Grain drying technology research and development achieved results in Vietnam
Rapid drying of high-moisture foods to safe storage of water is a key step in maintaining food quality and reducing post-harvest losses. In Vietnam, the safe moisture for long-term storage of rice is usually 14%. In the hot and humid climatic conditions of Southeast Asia, it is often difficult or even impossible to reduce grain moisture to 14% using conventional drying methods.
In order to solve the above problems, the Australian International Agricultural Research Center (ACIAR) has set up a grain drying project in Vietnam to research and develop a two-stage drying method for high-moisture foods, and has made some progress.
The nozzle bed drying system ACIAR97065 project "Developing a nozzle drying machine for two-stage grain drying method" was jointly undertaken by the State University of New South Wales, Australia and Vietnam Agriculture and Forestry University.
The jet bed dryer was chosen as the first stage drying technique because it is advanced compared to other methods. For example, the pressure required to pass through the nozzle bed is lower than the pressure through the fluidized bed, so that the air transmission does not require much power, thus saving energy. Moreover, the nozzle bed has a good gas connection, it can handle all kinds of grains of food and grain, with adjustable.
The experimental building was a triangular cross-section nozzle bed with a drying path depth of 4 meters. At inlet air temperatures of 80, 90, and 100 degrees Celsius, rice water could be reduced from 34% to 18% over 5-6 hours. The length depends on the original weight, moisture, and grain temperature. The grain temperature range at the end of the experiment is 50-60°C.
The experiment uses a relatively high temperature of the original inlet air (140-160°C) to dry for 1-2 hours and then 80-100°C hot air for drying. This method can reduce the grain moisture by 37% over approximately 5 hours. To 18%, the final grain temperature is 50°C. Early laboratory studies have shown that in order to minimize the breakage rate during processing of rice, it is necessary to keep the grain temperature below 50°C.
Based on the above experimental results, a hexagonal nozzle dryer was designed and built in the local area, which can hold 23.5 percent of the water in the rice at a time. The hexagonal bin consists of six separate units. A centrifugal fan provides dry air heated by diesel combustion. Each unit is designed to be used individually or in tandem, and hot air at the top of the dryer can be discharged or recycled as needed.
The two-stage drying method The two-step drying method is a method in which the high-moisture grain is rapidly dried to a moisture content of 18% in the first stage. At this time, a storage dryer is installed, and then mechanical ventilation is used to slowly reduce the moisture to 14%. This two-time drying method can maintain good food quality. The key to two-stage drying is to remove the free water from the rice at the fastest rate without affecting the color, shape, and other quality characteristics of the rice.
The concept of two-stage drying was first proposed in Vietnam as the 1994-1997 ACIAR90008 project. This project installed and successfully tested a series of warehouse drying machines with capacities of 80 tons to 400 tons (second stage technology). Now a new ACIAR project is studying the construction of a technically and economically viable first-stage dryer, and at the same time the test is being modified into a warehouse drying system with a grain thickness of 4 meters (formerly 2 meters).
Commercial companies in Thailand have used fluidized bed dryers extensively for the first stage of drying, and this dryer has been successfully sold to other countries and regions such as Guyana, Indonesia, Malaysia, Mexico, Philippines and China. Taiwan.
In order to solve the above problems, the Australian International Agricultural Research Center (ACIAR) has set up a grain drying project in Vietnam to research and develop a two-stage drying method for high-moisture foods, and has made some progress.
The nozzle bed drying system ACIAR97065 project "Developing a nozzle drying machine for two-stage grain drying method" was jointly undertaken by the State University of New South Wales, Australia and Vietnam Agriculture and Forestry University.
The jet bed dryer was chosen as the first stage drying technique because it is advanced compared to other methods. For example, the pressure required to pass through the nozzle bed is lower than the pressure through the fluidized bed, so that the air transmission does not require much power, thus saving energy. Moreover, the nozzle bed has a good gas connection, it can handle all kinds of grains of food and grain, with adjustable.
The experimental building was a triangular cross-section nozzle bed with a drying path depth of 4 meters. At inlet air temperatures of 80, 90, and 100 degrees Celsius, rice water could be reduced from 34% to 18% over 5-6 hours. The length depends on the original weight, moisture, and grain temperature. The grain temperature range at the end of the experiment is 50-60°C.
The experiment uses a relatively high temperature of the original inlet air (140-160°C) to dry for 1-2 hours and then 80-100°C hot air for drying. This method can reduce the grain moisture by 37% over approximately 5 hours. To 18%, the final grain temperature is 50°C. Early laboratory studies have shown that in order to minimize the breakage rate during processing of rice, it is necessary to keep the grain temperature below 50°C.
Based on the above experimental results, a hexagonal nozzle dryer was designed and built in the local area, which can hold 23.5 percent of the water in the rice at a time. The hexagonal bin consists of six separate units. A centrifugal fan provides dry air heated by diesel combustion. Each unit is designed to be used individually or in tandem, and hot air at the top of the dryer can be discharged or recycled as needed.
The two-stage drying method The two-step drying method is a method in which the high-moisture grain is rapidly dried to a moisture content of 18% in the first stage. At this time, a storage dryer is installed, and then mechanical ventilation is used to slowly reduce the moisture to 14%. This two-time drying method can maintain good food quality. The key to two-stage drying is to remove the free water from the rice at the fastest rate without affecting the color, shape, and other quality characteristics of the rice.
The concept of two-stage drying was first proposed in Vietnam as the 1994-1997 ACIAR90008 project. This project installed and successfully tested a series of warehouse drying machines with capacities of 80 tons to 400 tons (second stage technology). Now a new ACIAR project is studying the construction of a technically and economically viable first-stage dryer, and at the same time the test is being modified into a warehouse drying system with a grain thickness of 4 meters (formerly 2 meters).
Commercial companies in Thailand have used fluidized bed dryers extensively for the first stage of drying, and this dryer has been successfully sold to other countries and regions such as Guyana, Indonesia, Malaysia, Mexico, Philippines and China. Taiwan.
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