The four unit separation train shown in figure 1.1 has been designed to separate

Question

The four unit separation train shown in figure 1.1 has been designed to separate 1000 gmol/hr of a hydrocarbon feed containing 20% CH_4, 25 % C_2H_6, 40 % C_3H_8, and the rest C_4H_10 (molar basis) into five fractions. Given the indicated compositions (molar basis) and assuming that the recycle to unit I is 50% of bottoms from unit II (m_6 = 0.5 m_5), determine: Write all the possible material balance per system and sub-system. Determine how many known and unknowns are in the process. Solve for all flow rates and compositions.

Explanation / Answer

a) overall mass balance is given by:

m1=m4+m7+m8+m10+m11

for mass balance of fraction I

m1+m6=m2+m3

for mass balance of fraction II

m2=m4+m5

for mass balance of fraction III

m3=m9+m8

for mass balance of fraction IV

m9=m10+m11

b) unknown are: m4,m7,m8,m10,m11

known are: m1, x1,x2,x3,x4 in feed 1

x3 in stream 2

x1,x2 in stream 4

  x1,x3 in stream 7

  x4 in stream 8

x3,x4 in stream 10

x3,x4 in stream 9

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