Performance of Semi-Trailer Peanut Drying Units

Authors: Butts, Christopher - Chris; Lamb, Marshall

Submitted to: American Peanut Research and Education Society Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 7/7/2009
Publication Date: 7/16/2009
Citation: Butts, C.L., Lamb, M.C. 2009. Performance of Semi-Trailer Peanut Drying Units. American Peanut Research and Education Society Abstracts.

Interpretive Summary: None required.

Technical Abstract: The practice of forcing heated air through a deep bed of peanuts to remove moisture and preserve the quality of farmers stock peanuts has remained relatively unchanged since the 1960’s. Drying wagons or trailers were somewhat standardized to 2.4 m wide by 4.3 m long and with 1.3 m peanut depth. These trailers have been used reliably to cure peanuts in 4-t batches for many years. Trailers measuring 6.4 m long and capable of curing approximately 6 t of peanuts were introduced in the late 1980’s. Following plenum temperature guidelines with properly matched fan and burner units, these 4 and 6-t batches could be cured to moisture levels of 10% in less than 24 h consuming approximately 26.5 L of propane (21.7 m3 of natural gas) per ton of peanuts. Larger containers for curing farmers stock peanuts designed and converted from salvaged over-the-road semi-trailers were introduced in the West Texas growing region. These semi-trailer drying units are typically 13.7 m long with a 46-cm tall plenum and capable of curing peanuts in beds up to 2.3 m deep. Fans were sized appropriately to provide 10 m3/min per m3 of peanuts. As use of these drying units migrated to the southeastern U.S., fan capacity was increased to account for increased humidity of the region, along with the greater bed depth and maintain satisfactory drying performance. No data are published regarding the drying time, moisture gradients within the load, or energy consumption. Three semi-trailer dryers and a conventional 4-t dryer were equipped with gas vapor meters to determine natural gas consumption during the 2008 peanut harvest at a commercial peanut drying facility located in Quitman, GA. The entire drying facility was equipped with a network dryer control system that remotely sensed ambient temperature and relative humidity and set the plenum temperature of each dryer accordingly. This system maintained daily records of ambient temperature and relative humidity, and individual dryer temperatures. The facility used the peanut curing management software, PECMAN, to record drying data such as load identification, dryer used, initial and final moisture content, and the date and time of dryer initiation and completion, Buying point personnel recorded gas meter readings for each of the four dryers before starting and after stopping each load. During the 2008 peanut harvest, 1006 loads of peanuts were cured with an average 17.3% initial moisture content. The average cutoff moisture content was 10.5%. The average time required to dry a load of peanuts was 24.8 h. There was no significant difference in either the initial or final moisture content for the dryer type (semi-trailer or conventional). Twenty percent of the loads dried were semi-trailers. The average drying time for semi-trailer dryers was 26.5 h, and was not significantly different from the 24.4 h required to dry the conventional loads. Energy consumption was monitored on 59 loads during the season. Fifty-five (55) of those loads were semi-loads. Each load of peanuts required 5.33 m3 of natural gas per ton of peanuts with no significant difference due to size of the load. However, the semi-load required 26.2 kWh electrical energy per ton compared to 10.3 kWh/t for the conventional load. Total energy cost was calculated using a rate of $0.51/m3 of gas and $0.11/kWh. Total energy costs for the semi-trailer averaged $10.18/t compared to $7.85/t for the conventional dryer, but was not significantly different. Semi-dryer performance was also analyzed by dryer manufacturer and significant differences were found in operating costs. Differences were most likely due to differences in airflow per m3 of peanuts. As airflow rate increased, the drying time decreased, but not enough to offset the proportional increase in the gas consumption rate.