column heat balances to be modified, and energy recovery to the oil streams to improve. In this article, these four areas will be covered separately to highlight their role. Albeit CV1 is a highly integrated single system with all the related causes and effects, one thing cannot be changed without affecting everything else (see Figure 4 ). Focused capital revamps – finding creative solutions Focused capital revamps need to identify easy-to-build process flow scheme modifications that exploit underuti - lised equipment, minimise existing equipment modifica - tions, and circumvent existing equipment shortcomings. CV1’s vacuum system modifications were the single larg - est challenge and project cost. Its optimisation was critical to the success of the project. First-stage ejector process load is primarily process steam and condensable oil, hence both needed to be managed to minimise vacuum system investment. Because the unit processed external RGO containing a lot of light material, which affected ejector condensable load, processing some of the RGO in the atmospheric column would reduce ejector load (see Figure 5 ). However, this was not enough to reduce the size of the new inter-condensers. The new first-stage inter-con - denser needed to fit in the plot space used by the existing exchangers. In addition, ejector system CW supply flow rate could not be increased. Vacuum system modifications The vacuum column top pressure was operating at 50 mmHg absolute in the summer compared to a design of 18 mmHg absolute. Even though the process loads were less than design, the pressure was much higher than design. The high-pressure operation significantly reduced HVGO cutpoint and hindered the ability to process excess AR. A thorough troubleshooting effort was commissioned to understand why the vacuum system was not perform- ing per design. Pressure surveys conducted with highly accurate gauges determined the first-stage ejector was
Increased vacuum heater outlet temperature
Maximise energy recovery to oil streams
Column heat balance exibility
Vacuum system performance
Figure 4 Four areas highlighted
The downside to an HGO pumparound is that it reduces light gasoil (LGO) product (atmospheric diesel) yield due to reduced reflux between the two cuts (see Figure 3 ). 3 Shifting heat up the atmospheric column presented an opportunity to increase LGO up against heater constraints. Likewise, incremental LVGO (vacuum diesel) could be produced by shifting heat up the vacuum column. Shifting heat to the LVGO PA section increases condensing capacity, allowing maximum LVGO yield, but it also has a heat recov - ery penalty because MVGO PA draw is 500°F whereas LVGO PA draw is 275°F. The majority of the LVGO PA duty is rejected to air-cooled and water-cooled exchangers. CV1 is more complicated than most crude units because it processes external feed streams in addition to crude oil. The excess AR is cold and needs to be heated. This compli - cates preheat train heat recovery because a portion of the preheat train dduty must be used to preheat external AR and is not available for crude preheating. Increasing excess AR processing and shifting heat up to lower draw tempera - ture pumparounds in the atmospheric and vacuum columns were challenges to increasing the heater inlet temperatures. Meeting CV1’s processing objectives requires vacuum column operating pressure to decrease, vacuum heater outlet temperature to increase, atmospheric and vacuum
Diesel
RGO
+18.5 KBPD
Atmospheric column
RGO to Atmospheric column
Hydrocracker
FCC
LGO
Atmospheric heater
HGO
Preheat
Crude
Vacuum column
+10 KBPD Re nery AR
Coker feed
Vacuum heater
Preheat
Figure 5 RGO partially routed to atmospheric column
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