Double-circulation cascade refrigerating system

Abstract

The utility model discloses a double-circulation cascade refrigeration system, and belongs to the technical field of waste heat energy utilization, the double-circulation cascade refrigeration system comprises a waste heat refrigeration module, a low-temperature refrigeration module and a low-temperature refrigeration module, the waste heat refrigeration module comprises a generator, a condenser and an ammonia cooler, a gas outlet of the generator is connected with the condenser, the condenser is connected with the ammonia cooler, and the low-temperature refrigeration module is connected with the low-temperature refrigeration module. The low-temperature refrigeration module comprises a compressor and a heat exchanger, the heat exchanger is located between the waste heat refrigeration module and the low-temperature refrigeration module, a cold medium inlet of the heat exchanger is connected with an outlet of the ammonia cooler, a cold medium outlet of the heat exchanger is connected with an inlet of the ammonia cooler, and a heat medium of the heat exchanger is connected with the compressor. Stable work is still achieved when the waste heat load change interval is large, the heat exchange cost is reduced, poisonous, flammable and explosive media are prevented from entering final users, and the green hydrogen and green ammonia concepts and the production principle are met.

Description

Technical Field

[0001] The utility model relates to the technical field of waste heat energy utilization, and more specifically, to a double-circulation cascade refrigeration system. Background Art

[0002] The chemical industry is often labeled an "energy-intensive" sector, characterized by high energy consumption and low energy utilization. Therefore, within the current global trends of achieving carbon peak and carbon neutrality, energy conservation and consumption reduction, along with the goal of further improving energy utilization, have become the current priorities for the entire chemical industry. While waste heat utilization and energy conversion methods do not constitute new energy development, they are also forms of energy conservation and consumption reduction, and thus energy utilization, worthy of further research and development.

[0003] For some time, there have been various directions in energy utilization, such as the research and application of new heat transfer methods of thermal oil, the storage and utilization of molten salt, and the development of refrigeration utilization methods of low-level thermal energy of steam condensate.

[0004] At present, there are many cases of low-grade heat source applications in factories. Common processes include: 1. Direct use in the factory heat exchange station for heating offices and other living areas; 2. Waste heat power generation; 3. Waste heat cooling, etc.

[0005] However, due to the large fluctuations in the factory's waste heat load, resulting in poor energy stability, a single waste heat generator set cannot maintain normal operation. Additional steam accumulators are required to ensure normal operation of the unit during long periods of low load, which increases costs.

[0006] In summary, how to provide a heat exchange system that can meet the requirements of normal operation under the condition of large changes in factory waste heat load is an urgent problem to be solved by those skilled in the art. Utility Model Content

[0007] In view of this, the purpose of the present invention is to provide a dual-circulation cascade refrigeration system that can meet the requirements of a large range of waste heat load changes while still achieving stable operation, reducing heat exchange costs and improving energy utilization.

[0008] In order to achieve the above purpose, the present invention provides the following technical solutions:

[0009] A double-cycle cascade refrigeration system, comprising:

[0010] A waste heat refrigeration module, comprising a generator, a condenser and an ammonia cooler, wherein the gas outlet of the generator is connected to the condenser, and the condenser and the ammonia cooler are connected;

[0011] A low-temperature refrigeration module, wherein the low-temperature refrigeration module includes a compressor;

[0012] A heat exchanger is located between the waste heat refrigeration module and the low-temperature refrigeration module, the cold medium inlet of the heat exchanger is connected to the outlet of the ammonia cooler, the cold medium outlet of the heat exchanger is connected to the inlet of the ammonia cooler, and the hot medium of the heat exchanger is connected to the compressor.

[0013] Furthermore, the waste heat refrigeration module of the present invention also includes: a low-pressure cylinder, a lean-rich liquid heat exchanger and a solution pump, the lean-rich liquid heat exchanger is located between the generator and the low-pressure cylinder, the low-pressure cylinder is connected to the ammonia cooler, and the solution pump is located between the lean-rich liquid heat exchanger and the low-pressure cylinder.

[0014] Furthermore, the present invention adopts a two-stage compressor, and the low-temperature refrigeration module also includes a first-stage separator, a first-stage cooler, a second-stage separator, a second-stage cooler and a third-stage separator. The first-stage separator is connected to the first-stage inlet of the compressor, the second-stage separator is connected to the first-stage outlet of the compressor, the first-stage cooler is located between the compressor and the second-stage separator, the outlet of the second-stage separator is connected to the second-stage inlet of the compressor, the third-stage separator is connected to the second-stage outlet of the compressor, the second-stage cooler is located between the third-stage separator and the compressor, and the third-stage separator is connected to the heat medium inlet of the heat exchanger.

[0015] Furthermore, the utility model provides that the heat source temperature of the generator is 60-80 degrees.

[0016] Furthermore, in the present invention, the heat source of the generator is factory by-product steam or condensate.

[0017] Furthermore, in the present invention, the cold medium of the heat exchanger is saturated liquid ammonia, and the hot medium of the heat exchanger is gaseous CO2.

[0018] Furthermore, the present invention provides that the temperature of the liquid CO2 at the separator outlet is -35°C to -55°C, and the pressure is 0.6 to 1.5 MPa.

[0019] Furthermore, the present invention provides that the temperature of the liquid ammonia at the inlet of the heat exchanger is -10°C to -20°C, and the pressure is 0.1 to 0.5 MPa.

[0020] Furthermore, in the present invention, the pressure of the gaseous CO2 at the compressor outlet is 2.3-2.9 MPa.

[0021] Furthermore, in the present invention, the compressor is a centrifugal compressor and is driven by a high-voltage motor.

[0022] The utility model provides a dual-circulation cascade refrigeration system, in which the gas outlet of the generator is connected to the condenser, and a multi-component solution containing ammonia is contained in the generator. By heating the generator with an external heat source, ammonia is evaporated and passed to the condenser to be cooled into saturated liquid ammonia by circulating cooling water. The condenser is connected to the ammonia cooler, and the low-temperature refrigeration module includes a compressor. The heat exchanger is located between the waste heat refrigeration module and the low-temperature refrigeration module. The cold medium inlet of the heat exchanger is connected to the ammonia cooler outlet, and the cold medium outlet of the heat exchanger is connected to the ammonia cooler inlet. The hot medium of the heat exchanger is connected to the compressor. That is to say, saturated liquid ammonia enters the heat exchanger and generates heat exchange with the heat medium. After that, the saturated liquid ammonia absorbs the temperature and vaporizes and is sent to the condenser again for recirculation, and the cooled heat medium becomes provided to deep-cold users for cooling. The dual-circulation cascade refrigeration system has greatly expanded the heat exchange field. Ammonia is a toxic, flammable and explosive medium. It only circulates in the waste heat refrigeration module, avoiding toxic, flammable and explosive media from entering the end user, which is in line with the concept and production principles of green hydrogen and green ammonia. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0024] Figure 1 A schematic diagram of the overall system provided by the utility model;

[0025] Figure 2 This is a partial schematic diagram of the waste heat refrigeration module provided by the present utility model;

[0026] Figure 3 This is a partial schematic diagram of the low-temperature refrigeration module provided by the present utility model;

[0027] Figure 1-Figure 3 , the reference numerals include:

[0028] 1. Waste heat refrigeration module; 101. Condenser; 102. Generator; 103. Lean-rich liquid heat exchanger; 104. Solution pump; 105. Low-pressure cylinder; 106. Ammonia cooler; 2. Heat exchanger; 3. Low-temperature refrigeration module; 301. Compressor; 302. First-stage separator; 303. First-stage cooler; 304. Second-stage separator; 305. Second-stage cooler; 306. Third-stage separator. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0030] The core of the utility model is to provide a dual-circulation cascade refrigeration system, which can meet the requirements of a large range of residual heat load changes and still achieve stable operation, reduce heat exchange costs, and improve energy utilization.

[0031] Please refer to Figure 1-Figure 3 A double-cycle cascade refrigeration system includes a waste heat refrigeration module 1, a low-temperature refrigeration module 3 and a heat exchanger 2. The waste heat refrigeration module 1 includes a generator 102, a condenser 101 and an ammonia cooler 106. The gas outlet of the generator 102 is connected to the condenser 101, and the condenser 101 is connected to the ammonia cooler 106. The low-temperature refrigeration module 3 includes a compressor 301. The heat exchanger 2 is located between the waste heat refrigeration module 1 and the low-temperature refrigeration module 3. The cold medium inlet of the heat exchanger 2 is connected to the outlet of the ammonia cooler 106, the cold medium outlet of the heat exchanger 2 is connected to the inlet of the ammonia cooler 106, and the hot medium of the heat exchanger 2 is connected to the compressor 301.

[0032] It should be noted that the ammonia in the embodiment of the present invention can also be replaced by other media, such as propylene or Freon.

[0033] In addition, the present invention does not limit the model of the compressor 301. In some embodiments, the compressor 301 can be a positive displacement compressor 301 or a dynamic compressor 301, for example, a rotary compressor 301, a screw compressor 301 or a centrifugal compressor 301.

[0034] In addition, in the implementation of the present invention, the compressor 301 can select single-stage compression or multi-stage compression according to usage requirements.

[0035] When in use, the gas outlet of the generator 102 is connected to the condenser 101. There is a multi-component solution containing ammonia in the generator 102. By heating it with an external heat source, ammonia is evaporated and passed to the condenser 101 to be cooled into saturated liquid ammonia by circulating cooling water. The condenser 101 is connected to the ammonia cooler 106. The low-temperature refrigeration module 3 includes a compressor 301. The heat exchanger 2 is located between the waste heat refrigeration module 1 and the low-temperature refrigeration module 3. The cold medium inlet of the heat exchanger 2 is connected to the outlet of the ammonia cooler 106, and the cold medium outlet of the heat exchanger 2 is connected to the ammonia cooler 106. 6 inlet is connected, and the heat medium of heat exchanger 2 is connected to compressor 301. That is to say, saturated liquid ammonia enters heat exchanger 2, and heat exchange occurs between it and the heat medium. Then, the saturated liquid ammonia absorbs the temperature and vaporizes and is sent to condenser 101 for recirculation. The cooled heat medium becomes the cooling medium provided to deep-cold users. The double-circulation cascade refrigeration system has greatly broadened the heat exchange field. Ammonia is a toxic, flammable and explosive medium. It only circulates in the waste heat refrigeration module, avoiding the toxic, flammable and explosive media from entering the end user, which is in line with the concept and production principles of green hydrogen and green ammonia.

[0036] Please refer to Figure 2 In some embodiments, the waste heat refrigeration module 1 further includes: a low-pressure cylinder 105, a lean-rich liquid heat exchanger 103 and a solution pump 104. The lean-rich liquid heat exchanger 103 is located between the generator 102 and the low-pressure cylinder 105, and the ammonia cooler 106 is connected to the ammonia cooler 106. The solution pump 104 is located between the lean-rich liquid heat exchanger 103 and the low-pressure cylinder 105. That is, the heat source enters the generator 102, heats the solution multi-working medium in the generator 102, and evaporates most of the low-boiling-point ammonia in the solution. The gaseous ammonia vapor enters the condenser 101 and is cooled by the circulating cooling water into saturated liquid ammonia. The saturated liquid ammonia is pumped and pressurized out of the waste heat refrigeration module, and is reduced in pressure by the pressure reducing valve to become low-temperature liquid ammonia and enter the heat exchanger 2 to exchange heat with the heat medium in the heat exchanger 2, so that the temperature of the heat medium is reduced to a level where phase change liquefaction occurs, thereby achieving the purpose of one-time transfer of cold capacity. At this time, the low-temperature liquid ammonia absorbs heat in the heat exchanger 2 and evaporates into low-temperature gaseous ammonia, which returns to the waste heat refrigeration module. It is cooled into low-temperature liquid ammonia by circulating water in the ammonia cooler 106 and enters the low-pressure cylinder 105. At the same time, after part of the ammonia evaporates in the generator 102, the remaining lean solution enters the lean-rich liquid heat exchanger 103 to exchange heat with the rich solution in the low-pressure cylinder 105, and then throttles and reduces the pressure to enter the generator 102, absorbs low-temperature liquid ammonia and restores the solution to its original concentration. The lean solution increases its concentration due to the absorption of gaseous ammonia to form a rich solution, which is then pressurized by the solution pump 104 and enters the lean-rich liquid heat exchanger 103 to exchange heat with the lean solution, and then is sent to the generator 102 to continue circulating. The above is the ammonia circulation loop. It can be seen that ammonia is only circulated in the waste heat refrigeration module 1 at the front end, which prevents toxic, flammable and explosive media from entering the end user, thereby improving the safety of the entire system use process.

[0037] Please refer to Figure 3 In some embodiments, the compressor 301 is a two-stage compressor 301, and the low-temperature refrigeration module 3 further includes a first-stage separator 302, a first-stage cooler 303, a second-stage separator 304, a second-stage cooler 305, and a third-stage separator 306. The first-stage separator 302 is connected to the first-stage inlet of the compressor 301, the second-stage separator 304 is connected to the first-stage outlet of the compressor 301, the first-stage cooler 303 is located between the compressor 301 and the second-stage separator 304, and the outlet of the second-stage separator 304 is connected to the second-stage outlet of the compressor 301. The inlet is connected, the three-stage separator 306 is connected to the secondary outlet of the compressor 301, and the second-stage cooler 305 is located between the three-stage separator 306 and the compressor 301. The three-stage separator 306 is connected to the heat medium inlet of the heat exchanger 2, that is, the heat medium entering the heat exchanger 2 is first compressed by the compressor 301 to increase its pressure, which is beneficial to phase-liquid conversion during heat exchange. The use of multi-stage cooling and separation can separate the heat medium more thoroughly, while improving the efficiency of the heat medium phase-liquid conversion and reducing energy loss.

[0038] In some embodiments, the cold medium of heat exchanger 2 is ammonia, and the hot medium of heat exchanger 2 is CO2. That is to say, CO2 is used as the cryogenic medium used in the factory. Based on the above embodiment, the CO2 from the desulfurization / decarbonization section with a temperature of -30°C and a pressure of 0.7 MPa first passes through a first-stage separator 302 for solution separation. The separated gas enters the compressor 301 for primary compression, and then enters the first-stage cooler 303 for cooling, so that part of it becomes liquid CO2, and then passes through the second-stage separator 304 for gas-liquid separation. After separation, the separated gaseous CO2 enters the compressor 301 again for secondary compression. The compressed CO2 is cooled by the second-stage cooler 305 and separated into gas and liquid by the third-stage separator 306. Finally, the gaseous CO2 exchanges heat with liquid ammonia in the heat exchanger 2, and then undergoes phase change and liquefaction. It is mixed with the liquid CO2 separated by the first-stage separator 302, the second-stage separator 304 and the third-stage separator 306, and sent to the user as a cryogenic medium. This cycle is a CO2 gas-liquid conversion cycle, which can be used by the end user for cryogenic and low-temperature devices such as low-temperature methanol washing and ammonia synthesis.

[0039] At the same time, this dual-circulation cascade refrigeration system can be used in the current green ammonia device. Due to the volatility of upstream green hydrogen, the production load of the green ammonia device also fluctuates accordingly, and the required cooling capacity is also fluctuating. The advantage of this dual-circulation cascade refrigeration system is reflected in the load fluctuation. The dual-circulation heat exchange function eliminates most of the power consumption of dynamic equipment, so it can adapt to the use scenario with larger load fluctuations.

[0040] In some embodiments, the heat source of the generator 102 is factory by-product steam or condensate with a temperature of 60-80 degrees Celsius, and the ammonia in the multi-component solution can be heated by the steam or condensate to form ammonia vapor.

[0041] In other embodiments, the heat source of the generator 102 may also be a by-product of other heat sources in the factory.

[0042] In some embodiments, the heat exchanger 2 is of a kettle shell and tube type and is provided with a liquid level regulation and interlocking system.

[0043] In some embodiments, the compressor 301 is a centrifugal compressor 301 and is driven by a high-voltage motor. At the same time, an anti-surge backflow route is set at the outlet of the compressor 301 to return to the inlet of the compressor 301 to ensure the safe operation of the compressor 301.

[0044] In some embodiments, the temperature of the liquid CO2 at the separator outlet is -35°C to -55°C and the pressure is 0.6 to 1.5 MPa. The temperature of the liquid ammonia at the heat exchanger 2 inlet is -10°C to -20°C and the pressure is 0.1 to 0.5 MPa. The pressure of the gaseous CO2 at the compressor 301 outlet is 2.3 to 2.9 MPa. Compared to ammonia, the CO2 medium has a higher pressure and a larger molecular weight at ultra-low temperatures. Therefore, for the same cooling capacity, the CO2 gas transmission pipelines, valves, and fittings are much smaller than those of the latter. This achieves energy savings and cost reduction compared to traditional ammonia (or propylene) refrigeration compression, reduces investment, and provides safer operation, helping to lower production costs for enterprises.

[0045] That is to say, the key points of the embodiment of the present invention are: the gas outlet of the generator 102 is connected to the condenser 101, and there is a multi-component solution containing ammonia in the generator 102. By heating it with an external heat source, ammonia gas evaporates and flows to the condenser 101 to be cooled into saturated liquid ammonia by circulating cooling water. The condenser 101 is connected to the ammonia cooler 106, the low-temperature refrigeration module 3 includes a compressor 301, the heat exchanger 2 is located between the waste heat refrigeration module 1 and the low-temperature refrigeration module 3, the cold medium inlet of the heat exchanger 2 is connected to the outlet of the ammonia cooler 106, and the cold medium outlet of the heat exchanger 2 is connected to the outlet of the ammonia cooler 106. The port is connected to the inlet of the ammonia cooler 106, and the heat medium of the heat exchanger 2 is connected to the compressor 301. That is to say, saturated liquid ammonia enters the heat exchanger 2, and heat exchange occurs between it and the heat medium. After that, the saturated liquid ammonia absorbs the temperature and vaporizes and is sent to the condenser 101 for recirculation. The cooled heat medium becomes the cooling medium provided to deep-cold users for use. The double-circulation cascade refrigeration system has greatly broadened the heat exchange field. Ammonia is a toxic, flammable and explosive medium. It only circulates in the waste heat refrigeration module, avoiding toxic, flammable and explosive media from entering the end user, which is in line with the concept and production principles of green hydrogen and green ammonia.

[0046] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0047] The above is a detailed introduction to the dual-circulation cascade refrigeration system provided by the present invention. This article uses specific examples to illustrate the principles and implementation methods of the present invention. The description of the above examples is only intended to help understand the method and core concept of the present invention. It should be noted that for those skilled in the art, without departing from the principles of the present invention, various improvements and modifications can be made to the present invention, and such improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A double-cycle cascade refrigeration system, characterized in that: include: A waste heat refrigeration module (1), the waste heat refrigeration module (1) comprising a generator (102), a condenser (101) and an ammonia cooler (106), a gas outlet of the generator (102) being connected to the condenser (101), and the condenser (101) and the ammonia cooler (106) being connected; A low-temperature refrigeration module (3), the low-temperature refrigeration module (3) comprising a compressor (301); A heat exchanger (2), the heat exchanger (2) being located between the waste heat refrigeration module (1) and the low-temperature refrigeration module (3), the cold medium inlet of the heat exchanger (2) being connected to the outlet of the ammonia cooler (106), the cold medium outlet of the heat exchanger (2) being connected to the inlet of the ammonia cooler (106), and the hot medium of the heat exchanger (2) being connected to the compressor (301).

2. A dual-cycle cascade refrigeration system according to claim 1, characterized in that: The waste heat refrigeration module (1) further comprises: a low-pressure cylinder (105), a lean-rich liquid heat exchanger (103) and a solution pump (104); the lean-rich liquid heat exchanger (103) is located between the generator (102) and the low-pressure cylinder (105); the low-pressure cylinder (105) is connected to the ammonia cooler (106); and the solution pump (104) is located between the lean-rich liquid heat exchanger (103) and the low-pressure cylinder (105).

3. A dual-cycle cascade refrigeration system according to claim 2, characterized in that: The compressor (301) adopts a two-stage compressor (301), and the low-temperature refrigeration module (3) further comprises a first-stage separator (302), a first-stage cooler (303), a second-stage separator (304), a second-stage cooler (305), and a third-stage separator (306). The first-stage separator (302) is connected to the first-stage inlet of the compressor (301), the second-stage separator (304) is connected to the first-stage outlet of the compressor (301), the first-stage cooler (303) is located between the compressor (301) and the second-stage separator (304), the outlet of the second-stage separator (304) is connected to the second-stage inlet of the compressor (301), the third-stage separator (306) is connected to the second-stage outlet of the compressor (301), the second-stage cooler (305) is located between the third-stage separator (306) and the compressor (301), and the third-stage separator (306) is connected to the heat medium inlet of the heat exchanger (2).

4. A dual-cycle cascade refrigeration system according to claim 1, characterized in that: The heat source temperature of the generator (102) is 60-80 degrees.

5. A double-cycle cascade refrigeration system according to claim 4, characterized in that: The heat source of the generator (102) is factory by-product steam or condensate.

6. A dual-cycle cascade refrigeration system according to claim 1, characterized in that: The cold medium of the heat exchanger (2) is saturated liquid ammonia, and the hot medium of the heat exchanger (2) is gaseous CO2.

7. The dual-cycle cascade refrigeration system according to claim 3, characterized in that: The temperature of the liquid CO2 at the outlet of the three-stage separator (306) is -35°C to -55°C, and the pressure is 0.6 to 1.5 MPa.

8. The double-cycle cascade refrigeration system according to claim 6, characterized in that: The temperature of the liquid ammonia at the inlet of the heat exchanger (2) is -10°C to -20°C, and the pressure is 0.1 to 0.5 MPa.

9. The dual-cycle cascade refrigeration system according to claim 7, characterized in that: The pressure of the gaseous CO2 at the outlet of the compressor (301) is 2.3-2.9 MPa.

10. A dual-cycle cascade refrigeration system according to any one of claims 1 to 9, characterized in that: The compressor (301) is a centrifugal compressor (301) and is driven by a high-voltage motor.

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