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November 11, 2004 Sunflower Drying Tips for November
Based on average North Dakota temperatures and relative humidity, the equilibrium moisture content (EMC) of oil sunflowers is about 10 percent for November, 11 percent for December through February, 10 percent in March, 9 percent in April and 8 percent in May. For confectionary seeds it is about 14 percent for November, 15 percent for December through February, 14 percent in March, 11.5 percent in April and 10 percent in May. Sunflowers above this moisture content will gradually dry to the EMC based on temperature and relative humidity. The estimated natural-air drying time for 17 percent moisture in oil sunflowers, with October conditions of 47 degrees and 65 percent relative humidity, is about 27 days using an airflow rate of 1 cubic foot of air per minute per bushel. The drying time in November is about 47 days because of the reduced moisture-carrying capacity of the air at 27 degrees. Adding heat to warm the air 5 degrees reduces the final moisture content to about 8.5 percent and the drying time to about 32 days. Warming the air by 10 degrees reduces the final sunflower moisture content to about 7 percent and drying time to 36 days. Some supplemental heat will reduce the drying time, but more supplemental heat appears to lengthen the drying time. The estimated allowable storage time chart for cereal grains can also be used for estimates on oil sunflowers. Oil sunflowers at 15 percent moisture are equivalent to cereal grains at 20 percent moisture. The allowable storage time for 17 percent oil sunflowers at 40 degrees is about 60 days. Airflow through the sunflowers is required to keep them cool. The allowable storage time for 17 percent sunflowers at 60 degrees is only 15 days. Moisture meters will not give accurate readings for seed temperatures below about 40 degrees. To get an accurate reading, place the sunflower sample in a sealed container and allow it to warm to room temperature before taking the measurement. It’s also important to remember to adjust the temperature meter reading for seed temperatures above 40 degrees. The adjustment may be 3 percentage points for sunflowers near 40 degrees. Read and follow the operator’s manual for accurate readings. Sunflowers coming from a high- temperature dryer will have a moisture gradient that will generally cause the moisture meter to give a reading lower than the correct value. This causes what is commonly referred to as a moisture rebound so the sunflowers appear to increase in moisture after being placed in storage. To determine the amount of error, measure the sunflower moisture content coming from the dryer, place the sample in a sealed container for at least 12 hours and then recheck the moisture level. The cost of high-temperature drying is primarily the propane and the capital or fixed cost. The propane cost can be estimated on a per-point of moisture removed per-hundredweight basis by multiplying the propane price per gallon by 0.037. For a cross-flow column dryer, the expected propane cost, is about .048 cent per point of moisture per hundredweight using $1.30 propane. The estimated propane cost to dry sunflowers from 20 percent to 10 percent, using $1.30 propane, is 48 cents per hundredweight. The capital and fixed cost might be about 47 cents per hundredweight, so the total cost is 95 cents per hundredweight, or 48 cents plus 47 cents. On a per-point of moisture per-bushel basis, to estimate the propane cost, multiply the propane price by 0.012. For a cross-flow column dryer, the expected propane cost is about .016 cent per point of moisture per bushel using $1.30 propane. The estimated propane cost to dry sunflowers from 20 percent to 10 percent, using $1.30 propane, would be16 cents per bushel. The capital and fixed cost might be about 15 cemts per bushel, so the total cost is 31 cents per bushel, or16 cents plus15 cents. Any dryer using an open flame to heat the air poses a constant fire hazard. Fine fibers from sunflower seeds or other plant materials may be ignited by the burner and carried to the seeds, causing them to ignite. This fire hazard can be reduced by turning portable dryers into the wind so airborne fibers are blown away from the dryer intake and by pointing permanent dryers into the prevailing wind. A moveable air intake duct may be placed on the burner intake to draw clean air away from the dryer. The duct must be large enough not to restrict the airflow because the drying speed will be reduced if the airflow is reduced. The duct must be much larger than the fan diameter. Clean the dryer, air ducts and area around the dryer at least daily. Frequently remove the collection of sunflower lint on the dryer column and in the plenum chamber because the material becomes extremely dry and can be ignited during dryer operation. A major concern is that some sunflower seeds will hang up in the dryer or be stopped by an accumulation of material and become overdried. Make sure the dryer is completely cleaned after each batch, keep sunflower seeds moving and check a continuous-flow dryer regularly (hourly) to see that the sunflower seeds are moving. High-speed dryers are like a forge when a fire gets going. However, fires can be controlled if they are noticed immediately, which makes constant monitoring necessary. Many fires can be extinguished by shutting off the fan to cut off the oxygen. A little water applied directly to the fire at an early stage may extinguish it if shutting off the fan fails to do so. A fire extinguisher for oil-type fires should be used for oil sunflower fires. Many dryers are designed so that sunflowers can be unloaded rapidly in case of a fire and before the dryer is damaged. In some dryers, only the part of the dryer affected by the fire needs to be unloaded. ### Source:
Kenneth J. Hellevang, (701) 231-7243, kjh-eng@ndsuext.nodak.edu |
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North Dakota State University |
