早强剂对水泥稳定碎石材料干缩特性试验研究

以研究水泥稳定碎石路用材料的干缩特性为目的,在稳定碎石材料中掺入5%的水泥,再按水泥用量的0%、8%、10%、12%、14%、16%的早强剂(ESE-1型)替换水泥,研究不同早强剂掺量的水泥稳定碎石材料的失水率、干缩应变、干缩系数、失水率与干缩应变的关系.研究结果表明:早强剂能够降低材料的失水率、干缩应变、干缩系数,其中早强剂掺量为16%的材料抗干缩能力最强.故早强剂在提高材料早期强度和加快道路施工速度的同时,能够提高水泥稳定碎石材料的抗干缩能力,改善水泥稳定碎石材料因干缩造成的早期病害.     

Steam Drying of Products Containing Solvent Mixtures

Drying experiments with single, porous spheres wetted with mixtures of 2- propanol and water were performed using superheated steam, air, or steam-air mixtures as drying agent. Both the drying rate and the moisture composition were determined experimentally for different temperatures and compositions of the drying agent and for different initial compositions of the moisture. It is shown that evaporation of 2-propanol is enhanced by using superheated steam as drying agent instead of air due to steam condensing on the sample. While the overall drying rate increases with rising steam temperature, the evaporation rate of 2-propanol is hardly affected. When drying samples containing mixtures of 2- propanol and water, internal boiling can occur depending on the vapor-liquid equilibrium. Vapor generated inside the sample may cause mechanical dewatering of the sample which greatly increases the drying rate.     

Steam Drying of Products Containing Solvent Mixtures

ABSTRACT

Drying experiments with single, porous spheres wetted with mixtures of 2- propanol and water were performed using superheated steam, air, or steam-air mixtures as drying agent. Both the drying rate and the moisture composition were determined experimentally for different temperatures and compositions of the drying agent and for different initial compositions of the moisture. It is shown that evaporation of 2-propanol is enhanced by using superheated steam as drying agent instead of air due to steam condensing on the sample. While the overall drying rate increases with rising steam temperature, the evaporation rate of 2-propanol is hardly affected. When drying samples containing mixtures of 2- propanol and water, internal boiling can occur depending on the vapor–liquid equilibrium. Vapor generated inside the sample may cause mechanical dewatering of the sample which greatly increases the drying rate.     

2种方式干燥的天然橡胶干燥特性之研究

为探讨微波干燥天然橡胶新技术，分别在温度115℃下，采用电热烘箱产生热空气和微波干燥装置干燥湿天然橡胶胶粒，对二者的干燥特性及硫化胶性能进行对比分析研究。结果表明，微波干燥只需13．467min就可使胶料含水量降至0．791％，热空气干燥则需211min。天然橡胶微波干燥和热空气干燥主要包含失水率加速期、失水率减速期、失水率相对恒速期3个失水阶段。整个干燥过程中，微波干燥失水率较大，而热空气干燥失水率比较小。微波干燥天然橡胶硫化胶的耐热氧老化性能得到显著提高：其老化前后拉断伸长率变化率（-35％）和拉伸强度变化率（-59％）明显高于热风干燥天然橡胶硫化胶的拉断伸长率变化率（-62％）和拉伸强度变化率（-89％）。     

Formation of hollow granules from liquid marbles: Small scale experiments

Research into formation of hollow granules from liquid marbles is an emerging field in hydrophobic granulation. A liquid marble is formed by a network of self-assembled hydrophobic powder around a droplet, and this paper investigates the conditions required for forming hollow granules from a liquid marble precursor.Single drops of fluid were produced using a syringe and placed onto loosely packed powder beds of hydrophobic powders. Liquid marbles formed from several powder/liquid combinations were dried at several conditions to investigate the drying conditions required for formation of a stable hollow granule.The formation of stable hollow granules was found to depend on drying temperature and binder concentration. For HPMC and PVP binder, formation of hollow granule is proportional to binder viscosity and for HPC binder, this relationship is constant. Different combinations of powder and binder at both drying temperatures - 60 °C and 100 °C - had mixed success rates in forming hollow granules, but generally the success rate was improved by using higher drying temperatures, smaller particles or higher viscosity binder fluids.     

Agglomeration during the Drying of Fine Silica Powders, Part II: The Role of Particle Solubility

The effect of particle solubility and the dissolution rate on agglomeration was studied by drying silica and titania particles from aqueous slurries with pH values in the range of 2–12. The agglomerate strength and strength distribution were measured by a calibrated ultrasonic force, and the strength increased as the solubility and dissolution rate increased. Two silica powders of different particle size (60 nm and 500 nm) were studied, and smaller-sized particles formed stronger agglomerates. The drying rate of the powders was varied by using spray drying and tray drying, and slower drying was shown to lead to higher agglomerate strength. The agglomerate strength of titania powder (insoluble in water) was independent of pH, whereas the agglomerate strength of silica was dependent on pH. It was concluded that the solubility and dissolution rate are important parameters that govern the strength of agglomerates.     

THE RELATIVE INFLUENCE OF DIELECTRIC AND OTHER DRYING TECHNIQUES ON THE PHYSICO - MECHANICAL PROPERTIES OF A PHARMACEUTICAL TABLET EXCIPIENT. PARTI: COMPACTION CHARACTERISTICS.

The relative Influence of nine techniques for drying wet granulated microcrystal-lline cellulose (MCC) on the subsequent compaction characteristics was studied In terms of the tensile strength and corrected work of failure of the tablets. Wet granulation resulted in a substantial decrease in compatibility. However, the drying technique used was found to affect the degree of loss in compatibility. In general, microwave-vacuum drying using the “high” process type resulted in the production of granules with the highest compatibility followed by freeze drying and fluidized bed drying. Granules dried under ambient conditions, and granules tray dried to “just dry” or “over dried” conditions resulted In tablets possessing approximately comparable compatibilites, with the poorest compaction characteristics being exhibited by vacuum dried granules, in addition It was found that use of a “low” drying process type during microwave- vacuum drying yielded granules with inferior compaction characteristics to those dried by the “high” process type. Radio frequency drying was found to yield granules which produced tablets having slightly inferior tensile strength to tray dried material, although the tablet work of failure values were comparable. The effect of drying technique on the subsequent compaction characteristics was not found to be directly related to the moisture content of the granules.     

Evaporation and Diffusion Transport Properties and Mechanical Properties of Alginate Dried Film

The effects of alginate concentration and drying temperature on drying kinetics/characteristics of alginate solution and mechanical property of formed solid films were examined. Solid films were fabricated through thin-layer drying of 1 to 4%w/w sodium alginate solution at 40, 60, and 80°C using the solvent-evaporation method. The water weight loss profile of alginate solution undergoing drying was recorded with time. The polymer weight of all solid films was kept constant. The plasticity of films was evaluated using thermomechanical analyzer. The findings indicated that both constant rate and falling rate periods existed during drying of dilute alginate solution or at low drying temperature since both surface and core waters were available for drying. The falling rate period dominated in drying of an alginate solution of high polymer concentration and at high drying temperatures with internal diffusion being the governing transport phenomenon for water. In the latter, an exponential relationship between water content and drying time was obtained. The drying process of 4%w/w alginate solution at 60 and 80°C was relatively simple as there was only a single drying stage, viz. the falling rate period requiring no consideration of critical moisture content. The drying rate was faster than those obtained from the dilute alginate solution or conducted at low temperature, such as 40°C. The plasticity attributes of films prepared from 4%w/w alginate solution can be modulated to a degree similar to films prepared from dilute alginate solution or dried at low temperature via changing the drying temperature between 60 and 80°C.     

Structure of Crack in Thermally Dried Sludge Cake

We examined in this work the drying characteristics of wastewater sludge, considering the weight loss using an electronic balance and the morphology change of drying cake by an X-ray micro-computerized tomography scanner (micro-CT). The drying rates for sludge cake was 50-60% of the pure water test. The corresponding micro-CT images were scanned to explore the change in cake volume and development of internal crack over drying. The Otsu's method was applied to bilevel the scanned images, based on which the three-dimensional model for crack's internal structure was reconstructed. The cake porosity and the geometric factors of cracks, such as the compactness, the boundary fractal dimension, and the Sierpinski carpet fractal dimension, were evaluated. The shrinkage of cake volume and the development of internal crack occurred simultaneously. The skin layer formed by the former mechanism retards further drying. On the other hand, the internal cracks were shown to exhibit zigzagging with a noncircular cross section and fractal-like boundary, which should be able to enhance local drying. A possible role of change in crack structure on the rate of drying was discussed.     

Measurement of bound water content in sludge: The use of differential scanning calorimetry (DSC)

The bound water content of original and frozen activated sludge and an inorganic sludge were measured via differential scanning calorimetry (DSC) and drying tests. Original sludge contained a significant level of bound water which was reduced by about 50% after freeze/thaw treatment. A simple thermodynamic interpretation showed that liquid–solid binding strength played an important role in depression of the freezing point of bound water in a sludge. The choice of a threshold temperature in a DSC test was equivalent to definition of a threshold binding strength dividing bound/non-bound water content. The possible close relationship between the bound water content measured via DSC and the drying test is discussed. The importance for sample uniformity was also examined.     

Strength and morphology of solid bridges in dry granules of pharmaceutical powders

This is an experimental study of the tensile strength of solid bridges between primary particles comprising granules of lactose or mannitol. We report on two systems: granules prepared with ethanol granulating solutions, in which the base powders were at most sparingly soluble, and aqueous granulating solutions, in which the base powder solubility was large. Both systems were studied with and without hydroxypropylcellulose (HPC) or polyvinylpyrrolidone (PVP) or surfactants (Triton-X100, sodium lauryl sulfate or polysorbate 80) added to the granulating solution. The interparticle bridge strength was determined from the granule crush strength with a simple model that assumes that solid bridges form by evaporation of solvent from liquid bridges that maintain their shape during drying.Lactose granules prepared with pure ethanol are very weak, with crush strength comparable to that predicted by JKR theory, consistent with its negligible solubility. Mannitol, which is sparingly soluble, forms granules with bridge strength similar to the theoretical (Griffith) strength of a pure mannitol. Addition of HPC or PVP to the granulating solution produces bridges with strength comparable to that of pure polymer films. In comparison, the behavior of granules prepared with aqueous granulating solutions was much more complex due to the high saturation concentration of base powder. Granules produced with pure water had bridge strength approximately 20% of the theoretical strength. Addition of HPC or PVP to lactose granules increased the bridge strength modestly, but the strength was much smaller than that of the corresponding pure polymer films. Addition of HPC to mannitol granules had little effect on bridge strength, while PVP reduced bridge strength by approximately 30%. Addition of surfactants to the granulating solution also reduced dry bridge strength. These results reflect the complex microstructure and resulting mechanical properties of dry bridges produced by coprecipitation of the sugars and polymers (or surfactants).     

利用中低品位磷矿生产疏松状过磷酸钙的新方法

以中低品位磷矿为原料、采用矿浆浓酸法(湿法)生产疏松状过磷酸钙产品时,存在产品含水量控制不稳定、产品结块严重、全磷转化率低等问题。采用由表面活性剂、分散剂、水组成的液体过磷酸钙活化疏松剂与硫酸一起进入酸浆混合器中生产过磷酸钙产品,可使混合反应更彻底,产品的有效磷(以P2O5计)质量分数提高0.5%~1.0%,含水质量分数降低1.5%~3.0%,全磷转化率提高3%~7%,而且可减少熟化翻堆次数并缩短熟化时间,具有显著的经济和社会效益。     

THE RELATIVE INFLUENCE OF DIELECTRIC AND OTHER DRYING TECHNIQUES ON THE PHYSICO - MECHANICAL PROPERTIES OF A PHARMACEUTICAL TABLET EXCIPIENT. PARTI: COMPACTION CHARACTERISTICS.

The relative Influence of nine techniques for drying wet granulated microcrystal-lline cellulose (MCC) on the subsequent compaction characteristics was studied In terms of the tensile strength and corrected work of failure of the tablets. Wet granulation resulted in a substantial decrease in compatibility. However, the drying technique used was found to affect the degree of loss in compatibility. In general, microwave-vacuum drying using the “high” process type resulted in the production of granules with the highest compatibility followed by freeze drying and fluidized bed drying. Granules dried under ambient conditions, and granules tray dried to “just dry” or “over dried” conditions resulted In tablets possessing approximately comparable compatibilites, with the poorest compaction characteristics being exhibited by vacuum dried granules, in addition It was found that use of a “low” drying process type during microwave- vacuum drying yielded granules with inferior compaction characteristics to those dried by the “high” process type. Radio frequency drying was found to yield granules which produced tablets having slightly inferior tensile strength to tray dried material, although the tablet work of failure values were comparable. The effect of drying technique on the subsequent compaction characteristics was not found to be directly related to the moisture content of the granules.     

Structure of Crack in Thermally Dried Sludge Cake

Abstract

We examined in this work the drying characteristics of wastewater sludge, considering the weight loss using an electronic balance and the morphology change of drying cake by an X-ray micro-computerized tomography scanner (micro-CT). The drying rates for sludge cake was 50–60% of the pure water test. The corresponding micro-CT images were scanned to explore the change in cake volume and development of internal crack over drying. The Otsu's method was applied to bilevel the scanned images, based on which the three-dimensional model for crack's internal structure was reconstructed. The cake porosity and the geometric factors of cracks, such as the compactness, the boundary fractal dimension, and the Sierpinski carpet fractal dimension, were evaluated. The shrinkage of cake volume and the development of internal crack occurred simultaneously. The skin layer formed by the former mechanism retards further drying. On the other hand, the internal cracks were shown to exhibit zigzagging with a noncircular cross section and fractal-like boundary, which should be able to enhance local drying. A possible role of change in crack structure on the rate of drying was discussed.     

Partial acidulation of an ‘unground’ phosphate rock: I. Preparation and characteristics

Partially acidulated phosphate rocks were prepared from unground North Carolina phsophate rock and H₃PO₄ by (i) mixing phosphate rock with the requisite amount of H₃PO₄, (ii) mixing with a portion of the acid followed by adding the remaining acid during granulation and (iii) single-step acidulation and granulation. The degrees of acidulation were 20, 30, 40 and 50%. Only 20% and 30% acidulations were done by method (iii). The phosphate rock granulated readily on addition of H₃PO₄ either as in method (ii) or (iii) and the products did not need external drying before storage. The citric and water soluble P showed that from the viewpoint of acid-phosphate rock interaction all three methods of preparation were satisfactory. The granules were equally strong as or stronger than commercially available single or triple superphosphate samples tested. The percent degradation on abrasion was less than 4% compared to about 8% for superphosphate and 0.4% for triple superphosphate. A sand incubation study suggested an interaction in the partially acidulated phosphate rock between the monocalcium phosphate component and unreacted phosphate rock which initially increased the solubility of P.     

Obtaining granular NPK fertilizers from single superphosphate and urea

A laboratory study was conducted to elaborate methods for obtaining granular NPK fertilizers from mixtures of single superphosphate (SSP) with urea and potassium salts. Samples of products of various grades containing 32–39% fertilizer nutrients and some micronutrients (B, Cu, Co, Mo, Mn) were obtained and their characteristics determined. Instead of cured SSP the usage of a fresh den product was recommended to reduce environmental pollution. The best results were obtained by drying den superphosphate and neutralizing it with limestone before mixing it with other components. Granulation of mixtures should be carried out by the thermic method at 80–95°C, on account of the liquid phase from melting urea. The hardness of the granules obtained by this method, when stored in a dry room, remained satisfactory for 3 months.This paper is dedicated to the memory of Edgar Arumeel (1911–1993)     

Effect of Organic Binder Segregation on Sintered Strength of Dry-Pressed Alumina

The influence of binder systems on the structure and properties of alumina ceramics was examined. Two types of binders were used to prepare alumina granules by spray drying: poly-acrylic acid (PAA) and poly-vinyl alcohol (PVA). PVA segregated to the surface and subsurface of the granules, whereas PAA was homogeneously distributed. Compaction tests on a single granule showed that the PAA binder provides lower yield stress of granules than PVA. In the die compaction process, the relative density of the compact body started to increase at a lower pressure, and a more homogeneous internal structure was observed in the green compact prepared with the PAA binder than PVA. The homogeneous structure resulted in a sintered body with a strength of 580 vs 485 MPa when PVA was used.     

Effect of Humidity on NPK Fertilizer Drying

The drying process within rotary coolers during the manufacture of granular NPK fertilizer plays an important role in the production of fertilizer granules possessing both a low moisture content and low caking propensity. A theory for fertilizer drying has been developed which takes into account the low critical relative humidity of complex fertilizer found at high temperature. The theory proposes that the gradient between the partial vapour pressure of moisture in the air and the vapour pressure moisture adjacent to the surface of the fertilizer granule, is the rate controlling stage in the drying of hot granular fertilizer rather than the internal diffusion of moisture within the particle.     

MATHEMATICAL MODELLING AND APPARATUS ARRANGEMENTS OF DEEP DRYING PROCESS OF GRANULAR POLYMERS

ABSTRACT

A computer - aided analysis is made of the factors influencing the kinetics of the continuous deep drying of granular polymers on the basis of a two-level mathematical model. In terms of the lower (microkinetic) level, which deals with the drying of separate granules, consideration is given to the accuracy of determining the moisture diffusion coefficients in polymers as functions of temperature and concentration D=f(U,t). The expedience of employing the solution of linear and non-linear differential diffusion equations in microkinetic calculations is also considered. In terms of the macrokinetic level, which takes account of the influence of the hydrodynamic and heat-and-mass transfer drying conditions in the dryer, a numerical study is undertaken of how the kinetics is influenced by the granules’ dimension nonuniformity and by the difference in the granules’ residence time in the dryer. The results are graphically presented in generalised variables. The travel of 12 granular polymers in the shaft (column) dryers is experimentally studied depending on definite determining parameters. Accordingly, some recommendations aimed at ensuring the uniform drying are given. Presented are also the experimental results on the longitudinal mixing for different polymers for a continuous shaft dryer with a ring material layer and with the drying agent performing the radial motion. The findings make it possible to determine the mixing rate and to outline some practical recommendations. The investigations carried out allow one to find the rational construction of the dryer for the deep drying of granular polymers and to refine the kinetic calculations.     

Effect of Humidity on NPK Fertilizer Drying

ABSTRACT

The drying process within rotary coolers during the manufacture of granular NPK fertilizer plays an important role in the production of fertilizer granules possessing both a low moisture content and low caking propensity. A theory for fertilizer drying has been developed which takes into account the low critical relative humidity of complex fertilizer found at high temperature. The theory proposes that the gradient between the partial vapour pressure of moisture in the air and the vapour pressure moisture adjacent to the surface of the fertilizer granule, is the rate controlling stage in the drying of hot granular fertilizer rather than the internal diffusion of moisture within the particle.