Feed 2- benzene product 1- main product methane product 2- main product cumene bottom product-tail gas
The upper gas S 10 coming out of the tank is mainly methane and ethane.
And further condensed into two phases.
Ethane and carbon are the main components of tail gas and gas bottom.
Alkanes and propylene in liquid S 12 are refluxed to the reaction tank.
2 Selection of thermodynamic methods
In the chemical process simulation software PRO/II, you need to pass
There are few data about thermodynamic properties and known physical properties of the system.
The accuracy of estimation will be directly affected by the transfer characteristics.
Respond to the accuracy of simulation results. Select the appropriate physical method.
It is often the key step to determine the accuracy of simulation results, and the choice
Improper physical property method will get wrong calculation results. correct
In most refineries and petrochemical plants, the processed materials are
For hydrocarbon systems and petroleum fractions, it may contain some non-.
Hydrocarbon gases, such as hydrogen, air, carbon dioxide and nitric oxide.
Carbon, hydrogen sulfide, etc. These can be considered as nonpolar substances.
Quality. For nonpolar substances, the equation of state can be used to calculate.
Computational thermodynamic properties. So far, the position of publishing in literature
There are hundreds of equations, but only a dozen are commonly used.
Only 2 ~ 3 are the most important and fit this model best.
At present, different thermodynamic methods are selected for estimation.
211Soave-Redliofi-kwong equation of state (SRK
Equation)
Georgi Soave published this equation in 1972,
The calculation formula is as follows:
P =
radiogram
V - b
-
One (t)
V (V + b)
Where b = σ i.
Xi bi
bi = 0 108664RTci /Pci
Tci and PCI- critical temperature and critical pressure of component I
force
a(T)=σI
σj
XiXj(ai aj) 1/2( 1-Kij)
ai = aciαi
aci = 0 142747 (RTci ) 2 /Pci
αi
0 15 = 1+mi( 1-Tci
0 15 )
mi = 0 1480+ 1 1574ωI-0 1 176ωI
2
Ω Ω I-centrifugal coefficient of component I
Kij- binary interaction parameters of components I and J.
The Greek letter α was introduced to improve the steaming of pure components.
The prediction of steam pressure and the combined formula proposed by Kij.
Calculate A (T) to improve the pressure prediction of the mixture. manufacture
Application of chemical process simulation in distillation and reaction process
Predicting the mixture by Soave formula includes two steps: the first step
First, the acentric factor ωi of this component is for each component.
So that the vapor pressure of the components can be accurately predicted.
Measure; Second, the letter Kij is a binary interactive system composed of I and J.
The experimental data of the system enable the phase equilibrium to be launched.
Match. Input the parameters of each unit and the operation results after the original process conditions.
See table 1.
Table 1 selects the results of simulation operation of SRK equation.
Fluid name feed 1 feed 2 product 1 product 2 bottom
traffic
kmol h- 1 1300 197 350 759 104 403 132 172 147
raw material
Methane 015760100001986010000/005.
Ethane 01077010000101102601535.
Propane 0105701000010000105701293
Butane 0100901000010000101030.
Propylene 01281000+010030103401136.
Cumene 010000100010001784 8107×10-6.
Benzene 0100011000010000184001
2 12 Peng-Robinson equation of state (PR equation)
This equation was put forward by Peng and Robinson in 1976.
Come out, this is another cubic equation of state:
P =
radiogram
V - b
-
One (t)
V (V + b)
Where b = σ i.
Xibi
bi = 0 107780RTci /Pci
Tci and PCI- critical temperature and critical pressure of component I
force
a(T)=σI
σj
XiXj(ai aj) 1/2( 1-Kij)
ai = ac iαi
aci = 0 145724 (RTci ) 2 /Pci
αi
0 15 = 1+ni( 1-Tci
0 15 )
ni = 0 1480+ 1 1574ωI-0 1 176ωI
2
Ω Ω I-centrifugal coefficient of component I
Kij- binary interaction parameters of components I and J.
Substituting into the same data operation model as SRK equation, the result is
See Table 2.
Table 2 selects the simulation results of PR equation.
Fluid name feed 1 feed 2 product 1 product 2 bottom
traffic
kmol h- 1 1300 197 350 749 125 405 10 1 170 155
raw material
Methane 015760100001982010000/005.
Ethane 0107701000010130102801478.
Propane 01057 01000 01000 01059 01292
Butane 0100901000010000101029.
Propylene 01281000+010050103501195.
Cumene 010000100010001780 915×10-6.
Benzene 0100011000010000183001
Benedict Weber Rubin starling Identity Party
Cheng (BWRS equation)
This equation was put forward by Starling in 1973, and its calculation is common.
The type is:
P =ρRT + (B0 RT -
A0 C0
T2 -
E0
T4 )ρ2
+(Bus Rapid Transit System-
d
T
)ρ3 +α( a +
d
T
)ρ6
+
cρ3
T2 ( 1 + rρ2 ) exp ( - rρ2)
By operating this equation, the result is that the model is wrong.
Wrong.
According to these two methods, the ratio between the calculated results and the actual situation is calculated.
Compared with PR thermodynamic method, SRK thermodynamic method is in this model.
The type is closer to reality, so it is preferred.
3 process optimization
It can be easily modified by using chemical process simulation software.
Process parameters, so as to get a better process.
3 1 1 Change the feeding position of S4.
S4 is the liquid mixture after the initial mixed fluid is condensed and flashed.
Compound, change its position into the distillation column plate, comprehensive ratio
Compare the flow rate and concentration of each product and residual gas, thus obtaining
The best feeding point. The simulation results are shown in Table 3.
As can be seen from Table 3, according to the concentration of methane in the product and
Comparison of cumene content in tail gas at the best feeding position of raw material S4
Set as the 4th floor of the distillation column plate.
3 12 Change the heat exchange temperature of heat exchangers E3 and E4 after ammonia evaporation.
After changing the heat exchange temperature of heat exchangers E3 and E4, the product
Chemical Equipment Technology, Volume 28, No.4, Page 29, 2007
Table 3 selects the simulation results of PR equation.
Feed tower
Plate position
Methane flow
kmol h - 1
methane
concentrate
%
Cumene flow rate
kmol h - 1
cumin
concentrate
%
Tail gas cumene
content
× 10 - 6
Layer174813022981533151996577178810865.
The second floor is 7481305798155316130078138810683.
The third floor is 7481307198157316129378138810557.
The fourth floor: 7481307398157316129178138810547.
7481307598156316129078137810551.
7481307498156316128978137810556 on the 6th floor.
7 floors 7481307298155316128778137810552.
And the velocity and concentration of cumene in the tail gas and reflux flowing into the reaction tank.
The reflux flow also changes accordingly, and the results after operation are shown in Table 4.
Table 5, comprehensive comparison can get the best temperature control point.
Table 4 Change of heat exchange temperature of heat exchanger E3
temperature
℃
Cumene product
traffic
kmol h - 1
Cumene product
concentrate
%
Tail gas flow
kmol h - 1
Tail gas cumene
content
× 10 - 6
S 12 reflux
traffic
kmol h - 1
35 3 16 1 129 1 78 138 172 12960 8 10547 7 14290
40 3 16 1479 1 79 147 177 10329 8 10236 10 14540
45 3 16 18976 80 147 180 19907 8 10753 14 13566
50 3 17 140 18 8 1 139 184 13300 8 1 188 1 19 13543
55 3 17 19984 82 104 187 10697 8 13625 25 16565
60 3 18 13206 82 155 189 12 1 16 8 16035 38 14790
As can be seen from Table 4, with the heat exchange temperature of the heat exchanger E3
With the increase of temperature, the yield and concentration of cumene products increase, and the tail gas
The concentration of cumene also increased, but there was little change.
The reflux flow rate increases rapidly and the heat exchange temperature is 50℃.
Table 5 Change of heat exchange temperature of heat exchanger E4
temperature
℃
Cumene product
traffic
kmol h - 1
Cumene product
concentrate
%
Tail gas flow
kmol h - 1
Tail gas cumene
content
× 10 - 6
S 12 reflux
traffic
kmol h - 1
- 25 3 17 140 18 8 1 139 184 13300 8 1 188 1 19 13543
- 28 3 17 16092 8 1 1 19 182 18 178 4 10633 34 1552 1
- 29 3 17 17248 8 1 108 18 1 19248 3 10836 44 16888
- 30 3 17 18947 80 194 180 17796 2 12878 60 1 1557
- 3 1 3 18 1 14 12 80 177 179 1 1549 1 16735 83 19 138
- 32 3 18 15234 80 158 176 199 15 1 12 163 12 1 17759
Analysis of the data in Table 5 shows that the higher the temperature, the higher the temperature.
However, the higher the concentration of cumene in the product, the higher the cumene content in the tail gas.
The more the quantity, the lower the temperature and the lower the product concentration.
At the same time, the reflux flow also increases, and the load of the reflux pipeline also increases.
Bigger. Therefore, considering comprehensively, heat exchanger E4 is selected for cooling.
The outlet temperature is -30℃.
3 13 adjustment of benzene addition
According to the propylene content of the bottom liquid after distillation, consider again
Reflux the contents of propylene and benzene in the fluid, and adjust the amount of benzene added.
Quantity.
As can be seen from Table 6, with the increase of raw material benzene, the output
The output of propylene increased, but the concentration changed little.
The content of propylene in the gas has also increased. According to the data in Table 6, benzene
The addition amount is preferably controlled at 365 kmol/h.
Table 6 Adjustment of Benzene Addition
Benzene flow
kmol h - 1
Cumene product
traffic
kmol h - 1
Cumene product
concentrate
%
Tail gas flow
kmol h - 1
Tail gas cumene
content
× 10 - 6
S6 reflux
traffic
kmol h - 1
350 3 17 18947 80 194 180 17796 2 12878 60 1 1557
360 326 16796 8 1 109 17 1 19535 2 15423 49 10288
365 33 1 1075 1 8 1 1 17 167 1502 1 2 16837 44 1 1746
370 335 14825 8 1 125 163 1 1646 2 18253 39 19938
380 344 13002 8 1 143 154 14345 3 1 1396 32 16252
390 353 1 1362 8 1 16 1 145 18579 3 148 1 1 26 16930
3 14 data comparison before and after optimization
Compare the flow and concentration of products before and after optimization, as well as the tail
The content of toxic cumene in the gas can be seen from Table 7.
After optimization, the concentration of cumene in the product increased, and the tail gas
The content of cumene is also reduced to below the specified standard.
Table 7 Comparison of data before and after optimization
Methane flow
kmol h - 1
methane
concentrate
%
Cumene flow rate
kmol h - 1
cumin
concentrate
%
Tail gas flow
kmol h - 1
In the tail gas
Cumene content
× 10 - 6
Optimize
front
748 13057 98 155 3 16 1 1300 78 138 172 14739 8 10683
Optimize
After ...
748 13073 98 157 33 1 1075 1 8 1 1 17 167 1502 1 2 16837
4 conclusion
(1) The thermodynamic formula that best fits this model is selected.
Methods: The technological process was optimized.
(2) the concentration and flow of products are improved, and the tail gas
The content of cumene is also controlled within the specified range.
(3) It provides a theoretical basis for process control and is practical.
In the production process, the heat exchange temperature of the heat exchangers (E3, E4) can be adjusted.