Air separation device and preparation method for all-liquid production of nitrogen circulation process

Abstract

The invention relates to an air separation device and a preparation method for nitrogen circulation process full liquid preparation, comprising an air filter, an air compressor, an air precooling unit, an air purification unit, a nitrogen booster, a nitrogen compressor, a high-low temperature booster turbine expander and a deep cold separation cold box unit. The compressed air enters a lower tower after heat exchange in a main heat exchanger. After the circulating nitrogen passes through the nitrogen booster, a part of the circulating nitrogen passes through the main heat exchanger and then goes to a high temperature expander for expansion, and then is reheated by the main heat exchanger and then goes out of the deep cold separation cold box unit to the nitrogen booster inlet to complete the circulation. The other part of the circulating nitrogen passes through the high temperature expander booster end, the low temperature expander booster end and the main heat exchanger and is divided into being drawn from the bottom of the main heat exchanger and throttled by a throttle valve to enter the top of the lower tower and from the middle and lower part of the main heat exchanger to the expansion end of the low temperature expander for expansion. After expansion, the compressed air is separated in a gas-liquid separator, and then is reheated by the main heat exchanger and then goes out of the deep cold separation cold box unit to the nitrogen booster to complete the circulation, thereby meeting the large cooling capacity demand, reducing the energy consumption of the device and improving the product extraction rate.

Description

Technical Field

[0001] The invention belongs to the technical field of low-temperature air separation, and in particular relates to an air separation device and a preparation method for nitrogen circulation process full liquid preparation for reducing operating costs and device energy consumption. Background Art

[0002] In recent years, the demand for industrial gases such as oxygen and nitrogen has increased greatly, especially the demand for industrial gas products under different operating conditions, especially the demand for liquid products has increased year by year, increasing at a rate of 15% to 20% per year. Liquid air separation products have the advantages of convenient storage and supply, quality assurance, long transmission distance and wide range, and are increasingly recognized by the market, with great market potential, so the use of all-liquid air separation units has become the current trend. With the increasing convenience of national transportation, enterprises are pursuing more economic benefits. Liquid air products are increasingly sought after by the market for their good product quality, low transportation costs, high cost performance, and safe and convenient use. Therefore, the preparation and sale of liquid products have become a better choice for more gas companies. At the same time, liquid products can better adjust the imbalance between product supply and demand in various regions, and with the gradual standardization of the use of medical oxygen in the country, the use of all-liquid air separation units to produce medical oxygen has also become the mainstream.

[0003] The full liquid air separation unit adopts the low temperature distillation separation process method. Its core is to use the different boiling points of the components in the air to separate the components in the air mixture in the distillation tower, so as to obtain liquid products. Its basic principle is to use the adiabatic expansion refrigeration of the expander and the Joule-Thomson throttling refrigeration effect to expand and throttle the process gas of a certain pressure to produce a lower temperature, and recover the cold through heat exchange by the heat exchanger to separate the components in the air to obtain liquid products. Most of the cold capacity of the whole system is guaranteed by the adiabatic expansion of the expander. In order to prevent the impurity components in the air from solidifying at low temperature and blocking the heat exchanger channel and the sieve holes of the sieve plate distillation tower plate, the air entering the cold box needs to be pre-treated by the low temperature distillation method to remove the components in the air that can solidify at low temperature, such as CO2 and H2O.

[0004] The raw material of the air separation unit is air, and its main consumption is electricity. The energy consumption of the liquid air separation unit is very critical to gas companies and users, so how to further reduce energy consumption in this unit is particularly important. For air separation units using cryogenic distillation, energy consumption and extraction rate are also the main parameters for evaluating the economic and technical indicators of the unit. For all-liquid air separation units, reducing the energy consumption of the unit and increasing the extraction rate can effectively reduce production costs, which is beneficial to energy conservation and emission reduction, and is more conducive to improving the economic benefits of the enterprise.

[0005] At present, the process forms adopted for liquid air separation mainly include direct air expansion cycle refrigeration process, low-pressure external cycle expansion refrigeration process with pre-cooling, medium-pressure external cycle expansion refrigeration process and medium-pressure external cycle expansion refrigeration process with pre-cooling. There are many process forms, and the product extraction rate and energy consumption are also different. Summary of the invention

[0006] The object of the present invention is to overcome the deficiencies of the prior art in the above-mentioned process and to provide an air separation device and a preparation method for the nitrogen circulation process of full liquid production, which has low energy consumption and adopts high and low temperature expanders for double expansion refrigeration to finally obtain liquid oxygen and liquid nitrogen products, so as to reduce the operating cost and the energy consumption of the device.

[0007] The technical solution of the present invention is achieved in this way:

[0008] An air separation device for all-liquid production in a nitrogen cycle process, comprising an air filter, an air compressor connected to the air filter, an air precooling unit connected to the air compressor, an air purification unit connected to the air precooling unit, and a cryogenic separation cold box unit connected to the air purification unit, wherein the cryogenic separation cold box unit comprises a main heat exchanger connected to the air purification unit, a lower tower connected to the main heat exchanger, a subcooler connected to the lower tower, a condenser evaporator, and an upper tower;

[0009] Wherein, the air compressor inlet inputs the raw material atmosphere through the air filter, the air compressor outlet is connected to the air precooling unit inlet through the first pipeline, the air precooling unit outlet is connected to the air purification unit inlet through the second pipeline, the air purification unit outlet is connected to the bottom inlet of the lower tower through the third pipeline through the main heat exchanger, the bottom outlet of the lower tower is connected to the middle inlet of the upper tower through the cooler through the fourth pipeline through the first throttle valve, the top outlet of the lower tower is connected to the condenser evaporator inlet through the fifth pipeline, the sixth pipeline is connected to the fifth pipeline and is connected to the seventh pipeline of the deep cold separation cold box unit and the inlet of the nitrogen booster through the main heat exchanger, the seventh pipeline is connected to the inlet of the nitrogen booster and is connected to the outlet of the nitrogen compressor, and the outlet of the nitrogen booster is respectively connected to the eighth pipeline and the ninth pipeline;

[0010] The eighth pipeline is connected to the tenth pipeline through the high-temperature expander boost end filter, the high-temperature expander boost end, the high-temperature expander boost end cooler, the low-temperature expander boost end filter, the low-temperature expander boost end, and the low-temperature expander boost end cooler; the ninth pipeline is connected to the high-temperature expander expansion end inlet through the main heat exchanger and the high-temperature expander expansion end filter;

[0011] The tenth pipeline is connected to the eleventh pipeline and the twelfth pipeline respectively through the main heat exchanger, the eleventh pipeline is connected to the inlet of the expansion end of the low-temperature expander through the expansion end filter of the low-temperature expander, and the twelfth pipeline is connected to the upper inlet of the lower tower through the third throttle valve;

[0012] The expansion end outlet of the low-temperature expander is connected to the inlet of the gas-liquid separator through the thirteenth pipeline, the lower outlet of the gas-liquid separator is connected to the fourteenth pipeline through the fourth throttle valve, and the upper outlet of the gas-liquid separator is connected to the seventh pipeline through the fifteenth pipeline through the main heat exchanger and the deep cold separation cold box unit; the expansion end outlet of the high-temperature expander is connected to the lower middle inlet of the main heat exchanger through the sixteenth pipeline;

[0013] The lower outlet of the condenser evaporator is connected to the twenty-first pipeline, the twenty-first pipeline is connected to the twenty-second pipeline and the twenty-third pipeline respectively, the twenty-second pipeline is connected to the top inlet of the lower tower, the twenty-third pipeline is connected to the twenty-fourth pipeline through the cooler, the twenty-fourth pipeline is connected to the upper inlet of the upper tower through the second throttle valve, the twenty-fourth pipeline is connected to the fourteenth pipeline and the twenty-fifth pipeline respectively, the twenty-fifth pipeline exits the deep cold separation cold box unit, the lower outlet of the condenser evaporator is also connected to the twenty-sixth pipeline, the twenty-sixth pipeline exits the deep cold separation cold box unit;

[0014] The top outlet of the upper tower is connected to the twenty-seventh pipeline, the twenty-seventh pipeline is connected to the twenty-eighth pipeline and the twenty-ninth pipeline respectively through the subcooler and the main heat exchanger to exit the deep cold separation cold box unit, the twenty-eighth pipeline is connected to the inlet of the nitrogen compressor, the twenty-ninth pipeline is connected to the air precooling unit, the upper middle outlet of the upper tower is connected to the thirty-first pipeline, the thirty-first pipeline is connected to the thirty-second pipeline and the thirty-third pipeline respectively through the subcooler and the main heat exchanger, the thirty-second pipeline exits the deep cold separation cold box unit and is connected to the twenty-ninth pipeline, and the thirty-third pipeline exits the deep cold separation cold box unit and is connected to the air purification unit.

[0015] Furthermore, the lower tower is a sieve plate tower or a structured packing tower, the upper tower is a structured packing tower, and the main heat exchanger, condenser evaporator and subcooler are all vacuum brazed plate-fin heat exchangers.

[0016] Furthermore, the nitrogen generated at the top of the upper tower exits the cryogenic separation cold box unit through the twenty-seventh pipeline and is connected to the twenty-eighth pipeline and the twenty-ninth pipeline. The twenty-eighth pipeline is connected to the inlet of the nitrogen compressor, and after being pressurized by the nitrogen compressor, is connected to the seventh pipeline of the nitrogen booster inlet pipeline.

[0017] Furthermore, the process flow of the air separation unit is in the form of nitrogen circulation compression and high-low temperature turbine expander expansion refrigeration. The circulating nitrogen of the nitrogen booster comes from the upper tower and the lower tower respectively, or all comes from the lower tower; when the circulating nitrogen all comes from the lower tower, the liquid oxygen output is less and the liquid nitrogen output is more. When part of the circulating nitrogen comes from the upper tower and part of it comes from the lower tower, the liquid oxygen output increases and the liquid nitrogen output decreases. The two situations adjust the output ratio of liquid nitrogen and liquid oxygen respectively.

[0018] Furthermore, a portion of the circulating nitrogen passes through the main heat exchanger and is throttled through the third throttle valve to enter the lower tower, providing part of the cooling capacity for the process.

[0019] A method for preparing the nitrogen in an air separation unit with all-liquid preparation in the nitrogen circulation process, the preparation method is as follows:

[0020] Step 1), the raw material of this device is air. The air is first filtered by an air filter to remove impurities and then enters the air compressor for compression. The compressed air pressure is 0.49MPa. Then the air enters the air precooling unit through the first pipeline to wash and cool the air. The air is cooled to 10°C. Then, it enters the air purification unit through the second pipeline to remove CO2, H2O and some hydrocarbons. Then, it enters the main heat exchanger through the third pipeline to be cooled to about -173.6°C and then exits the main heat exchanger to enter the bottom of the lower tower to participate in distillation;

[0021] Step 2), after preliminary distillation in the lower tower, nitrogen with an oxygen content of less than 1ppm is obtained at the top of the tower, and oxygen-rich liquid air with an oxygen content of 37.85% is obtained in the kettle of the lower tower; a part of the nitrogen at the top of the lower tower enters the condenser evaporator through the fifth pipeline and is condensed into liquid nitrogen, and after passing through the twenty-first pipeline, a part of the liquid nitrogen flows back to the lower tower through the twenty-second pipeline as distillation reflux liquid, and another part of the liquid nitrogen enters the subcooler through the twenty-third pipeline, and after being supercooled, passes through the twenty-fourth pipeline and is throttled by the second throttle valve, and most of it enters the top of the upper tower as the reflux liquid of the upper tower to participate in distillation, and the other part passes through the twenty-fifth pipeline as a liquid nitrogen product to exit the cryogenic separation cold box unit; another part of the nitrogen at the top of the lower tower passes through the sixth pipeline through the main heat exchanger to be reheated to room temperature and exits the cryogenic separation cold box unit, and is then sent to the nitrogen booster through the seventh pipeline at the nitrogen booster inlet for pressurization;

[0022] The oxygen-rich liquid air containing 37.85% oxygen in the kettle of the lower tower is supercooled through the fourth pipeline and the supercooler, and then throttled through the first throttle valve and enters the upper middle part of the upper tower to participate in distillation. Part of the liquid oxygen from the upper tower is evaporated into oxygen in the condenser evaporator as the rising gas of the upper tower to participate in distillation, and part of it is discharged from the deep cold separation cold box unit as liquid oxygen product through the twenty-sixth pipeline. Low-pressure nitrogen is obtained at the top of the upper tower. The low-pressure nitrogen is reheated through the twenty-seventh pipeline, the supercooler and the main heat exchanger and then discharged from the deep cold separation cold box unit in two streams, one of which is discharged through the second pipeline. The twenty-ninth pipeline is used to cool the circulating water of the air precooling unit, and one stream is sent to the nitrogen compressor through the twenty-eighth pipeline, compressed to 0.43MPa by the nitrogen compressor, and then sent to the nitrogen booster through the seventh pipeline at the nitrogen booster inlet for boosting; the dirty nitrogen is obtained in the middle and upper part of the upper tower, and the dirty nitrogen is reheated and discharged from the deep cold separation cold box unit through the thirty-first pipeline, the subcooler and the main heat exchanger in two streams, one stream is connected to the twenty-ninth pipeline through the thirty-second pipeline, and the other stream is sent to the air purification unit through the thirty-third pipeline to be used as regenerated gas and then discharged;

[0023] Step 3), the circulating nitrogen is compressed to 2.9MPa by the nitrogen booster and then divided into two streams. One stream goes to the main heat exchanger through the ninth pipeline, is extracted from the middle of the main heat exchanger, and then goes to the expansion end of the high-temperature expander to expand. After expanding to 0.445MPa, it passes through the sixteenth pipeline and is reheated to room temperature through the main heat exchanger to exit the deep cold separation cold box unit, and then goes to the seventh pipeline at the entrance of the nitrogen booster. The other stream passes through the eighth pipeline, passes through the high-temperature expander booster end filter, the high-temperature expander booster end, the high-temperature expander booster end cooler, the low-temperature expander booster end filter, the low-temperature expander booster end, and the low-temperature expander booster end cooler to connect to the tenth pipeline and go to the main heat exchanger. After being cooled by the main heat exchanger, it is divided into two streams. One stream is cooled to -173.6 ℃ becomes liquid nitrogen, then it is extracted from the bottom of the main heat exchanger, throttled to 0.45MPa by the third throttle valve, and then enters the top of the lower tower through the twelfth pipeline to participate in distillation. The other stream is cooled to -98℃, extracted from the middle and lower part of the main heat exchanger, and goes through the eleventh pipeline and the expansion end filter of the low-temperature expander to the expansion end of the low-temperature expander for expansion. After expanding to 0.45MPa, it enters the gas-liquid separator through the thirteenth pipeline. The liquid nitrogen at the bottom of the gas-liquid separator passes through the fourth throttle valve and the fourteenth pipeline and is connected with the twenty-fourth pipeline and then enters the top of the upper tower. The nitrogen at the top of the gas-liquid separator goes to the main heat exchanger through the fifteenth pipeline, is mixed with the nitrogen in the sixteenth pipeline in the main heat exchanger, and is reheated out of the deep cold separation cold box unit, and then enters the seventh pipeline at the inlet of the nitrogen booster, and then is sent to the nitrogen booster for pressurization to complete the cycle.

[0024] The gas pressure after compression by the air compression system is 0.49MPa and the temperature is ~100℃; the gas temperature after cooling by the pre-cooling system is 8~13℃.

[0025] The temperature of the gas pressurized at the boosting end of the high and low temperature expander after being cooled by the boosting end cooler is 40°C.

[0026] The purity of the produced liquid oxygen product is greater than 99.6% O2, and the oxygen in liquid nitrogen and nitrogen gas is less than 1PPmO2.

[0027] The beneficial effects produced by the technical solution of the present invention are as follows:

[0028] The refrigeration system of the device adopts a double expansion form of a high-temperature booster turbine expander and a low-temperature booster turbine expander. The boosting medium nitrogen at the boosting end first passes through the boosting end of the high-temperature expander, and then passes through the boosting end of the low-temperature expander, which are connected in series; the expansion medium nitrogen at the expansion end of the high-temperature expander comes from the outlet of the nitrogen booster, and the expansion medium nitrogen at the expansion end of the low-temperature expander comes from the boosting end of the high and low temperature expanders. This process layout is conducive to the efficient and stable operation of the expander, and also makes full use of the expansion work of the turbine expander to re-pressurize the circulating nitrogen; the high and low temperature expanders use expansion nitrogen of different qualities to give full play to the refrigeration effect, which well meets the huge demand for cooling capacity of the full liquid air separation unit.

[0029] The liquid oxygen product is extracted from the condenser evaporator, and sent to the liquid oxygen storage tank after passing through pipelines and valves; the liquid nitrogen product is extracted from the top of the lower tower, supercooled by the cooler, and then throttled by pipelines and throttle valves, taken out from the pipeline separator connected to the top of the upper tower, and sent to the liquid nitrogen storage tank through a valve.

[0030] The lower tower adopts a high-efficiency sieve plate tower or a distillation tower with high distillation efficiency; the upper tower adopts a packed tower with good distillation effect, large operating flexibility, variable working condition operation, and can adapt to the switching production of liquid oxygen and liquid nitrogen products.

[0031] The main heat exchanger, condenser evaporator and subcooler are all aluminum finned heat exchangers with good heat exchange effect; the liquid nitrogen product is extracted at low pressure after being subcooled and throttled by the subcooler, which can increase the subcooling degree of the liquid nitrogen and reduce the gasification loss when entering the storage tank. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of the connection structure of the present invention.

[0033] 1. Air filter, 2. Air compressor, 3. Air precooling unit, 4. Air purification unit, 5. Nitrogen booster, 6. Nitrogen compressor, 7. High-temperature expander boost end filter, 8. High-temperature expander boost end, 9. High-temperature expander boost end cooler, 10. Low-temperature expander boost end filter, 11. Low-temperature expander boost end, 12. Low-temperature expander boost end cooler, 13. High-temperature expander expansion end filter, 14. High-temperature expander expansion end, 15. Low-temperature expander expansion end filter, 16. Low-temperature expander expansion end, 17. Deep cold separation cold box unit, 18. Gas-liquid separator, 19. Main heat exchanger, 20. Lower tower, 21. Condenser evaporator, 22. Upper tower, 23. Subcooler, 24. First throttle valve, 25. Second throttle valve, 26. Third throttle valve, 27. Fourth throttle valve, 101. First pipeline , 102, the second pipeline, 103, the third pipeline, 104, the fourth pipeline, 105, the fifth pipeline, 106, the sixth pipeline, 107, the seventh pipeline, 108, the eighth pipeline, 109, the ninth pipeline, 110, the tenth pipeline, 111, the eleventh pipeline, 112, the twelfth pipeline, 113, the thirteenth pipeline, 114, the fourteenth pipeline, 115, the fifteenth pipeline, 116, the sixteenth pipeline, 121, the twenty-first pipeline, 122, the twenty-second pipeline, 123, the twenty-third pipeline, 124, the twenty-fourth pipeline, 125, the twenty-fifth pipeline, 126, the twenty-sixth pipeline, 127, the twenty-seventh pipeline, 131, the thirty-first pipeline, 132, the thirty-second pipeline, 133, the thirty-third pipeline. DETAILED DESCRIPTION

[0034] The present invention will be further described and illustrated below in conjunction with specific examples and drawings.

[0035] like Figure 1As shown, an air separation device for all-liquid production in a nitrogen circulation process includes an air filter 1, an air compressor 2, an air precooling unit 3, an air purification unit 4, a nitrogen booster 5, a nitrogen compressor 6, a high-temperature expander boosting end filter 7, a high-temperature expander boosting end 8, a high-temperature expander boosting end cooler 9, a low-temperature expander boosting end filter 10, a low-temperature expander boosting end 11, a low-temperature expander boosting end cooler 12, a high-temperature expander expansion end filter 13, a high-temperature expander expansion end 14, a low-temperature expander expansion end filter 15, a low-temperature expander expansion end 16, a deep cold separation cold box unit 17, a gas-liquid separator 18, a main heat exchanger 19, a lower tower 20, a condenser evaporator 21, an upper tower 22, and a supercooler 23. , a first throttle valve 24, a second throttle valve 25, a third throttle valve 26, and a fourth throttle valve 27. The inlet of the air compressor 2 inputs the raw material atmosphere through the air filter 1. The outlet of the air compressor 2 is connected to the inlet of the air precooling unit 3 through the first pipeline 101. The outlet of the air precooling unit 3 is connected to the inlet of the air purification unit 4 through the second pipeline 102. The outlet of the air purification unit 4 is connected to the bottom inlet of the lower tower through the third pipeline through the main heat exchanger. The bottom outlet of the lower tower 20 is connected to the middle inlet of the upper tower 22 through the fourth pipeline 104 through the subcooler 23 and the first throttle valve 24. The top outlet of the lower tower 20 is connected to the condensation evaporation unit 20 through the fifth pipeline 105. The inlet of the device 21 is connected, the sixth pipeline 106 is connected to the fifth pipeline 105 and is connected to the seventh pipeline 107 of the inlet of the nitrogen booster 5 through the main heat exchanger 19 and the cryogenic separation cold box unit 17. The seventh pipeline 107 is connected to the inlet of the nitrogen booster 5 and is connected to the outlet of the nitrogen compressor 6. The outlet of the nitrogen booster 5 is respectively connected to the eighth pipeline 108 and the ninth pipeline 109. The eighth pipeline 108 is connected to the tenth pipeline 110 through the high-temperature expander boost end filter 7, the high-temperature expander boost end 8, the high-temperature expander boost end cooler 9, the low-temperature expander boost end filter 10, the low-temperature expander boost end 11, and the low-temperature expander boost end cooler 12. The ninth pipeline 109 is connected to the inlet of the high-temperature expander expansion end 14 through the main heat exchanger 19 and the high-temperature expander expansion end filter 13, the tenth pipeline 110 is connected to the eleventh pipeline 111 and the twelfth pipeline 112 through the main heat exchanger 19, the eleventh pipeline 111 is connected to the inlet of the low-temperature expander expansion end 16 through the low-temperature expander expansion end filter 15, the twelfth pipeline 112 is connected to the upper inlet of the lower tower 20 through the third throttle valve 26, the outlet of the low-temperature expander expansion end 16 is connected to the inlet of the gas-liquid separator 18 through the thirteenth pipeline 113, and the lower outlet of the gas-liquid separator 18 is connected to the fourteenth pipeline 114 through the fourth throttle valve 27,The upper outlet of the gas-liquid separator 18 is connected to the seventh pipeline 107 through the fifteenth pipeline 115 and the main heat exchanger 19 to exit the cryogenic separation cold box unit 17. The outlet of the high-temperature expander expansion end 14 is connected to the middle and lower inlet of the main heat exchanger 19 through the sixteenth pipeline 116. The lower outlet of the condenser evaporator 21 is connected to a twenty-first pipeline 121, and the twenty-first pipeline 121 is respectively connected to the twenty-second pipeline 122 and the twenty-third pipeline 123. The twenty-second pipeline 122 is connected to the top inlet of the lower tower 20. The twenty-third pipeline 123 is connected to the twenty-fourth pipeline 124 through the subcooler 23. The twenty-fourth pipeline 124 is connected to the upper inlet of the upper tower 22 through the second throttle valve 25. The twenty-fourth pipeline 124 is respectively connected to the fourteenth pipeline 114 and the twenty-fifth pipeline 125. The twenty-fifth pipeline 125 exits the cryogenic separation cold box unit 17. The lower outlet of the condenser evaporator 21 is also connected to the twenty-first pipeline 121. A twenty-sixth pipeline 126 is connected, the twenty-sixth pipeline 126 exits the cryogenic separation cold box unit 17, the top outlet of the upper tower 22 is connected to the twenty-seventh pipeline 127, the twenty-seventh pipeline 127 exits the cryogenic separation cold box unit 17 through the subcooler 23 and the main heat exchanger 19 and is respectively connected to the twenty-eighth pipeline 128 and the twenty-ninth pipeline 129, the twenty-eighth pipeline 128 is connected to the inlet of the nitrogen compressor 6, the twenty-ninth pipeline 129 is connected to the air precooling unit 3, the upper middle outlet of the upper tower 22 is connected to the thirty-first pipeline 131, the thirty-first pipeline 131 is respectively connected to the thirty-second pipeline 132 and the thirty-third pipeline 133 through the subcooler 23 and the main heat exchanger 19, the thirty-second pipeline 132 exits the cryogenic separation cold box unit 17 and is connected to the twenty-ninth pipeline 129, the thirty-third pipeline 133 exits the cryogenic separation cold box unit 17 and is connected to the air purification unit 4.

[0036] The lower tower 20 is a sieve plate tower or a structured packing tower, the upper tower 22 is a structured packing tower, and the main heat exchanger 19, the condenser evaporator 21 and the subcooler 23 are all vacuum brazed plate-fin heat exchangers.

[0037] The nitrogen generated at the top of the upper tower 22 is discharged from the cryogenic separation cold box unit 17 through the twenty-seventh pipeline 127 and is connected to the twenty-eighth pipeline 128 and the twenty-ninth pipeline 129. The twenty-eighth pipeline 128 is connected to the inlet of the nitrogen compressor 6, and after being pressurized by the nitrogen compressor 6, is connected to the seventh pipeline 107 of the inlet pipeline of the nitrogen booster 5.

[0038] The process flow of the air separation unit is nitrogen circulation compression and high and low temperature turbine expander double expansion refrigeration. The circulating nitrogen of the nitrogen booster 5 can come from the upper tower 22 and the lower tower 20 respectively, or all from the lower tower 20; when the circulating nitrogen comes all from the lower tower 20, the liquid oxygen output is less and the liquid nitrogen output is more. When part of the circulating nitrogen of the nitrogen booster 5 comes from the upper tower 22 and part from the lower tower 20, the liquid oxygen output increases and the liquid nitrogen output decreases. The two situations can adjust the output ratio of liquid nitrogen and liquid oxygen products respectively.

[0039] A portion of the circulating nitrogen in the process flow of the air separation unit passes through the main heat exchanger 19 and then is throttled through the third throttle valve 26 to enter the lower tower 20, providing part of the cooling capacity for the process.

[0040] A method for preparing a full liquid using the above-mentioned device is as follows:

[0041] Step 1), the raw material of this device is air. The air is first filtered out of impurities by the air filter 1 and then enters the air compressor 2 for compression. The compressed air pressure is 0.49MPa. Then, the air enters the air precooling unit 3 through the first pipeline 101 to wash and cool the air. The air is cooled to 10°C, and then enters the air purification unit 4 through the second pipeline 102 to remove CO2, H2O and some hydrocarbons. Then, the air enters the main heat exchanger 19 through the third pipeline 103 and is cooled to about -173.6°C. After that, the air exits the main heat exchanger 19 and enters the bottom of the lower tower 20 to participate in distillation.

[0042] Step 2), after preliminary distillation in the lower tower 20, nitrogen containing less than 1 ppm of oxygen is obtained at the top of the tower, and oxygen-enriched liquid air containing 37.85% of oxygen is obtained in the bottom of the lower tower 20. A portion of the nitrogen at the top of the lower tower 20 enters the condenser evaporator 21 through the fifth pipeline 105 and is condensed into liquid nitrogen. After the liquid nitrogen passes through the twenty-first pipeline 121, a portion of it flows back to the lower tower 20 through the twenty-second pipeline 122 as a distillation reflux liquid, and the other portion enters the supercooler 23 through the twenty-third pipeline 123, is supercooled, and then passes through the twenty-fourth pipeline 124. After throttling by the fourth throttle valve 27, most of it enters the top of the upper tower 22 as the reflux liquid of the upper tower 22 to participate in distillation, and another small portion passes through the twenty-fifth pipeline 125 as a liquid nitrogen product and exits the deep-cold separation cold box unit 17; another portion of the nitrogen at the top of the lower tower 20 passes through the sixth pipeline 106 and the main heat exchanger 19 to be reheated to room temperature and exit the deep-cold separation cold box unit 17, and then is sent to the nitrogen booster 5 for pressurization through the seventh pipeline 107 at the inlet of the nitrogen booster 5.

[0043] The oxygen-rich liquid air containing 37.85% oxygen in the bottom of the lower tower 20 is supercooled through the fourth pipeline 104 and the supercooler 23, and then throttled by the first throttle valve 24 and enters the upper and middle part of the upper tower 22 to participate in distillation. A part of the liquid oxygen from the upper tower 22 is evaporated into oxygen in the condenser evaporator 21 as the rising gas of the upper tower 22 to participate in distillation, and a part is discharged from the deep cold separation cold box unit 17 as a liquid oxygen product through the twenty-sixth pipeline 126, and low-pressure nitrogen is obtained at the top of the upper tower 22. The low-pressure nitrogen is reheated through the twenty-seventh pipeline 127, the supercooler 23 and the main heat exchanger 19 and then discharged from the deep cold separation cold box unit 17 and divided into two streams, one of which is sent to the air precooling unit 3 to cool the circulating water through the twenty-ninth pipeline 129, and the other is sent to the nitrogen compressor 6 through the twenty-eighth pipeline 128. After being compressed to 0.43MPa by the nitrogen compressor 6, it is sent to the nitrogen booster 5 for pressurization through the seventh pipeline 107 at the inlet of the nitrogen booster 5. The contaminated nitrogen gas is obtained in the middle and upper part of the upper tower 22. The contaminated nitrogen gas is reheated and discharged from the deep cold separation cold box unit 17 through the thirty-first pipeline 131, the subcooler 23 and the main heat exchanger 19. One stream is connected to the twenty-ninth pipeline 129 through the thirty-second pipeline 132, and the other stream is sent to the air purification unit 4 through the thirty-third pipeline 133 to be used as regenerated gas and then discharged.

[0044] Step 3), the circulating nitrogen is compressed to 2.9MPa by the nitrogen booster 5 and then divided into two streams, one stream goes to the main heat exchanger 19 through the ninth pipeline 109, is extracted from the middle of the main heat exchanger 19, passes through the high-temperature expander expansion end filter 13, and then goes to the high-temperature expander expansion end 14 to expand, expands to 0.445MPa, passes through the sixteenth pipeline 116, passes through the main heat exchanger 19 to be reheated to room temperature, and then goes to the deep cold separation cold box unit 17, and then goes to the seventh pipeline 107 at the entrance of the nitrogen booster 5; the other stream goes through the eighth pipeline 108, passes through the high-temperature expander boost end filter 7, the high-temperature expander boost end 8, the high-temperature expander boost end cooler 9, the low-temperature expander boost end filter 10, the low-temperature expander boost end 11, and the low-temperature expander boost end cooler 12, and then connects to the tenth pipeline 110 to go to the main heat exchanger 19, and is cooled by the main heat exchanger 19 and is divided into two streams, one of which is cooled to -173.6°C to become liquid nitrogen The liquid is extracted from the bottom of the main heat exchanger 19 and throttled to 0.45 MPa by the third throttle valve 26, and then enters the top of the lower tower 20 through the twelfth pipeline 112 to participate in distillation. The other stream is cooled to -98°C and extracted from the middle and lower part of the main heat exchanger 19, and then goes to the expansion end 16 of the low-temperature expander through the eleventh pipeline 111 and the expansion end filter 15 of the low-temperature expander for expansion. After expanding to 0.45 MPa, it enters the gas-liquid separator 18 through the thirteenth pipeline 113. The liquid nitrogen at the bottom of the gas-liquid separator 18 passes through the fourth throttle valve 27 and the fourteenth pipeline 114 and is connected with the twenty-fourth pipeline 124, and then enters the top of the upper tower 22. The nitrogen at the top of the gas-liquid separator 18 goes to the main heat exchanger 19 through the fifteenth pipeline 115, and is mixed with the nitrogen in the sixteenth pipeline 116 in the main heat exchanger 19, and then is heated out of the deep cold separation cold box unit 17, and then enters the seventh pipeline 107 at the inlet of the nitrogen booster 5, and then is sent to the nitrogen booster 5 for pressurization to complete the cycle.

Claims

1. An air separation device for all-liquid production in a nitrogen cycle process, comprising an air filter (1), an air compressor (2) connected to the air filter (1), an air precooling unit (3) connected to the air compressor (2), an air purification unit (4) connected to the air precooling unit (3), and a deep-cold separation cold box unit (17) connected to the air purification unit (4), characterized in that : The cryogenic separation cold box unit (17) comprises a main heat exchanger (19) connected to the air purification unit (4), a lower tower (20) connected to the main heat exchanger (19), a subcooler (23) connected to the lower tower (20), a condenser evaporator (21), and an upper tower (22); The inlet of the air compressor (2) is fed with raw material atmosphere through an air filter (1); the outlet of the air compressor (2) is connected to the inlet of the air precooling unit (3) through a first pipeline (101); the outlet of the air precooling unit (3) is connected to the inlet of the air purification unit (4) through a second pipeline (102); the outlet of the air purification unit (4) is connected to the bottom inlet of the lower tower (20) through a third pipeline (103) via a main heat exchanger (19); the bottom outlet of the lower tower (20) is connected to the upper tower (20) through a cooler (23) through a fourth pipeline (104) and a first throttle valve (24). (22) the middle inlet is connected, the top outlet of the lower tower (20) is connected to the inlet of the condenser evaporator (21) through the fifth pipeline (105), the sixth pipeline (106) is connected to the fifth pipeline (105) and is connected to the seventh pipeline (107) of the inlet of the cryogenic separation cold box unit (17) and the nitrogen booster (5) through the main heat exchanger (19), the seventh pipeline (107) is connected to the inlet of the nitrogen booster (5) and is also connected to the outlet of the nitrogen compressor (6), and the outlet of the nitrogen booster (5) is respectively connected to the eighth pipeline (108) and the ninth pipeline (109); The eighth pipeline (108) is connected to the tenth pipeline (110) via the high-temperature expander boost end filter (7), the high-temperature expander boost end (8), the high-temperature expander boost end cooler (9), the low-temperature expander boost end filter (10), the low-temperature expander boost end (11), and the low-temperature expander boost end cooler (12); the ninth pipeline (109) is connected to the inlet of the high-temperature expander expansion end (14) via the main heat exchanger (19) and the high-temperature expander expansion end filter (13); The tenth pipeline (110) is connected to the eleventh pipeline (111) and the twelfth pipeline (112) respectively through the main heat exchanger (19); the eleventh pipeline (111) is connected to the inlet of the expansion end (16) of the low-temperature expander through the expansion end filter (15) of the low-temperature expander; and the twelfth pipeline (112) is connected to the upper inlet of the lower tower (20) through the third throttle valve (26); The outlet of the expansion end (16) of the low-temperature expander is connected to the inlet of the gas-liquid separator (18) through the thirteenth pipeline (113); the lower outlet of the gas-liquid separator (18) is connected to the fourteenth pipeline (114) through the fourth throttle valve (27); the upper outlet of the gas-liquid separator (18) is connected to the seventh pipeline (107) through the fifteenth pipeline (115) through the main heat exchanger (19) and out of the deep-cold separation cold box unit (17); the outlet of the high-temperature expander (14) is connected to the middle and lower inlet of the main heat exchanger (19) through the sixteenth pipeline (116); The lower outlet of the condenser evaporator (21) is connected to a twenty-first pipeline (121), the twenty-first pipeline (121) is connected to a twenty-second pipeline (122) and a twenty-third pipeline (123), the twenty-second pipeline (122) is connected to a top inlet of the lower tower (20), the twenty-third pipeline (123) is connected to a twenty-fourth pipeline (124) through a cooler (23), the twenty-fourth pipeline (124) is connected to an upper inlet of the upper tower (22) through a second throttle valve (25), the twenty-fourth pipeline (124) is connected to a fourteenth pipeline (114) and a twenty-fifth pipeline (125), the twenty-fifth pipeline (125) exits the cryogenic separation cold box unit (17), the lower outlet of the condenser evaporator (21) is also connected to a twenty-sixth pipeline (126), the twenty-sixth pipeline (126) exits the cryogenic separation cold box unit (17); The top outlet of the upper tower (22) is connected to the twenty-seventh pipeline (127), and the twenty-seventh pipeline (127) passes through the subcooler (23) and the main heat exchanger (19) and exits the deep cold separation cold box unit (17) and is respectively connected to the twenty-eighth pipeline (128) and the twenty-ninth pipeline (129), the twenty-eighth pipeline (128) is connected to the inlet of the nitrogen compressor (6), and the twenty-ninth pipeline (129) is connected to the air precooling unit (3). The upper tower (22 ) is connected to the thirty-first pipeline (131), and the thirty-first pipeline (131) is connected to the thirty-second pipeline (132) and the thirty-third pipeline (133) respectively through the subcooler (23) and the main heat exchanger (19), and the thirty-second pipeline (132) is connected to the twenty-ninth pipeline (129) when it exits the cryogenic separation cold box unit (17), and the thirty-third pipeline (133) is connected to the air purification unit (4) when it exits the cryogenic separation cold box unit (17).

2. The air separation unit for all-liquid production of nitrogen by nitrogen cycle process according to claim 1, characterized in that: The lower tower (20) is a sieve plate tower or a structured packing tower, the upper tower (22) is a structured packing tower, and the main heat exchanger (19), condenser evaporator (21) and subcooler (23) are all vacuum brazed plate-fin heat exchangers.

3. The air separation unit for all-liquid production of nitrogen by nitrogen cycle process according to claim 1, characterized in that: The nitrogen generated at the top of the upper tower (22) is discharged from the cryogenic separation cold box unit (17) through the twenty-seventh pipeline (127) and is connected to the twenty-eighth pipeline (128) and the twenty-ninth pipeline (129). The twenty-eighth pipeline (128) is connected to the inlet of the nitrogen compressor (6), and after being pressurized by the nitrogen compressor (6), is connected to the seventh pipeline (107) of the inlet pipeline of the nitrogen booster (5).

4. The air separation unit for all-liquid production of nitrogen by nitrogen cycle process according to claim 1, characterized in that: The process flow of the air separation device is nitrogen circulation compression and high-low temperature turbine expander expansion refrigeration. The circulating nitrogen of the nitrogen booster (5) comes from the upper tower (22) and the lower tower (20) respectively, or all comes from the lower tower (20). When the circulating nitrogen comes all from the lower tower (20), the liquid oxygen output is small and the liquid nitrogen output is large. When part of the circulating nitrogen comes from the upper tower (22) and part of it comes from the lower tower (20), the liquid oxygen output increases and the liquid nitrogen output decreases. The two situations adjust the output ratio of liquid nitrogen and liquid oxygen respectively.

5. The air separation unit for all-liquid production of nitrogen by nitrogen cycle process according to claim 4, characterized in that: A portion of the circulating nitrogen passes through the main heat exchanger (19) and then is throttled through the third throttle valve (26) to enter the lower tower (20), thereby providing part of the cooling capacity for the process.

6. A method for producing nitrogen in an air separation unit by all-liquid production in a nitrogen cycle process according to any one of claims 1 to 5, characterized in that: The preparation method is as follows: Step 1), the raw material of the device is air. The air is first filtered through an air filter (1) to remove impurities and then enters an air compressor (2) for compression. The compressed air pressure is 0.49 MPa. The air then enters an air precooling unit (3) through a first pipeline (101) to wash and cool the air. The air is cooled to 10°C. The air then enters an air purification unit (4) through a second pipeline (102) to remove CO2, H2O and some hydrocarbons. The air then enters a main heat exchanger (19) through a third pipeline (103) to be cooled to about -173.6°C and then exits the main heat exchanger (19) to enter the bottom of a lower tower (20) to participate in distillation. Step 2), after preliminary distillation in the lower tower (20), nitrogen with an oxygen content of less than 1 ppm is obtained at the top of the tower, and oxygen-enriched liquid air with an oxygen content of 37.85% is obtained at the bottom of the lower tower (20); a portion of the nitrogen at the top of the lower tower (20) enters the condenser evaporator (21) through the fifth pipeline (105) to be condensed into liquid nitrogen, and after passing through the twenty-first pipeline (121), a portion of the liquid nitrogen flows back to the lower tower (20) through the twenty-second pipeline (122) as distillation reflux liquid, and the other portion of the liquid nitrogen enters the subcooler (23) through the twenty-third pipeline (123), and after being subcooled, After being throttled by the second throttle valve (25) through the twenty-fourth pipeline (124), most of the nitrogen enters the top of the upper tower (22) as the reflux liquid of the upper tower (22) to participate in distillation, and the other part passes through the twenty-fifth pipeline (125) to exit the cryogenic separation cold box unit (17) as a liquid nitrogen product; another part of the nitrogen at the top of the lower tower (20) passes through the sixth pipeline (106) through the main heat exchanger (19) to be reheated to room temperature and exits the cryogenic separation cold box unit (17), and then is sent to the nitrogen booster (5) through the seventh pipeline (107) at the inlet of the nitrogen booster (5) for pressurization; The oxygen-rich liquid air containing 37.85% oxygen in the bottom of the lower tower (20) is supercooled through the fourth pipeline (104) and the subcooler (23), and then throttled through the first throttle valve (24) to enter the upper middle part of the upper tower (22) to participate in distillation. A part of the liquid oxygen from the upper tower (22) is evaporated into oxygen in the condenser evaporator (21) and used as the rising gas of the upper tower (22) to participate in distillation, and a part of it is discharged from the deep-cold separation cold box unit (17) as a liquid oxygen product through the twenty-sixth pipeline (126). Low-pressure nitrogen is obtained at the top of the upper tower (22). The low-pressure nitrogen is reheated through the twenty-seventh pipeline (127), the subcooler (23) and the main heat exchanger (19), and then discharged from the deep-cold separation cold box unit (17) and divided into two streams, one of which is discharged through the twenty-seventh pipeline (127), the subcooler (23) and the main heat exchanger (19). The ninth pipeline (129) is used to cool the circulating water of the air precooling unit (3), and one stream is sent to the nitrogen compressor (6) through the twenty-eighth pipeline (128), compressed to 0.43 MPa by the nitrogen compressor, and then sent to the nitrogen booster (5) through the seventh pipeline (107) at the inlet of the nitrogen booster (5) for boosting; the contaminated nitrogen gas is obtained in the middle and upper part of the upper tower (22), and the contaminated nitrogen gas is reheated through the thirty-first pipeline (131), the subcooler (23) and the main heat exchanger (19) and is divided into two streams to be reheated and discharged from the deep-cold separation cold box unit (17), one stream is connected to the twenty-ninth pipeline (129) through the thirty-second pipeline (132), and the other stream is sent to the air purification unit (4) through the thirty-third pipeline (133) to be used as regenerated gas and then discharged; Step 3), the circulating nitrogen is compressed to 2.9 MPa by the nitrogen booster (5) and then divided into two streams. One stream passes through the ninth pipeline (109) to the main heat exchanger (19), is extracted from the middle of the main heat exchanger (19), passes through the expansion end filter (13) of the high-temperature expander, and then expands at the expansion end (14) of the high-temperature expander. After expanding to 0.445 MPa, it passes through the sixteenth pipeline (116) through the main heat exchanger (19) and is reheated to room temperature and exits the deep cold separation cold box unit (17), and then goes to the inlet of the nitrogen booster (5). The other stream passes through the eighth pipeline (108), passes through the high-temperature expander boost end filter (7), the high-temperature expander boost end (8), the high-temperature expander boost end cooler (9), the low-temperature expander boost end filter (10), the low-temperature expander boost end (11), and the low-temperature expander boost end cooler (12), and then connects to the tenth pipeline (110) and goes to the main heat exchanger (19). After being cooled by the main heat exchanger (19), it is divided into two streams. One stream is cooled to -173.6°C and becomes liquid nitrogen, and then is discharged from the main heat exchanger (19). The liquid is extracted from the bottom of the heat exchanger (19), throttled to 0.45 MPa by the third throttle valve (26), and then enters the top of the lower tower (20) through the twelfth pipeline (112) to participate in distillation. Another stream is cooled to -98°C and extracted from the middle and lower part of the main heat exchanger (19), through the eleventh pipeline (111), the expansion end filter (15) of the low-temperature expander, and then expanded to the expansion end (16) of the low-temperature expander. After expanding to 0.45 MPa, it enters the gas-liquid separator (18) through the thirteenth pipeline (113). The gas-liquid separator (18) ) The liquid nitrogen at the bottom passes through the fourth throttle valve (27) and the fourteenth pipeline (114) and is connected to the twenty-fourth pipeline (124) and enters the top of the upper tower (22). The nitrogen at the top of the gas-liquid separator (18) passes through the fifteenth pipeline (115) to the main heat exchanger (19), where it is mixed with the nitrogen in the sixteenth pipeline (116) and reheated. After exiting the deep cold separation cold box unit (17), it enters the seventh pipeline (107) at the inlet of the nitrogen booster (5) and is then sent to the nitrogen booster (5) for pressurization, completing the cycle.

7. The all-liquid preparation method of a nitrogen cycle process according to claim 6, characterized in that: The gas pressure after compression by the air compression system is 0.49MPa and the temperature is ~100℃; the gas temperature after cooling by the pre-cooling system is 8~13℃.

8. The all-liquid preparation method of a nitrogen cycle process according to claim 1, characterized in that: The temperature of the gas pressurized at the boosting end of the high and low temperature expander after being cooled by the boosting end cooler is 40°C.

9. The all-liquid preparation method of a nitrogen cycle process according to claim 1, characterized in that: The purity of the produced liquid oxygen product is greater than 99.6% O2, and the oxygen in liquid nitrogen and nitrogen gas is less than 1PPmO2.

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