Key Takeaways & Executive Findings
- •• • At 850 °C with steam flow 2 mL/min and N2 flow 75 mL/min, all biomass-coal gangue systems achieved peak syngas yields at a 5:5 mass ratio; the high-cellulose pine stick system produced the highest H2 yield (9.06 mmol/g) and H2+CO yield (15.25 mmol/g), with a H2 synergy index (SI) of 1.75, demonstrating efficient volatile reforming and offering a route to maximize hydrogen production from biomass wastes. • • The high-ash/K+ corn stover system exhibited the strongest CO synergy (SI = 1.22), attributed to catalytic Boudouard reaction, making it an ideal feedstock for CO-rich syngas production; this is critical for industries requiring CO as a chemical building block. • • The high-nitrogen soybean straw system achieved an optimal H2/CO ratio of 2.00, suitable for Fischer-Tropsch synthesis, but its high nitrogen content led to nitrogenous tars that suppressed overall syngas yield (Ysyngas = 13.00 mmol/g), highlighting a trade-off between syngas quality and quantity. • • Synergy indices varied significantly across systems: for H2, SI ranged from 1.43 (corn stover) to 1.75 (pine stick); for CO, from 0.97 (pine stick) to 1.22 (corn stover); for CH4, from 0.70 (pine stick) to 1.44 (soybean straw); these quantitative differences guide feedstock selection for targeted syngas composition.
Abstract
Biomass is a sustainable green coal alternative, and its thermochemical conversion, particularly hydrogen-rich gasification, offers an effective pathway for high-value utilization. Co-gasification of biomass with coal gangue enables synergistic utilization of carbon resources, with significant potential for emission reduction and efficiency enhancement. To elucidate how typical biomass components govern the gasification process, three feedstocks with distinct dominant characteristics were selected: pine stick (high cellulose), soybean straw (high nitrogen), and corn stover (high ash with abundant K+). Under fixed conditions (850 °C, steam flow 2 mL/min, N2 flow 75 mL/min), co-gasification with coal gangue was investigated. Results indicated that compositional differences led to distinct synergistic patterns and product distributions. All systems achieved the highest hydrogen yield at a 5:5 raw material mass ratio. The high-cellulose pine stick system yielded the most H2 (9.06 mmol/g) and H2+CO yield (15.25 mmol/g), exhibiting a 'three high, three low' advantage due to efficient volatile reforming. In contrast, the high-ash/K+ corn stover system showed the strongest synergy for CO (SI = 1.22), promoted by the catalytic Boudouard reaction. The high-nitrogen soybean straw system achieved an optimal H2/CO ratio (2.00) but suffered from suppressed syngas yield due to inhibitory nitrogenous tars. This study confirms that biomass composition—specifically cellulose, ash/K+, and nitrogen content—differentially regulates syngas production and synergy by steering dominant reaction pathways, providing a theoretical basis for targeted conversion of waste resources.
1. Introduction
Co-gasification of biomass with coal gangue addresses two pressing challenges: the low utilization rate of biomass (<20% in China) and the environmental burden of coal gangue. Conventional gasification of coal gangue alone suffers from low reactivity and high ash content, while biomass gasification often faces tar-related issues. The synergistic potential lies in complementarity: biomass pyrolysis radicals can cleave inert bonds in coal gangue, and alkali/alkaline-earth metals (AAEMs) in biomass ash can catalyze gasification reactions. However, the influence of biomass composition—cellulose, nitrogen, ash content—on the synergy and product distribution has not been systematically clarified.
This study fills that gap by selecting three biomass types with distinct dominant characteristics: pine stick (high cellulose), soybean straw (high nitrogen), and corn stover (high ash/K+). Under fixed conditions (850 °C, steam flow 2 mL/min, N2 flow 75 mL/min), co-gasification with coal gangue at varying mass ratios was performed. The results reveal that biomass composition steers dominant reaction pathways, leading to different optimal products and synergy intensities. This provides a theoretical basis for targeted conversion of waste resources, enabling process optimization for desired syngas compositions.
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NIU Yonghong, SHAO Qing, LI Hao, ZHANG Zaiwei (2026). Investigation of the synergistic mechanism during biomass and coal gangue co-gasification. Journal of Fuel Chemistry and Technology. https://doi.org/10.1016/S1872-5813(26)60637-8
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Frequently Asked Questions
What is the optimal biomass-to-coal gangue mass ratio for maximizing hydrogen yield, and how does it vary with biomass type?
All three biomass systems achieved peak hydrogen yield at a 5:5 mass ratio. The high-cellulose pine stick system produced the highest H2 yield (9.06 mmol/g), followed by corn stover (8.95 mmol/g) and soybean straw (8.66 mmol/g). This indicates that a 1:1 ratio is optimal for H2 production, but the absolute yield depends on biomass composition.
How does the ash content and K+ concentration in biomass influence the synergy for CO production?
The high-ash/K+ corn stover system exhibited the strongest CO synergy (SI = 1.22), attributed to K+ preferentially catalyzing the Boudouard reaction (C + CO2 → 2CO). This suggests that biomass with high ash and K+ content can enhance CO yield during co-gasification, making it suitable for CO-rich syngas applications.
What is the impact of nitrogen content in biomass on syngas yield and quality?
The high-nitrogen soybean straw system achieved an optimal H2/CO ratio of 2.00, which is ideal for Fischer-Tropsch synthesis. However, its overall syngas yield (13.00 mmol/g) was lower than that of pine stick (15.25 mmol/g) and corn stover (14.24 mmol/g), due to the formation of nitrogenous tars that inhibit gasification reactions. This trade-off must be considered when selecting biomass feedstocks.
What are the synergy indices for H2, CO, and CH4 across the three biomass systems, and what do they indicate?
For H2, synergy indices (SI) were 1.75 (pine stick), 1.56 (soybean straw), and 1.43 (corn stover), all indicating positive synergy. For CO, SI values were 0.97 (pine stick), 1.11 (soybean straw), and 1.22 (corn stover), with corn stover showing the strongest CO synergy. For CH4, SI values were 0.70 (pine stick), 1.44 (soybean straw), and 1.02 (corn stover), indicating that soybean straw promotes CH4 production. These indices quantify the synergistic effects and guide feedstock selection for desired syngas composition.
How does the synergistic mechanism differ among the three biomass types, and what are the dominant reaction pathways?
The synergy is governed by multiple pathways: radical activation (biomass pyrolysis radicals cleaving inert bonds in coal gangue), directed catalysis by AAEMs (K+ preferentially catalyzing Boudouard reaction, Ca2+ promoting water-gas shift), and catalytic tar cracking (coal gangue minerals cracking tars). The dominant pathway depends on biomass composition: high cellulose (pine stick) enhances volatile reforming, high ash/K+ (corn stover) promotes Boudouard reaction, and high nitrogen (soybean straw) leads to nitrogenous tar inhibition. This mechanistic understanding allows for targeted process optimization.
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