1. The utility model provides an use device of single rectifying column production pure nitrogen, the device comprises air compressor machine (3), precooling purification system, circulation nitrogen booster compressor (21), cold box system, connects through the pipeline each other, and wherein precooling purification system comprises air cooling tower (4), water cooling tower (5), cooling water pump (7), frozen water pump (9), cooling water set (10), molecular sieve adsorber (12) and regenerative heater (38), the cold box system comprises plate heat exchanger (14), low pressure rectifying tower (15), expander pressure boost end (18), pressure boost end aftercooler (19), condensation evaporator (22), expander expansion end (26), vapour and liquid separator (28) and liquid nitrogen subcooler (32), its characterized in that: the air compressor is characterized in that an air filter (2) is arranged in front of the air compressor (3), a pre-cooling purification system is arranged behind the air compressor, air enters the air turbine compressor (3) through the air filter (2) and is compressed to about 4bar, the air is sent to the pre-cooling purification system, the air is cooled in the pre-cooling purification system through an air cooling tower (4), impurities are removed through a molecular sieve (12), the air enters a cold box system, the air is cooled to be nearly saturated through a plate heat exchanger (14), the air enters a low-temperature rectifying tower (15) and is rectified to obtain low-pressure nitrogen and liquid air, the low-pressure nitrogen passes through the heat exchanger (14) and is reheated out of the cold box, a part of the low-pressure nitrogen is pressurized by an expander pressurization end (18) and then serves as a product, a part of the low-pressure nitrogen enters a circulating nitrogen compressor (21), a part of the nitrogen serves as a product, and a part of the nitrogen returns to the heat exchanger (14) and serves as expansion amount.

2. The apparatus for producing pure nitrogen using a single rectification column according to claim 1, wherein: the bottom of the low-pressure rectifying tower obtains low-pressure nitrogen (16) at the top of a low-pressure oxygen-enriched liquid air (17), the oxygen-enriched liquid air (17) is throttled to normal pressure and then sent into the evaporation side of a condensation evaporator (22), and is gasified after exchanging heat with the low-pressure nitrogen at the top of the low-pressure rectifying tower (15) to obtain polluted nitrogen (23), and the low-pressure nitrogen (16) is reheated by a plate heat exchanger (14) to reach a normal temperature and then is discharged out of a cooling box and divided into two strands: continuously pressurizing one strand of the mixture to 5-6 kilograms at a pressurizing end (18) of the expansion machine, feeding the mixture into a pressurizing end after-cooler (19), cooling the mixture to normal temperature, and feeding the cooled mixture into a user product nitrogen pipe network as a low-pressure nitrogen product (20); one of the recycle nitrogen compressors (21) continues to pressurize.

3. The apparatus for producing pure nitrogen using a single rectification column according to claim 2, wherein: the method is characterized in that low-pressure nitrogen sent to a circulating nitrogen booster (21) is pressurized to about 40 kg and then divided into two parts, one part is sent to a user pipe network as a medium-pressure nitrogen product (24), the other part is sent to a plate heat exchanger (14) as a medium-pressure expansion amount (25) to exchange heat with backflow waste nitrogen, an expansion end (26) of an expander is extracted from the middle part of the heat exchanger, the expanded liquid-carrying nitrogen (27) is sent to a gas-liquid separator (28), and liquid nitrogen (29) and low-pressure nitrogen (30) are obtained through separation.

4. The apparatus for producing pure nitrogen using a single rectification column according to claim 3, wherein: the liquid nitrogen (29) is divided into two parts, one part is used as reflux liquid nitrogen (31), the reflux liquid nitrogen flows back to the low-pressure rectifying tower to participate in rectification, one part is sent to a liquid nitrogen subcooler (32), the subcooled liquid nitrogen (33) is divided into two parts, one part is used as a liquid nitrogen product (34), one part is used as a subcooler cold source nitrogen (35) to be throttled to normal pressure, and the reflux liquid nitrogen exchanges heat with the liquid nitrogen (32) and then flows with the polluted nitrogen (23) in parallel to obtain the polluted nitrogen (36).

5. The apparatus for producing pure nitrogen using a single rectification column according to claim 4, wherein: and the polluted nitrogen (36) is reheated by the plate heat exchanger (14) and then is discharged from the cooling box, and is divided into two parts, wherein one part is used as a molecular sieve regeneration gas source (37) to a regeneration heater (38), and the other part is used as polluted nitrogen (8) for a water cooling tower.

6. Use of a device for producing pure nitrogen using a single rectification column according to any one of claims 1 to 5, characterized in that it comprises the following steps:

a) raw material air from the atmosphere is used as raw material gas, and is pressurized by an air turbine compressor to obtain high-temperature gas; cooling and adsorbing the high-temperature gas by a precooling purification system to obtain low-pressure air;

b) the low-pressure air enters a main heat exchanger in the cold box, is cooled to saturation temperature by the return gas and then enters a low-pressure rectifying tower to participate in rectification;

c) after the rectification by the low-pressure rectifying tower, obtaining low-pressure nitrogen at the top of the low-pressure rectifying tower and obtaining oxygen-enriched liquid air at the bottom of the low-pressure rectifying tower; the oxygen-enriched liquid is air-throttled to normal pressure and sent to the evaporation side of a condensation evaporator; the low-pressure nitrogen directly enters the main heat exchanger, exchanges heat with positive-flow low-pressure air, is reheated to normal temperature and then is sent out of the cold box;

d) the oxygen-enriched liquid air entering the evaporation side of the condensation evaporator exchanges heat with low-pressure nitrogen at the top of the rectifying tower, and then is vaporized to obtain dirty nitrogen, the dirty nitrogen is sent into a main heat exchanger for reheating and then is discharged out of a cooling box, a part of the dirty nitrogen is removed from a molecular sieve to be used as a regeneration gas source, and a part of the dirty nitrogen is removed from a water cooling tower to be used as cooling circulating water;

e) part of the low-pressure nitrogen out of the cold box is sent to the pressurization end of the expansion machine for pressurization and then is used as a low-pressure nitrogen product, and the rest of the low-pressure nitrogen is sent to the circulating nitrogen compressor for continuous pressurization;

f) after the low-pressure nitrogen is compressed by a circulating nitrogen compressor, the low-pressure nitrogen is extracted from the last stage and is cooled, one part of the low-pressure nitrogen is used as a medium-pressure nitrogen product, one part of the low-pressure nitrogen is sent to a main heat exchanger, is extracted from the middle part of the heat exchanger after exchanging heat with return gas, is sent to a gas-liquid separator after being expanded at the expansion end of a medium-pressure expander, and is separated to obtain low-pressure nitrogen and low-pressure liquid nitrogen;

g) the separated low-pressure nitrogen flows in parallel with the low-pressure nitrogen extracted from the top of the lower tower and then is sent to a main heat exchanger for reheating, part of the separated low-pressure liquid nitrogen is sent to the top of the lower tower to be rectified, and the other part of the separated low-pressure liquid nitrogen is sent to a liquid nitrogen subcooler as product liquid nitrogen and is discharged out of a cold box after exchanging heat with the returned normal-pressure nitrogen;

h) the normal pressure nitrogen gas which flows back in the liquid nitrogen subcooler is obtained by extracting a part of the product liquid nitrogen and throttling to the normal pressure, and the normal pressure nitrogen gas which is discharged from the subcooler and the normal pressure waste nitrogen gas at the evaporation side of the condensing evaporator flow in parallel and are sent to the main heat exchanger to be reheated and discharged from the cold box.

7. The use method of the apparatus for producing pure nitrogen by using a single rectification column as claimed in claim 6, wherein the low pressure rectification column in the rectification system is coupled with a condensation evaporator to realize heat exchange between the low pressure rectification column and the condensation evaporator, so as to keep the rectification process stable, and the cold source of the condensation evaporator is from the oxygen-rich liquid air at the bottom of the low pressure rectification column which is throttled to normal pressure; the low-pressure nitrogen discharged from the cold box after reheating can be extracted, a part of the low-pressure nitrogen is discharged from a pressurization end of the expansion machine to be pressurized and then is used as a low-pressure nitrogen product, and energy generated by expansion can be recovered by utilizing a braking motor at the pressurization end to produce electric energy; the low-pressure nitrogen of the reheating cold discharge box can be partially extracted from the middle part of the heat exchanger and sent into the low-pressure nitrogen expansion machine, and the low-pressure nitrogen expands to be close to normal pressure and then flows back to the main heat exchanger reheating cold discharge box to be used as a normal-pressure nitrogen product, and the pressurizing end of the low-pressure expansion machine can be matched with a machine type according to product requirements to select electricity recovery or pressurize the nitrogen to obtain the nitrogen product.

8. Use of a device for producing pure nitrogen using a single rectification column according to claim 6, characterized in that: according to the specification requirement of the nitrogen product, the nitrogen which is sent to the pressurization end of the expansion machine can be pumped from the circulating nitrogen press or the final stage, and the pressurized nitrogen can be used as the product or sent to a plate heat exchanger after being cooled and pumped to the expansion machine.

9. Use of a device for producing pure nitrogen using a single rectification column according to claim 6, characterized in that: the pressurized nitrogen fed into the circulating nitrogen booster can be completely pumped out from the final stage, or a nitrogen product with a required pressure grade can be pumped out from the middle part of the circulating nitrogen booster according to the product requirement, and an air source at the expansion end of the medium-pressure expansion machine can also be pumped out from the circulating nitrogen booster according to the product requirement.

Background

The nitrogen accounts for about 78% of the atmospheric components, is inactive and chemically inert, is an industrial gas with wide application fields, and is widely applied to the fields of chemical production, equipment manufacturing, food preservation, laser cutting and the like. The existing pure nitrogen production equipment mainly adopts a cryogenic rectification method, and cryogenic rectification separation has been used for hundreds of years as the method with the widest application range in the air separation field, and is widely applied to various industrial fields such as metallurgy, chemical engineering, glass, electronics and the like.

With the rapid development of various industrial technologies, the demand for nitrogen gas in the production process is rapidly increased. Meanwhile, along with the development trend of industrial diversification, the specification requirement of nitrogen products is more and more increased due to the diversification of the production process. Therefore, the air separation equipment process flow has wide application prospect, can adapt to extraction of a large amount of nitrogen with various specifications and can effectively reduce energy consumption.

Disclosure of Invention

The invention aims to provide a device for producing pure nitrogen by using a single rectifying tower and a using method thereof, and the method can greatly reduce the processing amount of raw material gas and reduce the exhaust pressure of a raw material gas compressor, thereby effectively reducing the energy consumption for nitrogen preparation. The purpose of the invention is achieved by the following technical scheme: the utility model provides an use single rectifying column combined cycle nitrogen compressor to produce device of a large amount of many specifications pure nitrogen, the device comprises air compressor machine, precooling purification system, circulation nitrogen booster compressor, cold box system, connects through the pipeline each other, and wherein precooling purification system comprises air cooling tower, water cooling tower, cooling water pump, frozen water pump, cooling water set, molecular sieve adsorber and regenerative heater, the cold box system comprises plate heat exchanger, low pressure rectifying column, expander pressure boost end, pressure boost end aftercooler, condensation evaporator, expander expansion end, vapour and liquid separator and liquid nitrogen subcooler, air compressor machine the place ahead is equipped with air cleaner, and the rear sets up precooling purification system, and air passes through air cleaner and gets into air turbine compressor internal compression to about 4bar after, sends into precooling purification system. Air is cooled by an air cooling tower in the precooling and purifying system, and enters a cold box system after impurities are removed by a molecular sieve. Air is cooled to be nearly saturated through a plate heat exchanger, then enters a low-temperature rectifying tower for rectification to obtain low-pressure nitrogen and liquid air, the low-pressure nitrogen is reheated through the heat exchanger and then exits a cold box, one part of the low-pressure nitrogen is sent to a pressurization end of an expander for pressurization to be used as a product, and the other part of the low-pressure nitrogen enters a circulating nitrogen compressor. After the nitrogen is pressurized by the circulating nitrogen compressor, one part of the nitrogen is used as a product, and the other part of the nitrogen returns to the heat exchanger to be used as expansion amount.

Preferably, the method comprises the following steps: the bottom of the low-pressure rectifying tower obtains low-pressure nitrogen from the top of a low-pressure oxygen-enriched liquid air, the oxygen-enriched liquid air is throttled to the normal pressure and then sent to the evaporation side of a condensation evaporator, the evaporation side exchanges heat with the low-pressure nitrogen at the top of the low-pressure rectifying tower and then gasifies the nitrogen to obtain polluted nitrogen, and the low-pressure nitrogen is reheated by a plate heat exchanger to the normal temperature and then is discharged from a cold box and divided into two strands: continuously pressurizing the other strand of the mixed gas to 5-6 kg at the pressurizing end of the expansion machine, feeding the mixture into a pressurizing end after-cooler, cooling the mixture to normal temperature, and feeding the cooled mixture serving as a low-pressure nitrogen product into a user product nitrogen pipe network; one of the recycle nitrogen compressors continues to pressurize.

Preferably, the method comprises the following steps: the low-pressure nitrogen of the recycle nitrogen booster is pressurized to about 40 kg and then divided into two parts, one part is used as a medium-pressure nitrogen product and sent into a user pipe network, the other part is used as a medium-pressure expansion amount and sent to a plate heat exchanger to exchange heat with backflow waste nitrogen, the expansion end of the expander is extracted from the middle part of the heat exchanger, the expanded gas with liquid nitrogen is sent into a gas-liquid separator, and liquid nitrogen and low-pressure nitrogen are obtained through separation.

Preferably, the method comprises the following steps: the liquid nitrogen is divided into two parts, one part is used as reflux liquid nitrogen, the reflux liquid nitrogen flows back to the low-pressure rectifying tower to participate in rectification, the other part is sent to a liquid nitrogen subcooler, the subcooled liquid nitrogen is divided into two parts, one part is used as a liquid nitrogen product, the other part is used as a subcooler cold source nitrogen to be throttled to normal pressure, and the reflux liquid nitrogen exchanges heat with the liquid nitrogen and then flows with dirty nitrogen in parallel to obtain dirty nitrogen.

Preferably, the method comprises the following steps: and the waste nitrogen is reheated by the plate heat exchanger and then discharged from the cooling box and divided into two parts, wherein one part is used as a molecular sieve regeneration gas source to a regeneration heater, and the other part is used as waste nitrogen for a water cooling tower.

The use method of the device for producing pure nitrogen by using the single rectifying tower comprises the following steps:

a) raw material air from the atmosphere is used as raw material gas, and is pressurized by an air turbine compressor to obtain high-temperature gas; cooling and adsorbing the high-temperature gas by a precooling purification system to obtain low-pressure air;

b) the low-pressure air enters a main heat exchanger in the cold box, is cooled to saturation temperature by the return gas and then enters a low-pressure rectifying tower to participate in rectification;

c) after the rectification by the low-pressure rectifying tower, obtaining low-pressure nitrogen at the top of the low-pressure rectifying tower and obtaining oxygen-enriched liquid air at the bottom of the low-pressure rectifying tower; the oxygen-enriched liquid is air-throttled to normal pressure and sent to the evaporation side of a condensation evaporator; the low-pressure nitrogen directly enters the main heat exchanger, exchanges heat with positive-flow low-pressure air, is reheated to normal temperature and then is sent out of the cold box;

d) the oxygen-enriched liquid air entering the evaporation side of the condensation evaporator exchanges heat with the low-pressure nitrogen at the top of the rectifying tower, the vaporized waste nitrogen enters the main heat exchanger, the waste nitrogen is reheated and then discharged from the cooling box, a part of the waste nitrogen is removed from the molecular sieve to be used as a regeneration air source, and a part of the waste nitrogen is removed from the cooling circulating water of the water cooling tower.

e) Part of the low-pressure nitrogen out of the cold box is sent to the pressurization end of the expansion machine for pressurization and then is used as a low-pressure nitrogen product, and the rest of the low-pressure nitrogen is sent to the circulating nitrogen compressor for continuous pressurization;

f) after the low-pressure nitrogen is compressed by a circulating nitrogen compressor, the low-pressure nitrogen is extracted from the last stage and is cooled, one part of the low-pressure nitrogen is used as a medium-pressure nitrogen product, one part of the low-pressure nitrogen is sent to a main heat exchanger, is extracted from the middle part of the heat exchanger after exchanging heat with return gas, is sent to a gas-liquid separator after being expanded at the expansion end of a medium-pressure expander, and is separated to obtain low-pressure nitrogen and low-;

g) the separated low-pressure nitrogen flows in parallel with the low-pressure nitrogen extracted from the top of the lower tower and then is sent to a main heat exchanger for reheating, part of the separated low-pressure liquid nitrogen is sent to the top of the lower tower to be rectified, and the other part of the separated low-pressure liquid nitrogen is sent to a liquid nitrogen subcooler as product liquid nitrogen and is discharged out of a cold box after exchanging heat with the returned normal-pressure nitrogen;

h) the normal pressure nitrogen gas which flows back in the liquid nitrogen subcooler is obtained by extracting a part of the product liquid nitrogen and throttling to the normal pressure, and the normal pressure nitrogen gas which is discharged from the subcooler and the normal pressure waste nitrogen gas at the evaporation side of the condensing evaporator flow in parallel and are sent to the main heat exchanger to be reheated and discharged from the cold box.

Preferably, the method comprises the following steps: a low-pressure rectifying tower in the rectifying system is coupled with a condensing evaporator to realize heat exchange between the low-pressure rectifying tower and the condensing evaporator, so that the stable operation of the rectifying process is kept, and a cold source of the condensing evaporator is from oxygen-enriched liquid air at the bottom of the low-pressure rectifying tower which is throttled to normal pressure; the low-pressure nitrogen discharged from the cold box after reheating can be extracted, a part of the low-pressure nitrogen is discharged from a pressurization end of the expansion machine to be pressurized and then is used as a low-pressure nitrogen product, and energy generated by expansion can be recovered by utilizing a braking motor at the pressurization end to produce electric energy; the low-pressure nitrogen of the reheating cold discharge box can be partially extracted from the middle part of the heat exchanger and sent into the low-pressure nitrogen expansion machine, and the low-pressure nitrogen is expanded to be close to the normal pressure and then flows back to the main heat exchanger reheating cold discharge box to be used as a normal-pressure nitrogen product, and the pressurizing end of the low-pressure expansion machine can be matched with a machine type according to the product requirement to select electricity recovery or pressurize the nitrogen to obtain the nitrogen product.

Preferably, the method comprises the following steps: according to the specification requirement of the nitrogen product, the nitrogen which is sent to the pressurization end of the expansion machine can be pumped from the circulating nitrogen press or the final stage, and the pressurized nitrogen can be used as the product or sent to a plate heat exchanger after being cooled and pumped to the expansion machine.

Preferably, the method comprises the following steps: the pressurized nitrogen fed into the circulating nitrogen booster can be completely pumped out from the final stage, a nitrogen product with a required pressure grade can be pumped out from the middle part of the circulating nitrogen booster according to the product requirement, and an air source at the expansion end of the medium-pressure expansion machine can be pumped out from the circulating nitrogen booster according to the product requirement.

The invention has the following characteristics:

1) the invention realizes the heat exchange between the low-pressure rectifying tower and the low-pressure condensing evaporator by coupling the low-pressure rectifying tower and the low-pressure condensing evaporator in the rectifying system, thereby keeping the stable operation of the rectifying process. The invention utilizes the oxygen-enriched liquid air at the bottom of the low-pressure rectifying tower as a self cold source after throttling, compared with the conventional air separation, the reduction of the oxygen content in the liquid at the evaporation side can effectively reduce the exhaust pressure of an air compressor, and the evaporated oxygen-enriched air is directly used as the sewage nitrogen to be used as a molecular sieve system to be used as a regeneration air source or cooling circulating water of a water cooling tower.

2) The invention has high extraction rate of nitrogen products, and the combination of the circulating nitrogen compressor and the medium-pressure expander ensures that a large amount of liquid nitrogen is filled into the low-pressure rectifying tower after expansion, thereby effectively adjusting the reflux ratio of the lower tower, improving the rectifying efficiency in the low-pressure tower and increasing the extraction rate of nitrogen.

3) The nitrogen product specification of the invention is diversified, and nitrogen with various specifications can be produced by coupling the system of the circulating nitrogen compressor and the expander set according to the requirement of the downstream process.

4) The invention can select the configuration form of a single medium-pressure expansion machine or a medium-pressure expansion machine and a low-pressure expansion machine through the coupling of the system of the expansion machine set, and can adjust the expansion amount and the yield of liquid nitrogen products in a great range according to the process requirements.

5) The invention relates to a single-tower nitrogen-making rectification system, which is simply matched with a compressor unit and an expansion unit and is flexibly adjusted.

The single-tower rectification method adopted by the invention can effectively improve the extraction rate of the single-tower single-making device, reduce the pressure discharge of the air compressor and reduce the energy consumption of the single-making device. The method has great freedom degree in process arrangement, and can optimize and configure the circulating nitrogen compressor and the expansion unit according to the specifications of different gas and liquid nitrogen products to reach the optimal energy consumption point. The characteristics of flexible operation and quick adjustment of a single rectifying tower are also reserved.

Drawings

Fig. 1 is a schematic structural view of the present invention.

Detailed Description

The invention will be described in detail below with reference to the following figures: as shown in fig. 1, a device for producing a large amount of multi-specification pure nitrogen by using a single rectification tower combined cycle nitrogen compressor, the device is composed of an air compressor 3, a precooling purification system, a cycle nitrogen booster 21 and a cold box system which are connected with each other through pipelines, wherein the precooling purification system is composed of an air cooling tower 4, a water cooling tower 5, a cooling water pump 7, a freezing water pump 9, a water chilling unit 10, a molecular sieve adsorber 12 and a regeneration heater 38, the cold box system is composed of a plate heat exchanger 14, a low pressure rectification tower 15, an expander supercharging end 18, a supercharging end after-cooler 19, a condensation evaporator 22, an expander expansion end 26, a gas-liquid separator 28 and a liquid nitrogen subcooler 32, an air filter 2 is arranged in front of the air compressor 3, the precooling purification system is arranged behind the air compressor 3, air enters the air turbine compressor 3 through the air filter 2 and is compressed to about 4bar, sending the mixture into a precooling purification system. The air is cooled by an air cooling tower 4 in the precooling and purifying system, and the impurities are removed by a molecular sieve 12, and then the air enters a cold box system. After being cooled to be nearly saturated by the plate heat exchanger 14, the air enters the low-temperature rectifying tower 15 for rectification to obtain low-pressure nitrogen and liquid air, the low-pressure nitrogen is reheated by the heat exchanger 14 and then exits the cold box, one part of the low-pressure nitrogen enters the booster end 18 of the expansion machine for boosting and then serves as a product, and the other part of the low-pressure nitrogen enters the circulating nitrogen compressor 21. After the nitrogen is pressurized by the recycle nitrogen compressor 21, a portion is taken as product and a portion is returned to the heat exchanger 14 as expansion.

The bottom of the low-pressure rectifying tower obtains low-pressure oxygen-enriched liquid air 17, the top of the low-pressure rectifying tower obtains low-pressure nitrogen 16, the oxygen-enriched liquid air 17 is throttled to the normal pressure and then sent into the evaporation side of a condensation evaporator 22, the evaporation side exchanges heat with the low-pressure nitrogen at the top of the low-pressure rectifying tower 15 and then is gasified to obtain polluted nitrogen 23, the low-pressure nitrogen 16 is reheated by a plate heat exchanger 14 to the normal temperature and then is discharged out of a cold box, and the cold box is divided into two strands: continuously pressurizing one strand of the mixture to 5-6 kilograms at a pressurizing end 18 of the expansion machine, feeding the mixture into a pressurizing end after-cooler 19, cooling the mixture to normal temperature, and feeding the cooled mixture into a user product nitrogen pipe network as a low-pressure nitrogen product 20; one of the recycle nitrogen compressors 21 continues to pressurize.

The low-pressure nitrogen gas sent to the circulating nitrogen booster 21 is pressurized to about 40 kilograms and then divided into two parts, one part is used as a medium-pressure nitrogen gas product 24 and sent to a user pipe network, the other part is used as a medium-pressure expansion amount 25 and sent to the plate heat exchanger 14 to exchange heat with the return waste nitrogen, the part is extracted from the middle part of the heat exchanger and sent to an expansion end 26 of an expander, the expanded nitrogen gas with liquid 27 is sent to a gas-liquid separator 28, and liquid nitrogen 29 and low-pressure nitrogen gas 30 are obtained through separation.

The liquid nitrogen 29 is divided into two parts, one part is used as reflux liquid nitrogen 31, the reflux liquid nitrogen flows back to the low-pressure rectifying tower to participate in rectification, one part is sent to a liquid nitrogen subcooler 32, the subcooled liquid nitrogen 33 is divided into two parts, one part is used as a liquid nitrogen product 34, one part is used as a subcooler cold source nitrogen 35 to be throttled to normal pressure, and the reflux liquid nitrogen exchanges heat with the liquid nitrogen 32 and then flows with the polluted nitrogen 23 in parallel to obtain polluted nitrogen 36.

And the waste nitrogen 36 is reheated by the plate heat exchanger 14 and then discharged from the cooling box, and is divided into two parts, wherein one part is used as a molecular sieve regeneration gas source 37 to a regeneration heater 38, and the other part is used as waste nitrogen 8 for a water cooling tower.

The use method of the device for producing pure nitrogen by using the single rectifying tower comprises the following steps:

a) raw material air from the atmosphere is used as raw material gas, and is pressurized by an air turbine compressor to obtain high-temperature gas; cooling and adsorbing the high-temperature gas by a precooling purification system to obtain low-pressure air;

b) the low-pressure air enters a main heat exchanger in the cold box, is cooled to saturation temperature by the return gas and then enters a low-pressure rectifying tower to participate in rectification;

c) after the rectification by the low-pressure rectifying tower, obtaining low-pressure nitrogen at the top of the low-pressure rectifying tower and obtaining oxygen-enriched liquid air at the bottom of the low-pressure rectifying tower; the oxygen-enriched liquid is air-throttled to normal pressure and sent to the evaporation side of a condensation evaporator; the low-pressure nitrogen directly enters the main heat exchanger, exchanges heat with positive-flow low-pressure air, is reheated to normal temperature and then is sent out of the cold box.

d) The oxygen-enriched liquid air entering the evaporation side of the condensation evaporator exchanges heat with the low-pressure nitrogen at the top of the rectifying tower, the vaporized waste nitrogen enters the main heat exchanger, the waste nitrogen is reheated and then discharged from the cooling box, a part of the waste nitrogen is removed from the molecular sieve to be used as a regeneration air source, and a part of the waste nitrogen is removed from the cooling circulating water of the water cooling tower.

e) Part of the low-pressure nitrogen out of the cold box is sent to the pressurization end of the expansion machine for pressurization and then is used as a low-pressure nitrogen product, and the rest of the low-pressure nitrogen is sent to the circulating nitrogen compressor for continuous pressurization;

f) and after the low-pressure nitrogen is compressed by a circulating nitrogen compressor, the low-pressure nitrogen is extracted from the last stage and is cooled, one part of the low-pressure nitrogen is used as a medium-pressure nitrogen product, one part of the low-pressure nitrogen is sent to a main heat exchanger, the low-pressure nitrogen exchanges heat with return gas and then is extracted from the middle part of the heat exchanger, the low-pressure nitrogen is sent to a gas-liquid separator after being expanded at the expansion end of a medium-pressure expander, and the low-pressure nitrogen and the low-pressure liquid nitrogen are obtained through separation.

g) The separated low-pressure nitrogen flows in parallel with the low-pressure nitrogen extracted from the top of the lower tower and then is sent to a main heat exchanger for reheating, part of the separated low-pressure liquid nitrogen is sent to the top of the lower tower to be rectified, and the other part of the separated low-pressure liquid nitrogen is sent to a liquid nitrogen subcooler as product liquid nitrogen and is discharged out of a cold box after exchanging heat with the returned normal-pressure nitrogen;

h) the normal-pressure nitrogen gas which flows back in the liquid nitrogen subcooler is obtained by extracting a part of the product liquid nitrogen and throttling to normal pressure, and the normal-pressure nitrogen gas which is discharged from the subcooler and normal-pressure waste nitrogen gas at the evaporation side of the condensing evaporator flow in parallel and are sent to the main heat exchanger to be reheated and discharged from the cold box;

as a preferred embodiment: the low-pressure rectifying tower and the condensing evaporator in the rectifying system are coupled to realize heat exchange between the low-pressure rectifying tower and the condensing evaporator, so that the stable operation of the rectifying process is kept, and a cold source of the condensing evaporator is from oxygen-enriched liquid air at the bottom of the low-pressure rectifying tower which is throttled to normal pressure.

As a preferred embodiment: the low-pressure nitrogen discharged from the cold box after reheating can be taken out, part of the low-pressure nitrogen is sent to the pressurization end of the expansion machine for pressurization and then is used as a low-pressure nitrogen product, and the energy generated by expansion can be recovered by utilizing a braking motor at the pressurization end to produce electric energy.

As a preferred embodiment: according to the specification requirement of the nitrogen product, the nitrogen which is sent to the pressurization end of the expansion machine can be pumped from the circulating nitrogen press or the final stage, and the pressurized nitrogen can be used as the product or sent to a plate heat exchanger after being cooled and pumped to the expansion machine;

as a preferred embodiment: the low-pressure nitrogen of the reheating cold discharge box can be partially extracted from the middle part of the heat exchanger and sent into a low-pressure nitrogen expansion machine, and the low-pressure nitrogen is expanded to be close to normal pressure and then flows back to the main heat exchanger reheating cold discharge box to be used as a normal-pressure nitrogen product, and the pressurizing end of the low-pressure expansion machine can be matched with a machine type according to product requirements to select electricity recovery or pressurize the nitrogen to obtain the nitrogen product;

as a preferred embodiment: the pressurized nitrogen fed into the circulating nitrogen booster can be completely pumped out from the final stage, or a nitrogen product with a required pressure grade can be pumped out from the middle part of the circulating nitrogen booster according to the product requirement, and an air source at the expansion end of the medium-pressure expansion machine can be pumped out from the circulating nitrogen booster according to the product requirement;

an apparatus for use in the process for reducing the energy consumption of air separation using a medium pressure distillation column, the apparatus comprising:

a feed air compression system for obtaining compressed air, the system comprising 1 air turbine compressor;

a recycle nitrogen compression system for obtaining compressed nitrogen, the system comprising 1 recycle nitrogen compressor;

a precooling and purifying system for cooling and adsorbing raw material air, which comprises 1 water cooling tower, 1 air cooling tower, 2 molecular sieves and 1 waste nitrogen heating device; an expansion refrigeration system for preparing the cold energy of the whole cryogenic rectification device, which at least comprises 1 medium-pressure booster turboexpander; a cryogenic rectification system for obtaining product gas, the system comprising 1 cryogenic heat exchanger, 1 low pressure rectification column, 1 condensing evaporator; an automatic control system for realizing the operation of the whole device comprises 1 set of DCS system, 1 set of valve, 1 set of measuring instrument and 1 set of component on-line analysis instrument.

Example (b): FIG. 1 shows an embodiment of a single-tower nitrogen cycle process for producing nitrogen products of various specifications, wherein:

feed air 1 from the atmosphere (with a component content of about O)₂：20.95%，Ar：0.932%，N₂: 78.118%) is filtered off from large-particle impurities by means of an air filter 2 and fed to a feed air turbine compressor 3 (hereinafter referred to as air compressor) in which it is compressed to approximately 4bar (absolute pressure)Force, the same applies hereinafter) and then sent to the air cooling tower 4 to be cooled to about 12 ℃.

Circulating cooling water 6 of the lower section of the air cooling tower 4 and the water cooling tower 5 comes from a public engineering system, cooling water of the lower section of the air cooling tower 4 enters the lower section of the air cooling tower after being pressurized by a cooling water pump 7, and chilled water of the upper section of the air cooling tower 4 enters the upper section of the air cooling tower after being subjected to heat exchange with returned sewage nitrogen 8 through the circulating cooling water 6 and the water cooling tower 5, is pressurized by a chilled water pump 9, is cooled by a water chilling unit 10 and then enters the upper section of the air cooling tower.

The cooled low-pressure air 11 enters a molecular sieve adsorber 12 to adsorb H₂O，CO₂And obtaining low-pressure air 13 after impurities are mixed, directly sending the low-pressure air into the plate heat exchanger 14 to be cooled to be close to the saturation temperature, then sending the low-pressure air out of the plate heat exchanger 14 to enter the bottom of the low-pressure rectifying tower 15 to participate in rectification.

After the rectification by the low-pressure rectifying tower 15, low-pressure nitrogen 16 is obtained at the top of the low-pressure rectifying tower, and low-pressure oxygen-enriched liquid 17 is obtained at the bottom of the low-pressure rectifying tower. And throttling the oxygen-enriched liquid air 17 to normal pressure, sending the oxygen-enriched liquid air to the evaporation side of the condensation evaporator 22, exchanging heat with low-pressure nitrogen at the top of the low-pressure rectifying tower 15, and gasifying to obtain polluted nitrogen 23. The low-pressure nitrogen 16 is reheated to normal temperature by the plate heat exchanger 14 and then is discharged out of the cooling box, and is divided into two parts: continuously pressurizing one strand of the mixture to 5-6 kg at a pressurizing end 18 of the expansion machine, then sending the mixture into a pressurizing end after-cooler 19, cooling the mixture to normal temperature, and sending the cooled mixture into a user product nitrogen pipe network as a low-pressure nitrogen product 20; one of the recycle nitrogen compressors 21 continues to pressurize.

The low-pressure nitrogen gas sent to the circulating nitrogen booster 21 is pressurized to about 40 kilograms and then divided into two parts, one part is sent to a user pipe network as a medium-pressure nitrogen gas product 24, the other part is sent to the plate heat exchanger 14 as a medium-pressure expansion amount 25 to exchange heat with the backflow waste nitrogen, the heat is pumped out from the middle part of the heat exchanger and sent to an expansion end 26 of an expansion machine, the expanded liquid-carrying nitrogen gas 27 is sent to a gas-liquid separator 28, and liquid nitrogen 29 and low-pressure nitrogen gas 30 are obtained through separation.

The liquid nitrogen 29 is divided into two parts, one part is used as reflux liquid nitrogen 31, and the reflux liquid nitrogen flows back to the low-pressure rectifying tower to participate in rectification. One part of the nitrogen enters a liquid nitrogen subcooler 32, the subcooled liquid nitrogen 33 is divided into two parts, one part is used as a liquid nitrogen product 34, one part is used as a subcooler cold source nitrogen 35 for throttling to normal pressure, and the reflux exchanges heat with the liquid nitrogen 32 and then flows with the polluted nitrogen 23 in parallel to obtain polluted nitrogen 36.

And the waste nitrogen 36 is reheated by the plate heat exchanger 14 and then discharged from the cooling box and is divided into two parts, wherein one part is used as a molecular sieve regeneration gas source 37 to a regeneration heater 38, and the other part is used as waste nitrogen 8 for a water cooling tower.

The invention provides a single-tower nitrogen circulation low-temperature rectification method which can be implemented and is suitable for large nitrogen product amount and also needs nitrogen with various specifications (3 bar (A)/5bar (A)/8bar (A)/20bar (A)/40bar (A)/65bar (A)) and a large amount of liquid nitrogen. The method overcomes the defects of low extraction rate of nitrogen, single specification and high energy consumption of the existing single-tower rectification nitrogen preparation device when preparing nitrogen, effectively reduces irreversible loss in the low-temperature rectification preparation process, fully utilizes the separation capacity of the rectification tower, greatly improves the extraction rate of the nitrogen preparation air separation device, and obviously reduces the energy consumption index of a unit product.