Development of optimal management schemes for in-bin drying of canola grain (rapeseed)

Abstract

As a management tool in grain drying and storage, a computer drying simulation model was developed, validated and used to investigate in-bin drying of canola grain (rapeseed) under typical weather conditions for a Canadian Prairie location. Different drying schemes with airflows of 0.5 to 2 m 3 min −1 per tonne, initial moisture contents of 13%, 16% and 19%, and three harvest dates in August, September and October were optimized by considering the total annual cost of drying for each scheme within set bounds of drying time (30 and 15 days) and grain spoilage. Continuous fan operation delivering an airflow of 1.0 to 2.0 m 3 min −1 per tonne of grain is adequate to successfully dry canola grain in 30 days or less when the initial moisture content of the grain is lower than or equal to 19% in August and September. Drying of grain in October requires supplemental heat. In September and October, however, supplemental heat must be added to air in order to successfully dry the product in 15 days or less. The drying time is about 50% higher when the drying front is allowed to sweep the entire grain bed (through-dry) as compared to drying grain to a bin average moisture content (average-dry). The combined drying cost and the hidden cost of over-drying grain (loss of weight) makes through-drying 30–100% more costly than average-drying. However, for long-term storage of the grain after drying, it is safer to dry all layers of the bin down to 8% through-dry. Small airflow rates of 0.5 m 3 min −1 per tonne show lesser drying costs but the drying time, risk and over-drying costs associated with these low airflow rates are significantly higher than for larger airflow rates. It is therefore, more economical to dry at airflow rate of 1.0–1.5 m 3 min −1 per tonne to minimize time delay in drying and these costs, especially over-drying cost in the through-dry policy. Amongst supplemental heat options, raising the ambient temperature by 5–10°C and maintaining plenum temperature at 20°C ensured complete grain drying in fall and are the most cost-effective schemes.