Real-time monitoring of drying parameters in semitrailers during peanut drying

Authors: Lewis, Micah; Trabelsi, Samir; NELSON, STUART - Retired ARS Employee

Submitted to: ASABE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: 6/8/2015
Publication Date: 7/26/2015
Citation: Lewis, M.A., Trabelsi, S., Nelson, S.O. 2015. Real-time monitoring of drying parameters in semitrailers during peanut drying. Acarology International Congress Proceedings. ASABE Paper No. 152189958, American Society of Agricultural and Biological Engineers, St. Joseph, MI.

Interpretive Summary: Peanut drying is an essential task that is carried out mainly at peanut buying stations 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. Peanuts must be dried below 10.5% kernel moisture content for grading, sale and storage. To facilitate drying, these pod peanuts are loaded into drying wagons or drying trailers. Then, dryers using propane or natural gas fuels are connected to the wagons and trailers 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% kernel moisture content. Knowledge of pertinent peanut drying parameters such as temperature and relative humidity of the ambient air, temperature and relative humidity of the air being blown into the peanuts, and kernel moisture content is essential in managing the dryer for optimal drying rate. The optimal drying rate is required to preserve quality and desired flavor. In the current peanut drying process, such parameters are elusive in real-time and are either not measured or only measured periodically by an operator. A peanut drying monitoring system, controlled by an embedded microcontroller, consisting of relative humidity and temperature sensors and a microwave moisture sensor was developed to monitor drying parameters in real-time. It was deployed during the 2014 peanut harvest season at a peanut buying point in central Georgia. It was placed in 45-ft drying semitrailers to monitor in-shell kernel moisture content, temperature of the drying peanuts, temperature and relative humidity of the exhaust air from the peanuts and relative humidity of the air being blown into the peanuts. In-shell kernel moisture content was monitored with a microwave moisture sensor with an accuracy of about ½% moisture content. In these trials, data were assessed to evaluate the uniformity of peanut drying. The movement of the drying front through the peanut bed was captured by real-time monitoring. Real-time monitoring of the drying parameters was also able to capture periods of nonbeneficial drying. During such periods kernel moisture content was observed to either remain constant or increase slightly, and relative humidity of the air being blown into the peanuts was above 70%. Eliminating these periods of nonbeneficial drying can save an average size buying station $22,000 annually. The peanut drying monitoring system is a valuable aid in providing the buying point personnel with real-time data that would allow them to make better informed decisions; therefore improving the efficiency of peanut drying by eliminating underdrying, overdrying and nonbeneficial drying. The monitoring system could also be incorporated into the drying system control to automate the operation with even better efficiency, saving operating costs and providing improved peanut quality for the benefit of growers, handlers, marketers and consumers.

Technical Abstract: The efficient control of drying parameters is essential to ensure that peanuts are dried at the optimal rate, preserving quality and desired flavor. The present peanut drying process has limitations in means for measuring parameters such as temperature and relative humidity of the air being blown into and exhausted from the peanuts in real-time or in a discrete manner. A sensor network, with an embedded microcontroller, consisting of relative humidity and temperature sensors and a microwave moisture sensor was developed to monitor such drying parameters in real-time. A previous version of the sensor network was field tested during the 2013 peanut harvest season, and positive results were observed. Drying parameters were measured and stored on a CompactFlash card every 12 seconds. In-shell kernel moisture content was determined with a standard error of prediction of 0.55% moisture when compared to the reference oven-drying method. After the addition of more sensors, two sensor networks were deployed during the 2014 peanut harvest season at a peanut buying station in central Georgia. They were placed in the 45-ft drying semi-trailers with one near the front of the trailer and the other near the back of the trailer. At both locations, pod and kernel moisture content, temperature of the drying peanuts, temperature and relative humidity of the air exhausted from the peanuts, and temperature and relative humidity of the air being blown into the peanuts were measured in real-time. Data from measurements at the two locations within each semi-trailer were time-stamped and used to assess the uniformity of peanut drying. Results show promise for the development of a system to monitor and control drying parameters in the field in real-time. Such a system has the potential for saving a buying station on average $22,000/year in propane and electric energy costs.