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United States Department of Agriculture

Agricultural Research Service

Title: Comparison of Dryer Control Strategies

Author
item Butts, Christopher

Submitted to: Peanut Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 20, 1996
Publication Date: N/A

Interpretive Summary: Tests were conducted to quantify the costs and benefits of curing peanuts using air heated so that the relative humidity was between 40 and 60%. Drying time increased from 18 hours to 29 hours when the carefully controlled drying technique was used. To handle the same amount of peanuts in the same amount of time as when the conventional drying method was used, a peanut buying point would have to purchase more dryers. This cost could be offset by savings in heating fuel and improved shelling characteristics. A buying point could save approximately $4.50 per metric ton of peanuts dried by using the improved control strategy. A sheller could improve net revenue on shelled peanuts by about $18 per metric ton of farmers stock peanuts cured using the improved drying technique.

Technical Abstract: Peanuts were mechanically cured from field moisture contents ranging from 11.5 to 32.8% wet basis to levels suitable for long-term storage using two dryer control strategies. The first control algorithm consisted of a constant thermostat setting of 39 C, while the second required manual thermostat control on an hourly basis such that theminimum plenum relative humidity was between 40 and 60% and the maximumplenum temperature was less than 39 C. The average drying rate using the variable thermostat set point of 0.3%/h was half that obtained with the constant set point. Average curing time for the variable thermostat setting was 56% longer than for the peanuts cured using the constant thermostat. Fuel consumption was reduced by approximately 30% using the variable set point. Kernel size distributions and milling quality indicated by bald kernels were significantly better for peanuts cured using the variable thermostat control. Increasing available dryers by 40% would allow the buying point manager to handle the same amount of peanuts during the same harvest interval. Economic analysis showed that the capital cost for additional drying equipment could be regained in the first year in energy savings alone. A sheller could realize an increase in net profits of approximately $18 per Mg of farmers stock peanuts cured by using a variable thermostat set point from increased shelled product value.

Last Modified: 9/1/2014
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