Parallel flow cryogenic freezer

Abstract

.Iadd.A cryogenic freezer for freezing products comprising an elongated horizontal tunnel, a conveyor extending therethrough, a liquid cryogenic spray at the outlet end of the conveyor, a plurality of substantially closed gas recirculating flow paths in series relationship along the length of the tunnel and individual fans in each recirculating flow path for causing gas contact with product being conveyed through the tunnel. .Iaddend.

What is claimed is: 
     
       1. A method for ultra-fast freezing of products with a cryogenic refrigerant including the steps of: (a) continuously moving said product to be frozen through an insulated tunnel along a predetermined path;   (b) continuously contacting said product with a cryogenic liquid in said tunnel to freeze the product while vaporizing the cryogenic liquid to form a cold gas;   (c) continuously collecting said cold gas resulting from said vaporization in a portion of said tunnel;   (d) continuously recirculating the major portion of said collected gas through a substantially closed path at least one-half of which closed path is parallel to and coincident with said predetermined path along a substantial extent thereof;   (e) continuously adding cold gas resulting from newly vaporized cryogenic liquid to said recirculation path;   (f) continuously removing some of said recirculated gas from said closed path in an amount which is substantially equal to the amount of cold gas continuously added to said recirculation path;   (g) maintaining the velocity of said recirculated gas in said closed path sufficient to cause turbulent flow of the gas in contact with said food product;   (h) collecting a minor portion of said cold gas in a reservoir immediately adjacent the outlet of said tunnel;   (i) detecting the level of said cold gas in said reservoir; and   (j) regulating the amount of recirculated gas which is removed from said substantially closed path as a function of said detected level.   
     
     
       2. The method as claimed in claim 1 wherein the step of continuously contacting said product with a cryogenic liquid comprises the step of spraying said product with liquid nitrogen. 
     
     
       3. A cryogenic freezer for ultra-fast freezing of products comprising: insulated wall means forming an elongated tunnel, conveyor means having at least one reach extending through the interior of said tunnel for conveying a food product through said tunnel, means positioned in said tunnel for contacting said food product with a cryogenic liquid whereby said product is frozen and substantially all of said liquid is vaporized to form a refrigerant gas, first and second partition means extending through different portions of said tunnel parallel to and in series along the length of said conveyor, said first and second partition means dividing said tunnel into respective first and second pairs of gas-product contact passages and gas return passages, the passages of each pair being in communication with each other at the ends of the respective partition means so as to form individual first and second recirculation paths located in series along said conveyor reach between the tunnel and said means for contacting the product with liquid, first passage means for continuously conducting newly generated refrigerant gas into said first recirculation path, second passage means for conducting some of the recirculated gas from said first path into said second path, third passage means for conducting some of the recirculated gas from said second path, and blower means for recirculating refrigerant gas through each of said substantially closed paths at a velocity sufficient to produce turbulent flow of the refrigerant gas in contact with the product on said conveyor reach. 
     
     
       4. The freezer as claimed in claim 3, wherein said blower means comprise first and second blowers respectively positioned in said first and second paths and wherein said second blower has a greater capacity in terms of cubic feet of gas moved per unit time than said first blower whereby a portion of said gas is drawn from said first path into said second path. 
     
     
       5. A freezer for ultrafast freezing of products with a cryogenic refrigerant comprising: insulated wall means forming an elongated tunnel, conveyor means having at least one reach extending through the interior of said tunnel for conveying a product through said tunnel, means positioned in said tunnel for contacting said product with cryogenic liquid whereby said product is frozen and substantially all of said liquid is vaporized to form a refrigerant gas, means in said tunnel forming a gas-product contact chamber, first passage means for conducting refrigerant gas into said chamber, second passage means for removing refrigerant gas from said chamber, flow control means in said second passage means for controlling the amount of refrigerant gas removed from said contact chamber, means forming a reservoir of refrigerant gas adjacent the product outlet end of said tunnel, means for detecting the level of refrigerant gas in said reservoir and producing a signal indicative of said level, and means actuated by said signal for regulating said flow control means. 
     
     
       6. The freezer as claimed in claim 5 wherein said gas-product contact chamber includes partition means extending through a substantial portion of said tunnel parallel to the direction of movement of said conveyor reach to form a recirculation path, and blower means for recirculating refrigerant gas through said path at a velocity sufficient to produce turbulent flow of the gas in contact with the product. 
     
     
       7. A cryogenic freezer for ultra-fast freezing of products comprising: insulated wall means forming an elongated tunnel, conveyor means having at least one reach extending through the interior of said tunnel for conveying a food product through said tunnel, means positioned in said tunnel for contacting said food product with a cryogenic liquid whereby said product is frozen and substantially all of said liquid is vaporized to form a refrigerant gas, partition means extending through a substantial portion of said tunnel parallel to the direction of movement of said conveyor reach dividing said tunnel into a gas-product contact passage surrounding said conveyor reach and a gas return passage, said contact and return passages being in communication with each other at the ends of said partition means to form a substantially closed recirculation path wholly within said insulation wall means, first passage means for continuously conducting newly generated refrigerant gas into said recirculation path zone, second passage means for continuously removing recirculated gas from said recirculation path, and blower means for recirculating said gas through said recirculation path at a velocity sufficient to produce turbulent flow of the refrigerant gas in contact with the product on said conveyor reach, said recirculation path being positioned between the tunnel inlet and said means for contacting the product with liquid, said blower means being positioned inside said insulated wall means forming said tunnel, said blower having an inlet in direct communication with one of said passages and an outlet in direct communication with the other of said passages whereby said gas is recirculated through said path and blower means wholly within the confines of said insulated wall means forming said tunnel. 
     
     
       8. The freezer as claimed in claim 7 wherein said blower comprises a centrifugal blower having flat, non-curved, radially extending blades for minimizing the effect of frost accumulation on said blades. .[.9. A cryogenic freezer for ultra-fast freezing of products with a cryogenic liquid comprising: (a) insulated wall means forming an elongated, horizontally extending tunnel having an inlet and an outlet;   (b) conveyor means having at least one reach extending through the interior of said tunnel for conveying a product to be frozen through said tunnel from said inlet to said outlet;   (c) means forming a liquid-product contact zone in said tunnel, said means including conduit means for introducing a cryogenic liquid refrigerant into said tunnel in contact with said product on said conveyor for freezing said product and vaporizing said liquid to form a refrigerant gas;   (d) passage means forming a plurality of distinct, substantially closed, recirculation paths for independently recirculating said refrigerant gas in each of said paths, said recirculation paths being adjacent each other in series along the length of said conveyor for successfully contacting the product on the conveyor with the gas recirculating in each path, all of said recirculation paths being positioned between said tunnel inlet and said liquid-product contact zone;   (e) passage means for conducting newly generated refrigerant gas from said liquid-product contact zone into the recirculation path adjacent thereto;   (f) passage means for conducting portions of the refrigerant gas from each recirculation path to the next recirculation path closer to said tunnel inlet such that the average temperature of the gas in each path increases in the direction of the tunnel inlet;   (g) passage means for exhausting a portion of the refrigerant gas from the recirculation path closest to said tunnel inlet; and   (h) gas flow producing means for recirculating the refrigerant gas in each of said recirculation paths at a velocity sufficient to produce turbulent   
     
     
        flow of the refrigerant gas in contact with the product..]. .[.10.  The cryogenic freezer as claimed in claim 9 wherein the gas flow producing means for each recirculation path have unequal flow capacities for producing flow of portions of refrigerant gas from one recirculation path to the next in the direction toward the tunnel inlet..]. .[.11. The cryogenic freezer as claimed in claim 9 further including means forming a reservoir of cold, dense refrigerant gas adjacent said tunnel outlet for producing a fluid seal against entrance of ambient air into the tunnel and against the exit of refrigerant gas through said tunnel outlet..]. .[.12. The cryogenic freezer as claimed in claim 9 wherein the flow of refrigerant gas in at least two of said plurality of recirculation paths is parallel to the direction of product movement along a substantial portion of said conveyor reach..]. .[.13. The cryogenic freezer as claimed in claim 12 including means for increasing and decreasing the volume of refrigerant gas flowing through said exhaust passage means, and means for sensing an operating condition of the freezer remote from said exhaust passage whereby said volume of exhausted gas is adjusted in accordance therewith..]. .Iadd. 14. A cryogenic freezer for ultra-fast freezing of products with a cryogenic liquid comprising: (a) insulated wall means forming an elongated, horizontally extending tunnel having an inlet and an outlet;   (b) conveyor means having at least one reach extending through the interior of said tunnel for conveying a product to be frozen through said tunnel from said inlet to said outlet;   (c) means forming a liquid-product contact zone in said tunnel, said means including conduit means for introducing a cryogenic liquid refrigerant into said tunnel in contact with said product on said conveyor for freezing said product and vaporizing said liquid to form a refrigerant gas;   (d) passage means forming a plurality of distinct, substantially closed, recirculation paths for independently recirculating said refrigerant gas in each of said paths, said recirculation paths being adjacent each other in series along the length of said conveyor for successfully contacting the product on the conveyor with the gas recirculating in each path, all of said recirculation paths being positioned between said tunnel inlet and said liquid-product contact zone;   (e) passage means for conducting newly generated refrigerant gas from said liquid-product contact zone into the recirculation path adjacent thereto;   (f) passage means for conducting portions of the refrigerant gas from each recirculation path to the next recirculation path closer to said tunnel inlet such that the average temperature of the gas in each path increases in the direction of the tunnel inlet;   (g) passage means for exhausting a portion of the refrigerant gas from the recirculation path closest to said tunnel inlet; and   (h) gas flow producing means for recirculating the refrigerant gas in each of said recirculation paths at a velocity sufficient to produce turbulent flow of the refrigerant gas in contact with the product, said gas flow producing means for each recirculation path having unequal flow capacities for producing flow of portions of refrigerant gas from one recirculation path to the next in the direction toward the tunnel inlet. .Iaddend.   
     
     
        .Iadd. 15.  The cryogenic freezer as claimed in claim 14 wherein the flow of refrigerant gas in contact with the product in at least two of said plurality of recirculation paths is parallel to the direction of product movement along a substantial portion of said conveyor reach. .Iaddend..Iadd. 16. The cryogenic freezer as claimed in claim 15 including means for increasing and decreasing the volume of refrigerant gas flowing through said exhaust passage means, and means for sensing an operating condition of the freezer remote from said exhaust passage whereby said volume of exhausted gas is adjusted in accordance therewith. .Iaddend.