Miller Magazine Issue: 131 November 2020

58 COVER STORY MILLER / November 2020 equilibrium is achieved and maintained. Forced fumi- gant recirculation creates overpressure in the bottom of a structure and under-pressure towards the top of the structure. Both pressure differences lead to leakage. Fu- migators realize the leakage (e.g. smell the gas around the fumigated area) and often stop recirculation to lim- it the leakage. Interruption of the recirculation leads to immediate equilibrium loss and leaves areas of the grain untreated. Figure 4 is a good illustration of all this. Use of wireless sensors has proved that gas concentra- tion varies between higher and lower points in a stack fumigation too. Phosphine is heavier than air and moves near the floor while higher areas get lower readings. The day-night fluctuation is observed in stack fumigations, especially when these happen in a warehouse lacking temperature control. Sometimes even forced recirculation is not enough to achieve gas equilibrium. Density differences in the prod- uct mass direct air currents through the easiest paths, leaving some parts of the mass with less gas (Figure 5). Plan a fumigation - or predict it? Good planning has always been part of successful fu- migation. But nowadays Artificial Intelligence and Indus- try 4.0 models allow the fumigator to predict the treat- ment and make adjustments in a virtual environment, even before opening a fumigant flask! Fumigation algo- rithms take into consideration multiple inputs given by Figure 5: Even with gas recirculation on from the beginning of the treatment, this fumigation never reaches full equilibrium in a 3000-ton metal silo.