IMPROVED FUMIGATION OF PARTICULATE COMMODITIES

摘要

When fumigating a bulk particulate commodity stored in a top-vented vertical silo (10) by slowly passing a gas containing a low concentration of a gaseous fumigant through the bulk mass, differences between the temperature, Tg, in the bulk mass (11) and the ambient temperature, Ta, outside the silo cause a "chimney effect" within the silo, and possible unwanted dilution of the fumigant. The chimney effect also occurs in other top-vented storage structures containing particulate commodities. To overcome the chimney effect, the fumigant-containing gas is supplied through a duct (18) to the base of the storage structure at a flow rate Qf (in m<3> sec<-1>) determined by the relationship (I) where g is the acceleration due to gravity (approximately 9.8 m sec<-2>); Pa is the atmospheric pressure expressed in Pascals; Ra is the gas constant for air (= 287 J kg<-1> K<-1>); Ta is in K; Tg is also in K; R is a resistance factor (in Pascals sec m<-2>) which depends upon the nature of the commodity in the storage structure; and A is the horizontal cross-sectional area of the storage structure, in square metres. This technique can also be used to maintain effective fumigation of a plurality of storage structures in a storage facility, from a single source of gaseous fumigant.