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 pilot study titled "Jetting Pre-oxidation Fluidized Bed Gasification Adapting to Caking Coal" was published in *Applied Energy* in 2013 (Volume 110, pages 276–284).
In traditional fluidized bed gasifiers, cohesive coal tends to clump together, which can disrupt the normal operation of the system. To address this issue, the Chinese Academy of Sciences introduced the concept of jet pre-oxidation fluidized bed gasification, specifically designed for coking coal. This innovative approach aims to improve the handling and gasification efficiency of difficult-to-process coal types.
The technology involves using an oxygen-containing gas to quickly transport fine coal particles (less than 5 mm in size) into the high-temperature dilute phase zone of the fluidized bed, where they are rapidly dispersed. The oxygen in the gas also helps oxidize the coal, reducing its stickiness. After pre-oxidation, the weakly cohesive semi-coke falls into the dense phase zone, where it reacts with the gasification agent—typically composed of O₂, CO₂, and water vapor. Based on these principles, a small-scale experimental setup with a processing capacity of 150 kg/h was developed after extensive laboratory testing to ensure the process is suitable for cohesive coal.
Figure 1: Fluidized bed pre-oxidation gasification principle and pilot test flow chart
The experiments successfully processed coal particles with a bonding index of 20, both under air and oxygen-enriched conditions. The calorific value of the produced gas ranged between 2.9 and 5.0 MJ/Nm³. However, the study found that if the oxygen supply from the raw material delivery system is too high, part of the gasification gas may be burned, thereby lowering the overall calorific value. The optimal oxygen supply ratio for the raw material delivery system was determined to be 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.
Table 1: Jet Pre-oxidation Fluidized Bed Gasification Small Test Conditions and Results
A: a1 and a2 represent the excess air ratios calculated for the total gasification agent, fuel jetting gas, and bottom fluidizing gas (excluding steam), respectively. Here, a = a1 + a2.
The results from the basic research and small-scale experiments thoroughly validated the feasibility and applicability of jet pre-oxidation fluidized bed gasification for treating cohesive coal. These findings provide a solid theoretical foundation and practical guidance for further development, optimization, and scaling up of the technology. This method offers a promising technical route for the clean and efficient utilization of cohesive coal.
This work 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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