JPS6314074A - Method of controlling operation of fractionating column in air separator - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for controlling the operation of a rectification column in an air separation apparatus.

[Prior art]

In air separation equipment that collects oxygen and nitrogen at the same time as air by cryogenic separation, nitrogen is collected from the top of the upper column of the double rectification column, liquid oxygen is collected from the bottom of the upper column, and argon is collected at the same time. Argon-containing gas is extracted from a side stream of the column and supplied to a crude argon column to collect argon.

When collecting argon, it is desirable that the composition of the gas supplied from the upper column of the rectification column to the crude argon column has a high argon concentration and a low nitrogen content, but the argon content in the air is small. In addition, argon's boiling point is between that of nitrogen and oxygen, and its relative volatility is low, making it relatively difficult to separate. Moreover, when operating a rectification column to maintain a relatively high argon yield,
It is necessary to operate the upper tower precisely. In other words, depending on the operation adjustment method, the concentration distribution of each component in the upper column changes and the operating state is disturbed, and as a result, the composition of the argon-containing gas extracted from the side stream of the upper column changes.
This may lead to disturbances in the operating conditions of the crude argon column and adversely affect the purity of the crude argon. Conventionally, methods for adjusting the operating conditions of the rectification column include (1) generating nitrogen by adjusting the flow rate of nitrogen extracted from the top of the upper column of the rectification column;

(11) The amount of feed air introduced into the air separation equipment, the throughput of the expansion turbine which is a cold generation engine, the amount of oxygen extracted from the bottom of the upper column of the rectification column, etc. are individually adjusted. Adjust the liquid level within the specified value.

It is carried out by etc.

[Problem that the invention seeks to solve]

However, according to method (i) mentioned above, the pressure in the upper column of the rectification column fluctuates in order to adjust the nitrogen flow rate, which disturbs the rectification state of the upper column and causes the argon-containing gas to be extracted from the side stream. In addition, in the method (11), the balance of the rectification column is disturbed and the concentration of the product, especially argon This caused fluctuations in the composition of the contained gas.

That is, an object of the present invention is to eliminate the drawbacks of the conventional operation control method in a rectification column of an air separation apparatus, and to operate the rectification column stably.

[Means for solving problems]

As a result of intensive studies to achieve this objective, the present inventors have found that the pressure inside the upper column can be maintained at a constant pressure by adjusting the amount of impure nitrogen gas extracted from the upper part of the upper column. Nitrogen is extracted in response to demand while maintaining the rectification column in a stable state, and at the same time, the expansion turbine flow rate, feed air flow rate, and Ratschman flow rate are set as specified in response to changes in the liquid level at the bottom of the upper column. The present invention was completed based on the discovery that the liquid level in the upper column can be adjusted while maintaining the balance of the rectification column by adjusting it according to the control law.

That is, the gist of the present invention is to provide an air separation apparatus in which feed air is compressed and cooled and then rectified in a double rectification column to extract oxygen, nitrogen, and argon. The pressure in the upper column is detected while extracting a predetermined amount of
The amount of impure nitrogen gas extracted from the top of the upper column is automatically adjusted to maintain the pressure constant, while the liquid oxygen level at the bottom of the upper column of the rectification column is detected and the liquid level is set at a predetermined level. The present invention relates to a method for controlling the operation of a rectification column in an air separation apparatus, characterized in that the flow rate of an expansion turbine, the flow rate of feed air, and the flow rate of Ratzmann are automatically adjusted according to a predetermined control law so as to maintain the flow rate within a certain value.

Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 shows an example of an air separation device for carrying out the present invention. In Fig. 1, the air separation device is composed of an air compressor A, a reversible heat exchanger B, a lower column C1 of a rectification column, an upper column D of the rectification column, an expansion turbine E, a crude argon column F, etc. . Raw air is compressed, cooled and purified through conduit 1 through air compressor A and reversible heat exchanger B, and then introduced into the bottom of rectification column C through conduit 1. In the lower column C, the condensed liquid air exchanges heat with the liquid oxygen at the bottom of the upper column of the rectification column in the condenser installed at the top of the column, descends, is supplied to the bottom of the lower column, and is fed into the column. Rectification is carried out by contacting the rising raw material air with gas-liquid on the tray. Lower tower C
Liquid nitrogen is removed from the top of the column and introduced as reflux via conduit 3 into the top of the upper column. Also, air is taken out from the center of the lower column C, and a part of it is introduced into the upper column from the center through the conduit S, the expansion turbine E, and the conduit 6. The fluid introduced into the rectification column through conduit 6 is called a Raschmann. Further, liquid air with a high oxygen concentration (liquid air with an oxygen concentration of about 10%) is extracted from the bottom of the lower column C and introduced into the upper column at a position slightly above the center through a conduit. In the upper column, gaseous oxygen generated by heat exchange with the condenser at the top of the lower column rises in the column together with rising gas, liquid air introduced from the lower column C, and liquid introduced as reflux liquid. Rectification is carried out in countercurrent contact with the rising gas on the tray due to the flow of nitrogen. Highly purified nitrogen is thus obtained from the top of the upper column and taken out through the conduit, and impure nitrogen is taken out through the conduit lO from a position slightly lower than the top. Also, high purity oxygen is obtained from the bottom and taken out through a conduit. Further, the sialbone-containing gas is withdrawn from a side cut stage at an appropriate position in the center of the upper column and introduced into the crude argon column F via conduit D.

In the air separation apparatus of the present invention, an upper air flow meter I and a Ratzmann flow meter I# are provided, and their respective signals are input into a computer, which constitutes a control system as shown in FIG. In other words, the pressure control system (
pctot).

Each flow control system (FCIOJ, FCIOJ, FCI
OJ), an operating condition setting system which is determined by taking into account material balance and heat balance from the operating state of the process, and an upper tower liquid level control system CLC201), and each control system works as follows.

The upper column pressure control system uses PID control to adjust the opening degree of a control valve r provided in a conduit io from which impure nitrogen gas is extracted so as to maintain the pressure in the upper column at a predetermined value. The flow rate control system operates the control valves H and H' using PID control under the given set value.
, H'' to adjust the flow rate.The operating condition setting system performs a so-called feedforward calculation that provides appropriate operating conditions obtained from the product demand and the heat balance of the air separation device.For example, when cold generation occurs, An appropriate setting value X for the flow rate of the expansion turbine, which is the engine, is obtained from the heat balance and is expressed by equation (1).

X-A, XAIR1A, XLO+A3XLA+A, XL
N... (1) However, AIR: Raw material air flow rate LO: Liquid oxygen generation amount LA: Liquid argon generation amount LN: Liquid nitrogen generation amount AI * A1 t A3 e A4: Coefficient However, based on equation (1) The calculated expansion turbine flow rate does not necessarily accurately maintain the heat balance in the air separation device, and the error appears as a fluctuation in the liquid level of liquid oxygen at the bottom of the upper column. Therefore,
In the liquid level control system, a liquid level controller (a geared PID controller) operates as a feedback element to compensate for errors in the feedforward calculation described above so as to maintain the liquid level within a certain range. In other words, the output of the liquid level controller is.

The value calculated from the operating condition setting system is added to the expansion turbine flow rate to provide a set value for the expansion turbine flow rate. ((
(2) formula) Also, the output of the liquid level controller is the raw material air flow rate.

For the Ratschmann flow rate, the respective set values are the sum of the coefficients in the output of the operating condition setting system and liquid level controller multiplied by , K, and the like.

(Formula (3), (4)) % formula % (2) However, Sv: Set value Mv: Output value X: Expansion turbine flow rate given by the operating condition setting system Y: Raw material air flow rate 2
: Ratschmann flow rate Here, K1, K are the raw material air flow rates at the output of the liquid level controller,
It is a weighted gain for the Rathman flow rate.

That is, when the expansion turbine flow rate changes by ΔE due to the liquid level control as a result of the liquid level change, the amount of change in the feed air flow rate and the Ratzmann flow rate are given by equations (5) and (6), respectively.

ΔA −ΔB X K, −・−−−−
...(51△R-ΔEXK, ...
Song・(6) Here, in order to operate the rectification tower stably.

For the gain, K2 is preferably set to a predetermined value within the range of 0.6≦1≦80, 0.0≦2≦O, and so on.

〔Example〕

The mode of control of the air separation apparatus of the present invention will be explained using FIGS. 3 to 7. 3rd~! In the figure, the symbol a is the liquid level in the upper column of the rectification column, b is the oxygen concentration in the argon-containing gas supplied from the intermediate stage of the upper column of the rectification column to the crude argon column via conduit 9, C is the flow rate of the expansion turbine, and d is the flow rate of the expansion turbine. The raw air flow rate, e, means the Ratschmann flow rate. The liquid level controller G employs a geared PID controller that sets a predetermined gap width to a target value of the liquid level and performs PID control when the liquid level exceeds the predetermined value. FIG. 3 is a trend diagram when only the expansion turbine flow rate is used as the manipulated variable with respect to upper tower liquid level fluctuations, that is, when 1=0 and K=0 in the present invention.

When the upper tower liquid level exceeds the lower limit, the expansion turbine flow rate increases accordingly, but the feed air flow rate and the Ratzmann flow rate remain constant. At this time, the rectification state in the upper column is disturbed and the oxygen concentration in the argon-containing gas tends to decrease. Recovery of the upper tower liquid level is also slow. FIG. q is a trend diagram when the expansion turbine flow rate and the raw material air flow rate are the manipulated variables and the amount of change in both manipulated variables is equal, that is, when = / and K2 = 0 in the present invention. When the liquid level exceeds the lower limit of the set value, the expansion turbine flow rate and feed air flow rate increase by the same amount, but the Lachman flow rate remains constant. At this time, the oxygen concentration in the argon-containing gas tends to increase. FIG. 5 is a trend diagram when the present invention is applied, that is, when the expansion turbine flow rate, the feed air flow rate, and the Lachman flow rate are adjusted at a certain ratio (K = 0.9, 2-0.k). . The upper tower liquid level is maintained within a predetermined value in a responsive manner without disturbing the oxygen concentration in the argon-containing gas.

6. The symbol f in the diagram is an indicator of nitrogen demand,
g is the flow rate of nitrogen generated from the rectification column, h is the amount of impure nitrogen extracted, 1 is the upper column pressure, and J is the nitrogen concentration in the argon-containing gas. FIG. 6 is a trend diagram when the amount of extracted impure nitrogen is not adjusted. That is, when the demand for nitrogen increases, since the amount of impure nitrogen extracted is constant, the pressure in the upper tower decreases, and therefore the nitrogen concentration in the argon-containing gas increases. FIG. 7 is a trend diagram when the present invention is applied, that is, when the amount of extracted impure nitrogen is adjusted so as to maintain the pressure in the upper column at a predetermined value. When nitrogen demand increases, the amount of impure nitrogen removed decreases to maintain the upper tower pressure at a predetermined value, and the amount of nitrogen generated increases as the demand increases, so the nitrogen concentration in the argon-containing gas remains constant. It does not change.

〔Effect of the invention〕

According to the present invention, in an air separation device that extracts oxygen, nitrogen, and argon by cryogenically separating feed air, the balance of the rectification column is not disturbed.

In other words, the pressure in the upper column is automatically maintained at a predetermined value and a predetermined amount of nitrogen is supplied without adversely affecting the purity of the product, especially the concentration of the argon-containing gas extracted from the upper column of the rectification column and supplied to the crude argon column. This makes it possible to maintain the liquid oxygen level in the upper column within a predetermined value.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an air separation device, FIG. 2 is a system diagram of a control mechanism of the present invention, and FIGS. 3 to 7 are diagrams showing control examples. A: Air compressor B: Reversible heat exchanger C: Lower column of rectification column D: Upper column of rectification column! =Flow rate detector
J: Pressure detector a: Liquid level in the upper column of the rectification column b: Oxygen concentration in the crude argon column feed gas C: Expansion turbine flow rate d: Raw material air flow rate e Niratubaman flow rate f: Index indicating the amount of nitrogen demanded g: Flow rate of nitrogen generated from the rectification tower h: Amount of impure nitrogen extracted l: Upper tower pressure j: Nitrogen concentration chart in the feed gas of the crude argon tower ni・reconciliation・so- vote 1・mB-connection porridge

Claims (1)

[Claims] In an air separation device that compresses and cools feed air and rectifies it in a double rectification column to extract oxygen, nitrogen, and argon, a predetermined amount of product nitrogen is extracted from the top of the upper column of the double rectification column, and The pressure is detected and the amount of impure nitrogen gas extracted from the top of the upper column is automatically adjusted to maintain the pressure constant, while the liquid oxygen level at the bottom of the upper column of the rectification column is detected and the A method for controlling the operation of a rectification column in an air separation device, characterized in that the flow rate of an expansion turbine, the flow rate of feed air, and the flow rate of Ratschman are automatically adjusted according to a predetermined control law so as to maintain the liquid level within a predetermined value.