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

4 19a and equations of table 44 analysis specify feed

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Unformatted text preview: mixture. Given: Feed mixture, of composition below, at 250oF and 500 psia. Pressure exiting valve = 300 psia. Find: (a) (b) (c) (d) Phase condition of feed. Temperature downstream of valve. Mole fraction vaporized across valve. Mole fraction compositions of vapor and liquid phases downstream of valve. Analysis: Use CHEMCAD process simulator with S-R-K method for K-values and enthalpies. Results are as follows: Stream Temperature, oF Pressure, psia Phase condition Mole fraction of feed Mole fractions: Ethylene Ethane Propylene Propane Isobutane n-Butane Feed 250 500 Liquid 1.00 Vapor from valve 207.6 300 Vapor 0.4043 Liquid from valve 207.6 300 Liquid 0.5957 0.02 0.03 0.05 0.10 0.20 0.60 0.0348 0.0491 0.0658 0.1260 0.1953 0.5290 0.0099 0.0171 0.0393 0.0823 0.2032 0.6482 Exercise 4.43 Subject and to Find: Algorithm for flash calculation when Ψ = V/F and P are specified. Given: Isothermal flash algorithm of Fig. 4-19a, and equations of Table 4.4. Analysis: Specify feed rate and composition, and values of Ψ = V/F and P. Use the isothermal flash algorithm of Fig. 4-19a as an inner loop. Guess the flash temperature and enter the inner loop. If the calculated Ψ = V/F is not the specified value, guess a new value of T = say 1.05 times the initial guess of T, and repeat the inner loop. For the next and subsequent iterations, k, apply the false position method to provide a new guess of T: T k + 2 = T k +1 + Ψspec − Ψ k +1 T k +1 − T k / Ψ k +1 − Ψ k This assumes that T is a linear function of Ψ = V/F. Iterate until the computed Ψ = V/F is within say 0.1% of the specified value. Exercise 4.44 Subject and to Find: Algorithms for flash calculations with 6 different sets of specified variables given in the table below. Given: Isothermal flash algorithm of Fig. 4-19a, and equations of Table 4.4. Assumption: All flashes are adiabatic. Analysis: The equations to be solved for each algorithm are those for the standard adiabatic flash procedure, where the specifications are outlet P and Q = 0. Rachford-Rice Eq. (3), Table 4.4: f1 = zi 1 − Ki =0 i =1 1 + Ψ Ki − 1 C Adiabatic energy balance, Eq. (4-19): f 2 = ΨhV + (1 − Ψ )hL − hF 1,000 (1) (2) For each of the 6 algorithms, we must choose a tear variable, the output variable for f1, and the output variable for f2. If K-values are composition-dependent, then outer loop iterations with f1 are necessary as in Fig. 4.19. Note that the specification of hF is equivalent to specifying TF or Q = 0. In some cases, it may be necessary to solve f1 and f2 simultaneously. Case Specifications Find 1 2 3 4 5 6 hF , P hF , T hF , Ψ Ψ, T Ψ, P T, P Ψ, Τ Ψ, P T, P hF , P hF , T hF , Ψ Output Variable in Tear f1 f2 Variable TV TV Ψ PV Ψ Ψ TV PV TV h F{T F} PV hF h F{T F} TV hF h F{T F} hF Ψ As an example of one of the algorithms, consider Case 1, which is equivalent to the standard adiabatic flash specification. The algorithm is shown in diagram form on the following page. Exercise 4.44 (continued) Analysis: (c...
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