EXAMINATION Luleå University of Technology

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1 EXAMINATION Luleå University of Technology Course: B0004K Course name: Unit Operations Date: Time: Aid: Del A: Inga hjälpmedel (no help materials) Del B: Christie J Geankoplis, Transport Processes and Separation Process Principles, 4th edition, Prentice Hall, Upper Saddle River, New Jersey, 2003 Coulson, J.M., Richardson, J.F., Backhurst, J.R., and Harker, J.H., Chemical Engineering Volume 1, Sixth Edition, Butterworth- Heinemann, Oxford, UK, Richardson, J.F., Harker, J.H., and Backhurst, J.R., Chemical Engineering Volume 2, Fifth Edition, Butterworth-Heinemann, Oxford, UK, Calculator Dictionary of choice Teacher on duty (complete telephone number): Mattias Grahn Teacher on duty (complete telephone number): Teacher on duty (complete telephone number): Teacher on duty (complete telephone number): Grade scale: Total number of questions and score: U: <30p; 3: 30-39,5p; 4:40-49,5p; 5: 50-60p 8+4 problems 60 points in total

2 Other information: General instructions Check that you have received all the tasks/questions. All new answers begin on a separate page. Print, write clearly; black or blue pen only. After examination The result of your examination are posted on your Student portal Examination results are posted within 15 workdays after the examination and no later den 12 workdays before next re-examination day. For the courses with more than 60 students taking the examination the results are posted within 20 workdays latest after the examination but no later than 12 workdays before the next re-examination day. Uppgifter till tryckeriet för tentor campus Luleå Projektnummer: Hur många sidor: Hur många ex: Dubbel eller enkelsidigt:

3 Luleå University of Technology Chemical Technology Svenska/(English) Tentamen i: Enhetsoperationer (del A) (Exam: Unit Operations (part A)) B0004K Totalt antal uppgifter (Total number of questions):8+4 Tentamensdatum: Lärare: M. Grahn ( ) Skrivtid(Time of Test): Poäng (Points): Del A: Teori (Part A: Theory) Del B: Problemlösning (Part B: Problem solving) Totalt (Total) 20 p 40 p 60 p Hjälpmedel (help materials): Del A: Inga hjälpmedel (no help materials) Del B: Christie J Geankoplis, Transport Processes and Separation Process Principles, 4th edition, Prentice Hall, Upper Saddle River, New Jersey, 2003 Coulson, J.M., Richardson, J.F., Backhurst, J.R., and Harker, J.H., Chemical Engineering Volume 1, Sixth Edition, Butterworth-Heinemann, Oxford, UK, Richardson, J.F., Harker, J.H., and Backhurst, J.R., Chemical Engineering Volume 2, Fifth Edition, Butterworth-Heinemann, Oxford, UK, Calculator Dictionary of choice OBS! Innan hjälpmedlen för del B får tas fram måste svaren till del A lämnas in. (Help materials to part B may not be used until the answers to part A are turned in)

4 A1. What is an azeotrope? A2. Sketch and label a figure showing the five steps of mass transfer in leaching. (2.5p) A3. How will the number of theoretical trays change in a distillation tower if the following parameters are changed? Motivate your answer! a. The reflux ratio is increased b. The relative volatility is decreased c. What are the limiting cases for the parameters in a) and b) A4. What is the difference between pasteurization and sterilization? (6p) A5. How does the number of trays in a distillation column vary with the reflux ratio? A6. What are the two phases formed in liquid-liquid extraction called? A7. Extraction can sometimes be used as an alternative to distillation. When is it preferable to use extraction instead of distillation as a separation process? A8. Show on an operating diagram the condition of minimum liquid flow rate for absorption. (1,5p)

5 Luleå University of Technology Chemical Technology Svenska/(English) Tentamen i: Enhetsoperationer (del B) (Exam: Unit Operations (part B)) B0004K Totalt antal uppgifter (Total number of questions):8+4 Tentamensdatum: Lärare: M. Grahn ( ) Skrivtid(Time of Test): Poäng (Points): Del A: Teori (Part A: Theory) Del B: Problemlösning (Part B: Problem solving) Totalt (Total) 20 p 40 p 60 p Hjälpmedel (help materials): Del A: Inga hjälpmedel (no help materials) Del B: Christie J Geankoplis, Transport Processes and Separation Process Principles, 4th edition, Prentice Hall, Upper Saddle River, New Jersey, 2003 Coulson, J.M., Richardson, J.F., Backhurst, J.R., and Harker, J.H., Chemical Engineering Volume 1, Sixth Edition, Butterworth-Heinemann, Oxford, UK, Richardson, J.F., Harker, J.H., and Backhurst, J.R., Chemical Engineering Volume 2, Fifth Edition, Butterworth-Heinemann, Oxford, UK, Calculator Dictionary of choice OBS! Innan hjälpmedlen för del B får tas fram måste svaren till del A lämnas in. (Help materials to part B may not be used until the answers to part A are turned in)

6 B1. Flue gas (in this case assumed to consist of air and SO 2 ) from a combustion plant contains 3% SO 2 by volume. A counter-current tray tower is used to remove the SO 2 from flue gas with water. The flue gas should have an SO 2 concentration less than 0.5% by volume when exiting the absorption tower. The tower works at 293 K and atmospheric pressure. The equilibrium curve can be approximated by: y = 23. 6x Where y is kmol SO 2 per kmol air and x is kmol SO 2 per kmol H 2 O. The flowrate of water is 0.67 kmol s -1 and the flow rate of air 0.03 kmol s -1. Determine the number of trays necessary to accomplish the separation. Hint: How is the concentration in volume percent related to the concentration in mol percent for a gas? (10p) B2. Slabs of a bone-dry solid with a density of 1600 kg m -3 are to be dried from an initial free- moisture content of 0.95 kg moisture per kg dry material to a final moisture content of 0.05 kg moisture per kg dry material. The drying is done batchwise in trays with dimensions 1 x 0.5 x 0.03 m (length x width x depth). Drying will be carried out by sweeping hot air across the trays and drying will thus only be from the top surface. Experiments under the given drying conditions have shown a critical free-moisture content of 0.70 kg moisture per kg dry material. The falling rate period is linear from the critical to the equilibrium moisture content. a. Calculate the total drying time if R C is 2 kg moisture h -1 m -2. b. What does the information provided by the drying-rate curve tell you about the material being dried? B3. Leaching of shark liver oil (10p) It has been suggested that shark liver oil might have anti cancer activity. A big nutraceutical company is going to launch a new health product based on shark liver oil and you have the position as their chief chemical engineer. You and your team of engineers will construct a counter current multistage leaching apparatus to extract the precious oil from granulated shark livers using ether as solvent. Your task now is to calculate the number of theoretical steps needed based on the data given below: The solids charge contains 0.35 kg oil/ kg exhausted livers and it is desired to obtain a 90 % oil recovery. 50 kg ether is used per 100 kg of untreated solids. The settling data is:

7 Weight fraction oil in underflow solution (kg oil/ kg solution) N ( kg extracted livers/ kg solution) (10p) B4. Benzene-Toluene Distillation A mixture of 40 mole per cent benzene with toluene is distilled in a continuous fractionating column equipped with reboiler and total condenser to give a product of 95 mole per cent benzene and a waste of 5 mole per cent benzene, using a reflux ratio of 4. Use equilibrium data on page 698, table , in Geankoplis textbook, 4:th edition and/or the equilibrium diagrams below and do the following: a) Using McCabe/Thiele method, determine the number of trays required and the position of the feed if supplied to the column as a liquid at the boiling point. b) Find the minimum reflux ratio possible. c) Find the minimum number of trays. d) If the feed is fed at 288 K, find the number of plates using reflux ratio of 4. Let the average latent heat of vaporization for the feed be 30 kj/mol and the average heat capacity be 1.84 kj/kg*k (Check the units carefully). Molecular mass of benzene = 78,1 g/mol, molecular mass of toluene = 92,1 g/mole. (10p)

8 Equilibrium diagram Benzene/Toluene System (1 atm) 1 0,9 0,8 Mole fraction benzene in vapour, ya 0,7 0,6 0,5 0,4 0,3 0,2 0, ,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1 Mole fraction benzene in liquid, xa

9 Equilibrium diagram Benzene/Toluene System (1 atm) 1 0,9 0,8 Mole fraction benzene in vapour, ya 0,7 0,6 0,5 0,4 0,3 0,2 0, ,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1 Mole fraction benzene in liquid, xa