高压浓相粉煤气力输送特性及信息熵分析

在输送压力可达4.0MPa,固气比高达450kg/m3的高压气力输送试验台上,用氮气进行粉煤高压浓相气力输送试验研究。分别在不同的输送差压、浓度和速度等条件下进行了输送试验,考察操作参数对煤粉固气比等气力输送特征参数的影响,用信息熵分析试验过程中采集到的压力波动时间序列,探讨流动稳定性和流型变迁过程中信息化趋势,建立信息熵和流型之间的关系。结果表明在输送差压增大的过程中,固气比和Shannon信息熵均增大;气体流量与Shannon信息熵和固气比之间呈现较好的规律性;不同流动形态的Shannon熵差异较大,不同流型之间的Shannon熵区分度较好。Shannon信息熵分析为研究高压浓相气力输送流型及其转变特性提供了一种行之有效的方法。     

高压密相气力输送煤粉输送速率通量及神经网络模拟

在高压密相气力输送中试试验台上,研究了输送压力P₁、总差压ΔP_T和流化风量Q_f等操作条件,以及煤粉平均粒径d_p、含水率W和煤粉种类等物性参数对煤粉输送速率通量ψ的影响规律。鉴于高压密相气固两相流的复杂性,在充分试验的基础上,先后采用原始BP神经网络和两种改进算法,对ψ进行模拟和预测,并比较各算法的优劣。研究结果表明:ψ随着P₁和ΔP_T的增大而增大,随着Q_f的增大而先增大后减小;ψ随着d_p和W的增大而减小,也受煤粉种类的影响;两种改进算法的BP网络可以对研究对象进行较好的模拟和预测,但收敛速度和预测精度不可兼得。试验结果将对高压密相气力输送系统的操作运行以及关键特征参数的模拟预测起到一定的指导作用。     

柱塞气固两相流输送特性

为了研究柱塞式气力输送气固两相流的输送特性,对实际的工业气力输送系统进行1∶1试验台改造,首先进行了粉煤灰在输送管内的流动模式试验;然后进行粉煤灰输送压力、输送质量流量特性试验;最后考察了主进气流量、补气流量、助吹气流量对粉煤灰输送量、固气比的影响。研究表明,柱塞式气力输送流动模式以密相栓柱流为主,其灰栓长度为0.8～2.3 m,移动速度约为2.8～11.3 m·s^-1;输送压力与输送流量呈双曲线特性,且随着气量的增加输送量增大;主进气流量起主导作用并与输送粉煤灰质量流量呈单调上升抛物线关系,与固气比呈上凸抛物线关系即先增大后减小。研究结果对柱塞式气力输送系统的工程设计、运行和理论研究提供依据并具有指导作用。     

上出料系统粉煤密相气力输送特性及其与下出料系统的比较

考察了气体进入方式和输送压力对上出料发料罐系统粉煤密相气力输送特性的影响,并比较了上出料和下出料发料罐系统的煤粉输送量、固气比和稳定性差异。结果表明,在上出料发料罐系统中,随锥部气增加,煤粉输送量和固气比呈先增加后减小趋势;随底部气和调节气增加,煤粉输送量和固气比呈减小趋势;随输送压力增加,煤粉输送量和固气比先明显增加后增加趋势减弱。与上出料发料罐系统相比,相同输送差压下,下出料发料罐系统具有较高的输送量和固气比,但二者均具有良好的输送稳定性。     

高压密相气力输送垂直弯管阻力特性

在输送压力可达4 MPa的气力输送实验台上,进行不同平均粒径煤粉的密相输送实验。从理论与实验两方面研究气固两相流流经弯管的压损随煤粉体积分数以及表观气速的变化规律。结果表明,高压密相输送中煤粉运动造成的能量损失是总压损的主要部分,且总压损随着煤粉体积分数的增加而增加。研究表明,相同质量流量下,随着表观气速的增加,弯管动能压损增加,摩擦压损降低;相同表观气速时,随着煤粉体积分数的增加,摩擦压损增加;固相摩擦系数与煤粉平均粒径及煤粉质量流量无明显关系,随着表观气速的增加略有下降。     

栓流密相气力输送特性的试验研究

为研究栓流密相气力输送气固两相流的输送特性,进行了粉煤灰在输送管内的流动模式试验和粉煤灰输送压力、物料流量特性试验.采用EcT技术测试了粉煤灰在输送管内的流动模式,并考察了主进气流量、补气流量、助吹气流量对物料流量、固气比的影响.研究表明:粉煤灰在输送管内的流动模式是以栓流密相为主,其灰栓长度为0.8～2.3 m,移动速度为2.8～11.3 m/s;输送压力与物料流量成双曲线特性,且随着空气流量的增加物料流量增大;主进气流量起主导作用,并与物料流量成单调上升抛物线关系,与固气比成上凸抛物线关系,即先增大后减小.     

高固气比状态下的粉煤气力输送

在自建的气力输送系统上,进行了高固气比状态下粉煤气力输送研究.分别在内径为15、20、32 mm的管道中进行了输送实验,考察了操作参数对粉煤质量流量、固气比、表观气速等气力输送特征参数的影响.结果表明,输送固气比达到200～580 kg•kg^-1;随气体流量增加,粉煤的质量流量增大,而固气比降低;与输送压力的影响相比,管径对粉煤质量流量的影响程度更为显著;给出了基于本系统描述各参数之间相互关系的经验方程,表明较小的气量和较大的输送管径更有利于实现高固气比状态下的粉煤气力输送.     

粉煤气化工业装置高压密相气力输送稳定性分析

选取煤粉高压密相气力输送系统关键操控参数作为研究对象,系统考察了工业装置煤粉输送密度、速度、流量的稳定性影响规律。结果表明,随着负荷的提高,煤粉输送管线密度、速度、流量波动均减小,稳定性提高;流化气量过大或过小均不利于提高稳定性;输送气量越高,稳定性越好。在实际工业生产中,还需要平衡各个参数对煤线的影响,以保证煤线在总体稳定的前提下,实现较大流量和较高浓度的输送。     

操控条件对煤粉密相气体输送特性影响

为了获得操控条件对煤粉密相气体输送的影响规律,在上出料输送装置中,各种操作参数,如锥部气流率、底部气流率、调节气流率、输送压力和输送压差对煤粉质量流率、固气比、煤粉速度和表观气速的影响进行研究。结果表明:当锥部气流率改变时,煤粉质量流量改变不超过8%,且其他输送参数改变也较小;当底部气流率为0,煤粉仍可实现输送。随着底部气流率的增加,输送量和固气比呈现下降趋势,但表观气速和煤粉流速却呈现相反的趋势;当调节气流率从0增加到0.9 m3/h时,输送量从1 548 kg/h增加到1 582 kg/h,仅增加2.2%,但表观气速、煤粉流速和固气比变化却较大;当压力大于1 000 kPa,压力对输送特性的影响变小;输送参数都随着输送压差的增加显著增加。研究结果将为大规模干煤粉气化技术的密相输送操作提供重要参考。     

基于静电与电容集成传感器的密相气力输送煤粉流动参数在线测量研究

提出了一种静电与电容传感器集成测量系统,用于监测低压下密相气力输送煤粉颗粒的流动参数(速度、浓度和质量流量)。在该系统中,环状静电传感器用于颗粒速度测量,螺旋电容传感器用于颗粒浓度测量。在不同工况下,对煤粉颗粒的流动参数进行了测量,并系统研究了输送系统运行参数(角阀开度、流化风量、补充风量和给料罐压力)对煤粉颗粒速度、浓度和质量流量的影响。结果表明,该系统能够对密相气力输送煤粉颗粒流动参数进行可靠的在线测量。     

Conveying Characteristics of Pulverized Coal in a Top‐Discharge Blow Tank System

Based on the experiments of pulverized coal pneumatic conveying using nitrogen as carrier, the influences of riser inlet height above the gas distribution plate, riser diameter, pulverized coal external moisture content, and supplemental gas flow rate on the conveying characteristics such as pulverized coal mass flow rate and solid‐gas ratio were investigated in a laboratory‐scale experimental setup of a top‐discharge blow tank under atmospheric pressure. There exists an optimal riser inlet height for a given top‐discharge blow tank. The supplemental gas is one of the critical factors affecting the conveying stability and continuity. A model for material mass flow rate prediction with errors ranging from –25 % to +15 % is presented.     

Effect of Operating Conditions on Discharge Characteristics of Petroleum Coke Powder from a Top-Discharge Blow Tank at High Pressure

Discharge experiments of petroleum coke powders were carried out in a pilot-scale top-discharge blow tank at high pressure. The effects of operating conditions (including fluidizing gas flow rate, blow tank pressure, differential pressure between blow tank and receiving tank, supplementary gas flow rate) on solid discharge rate and solid loading ratio were investigated. The results indicate that the maximum solid discharge rate corresponds to the most effective fluidization of the powders near the riser inlet when the fluidizing gas flow rate reaches a critical value. The solid loading ratio shows the same variation tendency as solid discharge rate with increasing fluidizing gas flow rate, which first increases then decreases. Increasing blow tank pressure can improve the fluidization of powders in the tank, which contributes to the increase of solid discharge rate; however, it would not change the basic discharge law. As the differential pressure between blow tank and receiving tank increases, the solid discharge rate increases, while the solid loading ratio first increases then decreases. Solid discharge rate and solid loading ratio both decrease as supplementary gas flow rate increases. A modified solid discharge rate prediction model is proposed for the top-discharge blow tank at high pressure with errors below ±12%.     

煤粉外水含量对上出料式发送罐供料特性的影响

在上出料式发送罐密相气力输送实验台上,研究了外水含量对煤粉供料质量流率、固气比以及供料稳定性的影响,获得了内蒙古褐煤的极限供料外水含量和最佳供料外水含量,并结合煤粉流动特性分析,探讨了煤粉极限供料外水含量和最佳供料外水含量的判别方法。结果表明：在初始外水含量为3.3%条件下,在上出料式发送罐壁面以及提升管入口处能够观察到明显的静电放电现象;当外水含量增加至10%时,发送罐内会出现煤粉结拱现象;实验所用内蒙古褐煤的极限供料外水含量在8.7%~10%之间,其最佳供料外水含量大约为4%,在最佳供料外水含量下煤粉供料质量流率和固气比均达到最大值,且供料稳定性最好;当外水含量为供料实验获得的最佳外水含量4%时,煤粉的流动函数达到最大值,同时黏附力达到最小值,煤粉的流动性也达到最佳。在外水含量由8.7%增加至10%的过程中,煤粉流动性由容易流动区域转为有黏性区域,流动性变差。当外水含量为10%时,煤粉处于有黏性区域,流动困难。与供料实验相比,通过剪切实验获得煤粉的流动函数和黏附力,可以作为工业应用中初步判别煤粉极限供料外水含量和最佳供料外水含量的便捷方法。     

工业级管道中粉煤浓相流动特性

分别以干燥空气和粉煤为输送载气和介质，在39 mm工业级水平不锈钢管内进行了浓相气固两相流动特性实验研究。高速摄像仪拍摄到的粉煤流型表明，浓相输送条件下存在分层流。在流化气和调节气协同作用下，工业级管道中的粉煤浓相输送规律与此两路气流流量密切相关，并获得了39 mm管径下的粉煤气力输送相图。与管径较小的20 mm水平不锈钢管输送结果的比较表明：较大管径条件下，输送压力对粉煤流率的影响更为显著，输送的经济气速相对较高；相同输送通量情况下，较大管径的输送单位管长压降低，且输送通量变化引起的单位管长压降变化也较为平缓。     

Study of the pressure drop of dense phase gas-solid flow through nozzle

Pressure drops are measured on different nozzles of various pipe sizes in dense phase pulverized coal pneumatic conveying. From the experimental results, we conclude that the effect of the gas phase nozzle pressure drop is negligible when comparing with the solid phase pressure drop in the experimental range. The main influence factors contributing to the nozzle pressure drop are gas and solid mass flow rate, solids loading ratio, and the diameters of the nozzle inlet and outlet. A new model was developed to predict the nozzle pressure drop in dense phase pneumatic conveying of pulverized coal based on the Barth's pneumatic conveying theory. The pressure drop predictions from the model are in good agreement with the experimental values. The model quantified the important influence factors of the nozzle pressure drop.     

Pneumatic transport characteristics of coarse size pulverized coal for the application of fast circulating fluidized bed gasification

The pneumatic transport characteristics of pulverized coal with very coarse grain size were investigated, especially related to fast circulating fluidized bed gasifier. The lock hopper system was used along with the top discharge blow tank technology to examine the transportation characteristics of pulverized coal. The most important factors among the pulverized coal transportation properties were mass flow rate of pulverized coal and the solid loading ratio, which changed with the amount of fluidization nitrogen and differential pressure between injection hopper and gasifier. The mass flow rate of the pulverized coal and the solid loading ratio were linearly proportional to changes in differential pressure, and were inversely proportional to changes in the amount of fluidization nitrogen. In the case of extended transport line, similar feeding characteristics were obtained by increasing the differential pressure while the level of fluidization nitrogen was kept constant. Pressure losses were observed with changes in the mass flow rate of pulverized coal, solid loading ratio, and the transport gas density in horizontal and vertical, both upward and downward, straight pipelines and at bends. Characteristics of pressure losses under various operating conditions were correlated with the nondimensional numbers such as the Reynolds number, Froude number, solid/gas density ratio, and solid loading ratio. Such correlations were reasonably consistent with the experimental results.