Progressive Freeze Concentration for Volume Reduction of Produced Water and Biodiesel Wastewater

One way to conserve fresh water resources is by reusing water from wastewater. For instance, water can be removed from wastewater through formation of ice crystal layers by progressive freeze concentration (PFC). The application of PFC to remove water from produced water and biodiesel wastewater was assessed through the final concentration of concentrated wastewater and purity of melted ice crystals. No PFC study has been done on these applications. In order to evaluate the efficiency of PFC, the effective partition constant (K) and separation efficiency (S_E) were calculated for the effect of stirring rate and coolant temperature. The results demonstrate that PFC is a more practical method for produced water, as compared to biodiesel wastewater which is based on the value of low K and high S_E.     

Modelling of heat transfer for progressive freeze concentration process by spiral finned crystallizer

This study presents a novel design for a spiral finned crystallizer which is the primary element of progressive freeze concentration (PFC) system,which simplifies the setup of the conventional system.After the crystallizer has been designed,the research experiments have been conducted and evaluated through a thorough analysis of its performance by developing a mathematical model that can be used to predict the productivity of ice crystal at a range of coolant temperature.The model is developed based on the basic heat transfer equation,and by considering the solution's and the coolant's convective heat transfer coefficient (h) under the forced flow condition.The model's accuracy is verified by making comparison between the ice crystal mass' experimental value and the values predicted by the model.Conseouentiv,the study found that the model helos in enhancing the PFC system.     

Review: Parametric Study on the Performance of Progressive Cryoconcentration System

Progressive cryoconcentration (PC) is gaining acceptance in solution concentration process as it could provide an easy separation and ice purification with relatively low energy. In fact, the advantages of PC process as compared to the other concentration methods have led the growth of related studies that aim to provide the best system or condition for the separation process involved. Apart from the provision of appropriate equipment, the PC process should also be conducted at its optimum conditions of operating parameters involved, which could give the highest separation efficiency. Hence, relationship between the parameters, which covers both manipulated and determinant parameters should be studied first. This review summarizes the previous conducted studies on the effect of various operating parameters on the PC performance, which includes effect of coolant temperature, solution flowrate, initial solution concentration, freezing time, ice crystal front growth rate, and stirring rate.     

冰晶尺寸及其对微波辅助冷冻干燥的影响

Freeze drying of an aqueous solution would result in the non-uniform distribution of solute concentration.Because ice is almost transparent to microwave, therefore such a non-uniform distribution may affect the microwave assisted freeze drying. The direct observation of the ice crystals formed under microscope reveals that the ice crystal sizes formed from de-ionized water depend on the cooling rate with fast cooling rate giving smaller ice crystals as expected. Once there is a sufficient amount of solute mixed with the de-ionized water, for example the reactive red,the size and its distribution are not very much dependent on either cooling rate or the final temperature provided there is sufficient time of cooling and the final temperature is not too low. The size of ice crystals formed within the solution of reactive red is usually below 100μm with a freezing rate of 1℃·min^-1 for a droplet of the size of less than 1 mm. A simplified simulation indicates that such a small ice crystal would not cause a significant non-uniform distribution of temperature for microwave assisted freeze drying. When the ice crystal size is larger than 5 mm, heat conduction from the solute concentrated region to the ice region mav need to be considered.     

高浓度尿素废水泠冻浓缩极限

冷冻浓缩技术是处理尿素厂废水和尿液等高浓度尿素废水的有效方法之一,浓缩极限的确定则是预测和评价该工艺最高水回收率和工作效率的必要条件.以尿素溶液为研究对象,采用差示扫描量热技术分析了溶液在冷冻过程中的相态变化规律,通过冷冻试验确定了溶液发生尿素共晶析出时的浓度;以尿液为对象,研究了确定高浓度尿素废水冷冻浓缩极限的方法.研究结果表明：尿素废水在达到浓缩极限之前,当尿素浓度高于26.3%时,继冰晶析出之后会共晶析出尿素;尿素废水在浓缩极限处呈玻璃态,由差示扫描量热分析可确定废水玻璃化转变温度、推算冷冻浓缩工艺最高水回收率;尿液的玻璃化转变温度为-108.33 ℃,相应的溶液浓度为57.92%,冷冻浓缩可达到的最高水回收率为97.75%.     

Ice-mould freeze casting of porous ceramic components

Porous, hollow ceramic components were produced by freeze casting technique. For this purpose aqueous slurries with high solid contents were prepared which were stable against freezing down to at least −5 °C. Ice cores were made by coating steel components with freezing water which were subsequently dip-coated with the ceramic suspensions. After freeze drying which removes both, the ice core and the frozen suspension liquid, and sintering, ceramic components with a high amount of open porosity including steel parts could be achieved. As an example hydroxyapatite was used for showing the opportunities of the freeze casting technology among others for applications in the field of bone replacement. The influence of the solid content of the hydroxyapatite slurries on the ice crystal growth has been investigated by means of compact hydroxyapatite bodies which were prepared by freeze casting using ice moulds with cylindrical cavities.     

Cell-friendly regulation of ice crystals by antifreeze organism-inspired materials

There is a dilemma between ice growth inhibition and cell-threatening sharp-edged ice formation, dominating an unfavorable efficiency of cell cryoprotection using ice control materials (ICMs). Herein, we design different-type antifreeze organism-inspired ICMs and show the cell-friendly regulation of ice crystals by a synergistic effect for cell cryoprotection. Preferred rapid adsorption of “high-diffusivity ICM” on the curved ice crystal surface induced by “ice-binding ICM,” owing to the Gibbs–Curie–Wulff theorem, promotes smooth-shaped and small ice crystal formation during the freeze–thaw cycle. Meanwhile, their intracellular and extracellular osmotic balance well protects the cryopreserved cells. All-round protection benefits cell survival to achieve a cryopreservation efficiency of 97%. After cryopreservation, ice-binding ICM exhibits double thermosensitive behaviors to directly encapsulate post-thaw cells by gels, to further support cell-based therapies. This work provides an in-depth understanding of cell cryoprotection, and paves the road to the development of even better ICMs for biospecimen cryopreservation.     

Freeze concentration of milk and saline solutions in a liquid–solid fluidized bed: Part I. Experimental

Fluidized bed freeze concentration is a novel technique that uses a fluidized bed heat exchanger (FBHE) to concentrate liquids through the process of freeze concentration. Ice formed on the cooled surface of the vertical heat exchanger is removed by particles fluidized inside the FBHE. In this paper, the operating conditions are reported for freeze concentration of saline solutions and milk in FBHE. The operation was tested with equilateral 4 mm and then 5 mm particles at different bed porosities, cooling rates and NaCl and milk concentrations. Experiments with NaCl solutions showed that the 5 mm particles were more aggressive than 4 mm in removing ice from the heat exchanger wall. Whilst particle size was considered responsible for this, the particle shape could have played a major role. A theoretical analysis on effect of FBHE parameters showed the size of particles to exert influence on FBHE performance. The result from experiments with skim milk and whole milk maintained the conclusions formed previously with NaCl experiments with regard to the effect of tested parameters on operational stability. However, the ice formed from milk was more difficult to remove than the ice formed from NaCl solutions. Whole milk showed even more resistance to ice removal. Skim milk was freeze concentrated from 13% to 27% TS content in these experiments. Installing a wash screen further improved the purity of separated ice.     

Freeze Purification of Water Utilizing a Cold Plastic Surface and Ice-Liquid Separation with a Centrifuge

Abstract

Freeze purification utilizing a cold plastic surface rather than a metallic surface may be advantageous. Plastics are more inert and weaker ice crystal nucleating agents, and possess low ice-plastic adhesion. Batch experiments were performed to test the viability of a freeze purification technique. One-liter samples of an aqueous feed solution containing 20 g/L sodium chloride were contacted with a 350-cm² area of polyethylene terephthalate surface at 256 K for 10 minutes. About 200 mL of ice-liquid mass was obtained. A centrifugal technique was utilized to separate solid ice crystals from adhering liquid. An average of 60 mL of solid ice containing 1.9 g/L salt was recovered. Ice crystal grain characteristics and conditions to improve efficiency of the freeze purification technique are discussed. A brief comparison with alternate freeze purification techniques is also mentioned.     

Keggin结构杂多酸盐结晶方法的探究

Keggin结构杂多酸盐的结晶方法：应用冷冻浓缩法,是将稀溶液中的水冻结并分离冰晶从而使溶质增浓的操作。应用不同浓度的氯化钠盐溶液凝点的不同,以控制冷冻浓缩过程的温度。探究对Keggin结构杂多酸盐浓度的设定,从而根据实验过程得到随温度降低的浓度变化曲线。分析各曲线,绘制非饱和溶液与饱和溶液浓度变化曲线图,最终得到最低温度相交点为此Keggin结构杂多酸盐的低共熔点,即结晶点。     

Bi-directional freeze casting of porous alumina ceramics: A study of the effects of different processing parameters on microstructure

Highly aligned lamellar ceramic scaffolds were produced using a bi-directional freeze casting technique. A specially designed, sloped copper mould was covered with a polymer to modulate the temperature field. Effects of different processing parameters (cooling rate, mould slope angle, ceramic solid loading and binder concentration) on lamellar orientation were systematically studied. The results showed that freezing under a dual temperature gradient produced highly aligned ceramic scaffolds. Increasing both the cooling rate and the mould slope angle increased the size of the ordered ceramic region. Using different alumina solid loadings in the initial suspension had little effect on the aligned lamellar structure. Increasing the binder concentration affected ice crystal growth in a highly aligned direction. Therefore, freeze casting using a dual temperature gradient can be used to fabricate highly aligned porous materials.     

Freeze Concentratton by Layer Crystallization

Layer crystallization in laminar falling films has been studied for freeze concentration applications. A binary mixture of water and sucrose has been tested in order to compare with literature results from suspension crystallizers. The concentration of sucrose in ice, which is a measure for loss of solute. were from 0.4 to 26.5% for bulk concenwlions of sucrose of 5 to 40%. respectively. The time averaged ice growth rates varied from 3. l0-7 l0 3-10-6 m/s. The results are related to expressions for maximum ice growth rate developed from the gradient criteria. Also an expression for maximum ice growth rate from irreversible thermodvnamics is oresented. Althoueh the exwrimental results show that one-step layercrystallization has amuch lower separation effect than suspension crystallizers with washcolumns, multistep layer crystallization could provide an economical favourable freeze concentration process. A multistep process that combines freeze concentration and reverse osmosis is proposed. A case study shows that it is possibleto reduce the investment costs to less than half of existing processes, for dewatering capacity of 700kg per hour. The energy consumption is also reduced.     

Freeze Concentratton by Layer Crystallization

ABSTRACT

Layer crystallization in laminar falling films has been studied for freeze concentration applications. A binary mixture of water and sucrose has been tested in order to compare with literature results from suspension crystallizers. The concentration of sucrose in ice, which is a measure for loss of solute. were from 0.4 to 26.5% for bulk concenwlions of sucrose of 5 to 40%. respectively. The time averaged ice growth rates varied from 3. l0-7 l0 3-10-6 m/s. The results are related to expressions for maximum ice growth rate developed from the gradient criteria. Also an expression for maximum ice growth rate from irreversible thermodvnamics is oresented. Althoueh the exwrimental results show that one–step layercrystallization has amuch lower separation effect than suspension crystallizers with washcolumns, multistep layer crystallization could provide an economical favourable freeze concentration process. A multistep process that combines freeze concentration and reverse osmosis is proposed. A case study shows that it is possibleto reduce the investment costs to less than half of existing processes, for dewatering capacity of 700kg per hour. The energy consumption is also reduced.     

In-situ X-Ray observations and thermal modeling of unidirectional and bidirectional freeze casting

Freeze casting is a cost effective, efficient, and versatile technique capable of producing 3D structures with controlled pore shapes, orientation of crystals, and components' geometries in many porous materials. Freeze casting of hydroxyapatite (HAP) has been widely applied to bone tissue engineering due to HAP's biodegradable, biocompatible, and osteoconductive properties. It provides interconnected porous structures with a relatively high mechanical strength. However, there are still many unexplained phenomena and features because of the complexity of the process. This study demonstrates the use of X-ray synchrotron micro-radiography for providing time-resolved, in-situ imaging of ice crystal growth in the HAP suspensions. The experimental results show the ice crystal growth behavior under unidirectional and bidirectional freeze casting conditions. The finite element modeling (FEM) of the freeze casting process has been used to predict the development of ice front position and temperature gradient in the suspensions during the freeze casting.     

夹套式MVR热泵蒸发浓缩系统性能分析

为解决具有高黏度、易结垢、强腐蚀性等特点的热敏性物料的蒸发浓缩,设计了夹套式MVR(机械蒸汽再压缩)热泵蒸发浓缩系统,并以水为实验介质进行了相关的实验研究。实验结果表明,温差、压缩比、蒸发量、传热系数、COP(制热性能系数)、SMER(单位能耗蒸发量)、绝热效率、容积效率等各项指标均受蒸发压力、压缩机频率、换热面积的影响;压缩机在频率50 Hz下运转时的系统性能大大优于低频率运转;单台蒸发釜在蒸发压力为 65～85 kPa之间运行较为合适,且不需要补热;两台蒸发釜完全可以同时应用于工业蒸发浓缩过程,但需要少量的补热;两者节能效果均十分显著。     

PSAFS絮凝剂处理印染废水的研究

印染废水是工业生产发生量大、危害严重且难以治理的三大废水之一,采用絮凝的方法处理印染废水,操作简单,经济适用。通过实验研制聚硅酸硫酸铝铁絮凝剂并处理印染废水,实验结果表明不仅克服了聚合氯化铝（PAC）处理水样后残留铝多和聚铁（PFC）稳定性较差的缺点,而且其絮凝效果较聚铝、聚铁更为优异。     

Prevention of crystallization fouling during eutectic freeze crystallization in fluidized bed heat exchangers

Eutectic freeze crystallization is a promising separation technique to produce salt and ice crystals with very high purities and requires less energy than competitive evaporative crystallization techniques. A drawback of this technique is crystallization fouling, which seriously reduces heat transfer rates. Solid–liquid fluidized bed heat exchangers may be attractive crystallizers for this purpose, since they have demonstrated to prevent severe crystallization fouling, for example of ice crystals. This paper presents crystallization experiments with a single-tube fluidized bed heat exchanger. A first experimental series showed that fluidized beds are also able to prevent salt fouling during cooling crystallization from KNO₃ or MgSO₄ solutions. A second series revealed that fouling during eutectic freeze crystallization is more severe than during separate salt or ice crystallization and is therefore difficult to prevent by the fluidized bed. The explanation for this phenomenon is that the salt crystallization process strongly reduces the solute mass transfer limitation for ice crystals growing on the wall resulting in an increased growth rate and more severe crystallization fouling. The addition of a non-crystallizing component strongly reduces fouling and enables to perform eutectic freeze crystallization in fluidized bed heat exchangers for industrial applications.     

基于电渗析的溶液再生传质模型及性能分析

电渗析溶液再生与传统热再生相比具有较大的节能潜力,近年来受到了越来越多的关注。目前有关电渗析溶液再生的研究主要都集中在系统层面的分析,而缺乏对电渗析传质机理的认识。为此,建立了描述电渗析在高浓度下的传质理论模型,并试验探究了不同电流密度、体积比及初始浓度对系统性能的影响。结果表明,模型和试验结果吻合很好,误差小于±4%。体积比越大时,系统再生性能越好,但溶液产量也越低;电流密度越大时,系统再生性能越好,但系统能耗也越高;初始浓度越高时,系统电流效率和再生性能越低,同时膜堆中浓差极化系数也越低。在实际应用时应权衡以上因素以实现更高的系统性能和效率。     

Influence of Freezing Temperature on Product Parameters of Solid Dosage Forms Prepared via the Freeze‐Casting Technique

The freeze‐casting technique was used to formulate porous solid bodies containing theophylline as an active pharmaceutical ingredient, potato starch as a filler and citric acid or saccharose as binding agents. Aqueous suspensions of the ingredients were frozen at three different temperatures. The aim of this work was to investigate the influence of the freezing temperature on the ice crystal growth rate of the suspensions and the resulting porosity of the freeze‐casted samples. The impact of the freezing temperature on the solidification of the suspensions was analyzed via contact angle measurements. The rate of ice crystal growth was expressed as an overall linear growth rate. The porosity of the freeze‐casted bodies was determined by high‐pressure mercury porosimetry. A close correlation was found between the freezing temperature and the investigated product parameters. Lower cooling temperatures resulted in higher final porosities. The lowest temperature, at which final product properties could be regulated by varying the cooling regimes, was –30 °C. The influence of the freezing temperature and the impact of the additives were not remarkable at a freezing temperature lower than –30 °C. Therefore, it can be concluded that the optimum freezing temperature of the suspensions investigated in this study is in the temperature range between –20 °C and –30 °C.     

液-液同向流中冰浆的形成

A new technique for ice slurry production was explored. Multiple small water-drops were formed in another immiscible chilled liquid by a single-nozzled atomizer and frozen in the fluidized bed by direct contact heat transfer. Experiments were conducted to investigate the dynamic behaviors of the ice crystal making system. The results demonstrate that the ice crystals could be produced continuously and stably in the vertical bed with the circulating coolant of initial temperature below -5℃. The size distribution of the ice crystals appears non-uniform, but is more similar and more uniform at lower oil flow rate. The mean ice crystal size rests seriously with the jet velocity and the oil flow rate. It decreases with decreasing the oil flow rate, and reaches the maximum at an intermediate jet velocity at about 16.5 m.s y. The ice crystal size is also closely related to the phenomenon of drop-coalescing, which can be alleviated considerably by reducing the flow rate or lowering the temperature of the carrier oil. However, optimization of liquid-liquid atomization is a more effective approach to produce fine ice crystals of desired size.