Equipment sizing distillation towers

Acetonitrile serves to greatly enlarge the spread of relative volatilities so that reasonably sized distillation equipment can be used to separate butadiene from the other components in the C4 fraction. The polar ACN acts as a very heavy component and is separated from the product without much difficulty.The feed stream is carefully hydrogenated to reduce the acetylene level rerun, and then fed to the single stage extractive distillation unit. Feed enters near the middle of the extractive distillation tower, while (lean) aqueous ACN is added near but not at the top. Butenes and butanes go overhead as distillate, with some being refluxed to the tower and the rest water washed for removal of entrained ACN. 

Chemical process equipment is of two kinds custom designed and built, or proprietary off the shelf. For example, the sizes and performance of custom equipment such as distillation towers, drums, and heat exchangers are derived by the process engineer on the basis of established principles and data, although some mechanical details remain in accordance with safe practice codes and individual fabrication practices. 

The philosophy of process intensification has been traditionally characterized by four words smaller, cheaper, safer, slicker. And indeed, equipment size, land use costs, and process safety are among the most important PI incentives. But process intensification can (and should) also be placed in a broader context—the context of sustainable technological development. Several years ago DSM published a picture symbolizing its own vision of process intensification (32), in which skyscraping distillation towers of the naphtha-cracking unit are replaced by a compact, clean, and tidy indoor plant (see Figure 3). The importance of PI for sustainable development and its role in the company s responsible business has been further stressed in a recent publication by the company s CEO, Peter Elverding (33). Here,... 

After the simulation file is augmented, the revised simulation is run and the results are sent to Aspen IPE. Note that the ASPEN PLUS and HYSYS.Plant simulators contain menu entries to direct the results to Aspen IPE. For details, the reader is referred to course notes prepared at the University of Pennsylvania (Nathanson and Seider, 2003), which are provided in the file. Aspen IPE Course Notes.pdf, on this CD-ROM. This section presents estimates of equipment sizes and purchase and installation costs using Aspen IPE for two examples involving (1) the depropanizer distillation tower presented on the CD-ROM (either HYSYS —> Separations —> Distillation or ASPEN PLUS Separations Distillation), and (2) the monochlorobenzene (MCB) separation process introduced in Section 4.4, with simulation results using ASPEN PLUS provided on the CD-ROM (ASPEN Principles of Flowsheet Simulation —> Interpretation of Input and Output —> Sample Problem). Just the key specifications and results are presented here. The details of using Aspen IPE for these two examples are presented in the file. Aspen IPE Course Notes.pdf... 

After the parameters for estimating equipment sizes and the utility parameters are adjusted, and a new steam utility is defined, the simulation units (blocks, modules, or subroutines) are mapped into Aspen IPE. In this case, there is only one distillation unit, Dl, to be mapped. The default mapping results in (1) a tray tower, (2) a shell-and-tube heat exchanger with a fixed tube sheet for the condenser, (3) a horizontal drum for the reflux accumulator, (4) a centrifugal reflux pump, and (5) a kettle reboiler with U tubes. 

Phase separation in macroscale equipment either uses density differences between the two fluids to drive the separation, as in settlers, or these differences play an important role in the technical layout of the separator, e.g. in distillation towers. In macroscopic two-phase flow, length scales vary between the size of the apparatus and the interface-dictated Laplace length scale /o/(g AQ)) of entrained bubbles or drops. The former is often on the order of meters, whereas the latter is on the order of millimeters. This significant disparity in length scales makes it virtually impossible to separate macroscopic two-phase flows in a single step. 

The light crude will define the design basis for the atmospheric section of the crude unit since its volume of distillates will exceed that which can be produced from the heavy crude. All equipment sizing will be based on heat and material balance data calculated for the various tight crude cases. As would be expected, the heavy crude will define the facilities for processing the atmospheric tower bottoms, either a vacuum unit or, if this is not planned, the reduced crude heat exchange equipment. To further complicate the... 

For a typical flowsheet, such as the DME (dimethyl ether) PFD in Figure B.1.1 i Appendix B), there are many decision variables. The temperature and pressure of each unit can be varied. The size of each piece of equipment involves decision variables (usually several per unit). The reflux in tower T-201 and the purity of the distillate fromT-202 are decision variables. There are many more. Clearly, the simultaneous optimization of all of these decision variables is a difficult problem However, some subproblems are relatively easy. If Stream 4 (the exit from the methanol preheater) must be at 154°C, for example, the choice of which heat source to use (Ips, mps, or hps) is easy. There is only a sin e decision variable, there are only three discrete choices, and the choice has no direct impact on the rest of the process. The problem becomes more difficult if the temperature of Stream 4 is not constrained. 

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