JPS583189B2 - Automatic control method for oxygen production in air separation equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for automatically controlling the amount of oxygen produced in an air separation device, and in particular, a method for automatically determining the amount of oxygen produced in accordance with fluctuations in the consumption amount at the place of use. This makes it possible to maintain an appropriate balance between production and consumption at all times.

After the war, with the dramatic increase in steel production and the establishment of oxygen utilization technology in the steelmaking process, oxygen consumption in the steel industry has continued to increase, and air separation equipment has also increased in recent years.
Large-scale engines with a capacity of 0,000 to 30,000 Nm/h are being installed.

As the main use of oxygen in the pig iron and steel making processes,
Examples include blast furnaces and converters.

As is well known, blast furnace operation is continuous, so the amount of oxygen used does not fluctuate over time; it is always constant and stable, and there are no particularly difficult problems in terms of supply and demand balance.

On the other hand, converter operation is performed intermittently in a batch manner and consumes a large amount of oxygen within a short period of time.

7711 In addition, due to the variety of operating conditions, such as changing the type of molten steel, reblowing, and simultaneous blowing of two units, a constant amount of oxygen is not consumed at all times, and it occurs rapidly and irregularly in a short period of time. It is normal for things to fluctuate.

As a means to absorb such fluctuations, it is common to install a large-capacity oxygen holder in the middle of the line connecting the air separation device and the place of use, such as a converter.

However, it is completely impossible to absorb fluctuations in consumption with the oxygen holder alone.3 Especially with conventional manual operation; well, changing the amount of oxygen produced requires skilled and laborious work. Therefore, it is not possible to accurately follow changes in usage.

Therefore, in consideration of the need to avoid operational problems due to insufficient supply at the user site, we manufacture more than the amount actually required at the user site, and excess oxygen remains unused. The reality is that we are forced to waste energy by dissipating it into the atmosphere.

In view of these circumstances, the present inventors have previously filed a patent application entitled "Automatic operation change method for air separation equipment" (Japanese Patent Application No.
No. 1-119534) provides a method for easily changing the amount of oxygen produced in a short time using a computer control system, making it possible to produce only the required amount of oxygen in response to fluctuations in consumption. This meets the need to avoid wasteful emissions into the atmosphere and save energy.

However, the above method is concerned with automating the actual change operation after the oxygen production amount is specified,
The task of determining and setting the amount of oxygen to be produced was still left to the operators.

This operator also has to take care of maintenance and other tasks, and is unable to monitor the production amount all the time, so we decided to go one step further and automatically determine the amount of oxygen produced. There was a strong demand for the establishment of a method to control this.

The present invention was made in response to such a request, and detects the pressure in the oxygen holder installed between the air separation device and the place of use at regular time intervals, and uses the detected value to detect the pressure in the oxygen holder. The pressure average value within a predetermined period of time is determined, and then the pressure change trend in the oxygen holder is determined based on the transition of the average value, and then the pressure change trend in the oxygen holder is determined based on this change trend and the predicted amount of oxygen usage over time that has been input in advance. After determining the current oxygen production volume and checking whether the calculated production volume is within the capacity of the equipment and whether the amount of other by-products can meet the demand, the final The system provides a new operating method that automatically determines and automatically controls the amount of oxygen produced, thereby freeing operators from cumbersome work.
This system maintains an appropriate oxygen supply and demand balance at all times, minimizes the amount of wasted oxygen that was conventionally released into the atmosphere, and significantly reduces the production energy required.

An example of pressure fluctuations in an oxygen holder installed on a line connecting an air separation device and a place where oxygen is used is as shown in FIG. 1 for a converter.

As mentioned above, in a converter, a large amount of oxygen is used in a short period of time due to batch operation, so the pressure inside the holder is determined by the period of the operation interval (usually about 30 minutes), as shown in the figure. The pressure inside the holder exhibits a sawtooth waveform, and during blowing when oxygen is blown into the converter, the pressure inside the holder decreases, and increases when blowing ends.

In addition, the internal pressure of the Holso is determined by its withstand pressure (for example, 25 kg
Approximately 15Kg7d must be operated to maintain a
Since it is required to hold the weight over 20g, it is usually about 20g.
K, 9/i. Operation is performed with the target value set at 9.

However, the pressure inside the holder shown in FIG. 1 fluctuates greatly above and below the target value of 20 kg/cm2g, and the balance between the amount of oxygen used and the amount of production is not stable.

This pressure fluctuation is 15 to 25K, as shown in Figure 2.
It is desirable to maintain a stable state around the target value of 20 KgΔRose between g/cm2g.

Such a stable state is achieved by detecting pressure changes within the holder, determining an appropriate amount of oxygen production, and balancing supply and demand.

In that case, the capacity of the holder should be adjusted so that it can follow sudden changes in the amount of oxygen used in the converter (for example, the capacity of the holder is such that it is possible to perform one or two blowing operations with only the amount of oxygen stored in the holder). Therefore, it is not necessary to pay attention to changes in pressure that occur in synchronization with the blowing cycle of the converter; it is sufficient to detect overall pressure changes.

Hereinafter, the treatment procedure according to the method of the present invention will be explained in detail using converter operation as an example.

First, as a first step, the pressure inside the holder is detected, and whether the pressure is rising or falling is automatically checked.

The pressure inside the holder has the characteristics shown in Table 1, and when the pressure remains constant, the amount used and the amount produced are equal, while when the pressure is rising or falling,
This indicates that the balance between supply and demand has collapsed.

If the pressure inside the holder has increased due to the above pressure detection,
Since the amount of oxygen produced exceeds the amount used, the amount of oxygen produced is reduced, and if it is decreasing, the amount of production is increased to make up for the shortage, thereby balancing supply and demand.

Detection of the pressure change inside the holder does not need to focus on changes that occur in synchronization with the blowing cycle of the converter as described above.
It is sufficient to target the overall pressure change.

This pressure detection can be performed as shown in FIG.

In the figure, line 1 represents the set value of the holder internal pressure, 2 represents the instantaneous value of the holder internal pressure measured by the pressure adjustment meter installed in the holder, and 3 represents the average value. be.

First, the integrated value of the pressure inside the holder sampled at a fixed period (△t) is read by the pressure integrator, and the read integrated value is transferred to the buffer (.Buffe) for calculating the pressure inside the holder.
r ) with the oldest data.

For example, at time (tn), data at time (tin-1) is replaced.

Then, using this data to be replaced, that is, the latest integrated data (at time t) and the oldest integrated data (at 'nyo time) in the buffer for calculating the holder internal pressure, calculate the average pressure in the holder using the following formula. .

Average pressure = {(latest integrated value) - (oldest integrated value)
) / ( {Sampling period (△t)} Supply and demand are balanced by controlling the supply and demand so that they match.

In order to achieve this supply and demand balance, in addition to the current pressure detection results in the holder obtained through the above procedure,
The final oxygen production amount is determined by considering changes in the operating status of the converter after that point and taking into account predicted fluctuations in supply and demand.

That is, the production plan of the converter is processed as feedforward, using the holder internal pressure as feedback.

For example, as shown in FIG. 4, if the average value 4 of the holder internal pressure falls below the set value 5, it is necessary to increase the oxygen production amount by the difference e at time t, and at the same time, in the future Check the converter production plan, and if blowing is scheduled to increase, add the predicted increase to the increase detected from the pressure change above, while if blowing is scheduled to decrease, The final amount of oxygen produced is determined by subtracting the corresponding amount.

If the finally determined oxygen production amount differs from the current production amount as described above, operational changes in oxygen production will be made in accordance with the difference.

When changing operations, it is necessary to check in advance whether the changed operating conditions satisfy the following conditions.

: (I) It is within the capacity of the air separation equipment itself, and it is also within the usable capacity of the component equipment such as the air compressor and expansion turbine; (■) The change in operation is due to a decrease in production volume. If so, other products (nitrogen, argon products, etc.) produced as by-products in the same equipment should not exceed the demand.

If any one of the above conditions is not satisfied, an alarm is generated to notify the operator, and the operation change operation is performed only when all conditions are satisfied.

In order to automatically perform the above operational changes in an air separation equipment equipped with a heat exchanger for liquefying feed air and separating it into oxygen and nitrogen using the difference in boiling points, it is necessary to , the quality of the produced product oxygen, nitrogen, etc. must not deteriorate; (b) it must not be affected by inappropriate control parameters; and (C) it must not be affected when operational changes should not be made (e.g. (e.g., when the operating conditions after the change exceed the capacity of the relevant equipment), the operation change can be detected as an abnormality, and (d) the end of the operation change can be detected quickly and accurately. It is hoped that all of the following will be met.

The new oxygen production amount can be adjusted by changing the operation under such conditions, for example, according to the method disclosed in the aforementioned patent application (Japanese Patent Application No. 119534/1982) by the present inventors.

According to the law, the ratio between feed air and product oxygen should be increased (a smaller ratio is advantageous in terms of operating efficiency, but a larger ratio is desirable to make the process more resistant to disturbances). , the process is brought into a sufficiently stable state, and the ratio is gradually reduced using the manipulated variable that ultimately works in the direction of decreasing the ratio, increasing the amount of product oxygen and nitrogen to return it to the normal value. When implementing operational changes to reduce operation, the computer system determines that (I) if an abnormality occurs in any indicator or control loop of the gas separation device;
Temporarily suspend operations change operations until normal conditions are restored.
(■) On the other hand, when the operation is changed, the unstable state continues immediately after the change is completed, so the period from the time when the change in operation reaches the change target value until the process stabilizes is set as the operation change prohibition time. The next operation change will not be accepted until (■) the operation change is completed when the operation amount that acts in the direction of decreasing the ratio of the last remaining raw material air flow rate and product oxygen gas flow rate is specified. It is detected by determining whether the operation has been operated up to the σ0 value, and a permissible time for operational changes corresponding to the σ0 operational change is set, and the presence or absence of an abnormality in the operational change is determined based on whether the operational change is completed within the corresponding allowable time. If the operation change does not reach the change target value within the allowable time, the operation change is completed in the current operating state and the operation change prohibition time is entered. can be done automatically.

After the above-mentioned operational change is completed, it takes a certain amount of time for the result to actually appear in the holder internal pressure.

Therefore, if control is continued without waiting for the pressure to change, over-control will occur, resulting in so-called over-hunting (
over hunting).

In order to prevent this, a certain pause period is provided after changing the amount of oxygen production, the pressure change is detected, and the control operation is temporarily paused until the change result appears in the holder internal pressure.

After the change result is confirmed, the control is restarted, and the process returns to the first step to repeat the series of operations starting from detecting the pressure inside the holder.

By performing the control as described above, the pressure inside the holder is maintained in a stable and good state regardless of fluctuations in the amount of oxygen used at the place of use.

FIG. 5 is a graph showing actual operation data in an oxygen holder for a converter (I is the conventional method, ■ is the method of the present invention). In the figure, the dashed line 6 is the target value, and the solid line 7 is the measured value. The dashed line 8 indicates the average value of the measured values 7.

As shown in the figure, in the conventional method, the measured values and their average values fluctuate greatly with respect to the target values (Figure I), whereas with the method of the present invention, the average value of the actual measured values is approximately It matches the target value, and the fluctuation range of the actual measured value △P2 is also the former fluctuation range △
It is recognized that it is smaller and more stable than 4P.

This kind of stable pressure change means that the amount of oxygen produced from the air separation equipment is accurately controlled to follow the fluctuations in the amount of oxygen used at the place of use, and that the two are in an appropriate balance. It means that there is.

Figure 6 is a graph illustrating the relationship between the air separation equipment and the oxygen consumption over time in the converter. This shows the case where control is performed using

In each figure, solid lines a and a' indicate the amount of oxygen produced, and solid line b indicates the actual amount of oxygen used in the converter.
The shaded area surrounded by and b means the amount of surplus oxygen that is unused and released into the atmosphere.

Note that the period between times P1 and P2 is a converter operation suspension period (oxygen non-use period) due to monthly inspections, etc.

In the past, as mentioned above, it was necessary to respond to the maximum usage amount at the place of use under the constraint that it was not possible to finely adjust the production amount in response to fluctuations in usage amount. As a result, a large amount of oxygen, which corresponds to the shaded area W surrounded by solid lines a and b in Figure 2, is unused and is wasted by being released into the atmosphere. However, according to the method of the present invention, the production amount can be accurately adjusted to follow the fluctuations in the usage amount, so the amount of surplus oxygen is determined by the area surrounded by the solid line a′ in the figure (■). As shown by W', the amount of oxygen is minimized, which corresponds to the area between a and a', and the production energy required for its production is reduced compared to the conventional method.

[Brief explanation of the drawing]

Figures 1 and 2 are diagrams schematically showing pressure changes in the oxygen holder, Figures 3 and 4 are diagrams explaining the fluctuations of the pressure set value, measured value, and their average value in the oxygen holder, and Figure 5 FIGS. 1 and 6 are diagrams illustrating changes in oxygen holder pressure in actual operation, and FIGS. 6 I and 6 are diagrams schematically showing changes over time in the amount of oxygen used and the amount of oxygen produced in converter operation.

Claims (1)

[Claims] 1. A method of automatically controlling the amount of oxygen produced in an air separation device according to the consumption amount at the place of use, which involves controlling the pressure of an oxygen holder installed in a line connecting the air separation device and the place of use. The pressure is detected at regular time intervals, the pressure average value within a predetermined time is determined based on the detected value, and the pressure change trend within the oxygen holder is determined based on the transition of the average value. Determine the amount of oxygen produced at that point based on the prediction of subsequent oxygen usage over time, and then determine whether the determined amount satisfies the capacity of the air separation device and the conditions required for the air separation device. automatic control of the amount of oxygen produced in an air separation device, characterized in that the amount of oxygen produced is changed to the determined amount of produced oxygen if the amount is satisfied, and an alarm is issued if the amount of produced oxygen is not satisfied. Method.