Questions and Answers of Analysis Synthesis And Design Of Chemical Processes

Use the approach given in Example 20.11 to determine the length of tubes necessary to vaporize an organic liquid (acetic acid at 1 bar) flowing inside a set of vertical ¾-in, BWG 16 tubes using
Repeat Problem 20.28 to find the length of a tube fitted with 2-in diameter, 1/16-in thick annular fins spaced a distance of 3/16-in apart.Problem 20.28Air (1 atm and 30°C) flows crosswise over a
Your assignment is to design a replacement condenser for an existing distillation column. Space constraints dictate a vertical-tube condenser with a maximum height (equals tube length) of 3 m. An
An air heater consists of a shell-and-tube heat exchanger with 24 longitudinal fins on the outside of the tubes. The tubes are 1.5-in, 14 BWG, and the fins are 0.75 mm thick and are 15 mm long. A
A 1–2 shell-and-tube heat exchanger has the following dimensions:Tube length: 20 ftTube diameter: 1-in, BWG 14 carbon steel (kcs = 45 W/m/K)Number of tubes in shell: 608Shell diameter: 35 inTube
A 1–2 S-T heat exchanger is used to cool oil in the tubes from 91°C to 51°C using cooling water at 30°C. In the design case, the water exits at 40°C. The resistances on the water and oil sides
Repeat Problem 20.35 if the oil side provides 80% of the total resistance to heat transfer.Problem 20.35A 1–2 S-T heat exchanger is used to cool oil in the tubes from 91°C to 51°C using cooling
Repeat Problem 20.35 for the case when the oil throughput must be increased by 25% but the cooling water flow rate remains unchanged from the base case. Determine the new outlet temperatures for both
For the situation in Problem 20.35, suppose that the flowrate of the process stream must be reduced while keeping the process exit temperature at 51°C. Therefore, it will be necessary to reduce the
A reboiler is a heat exchanger used to add heat to a distillation column. In a typical reboiler, an almost pure material is vaporized at constant temperature, with the energy supplied by condensing
In an S-T heat exchanger, initially ho = 500 W/m2/K and hi = 1500 W/m2/K. If the mass flowrate of the tube-side stream is increased by 30%, what change in the mass flowrate of the shell-side stream
A reaction occurs in an S-T reactor. One type of S-T reactor is essentially a heat exchanger with catalyst packed in the tubes.For an exothermic reaction, heat is removed by circulating a heat
In Problem 20.41, the reactor is now a fluidized bed where Dowtherm circulates through tubes in the reactor with the reaction in the shell. The Dowtherm then flows to a heat exchanger in which boiler
It is necessary to decrease the capacity of an existing distillation column by 30%. As a consequence, the amount of liquid condensed in the shell of the overhead condenser must decrease by the same
In the production of cumene from propylene and benzene, the feed propylene contains propane, which does not react with the benzene. The reaction occurs in the vapor phase. The separation section of
A reaction occurs in a well-mixed fluidized bed reactor maintained at 450°C. Heat is removed by Dowtherm A™ circulating through a coil in the fluidized bed. In the design or base case, the
In the process in Example 21.1, the vapor stream contains too much benzene, a valuable reactant. The feed flowrate of benzene is 102 kmol/h, while the flowrate of benzene in the liquid phase is
Sketch a T-xy diagram for an ideal, binary mixture.1. Illustrate a partial vaporization for a feed of 25 mol% of the more volatile component. Indicate the two phases in equilibrium, the bubble point,
Consider a gas-liquid separation in which acetone in air is absorbed into water to purify the exhaust air. The equilibrium is described by Raoult’s law, and the vapor pressure is given byAn
Sketch a P-xy diagram for an ideal, binary mixture.1. Illustrate a flash for a feed of 75 mol% of the more volatile component. Indicate the two phases in equilibrium, the bubble point, and the dew
A distillation column that has a total condenser and a partial reboiler is fed 500 kmol/h of an equimolar mixture of pentane and hexane. The feed is saturated liquid. It is necessary to produce
What are the physical assumptions of constant molar overflow? What are the consequences? To what types of systems does constant molar overflow typically apply?
State three reasons for requiring a high reflux ratio.Illustrate these on a McCabe-Thiele diagram.
How does the feed condition (saturated, superheated, subcooled) affect the reflux ratio for a given feed mole fraction? Illustrate the answer on McCabe-Thiele diagrams.
Estimate the efficiency of the distillation column in Example 21.4. The feed viscosity is 0.25 cP. Then calculate the number of actual trays in the column and the column height.Example 21.4A
Estimate the pressure drop in the column of Examples 21.4 and 21.5 if the weir height is 4 in.Examples 21.5Estimate the efficiency of the distillation column in Example 21.4. The feed viscosity is
What are the limiting cases for reflux ratio? Why are neither of these cases practical?
What is the best location for the distillation column feed?
Calculate the heat duty for the condenser and the reboiler and their required heat transfer areas. In the condenser, cooling water is used, entering at 30°C and leaving at 40°C. In the reboiler,
What happens if the feed to a distillation column is not at the optimum location? Illustrate this on a McCabe-Thiele diagram.
An air stream flowing at 1500 kmol/h containing benzene vapor is to be scrubbed in a packed bed using 1-in, ceramic Berl saddles using 250 kmol/h of hexadecane as the solvent. The mole fraction of
A distillation column requires 18 equilibrium stages that are 40% efficient. It has a partial reboiler.1. How many trays are in the column if there is a total condenser?2. How many trays are in the
Estimate the pressure drop through the column. To what weir height does this correspond?
Why are some distillation columns run at elevated pressures? State and explain as many reasons as you can.
Analyze the reboiler to determine how its performance is altered at 50% scale-down.
Why are some distillation columns run at vacuum? State and explain as many reasons as you can.
Using the results of Example 21.10, analyze the condenser for the scaled-down case.Example 21.10Analyze the reboiler to determine how its performance is altered at 50% scale-down.
An absorber is designed to be 20 m tall, and it is known that HoV is 4 m. The absorber is designed to treat 40 kmol/h of air containing acetone with a mole fraction of 0.002 and reduce the mole
The feed to a distillation column is significantly subcooled.What happens on the feed tray? What is the potential effect on column diameter? What is the effect on the reboiler and condenser duties?
The feed to a distillation column is significantly superheated. What happens on the feed tray? What is the potential effect on column diameter? What is the effect on the reboiler and condenser duties?
Explain the relationship between reflux ratio and the number of equilibrium stages in a distillation column.
The column in Example 21.12 is operating normally, but a 10% increase in air to be treated, to 44 kmol/h, is expected. How can column operation be changed to ensure the desired outlet mole fraction
What is flooding? What is loading? What is weeping?
Discuss the advantages and disadvantages of sieve trays versus bubble cap trays.
Why might vacuum columns be designed with a larger diameter above the feed compared to below the feed?
Does tray spacing have an effect on column diameter? Explain why or why not.
The feed to a column is to be saturated liquid. An initial design based on the column conditions below the feed shows that trays above the feed might be weeping. Suggest possible remedies.
Discuss the advantages and disadvantages of packed versus tray columns.
An existing distillation column is to be scaled up (increase throughput) without changing the distillate and bottom compositions. What happens to the reflux ratio? What problems might arise in the
For the distillation column in Problem 21.21, it is suggested to change the pressure of the column. Explain why this might work.Problem 21.21An existing distillation column is to be scaled up
For the distillation column in Problems 21.21 and 21.22, how can the pressure in the column be changed?Problem 21.22For the distillation column in Problem 21.21, it is suggested to change the
For the distillation column in Problems 21.21, 21.22, and 21.23, someone suggests that the column pressure can be increased by increasing the feed pressure. What is your response? Explain the
The preliminary design of a distillation column shows that it is flooding. If, for some reason, the diameter cannot be changed, suggest two other design modifications that could alleviate this
A colleague gives you a preliminary tray column design. It shows 12-in tray spacing with 8-in weirs. There are 30 actual trays, and the diameter is 5 ft. Comment on all aspects of this design and
A colleague gives you a preliminary tray column design. It shows 24-in tray spacing with 6-in weirs. There are 60 actual trays and the diameter is 5 ft. Comment on all aspects of this design and
What is a packing factor, and how does it affect packed column design?
What is the absorption (stripping) factor? How does it affect absorber (stripper) design?
State three operating conditions that favor absorption (i.e., make absorption easier). Provide a physical explanation for each condition.
State three operating conditions that favor stripping (i.e., make stripping easier). Provide a physical explanation for each condition.
An absorber is not performing as specified, meaning that the target outlet vapor composition is higher than desired. State as many possible reasons for this that you can identify, and explain why
A stripper is not performing as specified, meaning that the target outlet liquid composition is higher than desired. State as many possible reasons for this that you can identify, and explain why
Comment on the following statement: A transfer unit in a packed column is numerically equivalent to an equilibrium stage in a tray column.
What do height of a transfer unit and the number of transfer units indicate?
Explain the physical reason why, when the absorption or stripping factor is less than one, increasing the number of stages or increasing packed column height does not increase the recovery of solute.
What is the separation basis for distillation? What is the separating agent?
What is the separation basis for absorption? What is the separating agent?
What is the separation basis for extraction? What is the separating agent?
What is the separation basis for leaching? What is the separating agent?
For this problem, the feed is 60 mol% dimethyl ether (DME) and 40 mol% methanol. Assume that the equilibrium data provided are correct.1. A feed of 200 kmol/h is flashed at 5 bar and 50°C. What are
What is the separation basis for gas permeation membranes? What is the separating agent?
Cumene (isopropyl benzene) is manufactured from propylene and benzene. Most of the world’s supply of cumene is directly converted into phenol, which is a raw material for a variety of products such
A distillation column is fed 500 kmol/h of an equimolar mixture of pentane and hexane. The feed is saturated liquid.It is necessary to produce outlet streams containing 95 mol%pentane and 99 mol%
For this problem, the feed is 40 mol% heptane and 60 mol%ethylbenzene. A saturated liquid feed of 200 kmol/h is to be fractionated at atmospheric pressure to give a distillate containing 98 mol%
A feed of 500 kmol/h of methanol and ethanol are to be distilled at 2 bar. The feed is 60 mol% methanol, and the feed is 75% liquid and 25% vapor in equilibrium. The desired outlet compositions are
An absorber is designed to treat 40 kmol/h of air containing acetone with a mole fraction of 0.02 and reduce the mole fraction to 0.001. Pure water is the solvent, at a rate of 20 kmol/h. The column
CO2 is to be stripped from water at 20°C and 2 atm using a staged, countercurrent stripper. The liquid flowrate is 100 kmol/h of water with an initial mole fraction of CO2 of 0.00005. The inlet air
An air stream flowing at 1500 kmol/h containing benzene vapor is to be scrubbed using 25 kmol/h of hexadecane (C16H34) as the solvent. The mole fraction of benzene in the inlet gas is 0.010, and the
Sulfur dioxide (SO ) is removed from a smelter gas (which may be considered to have the properties of pure air) containing 0.80 mol% SO2 by absorption into a solution with the properties of pure
When coal is burned to form synthesis gas (syngas), which contains mostly CO, H2, H2S, and CO2, the H2S must be removed. The gas is called syngas because H2 and CO are the building blocks for
A wastewater stream at 35,000 kmol/h containing benzene at a mole fraction of 0.001 is to be strippied with air in a column operating at 2 bar and 25°C. The outlet water must contain no more than
Consider the removal of H2S only from air. The solvent has a molecular weight of 300, μ = 2.5 × 10-3 kg/m/s, σ = 30 dyne/cm2, and SG = 0.90. The partition coefficient for H2S between air and
For a simple first-order reaction, determine the relative change in reaction rate due to a change in temperature from 320°C to 350°C for the following reactions. Assume for Parts (a) and (b) that
A reaction between two components occurs in the gas phase and produces a single third component according to the following reaction:1. Write the form of the reaction kinetics for the forward and
Methanol can be produced from synthesis gas (syngas) by the following reaction:For the case when no inerts are present and for a stoichiometric feed, the equilibrium expression has been determined to
Consider the reaction of methanol to dimethyl ether (DME) via the gas-phase catalytic reaction using an amorphous alumina catalyst treated with 10.2% silica.There are no significant side reactions at
Comment on the following statement: “For reactions in equilibrium, if the forward reaction is exothermic, then an increase in temperature reduces the conversion, which means that the forward
Consider a simple liquid phase reaction in which reactant A is converted to product B. The reaction is second order in A and the kinetics are given by the equationA stream of material A of
Comment on the following statement: “For highly exothermic reactions, some form of heat exchange should be integrated within the reactor.”
A mixture of 5 moles of reactant A are introduced into a batch reactor by dissolving them in 100 L of solvent. The reaction of A to product B occurs by a first-order reaction of the formDetermine
Comment on the following statement: “For an exothermic reaction, if the temperature is increased at constant pressure with a fixed reactor size, the conversion decreases.”
Using the results from Example 22.4, Part (b), determine the conversion in the reactor if the flow pattern is laminar and not plug flow.Example 22.4Consider a simple liquid phase reaction in which
Sketch the T-Q diagram for an endothermic reaction in a PFR for 1. Countercurrent flow of HTM (heat transfer medium)2. Cocurrent flow of HTM What are the consequences on reactor size of choosing
It is known that for a certain third-order, gas-phase reaction, the rate of reaction doubles when the temperature goes from 250°C to 270°C. The form of the rate equation isIf the rate of reaction
Identify the main reactant and product process streams for the following:The styrene production facility shown in Figure B.3.1, Appendix B Table B.3.1 Stream Tables for Unit
Consider the following reactionafor the production of benzene via the homogeneous thermal dealkylation of toluene in the temperature range 700°C to 950°C:where the concentrations of reactants are
Consider the reaction scheme given in Equation (22.37) where P is the desired product, with both U and V as undesired by-products. Here it is assumed that the reactions occur in the gas phase. Assume
The synthesis of phthalic anhydride from o-xylene is considered. The following parameters and pseudo-firstorder reaction rate may be used for an approximate preliminary design of a shell-and-tube
An exothermic, liquid-phase reaction is to take place in a stirred tank reactor. The feed to the reactor (F) is pure A at 500 mol/min with a concentration of 10 mol/L. The volume of the reactor is
For the solution to Problem 22.7(a), and assuming that the reactor is packed with inert ceramic spheres, 5 mm in diameter with a voidage of 0.45, and that the reactor has a Length/Diameter ratio of
Consider the production of cumene (c) from the catalytic alkylation reaction of benzene (b) using propylene (p)— Reaction 1. A second undesirable reaction (Reaction 2) between propylene and cumene

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