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7.21: Untitled Page 166

  • Page ID
    18299
  • Chapter 7

    The cuts and enclosures based on observations I through VII are illustrated in Figure 7.6b where we see one redundant cut of Stream #2

    and an unnecessary cut of Stream #3. We can eliminate the latter with Figure 7.6b. Cuts for the construction of control volumes the control volumes illustrated in Figure 7.6c. There we see that we have avoided a cut of Stream #3 by enclosing the reactor and the absorber in Control Volume II; however, we have created redundant cuts of Stream

    #2, Stream #4 and Stream #5.

    We begin the analysis of this process with Eq. 7‐4 that takes the form A  6

    Axiom II

    N R

     0 ,

    J  C , H , O , N

    (7)

    JA A

    A  1

    and for the case under consideration, the atomic matrix is given by

    index-318_1.png

    index-318_2.png

    index-318_3.png

    index-318_4.png

    Material Balances for Complex Systems

    309

    Molecular Species  C H

    O

    CO

    H O C H O N

    2

    4

    2

    2

    2

    2

    4

    2

    carbon

     2

    0

    1

    0

    2

    0 

    hydrogen

    4

    0

    0

    2

    4

    0

    (8)

    oxygen

     0

    2

    2

    1

    1

    0 

    nitrogen

     0

    0

    0

    0

    0

    2 

    Figure 7.6c. Control volumes for the ethylene oxide production unit Given this form of the atomic matrix, we can express Eq. 7 as

     R

    C2H4

     R

    O

    2 0 1 0 2 0

    2

    0

     

    4 0 0 2 4 0  RCO

    0

    2

       

    (9)

    0 2 2 1 1 0 R

    0

    H

    2O

     

    0 0 0 0 0 2 

    0

    R

    C2H4O 

    RN

    2

    310