The present invention relates generally to apparatus adapted for use in transporting material through a heat exchange zone so as to bring the material in heat exchange contact with a heat exchange gas and, more particularly, to a substantially horizontal pellet cooler/dryer apparatus of the type employing an endless traveling grate conveyor wherein an improved support tray design is provided for carrying the pellets as they are conveyed through the heat transfer zone.
Applicant's assignee manufactures an apparatus, commonly known as a horizontal pellet cooler, wherein pellets of material such as animal food or other granular products are passed through a heat exchange zone on a endless traveling grate conveyor so as to contact the hot pellets received from the discharge of a pellet mill in contact with a cooling gas which is typically ambient air. An example of such a horizontal pellet cooler is presented in commonly assigned U.S. Pat. No. 4,344,524 of Glenn H. Flack and James R. Boose. As disclosed therein, the conventional horizontal pellet cooler generally consists of a housing defining a heat transfer chamber wherein there is positioned a substantially horizontally disposed endless traveling grate conveyor which may consist of one or more chains extending about a drive sprocket and an idler sprocket disposed in spaced relationship. A plurality of perforated metal carriers are mounted to the conveyor in juxtaposed relationship about the path of the conveyor chain to form an endless conveying belt having an upper surface which is used as the pellet carrying side, a descending turn-around end disposed about one sprocket, a substantially horizontal lower surface which serves as the return run, and an ascending turn-around portion disposed about the other sprocket. Hot, moist pellets are distributed on the perforated metal carriers forming the upper surface of the conveyor, and are cooled and dried as air is drawn through the perforations in the carrier tray as the pellets pass through the heat exchange chamber. The diameter of the perforations is selected to be smaller than the nominal size of the pellets being conveyed.
Recently, it has become a not uncommon practice in the production of animal feed pellets to spray coat the hot pellets discharged from the pellet mill with animal fat prior to passing same to the cooler. In the perforated tray type conveyors described hereinbefore, a problem has arisen in that the animal fat which has been sprayed on the hot pellets causes partial or complete blinding of the holes in the perforated trays. As a result, the air flow passing in heat exchange contact with the pellets as they traverse the cooler is reduced thereby resulting in improper cooling and increased maintenance to clean the trays.
One solution to the problem of the clogging of the air holes in such perforated trays with the animal fat is to provide solid, that is non-perforated, trays to carry the fat coated pellets through the heat exchanger of the pellet cooler. The use of such solid trays would reduce maintenance by eliminating the need to clean the fat clogged or partially blocked holes in the perforated trays. However, the use of solid trays presents the problem of insuring proper air flow through the pellets carried on the trays by providing appropriate gaps between adjacent trays while at the same time providing the air flow gaps in such a manner that the pellets do not fall through these large openings.