Method and apparatus for drying iron ore pellets

DETAILED DESCRIPTION OF THE INVENTION The present invention functions to improve drying at the top of the pellet bed by blowing at least one counter-current jet of hot air downwardly into the pellet bed.
The downwardly directed jet impinging against the top of the pellet bed in the updraft drying zone (UDZ) of the furnace has a higher flow velocity than the upward current of air.
The jet will thus overcome for an instant the upward movement of air in the air current, but because the upward movement of air is continuous, the downward jetting of air will not interfere with, i.
e.
, stop, the upward movement of air.
Each jet of air emerges from a slot typically about 3 inches above the pellet bed.
The impingement of the air jet against the pellets has a very noticeable effect compared to the current of air that is drawn through a bed of pellets as will be understood by those skilled in the art.
For one thing, it removes the boundary layer of gas at the surfaces of the pellets in the upper layers of the bed.
The following description focuses on the removal of water from the top portion of a pellet bed.
The invention is described by way of example, beginning with the first phase of a standard travelling grate furnace in solving some problems that occur in the updraft drying zone (UDZ) of a pelletizing furnace.
It will be assumed that the conveyorized furnace has 8-foot wide conveyor pallets and five windboxes 8 feet by 8 feet in the UDZ, for a total drying zone 40 feet long.
The pellets are assumed to have a mean diameter of 3/8 inch and a water content of 10%.
The jet action is provided by a series of slotted supply pipes or other type ducting installed across the top of the pellet bed.
Above the first windbox, the supply pipes are spaced as close to each other as practical, e.
g.
, three pipes per foot.
Each pipe or duct has a 3/8" to 1/241 wide slot or jet opening extending its entire length.
Each slot is on the bottom to enable hot air to be directed downwardly onto the pellet bed.
Each pipe is typically about 3 inches above the top of the pellet bed