Tips for efficient in-bin drying
A recent Alberta study compared grain drying systems on farms throughout the province. Results provide tips to improve fuel-use efficiency and reduce drying time and cost.
Farms can improve the efficiency of in-bin aeration drying systems with heated air, adequate air flow and exhaust fans.
This is based on results from a 2019-21 Alberta study, supported in part by Alberta Barley and the Alberta Wheat Commission, with funding from the Government of Canada and Alberta through the Canadian Agricultural Partnership. PAMI provided technical support while 3D Energy collected the data.
Cooperating farmers ran their drying and storage systems as they normally would. PAMI and 3D Energy compared systems based on energy use intensity, expressed as gigaJoules of energy consumed per tonne of moisture removed (GJ/t).
The final report available at teamalbertacrops.com describes the following considerations to improve fuel-use efficiency and reduce drying time and cost.
Hotter air reduces drying time: It takes a lot more energy to heat air to 30°C than to 10°C, but hotter air dries grain a lot faster. The increase in fuel consumption closely matches the increase in moisture removal, so that part of the equation is fairly even in terms of energy consumption. However, faster drying means the electric fans don’t have to run as long. This gives hotter air the advantage in terms of overall efficiency.
Direct or indirect heat source: In-bin systems can get supplemental heat from direct heaters mounted in-line with the fan or indirect heaters that supply heated air through a tube. PAMI and 3D Energy report that sample size is too low to confirm a difference, but indirect air has the advantage of lower relative humidity because moist exhaust is not included in the air supply.
Heat increases air’s capacity to dry: Air with lower relative humidity has more water holding (and therefore water removing) capacity. Adding heat lowers the relative humidity of incoming air. The report notes that increasing the temperature of the supply air by 30°C can reduce the air’s relative humidity from 100 per cent down to 14 to 16 per cent, which “increases the drying capacity of the air exponentially.”
Target air flow of 1.0 cfm/bu: Air flow for all systems in the study ranged from 0.65 to 1.20 cubic feet per minute per bushel (cfm/bu.). PAMI recommends 1.0 cfm/bu. for drying. Had air flow been well below the optimal target, drying efficiency would be a lot lower.
Adjust bin depth to maintain air flow: Static pressure for canola is higher than for wheat or barley, which is why canola tends to dry more efficiently when the bin is only partly filled. Fill grain to a point where airflow is close to 1.0 cfm/bu.
Add rooftop exhaust fans: For this study, bins with rooftop exhaust fans decreased energy consumption by approximately nine per cent when compared to bins with passive venting.
Energy choices
In all systems, natural gas was the lowest cost heating fuel based on energy used per tonne of moisture removed. Farms that anticipate large volumes of grain drying may want to inquire about a natural gas supply to the bin site. Diesel is the next best option, but it was about four times the price per bushel of grain dried. (Based on 2019 prices, average drying costs were 5¢ per bushel for natural gas systems, 21¢ for diesel and 27¢ for propane. Electricity was similar to propane.) The study concluded that “utilizing electric heating for grain drying should be avoided, as electricity has the highest operating costs and emissions, and would require a large infrastructure investment for service lines and transformers to be capable of the required demand need for grain drying.” Electricity is still needed to run the fans.