Efficient and energy-saving liquid nitrogen circulation refrigerating device

Abstract

The invention discloses an efficient energy-saving liquid nitrogen circulation refrigerating device which comprises a liquid nitrogen storage 1, a heat exchanger 2, a compressor 3 and a turbine expansion refrigerating machine 4. The invention relates to an efficient energy-saving liquid nitrogen circulating refrigerating device, which is integrated equipment for gasifying liquid nitrogen to produce high-pressure gas through heat exchange, driving a turbine expansion refrigerating unit under the pressure pushing of a compressor, or converting nitrogen into 100% liquid by adopting a method of compressing and deeply freezing the nitrogen. Each pipeline is provided with a temperature metering device, a pressure metering device, a flow metering device and the like and uploads the data to the control system, the control system adjusts operation parameters of the system according to monitoring data and carries out collection, the collected data are uploaded to a digital cloud, and the purpose of digital operation and maintenance is achieved.

Description

[0001] An efficient and energy-saving liquid nitrogen circulation refrigeration device comprises the following steps: reducing the temperature of a high-pressure nitrogen gas stream to below its critical temperature, and performing at least two liquid nitrogen cycles to provide at least part of the refrigeration required to reduce the temperature of the high-pressure nitrogen gas to below its critical temperature. Each such liquid nitrogen cycle includes compressing liquid nitrogen, cooling the liquid nitrogen, causing the cooled liquid nitrogen to expand through a turbine, and heat-exchanging and heating the turbine-expanded liquid nitrogen with the high-pressure nitrogen gas stream, so as to provide refrigeration for the high-pressure nitrogen gas stream. The improvement includes: at the completion of each liquid nitrogen cycle, the pressure of the liquid nitrogen is at least 12 atmospheres, wherein the liquid nitrogen forms a heat-exchange relationship with the high-pressure nitrogen gas stream, and the temperature of the liquid nitrogen is lower than the critical temperature of the high-pressure nitrogen gas.

[0002] The method according to claim 1, wherein the pressure is in the range of 12 to 20 atmospheres.

[0003] The method according to claim 2, wherein the temperature of the liquid nitrogen at the completion of turbine expansion is the saturation temperature at the said pressure or a temperature higher than the saturation temperature.

[0004] The method according to claim 1, wherein the high-pressure nitrogen gas below its critical temperature expands through a turbine to form a liquid product.

[0005] The method as claimed in claim 1, wherein the high-pressure nitrogen gas stream below its critical temperature undergoes at least two consecutive isenthalpic turbine expansions to produce a liquid and a flash gas; after each isenthalpic turbine expansion, the resulting flash gas is separated from the resulting liquid, and except for the last one, the liquid from each isenthalpic turbine expansion is the fluid that expands through a turbine in the immediately following isenthalpic turbine expansion, and at least part of the flash gas exchanges heat with the high-pressure nitrogen gas stream.

[0006] The method according to claim 5, wherein there is a single liquid nitrogen cycle, in which the liquid nitrogen forms a heat-exchange relationship with the nitrogen gas stream at a temperature below the critical temperature of nitrogen.

[0007] The method as claimed in claim 1, wherein when at least part of the flash gas exchanges heat with the high-pressure nitrogen gas stream, the temperature of the high-pressure nitrogen gas is lower than the temperature when the liquid nitrogen expanding through a turbine exchanges heat with the high-pressure nitrogen gas stream.

[0008] The method according to claim 1, wherein the liquid nitrogen is derived from the high-pressure nitrogen gas and recombined with it for compression.

[0009] The method according to claim 1, wherein there is a single liquid nitrogen cycle, in which the liquid nitrogen forms a heat-exchange relationship with the high-pressure nitrogen gas stream, and the temperature of the liquid nitrogen is lower than the critical temperature of the high-pressure nitrogen gas.

[0010] When providing refrigeration for a liquefied gaseous nitrogen stream, the following steps are included: reducing the temperature of a high-pressure nitrogen stream below its critical temperature, and performing at least two liquid nitrogen cycles to provide at least a part of the refrigeration required to reduce the temperature of nitrogen below its critical temperature, and then turbine-expanding the nitrogen to form a liquid nitrogen product. Each such liquid nitrogen cycle includes compressing the liquid nitrogen, cooling the liquid nitrogen, turbine-expanding the cooled liquid nitrogen, and performing heat exchange on the turbine-expanded nitrogen stream; the improvement includes the condition that at the end of each liquid nitrogen cycle, the pressure of the liquid nitrogen is at least 12 atmospheres, wherein the liquid nitrogen performs heat exchange with the nitrogen stream, and the temperature of the liquid nitrogen is lower than the critical temperature of nitrogen.

[0011] The method according to claim 10, wherein the pressure is in the range of 12 to 20 atmospheres.

[0012] Claims The method according to claim 11, wherein the temperature of the liquid nitrogen when it completes its work turbine expansion is the saturation temperature at the pressure or a temperature higher than the saturation temperature.

[0013] The method according to claim 10, wherein the nitrogen stream below its critical temperature undergoes at least two consecutive isenthalpic turbine expansions to produce liquid and flash gas; after each isenthalpic turbine expansion, the resulting flash gas is separated from the resulting liquid. Except for the last one, the liquid from each isenthalpic turbine expansion is the fluid turbine-expanded in the connected isenthalpic turbine expansion, and at least some of the flash gas performs heat exchange with the nitrogen stream, and at least some of the flash gas performs heat exchange with the nitrogen stream at a high-pressure nitrogen temperature lower than the temperature at which the liquid nitrogen performing work turbine expansion exchanges heat with the nitrogen stream.

[0014] The method according to claim 13, wherein the first isenthalpic turbine expansion is performed on the stream in the temperature range of 10 to -30 °C.

[0015] The method according to claim 10, wherein in at least one liquid nitrogen cycle for producing liquid nitrogen that performs work turbine expansion at a temperature higher than the critical temperature of nitrogen, the liquid nitrogen has a heat exchange relationship with the nitrogen stream at a temperature higher than the critical temperature of nitrogen.

[0016] The method according to claim 15, wherein in at least one liquid nitrogen cycle, the work turbine expansion of the liquid nitrogen cools the high-pressure nitrogen stream from an ambient temperature or a temperature close to ambient temperature to a temperature in the range of -180 to -196 °C.

[0017] The method according to claim 15, wherein the high-pressure nitrogen stream is also cooled by performing heat exchange with at least one refrigerant stream.

[0018] The method according to claim 10, wherein the liquid nitrogen is also nitrogen gas.

[0019] The method according to claim 10, wherein the nitrogen gas stream is supplied at a pressure of 12 atmospheres or less, and three liquid nitrogen cycles are employed.

[0020] The method according to claim 10, wherein the nitrogen gas stream is supplied at a pressure greater than 12 atmospheres, and two liquid nitrogen cycles are employed.

[0021] The method as claimed in claim 10, wherein in the liquid nitrogen cycle in which the liquid nitrogen causing the working gas to expand exchanges heat with the nitrogen gas stream at a temperature below the critical temperature of the nitrogen gas stream, the liquid nitrogen causing the working gas to expand provides cooling for the nitrogen stream, cooling it from an ambient temperature or a temperature close to ambient temperature to a temperature in the range of -100 to -130 °C.

[0022] The method according to claim 21, wherein only one liquid nitrogen cycle in which the liquid nitrogen causing the gas to expand exchanges heat with the nitrogen stream at a temperature below the critical temperature of nitrogen. Description of the Drawings, Figure 1 is a structural diagram of the present invention, Figure 2 is a flow chart of the present invention.

Claims

1. An efficient and energy-saving liquid nitrogen circulation refrigeration device includes the following steps: The temperature of a high-pressure nitrogen gas stream is reduced below its critical temperature, and at least two liquid nitrogen cycles are performed to provide at least a portion of the refrigeration required to reduce the temperature of the high-pressure nitrogen gas below its critical temperature. Each such liquid nitrogen cycle includes compressing liquid nitrogen, cooling the liquid nitrogen, turbine-expanding the cooled liquid nitrogen, and heat-exchanging and heating the turbine-expanded liquid nitrogen with the high-pressure nitrogen gas stream to provide refrigeration for the high-pressure nitrogen gas stream. The improvement includes that at the completion of each liquid nitrogen cycle, the pressure of the liquid nitrogen is at least 12 atmospheres, wherein the liquid nitrogen forms a heat-exchange relationship with the high-pressure nitrogen gas stream, and the temperature of the liquid nitrogen is lower than the critical temperature of the high-pressure nitrogen gas.

2. The method according to claim 1, wherein the pressure is in the range of 12 to 20 atmospheres. Among them, The temperature of the liquid nitrogen at the completion of turbine expansion is the saturation temperature at that pressure or a temperature higher than the saturation temperature. Wherein, the high-pressure nitrogen gas below its critical temperature is turbine-expanded to form a liquid product. Wherein, the high-pressure nitrogen gas stream below its critical temperature undergoes at least two consecutive isenthalpic turbine expansions to produce a liquid and a flash gas; after each isenthalpic turbine expansion, the resulting flash gas is separated from the resulting liquid, and except for the last one, the liquid from each isenthalpic turbine expansion is the fluid that is turbine-expanded in the immediately following isenthalpic turbine expansion, and at least a portion of the flash gas undergoes heat exchange with the high-pressure nitrogen gas stream.

3. The method according to claim 1, wherein there is a single liquid nitrogen cycle, and the liquid nitrogen forms a heat-exchange relationship with the nitrogen gas stream at a temperature below the critical temperature of nitrogen. When at least a portion of the flash gas forms a heat-exchange relationship with the high-pressure nitrogen gas stream, the temperature of the high-pressure nitrogen gas is lower than the temperature at which the liquid nitrogen that performs work in turbine expansion forms a heat-exchange relationship with the high-pressure nitrogen gas stream. Wherein the liquid nitrogen is derived from the high-pressure nitrogen gas and recombined with it for compression, and there is a single liquid nitrogen cycle, wherein the liquid nitrogen forms a heat-exchange relationship with the high-pressure nitrogen gas stream, and the temperature of the liquid nitrogen is lower than the critical temperature of the high-pressure nitrogen gas.

4. When providing refrigeration for a liquefied gaseous nitrogen stream, the following steps are included: The temperature of the high-pressure nitrogen stream is reduced below its critical temperature, and at least two liquid nitrogen cycles are performed to provide at least a portion of the refrigeration required to reduce the temperature of the nitrogen below its critical temperature, and then the nitrogen is turbine-expanded to form a liquid nitrogen product. Each such liquid nitrogen cycle includes compressing liquid nitrogen, cooling the liquid nitrogen, turbine-expanding the cooled liquid nitrogen, and heat-exchanging the turbine-expanded nitrogen stream; the improvement includes the condition that at the completion of each liquid nitrogen cycle, the pressure of the liquid nitrogen is at least 12 atmospheres, wherein the liquid nitrogen undergoes heat exchange with the nitrogen stream, and the temperature of the liquid nitrogen is lower than... the critical temperature of nitrogen. Wherein the pressure is in the range of 12 to 20 atmospheres.

5. The method according to claim 4, wherein the temperature at which liquid nitrogen completes its work turbine expansion is the saturation temperature at the said pressure or a temperature higher than the saturation temperature. Among them, the nitrogen gas stream below its critical temperature undergoes at least two consecutive isenthalpic turbine expansions to produce liquid and flash gas; after each isenthalpic turbine expansion, the resulting flash gas is separated from the resulting liquid. Except for the last time, the liquid from each isenthalpic turbine expansion is the fluid for turbine expansion in the connected isenthalpic turbine expansion, and at least some of the said flash gas exchanges heat with the nitrogen gas stream, and at least some of the said flash gas exchanges heat with the nitrogen gas stream at a high-pressure nitrogen gas temperature lower than the temperature of the liquid nitrogen for work turbine expansion in the heat exchange relationship with the nitrogen gas stream.

6. The method according to claim 5, wherein the first isenthalpic turbine expansion is carried out on the said stream within a temperature range of 10 to -30 °C. Among them, in at least one liquid nitrogen cycle for producing liquid nitrogen for work turbine expansion at a temperature higher than the critical temperature of nitrogen, liquid nitrogen has a heat exchange relationship with the nitrogen gas stream at a temperature higher than the critical temperature of nitrogen. Among them, in at least one liquid nitrogen cycle, the work turbine expansion liquid nitrogen cools the high-pressure nitrogen gas stream from the ambient temperature or a temperature close to the ambient temperature to a temperature within the range of -180 to -196 °C. And the high-pressure nitrogen gas stream is also cooled by exchanging heat with at least one refrigerant stream.

7. The method according to claim 6, wherein the nitrogen gas stream is supplied at a pressure of more than 12 atmospheres or lower, and three liquid nitrogen cycles are adopted. The nitrogen gas stream is supplied at a pressure greater than 12 atmospheres, and two liquid nitrogen cycles are adopted.

8. The method as claimed in claim 7, wherein in the liquid nitrogen cycle in which the liquid nitrogen for expanding the working gas exchanges heat with the nitrogen gas stream at a temperature lower than the critical temperature of the nitrogen gas stream, the liquid nitrogen for expanding the working gas provides cooling for the nitrogen gas stream, cooling it from the ambient temperature or a temperature close to the ambient temperature to a temperature within the range of -100 to -130 °C.

9. The method according to claim 8, wherein only one liquid nitrogen cycle for expanding the gas has a heat exchange relationship with the nitrogen gas stream at a temperature lower than the critical temperature of nitrogen.

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