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Questions and Answers of
Chemical Engineering
Derive Eq. (13-18b) starting with Eq. (13-18a). Yi,1E mi XiNR R () (13-18a) R/E=(mamg)1/2 (13-18b)
Single-stage systems \((\mathrm{N}=1)\) can be solved as countercurrent systems, Figure 13-4, or as crossflow systems, Figure 13-9. Develop the methods for both these designs. Which is easier? If the
Define \(\Delta\) and the coordinates of \(\Delta\) from Eqs. (13-38) and (13-39). Prove that points \(\Delta, \mathrm{E}_{\mathrm{j}}\), and \(\mathrm{R}_{\mathrm{j}+1}\) (passing streams) lie on a
Prove that the locations of streams \(\mathrm{M}, \mathrm{F}_{1}\), and \(\mathrm{F}_{2}\) in Figure 13-17 lie on a straight line. wt. frac. solute A M A XDF, XDM F2 B XDF2 wt. frac. diluent, D
Solve Problem 12.D22 with a mass balance and the Kremser equation.Data From Problem 12.D22We are adsorbing dichloromethane from air into water at \(25^{\circ} \mathrm{C}\) and \(10.0 \mathrm{~atm}\).
This problem is long and involves many calculations because it is a hand calculation of the matrix method for nonisothermal absorption. Suggestion: Set up everything on a spreadsheet. It makes
A laboratory steam stripper with 11 real stages is used to remove \(1000.0 \mathrm{ppm}\) (wt) nitrobenzene from an aqueous feed stream that enters at \(97.0^{\circ} \mathrm{C}\). Flow rate of liquid
Laboratory tests are being made prior to design of an absorption column to absorb bromine \(\left(\mathrm{Br}_{2}\right)\) from air into water. Tests were made in a laboratory packed column that is
Climate change is very much in the news. Engineers need to be heavily involved to control climate change. One approach is to capture carbon dioxide and sequester it. Write a two to three page
Feed gas is at \(1.0 \mathrm{~atm}\) and \(30.0^{\circ} \mathrm{C}\) and is \(90.0 \mathrm{~mol} \%\) air and \(10.0 \mathrm{~mol} \%\) ammonia. Flow rate is \(200.0 \mathrm{kmol} / \mathrm{h}\).
We wish to absorb two gas streams in an absorber. The main gas stream (stream A) is at \(15.0^{\circ} \mathrm{C}, 2.5 \mathrm{~atm}\), and has a flow rate of \(100.0 \mathrm{kmol} / \mathrm{h}\).
a. \(200.0 \mathrm{kmol} / \mathrm{h}\) of a liquid feed that is \(10.0 \mathrm{~mol} \%\) isopropyl alcohol and 90.0 \(\mathrm{mol} \%\) water is stripped in a column with five equilibrium stages.
We wish to absorb n-butane and n-pentane from a gas stream that is at \(25.0^{\circ} \mathrm{C}\) and \(1.0 \mathrm{~atm}\) and has a flow rate of \(100.0 \mathrm{kmol} / \mathrm{h}\). Feed is \(90.0
What is the designer trying to do in the extraction equipment shown in Figure 13-2 and listed in Table 13-1? Why are there so many types of extraction equipment and only two major types of equipment
Write your key relations chart for this chapter.
For Figure 13-24, suppose the raffinate concentration had to be obtained with exactly two equilibrium stages. This can be accomplished by changing amount of solvent used. Would we want to increase or
Extractors are analogous to strippers and absorbers; however, we ignore heat effects for concentrated extractors and assume they are isothermal, but concentrated absorbers and strippers typically
If extract and raffinate phases are totally immiscible, triangular diagrams can still be used. Explain how and describe what equilibrium diagrams will look like.
Based on their solubility parameters, do you think the following are miscible in water, ethanol, or diethyl ether?a. Furfuralb. Phenolc. Toluened. Epichlorohydrin
What situation in analysis of countercurrent extraction on triangular diagrams is superficially analogous to total reflux in distillation? How does it differ?
Study Figure 13-28. Explain what happens as S/F increases. What happens to \(\mathrm{M}\) ? What happens to \(\mathrm{E}_{\mathrm{N}}\) ? What happens to \(\Delta\) ? How do you find \(\Delta_{\min
Distillation systems rarely need pilot plant testing before design, but "design of the extraction column almost always requires pilot plant testing to provide data for accurate scale-up and design of
If an extraction column and a distillation column have the same feed rates, the extraction column will have a smaller diameter than the distillation column. Explain why.
In fractional extraction, what happens to solute \(\mathrm{C}\) ifa. \(\left(\frac{\mathrm{K}_{\mathrm{d}, \mathrm{c}} \mathrm{E}}{\mathrm{R}}\right)_{\text {top }}>1\) and
Sketch the two-stage countercurrent batch extraction process discussed in Section 13.6 after Eq. (13-27d).Equation (13-27d) Yfinal (FD,final /s,final) X final +(FS.initial Yinitial +FD.initial
How would you couple together crossflow and countercurrent cascades? What might be advantages of this arrangement?
The extract stream typically contains product (solute) dissolved in solvent. List as many ways as you can for recovering product and preparing solvent for recycle.
A five-stage countercurrent absorber is used to absorb acetone from air into water at \(3.0 \mathrm{~atm}\) pressure and \(20.0^{\circ} \mathrm{C}\). Total inlet gas flow rate is \(100.0
We are absorbing hydrogen sulfide at \(15.0^{\circ} \mathrm{C}\) into water. Entering water is pure. Feed gas contains \(0.12 \mathrm{~mol}_{2} \mathrm{H}_{2} \mathrm{~S}\). Recover \(97.0 \%\) of
Numerical instability of forms of the Kremser equation used to calculate \(\mathrm{N}\) can cause problems. Show that equations to calculate \(\mathrm{N}\) may have no answer because they would need
A steam stripper is operating isothermally at \(100.0^{\circ} \mathrm{C}\). Entering liquid stream contains \(0.02 \mathrm{~mol} \%\) nitrobenzene in water at \(100.0^{\circ} \mathrm{C}\). Flow rate
Absorb ammonia from air into water at \(20.0^{\circ} \mathrm{C}\) and \(1.5 \mathrm{~atm}\) pressure. Inlet water is recycled from a stripper and contains \(0.2 \mathrm{wt} \%\) ammonia. Gas flow
Design a stripping column to remove carbon dioxide from water by heating the water and passing it countercurrently to a nitrogen stream in a staged stripper. Operation is isothermal and isobaric at
We wish to absorb ammonia from an air stream using water at \(0^{\circ} \mathrm{C}\) and 1.3 atm. Entering water stream is pure water, and entering vapor is \(17.2 \mathrm{wt} \%\) ammonia. Recover
\(\mathrm{HCl}\) is being absorbed from two air streams into water in a countercurrent staged laboratory absorber at \(10.0^{\circ} \mathrm{C}\) and a pressure of \(2.0 \mathrm{~atm}\). Feed rate of
We are operating a stripper at \(0.75 \mathrm{~atm}\) pressure and \(25.0^{\circ} \mathrm{C}\) to strip \(1,2,3-\) trichloropropane from water using air as carrier gas. Inlet water contains 140.0 ppm
Dichloromethane and chloroform are being stripped from water into air at 1.2 \(\mathrm{atm}\) and \(25.0^{\circ} \mathrm{C}\). Feed water contains \(1000.0 \mathrm{ppm}(\mathrm{mol})\) of chloroform
An absorption column for laboratory use has been carefully constructed so that it has exactly four equilibrium stages and is being used to measure equilibrium data. Water is used as solvent to
Read Section 13.4 on crossflow in Chapter 13 before proceeding. We wish to strip \(\mathrm{CO}_{2}\) from a liquid solvent using air as carrier gas. Because air and \(\mathrm{CO}_{2}\) mixtures are
A water cleanup is stripping vinyl chloride from contaminated ground water at \(25.0^{\circ} \mathrm{C}\) and \(850.0 \mathrm{~mm} \mathrm{Hg}\) using a countercurrent, staged stripper. Feed is 5.0
A water stream is saturated with \(\mathrm{CCl}_{4}\) at \(25^{\circ} \mathrm{C}\) and contains \(155 \mathrm{ppm}\) (mol) of \(\mathrm{CHCl}_{3}\). The water stream is stripped with air at a
We plan to treat \(150.0 \mathrm{kmol} / \mathrm{h}\) of water that is saturated with carbon tetrachloride (the \(\mathrm{CCl}_{4}\) is at the solubility limit shown in Table \(12-2\) ) at
Argon and methane are absorbed from nitrogen into liquid ammonia at 252.3 \(\mathrm{K}\) and \(175.0 \mathrm{~atm}\) in an ammonia plant. Feed rate of gas is \(100.0 \mathrm{kmol} / \mathrm{h}\).
If the column uses sieve plates, what column diameter is required for the absorber in Problem 12.D16? Operate at \(75 \%\) of flood. Use \(0.6096 \mathrm{~m}\) tray spacing. Assume \(\eta=0.85\). The
A stripping column with 27 actual stages has an overall efficiency of 0.2 . Feed is \(100.0 \mathrm{kmol} / \mathrm{h}\) of liquid water that contains \(0.010 \mathrm{~mol}^{\%} \mathrm{CHCl}_{3}\).
Carbon dioxide dissolved in water makes the water slightly acidic. We desire to remove most of the \(\mathrm{CO}_{2}\) from \(10.00 \mathrm{kmol} / \mathrm{h}\) of water containing
0We need to remove \(\mathrm{H}_{2} \mathrm{~S}\) and \(\mathrm{CO}_{2}\) from \(1000.0 \mathrm{kmol} / \mathrm{h}\) of a water stream at \(0^{\circ} \mathrm{C}\) and \(15.5 \mathrm{~atm}\). 0Inlet
A gas-processing plant has an absorber and a stripper set up as shown in Figure \(12-2\), except both columns operate at \(25.0^{\circ} \mathrm{C}\) but are at different pressures. Absorber is at
We are adsorbing dichloromethane from air into water at \(25^{\circ} \mathrm{C}\) and \(10.0 \mathrm{~atm}\). pressure in a countercurrent absorber. The inlet vapor flow rate is 150 \(\mathrm{mol} /
Although most absorption equilibrium data follow the Arrhenius relationship, Eq. (12-4), some systems do not. Thus, one should always check before assuming the Arrhenius relationship is valid.Eq
Use Figure 11-6A (methanol product distillate from the first column, ethanol product distillate from the second column, and 1-propanol product bottoms of second column) to purify a ternary feed. Feed
A distillation column with a partial condenser and a partial reboiler is separating 1500.0 kmol/h of a 10.0 mol% ethane, 30.0 mol% n- butane, and 60.0 mol% n-pentane saturated liquid feed at 8.1 atm.
How can the direction of mass transfer be reversed as it is in a complete gas plant? What controls whether a column is a stripper or an absorber?
A tray distillation column that has been used in your plant for the separation of light hydrocarbons is no longer needed in that service. You can use the column for absorption of hydrocarbons in a
What assumptions are made to obtain the plot in Figure 12-16b? Does temperature need to be constant?Figure 12-16b Yo 0 0 V XN XB (RB + B) Equilibrium
As the system becomes dilute, L/G \(\rightarrow \mathrm{L} / \mathrm{V}, \mathrm{Y} \rightarrow \mathrm{y}\), and \(\mathrm{X} \rightarrow \mathrm{x}\). At what concentration levels could you safely
Explain how a stripper, shown in Figure 12-4, differs from the beer still distillation column shown in Figure 3-9.Figure 12-4Figure 3-9 V, y - Stripping Gas Feed LoXo N LNXN. Treated Liquid YN+I V
A stripper is unable to obtain the specified purity of outlet liquid. Outlet liquid impurity concentration can be decreased (which might allow one to reach or exceed specified purity) by doing which
Explain how the single assumption that "solutes are independent of each other" can specify more than one degree of freedom.
What is the practical distinction between proportional and linear? Consider the difference between Henry's law, \(y_{B}=\frac{H_{B}}{p_{\text {tot }}} x_{B}\), and the general expression for linear
The Kremser equation can be used for more than just determining the number of stages. List as many types of problems (in which a different variable is solved for) as you can. What variables would be
Many other configurations of absorbers and strippers can be devised. For example, there could be two feeds. Generate as many configurations as possible.
You want to use both cocurrent and countercurrent absorbers in a process. Sketch at least five ways of doing this. What are the advantages and disadvantages of each method?
Derive Eq. (12-43b).Equation (12-43) 4VRT 8.586VT Dia tray column Approximate 1.37 P
Derive an equation that is equivalent to Eq. (12-12) for \(\mathrm{L} /(\mathrm{mV})=1.0\) but in terms of liquid mole fractions.Equation (12-12) N = YN+1 Y1 L L for = 1 -10-0 mV -b
Derive an operating equation similar to Eq. (12-40b), but draw your balance envelope around the bottom of the column. Show that result is equivalent to Eq. \((12-40 b)\).Equation (12-40b) [x - 4x + x
Derive Eq. (10-4a) for dilute systems by determining \(\mathrm{N}_{\text {equil }}\) and \(\mathrm{N}_{\text {actual }}\) in Eq. (10-1) from appropriate forms of the Kremser equation.Equation
Occasionally it is useful to apply the Kremser equation to systems with a constant relative volatility. Where on the \(\mathrm{y}\) versus \(\mathrm{x}\) diagram for distillation can you do this?
For dilute systems, show that \((\mathrm{L} / \mathrm{V})_{\min }\) for absorbers and \((\mathrm{L} / \mathrm{V})_{\max }\) for strippers calculated from the Kremser equation agree with graphical
Repeat Example \(11-1\) except at \(400.0 \mathrm{kPa} . \mathrm{F}=1000.0 \mathrm{lb} \mathrm{mol} / \mathrm{h}, \mathrm{L} / \mathrm{D}\) \(=4.0\), distillate is \(99.9 \mathrm{~mol} \%
Estimate the 2020 cost of the condenser and the reboiler (shell and tube, floating head) for Problem 11.D1. Steam is available at 41.0 barg, but due to pressure losses, the steam is at
Determine steam and water operating costs per year and TAC for the distillation system described in Problems 11.D1 and 11.D2. Use 8000 h/year. Payback period is 3 years, and costs are based on 2020
Calculate steam and water operating costs per year for Example 11-1. Use \(8000 \mathrm{~h} /\) year. Calculate the TAC for Example 11-1. Payback period is 3 years, and costs are based on 2020 costs.
Calculate the cost of column plus trays, reboiler, and condenser for Example 11-1 using Luyben's cost data. The answers are in the example. In addition, calculate TAC for the entire system if
Repeat the residue curve analysis for Example 11-3 but using the flowsheet in Figure 11-7b. Arbitrarily use a recycle flow rate of 100.0 \(\mathrm{kmol} / \mathrm{h}\).Example 11-3Figure 11-7b We
Repeat the residue curve analysis for Example \(11-3\) but with no recycle:a. For the process in Figure 11-7A.b. For the process in Figure 11-7B. A F >> 1 2 I Recycle H VI L
a. If feed rate in Example 11-1 is doubled, what is total bare module capital cost (column plus trays and heat exchangers) in 2020? Use Eq. (11-4) and Table 11-2 for cost data.Example 11-1Example
Example 10-4 and Problem 10.D17 sized the diameter of a packed column doing the separation in Example 11-1. Suppose a \(15.0-\mathrm{ft}-\) diameter column is to be used. The 1.0 -in. ceramic Intalox
Estimate and compare the costs for \(8.5 \mathrm{~m}^{3}\) of carbon steel Pall ring random packing in 2020 using the data of Turton et al. (2018), Woods (2007), and Kister (2019) fora. \(2.5
Separate a feed that is \(10.0 \mathrm{~mol} \%\) benzene, \(55.0 \mathrm{~mol} \%\) toluene, 10.0 \(\mathrm{mol} \%\) xylene, and \(25.0 \mathrm{~mol} \%\) cumene. Use heuristics to generate four
Repeat Problem 11.D11 for an \(80.0 \%\) purity of the xylene product.Problem 11.D11Separate a feed that is \(10.0 \mathrm{~mol} \%\) benzene, \(55.0 \mathrm{~mol} \%\) toluene, 10.0 \(\mathrm{mol}
Update Table 11-1 by looking up current cost indices on the Internet or in Chemical Engineering magazine. TABLE 11-1. Average values of Chemical Engineering Plant Cost Index (CEPCI). Base year
Repeat the computer simulation proof of feasibility for Example 11-3 but use the flowsheet in Figure 11-7B. The input for the simulator should be based on the solution to Problem 11.D6. Try different
Repeat the computer simulation proof of feasibility for Example 11-3 but with no recycle. The input for the simulator should be based on the solution to Problem 11.D7.Example 11-3Data From Problem
A distillation column is being designed to process a feed that is 10.0 \(\mathrm{mol} \%\) ethanol and \(90.0 \mathrm{~mol} \%\) water. The feed rate is \(100.0 \mathrm{kmol} / \mathrm{h}\), and the
Draw an entirely thermally coupled system (extend Figure 11-6G) for Example 11-2.Figure 11-6GExample 11-2 G) C A B
Sketch possible column arrangements for separation of a fourcomponent system. Do not include sidestream products. Note that there are a large number of possibilities.
Multieffect distillation or column integration can be done with more than two columns. Use the basic ideas in Figures 11-2 and 11-3 to sketch as many ways of thermally connecting three columns as you
Show that Eq. (11-1) will plot as a straight line on log-log paper, and show that the exponent can be determined from a slope.Equation (11-1 Total capital cost = (Lang factor)(delivered equipment
If packing costs are directly proportional to the volume of packing, show that packing costs go through a minimum as L/D increases.
What restrictions on the values of \(\mathrm{K}_{1}, \mathrm{~K}_{2}\), and \(\mathrm{K}_{3}\) are necessary for Eq. (11-6) to follow the power law formula of Eq. (11-3)?Equation (11-6)Equation
A saturated vapor feed at \(1000.0 \mathrm{kmol} / \mathrm{h}\) of methanol \((5.0 \mathrm{~mol} \%)\) and water \((95.0 \mathrm{~mol} \%)\) is fed to a distillation column with 18 stages plus a
Biorefineries producing ethanol by fermentation have several distillation columns to separate the ethanol from the water. The first column, the beer still, is a stripping column that takes the dilute
We wish to distill \(0.10 \mathrm{kmol} / \mathrm{s}\) of a feed at \(25^{\circ} \mathrm{C}\) and \(15.0 \mathrm{~atm}\). The feed is \(10.0 \mathrm{~mol} \%\) ethane, \(35.0 \mathrm{~mol} \%\)
a. Repeat Problem 10.G3 except use the method shown in Figure 1018B to partially balance the column diameters. The liquid and vapor feeds have the same mole fractions as the feed in Problem 10.G3,
\(300.0 \mathrm{kmol} / \mathrm{h}\) of a saturated liquid feed that is \(40.0 \mathrm{~mol} \% \mathrm{n}\)-nonane (C9) and \(60.0 \mathrm{~mol} \% \mathrm{n}\)-decane (C10) at \(11.0 \mathrm{kPa}\)
Repeat the design of Part I, item 1, of Lab 10 including detailed tray and downcomer design except use Ballast V-1 valve trays.
Valve trays cost more than sieve trays. Why are valve trays often advertised as a way of decreasing tower costs?
What is the effect of increasing the feed temperature if \(L / D=1.15 \times\) \((\mathrm{L} / \mathrm{D})_{\min }\) ? Note that \((\mathrm{L} / \mathrm{D})_{\min }\) will change as feed temperature
Most of the values of the exponent \(\mathrm{n}\) in Table 11-3 are positive; however, the exponents for the cost of packing are negative. Explain why.Table 11-3 TABLE 11-3. Reference cost and sizes
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