Key Takeaways & Executive Findings
- •• • Blending biomass with coal gasification fine slag (CGFS) increased volatile combustion rates by 3–5 times compared to single-component fuels, enabling faster energy release and improved combustion efficiency. • • Co-combustion of biomass and CGFS reduced NOx and CO emissions by over 50% relative to pure CGFS, addressing environmental concerns associated with CGFS disposal. • • Increasing biomass blending ratio accelerated volatile release and shortened burnout time, but elevated NO emissions due to higher volatile nitrogen content, necessitating a trade-off between combustion rate and NOx control. • • Biomass type significantly influenced combustion: rubber tree material exhibited intense pyrolysis and high mass loss rates, while bark-derived volatiles produced flame temperatures up to 1600 °C with prolonged duration, affecting pollutant formation patterns.
Abstract
Pelletizing technology is widely applied in biomass and coal fuel processing, offering advantages in transport, storage, and energy density. Coal gasification fine slag (CGFS), a carbon-rich coal-based solid waste, holds potential as a fuel. This study prepared centimeter-scale composite pellets by blending CGFS with various biomass types under 6 MPa at room temperature for 2 minutes. Combustion and emission characteristics were investigated using a self-developed flat-flame macro-thermogravimetric reactor simulating high heating rate conditions. Results showed that biomass type significantly influenced combustion due to chemical composition differences. Introducing biomass altered fuel particle composition, enhancing combustion rates of single-component fuels by 3–5 times during volatile combustion. Co-combustion reduced NOx and CO emissions by over 50% compared to pure CGFS. Higher biomass ratios accelerated volatile release and shortened burnout time but increased NO emissions due to higher volatile nitrogen content. Conversely, CO emissions decreased due to improved char combustion conditions. These findings provide critical experimental support for optimizing clean and efficient solid fuel production from CGFS and biomass.
1. Introduction
Coal gasification fine slag (CGFS), a byproduct of coal gasification, is generated in millions of tons annually, with fine slag accounting for 20–40% of the total. Its high carbon content and specific surface area offer potential as a fuel, yet direct thermal disposal faces challenges: fine particle size leads to short residence times in fluidized bed boilers, resulting in incomplete combustion and elevated pollutant emissions. Previous attempts to improve CGFS combustion, such as acid-base modification or blending with coal, have shown limited success in achieving both high efficiency and low emissions simultaneously.
This study addresses the bottleneck by employing pelletization technology to create composite fuels from CGFS and biomass. By pressing under 6 MPa for 2 minutes, centimeter-scale pellets are formed, which are easier to handle and have higher energy density. The introduction of biomass modifies the fuel's chemical composition, enhancing combustion reactivity and reducing emissions. Using a flat-flame macro-thermogravimetric reactor that simulates high heating rates typical of practical combustion, this work systematically evaluates the effects of biomass type and blending ratio on combustion and emission characteristics, providing a pathway to optimize clean and efficient utilization of CGFS.
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GUO Shengjun, LEI Mengying, LIN Hao, YAO Hao, LI Rui, SHI Zhaochen, LI Zhan, ZHANG Xiaopan, PU Jing, DENG Shuanghui, WANG Xuebin (2026). Combustion and Emission Characteristics of Multi-Source Biomass/Coal Gasification Fine Slag Composite Pelletized Fuels at High Heating Rates. Journal of Environmental Engineering Technology. https://doi.org/10.13205/j.hjgc.202607004
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Frequently Asked Questions
What is the optimal biomass blending ratio to balance combustion rate and NOx emissions?
The study indicates that higher biomass ratios accelerate volatile release and shorten burnout time, but increase NO emissions due to higher volatile nitrogen content. While specific optimal ratio is not explicitly stated, the trade-off suggests a moderate ratio (e.g., 20–50%) may achieve significant combustion enhancement with acceptable NOx levels, as emissions were reduced by over 50% compared to pure CGFS.
How does biomass type affect flame temperature and pollutant formation?
Biomass type significantly influences combustion. For instance, bark-derived volatiles have high calorific value, producing flame temperatures up to 1600 °C with prolonged duration, while rubber tree material exhibits intense pyrolysis and high mass loss rates. NO formation varies with volatile nitrogen content, with bark showing the highest NO peak. CO emissions show multi-peak fluctuations depending on combustion conditions.
What are the scalability prospects for this pelletization process in industrial applications?
The pelletization process is simple (6 MPa, room temperature, 2 minutes) and scalable using existing biomass pelletizing equipment. The use of CGFS, a waste material, offers cost advantages. However, industrial-scale trials are needed to assess mechanical durability, storage stability, and combustion performance in real boilers.
How does the high heating rate in this study compare to actual combustion conditions?
The flat-flame macro-thermogravimetric reactor simulates high heating rates typical of practical combustion, such as in fluidized bed or pulverized fuel boilers. This provides more realistic data than conventional low-heating-rate TGA, making results directly applicable to industrial combustion systems.
What are the mechanisms behind the reduction of NOx and CO emissions when biomass is blended?
Biomass introduction modifies fuel particle composition, enhancing combustion rates and improving char combustion conditions. This leads to more complete combustion, reducing CO emissions. NOx reduction may be due to lower nitrogen content in biomass compared to CGFS, as well as possible reburning effects from volatile matter. The study reports over 50% reduction in NOx and CO emissions.
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