Figure 68  General Gas 13 – Fumigation Closed Loop

The system operates in closed-loop recirculation mode. Typically phosphide pellets are placed on top of the grain in the bin. A fan draws the fumigant-laden air from the top of the bin via the return header, 

It then pushes the air back into the bottom of the bin through the supply header. This creates a continuous upward flow of air with phosphine gas through the grain mass, ensuring uniform distribution and effective fumigation while minimising gas usage and emissions. 


For pressure loss calculation purposes the mixture between air and phosphine behaves essentially as air. All valves to the fresh air inlets remain closed (these are only opened later during the purge phase of the process) and the system is fully isolated and sealed (in closed-loop operation) during the exposure period.


A valve on pipe 14 is used to adjust the system operating performance so that the fan operates close to its BEP (Best Efficiency Point). 

A fitting on pipe 14 has been added to represent this valve. The fitting is named 'DP Set' and has a K factor of 10.