Understanding Grain Aeration Best Practices for Grain Storage
Understanding Grain Aeration Best Practices for Grain Storage 19 18 16 17 2 10 9 1 Ron Palmer Williston Wheat Show North Dakota State University Thurs, Feb 8, 2018 P. Eng. Ph. D. . ron. palmer@uregina. ca grain-aeration. com Indian Head Agricultural Research Foundation Western Grain Research Foundation
Objective • To build a fan controller or strategy that: – is Efficient – saves power, fan on only when necessary (if drying, fan on, if not drying, fan off) – Provides Safe Grain Storage – i. e. No spoilage • Cool grain • Dry grain Ø Dries Grain to market-dry levels Strategy Only run the fan when ambient air conditions will result in the drying of the grain; OR: only run the fan to make the grain as cold as possible? ? Or as SAFE as possible ? ?
Vapour Pressure Air surrounding kernel Grain kernel Water trying to get in Water trying to get out = Vapour Pressure Air = Vapour Pressure Grain • temperature • % moisture content • relative humidity • temperature • type & condition of grain When air vapour pressure is greater than grain vapour pressure, water enters the grain and WETTING occurs. When Vps are equal, EMC When grain vapour pressure is greater than the air vapour pressure, water evaporates from the grain into the air and we have DRYING
The Black Box Approach H 2 O IN Absol Humid in Black Box = Grain Bin Temp, RH H 2 O OUT Abs Humid Out Temp, RH If H 2 O IN < H 2 O OUT then turn FAN ON (drying) (Abs. Hum) ( Abs Hum) If H 2 O IN > H 2 O OUT then turn FAN OFF (wetting)
H 2 O 25 gr/m 3 Air goes in through the fan, passes through the grain, and exits the bin Amount of Air In = Amount of Air Out For every cubic meter of air that goes in, there is a cubic meter that exits at the top. Air holds water, Absolute Humidity grams per cubic meter (m 3) Example: Air entering has an Absolute Humidity of 20 gr/m 3 and exits the bin with an Absolute Humidity of 25 gr/m 3 Therefore for every cubic meter of air that passes through the bin, 5 grams of water are being removed. We are drying. How to determine Absolute Humidity? H 2 O 20 gr/m 3
Water in the Air Absolute Humidity grams of water per cubic meter gr/m 3 45 Saturation RH= 40 35 30 25 points 100% 75% 50% 25 RH = 75% RH = 50% 20 15 RH = 25% 10 5 -20 -10 0 0 10 20 Temperature of Air Degrees Celsius ⁰C 30 40
Get Absolute Humidity from T & RH • Use the graph Temp-->RH--> Abs. Hum • Use online calculator planetcalc. com/2167/ – Relative Humidity % 74 – Air Temperature ⁰ C 32 – it calculates the absolute humidity kg/m 3 . 025 • Use equation: Absolute Humidity = Saturation Humidity x RH =( 0. 000289 T 3 + 0. 010873 T 2 + 0. 311043 T + 4. 617135) x RH Absolute Humidity, a function of Temp & Relative Humidity
Example • Air In: 26 ⁰C, RH 80% Abs Hum 20 gr/m 3 • Exit Air: 32 ⁰C, RH 74% Abs Hum 25 gr/m 3 • For every cubic meter that flows through the bin, five grams of water are removed. • Let’s say our CFM is 3000. There are 35. 31 cubic feet in a cubic meter, so 85 m 3/min or 5098 m 3/hr x 5 gr/m 3 = 25, 488 gr/hr or 25. 488 kg/hr or 56. 17 lbs of water removed every hour.
Water in the Air Absolute Humidity grams of water per cubic meter gr/m 3 45 Saturation RH= 40 35 points 100% 75% 50% 25 30 25 20 5 gr H 20 RH = 75% RH = 50% 15 10 RH = 25% 5 -20 -10 0 0 10 20 Air In 26 ⁰C Temperature of Air Degrees Celsius ⁰C RH 80% 30 Air Out 32 ⁰C RH 74% 40
2 H 2 O removed (gr) per cubic meter of air flowing through bin Average Diurnal Drying Cycle of 19 trials 1. 5 Best Drying ~ 2 AM 1 0. 5 Drying to Wetting 9: 30 AM Wetting to Drying 6: 00 PM 0 1 -0. 5 -1 2 3 Night 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Hour of the Day Most Wetting Morning Noon Afternoon Evening
Night Drying Recommendation • Yard Light Rule (2010): On at night, you are bright On during the day, you will pay. • Requires no sensors, or calculations, or knowledge of grain type, temp, RH etc. • Turn off at 9 AM • Does not account for MC, air T or RH, nor grain T and therefore may not be the best.
200 How Do Temperature Cycles Line Up with Drying Cycles? 25. 6⁰ 3: 09 PM 150 Typical High 23. 5⁰ C ~ 3: 00 PM 25. 7⁰ 3: 09 PM Outside Air Temperature (⁰C) Grain Temperature 100 30 ⁰C 25 So a good control strategy would be to only run the fan when the grain is cooling Ie Outside Temp < Grain Temp Drying when grain temp is decreasing 20 15 0 10 1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64 67 70 73 76 79 82 85 88 91 94 97 100 103 106 109 112 115 118 121 124 127 130 133 136 139 142 145 148 151 154 157 160 163 166 169 172 175 178 181 184 187 50 -50 Cooling is Drying -100 Our data shows that cooling the grain by about 15⁰ C will lower the Moisture Content by 1% Heating the Grain Wets it 2. 6⁰ C 5: 09 AM Typical 11⁰ 5: 30 5 Our data shows that heating the grain By about 30⁰ C will increase MC by 1% 0
Cooling is Drying • Turn the Fan on if: (Air Temperature) < (Grain Temperature) The MC of the grain, and outside air RH are not accounted for, so again we could question: Is this the best? Can we also account for the MC and RH? This strategy requires a minimum of sensors – only the temperature of the grain. May want to further restrict – on if RH < 85%
Temperature Probes Temp and RH sensor - Good for when fan is running - Not good when fan stopped How do we get the T and RH of the air that will be exhausted? 1. T & RH sensor buried in grain 2. EMC Sampling ports for Grain Moisture Easy to get T and RH of the outside air.
Moisture Cables provide T & RH • If you have so called moisture cables, they will have temperature and RH sensors located every 4 feet. • When the fan is running we get the T & RH with a sensor located where the air exits the bin. • When the fan is stopped, use a sensor buried in the top layer of grain. This is what the exhaust air will be when the fan starts.
If you don’t have moisture cables, but only know the temperature of the grain by probing or temp cables • The temperature of the exhaust air will be the same as the grain temperature; but where will we get the RH of the exhaust air? • The exhaust air will be the air that is surrounding the grain right now. We have the temperature but we need the RH. • We will use Equilibrium Moisture Content (EMC) equations to get the RH.
EMC Equilibrium Moisture Content Grain put in a sealed container at a given MC and T Wait until equilibrium reached (grain and air at same T) Moisture Content (MC) Relative Humidity (RH) For each grain, graph MC vs. RH then find EMC equation Many have done this with slightly different equations Henderson, Chung, Pfost If you have a bin (considered sealed) that has been sitting with grain in it for awhile (equalized) and you know the T and MC you can plug this into an EMC equation to get RH = {… MC …. T } but only if the air is the same T as the grain • The operative word is equilibrium, the grain and air must be at the same T. Using this T and MC of grain, plug into EMC to get RH. Using this RH and grain T Absol Humid • •
How to Use EMC to determine drying conditions 1. Find the RH of the air inside the bin using EMC eq. for grain at T and MC 2. Calculate the saturation absolute humidity for air that is the same T as the grain 3. Find the absolute humidity of the air inside the bin by multiplying 1. x 2. 4. Calculate the saturation absolute humidity of the outside air at its T 5. Determine threshold RH by dividing 3. by 4. If the outside air has a RH that is less than the threshold RH, then we have drying conditions. 6. Fortunately all this math is done with the grain drying calculator. Simply enter the MC of the grain, its T and the outside temperature. The calculator will calculate threshold RH for a number of grains using the steps above. Find the grain in question, and its threshold RH. If the outside air has an RH that is lower than this then we have air that will dry your grain.
The Grain Drying Calculator • Input MC%, Grain Temp, Air Temp RHthres • planetcalc. com/4959/ Grain Moisture Content % 12 Grain Temperature ⁰ C 20 Air Temperature ⁰ C 32 Grain Threshold Relative Humidity Xxx xxx Canola (Henderson) 41. 5 Canola (Chung Pfost) 42. 0 Calculate
Absolute Humidity Water in the Air 45 grams of water per cubic meter gr/m 3 Consider Canola @ 12 % MC and 20 C It will equalize the air around it to have an RH of 81. 4% which has an absolute humidity of about 14 gr/m 3. If we blow air with an abs humidity < 14, we will get drying. If > 14 we will wet the canola. Saturation RH= 40 35 points 100% 75% 50% 25 30 25 20 15 10 RH = 75% Canola 12% MC RH = 50% 10 79. 6 15 80. 5 20 81. 4 25 82. 3 30 83. 1 RH = 25% 5 -20 -10 0 0 10 20 Temperature of Air Degrees Celsius ⁰C 30 40
Fan On: Abs. Hum Air < Abs. Hum Grain Air • Based on the idea that you will only turn the fan on if drying conditions exist. • Absolute Humidity from Temp and Rel Humid • Grain Drying Calculator • Relative Humidity of the Grain Air can be measured directly, or calculated from EMC • Ultimate strategy, but there is a degree of error in determining RH of grain air.
Objective • To build a fan controller or strategy that: – is Efficient – saves power, fan on only when necessary (if drying, fan on, if not drying, fan off) – Provides Safe Grain Storage – i. e. No spoilage • Cool grain • Dry grain Ø Dries Grain to market-dry levels Strategy Only run the fan when ambient air conditions will result in the drying of the grain; OR: only run the fan to make the grain as cold as possible? ? Or as SAFE as possible ? ?
SAFE STORAGE TIME (days) CEREAL GRAINS log 10 (safe days) = 6. 2 – 0. 3 MC% -. 07 ⁰C Fraser & Mu Grain Moisture Content germination reduced by 5% 14. 5% @ 30⁰C = 38 safe days 14. 5% @ 20⁰C = 128 safe days Temp⁰C 14. 5% @ 0⁰C = 1458 safe days 14% 15% <-5 5 10 15 > e ag r sto fe a S a 16% ar e y 17% 18% 19% 20% 21% 22% 23% 24% 2 80 -120 40 -60 20 -30 1 80 -120 40 -60 20 -30 10 -15 1 20 80 -120 40 -60 20 -30 10 -15 5 -8 25 80 -120 40 -60 20 -30 10 -15 5 -8 3 -5 30 40 -60 20 -30 10 -15 5 -8 3 -5 NOT SAFE 80 -120 40 -60 20 -30 10 -15 5 -8 VERY DANGEROUS 3 -5 5 5 -8 3 -5 3 -5 3 -5 3
SAFE STORAGE TIME (days) CEREAL GRAINS Grain Moisture Content Temp ⁰C 14% 15% 16% 17% 18% <-5 5 10 f e a S 15 ge a or t s > a ar e y 19% 20% 21% 22% 23% 24% 2 80 -120 40 -60 20 -30 1 80 -120 40 -60 20 -30 10 -15 5 -8 20 80 -120 40 -60 20 -30 10 -15 5 -8 25 80 -120 40 -60 20 -30 10 -15 5 -8 3 -5 30 40 -60 20 -30 10 -15 5 -8 3 -5 NOT SAFE 80 -120 40 -60 20 -30 10 -15 1 VERY DANGEROUS 3 -5 5 5 -8 3 -5 3 -5 3 -5 3
Co ld of o R Co Condensation: ld Ro o f Cold Air goes in through the fan, passes through the grain, and warms. Removes water from the grain. As it leaves the grain, it hits the cold roof. The warm moist air, cools rapidly as it hits the cold roof. It cooling air, reaches saturation and condensation occurs in the from of rain or frost. The condensed water falls or drips back onto the top of the grain and a crust is formed. Cold Air
Dripping and Crusting Flax harvested dry 8% MC, but it is warm 28⁰ C Nothing is done for a month, but decide to cool it down, by using night drying: yard light rule. Nights are getting cooler and going down to 8⁰C. Next morning lots of condensation on the inside roof. Did drying at night add water? Or, where did the water come from? The flax was dry? Plug numbers into calculator, 8% 28 C and we get 186% for THthres. What’s going on here? How can an RH be greater than 100% ? ?
Flax 28 C , 8 % MC EMC and RHemc is 52% Sat humidity @ 28 C is 28. 2 absolute humidity in the bin is 28. 2 x. 52 = 14. 8 gr/m 3 The air in the bin is 28 C, RH is 52%, and absolute humidity is 14. 8. When this air hits the roof, which is the same T as outside air, 8 C, it cools but keeps the same water 14. 8. But air at 8 C can’t hold that much water, the most it can hold is 7. 9. So for every cubic meter of air -30 -20 -10 grams of water per cubic meter gr/m 3 45 Water in the Air 40 Saturation RH= 100% Ws = 0. 000289 *T 3 + 0. 010873 * T 2 + 0. 311043 * T + 4. 617135 35 points 100% 75%the calculator When ever gives an 50% Rhthres > 100% we have 25 conditions for condensation on the inside of the roof and walls 30 25 RH = 75% RH = 50% 20 15 RH = 25% 10 5 0 0 10 Temperature of Air Degrees Celsius ⁰C 20 30 40
Condensation • Rule of Thumb: If the grain is warmer than the outside air by more than 5 or 6 ⁰C there will be condensation. • If the calculator gives a RH thres of 100% or more you will get condensation.
Absolute Humidity Water in the Air 45 grams of water per cubic meter gr/m 3 Consider Canola @ 12 % MC and 20 C It will equalize the air around it to have an RH of 81. 4% which has an absolute humidity of about 14 gr/m 3. If we blow air with an abs humidity < 14, we will get drying. If > 14 we will wet the canola. Saturation RH= 40 35 points 100% 75% 50% 25 30 25 20 15 10 RH = 75% Canola 12% MC RH = 50% 10 79. 6 15 80. 5 20 81. 4 25 82. 3 30 83. 1 RH = 25% 5 -20 -10 0 0 10 20 Temperature of Air Degrees Celsius ⁰C 30 40
Bottom Dries First • • The fan compresses the air Compressing the air, immediately heats it, 3⁰ Warmer air can and will hold more water As the air rises in the bin it decompresses Decompression – cooling Cooler Air can’t hold as much water, no drying Smaller fans, less compression, less top to bottom difference in drying.
-30 grams of water per cubic meter gr/m 3 45 Water in the Air 40 Saturation RH= 100% Ws = 0. 000289 *T 3 + 0. 010873 * T 2 + 0. 311043 * T + 4. 617135 35 points 100% 75% 50% 25 30 25 RH = 75% RH = 50% 20 15 RH = 25% 10 5 -20 -10 0 0 10 Temperature of Air Degrees Celsius ⁰C 20 30 40
First 24 Hours is Critical Average of 33 Runs 2007 – 2014 • • • First 24 Hours: Start End Difference Grain Temp ⁰C 26. 2 14. 6 11. 6 Moist Cont % 17. 65 16. 77 0. 88 Safe Days 6 32 26 Cooling/Drying 11. 6/0. 88 = 13. 18 ⁰C/%MC New Definition: Spoilage Index = Ʃ ( 1/ safe days) x 100 Example, if safe days is six, then after 3 days we will have an accumulated deterioration of: (1/6 + 1/6) x 100 = 50%, after 6 days : (6 x 1/6) x 100 = 100% of the way to 95% germination
Recommendation: Use your fans 1. All steel grain storage bins should be equipped with aeration storage bins. To prevent spoilage, the grain must be cooled, even if it is dry. The stored grain is very valuable, and cooling the grain ensures its safety and protects its quality. Even if the bin is not near grid power, a gen-set could be used to power the aeration fan for a couple of nights to cool the grain.
2. Smaller Fans: Power ~ Flow 3 ~ Pressure 2 $2300 10 HP 2, 150 CFM 3. 1 $1700 5 HP 1, 700 2. 2 $1100 2 HP 1, 200 1. 4 $900 1 HP 1, 000 1. 0 – Assume we use a smaller fan: 5 HP 1 HP: Flow is reduced, but not even half : 1, 700 to 1, 000 Power bill, reduced by 2/5. (Assume fan is on 2 X) Capital costs are reduced, half. Portable: A fan could easily be moved from bin to bin. Power delivery system, much smaller. Top/Bottom Drying reduced because less pressure drop and therefore less top/bottom temperature difference. • What is the hurry – just need to cool the grain down. • • •
3. Open bottom plenum. Air pressure drop can easily be can be measured across the plenum screen. A loss of 1 inch of water (static pressure measured with a manometer), or more going across our screen. What a waste. An open bottom screen would essentially reduce this loss in pressure to zero.
4. Turn Fan On Immediately Upon Filling Turn the Fan on the first day and night until 9: 00 the next morning. We observed time and time again that we got as much as a 1 % reduction in Moisture Content in the first 24 hours. This was even more evident when the grain came off the field hot. The fan should be turned on even as the bin is being filled. We want to get the grain cooled down immediately. Stop the spoilage as soon as possible.
5. Night Drying • This is for the farmer who has no sensors – not even temperature, and not planning on getting any. • Mindset = Get the grain as cold as possible, even if it is dry, Cold = Safe Yard Light Rule: On at night, you are bright, On during the day, you will pay
6. Use the Grain Drying Calculator If we know just a little bit -- let's say the Grain Temperature and the Grain Moisture Content; then one can use the Calculator to determine if drying will occur: www. planetcalc. com/4959/ The problem is that things keep changing, especially the outside T & RH, and it is tedious to be doing a calculation every hour and then running out to turn your fan on or off.
7. Air T Outside < Grain T AND RH outside < 80 to 70% Only need temperature of the grain. (thermistor) Can easily be realized with an inexpensive, simple controller Does not depend on Grain Type Theoretically it is not as good as an Absolute Humidity Controller, but its simplicity and reliability make it my choice. • Controls the fan automatically, on site with simple, inexpensive electronics. Electronics: a comparator and an actuator. • Start RH at 80% and slowly turn it down to 70% • The Absolute Humidity Controller requires the Grain Temp and RH as well as the Outside Air Temp and RH. The RH of the grain can be measured with a sensor, but it is not that accurate, and can easily be damaged with dirty air AND these sensors are much more expensive than the temperature sensor. The other way of obtaining the RH of the grain is through EMC equations, but then one must know the grain type, the temp of the grain, and the MC of the grain. This requires a computer. More money, more complication, and therefore less reliable. • •
8. Seal the Bin • All the strategies will produce grain that is cold and after you get your grain as cold as possible (-30 ⁰) VERY SAFE Seal all bin openings to: – Hold the cold in – Prevent warm spring breezes circulating around your grain with condensation • Grain will slowly warm up (1 ⁰C per week) • Keep pulling grain temp down “Keep it as cold as possible”
9. Take temperature of Grain, Half way Up To obtain the temperature of the grain, two thermistors should be placed in the center of the bin, just a little higher than half way up. Why two thermistors? For reliability and validation. If the two thermistors are reading the same value, then you can be assured that you have a reliable temperature value.
10. Invert Top Grain Cone The bottom always dries first, so one could remove a couple of hundred bushels from the bottom after a week or so. Especially if the grain went in with a MC that was more than 2 points higher than dry. In taking out the dry grain at the bottom, it would invert the cone at the top, and lower the overall depth as well as providing some mechanical movement, all to enhance the drying.
11. Supplemental Heat If MC more than 2. 5 points above dry. Use the natural higher temperatures of the day, along with the supplemental heat to put energy into the grain. Then cool with cold dry night air. Remember for every 15 °C – 1% MC. Also consider using #10.
Questions? planetcalc. com/4959/ Grain-Aeration. com Ron. palmer@uregina. ca Farmer’s Canola Bin Kelvington Sask 1600 bushels Dec 11, 2016
Supplemental Heat • Want to dry without condensation • Ideally want the top layer of grain to be no more than 6 ⁰C warmer than the outside air. • Can use the calculator to keep RH thres < 100 • Warming starts at the bottom and takes many hours to get to the top. The outside temp is changing, and it is hard to stay ahead of the curve. • Plenty of supplemental heat calculations on my blog grain-aeration. com
• Farmer, purchased a diesel heater, 75, 000 btu/hr. into a 5000 bushel bin - 3 HP fan. • Grain was 2 – 3% above dry Temperature Sensors every 4’ • Heat left on continuously, or cycled heating / cooling ? • Cycling - heater on (75, 000 btu/hr) until first 3 or 4 bottom sensors to 25 C. Then cooled the grain, using cold night air (5 C) got the grain down to 10. After a couple of cycles, he moved the entire contents of the bin to another bin. tipping? If the grain was still not dry he would go through another cycle. • Cycling much better than continuous. Why – vapour pressure. • When supplemental heat is applied continuously, the grain becomes more or less the same temperature as the air. As such the vapour pressures of each are more or less the same, and little drying occurs. On the other hand if the grain is warmed, and then cooled with cool or even cold air with very little vapour pressure; there will be lots of water being pushed out of the grain and into the air. Lot's of drying. Back to our old adage "Cooling is drying" and our data indicates our rule of thumb: "For every 15 C that the grain is cooled, 1% moisture will be removed.
Absolute Humidity Water in the Air 45 grams of water per cubic meter gr/m 3 Consider Canola @ 12 % MC and 20 C It will equalize the air around it to have an RH of 81. 4% which has an absolute humidity of about 14 gr/m 3. If we blow air with an abs humidity < 14, we will get drying. If > 14 we will wet the canola. Saturation RH= 40 35 points 100% 75% 50% 25 30 25 20 15 10 RH = 75% Canola 12% MC RH = 50% 10 79. 6 15 80. 5 20 81. 4 25 82. 3 30 83. 1 RH = 25% 5 -20 -10 0 0 10 20 Temperature of Air Degrees Celsius ⁰C 30 40
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