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Unformatted text preview: Modeling Distillation Columns Using Matlab This section provides a detailed discussion on the use of Matlab to model a binary distillation. Use the table of contents to go to the aspect you wish to explore. o Description of the system to be modeled o Overview of Matlab distillation functions o Building a McCabe-Thiele diagram o Minimizing the cost of a column Modeling Binary Distillation Using Matlab After flashing the reactor effluent, the liquid phase must be separated into streams that are primarily benzene, toluene and biphenyl. We will use Matlab programs to simulate one such distillation. The programs have the following restrictions: • There are only two compounds being separated, • VLE can be approximated by assuming ideal behavior of both phases, • Constant molar overflow of the liquid occurs throughout the column, • Ideal stages are set in the simulation. We will have to neglect the effects of both the light compounds methane and hydrogen as well as the heavy compound biphenyl on our separation. We will emphasize the influence of various operating parameters on the performance of the column and the costs associated with running the column. Cost data for the example are taken from Peters and Timmerhaus pages 371 to 376 . The liquid out of the flash at 2000 kPa and 300K will be taken as the product to be split. It was shown as stream 3 in the table: Inlet | Outlet Stream 1 | 2 3 Total Tmp K 929.00 | 300.00 300.00 State vapor | vapor liquid Enthalpy -50020930.3 | -176426148.5 7900057.8 -168526090.7 Compound Stream Flows toluene 28631.5 | 1039.2 27592.3 28631.5 hydrogen 795956.6 | 795431.9 524.7 795956.6 benzene 150568.2 | 16569.3 133998.8 150568.2 methane 2387533.0 | 2378826.1 8706.9 2387533.0 biphenyl 5726.3 | 0.2 5726.1 5726.3 Total 3368415.7 | 3191866.8 176548.9 3368415.7 Since we can only simulate binary fluids in the distillation modules, we will neglect the hydrogen and methane in this product and "lump" the biphenyl with the toluene. Thus our binary feed will have the composition: 0.8009 mol faction benzene and the rest toluene . We wish to produce 265 lb mol of benzene at a purity of 0.9997 and will assume we can do so with a feed of about 170 kg mols/hr. The main operating parameters that we can set in our distillation tower are: • pressure • number of ideal stages • location of the feed stage • column size • type of condenser: total or partial • reflux ratio Some of these parameters will be seen to be interrelated with our specifications. Thus we will find that in order to obtain the required purity, we may need to increase the reflux ratio or the number of stages. In fact we can achieve the desired separation by doing either. Economics will then settle on how much to increase each parameter....
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- Spring '11
- Distillation, reflux, minimum reflux ratio, reflux ratio, Mol fraction