A Novel Method for Determining the Void Fraction in Gas-Liquid Multi-Phase Systems Using a Dynamic Conductivity Probe

Conventional conductivity methods for measuring the void fraction in gas-liquid multiphase systems are typically affected by accuracy problems due to the presence of fluid flow and salinity.This study presents a novel approach for determining the void fraction based on a reciprocating dynamic conductivity probe used to measure the liquid film thickness under forced annular-flow conditions.The measurement system comprises a cyclone,a conductivity probe,a probe reciprocating device,and a data acquisition and processing system.This method ensures that the flow pattern is adjusted to a forced annular flow,thereby minimizing the influence of complex and variable gas-liquid flow patterns on the measurement results;Moreover,it determines the liquid film thickness solely according to circuit connectivity rather than specific conductivity values,thereby mitigating the impact of salinity.The reliability of the measurement system is demonstrated through laboratory experiments.The experimental results indicate that,in a range of gas phase superficial velocities 5–20 m/s and liquid phase superficial velocities 0.079–0.48 m/s,the maximum measurement deviation for the void fraction is 4.23%.

A Model on the Void Fraction in Liquid Slugs for Vertical Slug Flow

Aim To develop a hydrodynamic model on the void fraction in liquid slugs for gas liquid slug flow in vertical tubes. Methods Developing the model by considering the gas exchange between the Taylor bubble and the following liquid slug. Results Some experimental data are obtained to check the model. In comparison with previous published results, the predictions from this model are better and in good agreement with the experimental data. The error is within ±20%. Conclusion The proposed model can correctly predict the void fraction in liquid slugs for gas liquid two phase slug flow in vertical tubes.

单溶剂抽提分离FCC油浆影响因素分析

以大庆催化裂化(FCC)油浆为原料,N,N-二甲基甲酰胺(DMF)为抽提溶剂,采用三因素三水平BBD(box-behnken design)正交试验设计,考察分析抽提温度、剂油比和抽提时间对抽提油收率及芳香烃质量分数的影响,得到抽提油收率和芳烃质量分数与影响因素间的多项式回归模型。响应面法分析表明,单溶剂抽提分离FCC,抽提温度和剂油比对抽提结果有明显影响,且两者对芳烃质量分数具有交互作用,而抽提时间对抽提结果的影响不显著。模型分析表明,DMF抽提分离油浆的最优操作条件为抽提温度61.3℃、剂油比3.3,抽提时间35 min,模型预测结果与重复性验证试验具有非常好的一致性。

Void Fraction Distributions in Cold-gassed and Hot-sparged Three Phase Stirred Tanks with Multi-impeller

Vertical distributions of void fraction in gas-liquid and gas-liquid-solid stirred tanks have been measured in a fully baffled dished base vessel of 0.48 m diameter, using a conductivity probe. The impeller configuration （a hollow half elliptical blade dispersing turbine below two up-pumping wide blade hydrofoils, identified as HEDT＋2WHu） recommended in previous work has been used in this work. The operating temperatures were 24℃ and 81℃, identified as cold and hot respectively. The effects of superficial gas velocity, agitator speed and the corresponding power input on the local void fraction in two-phase systems are .investigated and discussed. Results show thatth-e increasing of agitator speed or gas flow rate leads to an increase in local-void fraction at the majority of measurement points in both cold and hot systems. However, the unifo,rmity of gas dispersion does not always in crease as the raising of agitator speed and power input. In either cold or hot sparged conditions, the two- and three-phase systems.have similar vertical profiles for void fraction, with maxima in similar locations; however, the void fractions are significantly lower in hot sparging than with cold. In cold operation the presence of particles leads to a lower void fraction at most points, although the local void fractions increase a little with the addition of solid particles at high temperature, in good agreement with the global gas holdup results, and the possible reasons are discussed in this paper. This work can give a better understanding of the differences between cold-gassed and hot-sparged three phase＇stirred tanks.

Void Fraction Measurement in Oil-Gas Transportation Pipeline Using an Improved Electrical Capacitance Tomography System

To measure the void fraction online in oil-gas pipeline, an improved electrical capacitance tomography (ECT) system has been designed. The capacitance sensor with new structure has twelve internal electrodes and overcomes the influence of the pipe wall. The data collection system is improved by using high performance IC (integrated circuit). Static tests of bubble flow, stratified flow and annular flow regime are carried out. Measurements are taken on bubble flow, stratified flow and slug flow. Results show that the new ECT system performs well on void fraction measurement of bubble flow and stratified flow, but the error of measurement for slug flow is more than 10%.

An Investigation on the Void Fraction for upward Gas-Liquid Slug Flow in Vertical Pipe

In order to investigate the influence of the entrance effect on the spatial distribution of phases, the experiments on gas-liquid two-phase slug flow in a vertical pipe of 0.03m ID were carried out by using optical probes and an EKTAPRO 1000 high speed motion analyzer. It demonstrates that the radial profile of slug flow void fraction is parabolic. Influenced by the falling liquid film, the radial profile curve of liquid slug void fraction in the wake region is also parabolic. Since fully turbulent velocity distribution is built up in the developed region,the void fraction profile in this region is the saddle type. At given superficial liquid velocity, the liquid slug void fraction increases with gas velocity. The radial profiles of liquid slug void fraction at different axial locations are all saddle curves, but void fraction is obviously high around the centerline in the entrance region. The nearer the measuring station is from the entrance, the farther the peak location is away from the wall.

Investigation of oil-air two-phase mass flow rate measurement using Venturi and void fraction sensor

Oil-air two-phase flow measurement was investigated with a Venturi and void fraction meters in this work. This paper proposes a new flow rate measurement correlation in which the effect of the velocity ratio between gas and liquid was considered. With the pressure drop across the Venturi and the void fraction that was measured by electrical capacitance tomography apparatus, both mixture flow rate and oil flow rate could be obtained by the correlation. Experiments included bubble-, slug-, wave and annular flow with the void fraction ranging from 15% to 83%, the oil flow rate ranging from 0.97 kg/s to 1.78 kg/s, the gas flow rate ranging up to 0.018 kg/s and quality ranging nearly up to 2.0%. The root-mean-square errors of mixture mass flow rate and that of oil mass flow rate were less than 5%. Furthermore, coefficients of the correlation were modified based on flow regimes, with the results showing reduced root-mean-square errors.

Gamma-ray attenuation technique for measuring void fraction in horizontal gas-liquid two-phase flow

The measurement of void fraction is of importance to the oil industry and chemical industry. In this article, the principle and mathematical method of determining the void fraction of horizontal gas-liquid flow by using a sin- gle-energy γ-ray system is described. The γ-ray source is the radioactive isotope of 241Am with γ-ray energy of 59.5 keV. The time-averaged value of the void fraction in a 50.0-mm i.d. transparent horizontal pipeline is measured under various combinations of the liquid flow and gas flow. It is found that increasing the gas flow rate at a fixed liquid flow rate would increase the void fraction. Test data are compared with the predictions of the correlations and a good agreement is found. The result shows that the designed γ-ray system can be used for measuring the void fraction in a horizontal gas-liquid two-phase flow with high accuracy.

萘系化合物对FCC油浆富含芳烃馏分油制备的针状焦组成和结构的影响

以石蜡基催化裂化油浆的富含芳烃馏分油为原料,添加不同萘系单体化合物(萘、1-甲基萘、四氢萘、十氢萘),通过两段焦化法制备针状焦。采用元素分析、傅里叶变换红外光谱、族组成分析等方法考察了萘系单体化合物对针状焦组成和结构的影响。结果表明,尽管在体系中添加的是小分子芳烃物种,随着萘系化合物含量的不断增加,对于碳质中间相的形成有着一定的促进作用;带有烷基侧链的芳烃通过自由基反应和氢转移反应可以提高体系的炭化活性,能够有效增加产物的缩合度;同时,具有环烷结构的芳烃也可通过开环反应和氢转移反应改变体系的流变性,降低体系黏度,从而降低产物缩合度。

Void fraction measurement and calculation model of vertical upward co-current air-water slug flow

The focus of this paper is on the measurement and calculation model of void fraction for the vertical upward co-current air-water slug flow in a circular tube of 15 mm inner diameter. High-speed photography and optical probes were utilized, with water superficial velocity ranging from 0.089 to 0.65 m·s^(-1)and gas superficial velocity ranging from 0.049 to 0.65 m·s^(-1). A new void fraction model based on the local parameters was proposed, disposing the slug flow as a combination of Taylor bubbles and liquid slugs. In the Taylor bubble region, correction factors of liquid film thickness Cδand nose shape CZ*were proposed to calculate aTB. In the liquid slug region, the radial void fraction distribution profiles were obtained to calculate aLS, by employing the image processing technique based on supervised machine learning. Results showed that the void fraction proportion in Taylor bubbles occupied crucial contribution to the overall void fraction. Multiple types of void fraction predictive correlations were assessed using the present data. The performance of the Schmidt model was optimal, while some models for slug flow performed not outstanding. Additionally, a predictive correlation was correlated between the central local void fraction and the cross-sectional averaged void fraction, as a straightforward form of the void fraction calculation model. The predictive correlation showed a good agreement with the present experimental data, as well as the data of Olerni et al., indicating that the new model was effective and applicable under the slug flow conditions.

An Experimental Study on the Void Fraction for Gas-Liquid Two-Phase Flows in a Horizontal Pipe

The flow patterns and the void fraction related to a gas-liquid two-phase flow in a small channel are experimentally studied.The test channel is a transparent quartz glass circular channel with an inner diameter of 6.68 mm.The working fluids are air and water and their superficial velocities range from 0.014 to 8.127 m/s and from 0.0238 to 0.556 m/s,respectively.The void fraction is determined using the flow pattern images captured by a high-speed camera,while quick closing valves are used for verification.Four flow patterns are analyzed in experiments:slug flow,bubbly flow,annular flow and stratified flow.For intermittent flows(bubbly flow and slug flow),the cross-sectional void fraction is in a borderline condition while its probability distribution function(PDF)image displays a bimodal structure.For continuous flows(annular flow and stratified flow)the cross-sectional void fraction behaves as a fluctuating continuous curve while the(PDF)image displays a single peak structure.The volumetric void fraction data are also compared with available predictive formulas,and the results show that the agreement is very good.An effort is also provided to improve the so-called Gregory and Scott model using the available data.

Distribution of void fraction for gas-liquid slug flow in aninclined pipe

In order to investigate the effect of inclination angle on the spatial distribution of phases, experiments on gas-liquid two-phase slug flow in an inclined pipe were carried out by using the optical probe and an EKTAPRO 1000 high speed motion analyzer. It has been demonstrated that the inclination angle and the mixture velocity are important parameters to influence the distribution of void fraction for upward slug flow in the inclined pipe. At high mixture velocity, the gas phase profile is axial symmetry in the cross-section of the pipe. This is similar to that for vertical slug flow. In contrast, most of the gas phase is located near the upper pipe wall at low mixture velocity. By measuring the axial variation of void fraction along the liquid slug, it can be concluded that there is a high void fraction wake region with length of 3～4D in the front of liquid slug. In the fully developed zone of liquid slug, the peak value of the void fraction is near the upper wall.

A MINI－CAPACITANCE PROBE FOR MEASURING THE LOCAL VOID FRACTION IN GAS－SOLID FLUIDIZED BEDS

A new mini-capacitance probe for measuring the local void frac-tion in gas-solid fluidized beds is developed in this paper. The measurementprincipleis analyzed. The structure of the probe , the spatial resolving powerand the influences of various paramete

Influences of physical properties of two-phase mixture on void fraction in an annular vessel

To keep the void fraction of two-phase hydrogen in the moderator cell of the cold neutron source (CNS)of China Advanced Research Reactor (CARR) to a specified range, an annular vessel with the same size as the actual moderator cell was used as test section. Deionized water and alcohol, sucrose, and sodium chloride solutions with different concentrations were used as working fluid to find out influences of physical properties, such as density, viscosity and surface tension, of the two-phase mixture on void fraction. The tests proved that the ratio of surface tension to density of liquid phase has great influence on void fraction: the larger the ratio, the smaller the void fraction.Since the ratio of surface tension to density of Freon 113 is lower than that of liquid hydrogen, Freon 113 can be used as a working fluid to study the void fraction in the two-phase hydrogen thermosiphon loop in the CNS of CARR and the results will be conservative.

FCC汽油窄馏分族组成及辛烷值与硫含量分布规律研究

采用实沸点蒸馏法对催化裂化(FCC)汽油进行了窄馏分切割,并对窄馏分的族组成、辛烷值、总硫及硫形态分布进行了测定。结果表明:窄馏分的烯烃质量分数在0.98%~57.08%,烯烃的含量随着馏分沸点的升高而显著降低,FCC汽油中约90%的烯烃(主要是C_(5),C_(6),C_(7))集中在<120℃的馏分中;正构烷烃质量分数在1.60%~5.17%,异构烷烃质量分数在18.98%~35.21%,环烷烃质量分数在4.19%~17.25%,烷烃含量随着馏分沸点的升高,呈中间高两头低的分布趋势,120~140℃馏分中烷烃含量最高;FCC汽油中占比约50%的烷烃集中在<70℃馏分和>150℃馏分中,70~150℃馏分中烷烃的分布比较均匀;窄馏分的芳烃质量分数为0~61.19%,其含量随着馏分沸点的升高而升高,约90%的芳烃集中在>120℃的馏分中,其中约76%的芳烃集中在<150℃的馏分中;FCC汽油中辛烷值呈现两头高中间低的分布,100~110℃馏分的辛烷值最低;FCC汽油中约90%的硫化物集中在>110℃馏分中。

Experimental Acoustic Determination of the Void Fraction in Two-Phase Flow in Horizontal Pipelines

In multi-phase flows, the phases can flow and arranged in different spatial configurations in the pipe, which called flow patterns. This type of flow is found in the oil, chemical and nuclear industries. For example, in the production and transport of oil and gas, the identification of the flow patterns are essential for answering those questions which are related to the economic return of the field, such as, measuring the volumetric flow, determining the pressure drop along the flow lines, production management and supervision. In offshore production, these factors are very important. This paper presents a new method for measuring the void fraction in horizontal pipelines, taking the air as gas in water-air two-phase flow. Through acoustic analysis of the frequency response of the pipe, the method gets the parameters to changes in runoff regime, in an experimental arrangement constructed on a small scale. The main advantages are the non-intrusive characteristic and easy to implement. The paper is composed of a qualitative experimental evaluation and transducers （microphone） which are used to analyze variations in the response accompanying variations in void and flow pattern changes. Changes are imposed and controlled by a two-phase flow experimental simulation rig, including a measurement cell constituted of an external casing that can isolate the measurement from the environmental background noise fitted with acoustic pressure transducers radially arranged, and the impact of a monitored excitation mechanism. The signals which captured by the microphones are processed and analyzed by checking their frequency contents changes according to the amount of air in the mixture.

水下抛石电阻率特性试验研究

研究旨在利用电阻率技术解决水下抛石坝(隐蔽性工程)隐患探测和质量评价等关键问题。采用四电极法分析了水下抛石在不同供电电压和空隙率条件下的电阻率特性,并建立了电阻率与水下抛石空隙率的经验公式。结果表明:水下抛石电阻率随供电电压(10~60 V)升高呈先衰减后逐渐趋于稳定的变化特征,且供电电压高于30 V时电阻率衰减程度显著降低;水下抛石电阻率随空隙率的增加逐渐减小并趋于稳定(两者间的关系可用递减型幂函数表征),且不同供电电压下电阻率随空隙率的变化规律与此类似;分别选用幂函数、指数函数及对数函数拟合电阻率与空隙率关系,发现幂函数拟合误差最小,考虑供电电压影响最终建立了水下抛石电阻率与空隙率的经验公式;进一步通过水下抛石坝模型试验验证了经验公式的可靠性。该经验公式可有效描述水下抛石分布的密实程度,从而快速识别水下抛石坝内部隐患。

基于IPSO-Elman的气液两相流含气率测量方法

为安全且非侵入式地测量气液两相流含气率,提出一种电阻层析成像(ERT)陈列电阻与Elman神经网络相结合的含气率测量方法。首先,为加快模型训练速度并避免数据冗余,使用主成分分析(PCA)算法对120维的阵列电阻特征降维。然后,在粒子群(PSO)算法中引入自适应惯性权重和非线性学习因子,并加入遗传算法(GA)的交叉和变异行为以加快算法收敛速度。最后,通过改进的粒子群(IPSO)算法优化Elman神经网络初始权值和阈值,并建立含气率测量模型。经对比实验发现,PCA-IPSO-Elman含气率测量模型的平均绝对百分比误差为2.92%,且训练时间较IPSO-Elman模型减少68.8%。说明所提方法可以达到预期的测量效果。

填料与CTST塔盘级配提高催化装置分馏精度的研究

介绍了板式和填料催化裂化装置分馏塔的特点及中国石油化工股份有限公司沧州分公司催化裂化装置分馏塔改造情况。经过顶循塔板更换填料、汽柴油分离段塔板更换填料等改造,形成填料与立体传质塔板(CTST)级配,分馏塔压降由0.049MPa降至0.041MPa,汽油终馏点由201.8℃提高至204.6℃,汽柴油重叠度降低,提高了分馏精度,汽油收率提高2.5个百分点,取得了良好的经济效益。装置改造后,分馏塔顶循段未发生结盐问题,装置运行正常。

沸腾床渣油加氢裂化装置结焦情况分析与操作优化

分析了沸腾床渣油加氢裂化装置易结焦堵塞的原因,介绍了某炼化公司沸腾床渣油加氢裂化装置易结焦区域和结焦典型症状,从原料、催化剂、反应和分馏工况等方面进行了优化。通过将原料渣油引入脱固油浆减缓结焦,动态调整渣油转化率控制装置结焦:加工中东高硫低氮原油所产渣油时,转化率可控制在75%以上;加工低硫中东原油所产渣油时,转化率控制在不大于70%;加工低硫高氮原油所产渣油时,转化率控制在不大于65%。每吨渣油原料置换新鲜催化剂0.90~0.95 kg,低控减压塔塔底液位(25%~30%),提高塔底物料返混流量以减少沥青质在塔底器壁生焦。优化操作后,常压塔底油总沉积物质量分数稳定小于0.2%,确保了装置在渣油高转化率下的长周期稳定运行。