Technology for monitoring and control of air flows inside metal silos during grain storage

Introduction. Preservation of grain crops in flat-bottomed metal silos is not possible without monitoring and control of air flows in the internal volume. In the silos with uncontrolled air flows, there is a redistribution of moisture and additional moistening of the grain surface layer that leads to losses of about 2% of grain. The aim of this work is to develop a technology for preventing the grain surface layer from humidifying during storage in metal silos. Materials and Methods. Under laboratory conditions, aerodynamic parameters of wheat and soybean grains were determined in the range of filtration rates less than 0.15 m/s. In metal silos, with a capacity of 2,000, 3,000 and 10,000 t, the temperature and relative humidity of the air inside at the top of the silos and outside were measured simultaneously. The temperature and relative humidity measurement period was 30 min for two and five months. Autonomous recorders were used for measurement. Results. A new objective standard of grain ventilation is proposed - minimum (critical) filtration rate, which ensures moisture removal outside the silo. The analytical studies produced an equation for calculating the weighted average filtration rate of air leaving the grain mass. The total air flow rate corresponding to the weighted average filtration rate will provide a filtration rate of at least critical over the entire surface and will exclude moisture settling. The periods of air saturation with moisture up to 100% in the supervisory space under the roof of the silo have been determined experimentally. The mechanism of heat emission up to the silo roof space from the depth of grain mass during storage has been clarified. Discussion and Conclusion. The algorithm for safe active ventilation of grain and roof space in metal silos is proposed. Limit values of relative humidity of atmospheric air are recommended, the use of which will exclude humidification of grain mass when ventilating actively in the range of temperature difference between grain and atmosphere up to 30 °С and more. The obtained data can be used by mechanical engineers in the manufacture of metal silos and by grain producers in the operation of the said silos.