JPH0794954B2 - Operating method of air liquefaction separation device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to optimum automatic operation change and process state such as product purity when automatically operating a plant such as an air liquefaction separation device using a computer. Monitoring
The present invention relates to an operation method for performing adjustment operation.

[Conventional technology]

 Fig. 10 shows an example of an air liquefaction separation device.

That is, the raw material air is compressed and pressurized to about 5 kg / cm ² by an air compressor through an air filter, and then cooled and washed in a water washing cooling tower. Next, it enters the heat exchanger and exchanges heat with product oxygen, product nitrogen and waste nitrogen, and is cooled to about -170 ° C.
It is led to the lower tower of the rectification tower. The air introduced into the lower tower is preliminarily rectified to obtain nitrogen gas rich in nitrogen at the top of the lower tower and becomes liquid air having an oxygen content of about 40% at the bottom of the lower tower.
The gas air extracted from the middle part of the lower tower enters the post-expansion turbine used for heat exchange with the raw material air in the heat exchanger, where cold is generated and then guided to the upper tower. On the other hand, liquid air accumulated at the bottom of the lower tower and liquid nitrogen containing a large amount of nitrogen accumulated at the top and the vicinity of the top are introduced into the middle, upper and vicinity of the upper tower respectively through conduits. Furthermore, rectification is separated in the upper tower, and product oxygen gas,
Product nitrogen gas is extracted from the top and waste nitrogen gas is extracted from the middle, and after heat exchange with the raw material air in the heat exchanger as described above, it is supplied to the outside. On the other hand, the raw material argon gas is extracted from the vicinity of the middle part of the upper tower and supplied to the crude argon tower through a conduit.

Although various proposals have been made in the past regarding the automation of the air liquefaction separation device configured as described above, the computer program becomes complicated, the required capacity increases, and it becomes uneconomical. Generally, a uniform control method is adopted. For example, regarding the automatic operation change, it is the automatic change of the oxygen generation amount which is the main product of the air liquefaction separation device, and the adjustment of the control valve necessary for the change including the amount of raw material air corresponding to this oxygen generation amount is performed. At the same time, the product nitrogen and argon generation amounts commensurate with the oxygen amount are determined, and when the oxygen generation amount is determined, other product generation amounts are also determined.

[Problems to be Solved by the Invention]

However, in such a method, since the production amount of oxygen and other products such as nitrogen and argon are always determined with respect to the production amount of oxygen, particularly in the field where the use amounts of oxygen, nitrogen and argon are not constant like the steel industry. However, the surplus product corresponding to the error will be emitted to the atmosphere and the operation will be continued, resulting in an increase in product manufacturing unit price.

On the other hand, in controlling the state of the air liquefaction separation device such as product purity and liquid oxygen level in the upper part of the rectification column, the conventional method of judging abnormal or normal recovery is absolute value control, so the air liquefaction separation device is particularly important. As described above, in a plant in which there is a time delay before changes in the purity and the like appear even if the control operation is performed, it is difficult to maintain the stability within a specified value by causing an overshoot phenomenon only by controlling the absolute value. In addition, the air liquefaction separation device has the characteristic of having a strong mutual interference action between the purities of each product and between the purities and the liquid oxygen liquid level in the upper column of the rectification column, and for example, oxygen purity control using a conventional computer. Like the method, a uniform control method such as increasing / decreasing the product oxygen generation amount or increasing / decreasing the raw material air amount does not always work well depending on the state of the air liquefaction / separation device. There is a problem that it is difficult to maintain the air liquefaction separation device in a stable manner.

Therefore, an object of the present invention is to eliminate the above-mentioned drawbacks of the conventional method and enable stable and economical operation.

[Means for Solving the Problems]

In changing the operation of the air liquefaction separation device which is controlled by a computer to produce oxygen, nitrogen or oxygen, nitrogen and argon, the operation change pattern for the individual increase / decrease operation of each product and the simultaneous increase / decrease operation of multiple products, The operation is changed by selecting it based on the setting value of each product which is separately input. Here, when the increase / decrease operation instruction is given during the abnormal adjustment, the increase / decrease operation instruction is validated if the current abnormality is recovered by the increase / decrease operation instruction,
If the current abnormality is in the direction of worsening (expansion), it is invalidated, while if an abnormality occurs during the operation change, the operation change is continued while performing adjustment for recovering the abnormality.

Also, when controlling the process amount using a computer,
The upper limit value, upper upper limit value, lower limit value, and lower and lower limit value are set for each process amount, and when the upper and lower limit values are exceeded, it is unconditionally judged as abnormal and error recovery is performed. When adjustment is started and the state value of each process is between the upper limit value and the upper limit value or the lower limit value and the lower limit value, the slope and the upper limit value or the lower limit value are changed from the actual state value for the past predetermined time. Predict the time to reach it, and if this time is within a predetermined value, judge that it is abnormal and start adjustment for abnormal recovery, while the adjustment causes the calculated slope to change (up → down, down). When it rises), the time required to reach the upper limit value or the lower limit value is calculated, and if it is within the predetermined value, it is judged that the operation has returned to normal and the adjustment operation ends.

[Action]

The first is to use an expert system for the computer, which enables the simple and economical operation of the following operating methods, which are said to be complicated and increase the capacity in conventional programs.

Secondly, when the operation is changed, conventionally the raw material air flow rate required for the product oxygen generation amount is calculated, and the raw material air flow rate corresponding to the product oxygen generation amount or other product flow rate or the adjustment valve for the stable operation of the device is used. Although the opening was adjusted, in the operation according to the present invention, the relationship between the raw material air flow rate required for product nitrogen or the raw material air flow rate required for argon is grasped, and the generation amount of each product is set freely. By establishing the minimum required raw material air flow rate to balance each product generation, and by grasping the relation of the optimal opening of the regulating valve required for stable operation of the equipment in the above balance, the relational expression It is stored in a computer and the production amount of each product can be arbitrarily selected, which enables flexible operation change and the most economical operation.

Third, in monitoring the process conditions such as the purity of the air liquefaction separation device, the liquid level in the rectification column, and the pressure, two values, an allowable value and an abnormal value, are set for the conventional absolute value control. By monitoring the state by the arrival time to these two values, not only feedforward control but also abnormal state ranking can be performed easily. By combining this rank and various control methods, the control performance can be further improved. Improve.

〔Example〕

FIG. 1 is a block diagram showing a system to which the present invention is applied, FIG. 2 is a schematic flowchart for explaining the overall operation of a computer system, and FIG. 3 is an example of the operation shown in FIG. FIG. 4 is a flowchart for specifically explaining an example of the operation shown in FIG.

In FIG. 1, 1 is a computer system, 2 is a measurement control device, 3 is an air liquefaction separation device (also called an oxygen plant),
4 is a CRT display and 5 is a printer. The computer system 1 for operating the oxygen plant 3 controlled by the measurement control device 2 has at least an expert system, and this expert system has a reasoning mechanism and an experienced operator who is experienced in operating the oxygen plant. It is composed of if-then rules and a knowledge base that expresses the specialized knowledge about the increase / decrease operation or the adjustment operation obtained from the equation. Then, the value obtained by the inference mechanism is given to the measurement control device 2, and at the same time, each time the inference is executed, the operator is notified of the value and the operation amount obtained by the inference, and the printer 5 prints them.

The expert system is activated by the operator inputting one or more of the product oxygen, product nitrogen, and crude argon (Ar) generation target values simultaneously from the operation monitoring screen 4, and the current flow rate (raw material air Amount, product oxygen amount, crude argon (Ar) amount and purity (product oxygen purity, product nitrogen purity, crude argon oxygen concentration), liquid oxygen (Lo) liquid level (level) at the bottom of the upper column, above the lower column The increase / decrease operation is performed based on the process data such as the valve opening for adjusting the flow rate of liquid nitrogen (reflux liquid) to the column and the knowledge base.

Here, when the operator uses the operation monitoring screen 4 to input the generated amount target value, it is checked whether or not there is an error. If there is no error in the input target value, each operation change pattern is automatically determined, such as an increase operation if the target value is larger than the current amount and a decrease operation if the target value is smaller than the current amount. The types of operation change patterns are shown below.

B) Increase of oxygen alone b) Decrease of oxygen alone c) Increase of nitrogen alone d) Decrease of nitrogen alone e) Increase of crude Ar alone f) Increase of crude Ar alone v) Increase of oxygen, increase of nitrogen h) Increase of oxygen, decrease of nitrogen i) Increase of oxygen , Nitrogen depletion Nu) Oxygen depletion, Nitrogen depletion Given a target value for single or multiple products,
The finally required air volume is obtained from the following equation.

Air amount = A1 · O ₂ amount + B1 (1) Air amount = A2 · (O ₂ amount + N ₂ amount + coarse Ar amount + B2) (2) Air amount = A3 · Coarse Ar amount + B3 (3) Where , A1 to A3 and B1 to B3 are constants, and O ₂ content, N
_The target value is used as the ₂ amount and the coarse Ar amount, and the present value is used for those that do not change, and the one having the largest value in the formulas (1) to (3) is the required air amount.

Further, when the increase / decrease instruction as described above is given, it is determined whether or not the operation is possible by using a table as shown in FIG. For example, in the case of increasing the amount of oxygen alone, if the product oxygen purity is stable or tends to improve, the operation is accepted. If it is determined that the designated operation cannot be performed as a result of the determination, the fact is notified to the operator and the operation is canceled.

If the required air amount is obtained in this way, the increase / decrease unit amount (1 step amount) of each product and the air amount (changed air amount) commensurate with the increase / decrease are increased / decreased a plurality of times at a certain time interval to generate a predetermined product. Increase or decrease the amount and the required amount of air to match it.

The formula for calculating the changed air volume is shown below.

(A) Change air amount = current air amount SV + A1 · oxygen increment / decrement unit (b) Change air amount = A1 · oxygen set value + B1 (c) Change air amount = A2 · (oxygen set value + nitrogen set value + current coarse Ar amount SV + B2) (d) Change air amount = current air amount SV + A3 / coarse Ar increment / decrement unit (e) Change air amount = A3 / coarse Ar amount set value + B3 Here, the set value is the increment / decrement unit amount to the current value of each product generation amount , SV is the current value of each product generation amount, and the increase / decrease unit is the increase / decrease unit amount in one step of each product generation amount.

How to use the above formula is as shown in FIG. That is,
As is clear from the figure, the above formulas (1) to (3) are roughly classified according to which formula has the maximum value as a result of calculation using the current value of each product generation amount. As a result of calculating the above formulas (1) to (3) using the target value, (a) to (e) depends on which formula has the maximum value.
Is the one to be selected.

Next, the relationship between each product generation amount and the opening degree of the reflux liquid control valve V1 will be described with reference to FIG.

That is, the range of O ₂ amount as shown in FIG. 7 and the air at that time
The valve opening is calculated by the following formula from the amount, O ₂ amount, N ₂ amount and constants K11 to K13, K21 to K23, K31 to K33. K11 to K13 are in the range (I), K21 to K23 are in the range (II), and K31 to K33 are in the range (II).
The constants of each quantity in I) are shown.

V1 valve opening = K11 * Air volume + K12 * O ₂ amount + K13 * N ₂ + amount constant V1 valve opening = K21 * Air volume + K22 * O ₂ amount + K23 * N ₂ + amount constant V1 valve opening = K31 * Air the amount + K32 * O ₂ amount + K33 * N ₂ + amount constant thereafter repeating the unit operation until the target generated value, and ends the process reaches the target value, inform the operator. The above operation is shown in FIG. 2 as an increase / decrease operation. Here, only the increasing / decreasing operation of the O ₂ amount is shown, and other increasing / decreasing operations are omitted.

When an abnormality as described below occurs during such an increase / decrease operation, the operation is continued while performing an adjusting operation for recovering the abnormality. The operation at this time is shown in FIG. 2 as the purity adjustment / monitoring during the increase / decrease operation, and a part of the contents is shown in FIG.

That is, oxygen purity, nitrogen purity, crude Ar purity, Lo level, etc. are monitored, and if an abnormality occurs, adjustment operation corresponding to each monitoring item is performed. Fig. 3 shows the purity monitoring operation during O ₂ increase / decrease. It shows that steps -1 to -4 are executed as a part. In other words, while it is the purity monitoring operation during the O ₂ reduction, the adjustment operation for abnormal recovery including the O ₂ reduction lock (see -2) is executed while monitoring the other items and their effectiveness. However, the increase / decrease operation is continued.

On the other hand, the expert system constantly monitors the plant status by a predetermined program in parallel with the above operation changing process. The operation at this time is shown in FIG. 2 as the purity monitoring / adjustment when the increase / decrease operation is not performed.

In this monitoring, process data such as purity and liquid level are sequentially collected, and when these are linearly approximated by the least squares method to predict the change tendency, first, the range as shown in Fig. 8 is set and judged. To do. In the figure, PH and PL indicate the upper and lower limits of the allowable range, and PHH and PLL indicate the upper and lower limits. Then, the following three patterns are determined to be abnormal during normal monitoring, and the others are normal.

i) If the current value is in the range 1 or 5.

ii) If the current value is in range 2 and

(: PHH is reached within the allowable time) iii) When the current value is in range 4 and

(: The PLL is reached within the allowable time) On the other hand, the following three patterns are judged to be recovered during the abnormal recovery judgment, and the other patterns are regarded as abnormal (not recovered).

i) When the current value is in range 3.

ii) If the current value is in range 2 and

(: PH is reached within the allowable time) iii) When the current value is in range 4 and

(: PL is reached within the permissible time) In other words, range 3 (see) is the permissible range, and ranges 1 and 5 are areas that are judged to be unconditionally abnormal, and PHH or Consider the time to reach the PLL, and judge it to be abnormal when it is predicted (or reference) to reach the PLL. Therefore, in the case of the same figure, it is not judged to be abnormal. This also applies to the case where it is judged to be recovered during the abnormal recovery judgment, and the case of or is considered to be the recovery, and the case of or is considered not to be recovered.

Then, if it is determined to be abnormal, it is determined whether or not the adjustment operation is necessary, and if it is not necessary, the monitoring is continued without doing anything, and if necessary, the adjustment operation is performed. At this time, in order to determine the operation amount and operate the operation end according to the degree of abnormality detected,
For example, if the operation amount is divided into 3 stages (ranks) and the PLL is reached in T1 to T2 hours (minutes), it is abnormal I, and the PLL is reached within T1 hours.
When it reaches to the abnormal condition II, when it has already entered the PLL, it is defined as the abnormal condition III, and by adjusting the operation amount individually for each of the abnormal conditions I to III, the adjustment operation is performed according to the degree of the abnormal condition. I am able to do that.

Further, when an increase / decrease operation instruction is input during the abnormal adjustment, it is determined from the above table whether the increase / decrease operation instruction is valid or invalid. The determination method is valid when the current abnormality is recovered by the increase / decrease operation instruction, and invalid when the current abnormality is deteriorated (expanded).

Furthermore, if abnormalities occur at the same time, such as oxygen purity and nitrogen purity or oxygen purity and crude LO (liquid oxygen) level,
Since a certain operation may amplify other abnormalities, it is determined whether or not the operation corresponding to each monitoring item can be performed.

For example, an example of adjusting the O ₂ purity when the oxygen purity and one of the other monitoring items become abnormal at the same time will be described with reference to FIG. First, it is determined whether or not the O ₂ purity is restored (see −1), and if not (N), it is determined whether or not the purity is lowered (see −2). As a result, if yes (Y), it is determined whether there is a margin to increase the air amount (see -3), and if no, it is determined whether there is a margin to reduce the O ₂ amount (see -4). . If there is no margin, it is judged whether it is Lo decline (see -5). If it is no, it is judged whether there is a margin to decrease the expansion turbine (ExpT), and (-6
If the answer is YES, the rank operation is performed (see -7). For example, as shown in FIG. 9, the rank operation is performed by individually determining the operation amount according to the ranks of abnormality I to abnormality III. At this time, if there is an operation amount equal to or more than the operation I, it is determined that "is there any margin?"

In addition, in the case of NO in step-2, it is judged whether or not the N ₂ purity has dropped (see -8), and if NO, it is judged whether or not there is a margin to decrease the air (see -9), and a margin is obtained. If so, reduce the amount of Air by one step (see -10), and adjust the reflux liquid control valves V1 and V2 according to the manipulated variables (see -11).

Furthermore, in the case of yes in step-3, after performing the rank operation (air increase), see -12), it is judged whether the N ₂ purity has dropped (see -13), and if no, the reflux liquid control valve. Adjust V1 and V2 according to the operation amount (see -14).

Although not shown, the adjustment operation described above is performed not only for nitrogen purity but also for nitrogen purity and crude LO level.

In this way, whether it is a decrease in Lo while adjusting the O ₂ purity (see -5) and whether the N ₂ purity has decreased (see
(See -8, 13) etc., so that adjustment operations are performed while considering other items as well, so stable and optimal operation is possible without adversely affecting other monitoring items (process amount). Becomes

In the above, the case where the air liquefaction separation device is mainly operated has been described, but it goes without saying that the present invention can be applied to the same general plant case.

〔The invention's effect〕

According to the present invention, not only the operation is standardized to avoid erroneous operation, but also it is possible to increase / decrease the product without being influenced by the proficiency of the operator, and as a result, the product can be stably and economically supplied. Benefits are obtained. Also, the product oxygen purity, product nitrogen purity
Monitoring and adjustment operations such as oxygen concentration in crude Ar, and complicated and advanced judgments such as whether or not the amount of product oxygen, product nitrogen, and crude Ar generated can be increased or decreased.
Also, since the simultaneous increase / decrease operations of product oxygen, product nitrogen, and crude Ar are automatically performed, there is also an advantage that a large amount of labor can be saved.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a system configuration example to which the present invention is applied, FIG. 2 is a schematic flow chart for explaining the overall operation of a computer system, and FIG. 3 is an example of the operation shown in FIG. FIG. 4 is a flow chart for explaining an example of the operation shown in FIG. 2, FIG. 5 is a configuration diagram showing a judgment table, and FIG. 6 is a formula and a method for obtaining the changed air amount. And FIG. 7 is an explanatory diagram for explaining how to determine the valve opening degree,
FIG. 8 is an explanatory diagram for explaining a monitoring method during normal times and abnormal times, FIG. 9 is a flowchart for explaining a rank operation, and FIG. 10 is a block diagram showing an outline of an oxygen plant. Explanation of symbols 1 ... Computer system, 2 ... Measurement control device, 3 ... Air liquefaction separation device (oxygen plant) 4 ... CRT, 5 ... Printer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nobuhiko Ando 1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Fuji Electric Co., Ltd. (72) Makoto Uekusa No. 1 Tanabe-taden, Kawasaki-ku, Kawasaki-shi, Kanagawa No. 1 within Fuji Electric Co., Ltd. (56) Reference JP-A-56-68777 (JP, A)

Claims (2)

[Claims] 1. An operation of an air liquefaction / separation device for producing oxygen, nitrogen or oxygen, nitrogen and argon under the control of a computer, and operation change patterns for individual increase / decrease operation of each product and simultaneous increase / decrease operation of plural products. When changing by selecting based on the setting value of each product separately input, when the increase / decrease operation instruction is given during abnormal condition adjustment, the current abnormality will be recovered by this increase / decrease operation instruction. Indicates that the increase / decrease operation instruction is valid, and the current abnormality has worsened (enlarged)
The operation method of the air liquefaction separation device is characterized in that, when an abnormality occurs during the operation change, the operation change is continued while the adjustment is performed to recover the abnormality while the operation is disabled. . 2. The method for operating an air liquefaction separation device according to claim 1, wherein the upper limit value, the upper limit value, and the upper limit value are oxygen, nitrogen or process amounts related to oxygen, nitrogen, and argon produced by the air liquefaction separator. Set the lower and lower limit values,
When the upper and lower limits or the lower and lower limits are exceeded, it is unconditionally judged as abnormal and adjustment is started for abnormal recovery, and the process quantity status value reaches the upper limit and upper limit or lower limit and lower limit. When it is between the lower limit value, the slope and the time to reach the upper upper limit value or the lower lower limit value are predicted from the actual state value of the past predetermined time, and when this time is within the predetermined value, it is judged as abnormal. While the abnormal time adjustment for abnormal recovery is started, the time until reaching the upper limit value or the lower limit value is obtained when the calculated slope changes (increase → decrease, descend → increase) as a result of the adjustment, A method for operating an air liquefaction separation device, characterized in that when this is within a predetermined value, it is judged that the operation has returned to normal and the adjustment operation at the time of abnormality is terminated.