John Edwards, P&I Design Ltd Dynamics Seminar Section 6 Continuous Distillation John Edwards, P&I Design Ltd August, 2014 www.chemstations.com 1

CONTINUOUS DISTILLATION SET UP DYNAMIC MODE www.chemcad.co.uk SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com CONTINUOUS DISTILLATION SET UP DYNAMIC MODE Switch to dynamic mode under convergence Set Run Time to 600 minutes with 0.5 minute step size Record desired streams 6 N-Pentane and 7 I-butane Select Run Time plot options Run from Initial State Plot results

DYNAMIC DISTILLATION SIMULATION DYNAMIC COLUMN CONFIGURATION www.chemcad.co.uk SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com DYNAMIC DISTILLATION SIMULATION DYNAMIC COLUMN CONFIGURATION

CONTINUOUS DISTILLATION RESULTS www.chemcad.co.uk SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com CONTINUOUS DISTILLATION RESULTS D6.02 page 134 CHEMCAD Job: FEEDCHANGEDCOLMDYNAMIC

CONTINUOUS DISTILLATION DYNAMIC COLUMN FEED CHANGE www.chemcad.co.uk SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com CONTINUOUS DISTILLATION DYNAMIC COLUMN FEED CHANGE Step change of feeds should be avoided as the column will take a long time to recover due to lags in the system. Feed forward control systems are used to adjust the column overheads and bottoms operation to compensate for feed changes and minimize upsets. Don’t expect steady state and dynamic mass balances to match exactly. Longer runs will produce closer matches. The simulation has not considered variable liquid hold up introduced by considering the effect of column internals.

DYNAMIC DISTILLATION SIMULATION DYNAMIC COLUMN FEED CHANGE www.chemcad.co.uk SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com DYNAMIC DISTILLATION SIMULATION DYNAMIC COLUMN FEED CHANGE CHEMCAD can calculate the holdup on each stage as a function of time using tray sizing and layout information. It cannot do this for packed columns, but the user can input holdup profiles for this situation. Condenser and reboiler holdups are handled differently. Calculated holdups can be used to make dynamic responses more realistic. Mass transfer geometries can be used to incorporate mass transfer effects into the flowsheet, further improving realism.

CONTINUOUS DISTILLATION SET UP DYNAMIC SIEVE TRAY COLUMN www.chemcad.co.uk SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com CONTINUOUS DISTILLATION SET UP DYNAMIC SIEVE TRAY COLUMN D6.03 page 134 CHEMCAD Job: FEEDCHANGEDCOLMDYNAMICSIEVETRAY Introducing column hold ups Pressure drop is constant during dynamic simulations. The Variable Pressure option would recalculate the top pressure at each time step.

CONTINUOUS DISTILLATION SET UP DYNAMIC TRAY COLUMN www.chemcad.co.uk SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com CONTINUOUS DISTILLATION SET UP DYNAMIC TRAY COLUMN

CONTINUOUS DISTILLATION DYNAMIC TRAY COLUMN RESULTS www.chemcad.co.uk SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com CONTINUOUS DISTILLATION DYNAMIC TRAY COLUMN RESULTS D6.03 page 136 Tray 24 selected for lower section temperature control

CONTINUOUS DISTILLATION FEED CHANGE - COLUMN BOTTOMS CONTROL www.chemcad.co.uk SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com CONTINUOUS DISTILLATION FEED CHANGE - COLUMN BOTTOMS CONTROL D6.04 page 137

CONTINUOUS DISTILLATION SPECIFY CONTROL LOOP AND STRATEGY www.chemcad.co.uk SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com CONTINUOUS DISTILLATION SPECIFY CONTROL LOOP AND STRATEGY

CONTINUOUS DISTILLATION SPECIFY REBOILER WITH DYNAMIC VESSEL www.chemcad.co.uk SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com CONTINUOUS DISTILLATION SPECIFY REBOILER WITH DYNAMIC VESSEL

CONTINUOUS DISTILLATION REBOILER LEVEL CONTROL RESULTS www.chemcad.co.uk SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com CONTINUOUS DISTILLATION REBOILER LEVEL CONTROL RESULTS D6.04 page 139 Initial High Level to prevent reboiler running dry Tune Level Control (Loop P = 25% I = 15 m)

CONTINUOUS DISTILLATION REBOILER FLOWS www.chemcad.co.uk SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com CONTINUOUS DISTILLATION REBOILER FLOWS D6.04 page 139

CONTINUOUS DISTILLATION FULL CONTROL MODEL www.chemcad.co.uk SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com CONTINUOUS DISTILLATION FULL CONTROL MODEL D6.05 page 140

CONTINUOUS DISTILLATION SPECIFY EQUIPMENT www.chemcad.co.uk SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com CONTINUOUS DISTILLATION SPECIFY EQUIPMENT

CONTINUOUS DISTILLATION REFLUX CONTROL www.chemcad.co.uk SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com CONTINUOUS DISTILLATION REFLUX CONTROL

CONTINUOUS DISTILLATION SCDS COLUMN SPECIFICATION www.chemcad.co.uk SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com CONTINUOUS DISTILLATION SCDS COLUMN SPECIFICATION

CONTINUOUS DISTILLATION RESULTS – COLUMN PROFILES www.chemcad.co.uk SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com CONTINUOUS DISTILLATION RESULTS – COLUMN PROFILES D6.05 page 145

CONTINUOUS DISTILLATION RESULTS – TEMPERATURE PROFILE www.chemcad.co.uk SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com CONTINUOUS DISTILLATION RESULTS – TEMPERATURE PROFILE

CONTINUOUS DISTILLATION RESULTS – STAGE 24 TEMPERATURE www.chemcad.co.uk SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com CONTINUOUS DISTILLATION RESULTS – STAGE 24 TEMPERATURE

CONTINUOUS DISTILLATION COLUMN OVERHEAD CONTROL www.chemcad.co.uk SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com CONTINUOUS DISTILLATION COLUMN OVERHEAD CONTROL D6.06 page 147

CONTINUOUS DISTILLATION COLUMN OVERHEAD CONTROL www.chemcad.co.uk SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com CONTINUOUS DISTILLATION COLUMN OVERHEAD CONTROL D6.06 page 147

CONTINUOUS DISTILLATION FEEDFORWARD CONTROL www.chemcad.co.uk SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com CONTINUOUS DISTILLATION FEEDFORWARD CONTROL D6.07 page 148

CONTINUOUS DISTILLATION FEEDFORWARD CONTROL www.chemcad.co.uk SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com CONTINUOUS DISTILLATION FEEDFORWARD CONTROL D6.07 page 149

CONTINUOUS DISTILLATION FEEDFORWARD CONTROL www.chemcad.co.uk SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com CONTINUOUS DISTILLATION FEEDFORWARD CONTROL D6.07 page 149

CONTINUOUS DISTILLATION RELIEF CONDITION www.chemcad.co.uk SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com CONTINUOUS DISTILLATION RELIEF CONDITION

CONTINUOUS DISTILLATION RELIEF CONDITION www.chemcad.co.uk SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com CONTINUOUS DISTILLATION RELIEF CONDITION

CONTINUOUS DISTILLATION RELIEF CONDITION www.chemcad.co.uk SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com CONTINUOUS DISTILLATION RELIEF CONDITION

CONTINUOUS DISTILLATION RELIEF CONDITION www.chemcad.co.uk SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com CONTINUOUS DISTILLATION RELIEF CONDITION INCREASING COLUMN PRESSURE REDUCES TEMPERATURE ∆T DUTY REDUCES FROM 3.9E06 to 2.5e06 kcal/h at relief Latent heat increases from 89.9 to 125 kcal/kg This effect reduces Relief flow by Factor 0f 1.4 Duty 3.9 e06 kcal/h requires 35141 kg/h Duty 2.5 e06 kcal/h requires 24269 kg/h Dynamic simulation predicts ≈ 6000 kg/h Dynamic simulation gives Better understanding of Distillation column behavior at relief conditions