Reactor-Separation TrainRecycle
Chapt. 8
Terry A. Ring
Use of Separation Units
Closing Recycle Loops
• Matrix Mathematics
• Without Recycle Loop
x
Unit Op
y
– [P] x = y
• Straight forward martix multiplication gives y
recycle
• With Recycle Loop
– [P] x + r [P] y = (1-r) y
x
Unit Op
• Non-linear model
• Non-linear matrix manipulation
y
[P] (x+ry)
Aspen Strategy
• Solve process sequentially without recycle
– Do no heat integration
• Add stream of simulated recycle
• Get all unit operations running correctly in the
sequence.
• Add heat integration
• Get all unit operations running correctly in
sequence
• Only then should you
– Eliminate Simulated Recycle
– Connect Actual Recycle
What does this Aspen Strategy Do?
• Initially all Calculations are of the type
– [P] x = y
• Heat integration makes this more
complicated but not significantly
• Only the Last Calculation is of the type
– [P] x + r [P]*[P] x = y
Flow Sheet
DCLPREC
LPVEN T
LPRET
HPVENT
HPSCRUB
LPSCRUB
DCVENT
SEP2
FLASH 4
RVENT
DCOVHD
DCHP
SCRUBRET
FLASH 3
RVAP
ACETIC
FSP LI T
B10
FLSHOVHD
DRYCOL
HVYNDS
REACTOR
CO
FLASH 1
DCBTMS
RLIQ
FLASH 2
WASTE
MEOH
DCREF
RECYCLE
Where To Purge?
• Purge at the point where the impurity has
the highest concentration.