床层高度对浓相气固流化床分选下限的影响研究

发布时间：2018-06-05 16:07

本文选题：浓相气固流化床 + 床层高度　；参考：《中国矿业大学》2017年硕士论文

【摘要】：在浓相气固流化床中,流化床床层高度是流态化技术的一个重要参数,直接影响着床层的流化行为。对于流化床选煤技术来说,床层太浅,分选空间不够,分层不好,影响分选效果;床层太高,易产生大气泡和腾涌现象,影响流化床稳定。而床层高度对于处于分选下限的细粒煤的影响较大,由于床层高度的增加,必然会影响分选下限,因此本文着重于探究浓相气固流化床中床层高度对分选下限的影响。从流态化角度出发,本试验以床层密度分布标准差、不均匀度为评价指标,探究了加重质颗粒大小模型、布风板压降、介质二维组分和流化数等因素对流态化的影响,并在确定以上因子为最佳条件的基础上,进一步探究不同床层高度下的流化特性、空隙率特性和密度空间分布,并揭示了不同床层高度下稳定流态化区域的变化特征,得出流化稳定区域S与床层高径比H/D的关系模型:从分选角度出发,本试验首先探索了各粒度级煤样的最大入料率rmax与煤样平均粒度级(?)的关系模型:rmax=0.004369(?)+0.05350基于此关系模型的斜率数值上,确定其实际入料率。在不同床层高度下、不同流化数下,分别对-10+8mm、-8+6mm、-6+5mm、-5+4mm、-4+3mm、-3+2mm、-2+1mm和-1+0.5mm八个粒度级煤样进行了分选试验。以灰分离析度和可能偏差为评价指标,得出相关结论:首先,在较大粒度级入料时,其分选效果在较大流化数下其分选效果更佳;而在较小粒度级入料时,其分选效果在较小流化数下其分选效果更佳。其次,在同一床层高度下,分选效果随入料煤样粒度级的减小而变差,较小粒度级的分选效果不理想。再次,随着浓相气固流化床床层高度的增大,各粒度级入料煤样的分选效果在变好,当床层高度增大到240mm时,其分选下限能达到-4+3mm粒度级。从次,从混合粒度级煤样入料的分选效果来看,与单粒级煤样入料分选效果相似,其粒度级、流化数与床层高度的关系与单粒级煤样入料的分选结果基本一致。最后,在较短的分选时间内,高床层流化床的分选效果不如低床层床,随着时间的增加,高床层床和低床层床的分选效果都开始变好,但是高床层床的变好幅度大于低床层床,高床层床的分选效果从不如低床层床,变化为超过低床层床的分选效果。从分析机理的角度出发,气速-压降、气固两相模型、散式流化区域和颗粒沉降理论等流态化理论对本试验中的流化及分选过程进行了阐明,并且从高速动态分析上对该结论进行了验证。
[Abstract]:The fluidized bed height is an important parameter of fluidization technology in dense phase gas-solid fluidized bed, which directly affects the fluidization behavior of fluidized bed. For fluidized bed coal preparation technology, the bed is too shallow, the separation space is not enough, the stratification is not good, and the separation effect is affected. The bed height has a great influence on the fine coal at the lower limit of separation. Because of the increase of bed height, it will inevitably affect the lower limit of separation. Therefore, this paper focuses on the study of the influence of bed height on the lower limit of separation in the dense phase gas-solid fluidized bed. From the point of view of fluidization, based on the standard deviation and non-uniformity of bed density distribution, the effects of aggravation particle size model, pressure drop of air distribution plate, two-dimensional composition of medium and fluidization number on fluidization were investigated. On the basis of determining the above factors as the best conditions, the fluidization characteristics, voidage characteristics and density spatial distribution at different bed heights are further explored, and the variation characteristics of stable fluidized areas at different bed heights are revealed. The relationship model between S and H / D ratio of bed height to diameter in fluidized stable region is obtained. From the separation point of view, the maximum feed rate (rmax) of coal samples of different granularity grades and the average grain size of coal samples are explored in this experiment. Based on the slope value of the model, the actual feed rate is determined. Under different bed height and different fluidization number, the coal samples of -108 mm ~ (-6) -8 ~ (6) mm ~ (-6) ~ (-5 mm) ~ (-54) mm ~ (-1) ~ (-3) ~ (-2) mm ~ (-2) 1mm and 1 ~ (-1) 0.5mm were separated from each other. Taking the degree of ash segregation and possible deviation as the evaluation index, the relevant conclusions are drawn: firstly, the separation effect is better under the larger fluidization number, but at the smaller granularity grade, the separation effect is better. The separation effect is better under the smaller fluidization number. Secondly, at the same bed height, the separation effect becomes worse with the decrease of the granularity level of the coal sample, and the separation effect of the smaller granularity level is not ideal. Thirdly, with the increase of the bed height of dense phase gas-solid fluidized bed, the separation effect of each granularity grade coal sample is becoming better. When the bed height increases to 240mm, the lower limit of separation can reach -4 3mm granularity level. From the point of view of the separation effect of mixed granularity grade coal sample, the separation effect is similar to that of single grain grade coal sample, and the relation among granularity, fluidization number and bed height is basically consistent with the separation result of single grain grade coal sample. Finally, in a short separation time, the separation effect of high bed fluidized bed is not as good as that of low bed. With the increase of time, the separation effect of high bed and low bed begin to improve, but the better range of high bed is larger than that of low bed. The separation effect of high bed is not as good as that of low bed, and the separation effect of high bed is higher than that of low bed. From the point of view of analysis mechanism, the fluidization and separation process in this experiment are expounded by the fluidization theory, such as gas-velocity pressure drop, gas-solid two-phase model, dispersed fluidization region and particle settlement theory. The conclusion is verified by high-speed dynamic analysis.
【学位授予单位】：中国矿业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TD94

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