UNIVERSITY OF TORONTO FA CUL TY OF APPLIED SCIENCE AND ENGINEERING . DEPARTMENT OF CHEMICAL ENGINEERING AND APPLIED CHEMISTRY

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1 NAME: STUDENT NUMBER: UNIVERSITY OF TORONTO FA CUL TY OF APPLIED SCIENCE AND ENGINEERING. DEPARTMENT OF CHEMICAL ENGINEERING AND APPLIED CHEMISTRY CHE 208 Process Engineering, Fall-2017 EXAMINER: Prof. Cathy (Ya-Huei) Chin Final Exam December 20, 2017 INSTRUCTIONS 1. Type D Exam (Course Text and a Single Aid Sheet are allowed) General scientific calculators are allowed (must be non-graphing and non-programmable) Faculty approved calculators include Casio 260, Sharp 520, Texas Instrument Write your name and student number at the top of the cover page. 3. Do not separate sheets. There are 20 pages, including the cover page. 4. The pages are printed on single side only. You may use the back side for calculation work. Identify the corresponding question for all written solution. 5. Calculations must be shown wherever and whenever required. Final answers without a quantitative proof will be rejected. 6. Answer all questions. The duration of the exam is 150 min. 7. Write clearly and legibly. 1

2 For evaluation use only DO NOT WRITE ON THIS SHEET QUESTION TOTAL MARKS la 5 lb 5 2a 5 2b 10 2c 5 2d 5 2e. 10 (BONUS) MARKS OBTAINED 3a 6 3b 21 3c 4.5 3d 3.5 4a 4. 4b 18 4c 4 4d 2 4e 2 TOTAL 100 2

3 Problem 1 [10 points]. A methanol-water mixture enters the Flash Drum, operating at 1 atm and an unknown temperature T. A T-x-y diagram for a methanol-water system at 1 atm is provided below. The exit mole fraction of methanol in the Vapor Stream is 0.3. Vapour Feed Flash Drum 110 Liquid u 90 b.o Cl) "O 85 a. E Cl) I ~ _ --,_ ~ ll '... - "'-. '1~..._ - r ~... ~ re ~ ' -- ~ i-a.. -., x,y (methanol liquid and vapor) mole fraction Part la [5 points]. If the temperature of the Flash Drum is decreased by 10 c, what is the mole fraction of methanol in the Liquid Stream? Show your work on the figure above. Part lb [5 points]. If the temperature of the Flash Drum is decreased by 10 c, the Vapor molar flow rate (V) from the Flash Drum will (select the correct answer): Increase Decrease Why? Explain in 1-2 sentences. 3

4 Problem 2 [ bonus points]. Figure 1 shows a gas blender. This gas blender has a capacity of 100 m 3 A vapour stream containing water and methanol (S2) is fed into this blender at a flowrate of2000 L s- 1 and 1 atm. This mixture stream is a saturated vapour with a dew point of91 Cat 1 atm. A valve (labeled Valve 3) regulating the flow of gas out of the tank maintains the tank pressure at 1 atm at all times. The system reaches steady-state for a period of hours prior to the next pr_ocess change. At a specific time, (let's set this time as zero time) t = 0, you open Valve 1. This valve regulates the flow of pure, superheated methanol vapour at 1 atm (S 1) into the gas blender. The molar flow rate is 110 mol s- 1 Both inlet streams S 1 and S2 have identical temperatures. S1: methanol S2: methanol + water Vl V2 V3 S3 Gas blender The gas constant (R): Gas constant R = L kpa moi- 1 K 1 = m 3 Pa moj- 1 K 1 = L atm moi- 1 K 1 Useful integral forms: Basic Forms (1) f udv = iu, - f vdu f - 1 -th: =! ln la:c + bl ax+b a Integrals of Rational Functions (3) (4) / 1 -dx=lnlxl X (2) I / I. d 1 (x+n)2 x=-~ (x+ a)"+' (x+ a)"dx=,n -:/:.-1 n+. 1 (5) (6) 4

5 Part 2a [5 points). Determine the molar flowrates of methanol and water in Stream 2 (S2). A T-x-y diagram for a methanol-water system is provided below, at a pressure of 1 atrn u 90 llj) QJ 'tj 85 C. E QJ I \ r _ " Ill ~ "" - ~ ~ Ill... ~ ~ - ~~ ~ a-..,_ - "-, ' -..._ '-... ~ """"'-- i ,...-- r-,... ~ x,y (methanol liquid and vapor) mole fraction 5

6 Part 2b [10 points]. Determine the time at which the outlet stream (Stream S3) would have a dew point of 85 C at 1 atm. 6

7 Part 2c [5 points]. Determine the composition of the outlet stream (Stream S3) after the mixing process reaches steady state. Part 2d [5 points]. Sketch the mole fraction of methanol and water in the tank, starting from one hour prior to the opening of Valve 1, to the final steady-state. Clearly label the time at which the valve was opened, the time at which the composition calculated.from Part 2b was reached, and the steady-state compositions. You should provide all the information to receive the full credit. Valve 1 is on fort> O 1/) C 0... u ro I..... Q) 0 ~ 0 Time 7

8 BONUS QUESTION: Part 2e [10 points]. A change in the specifications of the downstream process requires the outlet stream (Stream S3) to be condensed into liquid phase. To accomplish this, a cooling element was installed in the gas blender, to achieve simultaneous blending and cooling. Determine the minimum duty of the cooling element to achieve total condensation of the outlet vapour when the process is at steady-state. Clearly state the reference state, and indicate the path(s) selected to calculate the enthalpies of the streams. Average heat capacity, independent of temperature change: Cp, methanol (g) = 0.05 kj moi- 1 K- 1 Cp, water (g) = 0.03 kj mot- 1 K 1 Cp, methanol (1) = 0.09 kj moi- 1 K- 1 Cp, water (1) = 0.08 kj mot- 1 K 1 Heat of vaporization at 1 atm: ~Hvap, methanol = 36 kj mot- 1 mvap,water = 41 kj mo1-1 8

9 Problem 3 (35 points) Ammonia is reacted with oxygen to form nitric oxide, nitrogen, and water: The fresh stream containing liquid ammonia and liquid oxygen, at 300 K and 20 bar. This stream is combined with the recycle stream (S7) and fed into a reactor which is operated at 20 bar. The stream (S3) leaving the reactor contains 20 molls NH3, 30 molls 02, 20 molls NO, 20 molls N2, 10 mol/s H2O. All components in S3 are liquid at 275 K. The liquid goes through a throttling valve before the flash drum such that the pressure decreases from 20 bar to 1 bar, when reaching the flash drum. Only water is condensable in the flash drum which is operated at 1 bar. All the vapor is sent to S5 and 50% of the vapor products (Stream S5) leaves the process in S6. The components in S7 is compressed by a pump to 20 bar and return to the process. Assume the effect of shaft work in S7 is negligible for calculation. Below is a flow diagram for the process: S1 S2 S7 S3 ss Flash Drum (1 bar) S6 Reactor S4 Raoult's law: Yi *Ptotal = Xi *Pisat Antoine equation: log10 (P) = A - Bl(T + C), P = vapor pressure (bar), T = temperature (K) Component Antoine equation constants A B C NH NO N H Physical property table: Component Heat of Formation Specific Heat Capacity hr (liquid), kjlmol Cp (liquid), Jlmol K NH NO N H

10 Part3a (6 points). Determine the bubble point pressure in S3. 10

11 Part 3b (21 points). Complete the stream table Component OSI 0S2 0S3 0S4 nss 0S6 0S7 molls molls molls molls molls molls molls NHJ NO N H

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13 Part 3c (4.5 points). Determine the rate of heat transfer of the reactor in kj s- 1 (use negative sign for heat transferred from the system; positive sign for heat transferred to the system) To perform your calculations, use the following reference state: Component Reference state Temperature,.K Pressure, bar Phase NH liquid liquid NO liquid N liquid H liquid 13

14 Part 3d (3.5 points) Assuming ideal gases enter the recycle stream (S7), explain how does the adiabatic compression change the temperature, internal energy (U), and enthalpy (H) of the stream leaving the compressor? In a few sentences. 14

15 Problem 4 [30 points] In a boiler, a phenol (C6H6O) feed stream (SI) and a cyclohexane (C6H12) feed stream (S2) are mixed in a steady-state process. The mixture of phenol and cyclohexane (S3) exits the boiler at 250 C and 3 atm. This gas mixture (S3) and a stream of hydrogen (S4) are fed into a reactor, in which cyclohexane is produced from the reaction between phenol and hydrogen: The reactor is operated at 300 C and 3 atm, and the reaction reaches equilibrium at this condition (equilibrium constant Kp= I.66xIQ- 7 kpa- 3 ). The outlet stream (S5) leaves the reactor at 300 C and 1 atm. Other process data are: _Feed Stream 1 (SI): Feed Stream 2 (S2): Feed Stream 4 (S4): 14.1 kg/hphenol,30 C, 1 atm 4.2 kg/h Cyclohexane, 50 C, 1 atm 0.6 kg/h Hydrogen, 150 C, 3 atm All gases in this process can be considered as ideal gases. Neglect the kinetic energies of all streams. Sl S4 S2 BOILER S3 REACTOR S5 Heat transfer Heat transfer Melting points applied to 1-3 atm: Phenol: 41 C Cyclohexane: 7 C Water: 0 C Boiling points applied to 1-3 atm: Phenol: 182 C Cyclohexane: 81 C Water: 100 C Molar mass: Phenol: 94 g/mol Cyclohexane: 84 g/mol Hydrogen: 2 g/mol Water: 18 g/mol Heat of formation (ah:), at 25 C and 1 atm: Phenol: -165 kj/mol Cyclohexane: -158 kj/mol Hydrogen: 0 kj/mol Water: -286 kj/mol Average heat capacity <"c;}, independent of temperature change: Phenol: Solid: 127 J/(mol K) Liquid: 200 J/(mol K) Gas: 146 J/(mol K) Cyclohexane: Solid: 95 J/(mol K) Liquid: 122 J/(mol K) Gas: 169 J/(mol K) Hydrogen: Gas: 24 J/(mol K) 15

16 Water: Solid: 38 J/(mol K) Liquid: 75 J/(mol K) Gas: 34 J/(mol K) Phase transition data: Phenol: Heat of melting, llflm= 11 kj/mol Heat of vaporization, llflv= 59 kj/mol Cyclohexane: Heat of melting, llhm= 13 kj/mol Heat of vaporization, llhv= 29 kj/mol Water: Heat of melting, llflm= 6 kj/mol. Heat of vaporization, llflv= 41 kj/mol The gas constant (R): m 3 Pa/(mol K) L mm Hg/(mol K) L atm/(mol K) Factors for unit conversions: 1 m 3.= 1000 L 1 kg= 1000 g 1 atm = Pa= 760 mm Hg Part 4a (4 points]. Generate the molar balance equation used to solve for the extent ofreaction (fl, substitute known numerical values, but DO NOT solve. 16

17 Part 4b [18 points]. Knowing that the extent of the reaction is 40, complete the stream table below, specifically, fill in the 18 parentheses, which will be graded. References: C6H60(s), C6H12(l), H2(g), and H20(l) at 25 C and 1 atm. Substance S1 S2 S3 S4 S5 it fl it Fl it Fl it Fl it Fl -(mol/h) (kj/mol) (mol/h) (kj/mol) (mol/h) (kj/mol) (mol/h) (kj/mol) (mol/h) (kj/mol) Phenol ( ) ( ) ( ) ( ) ( ) ( ) Cyclohexane ( ) ( ) ( ) ( ) ( ) ( ) Hydrogen ( ) ( ) ( ) ( ) Water ( ) ( ) 17

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19 Part 4c [4 points]. Calculate the rate of heat transfer of the reactor in kj/h (use negative sign for heat transferred from the system; us~ positive sign for heat transferred to the system). 19

20 Part 4d [2 points]. Calculate the equilibrium conversion of phenol in the reactor. Part 4e [2 points]. If you increase the operation temperature of the reactor, the mole fraction of water in S5 will (circle the correct answer) a. Increase b. Decrease Why? Explain in 1-2 sentences. Congratulations! You have completed this course. Have a great winter break! 20

Furnace. 1. (10 points) mol/s 53.5% H2O CO2

Furnace. 1. (10 points) mol/s 53.5% H2O CO2 MEEBAL Exam 3 December 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.