Impact of agglomeration on crystalline product quality within the crystallization process chain

The quality of crystalline products, defined by e.g. purity or crystal size distribution (CSD), is primarily dominated by crystallization conditions but influenced by further downstream processes like solid‐liquid separation and drying also. Through uncontrolled agglomeration within the crystallization process chain the purity or CSD can be negatively affected. Therefore, in context of process optimization, missing knowledge of the impacts on the final product can lead to product batches out of specification. To increase the understanding of agglomeration and to provide insight into the relevance of holistic process optimization the agglomeration behavior of L‐alanine crystals is exemplarily quantified over the crystalline process chain. For the quantification the agglomeration degree (Ag) and the agglomeration degree distribution (AgD) are determined. The results show that the product quality achieved after crystallization is significantly affected by agglomeration during drying. Especially if washing after solid‐liquid separation is omitted, a broadening of the CSD is observed. Moreover, the evaluation by the AgD indicates that the final product can be ‐ despite similar characteristics of the CSD ‐ highly different. Consequently, it can be concluded that the characterization of the product quality by the CSD alone is insufficient and the quantification of agglomeration is essential for process optimization.     

Agglomeration of sub-micron particles by a non-thermal plasma electrostatic precipitator

Non-thermal Plasma agglomeration is presented as a promising process to reduce the number concentration of sub-micron particles in an acrylic duct, which included a saw-tooth electrode and a wire-plate electrostatic precipitator (ESP). The generated plasma by pulse-energized ESP, the particle agglomerations were controlled under operating conditions such as pulse voltages, pulse frequencies, dust loadings, and gas velocities. When gas velocity increased from 0.5 to 1 m s⁻¹ at 45 kV_p, 20 kHz, it was found that efficiency was increased. At gas velocity of 1 m s⁻¹, the sub-micron particle number reduction efficiency for all particle sizes was over 90% in ESP.     

凹凸棒黏土对燃煤PM2.5排放及团聚捕集特性影响

在固定床反应系统上考察凹凸棒黏土对燃煤可吸入颗粒物PM_2.5的排放及团聚捕集特性影响,分析凹凸棒黏土添加量以及添加凹凸棒黏土情况下燃烧气氛、燃烧温度和钙硫物质的量比等参数对燃煤PM_2.5的数量浓度、质量浓度以及团聚捕集率的影响规律。结果表明,煤燃烧过程中添加凹凸棒黏土可以显著降低PM_2.5排放浓度,凹凸棒黏土的添加量不宜超过3%(质量分数);空气气氛下燃烧产生的PM_2.5多于O₂/CO₂气氛;随着钙硫物质的量比的增大,PM₁的质量浓度减小,但PM_1~2.5的质量浓度增大,颗粒物的粒径有向更大粒径转移的趋势;燃烧温度的升高会促进PM_2.5各粒径范围颗粒物的生成,降低了凹凸棒黏土对PM_2.5团聚捕集率。     

A parametric study of cohesive particle agglomeration in a shear flow—numerical simulations by the discrete element method

In this study, we investigate numerically the shear-induced agglomeration of cohesive inertial particles in a simple shear flow. We conduct a series of numerical simulations by implementing a soft-sphere collision model. Post-processing tools are developed in-house to analyze the results of the simulations in terms of transient and terminal numbers of primary particles and agglomerates, magnitudes and distributions of agglomerate size, and fractal dimension as functions of the salient physical parameters. The obtained numerical results compared with existing transient models suggest that, as the system transitions from formation of duplets to larger agglomerates, in most cases the number of agglomerates in the system reveals clear maxima. The results also show evidence of agglomerate densification, as weaker agglomerates with lower fractal dimensions are broken up and stronger ones with higher fractal dimensions are formed. Furthermore, we found that a simple theoretical model proposed by, among others, Chimmili et al. is able to predict the temporal development of the agglomerate size properly.     

古诺竞争的选址模型研究

在Paul提出的圆环形城市模型基础上,通过引入成本分布函数,扩展了Pal和Matsushima的模型,建立了一个新的带有成本因子的选址与产量竞争的双寡头竞争模型.结果表明:如果成本分布函数是常数,那么两企业均衡地分布于圆环形城市将达到完美的纳什均衡;如果成本分布函数是严格凸函数,当运输系数较小时,企业将在产品成本分布函数最小点处集聚,并各自达到利润最大化.     

Characterization of palmitic and lauric acid aerosols from rapid expansion of supercritical CO2 solutions

Palmitic acid aerosols and lauric acid aerosols were generated by rapid expansion of supercritical CO₂ solutions. The particle properties were analysed by rapid-scan infrared spectroscopy in situ, by X-ray powder diffraction, with a scanning mobility particle sizer, and by scanning electron microscopy. Particles with irregular elongated shapes were found. Most particles and agglomerates have sizes between 250 and 750 nm. Fewer agglomerates with sizes up to several microns are observed. Our investigation reveals that strong agglomeration takes place at the Mach disc. Palmitic and lauric acid particles are both crystalline and most particles crystallize in the C-form.     

燃煤超细颗粒团聚模拟研究

针对煤燃烧过程中产生的超细颗粒有效控制问题,提出了一种配合中国目前电站除尘方式的新方法,其核心思想就是将一种表面具有较高粘附活性的团聚剂溶液喷入烟气中,使烟气中超细颗粒物团聚成较大颗粒物后能够被电站现有除尘装置所除去。为了证明这种方法的有效性,建立了模拟锅炉烟尘流动的小型团聚实验台并进行实验研究;在此基础上,模拟了团聚剂对超细颗粒物的团聚效果,计算结果表明:烟气流量、烟尘浓度、团聚剂流量和浓度等都是影响超细颗粒物团聚的重要因素;若保证烟气温度降低幅度在10℃以内,且烟气流量和烟尘浓度相同时,适当增加团聚剂的浓度或流量,可使超细颗粒物的团聚效率达到70%,为进一步实验研究提供理论依据。     

循环流化床收集器内颗粒团聚流动特性的研究

基于气固两相流理论和气溶胶动力学原理,建立流化床收集器(CFBA)内气体细颗粒聚团气固两相双流体模型。对不同入口气体速度、初始颗粒尺寸分布和不同颗粒团聚形成机理下收集器内颗粒聚团流动的流体动力特性进行数值模拟。研究结果表明湍流运动和剪切作用对颗粒聚团的形成起主要作用,布朗运动对颗粒团聚形成的影响可忽略不计。吸收颗粒可有效提高捕获细颗粒和颗粒聚团形成的能力。     

Identification of the Dispersion Behavior of Surface Treated Nanoscale Powders

The stability of highly acidic metal oxide surface treatments on rutile titanium dioxide nanopowders (40 nm nominal particle size) is examined. Dispersions are characterized in terms of their sedimentation behavior and light scattering pattern. Using elliptically polarized light scattering (EPLS), agglomerates are identified as fractal structures and size analysis is performed according to the measured fractal dimension. The effect of ultrasonication on agglomerate size and structure (compactness) is quantified for tungsten oxide and molybdenum oxide surface treatments, as well as untreated titanium oxide. Surface treatments are shown to increase dispersion stability, as witnessed by the decreased size of large agglomerates and sedimentation behavior. The EPLS fractal studies, combined with ultrasonication analysis, reveals information of agglomerate shapes, primary particle bonds and structures, and agglomerate growth mechanisms.