SU1414842A1 - Device for automatic control of hydrocarbon dehydrogenation process - Google Patents

Abstract

The invention relates to devices for the automatic control of hydrocarbon dehydrogenation processes occurring in fixed bed reactors, nat as an example in an oxidative de- process; hydrogenation of n-butylenes to davinyl, and can be used in the chemical and petrochemical industry in automating the processes of producing monomers. The aim of the invention is to increase the yield of the target product and reduce the specific steam consumption. The device contains a sensor (D) 1 and a temperature controller (P) 3 above the catalyst bed, D 8 steam consumption, D 15 and P 13 steam temperature at the outlet of the furnace, logic unit 18, which, depending on the readings D 1 and D 15, changes The fuel supply to the kiln is corrected by reading D 8. Another control loop contains D 21, 22, 23 in the catalyst bed, connected through the maximum temperature finder 20 to P 24, which affects the steam supply to the kiln. The task P 24 is formed depending on the standard deviation of the current maximum temperature from the specified value and the maximum allowable temperature. 1 hp f-ly. 2 or 3 table. ABOUT)

Description

Cb / fliie

 00 j; to

Nantes, gas Figure 1

The invention relates to devices for the automatic control of hydrocarbon dehydrogenation processes occurring in fixed bed reactors, for example, in the oxidative dehydrogenation of n-butylenes to divinyl, and can be used in the chemical and petrochemical industry in automating the production of monomers.

The purpose of the invention is to increase the yield of the target product and reduce the specific steam consumption.

FIG. 1 shows a block diagram of an I device; FIG. 2 is a block diagram I of a logic unit.

:

I The device contains a temperature sensor 1 over the catalyst bed, an oxidative dehydrogenation reactor 2 jn-butylenes to divinyl, a temperature controller 3 I above the catalyst bed, the first temperature setpoint 4 above the fuel; eMi key 5, memory 16, first adder 7, steam consumption sensor 8, steam superheating furnace 9, second adder 10, first block 11; delays, amplifier 12, steam temperature regulator 13 at the furnace exit, actuator 14 on the fuel gas supply line to the furnace, sensor

15 the temperature of the steam at the outlet of the furnace,; the first comparator 16, the second block 17

delays, logic unit 18, second comparator 19, maximum temperature finder 20 in the catalyst bed, temperature sensors 21-23 in the catalyst bed, maximum temperature controller 24 in the catalyst bed, calculating unit 25, counter 26, timer 27, second setpoint 28 of temperature in the catalyst bed, switch 29 third adder 30, fourth adder 31, inverter 32, third comparator 33, third setpoint 34 of the maximum allowable maximum temperature in the catalyst bed and actuator 35 for supplying steam to the furnace.

Logic unit 18 consists of AND 36 elements connected in parallel and the element OR NOT 37 (Fig. 2). Element 36 produces the output signal Y1 according to the scheme presented in Table 1 (XI and X2 are output signals of the first

16 and second 19 comparators, respectively).

Table 1

Element 37 produces an output signal Y2 according to the scheme presented in Table. 2

table 2

one

1 o

About 1

ABOUT

one

ABOUT

about

about about 1

25

thirty

five

0 | 5 0

t

By parallel connection of elements 36 and 37, the formation of a summed output signal Y is achieved in accordance with Table. 3

 The device is implemented on standard elements of the GPS system and microprocessor technology.

The device works as follows.

The signal from sensor 1 of temperature T above the catalyst bed in reactor 2 enters regulator 3, where it is compared with the set value from the first unit 4 of temperature T .. Regulator 3 in accordance with the PI of the control signal produces a control signal ..

The signal and through the key 5 and the storage device 6 is supplied to one of the inputs of the first sum. TOR 7, The signal from the steam consumption sensor 8 to the furnace 9 Gf, j is fed to one of the outputs of the second adder 10 and to the input of the first delay block 11, which inverts the input signal and outputs it to the other. The second input of the second adder with a time delay fB signal

C-Ghj.i).

The output signal of the second adder 10, having passed through the amplifier 12, is fed to the second input of the first adder 7 as a signal,

55

and.

Кз (С hi - G 4-1)

(i;

where is kj

gain of amplifier 12;

i - discrete points in time

with period S

The signals C, and Uj arrive at the inputs of the first adder 7, which forms the task of the regulator 13 of the steam temperature from the furnace 9 according to the formula

/

and

and, +

C.

The steam temperature regulator 13, in accordance with the PI-law of regulation, generates a control action on the actuator 1A on the fuel gas supply line to the furnace 9 "The signal from the steam temperature sensor 15 from the 9 T furnace is fed to the input of the Variable Regulator 13 temperature.pair, .to the first input of the first comparator 16 and to the input of the second delay block 17, which, at the second input of the comparator 16,

T signal

Ml-1

equal to the input with a time delay D. The first comparator 16 compares the values of the input signals T „; and T., and gives the result of the comparison in the form of a two-level logical signal of the gigantic unit 18 according to the condition

X. at the first entrance loH, O, with Tn, Tpj.,.; X, 1, at T ,, T j.,

(3)

The inputs of the second comparator 19

are coming

T signals

sensor 4 and temperature sensor 1 above the catalyst bed. As a result of comparing these signals, the comparator 19 generates a two-level logic signal X, which arrives at the second input of the logic unit 18, according to the condition

there is no need to change from the first catalyst

setting the steam temperature controller to 13 - this can lead to an increase in the mismatch and the time of the transition process in the channel.

Q FUEL gas - temperature | atura over the catalyst bed. The mismatch of the signals at the inputs of the logic unit 18 indicates that the flow rate of the fuel gas is the temperature PA

Xi Oh, with TTR ,,.; X2 1, at Ts.

(four)

Logic block 18 generates a decoded signal Y according to the scheme presented in Table 3.

Table 3

ten

Logic block 18 analyzes four possible situations:

a) steam temperature decreases

and the temperature above the catalyst bed is lower than the preset one;

b) the steam temperature increases and the temperature above the catalyst bed is higher than the desired one;

c) the temperature of the steam rises and the temperature above the catalyst bed is lower than the set one;

d) the steam temperature decreases and the temperature above the catalyst bed

1g above the target.

In cases a) and 6J, when the output signals of the comparators 16 and 9 X and X coincide, in order to eliminate the mismatch between the current and the set temperature above the catalyst bed, it is necessary to change the steam controller 13 to the appropriate direction. In this case, the logic unit 18 generates a control output

20

25

Y signal

the closing key, the cathode passes to the input of the first adder 7 through the storage device 6, which serves to memorize the last identified effect U (, controlling 2Q signal from the temperature regulator 3 above the catalyst bed.

In cases c) and d) to eliminate the mismatch between the current and the set temperature above the bed, control the steam temperature controller 13 - this can lead to an increase in the discrepancy and the time of the transition process in the channel.

Q FUEL gas - temperature | atura over the catalyst bed. The mismatch of the signals at the inputs of the logic unit 18 indicates that the flow rate of the fuel gas — the temperature pag pa received a disturbance and is processed by the regulator 13, / or did not have time to work out due to the delay of the previous control action U arriving at the input controller 13. In this case, the logic unit 18 generates the output signal Y 0, which opens the key 5. At the input of the adder 7, the former value of the control signal of the regulator 3 stored in the memory 6 remains.

This interaction of blocks 1-19 is aimed at reducing the negative impact on the quality of regulation

0

five

514

channel inertia Consumption of fuel gas — temperature above the catalyst bed by compensating for changes in the flow rate of the heat carrier (steam) by its temperature and taking into account 16-16 channel delay in the channel Steam temperature — temperature above the catalyst bed.

The latter is necessary in cases where the perturbation time (for example, a change in the composition or pressure of the fuel) is commensurate with or less than the net lag time in the channel. The vapor temperature is the temperature above the canalizer layer.

Next, the searcher 20 is the maximum temperature in the catalyst bed of the reactor 2 according to the signals from the sensors 21-23. temperature determines the maximum temperature T and sends it as a variable to the input of the maximum temperature controller 24. Task T | controller 24 is determined from the conditions:

T | Tust if TVCT + (5) TJ Tusg-36, if Tusg Zb7Tmchks, C6)

where TL-JCT is a task for T set from technological considerations, produced by the second unit 25 of the maximum temperature in the bed;

TMCIKC maximum permissible value Tj, after which thermal destruction of the catalyst occurs; & - the standard deviation of the temperature Tj. from given value T | for a certain period of time.

 The standard deviation of the controlled variable is calculated automatically by the computing unit 25 from the current measurements T | and Tj according to the formula

Jn (TK -T 2 te: -l. P-1

(7)

where n is an integer number of time points for which the dispersion is calculated, for example, 30, when the device is discretely 1 time per minute, Discrete time points are n drip

are in counter 26 and fed in

8426

also in computational unit 25. Counter 26 operates from timer 27. The output signal of computational unit is set to three times the value of the calculated standard deviation 36.

The output signal Tu, .- of the second temperature sensor 28 is supplied to

0 the first input to; the switch 29, to one of the inputs of the third adder 30 and to one of the inputs of the fourth adder 31. To the other input of the third adder 30 through the inverter 32 enters

5 the triple value of the standard deviation of the temperature control in the layer with the opposite sign (-Зй).

The input signals T УСТ, and (-36) are summed by the third adder 30 and arrive at the second input of the switch 29. The other input of the fourth adder 31 receives the triple value of the standard deviation of the temperature control in the layer 3. The input

5 signals 3.6. Are summed up by four. the adder 31 and go to one of the inputs of the third comparator. 33, to the other input of which from the third master 34 is fed the maximum

0 permissible maximum temperature in the catalyst bed; Comparator 33 compares the input signal values (T + 36) and Tddax and compares the result as a two-level logic signal Z fed to the control input of the switch 29, through which to the Input of the maximum temperature controller 24 in the catalyst bed, the signal T | in accordance with conditions (5) and (b).

The choice of the task to the controller 24 in accordance with the foregoing allows minimizing the probability of violations of the technological regime under the action of various disturbances on the temperature

reactor mode 2. Regulator is 24 to so1. . In accordance with the PI law of regulation

generates a control action, 50 supplied to the actuator 35 on the steam flow line to the furnace 9. Changes in steam flow to the reactor

2 changes the rate of reaction in the catalyst bed and the amount of the substance,

55 heat, and therefore the temperature in the layer. Reducing steam consumption leads to an increase in temperature T and vice versa, an increase in steam consumption reduces the temperature T.

35

40

45

Thus, the proposed automatic control device makes it possible to improve the quality of regulation of the most important technological parameters of the process and its efficiency as a whole due to more accurate suspension of the regulated technological mode. The increase in the efficiency of the process (for example, the production of divinyl) is expressed in terms of an increase in the yields of the target product to the missed and decomposed raw materials by 0.1% and a decrease in the specific steam consumption by 0.05 Gcal / t.

Formula of the invention

Claims (2)

1. An apparatus for automatically controlling the process of hydrocarbons dehydrogenation, comprising a series-connected sensor, a steam temperature controller at the furnace outlet, and an actuator for feeding fuel to the furnace, a sensor series-connected and. temperature controller above the catalyst bed of the reactor, temperature sensors in the catalyst bed of the reactor, connected to the maximum temperature of the seeker inputs, steam flow sensor in the furnace, furnace, steam supply actuator and computational unit, characterized in that increase the yield of the target product and reduce: specific steam consumption, it additionally contains a four-way adder, three temperature controllers, two delay units, three comparators, an inverter, a switch, a counter, a timer, a logic unit, an amplifier, a switch, a memory device, a maximum temperature controller in the catalyst bed of the reactor; the storage device is connected via its key with the output of the temperature controller above the catalyst bed, and the output to one of the inputs of the first adder, the other input through the amplifier is connected to the output of the second adder, connected by one input to the steam flow sensor, and the other to the same sensor. connected to the input Setting the steam temperature regulator at the furnace output, the first input of the computing unit through the counter is connected to the timer output, the finder's output — the maximum temperature is connected in parallel to the second input of the computing unit and to the input. The variable of the maximum temperature controller connected with its output the steam supply mechanism to the furnace, the output of the switch is parallel-connected to the input Setting the maximum temperature controller and the third input of the computing unit, the output of which is parallel to the first input of the fourth sum1-1ator and through the inverter to the first input of the third adder, the output of the second temperature setter is connected in parallel to the second inputs of the third and fourth adders and the first input of the comparator connected by its second input to the output of the third adder, and the third input to the output the third comparator, the first input of which is connected with the output of the third setter, and the second input - with the output of the fourth adder, the sensor for the temperature of steam at the outlet of the furnace is connected in parallel to the first the input of the first comparator and through the second delay unit to its second input, the output of the first setter parallel to cor is single with the input of the temperature controller above the catalyst bed of the reactor and with the first input of the second comparator connected by its second input to the temperature sensor above the catalyst bed of the reactor, and the output to the first input of the logic block Kaj whose second input is connected to the output of the first comparator, and the output of the logic unit is connected to the control input of the key. 2. The device according to claim 1, characterized in that the logic unit contains the elements AND and RSHI-NOT, the first inputs of which are connected to the output of the first comparator, the second inputs - with the output of the second comparator, and the outputs of the elements AND and OR-NOT connected to the control key input. OfnJ6 36 FIG. I From 19