Prof. Davide Manca – Politecnico di Milano Dynamics and Control of Chemical Processes
Solution to Lab #9
Shutdown of C4-C5 separation
section
RUN A DISTILLATION COLUMN USING HYSYS/UNISIM IN DYNAMIC MODE Data
Fluid package: Peng-Robinson
Feed: composition: 0.5 i-butane, 0.5 n-pentane.
molar flow: 113.4 kmol/h temperature: 327.3K pressure: 441 kPa feed tray: 5
Column type: trays with partial condenser #stages: 8
Top column pressure: 437 kPa Bottom column pressure: 444 kPa
Specify:
Molar component fraction: i-butane in the distillate 0.925 n-pentane in the bottom 0.95 Reflux rate: 69 kmol/h
Column Size Diameter: 0.9144 m Tray space: 0.6096 m
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Shutdown
To shutdown or startup a piece of equipment you can use the event scheduler (press ctrl + E)
Add
In our case the sequence of shutdown the column is:
1 – Reducing column rates
2 – Shutting down heating and cooling sources 3 – Stopping feed
4 – Draining liquids
5 – Preparing the column for opening to atmosphere So we have to add at least 5 sequences in the scheduler
Now we can modify the first, rename it as reducing rate.
Open it by pressing view, in sequence window you can add in series event.
Open it and in the condition page you can specify the event starting time (wait for a specific simulation time). It is recommended to start the shutdown sequence after 2 hours of simulation time, to check the steady state condition.
In the action list page you can add parallel actions
Model the single event in manual mode by a step change in the opening percentage valve value (e.g., every 30 min close 10% the valve).
Remember that, during the shutdown, all the controller should be in manual mode (except for which are in ramp controller).
In the action list press add:
Type: Set controller mode Select target: FIC-reflux New mode: man
Check new OP and write the percentage.
For the following steps do the same things, the logic of the sequences are reported in the following figures.
2 – Shutting down heating and cooling sources
You can also add a Ramp controller action providing the target SP and the ramp duration.
3 – Stopping feed
4 – Draining liquids
Use ramp controller to the strategy.
5 – Preparing the column for opening to atmosphere
This strategy can be simulated by controlling the pressure of the column. For that, you can add a valve in the vapor stream of the column condenser. And to introduce a ramp that goes back to the atmosphere pressure.
In the following table is reported the ramp duration and the starting time:
step Start time Ramp duration
1 2 h 5 h
2 2 h 10 h
3 2 h 20 h
4 7 h 2 h
5 21 h 1 h
To save the data and upload in excel, go in the databook window (press ctrl + D), strip charts, press historical for the datalogger that you want export, and press save to .CSV File. By doing so, you can create a csv file that you can open in excel.
