Dynamics mode results for the CC3 example simulation

Partial power failure results

With the trip of both reflux pumps and the continued availability of 50% of the air condenser fans, the reflux drum fills completely and floods the air cooler. The air cooler duty then drops to zero. In the following figure, the condenser duty is not available after 11 minutes and the column pressure begins to rise more steeply as a result.

Figure 3: Condenser duty and reflux drum level for partial power failure

Column relief begins at around 14 minutes and a peak of 12,500 kg/h occurs after 16 minutes, as shown in the following figure.

Figure 4: Column relief load for partial power failure

Total power failure results

The total power failure trips all pumps and all the condenser fan motors. With reduced natural convection airflow, we observe a lower condenser duty of 387 kW (around 31% of the design duty), as shown in the following figure.

Figure 5: Condenser duty and reflux drum level for total power failure

As the sump level decreases, the reboiler duties go to zero after 10 minutes, as shown in the following figure.

Figure 6: Reboiler duty and reflux drum level for total power failure

While we still see a condenser duty, the column starts relieving at around 7 minutes with a peak of 8,500 kg/h after 10 minutes, as shown in the following figure.

Figure 7: Column relief load for total power failure

Analysis

The partial power failure scenario has a higher relief load than the total power failure scenario because feed continues to flow to the column and provides low-boiling-point benzene to the reboiler.

The relief in the partial power failure scenario continues until an operator manually stops the feed or steam. There is only a momentary relief in the total power failure scenario because the initial benzene inventory in the column is consumed and there is no feed to replenish it.