Development of an eighth-scale grain drying system with real-time microwave monitoring of moisture content

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

Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/12/2019
Publication Date: 10/1/2019
Citation: Lewis, M.A., Trabelsi, S., Nelson, S.O. 2019. Development of an eighth-scale grain drying system with real-time microwave monitoring of moisture content. Applied Engineering in Agriculture. https://doi.org/10.13031/aea.13130.
DOI: https://doi.org/10.13031/aea.13130

Interpretive Summary: Oil seed products such as canola, safflower, soybean and sunflower and cereal grain products such as barley, corn, oats and wheat are stored in large, cylindrical bins after harvest. While in storage, the overall goal is to ensure that the products are kept at premium quality until distribution or processing. At the time of harvest, the moisture content of grain or seed is usually too high for safe storage and could result in spoilage or degradation. Therefore, it is important to accurately determine moisture content and dry them to acceptable levels. Guidelines for quality assurance include equilibrium moisture content and upper bounds for temperature and relative humidity. Grain drying bins can store up to 7,549 cubic meters of grain or seed, and the depth of material can be over 25 m deep. Present drying and storage operations depend heavily on human interaction including an operator to probe for samples and perform moisture content analysis with an external moisture meter. However, it is difficult to effectively monitor such massive volumes of material, and the moisture content can vary greatly at different heights. 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. During drying, there are three identifiable zones within the bed: the dry grain or seed zone is the bottom most layer, the drying zone is the layer that is currently drying, and the wet grain or seed zone is the highest layer that has yet to be dried. Often, the lower layers are overdried trying to dry the top layers because the top layers gain moisture from the bottom layers before they lose moisture. Real-time monitoring of moisture content of grain and seed in drying bins would greatly improve the efficiency with which they are dried and stored. This manuscript discusses the development of an eighth-scale grain drying system to automate such drying and provide continuous monitoring of moisture content and other drying parameters. The temperature of the air blown into the grain or seed was also controlled by the system. The system monitors relative humidity, moisture content and temperature at different heights within the drying grain or seed using eight temperature sensors, four relative humidity sensors and a microwave moisture sensor for moisture content determination in grain and seed. Original software was written to facilitate drying experiments and monitor drying parameters every 12 s with storage of data and display to a user. Preliminary results show monitoring at different heights within the drying bin were useful in observing the movement of the drying front through the 60-cm deep bed of wheat. Implementation of such monitoring systems would improve efficiency in the way cereal grain and oilseed are dried and stored. Operator dependence would be reduced, and a more effective way to monitor the entire volume of product would be made available.

Technical Abstract: After being harvested, cereal grain and oilseed are stored and dried in large cylindrical storage bins. Drying is necessary to prevent spoilage and degradation; however, because of the significant depth of material in the drying bin, a common 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 is limited to probing reachable locations to determine moisture content. Furthermore, since probing is done daily or every few days, the frequency is not enough to fully observe the dynamics of moisture content within the bin continuously, and the lower layers of grain or seed within the bin are susceptible to being overdried. By using a microwave moisture sensor operating at 5.8 GHz, developed within USDA ARS, the moisture content of the cereal grain or oilseed can be measured continuously, providing real-time moisture content with 12-second resolution. An automated, eighth-scale grain drying system was developed utilizing temperature and relative humidity sensors and the microwave moisture sensor at different heights within the grain bin to observe drying parameters and moisture migration as the grain or seed dried. Grain and seed moisture content was determined in real-time with a standard error of performance of 0.5 % moisture content when compared to the reference oven-drying method. Overall evaluation showed that the automated grain drying system is an effective solution for real-time monitoring of moisture content and other parameters during drying.