SPIRAL FREEZER WITH PRECOOLER

Abstract

A freezer includes a housing having a space therein for receiving a cryogenic gas, and an inlet and an outlet in communication with the space; a conveyor belt having an outer edge and being arranged for movement through the space for transferring a product from the inlet through to the outlet; a solid longitudinal member disposed in the space adjacent the outer edge for segregating the space into an upper chamber and a lower chamber; and a transfer duct operatively associated with the housing and having a first opening in communication with the upper chamber for receiving the cryogenic gas from the upper chamber and a second opening in communication with the lower chamber for expelling the cryogenic gas into the lower chamber.

Description

BACKGROUND

The present embodiments relate to spiral freezers and related processes wherein a cryogen gas is introduced into the freezer for chilling or freezing of products such as for example food products.

Exhaust gas from known cryogenic freezing systems is removed as waste and therefore typically 100% of the energy in the exhaust gas is wasted. Spiral freezing systems operate in an isothermal manner (at a constant temperature) and therefore, gas exhausted is usually at the operating temperature of the spiral freezer. This exhaust gas is usually at a temperature of −80° F. (−62.2° C.) to −120° F. (−84.4° C.).

It would therefore be desirable to use the exhaust gas of a spiral freezer or other type of freezer to capture gas for additional refrigeration for more efficient use of the freezer.

SUMMARY OF THE INVENTION

The present inventive embodiments described below include a precooler apparatus, which may be integrated with the existing spiral or other type of freezer, to utilize exhaust gas from the freezer to precool a product such as a food product, before entering the main or actual freezing chamber. Such construction and method provides efficiency gains for the freezer, e.g. less nitrogen (N₂) gas is used in the freezer without diminishing the freezer's capacity.

The present inventive embodiments can be used with a cryogen such as for example liquid or gaseous carbon dioxide (CO₂) or nitrogen (N₂).

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present inventive embodiments, reference may be had to the following drawing FIGURE taken in conjunction with the description of the embodiments, of which:

The FIGURE is a partial cross-sectional view of a spiral freezer having a precooler for the freezer of the present embodiments.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the FIGURE, a spiral freezer with precooler apparatus is shown generally at 10. The freezer 10 includes a housing 12 with a chamber 14 arranged therein for receiving a drum 16 for rotational movement within the chamber. The drum 16 is rotated about an axle 18 to which it is mounted; the axle connected to a drive mechanism 20 (such as a motor) mounted external to the housing 12. A conveyor belt 22 having an outer edge 23 or periphery is arranged for rotational movement in a spiral configuration about the drum 16. The conveyor belt 22 may be of the continuous type as shown in the FIGURE. The housing 12 includes an inlet 24 at a 26 side of the housing, and an outlet 28 at another side 30 of the housing. The inlet 24 and outlet 28 may optionally be disposed at opposed sides of the housing. The conveyor belt 22 is constructed and arranged with respect to the chamber 14 to introduce products 32, such as food products, through the inlet 24 in the direction of the arrows 34 into the chamber where the products are chilled or frozen for being removed from the chamber through the outlet 28.

A baffle 36 is disposed in the chamber 14 for segregating the chamber into an upper freezing zone 38 above the baffle, while the area below the baffle is a lower precooling zone 40. The freezing zone 38 occupies approximately seventy percent (70%) of the chamber 14, while the precooling zone occupies approximately thirty percent (30%) of the chamber, for example.

A cryogen, such as a cryogenic liquid or gas, for example nitrogen (N₂) or carbon dioxide (CO₂), is provided to the chamber 14 through the pipes 42,44 as indicated by the arrows 46,48, respectively. Each of the pipes 42,44 includes a respective valve 50,52 for controlling introduction of the cryogen into the chamber 14. If a cryogen liquid 46,48 is used such liquid will usually change phase into a gaseous form upon introduction into the chamber 14. By way of example only reference herein may be to a cryogenic gas, due to the phase change.

The conveyor belt 22 can be a mesh or solid construction, and can be formed from plastic, metal or a combination of both.

The housing 12 is provided with a precooling zone exhaust duct 54 constructed and arranged for example at the first side 26 proximate the inlet 24, and a freezing zone exhaust duct 56 constructed and arranged for example at the other side 30 proximate the outlet 28.

A transfer duct 58 is constructed and arranged with respect to the housing 12 to transfer the cryogenic gas 46,48 in the freezing zone 38 to the precooling zone 40 by circumventing the baffle 36. The baffle 36 is of solid construction, i.e. no cryogen gas is permitted to pass through the baffle. A fan 60 is disposed for rotational movement within the transfer duct 58 to draw the cryogenic gas 46,48 from the freezing zone 38 through the transfer duct into the precooling zone 40. The transfer duct 58 may be a pipe mounted to the sidewall 30, or may be integrally formed as part of the sidewall.

The baffle 36 is arranged in the chamber 14 so as not to interfere with the rotational movement of the drum 16 and the conveyor belt 22, and the continuous return arrangement of the belt between the zones 38,40.

A controller 62 is electronically connected as shown by the broken line 64 to the valves 50,52 and the fan 60. This arrangement permits the controller 62 to signal for the necessary flow rate of the cryogenic gas 46,48 to be introduced into the freezing zone 38 of the chamber 14 by controlling the openings of the valves and the speed of the fan 60.

The apparatus 10 prevents air or atmosphere external to the housing 12 from entering the inlet 24 and the outlet 28 by injecting 100% of the total mass flow into the freezing zone 38 and then allowing only 90% of the total mass flow to enter the precooling zone 40. There can always be a given flow rate of cryogen into the chamber 14. The flow rate can be designated as “X” (not shown in the FIGURE). The controller 62 opens or closes valves 50,52 to a specific orifice diameter so that the flow rate of cryogen into the apparatus 10 maintains a setpoint temperature in the upper freezing zone 38. Because the actual position of the control valves 50,52 is known, and the pressure and temperature of the cryogen 46,48 entering through the valves are known, the actually mass flow rate of the cryogen into the apparatus is also known. The controller 62 operates the fan 60 to draw a mass flow rate of 0.9×(90% of X). The fan 60 is operated by a variable speed motor (not shown), so varying the motor speed is directly proportional to the mass flow rate of gas drawn through the transfer duct 58 by the fan. Only 90% of the mass flow is drawn from the upper freezing zone 38 into the lower pre-cooling zone 40, because 10% of the gas must be allowed to exit the system under pressure at the outlet 28 of the apparatus 10. This is to prevent external warm air from entering the freezer apparatus. The remaining 90% of the mass flow, now in the lower precooling zone 40 below the baffle 36 is exhausted from the precooling zone exhaust duct 54 and/or a central exhaust port (not shown). A signal from the controller 62 which controls the variable speed fan 60 in conjunction with the valve 50,52 openings permits the apparatus 10 to maintain the necessary mass volume in the chamber 14. A remaining 10% of the cryogenic gas introduced into the chamber 14 at the freezing zone 38 can be exhausted through the outlet 28.

As the fan 60 draws the cryogenic gas 46,48 from the freezing zone 38 through the transfer duct 58 into the precooling zone 40, the gas comes in contact with the warmer product 32, which has entered the precooling zone from the inlet 24, to remove energy from the food product prior to it entering the freezing zone 38. The cryogenic gas provided from the transfer duct 58 into the precooling zone 40 can now be exhausted at the precooling zone duct 54 at a significantly warmer temperature (approximately −20° F. (−28.8° C.)), thereby increasing the overall efficiency of the apparatus 10. This is because the food product has been precooled in the precooling zone 40 such that a lesser amount of the cryogen gas 46,48 is necessary in the freezing zone 38 in order to reduce the temperature of the food product to that which is needed.

In the Example where the cryogenic gas 46,48 is introduced into the chamber 14 through the pipes 42,44, the gas is at −80° F. (−62.2° C.). There would therefore be a 9%-11% overall cryogen efficiency gained. If the upper freezing zone 38 was operated at −80° F. and the lower precooling zone 40 at −20° F., the following calculation is an Example comparing a conventional isothermal spiral freezer with the present embodiment, as an isothermal spiral freezer would operate and exhaust the gas at −80° F.(−80° F.−(−20° F.) is −60° F.). See the following Example.

Example

Conventional Isothermal Spiral Freezer Exhaust=−80° F.(−62.2° C.)

Dual Zone Precooler Spiral Freezer 10 Exhaust 54=−20° F.(−28.8° C.)

LN₂ Efficiency of Conventional Isothermal Spiral Freezer:

Assume liquid nitrogen @ 30 psig and at a saturated state entering the freezer.

LN₂ heat of vaporization=78.8 Btu/lb., therefore

total potential refrigeration=78.8 (Btu/lb)+0.24 (Btu/lb.*° F.)×ABS(−300−(−80)).

(the delta T or ΔT is =ABS(−320°−(−80°))F

˜0.24 Btu/lb.*° F. (specific heat of nitrogen gas).

˜ΔT=ABS(−300−(−80)), where −300° F.=Temp. of liquid nitrogen entering freezer, and −80° F.=Exhaust temp of gas exiting freezer.

78.8 Btu/lb.+0.24 (Btu/lb.*° F.)×(220)=131.6 Btu/lb.

LN₂ Efficiency of Dual Zone Precooler Spiral Freezer 10:

Assume liquid nitrogen @ 30 psig and at a saturated state entering the freezer.

90% of exhaust gas leaves freezer through exhaust duct 54 of precooler zone 40 at a temperature of −20° F.

10% of exhaust gas leaves freezer through exhaust duct 56 of freezing zone 38 at a temperature of −80° F.

Therefore, total potential refrigeration is:

$={78.8}_{\left(\mathrm{Btu}/lb\right)}+[\left(0.9\right)\left({\mathrm{.24}}_{\mathrm{Btu}/lb*F}\mathrm{ABS}\left(\text{-}300-\left(\text{-}20\right)\right)\right]+\hspace{1em}\left[\left(0.1\right)\left({\mathrm{.24}}_{\mathrm{Btu}/lb*F}\right)\mathrm{ABS}\left(\text{-}320-\left(\text{-}80\right)\right)\right]={78.8}_{\left(\mathrm{Btu}/lb\right)}+\left[\left(0.9\right)\left({\mathrm{.24}}_{\mathrm{Btu}/lb*F}\right)\left(280\right)\right]+\left[\left(0.1\right)\left({\mathrm{.24}}_{\mathrm{Btu}/lb*F}\right)\left(220\right)\right]={78.8}_{\left(\mathrm{Btu}/lb\right)}+{65.8}_{\left(\mathrm{Btu}/lb\right)}={144.6}_{\mathrm{Btu}/lb.}{144.6}_{\mathrm{Btu}/lb.}/{131.6}_{\mathrm{Btu}/lb.}=1.098\mathrm{or}9.8\%\mathrm{Cryogen}\mathrm{Efficiency}\mathrm{Gain}$

The 9.8% represents the overall increase in the capacity of the cryogen used in the apparatus 10 to absorb heat. This is referred to as the cryogen efficiency. Therefore, for the same mass flow rate of cryogen used in a conventional isothermal spiral freezer and in the dual zone freezer apparatus 10, the present apparatus 10 provides for the cryogenic gas 46,48 to remove 9.8% more heat from the apparatus.

As more cryogen gas 46,48 is introduced into the upper freezing zone 38, the controller 62 will increase the speed of the fan 60 which will increase the mass flow of cryogen into the lower precooling zone 40. The fan 60 is controlled by the controller 62 to pull or draw the cryogenic gas at a higher volumetric flow rate.

The baffle 36, in conjunction with the transfer duct 58, prevents the gas 46,48 in the freezing zone 38 from indiscriminately entering the precooling zone 40, by directing the gas to and through the duct 58 in a controlled flow depending upon the temperature to be used in the precooling zone.

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.

Claims

1. A freezer apparatus, comprising:

a housing having a space therein for receiving a cryogenic gas, and an inlet and an outlet in communication with the space;

a conveyor belt having an outer edge and being arranged for movement through the space for transferring a product from the inlet through to the outlet;

a solid longitudinal member disposed in the space adjacent the outer edge of the conveyor belt for segregating the space into an upper chamber and a lower chamber; and

a transfer duct operatively associated with the housing and having a first opening in communication with the upper chamber for receiving the cryogenic gas from the upper chamber and a second opening in communication with the lower chamber for expelling the cryogenic gas into the lower chamber.

2. The freezer apparatus of claim 1, further comprising a fan disposed in the transfer duct for moving the cryogenic gas from the upper chamber through the transfer duct into the lower chamber.

3. The freezer apparatus of claim 2, further comprising at least one passageway in communication with the upper chamber for introducing the cryogenic gas into the upper chamber, and a valve interposed in the at least one passageway for regulating flow of the cryogenic gas to the upper chamber.

4. The freezer apparatus of claim 3, further comprising a controller in communication with the valve and the fan for generating a signal to control the valve and the fan to regulate an amount of the cryogenic gas introduced into the upper chamber and a flow rate of the cryogenic gas.

5. The freezer apparatus of claim 1, further comprising a drum disposed in the space and having an exterior surface around which the conveyor belt moves.

6. The freezer apparatus of claim 1, wherein the conveyor belt comprises a surface area selected from the group consisting of a solid surface and a mesh surface.

7. The freezer apparatus of claim 1, wherein the transfer duct comprises a pipe mounted to a sidewall of the housing or optionally formed integral with the sidewall.

8. The freezer apparatus of claim 1, further comprising a first exhaust in communication with the lower chamber, and a second exhaust in communication with the upper chamber.

9. The freezer apparatus of claim 1, wherein the conveyor belt is arranged in a continuous loop.

10. The freezer apparatus of claim 1, wherein a pressure of an upper atmosphere in the upper chamber and another pressure of a lower atmosphere in the lower chamber are greater than an ambient pressure external to the housing.

11. The freezer apparatus of claim 1, wherein the cryogenic gas comprises at least one of nitrogen or carbon dioxide.