Method and equipment for producing air product based on cryogenic distillation

[0047]The present invention will be further described below through specific embodiments with reference to the accompanying drawings. These embodiments are only used to illustrate the present invention and do not limit the scope of protection of the present invention.

[0048]In the present invention, the term "raw air" refers to a mixture mainly containing oxygen and nitrogen.

[0049]The term "air product" refers to a gas whose composition is equal to or close to that of air, that is, nitrogen accounts for about 78% and oxygen accounts for about 21% by volume fraction. In the present invention, the main purpose of the air product is as the instrument gas or factory gas of the air separation device. Considering the safety of workers' operation, its composition should be as close as possible to the proportion of normal air.

[0050]The term "soil nitrogen" covers a gaseous fluid with a nitrogen content generally not less than 95 mole percent; the term "soil liquid nitrogen" refers to a liquid fluid with a nitrogen content generally greater than 95 mole percent.

[0051]The term "oxygen-enriched liquid air" refers to a liquid fluid with a mole percentage of oxygen greater than 30; the term "liquid air" refers to a liquid fluid with a mole percentage of oxygen not greater than 30; the term "liquid oxygen" covers a liquid with a mole percentage of oxygen greater than 99 Fluid, and the oxygen content in "liquid oxygen" is higher than that in "oxygen-rich liquid air".

[0052]The cryogenic rectification of the present invention is a rectification method performed at least partly at a temperature of 150K or lower. "Tower" here means a distillation or fractionation column or zone in which liquid and gas phases are contacted in countercurrent to effectively separate a fluid mixture. The operating pressure of the "first column" in the present invention is generally 5 to 6.5 bara, which is higher than the general operating pressure of the "second column" of 1.1 to 1.5 bara. The second tower can be installed vertically on top of the first tower or two towers can be installed side by side. The "first tower" is also generally called the medium pressure tower or the lower tower, and the "second tower" is also generally called the low pressure tower or the upper tower. The main condensing evaporator is generally located at the bottom of the "second tower", it can make the pure nitrogen produced at the top of the first tower heat exchange with the pure liquid oxygen produced at the bottom of the second tower to obtain pure liquid nitrogen at the top of the first tower. , While partially evaporating pure liquid oxygen. The main condensing evaporator types include shell and tube type, falling film type, immersion bath type, etc. The immersion bath type condensing evaporator can be used in the present invention.

[0053]The air pre-cooling system in the present invention is used to pre-cool the high-temperature air (70-120°C) discharged from the main air compressor to a temperature suitable for entering the air purification system (generally 10-25°C). High-temperature air generally contacts ordinary circulating cooling water and low-temperature water (usually 5-20°C) in the air cooling tower to exchange heat to achieve the purpose of cooling. Low-temperature water can be obtained by contacting ordinary circulating cooling water with gas products or by-products produced by air separation equipment, such as dirty nitrogen, or by using a refrigerator.

[0054]Air purification system refers to the dust, water vapor, CO in the air2, Purification devices for removing hydrocarbons, etc. In the present invention, pressure swing adsorption is generally used, wherein the adsorbent can be molecular sieve plus alumina or only molecular sieve.

[0055]In the main heat exchanger, the compressed, pre-cooled, and purified raw material air and the gas and/or liquid products produced by rectification undergo non-contact heat exchange, and are cooled to close to or equal to the rectification temperature of one column, generally lower At 150K. Common main heat exchangers include split type or integrated type. The main heat exchanger is divided into high pressure according to the suitable pressure range (>20bara pressure) and low pressure (<20bara pressure) heat exchanger. In the present invention, a high-pressure plate heat exchanger and a low-pressure plate heat exchanger or an integral combined heat exchanger can be used at the same time.

[0056]In the present invention, the ultra-low pressure is generally 1-2 bara, the low pressure is generally 2-10 bara, the medium pressure is generally 10-70 bara, the high pressure is generally 70-90 bara, and the ultra-high pressure is generally above 90 bara; the first nitrogen pressure is generally 2- 8bara, the second nitrogen pressure is generally 5-12bara, the third nitrogen pressure is generally 20-70bara, the fourth nitrogen pressure is generally 1-2bara, and the fifth nitrogen pressure is generally 70-99bara.

[0057]Such asfigure 1 As shown, the feed air 101 is pressurized to 6 bara by the main air compressor 4, and then pre-cooled and purified (pre-cooling system and purification system are not shown), sent to the low-pressure plate heat exchanger 72 and rectified from the first The 1.1 bara of ultra-low pressure nitrogen at the top of the second column 2 (at least part of the fourth nitrogen 1051) and the 1.15 bara of the dirty nitrogen 112 at the upper part of the second column 2 can optionally be combined with the low-pressure high-purity nitrogen from the top of the first column 1 (5.2 bara) A nitrogen gas 102) performs indirect heat exchange and is cooled to about -176°C and then sent to the lower part of the first column 1 for rectification. A part 1021 of the first nitrogen 102 extracted from the top of the first column 1 is optionally sent to the low-pressure plate heat exchanger 72 for heating, and the other part 1022 is sent to the high-pressure plate heat exchanger 71 to obtain a low-pressure high-purity nitrogen gas of 5.2 bara after heating. The product, optionally a part of 1022 and 1021 are combined and pressurized by the first nitrogen compressor 411, of which the first part is extracted from the intermediate stage of the first nitrogen compressor 411 to obtain 11.5bara medium-pressure high-purity nitrogen (the second nitrogen 103), In the second part, a 63.4bara medium-pressure high-purity nitrogen product (the third nitrogen 104) is obtained by pumping from the last stage of the first nitrogen compressor 411. At least a part of the third nitrogen 1041 is sent to the second nitrogen compressor 412 to continue to pressurize the medium-pressure high-purity nitrogen from the last stage of the first nitrogen compressor 411 to 85 bara; at least a part of the third nitrogen 1042 undergoes a high-pressure plate exchange After the heat exchanger 71 is partially cooled, it is expanded by the first nitrogen expander 121 to obtain 5.2 bara low-pressure high-purity nitrogen, at least a part of which (the fourth nitrogen 105a) is combined with the first nitrogen 102 extracted from the top of the first tower 1, at least The other part (the fourth nitrogen 105b) is sent to the top of the second column 2; at least a part of the third nitrogen 1043 is sent to the third nitrogen compressor 413 to continue the medium-pressure high-purity nitrogen from the last stage of the first nitrogen compressor 411 Pressurized to 99bara to obtain ultra-high-pressure high-purity nitrogen product (fifth nitrogen 106); at least a part of the fifth nitrogen is throttled to 85bara, which is the same pressure as at least a part of 1041 of the third nitrogen pressurized to 85bara, two strands After confluence, it is sent to the high-pressure plate heat exchanger 71. After the high-pressure plate heat exchanger 71 is cooled, high-purity liquid nitrogen (the first liquid nitrogen 1061) is formed, which is expanded and decompressed by the second nitrogen expander 122 to obtain a high-purity of 6 bara. Liquid nitrogen (second liquid nitrogen 1062). A part of the second liquid nitrogen 1062 can optionally be further expanded and reduced by the throttle valve 31 to obtain 5.3bara high-purity liquid nitrogen and sent to the top of the first tower 1 as reflux liquid; the second liquid nitrogen The other part of 1062 is supercooled by the cooler 8 and then sent to the top of the second tower 2 as reflux liquid. Draw 6 bara from the bottom of the first tower 1 containing 37% O2Part of the oxygen-enriched liquid air 108 is supercooled by the cooler 8 and then sent to the second tower 2 as reflux liquid, and at least a part is pressurized by the first pump 21 to obtain 11.6bara medium-pressure oxygen-enriched liquid air, which is then sent to the high pressure After the temperature of the plate heat exchanger 71 is raised, a gaseous medium-pressure oxygen-enriched liquid 1081 of 11.5 bara is obtained, which is mixed with the second nitrogen 103 of 11.5 bara extracted from the intermediate stage of the first nitrogen compressor 411 in the static mixer 9, and then adjusted The ratio of nitrogen and oxygen in the output medium pressure air product 109. Extract 1.4bara of liquid oxygen 107 (-180°C) from the main condensing evaporator 3, pressurize it by the second pump 22 to obtain 80bara of high pressure liquid oxygen 107, and then send it to the high pressure plate heat exchanger 71 to heat up to obtain 80bara of high pressure oxygen Product 110. 1.1 bara of ultra-low pressure nitrogen (at least part of the fourth nitrogen 1051) is extracted from the top of the second tower 2 through the cooler 8 and the low-pressure plate heat exchanger 72 to obtain the ultra-low pressure nitrogen product. The sewage liquid nitrogen 111 extracted from the first tower 1 is subcooled by the cooler 8 and then sent to the second tower 2 as reflux liquid. The 1.15bara sewage nitrogen 112 extracted from the second tower 2 is sequentially sent to the subcooler 8 and the low-pressure plate heat exchanger 72 for reheating.

[0058]In this embodiment, optionally, the oxygen-enriched liquid air 108 drawn from the bottom of the first tower 1 is pressurized to different pressure ranges by the first pump 21 with different heads, so as to output the air product with the same pressure as the second nitrogen gas. 109. Alternatively, the oxygen-enriched liquid 108 is pressurized to different pressure ranges by connecting different numbers of first pumps 21 in series to output air products 109 in different pressure ranges. Optionally, the first liquid nitrogen 1061 may be expanded and decompressed by the second nitrogen expander 122 and/or the throttle valve 31 and then sent to the top of the first column 1 and/or the second column 2. Alternatively, the high-pressure plate heat exchanger 71 and the low-pressure plate heat exchanger 72 may be replaced by an integral combined heat exchanger as the main heat exchanger. The first nitrogen expander 121 is braked by a second nitrogen compressor 412 connected to it; the second nitrogen expander 122 is braked by a generator 10 connected to it. In this embodiment, all kinds of materials flow through pipelines connected between equipment as the conveying medium.

[0059]figure 2 The embodiment shown is the same asfigure 1 The main difference is that the raw materials used to produce air products 109 are different.figure 2 , Choose the liquid air 113 in the first tower 1 to replacefigure 1 The oxygen-rich liquid at the bottom of the first column 1 is introduced into the first pump 21 for pressure increase.figure 2 The other parts of the illustrated embodiment are the same asfigure 1 The embodiments shown are the same. Both are examples of the realization of the present invention, but do not limit the spirit and scope of the present invention in any way. Specifically, infigure 2 In the illustrated embodiment, the feed air 101 is pressurized to 6 bara by the main air compressor 4, and then is pre-cooled and purified (the pre-cooling system and the purification system are not shown), and then sent to the low-pressure plate heat exchanger 72 and refined After distillation, the ultra-low pressure nitrogen from the top 1.1 bara of the second column 2 (at least part of the fourth nitrogen 1051) and the 1.15 bara dirty nitrogen 112 from the top of the second column 2 can optionally be combined with the low pressure and high pressure from the top of the first column 1 at 5.2 bara. Pure nitrogen (the first nitrogen 102) performs indirect heat exchange, is cooled to about -176°C and then sent to the lower part of the first column 1 for rectification. A part 1021 of the first nitrogen 102 extracted from the top of the first column 1 is optionally sent to the low-pressure plate heat exchanger 72 for heating, and the other part 1022 is sent to the high-pressure plate heat exchanger 71 to obtain a low-pressure high-purity nitrogen gas of 5.2 bara after heating. The product, optionally a part of 1022 and 1021 are combined and pressurized by the first nitrogen compressor 411, of which the first part is extracted from the intermediate stage of the first nitrogen compressor 411 to obtain 11.5bara medium pressure high purity nitrogen (the second nitrogen 103), The second part is extracted from the last stage of the first nitrogen compressor 411 to obtain a 63.4bara medium-pressure high-purity nitrogen product (the third nitrogen 104). At least a part of the third nitrogen 1041 is sent to the second nitrogen compressor 412 to continue to pressurize the medium-pressure high-purity nitrogen from the last stage of the first nitrogen compressor 411 to 85 bara; at least a part of the third nitrogen 1042 undergoes high-pressure plate exchange After the heat exchanger 71 is partially cooled, it is expanded by the first nitrogen expander 121 to obtain 5.2 bara low-pressure high-purity nitrogen, at least a part of which (the fourth nitrogen 105a) is combined with the first nitrogen 102 extracted from the top of the first tower 1, at least The other part (the fourth nitrogen 105b) is sent to the top of the second column 2; at least a part of the third nitrogen 1043 is sent to the third nitrogen compressor 413 to continue the medium-pressure high-purity nitrogen from the last stage of the first nitrogen compressor 411 Pressurized to 99bara to obtain ultra-high pressure and high-purity nitrogen product (the fifth nitrogen 106); at least a part of the fifth nitrogen is throttled to 85bara, which is the same pressure as at least a part of 1041 of the third nitrogen pressurized to 85bara, two strands After confluence, it is sent to the high-pressure plate heat exchanger 71. After the high-pressure plate heat exchanger 71 is cooled, high-purity liquid nitrogen (the first liquid nitrogen 1061) is formed, which is expanded and reduced by the second nitrogen expander 122 to obtain a high-purity of 6 bara. Liquid nitrogen (second liquid nitrogen 1062). A part of the second liquid nitrogen 1062 can optionally be further expanded and reduced by the throttle valve 31 to obtain 5.3bara high-purity liquid nitrogen and sent to the top of the first column 1 as reflux liquid; the second liquid nitrogen The other part of 1062 is supercooled by the cooler 8 and then sent to the top of the second tower 2 as reflux liquid. Draw 6 bara from the bottom of the first tower 1 containing 37% O2The oxygen-enriched liquid space 108 is supercooled by the cooler 8 and then sent to the second tower 2 as reflux liquid. Extract 6bara of liquid air 113 from the first column 1 (the mole percentage of oxygen is not more than 30), pressurize the first pump 21 to obtain 11.6bara of medium pressure liquid air, and then send it to the high-pressure plate heat exchanger 71 to obtain 11.5 after the temperature rises. The bara gaseous medium pressure liquid air 1131 is mixed with the 11.5bara second nitrogen 103 extracted from the intermediate stage of the first nitrogen compressor 411 in the static mixer 9 to adjust the nitrogen and oxygen content of the output medium pressure air product 109 proportion. Extract 1.4bara of liquid oxygen 107 (-180°C) from the main condensing evaporator 3, pressurize the second pump 22 to obtain 80bara of high pressure liquid oxygen 107, and then send it to the high pressure plate heat exchanger 71 to heat up to obtain 80bara of high pressure oxygen Product 110. 1.1 bara of ultra-low pressure nitrogen (at least part of the fourth nitrogen 1051) is extracted from the top of the second tower 2 through the cooler 8 and the low-pressure plate heat exchanger 72 to obtain the ultra-low pressure nitrogen product. Sewage liquid nitrogen 111 is extracted from the first tower 1 after being subcooled by the cooler 8 and then sent to the second tower 2 as reflux liquid. The 1.15bara sewage nitrogen 112 extracted from the second tower 2 is sequentially sent to the subcooler 8 and the low pressure plate heat exchanger 72 for reheating.

[0060]In this embodiment, optionally, the liquid air 113 extracted from the bottom of the first tower 1 is pressurized to different pressure ranges by the first pump 21 with different heads to output the air product 109 with the same pressure as the second nitrogen. Alternatively, the liquid air 113 is pressurized to different pressure ranges by connecting different numbers of first pumps 21 in series to output air products 109 in different pressure ranges. Optionally, the first liquid nitrogen 1061 may be expanded and reduced by the second nitrogen expander 122 and/or the throttle valve 31 and then sent to the top of the first column 1 and/or the second column 2. Alternatively, the high-pressure plate heat exchanger 71 and the low-pressure plate heat exchanger 72 may be replaced by an integral combined heat exchanger as the main heat exchanger. The first nitrogen expander 121 is braked by a second nitrogen compressor 412 connected to it; the second nitrogen expander 122 is braked by a generator 10 connected to it. In this embodiment, all kinds of materials flow through pipelines connected between equipment as the conveying medium.

[0061]image 3The embodiment shown is the same asfigure 1 The main difference is that the oxygen-enriched liquid air extracted from the first tower 1 is sent to the separation tank, and then the oxygen-enriched liquid air sent from the separation tank is used as the raw material for the production of air product 109.image 3In, a separation tank 11 is added. Since the separation tank 11 is set at a height corresponding to the second tower, and the first pump 21 is usually set on the ground, the separation tank 11 has a higher level than the first pump 21. The large static pressure difference increases the allowable NPSH of the pump, which is not easy to produce cavitation, and further increases the safety of pressurizing the oxygen-rich liquid air sent from the separation tank through the first pump.image 3The other parts in the illustrated embodiment are the same asfigure 1 The illustrated embodiment is the same. Both are examples of the realization of the present invention, but do not limit the spirit and scope of the present invention in any way. Specifically, inimage 3In the illustrated embodiment, the feed air 101 is pressurized to 6 bara by the main air compressor 4, and then is pre-cooled and purified (the pre-cooling system and the purification system are not shown), and then sent to the low-pressure plate heat exchanger 72 and refined After distillation, the ultra-low pressure nitrogen from the top 1.1 bara of the second column 2 (at least part of the fourth nitrogen 1051) and the 1.15 bara dirty nitrogen 112 from the top of the second column 2 can optionally be combined with the low pressure and high pressure from the top of the first column 1 at 5.2 bara. Pure nitrogen (the first nitrogen 102) performs indirect heat exchange, is cooled to about -176°C and then sent to the lower part of the first column 1 for rectification. A part 1021 of the first nitrogen 102 extracted from the top of the first column 1 is optionally sent to the low-pressure plate heat exchanger 72 for heating, and the other part 1022 is sent to the high-pressure plate heat exchanger 71 to obtain a low-pressure high-purity nitrogen gas of 5.2 bara after heating. The product, optionally a part of 1022 and 1021 are combined and pressurized by the first nitrogen compressor 411, of which the first part is extracted from the intermediate stage of the first nitrogen compressor 411 to obtain 11.5bara medium pressure high purity nitrogen (the second nitrogen 103), The second part is extracted from the last stage of the first nitrogen compressor 411 to obtain a 63.4bara medium-pressure high-purity nitrogen product (the third nitrogen 104). At least a part of the third nitrogen 1041 is sent to the second nitrogen compressor 412 to continue to pressurize the medium-pressure high-purity nitrogen from the last stage of the first nitrogen compressor 411 to 85 bara; at least a part of the third nitrogen 1042 undergoes high-pressure plate exchange After the heat exchanger 71 is partially cooled, it is expanded by the first nitrogen expander 121 to obtain 5.2 bara low-pressure high-purity nitrogen, at least a part of which (the fourth nitrogen 105a) is combined with the first nitrogen 102 extracted from the top of the first tower 1, at least The other part (the fourth nitrogen 105b) is sent to the top of the second column 2; at least a part of the third nitrogen 1043 is sent to the third nitrogen compressor 413 to continue the medium-pressure high-purity nitrogen from the last stage of the first nitrogen compressor 411 Pressurized to 99bara to obtain ultra-high pressure and high-purity nitrogen product (the fifth nitrogen 106); at least a part of the fifth nitrogen is throttled to 85bara, which is the same pressure as at least a part of 1041 of the third nitrogen pressurized to 85bara, two strands After confluence, it is sent to the high-pressure plate heat exchanger 71. After the high-pressure plate heat exchanger 71 is cooled, high-purity liquid nitrogen (the first liquid nitrogen 1061) is formed, which is expanded and reduced by the second nitrogen expander 122 to obtain a high-purity of 6 bara. Liquid nitrogen (second liquid nitrogen 1062). A part of the second liquid nitrogen 1062 can optionally be further expanded and reduced by the throttle valve 31 to obtain 5.3bara high-purity liquid nitrogen and sent to the top of the first column 1 as reflux liquid; the second liquid nitrogen The other part of 1062 is supercooled by the cooler 8 and then sent to the top of the second tower 2 as reflux liquid. Draw 6 bara from the bottom of the first tower 1 containing 37% O2The oxygen-enriched liquid space 108 is supercooled by the cooler 8 and then sent to the separation tank 11. A part of the oxygen-enriched liquid space sent from the separation tank 11 is sent to the second column 2 as reflux liquid, and at least a part of the enrichment sent from the separation tank 11 The oxygen liquid 114 is pressurized by the first pump 21 to obtain 11.6 bara of medium-pressure oxygen-enriched liquid air, and then sent to the high-pressure plate heat exchanger 71 to obtain 11.5 bara gaseous medium-pressure oxygen-enriched liquid 1141 after the temperature rises. The 11.5bara second nitrogen 103 extracted from the intermediate stage of a nitrogen compressor 411 is mixed in the static mixer 9 to adjust the ratio of nitrogen to oxygen in the output medium pressure air product 109. Extract 1.4bara of liquid oxygen 107 (-180°C) from the main condensing evaporator 3, pressurize the second pump 22 to obtain 80bara of high pressure liquid oxygen 107, and then send it to the high pressure plate heat exchanger 71 to heat up to obtain 80bara of high pressure oxygen Product 110. 1.1 bara of ultra-low pressure nitrogen (at least part of the fourth nitrogen 1051) is extracted from the top of the second tower 2 through the cooler 8 and the low-pressure plate heat exchanger 72 to obtain the ultra-low pressure nitrogen product. Sewage liquid nitrogen 111 is extracted from the first tower 1 after being subcooled by the cooler 8 and then sent to the second tower 2 as reflux liquid. The 1.15bara sewage nitrogen 112 extracted from the second tower 2 is sequentially sent to the subcooler 8 and the low pressure plate heat exchanger 72 for reheating.

[0062]In this embodiment, optionally, the oxygen-rich liquid air 114 sent from the separation tank 11 is pressurized to different pressure ranges by the first pump 21 with different heads, so as to output the air product 109 with the same pressure as the second nitrogen. Alternatively, the oxygen-enriched liquid air 114 is pressurized to different pressure ranges by connecting different numbers of first pumps 21 in series to output air products 109 in different pressure ranges. Optionally, the first liquid nitrogen 1061 may be expanded and reduced by the second nitrogen expander 122 and/or the throttle valve 31 and then sent to the top of the first column 1 and/or the second column 2. Alternatively, the high-pressure plate heat exchanger 71 and the low-pressure plate heat exchanger 72 may be replaced by an integral combined heat exchanger as the main heat exchanger. The first nitrogen expander 121 is braked by a second nitrogen compressor 412 connected to it; the second nitrogen expander 122 is braked by a generator 10 connected to it. In this embodiment, all kinds of materials flow through pipelines connected between equipment as the conveying medium.

[0063]Although the content of the present invention has been described in detail through the above preferred embodiments, it should be recognized that the above description should not be considered as limiting the present invention. After those skilled in the art have read the above content, various modifications and alternatives to the present invention will be obvious. Therefore, the protection scope of the present invention should be defined by the appended claims.