| China has abundant reserves of low-rank coal with high internal moisture content,such as lignite,which is difficult to be efficiently converted and utilized by coal-water slurry gasification technology.Entrained-flow gasification of pulverized coal is one of the important technologies for the conversion and utilization of low-rank coal,in which the moisture content of the pulverized coal is the key index.In this paper,the consolidation characteristics of Xinjiang Yili pulverized coal with different moisture contents under gas pressurization are firstly studied.And then the characteristics of dense phase pneumatic conveying of high moisture pulverized coal are investigated.The study provides an important basis for optimizing the moisture content of pulverized coal preparation and the design and operation of pressurized feeding units for low-rank coals with high internal water content.Finally,the influences of switching methods of parallel hopper feeding are systematically compared.The results are as follows:The influences of pressure,pressurization rate and moisture content on the consolidation characteristics of powders were quantitatively analyzed using pulverized coal with different moisture contents,and the consolidation mechanism of powders under gas pressurization was revealed.The results show that gas pressure has a significant compaction effect on the powder bed,and the compaction effect is mainly affected by the characteristics of the material and pressurization rate,but not related to the final pressure.The maximum compaction density is significantly affected by the pressurization rate,in the range of 1 kPa/s～100 kPa/s,the maximum compaction density increases with the increase of the pressurization rate,but the pressure when the pulverized coal reaches the maximum compaction density does not exceed 120 kPa.The maximum relative compaction density increases with the increase of the moisture content of pulverized coal.The kinetic model of compaction density versus pressurization time was established,with the deviation less than 3%.Finally,the consolidation mechanism of powders under gas pressurization is proposed by synthesizing the visualization analysis and the behaviors of compression and consolidation.For the demand of stable and controllable dense-phase pneumatic conveying of Xinjiang Yili pulverized coal with high internal water content,the influence of moisture content on the flowability of pulverized coal is systematically analyzed in the range of total moisture content from 0.5%to 21%.The parameters of flow characterization applicable to the dense-phase pneumatic conveying of pulverized coal are proposed,and the characteristics of dense-phase pneumatic conveying of low-rank coal with high internal water content are obtained.The results show that external water content is the main factor affecting the flowability of pulverized coal.Although the internal water of Xinjiang Yili pulverized coal is as high as 16%,its about 5%external water does not have a significant adverse effect on dense-phase pneumatic conveying,and still has good stability and controllability of dense-phase pneumatic conveying.Taking the switching process in the parallel hopper feeding system as the research object,the fluctuation characteristics of feeding under different switching methods are investigated,and the means of adding throttling parts in the aggregation pipeline to reduce fluctuation is proposed.The method of parallel hopper feeding satisfying entrained-flow gasification of pulverized coal is formed.And with the help of the dense phase pneumatic conveying system of the parallel hopper feeding of pulverized coal,the switching methods of parallel hopper feeding was verified. |
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