An infrared and hot-air grain drying system combines radiant heating with convective heat transfer to remove moisture from grain and other agricultural materials. The system described here consists of an automatically controlled infrared hot-air furnace and a multilayer hopper-type drying tower with tempering sections.
The equipment is intended for grain drying and can also be adapted for certain agricultural products and medicinal herbs. Its suitability depends on the material properties, required moisture content, production capacity, and operating conditions.
Self-regulating infrared hot-air furnace
Structural design
The furnace is described as having four concentric stainless steel cylinders that form three annular passages: an inner passage, a middle passage, and an outer passage.
A combustion chamber is located at the bottom center of the furnace. The hot combustion gases pass through the middle passage, moving upward and then downward, before flowing downward through the outer passage and leaving the furnace.
Cold air enters the outer passage from the top. It absorbs heat through the heat exchange surfaces before entering the inner passage for further heating. The air then passes through the central outlet duct, where it receives additional heat. According to the supplied equipment description, the outlet hot-air temperature can be controlled within a range of 50°C to 200°C.
High-temperature radiative coatings are applied to the inner and outer furnace walls and heat exchange surfaces. These coatings are intended to increase infrared emission from the heated surfaces.
Heating and drying principle
The combustion system heats the furnace walls and heat exchange surfaces. These surfaces transfer heat to the air and emit infrared radiation. When the radiation is absorbed by the grain or other material, it contributes to heating the material. The hot air also transfers heat by convection.
As the material heats up, moisture evaporates from its surface and moves outward from the interior. The airflow carries the resulting water vapor away from the drying area. The balance between radiant heating, convective heat transfer, moisture migration, and exhaust airflow determines the drying rate.
Combining infrared radiation with hot-air convection may improve heat transfer under suitable conditions. However, the actual drying rate and energy savings depend on the material, equipment design, operating parameters, and performance of the reference drying process. They should be established through testing rather than assumed from the heating method alone.
Multilayer hopper-type drying tower with tempering sections
Structural design
The drying tower consists of a top grain inlet, an array of funnel-shaped passages, a transverse hot-air supply system, exhaust outlets, and tempering sections.
Grain descends through the funnel array in successive streams. Hot air passes horizontally through the gaps between the passages. The supplied equipment description specifies an airflow velocity of 3 to 4 m/s for this arrangement.
The tower combines hot-air drying with intermittent tempering. This allows the grain to undergo successive drying and moisture redistribution stages rather than remaining continuously exposed to the drying air.
Drying stage
During drying, hot air passes across the falling grain streams, transferring heat to the grain and carrying away moisture.
The supplied process description lists hot-air temperature ranges of 180°C to 200°C for feed grain, 140°C to 160°C for food grain, and 60°C to 100°C for seed. These figures require confirmation against the specific equipment documentation and grain type before they are used as operating recommendations.
Safe drying conditions depend on the crop, intended use, initial moisture content, and dryer configuration. The temperature of the drying air must be distinguished from the temperature reached by the grain itself. Seed and malting grain generally require stricter temperature limits than grain intended for animal feed.
The process description specifies a drying period of approximately 30 minutes, during which the grain temperature reaches about 40°C. This should be treated as a stated operating example, not a universal cycle time or grain temperature for all crops.
Tempering stage
After the drying stage, the hot air is stopped and the grain rests for approximately one hour.
During tempering, moisture moves from wetter regions inside individual kernels toward drier regions, reducing moisture gradients within the grain. This redistribution helps moderate the effects of uneven drying and can reduce the risk of stress cracking when the drying process is properly controlled.
The length of the tempering period depends on grain type, initial moisture content, kernel temperature, and dryer design.
Repeated drying and tempering
The supplied operating sequence repeats the drying and tempering stages three times. The stated final moisture content is approximately 15%.
This moisture target is not appropriate for every grain or storage condition. The required final moisture content depends on crop type, intended use, storage temperature, and storage duration. It should be specified before the drying cycle is established.
Applications and system capacity
Grain drying systems
Large installations may integrate grain cleaning, drying chambers, and storage bins into one processing system. The supplied description gives a daily processing capacity of up to 300 tonnes for large systems.
Actual throughput depends on the grain type, initial and final moisture content, operating schedule, and equipment configuration. The stated capacity should therefore be confirmed against the manufacturer's technical specifications and the basis used to calculate daily throughput.
Smaller systems are also possible. Where demand is seasonal or individual users have limited annual operating hours, shared regional drying facilities or mobile drying services may be considered. The suitability of these arrangements depends on local demand, transport requirements, and equipment utilization.
Agricultural products and medicinal herbs
The infrared hot-air furnace may also be used with appropriately designed drying chambers for products such as tea, tobacco, wood ear mushrooms, daylilies, dried bamboo shoots, jujubes, dried persimmons, and preserved fruit. Potential applications also include medicinal materials such as Gastrodia, goji berries, ginseng, and deer antler.
Different materials require different drying temperatures, airflow conditions, residence times, and final moisture specifications. A process suitable for grain should not automatically be applied to herbs or other agricultural products without verifying product quality requirements.
The supplied description recommends spreading materials in layers approximately 30 mm thick, with adjustments according to material properties, to support effective infrared heating. This value should be treated as an application-specific guideline rather than a universal maximum. Suitable layer thickness depends on the material, infrared absorption characteristics, airflow, and drying chamber design.
Technical considerations
The main potential benefits of combining infrared radiation and hot-air convection are improved heat transfer, controlled moisture removal, and the ability to integrate drying with grain handling and tempering.
Product quality depends on maintaining appropriate drying conditions and allowing sufficient time for moisture redistribution. Excessive grain temperature or rapid moisture removal can damage kernels, reduce seed viability, or increase cracking, depending on the crop and its intended use.
For large-scale systems, capacity, energy use, air distribution, exhaust moisture removal, temperature measurement, and grain circulation should all be evaluated. Final operating settings should be established for the specific crop and equipment rather than applied uniformly across grain types.
Custom machining for industrial equipment
Beyond components used in agricultural drying systems, Hansheng Automation provides custom precision machining for non-standard industrial parts according to customer-supplied drawings. Our machining services also cover components for food processing and filling machinery, tobacco packaging equipment, yacht systems, and remote control racing cars. Each component is manufactured according to the specified dimensions, structural requirements, and drawing details.
