Helical conveyor freezer

Abstract

A food freezer having a thermally insulated enclosure wherein an endless conveyor having a lower loading section, a main helical section and an uppermost unloading section is primarily driven by engagement between its inner edge and the sidewall of a rotatable center cage, which includes a plurality of uniformly spaced apart vertical bars. The lower end of the center cage can be blocked, and a centrifugal blower is axially located at the upper end of the cage to suck gas from the interior of the cage and discharge it horizontally outward along the undersurface of the top wall so that it flows outward, then downward and, finally, radially inward in an overall generally toroidal pattern through the tiers of the helical belt section where it withdraws heat from the freezes the food products being carried therealong. Various arrangements, e.g., adjustable restrictors, are illustrated for creating vertical gradients in the radial inflow of gas through the helical section so that the cold gas flows inward at a greater rate in lower regions of the helical section than in the upper region. Cryogen injection devices for spraying a cryogen, such as liquid CO.sub.2 or liquid N.sub.2, radially inward to impinge upon the food products on the belt, may be located at selected positions about the perimeter and at various vertical levels. Radial inflow of gas adds to the effectiveness of the impinging spray against the food products; however, the overall freezer construction is also advantageously employed with mechanical cooling of the gaseous atmosphere via one or more heat exchange coils.