Patent Application
20130118202
The present inventive embodiments relate to apparatus and methods for using carbon dioxide (CO2) for chilling and freezing of products.
A large amount of energy is required to be used to compress CO2 gas into its liquid storage state of 280-300 lb. force per square inch gauge (psig). The potential energy of the gas is typically not used in a freezing process. In addition, there can be additional benefits gained from energy extraction via isentropic expansion and with the use of conventional subcooling technologies.
Currently, a maximum achievable cooling potential from saturated bulk stored liquid CO2 used for operating a CO2 freezer at −60 degrees F. (−51° C.) is approximately 125.5 btu/lb. Higher cooling efficiencies can be achieved by employing different freezing processes.
The present embodiments provide a hybrid refrigeration system which includes a cryogen direct injection apparatus and a closed loop mechanical refrigeration apparatus, wherein the mechanical refrigeration apparatus is driven by energy obtained from the cryogen refrigeration apparatus.
For a more complete understanding of the present embodiments, reference may be had to the following drawing figures taken in conjunction with the description of the embodiments, of which:
Referring to
The apparatus 10 may be used with a freezer 18, which includes a housing 15 having an inlet 20 and an outlet 22. An internal space 24 or chamber of the housing 15 may be divided into a plurality of zones as shown by example herein, i.e. Zones I, II, III. Dividers or baffles 25,27 may be disposed in the space 24 to divide the freezer 18 into a plurality of Zones I-III. A conveyor belt 26 for transporting product 28, such as for example food products, extends from the inlet 20 through the Zones I-III, and through to the outlet 22. The cryogen direct injection apparatus 12 is shown disposed in Zone I of the housing 15.
A bulk storage tank 30 contains liquid carbon dioxide (CO2) 32 therein. The storage tank 30 is pressurized. The liquid CO2 32 flows under the effect of pressure from the tank 30 through a pipe 34 into a heat exchanger 36, such as for example a shell and tube heat exchanger. The liquid CO2 flows through the heat exchanger 36 and then into a pipe 38 which is connected to another heat exchanger 40 disposed in Zone II of the freezer 18. A valve 39, such as an expansion valve, is disposed in the pipe 38. The liquid CO2 flows into the heat exchanger 40 which has a discharge outlet 42 connected to a pipe 44 that extends into Zone I.
Referring also to
Referring to
The compressor 50 is connected by a pipe 74 to the condenser 70, wherein the pipe 74 is constructed to provide subcooling within the condenser. Refrigerant is condensed in the condenser 70. A pipe 76 extends from an outlet of the condenser 70 to be connected to an evaporator 78 disposed in the Zone III of the freezer 18. A fan 80 is mounted in the Zone III for operation with the evaporator 78. A valve 82 is disposed in the pipe 76, and such valve can be a mechanical expansion valve.
An outlet of the evaporator 78 is connected to a pipe 84 which extends from the Zone III to be connected to the compressor 50.
Referring to
The liquid CO2 32 flows under the effect of pressure from the bulk storage tank 30 where it was stored at approximately 280 psia and 1.6 degrees F. (−17° C.) through the pipe 34 into the shell and tube heat exchanger 36 as shown by arrows 86. Exhaust gas 88 from freezing which occurs at the Zone II of the space 24 subcools the liquid CO2 in the heat exchanger 36 to a temperature of approximately minus 8° F. (−22.2° C.). The newly subcooled liquid CO2, as shown by arrows 90, moves through the pipe 38 and through the expansion valve 39 where its pressure and temperature are further reduced to 100 psia and minus 60° F. (−51° C.), respectively. This liquid CO2 continues along the pipe 38 into the heat exchanger 40 in the Zone II. The heat exchanger 40 is sized and shaped such that the liquid CO2 experiences a phase change so that it exits said heat exchanger as a gas with a temperature of minus 60° F. (−51° C.) at 100 psia, shown by arrows 92.
The pressurized gas 92 traveling along the pipe 44 enters the annular space 46 of the shaft 48 which causes the fan blade 52 to rotate as indicated by the arrows 56. In effect, the CO2 performs work during the process by driving the fan blades 52 to power the shaft 48, which in turn drives the compressor 50.
The CO2 44 remains pressurized to the point of injection from the nozzles 58 at the ends of the fan blades 52 into the Zone I, and such CO2 gas is discharged at a temperature as low as minus 109° F. (−78.3° C.) and as a gas-snow mixture. The discharge from the nozzles 58 is introduced into the Zone I of the freezer space 24, so as to provide cooling for the freezing process.
Power generated by the rotation of the fan blades 52 drives the compressor 50 as part of the closed-loop mechanical refrigeration apparatus 16. The apparatus 16 therefore does not need a separate motor or power unit to operate and move the cryogen refrigerant through said apparatus. The compressed refrigerant travels from the compressor 50 through the pipe 74 and into the condenser 70. The refrigerant is subcooled in the condenser 70 so that warmer CO2 exhaust gas exits to the atmosphere as indicated by arrows 96 in the pipe 72.
The refrigerant then travels to the pipe 76 and through the expansion valve 82 where its pressure and temperature are lowered. The refrigerant continues to proceed through the pipe 76 into the evaporator 78 which is disposed in the Zone III so as to cool said Zone. The refrigerant then travels from the evaporator 78 through the pipe 84 back through the compressor 50 for the process to continue.
The heat transfer which occurs from the heat exchanger 40 in the Zone II provides the exhaust gas 88 for the heat exchanger 36. The exhaust gas 88 is warmed by the heat exchanger 40 and passes through the pipe 60 where it is at approximately minus 60° F. (−51° C.) to be introduced into the inlet 64 of the heat exchanger 36, wherein the CO2 liquid flow 86 is at a temperature of approximately 1.6° F. (−16.9° C.) on a tube side of the heat exchanger. This provides subcooling of the CO2 liquid stream 86 in the pipe 34 from the storage tank 30 and warming of the CO2 gas stream 88. The CO2 gas stream 88 discharged from the heat exchanger 36 should be at a temperature of approximately minus 30° F. (−34.4° C.).
A plurality of heat transfer processes occur in the present embodiments. The processes contribute to a significantly higher utilization of stored energy and cooling capacity of the CO2. The present apparatus 10 provides for a hybrid freezing assembly, i.e. a closed-loop mechanical refrigeration assembly 16 powered by a cryogen direct injection assembly 12 to chill or freeze products, such as for example food products.
It will be understood that the embodiments described herein are merely exemplary, and that one skilled in the art may make variations and modifications without departing from the spirit and scope of the invention. All such variations and modifications are intended to be included within the scope of the invention as described and claimed herein. Further, all embodiments disclosed are not necessarily in the alternative, as various embodiments of the invention may be combined to provide the desired result.
