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10
ISSN 2522-1841 (Online) ISSN 0005-2531 (Print)
UDC 66.011/66.012:662.765
GLOBAL FLOWSHEET OF CONTROL ETHYLEN REGION OF A CHEMICAL-TECHNOLOGICAL COMPLEX ON PROCESSING CRACKING AND PYROLYSIS GASES WITH CONSIDERATION FOR NON-STATIONARITY OF THE PROCESSES
PROCEEDING IN IT
I.I.Osmanova
M.Nagiyev Institute of Catalysis and Inorganic Chemistry, NAS of Azerbaijan
agil-s@mail.ru Received 10.06.2019
The article presents a course and results of conducting the processes of ethylenic region of chemical technological complex according to the proposed earlier [1] flowsheet of their calculations under non-stationary conditions. The tasks of their optimal conduction have been decided and on the basis of work carried out general flowsheet of conducting ethylenic region of studied complex taking into account non-stationarity of the processes proceeding there, was developed.
Keywords: non-stationarity, conduction functions, production capacity, dynamics, activity, block-flowsheet, general flowsheet of conduction.
doi.org/10.32737/0005-2531-2019-4-76-83
The purpose of work consists in maintaining optimal production capacities of the target products in ethylenic region of chemical technological complex (CTC), found out for stationary conditions of their proceeding at optimization of CTC, not depending on reasons at which this stationarity is destroyed.
Fulfillment of work
According to a flowsheet of the basic actions, proposed in [1] to achieve the purpose set there are provided the results of their subsequent fulfillment for the concrete processes of ethylenic region. Regime parameters of the processes and denotions to them are presented references corresponding to each process.
Dealkylation of toluene with water va-
por [2]
1. Stoichiometric flowsheet of the process:
C6H5CH3 + 2H2O ^ C6H6 + CO + 3H2,
C6H5CH3 + HO ^ C6H6 + CO + 2H2,
C6H5CH3 + H2 ^ C6H6 + CH4 > 2C6H5CH3 ^^ CH3C6H4CH3 + C6H6
(1)
2. Stationary kinetic model:
w
BENZ
+ -
k1 P
kEFF ' TOL 1 + Ktol PTOL
k3 P P
kEFF1 TOL1 H,
k2 P
kEFF1 TOL 1 + KTOL PTOL
- +
1 + KTOL PTOL + PH
-w™T =
TOL
k P
kEFF ' TOL
1 + KTOL^TOL
k2 P
kEFF ' TOL 1 + KTOL PTOL
■ +
k P P
kEFFP TOLP H,
1 + KTOL PTOL + KH, PH
k4 P
kEFF ' TOL 1 + KTOL PTOL
W =
k1 P
kEFFP TOL
1 + KTOL PTOL
k2 P
kEFF ' TOL 1 + KTOL PTOL
k P P
kEFFP TOLP H,
1 + KTOLPTOL + KH, PH
wXYL =■
k4 P
kEFF ' TOL 1 + K tol PTOL
wCO =■
P
f-i Ti
wco =■
k P
keffP tol 1 + ktol PTOL
wch =■
k 1
kEFF ' TOL 1 + K tol PTOL
k3 P P
keff1 tol1 h,
(2)
1 + KTOL PTOL + P
kEFF = k0 ' exp
EJ
Eeff
RT
K = K 0 o I RT'
2
3. Equation of heat balance: dT
dl
= 0.
(3)
4. Function of deactivatisn of a catalyst:
0 = e"^a\ (4)
5. By introducing function of a catalyst's deactivation (3) into equation of benzene formation velocity
2
w
BENZ
k1 P
kEFF ' TOL 1 + Ktol PTOL
k P
kEFF ' TOL 1 + KTOL PTOL
■ +
k P P
kEFF1 TOL1 H
1 + KTOL ^TOL +
■0,
(5)
together with other equations of the system (2) constructed dynamic kinetic model.
6. Function of conducting - regression dependences of selectivity of benzene and xylene on additions of hydrogen and time of a catalysts work:
5benz=73.0071+0.5068M+0.003T, (6)
sxyl=-0.2770-0.1354M+0.0082T. (7)
The system of equations (2, 3) with consideration (4-7) is a complete mathematical model of the process for non-stationary conditions.
Suggested method of hydrogen additive to the reactionary mixture (TOL+H2O) in found out interval of their change (0.2-1.5) permits preserve production capacity of benzene at needed optima level (76.60/
7. Results of calculation: Table 1. Results of a catalysts work within 1000 hours (without additions of hydrogen)
Time of catalysts work, h 200 400 600 800 1000
Selectivity for benzene, % 76.6 75.8 75.0 74.4 73.2
Selectivity for xylenes, % 1.2 2.3 8.4 9.9 11.2
Table 2. The best yields of benzene at indicated additions of hydrogen to reactionary mixture at inlet into reactor
Volumetric velocity of feeding TOL+H2O+H2, h-1 Ratios Selectivity by benzene, % Selectivity by xylenes, %
TOL H2O H2
1800opt 1 4 - 76.6opt 7.5opt
1835 1 4 0.1 75.6 7.5
1872 1 4 0.2 76.0 7.4
1980 1 4 0.5 76.2 7.1
2070 1 4 0.75 76.5 6.9
2160 1 4 1 77.0 6.6
2250 1 4 1.25 77.1 6.5
2340 1 4 1.50 77.3 6.3
2430 1 4 1.75 75.5 8.4
Alkylation of benzene by ethylene [3]
1. Stoichiometric flowsheet of process:
B + E
k1
^EB,
EB + E
^PAB,
PAB + B
->2EB,
(8)
2 EB + B
^PAB.
2. Stationary kinetic model:
d^Ei d/
dX
PAB _
d/
( jP - A ) ( K1Cc XB - K2CcXEB ) , ^QCbXpab - KACCj X,
w/+B) w
KdG2J ( Yp - A) K2CcXeB + KCXBXEB - K3C£BX
2
EB
PAB
273Mg Yg FPW/
w
where
A = v^XB
(K3XBXPAB ~ K4XEB knB
nB Y l
KDWg
B = (K1XB + K2XEB )CknB
KDWg
d T
3. — = 0 (isotermic reactor). dl
(10) (11)
4. Conducting function 0=GET/GB:
0 = 0.3e-°-2T (design value) (12)
5. By introducing 9 into equation (9)
dX,
dl
( yP - A)(KiCk Xb - K 2Ck X EB )
+
W (i+b)
K3Ck Cb Xpab — K 4Ck CBXb
Wi
+
0
dynamic kinetic model of the process jointly with equation (10) was received. The system of equations (10), (11), (13) taking an account for (12) is a complete mathematical one of the process with consideration for non-stationarity of its proceeding.
6. Block-flowsheet of optimal conducting of the process in non-stationary conditions:
7. Results of calculation: Table 3. Comparison of well-known and proposed methods of proceeding process
№ Industrial method Proposed method
Inlet into alkylator, kg/h Yield, kg/h Inlet into alkylator, kg/h Yield, kg/h
Gf cc get gb gpab geb Gf cc get gb gpab Geb
1 420 5348.12 51477.17 4517.20 20976.56 420 5183.20 51134.52 4416 21071.91
2 420 5253.88 51178.45 4452.80 20803.20 420 5183.20 51134.52 4416 21106.58
3 420 5654.40 54473.20 4554.00 21063.24 420 5183.20 51134.52 4416 21063.24
4 420 4829.80 46477.94 4517.20 20629.84 420 5183.20 51134.52 4416 21071.91
5 420 5583.72 53858.18 4259.60 21037.24 420 5183.20 51134.52 4416 21149.92
6 420 5501.26 53067.44 4121.60 20993.90 420 5183.20 51134.52 4416 21167.26
7 420 5030.06 46978.74 4664.40 20673.18 420 4924.04 48577.79 4195.2 20954.89
8 420 5124.30 48481.15 4728.80 20716.52 420 3592.90 35495.44 3054.4 20868.21
9 420 5242.10 50677.65 4084.80 20794.53 420 3592.90 35495.44 3054.4 20846.54
By ratio of the concentrations of not reacted ethylene and benzene corrected are their amounts at inlet of alkylator to obtain at outlet from it demanded by project amount of ethyl benzene got for stationary conditions. Application of the proposed method of conducting makes it possible to increase by 1% of ethyl-benzene yields and decrease by 8-10% amounts of polyalkylbenzenes.
Dehydration of ethylbenzene to styrene [4].
1. Stoichiometric flowsheet of the process:
C8H10 — C8H8 + H2 CJHjq + H2 -o- C7H8 + CH4
C8H10 + H2 — C6H6 + C2H6
2. Stationary kinetic model:
dx2 _ ^ 1 ~ x2 ~ x5 .
(14)
dl
1 + x
2
dx5 1 X2 X5 ^ \
-5 = -2-T- ( x2 -x5 ),
dl 5 (1 + x2 )2 ( 2 5 ) '
x5 = x3 + x ; = k2 ß/ w0 ,
F
^ = k5ßCo/Wo ; ß = -.
Fo
3. Equation of heat balance:
(15)
(16)
dT
N
Q2dX2
dl Cp mid • NT - dl
(17)
C = C
C p mid CpH2O
M
M + (1 + x2
X2 ( Cp ct. + Cp H2 —
- +
) M + Cp eb.) +
(1 + X 2 )
C
4. Deactivation functions:
0 = 1 —
(1 — n) Ae-RT (NM)(t — T0 )
p eb.
1
1—n
(18)
5. By introducing 9 into the right part of equation (15):
dx2 ^ 1 X2 X5
dl 2 1 + x0
:0
(19)
dynamic kinetic model with equation (16) of the process was received.
6. Function of conducting - regression equations of dependences of ethylbenzene conversion to styrene X2 and selectivity of the process S on degree of dilution of feed stock by water vapor M, temperature of vapor feed stock mixture at inlet to reactor to and time of work of work setting x
X = 1.257042166 + 0.002389131 • M--0.001472064 • i0 —0.00000426802 • t
S = 0.79143 8979 + 0.003 849415 • M-0.000108156 • tn —0.00000528188 • t
(20)
(21)
The system of equations (16), (17), (19) with consideration for (18-21) is an entire mathematical model of the process for non-stationary conditions.
x
7. Results of calculation: Table 4. The optimal version of conducting the process
Conversion of ethyl benzene to styrene, X2; selectivity S, mol % Parameters Time of a catalyst's work, hours An average value of water vapor consumption for 5000 hours of a catalysts work
500 1000 1500 2000 2500 3000 3500 4000 45000 5000 AWv=3826.62 kmol/h
X2 =41 S=92 M 16.7 16.9 17.1 17.4 17.7 18.2 18.7 19.4 20.2 21.3 Gwv =68879.16 kq/h
ta 597.6 597.3 597.1 596.4 595.7 594.9 594.1 593.3 592.6 592.1
N 1 vw.v. 3483.62 3525.34 3567.06 3629.64 3692.22 3763.76 3900.82 4046.84 4213.72 4443.18
Table 5. Results of a catalyst's work after 5000 hours
Time of a catalyst's work, x, h Temperature of vapor feedstock mixture at inlet to a reactor, to, 0C Degree of dilution of feedstock by water vapor, M, mol/mol Conversion of ethylbenzene to styrene X2, %, mol Selectivity of the process, S %, mol
5000 592.1 21.3 41.0 92
5500 593.0 21.3 41.2 91.9
6000 594.0 21.3 41.3 91.85
6500 595.0 21.3 41.35 91.70
7000 596.0 21.3 41.3 91.60
7500 597.0 21.3 41.28 91.40
As we see, to keep up constant for whole period of work the optimal values of styrene yield at 41% and selectivity of the process at 92%, it is expedient to decrease mixture temperature at inlet to reactor from 597.6 at the beginning to 592.10C in the end of a catalyst's work and degree of delu-tion of feedstock by water vapor to increase simultaneously from 16.7 to 21.3.
It is radically differed from industrial way of carrying out the process, where to maintain activity of a catalyst they resort to increasing temperature of vapor feedstock mixture at inlet to a reactor, at the same time not changing delution degree of feedstock by water vapor that leads to sooner blocking of catalyst's surface by toxicants.
It is seen in the table that a rise temperature about by 40C for subsequent 2000 hours permits to increase a little yield, keeping up it within a frame of optimal, and though selectivity of the process with increase in temperature will decrease a little, however till 7000 hours the results of a catalyst's work may be considered satisfactory.
The proposed way of optimal conducting process will enable not decreasing styrene yield
not only to reduce expenditures for the process because of lesser consumption of water vapor in comparison with industrial by 25%, but also to prolong service term for 2000 hours work of a catalyst (7000 hours against 5000 hours at the plant). Result-is a tangible economic advantage.
Polymerization of styrene [5]
1. Stoichiometric flowsheet of the process:
(22)
2. Stationary kinetic model:
d t
10 (1 - x )
kEFF (1 Xm )\lii , \ jri \
l(1 + 6 xm ) F (Xm )
dxjdt = kd (1 - x ),
; (23) (24)
x _(10 -1) • J Mimc
XI t ; 10 _ A ^ fT0 ' kEFF kp
In
MoinicXrt
; ^ = №
kt = kt0 F (xm); 6 = -1;
to
ps
3. Equation of heat balance:
pVC = MstAH ^ p dt st dt
pot
(25)
dXm d t
W (1 — Xm\l(1 + 3 Xm ) F(Xm )
0, (27)
4. Function of non-stationarity:
equation (23)
jointly with (24) and (25) dynamic kinetic model of the process is received.
System of equations (24), (25), (27), with
c T . , • r\ • , • . v r.lu consideration of (26) is a complete mathemati-
5. Introducing 9 into the right part of the , ^
cal model of the process for non-stationary conditions.
0 = e-k a Nst1
(26)
6. Block-flowsheet of optimal conduction of the process in non-stationary conditions:
7. Results of calculation:
At difference of polystyrene productivity from its stationary value, changing a value of 9 on the account of increasing purity of the styrene feeded into a reactor or amount of initiator, we'll be able to regulate the process and obtain the required yield of a target product.
Conclusion
The developed algorithms of a choice for optimal conducting the processes of ethylene region with own non-stationarity function found out for each of them permit to calculate opera-tively the regimes of work in non-stationary industrial conditions for the purpose to receive demanded values of productivities of the target products obtained already at optimization of CTC, but in stationary conditions.
As the processes of ethylene region do not work synchronously and periods of changing catalyst's activity do not coincide in time, in addition the reasons of destroying stationarity in
each process are different, it is impossible to make up a general function of control for a whole region. However the mathematical models of the processes developed with consideration for non-stationary activity of catalyst's possess a flexible structure, i.e. in the course of time the process of self-adjustment of these models takes place. Adjusting mathematical models is carried out both periodically through certain intervals of time or disagreement between calculated and experimental values exceeds the definite values given beforehand. At similar approach the region becomes a flexible chemical-technological system maintaining own work capacity even at possible outward and inner effects.
A general flowsheet of control for ethylene region in CTC is shown in a Figure, where every process proceeding under non-stationary conditions corresponds to control block of its own, using non-stationarity function, concrete for this process.
General flowsheet for control of the ethylene region of CTC.
References
1. Osmanova I.I. Solution of the problems of non-stationarity of the processes of ethylene region of the chemical-technological complex on processing cracking and pyrolysis gases. Azerb. chem. journ. 2019. No 3. P. 75-83.
2. Aliyev A.M., Osmanova I.I., Balayev I.V., Huseynova A.M., Safarov A.R. The method of control for the process of dealkylating toluene by water vapor. Sci-enc. News. Sumgait University. 2018. No 3. P. 42-48.
3. Aliyev A.M., Osmanova I.I., Safarov A.R., Huseynova A.M., Aliyeva X.A. Blok-skhema optimal-nogo upravleniia protcessom alkilirovaniia benzola
Additional remarks for references
1. Cp mid - middle heat capacity of components, kcal/kmol-1-deg-1;
2. Cp st, Cp eb - heat capacities of styrene and ethylbenzene, kcal/kmol-deg.;
3. KD - constant of diffusion exchange;
4. K'eff - effective constant of j-th reaction velocity;
5. No - feeding velocity of ethylbenzene, kmol/h;
6. Nw.v. - amount of water vapor, kmol/h;
7. nB - mole velocity of benzene, mol/s;
8. pTOL - partial pressure of toluene;
9. wg, w\ - linear velocities of gas and
3 1
liquid flows, mol m- s- ;
KREKiNQ VO PiROLiZ QAZLARININ EMALININ KiMYOVi TEXNOLOJi KOMPLEKSiNiN ETiLEN REQiONU PROSESLORiNiN QEYRi-STASiONARLIGINI NOZORO ALMAQLA UMUMi
iDARO SXEMi
i.i.Osmanova
Maqalada KTK-in etilen regionu proseslarinin qeyri-stasionar §araitda avval taklif edilmi§ [1] sxemi uzra hesablanmi§ idara olunmasinin gedi§i va naticalari taqdim olunub. Proseslarin qeyri-stasionar §araitda optimal idara olunmasi masalasi hall olunub va aparilian i§ naticasinda KTK-in etilen regionunun qeyri-stasionar §araitda ba§ vermasini nazara almaqla umumi idara sxemi i§lanib hazirlanib.
Agar sozlar: qeyri-stasionar, idara olunma funksiyasi, mahsuldarliq, dinamika, aktivlik, blok-sxem, umumi idara sxemi.
ОБЩАЯ СХЕМА УПРАВЛЕНИЯ ЭТИЛЕНОВЫМ РЕГИОНОМ ХИМИКО-ТЕХНОЛОГИЧЕСКОГО КОМПЛЕКСА ПО ПЕРЕРАБОТКЕ ГАЗОВ КРЕКИНГА И ПИРОЛИЗА С УЧЕТОМ НЕСТАЦИОНАРНОСТИ ПРОТЕКАЮЩИХ В НЕМ ПРОЦЕССОВ
И.И.Османова
В статье представлены ход и результаты управления процессами этиленового региона ХТК по предложенной ранее [1] схеме их расчетов в нестационарных условиях. Решены задачи их оптимального управления и на основании проделанной работы разработана общая схема управления этиленовым регионом ХТК с учетом нестационарности протекающих в них процессов.
Ключевые слова: нестационарность, функции управления, производительность, динамика, активность, блок-схема, общая схема управления.
etilenom v nestatcionarnykh usloviiakh. Abstracts of Scien. conf. "Nagiye Readings" dedicated to the 110th anniversary of academician M.Nagiev. Baku. 2018. P. 133.
4. Aliyev A.M., Osmanova I.I., Safarov A.R., Huseynova A.M., Aliyeva Kh.A. Control of the process of ethylbenzene dehydration to styrene under non-stationary conditions. Azerb. chem. journ. 2018. No 1. P. 17-22.
5. Aliyev A.M., Osmanova I.I., Safarov A.R., Huseynova A.M., Balayev I.V. Control of the process of styrene polymerization in non-stationary conditions. Azerb. chem. journ. 2018. No 3. P. 33-37.
10. wBENZ, wXYL - benzene and xylene for-
2 1
mation velocity, mol m- h- ;
11. Wol - toluene summary conversion velocity, mol/(m .h);
12. XB, XPAB, XB - partial moles of benzene, polyalkylbenzene and ethylbenzene;
13. yl - special weight of liquid phase,
kg/m3;
14. Gf - expenditure of fresh catalyst's complex, kg/h;
15. NT - current amount of ethylbenzene, kmol/h.
