Analysis and evaluation on pressure fluctuations in air dense medium fluidized bed

Pressure fluctuations contribute to the instability of separation process in air dense medium fluidized bed, which provides a high motivation for further study of underlying mechanisms. Reasons for generation and propagation of pressure fluctuations in the air dense medium fluidized bed have been discussed.Drift rate and collision rate of particles were employed to deduce the correlation between voidage and pressure fluctuations. Simultaneously, a dynamic pressure fluctuation measuring and analysis system was established. Based on frequency domain analysis and wavelet analysis, collected signals were disassembled and analyzed. Results show gradually intensive motion of particles increases magnitudes of signal components with lower frequencies. As a result of violent particle motion, the magnitude of real pressure signal's frequency experienced an increase as air velocity increased moderately. Wavelet analysis keeps edge features of the real signal and eliminates the noise efficaciously. The frequency of denoised signal is closed to that of pressure signal identified in frequency domain analysis.

Numerical simulation and experimental verification of bubble size distribution in an air dense medium fluidized bed

Bubble size distribution is the basic apparent performance and obvious characteristics in the air dense medium fluidized bed (ADMFB). The approaches of numerical simulation and experimental verification were combined to conduct the further research on the bubble generation and movement behavior. The results show that ADMFB could display favorable expanded characteristics after steady fluidization. With different particle size distributions of magnetite powder as medium solids, we selected an appropriate prediction model for the mean bubble diameter in ADMFB. The comparison results indicate that the mean bubble diameters along the bed heights are 35 mm < D b < 66 mm and 40 mm < D b < 69 mm with the magnetite powder of 0.3 mm+0.15mm and 0.15mm+0.074mm, respectively. The prediction model provides good agreements with the experimental and simulation data. Based on the optimal operating gas velocity distribution, the mixture of magnetite powder and <1mm fine coal as medium solids were utilized to carry out the separation experiment on 6-50mm raw coal. The results show that an optimal separation density d P of 1.73g/cm 3 with a probable error E of 0.07g/cm 3 and a recovery efficiency of 99.97% is achieved, which indicates good separation performance by applying ADMFB.

RESEARCH ON DENSITY STABILITY OF AIRDENSE MEDIUM FLUIDIZED BED

In this paper on the basis of studying the distribution of fine Coal in the dense medAn fluidised bed. the optimai size range of fine coal, which constitutes a fluidized bed together with the dense medium, has been found. In the separating process the fine coal will continuously aeeumulate in fluidized bed, thus inevitably reducing the density of the bed.In order to keep bed density stable, the authors adopted such measures as split-now of used medium and complement of fresb dense medium.The experiment results in both lab and pilot systems of the air-dense medium fluidized bed show that these measures are effective and satisfactory. Then authors also have estabinbed some relative dynamic mathematical models for it.

Occurrence characteristics of mercury in high-mercury coal and distribution rule of mercury in products of an air dense medium fluidized bed

Mercury emitted from direct combustion of high-mercury coal does great harm to the environment. To make good use of high-mercury coal, it is necessary to study the occurrence characteristics of mercury in coal and high-efficient methods of mercury removal. In this paper, high-mercury coal of Guizhou Province of China was taken as an object to study the nature of mercury in coal and the rule of mercury removal by dry preparation method. Mercury mainly distributes in the medium and high density fractions, and has a good affinity with silicon, aluminum, iron, titanium, potassium, calcium, zinc, sodium and magnesium. It exists in minerals formed by these elements and presents significant correlation with ash in coal. After the high-mercury coal is separated by air dense medium fluidized bed, mercury content of clean coal is reduced to 1/10 of raw coal, while mercury content of gangue is increased to 3 times that of raw coal. This indicates that mercury in raw coal is rejected greatly by ADMFB and enriched in highdensity fractions. The rates of ash removal and mercury removal decrease with the density and present a very high correlation.

DRY CLEANING OF COAL WITH AIR DENSE MEDIUM FLUIDIZED BED

This paper deals with the experimental study of dry cleaning of coal with air dense medium fluidized bed. This technique opens up an efficient way of coal separation for vast areas in the country where water resources are in short supply or coals tend to slime seriously in wet process. Tests show that it can separate any kind of coal (6--50mm) efficiently. The probable error E, can reach 0.05--0.08. The separating density can be adjusted in the range of 1.0--2.0 g/cm^3. This technique brings about enormous economic benifits.

The Forming-Mechanism and Role of Creativity Thinking in Dry Coal Beneficiation of Coal with Air-Dense Medium Fluidized Bed

In this paper, the authors point out that the Creativity is an inevitable request in solving engineering and technological problems and that the coal beneficiation technology with air dense medium fluidized bed is a result of reversal thinking, and its forming mechanism is the use of other things for reference and the transplantation.

MECHANISM AND APPLICATION OF COAL DRY BENEFICIATION WITH AIR-DENSE MEDIUM FLUIDIZED BED

The mechanism of beneficiation with air dense fluidized bed has been theoretically studied in the paper. Focusing attention on the misplacing resources in separation process, the misplacing effects are divided into two parts called respectively as misplacing effect of viscosity and misplacing effect of motion. The proposed separation theory can reasonably explain the results of separation in different fluidization states. Experimental results in pilot and commercial plants showed that the air dense medium fluidized bed is a high efficiency dry cleaning technique. The dynamic stability of fluidized bed density is directly affected by the variation of fine coal content in fluidized bed and can be controlled in expected range through measurement of fluidized bed density and adjusting of split flow rate. With air dense medium fluidized bed, various coals of size 50—6 mm can be efficiently beneficiated. The separation density can be adjusted between 1.2—2.2 g/cm 3, and the probable error E p value is about 0.06.

Localisation and phase transition of acoustic waves in a soft medium containing air bubbles

We study via numerical experiments the localisation property of an acoustic wave in a viscoelastic soft medium containing randomly-distributed air bubbles. The behaviours of the oscillation phases of bubbles are particularly investigated in various cases for distinguishing efficiently the acoustic localisation from the effects of acoustic absorption caused by the viscosity of medium. The numerical results reveal the phenomenon of ＇phase transition＇ characterized by an unusual collective oscillation of bubbles, which is an effective criterion to unambiguously identify the acoustic localisation in the presence of viscosity. Within the localisation region, the phenomenon of phase transition persists, and a remarkable decrease in the fluctuation of the oscillation phases of bubbles is observed. The localisation phenomenon will be impaired by the enhancement of the viscosity factors, and the extent to which the acoustic wave is localised may be determined by appropriately analyzing the values of the oscillation phases or the amount of reduction of the phase fluctuation. The results are particularly significant for the practical experiments in an attempt to observe the acoustic localisation in such a medium, which is in general subjected to the interference of the great ambiguity resulting from the effect of acoustic absorption.

基于Altair Flux仿真的中压空气开关柜绝缘故障分析及优化

中压空气绝缘开关柜是电力系统中重要的电气设备,具有使用量多、分布广的特点,其稳定运行能力直接影响电力系统的安全可靠性及电网的正常供电。良好的绝缘性能对开关柜安全可靠地运行至关重要,文章以实际绝缘故障案例为研究对象,分析其绝缘故障产生的原因,利用AltairFlux仿真分析,提出了提高中压开关柜绝缘能力的改进优化措施及智能化预防方案,为今后开关柜设计提供一定的指导。

基于时间自动机的动力调度岗位培训仿真机理建模

针对大型风洞群中压空气系统存在调度机理复杂、岗位人员素质要求高、系统实操培训代价大等问题,实施基于时间自动机的动力调度岗位培训仿真机理建模。通过混杂系统理论提出适合大型风洞群中压空气调度的扩展时间自动机模型,基于先来先服务策略构建资源申请、机组工作等队列,建立调度器、就地执行器等核心机理模型,并采用UPPAAL工具对模型进行验证。结果表明:该模型的建立不仅为岗位人员掌握设备结构原理、积累实操经验提供有效手段,而且为建立风洞试验调度仿真系统、合理有效实施风洞动力调度岗位培训打下了基础。

跨介质航行器动力学前沿技术研究进展

近年来跨介质装备受到船舶与海洋、航空航天以及兵器等领域的高度重视,与跨介质航行器相关的总体方案、关键技术、研究方法以及使用效能等成为研究热点。文章阐述了跨介质航行器动力学相关研究背景,综述了航行器入水砰击、出入水流固耦合、跨介质仿生、跨介质动力与推进、新质跨介质装备、跨介质动力学试验与仿真技术等方面的最新研究成果和研究进展,并展望了跨介质航行器发展需要解决的若干前沿关键技术,以期为促进海空界面动力学与无人系统研究提供借鉴。

基于超材料的水声通信综述

近年来,声学超材料作为一种新型人工复合材料,凭借其强大的声学参数调控能力突破传统材料功能极限,在水下探测、目标识别、成像、导航和通信等领域展现出了广阔的应用前景。文章综述了利用超材料实现水声通信的研究进展,主要包括基于声轨道角动量的多路复用通信、基于声学超表面的波束操控实现的特定发射和接收端间的水声通信,以及水-空跨介质声通信,总结了其所涉及的关键技术,并对当前基于超材料的水声通信所面临的挑战和前景进行了展望。

超声波燃气表燃气-空气关系计量特性研究

作为新型电子式计量器具,超声波燃气表具有宽量程、无机械传动结构、灵敏度高等特点。燃气表的计量特性评价一般采用空气介质。因此,空气介质和燃气介质下计量性能的一致性至关重要。采用扩展不确定度U=0.25%(k=2)的活塞式实气流量标准装置,分别对流量范围为0.04~6m~3/h和0.025~4m~3/h的1.5级超声波燃气表的燃气-空气关系性能进行试验。试验结果表明:1~#、2~#、3~#G4超声波燃气表在流量点q_(min)的燃气-空气平均误差偏移相对较大,而4~#、5~#、6~#G2.5超声波燃气表在各流量点的误差发生普遍偏移。这分别是由零点漂移和错波现象引起的。因此,在超声波燃气表的检验检测和计量性能评价试验中建议增加燃气-空气关系项目。试验结果可为国内超声波燃气表的技术研发和检定方法改进等提供重要的数据参考。

基于粉管动压和煤粉分配的热态条件下中速磨煤机入口风量标定试验方法

针对中速磨煤机输运介质特点及入口管路、空间等限制,冷态纯空气条件下的测试方法无法保证磨煤机入口风量标定测试及时性的问题,热态运行工况下,选取流场稳定的磨煤机出口管道,采用等截面网格法测试各粉管动压和煤粉分配特性,并用循环迭代法获取风粉混合物流速,最终以实测的磨煤机出口风粉混合物流量与煤量、设计密封风量的差值对磨煤机入口风量进行标定。试验结果表明,在相同的实测原始数据基础上,采用上述方法获取的磨煤机入口流量更接近真实值,准确性较采用冷态纯空气条件下的计算结果提升约15百分点。该方法测试简单,实操性强,可有效提升中速磨煤机入口风量标定结果的准确性和及时性,同时,对相似工业环境中含粉气流流量的测试也有一定的指导作用。

分离器转速对中速磨煤机风粉分配的影响

针对磨煤机内部流场复杂且不均匀的问题,通过建立完整的中速磨煤机模型,采用CFD软件求解磨煤机内部流动方程,利用DPM迭代获取颗粒流动参数,探究了不同动态分离器转速下中速磨煤机内部流动情况和出口风粉分配特性。研究结果表明:一次风在磨煤机出口4根出粉管处分配特性较好且与试验结果相吻合;煤粉粒径较小时,4根出粉管的煤粉质量流量偏差较小,且随动态分离器转速提高变化不明显;随着粒径的增加,煤粉颗粒运动轨迹呈现为贴壁运动,4根出粉管的煤粉质量流量偏差逐渐增大;同时对于大粒径煤粉颗粒,随着动态分离器转速提高,4根出粉管煤粉质量流量偏差逐渐降低。

基于200 MW等级压缩空气储能系统中温与高温储热路线技术经济对比

压缩空气储能技术由于其规模大、效率高、环境友好等特点受到广泛关注,其中非补燃式压缩空气储能技术成熟,在运行过程中没有碳排放产生,国内已有多座非补燃式绝热压缩空气储能电站投运、在建和在规划中。然而,目前压缩空气储能系统的设计参数尚未形成统一的标准化体系,使得压缩空气储能在系统设计和性能优化面临诸多挑战。为此,对200 MW等级的压缩空气储能系统进行中温、高温储热系统方案设计,确定了关键设备参数与系统边界条件,并对中、高温储热系统方案进行了性能以及技术经济性分析对比。结果表明:高温储热系统在性能指标上优于中温储热系统,但在投资成本上高于中温储热系统。这表明在选择大容量压缩空气储能系统的储热技术路线时,需要根据具体应用场景和经济预算综合考虑。

低气压试验线缆密封方法研究及应用

飞机线束被誉为飞机的“神经系统”,担负着全机输配电功能和信号传输功能,随着发展,线缆和连接器越来越复杂且数量繁多,每一独立的系统设备都有一套复杂的线缆和冷却管等组成,冷却部分可能包含冷却通风管道、通油管道和液氮管道等。在进行低气压试验时,这类线缆经由低气压试验箱的引线孔伸延出箱外,需要进行密封处理才能使箱内达到要求的低气压环境。本文通过分析低气压漏气的原因,对不同的线缆和管道进行预处理和采取不同的密封方法和密封介质进行密封,并进行总结。

基于不同烹饪介质的空气炸锅对豇豆及其维生素C的影响

在普通空气炸锅上新增喷洒水雾的直流泵和喷洒油雾的电磁泵,研发一款具有双喷功能的空气炸锅。通过不同烹饪介质烹饪豇豆,采用荧光法测定烹饪完成后豇豆的维生素C含量,从而客观分析以水为介质的空炸或以油为介质的空炸或只有空气为介质的空炸对豇豆烹饪效果及其维生素C的影响,以验证双喷功能设计的可行性和有效性。豇豆在以水/油为介质的空炸条件下烹饪效果较好,且维生素C的含量和保留率均较高,其含量分别为(5.19±0.122)mg/100 g和(5.04±0.097)mg/100 g,其保留率分别为29.34%±1.513%和28.38%±0.985%,而只有空气介质的空炸条件下烹饪后的豇豆效果较差,且维生素C含量仅为(3.33±0.118)mg/100 g,保留率仅为17.75%±0.992%,这与水、油在烹饪过程中和食物发生理化作用密切相关。

空气/氮气温控介质在轮胎热机械性能测试中的探讨研究

DMA+1000动态力学分析仪广泛应用于热塑性与热固性塑料、橡胶等领域,主要用来测量黏弹性材料的力学性能与时间、温度或频率之间的关系,从而获得材料结构与分子运动的信息。测试模式主要有温度扫描、应力/应变扫描、蠕变/松弛扫描等模式,本项目首先在温度扫描的模式下,测试温度范围-40~70℃,最大力10 N,频率10 Hz,升温速率:2℃/min,静应变7%,动态应变0.25%,通过在室温(T_(0))以上把温控介质由液氮转换为空气,研究更换介质对0℃时的tanδ值、胶料的玻璃化转变温度Tg值以及60℃时的tanδ值尤其是60℃时的tanδ值的影响,研究得出更换介质对这三个值的影响范围均在统计学误差允许范围之内。另外,对介质切换的切换温度进行研究分析,通过对在T=T_(0)+3,T=T_(0)+5,T=T_(0)+8,T=T_(0)+10四个温度下进行空气切换研究得出在T=T_(0)+8进行空气的切换得出的试验曲线稳定性较好。

300 MW中温绝热压缩空气储能设计研究

近年来,绝热压缩空气储能技术引起了广泛关注。为了对绝热压缩空气储能进行设计,需要对其技术方案及技术参数进行研究。首先提出压缩空气储能系统的计算模型,并对模型进行对比验证。然后,以岩石硐库储气库的300 MW中温绝热压缩空气储能系统为例,比选得到透平机入口压力17 MPa、压力波动范围6 MPa为最优方案;并根据运行参数的计算,得到300 MW中温绝热压缩空气储能的设计方案。提出的建模过程及分析方法可以用于绝热压缩空气储能项目的设计。