Application of Electrical Capacitance Tomography to the Concentration Measurement in a Cyclone Dipleg

Accurate solid concentration measurement plays a key role in the process industry. Measurements analyzed offline can be used to estimate process efficiencies, to identify problems in a flow, and to validate computational models. Online measurements can be used for active control. Electrical capacitance tomography （ECT） is a unique measuring technique with great potential in multiphase flow measurement. Experimental studies are carried out on a solid concentration measurement in a cyclone separator dipleg, using ECT. In this experiment eight electrodes are selected for the ECT sensor that is placed on the straight tube of the dipleg. The fluctuating characteristics according to the screw feeder and the effect of the airflow rate from the top of the cyclone are analyzed. The feasibility andreliability of the method are verified by the experimental results.

The Physical Models of Cyclone Diplegs in Fluidized Beds

In most industrial fluidization units, two- or three-stage cyclone systems are used to clean the product gases. To return the solids to the bed, these cyclones are fitted with diplegs. By pass of gas from the bed through the dipleg is partially overcome by the back pressure build-up in the dipleg and by adding a trickle valve at the bottom of the dipleg. Diplegs of primary cyclones, operating at a high solid loading behave differently from diplegs of secondary and tertiary cyclones which operate at low solid loading. Both types have been investigated by pressure drop measurements, visual observation and by measurements of the air flow rate flowing up the riser. The primary dipleg was also studied using electrical capacitance tomography. The results are reported hereafter and will give a first indication towards the right design of the dipleg and the selection of the trickle valve. The influence of gas flow in the dipleg on the conversion in a catalytic fluidized bed reactor is found to be negligible.

Experimental analysis of pressure characteristics of catalyst powder flowing down a cyclone dipleg

An experiment was carried out for investigating pressure behavior of catalyst powders, with a Sauter mean diameter of 63.6 μm, flowing downward in a cyclone dipleg with 150 mm inner diameter and 9000 mm high. Time mean pressure and time series of pressure fluctua- tions were measured at different axial positions in the dipleg with particle mass fluxes ranging from 50.0 to 385.0 kg m-2s t. The experimental results showed that the time mean pressure in the dipleg increased progres- sively from the top section to the bottom section. The experimental phenomena displayed that the fluidization patterns in the dipleg can be divided into two types on the whole, namely the dilute-dense coexisting falling flow and the dense conveying flow along the dipleg. In the dilute- dense coexisting falling flow, the dilute phase region was composed of a length of swirling flow below the inlet of dipleg and a dilute falling flow above the dense bed level. With increasing particle mass flux, the dilute-dense coex- isting falling flow was gradually transformed to be the dense conveying flow, and the exit pressure of the dipleg increased considerably. The pressure fluctuations were closely related to the flnidization patterns inside the dipleg. In the dilute-dense coexisting falling flow, the pressure fluctuations in the dilute flow region originated from par- ticle clusters, propagating downward as a pressure wave; however, the pressure fluctuations in the dense flow region originated from rising gas bubbles, propagating upward. When the dense conveying flow was formed in the dipleg,the pressure fluctuations originated mainly from instability of the feed and the compressed gas, propagating down- ward. The standard deviation of the pressure fluctuations indicated that the intensity of pressure fluctuations first increased and then decreased with increasing particle flux.

Experimental study on the particle flow patterns in a cyclone dipleg with a trickle valve

An experimental apparatus including a dipleg and a trickle valve was established to simulate the operation of a suspended dipleg-trickle valve system of cyclone used in fluid catalytic cracking(FCC)unit.The flow regimes in the dipleg and the discharge modes in the trickle valve were studied by combining the observation of experimental phenomena with the analysis of transient pressure fluctuation.The results show that the flow regimes in the dipleg have two types-the dilute–dense phase coexisting falling flow and the dilute falling flow.Correspondingly,the trickle valve also has two discharge modes-the intermittent periodic dumping discharge and the continuous trickling discharge.The power spectrum density of pressure fluctuation displays that the gas–solids flow in the dipleg-trickle valve system is characterized by a low-frequency pulsation.The coherence coefficient explains the origin and propagation of pressure fluctuation in the system.Eventually,a map describing the flow regimes and discharge modes related to the operation parameters was proposed,which can provide a helpful guidance for the operation of cyclone dipleg-trickle valve system in FCC unit.

Concentration and angular velocity measurement in a cyclone separator dipleg using electrical capacitance tomography

Cyclone separator is one of the main parts of the circulating fluidized bed (CFB) boiler. The separation efficiency of the cyclone separator is very important to the whole boiler. Electrical capacitance tomography (ECT) is a unique measuring technique with great potential in multiphase flow measurement. Experimental studies are carried out on the measurement of volumetric concentration and angular velocity using ECT. The former is determined through image reconstruction method, and the latter is measured by cross-correlating the capacitance fluctuations caused by the conveyed solids. The distribution of void fraction in radial direction, the fluctuating characteristics, probability density function and the spectrum characteristics are analyzed. The feasibility and reliability of the method are verified by experimental results.

催化裂化装置沉降器跑剂原因分析及对策

对某炼油厂1.7 Mt/a催化裂化装置催化剂藏量和沉降器二级旋风分离器(顶旋)压力降快速下降及油浆固体含量快速上升等问题的原因进行了分析,并提出了解决措施。受台风过境的影响,该装置操作发生了波动,总催化剂藏量突然开始下降,沉降器顶旋压力降由正常的10.19 kPa降至8.98 kPa,油浆固体含量(油浆中固体颗粒的质量浓度)由正常的2~3 g/L增至28.41 g/L,最高上升至92.38 g/L。停工检查发现,顶旋的6个翼阀中有4个翼阀阀板被焦块卡住,翼阀不能正常开启和关闭,导致料腿堵塞不能排料,发生催化剂大量跑损的故障。经分析判断,堵塞料腿和翼阀的焦块是顶旋升气管外壁脱落的焦块。分析这些焦块产生的原理:重组分油气液滴沉积在器壁表面,发生脱氢缩合反应形成焦,后与催化剂颗粒结合逐渐增大、增厚。综合分析各种防焦措施,采用防焦导流片技术解决了顶旋升气管外壁结焦脱落的问题,保障了装置的长周期运行。

负压差立管内气固流动的不稳定性实验分析

负压差立管内气固两相流具有流动的不稳定性,比较典型的是颗粒流量的不稳定性. 实验表明这种不稳定性主要有两种形式,一种是流量偏移,流量从一个值逐渐或突然转变为另一个值,这种现象一般发生在立管的入口或出口,是颗粒失流化架桥产生的;另一种是流量振荡,流量在一定的范围内发生波动变化,即低频脉动流动,这是颗粒逆压力梯度流动压缩气体造成的. 负压差立管气固流动的不稳定性对工艺过程的运行具有潜在的危害性.

负压差立管内气固两相流的流态特性及分析

对于出口插入密相床的立管,管内气固两相的流动特点是下行的颗粒速度大于气体速度和颗粒的逆压差流动,颗粒下行是一个减速运动过程. 管内的气固两相流的流态有两种形式,当Gs<Gsc时,流态是稀密两相流态,气流上行;当Gs>Gsc时,流态是浓相输送流态,气流下行. 两种流态可以互相转变,主要取决于颗粒质量流率的大小. 负压差立管的流态变化与气固两相之间滑落速度和轴向压力的变化密切相关,滑落速度随颗粒质量流率的增加逐渐减小,而轴向压力则逐渐增大以平衡立管的负压差.

双级料腿循环流化床中颗粒停留时间分布的研究

双级料腿循环流化床垃圾焚烧炉采用分级转化技术,燃烧前脱氯,有效解决了高温腐蚀和二噁英造成的二次污染。该文采用不同的大颗粒物料来模拟垃圾中的不同组分,在双料腿循环流化床试验台中研究了颗粒的停留时间分布。结果表明,影响大颗粒停留时间的主要因素是循环流 率、表观流化气速、颗粒的密度和尺寸。循环流率增大,停留时间急剧降低。表观气速对停留时间影响较小。颗粒密度对停留时间的影响比尺寸要大。颗粒越轻,停留时间越短。根据实验结果,建立了两并联全混釜停留时间分布模型,模型计算结果与实验结果吻合较好。

肌电生物反馈综合治疗促进痉挛性双瘫型脑瘫患儿下肢运动功能的疗效观察

目的:观察神经康复重建疗法治疗痉挛性双瘫型脑瘫患儿下肢运动功能障碍的疗效。方法:24例痉挛性双瘫型脑瘫患儿随机分为治疗组和对照组,每组12例,所有患儿均接受Bobath技术、推拿、脑循环治疗。治疗组在以上基础上应用WOND2000F2型神经康复重建仪,对双下肢进行肌电触发的生物反馈刺激。在疗程开始与结束时,用改良的Ashworth量表测定患儿腓肠肌肌张力的变化、用关节量角器测量踝关节被动活动的角度变化,采用粗大运动功能测量量表(GMFM)中D和E功能区进行站立与步行功能评定。结果:治疗后,两组患儿的观察指标均有不同程度改善(P<0.01—0.001),但治疗组疗效优于对照组(P<0.05—0.01)。结论:神经康复重建治疗能降低痉挛性双瘫型脑瘫患儿的下肢肌张力,增加胫前肌肌力和踝关节活动度,明显提高下肢运动功能。

基于电容成像的料腿内气固两相流浓度测量

旋风分离器是循环流化床锅炉的主要组成部分,其分离效率是影响整个锅炉的重要因素之一。采用电容层析成像技术(ECT),对旋风分离器料腿中的固体颗粒体积浓度进行测量。这种测试方法的优点在于不破坏原有系统的运行特性,属于非侵入式、在线的快速测试技术。电容传感器均匀布置在分离器料腿直管上,电极数目为8。改变螺杆给料速度以及抽吸风量可改变给料浓度,通过对管道截面体积浓度、波动特性以及体积浓度平均测量结果的比较分析,证明这种方法可获得可靠的测量结果。

电容层析技术在旋风分离器及料腿中固体颗粒浓度、速度和流量测试中的应用

采用先进的电容层析成像技术和相关分析理论,对常温下旋风分离器及料腿中固体颗粒的浓度、速度和流量进行测试研究。浓度分布采用单层电容传感器,速度分布采用双层电容传感器得出相关流动信号,利用相关理论分析得出速度和流量。这种测试方法的优点在于不破坏原有实验系统的运行特性,属于非侵入式、在线的快速测试技术,能同时得出固体的断面浓度分布和流量。实验结果与称重计量测试结果吻合良好,说明电容相关技术测量流量的可行性和可靠性。

单回路循环流化床的压力平衡研究

为保证流化床装置正常运行,循环回路必须有一个适宜的压力平衡关系。在Φ800 mm×12 000 mm流化床装置上,用多点压力测量仪对固体颗粒单循环回路各部分的压力分布进行了实验研究。结果表明,颗粒单循环回路的压力平衡与装置的运行状态、颗粒的循环量密切相关。整个颗粒的循环回路压力曲线呈“8”字形分布,上部流化器内的压力高于料腿内的压力,下部流化器内的压力低于料腿内的压力。流化速度增大可使颗粒的循环量增加。流化器和料腿内空隙率沿高度的变化趋势是上部大下部小。循环回路的压力分布取决于流化器和旋风管的性质。

双级料腿循环流化床压力平衡分布的研究

该文在双级料腿循环流化床冷态实验装置中测定了不同工况下的压力平衡分布 ,详细分析了各种运行工况对压力平衡分布的影响。实验结果表明 :双级料腿循环流化床压力平衡主要依靠第二级循环料腿中物料的停留量来维持。调节压力平衡的关键是第二级循环料腿中脱氯床 (包括布风板和床层 )的阻力。通过压力平衡计算得到了脱氯床阻力的计算公式。

FCCU单级旋风分离器料腿的负压差和蓄压计算方法

催化裂化装置旋风分离器的料腿排料是一个负压差排料过程。由于对料腿有锁气排料和防止吹通的要求,料腿出口通常安装翼阀或插入密相床层,在料腿内部需要堆积一个料柱形成蓄压去平衡负压差。负压差是料腿出口外部同一水平面位置的床层压力与旋风分离器下部料腿入口处的压力之差。而蓄压是料腿内部上下两端(进出口位置)之间气固两相混合物的压力差。针对单级旋风分离系统料腿物料的流体力学状态进行分析,提出了负压差和蓄压的计算方法,指出料腿的排料条件是内部的蓄压大于其外部的负压差。某沉降器顶旋料腿悬挂在稀相床层中,该料腿内直径为200 mm,催化剂颗粒密度为1 500 kg/m3,料腿内密相段空隙率为76%,旋风分离器压力降(约等于料腿外部的负压差)5.6 k Pa,翼阀排料压力降0.35 k Pa,可计算出料腿内刚好形成排料能力的密相料柱的高度为1.685 m。

催化裂化装置旋风分离器料腿翼阀系统排料流态的实验分析

针对催化裂化装置旋风分离器料腿翼阀系统的排料过程,在150mm×5000mm料腿冷模实验装置中悬空安装翼阀,在颗粒质量流率0-50kg/（m^2·s）、负压差0-11kPa范围内进行系统的排料实验,考察负压差和颗粒质量流率对排料过程的影响。结果表明,料腿翼阀系统的排料流态有连续式滴流状排料和间歇周期性节涌状排料2种形式。负压差小、颗粒质量流率大,排料流态趋于连续式滴流排料;负压差大、颗粒质量流率小,排料流态趋于间歇式周期性排料。2种排料流态随负压差和颗粒质量流率的变化可以互相转换。根据实验数据还提出了旋风分离器料腿翼阀系统的排料相图。

细颗粒循环料腿的自力平衡原理及实验研究

本文介绍了一种固体细颗粒循环料腿的自力平衡结构模型（单气路式）及其工作原理，对该结构模型进行了流体力学分析，并分析了各种因素对自力平衡效果的影响趋势。在冷态模型装置上进行的实验测定验证了料腿的自平衡效果，并获得了与理论分析相一致的结论。由于该结构简单，无机械运动部件，并且易满足耐高温、耐高压及耐磨损等性能要求，特别是它能在较宽的工作范围内使料腿自力稳定，它的应用可望改善固体料循环控制的可操作性，从而对特定的工作系统有利。

FCCU串联旋风分离器料腿的负压差和蓄压计算方法

催化裂化装置旋风分离器的料腿排料是一个负压差排料过程,内部的颗粒需要从高处的低压区流向下部的高压区,此时需要借助于内部密相料柱的蓄压平衡外部的负压差保证排料。针对催化裂化装置再生器内两级串联旋风分离器料腿的不同安装结构形式,即第一级料腿插入密相床层,第二级料腿出口联接翼阀或插入密相床层或悬挂于稀相床层的情况,推导出了第一级料腿和第二级料腿的负压差和蓄压计算方法,并分析了形成排料的条件。计算分析表明,第一级料腿的负压差主要是第一级料腿插入密相床的深度压差和第一级旋风分离器的压力降之和,第二级料腿的负压差则主要为两级旋风分离器的压力降之和,第二级料腿的负压差大于第一级料腿的负压差。料腿的排料条件是料腿内部的蓄压大于等于其外部的负压差。

FCC沉降器粗旋风分离器的料腿泄气率

在粗旋冷态模型实验基础上,采用FLUENT 6.2流体力学计算软件对FCC沉降器粗旋内部的两相流动进行数值模拟,针对稀、密相流动分别采用颗粒随机轨道模型和双流体模型,探讨了气速、气体物性和固相颗粒浓度对FCC沉降器粗旋料腿泄气率的影响规律。结果表明,气速和固相颗粒浓度升高均导致粗旋料腿内外压差增大,料腿泄气率随之增大。随固相颗粒浓度增大,料腿泄气率上升的趋势先急后缓,与其固相颗粒浓度-压降关系相对应,料腿泄气率-固相颗粒浓度曲线和压降-固相颗粒浓度曲线显示的转折点质量浓度均为0.8 kg/m3;固相颗粒浓度对料腿泄气率的影响存在着2种作用机制,即下行颗粒群对气体的夹带作用和颗粒在粗旋内壁形成的不断增厚的灰层对气体实际流通横截面积的缩减作用。气体密度的增大会导致料腿泄气率增大;黏度增加在削弱气流的旋转能量的同时,增加了升气管短路流率,对料腿泄气率的增加具有正反两方面作用。综合操作参数、气体物性和结构尺寸等因素的影响,回归得到FCC沉降器粗旋料腿泄气率表达式。

旋风分离器料腿漏风对压降影响的实验分析

以直径300 mm的旋风分离器为实验对象,考察了在不同入口速度下料腿漏风量对旋风分离器压降的影响,并以此为基础,分析了某现场催化裂化装置旋风分离器压降出现的不稳定波动现象。实验结果表明,旋风分离器下部料腿是一个负压差立管,外部的压力大于料腿内的压力,易产生漏风,从而导致旋风分离器的压降降低。旋风分离器的压降随漏风量增大而降低,入口速度越低漏风量影响的作用就越明显。该旋风分离器的压降波动是由于不稳定的翼阀排料产生的漏风变化造成的。