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Reducing Grain Drying Costs
Scott SanfordSr. Outreach Specialist University of Wisconsin
Biological Systems EngineeringFocus on Energy / Rural Energy Issues
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Background
CornUS production 2004
11,807,217,000 bushel73,632,000 acres160 bushels per acreAverage Market Price: $1.95 per bushel
L.P. Gas (rural areas), Natural gas & ElectricityDrying costs
2005 – 30 to 35% higher than 20042004 – 25% higher than 2003
Record diesel fuel pricesLow cash prices – $1.40 to 1.77 per bushel
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Why Dry? Reduce moisture content so grain will not spoil.
13%11%13%Stored more than one year
13%12%14%Stored up to one year
13%13%15.5%Fed or marketed by June
13%13%18%*Fed by early Spring
Small grains
SoybeansCornStorage Period
* If maintained at temperatures less than 40 F
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Dry Clean GrainScreen before dryingScreen before storage
Less volume to dry Increased air flow in dryerLess materials to plug screens and aeration floors
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Dryer Energy EfficiencyNo dryer performance standardsLimited independent dryer test dataLimited research data
Buyer beware!
Rule of thumb fuel usage - High Temp. dryer w/o heat recovery
0.02 gallon propane/ bushel / % moisture removed0.018 Therms NG / bushel / % moisture removed0.01 kWh Electricity
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Types of DryersNames reflect air flow pattern
Cross-Flow Column Dryer (batch and continuous)
Batch bin dryers (high temperature)Bin DryersRoof Dryers
Mixed-flow dryers (Counter and concurrent flow)
In-Bin Continuous flow dryers (Counter-flow)
Ambient Air / Low temperature bin dryer (10ºF increase in air temperature)
Combination drying
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Cross-Flow Column Dryer
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Cross-flow Column DryerHeat Recovery Options
Scavenge Heat from hot corn to pre-heat inlet air to dryerReduces energy usage 10 to 20%
Duct exhaust air from cooling section to air intake of heaterAnd (optional)
Recovered from lower portion of drying section of dryer
OrReverse air flow through Cooling Section of dryer
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Duct Work for Heat Recovery
Heat Recovery Cooling section
Heat Recovery Lower Heating
Section
And
Cooling Section
Retro-fitting Dryer with Heat Recovery
Duct to Dryer Air Intake
Access needed for cleaning screens
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Reverse Flow Cooling
Courtesy of Zimmerman Dryers
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Reference: On-Farm Drying and Storage System, ASAE Publication
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Batch Bin DryersHigh temperature dryer
Typical drying temperatures 100 -160°FStirring device
Reduce drying costs by up to 25%Reduces over-dryingRun continuously during dryingRemove fines from floor before next batch
Important to screen out finesRestricts air flow through floor
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Bin Dryer with stirring device
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Mixed-Flow Dryer
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Mixed Flow Dryer - Air Flow PatternsGrain Flow Grain Flow
Grain FlowGrain Flow
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Reference: On-Farm Drying and Storage System, ASAE Publication
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In-Bin Continuous Flow Dryer Options
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In-Bin cooling
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In-Bin Cooling
Used with high-temperature full-heat dryerContinuous-flow or batch
Transfer hot grain (120 to 140°F) to storage bin
Moisture: 1 to 1.5% above desired storage moistureRemainder of drying occurs as grain cools Moisture reduction: ~0.2% per 10°F of temperature decrease
Start cooling fans immediately
Reduce fuel costs at least 10-15%
Increase dryer capacity about 33%Batch dryer – reduces batch time by 15-30 minutesContinuous-flow - ~50% more area for drying
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Dryeration
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DryerationTransfer hot grain (120 to 140°F) to cooling binMoisture: 2-3% above storage moisture contentGrain allowed to “Temper” for 4 to 12 hoursCool grain
Remainder of drying occurs as grain coolsMoisture reduction: ~0.4% per 10°F of temperature decrease
Transfer grain to storage bin
Energy savings: 15% - 25%Dryer capacity: increases up to 70%Improved grain quality
Fewer stress cracked kernels and breakageCracks Breakage
Rapid cooling 43.6% 11.3%Dryeration 7.6% 6.7%
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Reference: On-Farm Drying and Storage System, ASAE Publication
Ambient Air / Low Temperature Bin Dryer
Electrical Resistance
Heater
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In-Bin natural or low heat dryingForces ambient or warmed air (10°F temperature rise) through grain bed Batch / layered drying Energy efficient if dry weather
Early harvest advantageousHigh fan horsepower requirement over extended time
Three 10 HP blowers for 10,000 bushel bin30 to 45 with good weather - 90+ days if wet
1.25 cfm per bushel minimumEnergy: 100% electricityMaximum grain moisture ~ 22% - 24%Only handle grain onceStirring device – saves 20 – 25% in energy costs
Reduces over-drying Increases air-flowStirring 2 or 3 times maximum recommendedOver stirring can reduce air flow
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Combination drying
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Combination Drying
High Temperature drying down to 20-22% moistureContinuous-flow or batch
Transfer hot grain to low temperature bin dryer Start fans immediately and dry using natural air
Don’t Delay fan start!!!Capital cost higher – fans needed on all binsHigh drying capacityHigh quality grainUses more electricity but less LP or natural gasHigh energy efficiency –
~ 50% of energy use for cross-flow dryer ~ 75% LP gas or Natural gas~ 25% electricity
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Comparison of cooling / drying methods
In-dryer cooling $28.85 / 100 buIn-bin cooling $25.18 / 100 bu (12%)
Dryeration $20.90 / 100 bu (27%)
Combination drying $18.85 / 100 bu (35%)
Assumptions:Corn dried from 25.5% to 15.5%Energy Costs onlyElectricity $0.085 / kWhLP gas $1.40 / gallon
(Reference: Midwest Plan Service, MWPS-13, 1987)
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Dryer Maintenance
Keep screens and aeration floors cleanCheck and tighten beltsCheck burner operation –blue flameCalibrate moisture sensors and testersCheck that bearing mountings are tightLubricate as recommended by mfg.
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Moisture Sensors / TestersInaccurate readings
Spoilage / OverdryingReplace battery before season Testers not accurate
Above 22%underestimate hot grain (above 90F) by
at least 1 to 2 %.Checking Calibration:
Compare to certified unit (coop or feed mill)
Refer to Purdue U Fact Sheet #14
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Contact InformationScott Sanford
Sr. Outreach SpecialistFocus on Energy / Rural Energy Issues
Biological Systems EngineeringUniversity of Wisconsin – Madison
Wisconsin Energy Efficiency and Renewable Energy www.uwex.edu/energy