PTQ Q2 2024 Issue

Provisional nozzles

Light naphtha to SCAN finer Middle naphtha to MOG unit

Light naphtha to SCAN finer

Feed

Middle naphtha to U nionfining/ P latformer

LCO

ex41

HCO

Heavy naphtha to SCAN finer

Figure 7 Major unit modifications after revamping

product qualities. Also, the extension of the dividing wall should be properly designed to secure enough spare theo- retical stages to mitigate the effects of the deviations from ideality. Post-revamp process simulation results A simplified process flow diagram for Case 1 is shown in Figure 6 . This includes the material balance, the qualities of the three cuts, and the main operating data (pressure pro- file, temperature profile, and duties at both the reboilers). In particular, the revamped naphtha splitter converted to a DWC allows for an almost 25°C gap between light and heavy naphtha. The overlap between middle and heavy naphtha is as low as 8°C and consistently lower than the existing setup. Also, the content of C10 + aromatic compo- nents is far below the limits required by downstream units. Major units modifications Figure 7 shows the tower before the revamp on the left side, and the tower after the revamp on the right side. For easy interpretation, the new and/or modified equipment is red in colour. The tower has been completely retrofitted from top to bottom by replacing existing conventional trays with high-performance trays 7 and high-performance structured packing at the bottom of the tower. Two partition baffles have been installed: one in the middle-bottom portion of the large ID section of the tower, and one at the top of the small ID portion of the column. To minimise the welding to the tower wall with the final goal of minimising the instal - lation time at site, a tailor-made partition baffle has been implemented, also known as the ‘built-in dividing wall’. The built-in dividing baffle is made by a combination of thicker plate beams and lightweight bolted panels particu- larly suitable for revamp projects. Two-pass high perfor- mance trays 8 have been installed in the main fractionator

side of the wall and at the prefractionator above the feed. Four-pass high-performance trays 9 have been installed in the prefractionator below the feed. A tailor-made chimney tray has been installed above the partition baffle to control, by gravity, the internal reflux split between the prefraction - ator and main fractionator side of the dividing wall. The existing middle-cut draw-off nozzle has been blanked off and relocated a few trays above the existing one. A chimney tray has been installed below the bottom partition baffle to collect the liquid coming from both sides of the wall and feed the distributor above the bed of struc- tured packing. One new reboiler has been added at the bot- tom, and a new bottom pump has been added for the heavy naphtha draw-off, with associated piping and fittings. No modifications were required at the top condenser sys - tem, at the upper reboiler or at the feed preheat exchanger. Two new provisional nozzles have been installed above the partition baffle and blanked off. The purpose of these nozzles is for external reflux control (for future implemen - tation), but only in case the tower could not be operated smoothly with the supplied internal reflux control system. The existing unit control system has been maintained unchanged. All tower modifications and external equip - ment were implemented in 20 working days within the time frame of the planned unit turnaround. Conclusions The DWC transformation allowed for a consistent improve - ment of the fractionation of the three cuts, particularly between middle and heavy naphtha: from a 40°C overlap to a 2°C gap. The unit ran for more than seven years after the revamp without any significant issues. Last year, during the planned shutdown, the column was opened for inspection, and all the tower internals were found in place without any damage.

PTQ Q2 2024