SU1527156A1 - Method of controlling ammonia synthesis process - Google Patents

Abstract

The invention relates to the control of chemical processes, can be used in the industry for the production of mineral fertilizers and in the chemical industry in the production of ammonia and allows to increase the productivity of the process by improving the accuracy of controlling the composition of the circulation mixture. The control method is based on controlling the composition of the circulating mixture at the inlet of the ammonia synthesis column by changing the air supply to the second stage methane converter, taking into account the restrictions imposed on the maximum temperature value of the converted gas at the second stage methane converter output and on the maximum and minimum air values. 1 il.

Description

The invention relates to the field of controlling chemical processes. And it can be used in the mineral fertilizer industry and in the chemical industry in the production of ammonia.

The purpose of the invention is to increase the productivity of the process by increasing the accuracy of controlling the composition of the circulation mixture.

The drawing shows a system that implements the proposed method.

The control system and flowchart contain a first stage converter 1, a second stage converter 2, a synthesis column 3, a natural gas flow meter 4, a gas supply valve 5, a first regulator 6, a first setting device 7, a meter 8 for feeding air, a second regulator 9 , air supply valve 10, gas temperature meter 11 after the second stage converter, first, second, third, fourth, fifth and sixth threshold elements 12-17, first and second elements J8 and 19 coincidence, divider 20, first and second limiters 21 and 22, the third controller 23, the second unit 24, the functional unit 25 and the gauge 26 are the ratio between hydrogen and nitrogen.

The method is carried out as follows.

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Meter 4 is designed to measure the flow of natural gas. The first regulator 6 is designed to maintain a predetermined gas flow rate and may have a PID structure. The first setpoint 7 is designed to memorize the job of the SG on the flow rate of gas and gas introduced into the controller 6. The meter 8 is designed to form the air flow rate F. The second regulator 9 is designed to maintain the required air flow and may have a PID structure.

Valve 10 is designed to change the air supply. The meter 11 is designed to determine the temperature t of the gas after the second stage converter and can be implemented on the basis of a sensor with a thermocouple.

The first and second threshold elements 12 and 13 are designed to carry out inspections and, where B p is the first and second set points For air flow. When these conditions are met, signals are received at the two inputs of the coincidence element 18. The third threshold element 14 is designed to test, where B is the second temperature limit value after the second stage converter. When this condition is met, a signal is sent to the third input of element 18.

The fourth, fifth, and sixth threshold elements 15-17 are intended to carry out checks, respectively, where H and B are restrictions on the allowable air flow (,), B is the first temperature limit value after the second stage converter (B 7 V).

When the condition is fulfilled, the element 15 outputs the signal L to the first inputs of the limiters 21 and 22. When the conditions checked by the elements are fulfilled. 16 and 17, signals are received at the inputs of the second matching element 19.

The first coincidence element 18 CGD is assigned to generate an output signal f when signals are received at all its three inputs.

The second coincidence element 19 is intended to generate an output signal G when signals are received at all its two inputs.

The divider 20 is designed to determine the task 3 F controller 9

15 20

s - and 25 a jq, q

ds.

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dividing the value of the gas setting 3F by the value of i. A change in the value of ft leads to a change in

ZG

5 air supply since

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55

L

The first limiter 21 is designed to correct the setpoint of the regulator 9 depending on the signals L and G. If the input to the limiter 21 receives a signal to reduce air flow () and the signal L does not, it is accepted if a signal comes to increase air flow () and the G signal is not present, it is accepted. In the remaining cases, the signal as specified by the controller 9 does not change.

The second limiter 22 is intended to adjust the control on and. If 4 V O and there is no G signal, it is accepted. If there is no signal L, it is accepted. In the remaining cases, the control according to Ji does not change.

The third regulator 23 is designed to form a control by the magnitude of ft based on the condition of regulating the ratio between hydrogen and nitrogen relative to the reference entered into this regulator. The parameters of the regulator may vary in accordance with the change in the gas flow rate reference, for example, in a linear relationship. The second setpoint device 24 is intended for storing a predetermined value of p, and specifying ft by the value of the corresponding control.

The functional block is designed to determine the corrected value of the value of ip, multiply 4/3 by the K coefficient and then change d / 1 by the compensation value

At the same time (К-Р) а / 3, where, in the presence of a signal f, Р 1,

in other cases (K is the given coefficient, P is the compensation parameter),

Changes in the magnitude of the /) knots correspond to changes in the task of the discharge of the HEAVEN spirit, since 33F - - Zr

|

Since the adjusted change in air flow is

ZG

.th, then the corrected change in consumption will be. Therefore, the definition is adjusted to 5115271

l / 1 is adequate to multiplying the required change in air flow by a given coefficient K. One of the options for implementing block 25 can be the parallel connection of two chains in the first of which is a real differentiating link, the output of which is connected to

signal limiter, and in the second chain - amplifying link.

The operation of unit 25 can be somewhat improved if the amount of change in air flow during the control cycle is limited to the given maximum and minimum flow changes. For example: -N in | -Vd,, K - with

the presence of the signal f, in the remaining case x 1; )

at the same time,

where H and B are the specified allowable changes,

The meter 26 is designed to determine the value of the ratio between hydrogen and nitrogen in the synthesis cycle and can be implemented on the basis of an industrial chromatograph (gas analyzer).

Using the meter 26, the current value of the ratio between hydrogen and nitrogen is formed, which is fed to the input of the third regulator 23. With the help of the meter 11, the temperature value is formed after the second stage converter, which is fed to the inputs of the third and sixth threshold elements 14 and 17. With the help of the meter 8, the air flow value F is determined, which is fed to the input of the second controller, 9, to the inputs of the first, second, fourth and fifth threshold elements 12, 13, 15 and 16. Using the meter 4, the first controller 6 and the supply valve 5 ha for maintaining the gas supply equal to the task entered from the first setpoint 7; Using the first, second and third threshold elements 12-14 and the first coincidence element 18, generate a signal φ and feed the second input of the functional unit 25. With the help of the fifth and sixth the threshold elements 16 and 17 of the second element 19 coincidence produce a signal G and are fed to the second inputs of the limiters 21 and 22. With the help of the fourth

five

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five

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five

0

five

0

45

0

five

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the threshold element 15 generates a signal L and serves to the first inputs of the limiters 21 and 22. Using the third controller 23, they form a control by the value of the p-ratio of the tasks for the gas and air flow rates. Changes in the value of q correspond to changes in air flow due to the condition of controlling the composition of the mixture. With the help of the second limiter 22, the control over / s is corrected depending on the signals L and G. With the help of the functional block 25, first they give the corrected value of the control over / j, corresponding to the corrected change in air flow (K43F), then in accordance with the characteristic of the functional unit uf by the amount of compensation t, which causes a corresponding change in air flow / - (KP) - / 33F /.

If there is a limiter in the composition of the functional block, the control value in a number of cases after issuing the corrected control may be unchanged for some time. With the help of the second setter 24, the specified value of the value l is memorized. With the help of the divider 20, the reference to the controller 9 is determined, which is limited by the first limiter 21, and the controller 9 is outputted to the camera. The regulator 9 and the valve 10 are output to the camera. maintain air flow equal to task 3F.

There are various options for implementing the method. In particular, it is possible that the regulator directly changes the air flow, which is also corrected from the condition of the gas flow compensation. Then blocks 22, 24 and 20 are canceled.

Block 23 is connected to block 25, block 25 is connected to block 21. A compensator and an adder are introduced. The input of the compensator is connected to the output of block 7, and the output to the first input of the adder, to the second input of the adder, a signal is output from the block 21, and the output of the adder is connected to the controller's reference chamber. 9.

Thus, the magnitude of the air flow increase or decrease produced is adjusted, based on the condition that the quality of regulation is improved and in such a way that it does not lead to

/ 152716

emergency modes. In the case of the impossibility of such a correction for the object, the usual control is issued.

Claims (1)

The proposed method provides, in comparison with the known, higher quality control of the ammonia synthesis process, since it allows to increase the accuracy of controlling the composition of the mixture and prevent the occurrence of a number of pre-emergency modes. This leads to an increase in the stability of the process and an increase in its productivity. Invention Formula The method of controlling the ammonia synthesis process, including the regulation of the air supply to the second stage methane converter in relation to the specified flow rate of natural gas to the first stage methane converter, with correction for the composition of the circulation mixture at the inlet of the synthesis column, measurement and comparison of the current temperature value 15 eight - THOSE increase in process productivity by increasing the accuracy of controlling the composition of the circulation mixture, additionally compare the current temperature value of the converted Gas at the output of the second stage methane converter with the second limit value, with the current air flow rate being greater than the first and less than the second specified value and the current temperature value of the converted gas below the second limit value change the air supply, after a specified period of time change the air supply in against in the downstream direction, the current value of the air flow is compared with the upper and lower limit values, the direction of the change in the current value of the air flow is determined, with the current value of the air flow less than the lower limit value and the decrease of the converted gas at the air outlet current value air consumption is higher than the second stage upper methane graver with the first boundary value; comparing the current value of the air consumption with two given values, characterized in that, with a valuable value and an increase in the air consumption, air flow is stabilized at the current value. 0 71b6 five eight - THOSE increase in process productivity by increasing the accuracy of controlling the composition of the circulation mixture, additionally compare the current temperature value of the converted Gas at the output of the second stage methane converter with the second limit value, with the current air flow rate being greater than the first and less than the second specified value and the current temperature value of the converted gas below the second limit value change the air supply, after a specified period of time change the air supply in against in the downstream direction, the current value of the air flow is compared with the upper and lower limit values, the direction of the change in the current value of the air flow is determined, with the current value of the air flow less than the lower limit value and the increase in air flow stabilize the air flow at the current value.