A two-stage refrigeration system for carbon dioxide liquefaction

Abstract

The utility model provides a two -stage refrigeration system for carbon dioxide liquefaction. This carbon dioxide liquefaction two -stage refrigeration system includes: pre -cooler, aftercooler, superheater, main condenser, emptying condenser, emptying heat exchanger, reboiler, auxiliary reboiler, supercooler, primary throttle valve, secondary throttle valve, refrigerant compressor, refrigerant condenser, refrigerant receiving tank and supporting facilities. Based on the system can realize double temperature level refrigeration cycle, provides the cold quantity for the whole process of carbon dioxide liquefaction, reduces the heat exchange temperature gradient in the process of carbon dioxide liquefaction, to obviously promoted the heat exchange efficiency in the process of carbon dioxide liquefaction, reduced the liquefaction energy consumption.

Description

Technical Field

[0001] This utility model relates to the field of refrigeration technology, specifically a two-stage refrigeration system for carbon dioxide liquefaction. Background Technology

[0002] In carbon dioxide liquefaction technology, low-pressure (1.5–2.4 MPa) carbon dioxide liquefaction technology has been widely used in industry due to its advantages such as low energy consumption and high product purity. The core principle of this technology is to liquefy carbon dioxide gas at a lower pressure through low-temperature cooling. During the process, non-condensable gases (such as nitrogen and oxygen) have low solubility in liquid carbon dioxide, thereby reducing impurity residues and achieving efficient separation of carbon dioxide from impurities. The purity of liquid carbon dioxide can reach over 99.9%.

[0003] However, it is worth noting that the low-pressure method places extremely high demands on the cooling capacity of the refrigeration system (-35 to -40°C), and its energy consumption is significantly higher than other methods. Finding an optimized refrigeration system with lower energy consumption is key to solving this problem. Utility Model Content

[0004] In view of this, and to address the aforementioned problems, the purpose of this invention is to provide a two-stage refrigeration system for carbon dioxide liquefaction. Through heat exchange network design and the adoption of two-stage throttling and two-stage compression, the overall energy utilization rate of the system is improved, and the system's energy consumption is reduced.

[0005] To achieve the above objectives, this utility model provides a two-stage refrigeration system for carbon dioxide liquefaction, comprising: a precooler, an aftercooler, a superheater, a main condenser, a venting condenser, a venting heat exchanger, a reboiler, an auxiliary reboiler, a subcooler, a first-stage throttling valve, a second-stage throttling valve, a refrigerant compressor, a refrigerant condenser, a refrigerant receiving tank, and their connecting piping systems.

[0006] Specifically, the feed gas booster outlet is connected to the tube-side inlet of the precooler, the tube-side outlet of the precooler is connected to the feed gas compression inlet, the feed gas compression outlet is connected to the feed gas scrubbing inlet, the feed gas scrubbing outlet is connected to the tube-side inlet of the aftercooler, the tube-side outlet of the aftercooler is connected to the tube-side inlet of the superheater, the tube-side outlet of the superheater is connected to the CO2 purification inlet, and the CO2 purification outlet is connected to the CO2 liquefaction and purification inlet. The CO2 liquefaction and purification inlet is connected to the tube-side inlet of the reboiler; the tube-side outlet of the reboiler is connected to the tube-side inlet of the main condenser; the tube-side outlet of the main condenser is connected to the upper feed inlet of the distillation column; the top of the distillation column is connected to the tube-side inlet of the vent condenser; the tube-side outlet of the vent condenser is connected to the tube-side inlet of the vent heat exchanger; the tube-side outlet of the vent heat exchanger is connected to the tail gas discharge pipeline; the bottom liquid outlet of the distillation column is connected to the shell-side inlet of the reboiler; the shell-side inlet of the auxiliary reboiler is connected to the shell-side inlet of the reboiler; the shell-side outlet of the auxiliary reboiler is connected to the top shell-side outlet of the reboiler, and then connected to the bottom reboiler return port of the distillation column; the shell-side liquid phase outlet of the reboiler is connected to the tube-side inlet of the subcooler; and the tube-side outlet of the subcooler is connected to the CO2 liquid product output pipeline.

[0007] The refrigerant receiving tank outlet is connected to the shell-side inlet of the superheater. The superheater shell-side outlet is connected to the shell-side inlet of the vent heat exchanger. The vent heat exchanger shell-side outlet is connected to the tube-side inlet of the auxiliary reboiler. The tube-side outlet of the auxiliary reboiler is sequentially connected to the first-stage throttling valve and the first inlet of the top connector of the precooler. The first liquid-phase shell-side outlet of the precooler is connected to the shell-side inlet of the aftercooler. The aftercooler shell-side outlet is connected to the second inlet of the top connector of the precooler. The vapor-phase outlet of the top connector of the precooler is connected to the second-stage inlet of the refrigerant compressor. The second liquid-phase shell-side outlet of the precooler is sequentially connected to the second-stage throttling valve and the shell-side inlet of the vent condenser. The vent condenser shell-side outlet is connected to the first inlet of the top connector of the main condenser. The liquid-phase shell-side outlet of the main condenser is connected to the shell-side inlet of the subcooler. The subcooler shell-side outlet is connected to the second inlet of the top connector of the main condenser. The vapor-phase outlet of the top connector of the main condenser is connected to the first-stage inlet of the refrigerant compressor. The refrigerant compressor outlet is sequentially connected to the refrigerant condenser and the refrigerant receiving tank.

[0008] In the above system, preferably, the refrigerant is ammonia, propane, or an environmentally friendly Freon.

[0009] In the above system, preferably, the refrigerant compressor is a two-stage oil-injected screw compressor with a side suction port;

[0010] In the above system, preferably, the refrigerant condenser is an air cooler or a shell-and-tube heat exchanger;

[0011] In the above system, preferably, the tube-side outlet of the auxiliary reboiler is sequentially connected to the first inlet of the first-stage throttling valve and the top connector of the precooler, and the shell-side first liquid phase outlet of the precooler is connected to the shell-side inlet of the aftercooler, so as to provide refrigerant with a temperature of 0 to 10°C for the carbon dioxide liquefaction device.

[0012] In the above system, preferably, the shell-side second liquid phase outlet of the precooler is connected in sequence to the secondary throttling valve and the shell-side inlet of the vent condenser, the shell-side outlet of the vent condenser is connected to the first inlet of the top connector of the main condenser, and the shell-side liquid phase outlet of the main condenser is connected to the shell-side inlet of the subcooler, so as to provide refrigerant with a temperature of -28 to -35°C for the carbon dioxide liquefaction device.

[0013] In the above system, preferably, the gas phase outlet of the top connector of the main condenser is connected to the primary inlet of the refrigerant compressor to realize refrigerant circulation;

[0014] In the above system, preferably, the gas phase outlet of the top connector of the precooler is connected to the secondary inlet of the refrigerant compressor to realize refrigerant circulation.

[0015] The advantages and positive effects of this invention are as follows:

[0016] (1) The refrigerant is depressurized twice, providing the system with cooling capacity for two different cooling temperature requirements. Compared with existing single-stage single-condition refrigeration, the refrigeration system is more efficient and consumes less energy.

[0017] (2) The refrigerant gas after the refrigerant evaporates in the first stage of throttling returns to the second stage inlet of the refrigerant compressor, which reduces the energy consumption of the refrigerant compressor. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the process flow of this utility model.

[0019] The meanings of the codes in the diagram are as follows:

[0020] A. Raw material gas pressurization;

[0021] B. Raw material gas compression;

[0022] C. Raw material gas scrubbing;

[0023] D. CO2 purification;

[0024] E. The carbon dioxide liquefaction two-stage refrigeration system of this utility model;

[0025] 1. Precooler;

[0026] 2. Aftercooler;

[0027] 3. Superheater;

[0028] 4. Main condenser;

[0029] 5. Vent the condenser;

[0030] 6. Vent the heat exchanger;

[0031] 7. Reboiler;

[0032] 8. Auxiliary reboiler;

[0033] 9. Subcooler;

[0034] 10. Distillation column;

[0035] 11. Primary throttle valve;

[0036] 12. Two-stage throttle valve;

[0037] 13. Refrigerant compressor;

[0038] 14. Refrigerant condenser;

[0039] 15. Refrigerant receiving tank. Detailed Implementation

[0040] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of this utility model, the technical solution of this utility model is described in detail below, but it should not be construed as limiting the scope of implementation of this utility model.

[0041] Example

[0042] This embodiment provides a two-stage refrigeration system for carbon dioxide liquefaction.

[0043] Please see Figure 1The two-stage refrigeration system for carbon dioxide liquefaction includes: a precooler (1), an aftercooler (2), a superheater (3), a main condenser (4), a vent condenser (5), a vent heat exchanger (6), a reboiler (7), an auxiliary reboiler (8), a subcooler (9), a first-stage throttle valve (11), a second-stage throttle valve (12), a refrigerant compressor (13), a refrigerant condenser (14), a refrigerant receiving tank (15), and their connecting piping systems. Among them, the outlet of the raw gas booster (A) is connected to the tube inlet of the precooler (1), the tube outlet of the precooler (1) is connected to the raw gas compression inlet, the outlet of the raw gas compression (B) is connected to the raw gas scrubbing (C) inlet, the outlet of the raw gas scrubbing (C) is connected to the tube inlet of the aftercooler (2), the tube outlet of the aftercooler (2) is connected to the tube inlet of the superheater (3), the tube outlet of the superheater (3) is connected to the CO2 purification (D) inlet, and the outlet of the CO2 purification (D) is connected to the CO2 liquefaction and purification (E) inlet. The CO2 liquefaction and purification (E) inlet is connected to the tube-side inlet of the reboiler (7), the tube-side outlet of the reboiler (7) is connected to the tube-side inlet of the main condenser (4), the tube-side outlet of the main condenser (4) is connected to the upper feed inlet of the distillation column (10), the top of the distillation column (10) is connected to the tube-side inlet of the vent condenser (5), the tube-side outlet of the vent condenser (5) is connected to the tube-side inlet of the vent heat exchanger (6), and the tube-side outlet of the vent heat exchanger (6) is connected to the tail gas emission pipeline. The bottom liquid outlet of the distillation column (10) is connected to the shell-side inlet of the reboiler (7), the shell-side inlet of the auxiliary reboiler (8) is connected to the shell-side inlet of the reboiler (7), the shell-side outlet of the auxiliary reboiler (8) is connected to the top shell-side outlet of the reboiler (7), and then connected to the bottom reboiler return port of the distillation column (10). The shell-side liquid phase outlet of the reboiler (7) is connected to the tube-side inlet of the subcooler (9), and the tube-side outlet of the subcooler (9) is connected to the CO2 liquid product output pipeline.

[0044] The outlet of the refrigerant receiving tank (15) is connected to the shell-side inlet of the superheater (3), the shell-side outlet of the superheater (3) is connected to the shell-side inlet of the vent heat exchanger (6), the shell-side outlet of the vent heat exchanger (6) is connected to the tube-side inlet of the auxiliary reboiler (8), the tube-side outlet of the auxiliary reboiler (8) is sequentially connected to the first inlet of the first-stage throttle valve (11) and the top connector of the precooler (1), the first liquid phase outlet of the shell side of the precooler (1) is connected to the shell-side inlet of the aftercooler (2), the shell-side outlet of the aftercooler (2) is connected to the second inlet of the top connector of the precooler (1), and the top connector of the precooler (1) is connected to the first liquid phase outlet of the shell side of the precooler (1). The gas phase outlet of the connector is connected to the secondary inlet of the refrigerant compressor (13). The shell-side second liquid phase outlet of the precooler (1) is connected in sequence to the secondary throttle valve (12) and the shell-side inlet of the vent condenser (5). The shell-side outlet of the vent condenser (5) is connected to the first inlet of the top connector of the main condenser (4). The shell-side liquid phase outlet of the main condenser (4) is connected to the shell-side inlet of the subcooler (9). The shell-side outlet of the subcooler (9) is connected to the second inlet of the top connector of the main condenser (4). The gas phase outlet of the top connector of the main condenser (4) is connected to the primary inlet of the refrigerant compressor (13). The outlet of the refrigerant compressor (13) is connected in sequence to the refrigerant condenser (14) and the refrigerant receiving tank (15).

[0045] The refrigerant selected is ammonia, propane, or environmentally friendly Freon.

[0046] The refrigerant compressor is a two-stage oil-injected screw compressor with a side suction port.

[0047] The refrigerant condenser is either an air cooler or a shell-and-tube heat exchanger.

[0048] The tube-side outlet of the auxiliary reboiler is sequentially connected to the first inlet of the first-stage throttling valve and the top connector of the precooler. The first liquid phase outlet of the shell side of the precooler is connected to the shell-side inlet of the aftercooler, providing refrigerant with a temperature of 0 to 10°C to the carbon dioxide liquefaction unit.

[0049] The second liquid phase outlet of the precooler is connected in sequence to the secondary throttling valve and the shell inlet of the vent condenser. The shell outlet of the vent condenser is connected to the first inlet of the top connector of the main condenser. The liquid phase outlet of the main condenser is connected to the shell inlet of the subcooler. This provides refrigerant with a temperature range of -28 to -35°C to the carbon dioxide liquefaction unit, resulting in higher refrigeration system efficiency and lower energy consumption.

[0050] The gas phase outlet of the top connector of the main condenser is connected to the first-stage inlet of the refrigerant compressor to achieve refrigerant circulation.

[0051] The gas phase outlet of the top connector of the precooler is connected to the secondary inlet of the refrigerant compressor, realizing refrigerant circulation and reducing the energy consumption of the refrigerant compressor.

[0052] Principle of refrigerant cycle refrigeration system: Low-pressure gaseous refrigerant is pressurized by the refrigerant compressor (13) and mixed with the returning gaseous refrigerant. After being pressurized by the second stage, it enters the refrigerant condenser (14) and is cooled to 30-50°C. It then enters the refrigerant receiving tank (15) for buffering and is sent to the superheater (3), venting heat exchanger (6), and auxiliary reboiler (8) for successive cooling. The refrigerant temperature is 5-25°C. After being reduced and throttled to 0-10°C by the first stage, it flows into the precooler (1) and is then drawn from the precooler (1) to the aftercooler (2) to provide cooling capacity. After evaporation, the vapor phase is returned to the precooler (1) and together with the vapor phase generated by evaporation in the precooler (1), it is returned to the secondary inlet of the refrigerant compressor (13). The remaining refrigerant in the precooler (1) is reduced and throttled to -28 to -35°C through secondary pressure reduction and is then sent to the vent condenser (5) and the main condenser (4) in sequence. Part of the refrigerant is extracted from the main condenser (4) and sent to the subcooler (9) to provide cooling capacity. The vapor phase obtained after evaporation is returned to the main condenser (4) and together with the vapor phase evaporated in the main condenser (4), it is sent to the primary inlet of the refrigerant compressor (13).

[0053] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions, and alterations can be made to these embodiments without departing from the principles and spirit of the present invention, and all such changes fall within the scope of protection of this patent. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A two-stage refrigeration system for carbon dioxide liquefaction, characterized in that, include: The system comprises a precooler (1), an aftercooler (2), a superheater (3), a main condenser (4), a vent condenser (5), a vent heat exchanger (6), a reboiler (7), an auxiliary reboiler (8), a subcooler (9), a primary throttle valve (11), a secondary throttle valve (12), a refrigerant compressor (13), a refrigerant condenser (14), a refrigerant receiving tank (15), and their connecting piping systems. The outlet of the refrigerant receiving tank (15) is connected to the shell-side inlet of the superheater (3), the shell-side outlet of the superheater (3) is connected to the shell-side inlet of the vent heat exchanger (6), the shell-side outlet of the vent heat exchanger (6) is connected to the tube-side inlet of the auxiliary reboiler (8), the tube-side outlet of the auxiliary reboiler (8) is sequentially connected to the first inlet of the primary throttle valve (11) and the top connector of the precooler (1), and the first liquid phase outlet of the precooler (1) is connected to the shell-side outlet of the aftercooler (2). The inlet is connected, the shell-side outlet of the aftercooler (2) is connected to the second inlet of the top connector of the precooler (1), the gas phase outlet of the top connector of the precooler (1) is connected to the secondary inlet of the refrigerant compressor (13), the shell-side second liquid phase outlet of the precooler (1) is connected to the secondary throttle valve (12) and the shell-side inlet of the vent condenser (5) in sequence, the shell-side outlet of the vent condenser (5) is connected to the first inlet of the top connector of the main condenser (4), the shell-side liquid phase outlet of the main condenser (4) is connected to the shell-side inlet of the subcooler (9), the shell-side outlet of the subcooler (9) is connected to the second inlet of the top connector of the main condenser (4), the gas phase outlet of the top connector of the main condenser (4) is connected to the primary inlet of the refrigerant compressor (13), and the outlet of the refrigerant compressor (13) is connected to the refrigerant condenser (14) and the refrigerant receiving tank (15) in sequence.

2. The two-stage refrigeration system according to claim 1, characterized in that, The refrigerant compressor (13) is a two-stage oil-injected screw compressor with a side suction port.

3. The two-stage refrigeration system according to claim 1, characterized in that, The outlet of the refrigerant compressor (13) is connected to the shell-side inlet of the superheater (3), and the shell-side outlet of the vent heat exchanger (6) is connected to the tube-side inlet of the auxiliary reboiler (8).

4. The two-stage refrigeration system according to claim 1, characterized in that, The tube-side outlet of the auxiliary reboiler (8) is sequentially connected to the first inlet of the top connector of the first-stage throttle valve (11) and the precooler (1), and the shell-side first liquid phase outlet of the precooler (1) is connected to the shell-side inlet of the aftercooler (2).

5. The two-stage refrigeration system according to claim 1, characterized in that, The gas phase outlet of the top connector of the main condenser (4) is connected to the primary inlet of the refrigerant compressor (13).

6. The two-stage refrigeration system according to claim 1, characterized in that, The gas phase outlet of the top connector of the precooler (1) is connected to the secondary inlet of the refrigerant compressor (13).

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