Drying and Cooling Stored Grain and Preserving its Quality July 25, 2012 Dr. Greg Brenneman ISU Ag Engineering Specialist
Conditions that Lead to Storage Problems Grain that is too wet Grain that is too warm Trying to hold grain too wet, too warm, too long Fines accumulations Uneven grain temperatures in storage Grain not checked often enough
2012 Concerns - Aflatoxin A. flavus grows best in hot, dry years and warm nights. Storage conditions for A. flavus are 80-90 degrees, 18% mc and damaged corn. Aflatoxin never goes down in storage remains the same or increases. Check fields prior to harvest if suspected.
Scout for Aspergillus Scout at BL and prior to harvest. Sample moldy corn to check aflatoxin levels. Dry moldy corn to less than 15% immediately. Google aflatoxin in corn
Grain temp Corn MAX Allowable Storage Time - Days Corn Moisture Content degrees F 15 18 20 22 24 26 28 30 30 * * * 190 127 94 74 61 40 * 290 142 84 56 41 32 27 50 * 125 63 35 25 18 14 12 60 200 55 28 17 11 8 7 5 70 110 30 16 9 6 5 4 3 80 60 17 9 5 4 3 2 2 * - Allowable storage is greater than 300 days
Soybeans MAX Allowable Grain temp Storage Time - Days Soybean Moisture Content degrees F 11 13 15 17 19 21 23 25 30 * * * * 190 130 90 70 40 * * 200 90 60 40 35 30 50 * 230 90 50 30 15 12 10 60 * 120 50 25 15 10 8 7 70 200 70 30 14 8 6 5 4 80 140 40 15 7 4 3 2 2 * - Allowable storage is greater than 300 days
Corn Equilibrium Moisture Levels Temp 0 F Relative Humidity 40 50 60 65 70 80 90 40 11.0 12.7 14.5 15.5 16.4 18.7 21.7 50 10.5 12.2 13.9 14.8 15.7 17.9 20.9 60 10.1 11.7 13.3 14.1 15.1 17.2 20.1 70 9.7 11.2 12.8 13.5 14.5 16.6 19.4
Tem p 0 F Soybean Equilibrium Moisture Levels Relative Humidity 40 50 60 65 70 80 90 40 7.2 9.1 11.1 12.3 13.6 16.6 21.1 50 7.0 8.8 10.8 12.0 13.2 16.2 20.6 60 6.8 8.6 10.5 11.6 12.8 15.7 20.1 70 6.6 8.3 10.2 11.3 12.5 15.4 19.6
EMC (%) Safe Grain Moisture Content (ERH = 65%) 18 17 16 50 F 60 F 70 F 80 F 15 Winter Storage 14 13 Summer Storage Corn Soybeans 12 11 10 9 8-1 2 4 7 10 13 16 18 21 24 27 29 32 35 38 Temperature (C) Source: Purdue Univ.
Energy Efficiency Tips Use maximum drying temperature that does not damage the corn Energy requirements of a conventional high temperature cross-flow dryer as a function of drying air temperature and airflow rate. (University of Nebraska, about 1970) Airflow of Dryer Types Mixed Flow ~ 40 cfm/bu Cross-Flow ~ 70-90 cfm/bu Airflow rate affects drying rate Vacuum Cooling
Drying Energy Cost Estimation High Temperature Drying~210 F Assumes 2,500 Btu/lb water Propane cost / bu- point moisture = 0.022 x price/gal $ 0.033/bu-pt = 0.022 x 1.50/gal @ $1.50/gal propane, estimated propane cost to dry corn from 25% to 15% is $0.033/bu-pt x 10 pts = $0.33/bu.
Quantity of Propane Needed Propane gallons = 0.022 x bu. x point moisture Propane = 0.022 x 10,000 bu x 10 pts = 2200 gallons
Drying Time Natural Air 5-9 bu-pts / hour / hp 120 0 Air 50 bu-pts / hour / hp 160 0 Air 80 bu-pts / hour / hp Be careful with drying temps of 80 0 to 100 0 - corn can spoil faster than it dries
Fast Cooling Results in dry, cool grain that can go directly to market or into storage. Grain is still about 10 degrees F warmer than outdoor temperatures. Very little moisture loss during cooling. Subjects kernels to a lot of stresses that can result in cracking and breaking during handling.
In-Storage Cooling Hot grain is moved directly to storage and cooled slowly in the storage bin. Bin must be equipped with an aeration fan that is large enough to keep up with the dryer (need 12-15 cfm per bu/hr of dryer capacity). Large fans can be cycled on and off. Grain will lose 1 to 1.5 percentage points of moisture during cooling.
Dryeration Grain is moved to a cooling bin and tempered (kept hot without cooling) for 4 to 12 hours. Grain is cooled (usually in less than a day) and then moved to storage. Grain loses about ¼ percentage point of moisture for every 10 degrees F of cooling (often 2+ percentage points). Reduces stress cracks.
Grain Temp Differentials
Moisture Migration
Cooling Prevents Moisture Migration
How Long Does It Take to Cool Grain? Airflow rate is the key It takes about 15 cfm-hr/bu of fan operation Examples Drying fan 15 cfm-h/b 1.0 cfm/b = 15 hr Aeration fan 15 cfm-h/b 0.1 cfm/b = 150 hr Larger Bins Use electronic monitoring
Measuring Grain Temperature
Permanently Installed Grain Temperature Cables Cable Temperature sensor Temperature indicator Fan
Aeration Management Phase 1: Fall Cool Down Lower grain temperatures stepwise October November December 40-45 F 35-40 F 28-35 F Phase 2: Winter Maintenance Maintain temperatures with intermittent aeration January, February 28-35 F Phase 3: Spring Holding Keep cold grain cold Seal fans Ventilate headspace intermittently
Aerate Stored Grain (Spring) If grain isn t cooled below 30F, there might not be a need to warm it in the spring. If grain is cooled below 30F, it must be warmed in spring to prevent problems with condensation on the grain or frosting of equipment during summer. During grain warming, fans must be left on until warming is complete.
Aerate Stored Grain (Spring Grain must be dry. and Summer) Stored grain insects can be a problem, even in dry grain, if the temperature is too high. Avoid warming the grain above 50F. Avoid running aeration fans when the outdoor temp. is above 50F.
Cover Fans When Not Operating Prevents spring warm-up Keep snow & pests out Keep damp air out
Fines Management Fines are undesirable in stored grain because they increase airflow resistance and are easier for mold or insects to feed on. Clean grain before drying and storage. Or use a grain spreader to distribute fines throughout the grain mass. Or don t distribute fines and core bins to remove fines.
Checking Stored Grain Check every other week in winter. Check every week rest of year. Climb into the bin and feel for crusted, moist, sticky or warm grain. Probe the grain to with a thermometer checking for warm spots.
Correcting a Storage Problem Turn on the fan run until grain is cool Remove the problem grain Unload the entire bin
Work Safely Around Stored Grain! Use proper respiratory protection around dusty and/or moldy grain. Stay out of flowing grain. Watch out for bridged grain. Use fall protection when climbing bins or rail cars.
Keys to Successful Storage Store clean grain Dry grain to recommended moisture Aerate for a cool, uniform temperature Remove center cores of bins Check grain frequently Deal with any problems immediately
Where to go for more information www.iowagrain.org Google post-harvest crops minnesota http://www.ag.ndsu.edu/extension-aben/postharvest
Acknowledgments Managing Grain in Storage Bill Wilcke University of Minnesota Corn Storage and Drying Ken Hellevang North Dakota State University