(3) Induction System. A compressed air injector is used to produce a partial vacuum on the suction or inlet end of the pipe system, and to produce a pressure above atmospheric at the delivery end, thus avoiding the necessity for a discharger. This system, which is suitable for use with heavy sticky materials—such as hot sugar, saturated sand, finely ground heavy ores, spent oxide as used in gas works, etc.—is now being developed so as to make possible pneumatic conveyance of all manner of materials which are unsuitable for passing through the discharger, or air lock, of a suction system.
Factors influencing Design. In the strict sense of the term, “pneumatic conveying” really implies the conveyance of a quantity of material from one point to another, using air as the conveying agent. As will be seen from the above, the subject also embraces the removal of comparatively light dust produced in many industrial processes. Although the same name is implied in both cases, the methods to be adopted vary, and each case must be considered on its own merits.
With regard to a conveying plant proper, the points for consideration in the initial stages are as follows—
(1) The nature of the material to be handled and the quantity required in a given time.
(2) The size of the largest and smallest pieces of materials and the density of the material.
(3) The distance over which the material is to be conveyed.
(4) The difference in level between the point at which the material is fed into the system, and the point where it is delivered.
(5) The method and regularity of feeding the material into the system.
(6) The means to be adopted for separating the material from the conveying air at the desired point of delivery.
There is a very important distinction between plants in which the material passes through the fan or blower and those in which the conveying is carried out entirely under suction.