Multi-scale pressure analysis and fluidization quality characterization of dry dense medium fluidized bed
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摘要:
选煤是煤炭清洁加工利用的源头技术，干法选煤是干旱缺水地区与易泥化煤炭高效分选提质的重要途径。干法重介质流化床通过上升气流驱动加重质颗粒流化形成一定密度的气固流态化床层，实现对煤炭按密度分选，床层密度均匀稳定性即床层流化质量是决定分选精度的关键。受到气流、气泡、运动内构件、入料等多因素扰动，床层流化行为复杂多变，压力信号呈现出非均匀性、非线性、多尺度特征。基于干法重介质流化床压力信号的轴向差异传递与横向等效扩散特性，着重研究了床层轴向压差波动特征，提出流化质量定量表征方法。结果表明：基于时域分析可知，Geldart A类加重质颗粒床层总压降概率密度分布接近于正态分布；当床层散式膨胀时，由于颗粒间接触力的分布不均，概率密度呈现右偏且尖峰的偏离正态分布。通过频域分析发现，在床层膨胀区间的中末期，气泡主频主导了流化床的整个轴向区间；完全流化后的流化床，气泡主频仅控制着床层中部区域，床层浓度信号主频沿床层轴向分布变化明显。结合时域和频域信号分析结果，提出以轴向床层浓度主频为子区间波动标准差权重值的流化质量表征模型，可以综合评估干法重介质流化床的密度分布均匀性和稳定性，为干法重介质流化床分选密度稳态调控与精准分选提供有力支撑。
Abstract:Coal beneficiation is the source technology of clean processing and utilization of coal. Dry coal beneficiation is an important way for efficient separation and upgrading of easily sliming coal in arid area. Dry dense medium fluidized bed forms a certain density of gas-solid fluidized bed by updraft-driven heavy medium particles fluidization, thus achieving coal separation according to bed density. The uniformity and stability of bed density, namely the bed fluidization quality, is the key to determine the separation accuracy. Due to the disturbance of airflow, bubbles, moving internals, feeding and other factors, the fluidization behavior of the bed is complex and changeable, and the pressure signal shows non-uniformity, non-linearity and multi-scale characteristics. Based on the characteristics of axial differential transmission and lateral equivalent diffusion of pressure signal in dry dense medium fluidized bed, the fluctuation characteristics of axial differential pressure were studied emphatically, and a quantitative characterization method of fluidization quality was proposed. The results show that: Based on time domain analysis, the probability density distribution of total pressure drop in Geldart A type separation fluidized bed is close to normal distribution. When the bed is in the particulate expansion, due to the uneven distribution of contact force between particles, the probability density shows the right deviation and the peak, deviating from the normal distribution. Through frequency domain analysis, it is found that the dominant frequency of bubbles dominates the whole axial interval of fluidized bed at the later stage of bed expansion. After complete fluidization, the dominant frequency of bubbles only controls the central region of the bed. The dominant frequency of bed concentration signal changes obviously along the bed axial distribution. Combined with the results of time-domain and frequency-domain signal analysis, a fluidization quality characterization model was proposed, where the standard deviation of axial fluctuation is weighted and averaged, and the dominant frequency of sub-bed concentration is taken as the weight value. This model can comprehensively evaluate the uniformity and stability of density distribution of dry dense medium fluidized bed, and provide strong support for the steady-state control and accurate separation of dry dense medium fluidized bed.
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图 2 总床层压降标准差随气速的变化
Figure 2. Variation of standard deviation of total bed pressure with gas velocity
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图 3 总床层压降偏度随气速的变化
Figure 3. Variation of skewness of total bed pressure with gas velocity
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图 4 总床层压降峰度随气速的变化
Figure 4. Variation of kurtosis of total bed pressure with gas velocity
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图 5 初始流化时压差信号中的暂态空隙
Figure 5. Short-lived void reflected in differential pressure signal during initial fluidization
表 1 颗粒参数性质
Table 1 Parameter properties of particles
颗粒类型 平均粒径/
μm真密度/
(kg·m−3)堆密度/
(kg·m−3)最小流化速度/
(cm·s−1)Geldart A 83.20 4600 2540 0.83 
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表 2 不同流化流态下的理想特征频率
Table 2 Ideal characteristic frequency for different fluidization regimes
流化流态 单泡 多泡 爆发气泡 频率/Hz 0.64 3.18~6.37 1.11
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表 3 不同静床高下的理论自然振荡频率
Table 3 Theoretical natural oscillation frequency of different static bed heights
静床高/cm 70 60 50 40 30 自然振荡频率/Hz 0.57 0.66 0.80 1.00 1.32
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