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.     

菜豆种子薄层干燥的潜力分析

为探讨薄层物料脱水过程颗粒内部水分的迁移机理,考虑物料的非均质性及水分扩散系数在干燥过程的变化,利用扩散方程模型通过有限差分法数值模拟了菜豆种子的干燥过程,分析了物料内部温度场及湿度场的相互影响。结果表明,种皮是种子干燥过程最主要的传质阻力之一,菜豆种子子叶层的扩散系数是种皮层的3．2倍。根据物料颗粒内部的湿度分布,匹配一定的温度场,能够显著加快脱水过程,可以认为这是干燥极限过程,在一定程度上说明了强化、优化传热传质的方向与干燥潜力。     

Drying Kinetics of Instant Asian Noodles Processed in Superheated Steam

The objective for this work was to develop a novel technique for creating instant noodles by determining the drying kinetics of noodles undergoing simultaneous drying and processing using superheated steam. The mathematical model of moisture ratio was differentiated to determine the drying rates of noodles during processing. There was a constant rate drying period for all temperatures at a steam velocity of 1.5 m/s but there was no constant rate drying period at a steam velocity of 0.5 m/s. The constant rate drying period suggested by measurement of internal noodle temperature is much longer and well defined for all processing conditions than from the drying curves. The constant drying rate period, was nearly 200 s at 110°C but decreased to 50 s at 150°C. Equilibrium moisture content isobars were determined from mass changes during superheated steam processing. It was determined that isotherm equations for equilibrium moisture content in hot air systems may be utilized to model isobars in superheated steam systems.     

Some Considerations In Simulation Of Superheated Steam Drying Of Softwood Lumber

ABSTRACT

A mathematical model for high-temperature drying of softwood lumber with moist air has been modified and extended to simulate wood drying with superheated steam. In the simulation, differences between the two types of drying are considered, these include: external heat and mass transfer processes and calculation of equilibrium moisture content. The external mass transfer coefficient in the perheated steam drying was found to be much higher than that in the moist air drying, however, the heat ransfer coefficients for these two cases were of the same order. The predicted drying curves and wood temperatures from the superheated steam drying model were compared with experimental data and there was close agreement. Further studies will apply the model to development of commercial drying schedules for wood drying with superheated steam.     

微波干燥法测定过磷酸钙中的水分

提出用微波干燥法测定过磷酸钙中水分的含量,测定的精密度较高,操作简便,条件容易控制,分析速度快,RSD=(n=6)为1.23%。经多次试验证明,采用本法测定结果满意。     

Internal Mass Transfer during Isothermal Drying of a Porous Solid Containing Multicomponent Liquid Mixtures

Internal mass transfer in a porous solid partially saturated with multicomponent liquids has been experimentally and theoretically studied. Isothermal drying experiments were performed using a jacketed wind tunnel where the transient composition profiles and total liquid content of a cylindrical sample were determined. Sand samples wetted with the ternary liquid mixtures water-methanol-ethanol and 2-propanol-methanol-ethanol were dried at two different initial compositions and temperatures. A mathematical model including mass transfer by capillary movement of the liquid and interactive diffusion in both gas and liquid phase was developed. To simulate the capillary movement of liquid mixtures, parameters experimentally determined for single liquids where weighed according to liquid composition. A fairly good agreement between theoretical and experimental liquid composition profiles was obtained provided that axial dispersion is included in the model.     

Internal Mass Transfer during Isothermal Drying of a Porous Solid Containing Multicomponent Liquid Mixtures

Abstract

Internal mass transfer in a porous solid partially saturated with multicomponent liquids has been experimentally and theoretically studied. Isothermal drying experiments were performed using a jacketed wind tunnel where the transient composition profiles and total liquid content of a cylindrical sample were determined. Sand samples wetted with the ternary liquid mixtures water-methanol-ethanol and 2-propanol-methanol-ethanol were dried at two different initial compositions and temperatures. A mathematical model including mass transfer by capillary movement of the liquid and interactive diffusion in both gas and liquid phase was developed. To simulate the capillary movement of liquid mixtures, parameters experimentally determined for single liquids where weighed according to liquid composition. A fairly good agreement between theoretical and experimental liquid composition profiles was obtained provided that axial dispersion is included in the model.     

Aggregation in Solvent Extraction Systems Containing a Malonamide,a Dialkylphosphoric Acid and their Mixtures

Abstract

Aggregation phenomena in n-alkane solutions of di-n-hexylphosphoric acid (HDHP), N,N′-dimethyl-N,N′-dioctylhexylethoxymalonamide (DMDOHEMA), and their mixtures, were investigated by electrospray ionization–mass spectrometry (ESI-MS), vapor pressure osmometry (VPO), and small-angle X-ray and neutron scattering (SAXS and SANS). The objective of the study was to probe the formation of mixed HDHP-DMDOHEMA species before and after extraction of trivalent lanthanide and actinide (M³⁺) nitrates. The most important species formed by HDHP upon metal extraction has the composition M(DHP)₃(HDHP)₃(H₂O). These species exist as spherical aggregates of the reverse micelle type with a polar core diameter of ～ 7 Å and total diameter of ～ 11 to ～ 15 Å. The aggregation of DMDOHEMA is a progressive phenomenon, with an average aggregation number of ～ 2 in the 0.2 to 0.6 M range and larger aggregates forming at higher concentrations. The metal loaded DMDOHEMA aggregates can be considered as interacting spheres with a polar core diameter between ～ 11 and ～ 16 Å, depending on composition, a total diameter of up to ～ 25 Å, and a weight-average aggregation number of ～ 9. The results obtained in this work provide strong evidence for the formation of mixed aggregates when mixtures of HDHP and DMDOHEMA are used for the extraction of trivalent Ln and An cations. These mixed reverse micelles have a diameter between 19 and 24 Å with a polar core diameter of 10 and to 14 Å. The most recurrent micellar composition is 2 HDHP and either 4 or 5 DMDOHEMA molecules.     

Drying Rate Curves of Porous Solids in Steam and in Air under Low-Pressure Conditions

Drying of porous solids such as sintered glass beads, baked clay, and cemented glass balloons in both steam and air streams was investigated under low-pressure conditions. There was no significant difference between the normalized observed drying rate curves in air at low pressures of 0.71-1.19 kPa and those in steam at low pressures of 0.97-0.99 kPa. However, lower critical moisture contents and higher drying rates in superheated steam at subatmospheric pressures of 8.27-8.33 kPa were observed compared to those in steam at pressures in the range of 0.97-0.99 kPa. Moreover, two models were validated for the prediction of drying rate curves of sintered glass beads at subatmospheric and low pressures. The patterns of the drying rate curves, which depend on the drying medium and its pressure, were common to these materials.     

External Heat Transfer in Moist Air and Superheated Steam for Softwood Drying

In kiln drying of softwood timber, external heat and moisture mass transfer coefficients are important in defining boundary temperature and moisture content at the wood surface. In addition, superheated steam drying of wood is a promising technology but this has not been widely accepted commercially, partially due to the lack of understanding of the drying phenomena occurred during drying. In this work, experimental investigation was performed to quantify the heat transfer between wood surface and surrounding moist air or superheated steam. In the experiment, saturated radiata pine sapwood samples were dried using dry-bulb/wet-bulb temperatures of 60℃/50℃, 90℃/60℃, 120℃/71℃, 140℃/90℃, 160℃/90℃, 140℃/100℃ and 160℃/100℃. The last two schedules were for superheated steam drying as the wet-bulb temperature was set at 100℃. The circulation velocity over the board surface was controlled at 4.2m·s-1. Two additional runs (90℃/60℃) using air velocities of 2.4m·s-1 and 4.8m·s-1 were performed t     

Drying Rate Curves of Porous Solids in Steam and in Air under Low-Pressure Conditions

Drying of porous solids such as sintered glass beads, baked clay, and cemented glass balloons in both steam and air streams was investigated under low-pressure conditions. There was no significant difference between the normalized observed drying rate curves in air at low pressures of 0.71–1.19 kPa and those in steam at low pressures of 0.97–0.99 kPa. However, lower critical moisture contents and higher drying rates in superheated steam at subatmospheric pressures of 8.27–8.33 kPa were observed compared to those in steam at pressures in the range of 0.97–0.99 kPa. Moreover, two models were validated for the prediction of drying rate curves of sintered glass beads at subatmospheric and low pressures. The patterns of the drying rate curves, which depend on the drying medium and its pressure, were common to these materials.     

高沸醇木质素胺对菠萝蛋白酶的吸附

利用高沸醇木质素与二甲胺的曼尼希反应合成高沸醇木质素胺并探讨它对菠萝蛋白酶的吸附特性。结果表明,高沸醇木质素胺对菠萝蛋白酶的吸附量比高沸醇木质素的吸附量更大,胺基对菠萝蛋白酶的吸附起重要作用,而且吸附后的酶活性仍保持在较高的水平,有望成为菠萝蛋白酶固定化的潜在载体。     

Drying Behavior of Binary Mixtures of Solids

In this work, a model system zeolite NaY and kaolin (both from Aldrich®), and mixtures (1:4, 2:3, 3:2, 4:1) were studied. True and bulk densities, porosity, and specific surface area were determined for single solids and mixtures. Physical properties of mixtures were calculated from the mixing rule using mass fraction of each solid in the mixture. Calculated and experimental values presented perfect agreement for true density and specific surface area. For bulk density and porosity the mixing rule works well if the volumetric fraction is used, since the mixtures do not follow the mass proportion due to the different particle size distribution. The mixtures present the drying curves between those of the single solids according to their mass proportion. The results show that it is possible to use the mixing rule to evaluate some physical properties as well as the sorption isotherms and drying curves of binary mixtures of solids.     

Superheated Steam Vacuum Drying of Rubberwood

The effect of superheated steam vacuum drying (SSVD) on the drying time and mechanical properties of rubberwood was studied. Rubberwood boards with dimensions of 1000 mm × 76.2 mm × 25.4 mm were dried at 86.7–89.3 kPa vacuum pressure (14.6–12.0 kPa absolute) and temperatures of 60, 70, and 80°C. Superheated steam at 110°C was injected intermittently to relieve stress buildup in wood and eliminate cracking. The prong test was used to evaluate the initial acceptability of the dried wood and the mechanical properties of wood were measured. From this study, the total drying time was reduced from 168 h to less than 20 h (MC reduction from 0.80 to 0.06 db). In addition, compared to the reference values shown in the parentheses, the shear parallel-to-grain, the compression parallel-to-grain, the compression perpendicular-to-grain, the modulus of rupture (MOR), the modulus of elasticity (MOE), and the hardness for the optimum drying temperature of 70°C were 28.87 (11.0) MPa, 59.09 (32.0) MPa, 21.09 (5.0) MPa, 101.97 (66.0) MPa, 9838.5 (9240.0) MPa, and 6475 (4350) N, respectively. Thus, the vacuum-dried wood showed a 32% increase in hardness, a 12% increase in compression parallel-to-grain, and an 88% increase in shear parallel-to-grain.     

Comparison of Drying Rate Curves of Porous Solids in Superheated Steam to Those in Air

Drying of porous solids was experimentally investigated in superheated steam as well as in air. Drying rate curves, including critical moisture contents, in steam at subatmospheric pressure, were compared to those for air at atmospheric pressure; moreover, they were compared to those for steam at atmospheric pressure as well. The former comparison was carried out under conditions of sample temperatures of 41.8-42.5°C (which were nearly equal to saturation temperatures of 42.1-42.2°C at pressures of 8.23-8.30 kPa) for the constant rate period in steam and the corresponding sample temperatures of 42.0-45.0°C (which were close to the wet-bulb temperatures) for the constant rate period in air. There were distinct differences between normalized drying rate curves, including critical moisture contents in steam and in air at the above similar sample temperatures for materials of baked clay, firebrick, and cemented glass balloons over the minimum value of 8.3 × 10^-3 µm and up to the maximum value of 1.2 × 10² µm in cumulative pore-size distributions: longer constant rate periods and lower critical moisture contents in steam than in air, and higher drying rates in steam than in air for the falling rate period. Moreover, the latter comparison of the drying rates in steam at subatmospheric pressure to those in steam at atmospheric pressure revealed that the differences in normalized drying rates between subatmospheric pressure and atmospheric pressure were small for both materials under mild external conditions. These findings were common to the baked clay, firebrick, and cemented glass balloons over a wide range of pore-size distributions studied in the present work, as well as sintered coarse glass beads as previously reported.     

Comparison of Drying Rate Curves of Porous Solids in Superheated Steam to Those in Air

ABSTRACT

Drying of porous solids was experimentally investigated in superheated steam as well as in air. Drying rate curves, including critical moisture contents, in steam at subatmospheric pressure, were compared to those for air at atmospheric pressure; moreover, they were compared to those for steam at atmospheric pressure as well. The former comparison was carried out under conditions of sample temperatures of 41.8–42.5°C (which were nearly equal to saturation temperatures of 42.1–42.2°C at pressures of 8.23–8.30 kPa) for the constant rate period in steam and the corresponding sample temperatures of 42.0–45.0°C (which were close to the wet-bulb temperatures) for the constant rate period in air. There were distinct differences between normalized drying rate curves, including critical moisture contents in steam and in air at the above similar sample temperatures for materials of baked clay, firebrick, and cemented glass balloons over the minimum value of 8.3 × 10^?3 µm and up to the maximum value of 1.2 × 10² µm in cumulative pore-size distributions: longer constant rate periods and lower critical moisture contents in steam than in air, and higher drying rates in steam than in air for the falling rate period. Moreover, the latter comparison of the drying rates in steam at subatmospheric pressure to those in steam at atmospheric pressure revealed that the differences in normalized drying rates between subatmospheric pressure and atmospheric pressure were small for both materials under mild external conditions. These findings were common to the baked clay, firebrick, and cemented glass balloons over a wide range of pore-size distributions studied in the present work, as well as sintered coarse glass beads as previously reported.     

N-辛基-2- 吡咯烷酮表面活性剂复配体系的研究

研究了３０℃下Ｎ 辛基吡咯烷酮（Ｃ８Ｐ） 分别与十二烷基硫酸钠（ＳＤＳ） 、十六烷基三甲基溴化铵（Ｃ１６ ＴＡＢ）的水溶液表面张力随浓度的变化。计算这２ 种复配体系中的分子相互作用参数βσ、βＭ 值分别为－２ ．７０ ,－２ ．７８ ,－ １．２７,－ ０．８７,并比较了这２ 种复配体系的协同效应     

Surface Composition and Morphology of Particles Dried Individually and by Spray Drying

This study investigates how the morphology of spray-dried particles is related to the formulation and properties of the components in the formulation. Further, the scale effects in comparisons of levitation-dried single particles and spray-dried particles in a lab-scale spray dryer have been addressed. The Drying Kinetics Analyzer^TM generates single particles from a levitated drop under simulated spray-drying conditions. A set of surface-active polymers (bovine serum albumin, hydroxypropyl methyl cellulose, and triblock co-polymer Poloxamer), in combination with lactose, were analyzed for their dynamic surface properties in solution, and their effect on particle morphology and surface composition were determined by low-vacuum SEM and XPS analyses. The morphology obtained in spray drying was reproduced in the single-particle drying. The surface compositions were also similar, but higher levels of surface-active materials were found at the surface of the single particles as compared to the spray-dried particles. Further, the adsorption rate of surface-active compounds at the drop surface estimated by dynamic surface tension was found to be an important parameter to estimate the surface composition at different drying scales. The particle morphology was primarily determined by the surface rheological properties of the feed solution and, to a lesser extent, by the surface composition.     

Modeling Superheated Steam Vacuum Drying of Wood

A two-dimensional mathematical model developed for vacuum-contact drying of wood was adapted to simulate superheated steam vacuum drying. The moisture and heat equations are based on the water potential concept whereas the pressure equation is formulated considering unsteady-state mass conservation of dry air. A drying test conducted on sugar maple sapwood in a laboratory vacuum kiln was used to infer the convective mass and heat transfer coefficients through a curve fitting technique. The average air velocity was 2.5 m s^-1 and the dry-bulb temperature varied between 60 and 66°C. The ambient pressure varied from 15 to 11 kPa. Simulation results indicate that heat and mass transfer coefficients are moisture content dependent. The simulated drying curve based on transfer coefficients calculated from boundary layer theory poorly fits experimental results. The functional relation for the relative permeability of wood to air is a key parameter in predicting the pressure evolution in wood in the course of drying. In the case of small vacuum kilns, radiant heat can contribute substantially to the total heat transfer to the evaporative surface at the early stages of drying. As for conventional drying, the air velocity could be reduced at the latter stage of drying with little or no change to the drying rate.     

Modeling Superheated Steam Vacuum Drying of Wood

Abstract

A two-dimensional mathematical model developed for vacuum-contact drying of wood was adapted to simulate superheated steam vacuum drying. The moisture and heat equations are based on the water potential concept whereas the pressure equation is formulated considering unsteady-state mass conservation of dry air. A drying test conducted on sugar maple sapwood in a laboratory vacuum kiln was used to infer the convective mass and heat transfer coefficients through a curve fitting technique. The average air velocity was 2.5 m s^?1 and the dry-bulb temperature varied between 60 and 66°C. The ambient pressure varied from 15 to 11 kPa. Simulation results indicate that heat and mass transfer coefficients are moisture content dependent. The simulated drying curve based on transfer coefficients calculated from boundary layer theory poorly fits experimental results. The functional relation for the relative permeability of wood to air is a key parameter in predicting the pressure evolution in wood in the course of drying. In the case of small vacuum kilns, radiant heat can contribute substantially to the total heat transfer to the evaporative surface at the early stages of drying. As for conventional drying, the air velocity could be reduced at the latter stage of drying with little or no change to the drying rate.