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Supplemental Heating for Grain Storage

The fall of 2016, when an October snowfall followed by cool temperatures forced producers to come up with creative solutions for drying grain, is a cautionary tale that bears repeating as we head into harvest 2017. Spoiler alert: grain has to be managed as intensively when it is stored in the bin, as when it is being seeded and harvested.

It was a perfect storm last year, a unique combination of moisture and temperature that we might only see once every 10 or 15 years. Crops were coming off tough and producers who did not own grain-drying systems quickly discovered there were none available to rent. By November, many delivery points were full, so on-farm storage was the only option, but temperatures were too low to achieve safe storage moisture levels using natural air drying.

The solution for many producers was supplemental heating for stored grain, basically rigging their bin aeration systems with heaters in an attempt to lower the moisture to optimal levels. Increasing the temperature of the air dramatically increases its capacity to dry, but adding heat is a solution that carries big risks.

First, there is the safety issue. It goes without saying that any temporary heating system has the potential to result in damage or injury. The bigger risk, however, is that supplemental heating is tricky and can cause more harm than good.

Based on the information that is available today, which is dated and largely anecdotal based, it appears that the temperature window for effective supplemental heating is very narrow. To fill in this information gap, the Prairie Agricultural Machinery Institute, also known as PAMI (an organization providing innovative agriculture solutions) has a research proposal in the works that will be addressed later in this article, but what we know for sure is that hotter is not always better.

Building on what we know today, here are some basic recommendations for improving results and reducing risk when using supplemental heat:

  1. The air moving through the bin needs to be at least 10° Celsius for optimal drying potential, and should not exceed 20° Celsius to avoid high grain temperatures that can initiate spoilage.
  1. Use a fan with an airflow rate of at least 0.75 cubic feet per minute (CFM) per bushel. Anything lower could result in heating of the grain, which can initiate spoilage.
  1. Air flow can be improved by under filling the bin and leveling the cone, thereby reducing the static pressure and increasing airflow from the fan.
  1. Check that there is adequate ventilation at the top of the bin to allow moist air to escape.
  1. Rotate the bin’s contents frequently by removing at least one-third from the bottom and auguring it back in the top.
  1. Monitor the contents of the bin constantly.
  1. The size of the heater should be based on the desired temperature increase (which depends on the ambient temperature and the target temperature of between 10° and 20° Celsius) and the airflow rate from the fan.

Key to effective supplemental heating is ensuring that there is sufficient airflow through the bin. By way of comparison, a dedicated grain drying system is designed to provide 20-30 CFM of airflow per bushel of grain, while aeration systems, intended to cool and condition grain in the bin, generate anywhere from 0.1-1 CFM per bushel. Bin aeration systems simply do not have the capacity to move enough air through the bin for effective drying without heated air.

Insufficient airflow creates the potential to cook the grain closest to the heat source, while on the other side of the bin, spoilage from condensation in the headspace can reduce the quality of the grain to the point where it becomes worthless. To add insult to injury, the producer will then have to incur the cost of disposing of the lost crop. When you consider that a 5,000-bushel bin of canola could be worth $50,000, ineffective supplemental heating could jeopardize most or all of the year’s profit.

It all comes down to ensuring that the natural air-drying (NAD) system, with or without added heat, has an appropriately sized fan. In my discussions with producers about supplemental heating, the rule of thumb to achieve 1 CFM per bushel, the target airflow rate for NAD, is to use a fan that provides one horsepower for every 1,000 bushels of grain. To check the validity of this rule, we put it to the test in 18 scenarios with various grain types, grain depths and fan types, and here are the results: one hp/1,000 bushels provided 1 CFM per bushel only four times out of 18; and that, in my opinion, is not a passing grade.

So if one hp/1,000 bushels doesn’t work in most cases, what does?

The process of selecting the fan that will produce the best results is not an easy one. The airflow rate from fans of varying sizes depends on static pressure, a measure of the resistance to airflow, and static pressure is determined by four factors: the type of grain in the bin (the smaller the grain, the smaller the spaces between seeds that allow for air movement), the depth of the grain in the bin, the airflow rate produced by the fan, and the type of bin ducting.

These are not easy calculations to do, but they are necessary in order to reduce or prevent crop loss in the bin after a wet harvest season like we had in 2016. For a step-by-step explanation of the process, you can find a video entitled Selecting Fans for Grain Conditioning and Natural Air Drying on the crop storage page of the PAMI website (pami.ca).

As I mentioned earlier in this article, PAMI is proposing to expand the knowledge base around supplemental heating with natural air-drying with research into best management practices. The project has a number of objectives, all designed to help producers use supplemental heating without increasing damage to grain.

We will first scientifically determine how supplemental heat affects the drying rate and storage conditions of wheat and canola. It is important to note that while wheat and canola were chosen for the trial, the physics of drying applies to all types of grain.

Several kinds of heating systems are currently available and more are being introduced every year, but there has been little scientific evaluation of their efficiency. The information gained in the PAMI study will provide a baseline for evaluating economic factors, such as the number of fans and heater hours needed to establish good storage conditions. It will also improve the understanding of why the narrow temperature window for effective drying is so important, and thereby help producers make adjustments to their processes in an informed way.

A second objective is to determine the economic benefits of using supplemental heating with natural air-drying systems. We will look at both fixed and variable costs, and provide a comparison between managing damp grain with natural air drying only, heated air drying in a dedicated drying system, and natural air drying with supplemental heat using various fuel types.

Natural gas and propane are the most common fuels, but costs can range from $0.50-$3/hour for a 5,000-bushel bin, and drying can take one to five days. It is worthwhile considering alternatives; biomass like flax straw, oat hull pellets or wood chips may be more economical and environmentally conscious choices, and should be evaluated for viability.

The third aspect of the study will see us compile and disseminate best management practices for using supplemental heat with natural air drying. Existing information will be combined with new data from the proposed research to generate a list of best practices for managing damp grain stored on farm.

As we learn more about supplemental heat—its effectiveness and economics—there is potential for it to become a management tool producers can use in good years as well as bad. Efficient drying systems could widen the harvest window by allowing producers to avoid adverse weather and take crops off at a higher grade and slightly higher yield, knowing they can dry it in the bin. Research will give us the answers to these, and many other, questions.

By Joy Agnew


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