An investigation into the drying of oilseeds using ambient air and solar energy

Abstract

The generalized drying equation is developed by studying the characteristics of rapeseed for drying air temperature throughout a range of 30-60° C, an airflow range of 0.21 to 0.53 m³(s m²)⁻¹ and an initial moisture content range of 14 to 25% (d.b.).

The low-temperature Morey equilibrium drying model is modified using a generalized drying equation which is employed to analyse natural, supplemental and heated air drying.

The feasibility of natural air drying of oilseed rape is evaluated employing the modified equilibrium drying model. The two types of strategies of continuous fan and fan on when RH≤70% are used with both the hourly data for the years of 1968, 1971 and 1974 and average hourly data for 1960 to 1980. Complete drying down to 10% moisture content (w.b.) is achieved for rapeseed of up to 18% (d.b.) using all the airflow rates, initial moisture contents and of environmental data years. It has been shown that substantial energy saving is possible by using the strategy of switching the fan on when RH≤70%. It is observed that the average hourly data can be used if the real hourly data are not available.

The modelling of a single cover solar heat collector to accept the hourly ambient and radiation data to simulate the performance and predict the output is presented. The algorithm based on the 24-hour temperature rise required is developed to match the size of the collector to drying load. The feasibility of achieving complete drying using these models at the airflow rate of 180 m³(h m²)⁻¹ is also presented using historical hourly data for the harvesting seasons of 1968, 1971 and 1974. It has been shown that the amount of energy saved and the probability of achieving complete drying down to the safe storage moisture content of 10% (w.b.) are increased by employing the strategy of fan on when RH≤70% in solar assisted ambient air drying. The extra drying potential available in the ambient air when RH≤70% is used for energy saving when the solar collector is not operating.

The effect of drying on the physical properties and resistance to airflow are investigated for the moisture content range of 6.46 to 19.63% (d.b.). The relationships between the physical properties and the moisture content are presented. Drying air temperatures of up to 60° C have been shown to have no effect on the germination capacity of rapeseed at moisture contents of up to 24.98% (d.b.).