Compute the composition of the vapor and liquid when the wellstream feed is flas
ID: 592391 • Letter: C
Question
Compute the composition of the vapor and liquid when the wellstream feed is flashed to 500 psia and 120o F in a separator. Calculations should be made to at least 3 significant digits (i.e compositions should add to 1.000). All work must be shown for credit. You can use the equilibrium ratios from problem 5.
Separator (500 psia, 120o F)
Comp Feed Liquid Gas
C1 0.5
C2 0.15
C5 0.15
C6 0.1
C7 + 0.1
for more info, please go to sample test (it's question # 6)
http://www.pe.tamu.edu/barrufet/public_html/PETE310/sampleexams/Sample-Exam3b.pdf
thanks
Explanation / Answer
K = Y / X = constant
Separator
(500 psia, 120 F)
Comp
Feed
Liquid (X)
Gas (Y)
K (Y/X)
C1
0.5618
0.1188
0.7749
6.523
C2
0.1011
0.07
0.1161
1.659
C3
0.0787
0.106
0.0655
0.618
C4
0.0674
0.1397
0.0326
0.233
C5
0.0337
0.0871
0.008
0.092
C6
0.0225
0.0643
0.0024
0.037
C7+
0.1348
0.414
0.0005
0.001
Separator
Comp
Feed
K (Y/X)
C1
0.5
6.523
C2
0.15
1.659
C5
0.15
0.092
C6
0.1
0.037
C7+
0.1
0.001
Let F be the feed flow, G the vapor product flow and L the liquid product flow
Let G/F = Gf, and L/F = Lf
Mass Balance:
F = G + L
1 = G/F + L/F
1 = Gf + Lf … eqn (1)
Component Balance:
F * XF = G * Y + L * X
For C1:
F * 0.5 = G * Y1 + L * X1
0.5 = K1 * X1 * G/F + X1 * L/F
0.5 = X1 (K1 Gf + Lf)
Similarly for C2:
0.15 = X2 (K2 Gf + Lf)
For C5:
0.15 = X5 (K5 Gf + Lf)
For C6:
0.1 = X6 (K6 Gf + Lf)
For C7+:
0.1 = X7 (K7 Gf + Lf)
Xi = 1
X1 + X2 + X5 + X6 + X7 = 1
XFi / (KiGf + L) = 1
Using eqn (1) we get
XFi / (KiGf + 1 - Gf) = 1
XFi / (1 + Gf (Ki - 1)) = 1
0.5 / (1 + Gf (6.523 – 1)) + 0.15 / (1 + Gf (1.659 – 1)) + 0.15 / (1 + Gf (0.092 – 1)) + 0.1 / (1 + Gf (0.037 – 1)) + 0.1 / (1 + Gf (0.001 – 1)) = 1
Solving we get Gf = 0.574
Lf = 1 – 0.574 = 0.426
X1 = 0.5 / (K1 Gf + Lf)
= 0.5 / (6.523 * 0.574 + 0.426)
= 0.12
Y1 = X1 * K1 = 0.12 * 6.523 = 0.782
Similarly we can generate results as:
Separator
Comp
Feed, XF
K (Y/X)
Liquid
Gas
C1
0.5
6.523
0.120
0.782
C2
0.15
1.659
0.109
0.181
C5
0.15
0.092
0.313
0.029
C6
0.1
0.037
0.224
0.008
C7+
0.1
0.001
0.234
0.000
Y = X = 1
Separator
(500 psia, 120 F)
Comp
Feed
Liquid (X)
Gas (Y)
K (Y/X)
C1
0.5618
0.1188
0.7749
6.523
C2
0.1011
0.07
0.1161
1.659
C3
0.0787
0.106
0.0655
0.618
C4
0.0674
0.1397
0.0326
0.233
C5
0.0337
0.0871
0.008
0.092
C6
0.0225
0.0643
0.0024
0.037
C7+
0.1348
0.414
0.0005
0.001
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