Modelling of a Reactor Using Simulink

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  • Topic: Distillation, Fractional distillation, Fractionating column
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  • Published : February 23, 2013
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Chemical Engineering 367
Assignment 2
Aspen

Jason Miskin
16117190
A 28 staged distillation column with a reflux ratio of 30 and a total condenser was given in the problem statement. It is known that a total condenser and reboiler both count as a stage apart. Thus the total amount of theoretical stages is equal to 30. The problem statement schematic representration is redrawn. Consider the following distillation column setup: 1

2
11
15
25
29
Distillate
Liquid side stream
Vapour side stream
338.71°C
172.37 kPa
nC4: 14.08 kmol/hr
nC5: 19.53 kmol/hr
nC6:24.78 kmol/hr
nC8: 39.94 kmol/hr
19.53 kmol/hr
24.78 kmol/hr
14.08 kmol/hr
20 psia
25 psia

Feed stream

Bottoms

Figure 1: Schematic representation of theoretical column
Note that the feed-, vapour-, and liquid side streams are all moved a stage down. This is due to the total condenser that is considered a stagfe on its own (and it’s above all the other stages). It can be seen (from figure 1) that the feed stream, liquid stream and vapour stream are linked to stage 15, 11 and 25, respectively. It can also be seen that the pressure difference in the overall distillation clumn (from stage 1 [the condenser] to stage 30 [the reboiler]) is 5 psia. This will be the pressure drop that will be specified in Aspen (and the condenser pressure will be specified). It will be assumed that the feed stream is fed on stage. The previous mentioned information together with data from figure 1 will now be used in Aspen to model this distillation column. a)

The following product stream compositions, stage temperatures, reboiler and condeser duties and inter-stage flow rates and compositions (for the distillation column in figure 1) were found using Aspen, together with the Peng Robinson equation of state (thermodynamic model):

| | | | | | Compositions:| | |
Stage| Temp. [C]| P [Psia]| Heat duty [kW]| Liq. flow [kmol/hr]| Vap. flow [kmoll/hr]| Butane frac| Pentane frac| Hexane frac| Octane frac| 1|  |  |  |  |  |  |  |  |  |
2| 9.175| 1.379| -2351.37| 362.573| 0.000| 0.9799| 0.0201| 3.32E-08| 2.23E-20| 3| 11.641| 1.391| 0| 351.558| 376.653| 0.9416| 0.0584| 4.67E-07| 3.54E-18| 4| 17.444| 1.404| 0| 332.074| 365.638| 0.8402| 0.1598| 5.76E-06| 4.83E-16| 5| 27.674| 1.416| 0| 317.186| 346.154| 0.6214| 0.3786| 5.48E-05| 4.87E-14| 6| 37.622| 1.428| 0| 315.714| 331.266| 0.3428| 0.6569| 3.25E-04| 2.74E-12| 7| 43.030| 1.441| 0| 317.785| 329.794| 0.1637| 0.8351| 1.26E-03| 9.04E-11| 8| 45.351| 1.453| 0| 318.312| 331.865| 0.0910| 0.9050| 3.98E-03| 2.27E-09| 9| 46.699| 1.465| 0| 316.624| 332.392| 0.0669| 0.9216| 1.15E-02| 5.13E-08| 10| 48.400| 1.477| 0| 311.555| 330.704| 0.0595| 0.9084| 3.21E-02| 1.09E-06| 11| 51.685| 1.490| 0| 282.280| 325.635| 0.0577| 0.8576| 8.47E-02| 2.17E-05| 12| 57.724| 1.502| 0| 269.478| 315.890| 0.0577| 0.7410| 2.01E-01| 3.75E-04| 13| 66.377| 1.514| 0| 250.604| 303.088| 0.0583| 0.5576| 0.3794| 0.0047| 14| 79.890| 1.527| 0| 218.505| 284.214| 0.0596| 0.3581| 0.5413| 0.0411| 15| 102.437| 1.539| 0| 64.771| 252.115| 0.0632| 0.2014| 0.5209| 0.2144| 16| 102.654| 1.551| 0| 64.904| 0.051| 0.0638| 0.2018| 0.5203| 0.2140| 17| 102.870| 1.564| 0| 65.036| 0.184| 0.0645| 0.2022| 0.5197| 0.2136| 18| 103.083| 1.576| 0| 65.167| 0.316| 0.0652| 0.2026| 0.5190| 0.2132| 19| 103.295| 1.588| 0| 65.298| 0.447| 0.0659| 0.2029| 0.5184| 0.2128| 20| 103.506| 1.601| 0| 65.428| 0.578| 0.0666| 0.2033| 0.5177| 0.2124| 21| 103.714| 1.613| 0| 65.557| 0.708| 0.0673| 0.2037| 0.5171| 0.2120| 22| 103.923| 1.625| 0| 65.686| 0.837| 0.0679| 0.2040| 0.5165| 0.2116| 23| 104.153| 1.638| 0| 65.824| 0.966| 6.80E-02| 0.2044| 0.5163| 0.2113| 24| 104.641| 1.650| 0| 66.059| 1.104| 6.27E-02| 0.2025| 0.5222| 0.2127| 25|...
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