氨-水体系中硝酸钾结晶的生长特性

采用MSMPR结晶器研究了不同悬浮密度、氨水浓度和过饱和度下,KNO3在氨-水体系中的结晶动力学特性,并得到KNO3在氨水溶液中的结晶动力学模型.研究结果表明:随着悬浮密度的减少,晶体平均粒径增大,粒径分布变得均匀;氨的浓度增加,结晶成核 速率与生长速率均下降,晶体平均粒径减少,但粒径分布变均匀;随着过饱和度的加大,结晶成核速率与生长速率均增加,但晶体平均粒径减小,且粒径分布变差.研究结果可为硝酸钾生产工艺中结晶器的设计提供基础数据.     

基于晶体浓度分布的结晶过程放大研究

使用计算流体力学的方法,对不同大小流化床结晶器(FBC)内的流体动力学状态进行模拟。考察不同循环进料流速下,晶体颗粒在不同规模的结晶器内的悬浮状态,以此对结晶的放大过程进行分析。结果表明,晶体颗粒大小相同的情况下,结晶器中的晶体浓度分布基本取决于流化床内流体流动的能量。     

搅拌速度对氯化钾结晶影响的研究

通过MSMPR结晶器系统对纯氯化钾及加入光卤石母液后的溶液,采用不同的搅拌速度及不同的桨叶材料进行了氯化钾结晶动力学的研究,计算出了不同的搅拌速度及不同的桨叶材料下氯化钾结晶的基本动力学关系式,分析了氯化钾结晶过程中成核与生长速率的影响程度,为用光卤石生产氯化钾产品,提高其取得率及增大晶体粒度提供了理论依据.     

大粒度元明粉工艺技术装置设计探讨

市场的多样化需求,大粒度高品质元明粉将赢得竞争。探讨设计符合结晶学原理又易于改造或新建的蒸发结晶设备。控制好结晶过程是增产增效的重要手段。本文着重从结晶理论出发,对影响结晶粒度的因素进行分析,提出具有较强适应性的蒸发结晶器的设计。     

氯化钠结晶工艺优化设计

2011年我国国内医药用氯化钠产量已超10万t,产品基本采用多效真空蒸发结晶工艺,普通工艺生产的产品结晶在储存过程易出现板结,给流转、使用带来非常大的问题.通过对氯化钠生产过程中的成核、结晶理论进行分析,将套筒隔室武结晶技术和延时结晶技术相结合,使氯化钠产品晶体结构、粒度及品质有了很大的提高.通过研究表明,新工艺生产的氯化钠产品粒径达0.75 mm以上,晶体呈椭圆型（鱼籽状）,产品质量指标优于注射级氯化钠产品标准,是解决氯化钠结晶在储存过程板结、结晶生长致硬块化的很好途径.     

糖液物理场在制糖工业结晶中作用的研究

基于工业结晶过程的粒数衡算原理,本文作者首先提出,糖液物理场在蔗糖工业结晶中将明显地影响着产品的粒度分布。然后,通过对实际结晶体系的实验,作者进一步验证了运一观点,从而使人们可以从一含新的角度探讨工业结晶过程的粒度分布控制问题。     

添加剂对硫酸钠晶体粒度的影响

溶液结晶过程中,添加剂的加入对晶体的结晶动力学和热力学特征将产生一定的影响.文章研究了十二烷基苯磺酸钠和重铬酸钾作为添加剂对无水硫酸钠晶体粒度的影响.研究结果表明:十二烷基苯磺酸钠的加入增大了硫酸钠结晶过程的界面能,从而抑制自发成核过程的发生,促进晶体的生长,改善晶体的粒度.分别以十二烷基苯磺酸钠和重铬酸钾作为添加剂,在有效添加剂量为40mg/kg时,0.177mm以上硫酸钠筛上物分别为67.18%和51.12%.搅拌速度对硫酸钠晶体粒度有重要影响,正交实验确定的最佳结晶控制条件为:添加剂加入量40mg/kg、搅拌速度240r/min、晶种量40g、停留时间40min.     

悬浮状态下氯化钠晶体二次成核过程研究

实验利用60 L流化结晶装置,研究了悬浮状态下晶种粒度、流体循环速率以及循环时间对碰撞成核速率特征、规律及晶核粒度分布的影响.发现二次成核过程中,破碎机理占主导作用,碰撞后的晶体碎片具有连续分布;母晶粒度和循环速率不仅影响颗粒的碰撞能,而且对颗粒的悬浮状态及分布状况有明显作用;成核速率随晶种粒度及流体速度的增大而增加,循环时间对粒度较大晶体颗粒的二次成核有明显作用.     

光卤石分解制取KCl结晶过饱和度影响的研究

通过MSMPR结晶器系统对光卤石加水分解,采用不同的过饱和度进行氯化钾结晶动力学研究,建立了光卤石分解制取氯化钾结晶过程中氯化钾结晶动力学模型。探讨了氯化钾结晶过程中过饱和度对成核与生长速率的影响程度,为用光卤石生产氯化钾产品,提高其取得率及增大晶体粒度提供了理论依据。     

Online ice crystal size measurements during sorbet freezing by means of the focused beam reflectance measurement (FBRM) technology. Influence of operating conditions

In ice cream and sorbet manufacturing small ice crystals are desired to deliver a product with a smooth texture and good palatability. This research studied the influence of the operating conditions on the ice crystal size and the draw temperature of the sorbet during the freezing process. The evolution of ice crystal size was tracked with the focused beam reflectance measurement (FBRM) technique, which uses an in situ sensor that makes it possible to monitor online the chord length distribution (CLD) of ice crystals in sorbets containing up to 40% of ice. The refrigerant fluid temperature had the most significant influence on the mean ice crystal chord length, followed by the dasher speed, whereas the mix flow rate had no significant influence. A decrease in the refrigerant fluid temperature led to a reduction in ice crystal size, due to the growth of more small ice crystals left behind on the scraped wall from previous scrapings. Increasing the dasher speed slightly reduced the mean ice crystal chord length, due to the production of new small ice nuclei by secondary nucleation. For a given refrigerant fluid temperature and dasher speed, low mix flow rates resulted in lower draw temperatures, due to the fact that the product remains in contact with the freezer wall longer. High dasher speeds warmed the product slightly, due to the dissipation of frictional energy in the product, the effect of which was in part moderated by the improvement in the heat transfer coefficient between the product and the freezer wall.     

Crystallization Kinetics of Alpha-Lactose Monohydrate in a Continuous Cooling Crystallizer

The crystallization of alpha-lactose monohydrate in a continuous cooling crystallizer was investigated at various temperatures and super-saturations. The population balance model was used to analyze the product crystal size distribution as determined by the Coulter Multi-Sizer for each condition studied. Nucleation and growth values were thereby determined for each temperature and supersaturation. Kinetic models were then developed for both nucleation and growth to demonstrate the effects of the operating parameters. The results showed that the nucleation process had a temperature dependence with an activation energy of 17.0 kcal/mole and that nucleation increased with the 1.9 power of supersaturation and the 1.0 power of the suspension density (mass of crystals). The growth process was found to have a temperature dependence with an activation energy of 22.1 kcal/mole and to be a second order function of the supersaturation.     

蔗糖转化生产纯结晶果糖的工艺研究

本文研制出了一条以蔗糖为原料，生产纯结晶果糖技术路线。其工艺流程包括：①蔗糖的水解，②果糖、葡萄糖的分离，③果糖液精制，④果糖结晶。采用化学法分离果、葡糖浆，并得到了可进行果糖结晶的高质量的果糖液，克服了色谱分离技术要求高、在我国难以实现工业化的缺点。在进行果糖结晶前，对果糖液进行脱盐和脱色等精制处理。可根据不同的要求采取两种不同的结晶工艺，生产出两种结晶果糖产品。一种产品为小颗粒结晶果糖，另一种产品为大颗粒结晶果糖，其晶体颗粒大小达到０．２～０．３ｍｍ。两种结晶果糖产品果糖的结晶率可达到６０％。其纯度均超过试剂果糖纯度。采用本工艺流程，１００吨蔗糖可产２４．７吨结晶果糖，３２．５吨结晶葡萄糖，５３．８吨果葡糖浆。     

蔗糖结晶过程的粒度分布及其控制

蔗糖晶体的粒度是衡量其质量的重要指标之一。研究蔗糖结晶过程的晶体粒度分布对提高蔗糖质量和蔗糖连续结晶的实践具有明显的指导意义。本论文通过对晶体粒度的计量及结晶过程粒度分布的研究,着重分析了有关影响晶体生长分散的因素,从而指出控制蔗糖晶体粒度及其分布的途径。     

Evaluating the crystallization of lactose at different cooling rates from milk and whey permeates in terms of crystal yield and purity

The cooling rate of supersaturated lactose solution is one of the important parameters determining the yield and size distribution of lactose crystals. The influence of increasing cooling rate on lactose crystallization and quality of lactose crystals was evaluated in concentrated solutions prepared from deproteinized whey powder (DPW) and milk permeate powder (MPP). Concentrated permeates (DPW and MPP) with 60% (wt/wt) total solids were prepared by reconstituting permeate powders in water at 80°C for 2 h for lactose dissolution. Three cooling rates, 0.04°C/min (slow), 0.06°C/min (medium), and 0.08°C/min (fast) were studied in duplicate. A common rapid cooling step (80 to 60°C at 0.5°C/min) followed by slow, medium, and fast cooling rates were applied as per the experimental design from 60 to 20°C. After crystallization, the crystal slurry was centrifuged, washed with cold water, and dried. The dried lactose crystals were weighed to calculate the lactose yield. Final mean particle chord lengths were measured at the end of crystallization using focused beam reflectance measurement for slow, medium, and fast cooling rates, and observed to be not significantly different for DPW (27–33 µm) and MPP (31–34 µm) concentrates. Similarly, the lactose yield for slow, medium, and fast cooling rates in the DPW and MPP concentrates were in the range of 71 to 73% and 76 to 81%, respectively, and no significant difference between the 3 cooling rates was found. Qualitative analysis of dried lactose crystals exhibited no noticeable differences in the crystal purity with increasing cooling rate. This study evaluated the possibility of reducing the crystallization times by 8 h compared with current industrial practice without compromising the crystal yield and quality.     

Effect of Shear on the Rheology and Crystallization of Palm Oil

ABSTRACT:  This article reports on the impact of shear on crystallization upon cooling of palm oil. Samples were cooled down under shear from 70 to 10 °C, then kept at this temperature, while performing rheological measurements using a controlled shear rate rheometer and rheo-optical observations using optical microscopy and small-angle light scattering. Shear rates between 1 and 300 s⁻¹ were investigated. Two crystallization steps were observed, characterized by associated viscosity increases. The effect of shear on these 2 crystallization processes was investigated. Shear was shown to influence almost all of the steps of the structuring process of the crystallizing palm oil. The spherulite size and growth rate during the 1st crystallization are affected by shear. The onset time of the 2nd crystallization process strongly depends on the extent of shear. The steady state structures after the 1st and 2nd crystallization processes constituted of a suspension of aggregates of spherulites are controlled by the applied shear rate.
Practical Application: The texture of crystallized vegetal fats and subsequent end product properties depend on the structure developed during the crystallization process. This structuring process is strongly influenced by the thermo-mechanical history applied to the product (cooling rate, degree of undercooling, annealing time, application of flow). This article shows how the shear rate as well as extent of shear affects the different steps of the crystallization and aggregation processes in the case of palm oil after the 1st crystallization.     

Crystallization in Lactose Refining—A Review

In the dairy industry, crystallization is an important separation process used in the refining of lactose from whey solutions. In the refining operation, lactose crystals are separated from the whey solution through nucleation, growth, and/or aggregation. The rate of crystallization is determined by the combined effect of crystallizer design, processing parameters, and impurities on the kinetics of the process. This review summarizes studies on lactose crystallization, including the mechanism, theory of crystallization, and the impact of various factors affecting the crystallization kinetics. In addition, an overview of the industrial crystallization operation highlights the problems faced by the lactose manufacturer. The approaches that are beneficial to the lactose manufacturer for process optimization or improvement are summarized in this review. Over the years, much knowledge has been acquired through extensive research. However, the industrial crystallization process is still far from optimized. Therefore, future effort should focus on transferring the new knowledge and technology to the dairy industry.     

冷却速率对蔗糖连续冷却结晶过程的影响研究

考虑初级成核和二次成核的影响作用，借助于现代计算机技术研究蔗糖连续冷却结晶过程冷却速率对晶体群产品均匀率的影响规律，给出了最适冷却速率，并从理论上进行了探讨，以指导蔗糖连续冷结晶的操作运行。     

改善氯化钾结晶粒度的分析

针对察尔汗盐湖丰富的钾资源,青海盐湖发展公司对冷结晶提取的氯化钾结晶粒度从结晶的宏观和微观机理、影响结晶的因素、设备的选型、工艺参数的控制等多种因素分析了影响氯化钾结晶粒度的原因,并提出了技术的改进和建议。     

氢氧化镁结晶动力学研究

结晶动力学的研究是结晶器设计、结晶过程放大和优化的重要依据。文章研究了间歇反应过程中氢氧化镁结晶动力学,采用间歇动态法对结晶过程基本参数进行测试,根据粒数衡算和质量衡算关系,利用晶体成核生长经验公式拟合出氢氧化镁反应结晶动力学表达式。结果表明:氢氧化镁结晶过程晶体生长速率与粒度无关,得到了过饱和度、悬浮密度与成核速率之间的关系。     

Pretreatment of Hanford medium-curie wastes by fractional crystallization

Acceleration of the schedule for decontamination of the Hanford site using bulk vitrification requires implementation of a pretreatment operation. Medium-curie waste must be separated into two fractions: one is to go to a waste treatment and immobilization plant and a second, which is low-activity waste, is to be processed by bulk vitrification. The work described here reports research on using fractional crystallization for that pretreatment. Sodium salts are crystallized by evaporation of water from solutions simulating those removed from single-shell tanks, while leaving cesium in solution. The crystalline products are then recovered and qualified as low-activity waste, which is suitable upon redissolution for processing by bulk vitrification. The experimental program used semibatch operation in which a feed solution was continuously added to maintain a constant level in the crystallizer while evaporating water. The slurry recovered at the end of a run was filtered to recover product crystals, which were then analyzed to determine their composition. The results demonstrated that targets on cesium separation from the solids, fractional recovery of sodium salts, and sulfate content of the recovered salts can be achieved by the process tested.