陶瓷过滤管表面粉尘层清除过程的图像分析

Based on the analysis of high-speed video images, the detachment behavior of dust cake from the ceramic candle filter surface during pulse cleaning process is investigated. The influences of the dust cake loading,the reservoir pressure, and the filtration velocity on the cleaning effectiveness are analyzed. Experimental results show that there exists an optimum dust cake thickness for pulse-cleaning process. For thin dust cake, the patchy cleaning exists and the cleaning efficiency is low; if the dust cake is too thick, the pressure drop across the dust cake becomes higher and a higher reservoir pressure may be needed. At the same time there also exists an optimum reservoir pressure for a given filtration condition.     

Distributions of age, thickness and gas velocity in the cake of jet pulsed filters—application and validation of a generations filter model

Different imperfections are observed with jet pulsed filters. They manifest themselves most obviously in the curve of the pressure drop versus time. A convex pressure drop curve indicates cake compaction. But jet pulsed filters frequently show a concave rise of the pressure drop curve. This phenomenon is due to a strongly nonuniform cake area load on the filter and it is generally attributed to incomplete cake removal. Incomplete cake removal takes place when only a fraction of the total filter area is cleaned at the end of a filter cycle or when patchy cleaning prevails. Patchy cleaning means that a jet pulse removes the entire filter cake of only a fraction of the exposed filter area except for a thin adhesive dust layer.In this paper a filter model is proposed in which the different classes of cake thickness are understood to result from different cake generations. A cake becomes one generation older when it survives the jet pulse cleaning at the end of a filtration cycle, although the area that is occupied by the cake on the filter medium is diminished by the jet pulse.This generations filter model can be used to find the distributions of age, thickness and gas velocities in the cake from steady-state operational data. The steady-state, periodic model provides a complete basis for the simulation of heterogeneous gas/solid reactions in the cake of jet pulsed filters.In the model intermediate cake build up during the cleaning procedure is considered. There redeposition of removed filter cake also takes place, and its extent is estimated. The model can also serve to determine from macroscopic process data, if the cleaning system of a filter installation operates in the undesirable mode of patchy cleaning.Experiments from a pilot plant for dry flue gas cleaning are presented and the generations filter model is validated with the experimental data.     

Modelling pressure drop evolution on high temperature filters

A high temperature high pressure filtration facility is available at the ETSI-University of Seville, which allows testing different elements and cleaning reverse-flow pulse strategies using real coal ash under diverse operating conditions. The facility is capable of processing 850 Nm³/h gas flow rate at maximum temperature and pressure of 550 °C and 7.5 barg respectively. An extensive testing campaigns have been carried out with the aim of evaluating alternatives for hot gas filtration technologies and optimising the performance of commercial filtering elements.In this framework, this paper focuses on a semi-empirical model developed for predicting the rise of the pressure drop with time. The model is based on theoretical considerations and the application of the experimental data generated using four filtering elements (PTFE and 3MFB700 bag filters, DSN1020 and CS1150 rigid filters). Nonlinear regression has been used to estimate and validate the coefficient of the model (specific dust cake coefficient) with arbitraries relations between independent and dependent parameters, by using iterative estimation algorithms. This is a valuable tool to select the best filtration options and optimum cleaning strategies in high temperature applications. Investigations about the factors affecting the specific dust cake resistance coefficient (filtration velocity, temperature, filter medium) are also presented.     

Experimental investigation into compression properties of integrated coal gasification combined cycle fly ashes on a ceramic filter

The compression properties of IGCC (integrated coal gasification combined cycle) fly ash cake on a ceramic filter were carefully investigated under well-controlled conditions. Overall cake porosity and pressure drop of dust cake of three different particles of geometric mean diameters of 3.7, 6.2, and 12.1 Μm, and dynamic shape factors of 1.37, 1.57 and 1.65, respectively, were investigated, at face velocities of 0.02-0.06 m/s. Overall cake porosity was strongly dependent on face velocity, mass load, and particle size. The expressions for overall cake porosity, considering the compression effect, and pressure drop across the dust cake were developed with good agreement with experimental results.     

Effects of Operating Conditions on Pressure Drop in a Pulse-Jet Bagfilter for Coke Dust

A pilot-scale pulse-jet bagfilter was designed, built, and tested for the effects of four operating conditions (filtration velocity, inlet dust concentration, pulse pressure, and pulse interval time) on the total system pressure drop, using coke dust from a steel mill factory. Four models were used to predict the total pressure drop according to the operating conditions. These model parameters were estimated from the 192 experimental data points. The filtration velocity has been determined to be the most relevant variable affecting the pressure drop. An efficient operating condition considering the four variables is proposed from analysis of the dimensionless group model.     

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。     

Experimental study of cake formation on heat treated and membrane coated needle felts in a pilot scale pulse jet bag filter using optical in-situ cake height measurement

Pulse-jet bag filters are frequently employed for particle removal from off gases. Separated solids form a layer on the permeable filter media called filter cake. The cake is responsible for increasing pressure drop. Therefore, the cake has to be detached at a predefined upper pressure drop limit or at predefined time intervals. Thus the process is intrinsically semi-continuous. The cake formation and cake detachment are interdependent and may influence the performance of the filter. Therefore, understanding formation and detachment of filter cake is important. In this regard, the filter media is the key component in the system. Needle felts are the most commonly used media in bag filters. Cake formation studies with heat treated and membrane coated needle felts in pilot scale pulse jet bag filter were carried out. The data is processed according to the procedures that were published already [Powder Technology, Volume 173, Issue 2, 19 April 2007, Pages 93-106]. Pressure drop evolution, cake height distribution evolution, cake patches area distribution and their characterization using fractal analysis on different needle felts are presented here. It is observed that concavity of pressure drop curve for membrane coated needle felt is principally caused by presence of inhomogeneous cake area load whereas it is inherent for heat treated media. Presence of residual cake enhances the concavity of pressure drop at the start of filtration cycle. Patchy cleaning is observed only when jet pulse pressure is too low and unable to provide the necessary force to detach the cake. The border line is very sharp. Based on experiments with limestone dust and three types of needle felts, for the jet pulse pressure above 4 bar and filtration velocity below 50 mm/s, cake is detached completely except a thin residual layer (100-200 μm). Uniformity and smoothness of residual cake depends on the surface characteristics of the filter media. Cake height distribution of residual cake and newly formed cake during filtration prevails. The patch size analysis and fractal analysis reveal that residual cake grow in size (latterly) following regeneration initially on the base with edges smearing out, however, the cake heights are not leveled off. Fractal dimension of cake patches boundary falls in the range of 1-1.4 and depends on vertical position as well as time of filtration. Cake height measurements with Polyimide (PI) needle felts were hampered on account of its photosensitive nature.     

Zur Frage der optimalen Reinigungsbedingungen für Schlauchfilter mit DruckstossabreinigungInvestigations on optimal cleaning conditions for bag filters with pulse jet cleaning

Pressure drop, residual dust quantity, cleaning intensity as well as the time-dependent outlet dust concentration have been measured in a pulse-jetIn this paper, examples of the measuring results are given and correlations between the cleaning intensity and the outlet dust concentration are discusIt is shown that an optimum cleaning pressure exists at which the dust cake was completely removed. At this cleaning pressure the outlet dust concentra     

Clogging modeling in pleated filters for gas filtration

A model of clogging of a pleated filter in gas filtration is presented. The model is obtained by combining a semi-analytical model of the flow in a pleated filter and an empirical model of clogging of the planar filter medium applied locally along the pleated filter channels. The model takes into account the formation of a filtration cake of variable thickness at the porous wall of the pleated filter entrance channels and the resulting evolution of the entrance channels aperture distribution during the filtration/clogging process. Based on the numerical predictions, two main clogging scenarios are identified and analyzed. The optimum pleat density, defined as the pleat density maximizing the filter capacity, is determined and shown to be greater than the pleat density minimizing the pressure drop for a clean filter. Predictions of the evolution of overall pressure drop across the pleated filter due to clogging are compared with experimental data.     

Particle size effect on the filtration drag of fly ash from a coal power plant

In order to investigate the filtration properties of fly ash from a conventional coal power plant, the filtration drag across the dust cake over an absolute fiberglass filter element was measured. A fluidized bed column was utilized to obtain a well characterized particle stream. The cake resistance coefficient was analyzed by the equation proposed by Endo et al. [1998] in order to observe the effect of particle size and polydispersity. The filtration drag was measured for three kinds of particle stream having the geometric mean particle size of 3.15, 6.07, and 7.83 μm and the geometric standard deviation less than 1.44 in the practical operation conditions for the field applications of face velocity of 0.03–0.06 m/s and area dust load up to 0.2 kg/m². A dust cake of smaller particle size showed larger pressure drop even though the porosity was higher and presented high compressibility according to the face velocity. The particle polydispersity was also a dominant factor affecting the compressibility of the dust cake.     

A lab-scale study on the humidity conditioning of flue gas for improving fabric filter performance

A centrifugal separator was constructed to examine the effect of flue gas humidity on the adhesional force between fabric and collected dust. A lab-scale fabric filter sampling system (FFSS) was also manufactured by using a piece of flat fabric as a sample of bag material. In addition, an automatic control system for gas humidity was devised and installed in the FFSS, and, then, the following effects were studied: (i) the influence of gas humidity on the adhesional force between fabric and dust particles; (ii) the influence of gas humidity on the performance of fabric filter in terms of pressure drop, ΔP, dust removal efficiency, η, and specific cake resistance, K′₂; (iii) the variations in the composite-performance indices with gas humidity; and (iv) the influence of gas humidity on cleaning of dust-cake in terms of effective residual pressure drop. The main objectives were to determine the minimum and maximum values for the gas humidity range and to find the appropriate conditions for dust cleaning in terms of the critical value of effective residual pressure drop.     

气固并流式轴向移动床过滤器的压降特性

通过冷模实验,改变移动床表观气速、颗粒循环速率、入口气体含尘浓度等操作参数,研究了轴向移动床过滤器的压降特性和合适的操作条件,结合移动床内气固两相运动特点,修正了Ergun公式,在加尘条件下分析了床内滤饼对压降稳定性的影响。结果表明,在无尘负荷条件下(“纯”移动床操作),颗粒的循环速率由0增至2.26 kg/(m2?s)时,设备的压降减小0.03 kPa。表观气速为0.126 m/s、入口气体含尘浓度为89.10 g/m3时,移动床内滤饼形成和破损呈动态平衡,过滤500 s后,压降可稳定在0.88 kPa,此时设备具有较高的除尘性能,粉尘捕集效率可达96%以上。     

Determination of cake properties in ultrafiltration of nano‐colloids based on single step‐up pressure filtration test

The single step‐up pressure filtration test was developed to determine the pressure dependence of average specific resistance of the cake formed in ultrafiltration of a variety of nano‐colloids over a wide range of pressure drops across the cake. The values of the average specific resistance at extremely low pressures were obtained from only the flux decline data through the use of the distinct time variation of the pressure drop across the cake generated by using the ultrafiltration membrane with a high hydraulic resistance under the low filtration pressure in the first step of filtration. The values at higher pressures were obtained from the time variation of the filtration rate induced by a stepwise increase in the pressure. The correlations between the average specific cake resistance and the pressure drop across the cake were evaluated using only the flux decline data for a variety of different proteins and nanoparticles. © 2013 American Institute of Chemical Engineers AIChE J, 60: 289–299, 2014     

Simulation of operational behaviour of patchily regenerated, rigid gas cleaning filter media

Particle removal from hot process gases is frequently accomplished with regenerable ceramic filters. When regenerating such media periodically, the dust cake may be detached from parts of the filter surface while other regions remain intact (‘patchy cleaning’). The filtration process depends on how these patterns of incomplete regeneration evolve over a number of cycles, how they change the build-up of the new cake, and how they affect the pressure drop. A two-dimensional quasi stationary flow model is used to predict pressure drops as a function of regeneration efficiencies and regeneration patterns, taking into account the finite thickness and flow resistance of the medium itself. The effect of non-uniform cake build-up on the pressure rise during a filter cycle is also modelled for a partially regenerated filter. The calculations prove that the pressure drop rises faster for lower regeneration efficiencies and that also cycle times become briefer with lower regeneration efficiency. It can also be shown, that the regeneration pattern only influences the pressure drop curve at the very beginning of the filtration cycle but does not influence the filtration cycle times.     

Design and performance evaluation of vacuum cleaners using cyclone technology

A cyclone technology for a vacuum cleaner—axial inlet flow cyclone and the tangential inlet flow cyclone — to collect dusts efficiently and reduce pressure drop has been studied experimentally. The optimal design factors such as dust collection efficiency, pressure drop, and cut-size being the particle size corresponding to the fractional collection efficiency of 50% were investigated. The particle cut-size decreases with reduced inlet area, body diameter, and vortex finder diameter of the cyclone. The tangential inlet twin-flow cyclone has good performance taking into account the low pressure drop of 350 mmAq and the cut-size of 1.5 μm in mass median diameter at the flow rate of 1 m³/min. A vacuum cleaner using tangential inlet twin-flow cyclone shows the potential to be an effective method for collecting dusts generated in the household.     

Cake formation and growth in cake filtration

In this study we develop an experimental method to help understand the formation and growth of dust cakes. An on-line pressure-displacement measurement system is developed to measure the thickness of the dust cakes. A higher filtration superficial velocity resulted in a higher degree of compaction in the dust cakes and thus a higher specific cake resistance, hence a better collection efficiency could be achieved. The empirical equations for cake solidosity and specific cake resistance as a function of the filtration superficial velocity are derived. We find that the cake filter is influenced by the cake thickness and the filtration superficial velocity. The results of this study can be applied to granular bed filters for the removal of dust particulates in advanced coal-fired power systems.     

Modeling instantaneous pressure drop of pleated thin filter media during dust loading

In this paper, we present a modeling methodology for studying the effects of dust loading on the pressure drop across pleated filters. Our simulations demonstrate that there exists an optimum pleat count for clean filters at which pressure drop reaches a minimum regardless of the in-plane or through-plane orientation of the fibers. With the particle deposition included in the analysis, our results indicated that the rate of increase in pressure drop decreases with increase in the pleat count. We demonstrated that a higher pleat count results in a higher flow velocity inside the pleat channels causing more non-uniformity in the dust deposition across the pleat. Especially when particles are sufficiently large, the dust cake tends to form deeper inside the pleated channel when the pleat count is high. This effect is observed to be less pronounced when the pleats have a triangular shape. We also showed that if the dust cake permeability is higher than that of the filters fibrous media, the rate of increase in pressure drop does not always decrease with increase in the pleat count. Finally, by comparing filters having 15 pleats per inch, we observed that rectangular pleats are preferred over the triangular pleats when the particles are highly inertial, i.e., filtering high-speed large particles. When particle's inertia is small, our results indicate that triangular pleats cause less pressure drop, and so are recommended.     

Measurement and Simulation of Axial Velocity in a Filter Bag

The axial velocity in two different tests with pulse‐jet bag filters made of needle felts on a pilot‐scale test facility separating limestone dust from air under ambient conditions is measured and simulated at different cake area loads. Results reveal that the axial velocity profiles are not truly linear along the whole length of the bag. A nonuniform gas flow prevails when the bags are differently dust‐loaded. The same behaviors are observed even at the end of filtration cycles at different upper pressure drop limits. At the higher upper limit, the nonuniformity is stronger. Radial velocity profiles are nearly symmetric along the length of the bag.     

核电常规岛高低压加热器流动阻力计算问题讨论

针对高低压加热器流动阻力计算,对换热管摩擦阻力系数相关经验式进行了对比分析,并对U形管弯曲管道摩擦阻力系数计算及进出口局部阻力系数计算提出了新的建议。针对加热器壳程饱和蒸汽冷凝工况,阐明了壳程压降的主要影响是使壳程冷凝换热推动力下降,而壳程压降的主要构成则是进口局部阻力压降和防冲板阻力压降。基于蒸汽冲击防冲板的流动特征,提出了防冲板压降计算模型,该模型既反映了压降随防冲板距离管口远近而变化的特点,又与现有阻力系数经验取值有一致性,对设计应用有参考价值。     

Cake properties of nanocolloid evaluated by variable pressure filtration associated with reduction in cake surface area

A potential method has been developed for evaluating simultaneously both the average specific resistance and average porosity of the filter cake formed in unstirred dead‐end ultrafiltration of nanocolloids such as bovine serum albumin solution and silica sol. The method consists of variable pressure filtration followed by constant pressure filtration. The relation between the average specific cake resistance and the pressure drop across the cake was determined from the evolution of the filtration rate with time in the course of the variable pressure filtration period, based on the compressible cake filtration model. The average porosity was evaluated from the significant flux decline caused by a sudden reduction in the cake surface area in the middle of the constant pressure filtration period. The pressure dependences of both the average specific cake resistance and average cake porosity were obtained from only two runs which differed from each other in the pressure profiles. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3869–3877, 2014