Electrohydrodynamic Drying—A Concise Overview

Electrohydrodynamic (EHD) drying is a novel method of non-thermal processing. The drying can be carried out using either AC or DC high voltages. The thermodynamic considerations regarding the lowering of temperature under EHD drying include rapid rates of evaporation and exothermic interaction of the electric field with a dielectric material. Multi-point and plate electrode systems are efficient in accelerating drying of agricultural materials. Compared to hot air (convective) drying systems, EHD drying systems offer lower food production costs along with superior quality in terms of physiochemical properties such as color, shrinkage, flavor, and nutrient content. Compared to convective and freeze-drying, EHD drying systems, given their simpler design and lesser energy consumption, show great potential for bulk and industrial drying applications.     

Atmospheric Freeze Drying—A Review

This review article focuses on the development of atmospheric freeze drying (AFD): technological aspects, product possibilities, physical properties of products, drying kinetics, modeling, and simulation. The main motivation for developing atmospheric freeze drying as a new drying technology is the desire to reduce the energy consumption compared to vacuum freeze drying while maintaining a high product quality. One technical solution of atmospheric freeze drying is a combined atmospheric freeze drying and heat pump system with new environmentally friendly refrigerants. Temperature programs make it possible to customize products with desired qualities and properties, like retained color, instant properties, aroma, and nutritional value.     

Drying of Liquid Dispersions—A Unified Approach to Kinetics and Modeling

Abstract

The article presents a unified approach to interpretation of drying kinetics and modeling of the drying process for suspensions, solutions, emulsions and pastes. The approach is based on phenomenological analysis of temperature-moisture relationships T(X) with account for temperature plateaux that actually show-up, or could exist under certain drying conditions. In addition, a unified mathematical model is proposed that includes the differential equations for mass and heat diffusion along with their analytical solutions for a multi-layer plate, cylinder and sphere. Interconnections in the simultaneous heat-mass transfer, cross-effects and any other details of a real process are taken into account separately, by semi-empirical temperature-moisture function T(X). The principles of piece-wise multizone approximation of these temperature-moisture curves are presented. The hyperbolic and two-arc approximations for each separate zone are described. The set of 12 organic and inorganic materials either synthetic or of animal and plant origin such as meat processing sludge, heavy corn steep water, gelatin, starch, sugar, salt, combined latex emulsion, P-salt, gamma acid, dispersing and bleaching agents was taken as example for the development and validation of this approach.     

Drying of biofuels from the forest—A review

The literature during 2000–2016 about drying of biofuels from the forest has been reviewed. Biofuels constitute a low-cost energy resource that is likely to continue to increase and the dryers for such products should be simple, robust, and easy to operate. In 1970s and 1980s, rotary dryers and flash dryers were the most common types, and in 1990s, superheated steam (SHS) dryers became common. Maintenance costs and use of medium pressure steam for the SHS dryers are important topics to consider and one drawback for the rotary dryers is that high-temperature heat sources are used. The development during the last 15 years has moved toward moving bed dryers because of the possibility to use cheap low-temperature energy sources, robust design, and direct capacity control that is achieved by controlling the air temperature in the dryer. A price for the dry biofuel of 15–20 Euro/MWh has been indicated to make a dryer installation profitable based on no cost for the thermal energy and 40 Euro/MWh as the cost for the electrical energy. Shrinkage and the internal transport of moisture and heat in large particles of biofuels will need more considerations in the future. Fractionation of the biofuels, codrying with other products, the total cost for the drying process, environmental issues, and development of drying processes operating at high dew points are the other things to consider.     

Sorghum Allelopathy—From Ecosystem to Molecule

Sorghum allelopathy has been reported in a series of field experiments following sorghum establishment. In recent years, sorghum phytotoxicity and allelopathic interference also have been well-described in greenhouse and laboratory settings. Observations of allelopathy have occurred in diverse locations and with various sorghum plant parts. Phytotoxicity has been reported when sorghum was incorporated into the soil as a green manure, when residues remained on the soil surface in reduced tillage settings, or when sorghum was cultivated as a crop in managed fields. Allelochemicals present in sorghum tissues have varied with plant part, age, and cultivar evaluated. A diverse group of sorghum allelochemicals, including numerous phenolics, a cyanogenic glycoside (dhurrin), and a hydrophobic p-benzoquinone (sorgoleone) have been isolated and identified in recent years from sorghum shoots, roots, and root exudates, as our capacity to analyze and identify complex secondary products in trace quantities in the plant and in the soil rhizosphere has improved. These allelochemicals, particularly sorgoleone, have been widely investigated in terms of their mode(s) of action, specific activity and selectivity, release into the rhizosphere, and uptake and translocation into sensitive indicator species. Both genetics and environment have been shown to influence sorgoleone production and expression of genes involved in sorgoleone biosynthesis. In the soil rhizosphere, sorgoleone is released continuously by living root hairs where it accumulates in significant concentrations around its roots. Further experimentation designed to study the regulation of sorgoleone production by living sorghum root hairs may result in increased capacity to utilize sorghum cover crops more effectively for suppression of germinating weed seedlings, in a manner similar to that of soil-applied preemergent herbicides like trifluralin.     

Radio Frequency Heating—A Prospective Leather Drying System for Future

Abstract

Drying is one of the important operations influencing finished product quality and leather is no exception. Newer drying methods are being explored worldwide in order to enhance the productivity and quality. Radio frequency (RF) heating is being increasingly applied for industrial applications such as drying of wood, paper, and textiles. Investigations on the use of radio frequency heating for leather drying has been attempted in the present work which has led to promising results. Compared to conventional air-drying, RF heating produced leathers of comparable quality both at laboratory and semi-commercial scale trials. Leather drying by radio frequency heating has resulted in time reduction by more than 80%, at favorable energy costs.     

Applying Spray Drying to Customized Powder Manufacture

Spray drying is an important continuous industrial process for drying pumpable liquid formulations irrespective of their heat sensitivity, rheology, solids content and processing rate. Furthermore spray drying has the capability through drying chamber design, plant layout and mode of operation to produce dried products of specific particulate size and morphology. These are important aspects when spray drying technology is applied to the needs of customized powder manufacture. There are many examples in industry where spray dried powders have to meet stringent specifications set by such factors as end-product powder quality standards dictated by global competition, dry raw material characteristics required for optimum downstream processing, and dry materials handling to comply with environmental, health and safety issues. Spray drying is no longer regarded just as a convective industrial drying concept, but also as an integral part of modern manufacturing practices applying powder technology. This paper r     

Swell Drying: Coupling Instant Controlled Pressure Drop DIC to Standard Convection Drying Processes to Intensify Transfer Phenomena and Improve Quality—An Overview

Increasing globalization is driving agricultural production in developing countries toward better recovery levels and high additional value. A great opportunity is thus offered to emerging economies. By adopting appropriate and improved methods that allow better preservation, transport, and storage and that conform to the rigorous requirements and standards of organoleptic and nutritional quality as well as stringent hygienic criteria, emerging economies can derive significant benefits.

Drying of biological materials usually results in shrinkage. The impact of shrinkage is often highly prejudicial for both the function and use of these materials. On the one hand, shrinkage results in a sharp decrease in water diffusivity through the porous structure (for dehydration and rehydration processes). On the other hand, the compact structure of dried biological material is usually unsuitable in terms of organoleptic quality and is inadequate for grinding. Thus, it is becoming very important to include retexturing and structure-expanding processes in standard drying processes. To this end, the instant controlled pressure drop (DIC) technology has been proposed and successfully tested as a texturing process for partially dried materials, which should normally intensify the whole operation. The quality of the final product as well as the performance of the drying process can also be dramatically improved. Finally, for a large category of dried fruits and vegetables, and even freeze-dried materials, microbiological contamination and the presence of insects and larvae are serious problems. DIC technology can be used as an ultra-high-temperature treatment for a controlled decontamination. Such dried, expanded, and completely decontaminated products can be used as highly nutritional snacks. They can easily be ground to produce expanded granulated powders with excellent sensory, nutritional, functional, and textural properties.     

Steam Drying — History and Future

ABSTRACT

The concept of steam drying originates from the mid of the last century. However, a broad industrial acceptance of the technique has so far not taken place. The paper deals with applications of steam drying within certain industrial sectors where the technique has been deemed to have special opportunities. The applications discussed involve drying of fuels with high moisture contents, cattle feed exemplified by sugar beet pulp, lumber, paper pulp, paper and sludges.

Steam drying is compared to flue gas drying of biofuels prior to combustion in a boiler. With reference to a current installation in Sweden, the energy losscs, as manifested by loss of co-generation capacity, are discussed. The energy saving potential when using steam drying of sugar beet pulp as compared to other possible plant configurations is demonstrated. Mechanical vapour recompression applied to steam drying is analysed with reference to reported data from industrial plants. Finally, environmental advantages when using steam drying are presented.     

Optimization of the Spray Drying Operating Parameters—A Quick Trial-and-Error Method

This short communication reports an optimization approach to effectively determine suitable spray drying operating parameters for a pilot-scale dryer. The proposed optimization approach is essential, as pilot-scale investigations and medium-scale contract productions often involve usage of standard spray dryer units which is not specifically designed for the feed material used. This optimization approach was developed based on past studies on the effect and relationship of the many spray drying operating parameters and highlights two factors which has to be solved (or considered) chronologically: dripping problem, followed by product caking problem. Based on this proposed approach, an algorithm was developed in a case study to optimize an available spray dryer for our future experimental study on wall deposition. In this case, the operating parameters were determined under minimal experimental runs. This proposed optimization approach will be a useful tool for operators and experimenters utilizing spray dryers of similar type, particularly in exploring new feed materials. Depending on the optimization objectives and experimental limitations, different algorithms can be developed. Apart from that, interesting deposition pattern was also observed in the case study. This short communication also reported on the design of an internal rig for further studies on wall deposition.     

Retention of Vitamin C in Drying Processes of Fruits and Vegetables—A Review

This article presents a review of drying processes of fruits and vegetables in which vitamin C degradation was considered. Vitamin C is an important and essential nutrient for humans and it can be taken as an index of nutrient quality of processes. Many researchers have reported the effect of different drying methods and the influence of drying conditions on the vitamin C content. In addition, the effect of other parameters related to the sample structure or to pretreatments on the final quality of the dried product is discussed. Vitamin C degradation mechanisms proposed in the literature, models applied to describe its kinetics, and recent advances in drying processes aiming high retention of this nutrient are also provided.     

Sticky Region in Drying—Definition and Identification

Abstract

A device has been developed, to characterize the stickiness of materials prone to shearing that is based on torque measurement during intermittent stirring. Experiments were carried out, using materials of various origin, and over a range of moisture contents that span the pasty to free-flowing powder consistencies. To reflect the complex nature of stickiness, often noted by researchers during the drying of slurries and pastes, the concept is proposed, of a stickiness region, adjacent to the stickiness curve. Referring to the two-dimensional visualization of a drying process with evolving moisture content and material temperature, possible trajectories are suggested, to deal with the stickiness problem.     

Quantum Dots—From Synthesis to Applications in Biomedicine and Life Sciences

Imagine devices or particles so small that they are invisible to the naked eye. Imagine that such entities could be used to patrol our bodies and autonomously augment endogenous defense and repair mechanisms. Imagine the defeat of illness at a fraction of the current costs. Bionanotechnology is the field of science that deals with just that: the development of imaging, tracking, targeting, sensing, diagnostic, and eventually therapeutic capabilities based on particles in the nanometer range, i.e., “nanoparticles”. Within the extensive group of nanoparticles, semiconducting quantum dots play a central and prominent role. Quantum dots excel at a myriad of physical properties, most notably their fluorescent properties, such as high quantum yield, photo-stability, broad absorption spectra, and their remarkable size-dependent emission-tunability.     

Drying of Low-Rank Coal (LRC)—A Review of Recent Patents and Innovations

Despite being geographically dispersed, abundant, and accounting for almost half of the world's coal reserves, low-rank coals (LRCs) find limited use due to their high moisture content and high propensity for spontaneous combustion. Reducing the moisture content of low-rank coal enhances its heating value and reduces transportation costs, thus increasing its economic value. In addition, dried low-rank coals have been proven to improve plant efficiency, enhance safety, and reduce greenhouse gas emissions. Although numerous technologies for coal drying already exist, it is often challenging, if not impossible, to find one that is cost-effective in all aspects. When selecting a dryer for coal upgrading applications, factors such as particle size/size distribution, throughput, energy consumption, material handling capabilities, safety, carbon footprint, capital and operating costs, return on investment, etc., are important considerations. This article provides an overview of the patent literature along with the archival literature that deals with drying of coal as well as biomass, which is relevant to coal drying.