PTQ Q1 2023 Issue

C cut to NHT ISOM

C cut to NHT ISOM

Feed from CDU3/ CDU4

Feed from CDU3/ CDU4

C cut to NHT ISOM

Naphtha MS pool/CCR

ISOM/ Nap. pool/ MS pool

Naphtha splitter 2

Naphtha pool/ MS pool/CCR/GTU

Naphtha splitter 2

Naphtha splitter 1

Naphtha splitter 1

Bottoms to CCR

Bottoms to CCR

Figure 2 Post-reconfiguration of RFU splitters

Figure 1 Pre-reconfiguration of naphtha splitters

• ISOM feed had low amounts of C 6 components, which are active reactants in the ISOM unit (for RON improvement). To address these issues, different schemes were config - ured and simulated using Aspen Plus. Stream properties (quality and quantity) and the energy consumption of each configuration were compared with the existing configura - tion. Based on economic and operational benefits, one of these configurations was finalised and proposed for imple - mentation. The selected configuration was to convert RFU Splitter II into a divided wall column (DWC) so that RFU Splitters I and II can be operated in parallel and the ISOM naphtha splitter can be shut down. Objectives The main naphtha splitter objectives were as follows: • Increase RFU feed processing capacity from 4300 MTPD to 6000 MTPD by operating Splitters I and II in parallel con - figuration so that the ISOM naphtha splitter can be shut

down. Feed distribution to both the splitters will be opti - mised suitably to minimise the quantum of modifications and maximise product quality and yield • Maximise the quantity of top cut while minimising the benzene, C 6 naphthenes, and C₇+ hydrocarbons in it. This stream will be fed to the NHT-ISOM unit • Minimise the quantity of mid-cut and minimise over- lap with the top cut and bottom cut. This stream will be diverted to naphtha storage • Maximise the quantity of bottom cut while maximising the toluene in it. This stream will be fed to the NHT-CCR unit. Post-reconfiguration of RFU Post-reconfiguration, RFU Splitter I continues to operate as a conventional side-cut column, whereas Splitter II has been converted into a middle DWC. The RFU post-recon - figuration is shown in Figure 2 .

Details of major modifications done during the reconfiguration of the naphtha splitters

Sl. No.

Equipment category

Modifications done


Splitter I

Packing of top bed (10 layers) completely replaced with 13 layers of new type of packing. Bed height reduced (from 12 to 8 layers) for middle bed. 26 layers of packings reused without any change in bottom bed. All beds except bottom bed completely replaced with new structured packings and bed height reduced (from 27 layers to 13 layers) for bottom bed in stripping section of the column. A dividing wall was installed inside the column which runs between top and bottom beds. The dividing wall section runs approximately the middle third of the column.


Splitter II


New heat exchangers

MP steam/RFU feed preheater (No. 1) Splitter I/II top cooler (1 shell) splitter I/II Mid-cut cooler (2 shells) Splitter I/II bottom cooler (1 shell) RFU feed preheater condensate pot RFU Feed pumps (2 No.s) Splitter I reflux pumps (2 No.s) Splitter I mid-cut pump (1 No.) Splitter II mid-cut pumps (2 No.s)


New vessel


New pumps

Rated capacity of RFU post-reconfiguration is 6600 t/d with turndown of 40% for Splitters I and II.

Table 2


PTQ Q1 2023

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