4.3b Flowchart Scaling and Basis of Calculation Exercise 4.3-2.1: Scale-up of a

Question

4.3b Flowchart Scaling and Basis of Calculation Exercise 4.3-2.1: Scale-up of a Separation Process Flowchart Hydrogen can be produced using a process called coal gasification. It is desired to supply nearly pure oxygen to this process. Oxygen is separated from nitrogen out of the air (79 mol% nitrogen and 21 mol% oxygen) via a process known as cryogenic distillation. (a) A cryogenic distillation unit has a feed of 845 kgmo/hr air. The top stream has an overall flow rate of 632 kgmol/hr with a nitrogen mole fraction of 0.95. The bottom stream has an overall flow rate of 213 kgmol/hr with a nitrogen mole fraction of 0.31. The process is illustrated in the block diagram below. Scale up the system for a feed flow rate of 14200 kgmol air/hr. 632 kgmol air/hr 0.95 kgmol N/kgmol 0.05 kgmol Oz/kgmol 845 kgmol air/hr 0.79 kgmol N/kgmol 0.21 kgmol Oykgmol Home work 5.2 213 kgmol air/hr 0.31 kgmol No/kgiac 0.69 kgmol O-/kgnol

Explanation / Answer

Ans a

Feed flow rate = 14200 kmol air / h

Flow rate of N2 in feed = 0.79 x 14200 = 11218 kmol/h

Flow rate of O2 in feed = 0.21 x 14200 = 2982 kmol/h

Overall mass balance

Feed flow rate = top stream rate + bottom stream rate

X = Y + Z

14200 = Y + Z

Y = 14200 - Z

O2 balance

2982 = Y*0.05 + Z*0.69

2982 = ( 14200 - Z)*0.05 + Z*0.69

2982 = 710 - Z*0.05 + Z*0.69

2272 = 0.74 Z

Z = 3070.27 kmol air/h

Y = 14200 - 3070.27 = 11129.73 mol air /h

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