(a) Field of the Invention
This invention relates to pneumatic conveyor systems for conveying substantially dry materials over very long distances.
(B) Description of the Prior Art
Conventional pneumatic pipe conveyor systems transport materials in suspension by means of a high-velocity air stream. The principal uses for such pipe conveyor systems are for the transport of materials such as granular cork, bran, carbon black, copra, grain, wood chips, and saw dust. One such known system for transporting pulverized materials consists of a motor-driven pump and of a source of compressed air for fluidizing the material. The material itself is fed from a bin or hopper into a pump mechanism which is of the screw type. Compressed air is admitted from a cylindrical manifold into the discharge end of the screw, thus changing the material into a semi-fluid substance before allowing it to enter the transport line. The greatest present use of such a system is believed to be for transporting bulk cement.
Such a system is obviously restricted as to the types of materials that can be transported, especially over long distances. Since this system depends upon suspension of the materials in a high-velocity air stream, serious limitations are imposed due to pressure drop especially over long distances. Heavier materials fall out of the air stream and gradually cause pressure surges and clogging of the transport duct. As would be expected, the known systems operate more efficiently through straight runs and do not easily tolerate sharp bends and vertical sections.
Due to the required high-velocity air stream, the conventional systems also create severe dust problems at the discharge end of the conduit, thus requiring dust collectors which add to the expense of the system. Even the suction type of pneumatic conveyor also requires a dust collector at its discharge end.
Various other conveyor systems have been proposed in the patent literature, such as a pipeline having an impervious outer pipe and a porous inner pipe. However, the initial leakage of air pressure from and through the entire annulus into the porous transport pipe places a severe limitation on the length of the pipeline that can be used. For this reason such proposed systems have not been commercially acceptable.