatization, and decreases O-containing structures. Furthermore, steam can reduce the aliphatics content in tar while increasing the O-containing aromatics content. Additionally, the introduction of steam leads to a decrease in CH4 yield and an increase in H-2 yield, with changes in the H/C and O/C atomic ratios of the gas composition.