Nitrogen self-pressurizing air separation unit

Abstract

The invention discloses a nitrogen self-pressurizing air separation device, comprising an air compressor for compressing external air, a molecular sieve purification device for purifying air output by the air compressor, a pressurizing turbine expansion device for expanding and cooling the purified air, a distillation tower for separating the air passing through the pressurizing turbine expansion device into oxygen and nitrogen, and a heat exchanger for heat exchange of gas in the air separation device, wherein the distillation tower comprises an upper tower and a lower tower, a main condensing evaporator is arranged at the bottom of the upper tower, and the air separation device further comprises a liquid nitrogen evaporator, which is arranged lower than the main condensing evaporator; the invention can not only simultaneously meet the needs of users for nitrogen and oxygen products, but also its pressure and purity can meet the needs of users, thereby reducing the gas production cost.

Description

Technical Field

[0001] The present invention relates to an improvement of air separation equipment, and in particular to a nitrogen self-pressurizing air separation device which utilizes the static pressure of the liquid column of liquid nitrogen to increase the nitrogen pressure and self-pressurizes the nitrogen without raising the exhaust pressure of a matching air compressor. Background Art

[0002] Air separation equipment is widely used in the fields of petroleum, chemical industry, building materials, metallurgy and environmental protection. In the conventional molecular sieve purification and booster turbine expander refrigeration air separation process, in order to obtain the corresponding nitrogen product pressure, an air compressor with the corresponding exhaust pressure is required to match. If the user wants to increase the pressure of the nitrogen product, the exhaust pressure of the air compressor needs to be increased accordingly. In this way, both the investment cost and the operating cost will increase accordingly.

[0003] To this end, we have developed a nitrogen self-pressurizing air separation unit that uses the static pressure of the liquid nitrogen column to increase the nitrogen pressure, thereby self-pressurizing the nitrogen without raising the exhaust pressure of the matching air compressor. Summary of the invention

[0004] The present invention aims to provide a nitrogen self-pressurizing air separation device which utilizes the static pressure of the liquid column of liquid nitrogen itself to increase the nitrogen pressure and can self-pressurize the nitrogen without raising the exhaust pressure of the matching air compressor.

[0005] The technical scheme of the present invention is: a nitrogen self-pressurizing air separation device, comprising an air compressor for compressing external air, a precooling unit, a molecular sieve purification device for purifying the precooled air, a booster turbine expansion device for expanding and cooling the purified air, a distillation tower for separating the air passing through the booster turbine expansion device into oxygen and nitrogen, and a main heat exchanger and a subcooler for heat exchange of gas in the air separation device; the distillation tower comprises an upper tower and a lower tower, and a main condenser evaporator is arranged at the bottom of the upper tower; the air separation device also comprises a liquid nitrogen evaporator for condensing and evaporating the air purified by the molecular sieve purification device and the liquid nitrogen condensed by the main condenser evaporator into liquid air and nitrogen respectively, the liquid nitrogen evaporator is arranged below the main condenser evaporator, and the liquid air output end of the liquid nitrogen evaporator is connected to the lower tower.

[0006] Preferably, the processed air purified by the molecular sieve purification device is divided into two streams: one stream of air enters the main heat exchanger, and exits the main heat exchanger after being cooled by the reflux gas, wherein a portion of the air enters the liquid nitrogen evaporator to gasify the liquid nitrogen, and the other portion of the air directly enters the lower tower; another stream of air equivalent to the expansion amount enters the boost end of the expander, and then enters the main heat exchanger after being cooled by the cooler, and is extracted from the middle to enter the expansion end of the expander, and most of the expanded air is sent to the upper tower; after preliminary distillation in the lower tower, liquid air and pure liquid nitrogen are obtained, and the air is throttled after passing through the subcooler to enter the corresponding part of the upper tower; after further distillation in the upper tower, a liquid oxygen product is obtained at the bottom of the condenser evaporator.

[0007] Preferably, a connecting pipe for delivering liquid air to the upper tower is provided at the bottom of the lower tower, and a throttle valve is provided on the connecting pipe; the distillation tower is also provided with a liquid nitrogen output pipe connected to the main condenser evaporator and the liquid nitrogen outlet at the top of the lower tower, a gas nitrogen output pipe connected to the main condenser evaporator and the gas nitrogen outlet at the top of the lower tower, a liquid oxygen output pipe connected to the bottom of the upper tower, and a dirty nitrogen output pipe connected to the top of the upper tower; the liquid nitrogen output pipe is connected to the liquid nitrogen evaporator; the gas nitrogen output pipe is connected to the outside of the air separation device after passing through a heat exchanger; the dirty nitrogen output pipe is connected to the molecular sieve purification device after heat exchange in the heat exchanger.

[0008] Preferably, the liquid nitrogen evaporator is provided with a nitrogen outlet and a liquid nitrogen inlet which are arranged up and down and connected, and an air inlet and a liquid air outlet which are arranged up and down and are further connected, the liquid nitrogen inlet is connected to the liquid nitrogen output pipe, the air output end of the molecular sieve purification device is connected to the air inlet through a rear heat exchanger, the liquid air outlet is connected to the lower tower, and the nitrogen outlet is output outside the air separation device after passing through the heat exchanger.

[0009] Preferably, the nitrogen self-pressurizing air separation device further comprises a subcooler, and the connecting pipeline, the dirty nitrogen output pipe and the liquid nitrogen output pipe pass through the subcooler respectively.

[0010] Preferably, the nitrogen self-pressurizing air separation device further comprises a precooling device disposed between the air compressor and the molecular sieve purification device.

[0011] Preferably, the molecular sieve purification device comprises a molecular sieve adsorber and an electric heater.

[0012] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0013] 1. Through the height difference between the main condenser evaporator and the liquid nitrogen evaporator, the liquid nitrogen flowing into the bottom of the cold box is pressurized by the static pressure of the liquid column of the liquid nitrogen itself, so that the liquid nitrogen is self-pressurized to obtain nitrogen with a pressure increase of ≥0.1MPa. The increase in nitrogen pressure does not require the increase in the exhaust pressure of the air compressor, which greatly improves the safe operation cycle of the equipment; the pressure and purity of the obtained nitrogen can meet the needs of users, saving users' one-time investment, greatly reducing production costs, and creating higher profits for users;

[0014] 2. The full low-pressure molecular sieve adsorption process of the chiller effectively prevents moisture and carbon dioxide from entering the low-temperature equipment in the cold box. The operating pressure is low and it is safe and reliable;

[0015] 3. The booster turbine expansion device uses part of the pressurized air entering the device to expand and refrigerate. The expanded air is sent to the upper tower to participate in distillation, which improves the distillation efficiency and reduces the exhaust pressure of the air compressor. It essentially achieves a low-pressure process and achieves an energy-saving effect;

[0016] 4. The exhaust adjustment range of the air compressor is 75% to 105%, achieving the purpose of energy saving. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic diagram of the working principle of the nitrogen self-pressurizing air separation device of the present invention;

[0018] Among them: 1. air compressor; 2. molecular sieve purification device; 21. molecular sieve adsorber; 22. electric heater; 3. booster turbine expansion device; 31. booster; 32. expander; 4. heat exchanger; 5. distillation tower; 51. upper tower; 52. lower tower; 53. main condenser evaporator; 54 throttle valve; 55. connecting pipeline; 56. liquid nitrogen output pipe; 57. gas nitrogen output pipe; 58. liquid oxygen output pipe; 59. dirty nitrogen output pipe; 6. liquid nitrogen evaporator; 61. nitrogen outlet; 62. liquid nitrogen inlet; 63. air inlet; 64. liquid air outlet; 7. subcooler; 8. precooling device; 9. cold box; 10. booster air cooler. DETAILED DESCRIPTION

[0019] The technical content of the present invention is further described below in conjunction with the accompanying drawings:

[0020] like Figure 1 As shown, a nitrogen self-pressurizing air separation device includes an air compressor 1 for compressing external air, a molecular sieve purification device 2 for purifying the air output by the air compressor 1, a booster turbine expansion device 3 for expanding and cooling the purified air, a distillation tower 5 for separating the air passing through the booster turbine expansion device 3 into oxygen and nitrogen, and a heat exchanger 4 for heat exchange of gas in the air separation device; the heat exchanger 4 and the distillation tower 5 are located in a cold box 9.

[0021] The air separation device also includes the pre-cooling device 8 arranged between the air compressor 1 and the molecular sieve purification device 2, which is a chiller. The hot gas bypass valve assists in adjusting the cooling capacity of the system according to the changes in the cooling water temperature and the cooling water volume, and finally achieves the initial temperature of the cooling water to cool the air and stabilize the air temperature within the set range.

[0022] The air separation device also includes a liquid nitrogen evaporator 6 for condensing and evaporating the air purified by the molecular sieve purification device 2 and the liquid nitrogen separated by the distillation tower 5 into liquid air and nitrogen respectively. The liquid nitrogen evaporator 6 is located at the bottom of the cold box 9 and is arranged lower than the main condenser evaporator 53. The liquid air output end of the liquid nitrogen evaporator 6 is connected to the lower tower 52.

[0023] There are two booster turbine expansion devices 3 (one for use and one for standby), and the booster turbine expansion device 3 includes a booster 31 and an expander 32 that are coaxially arranged at opposite ends, wherein the booster 31 is located outside the cold box 9, and the expander 32 is located inside the cold box 9; the input end of the booster 31 is connected to the output end of the molecular sieve purification device 2, and the output end of the booster 31 is connected to the input end of the expander 32 after being cooled by the heat exchanger 4, and the output end of the expander 32 is connected to the upper tower 51; the work of the expander 32 is recovered by the booster 31 that is coaxially matched with the expander 32, so as to increase the inlet pressure of the expander 32, increase the enthalpy drop, reduce the amount of expanded air, and also increase the liquid product extraction amount of the entire air separation device.

[0024] A connecting pipe 55 for delivering liquid air to the upper tower 51 is provided at the bottom of the lower tower 52, and a throttle valve 54 is provided on the connecting pipe 55; the distillation tower 5 is also provided with a liquid nitrogen output pipe 56 connected to the main condenser evaporator 53 and the liquid nitrogen outlet at the top of the lower tower 52, a gas nitrogen output pipe 57 connected to the main condenser evaporator 53 and the gas nitrogen outlet at the top of the lower tower 52, a liquid oxygen output pipe 58 connected to the bottom of the upper tower 51, and a dirty nitrogen output pipe 59 connected to the top of the upper tower 51; the gas nitrogen output pipe 57 is connected to the outside of the cold box 9 after passing through the heat exchanger 4; the dirty nitrogen output pipe 59 is connected to the molecular sieve purification device 2 after heat exchange in the heat exchanger 4.

[0025] The liquid nitrogen evaporator 6 is provided with a nitrogen outlet 61 and a liquid nitrogen inlet 62 arranged up and down and connected, and an air inlet 63 and a liquid air outlet 64 arranged up and down and connected separately, the liquid nitrogen inlet 62 is connected to the liquid nitrogen output pipe 58, the air output end of the molecular sieve purification device 2 is connected to the air inlet 63 through the rear heat exchanger 4, the liquid air outlet 64 is connected to the lower tower 52, and the nitrogen outlet 61 is output outside the cold box 9 after passing through the heat exchanger 4; the air and liquid nitrogen undergo heat exchange in the liquid nitrogen evaporator 6, and are condensed and evaporated into liquid air and nitrogen respectively.

[0026] The cold box 9 is provided with a subcooler 7, and the connecting pipe 55, the dirty nitrogen output pipe 59 and the liquid nitrogen output pipe 56 pass through the subcooler 7 respectively.

[0027] The molecular sieve purification device 2 includes a molecular sieve adsorber 21 and an electric heater 22; wherein the molecular sieve adsorber 21 has one input end for inputting air that has passed through a chiller, another input end for inputting contaminated nitrogen that has been heated by the electric heater 22, one output end for discharging impurity gas, and another output end for outputting purified air. The molecular sieve adsorber 21 uses an optimized long-cycle molecular sieve adsorber, an advanced airflow distribution device and structure, and a simple and reliable anti-bias flow device, so that the bed structure is simple and reliable; meanwhile, the electric heater 22 adopts a unique vertical rod-shaped design to ensure a low failure rate and easy replacement.

[0028] During operation, air is input from the air inlet of the air compressor 1, cooled by the water chiller of the precooling device 8, and then enters the molecular sieve adsorber 21 to purify impurity gases such as CO2 and H2O. Most of the output gas enters the supercharger 31 of the supercharger turbine expansion device 3 for supercharging, and then passes through the supercharged air cooler 10 and is cooled by heat exchange with the reflux gas oxygen, pure nitrogen, and contaminated nitrogen therein, and then enters the expander 32 for refrigeration, and finally sent to the lower tower 52; another part of the gas directly enters the heat exchanger 4 to participate in the recovery of the cold energy of the reflux gas oxygen, pure nitrogen, and contaminated nitrogen, and then enters the liquid nitrogen evaporator 6 arranged at the bottom of the cold box through the air inlet 63, exchanges heat with the liquid nitrogen flowing down from the main condenser evaporator 53, and is cooled to full liquefaction while evaporating the liquid nitrogen and enters the lower tower 52;

[0029] In the lower tower 52, air is separated into nitrogen and oxygen-rich liquid air, and the rising gas nitrogen portion is liquefied into liquid nitrogen in the main condenser evaporator 53, while the liquid oxygen on the low-pressure side of the main condenser evaporator 53 is vaporized; part of the liquid nitrogen is retained as reflux liquid of the lower tower 52, another part of the liquid nitrogen is drawn out from the top of the lower tower 52 through the liquid nitrogen output pipe 56 and sent to the upper tower 51, and another part is sent to the liquid nitrogen evaporator 6;

[0030] The liquid air at the bottom of the lower tower 52 passes through the connecting pipe 55, is first subcooled by the subcooler 7, and then sent to the top of the upper tower 51 through the throttle valve 54 as reflux liquid;

[0031] The liquid nitrogen formed by the main condenser evaporator 53 enters the liquid nitrogen inlet 62 of the liquid nitrogen evaporator 6 at the bottom of the cold box 9 through the liquid nitrogen output pipe 56. The liquid nitrogen flowing into the liquid nitrogen evaporator 6 is evaporated by air by the static pressure of the liquid column of the liquid nitrogen itself. The pressure of the evaporated gaseous nitrogen increases by ≥0.1MPa, and is reheated in the heat exchanger 4 to room temperature and then sent to the outside of the cold box 9 for use.

[0032] The contaminated nitrogen is led out from the top of the upper tower 51 through the contaminated nitrogen output pipe 59, and is reheated by heat exchange with the liquid air in the connecting pipe 55 and the liquid nitrogen in the liquid nitrogen output pipe 56 in the subcooler 7, and then is reheated in the heat exchanger 4, sent out of the cold box 9, and is heated by the electric heater 22 as the regeneration gas of the molecular sieve adsorber;

[0033] A small portion of the contaminated nitrogen gas after reflux reheating is extracted and filled into the cold box 9 as sealing gas for the air separation device, so that a certain positive pressure is maintained in the cold box 9 to prevent the outside atmosphere from invading the cold box 9 and causing the insulation material of the cold box 9 to become damp, thereby reducing the thermal insulation effect.

[0034] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0035] 1. By setting the height difference between the main condenser evaporator and the liquid nitrogen evaporator, the liquid nitrogen pressure flowing into the liquid nitrogen evaporator is increased by utilizing the liquid column static pressure of the liquid nitrogen itself, so that the liquid nitrogen is self-pressurized to obtain nitrogen with a pressure increase of ≥0.1MPa. The increase in nitrogen pressure does not require increasing the exhaust pressure of the air compressor, which greatly reduces the operating energy consumption of the equipment; the pressure and purity of the obtained nitrogen can meet the needs of users, saving users' one-time investment, greatly reducing production costs, and creating higher profits for users;

[0036] 2. The full low-pressure molecular sieve adsorption process of the chiller effectively prevents moisture and carbon dioxide from entering the low-temperature equipment in the cold box. The operating pressure is low and it is safe and reliable;

[0037] 3. The booster turbine expansion device uses part of the pressurized air entering the device to expand and refrigerate. The expanded air is sent to the upper tower to participate in distillation, which improves the distillation efficiency and reduces the exhaust pressure of the air compressor. It essentially achieves a low-pressure process and achieves an energy-saving effect;

[0038] 4. The exhaust adjustment range of the air compressor is 75% to 105%, achieving the purpose of energy saving.

[0039] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with this technology to understand the content of the present invention and implement it. They cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A nitrogen self-pressurizing air separation unit, comprising an air compressor (1) for compressing external air, a precooling unit (8), a molecular sieve purification unit (2) for purifying the precooled air, a booster turbine expansion unit (3) for expanding and cooling the purified air, a distillation tower (5) for separating the air passing through the booster turbine expansion unit (3) into oxygen and nitrogen, and a main heat exchanger (4) and a subcooler (7) for heat exchange with gas in the air separation unit; the distillation tower (5) comprises an upper tower (51) and a lower tower (52), a main condenser evaporator (53) is provided at the bottom of the upper tower (51), and is characterized in that: The air separation device further comprises a liquid nitrogen evaporator (6) for condensing and evaporating the air purified by the molecular sieve purification device (2) and the liquid nitrogen condensed by the main condenser evaporator (53) into liquid air and nitrogen gas respectively. The liquid nitrogen evaporator (6) is arranged below the main condenser evaporator (53), and the liquid air output end of the liquid nitrogen evaporator (6) is connected to the lower tower (52).

2. The nitrogen self-pressurizing air separation unit according to claim 1, characterized in that: The processed air purified by the molecular sieve purification device (2) is divided into two streams: one stream enters the main heat exchanger (4), and exits the main heat exchanger (4) after being cooled by the reflux gas, wherein a portion of the air enters the liquid nitrogen evaporator (6) to gasify the liquid nitrogen, and another portion of the air directly enters the lower tower (52); another stream of air equivalent to the expansion volume enters the boosting end (31) of the expander, and then enters the main heat exchanger (4) after being cooled by the cooler (9), and is extracted from the middle to enter the expansion end (32) of the expander, and most of the air after expansion is sent to the upper tower (51); after the air is initially distilled in the lower tower (52), liquid air and pure liquid nitrogen are obtained, and after passing through the subcooler (7), the air is throttled and enters the corresponding part of the upper tower (51); after further distillation in the upper tower (51), a liquid oxygen product is obtained at the bottom of the condenser evaporator (53).

3. The nitrogen self-pressurizing air separation unit according to claim 1, characterized in that: A connecting pipe (55) for conveying liquid air to the upper tower (51) is provided at the bottom of the lower tower (52), and a throttle valve (54) is provided on the connecting pipe (55); the distillation tower (5) is further provided with a liquid nitrogen output pipe (56) connected to the main condenser evaporator (53) and the liquid nitrogen outlet at the top of the lower tower (52), a gas nitrogen output pipe (57) connected to the main condenser evaporator (53) and the gas nitrogen outlet at the top of the lower tower (52), a liquid oxygen output pipe (58) connected to the bottom of the upper tower (51), and a dirty nitrogen output pipe (59) connected to the top of the upper tower (51); the liquid nitrogen output pipe (56) is connected to the liquid nitrogen evaporator (6); the gas nitrogen output pipe (57) is connected to the outside of the air separation device after passing through the heat exchanger (4); the dirty nitrogen output pipe (59) is connected to the molecular sieve purification device (2) after heat exchange in the heat exchanger (4).

4. The nitrogen self-pressurizing air separation unit according to claim 3, characterized in that: The liquid nitrogen evaporator (6) is provided with a nitrogen outlet (61) and a liquid nitrogen inlet (62) arranged vertically and connected, and an air inlet (63) and a liquid air outlet (64) arranged vertically and connected. The liquid nitrogen inlet (62) is connected to a liquid nitrogen output pipe (56). The air output end of the molecular sieve purification device (2) is connected to the air inlet (63) via a rear heat exchanger (4). The liquid air outlet (64) is connected to the lower tower (52). The nitrogen outlet (61) is output outside the air separation device after passing through the heat exchanger (4).

5. The nitrogen self-pressurizing air separation unit according to claim 3, characterized in that: It also includes a subcooler (7), and the connecting pipe (55), the dirty nitrogen output pipe (59) and the liquid nitrogen output pipe (56) pass through the subcooler (7) respectively.

6. The nitrogen self-pressurizing air separation unit according to claim 1, characterized in that: It also includes a precooling device (8) arranged between the air compressor (1) and the molecular sieve purification device (2).

7. The nitrogen self-pressurizing air separation unit according to claim 1, characterized in that: The molecular sieve purification device (2) comprises a molecular sieve adsorber (21) and an electric heater (22).

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