JPH11142054A - Method and system for air liquefaction separation utilizing cold heat of liquefied natural gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To operate a system in safety without requiring any intermediate refrigerant by providing a detector for detecting the flammable components in nitrogen flowing through a passage connecting a rectification column, a circulation nitrogen compressor, a liquefied natural gas heat exchanger and a liquefied nitrogen storage tank thereby sustaining the compression pressure of circulation nitrogen at a low level. SOLUTION: Liquefied nitrogen in a passage 55 is subjected to pressure drop expansion through a valve 56 and introduced into a liquefied nitrogen storage tank 57 and flush gas is taken out from the upper part thereof and circulated through the passage 52 while being combined. Liquefied nitrogen stored temporarily in the liquefied nitrogen storage tank 57 is led out to a passage 59 and boosted by means of a liquefied nitrogen pump 60. Subsequently, it is subjected to pressure drop expansion and introduced through a passage 63 into a cold box 19a thence introduced to the top of an upper column 11 while being combined with liquefied nitrogen in a passage 26. A hydrocarbon analyzer 61 is provided in the passage 55 in order to detect/measure the quantity of hydrocarbon in high pressure liquefied nitrogen constantly. When it exceeds a specified level, an alarm is delivered immediately and a circulation nitrogen liquefying section 34 is stopped entirely.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air liquefaction separation apparatus and method using the cold of liquefied natural gas (hereinafter referred to as LNG), and more particularly, to a method for circulating nitrogen when LNG is supplied at a relatively high pressure. The present invention relates to an air liquefaction separation apparatus and method in which the pressure of the system is set lower than the supply pressure of the LNG and the safety of the apparatus is ensured.

[0002]

2. Description of the Related Art In a method in which air is liquefied and rectified and its components, such as oxygen, nitrogen, argon, etc., are collected as a gas or liquid product, the cold required for the system is covered by the cold of LNG to operate the apparatus. Various methods have heretofore been proposed. In other words, the cryogenic rectification / separation device for collecting gas products is required to supply the cold heat for cooling the device at the time of start-up necessary for the operation of the device, the cold heat required for the replenishment of hot end loss and intrusion heat during operation, and the collection of liquid product. In this case, in addition to the above, replenishment of cold heat taken out of the system as a liquid by the liquid product is provided by receiving supply from cold heat of LNG.

[0003] In this case, in a usual apparatus, the above-mentioned required cooling heat is generated by installing an expansion turbine, which is not necessary, so that the raw material air compression power can be saved by that amount, and the power consumption can be reduced. Most of the cost in air liquefaction and separation is power cost, and most of it is the cost of power for compressing feed air. Saves money.

However, since LNG is flammable and heat exchange with raw material air or product oxygen is not preferable, a circulating nitrogen system is provided so that circulating nitrogen at a higher pressure than LNG and LNG can be used.
Or heat exchange between the circulating nitrogen and LNG is further performed via a circulating refrigerant such as Freon, so that even if a heat exchanger leaks, flammable LNG will be produced in the raw material air, Care was taken not to mix them in or to enter the rectification column.

That is, in the heat exchanger of the pre-cooling section in the circulating nitrogen system, heat is exchanged between LNG and an intermediate refrigerant of chlorofluorocarbon or various gases, and nitrogen exchanged with LNG in the heat exchanger of the liquefaction section for liquefying nitrogen. Had heat exchanged at a higher pressure than LNG.

As a result, safety measures have been taken to prevent LNG from being mixed into nitrogen even if the heat exchanger cracks and leaks between fluids. That is, if LNG leaks into nitrogen, it may be concentrated in a portion of the rectification column where oxygen purity is high due to the boiling point and may explode, so the above measures have been taken. Further, as described above, conventionally, the pressure of the circulating nitrogen is set to be higher than the supply pressure of the LNG, so that a liquefied nitrogen storage tank is not usually provided in the circulation path.

[0007]

However, depending on the application of LNG, it may be supplied at a very high pressure,
In this case, the circulating nitrogen pressure must be compressed to a value equal to or higher than the pressure of the LNG, which causes a disadvantage that the compression power increases.

[0008] In recent years, the use of an intermediate refrigerant to cool the low-pressure portion of circulating nitrogen has recently become stricter from the viewpoint of protection of the global environment. And measures were needed.

Accordingly, the present invention provides an air liquefaction separation apparatus and method utilizing the cryogenic heat of liquefied natural gas which can keep the compression pressure of circulating nitrogen low and can operate the apparatus safely without using an intermediate refrigerant. It is intended to provide.

[0010]

In order to achieve the above object, an air liquefaction / separation apparatus utilizing the cryogenic heat of liquefied natural gas according to the present invention comprises an air liquefaction apparatus which liquefies air by utilizing the cryogenic heat of liquefied natural gas. In the separation device, at least one circulating nitrogen compressor for compressing nitrogen gas, and at least one liquefied natural gas heat exchanger for heat exchange between the circulating nitrogen and liquefied natural gas compressed by the circulating nitrogen compressor, A liquefied nitrogen storage tank for storing liquefied nitrogen cooled and liquefied by the liquefied natural gas heat exchanger, a path for introducing at least nitrogen gas from a rectification column to the circulating nitrogen compressor, a circulating nitrogen compressor and the liquefaction A path connecting the natural gas heat exchanger, a path connecting the liquefied natural gas heat exchanger and the liquefied nitrogen storage tank, a path connecting the liquefied nitrogen storage tank and the rectification tower, and nitrogen flowing through these paths. Flammable components A circulating nitrogen liquefaction unit provided with a detector for detecting the amount of the combustible component is a hydrocarbon measuring device, in particular, It is characterized in that a plurality of liquefied nitrogen storage tanks are provided.

Further, the air liquefaction / separation method of the present invention utilizing the cold heat of liquefied natural gas comprises compressing, purifying and cooling air, introducing the compressed air into a rectification column, rectifying and separating the air, and purifying at least one kind of air component gas. In the air liquefaction separation method of liquefying and rectifying air by supplying the required cold heat to the system using the cold heat of liquefied natural gas, at least a part of the nitrogen gas derived from the rectification column Is compressed, cooled and liquefied by heat exchange with liquefied natural gas, and at least a part of the generated liquefied nitrogen is stored in a liquefied nitrogen storage tank, and at least a part of the stored liquefied nitrogen is introduced into a rectification column and circulated. Detecting the content of combustible components in the circulating nitrogen and / or the stored liquefied nitrogen, and stopping the circulation of the circulating nitrogen when the detected value is equal to or more than a predetermined amount; Pressure It is characterized in that less than the supply pressure of the liquefied natural gas.

According to the above configuration, a liquefied nitrogen storage tank for storing liquefied nitrogen is provided in the circulating nitrogen liquefaction section, and an analyzer for detecting and monitoring hydrocarbons in nitrogen is provided. Even if there is a leak due to a crack or other trouble, the detector (hydrocarbon analyzer) can immediately detect this and stop the circulating nitrogen, so that the air separation section whose main equipment is the rectification tower is the hydrocarbon. Can be prevented from entering, and the circulating nitrogen can be circulated at a pressure lower than the supply pressure of LNG.

Further, by providing a liquefied nitrogen storage tank, it takes time for liquefied nitrogen containing a predetermined amount or more of hydrocarbons to be stored therein and reach the air separation unit.
By providing the hydrocarbon analyzer in the path connecting the liquefaction unit and the air separation unit, the possibility that the air separation unit enters the danger area of explosion is extremely low, and the safety of the entire apparatus can be sufficiently ensured.

Further, since the pressure of the circulating nitrogen can be made relatively low and the heat exchange between LNG and nitrogen can be made directly different, it is not necessary to use an intermediate refrigerant such as Freon. For this reason, the apparatus configuration is simplified, and the most suitable circulating nitrogen compressor can be selected from many types.

For example, if the pressure of the circulating nitrogen is selected to be 80 kg / cm ² G or higher, which is higher than LNG, a reciprocating compressor must be employed. , A turbo type can be used.

[0016]

FIG. 1 is a system diagram showing an embodiment of an air liquefaction / separation apparatus according to the present invention. Atmospheric air is introduced from the path 1 as raw material air at 29,500 Nm ³ / h, compressed to 5.5 kg / cm ² G by the air compressor 2 and led out to the path 3, and is cooled 4 (the after-cooler of the air compressor or the like). ), And is introduced into one of the paired MS adsorbers 5 used for switching. As the cooling water for the cooler 4, a cooling water that has been cooled to a low temperature by exchanging heat with low-temperature natural gas (vaporized LNG) by a separately provided heat exchanger (not shown) is used in accordance with the required cooling temperature.

The compressed and purified air from which the carbon dioxide and water contained therein have been removed by the MS adsorber 5 is introduced into the cold box 19a of the air separation unit 19 from the path 6 and enters the main heat exchanger 7, where it is subjected to main purification. The heat is exchanged with a low-temperature gas such as oxygen and nitrogen returning from the distillation tower 9, cooled, and discharged at −172 ° C. to be introduced into the lower part of the lower tower 10 of the main rectification tower 9 from the path 8.

The raw material air introduced into the lower tower 10 rises in the tower, comes into contact with the reflux liquid descending from the top in countercurrent gas-liquid state, performs rectification, and separates nitrogen into the upper part of the tower. At the bottom of the column, oxygen-enriched liquefied air distills. This oxygen-enriched liquefied air 16,500 Nm ³ / h is derived from the passage 12, expanded by the expansion valve 13 to about 0.4 kg / cm ² G, introduced into the middle part of the upper tower 11 from the passage 14, It is subjected to rectification in the column.

A part of the oxygen-enriched liquefied air in the path 14 branches to the path 15 and
7, the cooling heat is supplied by the condenser 17, and most of the gas is turned into gas, and the gas is introduced into the middle part of the upper tower 11 from the passage 18.

The nitrogen gas separated at the top of the lower column 10 is led out to a path 20 and branched, and one of the branches enters the main condensing evaporator 22 and the liquefied oxygen distilled off at the bottom of the upper column 11 and The liquid is liquefied by heat exchange, is led to the path 23, and is bisected. One is again introduced to the top of the lower column 10 and becomes the reflux liquid of the column. 3900 Nm ³ / h of the other branched liquefied nitrogen
From the path 26 via the path 24 and the expansion valve 25
At the top of 1 is introduced as reflux.

The other 8,800 Nm ³ / h of the nitrogen gas branched from the path 20 enters the main heat exchanger 7 via a path 21 and exchanges heat with the raw material air to reach a substantially normal temperature. A cold box 19a is drawn out from the tank 27 and passed through a control valve 28 to a circulating nitrogen liquefaction unit (circulating nitrogen system) 3 to be described later.
Go to 4.

In the upper tower 11, the liquefied oxygen distilled at the bottom of the tower exchanges heat with the nitrogen gas flowing through the gas-side flow passage in the main condensing evaporator 22, and is vaporized to become a rising gas. The liquefied nitrogen introduced into the top of the upper tower 11 and the oxygen-enriched liquefied air introduced into the middle of the tower become the reflux liquid of the upper tower 11 and flow down the tower, and the rising gas and the countercurrent gas-liquid The rectification is performed on contact.

As a result, 15,000 Nm ³ / h of the nitrogen gas separated at the top of the upper tower 11 is taken out to the passage 29 and exchanged heat with the raw material air in the main heat exchanger 7 to become substantially normal temperature, so that the cold box is formed. 19a is derived and the paths 31 and 3
From 2, it goes into the cold box 34 a of the circulating nitrogen liquefaction unit 34.

The liquefied oxygen separated at the bottom of the upper tower 11 is taken out through a passage 43 and stored in a liquefied oxygen storage tank 44. In addition, the exhaust gas in the middle and upper parts of the upper tower 11
0, the heat is recovered by the main heat exchanger 7, and the heat is led out of the system.

Further, an argon feed gas is withdrawn from the vicinity of the position where the argon concentration is highest in the middle part of the upper column 11 through a passage 35, introduced into the lower part of the crude argon column 16 and rectified. From the top of the argon tower 16, about 95-97% of argon is passed to the passage 37 in crude argon.

The crude argon derived from the crude argon tower 16 is passed through an argon heat exchanger 38 to an argon purifier 39.
And after purifying mainly the catalytic process, again passes through the argon heat exchanger 38 and enters the reboiler at the bottom of the high-purity argon column 40, liquefies itself and is discharged. And rectified in the middle of the column, and high-purity argon is distilled off at the bottom of the column. This high-purity liquefied argon is taken out through the path 41 and stored in the liquefied argon storage tank 42.

15,000 Nm of nitrogen gas at a pressure of 0.1 kg / cm ² G from the upper tower 11 led out to the path 31
³ / h, a part of which is 11,800 Nm3 / h
, And is taken out of the system as a product nitrogen gas from the path 33, and the other branched nitrogen gas is 32,000 Nm ³ /
h is introduced into the cold box 34a of the circulating nitrogen liquefaction section 34 from the path 32, and is first introduced into the LNG heat exchanger 45.
Enter a.

On the other hand, pressure 80 kg / cm ² G, temperature -1
LNG at 55 ° C. is introduced at 30 Ton / h from the path 46, a part of which is branched into the path 47a, introduced into the LNG heat exchanger 45a, and exchanges heat with the nitrogen gas introduced from the path 32 and flowing countercurrently. I do. The heat-exchanged nitrogen gas is
Cold box 3 from path 48 cooled to 135 ° C
4a is derived.

The cooled nitrogen gas in the passage 48 is introduced into a circulating nitrogen compressor 49 at -135 ° C. and is compressed at a low temperature to 4.7.
kg / cm ² G.
7. Merges with 4.7 kg / cm ² G of nitrogen gas 88,000 Nm ³ / h that has passed through the valve 28, and is introduced into the LNG heat exchanger 45 b through the path 51. In the LNG heat exchanger 45b, 8 branched from the path 46 to a path 47b.
Countercurrent heat exchange with 0 kg / cm ² G LNG, -135 ° C
And exits the cold box 34a through the path 52.

4.6 kg / cm ² G of the route 52, -13
12,000 Nm ³ / h of 5 ° C. nitrogen gas is introduced into the circulating nitrogen compressor 53 and compressed to 60 kg / cm ² G,
After being led out to the path 54 and again introduced into the cold box 34a, it is introduced into the LNG heat exchanger 45c and
80kg / cm ² G LNG introduced from c and flowing countercurrently
Then, the heat exchange temperature becomes −150 ° C., and the liquid is liquefied (the state of the supercritical condition is also referred to as a liquefied state) and led to the path 55.

The liquefied nitrogen 12,000 led out to the path 55
Nm ³ / h is reduced in pressure to about 2 kg / cm ² G by the valve 56 to reach −185 ° C., and is introduced into the liquefied nitrogen storage tank 57. The flash gas generated when expanded by the valve 56 is:
It is taken out from the upper part of the liquefied nitrogen storage tank 57, passes through the low-temperature gas path 66, merges with the path 52, and circulates.

The LNG heat exchangers 45a, 45b, 45
The natural gas which has been heated and gasified in step c to have a normal temperature is joined after the respective heat exchangers are led out, and is sent to the natural gas destination via the path 65.

The liquefied nitrogen 7500 Nm ³ / h temporarily stored in the liquefied nitrogen storage tank 57 is led out to a passage 59 and pressurized by a liquefied nitrogen pump 60.
The pressure is reduced and expanded to 3 kg / cm ² G, introduced into the cold box 19 a via the channel 63, combined with liquefied nitrogen 3600 Nm ³ / h in the channel 26, introduced into the top of the upper column 11, and refluxed in the upper column 11. It becomes liquid and supplies the required cold heat to the air separation unit. If the storage pressure of the liquefied nitrogen storage tank 57 is high enough to pump the liquid, the liquefied nitrogen pump 60 can be omitted.

The passage 55 is provided with a hydrocarbon analyzer (QIA) 61 which is a detector for detecting the amount of hydrocarbon which is a combustible component in nitrogen. The amount of hydrocarbons in nitrogen is constantly detected and measured. If the measured value exceeds a predetermined amount, an alarm is issued immediately and a signal is issued, and the entire circulating nitrogen liquefaction unit 34 (in the cold box 34a and in the circulating nitrogen compressor 4).
9, 53) is set to stop.

When it is detected that a small amount of LNG has entered the circulating nitrogen of the circulating nitrogen liquefaction unit 34, the order of closing various valves when the circulating nitrogen system is stopped can be considered in several ways. Since they are different, detailed description thereof is omitted.

Thus, the LNG heat exchanger 45a,
For example, even if a crack is generated in any of 45b and 45c and a small amount of LNG leaks into the circulating nitrogen, the hydrocarbon analyzer 61
Circulating nitrogen system was stopped due to
Does not reach the air separation unit 19.

Further, even if the liquefied nitrogen containing LNG leaked in a very small amount flows through the short-time path 55,
Since it is introduced and stored in the liquefied nitrogen storage tank 57, it reaches the main rectification column 9 (although not shown, a device for measuring the amount of hydrocarbons in liquefied oxygen is conventionally installed).
Even after a considerable time has passed, even if the hydrocarbon analyzer 61 fails and the discovery is delayed, a separate hydrocarbon measuring device (not shown) is provided to provide the hydrocarbon contained in the liquefied nitrogen in the liquefied nitrogen storage tank 57. If the amount of hydrogen is inspected at regular intervals, it does not matter. In addition, a hydrocarbon measuring device (not shown) is also provided on a route 63 from the liquefied nitrogen storage tank 57 to the main rectification column 9.
Is provided, the supply of hydrocarbon-containing liquefied nitrogen can be stopped before the accumulation of hydrocarbons in the main rectification column 9 starts.

By providing a plurality of the liquefied nitrogen storage tanks 57, the safety of the above steps can be further improved. That is, by using a plurality of liquefied nitrogen storage tanks 57 connected, for example, in series, or by using the receiving storage tank and the discharge storage tank separately, safer operation becomes possible. Even if a small amount of hydrocarbons enters one of the liquefied nitrogen storage tanks 57, the air separation unit 1
9 is capable of maintaining operation.

[0039]

As described above, according to the present invention,
A liquefied nitrogen storage tank for storing liquefied nitrogen is provided in the circulating nitrogen liquefaction section, and a detector for detecting and monitoring hydrocarbons in nitrogen is provided. Can be immediately detected by the detector, and by stopping the circulating nitrogen system, hydrocarbons can be prevented from entering the air separation section.
It can be formed to circulate at a pressure lower than the supply pressure of NG.

Furthermore, the provision of the liquefied nitrogen storage tank allows liquefied nitrogen containing a predetermined amount or more of hydrocarbons to be stored in the tank. It is very unlikely that the substance will enter and condense into an explosion, causing a danger of explosion, and safety can be ensured. Also, there is no need to use an intermediate refrigerant such as Freon.

Further, the pressure of the circulating nitrogen can be made relatively low, the heat exchange between LNG and nitrogen can be performed directly, the apparatus configuration becomes simple, and the circulating nitrogen compressor can be of many types. The most suitable one can be selected from

[Brief description of the drawings]

FIG. 1 is a system diagram showing one embodiment of an air liquefaction / separation apparatus of the present invention.

[Explanation of symbols]

2 ... Air compressor, 4 ... Cooler, 5 ... MS adsorber, 7 ...
Main heat exchanger, 9: Main rectification column, 10: Lower column, 11: Upper column, 13: Expansion valve, 16: Crude argon column, 17: Condenser, 19: Air separation unit, 19a: Cold box, 2
2: Main condensing evaporator, 25: expansion valve, 28: control valve, 34
... circulating nitrogen liquefaction unit (circulating nitrogen system) 34a ... cold box, 38 ... argon heat exchanger, 39 ... argon purifier, 40 ... high purity argon tower, 42 ... liquefied argon storage tank
44 ... liquefied oxygen storage tank, 45a, 45b, 45c ... LNG
Heat exchangers, 49, 53: circulating nitrogen compressor, 57: liquefied nitrogen storage tank, 60: liquefied nitrogen pump, 61: hydrocarbon analyzer (QIA), 62: control valve

Claims (5)

[Claims] 1. An air liquefaction / separation apparatus for liquefying air by utilizing the cold heat of liquefied natural gas, wherein at least one circulating nitrogen compressor for compressing nitrogen gas and circulating compressed by said circulating nitrogen compressor At least one liquefied natural gas heat exchanger for heat exchange between nitrogen and liquefied natural gas, a liquefied nitrogen storage tank for storing liquefied nitrogen cooled by the liquefied natural gas heat exchanger, and at least a rectification tower A path for introducing the nitrogen gas to the circulating nitrogen compressor, a path connecting the circulating nitrogen compressor and the liquefied natural gas heat exchanger, and a path connecting the liquefied natural gas heat exchanger and the liquefied nitrogen storage tank. Liquefied natural gas, comprising: a circulating nitrogen liquefaction unit provided with a path connecting the liquefied nitrogen storage tank and the rectification tower, and a detector for detecting the amount of combustible components in nitrogen flowing through these paths. Sky using the cold heat of Gas-liquid separation equipment. 2. The air liquefaction / separation apparatus according to claim 1, wherein the detector for detecting the amount of the combustible component is a hydrocarbon measuring device. 3. The air liquefaction / separation apparatus utilizing the cryogenic heat of liquefied natural gas according to claim 1, wherein a plurality of said liquefied nitrogen storage tanks are provided. 4. Air is compressed, refined, cooled and introduced into a rectification column, rectified and separated to collect at least one gas of air components as a product, and cryogenic heat required for the system is converted to liquefied natural gas. In the air liquefaction separation method in which air is liquefied and rectified by supplying it using cold heat, at least a part of the nitrogen gas derived from the rectification column is compressed, and heat exchange with liquefied natural gas is performed to liquefy and cool. At least a part of the liquefied nitrogen thus obtained is stored in a liquefied nitrogen storage tank, and at least a part of the stored liquefied nitrogen is introduced into a rectification column and circulated, and the circulated nitrogen and / or the combustible component contained in the stored liquefied nitrogen An air liquefaction / separation method using the cryogenic heat of liquefied natural gas, comprising detecting an amount and, when the detected value is equal to or greater than a predetermined amount, circulating the circulating nitrogen. 5. The method of claim 4, wherein the pressure of the circulating nitrogen is lower than the supply pressure of the liquefied natural gas.