共查询到18条相似文献,搜索用时 93 毫秒
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正压浓相气力输送系统是目前国内火电厂应用最为广泛的气力输送系统,该系统对运行的控制流程要求高、逻辑性强;其关键输送技术指标均采用模拟量进行检测,并实时控制.本文介绍的恒压输送系统,除了以上特点外,其独具的输送压力的动态实时调控功能,更是对控制系统提出更高的要求;阐述了DCS用于正压浓相恒压输送系统的典型设计. 相似文献
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张美玲 《中国新技术新产品》2010,(5):11-12
以聚丙烯酰胺为研究对象,在自行设计气力输送系统上,结合量纲和谐理论,分析了水平管段沿程阻力系数的影响因素,及各影响因素之间的关系。结果表明:在水平管段中,利用量纲和谐原理得到的规律与试验过程中直接观察到的试验现象吻合,证明量纲和谐原理可以应用于聚丙烯酰胺在水平管道中流动及阻力特性试验研究中。在聚丙烯酰胺水平管段浓相输送中,影响沿程阻力系数的各参数的指数与物料的质量流量存在线性关系,这个结论为今后聚丙烯酰胺的气力输送提供了有力的理论依据。 相似文献
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分析了炭黑在气力输送过程中的破碎机理。通过实验,介绍了气力输送系统中炭黑的种类和炭黑的物性对炭黑的破碎的影响,指出气力输送系统的输送管路长度和布置以及输送参数如输送压力和输送速度等的变化直接影响着炭黑的破碎率的大小。为更好地解决炭黑在气力输送中存在的问题,优化炭黑气力输送系统的设计提供了依据。 相似文献
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分析了炭黑在气力输送过程中的破碎机理.通过实验.介绍了气力输送系统中炭黑的种类和炭黑的物性对炭黑的破碎的影响.指出气力输送系统的输送管路长度和布置以及输送参数如输送压力和输送速度等的变化直接影响着炭黑的破碎率的大小.为更好地解决炭黑在气力输送中存在的问题,优化炭黑气力输送系统的设计提供了依据. 相似文献
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Pneumatic conveying is widely used for transporting bulk solids in chemical, process and agricultural industries. It is environmentally friendly, flexible and can be fully automated. But it can also involve high power consumption, wear, abrasion, blockage and particle degradation. Hence understanding the physics can help to optimise design and operation. Conveying in a horizontal pipe involves complex multiphase flows, potentially with lean and dense phase regions, stationary particles and blockage.The Distinct Element Method (DEM) is a powerful tool to study granular dynamics. It models interactions at the particle level and reproduces the assembly physics. This paper presents a 3D DEM model to predict pressure drop, flowrate and flow patterns in pneumatic conveying. The inter-particle forces are modelled using the spring-dashpot-slider analogy. A novel gas flow model is developed. The pipe is divided into sections. In each section a lean and dense region is determined on a voidage criterion based on particle positions. Given the pressure at the boundaries, the fluid flow is determined assuming steady state conditions. This uses the Ergun equation for the flow through the dense phase and the equations of Wen and Yu for modified single spheres and wall resistance for the lean phase. It uses an iterative algorithm adjusting the fluid flowrate so that the pressure in each section is the same in the dense phase and lean phase and maintaining the boundary pressures. Once the fluid flow profile has been calculated the fluid drag on each particle can be determined. The results compare well with experimental data relating pressure gradient and solid and gas flowrates from Molerus (1993), Molerus (1996). Flow patterns for all the flow regimes, fully suspended flow, strand flow, slug flow, and conveying over stationary layer are observed. 相似文献
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密相气力输送系统中几种气量控制方式的比较 总被引:1,自引:0,他引:1
从调压范围、压力特性和流量特性方面介绍了减压阀的主要性能,讨论了气力输送交流中减压阀的选择和调节,分析了密相气力输送系统中各种气量控制方法,对其各自的优缺点进行了详细讨论,重点分析减压阀及减压阀与拉法尔联合气量控制系统的优、缺点,表明可调式拉法尔管是今后气力输送气量控制发展的方向。 相似文献
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射流管在气力输送中的应用 总被引:2,自引:0,他引:2
对物料气力输送的各种供料方式的性能、特点和使用场合进行了比较 ,重点讨论了传统文丘里供料器实际应用中存在的问题 ,介绍了几种国内外新型的文丘里供料器结构及其特点和用途。指出采用组合式供料器 ,即将文丘里供料器与机械旋转式连续供料器进行组合使用 ,可以同时改善它们两者单独使用时存在的问题。文中介绍了LAVAL管密相输送气量控制方面的应用 ,指出LAVAL管在气力输送中主要起稳定空气流量和压力的作用 ,使输送过程稳定、均匀 ,并简要介绍了气力输送系统的设计方法和步骤 相似文献
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Pneumatic conveying of bulk materials has become an important technology in many industries: from pharmaceuticals to petro-chemicals
and power generation. Particulate segregation has been investigated in many solids handling processes. However, little work
has been published on the segregation and mixing in pneumatic conveying pipelines, particularly in dense phase pneumatic conveying.
Due to the character of dense phase flow, it is difficult to investigate the segregation in a flowing plug. A sampling device
was designed and built to take samples from the pneumatic conveying pipeline after “catching a plug”. Several experiments
were conducted over a range of gas–solids flow conditions with 3 mm nylon pellets and 3 mm ballotini as a segregating mixture.
Experimental data combined with video footage were analysed to describe the segregation and mixing of solids plugs in pipes.
This investigation provides initial research on establishing a segregation index in a flowing plug. A gas–solids two-dimensional
mathematical model was developed for plug flow of a nylon-glass particulate mixture in a horizontal pipeline in dense phase
pneumatic conveying. The model was developed based on the discrete element method (DEM). The model was used to simulate the
motion of particles both in a homogeneous flow and as binary mixtures taking into account the various interactions between
gas, particles and pipe wall. For the gas phase, the Navier Stokes equations were integrated by the semi-implicit method for
pressure-linked equations (SIMPLE) using the scheme of Patankar employing the staggered grid system. For the particle motion
the Newtonian equations of motion of individual particles were integrated, where repulsive and damping forces for particle
collision, the gravity force, and the drag force were taken into account. For particle contact, a model with a simple non-linear
spring and dash pot model for both normal and tangential components was used. This model employed a mixture of 3 mm pellets
and ballotini as virtual materials with properties of nylon and glass. The results from the model are discussed and compared
with experimental work and show qualitative agreement. Further modelling and experimental work in key areas is proposed. 相似文献
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David Mills 《Granular Matter》2004,6(2-3):173-177
For fine powdered materials, capable of being conveyed in dense phase, a conveying region exists in which instability in flow and pipeline blockage can occur if the pressure gradient available is insufficient to maintain a minimum value of solids loading ratio. A reduction in material flow rate can also lead to pipeline blockage in this region. Conveying trials under-taken with cement are used to illustrate the nature of the problem. 相似文献
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Hui Li 《Particulate Science and Technology》2000,18(3):187-198
In order to prevent flow blockage phenomenon and to reduce the impact of particles on the wall of the bend, an experimental study of the swirling flow pneumatic conveying system with a horizontal curved pipe was carried out in this work. The experiment was performed in a 90-deg pipe bend with pipe diameter 75 mm and centerline curvature ratio 12. The straight pipes with 75 mm inside diameter at the upstream and downstream of the bend were 1.3 m and 4.0 m in lengths, respectively. The initial swirl number was varied from 0.22 to 0.60, the mean air velocity from 10 to 20 m/s, and the solid mass flow rate from 0.07 to 0.68 kg/s. It is found that in the lower air velocity range, the overall pressure drop of the swirling flow pneumatic conveying shows a lower tendency than that of axial flow pneumatic conveying. The minimum air velocities can be decreased by using the swirling flow pneumatic conveying. From the visualization of particle flow patterns, the impact of particles on the wall of the bend can be reduced using the swirling flow. 相似文献
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HUI LI 《Particulate Science and Technology》2013,31(3):187-198
ABSTRACT In order to prevent flow blockage phenomenon and to reduce the impact of particles on the wall of the bend, an experimental study of the swirling flow pneumatic conveying system with a horizontal curved pipe was carried out in this work. The experiment was performed in a 90-deg pipe bend with pipe diameter 75 mm and centerline curvature ratio 12. The straight pipes with 75 mm inside diameter at the upstream and downstream of the bend were 1.3 m and 4.0 m in lengths, respectively. The initial swirl number was varied from 0.22 to 0.60, the mean air velocity from 10 to 20 m/s, and the solid mass flow rate from 0.07 to 0.68 kg/s. It is found that in the lower air velocity range, the overall pressure drop of the swirling flow pneumatic conveying shows a lower tendency than that of axial flow pneumatic conveying. The minimum air velocities can be decreased by using the swirling flow pneumatic conveying. From the visualization of particle flow patterns, the impact of particles on the wall of the bend can be reduced using the swirling flow. 相似文献