RU1810727C - Method for automatic control of rectification process in air - distributing plant - Google Patents

Abstract

Usage: cryogenic technique, in particular the control of the rectification process in air distribution plants. SUMMARY OF THE INVENTION: Automatic control is carried out by stabilizing the concentrations of dirty and pure nitrogen reflux and the pressure in the upper column. Information on the concentration of production gaseous pure nitrogen, dirty and pure nitrogen reflux is used to generate correction signals of the vapor pressure stabilization system in the column, which allows to increase the accuracy of regulation of the rectification process. 3 ill. ate with

Description

The invention relates to the management of distillation columns and can be used, for example, in cryogenic technology.

The purpose of the invention is to increase the accuracy of the regulation of the rectification process and to obtain a gaseous production pure nitrogen of the required concentration.

The proposed method for automatically controlling the rectification process in an air separation unit is carried out using the device shown in FIG. 1; in FIG. Figure 2 shows a graphical dependence of the concentration of production nitrogen on the consumption of waste nitrogen with a change in the concentration of pure nitrogen reflux: Fig. 3 shows the same dependence YA f (VOA) with a change in the concentration of dirty nitrogen reflux.

The device contains a lower distillation column NRK1, an upper distillation column VRK2 with lines of side flows of dirty and pure nitrogen reflux, gaseous production nitrogen, waste nitrogen and production oxygen, a condenser-evaporator 3, built between NRK1 and VRK2. subcooler 4, actuators 5, 6, 7, 8, 9, level sensor 10. oxygen concentration sensors 11, 12,13, 14, pressure sensor 15, regulators 16, 17, 18. 19, 20, corrective regulators 21 .22, 23, delay elements 24, 25 and adder 26.

In the lines of the side flows of bottoms liquid, dirty and pure nitrogen reflux, the executive bodies 5, 6, 7, respectively, with regulators 16.17 connected to them, are installed. 18. Sensors

00

about VI to VI

the oxygen concentrations 11 and 12 are set in dirty and pure nitrogen reflux lines and are connected to the regulators 17 and 18, respectively, while in the circuit between the sensor 11 and the regulator 17, a co-regulating regulator 21 is connected through the delay element 24, and in the circuit between the sensor 12 and the regulator 18 - through the delay element 25 the correction regulator 22 is turned on. The production nitrogen concentration sensor 14 is installed at the outlet of the upper part of the BPK2 and connected to the correction regulator 23, and the vapor pressure sensor 15 is installed at the level of the rejection line - nitrogen in VRK2 and is connected to the regulator 20, to which the correcting regulators 21, 22, and 23 are connected via the adder 26. The regulator 20 is connected to the executive body 9 in the waste nitrogen withdrawal line. The bottoms liquid level sensor 10 is connected through the regulator 16 to the actuator 5, and the oxygen concentration sensor 13 installed in the condenser-evaporator 3 is connected to the regulator 19 connected to the actuator 8 in the production oxygen extraction line.

The distillation process and its regulation are carried out as follows: air under pressure is supplied to the lower distillation column 1, in which it is subjected to preliminary separation, as a result of which bottoms and nitrogen reflux are formed in the column. The bottom liquid is sent through a subcooler 4 to the middle of the upper distillation column 2, and its flow rate is regulated in accordance with the change in the liquid level in the bottom column 1 cube (see Fig. 1, actuator 5, regulator 16, sensor 10).

In the process of distillation, the upper column 2 is irrigated by using a stream of pure nitrogen reflux generated in the condenser-evaporator 3 cooled in a subcooler 4 and a side stream of dirty nitrogen reflux from the middle of column 1. Pure nitrogen reflux is supplied through an actuator 7 to the top of the column 2, and the lateral flow of nitrogen reflux is to the level of waste nitrogen withdrawal through the actuator 6. When air is separated, pure gas production nitrogen and liquid production oxygen are obtained, d which is carried out from the upper portion of the column 2 and from kondensatora- evaporator 3, and a production rate of oxygen is controlled depending on variations of its concentration, for which purpose

they use an actuator 8, a regulator 1.9, and an oxygen concentration sensor 13 installed in a condenser-evaporator 3.

The proposed method for controlling the rectification process in an air separation unit is implemented as follows. Under the influence of disturbing influences, a violation of the regime occurs.

the operation of the installation, which can lead to a decrease in the quality of the final products. To maintain the set parameters of production nitrogen, oxygen, respectively, the nitrogen concentration in the side flows of dirty and pure nitrogen reflux is measured by the corresponding oxygen concentration sensors 11 and 12. If the concentration of nitrogen in the side stream of dirty phlegm deviates from the set value, its flow rate is changed in the upper column 2 so that the desired value is restored, in addition, when the current value of the nitrogen concentration in pure nitrogen deviates from the set value, they change

its flow rate before recovery given value. The irrigation regime of the upper column 2 is regulated using the regulators 17 and 18, which act on the executive bodies 6 and 7, respectively, which change the flow rate of dirty and pure nitrogen reflux,

However, the process of stabilizing the nitrogen concentration in the clean and side stream of the dirty nitrogen reflux is inertial,

5, compensation of external disturbances occurs slowly, and during this time, the concentration of pure gaseous production nitrogen from the norm may deviate. It is also known that an increase in the oxygen concentration in these streams is associated with a decrease in the steam flow rate in the NRC and, consequently, the need to reduce the steam flow rate in the NRC. Moreover, a spontaneous change in steam flow

5 is not enough, additional regulation is needed. Therefore, the vapor pressure in the upper column 2 is measured at the level of waste nitrogen by the pressure sensor 15, and then the flow rate of the waste is regulated

0 nitrogen through the actuator 9, so that the preset pressure value set in the regulator 20 is restored. Restoring the operating mode in the overhead distillation column 2 is accompanied by a transient process during which it is necessary to take into account dynamic relationships between the control actions, which can also degrade the concentration of end products. Therefore, in the proposed method, the current value of the oxygen concentration in the production nitrogen is constantly measured and the value of the stabilized pressure setting is corrected depending on the mismatch signals of the current and the set values of the production nitrogen concentration, side stream of dirty nitrogen reflux and pure nitrogen reflux, and the control effect of the concentration of pure nitrogen reflux formed in the correcting regulator 22, is shifted in time by the value of An, which is set by the delay element and 25, choosing its value equal

DP Hz -tz1,

where Hz is the channel delay time of the concentration of pure nitrogen reflux and gaseous production pure nitrogen; Tz1 is the channel delay time of the waste nitrogen flow rate and the concentration of production nitrogen.

The control action of the concentration of the lateral flow of dirty nitrogen reflux, formed in the correcting regulator 21, is shifted in time by the value of Дт2, which is set by the delay element 24, choosing its value equal to

DT2 G21 -G31,

where G21 is the channel delay time of the side stream concentration of nitrogen reflux and the concentration of gaseous production pure nitrogen.

The control action on the concentration of pure gaseous production nitrogen is formed by the correcting regulator 23 in accordance with the signal from the oxygen concentration sensor in the production nitrogen 14. Electric signals corresponding to control actions previously biased in time are sent to the adder 26, while compensating thereby the inertia of the control circuits, which have different delay times. After the operation of algebraic summation, the final command signal is fed to the controller 20, which acts on the executive body 9. Thus, with the help of Дл and Дг2 they compensate for the inertia of the control system, which provides a significant reduction in the transition process time and increases the accuracy of regulation of the process of stabilization of the concentration products.

A device that implements a method for automatically adjusting the rectification process (described earlier in the statics) works as follows. Electrical signals from oxygen concentration sensors 11, 12 and 14 are respectively supplied to a regulator 17, an additionally introduced regulator 18 and a correcting regulator 23, in which control signals are generated when the value of the guessed nitrogen concentration deviates. These signals

5 come from the regulators 17 and additionally 18 respectively to the executive bodies 6 and 7, which change the flow rates of nitrogen reflux in BPK2 until it is established in the regulators 17 and 18

0 given value of concentration. An electrical signal from pressure sensor 15 is supplied to a regulator 20, which, when the pressure value deviates from the reference, generates a control signal supplied to the actuator 9, which changes the waste nitrogen flow rate until the set pressure value is restored. Thus, the regulator 20 controls the vapor pressure in the WRC 2. regulator

0 17 stabilizes the nitrogen concentration in the side stream of dirty nitrogen reflux, and the additionally introduced, according to the claimed device, regulator 18 stabilizes the nitrogen concentration in the side

5 flow of pure nitrogen reflux at the entrance to the WRC 2. The interaction of these regulatory circuits compensates for the significant inertia of the control object.

In order to coordinate the time of transients in the control system, according to the claimed device, corrective circuits operating in this way are introduced. The signal from the oxygen concentration sensor 11 through the delay element 24

5 is fed to the input of the correcting controller 21, in which, when the specified voltage value is exceeded, a mismatch signal is generated proportional to the deviation of the current concentration

0 nitrogen in dirty nitrogen reflux. In correction adjuster 22, a mismatch signal is generated similarly proportional to the deviation of the nitrogen concentration in pure nitrogen reflux. These signals are delayed for a predetermined time and arrive at the adder 26 simultaneously with the error signal from the correction controller 23, to which the electric signal of the oxygen concentration sensor in the production nitrogen 14 is supplied.

in the adder 26, the electrical mismatch signals are added algebraically and the resulting electrical signal is fed to the input of the controller 20, which generates a control action on the actuator 9, which changes the flow rate of the waste nitrogen from the WRC 2.

Thus, taking dynamic relationships between different control actions into account allows eliminating the destabilizing effect of disturbances in transient conditions during operation of the air separation unit.

The relationship between the adjustable parameters and the regulatory actions is shown in FIG. 2, 3, which shows the dependence of the concentration of pure nitrogen YA on the consumption of waste nitrogen VOA when changing the concentration of pure nitrogen phlegm Hfl 4 as a parameter (see Fig. 2) and the concentration of dirty nitrogen reflux Hflg (Fig. 3).

Using the proposed method maintains a predetermined concentration of production gaseous pure nitrogen due to the introduction of anticipatory actions, which allows to increase the accuracy of automatic control of the rectification process.

Claims (1)

The claims A method for automatically controlling the rectification process in an air separation unit by measuring the concentration of the side stream of dirty nitrogen reflux and changing this concentration by exposing the stream to the top distillation column, characterized in that, in order to increasing the accuracy of regulation of the rectification process and obtaining gaseous production pure nitrogen, the required concentration, in addition measure the current value of the concentration of production gaseous pure nitrogen, the concentration of the side stream of pure nitrogen reflux and the vapor pressure in the upper distillation column, stabilize the concentration of pure nitrogen reflux, acting on its flow rate to the upper distillation column, stabilizes the vapor pressure in this column, affecting the flow rate of waste nitrogen, and the value of the vapor pressure setting is adjusted depending on the mismatch signals of the current and preset values of the concentration of gaseous production pure nitrogen, side flows gr and clean nitrogen reflux, while the effect of the concentration of the side stream of pure nitrogen phlegm is shifted by the value of Dgm TC - Gz1, and the effect of the concentration of the side stream of dirty nitrogen phlegm is shifted by LT2 G21 - G31; where Hz is the delay time along the concentration channel of pure nitrogen reflux and gaseous production pure nitrogen; G31 — delay time along the channel for the flow of waste nitrogen and the concentration of gaseous production pure nitrogen;  G21 is the time lag along the concentration channel of the side stream of dirty nitrogen reflux and the concentration of gaseous production pure nitrogen. about 6 Fie. 2 8 10 Upl-103 ol Vqa vac Editor Tehred M. Morgenthal Proofreader N.Korol Order 1438 Mintage Subscription VNIIIPI of the State Committee for Inventions and Discoveries under the USSR SCST 113035, Moscow, Zh-35. Rauska nab .. 4/5 Production and Publishing Plant Patent, Uzhhorod, 101 Gagarin St.