尿素熔融喷浆造粒工艺在复混肥生产中的应用

介绍了在团粒法工艺的基础上,将尿素熔融成尿液进行喷浆造粒生产复混 肥过程中存在的问题,分析产生的原因并提出改进措施,对改造效果进行了总结。     

In situ UV–Vis spectroscopy in gas–liquid–solid systems

This paper presents the use of ultraviolet–visible spectroscopy (UV–Vis) spectroscopy in a slurry of particles, a packed bubble column, and a trickle bed to assess the changes in the state of an active component on the surface of the solid support. As a model system, insoluble pH indicators deposited on the particles and on a solid foam packing (used as the packing material in the packed bubble column and the trickle bed) are used which fluoresce different UV–Vis spectra according to the liquid pH. The experimental results indicate that for the slurry the UV–Vis spectra obtained from the moving particles can be used to characterize the state of the pH indicator and to determine the transition point. The UV–Vis spectra can also be used to characterize the concentration of particles. Bubbles in the packed bubble column result in disturbances in the UV–Vis spectra collected from the pH indicator adsorbed to the solid surface and this interference is removed successfully with a newly developed tolerance-and-averaging method. In the trickle bed the liquid film flowing over the solid surface does not disturb the UV–Vis spectra. An abrupt change in the state of the pH indicator is therefore observed successfully.     

聚丙烯淤浆液的流变特性以及与搅拌功率的关系

粗分散的聚丙烯的淤浆液,由于动力上不稳定,特别是粘度测定中出现“壁效应”,是无法用一般粘度计来测定其流变特性的。 作者应用Brabender型粘度计定性地确定了聚丙烯淤浆液属于典型的宾汉型流体,然后利用化工上常用的螺带搅拌槽探讨了宾汉流体的搅拌功率准数与雷诺数的关系,求得聚丙烯淤浆液塑性粘度值和屈服值,为丙烯液相本体聚合过程的传热、混合、搅拌等方面提供了基础数据。     

T型微通道内浆料体系中气泡生成行为与尺寸预测

实验研究了T型微通道内浆料中气泡的生成过程和尺寸。聚丙乙烯微球浆料和N₂分别为连续相和分散相。气泡的生成过程可分为三个阶段：膨胀阶段、挤压阶段和快速夹断阶段。随着浆料浓度的增大,膨胀阶段时长几乎没有变化,挤压阶段显著缩短,而快速夹断阶段略有缩短。在膨胀阶段和快速夹断阶段,气泡颈部宽度与无量纲剩余时间均呈幂率关系,而挤压阶段气泡颈部宽度与时间呈线性关系。考察了浆料浓度、气相和浆料流量对气泡生成尺寸的影响。结果表明气泡尺寸随气相流量的增大而增大,随液相流量和浆料浓度的增大而减小。     

Steady‐state behavior of liquid fuel hydrazine decomposition in packed bed

A general theoretical model is presented to analyze the steady‐state decomposition process of liquid monopropellants in packed beds for thruster systems. Additionally, an experiment studying the decomposition of liquid hydrazine in a packed bed is used to validate this model. The liquid droplet evaporation rate is determined through calculating the gas‐liquid mass transfer for the mixture temperatures lower than the liquid propellant boiling point and solving the gas‐liquid or liquid‐solid heat transfer equations at the temperature exceeding the boiling point. The process of liquid propellant decomposition in packed beds are simulated based on the Naive–Stokes equation for the mixture model integrated with the developed liquid evaporation rate, in which both the heterogeneous catalytic reaction coupled with the diffusion of reactants in the pore of catalyst, and the homogenous decomposition reactions are considered. The calculated results for the axial distribution of the temperature are in good agreement with the experimental data. © 2014 American Institute of Chemical Engineers AIChE J, 61: 1064–1080, 2015     

铁黄合成体系流变特性

针对碱法铁黄制备过程,研究了体系的流变特性．在反应初期铁黄合成体系粘度较小,随反应进行体系粘度显著增大,在反应中后期反应液为满足幂指数规律的假塑性流体,并具有很强的剪切稀化行为．反应温度、碱比、搅拌转速和通气量等通过改变粒子的生成过程和粒子的形态来改变铁黄合成体系的流变特征．在铁黄合成体系中加人硅酸纳会使体系粘度显著下降,流变特性随之发生变化．     

Mechanism and Simulation of Removal Rate and Surface Roughness During Optical Polishing of Glasses

Glass optics with ultra‐low roughness surfaces (<2 Å rms) are strongly desired for high‐end optical applications (e.g., lasers, spectroscopy, etc.). The complex microscopic interactions that occur between slurry particles and the glass workpiece during optical polishing ultimately determine the removal rate and resulting surface roughness of the workpiece. In this study, a comprehensive set of 100 mm diameter glass samples (fused silica, phosphate, and borosilicate) were polished using various slurry particle size distributions (PSD), slurry concentrations, and pad treatments. The removal rate and surface roughness of the glasses were characterized using white light interferometry and atomic force microscopy. The material removal mechanism for a given slurry particle is proposed to occur via nano‐plastic deformation (plastic removal) or via chemical reaction (molecular removal) depending on the slurry particle load on the glass surface. Using an expanded Hertzian contact model, called the Ensemble Hertzian Multi‐gap (EHMG) model, a platform has been developed to understand the microscopic interface interactions and to predict trends of the removal rate and surface roughness for a variety of polishing parameters. The EHMG model is based on multiple Hertzian contacts of slurry particles at the workpiece–pad interface in which the pad deflection and the effective interface gap at each pad asperity height are determined. Using this, the interface contact area and each particle's penetration, load, and contact zone are determined which are used to calculate the material removal rate and simulate the surface roughness. Each of the key polishing variables investigated is shown to affect the material removal rate, whose changes are dominated by very different microscopic interactions. Slurry PSD impacts the load per particle distribution and the fraction of particles removing material by plastic removal. The slurry concentration impacts the areal number density of particles and fraction of load on particles versus pad. The pad topography impacts the fraction of pad area making contact with the workpiece. The glass composition predominantly impacts the depth of plastic removal. Also, the results show that the dominant factor controlling surface roughness is the slurry PSD followed by the glass material's removal function and the pad topography. The model compares well with the experimental data over a variety of polishing conditions for both removal rate and roughness and can be extended to provide insights and strategies to develop practical, economic processes for obtaining ultra‐low roughness surfaces while simultaneously maintaining high material removal rates.     

Experimental study of rheological properties of solid propellant slurry at low-shear rate and numerical simulation

The steady state rheological properties of a three-component hydroxyl-terminated polybutadiene binder (HTPB) solid propellant slurry at low shear rate were investigated using a rotational rheometer. The data were analyzed and the rheological characteristics of the slurry were determined. The effect of shear rate on apparent viscosity and shear stress as well as the viscosity–time effect of the slurry were also analyzed. Herschel–Bulkley (H-B) model was applied for the simulation of the flow process of a two-dimensional container using CFD Ansys-polyflow software. Experimental results showed that solid propellant slurry had yield pseudoplasticity. Yield characteristics were determined based on the fact that when shear stress was greater than yield stress, the slurry began to flow and the relationship between shear stress and shear rate obeyed power law function. Simulation results further verified the correctness of experimental results.     

Mathematical modeling and analysis of an interfacial polycarbonate polymerization in a continuous multizone tubular reactor

A detailed mathematical model is presented to describe the steady state behavior of a continuous multizone tubular reactor for the synthesis of aromatic polycarbonate by interfacial polycondensation mechanism. In this process, bisphenol‐A dissolved in a dispersed aqueous phase reacts with phosgene dissolved in a continuous organic phase and hence, the reaction initiates at the interface of the two phases. A liquid‐liquid mass transfer process is incorporated into a reaction kinetic model to calculate the reaction rates and polymer molecular weight distribution. The kinetic model has also been used in developing a steady state multizone tubular reactor model for continuous production of polycarbonate. The model simulations are compared with proprietary plant data and excellent agreement has been obtained. POLYM. ENG. SCI., 58:438–446, 2018. © 2017 Society of Plastics Engineers     

Processing defects and their relevance to strength in alumina ceramics made by slip casting

Al₂O₃ made by slip casting inherently contained the elongated and the spherical shaped defects. The pores of elongated shape were formed through the liquid flow during the casting process, since they were found in all slip cast specimens and not found in the spontaneously dried specimen where no rigorous flow of water happened. The formation of these defects was insensitive to the slurry properties. The origin of spherical pores was likely due to the entrapped air bubbles during de-airing procedure. Their removal by de-airing was easy for a dispersed slurry having a low viscosity, but difficult for a flocculated slurry of high viscosity. The Weibull's plots for the flexural strengths are essentially the same in the region of high strengths. Specimens made from the flocculated slurry contain a higher concentration of the spherical pores, and some of the resultant specimens have low strength. The lower strength of those ceramics has been ascribed to more detrimental defects, i.e. the spherical ones.     

石灰石-石膏法烟气脱硫过程中细颗粒物形成特性

利用石灰石-石膏湿法烟气脱硫模拟试验装置分析探讨脱硫净烟气中细颗粒物物性与脱硫浆液中晶体粒度分布、浓度、形貌及元素组成间的关系,并试验考察了烟气组分及脱硫工艺条件对脱硫净烟气中细颗粒物排放的影响。结果发现:石灰石-石膏湿法烟气脱硫过程中可生成大量亚微米级细颗粒,生成的细颗粒物性与脱硫浆液中晶体物性存在密切关系,脱硫操作参数如空塔气速、液气比等对脱硫浆液液滴夹带量存在显著影响;脱硫浆液蒸发夹带是石灰石-石膏法脱硫过程中生成细颗粒物的主要来源,通过抑制细小石膏晶粒的形成及优化脱硫工艺参数可减少石灰石-石膏湿法脱硫过程中细颗粒的形成。     

The effects of mass transport and chemical reaction on pollutant removal in a three-phase slurry adsorber-reactor

The analysis of the effects of mass transport and chemical reaction on pollutant removal from a gas-phase in a three-phase slurry adsorber-reactor is presented. A mathematical model, consisting of four coupled differential equations, was developed to describe the process and solved numerically. The modeling assumptions included: perfect mixing in the three-phase slurry, Henry's law, a linear adsorption isotherm and a second order, irreversible chemical reaction. The model was found to adequately represent limited existing experimental data and to qualitatively predict the effects of the various transport coefficients on the pollutant removal efficiency of the process. The model was also used for design analysis. Although the model-process achieved significant pollutant removal for representative operating conditions, the percent removal was ultimately limited by mass transport from the gas bubbles to the liquid slurry.     

A scale-up strategy for low-temperature methanol synthesis in a circulating slurry bubble reactor

Slurry bubble column reactors are being increasingly utilized in the large-scale conversion of coal or natural gas to liquid hydrocarbons and alcohols. A new suite of tools for developing low-temperature methanol synthesis in circulating slurry bubble reactors is explored in this study. The scale-up strategy consisting of hydrodynamics in cold flow units, catalyst performance evaluation in an autoclave, and process investigation in a pilot-scaled circulating slurry bubble reactor is presented. This methodology should be helpful for designing and scaling-up the low-temperature methanol synthesis and other related processes in slurry bubble column reactors, which will enhance and speed them towards commercial application.     

Ab inito and FTIR Studies of HfSiCNO Processed from the Polymer Route

The reactions between polysilazane and hafnium‐butoxide precursors are followed from the liquid, to the cross‐linked, and finally to the ceramic state by infrared spectroscopy. We find evidence of formation of Hf–N bonds in the liquid state, and Hf–O–Si bonds in the cross‐linked polymer state. Results from ab inito calculations for the ceramic state are presented. They show that Hf behaves like Si, forming bonds with C, N, and O in proportion of the Hf/Si ratio in the compounds. The average values of such bonds formed by Hf, relative to silicon, are 11.2, 17.8, and 24.4%, which is in reasonable agreement with the overall Hf/Si ratio in the samples (8%, 15% and 22%). It is concluded that it is appropriate to express the composition of these compounds in terms of the Hf/Si ratio. The X‐ray data that show the emergence of weak diffraction peaks for monoclinic HfO₂ when the Hf/Si ratio is 0.22, but not at lower concentrations of Hf [K. Terauds and R. Raj, J. Am. Ceram. Soc., 96 , 2117–2123 (2013)].     

Compact Formation during Colloidal Isopressing

In colloidal isopressing, a preconsolidated slurry with a high relative density (∼0.58) is converted into an elastic body (compact) under the influence of an isostatic pressure. Experiments suggest that during isopressing, the preconsolidated slurry is separated from the elastic body by a transition plane that rapidly moves into the preconsolidated slurry, leaving behind the elastic body which is formed against a piece of porous material present within the rubber mold. The porous material will accommodate the liquid phase squeezed out of the preconsolidated slurry, allowing for the conversion to the denser elastic body (∼0.63). The results of experiments with varied isopressure are compared with simulations based on a filtration model. The good agreement indicates that colloidal isopressing can be considered a special case of consolidation via pressure filtration. Compared with conventional pressure filtration, the extremely rapid consolidation is due to the high relative density of the preconsolidated slurry used to fill the mold as well as the high applied isopressure. The simulation used here is a useful tool in the design and understanding of shape forming by colloidal isopressing and shows how process variables such as particle size, relative density, and applied pressure influence compact formation time.     

Use of capillary suction apparatus for estimating the averaged specific resistance of filtration cake

A method for estimating the averaged specific resistance of filtration cake, which avoids the necessity of measuring the liquid invasion volume in capillary suction apparatus (CSA) experiments, is proposed. When insufficient slurry is used, the slurry will exhaust during an experiment and the curve of wet front radius versus time shows transition. The transition point shifts according to the slurry concentration, cake specific resistance and the CSA parameters. Based on the wet front radius and the capillary suction time (CST) of the transition point, the liquid saturation under the inner cylinder can be estimated and the averaged specific resistance of cake calculated without the liquid invasion volume data. The proposed method agrees well with vacuum filtration data.     

Inhibition of liquid Si infiltration into carbon-carbon composites by the addition of Al to the Si slurry pre-coating: mechanism analysis

The mechanism of the inhibition of liquid Si infiltration (LSI) into a two-dimensional carbon-carbon composite (2D-C/C) by the addition of Al to the Si slurry pre-coating was investigated. It was shown by means of a vapor treatment experiment designed intentionally that the surface composition of the inner pores beneath the Si slurry pre-coating before the occurrence of LSI was pure carbon and SiC, while before the occurrence of the LSI with the Si-6 wt.%Al slurry pre-coating, the surface composition of the inner pores was Al₄C₃, SiC and a small amount of pure carbon. The formation of the SiC and the Al₄C₃ was the result of the evaporation of almost all the Al additive and a little Si during the heating. For reactive infiltrations, reactions at the vapor-liquid-solid triple line are believed to affect the final infiltration depth. Faster reactions at the triple line lead to faster infiltration velocity and hence deeper reactive infiltration. The reaction at the triple line for the LSI with the Si-6 wt.%Al slurry pre-coating was mainly between liquid Si and the surface Al₄C₃, which was probably slower than the reaction of liquid Si with the pure carbon at the triple line corresponding to the LSI with the Si slurry pre-coating. Therefore, the extent of the penetration of liquid Si during the LSI with Si-6 wt.%Al slurry pre-coating was lower than that with the Si slurry pre-coating.     

Tailored macro-pores during the formation of C/C-SiC via liquid phase pyrolysis

The synthesis of C/C-SiC via liquid silicon infiltration (LSI) with thermoplastic carbon precursors can lead to the formation of macropores in the C/C state. The macro-pore pattern formation can be controlled and used as a new level in microstructure for ceramic matrix composites. The pore formation occurs in the CFRP state with the remelting of the thermoplastic matrix and can be fixed to the C/C state after liquid phase pyrolysis. The macro-pores are primarily induced by a non-linear elastic recovery of the fiber preform and not via gas formation and release during pyrolysis. The formation of the macroporosity is described and explained. These pores can be tailored by process control in size and shape. The pore shapes can vary from isolated spherical pores to an interconnected tube like macro-pore network. The relationship between starting setting variables of the fiber preform, the process conditions, and the resulting structure are discussed.     

浆料催化精馏合成碳酸二甲酯的模拟研究

以浆料催化精馏酯交换合成碳酸二甲酯实验为基础,应用Aspen Plus软件建立了浆料催化精馏合成过程的稳态模型并进行研究。研究结果表明,模型的计算值与实验值吻合良好。通过计算机模拟还得到了实验难以测定的塔内温度分布、塔内气液相流率及组成和碳酸二甲酯在各板的生成速率的变化规律。     

Study of the Characteristics of Methanol Synthesis in a Recirculation Slurry Reactor – A Novel Three‐Phase Synthesis Reactor

A process feasibility analysis on the liquid phase methanol synthesis (LPMeOH^TM) process was performed in a recirculation slurry reactor (RSR). In the three‐phase RSR system, a fine catalyst is slurried in the paraffin and this catalyst slurry is continuously recirculated through the nozzle from the slurry sector to the entrained sector by a pump. The syngas is fed concurrently with the downward flow of slurry to form the methanol product. A laboratory scale mini‐pilot plant version of a recirculation slurry reactor system was successfully designed and built to carry out process engineering research, and in addition, an identical cold model was built to measure the mass transfer coefficient in the recirculation slurry reactor. The effects of operating conditions, including temperature, pressure, gas flow rate and catalyst slurry recirculation flow rate on the productivity of methanol were studied. This experimental data helps the scale‐up and commercialization of the methanol synthesis process in recirculation slurry reactors.