Separation Process Principles- 2n - Seader & Henley - Solutions Manual

Then n d unit with sidestream 2 n 2c 6 2 2

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Unformatted text preview: ) (2) NR = 6 and NA = 0 Therefore, Eq. (1) becomes, ND ND all elements Let N1 = number of rectifying stages and N2 = number of stripping stages. Using the values of ND for the elements in Table 5.3: Rectifying section 2N 1 + 2C + 5 Feed stage with heat transfer 3C + 8 Stripping section 2N 2 + 2C + 5 Partial reboiler C+4 N D e = 2(N1 + N2) + 8C + 22 (3) all elements Substituting Eq. (3) into (2), N D unit = 2 N 1 + N 2 + 8C + 22 − 6 C + 2 = 2 N1 + N 2 + 2C + 10 (4) However, in Operation (e) of Table 5.4, the feed stage and the partial reboiler are counted in N. Therefore, N1 + N2 = N - 1 - 1 = N - 2. Substituting this into Eq. (4), gives ( N D )unit = 2( N − 2) + 2C + 10 = 2 N + 2C + 6 which verifies the result given in Table 5.4. (5 Exercise 5.29 (continued) Analysis: (continued) If a vapor sidestream is added, we add 2 degrees of freedom, one for the location and one for the sidestream flow rate. Then, ( N D ) unit with sidestream = 2 N + 2C + 6 + (2) = 2 N + 2C + 8 Operation (f), reboiled stripper: Using the values of ND for the elements in Table 5.3: Section of N - 1 stages Partial reboiler 2(N - 1) + 2C + 5 C+4 N D e = 2N +3C + 7 (6) all elements Substituting Eq. (3) into (2), with NR = 2 and NA = 0, ( N D )unit = 2 N + 3C + 7 − 2 ( C + 2 ) = 2 N + C + 3 If a vapor sidestream is added, we add 2 degrees of freedom, then, ( N D )unit with sidestream = 2 N + C + 3 + (2) = 2 N + C + 5 (7) Exercise 5.30 Subject: Verification of numbers of degrees of freedom for one operation, and effect of adding a liquid sidestream.. Given: Degrees of freedom for operation (h) in Table 5.4. Find: Verify value of ND and determine effect of adding a liquid sidestream Analysis: Operation (h), extractive distillation: From Eq. (5-70), N D unit = ND e − NR C + 2 + N A (1) NR = 13 and NA = 0 Therefore, Eq. (1) becomes, N D unit = (2) all elements ND all elements e − 13(C + 2) Let N1 = number of rectifying stages above the MSA feed, N2 = number of intermediate stages between the MSA feed and the feed, N3 = number of stripping stages. Using the values of ND for the elements in Table 5.3: Total condenser C+4 Reflux divider C+5 Rectifying section 2N 1 + 2C + 5 MSA Feed stage with heat transfer 3C + 8 Intermediate section 2N 2 + 2C + 5 Feed stage with heat transfer 3C + 8 Stripping section 2N 2 + 2C + 5 C+4 Partial reboiler N D e = 2(N1 + N2 + N3 ) + 15C + 44 (3) all elements Substituting Eq. (3) into (2), N D unit = 2 N 1 + N 2 + N 3 + 15C + 44 − 13 C + 2 = 2 N 1 + N 2 + N 3 + 2C + 18 (4) However, in Operation (h) of Table 5.4, the two feed stages and the partial reboiler are counted in N. Therefore, N1 + N2 + N3 = N - 3. Substituting this into Eq. (4), gives (5) ( N D )unit = 2( N − 3) + 2C + 18 = 2 N + 2C + 12 which verifies the result in Table 5.4. If a liquid sidestream is added, we add 2 degrees of freedom, then, ( N D )unit with sidestream = 2 N + 2C + 12 + (2) = 2 N + 2C + 14 Exercise 5.31 Subject: Alternative design variables for distillation Given: Distillation design variables in Table 5.4 Find: Conditions under which the alternative varia...
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