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. The moisture content of rice harvested in the wet season can reach more than 30%. Wet weather is not conducive to drying, and it is very difficult to find sufficient space and labor for drying. At this time, the food must be dried by mechanical drying to avoid possible losses.
Rapid precipitation of high-moisture foods to 14% consumes a lot of energy, and in the season of concentrated harvesting, existing dryers are difficult to meet in order to handle large amounts of high-moisture food in a short period of time.
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.
One and two-stage drying method
In this method, the high-moisture grain is quickly dried to a moisture content of 18% in the first stage. At this time, a warehouse drier is installed, and 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).
In Vietnam, the flat bed dryer is the most common dryer type. It is a set of dryers, generally with a processing capacity of 4 tons or 8 tons of grain, not a fast dryer, so it is not suitable for the first stage drying of the two-stage drying method.
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.
Second, nozzle drying system
The 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.
After completing the assembly and testing at the University of Agriculture and Forestry, the system was delivered to the farm in Can Tho Province for a real-life trial.
Third, potential benefits
The widespread application of two-stage drying will bring great benefits to Vietnam's rice industry. Vietnam is now an important rice exporter, but its product quality needs improvement. In fact, in order to meet acceptable standards in the export market, many rices require secondary processing, adding extra costs. Two-stage drying can help Vietnamese rice to improve overall quality levels, especially in terms of reducing crushing rate and raising rice grade. Rapid drying will also reduce the potential for mildew caused by microorganisms and the deterioration caused by biochemical reactions. In the case where the moisture content exceeds 18% and the environmental temperature and humidity are high, these two factors have a great influence on the shelf life of rice, so the improvement of drying technology will effectively improve the economic benefits of the country and farmers.
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. The moisture content of rice harvested in the wet season can reach more than 30%. Wet weather is not conducive to drying, and it is very difficult to find sufficient space and labor for drying. At this time, the food must be dried by mechanical drying to avoid possible losses.
Rapid precipitation of high-moisture foods to 14% consumes a lot of energy, and in the season of concentrated harvesting, existing dryers are difficult to meet in order to handle large amounts of high-moisture food in a short period of time.
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.
One and two-stage drying method
In this method, the high-moisture grain is quickly dried to a moisture content of 18% in the first stage. At this time, a warehouse drier is installed, and 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).
In Vietnam, the flat bed dryer is the most common dryer type. It is a set of dryers, generally with a processing capacity of 4 tons or 8 tons of grain, not a fast dryer, so it is not suitable for the first stage drying of the two-stage drying method.
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.
Second, nozzle drying system
The 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.
After completing the assembly and testing at the University of Agriculture and Forestry, the system was delivered to the farm in Can Tho Province for a real-life trial.
Third, potential benefits
The widespread application of two-stage drying will bring great benefits to Vietnam's rice industry. Vietnam is now an important rice exporter, but its product quality needs improvement. In fact, in order to meet acceptable standards in the export market, many rices require secondary processing, adding extra costs. Two-stage drying can help Vietnamese rice to improve overall quality levels, especially in terms of reducing crushing rate and raising rice grade. Rapid drying will also reduce the potential for mildew caused by microorganisms and the deterioration caused by biochemical reactions. In the case where the moisture content exceeds 18% and the environmental temperature and humidity are high, these two factors have a great influence on the shelf life of rice, so the improvement of drying technology will effectively improve the economic benefits of the country and farmers.