Estimating costs of nonbeneficial dryer operation by using a peanut drying monitoring system

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: 2/16/2018
Publication Date: 5/22/2018
Citation: Lewis, M.A., Trabelsi, S., Nelson, S.O. 2018. Estimating costs of nonbeneficial dryer operation by using a peanut drying monitoring system. Applied Engineering in Agriculture. 34(3):491-496.

Interpretive Summary: Peanut drying is a postharvest process that is required to remove moisture from freshly harvested, unshelled peanuts. They must be dried to reduce the peanut kernel moisture content to 10.5% or less for sale and safe storage to prevent the development of mold and potential toxins produced by some molds. Even though left in windrows in the field to dry naturally before combing, peanuts still have more than 20% kernel moisture content when delivered to the peanut buying points. A recently developed microwave sensor can instantaneously provide the moisture content of the kernels in unshelled peanuts. Therefore such kernel moisture sensors were used along with temperature and relative humidity sensors in developing monitoring systems to study the behavior of peanuts during the drying process. Such peanut drying monitoring systems have been field tested at a commercial peanut buying point in central Georgia during the past few harvest seasons. The monitoring systems were placed near the top of the peanut loads in semitrailers to monitor drying dynamics as the peanuts dried. The monitoring systems provided a continuous profile of kernel moisture content, temperature and relative humidity of the exhaust air, peanut bed temperature and relative humidity of the input air. During these studies, periods of nonbeneficial dryer operation were revealed when no moisture loss was noted in the peanuts. Since operation of the dryer during such periods results in wasted energy, the data were further examined to estimate the costs for propane and electric energy resulting from nonbeneficial drier operation. Estimating costs based on current prices for propane and electric energy, nonbeneficial drier operation would cause a peanut buying point to accumulate unnecessary expenses for propane and electric energy that could total up to $3,250 annually for an average-size buying point. The implementation of peanut drying monitoring systems including microwave kernel moisture sensors would provide buying-point personnel necessary information allow them to better control dryer settings to optimize drying. This would provide considerable savings in energy costs and would also improve peanut quality and safety by preventing the development of molds and aflatoxin for the benefit of the peanut industry and consumers.

Technical Abstract: Knowledge of kernel moisture content during peanut drying is important to ensure that the bed of peanuts is dried appropriately. However, the lack of a commercially available, industry-accepted solution for real-time kernel moisture content determination during peanut drying makes its detection cumbersome and laborious. Samples of unshelled peanuts are extracted from the semitrailer by an operator periodically, and the samples have to be cleaned and shelled to determine kernel moisture content with the official meter. A peanut drying monitoring system that includes a microwave kernel moisture sensor, developed within the USDA ARS, provides a means for monitoring in-shell kernel moisture content in real-time. The system determines kernel moisture content with a standard error of prediction (SEP) of 0.55% moisture content when compared to the reference oven-drying method. During recent peanut harvest seasons, peanut drying monitoring systems were placed in 13.7-m (45-ft) drying semitrailers. As the peanuts dried, 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 every 12 seconds. The continuous data, provided by the monitoring systems, were useful in observing the loss of moisture by the peanuts throughout drying. The data also revealed periods of at least 3 hours in during which dryer operation did not result in loss of moisture from the peanuts; thus, identifying nonbeneficial dryer operation. Such periods can cause a peanut buying point to accumulate unnecessary expenses in for propane and/or electric energy expenses per semitrailer, which can total from $4,000 to $8,000 annually for an average-size buying point.