JP2002139277A - Control method and control device for air liquefying and separating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control method and a control device capable of responding quickly and stably to the change of demand of product gas in an air liquefying and separating device while maintaining the purity of the product. SOLUTION: When the amount of a product collected from the air liquefying and separating device is increased or decreased, an objective value is achieved employing a fundamental increasing and decreasing value, increasing or decreasing the flow rate set value of a fluid except the product linearly in proportion to the increasing or decreasing amount of the product, an increase compensating value, decreased with a big decreasing degree at first after arriving at the predetermined maximum compensating value and, thereafter, with the decreasing degree reduced gradually and arriving at zero finally, and a decrease compensating value, increased with a big increasing degree at first after arriving at the predetermined minimum compensating value and, thereafter, increased with the degree of increase reduced gradually and arriving at zero finally.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control method and a control apparatus for an air liquefaction / separation apparatus, and more particularly, to a method for controlling the amount of product produced in a steel mill or the like who is a user who consumes industrial gases such as oxygen, nitrogen and argon. The present invention relates to a control method and a control device for an air liquefaction / separation device capable of quickly responding to a large change.

[0002]

2. Description of the Related Art In order to cope with large fluctuations in the amount of oxygen gas used repeatedly at steelworks, etc., which are users of mass consumption of oxygen gas, a liquefied oxygen storage tank and a liquefied nitrogen storage tank are attached to an air liquefaction / separation apparatus. A method of performing an operation of increasing or decreasing a supply amount is known. One example of this driving method is shown in FIG.
4 will be described.

First, an air liquefaction / separation apparatus for separating at least oxygen and nitrogen by a cryogenic air liquefaction / separation method using double rectification includes a lower tower (high pressure tower) 1 and an upper tower (low pressure tower).
2, a double rectification column having a condensing evaporator 3, a main heat exchanger 4 for cooling raw air, and an expansion turbine 5 for generating cold
The air liquefaction / separation apparatus is provided with a liquefied nitrogen storage tank 6 and a liquefied oxygen storage tank 7 as equipment for responding to an increase or decrease in product oxygen gas.

[0004] Compressed, purified and cooled raw material air (AI
R) is introduced from the main heat exchanger 4 to the lower part of the lower column 1 through the path 11 and rectified in the lower column 1 to obtain nitrogen gas (medium pressure nitrogen gas) at the top of the column and oxygen content at the bottom of the column. Is separated from the liquefied air enriched. The liquefied air flows from the bottom
2 through the subcooler 13 and the valve 14 and introduced into the middle stage of the upper tower 2.

[0005] The medium-pressure nitrogen gas is extracted from the lower tower top to the path 15, a part thereof is branched to the path 16 and introduced into the condensing evaporator 3, and the remainder is passed through the path 17 for main heat exchange. After entering the heat exchanger 4, the pressure is increased by the blower 19 through the passage 18, cooled by the after cooler 20, again flows through the main heat exchanger 4, extracted from the intermediate portion of the main heat exchanger 4, and passed to the expansion turbine 5. be introduced. The low-pressure nitrogen gas that has generated cold in the expansion turbine 5 is introduced into the main heat exchanger 4 three times through the paths 21 and 22, and is led out of the system as a product nitrogen gas (GN) from the path 23.

The nitrogen gas introduced into the condensing evaporator 3 is liquefied by the condensing evaporator 3 to become liquefied nitrogen.
It is extracted to 4. Part of the liquefied nitrogen in path 24 is
5 and becomes the reflux liquid of the lower tower 1, and the remaining liquefied nitrogen is passed from the passage 26 through the subcooler 27 and the valve 28 to the upper tower 2.
Introduced at the top.

The liquefied air and liquefied nitrogen flowing into the upper tower 2 are rectified in the upper tower 2 and separated into nitrogen gas (low-pressure nitrogen gas) at the top of the tower and liquefied oxygen at the bottom of the tower. The low-pressure nitrogen gas at the top of the tower is withdrawn through a path 29 and is cooled by subcoolers 27 and 13.
And merges from the path 30 to the path 22 to form the path 23
From the system as product nitrogen gas (GN).

The liquefied oxygen at the bottom of the upper tower flows into the condensing evaporator 3 via the path 31, evaporates and becomes oxygen gas, and is led out to the path 32. The gas becomes a rising gas, and the remaining oxygen gas flows into the main heat exchanger 4 through the passage 34, and is discharged from the system as a product oxygen gas GO from the passage 35 after the temperature is increased.

In the air liquefaction / separation apparatus thus formed, if the demand for the product oxygen gas exceeds the oxygen gas production capacity of the air liquefaction / separation apparatus and becomes the oxygen gas production capacity plus the α amount, As shown in FIG.
The flow rate of the medium-pressure nitrogen gas flowing from the top to the main heat exchanger 4 via the path 15 and the path 17 is reduced by β (−β), and this reduced amount is added to the nitrogen gas flowing from the path 16 to the condensing evaporator 3 ( + Β), and is liquefied in the condensation evaporator 3. The liquefied nitrogen whose β amount has increased is branched from the condensing evaporator 3 through a path 24 and a path 26 to a path 36 toward the liquefied nitrogen storage tank 6, and a valve 37 is provided.
And stored in the liquefied nitrogen storage tank 6.

At the same time, the liquefied oxygen in the liquefied oxygen storage tank 7 is
The amount of α is supplied to the condensing evaporator 3 by the pump 38 through the path 39 and the valve 40 (+ α), and is vaporized by the condensing evaporator 3 to be oxygen gas. Thereby, the amount of product oxygen derived from the condensing evaporator 3 via the path 32, the path 34, the main heat exchanger 4, and the path 35 can be increased by α. At this time, the rising gas amount and the descending liquid amount in the upper tower 2 do not change even if the product oxygen gas amount is increased by α, so that the same state as before the product oxygen increase is maintained.

On the other hand, when the demand for the product oxygen gas falls below the oxygen production capacity of the air liquefaction / separation apparatus and becomes the product oxygen gas production capacity minus α, as shown in FIG. The flow rate of the medium-pressure nitrogen gas flowing from the top to the main heat exchanger 4 via the path 15 and the path 17 is increased by β (+ β), and the increased amount is reduced from the nitrogen gas flowing from the path 16 to the condensing evaporator 3. (-Β). As a result, the amount of liquefied nitrogen generated in the condensing evaporator 3 is reduced by β amount. Therefore, by supplying liquefied nitrogen in the liquefied nitrogen storage tank 6 through the pump 41, the path 42, and the valve 43 (+ β), Maintain the same amount of liquefied nitrogen introduced into the reactor.

At this time, in the condensing evaporator 3, since the amount of evaporation of the liquefied oxygen decreases by the amount of α due to the decrease of the amount of nitrogen gas by β, the amount of product oxygen gas derived from the path 32 via the path 35 is reduced by the amount of α Will decrease. Since the liquefied oxygen becomes excessive in the condensing evaporator 3, the surplus liquefied oxygen α is withdrawn from the condensing evaporator 3 to the path 44,
7. Store in the liquefied oxygen storage tank 7 through the valve 45. Also in this case, the ascending gas amount and the descending liquid amount in the upper tower 2 do not change, and the same state as before the product oxygen reduction is maintained.

As described above, in the conventional air liquefaction / separation apparatus, the operation of increasing or decreasing the amount of product oxygen gas is performed by converting liquefied oxygen to liquefied nitrogen or by converting liquefied nitrogen to liquefied oxygen. ing. That is,
The operation of increasing or decreasing the amount of product oxygen gas by cold transfer between liquefied oxygen and liquefied nitrogen is performed. Also, by increasing or decreasing the medium pressure nitrogen gas from the top of the lower tower 1 to the main heat exchanger 4, the rising gas flow rate and the descending liquid flow rate of the upper tower 2 are kept constant. Thus, the operation of increasing or decreasing the amount of product oxygen gas can be performed in a short time without lowering the product yield.

In FIGS. 15 and 16, FIG.
The same reference numerals are given to the same components as those described above, and the detailed description is omitted.

[0015]

However, in the above-described operation method, if the increase or decrease of the medium-pressure nitrogen gas amount causes the increase or decrease of the flow rate of the expansion turbine 5, the flow of the hot fluid and the cold fluid in the main heat exchanger 4 is reduced. The flow balance changes greatly. For example, when the flow rate of the expansion turbine 5 decreases,
That is, when increasing the product oxygen gas, the air temperature at the outlet of the main heat exchanger 4 increases, and when the flow rate of the expansion turbine 5 increases, that is, when decreasing the product oxygen gas, the air temperature at the outlet of the main heat exchanger 4 increases. The air temperature will be lower.

As shown in FIG. 16, the main heat exchanger 4
And a branch path 46 is provided in the path 18 of the medium-pressure nitrogen gas flowing from the blower 19 to the expansion turbine 5, and the amount of the medium-pressure nitrogen gas derived from the branch path 46 is changed to + β and −β. Even when the amount of nitrogen gas flowing to the expansion turbine 5 is kept constant, due to the difference in latent heat between liquefied nitrogen and liquefied oxygen in the condensing evaporator 3, the medium pressure nitrogen Since the increase / decrease amount β of the gas is larger, the flow ratio between the hot fluid and the cold fluid in the main heat exchanger 4 changes greatly, and as a result, the air temperature at the outlet of the main heat exchanger 4 changes. .

Since the heat capacity of the main heat exchanger 4 is large, the rate of change of the temperature is very slow and it takes time to stabilize, and the temperature change at the outlet of the main heat exchanger is large. There was a problem that the excess and deficiency of the cold occurred.

[0018] Specific phenomena and examples are:
When increasing the raw gas flow rate, the air temperature at the outlet of the main heat exchanger
Is below the specified temperature, that is, does not rise to the specified temperature
Since the state will continue for a while, the condensing evaporator 3
The amount of liquefied oxygen evaporated decreases, and the rising gas in the upper
Will be added. Therefore, during this time,
In order to keep the rising gas flow constant, supply the product oxygen gas at the specified flow rate.
And the liquid in the condensing evaporator 3 cannot be increased.
Liquefied oxygen becomes excessive due to a reduction in the amount of vaporized oxygen.
Normally, product oxygen gas is 35000Nm³/ H production regulation
The product oxygen gas is 100
00Nm³/ H increased to 45,000 Nm ³/ H
In the case of 2-3 hours, 2000-3000Nm³/ H products
Insufficient oxygen gas, 2000-3000Nm³/ H liquid
Oxygenation becomes excessive.

On the other hand, when reducing the amount of product oxygen gas, the air temperature at the outlet of the main heat exchanger continues to be higher than the specified temperature, so that the amount of liquefied oxygen evaporated in the condensing evaporator 3 increases and the upper tower 2 Gas rises in excess. Therefore, during this time, the product oxygen gas flow rate cannot be reduced to the specified flow rate in order to keep the rising gas flow rate of the upper tower 2 constant,
In addition, liquefied oxygen becomes insufficient due to an increase in the amount of liquefied oxygen evaporated in the condensation evaporator 3. On the scale of the air liquefaction separator, the product oxygen gas is 10,000 Nm
^{When the} weight is reduced to 35000 Nm ³ / h by ³ / h,
3 hours becomes excessive oxygen product gas 2000~3000Nm ³ / h, a shortage of liquid oxygen of 2000~3000Nm ³ / h.

Accordingly, the present invention provides a method for increasing or decreasing the amount of product gas in an air liquefaction / separation apparatus, which can quickly and quickly maintain a product purity with respect to a change in the amount of product gas demand.
It is an object of the present invention to provide a control method and a control device capable of stably responding.

[0021]

In order to achieve the above object, a control method of an air liquefaction / separation apparatus according to the present invention uses compressed, purified and cooled raw material air by using a lower tower, an upper tower and a condensing evaporator. In the control method of the air liquefaction separation device that separates at least oxygen and nitrogen by the cryogenic air liquefaction separation method by the double rectification, when the amount of the product collected from the air liquefaction separation device is increased or decreased, the amount of the product is increased or decreased. In accordance with, the flow rate set value of the fluid other than the product, a basic increase and decrease value that linearly increases and decreases in proportion to the increase and decrease of the product, and after reaching a predetermined maximum correction value with a rapid increase, first An increase correction value that decreases with a large decrease, then decreases with a gradually decreasing decrease, and finally changes to zero, and after reaching a predetermined minimum correction value with a rapid decrease, Increase at a large rate, then gradually It is characterized by configured using the reduction correction value that varies so as to be finally zero increases with smaller increases degree.

Further, in the above control method, when the amount of the product oxygen gas is increased, the increase in the amount of the product oxygen gas is caused by a delay in the temperature change of the raw material air cooled by performing heat exchange with the product oxygen gas. On the basis of the signal, 1) the flow rate set value of the raw air is corrected to the target value by the increase correction value, and 2) the flow rate set value of the nitrogen gas derived from the top of the lower tower is set to the decrease correction value. 3) At least one of 1), 2) and 3), wherein the set value of the flow rate of liquefied nitrogen introduced into the upper tower is corrected to the target value by the decrease correction value. It is characterized by performing one.

When the amount of the product oxygen gas is reduced, a delay in the temperature change of the raw material air cooled by performing heat exchange with the product oxygen gas is determined based on the decrease signal of the product oxygen gas. 1) The set value of the flow rate of the raw air is corrected to the target value by the decrease correction value. 2) The set value of the flow rate of the nitrogen gas derived from the lower tower top is corrected to the target value by the increase correction value. 3) Correcting the set value of the flow rate of the liquefied nitrogen introduced into the upper tower to the target value by using the increase correction value, and performing at least one of 1) 2) 3) It is characterized by.

Further, in the above control method, when increasing the product oxygen gas amount, the liquefied oxygen introduced from the liquefied oxygen storage tank provided outside the system and introduced into the condensing evaporator is derived from the top of the lower column. The nitrogen gas introduced into the condensing evaporator is heat-exchanged and vaporized to form a part of the product oxygen gas. 1) The set value of the flow rate of the raw air is corrected by the increase correction value. A surplus of liquefied air generated by a temporary increase in the amount of raw material air is stored at the bottom of the lower tower as a target value. 2) The set flow rate of nitrogen gas derived from the lower tower is reduced by the decrease. The target value is corrected by the correction value, and the excess liquefied nitrogen generated by the temporary decrease of the nitrogen gas is stored in a liquefied nitrogen storage tank provided outside the system. 3) The flow rate of the liquefied nitrogen introduced into the upper tower Set value The surplus of the liquefied nitrogen generated by the temporary decrease of the liquefied nitrogen is stored in a liquefied nitrogen storage tank provided outside the system. It is characterized in that either one is performed.

Further, when reducing the amount of product oxygen gas, a part of the product oxygen gas is liquefied by liquefied nitrogen introduced from the liquefied nitrogen storage tank provided outside the system and introduced into the condensing evaporator, and the generated liquefied While oxygen is stored in a liquefied oxygen storage tank provided outside the system, 1) the flow rate set value of the raw material air is
The target value is corrected by the decrease correction value, and the shortage of the liquefied air generated by the temporary decrease of the raw air amount is supplemented by the liquefied air stored at the bottom of the lower tower.
2) The set value of the flow rate of the nitrogen gas derived from the top of the lower tower is corrected to the target value by the increase correction value, and the shortage of the liquefied nitrogen caused by the temporary increase of the nitrogen gas is determined by the liquefied nitrogen. 3) The set value of the flow rate of liquefied nitrogen introduced into the upper tower is corrected by the increase correction value to a target value, and the shortage of liquefied nitrogen caused by the temporary increase of the liquefied nitrogen is calculated. A method for controlling an air liquefaction / separation device, wherein at least one of 1), 2) and 3) is carried out in a liquefied nitrogen storage tank provided outside the system.

The control device of the air liquefaction / separation apparatus of the present invention comprises:
The compressed, purified and cooled raw material air is subjected to flow control in an air liquefaction / separation unit that separates at least oxygen and nitrogen by a cryogenic air liquefaction / separation method based on double rectification using a lower tower, an upper tower and a condensing evaporator. A control device for performing, the product amount increase / decrease signal generating means for generating a signal for increasing / decreasing the product oxygen gas sampling amount, and a product amount other than the product oxygen gas based on the signal from the product amount increase / decrease signal generating means Basic increase / decrease value setting means for setting a basic increase / decrease value for linearly increasing / decreasing a flow rate set value of the fluid in proportion to an increase / decrease amount of the product oxygen gas, and a predetermined maximum correction of the flow rate set value at a rapid increase degree After reaching the value, an increase correction value setting means for setting an increase correction value that initially decreases with a large decrease degree, then decreases with a gradually decreasing decrease degree, and finally changes to zero. Great decrease After reaching a predetermined minimum correction value, a reduction correction value is set which initially increases with a large increase, then increases with a gradually decreasing increase and finally changes to zero. Means and
1) a raw air flow control means for controlling the flow rate of the raw air, 2) a nitrogen gas flow control means for controlling the flow rate of nitrogen gas derived from the top of the lower tower, 3) the flow rate of liquefied nitrogen introduced into the upper tower Liquefied nitrogen flow control means for controlling the
It is characterized by having at least one of 1), 2) and 3).

Further, the air liquefaction / separation apparatus introduces into the system an amount of liquefied oxygen corresponding to a shortage of product oxygen gas generated when the amount of sampled product oxygen gas is increased. A liquefied oxygen storage tank for extracting and storing surplus liquefied oxygen generated when the amount is reduced, and a surplus liquefied nitrogen generated in the system when the amount of product oxygen gas collected is increased. A liquefied nitrogen storage tank for introducing and storing in the system an amount of liquefied nitrogen corresponding to the deficiency of liquefied oxygen generated when reducing the amount of product oxygen gas extracted and stored in the system It is characterized by.

The air liquefaction / separation apparatus may further include a liquefied air storage tank for compensating for fluctuations in the amount of liquefied air generated due to an increase or decrease in the amount of product oxygen gas collected, from the bottom of the lower tower or the bottom of the lower tower. It is characterized by being provided in the middle of the path for supplying liquefied air to the tower.

[0029]

FIG. 1 is a system diagram showing one embodiment of an air liquefaction / separation apparatus to which the control method and control apparatus of the present invention are applied. The basic configuration of the air liquefaction / separation apparatus shown in FIG. Therefore, the same components as those in FIG. 14 are denoted by the same reference numerals, and detailed description is omitted.

As before, the raw air (AIR) is compressed by an air compressor to adsorb and remove water and carbon dioxide, and then introduced into the main heat exchanger 4 through a passage 10 and cooled to a predetermined temperature. Then, it is introduced into the lower part of the lower tower 1 through the path 11. In the lower tower 1, medium-pressure nitrogen gas is separated at the top, and liquefied air is separated at the lower part. The liquefied air extracted to the path 12 is introduced into the middle part of the upper tower 2 after decompression by the valve 14, and Is separated into oxygen and nitrogen.

Part of the medium-pressure nitrogen gas at the top of the lower tower is returned to the main heat exchanger 4 via a path 17, pressurized by a brake blower 19 of the expansion turbine 5, and then cooled to a normal temperature by a cooler 20. After being cooled again to a predetermined temperature in the main heat exchanger 4, it is introduced into the expansion turbine 5 to generate cold required for the present apparatus. Thereafter, it is collected from the passage 23 as low-pressure nitrogen gas.

On the other hand, the medium-pressure nitrogen gas branched from the path 15 to the path 16 is introduced into the condensing evaporator 3, where it undergoes heat exchange with liquefied oxygen to become liquefied nitrogen. After the liquefied nitrogen generated here is led out to the path 24, a part thereof is returned to the lower tower 1 via the path 25 as a reflux liquid of the lower tower 1. The remaining liquefied nitrogen is introduced into the upper part of the upper tower 2 after being depressurized by a valve 28 as a reflux liquid of the upper tower 2 via a passage 26.

In the upper tower 2, oxygen and nitrogen are separated,
Oxygen is collected from the bottom and nitrogen from the top.
Liquefied oxygen is led out from the lower part of the upper tower 2 through a path 31 and introduced into the condensing evaporator 3, where it is heat-exchanged with the medium-pressure nitrogen gas and vaporized, and is led out from a path 32. Route 3
A portion of the oxygen gas from 2 returns from the main heat exchanger 4 from the path 34 as the product oxygen gas GO and is collected from the path 35. On the other hand, the remaining oxygen gas branched from the path 32 to the path 33 is introduced into a lower part of the upper tower 2 as a rising gas of the upper tower 2.

The nitrogen gas led out from the top of the upper tower 2 to the passage 29 joins with the low-pressure nitrogen gas leaving the expansion turbine 5 and returns to the main heat exchanger 4 to be taken out from the passage 23. . Further, in the present embodiment, the waste gas WG is extracted from the upper part of the upper tower to the path 47, passes through the subcoolers 27 and 13, further passes through the main heat exchanger 4, and is led out from the path 48.

Next, a description will be given of a case where the operation for increasing or decreasing the amount of product oxygen gas is performed using the liquefied nitrogen storage tank 6 and the liquefied oxygen storage tank 7 attached to the air liquefaction / separation apparatus. First, the liquefied nitrogen in the liquefied nitrogen storage tank 6 is supplied from the liquefied nitrogen pump 41 to the upper part of the upper tower 2 through the passage 42 when the product oxygen gas is reduced. On the other hand, when increasing the product oxygen gas, the lower tower 1
The amount of medium-pressure nitrogen gas sent to the condensing evaporator 3 from the top of
The increased amount of the liquefied nitrogen liquefied in the condensing evaporator 3 is supplied to the path 2
6 branches into a path 36 and is introduced into the liquefied nitrogen storage tank 6.

The liquefied oxygen in the liquefied oxygen storage tank 7 is supplied from the liquefied oxygen storage tank 7 through the liquefied oxygen pump 38 to the condensing evaporator 3 or the lower part of the upper tower 2 through the liquefied oxygen pump 38 when the product oxygen gas is increased. After vaporization in the condensing evaporator 3,
It is collected as the product oxygen GO via the route 34 and the route 35. On the other hand, when the product oxygen gas is reduced, the liquefied oxygen that could not be vaporized by the condensing evaporator 3 is introduced into the liquefied oxygen storage tank 7 via the path 44.

In the operation control of such an air liquefaction / separation apparatus, as shown in FIG. 1, a feed air flow controller 51 is provided in the feed air path 10 as a controller for performing an increase / decrease operation of the product oxygen gas. The product oxygen gas flow controller 52 in the product oxygen gas path 35, the low pressure nitrogen gas flow controller 53 in the low pressure nitrogen gas path 23, the expansion turbine flow controller 54 at the inlet of the expansion turbine 5, and the upper tower. A liquefied nitrogen flow controller 55 is provided in the valve 28 of the path of the refluxed liquefied nitrogen supplied to the upper column 2, a liquefied air flow controller 56 is provided in the valve 14 of the liquefied air supplied to the upper tower 2, and a liquefied oxygen storage tank. 7
A delivery liquefied oxygen flow controller 57 is provided at a valve 45 portion of a path for sending out liquefied oxygen, and a delivery liquefied nitrogen flow controller 58 is provided at a valve 37 portion of a route for sending liquefied nitrogen to the liquefied nitrogen storage tank 6.
The injection liquefied nitrogen flow controller 59 is provided at the valve 43 in the path for injecting liquefied nitrogen from the liquefied nitrogen storage tank 6 to the upper tower 2, and the valve 40 is provided in the path for injecting liquefied oxygen from the liquefied oxygen storage tank 7 to the condensing evaporator 3. The injection liquefied oxygen flow controller 60 is further
An upper tower top pressure controller 61 for controlling the pressure at the top of the upper tower 2 is provided in the waste gas path 48, and the flow rate of each fluid is adjusted by each of these controllers, whereby the product oxygen gas is controlled. Flow control and pressure control corresponding to demand fluctuations are performed.

The basic control is that when the product oxygen gas is increased or decreased, a fluid other than the product oxygen gas whose flow rate should be increased or decreased according to the increase or decrease of the product oxygen gas amount, for example, a raw material air or a medium-pressure nitrogen gas. The flow rate set value is determined by a basic increase / decrease value that is linearly increased / decreased in proportion to the increase / decrease amount of the product oxygen gas. In the present invention, in addition to the basic increase / decrease value, by using the increase / decrease correction value, the delay in the temperature change of the raw air at the outlet of the main heat exchanger and the temporary excess / deficiency of the cold are compensated. I have.

When performing the operation of increasing the amount of product oxygen gas, specifically, at least one of the following three cases of operation control is performed to delay the temperature change of the raw air at the outlet of the main heat exchanger. And temporary overcooling.

Case 1 During a period in which the raw material air temperature at the outlet of the main heat exchanger 4 is lower than the specified temperature, the flow rate set value of the air flow controller 51 is
In response to the product oxygen gas increase signal, as shown in FIG.
After reaching the predetermined maximum correction value Rmax by rapid increase of E, initially changes as decreased in large decrease of D _L, the finally zero decreases thereafter gradually decrease rate of decrease D _S Set value to which the increase correction value is added. By controlling the flow rate of the raw air in this way, the shortage of the amount of liquefied oxygen evaporating in the condensing evaporator 3 is compensated for, the rising gas flow rate in the upper tower 2 is kept constant, and the excess liquefied air in the lower tower 1 is increased. The temporary excess of cold is treated by storing the fraction in the middle of a path 12 for supplying liquefied air from the bottom of the lower tower 1 or the bottom of the lower tower to the upper tower, thereby processing the temporary excess of the cold.
Make the descending liquid flow rate constant.

Case 2 During a period in which the temperature of the raw material air at the outlet of the main heat exchanger 4 is lower than the specified temperature, the flow rate set value of the expansion turbine flow controller 54 is changed according to the product oxygen gas increase signal as shown in FIG. as shown, after reaching a rapid decrease of the predetermined minimum correction value Rmin in D, initially increases with significant increase of E _L, and finally zero increases thereafter gradually decrease the increase of E _S It is set to a value obtained by adding a decrease correction value that changes as follows. By controlling the flow rate of the expansion turbine 5 as described above, the shortage of the amount of liquefied oxygen evaporating in the condensing evaporator 3 is compensated for, and the rising gas flow rate of the upper tower 2 is kept constant. The set value of the flow rate is a set value to which the increase correction value shown in FIG. 2 is added, and the surplus amount of liquefied nitrogen derived from the condensing evaporator 3 with the temporary decrease of the flow rate of the expansion turbine is stored in the liquefied nitrogen storage tank 6. The excess liquid is treated to keep the descending liquid flow rates of the upper tower 2 and the lower tower 1 constant.

Case 3 During the period when the temperature of the raw material air at the outlet of the main heat exchanger 4 is lower than the specified temperature, the flow rate set value of the reflux liquefied nitrogen flow controller 55 is set by adding the decrease correction value shown in FIG. Value,
The flow rate of the descending liquid from the top of the upper tower 2 is also reduced in accordance with the decrease in the flow rate of the rising gas in the upper tower 2 to suppress the disturbance in the flow rate ratio between the rising gas and the descending liquid in the upper tower 2, The flow rate set value is a set value to which the increase correction value shown in FIG. 2 is added, and the excess amount of liquefied nitrogen accompanying the temporary decrease in the flow rate of the liquefied liquefied nitrogen is stored in the liquefied nitrogen storage tank 6 to process excess cold. The flow rate of the descending liquid in the lower tower 1 is made constant.

When the operation of reducing the product oxygen gas is performed, control delay reverse to that in the case of increasing the amount of oxygen is added to temporarily delay the temperature change of the raw air at the outlet of the main heat exchanger 5 and temporarily reduce the temperature. Insufficient cold can be compensated.

Case 1 During the period when the raw air temperature at the outlet of the main heat exchanger 4 is higher than the specified temperature, the flow rate set value of the air flow controller 51 is
A set value obtained by adding the decrease correction value shown in FIG. 3 is used to suppress the increase in the amount of liquefied oxygen evaporated in the condensing evaporator 3 to keep the rising gas flow rate in the upper tower 2 constant, and to determine the shortage of liquefied air in the lower tower. The liquefied air stored in the bottom of the column 1 is used to compensate for the temporary shortage of the cold, and the flow rate of the descending liquid in the upper column 2 is made constant.

Case 2 During the period when the raw air temperature at the outlet of the main heat exchanger 4 is higher than the specified temperature, the flow set value of the low-pressure nitrogen gas flow controller 53 is changed to the set value obtained by adding the increase correction value shown in FIG. In addition to suppressing the increase in the amount of liquefied oxygen evaporating in the condensing evaporator 3 and keeping the rising gas flow rate of the upper tower 2 constant, the set value of the reflux liquefied nitrogen flow rate controller 55 is set to With the added set value, the descending liquid flow rate of the lower tower 1 is made constant with respect to the decrease in the amount of liquefied nitrogen generated in the condensation evaporator 3,
Further, the set value of the injection liquefied nitrogen flow controller 59 is
Is set to a value obtained by adding an increase correction value to refrigeration liquid nitrogen in the upper tower 2 to compensate for the decrease in liquefied liquefied nitrogen.

Case 3 During a period in which the temperature of the raw material air at the outlet of the main heat exchanger 4 is higher than the specified temperature, the set value of the injected liquefied nitrogen flow controller 59 is set to a value obtained by adding the increase correction value shown in FIG. In order to cope with the cold shortage, the descending liquid flow rate from the top of the upper tower 2 is increased in accordance with the increase of the ascending gas flow rate of the upper tower 2,
The disturbance of the flow ratio between the ascending gas and the descending liquid is suppressed.

The operation control of the case 3 is different from the idea of the other cases in which the flow rates of the ascending gas and the descending liquid in the upper tower 2 are always kept constant. The descending liquid flow rate is also changed in the same direction, based on the idea that the flow rate ratio between the ascending gas and the descending liquid in the upper tower 2 is not largely destroyed.

Although the above description has been limited to the collection of oxygen and nitrogen as products, it goes without saying that the present invention can also be applied to an air liquefaction separator for collecting argon.

[0049]

EXAMPLE A simulation was performed at the time of rated operation and at the time of oxygen increase operation using an air liquefaction / separation apparatus having the structure shown in FIG. This air liquefaction separation device is shown in FIG.
The crude argon column 71 and the crude argon condenser 72 were added to the air liquefaction / separation apparatus having the lower tower 1, the upper tower 2, the condensing evaporator 3 and the liquefied nitrogen storage tank 6 and the liquefied oxygen storage tank 7 shown in FIG. A three-tower air liquefaction and separation apparatus,
The crude argon tower 71 has a lower part in the middle part of the upper tower 2 and a path 73 for supplying the argon raw material gas from the upper tower 2 to the crude argon tower 71, and a path 74 for returning the bottom liquid of the crude argon tower 71 to the upper tower 2. In the upper part of the tower, a route 75 for leading out the crude argon gas and a route 7 for returning the liquefied argon liquefied by the crude argon condenser 72 to the crude argon tower 71 are provided.
6 are provided.

The crude argon condenser 72 has a passage 77 for introducing a part of the crude argon gas led out to the passage 75 to the crude argon condenser 72, and a passage 76 for returning liquefied argon to the crude argon column 71. And a path 78 for introducing the liquefied air extracted from the lower part of the lower tower 1 to the crude argon condenser 72 and a path 79 for leading out the air vaporized by the crude argon condenser 72.

The crude argon gas A led to the path 75
r is partially branched to the path 77, and the remaining crude argon gas passes through the main heat exchanger 4 from the path 80, is collected through the path 81, and the crude argon flow controller 82. Further, the air in the path 79 is introduced into the middle stage of the upper tower 2.

The other configuration is partially different, for example, the condensing evaporator 3 is integrally provided at the bottom of the upper column 2. However, the configuration differs from that of the air liquefaction separation apparatus shown in FIG. Since they are formed in substantially the same manner, the same or substantially the same components as those of the device shown in FIG. 1 are denoted by the same reference numerals, and detailed description is omitted.

In the apparatus of the present embodiment, the conditions of the raw material air are as follows: pressure: about 5.5 bar (550 kPa);
° C and a flow rate of 167000 Nm ³ / h. During rated operation (MODE1) and during operation of increasing product oxygen gas (MODE1)
Table 1 shows the main process values in the steady state in 2). In Table 1, the rising gas flow rate of the upper tower 2 in MODE 2 is maintained at the same level as that of MODE 1 by reducing the flow rate of the expansion turbine 5, and the descending liquid flow rate of the upper tower 2 in MODE 2 is equal to the excess liquefied nitrogen. Is led to the liquefied nitrogen storage tank 6 to maintain the same amount as MODE1. The expansion turbine 5 in MODE 2
Is reduced to about 40% of MODE1, so that the air temperature at the outlet of the main heat exchanger 4 of MODE2 is 3K lower than MODE1. In addition, since the flow rate of each part related to crude argon is maintained constant,
It is omitted in Table 1.

[0054]

[Table 1]

In this apparatus, in the state of MODE1, 2
At the time of running for all hours, all the controller set values that needed to be changed toward the target value of MODE2 were changed linearly in 10 minutes. Thereafter, the operation was performed for 6 hours in the state of MODE2, and then the operation was returned to the original MODE1 in 10 minutes. Simulations were performed for the state of each part at this time for the case where the method of Case 1 was used and the case where the state was performed by the conventional method.

As shown in FIG. 5, the flow rate of the product oxygen gas increases and decreases in 10 minutes from the start of the increase and decrease, and the flow rate of the expansion turbine also increases in 10 minutes from the start of the increase and decrease as shown in FIG. The flow rate was increased or decreased.

First, in the conventional method, if the flow rate of the raw air is kept constant as shown by the broken line A in FIG.
As shown by the dashed line A in FIG. 8, the delay in the change of the air outlet temperature caused by the problem of the heat capacity of the main heat exchanger occurs, and as shown by the dashed line A in FIG. The volume has not reached the specified volume for several hours. Therefore, the rising gas flow rate of the upper tower fluctuates as shown by the dashed line A in FIG. 10, and as a result, the product oxygen gas purity (oxygen concentration) greatly decreases as shown by the dashed line A in FIG. The oxygen concentration and nitrogen concentration in FIG.
As shown by the broken line A in FIG.

On the other hand, when the operation is performed by the method of Case 1 in which the delay in the change of the air outlet temperature caused by the problem of the heat capacity of the main heat exchanger is controlled and compensated, the air flow rate is corrected as shown by the solid line B in FIG. Therefore, as shown by the solid line B in FIG. 8, although the change in the air outlet temperature of the main heat exchanger is almost the same as the conventional one, the amount of liquefied oxygen evaporated in the condensing evaporator is shown by the solid line B in FIG. Thus, the amount has almost reached the specified amount in 10 minutes. As a result, the rising gas flow rate of the upper tower becomes substantially constant as shown by the solid line B in FIG. 10, and the purity change of the product is within the allowable range as shown by the solid lines B in FIGS. 11, 12 and 13, respectively. It is suppressed.

Also, when the product oxygen gas is reduced, that is, in the transition from MODE2 to MODE1 (after the eighth hour in each figure), the flow rate of the raw air is controlled as shown by the solid line B in FIG. As shown by the solid line B in FIGS. 9 and 10, the evaporation amount of liquefied oxygen in the condensing evaporator and the ascending gas flow rate in the upper tower become substantially constant, and as shown by the solid line B in FIGS. It can be seen that the change is also small.

Although not shown here, it has been confirmed by simulation that the operation methods of Case 2 and Case 3 are more effective than the conventional method.

[0061]

As described above, according to the present invention,
Respond to fluctuations in demand for product oxygen gas due to cold transfer between liquefied oxygen and liquefied nitrogen by suppressing turbulence caused by delay in following the air temperature at the outlet of the main heat exchanger, and responding quickly without impairing product purity Can be. In particular, as shown in the embodiment, the present invention is effective when a speed is required such that the demand fluctuation of the product oxygen gas changes by 30% of the product amount in about 10 minutes. Further, when the present invention is applied to the flow rate of the raw material air, it is possible to suppress a temporary fluctuation in the gas flow rate in the upper tower, which is caused by a delay in the change of the raw material air temperature at the outlet of the main heat exchanger. Further, when the present invention is applied to the nitrogen gas derived from the lower tower top, the gas is supplied to the upper tower in the same direction as the temporary fluctuation of the upper tower rising gas flow rate caused by the delay of the air temperature change. By changing the descending liquid flow rate, the collapse of the flow ratio between the ascending gas flow rate and the descending liquid flow rate in the upper tower can be suppressed. In addition, when the present invention is applied to the flow rate of liquefied nitrogen supplied to the upper tower, it is possible to appropriately process temporary excess / deficiency of cold caused by a delay in air temperature change.

[Brief description of the drawings]

FIG. 1 is a system diagram showing one embodiment of an air liquefaction / separation device to which a control method and a control device of the present invention are applied.

FIG. 2 is a diagram illustrating an example of an increase correction value.

FIG. 3 is a diagram illustrating an example of a decrease correction value.

FIG. 4 is a system diagram showing an air liquefaction / separation device used in Examples.

FIG. 5 is a diagram showing a change in a product oxygen gas flow rate.

FIG. 6 is a diagram showing a change in an expansion turbine flow rate.

FIG. 7 is a diagram showing a change in a raw material air flow rate.

FIG. 8 is a diagram showing a change in outlet air temperature of a main heat exchanger.

FIG. 9 is a diagram showing a change in a liquefied oxygen evaporation amount of a condensing evaporator.

FIG. 10 is a diagram showing a change in a rising gas flow rate of an upper tower.

FIG. 11 is a diagram showing a change in oxygen concentration of product oxygen gas.

FIG. 12 is a diagram showing a change in oxygen concentration in crude argon.

FIG. 13 is a diagram showing a change in nitrogen concentration in crude argon.

FIG. 14 is a system diagram showing an example of a conventional air liquefaction / separation apparatus provided with a liquefied oxygen storage tank and a liquefied nitrogen storage tank, illustrating a state when a product oxygen gas is increased.

FIG. 15 is a system diagram similarly illustrating a state when the product oxygen gas is reduced.

FIG. 16 is a system diagram showing another configuration example of the conventional air liquefaction / separation apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Lower tower, 2 ... Upper tower, 3 ... Condenser evaporator, 4 ... Main heat exchanger, 5 ... Expansion turbine, 6 ... Liquefied nitrogen storage tank, 7 ... Liquefied oxygen storage tank, 51 ... Raw material air flow controller, 52 ... Product oxygen gas flow controller, 53 ... Low pressure nitrogen gas flow controller, 54
... Expansion turbine flow controller, 55 ... Refluxed liquefied nitrogen flow controller, 56 ... Liquefied air flow controller, 57 ... Delivered liquefied oxygen flow controller, 58 ... Delivered liquefied nitrogen flow controller, 59 ... Injected liquefied nitrogen flow controller , 60: injection liquefied oxygen flow controller, 61: upper tower top pressure controller, 71: crude argon column, 72: crude argon condenser, 82: crude argon flow controller

Claims (8)

[Claims] 1. An air liquefaction separation of compressed, purified and cooled raw material air by a cryogenic air liquefaction separation method by double rectification using a lower tower, an upper tower and a condensing evaporator. In the control method of the device, when increasing or decreasing the amount of product collected from the air liquefaction separation device, according to the increase or decrease of the amount of product, the flow rate set value of the fluid other than the product,
A basic increase / decrease value that increases / decreases linearly in proportion to the increase / decrease amount of the product, and after reaching a predetermined maximum correction value with a rapid increase, first decreases with a large decrease and then gradually decreases. And an increasing correction value that decreases to finally become zero and a sudden decreasing degree that reaches a predetermined minimum correction value, then increases at a large increasing rate at first, and then gradually decreases. And a decrease correction value that increases so as to finally become zero. 2. The method for controlling an air liquefaction / separation apparatus according to claim 1, wherein when the amount of product oxygen gas is increased, heat exchange with the product oxygen gas causes a delay in a change in temperature of the raw material air cooled. On the other hand, based on the increase signal of the product oxygen gas amount, 1) the set value of the flow rate of the raw air is corrected to the target value by the increase correction value. 2) The flow rate set value of the nitrogen gas derived from the lower tower top is corrected by the decrease correction value to be a target value. 3) The set value of the flow rate of the liquefied nitrogen introduced into the upper tower is corrected by the decrease correction value to obtain a target value. A method for controlling an air liquefaction / separation apparatus, wherein at least one of the methods is implemented. 3. The method for controlling an air liquefaction / separation apparatus according to claim 1, wherein when the amount of product oxygen gas is reduced, a delay in temperature change of the raw material air cooled by performing heat exchange with the product oxygen gas. On the other hand, based on the decrease signal of the product oxygen gas amount, 1) the set value of the flow rate of the raw air is corrected by the decrease correction value to a target value. 2) The set value of the flow rate of the nitrogen gas derived from the top of the lower tower is corrected by the increase correction value to obtain a target value. 3) The set value of the flow rate of the liquefied nitrogen introduced into the upper tower is corrected by the increase correction value to obtain a target value. A method for controlling an air liquefaction / separation apparatus, wherein at least one of the methods is implemented. 4. The method for controlling an air liquefaction / separation apparatus according to claim 1, wherein when increasing the amount of product oxygen gas, the liquefied oxygen introduced from the liquefied oxygen storage tank provided outside the system and introduced into the condensing evaporator. Is vaporized by heat exchange with nitrogen gas introduced from the top of the lower tower and introduced into the condensing evaporator to form a part of product oxygen gas. 1) The set flow rate of the raw air The excess value of the liquefied air generated by the temporary increase in the amount of the raw air is stored at the bottom of the lower tower. 2) The set value of the flow rate of the nitrogen gas derived from the lower tower is corrected to the target value by the decrease correction value, and a surplus of liquefied nitrogen generated by the temporary decrease of the nitrogen gas is provided outside the system. Store in a liquefied nitrogen storage tank. 3) The set value of the flow rate of the liquefied nitrogen introduced into the upper tower is corrected to the target value by the decrease correction value, and an excess amount of the liquefied nitrogen generated by the temporary decrease of the liquefied nitrogen is provided outside the system. Store in a liquefied nitrogen storage tank. A method for controlling an air liquefaction / separation apparatus, wherein at least one of the methods is implemented. 5. The method for controlling an air liquefaction / separation apparatus according to claim 1, wherein when reducing the amount of product oxygen gas, the liquefied nitrogen introduced from the liquefied nitrogen storage tank provided outside the system and introduced into the condensation evaporator. Liquefies part of the product oxygen gas,
The generated liquefied oxygen is stored in a liquefied oxygen storage tank provided outside the system. 1) The set value of the flow rate of the raw air is corrected to the target value by the reduction correction value, and the amount of the raw air is temporarily reduced. The shortage of liquefied air generated by the above is supplemented by liquefied air stored at the bottom of the lower tower. 2) The set value of the flow rate of nitrogen gas derived from the lower tower is corrected to the target value by the increase correction value, and a shortage of liquefied nitrogen caused by the temporary increase of the nitrogen gas is stored in the liquefied nitrogen storage tank. refill. 3) The set value of the flow rate of liquefied nitrogen introduced into the upper tower is corrected to the target value by the increase correction value, and a shortage of liquefied nitrogen caused by the temporary increase of the liquefied nitrogen is provided outside the system. Store in a liquefied nitrogen storage tank. A method for controlling an air liquefaction / separation apparatus, wherein at least one of the methods is implemented. 6. Air liquefaction separation of compressed, purified and cooled raw material air by a cryogenic air liquefaction separation method by double rectification using a lower tower, an upper tower and a condensing evaporator. A control device for adjusting a flow rate in the device, wherein a product quantity increase / decrease signal generating means for generating a signal for increasing / decreasing a product oxygen gas collection quantity, and a signal from the product quantity increase / decrease signal generating means. Basic increase / decrease value setting means for setting a basic increase / decrease value for linearly increasing / decreasing the flow rate set value of the fluid other than the product oxygen gas in proportion to the increase / decrease amount of the product oxygen gas; After reaching the predetermined maximum correction value, the increase correction value sets an increase correction value that initially decreases with a large decrease degree, then decreases with a gradually decreasing decrease degree, and finally changes to zero. Setting means; After reaching the predetermined minimum correction value with a sharp decrease, the decrease correction value is set to increase at a large increase at first, then increase at a gradually decreasing increase, and finally change to zero. Means for controlling the flow rate of the feed air; 2) a flow rate control means for controlling the flow rate of the nitrogen gas derived from the top of the lower tower; and 3) a flow rate control means for controlling the flow rate of the feed gas. A control device for an air liquefaction / separation device, comprising at least one of liquefied nitrogen flow rate control means for controlling a flow rate of liquefied nitrogen introduced into an upper tower. 7. The air liquefaction / separation apparatus introduces into the system an amount of liquefied oxygen corresponding to a shortage of product oxygen gas generated when increasing the amount of product oxygen gas collected, and collects the product oxygen gas. A liquefied oxygen storage tank for extracting and storing surplus liquefied oxygen generated when the amount is reduced, and a surplus liquefied nitrogen generated in the system when the amount of product oxygen gas collected is increased. A liquefied nitrogen storage tank for introducing and storing in the system an amount of liquefied nitrogen corresponding to the deficiency of liquefied oxygen generated when reducing the amount of product oxygen gas extracted and stored in the system The control device for an air liquefaction separation device according to claim 6, characterized in that: 8. The air liquefaction / separation apparatus includes a liquefied air storage tank for compensating for a change in the amount of liquefied air generated due to an increase or decrease in the amount of product oxygen gas collected, from the bottom of the lower tower or the bottom of the lower tower. 7. The control device for an air liquefaction / separation device according to claim 6, wherein the control device is provided in the middle of a path for supplying liquefied air to the tower.