Patent GB-1139701-A (GB)
Title: Method and apparatus for flash freezing various products
IPC: F25D3/11
Filed: 1966-01-21
Abstract: 1,139,701. Refrigerators. INTEGRAL PROCESS SYSTEMS Ino. 21 Jan., 1966 [15 Sept., 1965], No. 2899/66. Addition to 1,029,254. Heading F4H. Articles conveyed along a path through a process chamber are sprayed with liquid nitrogen at a first region and part of the gas generated is recirculated to the chamber to establish a flow of mixed fresh and returned gas and, in a second region upstream of the first to establish a transverse flow of returned gas. As illustrated in Fig. 1 articles are passed on conveyers through a process chamber formed by a main chamber 4 and entrance and exit tunnels 2 and 6, and are cooled by liquid nitrogen fed to sprays 18 through a pipe 20 including a valve controlled by a temperature senser 42. Gas is withdrawn by a fan 26 and is in part recirculated to the spraying region through pipes 34 and in part passed through a pipe 36 to form gas curtains at the chamber entrance and exit and to feed pipes 64 admitting gas to the tops of the entrance and exit tunnels. Gas is withdrawn from the bottoms of the entrance and exit tunnels by a fan 74 and together with gas passed from the fan 26 through a pipe 76 is wasted through a pipe 78. The main process chamber, the entrance and exit tunnels, and the pipes 20 and 36 are of double walled construction and are connected to a vacuum pump 54. The entrance and exit tunnels may be provided with gates at one or both ends to allow isolation of the tunnels during shutdown and start up periods. In another embodiment (Fig. 3), articles are conveyed through a chamber 101 and are sprayed with liquid nitrogen from a pipe 108. A fan 128 withdraws fresh gas from the chamber as indicated at 131 and also withdraws gas from a plenum 120 communicating through openings 120R with an intermediate region of the chamber. The withdrawn gases are passed by the fan through a duct 128D to establish a gas curtain across the exit end of the chamber and to feed a plenum 119 communicating with the intermediate region through adjustable nozzles 119N. A further fan 123 recirculates gas through an upstream region of the chamber between plenums 117, 118 having adjustable nozzles 117N and inlet openings 118R respectively. Part of the output of fan 123 is wasted through a valve controlled duct 126 to cause a migration of gas as indicated at 132 from the intermediate to the upstream region. The fan 123 also establishes a gas curtain across the entrance end of the chamber. The conveyer 102 is of open mesh construction and liquid nitrogen is sprayed from below as well as above the conveyer, Fig. 4 (not shown). The liquid nitrogen is sprayed at a rate in excess of that required for flashing and excess liquid is collected in a tray (110) for recirculation to the sprays. The chamber is operated at substantially atmospheric pressure and top up liquid nitrogen is supplied through a valve controlled pipe (116) to the tray ( 110) to give additional flashing. The chamber has an annular insulation space (105) which is evacuated. Insulated end pieces 106 and 107 are provided. Articles suitable for freezing in the apparatus are listed and operating temperatures are disclosed.