System and method for vapor control in cryogenic freezers

Abstract

A cryogenic freezer with cryogenic vapor control is disclosed. The cryogenic freezer is characterized in that the vapor control system is adapted to control the speed of the transition fan which moves some of the cryogen from a first cryogenic freezer to a second freezer in response to differences between the temperature of the process room, operating temperature of the cryogenic freezer; and a temperature of the exhaust. By adjusting the transition fan speed in response to such temperature differences the vapor control system operates to limit the flow of air from the process room into the freezer and also limits cryogen vapor flow from the freezer to the process room.

1 . A cryogenic freezer system comprising:
 a freezer compartment having an entrance, an exit and a conveyor disposed therein for treating a food product;   a cryogen supply subsystem adapted to provide a cryogen to treat the food product within the freezer compartment;   an exhaust subsystem, including an exhaust fan disposed proximate the entrance of the freezer compartment;   a transition fan disposed proximate the exit of the freezer compartment;   a control subsystem operatively coupled to the cryogen supply subsystem and adapted to control the cryogen introduced into the freezer compartment and the transition fan in response to selected inputs; and   a plurality of temperature sensors coupled as inputs to the control subsystem, said temperature sensors adapted to ascertain a temperature of the process room, an operating temperature of the freezer compartment; and a temperature of the exhaust;
 wherein the control subsystem is adapted to govern the transition fan in response to a temperature difference between the temperature of the process room and the temperature of the exhaust. 
   
   
   
       2 . The system of  claim 1  wherein the control subsystem is further adapted to govern the transition fan in response to the temperature difference between the operating temperature of the freezer compartment and the temperature of the exhaust. 
   
   
       3 . The system of  claim 1  wherein the control subsystem is further adapted to govern the transition fan to maintain the exhaust temperature above 0 degrees Centigrade. 
   
   
       4 . The system of  claim 1  wherein the exhaust subsystem further comprises a plate disposed beneath the conveyor belt proximate the entrance and wherein the plate directs a portion of the cryogen vapor flow within the freezer to the exhaust fan. 
   
   
       5 . The system of  claim 1  wherein the exhaust subsystem further comprises an exhaust pickup and a vapor focusing tunnel disposed proximate the entrance of the freezer wherein the exhaust pickup and vapor focusing tunnel limit the flow of air from a process room into the freezer compartment and further limits cryogen vapor flow from the freezer compartment to the process room. 
   
   
       6 . The system of  claim 1  wherein the exhaust subsystem further comprises an exhaust duct and a flow sensing device disposed in the exhaust duct, said flow sensing device adapted to provide an input to the control subsystem. 
   
   
       7 . The system of  claim 1  further comprising a second freezer compartment adjacent the exit of the freezer compartment and wherein the transition fan is adapted to direct cryogen flow from within the freezer compartment to the second freezer compartment. 
   
   
       8 . The system of  claim 7  wherein the second freezer compartment is a mechanical freezer and the cryogen flow to the second freezer provides a supplemental cryogen refrigeration capacity to the mechanical freezer. 
   
   
       9 . The system of  claim 7  wherein the freezer compartment is a cryogenic tunnel freezer and the second freezer compartment is a spiral freezer. 
   
   
       10 . The system of  claim 1  further comprising a second freezer compartment adjacent the exit of the freezer compartment and wherein the transition fan is adapted to direct cryogen flow from within the freezer compartment to the second freezer compartment or evacuate the cryogen vapor from the cryogenic freezer system in response to commands from the control subsystem. 
   
   
       11 . A method of controlling a cryogenic freezer system comprising the steps of:
 injecting a cryogen into a freezer compartment, said freezer compartment having an entrance, an exit and a conveyor disposed therein for treating a food product;   directing a portion of the cryogen vapors in said freezer compartment via an exhaust fan to an exhaust disposed proximate the entrance to the freezer compartment and directing the remainder of the cryogen vapors in said freezer compartment to a second freezer compartment via a transition fan;   monitoring the operating temperatures associated with the cryogenic freezer system including a temperature of the process room, an operating temperature of the freezer compartment, and a temperature of the exhaust;   controlling the injection of cryogen into the freezer compartment in response to a temperature difference between the temperature of the freezer compartment and the temperature of the exhaust; and   controlling the operation of the transition fan in response to a temperature difference between the temperature of the process room and the temperature of the exhaust.   
   
   
       12 . The method of  claim 11  further comprising the step of controlling the operation of the transition fan in response to a temperature difference between the operating temperature of the freezer and the temperature of the exhaust. 
   
   
       13 . The method of  claim 11  wherein the step of controlling the operation of the transition fan further comprises controlling the transition fan to maintain the exhaust temperature above a prescribed threshold. 
   
   
       14 . The method of  claim 11  wherein the step of directing a portion of the cryogen vapors in said freezer compartment to an exhaust disposed proximate the entrance further comprises directing the cryogen vapors from the freezer compartment to an exhaust pickup and concurrently directing any infiltrating process room air to the exhaust pickup thereby limiting the flow of air into the freezer compartment and limiting cryogen vapor flow from the freezer compartment to the process room.