Characterization of the gas pulse frequency,amplitude and velocity in non-steady dense phase pneumatic conveying of powders

Current modelling techniques for the prediction of conveying line pressure drop in low velocity dense phase pneumatic conveying are largely based on steady state analyses. Work in this area has been on-going for many years with only marginal improvements in the accuracy of prediction being achieved. Experimental and theoretical investigations undertaken by the authors suggest that the flow mechanisms involved in dense phase conveying are dominated by transient effects rather than those of steady state and are possibly the principal reasons for the limited improvement in accuracy. This paper reports on investigations on the pressure fluctuation behaviour in dense phase pneumatic conveying of powders. The pressure behaviour of the gas flow in the top section of the pipeline was found to exhibit pulsatile oscillations. In particular, the pulse velocity showed variation in magnitude while the frequency of the oscillations rarely exceeded 5 Hz. A wavelet analysis using the Daubechie 4 wavelet found that the amplitude of the oscillations increased along the pipeline. Furthermore, there was significant variation in gas pulse amplitude for different types of particulate material.

Experimental study of the blockage boundary for dense-phase pneumatic conveying of powders through a horizontal slit

The estimation of the blockage boundary for pneumatic conveying through a slit is of significant importance. In this paper, we investigate the characteristics for blockage of powder （48 gLm average diameter） through a horizontal slit （1.6 m × 0.05 m × 0.002 m）. The results show that the required critical solid mass flow rate increases as the superficial air velocity increases superficial air velocity. The solid loading ratio and superficial air velocity displayed a decreasing power law relationship. This finding agrees with existing theory and experimental results. However, a minimum inlet solid loading ratio exists. When the air velocity is greater than the corresponding air velocity of the minimum solid loading ratio, the solid loading ratio exhibits an increasing trend in power law. We also found that when the inlet conveying pressure increased, the critical solid mass flow rate required for blockage, the inlet solid loading ratio, and the minimum inlet solid loading ratio increased.

An assessment of steady-state conditions in single slug horizontal pneumatic conveying

This study used a 3D coupled CFD–DEM model to assess how slugs tend towards steady state in single slug horizontal pneumatic conveying.Initial slug length,inlet velocity and initial stationary layer fractions were systematically varied for a total of 72 simulations.Previously made observation that slugs tend towards a steady state was confirmed via a theoretical derivation.The derivation shows that slugs move towards their steady state lengths exponentially.This allowed for a calculation of a characteristic time scale which is a measure of how quickly a slug tends towards the steady state.The theoretical estimate which is a function of slug porosity,steady length,velocity and stationary layer fraction has good agreement with simulated results.A link between steady slug length and solids loading ratio was also shown.

Predicting the mode of flow in pneumatic conveying systems—A review

An initial prediction of the particulate mode of flow in pneumatic conveying systems is beneficial as this knowledge can provide clearer direction to the pneumatic conveying design process. There are three general categories of modes of flow, two dense flows： fluidised dense phase and plug flow, and dilute phase oniy. Detailed in this paper is a review of the commonly used and available techniques for predicting mode of flow. Two types of predictive charts were defined： basic particle parameter based （e.g. particle size and density） and air-particle parameter based （e.g. permeability and de-aeration）. The basic particle techniques were found to have strong and weak areas of predictive ability, on the basis of a comparison with data from materials with known mode of flow capability. It was found that there was only slight improvement in predictive ability when the particle density was replaced by loose-poured bulk density in the basic parameter techniques. The air-particle-parameter-based techniques also showed well-defined regions for mode of flow prediction though the data set used was smaller than that for the basic techniques. Also, it was found to be difficult to utilise de-aeration values from different researchers and subsequently, an air-particle-based technique was developed which does not require any de-aeration parameter in its assessment.

Energy loss at bends in the pneumatic conveying of fly ash

An accurate estimation of the total pressure drop of a pipeline is important to the reliable design of a pneumatic conveying system. The present paper presents results from an investigation into the modelling of the pressure drop at a bend in the pneumatic conveying of fly ash. Seven existing bend models were used （in conjunction with solids friction models for horizontal and vertical straight pipes, and initial acceleration losses） to predict the total pipeline pressure drop in conveying fly ash （median particle diameter： 30 }zm; particle density： 2300 kg/m^3; loose-poured bulk density： 700 kg/m3） in three test rigs （pipelines with dimensions of 69 mm inner diameter （I.D.） × 168 m length; 105 mm I.D. × 168 m length; 69 mm I.D. × 554 m length）. A comparison of the pneumatic conveying characteristics （PCC） predicted using the seven bend models and experimental results shows that the predicted total pipeline PCC and trends depend on the choice of bend model. While some models predict trends that agree with the experimental results, other models predicted greater bend pressure drops for the dense phase of fly ash than for the dilute phase. Models of Pan, R. （1992）. Improving scale-up procedures for the design of pneumatic conveying systems. Doctoral dissertation, University of Wollongong, Australia, Pan, R., ＆ Wypych, P.W. （1998）. Dilute and dense phase pneumatic conveying of fly ash. In Proceedings of the sixth International Conference on Bulk Materials Storage and Transportation （pp. 183-189）, Wollongong, NSW, Australia and Chambers, A.J., ＆ Marcus, R.D. （1986）. Pneumatic conveying calculations. In Proceedings of the second International Conference on Bulk Materials Storage and Transportation （pp. 49-52）, Wollongong, Australia reliably predicted the bend losses for systems conveying fly ash over a large range of air flows.

高压密相气力输送固相流量的实验与GRNN网络预测

煤粉高压密相气力输送是气流床加压气化的关键技术之一。在输送压力可达3.7MPa,管路固气比可达660kg/m3的气力输送实验台上进行系统的研究,考察输送压力、输送差压、流化风量、充压风量、补充风量、煤粉含水率等条件对固相质量流量的影响。结果表明:固相流量随着输送差压的增大而增大;随着流化风量的增大而先增大后趋向于某一定值;注入风量一定时,随着充压风量的增大而先减小后增大;与补充风量的大小基本无关;随着煤粉含水率的增大而减小。同时建立广义回归神经网络(GRNN)对固相流量进行了有效预测,最大预测误差在2.3%以内。上述工作将为系统的控制和运行提供一定的指导,同时为深化高压密相气力输送的研究奠定基础。

高炉煤气全干法除尘灰的输送工艺分析

介绍了高炉煤气全干法除尘灰的三种输送工艺,并从投资、能耗、环保等方面进行了综合比较分析,得出了采用浓相气力输送工艺目前最为合理、经济、环保。

密相气力输送水平料栓作用力分析

密相气力输送技术已成为输送固体物料的新途径,其一个重要指标就是输送系统的稳定性,输送过程是否稳定主要看输送管道的振动。要想使输送系统更加稳定,必须对密相输送过程进行分析,找到管线振动的来源,从而控制好输送过程中的参数,进而解决管道振动的问题。

长距离正压浓相气力输送水泥粉体的能耗分析

在1∶1的240m管长的气力输送系统上,输送水泥粉体物料,以压缩空气作为输送动力,进行了浓相气力输送的试验研究。在试验基础上得出了固气质量比、输送压力、输送速度和管道布置形式等因素对浓相气力输送过程能耗的影响规律,并在此基础上给出了气力输送过程中降低能耗的关键点,为浓相气力输送系统的能耗分析与系统设计提供了良好的指导。