Optimization of a device for the fumigation process

It has been optimized a device that performs the dried agricultural products disinfestation by fumigation process with phosphine gas. Moreover, it allows to completely exhaust the active principle contained in the pellets of magnesium and aluminium phosphide used in the fumigation process, and to complete the phosphine production process, ordinarily of 5 days, in 2 days. Further, the device results particularly convenient during the fumigation process performed in cold periods; in facts, it is equipped with a pellets heating device that improves the phosphine production. Further it allows the continuous remixing of the pellets during the fumigation process and the control of the humidity by mean of water injection. The prototype is composed of : - cylindrical tray in stainless steel, containing the pellets of magnesium and aluminium phosphide, and it is connected to an electrical heater with a thermostatic device for the tray temperature control; - electric engine for the rotation of the cylindrical tray; - two bars that sustain 5 harmonic steel sheets with the extremity folded up downward with an angle of 90°. Such sheets, thanks to their elasticity, follow the fund of the tray. Besides they are of different length, so that they allow a good remixing. By mean ANSYS code it has been possible also to evaluate the goodness of the performed remixing. - a water sprinkler connected to an electrical valve that performs the environmental hygrometric control. In such way the value of the environmental humidity is kept optimal to have the maximum phosphine production and therefore the considered process results very fast. In the definition of the device geometries it has been used a 3D CAD program: Solid Works. It has allowed to define a parametric model of the considered device. Some experimental tests have been performed to determine the amount of water flow to obtain the optimal humidity value and to avoid dangers of fires caused by the pellets, sprinkling a water quantity ranged from 1/40 to 10 ml for every ¼ of round of the cylindrical tray. Moreover some tests have been performed to determine the optimal heating temperature considering 4 different temperatures: 30, 40, 50, 60 °C, and evaluating the phosphine quantity produced in such conditions. Besides the process of remixing has been optimized, performed by the steel sheets opportunely shaped. All of this has allowed to completely exhaust the magnesium and aluminium phosphide contained in the inlet pellet