JPH0814459B2 - Air liquefaction separation method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an air liquefaction separation method for collecting oxygen, nitrogen, argon or the like, and an air liquefaction separation method for efficiently collecting mainly oxygen ashes at a relatively high pressure. Regarding

[Conventional technology]

As a method for liquefying and separating air using a double rectification column to mainly collect oxygen gas, the method shown in the system diagrams of FIGS. 4 and 5 is known.

First, in FIG. 4, the compressed raw material air A is cooled to near the liquefaction temperature in the heat exchanger 1 and introduced into the bottom of the lower column 3 of the double rectification column 2 to generate nitrogen gas NH in the lower column 3. And liquefied air LA. The separated liquefied air LA is introduced into the middle stage of the upper tower 6 through the subcooler 4 and the valve 5, and is further rectified and separated into nitrogen gas NL and liquefied oxygen LO.

This liquefied oxygen LO exchanges heat with the nitrogen gas NH introduced from the upper part of the lower tower 3 in the main condenser 7 arranged at the bottom of the upper tower 6, and is vaporized to become oxygen gas GO and rise in the upper tower 6. It becomes gas. Part of the liquefied oxygen LO is discharged from the main condenser 7, decompressed by the valve 8 and introduced into the dip-type sub-condenser 9 provided separately from the main condenser 7, and introduced from the upper part of the lower tower 3. It is vaporized by exchanging heat with the nitrogen gas NH, which is converted into oxygen gas GO, and then introduced into the heat exchanger 1 to exchange heat with the raw material air A to reach room temperature and is taken out as a product.

A part of the nitrogen gas NH separated in the lower tower 3 is led out of the tower, and the rest is introduced into the main condenser 7 and the sub-condenser 9 to exchange heat with the liquefied oxygen LO to be condensed and liquefied to be liquefied. Nitrogen LN
Becomes A part of this liquefied nitrogen LN is again introduced into the upper part of the lower tower 3 to become the reflux liquid of the lower tower 3, and the remaining liquefied nitrogen LN
Is introduced into the upper part of the upper tower 6 through the supercooler 4 and the valve 10 and becomes the reflux liquid of the upper tower 6.

In addition, a part of the nitrogen gas NH discharged outside the tower is introduced into the heat exchanger 1 and exchanges heat with the raw material air A to raise the temperature to an intermediate temperature, and then adiabatically expanded in the expansion turbine 11 to cool the cold. The generated nitrogen gas NP of low temperature and low pressure is again introduced into the heat exchanger 1 and exchanges heat with the raw material air A to reach room temperature.

The nitrogen gas NL derived from the upper part of the upper tower 2 is heat-exchanged with the liquefied air LA and the liquefied nitrogen LN in the subcooler 4,
It is introduced into the heat exchanger 1 by merging with the nitrogen gas NP that has been made low temperature and low pressure in the expansion turbine 11.

Further, in the one shown in FIG. 5, the dip type sub-condenser 9 is arranged below the main condenser 7, and the heat source for vaporizing the liquefied oxygen LO is used as the source air A having a temperature higher than that of the nitrogen gas NH. Is introduced into the sub-condenser 9 to increase the internal pressure by using the liquid depth pressure (liquid head) of the liquid oxygen LO due to the difference in position to increase the internal pressure of the oxygen gas.
This is an increase in GO outflow pressure.

[Problems to be Solved by the Invention]

These air liquefaction separation methods reduce the power consumption
Although it is desired to improve the separation efficiency or increase the pressure of the sampled gas, the former method uses the main condenser and the dip-type sub-condenser to vaporize the liquefied gas using nitrogen gas from the same lower column. Therefore, the pressure of the oxygen gas discharged from the sub-condenser must be reduced, and the operating pressure of the lower column must also be maintained at a pressure that allows heat exchange with oxygen in the sub-condenser. It was difficult to reduce the power consumption by lowering the pressure.

For example, if the operating pressure of the upper tower is 0.36 kg / cm ² G and the composition of liquefied oxygen that accumulates in the main condenser at the bottom of the upper tower is 85% O ₂ , its boiling point is -183.6 ° C, and the oxygen gas composition in equilibrium with it. Is 61% O ₂ . The composition of oxygen gas introduced from the upper tower to the sub-condenser and vaporized and discharged is 85% O ₂ which is the same as the liquefied oxygen at the bottom of the upper tower, and the liquefied oxygen in equilibrium with this is 96% O ₂ Becomes

The boiling point of liquefied oxygen in the sub-condenser is -182.5 ° C when the pressure required for discharging the vaporized oxygen gas to the outside of the system through the heat exchanger is 0.19 kg / cm ² G. When the temperature difference between liquefied oxygen and nitrogen gas that exchange heat in the sub-condenser is 1.8 ° C, the condensation temperature of nitrogen gas is -180.7 ° C, and in order to condense and liquefy nitrogen gas at this temperature, the pressure of nitrogen gas, that is, The operating pressure of the lower tower must be 3.5 kg / cm ² G, and the compression pressure of the raw material air should be a pressure loss on the way.
It will be 3.8 kg / cm ² G.

As described above, the operating pressure of the lower column was determined by the vaporization temperature (boiling point) of liquefied oxygen in the sub-condenser, so that the operating pressure of the lower column could not be lowered any further.

Further, in the latter method, since the vaporization of liquefied oxygen in the dip type sub-condenser is performed at a high pressure, the raw material air must be used as the gas on the condensation side, and the raw material air is liquefied in the sub-condenser. Since the amount of gas rising in the lower column and the amount of reflux liquid descending are small, and the amount of gas rising further is small, there is not enough heat source to vaporize liquefied oxygen in the main condenser at the lower part of the upper column. The amount of rising gas also decreases and the rectification efficiency decreases.

Therefore, in the present invention, a sub-condenser is provided in addition to the main condenser to vaporize the oxygen gas collected as a product, and the fluid liquefied in the sub-condenser is used as nitrogen gas from the upper part of the lower column to deteriorate the rectification conditions. To prevent the deterioration of the separation efficiency and to increase the pressure of the nitrogen gas by the expansion turbine braking blower to obtain the temperature difference in the sub-condenser and reduce the operating pressure of the double rectification column to reduce the power source. It is an object of the present invention to provide an air liquefaction separation method which can reduce the unit and can collect product oxygen gas at high pressure.

[Means for solving the problem]

In order to achieve the above object, the present invention provides an air liquefaction separation method using a double rectification column comprising an upper column, a lower column and a main condenser, wherein the first invention is a dip type provided separately from the main condenser. Liquefied oxygen in the lower part of the upper tower is introduced into the sub-condenser to vaporize it, and nitrogen gas is discharged from the upper part of the lower part of the double rectification column to raise the temperature. It is introduced into a braking blower of an expansion turbine for adiabatic expansion, the pressure is increased, and after cooling again, it is introduced into the sub-condenser, condensed, discharged, depressurized, and then introduced into the upper part of the lower tower or the upper part of the upper tower. According to the second aspect of the invention, the dry type sub-condenser provided separately from the main condenser introduces liquefied oxygen in the lower part of the upper column to cause the liquid oxygen to flow down and vaporize the nitrogen gas. After derivation and temperature rise,
After introducing into a braking blower of an expansion turbine that adiabatically expands a part of the nitrogen gas derived from the upper part of the lower tower to raise the pressure and cool it again, it is introduced into the sub-condenser to be condensed and discharged to reduce the pressure. It is characterized in that it is introduced into the upper part of the tower or the upper part of the upper tower.

[Work]

As a result, since the pressure and temperature of the sub-condenser can be increased regardless of the operating pressure of the lower column of the double rectification column, the pressure of the lower column, that is, the compression pressure of the raw material air can be lowered, and the power consumption can be reduced. , The product oxygen gas sampling pressure can be increased. Further, nitrogen gas in the upper part of the lower tower is used as a heat source of the sub-condenser, and after decompressing after being condensed in the sub-condenser, the whole amount is introduced into the upper part of the lower tower or the upper part of the upper column as a reflux liquid, so the rectification efficiency Does not decrease.

Moreover, since the fluid to be adiabatically expanded by the expansion turbine is a part of the nitrogen gas derived from the upper part of the lower tower, the rectification efficiency does not decrease as compared with the case where air is used as the fluid, and the yield of product oxygen is reduced. improves.

Further, in the second invention, since the dry type sub-condenser is adopted, the liquid depth of liquefied oxygen is eliminated, the boiling point rise due to the liquid pressure is eliminated to improve the vaporization efficiency, and the temperature of the nitrogen gas on the condensation side is lowered. The operating pressure of the lower tower can be further reduced.

〔Example〕

An embodiment of the present invention will be described below with reference to the system diagrams shown in FIGS. The same elements as those in the conventional example are designated by the same reference numerals, and detailed description thereof will be omitted.

First, in the first embodiment shown in FIG. 1, the liquefied oxygen LO, which has been rectified and separated in the double rectification column 2 in the same manner as in the conventional example, is led out from the bottom of the upper column 6, and passed through the valve 8 to the main condenser. It is introduced into a dip type sub-condenser 9 provided separately from 7.

As the gas on the condensation side that serves as a heat source for vaporizing the liquefied oxygen LO, the nitrogen gas GN obtained by pressurizing the nitrogen gas NH derived from the upper part of the lower tower 3 is used. That is, part of the nitrogen gas NH derived from the upper part of the lower tower 3 is in the passage of the heat exchanger 1.
It is introduced into 1a and exchanges heat with the raw material air A to raise the temperature, and becomes nitrogen gas N1 at approximately room temperature. This nitrogen gas N1 is compressed by the expansion turbine braking blower 12 operated by the rotational force of the expansion turbine 11 that adiabatically expands a part of the nitrogen gas NH derived from the upper part of the lower tower 3, and has a pressure higher than the operating pressure of the lower tower 3. Becomes nitrogen gas N2. Next, in the cooler 13, the temperature rise caused in the pressure increasing step is lowered to approximately room temperature by water cooling or the like,
Further, it is introduced into the passage 1b of the heat exchanger 1 to be cooled to near the liquefaction temperature, becomes low temperature pressurized nitrogen gas GN, and is introduced into the sub-condenser 9 as a heat source for vaporizing the liquefied oxygen LO, and condenses itself. It liquefies to liquefied nitrogen LN, and valve 14
After being decompressed by, it is returned to the upper part of the lower tower 3 and becomes the reflux liquid of the lower tower 3.

Appropriate values are selected for the pressure and flow rate of the nitrogen gas GN depending on the composition and flow rate of the oxygen gas GO, the vaporization pressure, the power generated by the expansion turbine, and the like. For example, lower tower 3
If the pressure of the nitrogen gas NH derived from is increased to 4.8 kg / cm ² G of nitrogen gas GN, the condensing temperature (boiling point) becomes -177.4 ° C, and the liquefied oxygen LO is heated and vaporized at a high temperature accordingly. Can be made. That is, as in the conventional example, the sub-condenser 9
The composition of the oxygen gas GO vaporized at 85% O ₂ and the operating pressure of the upper tower 6 is 0.36 kg / cm ² G, and the pressure of the oxygen gas GO vaporized at the sub-condenser 9 is operated at the upper tower 6. Pressure 0.36kg / c
Even at a pressure equal to m ² G, its boiling point is −181.2 ° C., so it can be vaporized with a margin.

Further, the temperature of the nitrogen gas NH in the lower tower 3 is set to the main condenser 7
Since it suffices to vaporize the liquefied oxygen LO to liquefy itself,
Since the temperature of the liquefied oxygen LO is -183.6 ° C, -181.8 ° C
The pressure in the lower tower can be reduced to 3.1 kg / cm ² G. As a result, the compression pressure of the raw material air A can be lowered from 3.8 kg / cm ² G of the conventional example to 3.4 kg / cm ² G by including a pressure loss on the way, and the power consumption rate can be reduced by about 5%. Further, since the rectification conditions are improved as compared with the conventional method, the feed air amount can be reduced by about 10%.

Further, in this embodiment, liquefied nitrogen condensed in the sub-condenser 9 is used.
Since LN is returned to the lower tower 3 to be a reflux liquid and a fluid to be adiabatically expanded by the expansion turbine 11 is a part of the nitrogen gas NH derived from the upper portion of the lower tower 3, compared to the case where air is used as the fluid, The reflux liquid and the rising gas required for the operation of the lower tower 3 are not reduced, the rectification efficiency is not reduced, and the product oxygen yield is improved.

The heat exchanger 1 may be a reversible heat exchanger having a function of removing carbon dioxide gas and water in the raw material air A.

FIG. 2 shows a second embodiment of the present invention, in which a dip type sub-condenser 9 is arranged below the main condenser 7 as compared with FIG. The liquid pressure of is increased by its own weight, whereby the liquid oxygen LO is introduced into the sub-condenser 9 and the oxygen gas GO is obtained at a pressure higher than that of the main condenser 7.

As described above, if the pressure of nitrogen gas GN is 4.8 kg / cm ² G and the condensation temperature is -177.4 ° C, the temperature of liquefied oxygen LO is -179.2 ° C.
The temperature of oxygen gas GO can be increased to ℃, and the pressure of oxygen gas GO is 0.2kg / cm.
It can be from ² G to 0.66 kg / cm ² G.

As a result, the product oxygen gas can be supplied at a higher pressure, and when a booster is provided downstream, the power of this booster can be reduced and the booster can be downsized.

Further, in this embodiment, the liquefied nitrogen LN from the sub-condenser 9 is used.
Is cooled in the subcooler 4, depressurized through the valve 15, and introduced into the upper stage of the upper tower 6 to form a reflux liquid for the upper tower 6.
Incidentally, it is possible to freely select whether the liquefied nitrogen LN is introduced into the upper tower 6 or returned to the upper part of the lower tower 3 in the same manner as in the first embodiment.

FIG. 3 shows a third embodiment of the present invention, which is a sub-condenser.
By using 16 as a dry type, by vaporizing the liquefied oxygen LO while flowing it down, the liquid depth of the liquefied oxygen LO is eliminated, the boiling point rise due to the liquid pressure is eliminated, the vaporization efficiency is increased, and the temperature of the nitrogen gas GN on the condensation side is lowered. The operating pressure is further reduced.

The heat source of the sub-condenser 16 is the nitrogen gas GN which is discharged from the upper part of the lower tower 3 and heated in the heat exchanger 1, then pressure-increased in the braking blower 12 and cooled in the heat exchanger 1 again. The gas GN is condensed in the sub-condenser 16 and decompressed by the valve 14, and then introduced into the upper part of the lower tower 3 as a reflux liquid.

The liquefied nitrogen LN condensed in the sub-condenser 16 may be introduced into the upper part of the upper tower 6 as a reflux liquid after depressurization as in the embodiment of FIG.

In addition, although one heat exchanger is used in each of the above-described embodiments, another heat exchanger may be provided in the circulation system of nitrogen gas which is a heat source of the sub-condenser.

As described in each of the above examples, by increasing the pressure of nitrogen gas regardless of the operating pressure of the lower column and using it as a heat source for vaporizing liquefied oxygen in the sub-condenser, the vaporizing pressure of oxygen gas can be increased and the lower column The power consumption per unit can be reduced by lowering the pressure of, and when the oxygen gas is sent to other products as a product, the power consumption per unit of the compressor can also be reduced.

It should be noted that an independent compressor may be used to pressurize the nitrogen gas that is a heat source in the sub-condenser, but the independent compressor causes an increase in cost, and thus is inferior to the method of the present invention that effectively uses the expansion turbine braking power. . Also, the composition of oxygen or nitrogen is determined by the quality of the product to be collected and the mass balance,
The method of the present invention can be applied regardless of the purity.

〔The invention's effect〕

The air liquefaction separation method of the present invention, as described above,
Liquefied oxygen in the lower part of the upper column was introduced into a dip or dry type sub-condenser installed separately from the main condenser to vaporize it, and nitrogen gas was discharged from the upper part of the lower column of the double rectification column to raise the temperature. Introducing into the braking blower of the expansion turbine for adiabatically expanding a part of the nitrogen gas derived from the lower tower upper part, boosting the pressure, cooling again, and then introducing it into the sub-condenser and condensing it to depressurize it; Since it is introduced into the upper part of the lower tower or the upper part of the upper tower, the pressure of nitrogen gas, which is the heat source for vaporizing liquefied oxygen in the sub-condenser, can be raised to raise the condensation liquefaction temperature, and the vaporization pressure of liquefied oxygen in the sub-condenser can be increased. When the oxygen gas is collected as a product and the sampling pressure is increased and the compressed gas is sent, the basic unit of the compressor can be reduced and the cost can be significantly reduced.

Further, since the pressure and temperature of the sub-condenser can be increased regardless of the operating pressure of the lower tower, the pressure of the lower tower, that is, the compression pressure of the raw material air can be lowered, and the power consumption rate can be reduced. further,
Since the liquefied nitrogen after being condensed in the sub-condenser is decompressed and the whole amount thereof is introduced into the upper part of the lower column or the upper part of the upper column as a reflux liquid, the rectification efficiency is not lowered.

Moreover, since the fluid to be adiabatically expanded by the expansion turbine is a part of the nitrogen gas derived from the upper part of the lower tower, the rectification efficiency does not decrease as compared with the case where air is used as the fluid, and the yield of product oxygen is reduced. improves.

Further, in the second invention, since the dry type sub-condenser is adopted, the liquid depth of the liquefied oxygen is eliminated, the boiling point rise due to the liquid pressure is eliminated to improve the vaporization efficiency, and the temperature of the nitrogen gas on the condensation side is lowered. The operating pressure of the lower tower can be further reduced.

[Brief description of drawings]

1 to 3 show an embodiment of the present invention.
FIG. 1 is a system diagram showing a first embodiment, FIG. 2 is a system diagram showing a second embodiment in which a sub-condenser is arranged below, and FIG. 3 is a third embodiment using a dry type sub-condenser. 4 and 5 are system diagrams showing conventional examples. 1,17 …… Heat exchanger, 2 …… Double rectification tower, 3 …… Lower tower, 6
...... Upper tower, 7 …… Main condenser, 9 …… Dip type sub condenser, 11 …… Expansion turbine, 12 …… Expansion turbine braking blower, 13 …… Cooler, 16 …… Dry type sub-condensation Bowl, A ...
... Raw air, GN, NH, NL, N1, N2 ... Nitrogen gas, GO ... Oxygen gas, LN ... Liquefied nitrogen, LO ... Liquefied oxygen

Claims (2)

[Claims] 1. An air liquefaction separation method using a double rectification column comprising an upper column, a lower column and a main condenser, wherein a liquefied oxygen in the lower part of the upper column is supplied to a dip type sub-condenser provided separately from the main condenser. While introducing and vaporizing, nitrogen gas is discharged from the upper part of the lower part of the double rectification column to raise the temperature, and then a part of the nitrogen gas derived from the upper part of the lower part column is adiabatically expanded and introduced to the braking blower of the expansion turbine. A method for air-liquefaction separation, which comprises increasing the pressure and cooling again, introducing the condensed gas into the sub-condenser, discharging it, decompressing, and introducing into the upper part of the lower column or the upper part of the upper column. 2. An air liquefaction separation method using a double rectification column comprising an upper column, a lower column and a main condenser, wherein a liquefied oxygen in the lower part of the upper column is supplied to a dry type sub-condenser provided separately from the main condenser. Introduces nitrogen gas from the upper part of the lower part of the double rectification column to raise the temperature, and then adiabatically expands part of the nitrogen gas derived from the upper part of the lower part of the double rectification column. After pressurizing and cooling again, it is introduced into the sub-condenser to be condensed and discharged to reduce the pressure,
An air liquefaction separation method, characterized by introducing into the upper part of the lower tower or the upper part of the upper tower.