Recently, a research team led by Xu Guangwen at the Institute of Process Engineering, Chinese Academy of Sciences, made significant progress in the treatment of cohesive coal using jet pre-oxidation gasification technology. Their findings were published in *Applied Energy* in 2013 (Volume 110, pages 276–284), titled "Pilot Study on Jetting Pre-oxidation Fluidized Bed Gasification Adapting to Caking Coal." This study introduced an innovative approach to address challenges commonly faced in traditional fluidized bed gasifiers, where cohesive coal tends to agglomerate and disrupt normal operations.
To tackle this issue, the team developed a novel technique known as jet pre-oxidation fluidized bed gasification. The process involves using oxygen-containing gas to rapidly transport fine coal particles (less than 5 mm in size) into the high-temperature dilute phase zone within the fluidized bed. This helps disperse the coal efficiently while allowing the oxygen to partially oxidize the thermoplastic material in the coal. The resulting weakly cohesive semi-coke then falls into the dense phase zone, where it reacts with the gasification agent—typically composed of O₂, CO₂, and water vapor.
Based on this principle, the researchers built a small-scale experimental setup capable of processing up to 150 kg/h of coal. The system was tested with coal having a bonding index of 20 under both air and oxygen-enriched conditions. The generated syngas had a calorific value ranging between 2.9 and 5.0 MJ/Nm³. However, the study found that excessive oxygen supply from the raw material delivery system could lead to partial combustion of the gas, thereby lowering the energy content of the final product.
The optimal oxygen supply for the raw material delivery system was determined to be around 37% of the total oxygen used in the gasification process. Additionally, increasing the oxygen concentration in the dense phase gasification agent to 30% significantly improved the gasification rate and carbon conversion efficiency, especially for low-reactivity coals.
Figure 1: Fluidized bed pre-oxidation gasification principle and pilot test flow chart
Table 1: Jet Pre-oxidation Fluidized Bed Gasification Small Test Conditions and Results
In the table, a1 and a2 represent the excess air ratios calculated for the total gasification agent, fuel jetting gas, and bottom fluidizing gas (excluding steam), respectively. The sum of these values gives the overall excess air ratio (a = a1 + a2).
The laboratory studies and small-scale experiments demonstrated that the jet pre-oxidation fluidized bed gasification technology is not only feasible but also highly effective for handling cohesive coal. These results laid a solid foundation for further development, process optimization, and large-scale implementation of the technology. Moreover, the method offers a promising pathway for the clean and efficient utilization of coking coal, which is crucial for sustainable energy production.
This research was supported by the National Science and Technology Support Project (Grant No. 2009BAC64B05) and the Scientific and Technological Pilot Project of the Chinese Academy of Sciences (Grant No. XDA07050400).
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