无机陶瓷膜澄清食醋工艺研究

为了除去老陈醋中的细菌和沉淀物,采用无机陶瓷膜对含有菌体和沉淀物的老陈醋进行过滤实验研究。通过研究无机陶瓷膜平均孔径、跨膜压差、膜面流速、操作温度、料液浓缩比、流动状态等操作条件对老陈醋过滤效果的影响,确定了适宜的工艺分离条件:膜孔径100 nm、室温(30℃以下)、跨膜压差0.14 MPa、雷诺数5 000、膜面流速2.0 m/s、最大浓缩倍数为9。在适宜的工艺分离条件下,平均通量可达40 L/(m2.h);过滤后食醋的理化和卫生指标均符合国家标准,且放置2年后无沉淀现象。因此,采用无机陶瓷膜澄清食醋在技术上是完全可行的方法。     

Preparation of alumina membranes for micro- and ultrafiltration applications

Abstract

A very thin disc type ceramic membrane (0·3-0·8 mm thickness, 25-30 mm diameter) made of pure alumina and suitable for microfiltration applications has been prepared by a tape casting process. A sol coating was applied to the disc to form an ultrafiltration membrane. T he pore size of the membrane could be varied in the range 0·1-0·7 μ m and porosity in the range 25-55% by optimising the ex perimental parameters. The most important factor for determining the pore size of the membrane was found to be the initial particle size distribution of the ceramic powder. Firing temperature and soaking time are other crucial parameters affecting volumetric porosity. Water permeability through the membrane under suction and under positive pressure is comparable with that of ceramic membranes prepared by conventional methods. In addition, a typical membrane shows a very narrow pore size distribution in the range 0·1-0·4 μm, with a median pore size of 0·28 μm. A very sharp drop in the pore size distribution pattern around 0·4 μm indicates that no pores larger than this exist. This implies that all particles with radius > 0·4 μm are trapped in the membrane, providing excellent separation efficiency. Results of microbial separation tests confirmed the possibility of micro-organism separation through these membranes.     

Periodic open-cell foams: Pressure drop measurements and modeling of an ideal tetrakaidecahedra packing

Periodic open-cell foams of ideal tetrakaidecahedron geometry were manufactured by selective electron beam melting (SEBM) and characterized with respect to the morphological parameters, namely strut diameter, window diameter and porosity. The pressure drop over these periodic foam samples of different pore size and porosity was determined experimentally. The basic form of the Ergun equation (which contains no empirical coefficients) was modified to develop a new correlation for the prediction of the pressure drop in periodic open-cell foams of ideal tetrakaidecahedron geometry. The correlation was successfully validated by the experimental results of the pressure drop measured for the periodic open-cell foam samples. With the new correlation it is possible to predict the pressure drop in periodic open-cell foams by using only two geometrical parameters, namely the open porosity and the window diameter.The applicability of the new correlation for a large range of porosities was examined by comparing the experimental and simulated friction factors for the porous media with both high (foam structure) and low porosities (packed beds) for a large range of the Reynolds number. It was demonstrated that the correlation can successfully predict the pressure drop of foam structures as well as packed beds.     

Experimental study on the effects of big particles physical characteristics on the hydraulic transport inside a horizontal pipe

This paper presents an experimental study of the physical characteristic effects of large particles on hydraulic transport in a horizontal pipe. The particles are spherical and are large with respect to the diameter of the pipe (8%, 10%, 16%and 25%). Experiments were done to test the important parameters in solid transport (pressure, velocity, etc.). As a result, the relationship between the pressure gradient forces and the mixture velocity was sub-stantially different from the pure liquid flow. However, in a single-phase flow a monotonous behavior of the pres-sure drop curve is observed, and the curve of the solid particle flow attains its minimum at the critical velocity. The regimes are characterized with differential pressure measurements and visualizations.     

Characteristics of solid suspensions in a bubble column without and with draft tube

In order to investigate the suspension behaviour of solid particles in bubble columns without and with draft tube, minimum gas velocities for generating and maintaining complete solid suspension were determined. Experiments were carried out in a bubble column with a diameter of 200 mm and a height of 2 500 mm. The bubble column could be equipped with a draft tube with a diameter of 120 mm and a length of 1 500 mm. The state of suspension was determined by measuring the hydrostatic pressure as a result of suspended solid particles with an inductive pressure gauge. Solid content ε_s, solid density ?_s, particle size d_p, particle shape, particle size distribution, and solid wettability were varied. Furthermore measurements of integral gas holdup were carried out.     

Insights into the calcination temperature and loading amount of the catalyst support (TiO2) in the fibrous ceramic-based catalytic filter element prepared by microwave drying

The fibrous ceramic-based catalytic filter element (CFE) is a promising multifunctional material capable of simultaneously removing dust and NO_x from hot gases. In this study, various calcination temperatures and titanium sols with different solid contents were used to prepare CFEs based on microwave drying, and their influences on the catalytic performance were experimentally investigated. The results showed that both the calcination temperature and the solid content of the titanium sol had important impacts on the catalytic activity. As the calcination temperature increased, the particle size, crystallite size, and average pore diameter of the loaded catalyst support (TiO₂) increased, while the specific surface area decreased, ultimately resulting in a decline in the catalytic activity. However, a suitable calcination temperature ranging from 300 to 400 °C was required to achieve a good combination between the catalyst and the fibrous ceramic and a relatively uniform mesoporous structure. Furthermore, the increase in the solid content gave rise to a corresponding increase in the TiO₂ loading amount, which increased the pressure drop and reaction surface area of the CFE. Excessive vanadium content caused by insufficient catalyst support induced side reactions of NH₃ oxidation under high-temperature conditions, thereby reducing catalytic activity. Therefore, the preferred calcination temperature and solid content were set at approximately 300–400 °C and 8 wt%, respectively. The final prepared CFE demonstrated superior catalytic performance and adaptable gas velocity properties.     

Towards a more realistic modeling of solid foam: Use of the pentagonal dodecahedron geometry

The geometric structure of a solid foam is approached using a pentagonal dodecahedron as the unit cell. Important properties of the foam (specific surface area, pressure drop, external fluid-solid mass transfer) are well represented and successfully compared with experiments. The approach enables accounting for triangular or cylindrical struts and solid accumulation at their meeting points. Knowledge of the void fraction and mean strut diameter (or pore diameter) are sufficient for estimating any geometric characteristics. The model has been tested with foams of porosity ranging from 0.75 to 0.98.     

Volume Image Analysis of Ceramic Sponges

The three‐dimensional structure of monolithic networks such as ceramic sponges and their geometrical dimensions are part of the fundamentals necessary for investigation in most possible applications in chemical engineering. A volume imaging method must be applied to determine this structure and to measure features such as the specific surface area and the pore diameter. Magnetic Resonance Imaging was chosen for such measurements in this study. The analysis of volume images is performed with various methods based on different principles, which are compared with each other as well as with data generated by conventional techniques and from literature models.     

Investigations of reticulated porous alumina foam ceramics based on different coating techniques with the aid of μCT and statistical characteristics

Alumina foam ceramic filters were prepared due to the “replica technique”. The parameters of the two coating steps were varied to find the optimal processing route to prepare ceramic foam filters with a good homogeneous distribution of the strut thickness. Different additives for the slurry for the impregnation (first coating) step were investigated with the aid of rheological measurements. For the second coating step spraying as well as centrifuging techniques with different processing parameters were studied. The sintered foam structure (strut diameter, pore size and porosity) was characterized with the aid of CT-images and described with an image analysis software and statistical tools.     

高温陶瓷过滤管性能退化建模及实时寿命预测

高温陶瓷过滤管由内部孔径较大的支撑体和外部孔径较小的过滤膜双层结构构成,在实际应用中,存在大量粒径较小的粉尘颗粒,会穿过过滤膜沉积到支撑体内部,脉冲反吹无法有效清除. 因支撑体内颗粒沉积及管壁外残余粉尘层不断压缩,使陶瓷过滤管渗透率不断下降,残余压降逐渐增加。本工作基于高温陶瓷过滤管壁内颗粒沉积特性及残余粉尘层压缩不可直接观测的特点,结合贝叶斯估计理论,利用过滤管运行期间采集的残余压降数据,提出一种基于状态空间模型的过滤管性能退化建模方法。该方法能融入最新采集到的残余压降数据,实时对模型参数进行更新,可对陶瓷过滤管的剩余寿命进行实时预测,同时对陶瓷过滤管剩余寿命的失效概率密度分布及陶瓷过滤管的退化状态变化率进行预测。对某高温试验装置及壳牌煤气化装置中的陶瓷过滤管残余压降分析表明,预测剩余寿命准确率随残余压降数据增加而逐渐增加,后期预测准确率高于95%,且陶瓷过滤管退化状态变化率逐渐变小,与陶瓷过滤管残余压降前期增加快后期增加慢的现象一致。     

Flow characteristics of surfactant stabilized water-in-oil emulsions

In this paper, an investigation was carried out to study the effect of water fraction and flow conditions on the flow characteristics of surfactant stabilized water-in-oil emulsion. Pressure drop measurements were conducted in 2.54-cm and 1.27-cm horizontal pipes. The influence of water fraction and the flow conditions on emulsion stability, type, conductivity, droplet size distribution, viscosity and pressure drop were reported. The results showed a significant increase in the emulsion stability, viscosity and pressure drop with increasing water fraction up to 70%. In addition, shear thinning behavior was observed for the emulsions especially at high water fractions. Furthermore, pressure drop measurements of high concentrated emulsions showed pipe diameter dependency especially at high Reynolds (Re) numbers. Moreover, drag reduction was observed with decreasing water fraction. The viscosity of surfactant-stabilized water-in-oil emulsions was modeled with a modified fluidity-additivity model.     

CFD Simulation of Mass Transfer Efficiency and Pressure Drop in a Structured Packed Distillation Column

The pressure drop and mass transfer efficiency for two‐phase flow in a structured packed column were simulated using a commercial CFD package, CFX version 10. The distillation of the methanol/isopropanol system was carried out in a 0.073 m diameter column, with an element composed of a ceramic structured packing and 0.053 m in height. The Height Equivalent to Theoretical Plate (HETP) value varied from 0.106–0.146 m. Pressure drop experiments were measured with an air/water system. The pressure drops at the flooding and loading points were ca. 173 and 580 Pa/m of packing, respectively. HETPs and pressure drops calculated from the Computational Fluid Dynamics (CFD) model were compared to their experimental counterparts. The average relative error between CFD predictions and the experimental data for the prediction of dry pressure drop, irrigated pressure drop and mass transfer efficiency are 20.3 %, 23 % and 9.15 %, respectively. In all cases, the CFD predictions show a good agreement with the experimental data, indicating that CFD is a reliable, cost saving and suitable technique for the design and optimization of separation processes.     

Synthesis of macroporous silica from solid-stabilised emulsion templates

We have investigated the microstructures of the solid residue left behind after the evaporation of solid-stabilised emulsions. The correlation between the microstructure and the properties and preparation conditions of the emulsions will be thoroughly discussed. The type of microstructure is related to the conditions (oil type, oil content, particle type, particle concentration and emulsion type) of the initial emulsion. Solid residues left after evaporation of oil-in-water emulsions containing volatile oils (relative to water) show a “knobbly” microstructure. When oils with similar or lower vapour pressure to that of water were used, “sponge-like” structures were obtained. For emulsions containing volatile oils, the mean drop diameter is similar to the mean pore diameter, whereas when oils with low vapour pressure are used, the pores are much smaller. Finally, this paper will illustrate that stable toluene-in-water emulsions leave porous microstructures, whereas water-in-toluene emulsions and emulsions close to the phase inversion show sheet-like or “knobbly” structure.     

CFD and experimental studies of liquid weeping in the circular sieve tray columns

Sieve trays are widely used in fractionating devices like tray distillation towers existing in separation and purification industries. The weeping phenomenon that has a critical effect on the efficiency of tray towers was studied by a numerical model and some experiments. The experiments were carried out in a pilot scale column with the diameter of 1.22 m that includes two test trays and two chimney trays. Weeping rates and some hydraulic parameters were measured in sieve trays with the hole area of 7.04%. Furthermore, the total weeping rate and weeping rate in inlet and outlet halves of the test tray were determined. It was also used an Eulerian–Eulerian computational fluid dynamics (CFD) method for the present study. The model was able to predict the dry tray pressure drop, total pressure drop, clear liquid height, froth height, and weeping rate simultaneously. Furthermore, the obtained CFD results were in a good agreement with the experimental data in terms of pressure drop and the model properly predicted several hydraulic parameters like the liquid weeping behavior along the tray.     

液体燃料合成浆态反应器内部过滤的研究

在液体燃料合成浆态搅拌反应器中设置了以金属烧结板为过滤介质的内过滤器,实现固液分离。研究了压降、温度、搅拌转速、固含率、过滤介质孔径及颗粒粒径对过滤速率的影响。实验结果表明:在浆态反应器中进行内过滤可以得到澄清稳定的滤液;随着操作进行,滤饼厚度达到动态平衡,过滤速率最终趋于稳定;过滤速率随着压降、温度、过滤介质孔径、颗粒粒径的增大及搅拌转速、固含率的减小而增大。应用因次分析法建立过滤模型,通过麦夸特算法对实验数据进行最优拟合得到模型的参数值,统计检验以及模型计算值与实验值的比较表明该模型可靠。     

Performance of Spray,Sieve Tray,and Packed Contactors for High Pressure Extraction

Abstract

The performance of various contactors in high pressure extraction service was studied. The mass transfer efficiency of a spray column and columns filled with sieve trays, 1.27 cm ceramic Raschig rings, and no. 15 metal Intalox saddles were obtained from a “windowed” high pressure extraction column with an internal diameter of 9.88 cm and a column height of 168 cm. The extraction column has an internal diameter of 9.88 cm and a contacting height of 168 cm. Glass windows in the extractor allowed visual observation and photography. Supercritical and liquid carbon dioxide were used to extract isopropanol from water at pressures of 81 to 150 atmospheres and 297 to 318 [ddot]K. The sieve tray extractor yielded the highest mass transfer efficiency followed closely by Raschig rings and metal Intalox saddles. The spray column was by far the least efficient. The mass transfer efficiency was observed to be independent of the operating conditions studied in this work. Sauter mean drop diameters and dispersed phase (free) hold-up were also obtained in this work. These data will provide a reliable high pressure mass transfer and hydraulic database for future correlation and design efforts.     

Synthesis of bone-like structured foams

Here we present a processing route to produce multi-structured ceramic foams based on the combination of particle-stabilized foams with polymeric sponges to produce positive and negative templating structures. Polyester sponges are infiltrated with freshly produced calcium aluminate–alumina foams and upon sintering either positive templating structures are produced when wetting the sponges, or negative templating foams with a percolating pore network are obtained when completely filling the sponges. Additionally, by combining different layers of these particle-stabilized foam infiltrated sponges, various different structures can be produced, including sandwich structures, pore size gradients, and ceramic bone-like structures applying to different types of bone. The particle-stabilized foams used were in situ self-hardening calcium aluminate cement enriched alumina foams to obtain crack-free samples with pore interconnections and tailorable pore sizes.     

Preparation and characterization of bacterial cellulose sponge with hierarchical pore structure as tissue engineering scaffold

Bacterial cellulose (BC) is believed to be a promising and cost-efficient nano-scaffold for tissue engineering. However, the pore size of BC is not big enough for cell ingrowth, which restricts its practical usage as tissue engineering scaffold. In this work, novel porous BC sponges were obtained through emulsion freeze-drying technique. Results of scanning electron microscopy (SEM) and mercury intrusion porosimeter showed that the resulted BC sponges were composed of nanofibrills with hierarchical pore structure consisting of large pores (from 20 to ~1,000 μm in diameter) and nano pores (down to ~4 nm in diameter). BC sponges possessed high surface area (92.81 ± 2.02 m²/g) and sufficient porosity (90.42 ± 0.24%). Additionally, the size and shape of BC sponges could be easily controlled by using appropriate molds. We also demonstrated that BC sponges had excellent cell compatibility as fibrous synovium-derived mesenchymal stem cells (MSCs) could proliferate well on and inside the BC sponges and the maximum ingrowth distance was 150 μm after cultured for 7 days.     

陶瓷过滤管管壁内气体流动的LBM并行模拟

采用格子Boltzmann方法,编制并行程序,计算了陶瓷过滤管管壁内的流体流动,从微观角度对滤管多孔介质结构内的流动进行分析。以陶瓷过滤管管壁扫描电镜图片为基础,根据实际滤管的厚度,确定计算中的多孔介质结构。分析了无膜滤管微细通道内的速度及压力随入口参数的变化情况以及多孔介质结构对速度的影响,给出了压力沿滤管厚度方向的变化曲线;分析了有膜滤管内的流动情况,给出了压力变化曲线,由计算结果可知,滤膜压降占滤管压降的比例较大。对过滤管微孔结构内流动的研究,可为陶瓷过滤管的性能优化提供理论指导。