Run the Problem

If you run the problem, make a change in a parameter, and run the problem again, Aspen Plus will use the first solution as the starting guess for the second problem. If you do not want this to happen, choose Run/Reinitialize or the reinitialize button mJ, and the starting values are put back to the default values (flow rates are usually zero). You can also do the iterative calculations one unit at a time by choosing the Run/Step menu or Ctrl + F5 or the open triangle. 

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Run the calculation again with TS 2 = 1290 K. Plot the CH4 mole fraction against height at distances x = 1, 2, 3,4, and 5 cm. Make similar plots for CO2. Use the CO2 plot at x = 1 cm to estimate the boundary layer thickness at this point downstream. Re-run the problem with average velocity set to 5000 cm/s, and make plots as above. How does the boundary layer thickness <5 scale with velocity That is, if 5 scales as vn, find the approximate value of n. How did the CH4 conversion efficiency change as the velocity was increased ... 

Step 4 To run the problem shown in Table 4.1, you change the function to the following ... 

Step 3 Next, replace the in the m-file and run the problem from an initial guess... 

Since the desired separation is not achieved, you must run the problem again with 26 stages and a higher reflux ratio choose 5. This time 94.2 lb mol/h of propane goes out in the top stream. Increasing the reflux ratio to 7.5 gives 98.2 lb mol/h of propane, and a reflux ratio of 10 gives 99.2 lb mol/h of propane. 

Step 3 Next create an m-file that provides the script to run the problem. These commands can also be typed in the command window, but when you have several commands that you will use over and over, it is more convenient to create a script that can run all the commands with one message from you. 

To run the problem, choose the blue in the new window and click OK or click on the closed triangle r fr. (If some data is not yet specified, the program will tell you.) By choosing the N button, you get the most information back from the computer, including information about convergence, as shown in Figure C.8. 

To run the problem with different conditions, look for the word AU in a white box (see it in Fig. C.2). The options are All, Input, Results scroll down to Input and make your changes using the menu on the left. Click the button to re-run the problem. 

Finally, Figures 14.9 through 14.11 show a comparison between optimal control and state variable profiles, as function of the objective function weights. In the first case, we have run the problem with co, = 1 x 10 and 0)2=2x 1(F, while in the second... 

A MATLAB program ex41.m has been created to solve this problem. The differential equations are defined in file model41.m. Results of running the problem are shown in Figure 4.3. The maximum amount of monochlorobenzene occurs at 0.78 hours and that for dichlorobenzene at 1.75 hours. 

Additional theoretical investigations of the intraparticle deactivation problem, which unfortunately we cannot treat in detail here, have been reported by Luss and co-workers (28,29) on the modification of selectivity upon poisoning, and by Hegedus (30) on the combined influence of interphase and intraparticle gradients on deactivation It is of interest that deactivation in certain instances can actually have beneficial results on selectivity and in the long run the problem may be to achieve the best balance between diminished activity and enhanced selectivity such results are reminiscent of those pertaining to deactivation of bifunctional catalysts (19,20) ... 

The way in which the calculation is performed is also important. Unrestricted calculations will allow the system to shift from one spin state to another. It is also often necessary to run the calculation without using wave function symmetry. The calculation of geometries far from equilibrium tends to result in more SCF convergence problems, which are discussed in Chapter 22. 

The raw data collected during the experiment are then analyzed. Frequently the data must be reduced or transformed to a more readily analyzable form. A statistical treatment of the data is used to evaluate the accuracy and precision of the analysis and to validate the procedure. These results are compared with the criteria established during the design of the experiment, and then the design is reconsidered, additional experimental trials are run, or a solution to the problem is proposed. When a solution is proposed, the results are subject to an external evaluation that may result in a new problem and the beginning of a new analytical cycle. 

For the first time through a liqmd-liquid extrac tion problem, the right-triangular graphical method may be preferred because it is completely rigorous for a ternary system and reasonably easy to understand. However, the shortcut methods with the Bancroft coordinates and the Kremser equations become valuable time-savers for repetitive calculations and for data reduction from experimental runs. The calculation of pseudo inlet compositions and the use of the McCabe-Thiele type of stage calculations lend themselves readily to programmable calculator or computer routines with a simple correlation of equilibrium data. 

Selection of Equipment If a new product is being considered, the preliminaiy study must be highly detailed. Laboratory or pilot-plant work must be done to establish the controhing factors. The problem is then to select and instaU equipment which 1 operate for quantity production at minimum overall cost. Most equipment vendors have pilot equipment available on a rental basis or can conduct test runs in their own customer-demonstration facilities. 

Direct-Current Motor Control Control for dc motors runs the gamut from simple manual line starters to elaborate regulating systems. Only the starting problems are considered here since variable-speed drives and regulating systems are discussed elsewhere. 

The checkers obtained erratic results in this step, possibly because of surface effects or trace impurities in the pressure vessel. In two other runs, only 16.8-18.8 g of crude product were obtained. In one case, high boiling oligomers were formed, but none of the desired product was produced. Impurities in the diene or dienophile did not appear to be the problem since runs which employed recrystallized 3-acetyl-2(3H)-oxazolone and redistilled 2,3-dimethyl butadiene also gave variable results. 

The submitters report no problems in running the entire procedure on four times the scale described here. 

The problem of spare parts is an inherent phase of the maintenance business. The high costs of replacement parts, delivery, and in some instances, poor quality, are problems faced daily by everyone in the maintenance field. The cost of spare parts for a major power plant or refinery runs into many millions of dollars. 

There are many types of failures assoeiated with a gas turbine, sinee these units are very eomplex in their overall makeup. The failures in the hot seetion far outnumber the problems in the eompressor due to the high temperatures assoeiated with the hot seetion. Hot-seetion failures are usually eonneeted to problems assoeiated with fuels. Turbine failures ean be very eostly, the average eost runs about 500,000 for units between 10 and 50 MW and about 700,000 for units above 50 MW. These average failures result in downtime of between 12 and 16 weeks. The type of operation the unit experienees is a major faetor in the problem. The unit has a more trouble-free operation if it is a baseload unit. 

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