Ave’s = 850, Std Dev’s = 50, USL’s = 1000, DNS’s = 3σ
Fraction of Samples
1000
800
600
400
200
0
–200
–400
–600
–800
–1000
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
–ppm Light Key in Bottoms (Tray Temp) ppm Heavy Key in Distillate
Figure 7.6 Optimum economic return from distillation column.
Std Dev’s = 50, USL’s = 1000, DNS’s = 6σ
Fraction of Samples
1000
800
600
400
200
0
–200
–400
–600
–800
–1000
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
–ppm Light Key in Bottoms (Tray Temp) ppm Heavy Key in Distillate
Figure 7.5 Reduction of variability in distillation column.
64 ◾  Distillation Control, Optimization, and Tuning