Cryogenic freezing tunnel

Abstract

A cryogenic food product freezing tunnel comprising a stationary structure including an entrance end housing section, a tunnel housing cover, and an exit end housing section, a conveyor to transport food products through the tunnel housing, a spray header to spray a liquid cryogen onto the food products near the exit end of the tunnel, and an exhaust plenum to exhaust cryogen gas from the entrance end. The base of the tunnel housing is a series of U-shaped modular units arranged end-to-end and suspended from the stationary structure by individual hydraulic elevators, movable between a lowered, open service position and a raised position sealed against the housing cover and the end housing sections. Each end base unit is lowered outwardly and downwardly to its service position and is raised along the same path; the base units are lowered in predetermined sequence, end units before center units, and are raised in the reverse sequence. The base units are held sealed to the stationary structure by constant pressure applied by the elevators, using double-bulb silicone gaskets with bonded polyfluoroethylene coverings. Each base unit includes plural sub-modules joined by shielded external expansion slip joints with a continuous interior sheet metal covering. The cover is of modular construction with polyfluoroethylene coated silicone gaskets of clothes-pin configuration between modules. The spray header is a large tube with liquid discharge nozzles below and gas relief nozzles above; excess liquid cryogen is collected in a very long pan below the header and the upper run of the conveyor belt is guided down and up very mild inclines to skim the surface of liquid cryogen in the pan. Insulated doors on the ends of the tunnel and an automatically controlled exhaust damper permits standby for extended periods. The conveyor belt supports are also of sub-modular construction.