Minimum energy to dry barley without mould growth in near ambient driers

Abstract

Dynamic programming methods are used to calculate the minimum energy required by fans and heaters to dry barley without the risk of mould growth, in grain driers using near-ambient air. Minimum values are obtained for moisture contents (dry basis) in the range 0·24–0·34, with airflows of 0·05–0·2 m/s through grain, beds 1, 3 and 5m deep. However not all possible combinations of these parameters are considered; in particular, the extreme cases of large moisture content, deep bed and low airflow are avoided. Weather records for the years 1969–1978 from Turnhouse, near Edinburgh, were used. These minimum values of energy consumption cannot be attained in practice because they require a knowledge of future weather conditions. However, for beds 3 m deep a comparison is made between the minimum values of energy consumption and the values attained with three practical methods of control. No supplementary heat was used in these practical methods of control because it is shown that they cause a large increase in energy consumption and because heaters are not generally recommended in Britain. One of these control methods minimizes average consumption over the years. Another method uses relative humidity to control the drier. It is shown that with both these control methods the energy consumption is approximately 1·05–1·18 times the minimum value. Calculations for a continuous ventilation strategy show that this uses much more energy than the other two methods of control; approximately 1·11–1·54 times the minimum value.