Utilization of rice-husk packed beds as fine dust collectors at heavy dust loadings

Typical rice mills generally generate tonnes of biomass which is rice husks and a significant quantity of coarse and fine dusts from the paddy, resulting in public health concern. Instead of normal air cyclones which are not efficient for collecting fine soft-hair (detached pubescence) particles smaller than a few microns, a new system using packed beds of rice husks was developed for collection fine dusts. It was found that the rice-husk packed beds could exhibit an effective performance in capturing fine dusts at various dust loadings with collection efficiency higher than 85% by mass. The filtrating phenomenon could be observed as an integrated effect of cake and deep-bed filtrations due to the heavy dust loads, agglomeration of dusts, and cohesion between the dusts and bed of irregularly shaped rice husks. Both the pressure drop across the bed and the overall filtration efficiency remarkably increased at the initial clean stage, then increased more slowly due to the recurrent fracture of the dust cake layer.     

Filter Clogging by Bimodal Aerosol

Pressure drop evolution during filtration of bimodal aerosol was studied experimentally. A low-pressure drop pre-filter upstream of the actual collection filter was demonstrated to significantly reduce the pressure drop growth rate, when the aerosol is dominated by coarse particles. The pressure drop evolution during depth-filtration, that took place mainly in a pre-filter, could be predicted by adding up the separately measured contributions from the unimodal fine and coarse aerosols. However, the cake filtration (pre-filter was not used) of coarse particles alone resulted in a faster clogging rate as compared to the same amount of coarse particles accompanied with fine particles (mass ratio coarse:fine 3:1). Apparently, fine particles deposited on coarse particles affect their surface properties and thus the porosity of the cake formed.     

蒸汽射流压力振荡主频分析及强度特性

对蒸汽质量流率298~865 kg·m^-2·s^-1,水温20~70℃的蒸汽射流压力振荡特性进行了实验研究。发现压力振荡特殊主频与汽羽周期性鼓胀和收缩的频率一致。随着凝结形态由在凝结振荡区向稳定凝结区的转变,振荡频率随蒸汽质量流率的增加先增大后减小,振荡主频随冷却水温的升高而下降。振荡幅值的变化与频率变化相反。基于实验结果和分析,给出计算压力振荡量纲1方均根幅值的实验关联式,并在蒸汽质量流率370~865 kg·m^-2·s^-1,水温20~60℃的参数范围内与实验值对比,预测误差在±30%以内。     

DMLS微型换热器内纳米粒子浓度对Al2O3/R141b流动沸腾压降的影响

为探究纳米粒子浓度对纳米流体制冷剂在微细通道中流动沸腾气液两相压降影响,运用超声波振动法制备质量分数为0.05%、0.1%、0.2%、0.3%、0.4%均匀、稳定的Al₂O₃/R141b纳米流体制冷剂,在直接激光烧结（DMLS）微型换热器中,设计系统压力为176 kPa,纳米流体制冷剂入口温度为40℃,在热通量21.2~38.2 kW·m^-2和质量流率183.13~457.83 kg·m^-2·s^-1工况下,研究纳米粒子浓度对Al₂O₃/R141b纳米流体制冷剂流动沸腾气液两相压降影响。研究结果表明：纳米粒子浓度对纳米流体制冷剂在微细通道中流动沸腾气液两相压降有显著影响,气液两相压降随纳米流体制冷剂的纳米粒子浓度增加而减少,在纯制冷剂中R141b加入纳米粒子Al₂O₃,不同质量分数的纳米流体制冷剂流动沸腾气液两相压降降低5.5%~32.6%;通过SEM和表面静态接触角测试方法,发现纳米流体制冷剂沸腾气液两相压降随质量分数增加而减少的原因是纳米颗粒沉积在通道表面,增加了微通道表面的润湿性;对比国际上3种比较经典流动沸腾两相压降模型,并基于Qu-Mudawar关联式和Zhang关联式进行修正,得出两相压降结果的85%数据点位于修正后的关联式模型值的±15%范围之内,同时实验结果与修正后的模型结果偏差MAE值为11.7%,说明修正后关联式能有效预测本工况下实验值。     

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.     

载气增湿蒸发技术处理切削废液的研究

利用空气作为载气,采用蒸发塔进行了载气增湿蒸发浓缩切削废液的实验,探究了操作条件对蒸发过程的影响。随着载气流量的增加,容积传质系数、蒸发量和整塔压降均增大,出口载气VOC浓度减小;随着载气温度、循环流量的增加,容积传质系数、蒸发量、整塔压降和出口载气VOC浓度均增大。实验条件下容积传质系数及蒸发量最大达到了13.95 g·（m³·s）^-1和3.39 kg·h^-1;出口载气VOC浓度最大为6.2 mg·L^-1,小于《大气污染物综合排放标准》中规定值。研究结果表明载气增湿蒸发工艺能有效浓缩切削废液,为工业化应用奠定了基础。     

基于流型的R290水平管内流动沸腾压降实验研究

丙烷(R290)作为一种性能优异的自然制冷剂,其两相流动压降特性在换热器设计及制冷系统优化等方面起到重要作用,而且目前对于低质量流率以及低饱和压力条件下的压降分析相对较少,且仅有少数研究结合流型进行分析。因此,开展了R290在内径6 mm的水平光管内压降特性实验研究。在如下实验工况范围内,质量流率70~190 kg·m^-2·s^-1,热通量10.6~73.0 kW·m^-2,饱和压力0.215~0.415 MPa,干度0~1,获取了压降实验数据,并进一步基于实验工况以及流型分析了加速压降、两相摩擦压降的变化趋势。对比了现有的摩擦压降关联式并基于Friedel模型,使用Re_v/Re_l 和液相Froude数Fr表征气液相相互作用,获取了一个新的基于流型的两相摩擦压降关联式。新模型可以很好地预测R290实验数据,预测结果的平均相对偏差(ARD)为-0.2%,平均绝对相对偏差(AARD)为5.2%,λ_30%为97.9%。对比文献中的实验数据,10组数据预测结果的ARD为10.0%,AARD为19.3%,λ_30%为80.3%,由此可见新模型具有一定的预测精度和适用性。     

分散颗粒和超声场对鼓泡塔内传质性能的影响

用双电导探针气泡特征参数测量系统实时测定超声场与分散颗粒(活性炭)对鼓泡塔水+CO₂体系气泡Sauter直径和体积传质系数影响的变化规律。实验结果表明:无活性炭颗粒添加时,多频超声场比单频超声场更有利于提高体积传质系数,输入功率为100 W、组合超声频率为20-50-100 kHz时,体积传质系数增幅达40%~64%;加入活性炭颗粒后,体积传质系数随加入活性炭固含量的增大呈现先增大后逐渐减少的趋势,气泡Sauter直径变化规律相反,当体系中活性炭固含量为1.0 kg·m^-3时,传质增强最明显。体积传质系数随加入活性炭粒径的减小呈现增大的趋势。与无活性炭颗粒(d_s=0)比较,活性炭(固含率1.0 kg·m^-3)粒径d_s=38 μm时,液相体积传质系数在扣除吸附传质效果后仍增大1.58倍,同时引入超声场后,当组合超声频率为20-50-100 kHz,超声功率100 W时,液相体积传质系数增大2.02倍,可见超声场和分散颗粒对气液传质有显著的协同强化作用。     

圆管内超临界CO2的阻力特性

对超临界二氧化碳在圆管内流动时的压降和摩擦系数进行了实验研究。实验段长为2000 mm,内径为10 mm。该实验压力范围为8～16 MPa,质量流量范围为1000～1525 kg·m^-2·s^-1,内壁热通量范围为96.5～283.2 kW·m^-2。得到了不同工况下竖直圆管内流动阻力的变化规律,分析了压力、质量流速、主流焓值和热通量对圆管内摩擦阻力的影响。实验结果表明摩擦压降随着质量流量和压力的增加而显著增加,特别是当主流焓值超过拟临界焓值后,其增加的速度变得更加剧烈,同时发现热通量对摩擦压降的影响较小。对于预测常物性摩擦因子的经验关联式并不能预测超临界CO₂的摩擦因子。因此提出了一个新的经验关联式,其实验数据在±20%误差范围内占83.31%。     

The influence of conditioning and regeneration on the separation behaviour of rigid surface filters for the separation of particles from gases

Rigid ceramic filter media can be used for the separation of particles from gas streams at elevated temperatures. In order to characterize comparatively the separation behaviour of differently structured filter media over a multitude of filtration cycles, experiments were performed in a filter test rig. The filter test rig used is built in accordance with VDI guideline 3926 and equipped with a special type of optical particle counter, which has the advantage of measuring both the particle size and the particle concentration simultaneously and in situ on the clean gas side.

It is demonstrated that by far largest share of the particles reaches the clean gas as a result of the filter regeneration process. During the subsequent formation of the dust cake, the particle penetration is almost zero. The regeneration parameters, actually in essence only the tank pressure, possess the decisive influence on the separation behaviour. In the course of a filtration experiment, the number of particles reaching the clean gas reduces with the increasing number of filtration cycles due to the filter conditioning. The particles arriving in the clean gas during regeneration are extremely fine. The mean particle size is almost entirely independent of the regeneration conditions and the filter cycle number. The fine particulate emissions measured here are an anthropogenic source of particulate matter in ambient air. They have to be considered as relevant with respect to the new standards of ambient air quality (PM 10 and PM 2.5).

It is shown that membrane-coated ceramic filter media at identical operating conditions exhibit, as expected, a better separation and regeneration behaviour than fibrous ceramic, open-pored filter media. However, the advantages are at the expense of a 10 times higher pressure loss, which is essentially attributed to the membrane layer.     

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。     

聚偏氟乙烯/聚二甲基硅氧烷渗透气化膜在丁醇分离中的应用

通过相转化法制备PVDF多孔支撑膜,在其上涂覆致密的PDMS分离层制备得到PVDF/PDMS复合膜,用于丁醇的分离纯化。以丁醇水溶液为原料液,流速为1.6 L·min^-1,丁醇浓度为15 g·L^-1,温度为37℃时, PVDF/PDMS复合膜的总通量为158.2 g·m^-2·h^-1,分离因子为17.3。向丁醇水溶液中按丁醇：丙酮：乙醇比例为6：3：1添加丙酮和乙醇模拟发酵液,PVDF/PDMS复合膜的总通量升高到189.5 g·m^-2·h^-1,分离因子降低到14.8。进一步考察了以丙酮-丁醇-乙醇（ABE）发酵液为原料液的渗透气化膜分离性能,发酵液中不存在菌体时,PVDF/PDMS复合膜的总通量和分离因子分别为120.2 g·m^-2·h^-1和19.7,而菌体存在时,复合膜的总通量和分离因子分别为122.1 g·m^-2·h^-1和16.7。与PDMS均质膜相比,PVDF/PDMS复合膜在丁醇分离过程中的分离性能有了显著的提升, 具有潜在的应用价值。     

粉尘沉积形成滤饼结构的分形研究

粉尘在过滤过程中,随过滤时间的增加,在过滤介质内部不断沉积形成滤饼,目前人们还主要从过滤的整体行为的角度去研究过滤问题,由于测试手段和研究方法的限制,对直接决定过滤行为的滤饼结构则研究很少。然而,要想深化对过滤机理的认识,揭示滤饼中粉尘颗粒之间的相互作用力与形成滤饼孔隙率的关系,了解滤饼中"尘滤尘"的机理,以提出提高粉尘捕集效率,减少过滤阻力,寻求强化清灰的措施,就必须对滤饼的内部结构进行研究。通过对滤饼结构进行分形研究,寻求滤饼结构分形维数与物料的比表面积及各操作条件的关系,探索滤饼孔隙率、滤饼厚度及粉尘颗粒直径、粒径分布与滤饼分形维数的关系。     

Experimental Study on the Loading Characteristics of Needlefelt Filters with Micrometer-Sized Monodisperse Aerosols

In this work, three types of needlefelt filters, made of Polyester (PE), Ryton Sulfar (RS), and Polyaramid (PA), were tested to in- vestigate the aerosol loading characteristics of fabric filters when challenged with micrometer-sized monodisperse potassium sodium tartrate (PST) particles. A fibrous filter with packing density of 9%, thickness of 0.38 mm, and fiber diameter of 5.1 θ m was included for comparison. A vibrating orifice monodisperse aerosol generator was used to produce three different sizes (5, 10, and 20 θ m) of PST particles for aerosol loading experiment. An ultrasonic atomizing nozzle and a TSI constant output nebulizer were used to generate polydisperse PST particles for the aerosol penetration test. The aerosol penetration of submicrometer-sized particles through the filters was measured by using a Scanning Mobility Particle Sizer. An Aerodynamic Particle Sizer was used to measure the penetration fraction of aerosol particles larger than 0.8 θ m. The pressure drop across the filter was monitored by using pressure transducers, which were calibrated against an inclined manometer. Airflows of 5, 10 , 20, and 30 cm/s were used to study the flow dependency. The aerosol penetration results showed that the particles larger than 3 θ m did not penetrate the clean fabric filters tested in the present study. The loading curves (plots of pressure drop against sampling time) displayed three regions: an initial region of fast increase, a transition region, and a final linear region after the dust formation point. After the formation point of the dust cake, both fabric and fibrous filters shared the same slope (of the loading curves). The slope of different regions of the loading curves was determined by many factors, such as size of challenge aerosol, face found to be critical to the performance of the fabric filters. In order lower porosity, which caused an extra rise in pressure drop across velocity, surface treatment, and the compressibility of the dust cake forming on the filter. The method of final surface treatment was to avoid the unnecessary rise in air resistance, the melting clumps formed during final surface treatment should be as thin and narrow as possible, just enough to support the filter bag cleaning. From the standpoint of filter quality and energy consumption, the low filtration velocity has to be adopted whenever possible, because high filtration velocity not only led to lower filter quality (in particular for submicrometer-sized particles) but also created dust cake of lower porosity, which caused an extra rise in pressure drop across thet dust cake.     

Influence of pulsing-air injection distance on pressure drop in a coke dust bagfilter

The effect of the pulsing-air injection distance between the nozzle and venturi on total pressure drop was investigated in a pilot-scale pulse-jet bagfilter for coke dust of a steel mill factory. Theoretical and empirical models were used to predict the pressure drop. The empirical model contains two parameters—dust cake resistance and exponent of areal mass density—to be estimated by experiment. The optimum injection distance for minimizing the total pressure drop was evaluated by 64 experimental data at a fixed filtration velocity and pulse pressure in the practical ranges of dust concentration and pulse interval time. The dust cake resistance shows a minimum value at the optimum injection distance. The empirical model is in good agreement with the experimental data, showing a correlation coefficient of 0.952.     

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.     

十二醇-癸酸-纳米粒子复合相变材料传热性能

针对有机相变材料热导率低的共性,以质量比为58.47:41.53的脂肪烃类低共熔有机物十二醇(DA)-癸酸(CA)为基液,添加纳米粒子MWNT、Cu、Al₂O₃及分散剂SDBS制备出纳米复合相变材料,从纳米粒子种类、添加浓度及超声时间方面研究其对复合有机相变材料热物性的影响。实验发现MWNT、Cu、Al₂O₃的添加都可以不同程度上提高DA-CA的热导率。当超声时间为50min、纳米粒子浓度均为0.1g·L^-1时3种纳米复合材料的热导率大小依次是:MWNT>Al₂O₃>Cu。最优例:超声分散时间90min,DA-CA+MWNT(0.1g·L^-1)+SDBS(0.2g·L^-1)的热导率最大,为0.3602W·m^-1·K^-1,相较DA-CA提高了20.5%,在不影响基液热物性的基础上具有良好的热稳定性。     

水平微细管内CO2流动沸腾压降特性

对CO₂在内径1.5 mm水平微细管内流动沸腾换热摩擦压降特性进行了实验研究。实验工况：热通量（7.5～30 kW·m^-2）、质量流率（300～600 kg·m^-2·s^-1）、饱和温度（-40～0℃）。实验结果表明：热通量的增加对摩擦压降影响很小,几乎为零;质量流率是影响摩擦压降的最主要因素;随着饱和温度的升高摩擦压降减小;干度对摩擦压降影响主要由管内流型变化导致。将实测摩擦压降变化趋势绘制于CO₂流态图中,比较发现理论预测摩擦压降最大值落在环状流末端区域。实验过程中对各个工况管内流态进行可视化研究,理论分析所采用的流态形式与实际CO₂在微细通道内所具有的流态类型基本一致。     

Improvements to dust filtration through acoustic agglomeration and atomization

Based on the theories of acoustic agglomeration and dust wet removal, an experimental apparatus was constructed to study the combined effects of acoustic agglomeration and atomization humidification in the pretreatment process to analyze the filtration performance of filter material. According to the concentration of coal-fired fly ash chosen in the experiments, the proper amount of atomization humidification and the proper sound pressure level (SPL) were determined. Under the relative humidity (RH) of 69% and with SPL in the range of 100 dB to 135 dB, the removal efficiency of fly-ash, the compressibility of the fly-ash particle layer on the filter media, and the performance of pulse filter cleaning were studied. The results indicate that the combined effects of sound fields and atomization humidification can effectively remove PM₁₀ and PM_2.5, and change the interaction and movement of particles, which can improve the pore structure of the fly-ash particle layer and increase the porosity of the dust layer. The results also indicate that with the proper amount of atomization humidification and appropriate SPL, the joint acoustic-atomization pretreatment can delay the filter material blocking, which reduces the pulse filter cleaning frequency and extends the filter cleaning cycle. It can also reduce the residual resistance after filter cleaning and prolong the operating lifetime of the filter media.

© 2017 American Association for Aerosol Research     

Effect of Bi-Modal Aerosol Mass Loading on the Pressure Drop for Gas Cleaning Industrial Filters

The typical size distribution of emission particulates is bi-modal in shape with particles in the fine mode (< 2.0 w m) and the coarse mode. An experimental study of pressure drop across industrial gas cleaning filters has been conducted using a particle mixture of fine alumina and coarse Arizona dusts with a rotating aerosol disperser to generate the bi-modal test aerosol. Pressure drop increased linearly with increasing mass loading. The pressure drop was found to be strongly dependent upon the mass ratio of fine to coarse particles. The measured specific resistances of HEPA filters at a given face velocity of 5 cm/s were 1.18 2 10 6 , 5.89 2 10 5 , 4.67 2 10 5 , 2.65 2 10 5 , and 1.18 2 10 5 s -1 for the mass ratio of fine to coarse particles of fine only, 50%:50%, 25%:75%, 10%:90%, and coarse particles only, respectively. The pressure drop across the loaded filter increased with increasing face velocity. The larger the mass ratio of fine to coarse particles and the higher the face velocity are, the faster pressure drop rises. The fine particles and the greater inertia of the particle moving fast would cause a denser cake formation on the filter surface, resulting in a greater specific resistance to the gas flow.