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engineering
chemical engineering
Questions and Answers of
Chemical Engineering
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
For a ternary separation that has modest required B purity and low concentration of \(\mathrm{C}\) in the feed, we should consider scheme 11-6I as a possibility. If the side withdrawal does not
Schemes 11-6E and 11-6F accomplish the same task of removing and purifying an intermediate component.a. What factors enter into the decision to use scheme \(11-6 \mathrm{~F}\) instead of \(11-6
Sketch a divided-wall column for an ideal four-component (A, B, C, D) separation with component A most volatile and D least volatile.
It is common to design columns at reflux ratios slightly above (L/D) opt. Use a curve of total cost/yr vs. L/D to explain why there is not a large cost penalty if L/D > (L/D)opt.
What happens to economies of scale if the feed rate is half the design value?
The following statement occurs in the text: "Within the careers of current chemical engineering students, maximum energy conservation in chemical plants may be legally required." Although plant
Referring to Figure 11-3, if D1 is the feed to column 2, explain what conditions are necessary for this system to work.Figure 11-3 F F2 2 B2 D
The multieffect distillation system shown in Figure 11-4 appears to be able to cut energy use in half; however, the reduction is not this large. Explain why.Figure 11-4 F PL D, D Reflux B PH
To estimate future values of the cost indices, one is tempted to assume that the average value for the year occurred at midyear (June 30-July 1) and that the linear fit to the recent data can be
The use of components in the feed as solvents for extractive or azeotropic distillation or extraction is recommended even if they are not the best solvents for standalone separations. Explain the
Preheating the feed often increases the number of stages required for the separation ( \(\mathrm{F}, \mathrm{z}, \mathrm{x}_{\mathrm{D}}, \mathrm{x}_{\mathrm{B}}, \mathrm{L} / \mathrm{D}\) constant).
We are separating an ethanol-water mixture in a column operating at atmospheric pressure with a total condenser and a partial reboiler. Constant molal overflow (CMO) can be assumed, and reflux is a
Repeat Problem 10.E1, except design a packed column using 1-in. metal Pall rings. Do the calculations at the top of the column. Approximate HETP for ethanol-water is \(0.366 \mathrm{~m}\). At
You need to temporarily increase the feed rate to an existing column without flooding. Since the column is now operating at about \(90 \%\) of flooding, you must vary some operating parameter. The
Show that staged column diameter is proportional to (feed rate) \({ }^{1 / 2}\) and to \((1+\mathrm{L} / \mathrm{D})^{1 / 2}\).
If the packing factor were unknown, you could measure \(\Delta p\) at a series of gas flow rates. How would you determine the packing factor \(\mathrm{F}\) from these data?
Using a McCabe-Thiele diagram for a binary system, show why the purity will be reduced compared to the base case if \(\mathrm{N}\) and L/D are constant and one of the diameter balancing methods in
Using a McCabe-Thiele diagram for a binary system, show why increasing \(\mathrm{N}\) may not be sufficient to keep purity constant compared to the base case if the diameter balancing method in
Repeat Example 10-1 for an average column pressure of \(400.0 \mathrm{kPa}\).Example 10-1 A sieve plate distillation column is separating a feed that is 50.0 mol% n-hexane and 50.0 mol% n-heptane.
Repeat Example 10-2, except calculate the diameter at the bottom of the column. For n-heptane: \(\mathrm{MW}=100.2\), bp \(98.4^{\circ} \mathrm{C}\), sp gravity \(=\) 0.684 , viscosity
The calculations in Example 10-3 were done for conditions at the top of the column. Physical properties will vary throughout the column, but columns are normally constructed with identical trays,
We wish to repeat the distillation in Examples 10-2 and 10-3 except using valve trays. The valves have a 2-in. diameter head. For the top of the column, estimate the pressure drop vs. hole velocity
We are testing a new packing for separation of benzene and toluene. The column is packed with \(3.5 \mathrm{~m}\) of packing and has a total condenser and a partial reboiler. Operation is at \(760.0
You have designed a sieve tray column with \(0.3048-\mathrm{m}\) tray spacing to operate at a pressure of \(1.0 \mathrm{~atm}\). The value of the flow parameter is \(\mathrm{F}_{\mathrm{lv}}\)
A sieve tray column with \(0.4572-\mathrm{m}\) tray spacing is designed to operate at \(p=4.0 \mathrm{~atm}\). The value of the flow parameter is \(\mathrm{F}_{1 \mathrm{v}}=0.71\), and the flooding
\(1000.0 \mathrm{kmol} / \mathrm{h}\) of a saturated vapor feed that is \(60.0 \mathrm{~mol} \%\) methanol and \(40.0 \mathrm{~mol} \%\) water is distilled in a sieve plate column operating at \(75
The effect of liquid maldistribution in packed columns can be explored with a McCabe-Thiele diagram. Assume that a packed distillation column is separating a saturated liquid binary feed that is
We wish to distill an ethanol-water mixture to produce \(2250.0 \mathrm{lbm}\) of distillate product per day. The distillate product is \(80.0 \mathrm{~mol} \%\) ethanol and \(20.0 \mathrm{~mol} \%\)
\(10.0 \mathrm{kmol} / \mathrm{h}\) of a saturated vapor feed that is \(23.5 \mathrm{~mol} \%\) water with the remainder nitromethane is sent to an enricher that is packed with 1.524 \(\mathrm{m}\)
Repeat Problem 10.D9, calculating the diameter at the top, but condense the feed to a saturated liquid. Determine \((\mathrm{L} / \mathrm{D})_{\min }\) and \(\mathrm{L} / \mathrm{D}=\) \(1.43
a. We are distilling methanol and water in a column packed with 1-in. ceramic Berl saddles. The bottoms composition is \(0.01 \mathrm{~mol} \%\) methanol. A total reboiler is used. The column
Repeat Problem 10.D14a, except determine the diameter of a sieve plate column operating at \(80 \%\) of flooding velocity. Use a \(0.3048-\mathrm{m}\) tray spacing and \(\eta=0.85\). The liquid
Repeat Example 10-4, except calculate the diameter at the bottom of the column.Example 10-4 A distillation column is separating n-hexane from n-heptane using 1-in. ceramic Intalox saddles. The
You have designed a packed column at \(1.0 \mathrm{~atm}\). The flow parameter \(\mathrm{F}_{\mathrm{lv}}\) has a value of 0.2 . The calculated gas flux at flooding is \(0.50 \mathrm{lbm}
Repeat Problems 10.D13 and 10.D13 using the two-enthalpy feed method in which a portion of the feed is condensed to a saturated liquid and the remainder is still a saturated vapor. Select the amount
An atmospheric column with 25 real stages is operating with a pressure drop of 0.6 in. of water per stage. Assume pressure drop in the condenser and the reboiler is \(1.2 \mathrm{in}\). of water
Repeat Problem 10.D14, except calculate the diameter at the top of the column.Problem 10.D14a. We are distilling methanol and water in a column packed with 1-in. ceramic Berl saddles. The bottoms
Repeat Problem 10.D9, part a only, except at \(1.50 \mathrm{~atm}\). The Antoine equation constants to determine the vapor pressure of methanol are in Table 2-3. Other physical properties are in
A vacuum column with 25 real stages is operating with a pressure drop of \(0.3 \mathrm{in}\). of water per stage. Assume pressure drop in the condenser and the reboiler is 0.6 in. of water each. The
Repeat the alternative solution to Example 2-4 but use 2-in. metal Pall rings.Example 2-4 A vertical flash drum is to flash a liquid feed of 1500 lbmol/h that is 40 mol% n-hexane and 60 mol% n-octane
What effect does increasing the spacing between trays have on:a. Column efficiency?b. \(\mathrm{C}_{\mathrm{sb}, \mathrm{f}}\) and column diameter?c. Column height?d. Maintenance?
Several different column areas are used in this chapter. Define and contrast: total cross-sectional area, net area, downcomer area, active area, and hole area.
Calculate the pressure drop in \(\mathrm{kPa}\) from the head of clear liquid.
The paragraph following Eq. (10-30) states, "With saturated liquid feeds, downcomers are designed for the stripping section where the liquid flow rate is largest." Why not design downcomers with
As shown by the Leaning Tower of Pisa, towers that do not have a proper footing can develop a significant lean. Even if a distillation tower is structurally sound, leaning away from being vertical
Beer stills are distillation columns that process the raw feed from fermentation. This feed includes cells and cell debris in addition to ethanol and water. Why are sieve plates with
Intermediate feeds should not be introduced into a downcomer. Explain why.
What are the characteristics of a good packing? Why are marbles a poor packing material?
Why do intermediate reboilers make start-up more difficult?
Structured packings work very well in vacuum and atmospheric pressure distillation columns, but sometimes structured packings do not work well in high-pressure columns. What is different about
The original publication of Figure 10-15 (Fair and Matthews, 1958) did not cite any equations, and equations probably were not available, but when the curves were fit statistically, Eqs (10-10) were
Refer to Table 10-4.a. Which is more desirable, a high or low packing factor, \(\mathrm{F}\) ?b. As packing size increases, does \(\mathrm{F}\) increase or decrease? What is the functional form of
Distillation columns have been installed on ships. What are the likely effects of the ship's motion on the performance of the distillation column? Would you recommend use of random packing,
One type of valve is shown in Figure 10-1. Brainstorm alternative ways in which valves could be designed.Figure 10-1
Generate other ways of contacting in packed columns.
a. A farmer friend of yours is going to build his own distillation system to purify ethanol made by fermentation. He wants to make his own packing. Suggest 30 different things he could make or buy
If trays are good, random packing is good, and structured packing is good, why not combine them? Think of at least ten ways you might do this.
Develop a spreadsheet for a simple binary Rayleigh distillation that uses Eq. (9-13) but can be used for systems where \(\alpha\) is not constant. Because \(\alpha\) is not constant, calculate the
Solve Example 9-2 with a spreadsheet using Eq. (9-18) over the following ranges of methanol mole fraction: 1.0 to \(0.9,0.9\) to \(0.7,0.7\) to \(0.5,0.5\) to 0.3 , and 0.3 to 0.1 . *Answers are in
We wish to do a constant mole batch distillation of 100 moles of feed that is pure water \(\left(x_{W}=1\right)\) to exchange the solvent to obtain the nonvolatile solute in a mixture that is 0.01
Challenging! Develop a spreadsheet with VBA to solve the following problem. A simple batch distillation of the system n-butane, n-pentane, and n-hexane is planned. \(1.0 \mathrm{kmol}\) of a feed
We are doing a single-stage, batch steam distillation of 1-octanol. The unit operates at \(760 \mathrm{~mm} \mathrm{Hg}\). The batch steam distillation is operated with liquid water present. The
We are separating 100 moles of a feed that is \(60.0 \mathrm{~mol} \%\) methanol and \(40.0 \mathrm{~mol} \%\) water by batch distillation in a system with a still pot and a column that has one
In inverted batch distillation (Diwekar, 1995; Robinson and Gilliland, 1950; Sorensen, 2014) the charge of feed is placed in the accumulator at the top of the column (Figure 9-9). Liquid is fed to
A nonvolatile solute is dissolved in \(1.0 \mathrm{kmol}\) of methanol. We wish to switch the solvent to water. Because the solution is already concentrated, a first batch distillation to concentrate
A simple batch distillation is used to process \(1.0 \mathrm{kmol}\) of methanol-water feed into three distillate fractions and a waste. The initial feed has \(\mathrm{x}_{F, \mathrm{M}}=\) 0.50 mole
A simple batch distillation separates \(0.6 \mathrm{kmol}\) of a binary feed that is 70.0 \(\mathrm{mol} \%\) methanol and \(30.0 \mathrm{~mol} \%\) water. The final still pot is \(10.0 \mathrm{~mol}
A simple batch still (one equilibrium stage) separates 100 moles of a 10.0 \(\mathrm{mol} \%\) methanol and \(90.0 \mathrm{~mol} \%\) water feed. The final bottoms concentration is \(1.0
A distillation system with a still pot plus a column with one equilibrium stage is used to batch distill \(1.0 \mathrm{kmol}\) of a \(57.0 \mathrm{~mol} \%\) methanol and 43.0 \(\mathrm{mol} \%\)
A simple batch distillation (Figure 9-1) is separating \(8.00 \mathrm{kmol}\) of a feed that is \(40.0 \mathrm{~mol} \%\) water and \(60.0 \mathrm{~mol} \% \mathrm{n}\)-butanol. The batch
\(3.0 \mathrm{kmol}\) of feed containing \(52.0 \mathrm{~mol} \%\) water and \(48.0 \mathrm{~mol} \% \mathrm{n}\)-butanol is charged to the still pot of a simple batch distillation system (Figure
A simple batch still is separating a feed that is \(60.0 \mathrm{~mol} \% 1,2\) dichloroethane and \(40.0 \mathrm{~mol} \%\) 1,1,2-trichloroethane. Pressure is \(1 \mathrm{~atm}\). The relative
A batch distillation system with a still pot and one equilibrium stage (two equilibrium contacts total) distills a feed that is \(10.0 \mathrm{~mol} \%\) water and \(90.0 \mathrm{~mol} \%
\(10.0 \mathrm{kmol}\) of a feed with \(\mathrm{x}_{\mathrm{F}}=0.4\) (mole fraction methanol) and the remainder water is sent to a batch distillation system with a large still pot that is an
We wish to batch distill a mixture of 1-butanol and water. This system has a heterogeneous azeotrope (see Chapter 8), so we use the system shown in Figure 9-10. The bottom liquid layer from the
4.0 kmoles of a feed that is 0.60 mole fraction acetone and 0.40 mole fraction ethanol is batch distilled in a system with a still pot (an equilibrium contact), a column that acts as one equilibrium
A constant-mole batch distillation is used to change from a pure nbutanol solvent to a solvent that is \(60.0 \mathrm{~mol} \% \mathrm{n}\)-butanol and \(40.0 \mathrm{~mol} \%\) water. If the initial
A nonvolatile pharmaceutical is dissolved in a solution that is \(90.0 \mathrm{~mol} \%\) acetone and \(10.0 \mathrm{~mol} \%\) ethanol. A constant volume batch distillation is used to switch the
Repeat Problem 9.D4 except use Figure 9-10 as long as the distillate is in the two-phase region and then convert to simple batch distillation by bypassing the liquid-liquid settler. Compare the
Suppose you are doing a batch steam distillation of a mixture that has two volatile organic compounds, n-octane and \(n\)-decane, that are immiscible in water plus a nonvolatile organic compound that
\(12.0 \mathrm{kmole}\) of a mixture \(40 \mathrm{~mol} \%\) water and \(60 \mathrm{~mol} \% \mathrm{n}\)-butanol at 1.0 atm pressure is batch distilled in a system with an equilibrium still pot and
\(10.0 \mathrm{kmol}\) of a \(40.0 \mathrm{~mol} \%\) methanol and \(60.0 \mathrm{~mol} \%\) water mixture is processed in a normal batch distillation system with a still pot that acts as an
A nonvolatile solute is dissolved in \(1.0 \mathrm{kmol}\) of methanol. We wish to have the solute in \(1.0 \mathrm{kmol}\) of solution that is \(99.0 \mathrm{~mol} \%\) water and 1.0 \(\mathrm{mol}
A differential condensation [see Eq. ( \(9-15)\) ] is done for a binary mixture of ethanol and water. The feed is \(0.50 \mathrm{kmol}\) of vapor that is \(10.0 \mathrm{~mol} \%\) ethanol. The
\(1.5 \mathrm{kmol}\) of feed one that is \(40.0 \mathrm{~mol} \%\) methanol and \(60.0 \mathrm{~mol} \%\) water and \(1.0 \mathrm{kmol}\) of feed two that is \(20.0 \mathrm{~mol} \%\) methanol and
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