Drying corn is a crucial step during harvest and essential for ensuring its preservation and quality. However, this process can be costly, particularly in terms of energy. In a context where agricultural production costs continue to rise, it is essential to find ways to dry corn efficiently while controlling expenses.
In this article, we will present the key points to watch out for to optimize the drying process, reduce costs, and maximize return on investment. As they say, the calculation is worth the work!
Corn drying: the main principles
La récolte du maïs
In Quebec and Ontario, corn is typically harvested at high moisture levels, often between 22% and 28%. However, to ensure good preservation and prevent the development of mold or grain deterioration, it is necessary to reduce this moisture content to about 13-15%.
In Quebec, the maximum moisture content accepted at delivery varies from 14.5% to 15.5%, depending on the buyer. Delivering corn below this threshold results in economic loss for the producer, mainly due to increased drying costs and loss of water weight. For all practical purposes, 1% moisture represents 1% of the weight at delivery. So for the same volume of grain, if you deliver your corn at 14.5% instead of 13.5%, you gain an additional 1% net profit.
Dry weight = Wet weight * (100 - % initial moisture) / (100 - % target moisture)
To convert a ton (1,000 kg) of corn at 25% moisture:
Conversion to 14.5%: Dry weight = 1,000 (100 - 25) / (100 - 14.5) = 1,000 75 / 85.5 = 877.19 kg
Conversion to 15.5%: Dry weight = 1,000 (100 - 25) / (100 - 15.5) = 1,000 75 / 84.5 = 887.57 kg
Comparison between 14.5% and 15.5%: Difference: 887.57 - 877.19 = 10.4 kg Proportion: 10.4 / 877.19 = 1.17%
To obtain a dry grain, the temperature must be increased during drying. The higher the temperature of the grain during drying, the more its properties are affected. Overheating grain directly affects the quality of your corn.
An important fact to consider; the drier the grain, the more fragile it is, and therefore more prone to damage during handling. Storing and handling grain that is too dry can affect the grading of your grain, as well as your harvest revenues.
Principle of propane drying
As presented on the Ontario Ministry of Agriculture, Food and Agri-Business and Ministry of Rural Affairs (OMAFRA) website, to dry 1,134 kg of wet corn to 25% with a standard continental cross dryer, you'll need 34 L of propane. This will remove 134 kg of water, or 10% moisture (25%-15%).
Approximate fuel consumption values for drying one tonne of corn in a continuous cross-flow dryer. Source: OMAFRA
Drying phase
Contrary to popular belief, drying is not a linear process. In other words, if we plot the drying process on a graph, we'll find a curve (phase 3) where the closer we get to the target moisture content (14%-15%), the longer the drying time. This is easily explained by the distribution of moisture in the grain. At the start of the drying process, surface moisture quickly leaves the grain. But when the aim is to extract moisture from the center of the grain, the water needs more time to migrate outwards.
Grain drying can be defined in 3 main stages:
Heating
Surface drying
Deep drying
During the heating phase (phase 1), the dryer gradually heats the grain to transpiration temperature. Once reheated, the grain will transpire strongly, enabling rapid and efficient drying.
The surface drying stage (phase 2) is marked by a drying plateau. In fact, the drying plateau represents the maximum speed at which the dryer can extract water. In other words, the drying speed is the limit of your dryer.
Then comes the deep drying phase (phase 3), where drying efficiency gradually decreases.
The green curve represents grain moisture,
while the blue curve represents the speed at which the corn dries.
How to reduce drying costs?
The last ⅓ of moisture costs the ⅔ of drying costs.
Do you know a grower with a bin dryer? Has he ever said to you, “In the end, it just doesn't finish finishing!” That's perfectly normal. Because the last 1/3 of moisture takes much longer. because you have to give the moisture in the center of the grain time to migrate to the surface.
Although the graph above is not exactly to scale, by dividing the height of the curve into 3 parts, the last ⅓ of the drying process comes almost halfway through the full drying period. We can well imagine that the drying process is far from constant, and that it takes a long time to finish. So what happens if your grain passes through your dryer at a constant speed?
Well, if you measure the air coming out of your dryer, you'll notice that the air at the bottom is still dry. This means that your dryer is not 100% efficient. For this reason, dryer manufacturers add air recirculation to the bottom of the dryer. You'll save 15% in energy!
Harvest Early and Save Big!
Contrary to popular belief, leaving corn in the field to dry out is not a good idea. A study* conducted in Nebraska over 5 years shows a systematic yield loss of 9 bushels per acre (0.6 t/ha) when harvesting is delayed. With corn at $250/t, we're talking about $134/ha. Food for thought!
This loss can be explained by several factors, such as :
by shelling on the nose of the threshing machine
Grain breathing
Cobs on the stalk
Mould growth
Pests such as insects and animals
In our climate, the longer we wait for grain to dry in the field, the later the season, and the colder it gets. Which also means your propane costs will rise. For example, if the average temperature drops by 10 degrees Celsius, you'll need more propane to heat the air mass drawn into the dryer. This means a 15% increase in consumption.
Calculation of the additional energy consumption cost:
Plenum temperature: 176 degrees Fahrenheit => 80 degrees Celsius
Warm average temperature: 15 degrees Celsius
Cold average temperature: 5 degrees Celsius
Additional drying cost: (80 - 5) / (80 - 15) = 1.15%
A clean dryer for optimal performance
It's not uncommon to see a build-up of bran on the top of continuous dryers. But did you know that this dirt prevents your dryer from breathing properly? In fact, although this dirt may be light, it can be responsible for a loss of efficiency of up to 10%!
A good practice is to clean your dryer every 3 days. Or at least, as soon as you notice an accumulation of fine particles on the top of the dryer. How do you do it? Simply wash the top section with a pressure washer. Just give it a quick blast to loosen the dirt and clean the dryer's pores. Don't worry, a few drops of water won't moisten your grain - it's already sweating!
*Phantom Yield Loss in Corn - A Five-Year Nebraska Field Study, Written by John Mick, Pioneer Agronomy Sciences, site web: site web: https://www.pioneer.com/us/agronomy/phantom-yield-loss-corn.html
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