The Water Stripper Tower

This month we feature a scenario from our work in the petrochemical industry.

Welcome to our featured scenario of the month! This month’s featured ShadowBox scenario was authored by Ron Besuijen in collaboration with the ShadowBox team for the petrochemical industry. This scenario demonstrates one way we have developed training for technical, process-based domains.

As you read through the scenario, think carefully about how you would handle the situation – what stands out to you, what do you think is going on, and what would your priorities be if you found yourself in this situation? We suggest recording your choices and decision rationale so that you can compare your decisions with the experts at the end of the scenario.

Scenario background: 

The following scenario requires an understanding of basic distillation principles. 

The below image is a schematic of a basic water stripper. Live steam is injected into the trayed Stripper tower (see ‘LP Stm,’ controlled by ‘FC205’ at the bottom of the tower). As the water (labeled ‘WATER’ in the top left of the diagram, controlled by ‘LC101’) drains down through the trays any dissolved hydrocarbons are driven overhead and flow through the vent (see ‘VENT’ in the top right of the diagram). Stripped water flows out of the tower and continues downstream (see ‘WATER’ in the bottom right, controlled by ‘FC202’.)

Process variable descriptions

Vessel V101 – Water Storage 

Stripper Tower T201 – Removes dissolved vapors from the water. 

LC101 – Controls the level by directly manipulating the valve on the outlet.  

FC205 – Controls the steam flow into the tower. 

LC201 – Cascades to FC202. 

Exercise: Identify Control Elements       

The tower level (as shown by LC201) is controlled by adjusting the set point of the flow leaving the tower bottoms (controlled by FC 202).

Decision Point #1  

Select the top four variables that you would monitor to ensure stable Stripper Tower operation.

The level of Vessel 1.
The water flow into the tower.
The level of the stripper tower.
The flow through the tower vent.
The steam flow to the tower.
The water flow out of the tower.
The delta pressure of the tower.

Take a moment to consider your reasons for your decision.

The Scenario Continues…

Review the four images below. The values of key variables are indicated by the trend lines in the lower right of the screen. See if you can determine what the problem might be.

Decision Point #2

What is your assessment of the situation?

Rank the following items from 1 = most likely (top) to 5 = least likely (bottom). 

FV202 is malfunctioning.
LC201 is failing.
FV205 is cycling.
The stripper tower tray is damaged.
The FC202 transmitter is failing.

Take a moment to consider your reasons for your decision.

Decision Point #3

What are the most important actions to take at this moment?

Select only the three most important actions you would take and rank them from 1 = most important (top) to 3 = least important (bottom). 

Place FV202 into manual.
Increase the feed to the stripper tower.
Stop the steam flow to the stripper tower.
Have an outside operator check the local level indicator.
Reduce the FV202 output to recover the level in T20.

Take a moment to consider your reasons for your decision.

Click the link below to see how your choices compared with the experts!

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