Entering Feed Stream Data

Condenser. Use the dropdown menu to select Total. If the distillate were removed as a vapor, Partial-Vapor should be selected. 

Reboiler. Both the kettle and the thermosyphon reboilers are partial reboilers (the vapor from the reboiler is in equilibrium with the liquid bottoms product withdrawn), so it does not matter which you select. 

Convergence. The standard method works well in hydrocarbon systems. An alternative method must be used in highly nonideal systems. We select Strongly non-ideal liquid for this example. 

Operating Specifications. A standard distillation column with two product streams has two degrees of freedom once the feed, pressure, number of stages, and feed stage location have been fixed. There are several alternative ways to select these 

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After entering feed stream data, the next step is to enter data needed in the decanter block. Clicking on Blocks and DECANTER and Input on the left-hand side of the Data Browser opens the window shown in Figure 3.56. The first page tab is Specifications, on which operating pressure and another one decanter specification need to be specified. We select the... 

Carry out a reactor design analysis of the fed batch process described below in which the volumetric flow rate of the entering feed stream is held constant Use the following data and assumptions as guides in your analysis... 

In distillation calculations, molar flowrates and compositions are usually employed. Let us assume that the fresh feed flowrate is lOOkmol/h, the feed temperature is 25°C, and the feed pressure is 1.3 atm. These are entered in the middle of the window. The feed composition is 50 mol% IPA and 50 mol% water to represent a typical waste stream from semiconductor industry. The composition can be entered in terms of mole or mass fractions, or it can be entered in terms of component molar or mass flowrates. In our example, we use the dropdown arrow to change to Mole-Frac and enter the appropriate values. Repeat the same procedure to enter the feed-stream data of the entrainer feed (FFl) as can be seen in the flowsheet given in Figure 3.1. 

The next task at hand is entering the known data into the simulation. We will begin with the feed stream data. Double click on SI and the Stream Data screen will appear. Click on Flowrate and Composition, then Individual Component Flowrates, and then enter in all the given feed flow rates. Once this is done, click OK and the Stream Data screen should reappear with Flowrate and Composition now outlined in blue. The two streams each containing ethanol and water is mixed together at 5 atm pressure and 25°C. 

Effective temperatures. When extracting stream data to represent the heat sources and heat sinks for the heat exchanger network problem, care must be exercised so as to represent the availability of heat at its effective temperature. For example, consider the part of the process represented in Figure 19.8. The feed stream to a reactor is preheated from 20°C to 95°C before entering the reactor. The effluent from the reactor is at 120°C and enters a quench that cools the reactor effluent from 120°C to 100°C. The vapor leaving the quench is at 100°C and needs to be cooled to 40°C. The quenched liquid also leaves at 100°C but needs to be cooled to 30°C. How should the data be extracted ... 

The interpretation of the F(t) curve as the probability that a fluid element entering the reactor at time zero has left by time t may be used to indicate how the curve may be generated from experimental data. Let us consider the case where at time zero one makes a step change in the weight fraction tracer in the feed stream from Wq to w o A generalized stimulus-response curve for this system is shown in Figure 11.2. 

The irreversible enzyme-catalyzed reaction 2A B -I- C is to be carried out in the hquid phase in a tubular reactor. The feedstock contains A at a concentration of300 g/L and enters at a temperature of 25°C. The density of the feed stream is 0.95 kg/L and its volumetric flow rate is 0.8 m /h. Thermochemical data indicate that at 25°C, the standard heat of reaction is -200 cal/g of A reacting. Experimental measurements indicate that the heat capacity of the liquid is essentially 0.92 cal/(g-°C), regardless of the extent of reaction. Bench-scale measurements indicate that over the temperature range of interest, the dependence of the first-order rate constant on temperature is given by k = 3.0 -I- 0.6(r - 25) for k in h" and T in °C. 

El. A laboratory steam stripper with 11 real stages is used to remove 1000 ppm (wt) nitrobenzene from an aqueous feed stream which enters at 97°C. The flow rate of the liquid feed stream is Ljjj = F =1726 g h. The entering steam rate was measured as S = 99 hr. The leaving vapor rate was measured as = 61.8 h. Column pressure was 1 atm. The treated water was measured at 28.1 ppm nitrobenzene. Data at 100°C are in Problem 12.D4. Molecular weights are 123.11 and 18.016 for nitrobenzene and water, respectively. What is the overall efficiency of this column ... 

D16. Acetic acid is being extracted from water with butanol as the solvent. Operation is at 26.7°C and equilibrium data are in Table 13-3. The feed is 10.0 kg/min of an aqueous feed that contains 0.01 wt frac acetic acid. The entering solvent stream is butanol with 0.0002 wt frac acetic acid. The flow rate of the solvent stream is 8.0 k mim The column has 6 equilibrium stages. Find the outlet weight fractions. Assume butanol and water are immiscible. 

D28. We are extracting acetic acid from water with isopropyl ether at 20°C and 1 atm pressure. Equilibrium data are in Table 13-5. The column has three equilibrium stages. The entering feed rate is 1000 kg h. The feed is 40 wt % acetic acid and 60 wt % water. The exiting extract stream has a flow rate of 2500 kg h and is 20 wt % acetic acid. The entering extract stream (which is not pure isopropyl ether) contains no water. Find ... 

PRO/II is capable of handling multiple reactions. The same procedure of Example 3.2 is used here. First, perform the process flow sheet of the conversion reactor and specify the feed stream with the given total flow rate and compositions, Temperature is 350°C and pressure is 30 atm. Under the Reactions input menu, select Reaction Data and enter the two reactions as shown in Figure 3.29. Select reaction set R1 from the Reaction set Name of the pull-down menu. Click on Extent of Reaction and specify 100% conversion (fractional conversion is 1) for... 

Under Properties, Specifications, select the base property method. Since these components are liquids, NRTL thermodynamic package is the most convenient fluid package. Install CSTR reactor under Reactors in the model library, and connect inlet and exit streams. Specify the feed stream conditions and composition. Input the reactor specifications double click on the reactor block. The reactor Data Browser opens. Specify an adiabatic reactor and the reactor volume to 4433 liters the value obtained from hand calculations (Figure 5.11). Add the reactions to complete the specifications of the CSTR. Choose the Reactions block in the browser window and then click on Reactions. Click New on the window that appears. A new dialog box opens enter a reaction ID and specify the reaction as Power Law. Then click on Ok. The kinetic data are very important to make Aspen converge. Mainly specifying accurate units for pre-exponential factor A, is very important (see the k value in Figure 5.12). The value MUST be in SI units. 

The Absorber column is selected from Ratefrac in the Column subdirectory. After specifying feed streams, the following data (obtained from hand calculation) should be entered in the column block specifications window ... 

One of the key pieces of data is the composition of products leaving the reactor. The reactor effluent vapor entering the main fractionator contains hydrocarbons, steam, and inert gases. By weight, the hydrocarbons in the reactor overhead stream are equal to the fresh feed plus recycle minus the portion of the feed that has been converted to coke. If the feed can contain water, it should be analyzed for and corrected. 

The precise location of the feed point will affect the number of stages required for a specified separation and the subsequent operation of the column. As a general rule, the feed should enter the column at the point that gives the best match between the feed composition (vapour and liquid if two phases) and the vapour and liquid streams in the column. In practice, it is wise to provide two or three feed-point nozzles located round the predicted feed point to allow for uncertainties in the design calculations and data, and possible changes in the feed composition after start-up. 

The data and equations are entered into locations in the spread sheet as follows The first five rows are used for labels and constants the first column is used for labels and stream numbers. Each location that will contain a number is initialized to zero. The value 100, the carbon monoxide feed rate in mol/h,... 

When the values above for nitrous oxide, organic waste, and aqueous waste are entered in the spreadsheet, the mass balance shows 101 MT of product for every 100 MT of feed. This is not perfectly closed but is good enough at this stage in the analysis. The error is most likely in the organic or aqueous waste streams and will have little impact on the economic analysis. This should, of course, be revisited when better process yield data and a converged process simulation are available. 

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