FREEZING AND MULTI-STAGE FREEZING METHOD USING GAS AS REFRIGERANT

Abstract

A freezing method using a gas as a refrigerant, comprising: step 1: using a colorless, tasteless, and non-toxic liquid gas or supercritical gas as a refrigerant for freezing; step 2: immersing a product to be frozen in the liquid gas or the supercritical gas until the center temperature of the product to be frozen reaches the temperature of a freezing stage; and step 4: taking out the product to be frozen and transferring it to a frozen storage low temperature environment for storing. A multi-stage freezing method using a gas as a refrigerant, comprising: step 1: dividing the freezing process for a product to be frozen into at least two freezing stages; step 2: sequentially performing freezing operations corresponding to each of the freezing stages on the product to be frozen; and step 3: transferring, after balancing the pressure of the product to be frozen with the atmospheric pressure, the product to be frozen to the frozen storage low temperature environment for storing.

Claims

1. A freezing method using gas as refrigerant, comprising the following steps: Step 1: cooling the refrigerant down to a predetermined immersion temperature, wherein the refrigerant is a colorless, odorless and non-toxic liquefied gas or supercritical gas, and said immersion temperature is lower than a frozen stage temperature of a food product to be frozen; Step 2: immersing the food product into the liquefied gas or supercritical gas, until a central temperature of the food product reaches the frozen stage temperature; when performing step 2, performing temperature-controlled refrigeration cycles to the liquefied gas or supercritical gas so that the liquefied gas or supercritical gas is always maintained at the predetermined immersion temperature, and also imposing pressure consistently to the liquefied gas or supercritical gas so that the liquefied gas or supercritical gas is always maintained in a liquefied or supercritical condition; Step 3: after the central temperature of the food product reaches the frozen stage temperature, separating the food product from the liquefied gas or supercritical gas, causing a pressure of the food product to be balanced with atmospheric pressure, and finally taking out and transferring the food product into a low temperature environment for freeze storage.

2. The method of claim 1, wherein before transferring the food product into the low temperature environment for freeze storage in step 3, applying ice coating on the food product after the food product is taken out.

3. A multi-stage freezing method using gas as refrigerant, comprising the following steps: Step 1: dividing a freezing process of a food product to be frozen into at least two freezing stages; determining a frozen stage temperature of each of the freezing stages; preparing a kind of colorless, odorless and non-toxic liquefied gas or supercritical gas for each freezing stage as the refrigerant of the respective freezing stage; and cooling each refrigerant of each freezing stage into a stage immersion temperature predetermined for the respective freezing stage, wherein the stage immersion temperature of each freezing stage is lower than the frozen stage temperature of the same respective freezing stage and higher than the frozen stage temperature of a next freezing stage; Step 2: based on a temperature sequence of the frozen stage temperatures of the freezing stages, performing freezing procedures of the food product in the freezing stages in sequential order, wherein after the freezing procedures in one freezing stage is finished, the food product is transferred to the next freezing stage for a next stage of freezing procedures in the refrigerant used in the next freezing stage, until all freezing procedures of all freezing stages are finished; the freezing procedures are as follows: immersing the food product into the refrigerant of a current freezing stage, until a central temperature of the food product reaches the frozen stage temperature of the current freezing stage; after that separating the food product from the refrigerant of the current freezing stage; when performing the freezing procedures, performing temperature-controlled refrigeration cycles to the refrigerant of the current freezing stage so that the refrigerant of the current freezing stage is always maintained at the predetermined stage immersion temperature of the current freezing stage, and also imposing pressure consistently to the refrigerant of the current freezing stage so that the refrigerant of the current freezing stage is always maintained in a liquefied or supercritical condition; Step 3: when all the freezing procedures of all the freezing stages are finished, causing a pressure of the food product to be balanced with atmospheric pressure, and finally transferring the food product into a low temperature environment for freeze storage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0036] The present invention will be further described in detail below with reference to some embodiments.

Embodiment 1

[0037] Liquefied carbon dioxide is used as the refrigerant for immersion freezing. The immersion temperature of the refrigerant is set to be 50 C. The frozen stage temperature of the food product to be frozen is 18 C. The current embodiment comprises the following steps:

[0038] Step 1: cooling the liquefied carbon dioxide down to 50 C.;

[0039] Step 2: filling a freeze tank with the cooled liquefied carbon dioxide; immersing the food product into the liquefied carbon dioxide, until a central temperature of the food product reaches 18 C.; when performing step 2, performing temperature-controlled refrigeration cycles to the liquefied carbon dioxide so that the liquefied carbon dioxide is always maintained at 50 C. (in actual practice, due to various constraints such as the refrigeration apparatus being used, the temperature actually maintained may differ, and a difference within a range of 5 C. will be normally considered an acceptable range of difference), and also imposing a working pressure of 3.0 MPa consistently to the liquefied carbon dioxide so that the liquefied carbon dioxide is always maintained in a liquefied condition;

[0040] Step 3: after the central temperature of the food product reaches 18 C., separating the food product from the liquefied carbon dioxide, causing a pressure inside the freeze tank to be balanced with atmospheric pressure, and then opening the freeze tank, and finally taking out and transferring the food product into a low temperature environment for freeze storage.

[0041] Further, before transferring the food product into the low temperature environment for freeze storage in step 3, applying ice coating on the food product taken out from the freeze tank after taken out.

Embodiment 2

[0042] Supercritical air is used as the refrigerant for immersion freezing. The immersion temperature of the refrigerant is set to be 65 C. The frozen stage temperature of the food product to be frozen is 60 C. The current embodiment comprises the following steps:

[0043] Step 1: cooling the supercritical air down to 65 C.;

[0044] Step 2: filling a freeze tank with the cooled supercritical air; immersing the food product into the supercritical air, until a central temperature of the food product reaches 60 C.; when performing step 2, performing temperature-controlled refrigeration cycles to the supercritical air so that the supercritical air is always maintained at 65 C. (in actual practice, due to various constraints such as the refrigeration apparatus being used, the temperature actually maintained may differ, and a difference within a range of 5 C. will be normally considered an acceptable range of difference), and also imposing a working pressure of 5.2 MPa consistently to the supercritical air so that the supercritical air is always maintained in a supercritical condition;

[0045] Step 3: after the central temperature of the food product reaches 60 C., separating the food product from the supercritical air, causing a pressure inside the freeze tank to be balanced with atmospheric pressure, and then opening the freeze tank, and finally taking out and transferring the food product into a low temperature environment for freeze storage.

Embodiment 3

[0046] Liquefied carbon dioxide is used as the refrigerant for immersion freezing. The immersion temperature of the refrigerant is set to be 50 C. The frozen stage temperature of the food product to be frozen is 18 C. The current embodiment comprises the following steps:

[0047] Step 1: cooling the liquefied carbon dioxide down to 45 C.;

[0048] Step 2: filling a freeze tank with the cooled liquefied carbon dioxide; immersing the food product into the liquefied carbon dioxide, until a central temperature of the food product reaches 18 C.; when performing step 2, performing temperature-controlled refrigeration cycles to the liquefied carbon dioxide so that the liquefied carbon dioxide is always maintained at 45 C. (in actual practice, due to various constraints such as the refrigeration apparatus being used, the temperature actually maintained may differ, and a difference within a range of 5 C. will be normally considered an acceptable range of difference), and also imposing a working pressure of 3.0 MPa consistently to the liquefied carbon dioxide so that the liquefied carbon dioxide is always maintained in a liquefied condition;

[0049] Step 3: after the central temperature of the food product reaches 18 C., separating the food product from the liquefied carbon dioxide, causing a pressure inside the freeze tank to be balanced with atmospheric pressure, and then opening the freeze tank, and finally taking out and transferring the food product into a low temperature environment for freeze storage.

[0050] Further, before transferring the food product into the low temperature environment for freeze storage in step 3, applying ice coating on the food product taken out from the freeze tank.

Embodiment 4

[0051] Supercritical air is used as the refrigerant for immersion freezing. The immersion temperature of the refrigerant is set to be 55 C. The frozen stage temperature of the food product to be frozen is 50 C. The current embodiment comprises the following steps:

[0052] Step 1: cooling the supercritical air down to 55 C.;

[0053] Step 2: filling a freeze tank with the cooled supercritical air; immersing the food product into the supercritical air, until a central temperature of the food product reaches 50 C.; when performing step 2, performing temperature-controlled refrigeration cycles to the supercritical air so that the supercritical air is always maintained at 55 C. (in actual practice, due to various constraints such as the refrigeration apparatus being used, the temperature actually maintained may differ, and a difference within a range of 5 C. will be normally considered an acceptable range of difference), and also imposing a working pressure of 5.2 MPa consistently to the supercritical air so that the supercritical air is always maintained in a supercritical condition;

[0054] Step 3: after the central temperature of the food product reaches 50 C., separating the food product from the supercritical air, causing a pressure inside the freeze tank to be balanced with atmospheric pressure, and then opening the freeze tank, and finally taking out and transferring the food product into a low temperature environment for freeze storage.

Embodiment 5

[0055] Supercritical nitrogen is used as the refrigerant for immersion freezing. The immersion temperature of the refrigerant is set to be 60 C. The frozen stage temperature of the food product to be frozen is 55 C. The current embodiment comprises the following steps:

[0056] Step 1: cooling the supercritical nitrogen down to 60 C.;

[0057] Step 2: filling a freeze tank with the cooled supercritical nitrogen; immersing the food product into the supercritical nitrogen, until a central temperature of the food product reaches 55 C.; when performing step 2, performing temperature-controlled refrigeration cycles to the supercritical nitrogen so that the supercritical nitrogen is always maintained at 60 C. (in actual practice, due to various constraints such as the refrigeration apparatus being used, the temperature actually maintained may differ, and a difference within a range of 5 C. will be normally considered an acceptable range of difference), and also imposing a working pressure of 3.5 MPa consistently to the supercritical nitrogen so that the supercritical nitrogen is always maintained in a supercritical condition;

[0058] Step 3: after the central temperature of the food product reaches 60 C., separating the food product from the supercritical nitrogen, causing a pressure inside the freeze tank to be balanced with atmospheric pressure, and then opening the freeze tank, and finally taking out and transferring the food product into a low temperature environment for freeze storage.

Embodiment 6

[0059] Supercritical air is used as the refrigerant. The freezing process is divided into two freezing stages. The stage immersion temperatures of the two freezing stages are 55 C. and 105 C. respectively, and the corresponding frozen stage temperatures of the two freezing stages are in sequence 50 C. and 100 C. respectively. The current embodiment comprises the following steps:

[0060] Step 1: dividing the freezing process of a food product to be frozen into two freezing stages; wherein the frozen stage temperature of the first freezing stage is 50 C., and the frozen stage temperature of the second freezing stage is 100 C.;

[0061] Step 2: preparing a portion of supercritical air for each freezing stage as the refrigerant of the respective freezing stage; cooling the refrigerant of the first freezing stage to 55 C., and cooling the refrigerant of the second freezing stage to 105 C.;

[0062] Step 3: filling a freeze tank with the cooled refrigerant of the first freezing stage; immersing the food product into the refrigerant of the first freezing stage, until a central temperature of the food product reaches 50 C.; during the first freezing stage, performing temperature-controlled refrigeration cycles to the refrigerant of the first freezing stage so that the refrigerant of the first freezing stage is always maintained at 55 C. (in actual practice, due to various constraints such as the refrigeration apparatus being used, the temperature actually maintained may differ, and a difference within a range of 5 C. will be normally considered an acceptable range of difference), and also imposing a working pressure of 5.2 MPa consistently to the refrigerant of the first freezing stage so that the refrigerant of the first freezing stage is always maintained in a supercritical condition;

[0063] Step 4: when the central temperature of the food product reaches 50 C., separating the food product from the refrigerant of the first freezing stage, and then filling the freeze tank with the cooled refrigerant of the second freezing stage, immersing the food product into the refrigerant of the second freezing stage, until the central temperature of the food product reaches 100 C.; during the second freezing stage, performing temperature-controlled refrigeration cycles to the refrigerant of the second freezing stage so that the refrigerant of the second freezing stage is always maintained at 105 C. (in actual practice, due to various constraints such as the refrigeration apparatus being used, the temperature actually maintained may differ, and a difference within a range of 5 C. will be normally considered an acceptable range of difference), and also imposing a working pressure of 5.2 MPa consistently to the refrigerant of the second freezing stage so that the refrigerant of the second freezing stage is always maintained in a supercritical condition;

[0064] Step 5: after the central temperature of the food product reaches 100 C., separating the food product from the refrigerant of the second freezing stage, causing a pressure inside the freeze tank to be balanced with atmospheric pressure, and then opening the freeze tank, and finally taking out and transferring the food product into a low temperature environment for freeze storage.

Embodiment 7

[0065] Supercritical nitrogen and liquefied nitrogen are used as refrigerants. The freezing process is divided into four freezing stages. The stage immersion temperatures of the four freezing stages are 50 C., 100 C., 145 C., and 193 C. respectively, and the corresponding frozen stage temperatures of the four freezing stages are in sequence 45 C., 95 C., 140 C., and 190 C. respectively. The current embodiment comprises the following steps:

[0066] Step 1: dividing the freezing process of a food product to be frozen into four freezing stages; wherein the frozen stage temperature of the first freezing stage is 45 C., the frozen stage temperature of the second freezing stage is 95 C., the frozen stage temperature of the third freezing stage is 140 C., and the frozen stage temperature of the fourth freezing stage is 190 C.;

[0067] Step 2: preparing a portion of supercritical nitrogen for each of the first three freezing stages as the refrigerants of the respective freezing stages, and preparing a portion of liquefied nitrogen for the fourth freezing stage as the refrigerant of the fourth freezing stage; cooling the refrigerant of the first freezing stage to 50 C., cooling the refrigerant of the second freezing stage to 100 C., cooling the refrigerant of the third freezing stage to 145 C., and cooling the refrigerant of the fourth freezing stage to 193 C.;

[0068] Step 3: filling a freeze tank with the cooled refrigerant of the first freezing stage; immersing the food product into the refrigerant of the first freezing stage, until a central temperature of the food product reaches 45 C.; during the first freezing stage, performing temperature-controlled refrigeration cycles to the refrigerant of the first freezing stage so that the refrigerant of the first freezing stage is always maintained at 45 C. (in actual practice, due to various constraints such as the refrigeration apparatus being used, the temperature actually maintained may differ, and a difference within a range of 5 C. will be normally considered an acceptable range of difference), and also imposing a working pressure of 3.6 MPa consistently to the refrigerant of the first freezing stage so that the refrigerant of the first freezing stage is always maintained in a supercritical condition;

[0069] Step 4: when the central temperature of the food product reaches 45 C., separating the food product from the refrigerant of the first freezing stage, and then filling the freeze tank with the cooled refrigerant of the second freezing stage, immersing the food product into the refrigerant of the second freezing stage, until the central temperature of the food product reaches 95 C.; during the second freezing stage, performing temperature-controlled refrigeration cycles to the refrigerant of the second freezing stage so that the refrigerant of the second freezing stage is always maintained at 100 C. (in actual practice, due to various constraints such as the refrigeration apparatus being used, the temperature actually maintained may differ, and a difference within a range of 5 C. will be normally considered an acceptable range of difference), and also imposing a working pressure of 3.6 MPa consistently to the refrigerant of the second freezing stage so that the refrigerant of the second freezing stage is always maintained in a supercritical condition;

[0070] Step 5: when the central temperature of the food product reaches 95 C., separating the food product from the refrigerant of the second freezing stage, and then filling the freeze tank with the cooled refrigerant of the third freezing stage, immersing the food product into the refrigerant of the third freezing stage, until the central temperature of the food product reaches 140 C.; during the third freezing stage, performing temperature-controlled refrigeration cycles to the refrigerant of the third freezing stage so that the refrigerant of the third freezing stage is always maintained at 145 C. (in actual practice, due to various constraints such as the refrigeration apparatus being used, the temperature actually maintained may differ, and a difference within a range of 5 C. will be normally considered an acceptable range of difference), and also imposing a working pressure of 3.6 MPa consistently to the refrigerant of the third freezing stage so that the refrigerant of the third freezing stage is always maintained in a supercritical condition;

[0071] Step 6: when the central temperature of the food product reaches 140 C., separating the food product from the refrigerant of the third freezing stage, and then filling the freeze tank with the cooled refrigerant of the fourth freezing stage, immersing the food product into the refrigerant of the fourth freezing stage, until the central temperature of the food product reaches 190 C.; during the fourth freezing stage, performing temperature-controlled refrigeration cycles to the refrigerant of the fourth freezing stage so that the refrigerant of the fourth freezing stage is always maintained at 193 C. (in actual practice, due to various constraints such as the refrigeration apparatus being used, the temperature actually maintained may differ, and a difference within a range of 5 C. will be normally considered an acceptable range of difference), and also imposing a working pressure of 3.6 MPa consistently to the refrigerant of the fourth freezing stage so that the refrigerant of the fourth freezing stage is always maintained in a liquefied condition;

[0072] Step 7: after the central temperature of the food product reaches 190 C., separating the food product from the refrigerant of the fourth freezing stage, causing a pressure inside the freeze tank to be balanced with atmospheric pressure, and then opening the freeze tank, and finally taking out and transferring the food product into a low temperature environment for freeze storage.

[0073] The present invention is illustrated and described by using the above embodiments and their alternative configurations. However, it should be understood that various changes and modifications are possible provided that they are not deviated from the scope of the spirit of the present invention. Therefore, it should be understood that, the present invention is only limited by the claims and their equivalents, and should not be otherwise limited no matter in what sense.