Assessment of real-time, in-shell kernel moisture content monitoring with a microwave moisture meter during peanut drying

Authors: Lewis, Micah; Trabelsi, Samir; NELSON, STUART - Collaborator

Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/11/2014
Publication Date: 10/1/2014
Citation: Lewis, M.A., Trabelsi, S., Nelson, S.O. 2014. Assessment of real-time, in-shell kernel moisture content monitoring with a microwave moisture meter during peanut drying. Applied Engineering in Agriculture. 30(4):649-656.

Interpretive Summary: Peanut drying is an essential task that takes place at peanut buying stations and shelling plants, preceding the grading process. Although peanuts are left in windrows to dry naturally before being harvested with combines, they arrive at buying stations considerably high in moisture content. Therefore, it is imperative for peanuts to be dried below 10.5% kernel moisture content for grading and storage purposes. To facilitate the drying process, peanuts are loaded into drying wagons. Then, dryers using propane or natural gas fuels are connected to the wagons through canvas ducts, and heated air is blown into the airspace below the bed of peanuts. The air is forced up through the peanuts to decrease their moisture content. Peanuts are dried in this fashion until they are expected to have less than 10.5% moisture content. Then, a representative sample of peanuts is extracted from the wagon and taken to be graded. While being graded, if the kernel moisture content is determined to be more than 10.5%, the sample is marked with a label, “NO SALE”, and the corresponding lot of peanuts has to be taken back to the drying shed and further dried. Modern peanut drying processes utilize decision support software based on modeling and require substantial human interaction for moisture sampling. The samples must be taken, shelled and cleaned before testing for kernel moisture content with current moisture meters. The kernel moisture content is the main parameter of interest in the drying process, and it is the only parameter, besides temperature, that the drying system is working to control. However, since it is difficult to obtain, the control for kernel moisture content is often indirect and misguided. These procedures increase the likelihood of peanuts being overdried or underdried. This research assessed the performance of a peanut drying control system utilizing a microwave moisture meter, developed within USDA, ARS, to monitor the moisture content of the peanut kernels in the drying bed without having to shell samples for moisture testing. The kernel moisture content and atmospheric conditions served as continuous inputs to the controller, and thus, air temperature and drying time were controlled automatically. Three different peanut drying trails were run with varying initial kernel moisture contents and atmospheric conditions. to evaluate the performance of the drying system. Standard errors of prediction were evaluated to compare the kernel moisture content values provided by the microwave moisture meter with those determined by the oven drying reference method. In-shell kernel moisture content was determined in real-time with a standard error of less than 0.55% moisturecontent compared to the reference oven-drying method. Overall evaluation demonstrated that the automated drying system is an effective solution for user-independent dryer control and real-time, in-shell kernel moisture content monitoring. Implementation of the automatic control will reduce overdrying and underdrying, preserve the quality of peanuts, and minimize energy consumption through efficient control of the heater. In this paper, a quarter-scale drying system with automated control was discussed. Results show promise for large-scale implementation. When implemented commercially, such control systems would save significant labor and energy costs while improving product quality for the peanut industry and consumers.

Technical Abstract: The present-day peanut drying process lacks the capability of kernel moisture content determination in real-time. Samples of peanut pods have to be taken from the drying trailer, cleaned and shelled by an operator to test for the kernel moisture content. The frequency with which the operator samples the drying trailer to determine kernel moisture content determines the accuracy of the drying process in reaching the targeted kernel moisture content. However, by using a microwave moisture meter, developed within USDA ARS and operating at power levels of a few milliwatts, the moisture content of the peanut kernel can be determined without having to shell the peanut pods. An automated quarter-scale drying system, equipped with the microwave meter, was developed and tested, and it has demonstrated effective control of the drying process and accurate real-time monitoring of kernel moisture content. The objective of this study was to evaluate the performance of the drying system with varying initial kernel moisture contents and atmospheric conditions. Therefore, three different trails were run where such conditions were varied. Analysis of variance was performed, and standard errors of prediction were evaluated to compare the kernel moisture content values predicted by the microwave moisture meter to those determined by the oven method. In-shell kernel moisture content was determined in real-time with a standard error of performance = 0.55% moisture when compared to the reference oven-drying method. Overall evaluation demonstrated that the automated drying system is an effective solution for user-independent dryer control and real-time, in-shell kernel moisture content monitoring.