Assignment 3 (Winter, 2017 ) PDF

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DEPARTMENT OF CHEMICAL & MATERIALS ENGINEERING

ChE 416

Equilibrium Stage Processes

Winter 2017

Correction (updated on Feb 09): Corrections have been made for Q4 (c) and number disorder of Q2 and Q4. Assignment 3 (Due 4:00pm, Feb. 15, 2017) Q1. Murphree Efficiency and Binary Distillation using McCabe Thiele method (25 marks) Use enclosed y-x diagram for your solution [20+5] A distillation column with a total condenser and a partial reboiler is separating methanol and water. Feed is a super-heated vapor where 3 moles of feed vaporize 2 mole of liquid. Feed rate is 100 mol/h, and a feed composition is 60% methanol. The column separates this feed into a liquid distillate product of 96 mol% methanol and liquid bottom product of 96 mole% water. The column operates at 1 atm. The y-x diagram for the system is enclosed (Figure 1). L/V is equal to 0.75. Determine the number of trays and optimal feed tray location for the actual column at 75% Murphree vapor -tray efficiency by the McCabeThiele method. Q2. Optimal side-stream location [2+2+6+4+2+4+5] Following figure shows a distillation column assuming that methanol (M) and ethanol (E) form an ideal solution with a constant relative volatility of 1.745. Please see Figure 2 for equilibrium data.

a) Calculate D and B b) Determine reflux ratio (R) c) Calculate the following flow rates of all three sections: Top section: V, L 1

DEPARTMENT OF CHEMICAL & MATERIALS ENGINEERING

ChE 416

d)

e) f) g)

Equilibrium Stage Processes

Winter 2017

Intermediate section: V, L Bottom section: and From the mass and/or component balance show the intermediate operating line in terms of y = mx + c, where m is the slope of the operating line and c is the intercept. Find the value of m and c From the balance around reboiler show the bottom operating line in terms of y = mx + c. Find the value of m and c Determine the optimal feed and side stream locations Determine the number of equilibrium stages

Q3. Multiple feed streams using McCabe Thiele method [6+2+6+4+5+2] There are two feed streams A and B at their corresponding bubble points available in a plant. The streams consist of binary mixtures of methanol and water whose characteristics are given in Table1. You are given an assignment to design a distillation column, which is expected to produce a top product of 95% methanol and a bottom product of 95% water. There is a high premium on distillation equipment cost and you are expected to keep the number of plates the minimum. The equilibrium data is given in Figure 1. Your supervisor fixes the reflux ratio L/D = 2.0 and asks you to explore the following two conditions: (i) Case 1. Mix the two streams A and B, bring them to their bubble point and then have one feed to the column. (ii) Case 2. Feed the two streams at two different places in the column. Table 1: Characteristic of the two streams. Stream Flow rate [mol/h] Composition A 100 x = 0.5 B 100 x = 0.4 a) For case 1, calculate D, B and determine the number of stages b) For case 2, find the followings: i) Calculate D and B ii) Calculate all the flow rates in all three sections: V, L, V, L, and iii) From the mass and/or component balance show the intermediate operating line in terms y = mx + c, where m is the slope of the operating line and c is the intercept. Find the value of m and c iv) Determine the number of stages

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DEPARTMENT OF CHEMICAL & MATERIALS ENGINEERING

ChE 416

Equilibrium Stage Processes

Winter 2017

c) Which of the above two cases will give you the minimum number of trays? Support your answers with the proper McCabe-Thiele diagrams. Q4. Open steam using McCabe Thiele method [4+12+4+5] We are separating a mixture containing methanol and water in a distillation column using open steam heating and a partial condenser. Feed is a super-heated vapor where 2 moles of feed vaporize 1 mole of liquid. Feed rate is 250 mol/h, and a feed composition is 80% methanol. Distillate composition is yD=0.96 and bottoms composition is xB=0.1. Use a reflux ratio, L/D = 1.84. The equilibrium data are given in Figure 1. a) b) c) d)

Find the optimum feed plate location. Determine the total number of equilibrium stages needed. Find the composition of the liquid leaving the 4th stage below the partial condenser. Determine steam rate in kg/h and distillate rate in kmol/h

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DEPARTMENT OF CHEMICAL & MATERIALS ENGINEERING

ChE 416

Equilibrium Stage Processes

Winter 2017

Figure 1. Equilibrium data for methanol and water at 1 atm

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DEPARTMENT OF CHEMICAL & MATERIALS ENGINEERING

ChE 416

Equilibrium Stage Processes

Winter 2017

Figure 2. Equilibrium data for methanol and ethanol at 1 atm

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