Food Drying and Dewatering

ABSTRACT

Food drying and dewatering raises a growing interest because of increasing requirements in quality, specially in the production of ingredients and additives for food formulation. Heat and mass transfers, as well as mechanical phenomena and reactions kinetics induced by these transfers must be more and more carefully controlled during drying and storage.

This chapter relates recent advances in

- drying of solids

- spray-drying

- drum-dryine

- superheateded steam drying

- osmotice dehydration

- hot oil immersion drying     

Pervaporation for Drying and Dewatering

Dewatering denotes moisture removal from materials and it is a more general term than drying. In dehydration and drying technology, a growing role of modern techniques used either separately or in hybrid solutions is observed. Membrane techniques find many industrial applications in this field. Based on available literature, examples of dehydration on membranes, important from the viewpoint of energy saving, environmental protection, and recoverable energy sources, are presented in this study. Special attention is given to the process of pervaporation as the most modern and promising technique for azeotropic mixture separation to be used in dehydration of solvents, including alcohols, and removal of volatile organic compounds from sewage, concentration of aromas, and separation of multicomponent systems.     

Pervaporation for Drying and Dewatering

Dewatering denotes moisture removal from materials and it is a more general term than drying. In dehydration and drying technology, a growing role of modern techniques used either separately or in hybrid solutions is observed. Membrane techniques find many industrial applications in this field. Based on available literature, examples of dehydration on membranes, important from the viewpoint of energy saving, environmental protection, and recoverable energy sources, are presented in this study. Special attention is given to the process of pervaporation as the most modern and promising technique for azeotropic mixture separation to be used in dehydration of solvents, including alcohols, and removal of volatile organic compounds from sewage, concentration of aromas, and separation of multicomponent systems.     

Dewatering and Drying Methods for Microalgae

Microalgae can efficiently fix carbon dioxide through their phototropic metabolism, and have been recognized as a promising bioresource for animal feed, health food, fuel, cosmetic, and pharmaceutical products. However, since microalgae in cultivated medium have a low biomass concentration (0.1–1% w/w), both harvesting and concentration of microalgal biomass are often required prior to the production of commercial products. Efficient and cost-effective dewatering and drying methods for microalgae heavily affect the overall energy consumption and production cost of microalgal products. This review describes the characteristics of commonly used dewatering and drying technologies, and critically evaluates the feasibility for their use to treat microalgal biomass. No single dewatering or drying method can satisfactorily handle all types of microalgae. The suitability of each method depends on the properties of the microalgae suspension, the required process design, the quality of the end product, and the related capital and production costs.     

海底天然气管道排水和干燥工艺若干问题分析

为了防止投产过程中形成水合物堵塞管道,天然气管道在投产之前必须进行排水和干燥处理。而海底天然气管道不能像陆上管道一样进行分段施工干燥,加大了干燥的难度。由于我国的海底管道干燥工艺起步较晚,干燥过程中存在窜漏、卡堵、清管器速度难以控制、无内涂层管道排水干燥效果差等技术问题。分析了上述问题的起因,并结合一些国内外具体投产实例提出了相应的解决方法。为我国海底天然气管道的干燥提供了可借鉴的经验。     

变性淀粉脱水及气流干燥系统的控制策略优化

根据工作原理将变性淀粉脱水及气流干燥的工艺分成两部分来研究.通过在线预估得到淀粉压滤脱水环节的生产速率,将该速率进行适当的转换以确定下游气流干燥环节的干燥速度,并对气流干燥环节的最终成品水分和相关的尾气温度做一定程度的控制优化,使得整条生产线在优化产能的同时,提高成品含水率的稳定性和产品质量.对比试验证明了该系统相对于原系统的优越性.     

Effect of Drying and Dewatering on Yttria Precursors with Transient Morphology

The influence of drying and dewatering of a yttrium hydroxynitrate precursor with transient morphology was investigated. The ability of this precursor to form soft agglomerated nanoparticles after calcination is dependent on the dewatering method. Freeze drying leads to finer particles than other dewatering methods that involve removal of the solvent from its liquid state. As water is directly removed by sublimation during freeze drying, this method inhibits the formation of solid bridges between hydroxynitrate platelets. These bridges, which form with the other dewatering methods, destabilize the spheroidization process of the platelets during subsequent firing at high temperatures.     

Mechanical Dewatering and Thermal Drying of Sludge in a Single Apparatus

This article describes the Centridry® technology (marketed in the UK by Euroby Ltd.) used at the Monsanto wastewater treatment plant in Antwerp, Belgium, for handling excess wastewater-activated sludge. In one single enclosed machine, sludge with an initial solids concentration of 1.5 to 4% w/w dry substance is mechanically dewatered with a high-solids decanter centrifuge and thermally dried in a flash dryer, yielding a final product with a concentration of solids ranging from 80 to 95% w/w dry substance. Operational experience with varying sludge characteristics affecting the fouling sensitivity of the system is presented for the Centridry technology at the Monsanto plant in Antwerp.     

离心干燥机在聚合物颗粒脱水干燥中的应用和发展

主要介绍离心干燥机在聚合物造粒加工后处理中的应用、发展及国内外现状。对比Gala和caner Day两大公司相关产品结构的差异,简述其脱水、干燥的基本原理及结构特点。尽管该机械已经得到大量工程应用,但缺乏详细的设计理论。深入开展相关理论研究对于正确选型和开发我国自主知识产权的高效率机器至为重要。     

Energy and Quality Aspects of Food Drying

High energy consumption and increasing consumers interest in new products are two problems worthy of note in the drying of food. Difficulties in producing high-quality food and degrading transformations of the material during drying are mentioned. The kinetics of quality degradation due to drying is described. The role of water activity in maintaining product quality is emphasized. Examples of drying methods and tendencies toward a reduction in quality degradation of dried food products are shown.     

The Spray Drying of Food Flavors

Abstract

Spray drying is the most commonly used technique for the production of dry flavorings. In spray drying, an aqueous infeed material (water, carrier, and flavor) is atomized into a stream of hot air. The atomized articles dry very rapidly, trapping volatile flavor constituents inside the droplets. The powder is recovered via cyclone collectors. Flavor retention is quite satisfactory if dryer operating parameters are properly chosen. Flavor retention is maximized by using a high infeed solids level, high viscosity infeed, optimum inlet (160–210°C) and high exit (>100°C) air temperatures, and high molecular weight flavor molecules. The shelf life of oxidizable flavor compounds is strongly influenced by the flavor carrier.     

Electro-Kinetic Technology as a Low-Cost Method for Dewatering Food By-Product

Increasing volumes of food waste, intense environmental awareness, and stringent legislation have imposed increased demands upon conventional food waste management. Food by-products that were once considered to be without value are now being utilized as reusable materials, fuels, and energy in order to reduce waste. One major barrier to the valorization of food by-products is their high moisture content. This has brought about the necessity of dewatering food waste for any potential re-use for certain disposal options. A laboratory system for experimentally characterizing electro-kinetic dewatering of food by-products was evaluated. The bench scale system, which is an augmented filter press, was used to investigate the dewatering at constant voltage. Five food by-products (brewer's spent grain, cauliflower trimmings, mango peel, orange peel, and melon peel) were studied. The results indicated that electro-kinetic dewatering combined with mechanical dewatering can reduce the percentage of moisture from 78% to 71% for brewer's spent grain, from 77% to 68% for orange peel, from 80% to 73% for mango peel, from 91% to 74% for melon peel, and from 92% to 80% for cauliflower trimmings. The total moisture reduction showed a correlation with electrical conductivity (R² = 0.89). The energy consumption of every sample was evaluated and was found to be up to 60 times more economical compared to thermal processing.     

常压吸附流化冷冻干燥技术的研究与探索

阐述了常压吸附流化冷冻干燥与真空冷冻干燥的原理、特点、研究概况和能耗分析,提出常压吸附流化冷冻干燥可能成为一种新型冷冻干燥技术而具有较高的研究开发价值.     

Advanced Exergy Analysis of a Heat Pump Drying System Used in Food Drying

Exergy analysis has been used as a powerful tool to study and optimize various types of energy systems. However, the methodology of splitting the exergy destructions (the so-called advanced exergy analysis) allows for a further understanding of the exergy destruction values to improve the system efficiency. In this study, advanced exergy analysis was applied to a pilot-scale heat pump drying system used in food drying for the first time to evaluate its performance at different drying temperatures. The results showed that inefficiencies within the compressor and condenser were mainly due to the internal operating conditions and the efficiencies in the evaporator and heat recovery system could be improved by structural improvements of the whole system and remaining system components.     

Power Ultrasound Mass Transfer Enhancement in Food Drying

Power ultrasound application could constitute a way to enhance food drying in order to improve not only mass transfer but also product quality, since it does not significantly heat the material. The main aim of this work was to assess the influence of power ultrasound on the mass transfer process during drying of different products, carrot, persimmon and lemon peel.Convective drying kinetics were carried out with ultrasound (US experiments 21.8 kHz, 75 W), or without ultrasound application (AIR experiments) at air velocities ranging between 0.5–12 m s⁻¹. Different geometries were used for each of the products: cubes in carrots (2 L = 8.5 mm), cylinders in persimmon (2 L = 30 mm and 2 R = 13 mm) and slabs in lemon peel (L = 10 mm). Drying kinetics were modelled by considering different diffusion models according to the geometry.The results show that air velocity and raw material characteristics play a role in convective drying kinetics assisted by power ultrasound. Power ultrasound increased effective moisture diffusivity at low air velocities for all the products. However, in the case of lemon peel, ultrasound also improved the drying rate at high air velocities. This behaviour may be explained by the disruption of the acoustic field at high air flow rates and the different level of intensity required due to the structure of the products. Therefore, the raw material constitutes an important variable to establish the influence of power ultrasound on convective drying.     

基于PLC控制的全自动污泥脱水干化系统设计

随着我国污水处理产业的快速发展,也带来了污泥产量的迅速增加。文章以市政污泥为例,模块化设计污泥压滤、干化设备,并应用PLC系统控制整个操作流程,实现工作系统全自动运行方式,保证了处理污泥全过程的安全性及可控性。这一设计系统也为其它环保设备模块化设计提供参考。     

CFD 在食品干燥过程及其干燥设备设计中的应用

CFD是通过计算机数值计算和图像显示以定量描述流场的数值解,从而对物理问题进行分析研究。CFD兼有理论性和实践性的双重特点,其主要用途是对流态进行数值仿真模拟计算,能够对流态的温度场、速度场、浓度场等进行有效的指导和预测。本文综述了CFD数值模拟在食品干燥过程中以及干燥设备设计中的应用和发展前景。     

Encapsulation Efficiency of Food Flavours and Oils during Spray Drying

Microencapsulation is a rapidly expanding technology which is a unique way to package materials in the form of micro- and nano-particles, and has been well developed and accepted within the pharmaceutical, chemical, food and many other industries. Spray drying is the most commonly used encapsulation technique for food products. A successful spray drying encapsulation relies on achieving high retention of the core materials especially volatiles and minimum amounts of the surface oil on the powder particles for both volatiles and non-volatiles during the process and storage. The properties of wall and core materials and the prepared emulsion along with the drying process conditions will influence the efficiency and retention of core compounds. This review highlights the new developments in spray drying microencapsulation of food oils and flavours with an emphasis on the encapsulation efficiency during the process and different factors which can affect the efficiency of spray drying encapsulation.     

常压吸附流化冷冻干燥技术的研究与探索

阐述了常压吸咐流化冷冻干燥与真空冷冻干燥的原理，特点，研究概况和能耗分析，提出常压吸附流化冷冻干燥可能成为一种新型冷冻干燥技术而具有较高的研究开发价值。