Real-time monitoring of moisture within an eighth-scale grain bin during drying

Authors: Lewis, Micah; Trabelsi, Samir; NELSON, STUART - US Department Of Agriculture (USDA)

Submitted to: ASABE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: 6/30/2018
Publication Date: 7/29/2018
Citation: Lewis, M.A., Trabelsi, S., Nelson, S. 2018. Real-time monitoring of moisture within an eighth-scale grain bin during drying. ASABE Annual International Meeting. ASABE Paper Number: 1801664.

Interpretive Summary: Cereal grains such as corn, wheat, barley, oats, and oilseeds such as soybeans, canola, sunflower and safflower, are often stored in large, cylindrical bins after harvest. When their moisture contents at harvest are too high for extended storage, they must be dried to safe storage levels. Often, they are dried in the same bins in which they are stored. The overall goal is to ensure that the product quality is preserved until distribution or processing. Cereal grain and oilseed are dried by aeration, a process in which ambient or heated air is forced up through the material to achieve loss in moisture. Temperature and relative humidity are important parameters as well as moisture content in drying operations. Air entering the grain or seed at the bottom of the bin picks up moisture from the material being dried and is less effective in drying as it moves up through the bin to the exhaust vents at the top. Therefore, overdrying the bottom layer while trying to dry the top layer can be a significant problem. Presently operators use probes to obtain grain and seed samples for moisture content testing at certain bin locations. However, the locations that are reachable are limited. Also, since such probing is done daily or every few days, moisture content determination is not frequent enough to observe the dynamics of moisture content within the bin continuously. Real-time monitoring of moisture content, temperature, and relative humidity of drying air would greatly improve the efficiency with which grain and seed can be dried. This paper describes the development of an eighth-scale grain drying system for studying grain and seed drying in the laboratory. It includes a microwave moisture sensor for real-time determination of moisture content. Drying parameters such as temperature and relative humidity at different locations are also monitored. The temperature of the air blown into the grain or seed is also controlled. This system shows promise in automating the drying process in grain bins. The eighth-scale grain drying bin system was designed and constructed. Original software was created to facilitate drying experiments and display drying parameters in real-time. A microwave moisture sensor was used to measure moisture content every 12 seconds as wheat dried. Preliminary results show the movement of the drying front through a 60-cm deep bed of wheat. Results also show that the wheat was effectively dried and monitored. Overall evaluation showed that the automated grain drying system is an effective solution for real-time monitoring of moisture content during drying. In future experiments, more temperature sensors will be added to provide better resolution of the movement of moisture through the drying bed. Experiments will also be conducted with other materials such as corn and soybeans. Implementation of such monitoring and control systems would improve efficiency with which cereal grain and oilseed are dried and stored. Operator dependence would be reduced, and a more effective way to monitor the entire volume of material would provide energy and cost savings while maintaining better quality in the products with subsequent benefits to both producers and consumers.

Technical Abstract: After cereal grain and oilseed are harvested, they are stored and dried in large cylindrical storage bins. Such bins can have a diameter ranging from 4.6 to 18.3 m and height ranging from 4.6 to 28.7 m. Grain or oilseed within the bins are dried by forcing ambient or heated air up through them. The moist air escapes through vents within the conical roof. Since the contents of the bin can be more than 15.2 m deep, a significant problem in grain and oilseed drying is overdrying the bottom layer while trying to dry the top layer. This is due to insufficient knowledge of moisture throughout the bin. Presently, an operator probes certain locations to determine moisture content; however, the locations that are reachable are limited. Also, since such probing is done daily or every few days, moisture content determination is not frequent enough to observe the dynamics of moisture content within the bin continuously. By using a microwave moisture sensor operating at 5.8 GHz, developed within USDA ARS, the moisture content of the grain or oilseed can be measured continuously at multiple locations, providing real-time moisture content with 12-second resolution during drying. An automated, eighth-scale grain drying system was developed using microwave moisture sensors at different heights within the bin to observe moisture migration as grain or oilseed dried. Samples were extracted to conduct moisture tests using the reference oven drying method in order to assess the accuracy of moisture content determined by the microwave sensors. Overall evaluation showed that the automated grain drying system is an effective solution for real-time monitoring of moisture content during drying.