SOME CRITERIA OF SPRAY DRYER DESIGN FOR FOOD LIQUID

Spray drying has many applications for a wide variety of dried food powders. The quality of spray dried food is quite dependent on the atomization characteristics and the heat and mass transfer on drops inside the spray dryer. This paper deals with some design criteria of the spray dryer such as the atomizer, the drop trajectory and the heat/mass transfer between the drop and the drying air.     

EFFECT OF THE DROPLET AGGLOMERATION ON THE DESIGN OF SPRAY DRYER TOWERS

ABSTRACT

The agglomeration of water droplets along the distance from the atomising nozzle was determind experimentally. The effect of the droplet agglomeration upon the required height of the spray dryer is computed for different nozzle sizes and different gas temperatures.     

喷雾干燥设备设计的数学模拟法

系统论述了喷雾干燥器内粒子的运动状态与风场流动特性及其数学模型的建立过程,在传递理论的基础上根据马歇尔方程计算了干燥过程中粒子与干燥介质之间的传质传热,通过求解粒子在干燥室内的运动方程而进行喷雾干燥设备设计的粒子运动轨迹法及设计计算程序的计算机实现过程,并用实验数据及理论解对程序的可靠性进行了论证。     

FUNDAMENTALS OF LIQUID SPRAY TECHNIQUES

Two twin forced convection dryers of 1.5 m³ were built in Majorca (Spain). They are of a mixed kind, with solar air collectors and a green house type chamber. A wooden frame supports polycarbonate walls. After two years operation they have been proven weather resistant. Six solar air collectors 2.12 × 1.05 m were used in each dryer.

Apricots were processed in both dryers and at open sun. Three different tray heights were tested 5, 9 and 12 cm. The best results were obtained with 12 cm trays. Recycling part of the exhaust air improves the efficiency of the dryer. Blanching the fruits makes no difference to the dehydration rate. The rate of SO₂ loss during the drying process is higher within the chamber.     

OBSERVATIONS OF FLOW PATTERNS IN A SPRAY DRYER

ABSTRACT

Experiments have been performed on a pilot scale, cylinder-on-cone spray dryer fitted with a vaned-wheel atomiser to observe air flow patterns, with and without water spray. A combination of tufts, smoke streams and a laser light sheet, was used to provide information about regions of recirculation, flow stability, spray trajectories and wall deposition. While atomiser-induced swirl dominated the flow patterns under typical operating conditions, some instability was observed, although different in type, for situations with and without atomiser rotation. Clockwise eddies were observed to form and collapse between the wall and the strongly anti-clockwise swirling core created by anti-clockwise atomiser rotation. Without swirl, large portions of the recirculation zones at the walls were observed to have a weak tendency to change randomly between clockwise, anticlockwise and chaotic behaviour.     

RECENT PROGRESS OF SPRAY DRYING IN CHINA

Abstract

The development of spray drying technique during past 10 years in China is reviewed. Main achievements in research, development and utilization of three types of atomization are described and summarized. General trend of spray drying research and development in 21st century is forecasted.     

微型台式喷雾干燥器的研制

介绍一种目前国内最小、性能优良的喷雾干燥装置 ,该机经鉴定认为填补了国内空白 ,技术水平处于国内领先 ,可以作为各大专院校、科研院所、大中型企业的探测性试验研究或生产前小试装置。     

RECENT PROGRESS OF SPRAY DRYING IN CHINA

The development of spray drying technique during past 10 years in China is reviewed. Main achievements in research, development and utilization of three types of atomization are described and summarized. General trend of spray drying research and development in 21st century is forecasted.     

LEAFLASH SPRAY DRYER: INVESTIGATION OF THE ATOMIZATION PROCESS

The atomization process of the LEAFLASH spray dryer has been investigated by laser diffractometry and video imaging. The LEAFLASH atomizer is a particular pneumatic nozzle where the pressurized gas is the hot drying air. The drying and the atomization processes are interrelated in the spray dryer. Consequently the mixing of the liquid droplets and the drying medium is very efficient, permitting to work with short drying duration and reduced chamber volume. The mean diameter and the drop size distribution are measured at the outlet of the nozzle by laser diffraction. We studied the coupling effects of the air temperature (150 to 300° C) and pressure (1.20 to 1.50 bars abs) and of the dry matter content of the liquid feed (aqueous maltodextrin solution, 20 to 55% w/ w) on the droplets/ size distribution and on the general pattern of the spray. Analyses of video images of the generated spray give the general pattern of the spray and an estimation of the liquid velocity     

喷干塔五种燃煤方式的综合分析

本文根据实际使用效果,分析介绍了喷干塔五种燃煤方式的工作原理及特点,并从粉料工艺性能,燃煤适应性,操作及控制,建设投资,运行成本等方面进行了综合分析。     

SOME ASPECTS OF SPRAY FORMATION BY PNEUMATIC NOZZLES

A study of spray formation in a pneumatic nozzle With external mixing is pre- sented. The mast importent parameters are highlighted and their influence on the mean drop diameter and size distribution is examined. A theoretical approach is outlined which yields several exponential models containing all important parame- ters in dimensionless form. The most appropriate model for drop size prediction is recommended after experimental verification and comparison with several previously published models. Special attention was paid to development of s simple model which makes its practical application easier.

Unlike the mean drop diameter, the size distribution was found to be much less affected by the operating parameters. The Rosin-Rammler distribution can be used to characterize the experimental results within the range covered. The coefficient of polydispersity was found to be practically unaffected by the operating parameters.     

DESIGN AND TESTING OF A COMBINED CONDUCTION-CONVECTION ROTARY PADDY DRYER

ABSTRACT

A rotary drum dryer prototype was designed, fabricated and tested to combine convection drying with conduction heating of paddy to increase moisture reduction rates. Ambient air forced inside the drum counter-flow to the direction of the cascading grains brought about “dryeration” of the hot grains, resulting in cooler grain output and increased moisture reduction rates. Its partial drying capacity doubled that of the benchmark pre-dryer at 5?rpm drum speed and quadrupled at 7?rpm, requiring only a single-pass operation. Tests using freshly harvested and re-wetted paddy showed that partial drying capacity, final moisture content and moisture reduction rate were all significantly affected by counter-flow air velocity, Its overall thermal efficiency was also 50% higher.     

A SYSTEMATIC APPROACH FOR INVESTIGATION OF SPRAY DRYING PROCESSES

Abstract

A systematic approach is developed for investigation of spray drying processes for chemical and biological systems. The approach involves an in-depth study of atomizer performance, spray dryer parametric sensitivity, spray-dried powder properties, thermal inactivation and post-drying properties. The approach helps considerably in rational design of spray drying experiments and in investigation and optimization of various process aspects of spray drying of chemical and biological systems, leading to large savings in labor, cost and time.     

USE OF COMPUTATIONAL FLUID DYNAMICS TECHNIQUES TO ASSESS DESIGN ALTERNATIVES FOR THE PLENUM CHAMBER OF A SMALL SPRAY DRYER

The inlet region of a pilot-scale, co-current spray dryer was simulated using the proprietary Computational Fluid Dynamics (CFD) codes, CFX4 and CFX5. Several design alternatives were considered for correcting uneven inlet air distribution, which is known to influence spray dryer performance and airflow patterns. The simulations were used to assess each alternative prior to construction, assuming isothermal and incompressible flow conditions. Experimental measurements were compared with the simulation results for the original and one modified design.

Drying air is supplied to this dryer via an overhead pipe feeding an annular plenum chamber, of diameter 400 mm, surrounding the atomiser. A distributor plate with two concentric rings of 50 holes, each of 5 mm diameter, forms the base of the plenum chamber. A three-dimensional grid was required to model each of the 100 holes separately and to consider the asymmetric flow behaviour. The resulting grid consisted of about 532,000 cells. The CFD simulations proved useful in predicting the trends in flow distributions in each of the designs.     

USE OF COMPUTATIONAL FLUID DYNAMICS TECHNIQUES TO ASSESS DESIGN ALTERNATIVES FOR THE PLENUM CHAMBER OF A SMALL SPRAY DRYER

The inlet region of a pilot-scale, co-current spray dryer was simulated using the proprietary Computational Fluid Dynamics (CFD) codes, CFX4 and CFX5. Several design alternatives were considered for correcting uneven inlet air distribution, which is known to influence spray dryer performance and airflow patterns. The simulations were used to assess each alternative prior to construction, assuming isothermal and incompressible flow conditions. Experimental measurements were compared with the simulation results for the original and one modified design.

Drying air is supplied to this dryer via an overhead pipe feeding an annular plenum chamber, of diameter 400 mm, surrounding the atomiser. A distributor plate with two concentric rings of 50 holes, each of 5 mm diameter, forms the base of the plenum chamber. A three-dimensional grid was required to model each of the 100 holes separately and to consider the asymmetric flow behaviour. The resulting grid consisted of about 532,000 cells. The CFD simulations proved useful in predicting the trends in flow distributions in each of the designs.     

磷酸氢钙的大型气流干燥装置设计

介绍了一种大型气流干燥磷酸氢钙的工业生产流程,对干燥管内颗粒和空气的干燥特性进行了模拟和计算机辅助设计,模拟设计结果与实际生产情况较吻合。     

MICROENCAPSULATION OF EMULSIFIED HYDROPHOBIC FLAVORS BY SPRAY DRYING

The retention of emulsified flavor during spray drying was investigated under various compositions of feed liquid. Drying of the emulsion solution was carried out in a spray dryer, equipped with a centrifugal atomizer. The retention of d-limonene during spray dying was nearly hundred percent independent of the composition of the feed liquid, whereas the retention of ethyl butyrate emulsified by gum arabic (GA) was much lower (0–20%). The retention of ethyl butyrate was markedly dependent on the concentration of maltodextrin and the type of emulsifier, indicating that the stability of emulsion is a controlling factor for flavor retention. The use of mixing emulsifiers, adjusting of density of ethyl butyrate, and the addition of 1% gelatin were quite effective procedures to improve the retention of ethyl butyrate, particularly when emulsified by GA.     

白炭黑干燥工艺介绍

讲述了目前国内常见的几种白炭黑的干燥工艺,并就每一种干燥工艺的优点及不足作了论述,为白炭黑干燥工艺的选择提供了参考;对今后白炭黑干燥工艺的发展趋势及热源的选择进行了探索     

MICROENCAPSULATION OF EMULSIFIED HYDROPHOBIC FLAVORS BY SPRAY DRYING

The retention of emulsified flavor during spray drying was investigated under various compositions of feed liquid. Drying of the emulsion solution was carried out in a spray dryer, equipped with a centrifugal atomizer. The retention of d-limonene during spray dying was nearly hundred percent independent of the composition of the feed liquid, whereas the retention of ethyl butyrate emulsified by gum arabic (GA) was much lower (0-20%). The retention of ethyl butyrate was markedly dependent on the concentration of maltodextrin and the type of emulsifier, indicating that the stability of emulsion is a controlling factor for flavor retention. The use of mixing emulsifiers, adjusting of density of ethyl butyrate, and the addition of 1% gelatin were quite effective procedures to improve the retention of ethyl butyrate, particularly when emulsified by GA.     

MODELING AND OPTIMIZATION FOR DESIGN UNDER PRODUCTION PLANNING CRITERIA IN MULTIPRODUCT DEHYDRATION PLANTS

ABSTRACT

The design problem of a multiproduct dehydration plant involving continuous conveyor-belt dryers utilised for the dehvdration of agricultural products over a fmite tim horizon, is presented. The peculiarities of the problem under demand-varying market patterns and time-variable market prices of raw materials are underlined. Limitations imposed by storage capacity, custormer orders, and constraints dictated by the process itself, are also taken into consideration. The overall problem is cast into a MINLP formulation involving the total annual cost of the plant as its objective function. This was infered by deducing the mathematical model of conveyor-belt dryers. Repeated evaluation of the total annual cost for various structures and operating points, allowed the determination of overall performance characteristic operational and structural curves. approximated by suitable mathematical expressions. A test case is presented in order to demonstrate the effectiveness of the proposed approach.