Solution of the problems of non-stationarity processes in ethylene region of a chemical technological complex on processing the cracking and pyrolysis gases Текст научной статьи по специальности «Математика»

ISSN 2522-1841 (Online) ISSN 0005-2531 (Print)

AZERBAIJAN CHEMICAL JOURNAL № 3 2019

75

UDC 66.011/66.012:662.765

SOLUTION OF THE PROBLEMS OF NON-STATIONARITY PROCESSES IN ETHYLENE REGION OF A CHEMICAL TECHNOLOGICAL COMPLEX ON PROCESSING THE CRACKING AND PYROLYSIS GASES

I.I.Osmanova

M.Nagiyev Institute of Catalysis and Inorganic Chemistry [email protected] Received 14.03.2019

Dynamics of the processes in the greatest - ethylene region of chemical-technological complex has been studied, the functions taking into account non-stationarity of the processes has been chosen, their dynamic kinetic model were constructed, and on the basis of entire mathematical descriptions there have been decided the tasks of their optimal control. This in result enabled to fulfill the goal to be achieved -to maintain the optimum production capacity of the target products found out at optimization of chemical-technological complex for stationary conditions of their proceeding.

Keywords: non-stationarity, functions of deactivation, of control, productivity capacity, dynamics, catalyst, activity, block-flowsheet, cracking andpyrolysis gases.

https://doi.org/10.32737/0005-2531-2019-3-75-83

Introduction

To answer the Republics demands olefins obtained from cracking and pyrolysis gases from BNZ named after H.Aliyev and equipment EP-300 of Sumgait plant Ethylene-Polyethylene and their rational using in the Institute of Catalysis and Inorganic Chemistry, named after M.Nagiev, Azerbaijan National Academy of Sciences there have been developed the chemical-technological complex (CTC) on co-processing of these gases. Functioning of such CTC will permit to achieve the needed productivity capacity of the target products, the Republic demands, will minimum expenditures Calculation of the processes entering CTC has been made by mathematical models constructed for stationary conditions of their proceeding. However, the processes considered in CTC, both catalytic and non-catalytical, often take place in conditions of non-stationarity caused by various reasons [7]. Depending on conclusions of running the processes, change in their activity in time occurs differently decreasing reactors production activity, term of catalysts operation, selectivity of the process.

Our task consists in that data on optimal productivities capacity of the target products obtained at optimization of an entire CTC and meeting the Republics need in them, woaldut be destroyed because of possible non-stationarity of the processes. This can be provided by introducing into the kinetic models of stationary processes the

corresponding functions of non-stationarity, and on their basis to operate them by the entire mathematical models of the processes, each taken separately.

Fulfillment of work

Based on work done the article offers the flow sheet of these basic actions which were implemented for each process of the region for obtaining demanded results, namely:

1. design of a stoichiometric flowsheet of the process on the basis of experimental data;

2. working out the kinetic models of the process on the basis of stoichiometric flow sheet;

3. making up complete mathematical model of the process for stationary conditions on the basis of kinetic model and studying heat and hydrodynamic conditions in a reactor;

4. choice of the functions of process non-stationarity based on studying its reasons;

5. receiving dynamic mathematical model of the process;

6. working out algorithm of operating the process using non-stationary mathematical description;

7. obtaining results of operating the process in non-stationary conditions.

Below there are cited the results of the successive fulfillment of suggested scheme for the concrete processes of ethylene region in CTC. The regime parameters of the process and designations to them are offered in references corresponding to each process.

Pyrolysis of ethane [1, 2]

1. Stoichiometric scheme of the process

C2H6 <—- C2H4 + H2

C2H4 + 2H < - > 2CH4

C2H4 - > 1 C4H6 + 1C4H8 + 1C4H10 + 1H2 k 1

C2H4 —^H + H2

(1)

C2H4-^ C2H2 + H2

C2H4 ——■ 2C + 2H2

k 143 57 93

CH. + - —-CH +--CH +--H

2 4 2 6 150 3 6 150 3 8 150 2

C + HO ——— CO + H2

co+ho ———co+H

2. Stationary kinetic model

dn

CH,

d/

2H = -u

k1WCH + k7nc2H6 "c2H,, S «-(V KP1) «C2H4 «H2 W^^ S «

dn,

CH

d/

?H4 -1

24 = u n,

c,H 1 k1 «CH /nCH - (VKP1) "H PRTS «- k

n

//RT S «

(v KP2 y>

X("C2H4 /«C2H4 ) P/RT S « - k3 - k4 - k5 - k6 - k7 nCH pRTS '

dn

d/

^ = U-1

k1«C2H6 +(KlKp2 ) nC2H4PIRTS n

+ «

( kj Kp1) «H2 p/RT S «

- 2k

n

PI RT S n +1/8 k3 + k4 + k5 + 2k6 +(93150 ) k7«cH PRT Sn

+n

dnr

H,OP (k8«C + k9nC0 )/RT S «

d/

^ = 2k2 u-1

n

n

x 2 /- x 2

nJ -(1/Kp2)^nchSn

(2)

^ = (14)u-VchV "C^ =(18)uks«

d/

d/

dnr tt

1 I, ™ C4H10

-2H4 '

d/

= (V8)u~%nc2H4, ""chJ" = (V3)u~Vc2H4>

2

2

f \

dnc1nJdl — u~%nc2H4 ' dnc/dl — u 1 - k8nGnH2GZnt

V ! y

dnCÄ /d/ = (l43/l5O)w _lk. dn^ /d/ — (57/l5O)u 1k•

U ^^^ TT n.

7 C2H4 C2H6

^^^ Z n,

U TT n^ TT

/ C2H4 C2H6

^^^ Z n,

dneJd/

— u nH O p(k8nc k9 ncO )/ ^^ Z n,

dnC^d/ — U ^k9nCOnHOPIRTZ ^ .

3. Equation of heat balance and hydrodynamics g™' ~

nonst

H4

dT d!

^h q - Zr^

ÄJ

J

Z

fz0

Z«! + Z An

M L-i 'Lu 1

1 1

C

P1

(3)

— —-2160.4 • 10 " dL

1 +

30d

^ <§c,:

v 0 y -1 o^ins

Pd5

(4)

4. Account of the process non-stationaryity Equation of cokeformation rate:

rC — ^ — kl • C4+ — k0ieXP C4+

(5)

increase in coke thickness for time break Ax: r Ax

At — ■

Pc

change of pipe diameter as a result of coke deposit:

(6)

Ad — d° - df — 2 • Atr

ins ins uns G

(7)

5. Equation of pressure loss in dynamic conditions:

— —-2160.4 •lO-dL

/1+ 3OdL (x) )

+

V lo

Lo J P fe to)5'

h

2iJ-6

6. Function of control: - regressive dependences of ethylene yield on time of stove work x(X1), reactor leading g°2H6() and change of pressure in it

AP(X3):

7cal=0.1094X1+0.4853X2-316.128^X3 (9)

Y cal = -5646 + 21.24 Ycal - 0.022957^ +

+8.256 • 10-6 Yc3al. (10)

The system of equations (2), (3), (8) with account of (9), (10) is a complete mathematical model of the process for non-stationary conditions.

Block-scheme of process operation in non-stationary conditions:

7. Results of calculation:

Table 1. The course and results of calculation of non-stationary process of ethane pyrolysis_

* H" 1) e H Load of reactor 0 SC2H6 , Kg/h, X2 Change of pressure AP, atm, X3 Decreasing of inner diameter Adins, m Final diameter, J "ins , m e M § o c S s < m 1) S '5o i â Pressure at inlet to reactor, P0, atm Pressure at outlet from reactor, P, atm Yield of ethylene g exs S C2H4 Y ± exs Yield of ethylene cal S C2H4 Y (5) Y cal Relative error (4, -4?) i-100% Yield of ethylene scal s c2h4 — (6) y ca) Relative error ks-Yfi)

Y,,

100 2504 0.904 0.00424 0.1280 2.12 3.245 2.341 900.14 940.35 -4.46 898.3 0.2073

200 2510 1.088 0.00898 0.1232 4.50 3.253 2.165 901.1 896.04 0.56 899.1 0.217

300 2526.8 1.252 0.01274 0.1195 6.40 3.274 2.022 899.5 863.28 4.02 898.1 0.1536

400 2619.3 1.438 0.01605 0.1162 8.02 3.395 1.958 900 860.31 4.41 897.9 0.235

500 2993.8 1.922 0.02030 0.1119 10.20 3.878 1.956 901.13 899.99 0.12 899.1 0.2226

600 3057.6 2.018 0.02410 0.1081 12.05 3.970 1.952 900.46 911.55 -1.23 899 0.1669

700 3086.4 2.05 0.02950 0.1027 14.75 4.000 1.950 900.61 926.35 -2.86 898.6 0.2222

Yield of ethylene is maintained at demanded stationary level (»900 kg/h) and limit for end pressure is not destroyed.

Ethylene polymerization [3]

1. Stoichiometric scheme of the process

nA ^(A)„

2. Stationary kinetic model:

dX = ["Ar [ M]„exp b ]■ Ty"2

| = -A, [M]„exp [- b2 ] y.

3. Equation of heat balance

(11)

(12)

(13)

dT r

— = ^exp dl

v 1 J

xy/2 + «4 (T - T0 ), (14)

x

= [M^[M]o,

y = [l Mm]o,

b =-(er + tVtp)/ R, b2 = EjR; a3 = Ar [M]o Qr ;

a4 = -

4 K nd2msCpp

4. Function of non-stationarity

Í EmA Ae RT

0 = e

tR'b-FC2HA

(15)

5. Dynamic kinetic model (equations (16) and (13))

dx

d7

-Ar [M]o expf-bTy^2

0. (16)

The system of equation (16), (13), (14) with account of (15) is a complete kinetic model of the process for non-stationary conditions.

6. Block-scheme of process operating in non-stationary conditions:

7. Results of calculation In case productivities of polyethylene don't agree with its stationary value the process is regulated by change of value 9 on the account of change in turn of amount of ethylene gc H and initiator gin, passed into polymerizator. Direct hydration of ethylene [4]

1. Scheme of forming ethyl alcohol CH2 = CH2 + HO ^ CH3 - CH2OH (17)

2. Stationary kinetic model of the process dn k

dt "

( n0 - n

_H2O_P

0,0 n + n - n

V C2H4 H2O

1

\2

( n0 - n

C2H4_

0 , 0 n + n - n

V C2H4 H2O

P-

-K-2

у

> 'n0 + n0 -n )

eq 0

n - n

H2O у

PI n0 + n0 )

C2H4 H2O

In

3. Equation of heat balance and pressure loss:

dT

Z r^HR

PcatnD2 dl

- Öh

(18)

(19)

dP dl

. —

150 Re

-1.75

Z nCPi

1=1

PgasU2 (! - S)

pgS

0.987 -10-5. (20)

3. Function of operation:

G

1) 9 = —cuL (without additions of phosphorus

G

acid);

(21)

G + G G 9' = cur _. add = (with additions of phos-

Ginit

phorus acid)

G-

(22)

4. Dynamic kinetic model:

dn _ dt (

к • 9

.„0

n - n

H2O_P

0,0 n +n -n

V C2H4 H2O у

(n +n° -n)2

V C2H4 H2O J

P ( n + n ) .

\ C2H4 H2O J

i n° - n

C2H4_

0 , 0 n + n - n

V C2H4 H2O

P - K-1

eq 0

n - n

H2O у

(23)

6. Regressive dependence of the current value of phosphorus acid on time:

>=Gcur=/(T)=0.00lT-2.328T+6543.

(24)

The system of equations (23), (17), (20) with account of (21-24) is a complete non-stationary mathematical model.

Output of ethyl alcohol is maintained at stationary level with loss expenditures for consumption of phosphorus acid (291.6 in proposed method against 637.5 - in industrial one).

As the results of operating the processes N 1, 2 and 3, the use of own function of non-stationarity chosen for every process, permitted to preserve productivities of the purpose products at optimum, stationary level found out at optimization of entire CTC.

X

2

n

CH

HO

2H4

7. Results of calculation:

Table 2. Comparison of results of calculating hydration process in industrial and proposed ways of its implementation

Industrial way Proposed way

Time breaks of catalyst work Rate of removing phos. acid kg/h Amount of removed phos. acid for every 50 hours,kg Current amount of phos. acid Gcur, kg Control function (without additions) e = Gcu. Glml Additions of phos.acid Gadd, kg Current amount of phos.acid Gcur = Gcur + Gadd, kg Control function (with additions) e = GCur/G1nit

0 0 0 6534 1 - - -

0-50 2.00 100 6434 0.9847 - - 0.985

50-100 1.95 97.5 6336.5 0.9698 66.8 6403.3 0.98

100-150 1.9 95.0 6241.5 0.9552 - - 0.98

150-200 1.8 90 6151.5 0.9415 58.3 6209.8 0.961

200-250 1.7 85 6066.5 0.9285 - - 0.98

250-300 1.4 70 5996.5 0.9177 89.1 6085.6 0.966

300-350 1.2 60 5936.5 0.9086 - - 0.98

350-400 1.0 50 5886.5 0.9009 77.4 5963.9 0.967

400-450 0.8 40 5846.5 0.8947 - - 0.98

450-500 0.2 10 5836.5 0.8932 - - 0.98

Z697.5 Z291.6

Oxidative conversion of ethyl alcohol into vinegar acid [5]

1. Stoichiometric scheme of the process 1 k

c2h5oh+1 o kl > ch3cho+ho 1k

CHCHO + - O k2 > CHCOOH

2

C2H5OH + CH3COOH ^ > CH3COOC2H5 + HO 1 k

CH3CHO + 210 k4 > 2CO2 + 2H2O

2. Stationary kinetic model of the process:

N dAj _ kbbPPt

pcat• nD- d/ N(1+Vi + K4P2+ bp + Ö4P5)

N0 k2b2A/p2"b4P - k3b1b3PP4

Pcat • ^D2 d/ N10 (l + b^ + b2,P + bP + b4

№ dA3 _ kpbPjï - k2b2^P2bAP5 - k4b4PsP2 (1 + bj + b2yP; + b3P4 + b4Ps ) pcat • ^ d/ N0 (1 + bP + b2VP + b3P4 + b4P5)2

N0 dX4 _ 2k4 P2b4 Ps

. —

ÄHR N0-^ — + a (T - Tr )

dT_ R 1 pcat nD2 dl ( r ).

PcatnD2 dl (^A + Cp4«4 + Cp3«3 + Cp7n7 )'

. -

dl v Re J dpge

nD2 d/ N° (1 + b^ + b2jP2 + b,P, + b,P5)2 (26)

pcat.nDL dl N-0 (1+b-P- + b2,/p++ b4P5)

3. Equation of heat balance and pressure bosses:

4

y r ahr

N0 dT yj ^^ a (T - Tr (27)

nD dl „ „

Pk Z A nCPi

4 1=1 i=1

f150 ,1.751. (l-e). 0.987.10-5 (28)

dl ^ Re ) dpge

Etherification of vinegar acid by ethyl alcohol [5]:

1. Stoichiometric scheme of the process;

c2h5oh + ch3cooh ^ ch3cooc2h5 + ho (29)

2. Stationary kinetic model of the process;

N° dX _k\b2P2 (1 - X )(tp- X)_

pcat. ^ dl = N0(1 + b^ P + b2 ^P)2(1 + 9)2 Kcat 4 1 + 9 1 + 9

3. Equation of heat balance and pressure losses: To 4 dx

(30)

(150 + 1.7S ] P-£ ) 0.987-10-s. (31)

Results of calculation the optimum out pus have been found out on the purpose products of two letter processes. As the processes of oxidative conversion of ethyl alcohol into vinegar acid and esterification of vinegar acid by ethyl alcohol within 50 hours of a catalysts work of clinoptilo-lite and P-zeolite display stable activity, then at calculation of region there were used mathematical models cited for stationary conditions.

Conclusion

The proposed in the work list of main actions which should be fulfilled for preserving stability of work of chemico-technological system, way serve as a guide for calculation of any region of CTC, including the processes with possible non-stationarity of their proceeding.

References

1. Aliyev A.M., Osmanova I.I., Mammadov E.M.,

2. Safarov A.R., Huseynova A.M. Development of kinetic models of non-stationary processes with consideration for characteristic features of changing catalyst activity. Chem. Ind. St. Petersburg. 2013. V. 95. No 2. P. 64-75.

3. Aliyev A.M., Osmanova I.I., Safarov A.R., Huseynova A.M., Yariev V.M. Equation of the processes of ethane pyrolysis in non-stationary conditions. Azerb. Chem. Journ. 2017. No 2. P. 10-15.

4. Aliyev A.M., Osmanova I.I., Safarov A.R., Huseynova A.M. Development of non-stationary mathematical model of the processes of ethylene polymerization. Azerb. Chem. Journ. 2017. No 3. P. 20-23.

5. Aliyev A.M., Osmanova I.I., Safarov A.R., Huseynova A.M., Ismaylov A.Q. Control of the processes of direct ethylene hydration with consideration for dynamics of its proceeding. Azerb. Chem. Journ. 2017. No 4. P. 17-24.

6. Safarov A.R. Modeling and optimization of the processes of obtaining vinegar acid and ethyl-acetate by combined technology. Synopsis of dis. cand. of techn. sci. Institute of Chemical Problems. ANAS, Baku, 2006. 26 p.

РЕШЕНИЕ ВОПРОСОВ НЕСТАЦИОНАРНОСТИ ПРОЦЕССОВ ЭТИЛЕНОВОГО РЕГИОНА ХИМИКО-ТЕХНОЛОГИЧЕСКОГО КОМПЛЕКСА ПО ПЕРЕРАБОТКЕ ГАЗОВ КРЕКИНГА И

ПИРОЛИЗА

И.И.Османова

Изучена динамика процессов самого большого - этиленового региона ХТК, выбраны функции, учитывающие нестационарность процессов, составлены их динамические кинетические модели и на основе полных математических описаний решены задачи их оптимального управления, что в итоге позволило выполнить поставленную цель - сохранить оптимальные производительности целевых продуктов, найденных при оптимизации ХТК для стационарных условий их протекания.

Ключевые слова: нестационарность, функция дезактивации, управление, производительность, динамика, активность катализатора, блок схема.

krekínq va pírolíz qazlarinin emalinin kímyoví texnolojí kompleksínín etílen

REGÍONUNA DAXÍL OLAN PROSESLORÍNÍN QEYRÍ-STASÍONARLIGI MOSOLOLORiNiN HOLLi

i.i.Osmanova

KTK-in an böyük - etilen regionu proseslarinin dinamikasi öyranilib, proseslarin qeyri-stasionarligini nazara alan funksiyalar seçilib, onlarin dinamik kinetik modellari tartib va tam riyazi tasvir asasinda onlarin optimal idara edilmasi masalasi hall olunub ki, bu da naticada qarçiya qoyulmuç maqsadi - maqsadli mahsullarin KTK-in stasionar çaraitda optimallaçdinlmasi zamani alinan mahsuldarligini sabit saxlamaq masalasini hall etmaya imkan verdi.

Açar sözteri: qeyri-stasionarliq, deaktivasiya funksiyasi, idar3etm3, mahsuldarliq, dinamika, katalizatorun aktivliyi, blok-sxem.

Additional remarks for references

1. dins - inside diameter of tube, m;

2. - diameter in the end of time's interval;

3. Ein - energy of activation of initiator's decomposition, kJ/mol;

4. gcXh„> gCl - experimental and calculated yield

of ethylene, kg/h;

5. gin - current amount of initiator, kmol/h;

6. g,

nonst opt

- non-stationary and optimal amounts

of polyethylene, kmol/h;

7. Gcur, Ginit - current and initial amounts of phosphorus acid, kg;

8. Gadd - additions of phosphorus acid, kg;

9. Pf - pressure at outlet from reactor, atm;

10. Qh - warmth of heating of ethylene, kkal/mol;

11. Tr - temperature of refrigerant, K;

12. Ycal, Ycai - regressive dependence of ethylene yield;

13. pcat, pgas - densities of catalizator and gas, kg/m3;

14. Keq - constant of equilibrium.