JPH0372908B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method and apparatus for producing nitrogen gas, which uses compressed air as a raw material and produces a nitrogen gas product using a single rectification column. [Prior Art] This type of nitrogen gas production method and production equipment using a single rectification column uses nitrogen gas taken out from the top of the rectification column as a cooling source for the main heat exchanger, and then uses this heat A technique is conventionally known in which nitrogen gas heated to room temperature by exchange is extracted as a low-pressure product nitrogen gas having approximately the same pressure as the raw material air (for example, Japanese Patent Publication No. 54-39830). In the case of this conventional technology, it is possible to rectify and separate nitrogen gas from the feed air by the partial condensation effect caused by the contact between the feed air supplied from the bottom of the rectification column and the reflux liquid descending from the top of the rectification column. However, the recovery rate of nitrogen gas relative to the amount of raw material air is still low, and if we look at the yield with current nitrogen gas production equipment, it is 37% to 48% as shown in the table below.
The yield is about 100%.

[Problem that the invention seeks to solve]

When we examine the conventional nitrogen gas production method and low-temperature generator mentioned above, we find that the former nitrogen gas production method has a low yield of nitrogen gas, which tends to increase costs, and the latter low-temperature generator Since the structure is such that nitrogen gas is rectified in the rectification column and taken out from the top of the column, it is mixed into the feed air supply path and rectified again, so the yield of nitrogen gas relative to the amount of feed air is low. Even if the nitrogen gas is increased to some extent, the purity cannot be increased to the extent that the nitrogen gas can be used as a product gas, and there is a problem that it cannot be used as a method for producing a product nitrogen gas. The first object of the present invention is to improve the yield of nitrogen gas by effectively utilizing the low-pressure nitrogen gas taken out as a product, to reduce the manufacturing cost per unit amount, and to reduce the production cost of nitrogen as a product. The second purpose is to provide a manufacturing method that can obtain nitrogen gas of sufficient purity as a gas, and the second purpose is to
It is an object of the present invention to provide a production apparatus that can continuously produce a nitrogen gas product while achieving the objective. [Means for Solving the Problems] The method for producing nitrogen gas according to the first invention uses compressed air as a raw material, removes moisture, carbon dioxide, etc., and then cools it to near the liquefaction point in a main heat exchanger. In a nitrogen gas production method in which nitrogen gas is supplied to a rectifying type rectification tower, product nitrogen gas is taken out from the top of the tower by rectification, and then led out of the production system, the nitrogen gas taken out from the top of the rectification tower is supercooled. The nitrogen gas is then used as a cooling source for the main heat exchanger to warm it to room temperature, compress at least a portion of this nitrogen gas, and then return at least a portion of it to the main heat exchanger to cool it to near the liquefaction point. , the cooled nitrogen gas is supplied to a lower part of the rectification column than the auxiliary rectification section disposed below the feed air intake section, and the supplied nitrogen gas is passed to the bottom of the rectification column. The gas vaporized in the impure liquid oxygen reservoir by being supplied to the top of the reboiler provided in the impure liquid oxygen reservoir is introduced into the raw material air intake through an auxiliary rectification section located below the raw material air intake section of the rectification column. At the same time, the liquid nitrogen is completely liquefied by heat exchange with the impure liquid oxygen in the impure liquid oxygen storage section, and is taken out from the bottom of the reboiler, and after supercooling in the supercooler. It is characterized in that it is expanded and supplied as a reflux liquid to the upper part of the rectification column, and that refrigeration is separately supplied during the entire process, and its functions and effects are as follows. [Operation] The cold energy of the nitrogen gas taken out from the top of the rectification column is used as a cold source in the supercooler and main heat exchanger to heat the nitrogen gas to a set temperature. At least a portion of this nitrogen gas is compressed, and after at least a portion of the compressed nitrogen gas is cooled by main heat exchange, it is supplied to a reboiler at the bottom of the rectification column. By heat exchange between the nitrogen gas and the impure liquid oxygen in this reboiler, the impure liquid oxygen is heated and the nitrogen gas is completely liquefied. The gas that evaporates as the impure liquid oxygen is heated rises while contacting the liquid nitrogen (reflux liquid) descending in the rectification column in a countercurrent state, the oxygen liquefies and descends, and the nitrogen-rich gas is It rises and rectification takes place. On the other hand, the liquefied liquid nitrogen is taken out from the bottom of the reboiler, supercooled in a supercooler, expanded, and then supplied to the top of the rectification column as a reflux liquid, which is necessary to separate the nitrogen component from the feed air. This helps further improve nitrogen gas yield. In addition, the cold energy of the nitrogen gas taken out from the top of the rectification tower is used as a cold source in the supercooler and main heat exchanger, and at least a part of the compressed nitrogen gas is cooled in the main heat exchanger. After that, when supplying the air to the rectification tower, the raw air to the rectification tower is routed through a separate route from the supply route, and the raw air intake section of the rectification tower is completely separated by an auxiliary rectification section. Since the nitrogen gas is supplied to various locations, it can be used as a cold source for improving the yield without reducing the purity of the nitrogen gas at all. [Effect of the invention] Therefore, the nitrogen gas taken out from the top of the rectification tower is used as a cold source in the supercooler and the main heat exchanger, and then the nitrogen gas is compressed and cooled to produce raw air. By supplying it to the reboiler below the intake position and using it as a heating source for the impure liquid oxygen at the bottom of the rectification column, and using the liquid nitrogen liquefied in this reboiler as a reflux liquid, Compared to the production method described above, it is possible to improve the yield of nitrogen gas, that is, to reduce the production cost per unit amount. In addition, when the nitrogen gas taken out from the top of the rectification tower is used as a cold source and then supplied to the rectification tower again, it is completely separated from the feed air. It can be used as a cold source for improving the yield without reducing the purity of the nitrogen gas at all, and as a result, a highly pure nitrogen gas suitable for use as a product nitrogen gas can be obtained. [Means for Solving the Problems] The characteristic configuration of the nitrogen gas production apparatus using a single distillation column according to the second invention is that it includes a feed air supply section for supplying compressed air as a raw material, and a single distillation column. A single rectification column equipped with a distillation column and a heat exchanger that cools the air supplied to the rectification column to near the liquefaction point using nitrogen gas taken out from the top of the column as a cooling source. A nitrogen gas production apparatus using a nitrogen gas production apparatus is provided with the configurations described in [A] to [D] below. [B] The raw air supply section is composed of an air compressor that compresses and supplies raw air, and a carburization/drying unit that removes moisture, carbon dioxide, and the like. [B] The main heat exchanger compresses at least a portion of the nitrogen gas that is heated by exchanging the nitrogen gas supplied from the top of the rectification column with the air supplied from the decarburization/drying unit. Then, the compression circuit that supplies the main heat exchanger is connected again. [C] The rectification column is provided with a feed air intake section between the main rectification section and the auxiliary rectification section, and an impure liquid oxygen reservoir section equipped with a condenser at the top of the column and a reboiler at the bottom of the column. It is arranged,
Furthermore, a nitrogen gas intake path is connected to supply nitrogen gas supplied from the main heat exchanger via the compression circuit to the top of the reboiler of the impure liquid oxygen reservoir, so that the gas vaporized in the impure liquid oxygen reservoir is connected. The liquid nitrogen is raised to the main rectification section of the rectification column through the auxiliary rectification section of the rectification column, and the liquid nitrogen, which has been completely liquefied by heat exchange with impure liquid oxygen in the impure liquid oxygen storage section, is sent to the bottom of the reboiler. It is configured to be taken out from the [d] In the rectification column, liquid nitrogen that has been completely liquefied by heat exchange with impure liquid oxygen in the impure liquid oxygen storage section is taken out from the bottom of the reboiler, supercooled in the supercooler, expanded, and purified. A reflux path for supplying reflux liquid is connected to the upper part of the distillation column. The functions and effects of the above configuration are as follows. [Operation] The cold energy of the nitrogen gas taken out from the top of the rectification column is used as a cold source in the supercooler and main heat exchanger to heat the nitrogen gas to a set temperature. At least a portion of this nitrogen gas is compressed through a compression circuit and then returned to the main heat exchanger, and the nitrogen gas supplied from the main heat exchanger is further supplied to the top of the reboiler of the impure liquid oxygen storage section. The nitrogen gas intake passage is connected so that the air is processed in a system completely separate from the raw air supplied to the air intake section located between the main rectification section and the auxiliary rectification section. has been done. The gas vaporized in the impure liquid oxygen reservoir is caused to rise to the main rectification section of the rectification column through the auxiliary rectification section of the rectification column, and undergoes heat exchange with the impure liquid oxygen in the impure liquid oxygen reservoir. The liquid nitrogen that has been completely liquefied is taken out from the bottom of the reboiler, passed through a reflux path, supercooled in the supercooler, expanded, and supplied to the upper part of the rectification column as a reflux liquid. [Effect of the invention] Therefore, the nitrogen gas taken out from the top of the rectification tower is used as a cold source in the supercooler and the main heat exchanger, and then the nitrogen gas is compressed and cooled to produce raw air. By supplying it to the reboiler below the intake position and using it as a heating source for the impure liquid oxygen at the bottom of the rectification column, and using the liquid nitrogen liquefied in this reboiler as a reflux liquid, This apparatus has a higher yield of nitrogen gas than the production apparatus of 1, and has the effect of continuously producing nitrogen gas products at low cost. In addition, the nitrogen gas used as a cooling source can be completely separated from the raw air when it is resupplied to the rectification column.
Product nitrogen gas can be obtained without reducing the purity of nitrogen gas at all. [Example] Hereinafter, a method and apparatus for producing nitrogen gas according to the present invention will be explained based on FIG. 1. Raw air from which dust has been removed by an air filter (not shown)
After compressing GA to the pressure required for air separation operation (for example, 4.7 Kg/cm2G) in compressor 1, this compressed raw air GA is passed through pipe P1 to compressor 1.
The air is also supplied to the carburization/drying unit 2 that constitutes the raw air supply section. This carburization/drying unit 2
In this case, the compressed feed air GA is cooled to room temperature in the aftercooler, then cooled to approximately 5℃ in the refrigeration equipment, and then supplied to one of the two molecular sieve towers to cool down the air in the feed air GA. Adsorbs and removes carbon dioxide and moisture. Meanwhile, waste gas (impure oxygen gas) that has passed through the main heat exchanger 3 (described later) is supplied to the other molecular sieve tower for regeneration. Carbon dioxide, moisture,
Pipe P for raw air GA from which other impurities have been removed
2 to the main heat exchanger 3, and after being cooled to near the liquefaction point, it is supplied to the raw air intake section 4a at the bottom of the rectification column 4 through the pipe P3. In addition, liquid nitrogen, which is an example of a cold source, is placed at the top of the rectification column 4.
LN2 is supplied through pipe P4, and in the main rectification section 4b in the rectification column 4, the feed air GA rising from the bottom and the liquid nitrogen (reflux liquid) descending from the top in the rectification column 4 are placed in a countercurrent state. Contact with raw air
Oxygen is liquefied from GA and nitrogen gas GN2 is separated by rectification. Nitrogen gas GN taken out from the top of the rectification column 4
2 is supplied to the subcooler 5 through piping P5, and further to the main heat exchanger 3 through piping P6, and nitrogen gas is
The cold energy of the GN2 is used as a cold source in the supercooler 5 and the main heat exchanger 3, and the nitrogen gas GN2 is heated to room temperature. At least a part of the room temperature nitrogen gas GN2 taken out from the main heat exchanger 3 through the low-pressure product nitrogen gas pipe P7 is supplied to the compressor 6 through the pipe P8, and the raw material
Low pressure product nitrogen gas GN2 (e.g. 4.0Kg/cm2G) with almost the same pressure as GA is mixed with medium pressure (e.g. 9.0Kg/cm2G).
2G). Piping P9 for intermediate pressure product nitrogen gas from the compressor 6
At least a part of the compressed nitrogen gas taken out through the pipe P10 is returned to the main heat exchanger 3 through the pipe P10, and after being cooled to near the liquefaction point, it is passed through the pipe P11 into the impure liquid oxygen reservoir section 4c at the bottom of the rectification column 4. It is fed to the top of the reboiler 7 provided. In other words,
The pipes P7, P8, P9 and the compressor 6 constitute a compression circuit according to the present invention, and the pipe 11 constitutes a nitrogen gas intake path. Then, nitrogen gas GN2 and impure liquid oxygen LO in the reboiler 7
By heat exchange with LO2, the impure liquid oxygen LO2 is heated, and the nitrogen gas GN2 is completely liquefied. This impure liquid oxygen LO2 is evaporated as it is heated, and the gas is passed through the rectification tower 4 through an auxiliary rectification section 4d interposed between the raw air intake section 4a and the impure liquid oxygen storage section 4c of the rectification tower 4. The oxygen rises to the top of the column and comes into contact with the liquid nitrogen (reflux liquid) descending in the rectifying column 4 in a countercurrent state, and the oxygen liquefies and descends, and the nitrogen-rich gas moves upstream to perform rectification. . Such a two-stage rectification action in the auxiliary rectification section 4d and the main rectification section 4b can improve the yield of nitrogen gas GN2. The liquid nitrogen LN2 taken out from the bottom of the reboiler 7 through the pipe P12 is supplied to the supercooler 5, and after supercooling the liquid nitrogen LN2, it is led to the pipe P13 having an expansion valve 8, expanded, and sent to the rectification column 4. The reflux liquid is supplied to the top of the reflux liquid. In other words, the pipes 12 and 13 constitute a reflux path. In addition, the impure liquid oxygen LO2 taken out from the lower part of the impure liquid oxygen storage section 4c of the rectification column 4 is transferred to the pipe P
14 to the supercooler 5, impure liquid oxygen
After supercooling LO2, pipe P with expansion valve 9
15, expand it, and supply it to the condenser 10 provided at the top of the rectification column 4. The impure liquid oxygen LO2 evaporated under reduced pressure in the condenser 10 exchanges heat with the low-temperature nitrogen gas GN2 present in the upper part of the rectification column 4, and a part of the low-temperature nitrogen gas GN2 is liquefied and descends as a reflux liquid. . Impure oxygen gas evaporated in the condenser 10
GO2 is supplied to the subcooler 5 through piping P16, and further to the main heat exchanger 3 through piping P17,
The cold energy of the impure oxygen gas GO2 is used as a cold source in the subcooler 5 and the main heat exchanger 3.
The waste gas GO2, which is impure oxygen gas that has been warmed to room temperature as a result of this cold release, is supplied to the unused molecular sieve tower of the decarburization/drying unit 2 through pipe P18, and is used as regeneration gas before being externalized. is released. There are three ways to take out the product nitrogen gas GN2 depending on valve control: [B] The required amount of nitrogen gas GN2 heated to room temperature in the main heat exchanger 3 is taken out as a low-pressure product nitrogen gas GN2 having approximately the same pressure as the raw material air GA, and the remainder is compressed and returned to the main heat exchanger 3. Method. [B] A method of compressing the nitrogen gas GN2 heated to room temperature in the main heat exchanger 3, taking out the required amount as a medium-pressure product nitrogen gas GN2, and returning the remainder to the main heat exchanger 3. [C] The required amount of the nitrogen gas GN2 heated to room temperature in the main heat exchanger 3 is taken out as a low-pressure product nitrogen gas GN2 having approximately the same pressure as the raw material air GA, and the remaining portion is compressed and the required amount is further heated to medium pressure. A method of taking out the product nitrogen gas GN2 and returning the remainder to the main heat exchanger 3. In the above example, liquid nitrogen LN2 was supplied from the outside to the upper part of the rectification column 4 as a method of separately replenishing cold during the entire process, but the method is not limited to this replenishment method, and for example, As shown in FIG. 2, a part of the raw air GA taken out from the middle of the raw air supply system of the main heat exchanger 3 through the piping P19 is adiabatically expanded in the expansion turbine 11, and then from the expansion turbine 11 to the piping Piping P17 for the waste gas (impure oxygen gas) system where the cold raw material air GA taken out through P20 passes through the supercooler 5
Then, a part of this raw air GA may be supplied as a cold source for the main heat exchanger 3. In addition, in the above-mentioned embodiment, the production uses two compressors: the compressor 1 that compresses the raw material air, and the compressor 6 that compresses the nitrogen gas that is first heated to room temperature in the main heat exchanger 3. Although the means have been described, the present invention is not limited thereto. In other words, considering the pressure levels of these two compressors 1 and 6, it is possible to achieve one compression by using the low pressure stage of the same compressor for raw air compression and the high pressure stage for nitrogen gas compression. It can also be used for both purposes.

[Brief explanation of drawings]

1 and 2 show an embodiment according to the present invention, FIG. 1 is a piping system diagram showing a nitrogen gas production device, and FIG. 2 is a piping system diagram showing another embodiment of the nitrogen gas production device. . 1... Compressor, 2... Carburization/drying unit, 3
... Main heat exchanger, 4 ... Rectification column, 4a ... Raw air intake section, 4b ... Main rectification section, 4c ... Impure liquid oxygen reservoir section, 4d ... Auxiliary rectification section, 5 ... Supercooler, 7...Reboiler, 10...Condenser, 1
1... Expansion turbine, P11... Nitrogen gas intake path, P7... Compression circuit, P12, P13... Reflux path.

Claims (1)

[Scope of Claims] 1 Compressed air is used as a raw material, and after removing moisture, carbon dioxide, etc., it is cooled to near the liquefaction point in a main heat exchanger 3, and then supplied to a single rectification type rectification column 4, where it is refined. This is a nitrogen gas production method in which product nitrogen gas is taken out from the top of the column by a distillation column and led out of the production system, and the nitrogen gas taken out from the top of the rectification column 4 is sent to the supercooler 5 and the main heat exchanger 3. It is used as a cold source to warm up to room temperature, compress at least a portion of this nitrogen gas, and then return at least a portion of it to the main heat exchanger 3 and cool it to near the liquefaction point. The gas is supplied to a lower part of the rectifying column 4 than the auxiliary rectifying section 4d disposed below the raw air intake section 4a, and the supplied nitrogen gas is transferred to the impure liquid at the bottom of the rectifying column 4. Oxygen storage section 4c
The gas vaporized in the impure liquid oxygen storage section 4c is supplied to the top of the reboiler 7 provided in While rising to the main rectification part 4b above the intake part 4a,
Liquid nitrogen, which has been completely liquefied by heat exchange with the impure liquid oxygen in the impure liquid oxygen storage section 4c, is taken out from the bottom of the reboiler 7, supercooled in the supercooler 5, expanded, and sent to the top of the rectification column 4. A method for producing nitrogen gas using a single rectification column, which is characterized in that it is supplied as a reflux liquid to the nitrogen gas, and that refrigeration is separately supplied during the entire process. 2. The method for producing nitrogen gas using a distillation tower according to claim 1, wherein the separately supplied cold is liquid nitrogen supplied to the upper part of the rectification tower 4 from the outside. 3 The separately replenished cold is taken out from the middle of the main heat exchanger 3 and expanded in the expansion turbine 11, and then transferred to the condenser 10 provided at the upper part of the rectification column 4.
According to claim 1, which is part of the raw material air that is combined with impure oxygen gas, which is waste gas taken out from A method for producing nitrogen gas using the single rectification column described above. 4. The required amount of nitrogen gas heated to room temperature in the main heat exchanger 3 is taken out as a low-pressure product nitrogen gas having approximately the same pressure as the raw material air, and the remainder is returned to the main heat exchanger 3 after being compressed. A method for producing nitrogen gas using the single rectification column according to item 2 or 3. 5. Compressing the nitrogen gas heated to room temperature in the main heat exchanger 3, taking out the required amount as intermediate pressure product nitrogen gas, and returning the remainder to the main heat exchanger 3. A method for producing nitrogen gas using the single rectification column according to item 3. 6. Take out the required amount of the nitrogen gas heated to room temperature in the main heat exchanger 3 as a low-pressure product nitrogen gas with approximately the same pressure as the raw material air, compress the remainder, and further take out the required amount as a medium-pressure product nitrogen gas. A method for producing nitrogen gas using a single rectification column according to claim 2 or 3, wherein the nitrogen gas is extracted and the remainder is returned to the main heat exchanger 3. 7 A raw air supply unit for supplying compressed air as a raw material, a single rectification type rectification tower 4, and a nitrogen gas taken out from the top of the rectification tower 4 as a cooling source to the rectification tower 4. It is equipped with a heat exchanger 3 that cools the supplied air to near the liquefaction point, and also includes the following [A] ~
A nitrogen gas production device using a single rectification column having the configuration described in [d]. [B] The raw air supply section is comprised of a compressor 1 that compresses and supplies raw air, and a decarburization/drying unit 2 that removes moisture, carbon dioxide, and the like. [B] At least a portion of the nitrogen gas supplied from the top of the rectification column 4 is heated by exchanging the nitrogen gas supplied from the top of the rectification column 4 with the air supplied from the decarburization/drying unit 2 to the main heat exchanger 3. , compression circuits P7, P8, and P10 are connected for compressing the heat and supplying it again to the main heat exchanger 3. [C] The rectification column 4 is equipped with a raw air intake section 4a between the main rectification section 4b and the auxiliary rectification section 4d, and is equipped with a condenser 10 at the top of the column and a reboiler 7 at the bottom of the column. A liquid oxygen reservoir 4c is provided, and the nitrogen gas supplied from the main heat exchanger 3 via the compression circuits P7, P8, P10 is transferred to the impure liquid oxygen reservoir 4.
A nitrogen gas intake path P11 is connected to the top of the reboiler 7 of c, and the gas vaporized in the impure liquid oxygen storage section 4c is passed through the auxiliary rectification section 4d of the rectification column 4 to the rectification column 4. Main distillation section 4b
The liquid nitrogen is completely liquefied by heat exchange with the impure liquid oxygen in the impure liquid oxygen storage section 4c and taken out from the bottom of the reboiler 7. [d] In the rectification column 4, liquid nitrogen that has been completely liquefied by heat exchange with the impure liquid oxygen in the impure liquid oxygen storage section 4c is taken out from the bottom of the reboiler 7 and supercooled in the supercooler 5. Reflux path P1 that is expanded and supplied to the upper part of the rectification column 4 as a reflux liquid
2, P13 is connected.