MEEBAL Exam 2 November 2012 Show all work in your blue book. Points will be deducted if steps leading to answers are not shown. No work outside blue books (such as writing on the flow sheets) will be considered. No outgoing text messages are allowed during the exam. You must use given stream numbering in the problems (no points given if different numbering system is used). Report all answers with three significant digits. You are allowed to use one page of notes and a calculator (no textbooks, computers or tablets such as iPads are allowed). You must pass in your test sheet (with your name on the sheet) with your blue book for your exam to be graded. 1. (25 points)

Solid soybean residue (Stream 1) which contains 0.80 kg liquid hexane/kg dry solids is contacted in a dryer with nitrogen (Stream 2) that enters at 85 °C. The mass flow rate of entering dry solids in Stream 1 is 100 kg/s. The solids leave the dryer containing 0.05 kg liquid hexane/kg dry solids in Stream 3, and the gas (Stream 4) leaves the dryer at 80 °C and 1.0 atm with a relative saturation of 65%. Stream 4 is fed to a condenser in which it is compressed to 5.0 atm and cooled to 28 °C enabling some of the hexane to be recovered as condensate (Stream 6). There is no nitrogen in Stream 6. The gas stream leaving the condenser that contains hexane and nitrogen (Stream 5) is then split into an outlet stream (Stream 7) and a recycle stream (Stream 8) in the ratio of 1:9. The recycle stream (Stream 8) is heated to 85 °C and combined with the nitrogen entering in Stream 2.The molecular weight of hexane is 86 g/mol. Antoine Equation Constants for Hexane: A = 6.87776, B = 1171.580, C = 224.366 (T in °C, P in mm Hg) Calculate:

a. (5 pts) Mole fraction of nitrogen in Stream 4 b. (5 pts) Mole fraction of hexane in Stream 5 c. (5 pts) Molar flow rate of Stream 4 (kmol/s) d. (5 pts) Molar flow rate of Stream 6 (kmol/s) e. (5 pts) Ratio of the molar flow rate of Stream 9 relative to that of Stream 2 (n9/n2)

MEEBAL Exam 2 November 2012 2. (25 points)

100 mol/s of a mixture (Stream 1) containing 60 mol% acetone (Ac) and the balance acetic acid (AA) are fed to a continuous distillation column at 1 atm. The overhead stream from the column (Stream 2) is a vapor that passes through a condenser. The condensed liquid (Stream 4) is split equally into two streams with Stream 5 being taken off as the distillate and Stream 6 is returned to the column as reflux. The bottom stream from the column (Stream 3) is a liquid that is partially vaporized in a reboiler. The liquid stream emerging from the reboiler (Stream 7) is taken off as the bottoms product and the vapor (Stream 8) is returned to the column. The specific enthalpy of Stream 3 is 10 kJ/mol. Calculate:

a. (5 pts) Molar flow rate (mol/s) of Stream 5 b. (5 pts) Heat removed (QC) in the condenser (kW) c. (5 pts) Heat input (QR) required to the reboiler (kW) d. (5 pts) Molar flow rate (mol/s) of Stream 8 e. (5 pts) Molar composition of Stream 3 (mole fractions)

Stream No. Stream Name Stream Data

1 Feed Liquid, 67.5 °C, 60 mol% Ac, 40% AA 2 Overhead Vapor, 63.0 °C, 96% Ac, 4 % AA 5 Distillate Liquid, 56.8 °C, 96% Ac, 4% AA 7 Bottoms Liquid, 98.7 °C, 15.5% Ac, 84.5% AA 8 Boilup Vapor, 98.7 °C, 54.4% Ac, 45.6% AA

Specific enthalpy Ĥ (kJ/mol)

T (°C) Acetone (Ac) Acetic Acid (AA) Ĥl Ĥv Ĥl Ĥv 56.8 0 30.15 0 23.95 63.0 0.8577 30.64 0.8117 28.48 67.5 1.481 30.97 1.402 28.80 98.7 5.795 33.25 5.489 31.05

MEEBAL Exam 2 November 2012 3. (25 points)

A mixture of pentane vapor and air (Stream 1) flows into a condenser through a duct of diameter 80 cm at a velocity of 4 m/s. The temperature of Stream 1 is 60 °C, the pressure is 1.5 atm, and the dew point is 25 °C. The gas is cooled in the condenser at constant pressure. 70% of pentane in the feed is condensed and leaves as Stream 3, while the uncondensed pentane vapor and air leave in Stream 2. Antoine Equation Constants for pentane: A = 6.73457, B = 992.019, C = 229.564

Tb, pentane = 36.07 °C

Heat of vaporization of pentane at Tb= 25.77 kJ/mol

cp, Pentane (l) = 155.4*10-3 + 43.68*10-5 T (kJ/mol) cp, Pentane (v) = 114.8*10-3 + 34.09*10-5 T (kJ/mol) cp, Air = 28.94*10-3 + 0.4147*10-5 T (kJ/mol) Calculate:

a. (5 pts) Mole fraction of pentane in Stream 1 b. (5 pts) Mole fraction of pentane in Stream 2 c. (5 pts) Outlet condenser temperature (°C) d. (5 pts) Cooling rate (QC, kW) e. (5 pts) Fraction of pentane that would condense (n3,P/n1,P) if the outlet condenser temperature is 16 °C and the

condenser pressure is 1.5 atm

1  

 1  

 3  

 2  

Condenser

P=1.5 atm

QC

Pentane (v) Air

4 m/s 80 cm ID T=60 ºC P=1.5 atm

Pentane (v) Air

Pentane (l)

MEEBAL Exam 2 November 2012 4. (25 points)

400 mol/s of a hydrocarbon mixture containing 80 mol% CH4, 10% C2H6 and 10% C3H8 in Stream 1 is burned in an adiabatic furnace with 25% excess air (Stream 2). The inlet temperatures of Streams 1 and 2 are 25 ºC and 200 ºC, respectively. The three hydrocarbon components are completely consumed, and all of the combustion reactions should be considered as primary reactions. Water exits as a vapor in Stream 3, and the heats of combustion assume that water is a liquid. The pressure of all streams is 1 atm. cp, CO2 = 50.0 J/(mol-K) cp, H2O (v) = 38.5 J/(mol-K) cp, O2 = 33.1 J/(mol-K) cp, N2 = 31.3 J/(mol-K)

ΔHc, CH4 = -890.36 kJ/mol ΔHc, C2H6 = -1559.9 kJ/mol ΔHc, C3H8 = -2220.0 kJ/mol \

Heat of vaporization of water at Tb = 44.013 kJ/mol

Antoine Equation Constants for water: A= 7.96681, B= 1668.210, C= 228.0 Calculate:

a. (5 pts) Molar flow rate (mol/s) of Stream 2 b. (5 pts) Mole fractions of components in Stream 3 c. (5 pts) Temperature of Stream 3 (ºC) d. (5 pts) Degrees of superheat for water in Stream 3 (ºC) e. (5 pts) Outlet temperature of Stream 3 if 200% excess air is fed in Stream 2

 1  

 2

 

 3

   

Furnace P=1 atm

 

80 mol% CH4 10% C2H6 10% C3H8 400 mol/s T=25 ºC

Air T=200 ºC

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