Test Bank for Computer Methods in Chemical Engineering, 1e by Nayef Ghasem

TEST BANK

1.2 Compressibility Factors Fifty cubic meters per hour of methane flow through a pipeline at 40.0 bar absolute and 300.0 K. Estimate the mass flow rate.

UniSim solution (Fig. 1.3) In the molar flow rate cell, set the volumetric flow rate to 50 m3/h.

Equation of state: Peng Robinson.

Fig. 1.3 stream conditions The compressibility factor (Z) = 0.9199

Fig. 1.4 Compressibility factor

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PRO/II simulation (Fig. 1.5)

Fig. 1.5 PRO/II generated the molar flow rate of 50m3/h of methane.

Fig. 1.6 Compressibility factor (Z)

1.3 Use of Raoult’s law A liquid mixture contains 40 % (mole percent) benzene, and balance is toluene equilibrium with its vapor at 30.0°C. What are the system pressure and the composition of the vapor? Use Unisim, PRO/II, and Aspen Plus.

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UniSim solution (Fig. 1.7) The system is at its boiling pressure at 30oC. The fluid package is NRTL.

Fig. 1.7 Flash unit in Hysys PRO/II simulation (Fig. 1.8)

Fig. 1.8 Flash unit in PRO/II

1.4 Use of Raoult’s law A liquid mixture contains an equal molar of benzene, and toluene is in equilibrium with its vapor at 0.12 atm. What are the system temperature and the composition of the vapor? Use Unisim, PRO/II, and Aspen Plus.

Hysys solution (Fig. 1.9) The bubble temperature at 0.12 atm Fluid package: NRTL I am using the separator from the object palette of Hysys.

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Fig. 1.9 Bubble point temperature of Benzene/Toluene mixture.

PRO/II simulation (Fig. 1.10)

Fig. 1.10 Bubble point temperature of B/T generated by PRO/II 1.5 Use of Henry’s law A gas containing 1.00 mol% of ethane, the balance is methane, is contacted with water at 20.0°C and 20.0 atm. Estimate the mole fraction of dissolved ethane and methane UniSim, PRO/II, and Aspen Plus.

Hysys solution (Fig. 1.11) Fluid package: Peng Robinson

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Fig. 1.11 Process flowsheet generated with Unisim PRO/II simulation (Fig. 1.12)

Fig. 1.12 Process flow sheet generated by PRO/II 1.6 Use of Henry’s law A gas containing 15.00 mol% of CO2 and the balance is methane is contacted with water at 20.0°C and 20.0 atm. Estimate the mole fraction of dissolved CO2 in water using Hysys, PRO/II, and Aspen Plus.

Hysys solution (Fig. 1.14) Using mixer and separator and Peng Robinson 6

Fig. 1.13 Process flowsheet of problem 6 PRO/II results (Fig. 1.14)

Fig. 1.14 PRO/II results 1.7 Dew point calculation Find the dew point temperature for a mixture of 45 mol% n-hexane, 30 % n-heptane, 15 % noctane, and 10 % n-nonane at 2.0 total atm pressure.

UniSim solution (Fig. 1.15) The dew point is calculated (using Hysys, Peng Robinson) by setting the vapor/phase ratio = The dew point temperature is 131.7oC (Fig. 1.15).

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Fig. 1.15 Dew point found with Unisim PRO/II results (Fig. 1.16)

Fig. 1.16 Dew point of gas mixture found by PRO/II. 1.8 Bubble point calculation Find the Bubble point temperature for a mixture of 45 mol% n-hexane, 30 % n-heptane, 15 % n-octane, and 10 % n-nonane at 5.0 total atm pressure.

Hysys solution (Fig. 1.17) For bubble point calculation, the vapor/phase ratio = 0. The bubble point = 153.3 oC (Fig. 1.17).

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Fig. 1.17 Bubble point at 5 atm PRO/II results (Fig. 1.18)

Fig. 1.18 Gas mixture bubble point at 5 atm 1.9 Vapor pressure of gas mixture (Fig. 1.19) Find the vapor pressure for the binary mixture of 50 mol% n-hexane and 50 % n-heptane at 120oC. Hysys solution (Fig. 1.19) 9

The vapor pressure is calculated by setting the vapor/phase ratio= 0

Fig. 1.19 UniSim generated worksheet vapor pressure for the binary gas mixture.

PRO/II results (Fig. 1.20).

Fig. 1.20 Vapor pressure of n-hexane/n-heptane found with PRO/II. 1.10 Vapor pressure of the gas mixture Find the vapor pressure for the pure components and the mixture of 35 mol% n-hexane, 30 % n-heptane, and 35 % n-octane at 150oC. Hysys solution: Vapor pressure of pure hexane = 750.267 kPa Vapor pressure of pure n-heptane = 372.53 kPa Vapor pressure of pure n-octane = 190.26 kPa Vapor pressure of the mixture = 429.06 kPa (Fig. 1.21).

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Fig. 1.21 vapor pressure of gas mixture calculated with UniSim PRO/II simulation (Fig. 1.22)

Fig. 1.22 PRO/II generated the vapor pressure of gas mixture calculated with PRO/II.

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Chapter 2 2.1 Pressure drop through a smooth pipe Water is flowing in a 15 m smooth horizontal pipe at 8m3/h and 35oC. The density of water is 998 kg/m3, and the viscosity of water is 0.8 cp. The tube is Schedule 40, 1-inch nominal diameter (2.66 cm ID). Water inlet pressure is 2 atm. Calculate pressure drop.

Unisim Solution Using Hysys: fluid package: ASME steam The pressure drop = 73.96 kPa

Fig. 2.1 UniSim generated pressure drop through the pipe, solved with UniSim. PRO/II solution (Fig. 2.2)

Fig. 2.2 Pressure drop through smooth pipe solved by PRO/II 2.2 Pressure drop in a horizontal pipe

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Calculate the pressure drop of water through a smooth horizontal pipe 50 m long. The inlet pressure is 100 kPa, the average fluid velocity is 1.0 m/s, and the pipe diameter is 10 cm, relative pipe roughness is zero. Fluid density is 1.0 kg/L, and viscosity is 1.0 cP. Unisim Solution (Fig. 2.3) The volumetric flow rate: cross sectional area × velocity = 36 m3/h Pressure drop = 6.47 kPa Assume outer diameter as 11 cm; the exterior does not affect pressure drop.

Fig. 2.3 Pressure drop through 50 m smooth pipe PRO/II solution (Fig. 2.4)

Fig. 2.4 Pressure drop through 50 m smooth pipe solved with PRO/II

2.3 Pressure drop in a pipe with elevation Calculate the pressure drop of water through a pipe 50 m long (relative roughness is 0.01 m/m).

The inlet pressure is 100 kPa, the average fluid velocity is 1.0 m/s. The pipe diameter is 10 cm.

Fluid density is 1.0 kg/L, and viscosity is 1.0 cP. The water is discharged at an elevation 2 m higher than the water entrance.

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Unisim solution (Fig. 2.3) The problem is the same as that of Problem 2.4.2 except for the change in elevation, and this is to show that 2 m of change in elevation makes a big difference in pressure drop (25.96 kPa)

Fig. 2.5 Pressure drop through 2 m elevated pipe, solved with Unisim PRO/II solution

Fig. 2.6 Pressure drop in a smooth pipe, elevation = 10 m 2.4 Pumping of natural gas in a pipeline Natural gas contains 85 mole% methane, and 15 mole% ethane is pumped through a horizontal schedule 40, 6-in-diameter cast-iron pipe at a mass flow rate of 363 kg/hr. If the pressure at the pipe inlet is 3.5 bars and 25oC, the pipe length is 20 km downstream, assume incompressible flow. Calculate the pressure drop across the pipe using Hysys, Aspen Plus, and PRO/II. Hysys simulation (Fig. 2.7) Fluid package: Peng Robinson Pressure drop: 19.23 kPa

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Fig. 2.7 UniSim generated pressure drop of natural gas through 20 km.

PRO/II simulation (Fig. 2.18)

Fig. 2.8 Pressure drop through 20 km smooth pipe 2.5 Compression of the gas mixture The mass flow rate of a gas stream 100 kg/h of feed contains 60 wt% methane and 40 % ethane at 20 bar, and 35oC is being compressed to 30bar (use PR fluid package). Determine the temperature of the exit stream in degree C. Unisim Solution: Fluid Package: Peng Robinson Exit temperature = 70.18

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Fig. 2.9 UniSim generated compression of the natural gas stream, 100% adiabatic efficiency.

Fig. 2.10 UniSim generated the compression of the natural gas stream, 100% adiabatic efficiency, PRO/II. 2.6 Compression of Nitrogen Find the compressor horsepower required to compress 100 kmol/h of nitrogen from 1atm and 25oC to 5 atm.

Hysys solution (Fig. 2.11) Fluid package: PR Compressor horsepower = 187.2 kW

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Fig. 2.11 UniSim generated the process flow sheet for nitrogen gas compression from 1 to 5 atm.

PRO/II simulation (Fig. 2.12)

Fig. 2.12 PRO/II generated stream table of the compression of nitrogen gas from 1 to 5 atm, generated with PRO/II. 2.7 Pumping of pure water Pure water is fed at 45.36 kg/h into a pump at 121°C, 308 kPa. The exit pressure is 8375 kPa. Plot the adiabatic pump efficiency versus the energy required using UniSim/Hysys (the suitable fluid package is ASME Steam) or any other software package.

Hysys Solution (Fig. 2.13) Fluid package: ASME steam 17

To plot adiabatic efficiency versus energy required, use: Tools>> Data book>>Insert>> • Add adiabatic efficiency • Heat flow

Fig. 2.13 Heat flow versus adiabatic efficiency PRO/II simulation (Fig. 2.14)

Fig. 2.14 Pumping of liquid water

2.8 Pumping of water to the top of the building Calculate the size of the pump required to pump 100 kmol/min of pure water at 1 atm and 25oC to the top of a building 12 m high.

Hysys Solution (Fig. 2.15)

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The pressure at the exit of the pump is the head pressure + Patm So the exit pressure is approximately 1.2 atm + 1atm = 2.2 atm

Fig. 2.15 Energy required pumping

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Chapter 3 3.1 Cumene reaction Cumene is produced from the reaction of benzene and propylene at 25oC and 1 atm. Inlet mass flow rate of benzene is 1000 kg/h and propylene 180 kg/h. Assume 45% completion of the limiting reactant. Calculate molar flow rates of the product stream.

C6 H6 (benzene) + C3H6 ( propene) ⎯⎯→C9 H12 (cumene) Hysys simulation (Fig. 3.1) Fluid package: PRSV Isothermal: 25 oC Limiting component: propylene System: Conversion reactor

Fig. 3.1 Results obtained with Hysys PRO/II results (Fig. 3.2)

Fig. 3.2 PRO/II generated PFD and stream summary.

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3.2 Nitric oxide production Ammonia is burned to produce nitric oxide. The fractional conversion of the limiting reactant is 0.6 NH3, and O2 is in equal molar proportion; the total inlet flow rate is 100 kmol/h. The operating temperature and pressure are 25oC and 1.0 atm. Calculate exit molar flow rates.

Assume the reactor is operating adiabatically.

Hysys simulation (Fig 3.3) Select components are shown in the reaction below: 4NH3 + 5O2 ⎯⎯→4NO + 6H 2O Fluid package: PRSV Limiting reactant: Oxygen

Fig. 3.3 conversion reactor stream conditions PRO/II simulation (Fig. 3.4)

Fig. 3.4 PRO/II simulation results 21

3.3 Multiple reactions Feed enters a conversion reactor at 350oC, 30 atm, and a molar flow rate of 7600 kmol/h. The feed molar fractions are 0.098 CO, 0.307 H2O, 0.04 CO2, 0.305 Hydrogen, and 0.25 Methane.

The reactions are taking place in series. Assume 100% conversion of methane and carbon monoxide, neglect pressure drop across the reactor. Calculate the molar flow rates of the product components. The reactions are taking place in an isothermal conversion reactor: CH 4 + H2O ⎯⎯→3H2 + CO

CO + H2O ⎯⎯→CO2 + H2 Hysys simulation (Fig. 3.5) Fluid package: Peng Robinson Isothermal conversion reactor The reactions are ranked 0 and 1, such that reaction 1 starts then reaction two

Fig. 3.5 gas shift reaction results, Unisim PRO/II Results (Fig. 3.6)

Fig. 3.6 Conversion reactor results with PRO/II 22

3.4 Gas-phase reaction The gas-phase reaction proceeds with 80% conversion. Estimate the heat that must be provided or removed if the gases enter at 400oC and leave at 500oC. The following response is taking place: CO2 + 4H2 → 2H2O + CH4

Hysys simulation (Fig. 3.7) Basis: 100 kgmol/h of the feed stream Assume that feed component CO2 and H2 enters the reactor on a stoichiometric basis

Fig. 3.7 Heat release from conversion reactor PRO/II simulation (Fig. 3.8)

Fig. 3.8 Reaction results generated with PRO/II 23

3.5 Burn of carbon monoxide Carbon monoxide (CO) at 10oC is completely burned at 1 atm pressure with 50% excess air fed to a burner at a temperature of 540oC. The combustion products leave the burner chamber at a temperature of 425oC. Calculate the heat evolved, Q, from the burner.

Hysys simulation (Fig. 3.9) Basis: 100 kmol/h of feed gas Fluid package: Peng Robinson Reaction: 𝐶𝑂 + 0.5𝑂2 → 𝐶𝑂2 Feed stream contains air (21 mol% Oxygen and 79 mol% Nitrogen) Total inlet oxygen = 0.5 theoretical + theoretical O2 Theoretical O2 = 0.5(100) = 50 kgmol/h Total inlet oxygen = 0.5 theoretical + theoretical O2 =100 kmol/h Total inlet air = 100/0.21 = 476.12 kmol/h

Fig. 3.9 Conversion reactor heat release PRO/II simulation (Fig. 3.10)

Fig. 3.10 conversion reactor stream property, PRO/II

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3.6 Production of Ketene from acetone Pure acetone reacts isothermally to form ketene and methane at 2 atm and 650oC. The percent conversion of acetone is 70%. Calculate the reactor exit rate of acetone, ketene, and methane.

Calculate the heat added or removed from the reactor. As a basis, assume 100 kmol/h of pure acetone. Note that 1 mole of acetone reacts to form one mole of ketene and one mole of methane.

Hysys simulation (Fig. 3.11) Fluid package: PRSV System: conversion reactor Basis: 100 kgmol/h of pure acetone

Fig. 3.11 conversion of acetone PRO/II results (Fig. 3.12)

Fig. 3.12 Ketene conversion material balance

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3.7 Production of Dimethyl ether (DME) The production of DME is via the catalytic dehydration of methanol. A feed stream of 134.2 kmol/h at 250oC and 1470kPa contains 0.97 methanol, 0.02 ethanol, and 0.01 steam to an adiabatic conversion reactor. If the single-pass conversion is 90%, calculate the molar flow rate of the exit stream. Use UniSim/Hysys software and the PRSV fluid package and compare the software predictions with manually calculated results.

Fig. 3.13 DME production in a conversion reactor 3.8 Toluene production from heptane The catalytic dehydrogenation of n-heptane produces toluene. The reaction is taking place isothermally in a conversion reactor. The feed stream is at 430oC, 1 atm, and 100 kmol/h (pure n-heptane). The single-pass conversion of n-heptane is 20%. Calculate the molar flow rate of the exit stream. The catalytic dehydrogenation reaction: 𝐶7𝐻16 → 𝐶6𝐻5𝐶𝐻3 + 4𝐻2 Use UniSim/Hysys software (Peng-Robinson) and the PRSV fluid package and compare the software predictions with manually calculated results.

Fig. 3.14 Toluene production in conversion reactor and material balance 3.9 Ketene Production from acetic acid Catalytic cracking of acetic acid at 700oC and 1 bar pressure produces ketene as an intermediate product via the following primary reaction with low conversion (6%): 26

𝐶𝐻3𝐶𝑂𝑂𝐻 → 𝐶𝐻2𝐶𝑂 + 𝐻2𝑂 The side reaction is with higher conversion (74%): 𝐶𝐻3𝐶𝑂𝑂𝐻 → 𝐶𝐻4 + 𝐶𝑂2 The feed stream is pure acetic acid fed to a conversion reactor at a rate of 100 kgmol/h, 1 bar, and 300oC. Calculate the required heating rate using UniSim/Hysys (PRSV fluid package) software or any other available software packages (e.g., PRO/II, Aspen Plus, SuperPro, and Aveva Process Simulation).

Fig. 3.15 UniSim generated PFD and stream summary of the acetic acid to ketene conversion material balance.

3.10 Methane production Methane produced from the reaction of carbon monoxide and hydrogen via the following reactions 𝐶𝑂 + 3𝐻2 → 𝐶𝐻4 + 𝐻2𝑂 The feed flow rate is 100 kmol/h carbon monoxide and 300 kmol/h hydrogens at 550oC and 1000 kPa. The single-pass conversion of CO is 80%, the reaction is taking place in an adiabatic conversion reactor. Determine the reactant exit temperature. Compare the manually calculated result with software predictions using UniSim/Hysys (Peng Robinson) software or any other available software packages (e.g., PRO/II, Aspen Plus, SuperPro, and Aveva Process Simulation).

Fig. 3.16 UniSim generated PFD and stream summary of the methane production process in a conversion.

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Chapter 4 4.1 Hot water-cold water heat exchanger Design a shell and tube heat exchanger for hot water at 12.6 Kg/s and 344.261 K is cooled with 25.2 Kg/s of cold water at 305.372 K, which is heated to 322.04 K in a counter-current shell and tube heat exchanger. Assume that the exchanger has 6.096 m steel tubes (Thermal conductivity of steel is 45 W/(m K), 0.01905 m. OD, and 0.015748 m. ID.) The tubes are on 0.0254 m square pitch (The appropriate fluid package is NRTL-Ideal).

Solution Hysys simulation (Fig. 4.1, Fig. 4.4)

Fig. 4.1 Process flow sheet and stream summary

Fig. 4.2 Rating/tube side

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Fig. 4.3 Rating/shell

Fig. 4.4 Performance page PRO/II simulation (Fig. 4.5)

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Fig. 4.5 UniSim generated the process Process flowsheet caused by PRO/II Hand calculations/Visual Basic (Fig. 4.6)

Fig. 4.6 VB program

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4.2 Heating of Natural gas with hot water Hot water at 388.706 K is used to heat 14.5 kg/s of natural gas (60% methane, 25% ethane, 15% propane) at 3447.38 KPa from 300 K 308.15 K. The heating water is available at 394.261 K and 620.528 kPa with a flow rate of 3.8 kg/s. Hot water is flowing on the shell side. Assuming 𝑚2.𝐾 that the fouling factor for water is 3.52 × 10−4 . Design a shell and tube heat exchanger 𝑊

for this purpose. (The proper fluid package is NRTL-SRK).

Hysys calculation (Fig. 4.7-4.8)

Fig. 4.7 Result generated with Hysys

Fig. 4.8 Heat exchanger performance PRO/II simulation

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Fig. 4.9 Design of shell and tube heat exchanger using PRO/II Hand calculations Typical gas velocities are 50-100 ft/s

Fig. 4.10 Vb program, hand calculation

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4.3 Cooling Diethanolamine solution in sweetening plant Design a shell and tube heat exchanger to cool 6.3 kg/s of diethanolamine (DEA) solution (0.2 mass fractions DEA/0.8 water) from 335.372 K to 318.15 K by using water at 298.15 K heated to 310.928 K. Assume that the tube inside fouling resistance is 3.52×10-4 m2K/W, and shell side fouling resistance is 3.52×10-4 m2K/W. Compare design results with Example 4.1 (The suitable fluid package is NRTL-SRK).

Hysys simulation

Fig. 4.11 process flowsheet and stream summary with Hysys

Fig. 4.12 Heat exchanger performance

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Fig. 4.13 PRO/II simulation of DEA/water heat exchanger Hand calculation

Fig. 4.14 Exchanger design generated by VB program

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4.4 Cooling ethylene glycol in the dehydration process Design a shell and tube heat exchanger for 12.6 kg/s of ethylene glycol (EG) at 394.26K cooled to 327.594 K using cooling water heated from 305.37 K to a temperature of 322.039 K. The shell side fouling resistance is 7.04×10-4 m2K/W, and tube side fouling resistance is also 7.04×10-4 m2K/W. Compare results with Example 4.2. (The suitable fluid package is NRTLSRK).

Fig. 4.15 Heat exchanger performance

Fig. 4.16 Heat exchanger performance

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Fig. 4.17 Ethylene Glycol /water exchanger simulated by PRO/II

Hand calculations

Fig. 4.18 water/ethylene glycol exchanger 4.5 Rich glycol – lean glycol heat exchanger 36

Rich glycol (TEG) from the absorber at 4.14 kg/s and 291.483 K is exchanging heat with 4.03 kg/s lean glycol from the air cooler at 333.15 K and leaving 301.483 K. Design a shell and tube heat exchanger for this purpose. (The suitable fluid package is NRTL-SRK).

Fig. 4.19 Process flowsheet

Fig. 4.20 Heat exchanger performance

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Fig. 4.21 Rich TEG/Lean TEG exchanger simulated with PRO/II 4.6 Shell side heat transfer coefficient (McCabe page 441) A shell and tube heat exchanger is used to heat 12.6 kg/s of benzene is heated from 277.594 K to 299.817 K in the shell side heat exchanger using 12.6 kg/s hot water 355.372 K., The exchanger contains 828 tubes, 0.01905 m. OD, 3.6576 m long on 0.0254 m. square pitch. The baffles are 25% cut, and baffle spacing is 0.3048 m. the shell side is 0.889 m. Calculate the shell sheat transfer coefficient using the Donohue equation (4.18) and compare it with Equation 4.14 (The proper fluid package is NRTL).

Fig. 4.22 Process flowsheet of problem 4.6 generated by Hysys

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Fig. 4.23 Heat exchanger performance

Fig. 4.24 Benzene/water exchanger simulated by PRO/II Hand calculation

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Fig. 4.25 Benzene/water exchanger design 4.7 Heat exchanger for ethylbenzene and styrene Design a shell-and-tube heat exchanger to preheat a stream of 8.34kg/s containing equal amounts of ethylbenzene and styrene from 283.15 K to 370.372 K. Heat supply is medium saturated steam at 388.706 K at a flow rate of 10kg/s and atmospheric pressure. Additional data: Density = 856 kg m3 Viscosity = 0.4765 cP Specific heat = 0.428 kcal/kg °C Thermal conductivity = 0.133 kcal/h m °C The suitable fluid package is NRTL. Hysys solution

Fig. 4.26 Streams summary 40

Fig. 4.27 Heat exchanger performance PRO/II simulation

Fig. 4.28 Ethylbenzene, styrene/steam exchanger, simulated with PRO/II 4.8 Heating of methanol liquid mixture A liquid mixture of 134.2 kmol/h (0.97methanol, 0.02 ethanol, 0.01 water) enters a tube side of a shell and tube heat exchange at 25oC, and 1520 kPa is heated to 155oC using 1000 kgmol/h high-pressure steam at 15 atm. The exit high-pressure steam temperature is 160oC. Using UniSim/Hysys software package (PRSV), determine the inlet steam temperature. Neglect heat losses and pressure drop in the heat exchanger.

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Fig. 4.29 Heating of methanol liquid in exchanger simulated with UniSim 4.9 Cooling of dimethyl ether (DME) The DME gas mixture 100 kgmol/h (50 mol% DME, 35% H2O, 10% methanol, 5% ethanol) exits a reactor at 250oC and 1470 kPa is utilized to heat a methanol gas stream of 134 kmol/h (0.97methanol, 0.02 ethanol, 0.01 water) from 25oC and 1520 kPa to 200oC. Using UniSim/Hysys software package (PRSV), determine the DME exit stream temperature.

Neglect heat losses and pressure drop in the heat exchanger.

Fig. 4.30 Cooling of DME exchanger simulated with UniSim 4.10 Cooling of benzene/toluene liquid mixture The saturated liquid mixture (12 kgmol/h) of benzene and toluene (50% benzene) at 1 atm cooled to a temperature of 30oC using cooling water in a shell and tube heat exchanger. The cooling water inlet temperature is 15oC and 1 atm pressure, and the temperature increases in the heat exchanger to 25oC. Neglect heat losses and pressure drop in the heat exchanger. Using UniSim/Hysys, determine the cooling water inlet flow rate. Use the hot stream into the tube side and the cooling water into the shell side. Use PRSV for the fluid package.

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4.31 Cooling of benzene/toluene liquid mixture.

Chapter 5 5.1 Volume of CSTR reactor The inlet molar feed rate to the CSTR reactor is 50 kgmol/h ethanol, 50 kmol/h diethylamine, 100 kgmol/h water. The reaction is second order concerning ethanol, and the rate constant, k, A(ethanol) + B(diethylamine) ⎯⎯k→C(triethylamine + D(water) kJ   Where, k = (4775 m 3 -10000 kmol /RT )e 



kmol.h

Find the reactor volume that achieves 90% conversion of ethanol: a. If the reactor is isothermal. b. If the reactor is adiabatic. c. Compare the results in a & b.

Hysys Solution (Fig. 5.1) 1.

2.

3. a. b. c. d. e.

Open new case and select components Fluid package: NRTL Build the reaction Rate: kinetic A = 4775 m3/kmol h E= 10000 kJ/kmol Liquid phase Base component: Ethanol

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Fig.5 1 Stoichiometric page

Fig. 5.2 Reaction phase

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Fig. 5.3 reaction rate constant Assume room temperature and atmospheric pressure (i.e. 25oC, 1 atm) Adjust the reactor volume until 90% conversion is achieved

Fig. 5.4 Reactor volume required to achieve 90% conversion The answer looks like Fig. 5.5

Fig. 5.5 Stream summary

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PRO/II simulation (Fig. 5.6) Fluid package: NRTL

Fig. 5.6 CSTR reactor simulated with PRO/II 5.2 Conversion in PFR reactor 100 kgmol/h of acetone is fed to an isothermal plug flow reactor (PFR). The inlet temperature and pressure of the feed stream is 750oC and 1.5 atm, respectively. The reaction is taking place in vapor phase. Acetone ( CH3COCH 3 ) is cracked to ketene ( CH 2CO ) and methane ( CH 4 ) according to the following reactions: CH3COCH3 ⎯⎯→CH2CO + CH4 The reaction is first order with respect to acetone and the specific reaction rate can be expressed by

( )

k = 8.21014 s−1 e

−2.845105 (kJ / kmol) RT

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Calculate the reactor volume required to achieve 45% of limiting components.

Hysys Solution (Fig. 5.7 – 5.12) 1. Add components 2. Fluid package: PRSV 3. Build the reaction

Fig. 5.7 Reaction stoichiometric and reaction order

Fig. 5.8 Reaction base components conditions

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Fig. 5.9 Forward reaction rate constants

Fig 5.10 Isothermal plug flow reactor conversion

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Fig. 5.11 Reactor volume to achieve 40% conversion

Fig. 5.12 Stream summaries

PRO/II simulation (Fig. 5.13. 5.14)

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Fig. 5.13 Process flowsheet

Fig. 5.14 Reaction rate

5.3 Styrene production Styrene is made from the dehydrogenation of ethylbenzene in a plug flow reactor, C8 H10 → C8 H8 + H2 The feed consists of 780 kmol/h ethylbenzenes, the reaction is isothermal, inlet temperature and pressure are 600oC, and 1.5 atm, respectively. The reaction rate is first order concerning ethylbenzene. Calculate the percent conversion of ethylbenzene if the reaction occurs in a 150 m3, 3 m length plug flow reactor. The reaction rate is: r = −kPEB , where PEB is the partial pressure of ethylbenzene. kmol exp− 90000 kJ / RT  The specific reaction rate constant, k = 200 3   m skP a kmol Hysys Solution (Fig.5.15 to 5.20) 1. Add components 50

2. Fluid package: Peng Robinson 3. Build the reaction

Fig. 5.15 reaction stoichiometric and reaction order

Fig. 5.16 Base components

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Fig 5.17 Reaction rate constant

Fig. 5.18 Isothermal reaction actual percent conversion

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Fig. 5.19 Reactor volume and length

Fig. 5.20 Stream summaries PRO/II simulation (Fig. 5.21-5.22)

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Fig. 5.21 Kinetic data, PRO/II

Fig. 5.22 Stream summary (V=150 m3) 5.4 Ethylene production Ethylene is produced by dehydrogenation of ethane in an isothermal plug flow reactor at 800oC and 3 atm. The reaction taking places is C2H 6 ⎯⎯K1→C2 H 4 + H 2 Reaction rate: r1 = k1CC2H 6 The specific reaction rate constant: k = 4.651013 (s−1) exp(−2.7 105

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kJ / RT ) kmol

Find the reactor volume that is required to achieve 65 % conversion of ethane. a. What if the reaction is taking place isothermally. b. What if the reaction is taking place in an adiabatic reactor. c. Discuss results in pars a and b.

Hysys Solution (Fig. 5.23-5.28) 1. Select components involved in the reaction process 2. Fluid package: Peng Robinson 3. Build reaction rate

Fig. 5.23 reaction stoichiometric coefficients

Fig. 5.24 Reaction phase

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Fig. 5.25 Reaction rate constants

Fig. 5.26 Reactor dimensions

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Fig. 5.27 Reaction percent conversion

Fig. 5.28 Process flow sheet and streams’ summary PRO/II simulation (Fig. 5.29, Fig. 5.30)

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Fig. 5.29 Plug flow reactor process flowsheet (L= 2.5 m, D = 0.431m)

Fig. 5.30 Kinetic data enters to PRO/II

5.5 Catalytic reaction Consider the multiple reactions that take place in PFR; the reactions parameters are shown in Table 5.8 CH4 + H2O  3H2 + CO

CO + H2O  H2 + CO2 Reaction rate

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r1 =

− Ea1 R*T

b * A1 * e PCH 4 (1 + K a * PH ) 2

− Ea2

r2 = b * A2 * e

R*T

( y CH 4 * yH 2O −

yCO * yH 2

K

2

)

eq2

Where b is the bulk density, A1 ,A2 is the pre-exponential factor or Arrhenius constant of the first and second reactions, respectively. Ea1 Ea2 , are the activation energy of the first and second reactions, respectively. Where k a is an absorption parameter, and yi is the mole fraction of component i .

Table 5.8 reaction constant

b 1200 Kg/m3 A1 5.517 106 mol/kg s atm Ea1 1.849 108 J/mol R 8.314 J/mol/K P 30.0 atm Ka 4.053 atm-1 A2 4.95108 mol/kg/s Ea2 1.163 105 J/mol Keq2 e-4.946+4897/T (T in K)

Feed enters the reactor at 350 oC, 30 atm, and 2110 mol/s with feed mole fractions; 0.098 CO,0.307 H2O, 0.04 CO2, 0.305 Hydrogen, 0.1 Methane, 0.15 Nitrogen.

Hysys Solution (Fig. 5.31-5.55) 1. Open new case in Hysys, select components involved in the reaction, close component windows and click on fluid package tab and select “Peng Robinson” fluid package, the click enter the simulation environment.

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Figure 5.31 Component selection page 2. Click on the flowsheet on the Hysys tool bar and select Reaction Package.

3. Select Heterogenous reaction and name it “Rxn-1.”

Figure 5.32 Stoichiometric page of the catalytic reaction 4. The reaction phase tells HYSYS in which stage the reaction is to take place. Your options for this are: Overall -- reaction occurs in all Phases Vapour Phase -- reaction only occurs in the Vapour Phase.

Liquid Phase -- reaction only occurs in the Light Liquid Phase.

Aqueous phase -- reaction only occurs in the Heavy Liquid Phase.

Combined liquid -- reaction occurs in all Liquid Phases.

Basis: Partial pressure because the reaction rate is a function of partial pressure

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Base Component: Methane, Hysys default component is the component of stoichiometric coefficient equal 1.

Reaction Phase: the reaction took place in the gas phase Basis unit: atm, Rate unit: kg mol/m3.s

Fig. 5.33 basis page 5. Select reaction phase as vapor or overall The Basis Page should look like this:

Figure 5.34 Basis page 6. On the Numerator Page, you shall begin filling in the information that will tell HYSYS the actual form of the rate equation. See kinetic help window below,

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Figure 5.35 Kinetic equation help menu 7. The Activation Energy, E = 1.849E8 J/mol, of the reaction may be entered as E of the forward reaction. The number you enter into A for the forward reaction must be the product of b and km divided by 1000 (the units need to be in kg mole/m3/s, not mole/m3/s), equal to 6620400. It should look something like this:

Figure 5.36 Numerator page 8. Note that the status has changed to Ready. On the denominator page, enter Kh = 4.053 into A, set E equal to 0, and put a 1.0 under hydrogen.

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Figure 5.37 Denominator page 9. Close the window, open a simple rate reaction.

Figure 5.38 Stoichiometry page 10. Add the components and the stoichiometric coefficients like we did for the first reaction, then move to the Basis Page.

63

Figure 5.39 simple rate basis menus 11. On the Basis Page, set the basis to Mole Fraction, the reaction phase to Overall or Vapour Phase, and the reaction units to kmol/m3-s. Moving on to the Parameters Page, we see that the Kinetics Help is already on the page this time. Enter A = 5.94e8 (bulk density*A/1000) and E = 1.163E5 J/mol. For the rest, we need to use the expression in the chart for Keq2: Keq2 = e-4.946 + 4897/T. Note that the natural log of this is what we want to enter into Hysys. Therefore, A' = -4.946 and B' = 4897. The T used in their expression is always in Kelvin.

Figure 5.40 Simple rate Parameters page 12. Close his window and return to the Reactions Page of the Simulation Basis Manager. Add both reactions to a reaction set.

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Figure 5.41 Reaction set 13. Close the window; UniSim/Hysys Reaction page should look like Figure 5.16:

Figure 5.42 Simulation basis managers 14. If you open your reaction set from the simulation basis manager, your reaction page should look like figure 5.17

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Figure 5.43 Simulation basis managers 15. On the feed’s conditions page, set the temperature to 350 oC, the pressure to 30 atm, and the total flowrate to 2110 moles/s (7596 kmol/hr).

Figure 5.44 Feed stream conditions Fill out the compositions as shown below.

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Figure 5.45 feed input composition 16. Palette adds a Plug Flow Reactor to the flowsheet and connects the Feed and Product streams from the object.

17. Double Click on the PFR. On the parameters page, set the Pressure Drop to 0.

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Figure 5.46 Pressure drop parameters window 18. On the sizing page, fill in the reactor volume dimensions.

Figure 5.47 PFR tube dimensions 68

19. Click the “Reactions” tab. Enter your reaction set, in this case, “Set-1,” as shown in Figure 5.23.

Figure 5.48 Converged PFR

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Figure 5.49 Reaction set 20. Click on the Performance tab to see the results:

Figure 5.44 Temperature versus reactor length

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5.6 Production of trans-butane Pure cis-2-butene reacts to produce trans-2-butene in a continuous stirred tank reactor at 100 kgmol/h, 10 bar, and 25oC. Calculate the volume required to achieve 90% conversion. The reaction rate: 𝑟𝐴 = −𝑘𝐶𝐴, 𝑘 = 0.004 𝑠−1 Use UniSim software or other available software packages to simulate the reaction process (Peng Robinson is a suitable fluid package).

Figure 5.45 UniSim generated process flow diagram and stream summary of Problem 5.6 5.7 Production of propylene glycol Propylene glycol resulted from the reaction of propylene oxide, and an excess amount of water in a 2 m3 stirred tank reactor (CSTR) operating isothermally at atmospheric pressure and 25oC. The combined water, ethylene oxide mixture, is fed at a 500 kgmol/h consisting of 80% water, and the balance is ethylene oxide. 𝐶3𝐻6𝑂 + 𝐻2𝑂 → 𝐶3𝐻8𝑂2 The reaction rate is first order concerning propylene oxide, and the reaction rate constant is 𝑘𝐽 75330 𝑘𝑚𝑜𝑙 𝑘 = 1.7 × 1013 exp ( ) 𝑅 Use UniSim/Hysys (NRTL) to find the ethylene oxide conversion. Consider kinetic reaction type, the reaction phase is a combined liquid, and the base component is ethylene oxide.

71

Figure 5.46 UniSim generated process flow diagram and stream summary of Problem 5.7.

5.8 Ethylene production Determine the volume necessary to produce ethylene from cracking a feed stream of 100 kgmol/h of pure ethane. The reaction is irreversible and elementary. The Plug flow reactor (50 m3) operates isothermally at 880oC and a pressure of 5 atm. 𝐶2𝐻6 → 𝐶2𝐻4 + 𝐻2 The reaction rate is first order concerning ethane. The Arrhenius constant, A = 1.3×1013 and activation energy, E=3.5×105 kJ/kmol. Using UniSim/Hysys, determine the fraction conversion of ethane to ethene. The appropriate fluid package is Peng-Robinson, which uses the kinetic reaction type, and the reaction is in the vapor phase.

Figure 5.47 UniSim generated process flow diagram and stream summary of Problem 5.8.

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5.9 Ketene production Calculate the PFR reactor volume to achieve 15% conversion of acetone to ketene and methane.

The reactor is operating in adiabatic conditions. The following reaction is taking place: 𝐶𝐻3𝐶𝑂𝐶𝐻3 → 𝐶𝐻2𝐶𝑂 + 𝐶𝐻4 The reaction is irreversible and elementary; the reaction rate constant is 𝐽 −2.85 × 10 5 ( 𝑚𝑜𝑙) −1 14 ) 𝑘(𝑠 = 8.2 × 10 exp ( ) 𝑅𝑇 The feed rate is 138 kgmol/h acetone at 730oC and 150 kPa. Use UniSim/Hysys to find the reactor volume. The recommended fluid package is PRSV; consider kinetic reaction type and vapor phase.

Figure 5.48 UniSim generated process flow diagram and stream summary of Problem 5.9 5.10 Production of isobutene Normal butane isomerized to isobutene in a CSTR reactor. This irreversible elementary reaction is carried out adiabatically in the liquid phase under high pressure using a liquid catalyst with a specific reaction rate of 0.5s-1. The feed enters at 330 K and 1 atm. Calculate the PFR volume necessary to process 160 kmol/h at 70% conversion of a mixture of 90 mol % n-butane and 10 mol % i-pentane, which is considered inert. Simulate the CSTR in UniSim/Hysys (NRTL); the reaction phase is overall.

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Figure 5.49 UniSim generated process flow diagram and stream summary of Problem 5.10.

Chapter 6 6.1 Shortcut Distillation The feed to a distillation column is at 207°C and 13.6 atm enters at 577 kmol/h with the following compositions in mole fraction: Ethane 0.0148, propane 0.7315, i-butane 0.0681, nbutane 0.1462, i-Pentane 0.0173, n-pentane 0.015, n-hexane 0.0071. HK in the distillate is an i-butane 0.02-mole fraction; LK in the bottom is propane 0.025-mole fraction for reflux ratios of 1.5. Use UniSim (the suitable fluid package is PR) or any other software package to calculate the minimum reflux and column performance.

Hysys Solution Defining Simulation Basis 1. Start new case 2. Add the component: ethane, propane, i-butane, n-butane, i-pentane, n-pentane, n-hexane 3. Select the Peng Robinson as fluid package 4. Enter simulation environment Adding the feed stream Add a material stream with the following data In this cell Enter Name Feed Temperature 207oC Pressure 13.6 atm 74

Flow Rate Component Ethane Propane i-butane n-butane i-pentane n-pentane n-hexane

577 kmol/h Mole Fraction 0.0148 0.7315 0.0681 0.1462 0.0173 0.0150 0.0071

Adding the unit operation Short Cut Distillation column 1. Double click on the Distillation column button in the object Palette.

2. Complete the view (Fig. 6.1).

Fig. 6.1 Connection page 3. Press the Parameter button 4. Supply the following information to the Parameter page (Fig. 6.2).

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Fig. 6.2 Parameters page

The result can be viewed from Performance tab (Fig. 6.3).

Fig. 6.3 Performance page

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PRO/II simulation (Fig. 6.4, Fig. 6.5)

Fig. 6.4

Summary of Underwood calculations

Fig. 6.5 Process flowsheet of the shortcut distillation method

6.2 Rigorous Distillation Column The feed to a distillation column is at room conditions (T = 25°C, P = 1 atm). The concentration of the feed stream is 50% ethanol, 50% iso-propanol in mass fractions. The feed is at a rate of 74 kg/h. We will assume a load of 35.169 kW for the reboiler heat duty, assume the number of trays to be 24, and the reflux ratio equals 3. Find the conditions of the exit streams. Use UniSim (the suitable fluid package is NRTL) or any other software package to calculate the minimum reflux and column performance.

Defining Simulation Basis 1. Start new case 2. Add the component: ethanol, iso-propanol 3. Select the NRTL as a fluid package 4. Enter simulation environment 77

Adding the feed stream Add a material stream (Temperature, pressure, flow rate, and composition).

Adding the unit operation Distillation column 1. Double click on the Distillation column button in the Object Palette.

2. Complete the view as shown below (Fig. 6.6)

Fig. 6.6 Connections page 3. Press the Next button to proceed to the next page 4. Supply the following information to the pressure estimate page.

Condenser pressure = Reboiler pressure = Feed pressure = 1 atm (Fig. 5.7)

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Fig. 6.7 Column pressure 5. Press the Next button to proceed to the next page Optional not required (Fig. 6.8).

Fig. 6.8 Temperature optional page 6. Press the Next button to proceed to the next page 7. Supply value of reflux ratio (Fig. 6.9).

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Fig. 6.9 Reflux ratio page

8. Press the Done button When the done button pressed, HYSYS will open the Column Property View window 9. Access the monitor page from the Design tab.

Fig. 6.10 Monitor page To converge the column 1. Press Add Specification button to create a new specification 2. Select Column Duty from the list that appears (Fig. 6.11).

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Fig. 6.11 Specs selection page 3. Press Add Specification button 4. Complete the specs as shown in Figure 6.12.

Fig. 6.12 Duty spec selection page 5. Close the window 6. Go to the monitor page. Deactivate the Distillate Rate as an active specification and activate the Duty specification, which was created Once the column has converged, the result viewed from the Performance tab (Fig. 6.13)

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Fig. 6.13 Distillation column performance page PRO/II simulation (Fig. 6.12)

Fig. 6.14 process flowsheet of rigorous distillation, PRO/II 6.3 Rigorous Distillation Column Repeat Example 6.2; assume that the reboiler duty is unknown. The overhead ethanol concentration is 0.55. What is the amount of the reboiler load in kW?

Solution 1. Go to the monitor page. Deactivate the Duty as an active specification 2. Press Add Specification button to create a new specification 3. Select Column Component Fraction from the list that appears (Fig. 6.15).

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Fig. 6.15 Add specs page 7. Press Add Specification button 8. Complete the specs (Fig. 6.16).

Fig. 6.16 Parameters specs page 9. Close the window 10. Go to the monitor page. Activate the Component Fraction specification, which was created Once the column has converged, the result viewed from the Performance tab (Fig. 6.17).

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Fig. 6.17 Performance page PRO/II simulation (Fig. 6.18-6.19).

Fig. 18 Continuous distillation with ethanol mass fraction in the distillate is 0.55

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Fig. 6.19 Reboiler heat duty 6.4 Rigorous Distillation Column Repeat example 6.2; in this case, calculate the reflux ratio that would given an ethanol concentration of 80% with a reboiler duty of 300,000 Btu/hr (8.069e+4 kcal/h) is to be calculated.

Solution 1. Go to the monitor page. Deactivate the Component Fraction and Reflux Ration as active specifications 2. Press Add Specification button to create a new specification 3. Select Column Duty from the list that appears (Fig. 6.20).

Fig. 6.20 Specs page

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4. Press Add Specification button 5. Complete the specs as shown in the following figure (Fig. 6.21).

Fig. 6.21 Specs value unit selection 6. Close the window 7. Press Add Specification button to create a new specification 8. Select Column Duty from the list that appears (Fig. 6.22).

Fig. 6.22 Specs value 86

9. Press Add Specification button 10. Complete the specs as shown in the following figure 11. Close the window 12. Go to the monitor page. Activate the Component Fraction specification, which was created Once the column has converged, the result is viewed from the Performance tab (Fig 6.23).

Fig. 6.23 Performance page PRO/II simulation (Fig. 6.22-Fig. 6.23)

Fig. 6.24 Ethanol mass fraction of 0.8 and reboiler duty 300000 Btu/h

Fig. 6.25 Reflux ratio

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6.5 Separation of benzene, toluene, and trimethyl-benzene Use a distillation column with a partial reboiler and a total condenser to separate a mixture of benzene, toluene, and trimethyl-benzene. The feed consists of 0.4-mole fraction benzene, 0.3mole fraction toluene, and trimethyl-benzene balance. The feed enters the column as a saturated vapor and separated 95% of the distillate’s toluene and 95% of the bottom’s trimethyl benzene.

The column operates at 1 atm, the top and bottom temperatures are 390 and 450 K, respectively. a. Find the number of equilibrium stages required at total reflux. b. Find the minimum reflux ratio for the previous distillation problem using the Underwood method. c. Estimate the total number of equilibrium stages and the optimum feed-stage location if the actual reflux ratio R equals 1. d. Use UniSim software (the suitable fluid package is PRSV) or any other software package to calculate the minimum reflux ratio and column performance.

Hand calculation using the shortcut method Bases Components Benzen Toluene(Lk) Trimethyl Benzene(Hk) Total

Xif 0.4 0.3

100 F* Xif 40 30

D*XiD 40 28.5

XiD 0.571428571 0.407142857

W*Xiw 0 1.5

Xiw 0 0.05

0.3 1

30 100

1.5 70

0.021428571 1

28.5 30

0.95 1

PvTop

Pvbottom

α top

4.502890173

1.67

6.3

α Bottom

3.4

0.779

3.4

α average

3.91277735

0.173

1

N min

4.316576142

Part B: Find the minimum reflux ratio for the previous problem using the Underwood method.



n

i=1



n

i=1

i x if i −  i x if i − 

= 1− q = 1+ R min

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αB αT α TMB

TOP 9.653 4.503 1

assume theta Rmin

αB αT α TMB

BOTTOM 6.3 3.4 1

α AVG 7.7984 3.9127 1

2.211 1 0.7156

Part C: Estimate the total number of equilibrium stages and the optimum feed-stage location if the actual reflux ratio R equals 1 (Fig. 6.26).

Fig. 6.26 Gilliland correlation page

Rmin = 0.7156 and Ro = 1 Nmin= 4.32 Using Gilliland correlation N- Nmin/ N+ 1= 0.5 N = 9.64 Using Kirkbride empirical relation: Log (Nabove / Nbelow) = 0.206 Log [(XHF / XLF) (W / D) (XLW / XHD)2] Log (Nabove / Nbelow) = 0.206 Log [(0.3 / 0.3) (30 / 70) (0.05/ 0.02)2] Log (Nabove / Nbelow) = 0.088 (Nabove / Nbelow) =1.22 Nabove = 1.22Nbelow Nabove + Nbelow = N 1.22Nbelow + Nbelow = N Nbelow = 3.582 Nabove = 4.2657 89

Fig. 6.27 VB program Solution (using Hysys): 1. Choose the components: benzene, toluene and trimethyl-benzene (6.28).

Fig. 6.28 Component selection page 2. Choose the fluid package: Peng-Robinson (Fig. 6.29).

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Fig. 6.29 Fluid package selection page

3. Chose the distillation column: Short Cut Distillation (Fig. 6.30)

Fig. 6.30 UniSim generated shortcut distillation column.

4. Specify the feed: vapor/phase fraction = 1, pressure = 1 atm, molar flow = 100 kmole/h, composition (Fig. 6.31-6.33).

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Fig. 6.31 Stream conditions

Fig. 6.32 Stream conditions 92

4. Specify the mole fraction of the LK in the bottom and the HK in Distillate. Specify the pressure of the condenser and reboiler (Design → Parameters).

Fig. 6.33 Process flowsheet and stream summary

TB in the Distillate = (1.5)/(1.5+28.5+40) = 0.02 T in the Bottom= (1.5)/(1.5+28.5) = 0.05 A) Equilibrium stages required at total reflux = 3.739 B) Minimum reflux ratio = 0.634

Fig. 6.34 Parameters page

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Fig. 6.35 Parameters page

6. Put External reflux ratio =1, the total number of equilibrium stages = 8.029, and optimal feed stage = 4.425.

Fig. 6.36 Parameters page 94

PRO/II simulation (Fig. 6.37, 7.38)

Fig. 6.37 PRO/II generated the shortcut results.

Fig. 6.38 Minimum reflux ratio Conclusion There is a slight difference between the hand calculation values and the Hysys results. The assumption used in hand calculations for the lighter than the light key (benzene) is equal to zero, but with Hysys it was a 0.036-mole fraction.

6.6 Separation of hydrocarbon mixtures A mixture with 4% n-C5, 40% n-C6, 50% n-C7, and 6% n-C8 distilled at 1 atm with 98% of nC6 and 1 % of n-C7 recovered in the distillate. Use UniSim (the suitable fluid package is PR) or any other software package to calculate the minimum reflux ratio for a liquid feed at its bubble point.

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Manual calculations: The solution is performed by using excel to find the results like the following: 1- Inserting the data related to each component, then plot the graph for k values.

2- Insert the component to find at the end of the products, which should be = to the feed.

3- Again find the bubble point to the system to find L minimum, then find the R minimum.

Table 6.1. Fittings of K values as a function of temperature A K(n-C5) K(n-C6) K(n-C7) K(n-C8)

B -6.67E-05 4.17E-06 -1.49E-06 7.76E-07

C 1.40E-02 -6.31E-04 6.69E-04 -3.4E-05

d -8.98E-01 5.92E-02 -5.74E-02 -1.04E-03

2.00E+01 -1.42E+00 1.645 0.135

Fig. 6.39 calculation to find the amount of the products Comp n-C5 n-C6 (LK) n-C7 (HK) n-C8

xif 0.04 0.4 0.5 0.06

Check

F xif DxiD xiD W xiw xiw 0.04 0.04 0.091533 0 0 0.4 0.392 0.897025 0.008 0.01421 0.5 0.005 0.011442 0.495 0.879218 0.06 0 0 0.06 0.106572 F D ∑xiD W ∑xiw 1 0.437 1 0.563 1 F=D+W 1

Table 6.3. Calculation to find R minimum L min /f=[(LK recovery on top)-(1HK recovery in bottom)*aAB]/(aAB-1) 0.622 f=1 T bubble assumed

79.75548 96

l min R min

0.622 1.423341

Comp n-C5 n-C6 (LK) n-C7 (HK) n-C8

Xif 0.04 0.4 0.5 0.06

Ki yi=Ki xif 3.58055 0.143222 a AB 1.403296 0.561318 1.992868 0.563327 0.281664 0.230022 0.013801 1.000005

Table (6.4):Equation used in calculation F xif Xif *F DxiD of light key recovery*F Xif Xid Dxid/D Xiw W xiw/ W Ki of light key/Kiof a AB heavy key R min Lmin/D

Fig. 6.40 VB program Hysys program (Fig. 6.41) - Insert components and choose the PRSV fluid package.

- Put shortcut column and name the streams.

- Insert data given in the feed with considering mole fraction of the composition.

- Put data given in the parameter in the shortcut method.

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-

See the results.

Fig. 6.41 amount of the products in the top and bottom

Fig. 6.42 UniSim calculated the minimum reflux ratio.

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Fig. 6.43 UniSim shortcut column generated distillation column performance.

Conclusions: The results seem to be the same between hand calculation and Hysys.

PRO/II simulation (Fig. 6.44)

Fig. 6.44 PRO/II simulation

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Fig. 6.45 Column specifications

6.7 Separation of the multi-component gas mixture A feed at its bubble point temperature is fed to a distillation column. The feed contains propane (C3), n-butane (n-C4), i-butane (i-C4), n-pentane(n-C5) and i-pentane(i-C5). The mole % of components in the feed is respectively 5%, 15%, 25%, 20% and 35%. The operating pressure of the column is 405.3kPa. 95% of the i-C4 is recovered in the distillate (top), and 97% of the n-C5 is recovered in the bottom. Determine the top and bottom flow rats and composition, minimum reflux ratio, and the minimum number of trays at a reflux ratio of 2.25.

Hand calculations The problem needs many iterations to solve this problem twice, once by excel and the other method by Hysys.

The method used here is the shortcut method. Shortcut calculation methods for the approximate solution of multi-component distillation are pretty helpful for the following reasons: • To study a large number of cases (rapidly).

• To determine optimum conditions (approximately).

• To provide fast information for cost estimation.

There are some assumptions for shortcut method calculations which are listed below: • The designer usually chooses 2.0 components in which recoveries in D & W are a good index of the separation.

•

These components are called Key-Components.

•

The Key-components must differ in volatility.

•

The more volatile is called the light key.

•

The less volatile is called the heavy key.

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•

The designer arbitrarily assigns small values XDH & XWL for top and bottom products.

•

All comp’s that are lighter than the light key will be recovered entirely in the top product.

•

All comp’s that are heavier than the heavy key will be recovered in the bottom product.

•

Usually, key components are adjacent in the rank order of volatility (sharp separation).

•

The key components are the only components that appear in both products.

•

Calculations:

a) the distillate and bottom flow rates are shown in the table below:

Comp n-C3 i-C4 n-C4 i-C5 n-C5

xif

Xi*F 0.05 0.15 0.25 0.2 0.35 1

50 150 250 200 350 1000

D 50 150 237.5 6 0 443.5

Xid B Xib 0.11274 0 0 0.338219 0 0 0.535513 12.5 0.022462 0.013529 194 0.348607 0 350 0.628931 1 556.5 1

where xif is the composition of components in the feed, xi*F is the flow rate of each composition in the feed, D is the flow rate of the distillate assuming that all components lighter than the lighter key (which is n-C4 here) are totally transferred to the top, 95% of the light key is recovered in the top, 3% of the heavy key (i-C5) is recovered in top and the heavier than the heavy key is totally recovered in the bottom. The summation of all of this flow rates are the distillate.

Moreover, the composition of each component is found by dividing each flow rate by the total flow rate. These procedures are the same for B (bottom) flow rate and compositions. b) The minimum reflux ratio is calculated by the underwood method which uses the two equations below: ∑(αi*Xif/ αi-Φ)=1-q ∑(αi*Xid/ αi-Φ)=1+Rmin In the first equation q is the feed quality and αi is the average volatility for each component. Φ is calculated first from the first equation by iterations in excel if q is known. As mentioned before, the feed is at its bubble point and the q value for this condition is = 1. Average volatility are calculated for both top and bottom by the following equation: αi= ki / kb; where k is the vapor – liquid equilibrium constant (distribution coefficient) and the kb is the constant for the heavy key. The k values are represented in correlations which are temperature dependent. The correlations for each component are listed below: • C3: 0.0002T2+0.0021T+1.2774 101

•

i-C4: 0.0001T2+0.0084T+0.2417

•

n-C4: 0.0002T2-0.008T+0.656

•

i-C5: 6*10^-5T2+0.0009T+0.1355

•

n-C5: 0.0002T2-0.0205T+0.9738

The temperatures for the top and bottom are found by convergence using the solver in excel.

The target cell is setting the summation of x or y, depending on if it is done for top and bottom, equal to zero by changing the temperature cell. The tables below show the top and bottom calculations: Note that the Yid and xif are the compositions calculated in the xid and xiw: Td Comp n-C3 i-C4 n-C4 i-C5 n-C5

59.43641109 Yid 0.112739572 0.338218715 0.535512965 0.013528749 0 1

ki 2.108754 1.094235 0.887046 0.400954 0.461891

Xid 0.053463 0.309092 0.603704 0.033741 0 0.999999

Tb Comp n-C3 i-C4 n-C4 i-C5 n-C5

104.9130239 Xif 0 0 0.022461815 0.348607367 0.628930818 1

ki 3.699066 2.223644 2.018044 0.890326 1.024432

Yid 0 0 0.045329 0.310374 0.644297 1

The table below shows the calculation of alpha: alpha bottom alpha top alpha avg 4.154730647 5.259341 4.674520977 2.497560409 2.729078 2.610753949 2.26663458 2.212339 2.239322186 1 1 1 1.150624837 1.15198 1.151302207

Where alpha average is calculated by using αL av = (αLD αLW)0.5, by applying these equations, the values of phi and Rmin are: Phi 1.575 102

Rmin

1.804151

c) Nmin is calculated by the following equation: Nmin = Log [(XLD/XHD)(XHW/XLW)] / Log (αL av) •

XLD: mole fraction of light key in the distillate.

•

XLW: mole fraction of light key in the bottom.

•

XHD: mole fraction of heavy key in the distillate.

•

XHW: mole fraction of heavy key in the bottom.

•

αLav: average value of αL of the light key.

•

αLD: top temperature (i.e., dew point) of the tower.

•

αLW : bottom temperature (i.e., bubble point) of the column.

By applying the above equation Nmin=7.96

Hysys simulation (Fig. 6.46) In Hysys, the package data used is PRSV, and the distillation column is the shortcut. Specify the feed composition, temperature, pressure, reflux ratio, light and heavy keys in the bottom, and distillate. Also, the condenser and reboiler pressure should be specified, which is assumed to be the same as the feed pressure. The results are shown below for part a:

Fig. 46 Shortcut column, Hysys

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Fig. 6.47 Column performance b) Rmin=1.011 c) Nmin=5.754 PRO/II simulation (Fig. 6.48)

Fig. 6.48 PRO/II results

Fig. 6.49 summary of underwood calculations, PRO/II Conclusions 104

There are minor differences between the two answers.

6.8 Separation of methanol, water, phenol a distillation column utilized to separate a mixture of methanol, water, and phenol. The feed stream is at 65oC and 1.7 bar, the inlet mass flow rate is 4530 kg/h, the stream component mass fractions are 0.6, 0.39, and 0.01 for methanol, water, phenol, respectively. Use the shortcut distillation method to determine the minimum reflux ratio, and for the fluid package, use NRTL-RK. The distillate’s expected methanol recovery is 99% methanol (LK) and water 1% (HK). Assume the condenser pressure is at 1.1 bar and reboiler pressure at 1.7 bar.

Solution

Figure 6.50. UniSim generated the shortcut column the minimum reflux ratio (0.899) for the case described in problem 6.8.

6.9 Separation of Dimethyl ether (DME) Dimethyl ether at a feed rate of 135 kgmol/h (55oC and 1040kPa) contains 44mol% DME, 46%, 8% methanol, and 2% ethanol is separated in 5 trays distillation column. It is desired to achieve 60 kmol/h as the top product containing a DME mole fraction of more than 98%. The reflux ratio is 2. Use UniSim/Hysys software package (PRSV) to simulate the distillation column and fined the DME mole fraction in the distillate.

Solution

105

Figure 6.51. UniSim generated process flow sheet and stream summary of the case described in Problem 6.9.

6.10 Separation of ethanol from methanol/ethanol/water liquid mixture A feed to a distillation column is 75 kgmol/h at 50oC, and 740 kPa contains 80 mol% water, 17% methanol, 3% ethanol. Use the shortcut column in UniSim/Hysys (PRSV) to obtain 99% ethanol in distillate and 99% methanol in the bottom. Calculate the minimum reflux ratio.

Using a reflux ratio of 1.5 times the minimum reflux ratio, find the actual number of trays.

106

Figure 6.52. UniSim generated process flow sheet and stream summary of the case described in Problem 6.10

Figure 6.53. UniSim generated the performance of the shortcut column of the case described in Problem 6.10.

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Chapter 7 Problem 7.1 Absorption of ammonia in the packed tower Ammonia NH3 is absorbed by water in a packed column. The inlet polluted air stream is 20,000 ppm NH3. The air stream flow at a 7 ft3/min rate, and the column operate at 70oF and 1 atm.

The inlet water is pure flowing at a rate of 500 ml/min. The concentration of ammonia in the exit air should not exceed 250 ppm. The packing consists of ceramic Raschig rings, length 3/8 inch, width 3/8 inch, wall thickness 1/16 in, weight 15 lbs/cubic foot, equivalent spherical diameter is 0.35 inch, 0.68 void fraction. The packed column consists of 4 inch ID by a 36-inch long section of borosilicate pipe. Determine the number of transfer units, column diameter, and column height, and then verify your answer with simulation results obtained from Hysys, PRO/II, Aspen, and SuperPro designer software packages.

7.1.1 Manual calculations The concentration of ammonia in the inlet and exit air is: Concentration of NH3 in air feed = 20,000 ppm Concentration of NH3 in effluent air = 250 ppm Gas inlet molar flow rate:  7 ft3  28.32 L  1 gmol  (460 + 32) R   ft3  22.4 L  (460 + 70) R  = 8.125 gmol / min Gm =  min      Liquid molar flow rate:  500 ml  1 g  1 gmol  Lm =  min   18 g  = 27.8 gmol / min ml     NH 3 mole fraction in water feed (fresh water)

xB = 0 NH 3 mole fraction in inlet air: y =

20,000 /(17 g NH 3 / mol )

= 0.034 1,000,000 /(29 g air / mol ) Ammonia mole fraction in exit air: A

250 /(17 g / mol ) = 0.00043 1,000,000 /(29 g / mol ) Ammonia/water vapor-liquid equilibrium data at various temperatures are available in Perry’s Handbook. From these data, a Henry’s Law constant can be derived. Assuming T = 50 oF, the partial pressure, PNH over 0.05 mole fraction aqueous ammonia = 0.47 psia, hence mole yB =

3

fraction 0.47 psia y= = 0.0319 14.7 psia y 0.0319 y=K x K = = = 0.638 H H x 0.05 Hence the equilibrium line y = 0.638 x Operating line x = (V / L) y − yB The number of transfer units (NTU) can be calculated using the following two methods

108

0.034

0.034

0.034

dy dy dy =  =  NTU =  * y − y 0.00043 y − (0.63x) 0.00043 y − (0.63(V / L) y − yB ) 0.00043 0.034

0.034

dy dy =  NTU =  y − (0.63(8.125 / 27.8) y − 0.00043 ) 0.00043 0.816 y + 0.00027 0.00043

NTU =

1 1 0.034 ln0.816 y + 0.00027 0.00043 = (− 3.575 − (−7.394)) = 4.67 0.816 0.816

Second method:  yi − mxi  1  1  ln  1− AF  + AF  y − mx  i   o  NTU =  1 1− AF L 27.8 AF = = = 5.363 mV 0.638x8.125  0.034 − 0  1  1  ln  0.00043 − 0 1 − 5.363  + 5.363     = 5.12 NTU =  1 1− 5.363 Determining Column Diameter: The tower diameter may be determined using the modified generalized pressure drop correlation presented in Figure 1.5.

The x-axis X axis  L  G = G   L  27.8 mol  18 1b  min lbmol 3 = Xaxis =   0.0711b / ft 0.0715  8.15 mol 29 lb  62.4lb / ft 3    min lbmol   The Ordinate value (Y-axis) in the graph is expressed as [10]

(G )  F  = 2

Y

axis

f

p

 L G gc

0.2 L

  = 10^ −1.668 −1.085(log 0.0715) − 0.297(log 0.0715) = 0.153

Yaxis = 10^ −1.668 −1.085(log Xaxis ) − 0.297(log Xaxis )

2

Yaxis Equation 1.18 may then be rearranged to solve for Gf:    g (Y )  G = L G c axis  f 0.2   Fp(L )  Substituting needed values:

109

2

0.5

(62.4lb / ft 3 )(0.071lb / ft 3 )(32.2 ft / s 2 )(0.153)  Gf =   = 0.265 lb / s. ft 0.2 (318)(1)(0.893 )   2 The cross-sectional area of the tower (ft ) is calculated as:  mol 1min  29 g  1lb  8.125 G MW  60 s  mol  454 g   min     = 0.047 ft 2 m G A= = 2 f Gf (0.7)(0.265lb / ft s) The tower diameter: Dt =

4A



=

4 0.047



=0.245 ft

Estimation of Column Height For this purpose, the method used to calculate the height of the overall transfer unit is based on estimating the height of the gas and liquid film transfer units, HL and HG, respectively: [4] 1 HL Htu = HG + AF The following correlations may be used to estimate values for HL and HG: [13] The height of gas transfer unit, H G H =  ( f G f )  G  G  ( L )   G DG f G f = 0.265lb / ft2 s  gmol  1min  1lbmol  18lb   454 gmol  lbmol  Lm 27.8 min  60 s    L = = = 0.39 lb / s. ft 2 f A 0.047 ft 2 0.45   0.265lb     0.7 ft 2 s    0.044 lb / ft h 2.32  0.47 = 1.18 ft HG =   0.39lb  ( 0.071lb / ft 3 )(0.914 ft 2 / h)     2    ft s   The height of liquid transfer unit, H L b  Lf  L  H L = a DL  L  Substitute the needed value; 0.46  s  0.39 lb    3600   h  ft 2 s   H = 0.00182   L 2.16lb / ft .h     

2.16lb ft h 2

2   62.4lb  1 ft   3600 s  −5 cm   1.76   10  3 s  30.48cm   h   ft 

The height of transfer of unit is: H L = 0.8 ft The depth of packing is calculated as follows: 1 HL Htu = H G + AF 110

1 (0.8 ft) = 1.33 ft 5.363 The total height of the column H pack = Ntu  Htu = 5.121.33 = 6.8 ft (2.1m) Htu = 1.18 ft +

7.1.2 Hysys/Unisim Simulation Login to Hysys, select the components; air, ammonia, and water. Peng-Robinson is used as the thermodynamic fluid package (Fig. 7.1-7.2).

Fig. 7.1 Process flow sheet and stream summary

Fig. 7.2 Packing results

111

7.5.3 Pro/II simulation (Fig. 7.3).

Fig. 7.3 Absorber flowsheet, PRO/II 7.1.3 Aspen Plus Simulation From the model library, select RadFrac. ABSBR2 is selected from the column subdirectory and by clicking on the down arrow on the right side of the RadFrac icon. Connect two feed streams (Gas in and liquid in) and two product streams (gas out and liquid out. Using the ABSBR2, the feed streams need to be specified. The number of trays and feed streams, exit stream tray locations must be specified, and column pressure will be entered. Using this column with 5 trays, almost complete removal is achieved. Results are different from hand calculations.

The gas inlet is in the 6th stage. The stream summary is shown in Figure 7.4.

Fig. 7.4 Stream summary using RadFrac column Using the radfrac column, the results look better and close to hand calculations. Additional information is required. The following information is required: 1. Feed streams condition (Temperature, pressure), flowrate and compositions.

2. Column packing specifications (random ceramic raschig rings, 0.25 inch) 112

3. Number of trays (5 trays) and stream tray locations 4. Column diameter ( 0.08 m) and column total height (2 m) Hand calculation values are used. The results are shown in Figure 7.5. Results were in good agreement with hand calculation.

Fig. 7.5 Process flowsheet and stream summary using radfrac column 7.1.4 SuperPro Designer simulation Using the absorber column under unit procedures, select a proximately 99.2% removal of ammonia is required. Feed streams need to be fully specified. Liquid and gas diffusivity is taken from hand calculations Henry’s law constant, H = 1.7 10−5 atm.m3 / gmole The process flowsheet is shown in Figure 7.6.

113

Fig. 7.6 Stream summary The calculated height and number of transfer units are shown in Figure 7.7.

Fig. 7.7 height and number of transfer units The calculated column diameter and height are shown in Figure 7.8.

Fig. 7.8 Column diameter and height

7.2 Absorption of acetone from the air using water Acetone is being absorbed from the air by pure water in a packed column designed for 80% of flooding velocity at 293 K and 1atm pressure. The inlet air contains 2.6 mol% acetone and outlet 0.5 mol% acetone, and the total gas inlet flow rate is 14.0 kmol/h. The pure water inlet 114

flow is 45.36 kmol/h. The column is randomly packed with ceramic raschig rings, 1.5-inch nominal diameter. Calculate the packed column height and verify your answer with Hysys/Unisim, Pro/II, and Aspen and SuperPro designer.

7.2.1 Hand calculation Follow the same method using in Problem 1.

7.2.2 Hysys/Unisim simulation Follow the following steps in the simulation of the gas absorber with Hysys: open a new case in Hysys and select all components involved in the process. Click on the Fluid package tab and set Sour PR, then click Enter to Simulation Environment”. From the object pallet, select the Absorber icon and click inside the PFD simulation environment. Double click on the absorber and fill in the inlet and exit streams. Click on the Next> button to fill in the top and bottom stage pressures. Click the Next> button again and fill in the top and bottom optional stage temperatures if known. Close the Expert menu by clicking the Done button; notice that the streams are light blue, which means these streams are not specified. Double click on inlet gas stream and solvent stream and fill in temperature, pressure, flow rates, and compositions. The solvent stream is established, the color is changed to dark blue. Double Click on the gas in the stream and enter T, P, and flow rate. Double click on the column PFD, and click Run to start the calculation. The column is now Converged, and the red un-converged slip changes to green converged slip. Close the column windows. The absorber is ready; notice that all stream colors are changed to dark blue, as shown in Figure 7.9.

Fig. 7.9 Absorber process flow sheet and stream summary Calculation of Column Diameter and Height: The results that are obtained at this point do not represent a proper model for our gas absorption column because the simulation was run using trays, not packing. To replace trays with packing, from Tools in the tool menu, select Utilities and select Tray sizing. Click on Add Utilities.

Double click on Tray Sizing-1 under the Available Utilities. A tray-sizing window should pop up. Name the utility as packing. Click on the Select TS… button. Select TS-1, then click on the OK button. Click on; Next, and then on; Complete Auto Section. In the section results, find the diameter and the height of the column. Make sure to go back to the Absorber PFD and double click on the absorber and rerun it to execute the new column setting the change from tray to the backing. Even though Hysys calculates automatically, it is better to click on the columns run button before recording the results. While on the Tray sizing design page, click the Performance tab and select packing to see the results shown in Figure 7.10.

115

Fig. 7.10 Absorber specification 7.2.3 Pro/II simulation (Fig. 7.11, 7.12)

Fig. 7.11 Acetone absorption from the air using water

Fig. 7.12 Column performance generated by PRO/II 116

7.2.4 Aspen Plus simulation Logon to AspenPlus; from the Column subdirectory, RateFrac block is selected. RateFrac can simulate actual tray and packed columns. A column consists of segments. Segments refer to a portion of filling in a packed column or one or more trays in a tray column. The RateFrac block is selected from the Column subdirectory and placed in the process flowsheet area. Attach the liquid inlet and gas inlet streams to the feed port, and then attach the gas outlet to the distillate port and the liquid outlet to the bottoms port (Figure 7.13).

Fig. 7.13 Packed bed absorber process flowsheet Once the flowsheet is completed; click the Next button; fill in column specifications, accounting and description. Click Next; in the component’s screen (Acetone, water, air). On the next screen, choose a Property Method from the list by pressing the drop-down button to the right of the box. In this example, the NRTL is selected. In the gas inlet stream, specify temperature (293K), pressure (1 atm), flowrate (14.014 kmol/h), and composition (0.026 acetone, 0.974 for air, 0 for water). In the inlet liquid stream, the temperature is 293 K, pressure is 1 atm, and the molar flow rate of inlet pure liquid water is 45.36 kmol/h. In the next screen, the input sheet for the absorber block will appear. A column consists of segments that are used to evaluate mass and heat transfer rates between contacting phases. The height of the part should not be less than the average size of the packing used. In this example number of pieces is 10. For absorber, no condenser or reboiler is needed; none is selected for Condensor and reboiler. Click on the Pressure tab for the pressure type specification Top/Bottom and enter 1 atm pressure (Figure 7.14).

Fig. 7.14 number of segments Click the Next button, which brings you to the tray specification sheet. Since our column consists of packing rather than trays, choose PackSpecs from the data browser at the left. You will be brought to the packing specification for the tower. The pack segment number starts at 1, which is the top packed section of the column. Enter the value of the total packing height in order for the AspenPlus simulation to run. This estimated value will be overridden in the Design Specs area of the program, where the height will be varied to satisfy entered mole fraction values (7.15).

117

Fig. 7.15 Packed column specifications The diameter input screen should appear next. Since the value of the diameter is not known.

AspenPlus can calculate the diameter based upon the percent flooding of the column. Choose Use calculated diameter and enter the value as shown in Figure 7.14. Here 1 meter is being used (Fig. 7.16).

Fig. 7.16 Packed bed diameter Enter the design Specification menu, and determine the height of the column that achieves a 0.005-mole fraction of acetone in the exit gas stream. Scroll down the data browser and choose Flow sheeting Options and then Design Specs. Click the New button on the screen that appears.

The design spec of DS-1 will appear and select OK to accept and then select a name Acetone concentration ACON and then click on the Edit button (Figure 7.17).

118

Fig. 7.17 Selected variable category Click on Spec tab and define the design specifications as shown in Figure 7.18.

Figure 7.18 Design specification expression Click on the Vary tab and define the packing type, block name, and variable. Access to the list of manipulated variables can be accessed by clicking on the down button to the left of the variable blank. Short descriptions of the inconsistent abbreviations are given as each variable’s variable names are highlighted (Figure 7.17). All required input has now been entered, and the simulation can be run. The results screen is shown in Figure 7.18. In the area labeled ID1, enter 1; this refers to the column number. In the area label ID2, enter 1; this refers to the starting stagnant number. For the manipulated variable limits, in this case, the packing height is between 1 to 10 meters (Fig. 7.19).

Fig. 7.19 Manipulated variable 119

The next screen shown in Figure 7.18 asks to specify the location of feed inlets and outlets.

Notice that the number eleven for the inlet gas because the convention for stream location is above the segment (Fig. 7.20).

Fig. 7.20 Material stream locations The process flowsheet and stream summary is shown in Figure 7.21

Figure 7.21 Process flowsheet and stream summary The value of packing height that satisfied our design conditions was 1.85 meters. This value is close to the value of packing height of 1.94 meters calculated by hand calculations (Fig. 7.22).

120

Fig. 7.22 Aspen Plus calculated packing height 7.2.5 SuperPro Designer Absorption is selected from Unit Procedures, then Absorption/Stripping, and then select Absorption. Under the Tasks menu, choose Edit Pure Component, and then select acetone.

Water, oxygen, and nitrogen are already there (Fig. 7.23-7.25).

Figure 7.23 Inlet gas stream composition

Fig. 7.24 Absorber process flow sheet and stream

Fig. 7.25 Packed bed column height

121

7.3 Stripper A measure of 100 kgmol/h of feed gas at 17 atm and 100°C, containing 3% ethane, 20% propane, 37% n-butane, 35% n-pentane, 5% n-hexane, is to be separated such that 100% ethane, 95% propane, and 1.35% n-butane of the feed stream are to be recovered in the overhead stream. Use stripper to find the molar flow rates and compositions of the bottom stream. Use UniSim to simulate the absorption column (Use Peng Robinson as the suitable fluid package).

Solution Define the feed stream (Fig. 7.26-7.35).

Fig. 7.26 Feed stream conditions

Fig. 7.27 Feed stream composition Select stripper from the object pallet and place it on the PFD

Fig. 7.28 Splitter icon in the object pallet Double click on the splitter icon, in the connection page define inlet and exit streams, and do not forget to install an energy stream.

122

Fig. 7.29 Splitter connections page In the split, the page defines the percentage exit in the overhead product stream.

Fig. 7.30 Splits page The page of parameters defines the overhead pressure as the same as the feed pressure. The overhead vapor fraction is 1.0. The bottom vapor fraction is 0.0.

123

Fig. 7.31 Stripper parameters page Define pressure drop across the column as 0.25 atm

Fig. 7.32 Set connections page

124

Fig. 7.33 Set operator parameters

Close splitter windows.

Fig. 7.34 Stripper PFD with the Set operator Use a set unit to set the pressure drop across the column.

Select the variable target pressure as stream B Select source pressure as stream D Click on the Parameters tab to specify the pressure drop as 0.25 atm and offset the multiplier as 1.

Splitter is now ready and converged

Fig. 7.35 worksheet windows PRO/II simulation (Fig. 7.36)

125

Fig. 7.36 Shortcut distillation in PRO/II 7.4 Absorption of CO2 from Gas stream in a fermentation process Ethanol is absorbed from a gas stream in a fermentation process. The gas stream contains 2mole percent ethanol, and the balance is CO2. All streams enter at 30 oC, and the process is isobaric at 1 atm. The entering gas flow rate is 1000 kg mol/hr. The water flowrate in is 2000 kg mol/hr with no ethanol. Use 60% Murphree Tray efficiencies. Determine the number of stages required to absorb 95% of the ethanol from the air stream using water as the absorption media.

Unisim simulation (Fig. 7.37)

Fig 7.37 Absorber stream summary PRO/II simulation (Fig. 7.38)

126

Fig. 7.38 Absorber process flowsheet generated with PRO/II 7.5 Absorption of CO2 from a gas stream using methanol A gas stream at 100°C and 6000 kPa pressure enter a gas absorber. The primary objective of the CO2 absorber is to absorb CO2 contained in the feed stream by contacting counter-currently with methanol solvent in an absorber. The gas stream (0.35 CO, 0.002 H2O, 0.274 CO2,0.37 H2,0.002 CH4, and 0.002 N2) is flowing at a rate of 100 kmol/h. Methanol at 30°C and 6000 kPa is used as an absorbent solvent. The molar flow rate of methanol liquid is 330 kmol/h.

Determine the number of theoretical trays required to achieve a fraction of 0.06 CO2 in the exit stream, column diameter, and height. Use UniSim or any other software package to simulate the absorption column. The suitable fluid package is PRSV. Unisim simulation (Fig. 7.39)

Fig. 7.39 Absorber process flowsheet PRO/II simulation (Fig. 7.40)

127

Fig. 7.40 Absorber column, results generated by PRO/II 7.6 Absorption of SO2 from air Using pure Polluted air fed to the bottom of an absorption column at a rate of 100 kmol/h (0.03 SO2, 0.97 air) at 30oC and 1atm. Pure water at a flow rate of 10000 kgmol/h and 30oC and 1atm is used as absorbent. Use UniSim/Hysys (fluid package Peng Robinson) to estimate the composition of SO2 in the clean air.

Solution

Fig. 7.41 UniSim generated absorber process flow diagram and stream summary, the case described in problem 7.6 7.7 Absorption of H2S from Natural gas Using pure water Polluted air fed to the bottom of an absorption column at a rate of 100 kmol/h (0.05 H2S, 0.95 CH4) at 30oC and 1atm. Pure water at a flow rate of 10000 kgmol/h and 30 oC and 1atm is used as absorbent. Using UniSim/Hysys (fluid package Sour PR) to estimate the composition of H2S in the clean air.

Solution

128

Fig. 7.42 UniSim generated absorber process flow diagram and stream summary, the case described in problem 7.7 7.8 Absorption of H2S from Natural gas Using Propylene carbonate Sour Natual gas fed to the bottom of an absorption column (10 stages) at a rate of 100 kmol/h (0.05 H2S, 0.95 CH4) at 30oC and 1atm. The solvent composed of 80% propylene carbonate and 20% water at a flow rate of 10000 kgmol/h and 30 oC and 1atm is used as absorbent. Use UniSim/Hysys (fluid package Sour PR) to estimate the composition of H2S in the treated natural gas.

Solution

Fig. 7.43 UniSim generated absorber process flow diagram and stream summary, the case described in problem 7.8.

7.9 Absorption of CO2 from Natural gas Using Diethanolamine (DEA) Sour natural gas fed to the bottom of an absorption column (10 stages) at a rate of 100 kmol/h (0.15 CO2, 0.85 CH4) at 30oC and 10 atm. The solvent is composed of 10 wt% DEA in water at a flow rate of 7000 kgmol/h and 30 oC and 10 atm (absorbent). Use UniSim/Hysys (fluid package Amine Pkg) to estimate the composition of CO2 in the treated natural gas. Compare the exit treated methane with the one treated in 7.8 using the different absorbents.

129

Solution

Fig. 7.44 UniSim generated absorber process flow diagram and stream summary, the case described in problem 7.9.

7.10 Absorption of acetic acid A feed stream (100 kg/h) enters the bottom of an absorption column (5 stages) at 40oC and 10 atm. The absorber uses pure water (150 kg/h) at 25oC and 10 atm to absorbed acetic acid from a gas mixture, a mass fraction of 98% CO2, 1.4% N2, and 0.6% acetic acid. Use UniSim/Hysys (NRTL) to simulate the absorption process and find the treated stream’s composition.

Solution

Fig. 7.45 UniSim generated absorber process flow diagram and stream summary, the case described in problem 7.10.

130

Chapter 8 8.1 Extraction of Acetone from water by MIBK A counter-current liquid-liquid extractor is used to remove acetone from a feed that contains 50% acetone (A), 50 wt% water (B). Pure methyl isobutyl ketone (MIBK) is used as the solvent in this separation at a flow rate of 80 kg/ hr. A feed flow rate of 100 kg/hr is to be treated. It is desired to have a final raffinate of 4 wt% acetone. The operation takes place at 25° C and 1 atm.

Determine the number of stages necessary for the separation as specified Solution Initial Setup: 1. Star Start a new case in HYSYS 2. Select Acetone, Water, and MIBK for the components 3. Use the NRTL Fluid Package.

4. For Liquid-Liquid Extraction cases, the binary coefficients of the components have to be checked.

If some of the coefficients are not specified by HYSYS, a fatal error will occur, and the process cannot be simulated. To check the Binary Coefficients, simply click the “Binary Coeffs” tab (Fig. 8.1).

Fig. 8.1 Binary coefficient selection page 5. Some of the coefficients are not specified since some of the tabs are left blank. There are several ways to fix this. First, the coefficients can either be looked up or experimentally determined and then entered straight into the appropriate box. Or, HYSYS can estimate the unknown coefficients using equilibrium relationships. To do that, select either “UNIFAC VLE” or “UNIFAC LLE” and then clicking on the tab “Unknowns Only.” In Liquid-Liquid Extraction processes, UNIFAC LLE is the appropriate estimation to use. Close the Binary Coefficient window, and enter the simulation environment (Fig. 8.2).

131

Fig. 8.2 Activity model interaction parameters

Close and enter the simulation environment, select extraction column, connect feed, solvent, extract, and raffinate (a raffinate is a liquid stream that remains left after the extraction with the immiscible liquid to remove solutes from the original liquid). In the solvent extraction, the two liquids must be immiscible. The process flow sheet and stream summary is shown in Figure 3 below. The number of stages is 2 (Fig. 8.3).

Fig. 8.3 Stream summary PRO/II simulation Select component (Acetone, water, MIBK) Select the fluid package and make the necessary changes in the fluid package (Fig. 8.4)

132

Fig. 8.4 K-value (LLE) NRTL should be specified The results are shown below (Fig. 8.5)

Fig. 8.5 Process flowsheet and stream summary 8.2 Extraction of acetone using pure Trichloroethane In a continuous counter-current extraction column, 100 kg/h of a 30 wt % acetone, 70 wt % water solution is to be reduced to 10 wt % acetone by extraction with 100 kg/h of pure 1,1,2 Trichloroethane (TCE) at 25oC and 1 atm: Find the number of mixer settlers required.

Hysys solution (Fig. 8.6) Fluid package: UNIQUAQ Solution: 1 stage will be enough to reduce the concentration to 0.1 mass fraction acetone

133

Fig. 8.6 Process flowsheet and stream summary

PRO/II simulation (Fig. 8.7) Fluid package: UNIFAC Two liquid phases

Fig. 8.7 Process flowsheet and stream summary generated by PRO/II 8.3 Extraction of acetone from water using MIBK A counter-current extraction plant is used to extract acetone from 100 kg/hr of feed mixture.

The feed consists of 20 wt% acetone (A) and 80 wt% water (w) employing methyl isobutyl ketone (MIK) at a temperature of 25oC and 1 atm. 100 kg/h of pure solvent (MIK) is used as the extracting liquid. How many ideal stages are required to extract 90% of the acetone fed?

What are the extract and raffinate mass flow rates, and what are the compositions?

Solution Hysys simulation (Fig. 8.8) Fluid package: NRTL

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Fig. 8.8 UniSim generated process flowsheet and stream summary.

PRO/II simulation (Fig. 8.9) Fluid package: NRTL

Fig. 8.9 Process flowsheet and stream summary generated by PRO/II 8.4 Extraction of acetone from water using 1,1,2 Trichloroethane A counter-current extraction column is used to extract acetone from water in a two feed stream using 50 kg/h of 1,1,2 Trichloroethane to give a raffinate containing 10.0 wt% acetone. The feed stream (F1) is at a rate of 75 kg/h, including 50% acetone, 50wt% water. The second feed (F2 ) is 75 kg/h containing 25 wt% acetone and 75 wt% water. The column is operating at 25 o C and 1 atm. Calculate the required equilibrium number of stages and the location of the feed stages Hysys solution (Fig. 8.10) Fluid package: UNIQUAQ The number of stages required is 2

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Fig. 8.10 Process flowsheet and stream summary with Hysys PRO/II simulation (Fig. 8.11) Fluid package: UNIFAC The number of stages required is 3.

Fig. 8.11 Process flowsheet and streams summary with PRO/II 8.5 Extraction of acetic acid from water using isopropyl ether 100kg of an acetic acid and water mixture containing 30wt% acid is to be extracted in three stages extractor with isopropyl ether at 20 oC using 40 kg of the pure solvent. Fresh solvent at 40 kg/h of pure solvent is added to the second stage (Fig. 8.12).

Determine the composition and quantities of the raffinate and extract streams.

Figure 8.12 Process flowsheet of Problem 8.5.

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Hysys simulation (Fig. 8.13) Fluid package: NRTL

Fig. 8.13 Process flowsheet and stream summary PRO/II simulation (Fig. 8.14)

Fig. 8.14 Process flowsheet, PRO/II

8.6 Extraction of acetone in two stages A mixture mass flow rate of 100 kg/h contains 0.24 mass fraction acetone, and 0.78 water is extracted by 50 kg/h of methyl isobutyl ketone in two stages counter continuous current extractor. Determine the amount and composition of the extract and raffinate phases.

Hysys solution (Fig. 8.15)

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Fig. 8.15 Process flowsheet and stream summary generated by Hysys PRO/II simulation (Fig. 8.16)

Fig. 8.16 Process flowsheet and stream results using PRO/II 8.7 Three stage extractor continuous extractor A three-stage counter-current extractor is used to extract acetic acid from water by isopropyl ether. 40 kg/h of the solution containing 35 wt% acetic acids in water is contacted with 40 kg/h of pure isopropyl ether. Calculate the amount and composition of the extract and raffinate layers.

Hysys simulation (Fig. 8.17)

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Fig. 8.17 Process flowsheet and stream summary generated with Hysys PRO/II simulation (Fig. 8.18) Fluid package: NRTL

Fig. 8.18 Process flowsheet using PRO/II 8.8 Extraction of acetic acid with pure isopropyl ether 100 kg/h of an aqueous feed solution of acetic acid contains 30 wt% acetic acids, and 70 wt% water is to be extracted in a continuous counter-current extractor with pure isopropyl ether to reduce the acetic acid concentration to 5 wt% in the final raffinate. If 2500 kg/h of pure isopropyl ether is used [1], determine the number of theoretical stages required.

Hysys simulation (Fig. 8.19)

Fig. 8.19 results generated with Hysys PRO/II simulation (Fig. 8.20)

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Fig. 8.20 Process flowsheet and stream conditions generated with PRO/II 8.9 Extraction of acetic acid with pure isopropyl ether An aqueous feed solution of acetic acid contains 30 wt% acetic acids, and 70 wt% water is to be extracted in a continuous counter-current extractor with pure isopropyl ether to reduce the acetic acid concentration to 5 wt% in the final raffinate. If 1000 kg/h of pure isopropyl ether is used, determine the number of theoretical stages required. Compare the number of theoretical stages with example 8.8 and the effect of the amount of solvent on the required number of theoretical stages.

Hysys simulation (Fig. 8.21)

Fig. 8.21 Stream results generated with Hysys PRO/II simulation (Fig. 8.22)

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Fig. 8.22 Process flowsheet and steam results generated with PRO/II.

8.10 Extraction of acetic acid with nonpure isopropyl ether An aqueous feed solution of acetic acid contains 30 wt% acetic acids, and 70 wt% water is to be extracted in a continuous counter-current extractor with pure isopropyl ether to reduce the acetic acid concentration to 5 wt% in the final raffinate. If 1000 kg/h of 90 wt% isopropyl ether and 10.0 wt% acetic acids are used, determine the number of theoretical stages required.

Compare the number of stages with Example 8.9 and the effect of the amount of solvent on the required stages.

Hysys simulation (Fig. 8.23)

Fig. 8.23 using not pure solvent PRO/II simulation (Fig. 8.24)

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Fig. 8.24 Process flowsheet

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Chapter 9 9.1 Ethyl chloride production in an adiabatic reactor Ethyl chloride is produced by the gas-phase reaction of HCl with ethylene over a copper chloride catalyst supported on silica. The feed stream is composed of 50% HCl, 48 mol% C2H4, and 2.0 mol% N2 at 100 kmol/hr., 25oC, and 1 atm. Since the reaction achieves only 80 mol% conversions, the ethyl chloride product is separated from the unreacted reagents, and the latter is recycled. The chemical reaction is taken place in an adiabatic reactor. The separation is achieved using a distillation column. A portion of the distillate withdrawn in the purge stream prevents the accumulation of inert in the system. Design a process for this purpose using Hysys, PRO/II, Aspen Plus, and SuperPro software packages. Compare the result with example 9.1.

Hysys Simulation (Fig. 9.1) Fluid package: Peng Robinson

Fig. 9.1 UniSim generated the ethylene chloride production process.

PRO/II simulation (Fig. 9.2) Fluid package: Peng Robinson 143

Fig. 9.2 PRO/II generated the ethylene chloride production process.

9.2 Ethylene production in an isothermal reactor Ethylene is produced using ethane cracking at 800oC. Assume the reaction is taken place in an isothermal conversion reactor where ethane single-pass conversion is 65%. Develop a process flow sheet for the production of ethylene. Use one of the available software packages to perform the material and energy balance of the entire process.

Hysys Simulation (Fig. 9.3)

Fig. 9.3 Ethylene production process flowsheet using a splitter

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Figure 9.3aa Ethylene production using fractional distillation

PRO/II simulation (Fig. 9.4)

Fig. 4 PRO/II stimulation of ethylene production process

9.3 Ammonia synthesis process in an adiabatic reactor Ammonia is synthesized through the reaction of nitrogen and hydrogen in an adiabatic conversion reactor. The feed stream to the reactor is at 400oC. Nitrogen and hydrogen are feedin stoichiometric proportions. The single-pass fractional conversion is 0.15. The product from the convertor is condensed, and ammonia is produced in liquid form. The unreacted gases are recycled. The reactor effluent gas is used to heat the recycled gas from the separator in a combined reactor effluent/recycle heat exchanger. Construct a process flow diagram and use one of the available software packages to simulate the process.

Hysys simulation (Fig. 9.5) 145

Fig. 9.5 Adiabatic Ammonia synthesis process flowsheet

PRO/II simulation (Fig. 9.6)

Fig. 9.6 PRO/II result of the adiabatic ammonia production process 9.4 Ammonia synthesis process in an isothermal reactor Hysys simulation (Fig. 9.7) Repeat problem 9.2.3; in this case, the reaction is taking place at 400oC. 146

Fig. 9.7 Isothermal conversion reactor

PRO/II simulation (Fig. 9.8)

Fig. 9.8 Isothermal conversion reactor for ammonia production generated with PRO/II 9.5 Methanol dehydrogenation Methanol at 675 oC and 1 bar is fed at a rate of 100 kmol/h to an adiabatic reactor where 25% of it is dehydrogenated to formaldehyde (HCHO). Calculate the temperature of the gases leaving the reactor and separate the component where methanol is recycled, and almost pure formaldehyde is produced.

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Hysys simulation (Fig. 9.9)

Fig. 9.9 Hysys simulation of the methanol dehydrogenation process PRO/II Simulation (Fig. 9.10)

Fig. 9.10 PRO/II generated the PFD and stream summary of the methanol dehydrogenation process.

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