Apparatus and process for drying granular products

An apparatus for removing moisture from a granular product, said apparatus comprising:

• a drying tank having an enclosing side wall and a tubular portion that is surrounded by the side wall such that a generally annular drying chamber exists between the side wall and the tubular portion, the tubular portion being formed from a material that is transparent to microwave energy and having its interior exposed to and filled with air at substantially atmospheric pressure;
• at least one drying column in the drying cavity of the drying vessel, the drying column being tubular and having walls that are transparent to microwave energy;
• meand for directing a granular product into the upper end of the drying column, whereby the product will descend through the column under the influence of gravity;
• a collecting tank connected to the lower end of the drying vessel for receiving the granular product after it passes out of the drying column;
• means for isolating the interiors of the drying vessel and the collecting tank from the surrounding atmosphere;
• means for evacuating air and other gases from the interiors of the drying vessel and collecting tank;
• a launcher unit located at one end of the tubular portion of the drying vessel, and being capable of producing microwave energy;
• and a waveguide-radiator formed from metal and being in a tubular configuration with one of its ends located at the launcher unit for receiving microwave energy produced at the launcher, the waveguide-radiator extending into the hollow interior of the tubular portion for the vessel and having apertures presented toward the transparent walls of the tubular portion so that microwave energy can escape from the waveguide-radiator and pass through the transparent walls of the tubular portion to dry the granular product in the drying column.

A process for drying a granular product, said process comprising:

• introducing the product into a generally annular drying cavity that is enclosed by walls, two of which are generally concentric, with the inner of the two concentric walls being transparent to microwave energy and having its radially inwardly presented surface exposed to and at the same pressure as the ambient atmosphere;
• evacuating air from that cavity so that the pressure within the cavity is substantially less than atmospheric;
• within a region of substantially atmospheric pressure, generating microwave energy of a frequency capable of exciting molecules of water;
• and while still in the region of atmospheric pressure directing the microwave energy through the transparent wall such that it enters the drying cavity and evaporates moisture from the product.