Airflow key to in-bin drying

This two-year project on canola and wheat found that adding supplemental heat to natural air drying (NAD) systems can be a lower-capital alternative to dedicated heated-air dryers, but careful management is required to keep operating costs comparable to that of a dedicated dryer system.

First year trials, using bench-scale test bins, compared the effect of air flow rate on supplemental heating with NAD compared to NAD without added heat.

Second year trials assessed the rate of drying with supplemental heat at three different temperature increases.

All trials were planned to occur in mid-late fall to ensure the ambient conditions were representative of conditions where supplemental heating is typically used. Moisture content, grain weights, and grain temperature data from each bin were recorded for the six treatments (three airflow rates and two temperatures). Ambient temperature and humidity data were averaged for the three standard bins at the fan intake as well as for the three bins with supplemental heat.

First year results indicated that adding 10°C of heat when ambient conditions are cool and damp will increase the drying rate, as long as the airflow rate is at a minimum of one cubic foot per minute per bushel (cfm/bu.) and sufficient to move the moisture all the way through the grain bulk. Airflow rate has an impact on drying rate, particularly for wetter grain. Airflow rate will depend on the type of fan used, the density of the grain and grain depth within the bin. (If airflow is too low, consider removing some grain from the bin.)

The trials also showed that over-drying at the bottom of the bin may not be avoidable, therefore an average dry moisture should be targeted, followed by mixing the grain.

Second year trials showed that a 10°C increase in temperature is adequate as long as the result is a plenum temperature of greater than 5°C. However, if sub-zero ambient conditions are being experienced for prolonged periods of time, then higher temperature increases would be required. Based on the observed rates of drying for both canola and wheat in the trials, supplemental heating with a NAD system may not be suitable for starting grain moisture contents more than three percentage points above “dry” because an increased risk of spoilage is possible. Careful monitoring or reduced grain bed depths can help mitigate this risk if a heated-air dryer is not available.

Fuel comparison. The study included an economic assessment of supplemental heating with various fuel types. It found that fuel type has the greatest impact on operating costs. Natural gas has lower cost than diesel and propane, however, access to natural gas can be capitally hindering in certain regions. Estimated efficiencies for NAD systems with supplemental heat range from 50 to 75 per cent compared to efficiencies of 40 to 55 per cent for dedicated heated-air drying systems.