CHE 441 ______LAST NAME, FIRST Problem set #91,2,3
1. Run the program Microplant as an Expert Troubleshooter and turn in the last display of the program.
2. A continuous fractionating column is required to separate a mixture containing 0.40 mol fraction n-heptane (MW= 100) and 0.60 mol fraction n-octane (MW = 114) into overhead products of 99 mol% heptane and bottom products of 1 mol% heptane. The column is to operate at a pressure of 101.3 kN/m2 with a pressure drop across the tower of 25 kPa. The feed is a saturated mixture with 30% vapor, and is supplied to the column at 0.070 kgmol/s.The reflux ratio (L/D) is 2.5 and the fraction of the cross sectional area available for vapor flow is 0.88. If the vapor velocity is 0.8 m/s, determine the required diameter based on the conditions at the bottom of the tower where you can use pure n-octane for the evaluation of vapor density. Vapor pressure for n-octane ln P*(kPa) = 14.2368 - 3304.16/(T(K) - 55.2278) Gas constant R = 8314 m3Pa/kgmol K.
3. Acetone is to be recovered from a 5 mole % acetone-air mixture by scrubbing with pure water in a packed tower using countercurrent flow. The liquid rate is 2.85 kg/m2s and the gas rate is 1.5 kg/m2s. The overall absorption coefficient K a may be taken as 1.5x10-2 kmol/m3s. The pressure of y the system is 101.3 kPa. What should be the height of the tower to removed 98% of the acetone? Equilibrium data: y 0 0.0099 0.0196 0.0361 0.0400 0.0500 x 0 0.0076 0.0156 0.0306 0.0333 0.0417 where y = mole fraction acetone is air, x = mole fraction acetone in water Molecular weight of air is 29. Molecular weight of acetone is 58.1.
4. A shell-and-tube heat exchanger with two tube passes is to heat 20,000 kg/h of water from 25 to 84oC by hot engine oil flowing through the shell. The oil makes a single shell pass, entering at 160oC and leaving at 94oC, with a heat transfer coefficient of 500 W/m2K. The heat exchanger contains 100 steel tubes of 22.9-mm inside diameter and 25.4-mm outside diameter. The inside heat transfer coefficient is 3210 W/m2K. Neglecting fouling coefficients, determine the required tube length. 3 Data: Water: Cp = 4182 J/kgK, density = 998.1 kg/m Steel: k = 40 W/mK
1,1 Peters and Timmerhaus, Plant Design and Economics for Chemical Engineers, Fourth Edition, McGraw Hill 2,32 Fundamentals of Heat and Mass Transfer by Incorpera and Dewitt. 3 Transport Processes and Unit Operations by Jeankoplis. 5. Ethyl acetate is an extensively used solvent and can be formed by the vapor-phase esterification of acetic acid and ethanol: CH3COOH + C2H5OH C4H8O2 + H2O The reaction was studied using a microporous resin as a catalyst in a packed-bed reactor. The reaction is first-order in ethanol and pseudo-zero-order in acetic acid. For an equal molar feed rate of acetic acid and ethanol the specific reaction rate is 2.2 L/g catmin. The total molar feed rate is 10 mol/min, the initial pressure is 10 atm, the temperature is 118oC, and the pressure drop parameter, , equals 0.01 g-1. The pressure drop can be determined from
= P0(1 + X) a) Calculate the maximum weight of catalyst that one could use and maintain an exit pressure above 4 atm. b) The catalyst weight and the conversion in the reactor is related by the following equation
= k(1 W)1/2
For CA0 = 0.156 mol/L, determine the catalyst weight required for 50% conversion.
6. A heat exchanger is to be constructed by forming copper tubing into a coil and placing the latter inside an insulated steel shell. In this exchanger, water will flow inside the tubing, and a hydrocarbon vapor at a rate of 0.126 kg/s will be condensing on the outside surface of the tubing. The inside and outside diameters of the tube are 0.0127 and 0.0152 m, respectively. Inlet and exit temperatures for the water are 10 and 32oC, respectively. The heat of condensation of the hydrocarbon at a condensing temperature of 88oC is 335 kJ/kg, and the heat transfer coefficient for the condensing vapor is 1420 W/m2K. Heat losses from the shell may be neglected. What length of copper tubing will be required to accomplish the desired heat transfer? 3 -4 Data: Water: Cp = 4151 J/kgK, density = 997 kg/m , viscosity = 9.94×10 kg/ms, 0.8 1/3 k = 0.61 W/mK, Pr = 6.76, hi = (k/Di)(0.023Re Pr ) Copper: k = 385 W/mK
7.4 For a process, the following process streams must be cooled or heated:
Stream Cp Tin Tout Number (Btu/hroF) (oF) (oF) 1 4000 600 320 2 4000 470 280 3 3000 340 580 4 5000 300 480
Use the MUMNE algorithm for heat-exchanger networks and a minimum approach temperature of 20oF. a. Determine the temperature interval diagram. b. Determine the cascade diagram, the pinch temperature, and the minimum hot and cold utilities. If there is a choice, for the sake of uniformity, choose the larger values for the pinch temperatures. c. Determine the minimum number of heat exchangers above and below the pinch. d. Determine the heat-exchange network above the pinch. e. Determine the heat-exchange network below the pinch.
4 Turton et al, Analysis, Synthesis, and Design of Chemical Processes, Prentice Hall, 2012, pg 543.