THE CURRENT SITUATION OF GRAIN DRYING IN CHINA

Drying is an important technology widely used in the processing of such products as grain, food and other agricultural materials. In recent years the drying industry in China is in a fast developing period and the amount of grain dryers is increasing every year. The grain drying technology is also improving. In this paper the present situation of grain drying technology and grain drying equipment is presented. The type, structure and characteristics of most widely used grain dryers are described. Some recommendations for further development are given.     

THE CURRENT SITUATION OF GRAIN DRYING IN CHINA

Abstract

Drying is an important technology widely used in the processing of such products as grain, food and other agricultural materials. In recent years the drying industry in China is in a fast developing period and the amount of grain dryers is increasing every year. The grain drying technology is also improving. In this paper the present situation of grain drying technology and grain drying equipment is presented. The type, structure and characteristics of most widely used grain dryers are described. Some recommendations for further development are given.     

DRYING R D IN THE F.R. GERMANY

This paper summarizes the developments in the field of drying within the Federal Republic of Germany. The main areas on the scientific side (software) as well as those on the manufacturing'side (hardware) are discussed. This survey covers the period, 1976-1986.

On the theoretical side, research and development activities have focussed on convective and contact drying, modelling of contact dryers, selective drying of products with solvents, drying of mixtures and relevant topics in the field of ad-and desorption. On the hardware side, design to fit a changing framework (environment, energy, legislation, etc.), integration of up-and downstream equipment, detail improvements and new types of dryers (as well as applications of otherwise known equipment to drying) have been the major developments. A list of West German manufacturers of drying equipment is also in-cluded as an Appendix.     

DRYING OF OILSEEDS

Drying of oilseeds is a post harvest operation required for safe storage of harvested seeds. Oilseeds have gained importance in India over the last few years. Fluidized bed (FB) drying and Spouted Bed (SB) drying of oilseeds were studied as potential dryers for these seeds. Experimental pilot fluidized bed dryers were developed and a 2 TPH capacity (mustard seed) FB dryer plant was designed and installed in the lab. Experimental units and a pilot spouted bed dryer were also developed. The dryer units and the plant have been extensively tested and satisfactory drying performance has been achieved. Drying data and drying characteristics have been generated for different oilseeds such as mustard, sunflower, soybean and groundnut etc. The drying rates in different regimes of drying characterized by constant rate and falling rate periods have been evaluated. The salient results of the work are briefly outlined.     

Heating/Drying Using Particulate Medium : A Review Part II. Equipment

ABSTRACT

This paper presentS an overview of particulate medium dryers developed to evaluate the drying of grains using heated particulate media. Components of particulate medium heating and drying equipments as well as the devices employed to conduct the materials through the machine are described. How these components accomplish the basic processes involved in conduction/particulate medium heating is also explained.

To characterize the performance of these dryers based on criteria developed for farm level dryers was not possible because of the different methods employed by researchers and the various conditions the equipment were subjected to. So in order to assess the operating characteristics of each design. the dryers were compared based on their ability to remove moisture and their thermal and drying efficiency. Comparison was made on the methods utilised by each design to accomplish heating of the medium, mixing the medium with grain, the separation of the medium from grain, and the means of recirculating the medium.

Several studies conducted to evaluate the different parameters which influence drying using heated particulates are discussed. The granular media used in heating the grain and the corresponding types of grains used in the tests are also presented.     

Heating/Drying Using Particulate Medium : A Review Part II. Equipment

This paper presentS an overview of particulate medium dryers developed to evaluate the drying of grains using heated particulate media. Components of particulate medium heating and drying equipments as well as the devices employed to conduct the materials through the machine are described. How these components accomplish the basic processes involved in conduction/particulate medium heating is also explained.

To characterize the performance of these dryers based on criteria developed for farm level dryers was not possible because of the different methods employed by researchers and the various conditions the equipment were subjected to. So in order to assess the operating characteristics of each design. the dryers were compared based on their ability to remove moisture and their thermal and drying efficiency. Comparison was made on the methods utilised by each design to accomplish heating of the medium, mixing the medium with grain, the separation of the medium from grain, and the means of recirculating the medium.

Several studies conducted to evaluate the different parameters which influence drying using heated particulates are discussed. The granular media used in heating the grain and the corresponding types of grains used in the tests are also presented.     

COMBINED INNOVATIVE HEAT PUMP DRYING TECHNOLOGIES AND NEW COLD EXTRUSION TECHNIQUES FOR PRODUCTION OF INSTANT FOODS

There is an increased demand for convenient foods including ready-to-eat and instant products. These products are desired with minimum concentration of synthetic chemicals. This creates challenges for the food industry and dryers manufactures to develop new technologies to process difficult-sensitive materials and to supply final products with high quality and improved properties. Fruits and vegetables are mainly composed of water, carbohydrates, proteins and lipids. Due to modification of chemical and physical bonds the compounds the material becomes viscous and sticky during processing. Conventional dryers have limitations in handling such sensitive materials. Heat pump dryers have been applied in the production of a diversity of ready-to-eat foods and dried instant products for the last five years at SINTEF-NTNU. Besides being energetically efficient and environmentally friendly, the heat pump drying technology provides a wide range of drying conditions as required to produce powders with improved characteristics. This work describes the new technologies and processing line for the production of instant foods as well as the measurements on the properties and quality attributes for raw, intermediate and final instant products.     

稻谷通风干燥装备研制和应用

阐述了我国粮食干燥技术与设施的发展现状,分析了传统快速烘干机烘干稻谷的弊端,简要介绍了粮食低温通风干燥理论,研发了多环立式深层粮食径向通风干燥新的技术装备。该技术装备打破了国内外粮食机械通风干燥粮层不能超过4m的极限。将网架式薄壁通风管道装置应用于粮层堆厚12m的砖筒仓内进行整仓稻谷机械通风干燥。实现了粮食通风干燥过程的智能、远程、实时、动态监控和管理。技术装备经两年多的生产实践,运行安全可靠,经济和社会效益显著。     

DRYING R D IN THE F.R. GERMANY

This paper summarizes the developments in the field of drying within the Federal Republic of Germany. The main areas on the scientific side (software) as well as those on the manufacturing'side (hardware) are discussed. This survey covers the period, 1976-1986.

On the theoretical side, research and development activities have focussed on convective and contact drying, modelling of contact dryers, selective drying of products with solvents, drying of mixtures and relevant topics in the field of ad-and desorption. On the hardware side, design to fit a changing framework (environment, energy, legislation, etc.), integration of up-and downstream equipment, detail improvements and new types of dryers (as well as applications of otherwise known equipment to drying) have been the major developments. A list of West German manufacturers of drying equipment is also in-cluded as an Appendix.     

A Novel Design of Crop Dryer for Use in Developing Countries

The dryer is required for drying of grain as well as drying of the processed products in small catchment agro processing centers in the developing world. However, due to varied material characteristics of grain and secondary processed product, two entirely different types of dryers are required. The grain is dried in a recirculatory dryer, whereas processed product is dried in a tray dryer, where it is frequently mixed and trays are also intermittently changed. To avoid the need for two dryers, a novel design of a low-cost hot air dryer was developed where just by changing the trays the dryer can be converted from an LSU grain dryer to a tray-type product dryer. The dryer was tested for drying soybean grain as well as processed soy products like blanched soybean dal and soyflakes. The capacity of the dryer was 100 kg/batch in a tray dryer with each tray accommodating 10 kg of wet material. In case of LSU mode, the capacity of the dryer was 250 kg of grain per batch. The drying time required was 5 h for 250 kg of wet soybean from 24 to 10% moisture content, whereas in a tray dryer 100 kg blanched soybean dal was dried from 60 to 10% in 5 h and 100 kg of soyflakes from 25% moisture content to 10% moisture in 1.75 h. The cost of the dryer is estimated at US$580.00 and it can be fabricated in a moderately equipped workshop in developing countries.     

A Novel Design of Crop Dryer for Use in Developing Countries

The dryer is required for drying of grain as well as drying of the processed products in small catchment agro processing centers in the developing world. However, due to varied material characteristics of grain and secondary processed product, two entirely different types of dryers are required. The grain is dried in a recirculatory dryer, whereas processed product is dried in a tray dryer, where it is frequently mixed and trays are also intermittently changed. To avoid the need for two dryers, a novel design of a low-cost hot air dryer was developed where just by changing the trays the dryer can be converted from an LSU grain dryer to a tray-type product dryer. The dryer was tested for drying soybean grain as well as processed soy products like blanched soybean dal and soyflakes. The capacity of the dryer was 100 kg/batch in a tray dryer with each tray accommodating 10 kg of wet material. In case of LSU mode, the capacity of the dryer was 250 kg of grain per batch. The drying time required was 5 h for 250 kg of wet soybean from 24 to 10% moisture content, whereas in a tray dryer 100 kg blanched soybean dal was dried from 60 to 10% in 5 h and 100 kg of soyflakes from 25% moisture content to 10% moisture in 1.75 h. The cost of the dryer is estimated at US$580.00 and it can be fabricated in a moderately equipped workshop in developing countries.     

COMBINED INNOVATIVE HEAT PUMP DRYING TECHNOLOGIES AND NEW COLD EXTRUSION TECHNIQUES FOR PRODUCTION OF INSTANT FOODS

ABSTRACT

There is an increased demand for convenient foods including ready-to-eat and instant products. These products are desired with minimum concentration of synthetic chemicals. This creates challenges for the food industry and dryers manufactures to develop new technologies to process difficult-sensitive materials and to supply final products with high quality and improved properties. Fruits and vegetables are mainly composed of water, carbohydrates, proteins and lipids. Due to modification of chemical and physical bonds the compounds the material becomes viscous and sticky during processing. Conventional dryers have limitations in handling such sensitive materials. Heat pump dryers have been applied in the production of a diversity of ready-to-eat foods and dried instant products for the last five years at SINTEF-NTNU. Besides being energetically efficient and environmentally friendly, the heat pump drying technology provides a wide range of drying conditions as required to produce powders with improved characteristics. This work describes the new technologies and processing line for the production of instant foods as well as the measurements on the properties and quality attributes for raw, intermediate and final instant products.     

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.     

Review of: “Impregnation,Drying and Adhesive Coating Equipment”by Konovalov 7.1. and Koval A.M. Khimia,Moscow, 1989, 222 p. (in Russian)

Zeolites have potential to increase efficiency of medium-temperature drying in the food industry. This work concerns the comparison between conventional dryers and dryers using air dehumidified by zeolite. Steady-state mass and energy balances have been used and the work concerns drying temperatures ranging from 52 to 70°C. Process integration based on pinch analysis has been applied and nine different heat exchanger networks for energy recovery are compared. Results indicated that dryers using air dehumidifier by zeolites are 10–18% more efficient than conventional dryers.     

Research on Modeling and Simulation of Mixed Flow Grain Dryer

Mathematical modeling and computer simulation of grain drying are the major emphasis of grain drying research in CAU (China Agricultural University). Since 1988, research on simulation of concurrent flow, counterflow, cross-flow, and mixed-flow grain dryers has been accomplished. The developed mixed-flow grain drying software has been used in analysis of dryer performance, design, and optimization of new grain dryers and management of existing ones. Effect of size, shape, number of rows, and arrangement of air duct on the performance of a mixed-flow grain dryer has been studied.     

PHYSICAL PROPERTIES OF RICE RELATED TO DRYING THE GRAIN

Stresses in the rice grain can be produced by mechanical equipment such as the combine, elevator, auger and the rice mill. There are, however, other and more insidious means of producing severe stresses in the grain with moisture and thermal gradients. Moisture gradients can be found 1) in the field on a humid night before harvest, 2) in a hopper of freshly harvested rice containing high-, low- and intermediate-moisture grains, and 3) in certain types of dryers ahead of the drying front. A single high humidity exposure of rough rice at storage moisture can be very detrimental to the quality of the grain. Other steep moisture gradients can be produced by rapidly drying high-moisture rice, With time, after drying, the gradients cause moisture to diffuse from the center to the surface thus causing 1) the moisture gradient to decrease, 2) the grain surface to gain moisture and expand, 3) the grain interior to lose moisture and contract, and 4) the grain to fissure several hours after it has been dried. Fissured rice will usually break when it is milled.     

Application of Computational Fluid Dynamics for Simulation of Drying Processes: A Review

In recent years, computational fluid dynamics (CFD) has been used increasingly to improve process design capabilities in many industrial applications, including industrial drying processes. Drying of food and beverage products, industrial and municipal wastewater sludge, and other manufacturing and environmental products is done regularly in order to enhance the quality and life span of these products and to facilitate their use, storage, and transportation. With recent advancements in mathematical techniques and computer hardware, CFD has been found to be successful in predicting the drying phenomenon in various types of industrial dryers, which utilize all forms of drying operations including spray, freeze, and thermal drying techniques. The CFD solutions are being used to optimize and develop equipment and processing strategies in the drying industry, replacing expensive and time-consuming experimentations. However, a comprehensive review on the application of CFD for the design, study, and evaluation of industrial dryers is not yet available. A comprehensive review of the current literature on the use of CFD models in both industrial and lab-scale drying applications is presented in this article. The use of Eulerian-Eulerian and Eulerian-Lagrangian models in the study of the drying kinetics for gas–solid multiphase flow systems is fully discussed. Merits and disadvantages of using various CFD models in the design of industrial dryers are illustrated and the scope of their applicability is also discussed.     

Solids transport in mixed-flow dryers

Mixed-flow dryers are broadly used in worldwide agriculture for the drying of grain, corn and rice but are also applied in industry. Although this drying process is well established, there is still a need to optimize the dryer apparatus. Unfavorable design can cause uneven mass flow and air flow distributions, broad residence time distributions and, hence, inhomogeneous drying histories of the particles resulting in non-uniform drying. The transport of solids in mixed-flow dryers has not yet been sufficiently considered and investigated. Therefore, the objective of this study is to derive basic equations on particle flow in mixed-flow dryers which are practically operated in the interrupted flow regime and equipped with discharge gates. The function of the discharge gate, the discharge characteristic and the solids mass flow rate were studied by varying the discharge and standstill times, respectively. The experiments were conducted at a semi-technical dryer test station with a transparent acrylic glass front wall using wheat as bed material. The fundamentals developed serve as a basis for further theoretical and experimental investigations. The future goal is to improve apparatus design and process control so as to homogenize the drying process, to increase energy efficiency and to save product quality.     

EFFECT OF MATURITY AND HARVEST METHOD ON DRYING RATE OF WHEAT

Drying rates of cereals have a significant influence on the drying capacity of dryers. Drying rates are influenced by the variety and type of cereal, past history of the grain, maturity at harvest and the harvest method. The effect of the last two parameters on the drying rate of wheat was investigated by drying a single-kernel-thick layer of wheat in an experimental dryer. The laboratory results indicated that grain in the swath had a higher drying rate than grain standing in the field on a particular day of harvest. The effect of maturity or harvest date on the drying rate did not show any particular trend. In the field, the grain in the swath dried faster than grain standing in the field.     

Experiments on Hot-Air Drying of Wheat in a Semi-Technical Mixed-Flow Dryer

Although mixed-flow grain dryers are widely used, there is still a need to optimize the process control as well as the dryer apparatus. Fluctuations of the grain moisture content at the dryer entrance are still a major problem resulting in quality and economic losses due to under- or overdrying. Therefore, a mathematical model for heat and mass transfer in a mixed-flow dryer has been developed. Practical drying experiments were carried out at a semi-technical dryer test station that was operated quasi-continuous. The measurements reveal the complexity of the mixed-flow drying process. First predicted results are in satisfactory agreement with data.