JPH03199882A - Operation of plant including air liquefying and separating device - Google Patents

Abstract

PURPOSE:To permit safe and economical operation by a method wherein an operation changing pattern for the individual increasing or decreasing operation of respective products and the simultaneous increasing or decreasing operation of a plurality of products are selected based on the set values of respective products, inputted through other routs, to effect an operation for changing the operations. CONSTITUTION:A computer system 1, operating an oxygen plant 3 controlled through a measurement control device 2, is provided with an expert system while the expert system is started by a method wherein either one or a plurality of objective values of the generating amount of product oxygen, product nitrogen and crude argon is inputted simultaneously from an operation monitoring picture 4 by an operator and effects increasing and decreasing operation based on process data, such as the flow rate, the purity, the level of liquid oxygen in the bottom part of an upper tower, the opening degree of a valve regulating the flow rate of liquid nitrogen from a lower tower into the upper tower and the like of the present time, and a knowledge base. In this case, when the objective value of the generating amount is inputted by the operator employing the operation monitoring picture 4, the objective value is checked whether there is any error or not. When there is no error, the value is compared with a present amount and when the objective value is larger, respective operation changing patterns are judged automatically so as to effect the increasing operation but when the objective value is smaller, said patterns are judged automatically so as to effect the decreasing operation.

Description

[Detailed Description of the Invention] [Industrial Field of Application] This invention is aimed at automatically operating a plant such as an air liquefaction separation device using a computer, and determining process conditions such as optimal automatic operation changes and product purity. monitoring/
This invention relates to an operating method for performing adjustment operations.

[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/- by an air compressor through an air filter, and then cooled and washed in a water washing cooling tower. Next, it enters a heat exchanger, exchanges heat with product oxygen, product nitrogen, and waste nitrogen, is cooled to about 1.70°C, and is led to the precision measurement column lower column. The air introduced into the lower column is preliminarily measured, and nitrogen-rich nitrogen gas is obtained at the top of the lower column, and liquid air with an oxygen content of approximately 40% is obtained at the bottom of the lower column. Note that the gaseous air extracted from the middle part of the lower tower is used for heat exchange with raw material air in a heat exchanger, and then enters an expansion turbine, where it is cooled and then guided to the upper tower. On the other hand, the liquid air accumulated at the bottom of the lower column and the liquid nitrogen containing a large amount of nitrogen accumulated at the top and near the top are guided through conduits to the middle, upper, and vicinity of the upper column of the upper column, respectively. Furthermore, it is precisely measured and separated in the upper tower, and the product oxygen gas is released from the bottom of the upper tower.

Product nitrogen gas is extracted from the top and waste nitrogen gas is extracted from the middle, and after heat exchange with raw air in the heat exchanger as described above, it is supplied to the outside. On the other hand, raw argon gas is extracted from near the middle of the upper column and supplied to the crude argon column through a conduit.

Although various proposals have been made for automating air liquefaction separation equipment configured in this way, the computer program becomes complicated, the required capacity increases, and it becomes uneconomical. Generally, a uniform control method is used. For example, automatic operation changes involve automatic changes in the amount of oxygen generated, which is the main product of air liquefaction separation equipment, and adjustments are made to the control valves necessary to change the amount of feed air to match this amount of oxygen generated. In addition, the amount of product nitrogen or argon generated is determined in accordance with the amount of oxygen, and once the amount of oxygen generated is determined, the amounts of other products generated are also determined.

[Problem to be solved by the invention]

However, in this method, the amount of other products such as nitrogen or argon generated is always fixed in relation to the amount of oxygen generated, so this method is particularly useful in fields such as the steel industry where the amounts of oxygen, nitrogen, and argon used are not constant. , the operation will continue while the surplus product corresponding to the error is dissipated into the atmosphere, resulting in an increase in the unit manufacturing cost of the product.

On the other hand, the conventional method of determining abnormality or return to normality is absolute value control in controlling the state of the air liquefaction separation equipment, such as product purity and liquid oxygen level in the upper column of the rectification column. In plants such as those in which there is a time delay before a change in purity, etc. appears even after control operations are performed, absolute value management alone causes an overshoot phenomenon, making it difficult to maintain stability within the specified value.

In addition, air liquefaction separation equipment is characterized by strong mutual interference between the purity of each product and between the purity and the liquid oxygen level in the upper column of the rectification column. How to increase or decrease the amount of product oxygen generated,
Alternatively, a uniform control method such as increasing or decreasing the amount of raw air may not necessarily work depending on the condition of the air liquefaction separation device, and the purity of other products may also be affected, so purity control is also required. There are problems such as difficulty in stably maintaining the air liquefaction separation device.

Therefore, an object of the present invention is to eliminate the drawbacks of the conventional system as described above and to enable stable and economical operation.

[Means to solve the problem]

Oxygen, nitrogen or oxygen controlled by computer.

When changing the operation of the air liquefaction separation equipment that produces 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 change operation is performed by selecting based on the setting values of each product that are manually input separately.

Here, when an increase/decrease operation instruction is given during abnormality adjustment, if the increase/decrease operation instruction is in the direction of recovering from the current abnormality, the increase/decrease operation instruction is valid, and the current abnormality is worsened (expanded). If an abnormality occurs during operational changes, the operational changes will be continued while making adjustments to recover from the abnormalities.

In addition, when controlling the process amount using a computer,
Upper limit value and upper limit value for each process quantity.

The lower limit value and ff limit value are set, and when the upper limit value or ff limit value is exceeded, it is unconditionally determined to be abnormal and adjustment for abnormality recovery is started, and the state value of each process is set as the upper limit value. When the value is between the upper upper limit value or the lower limit value and the ff limit value, the slope and the time until reaching the upper upper limit value or the ff limit value are predicted from the actual state value of the past predetermined time, and this time is calculated as the predetermined value. If it is within the value, it is determined that there is an abnormality and adjustment is started to recover from the abnormality, while as a result of the adjustment, when the calculated slope changes (rise → fall, fall - rise>), the upper limit or lower limit is reached. If the time is within a predetermined value, it is determined that the adjustment has returned to normal and the adjustment operation is completed.

Furthermore, when controlling an air liquefaction separation device that produces oxygen, nitrogen, or oxygen, nitrogen, and argon, if the process quantities, including oxygen purity and nitrogen purity, or oxygen purity and rectification tower liquid oxygen level, become abnormal at the same time. The operation is performed by selecting the optimum operating end and operating amount without interfering with each other and causing adverse effects.

[Effect]

The first is the use of an expert system in the computer, which enables the following operating methods, which are said to be complex and increase capacity with conventional programs, to be
Made easy and economical to implement.

Second, when changing operations, conventionally, the feed air flow rate required for the amount of product oxygen generated was calculated, and the feed air flow rate corresponding to the amount of product oxygen generated, or other adjustment valves necessary for product flow rate and stable operation of the equipment, was calculated. However, 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 understood, and the generation amount of each product can be freely set. By supplying the minimum necessary raw material air flow rate to balance each product generation, and by understanding the relationship between the optimal opening degree of the regulating valve necessary for stable operation of the equipment in the above balance, the relational expression can be calculated. The amount of each product generated can be arbitrarily selected by storing it in the computer, allowing for flexible operational changes and the most economical operation.

Thirdly, when monitoring process conditions such as the purity of the air liquefaction separation device or the liquid level and pressure in the rectification column, two values, an allowable value and an abnormal value, are set in contrast to the conventional absolute value control. By monitoring the condition based on the time it takes to reach these two values, it is possible to perform not only feedforward control, but also to easily rank abnormal conditions. By combining this ranking with various control methods, control performance can be further improved. improve.

Fourth, in the control of process conditions such as purity or liquid level in a rectification column, for example, in the case of purity control of product oxygen purity, the control operation type is an increase or decrease in the amount of product oxygen generated.
Multiple operation types such as increase/decrease of feed air flow rate and expansion turbine air volume are provided, and the operation varies depending on the degree of the above abnormality rank, such as when there is an abnormality in only the product oxygen purity, multiple abnormalities such as product oxygen purity and product nitrogen purity, etc. By automatically selecting and executing the control operations that have been performed, mutually interfering operations such as one control requiring another control can be prevented, and stable operation can be achieved.

〔Example〕

Fig. 1 is a block diagram showing a system to which this invention is applied, Fig. 2 is a schematic flowchart for explaining the overall operation of the computer system, Fig. 3 is an explanation of an example of the operation indicated by 0 in Fig. 2. FIG. 4 is a flowchart for concretely explaining an example of the operation indicated by ■ in FIG. 2.

In Figure 1, ■ is a computer system, 2 is a measurement control device, 3 is an air liquefaction separation device (also called # elementary plant),
4 is a CRT display, and 5 is a printer. In addition,
A computer system 1 that operates an oxygen plant 3 controlled via a measurement control device 2 has at least an expert system, and this expert system has a reasoning mechanism and a skilled operator with extensive experience in oxygen plant operation. It consists of a knowledge base that expresses specialized knowledge regarding increase/decrease operations or adjustment operations in the form of if'' then rules and mathematical formulas.
The value obtained by the inference mechanism is given to the measurement control device 2, and at the same time, the value obtained by the inference and the amount of operation are notified to the operator each time the inference is executed, and are printed by the printer 5.

The expert system is started by the operator inputting the generation amount target value for one or more of the generation amounts of product oxygen, product nitrogen, and crude argon (Ar) from the operation monitoring screen 4, and inputs the current flow rate (raw air amount, product oxygen amount, crude argon (Ar) amount), purity (product oxygen purity, product nitrogen purity, oxygen concentration in crude argon), liquid oxygen (LO) level at the bottom of the upper column, from the lower column to the upper column. Increase/decrease operations are performed based on process data such as the valve opening degree that adjusts the flow rate of liquid nitrogen (reflux liquid) to the column and the above knowledge base.

Here, when the operator inputs the generation amount target value using the operation monitoring screen 4, it is checked to see if there are any errors. 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. The types of operation change patterns are shown below.

B) Increase the amount of oxygen alone C) Increase the amount of nitrogen alone C) Increase the amount of nitrogen alone 1 2 d) Reduce the amount of nitrogen alone e) Increase the amount of crude Ar alone) G) Increase the amount of oxygen, increase the amount of nitrogen CH)! 2 elemental weight loss, nitrogen weight loss W) Oxygen weight loss, nitrogen weight loss N) Oxygen weight loss, nitrogen weight loss If the generation target value for a single product or multiple products is given,
The finally required air (A i r) Ji is calculated from the following equation.

Air amount - AI'02 amount + Bl ・ (1) A
ir amount = A2 (Ch amount 10 N2 amount 10 coarse Ar amount 10 B2)
...(2) Air amount - A3 - Crude Ar amount + B3 - (3) Here,
A1-A3 and B1-B3 are constants, 02 amount, N
The target value is used as the 2 amount and the coarse Ar amount, and the current value is used if the amount is not changed, and the largest value in equations (1) to (3) is taken as the required air amount.

Further, when the above-mentioned increase/decrease instruction is given, it is determined whether the operation is possible or not 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 improving, the operation will be accepted. If it is determined that the specified operation is not possible, the operator is notified of this and the operation is canceled.

Once the required amount of air is determined in this way, the unit amount of increase/decrease (one step amount) for each product and the corresponding amount of air (changed air amount) are increased/decreased multiple times at the same time intervals until the specified amount of product is generated. Then, increase or decrease the amount of air to the required amount.

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

(a) Changed air amount = Current air amount SV + AI / Oxygen increase/decrease unit (b) Changed air amount = AI / Oxygen set value 1 B1 (C) Changed air amount - A2 (Oxygen set value 10 Nitrogen set value + Current crude A
r amount sv + B2) (d) Changed air amount - current air amount SV + A3・Rough Ar increase/decrease unit 3 4 (e) Changed air amount - A3・Rough Ar amount set value 10 B3 Here, the set value is the current amount of each product generated. The value obtained by adding the unit amount of increase or decrease to the value, SV, indicates the current value of the amount of each product produced, and the unit of increase or decrease indicates the unit amount of increase or decrease in the amount of each product produced in one step.

The usage of the above formula is as shown in FIG. That is,
As is clear from the figure, the equations (1) to (3) above are roughly classified based on which equation has the largest value as a result of calculation using the current value of each product generation amount, and then Above (1
) to (3) are calculated using target values, and one of (a) to (e) is selected depending on which formula has the largest value.

Next, the relationship between the amount of each product generated and the opening degree of the reflux liquid regulating valve V1 will be explained with reference to FIG.

In other words, the range of 02 amount as shown in Fig. 7 and the A at that time.
ir amount, 02 amount, N2 amount and constant 11~13, 21
to 23. The valve opening degree is calculated from 31 to 33 using the following equation. In addition, K11-Kl3 shows a large constant in the range (I), 21 to 23 in the range (11), and K31-33 in the range (1).

V1 valve opening = 11*Air amount 12' kOz amount + 13')'N2 amount + constant V1 valve opening = 21*Air amount + 22*02 amount + 2
3 * NZ amount + constant v1 valve opening = 31 * Air amount 10 + 32'l'Oz amount +
33*N2 amount 10 constant Thereafter, unit operations are repeated until the target generation value is reached, and when the target value is reached, the process is terminated and the operator is notified of this fact. The above operation is shown in FIG. 2 as an increase/decrease operation. Here, only the increasing/decreasing operations of the 02 amount are shown, and other increasing/decreasing operations are omitted.

If an abnormality as described below occurs during such an increase/decrease operation, the operation is continued while carrying out adjustment operations to recover from the abnormality. The operation at this time is shown in FIG. 2 as purity adjustment and monitoring during the increase/decrease operation, and a part of its contents is shown in FIG.

That is, oxygen purity, nitrogen purity, crude Ar purity, and Lo
It monitors the level, etc., and if an abnormality occurs, it performs adjustment operations corresponding to each monitoring item.
Figure 3 shows 11 as part of the purity monitoring operation during 02 reduction.
This indicates that the steps from ~■-4 are to be executed.

In other words, while monitoring the purity of the ozM amount, while considering the monitoring of other items and their effectiveness, and while performing adjustment operations for abnormality recovery including the 02 weight loss lock (see ■-2). , the increase/decrease operation continues.

On the other hand, the expert system constantly monitors the plant status using a predetermined program in parallel with the above-described operation change processing. The operation at this time is shown in FIG. 2 as purity monitoring/adjustment when no increase/decrease operation is being performed.

For this monitoring, process data such as purity and liquid level are collected sequentially, and the process data is linearly approximated using the least squares method to predict the change trend. First, a range as shown in Figure 8 is set and judgment is made. 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, respectively. The following three patterns are determined to be abnormal during normal monitoring, and the others are considered normal.

i〉If the current value is in 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 ■.

(■: PLL is reached within the allowable time) On the other hand, the following three patterns are determined to be recovery during abnormality recovery determination, and the rest are considered to be abnormal (not recovered).

i) 'Current value is in range 3.

ii) When the current value is in range 2 and [phase].

([Phase]: PH is reached within the allowable time>iii) When the current value is in range 4 and @.

(0: PL is reached within the allowable time) In other words, range 3 (see ■, ■) is the allowable range, range 1.5
is an area that is unconditionally determined to be abnormal, and the time to reach PHH or PLL is considered only when it is in range 2.4, and it is determined to be abnormal when it is predicted to reach PHH or PLL (see ■ or ■). 7 8 In the past, cases marked ■ and ■ in the same figure are not judged to be abnormal. This is also the case when determining recovery during abnormality recovery determination; [phase] or 0 is considered to be recovery, and ■ or @ is considered not to be recovery.

Then, if it is determined that there is an abnormality, it is determined whether or not an adjustment operation is necessary, and if it is not necessary, monitoring is continued without doing anything in particular, and if necessary, the adjustment operation is performed. At this time, in order to determine the amount of operation and operate the operating end according to the degree of the detected abnormality,
For example, the operation amount is divided into three stages (ranks), and T1 to T2 are
If the PLL is reached in time (minutes), it is considered an abnormality ■, if it reaches the PLL within T1 hours, it is an abnormality ■, and if it has already entered the PLL, it is an abnormality ■, and the manipulated variable for each abnormality 1 to abnormal By determining the values individually, it is possible to perform adjustment operations according to the degree of abnormality.

Further, if an increase/decrease operation instruction is received during abnormal adjustment, it is determined whether the increase/decrease operation instruction is to be valid or invalid based on the above table. The determination method is valid if the current abnormality will be recovered by this increase/decrease operation instruction, and invalid if the current abnormality is in the direction of worsening (expansion).

Furthermore, oxygen purity and nitrogen purity or oxygen purity and crude LO (
When abnormalities occur at the same time, such as in liquid oxygen (liquid oxygen) levels, it is determined whether or not it is okay to carry out the operations corresponding to each monitoring item, since certain operations may amplify other abnormalities.

For example, in the example of 02 purity adjustment when oxygen purity and one of the other monitoring items become abnormal at the same time,
This will be explained with reference to the figures. First, it is determined whether the 02 purity has returned (see ■-1), and if not (N), it is determined whether the purity has decreased (see ■2). The result is yes (Y)
If so, determine whether there is room to increase the amount of Air (see ■3); if no, determine whether there is room to reduce the amount of 02 (see ■-4). L if you can't afford it
If no, determine whether there is room to reduce the expansion turbine (E x p T) (see ■-6); if yes, perform rank operation (■- (see 7). The rank operation 9 0 is performed by individually determining the operation amount according to the rank of abnormality (1) to abnormality (2), as shown in FIG. 9, for example. At this time, the judgment of "Is there enough margin?" is, if the amount of operation is greater than operation I,
We will set it to ``with some leeway''.

In addition, if No in step ■-2, determine whether the Nz purity has decreased (see ■-8), and if No, Ai
Determine whether there is enough room to reduce Air (see ■-9), and if there is room, reduce Air by one step (see ■-10).
, reflux liquid control valve Vl.

Adjust V2 according to the operation amount (see ■-11).

Furthermore, if YES in step ■-3, rank operation (
After increasing the air flow (see ■-12), determine whether the N2 purity has decreased (see ■-13). If no, adjust the reflux liquid control valves Vl and V2 according to the operating amount (see ■-13).
(See ■-14).

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

In this way, while adjusting the 02 purity, we also take into account other items such as whether the LO is low (see ■-5) and whether the N2 purity has decreased (see ■-8, 13). Since the adjustment operation is executed, stable and optimal operation is possible without adversely affecting other monitoring items (process quantities).

Although the above description has mainly been given to the case where an air liquefaction separation device is operated, it goes without saying that the present invention can also be applied to similar plants in general.

〔Effect of the invention〕

According to this invention, not only operations are standardized and erroneous operations are avoided, but it is also possible to increase or decrease the number of products regardless of the operator's proficiency, and as a result, products can be supplied stably and economically. Benefits can be obtained. In addition, it is possible to improve product oxygen purity, product nitrogen purity, and
Monitoring and adjusting operations such as the oxygen concentration in crude Ar, complex and advanced judgments such as whether to increase or decrease the amounts of product oxygen, product nitrogen, and crude Ar generated, and simultaneous increase/decrease operations of product oxygen, product nitrogen, and crude Ar. etc. are performed automatically, which has the advantage of making it possible to significantly save labor.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing an example of a system configuration to which the present invention is applied, Fig. 2 is a schematic flowchart for explaining the overall operation of the computer system, and Fig. 3 is an example of the operation indicated by ■ in Fig. 2. FIG. 4 is a flowchart for explaining an example of the operation indicated by ■ in FIG. 2, FIG. 5 is a configuration diagram showing a determination table, and FIG. An explanatory diagram for explaining how to determine the valve opening degree, FIG. 7 is an explanatory diagram for explaining how to determine the valve opening degree,
FIG. 8 is an explanatory diagram for explaining the monitoring method during normal and abnormal times, FIG. 9 is a flowchart for explaining rank operation, and FIG. 10 is a block diagram schematically showing the oxygen plant. Code explanation 1... Computer system, 2... Measurement control device, 3.
・・Air liquefaction separation device (oxygen plant) 4・・CRT
. 5...Printer. 3 Figure 2 JP-A-3-199882 (8)

Claims (1)

[Claims] 1) In changing the operation of an air liquefaction separation device that is controlled by a computer to produce oxygen, nitrogen, or oxygen, nitrogen, and argon, an individual increase/decrease operation of each product and a simultaneous increase/decrease operation of multiple products are performed. 1. A method for operating an air liquefaction separation apparatus, comprising selecting an operation change pattern for the above-mentioned products based on separately input set values for each product and performing an operation change operation. 2) When an instruction to increase or decrease is given during abnormal adjustment,
If this increase/decrease operation instruction causes the current abnormality to recover, the increase/decrease operation instruction is valid; if the current abnormality worsens (expands), it is invalidated; however, if an abnormality occurs during operational changes, 2. The method of operating an air liquefaction separation apparatus according to claim 1, wherein the operation change is continued while making adjustments to recover from the abnormality. 3) When controlling process quantities using a computer, set an upper limit value, an upper upper limit value, a lower limit value, and a lower lower limit value for each process quantity, and when the upper upper limit value or the lower lower limit value is exceeded, If 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, it will unconditionally determine that it is abnormal and start adjustment for abnormality recovery. The slope and the time to reach the upper upper limit or lower lower limit are predicted from the state value, and if this time is within a predetermined value, it is determined that there is an abnormality and adjustment is started to recover from the abnormality. As a result, the slope calculated above changes (
(rise → fall, fall → rise), the time required to reach the upper limit value or lower limit value is determined, and if this is within a predetermined value, it is determined that normality has returned and the adjustment operation is terminated. how to drive. 4) When operating an air liquefaction separation device that produces oxygen, nitrogen, or oxygen, nitrogen, and argon, if the process amount including oxygen purity and nitrogen purity or oxygen purity and rectification tower liquid oxygen level becomes abnormal at the same time. , a method of operating an air liquefaction separation device characterized by selecting and operating an optimal operating end and operating amount without interfering with each other and having adverse effects.