Simultaneous monitoring of stored grain with relative humidity, temperature, and carbon dioxide sensors

Grain moisture content (MC) and temperature (T) are the primary factors affecting grain deterioration in storage. If these factors are not properly monitored and controlled, grain quality can deteriorate quickly due to mold growth and insect infestation. This research examined use of relative humidity (RH), T, and carbon dioxide (CO₂) sensors for their suitability to determine adverse storage conditions of wheat. A mock-up storage system was constructed and used to simulate a wheat storage bin 6.86 m high. Sensors for T, RH, and CO₂ measurement were placed at various depths in the storage. High-moisture grain, comprising about 11% of the grain volume, was placed in the top section of the bin. Wheat was aerated with the high-moisture grain conditioned to nominal MCs of 14%, 16%, and 18% wet basis (MC_wb) and the remaining grain at approximately 11% MC_wb. Sensors monitored air conditions during the entire storage period. Aeration was provided over 3-h periods at rates of 0.083 m³/min/tonne (eight experiments) and 0.166 m³/min/tonne (one experiment). Airflow was from top to bottom of the bin. CO₂ sensors were effective in indirectly detecting moist grain conditions due to the large amount of CO₂ generated from the wet grain. CO₂ measurement was less effective as grain temperature was reduced as a result of aeration. CO₂ levels monitored at the exhaust of the aeration duct were generally adequate in determining adverse storage conditions. The equilibrium moisture content (EMC) of wheat, determined from RH and T, gave reasonably accurate measurements of grain MC. EMC measurements were also effective in determining moisture changes in the grain due to the moisture front movement from the high-moisture grain.