PTQ Q1 2023 Issue

Reconfiguration of naphtha splitters using divided wall column technology Integration of DWCs into existing refining configurations reduces energy consumption and GHG emissions in distillation systems while also lowering operating costs

Ratheesh S Bharat Petroleum Corporation Limited (BPCL)

D istillation systems are responsible for the highest amount of energy consumption in refineries. Use of fossil fuels is responsible for environmental problems such as global warming and air pollution, causing health problems and affecting the quality of life of populations. Technologies coupled with improved energy efficiency can support a more sustainable energy system with fewer car- bon emissions. The most effective way to reduce greenhouse gas (GHG) emissions is to reduce the consumption of fossil fuels. The BPCL Mumbai Refinery (MR) is committed to pioneering energy conservation stewardship and envi- ronmental protection in the oil and gas industry through innovative approaches. Reconfiguration of the Mumbai refinery naphtha splitters was such an attempt to reduce fuel consumption. Naphtha management is crucial for improving the overall gross refining margin (GRM) of a refinery. Naphtha can be managed by effective separation and upgradation and by optimising the blending strategies, which minimises overall naphtha production. MR consists of two crude distillation units (CDUs), namely CDU-3 and CDU-4. The refinery had three naphtha splitters, namely the reformer feed prepara- tion unit (RFU) Splitter I, RFU Splitter II, and the isomeri - sation unit (ISOM) naphtha splitter, to split 6000 tons/day of stabilised naphtha from the CDUs into light and heavy components. RFU Splitters I and II were operating in a series config - uration wherein Splitter I bottoms were fed to Splitter II. Along with its scheduled turnaround for maintenance and inspection activities, the RFU had also undergone a recon - figuration in Sept-Oct 2021 to enhance its feed processing capacity from 4300 t/d to 6000 t/d through modification of column internals. With the post-reconfiguration of its RFU naphtha splitters, MR can operate Splitters I and II in

a parallel configuration, thereby shutting down the ISOM naphtha splitter to conserve energy and reduce emissions. Background Straight-run naphtha from the stabiliser bottoms of both CDU-3 and CDU-4 is received by the naphtha splitters. The quantity and quality of naphtha depends on the type of crude. Typically, naphtha generated from Bombay High (BH) crude contains a high amount of benzene, whereas naphtha generated from Middle East crude contains rela - tively lower benzene. For upgradation purposes, naphtha has to be separated into ISOM feed (C5 and C6 with low benzene content) and CCR feed (C7+). In the pre-reconfiguration scenario, the RFU, with a series configuration of the two splitters, was processing 4300 t/d of stabilised naphtha, and the ISOM naphtha splitter was pro - cessing 1700 t/d of stabilised naphtha. Details of these col - umns (pre-reconfiguration) are provided in Table 1 . Top cuts (C5-85ºC) from RFU Splitter I and the ISOM naphtha splitter were routed to the naphtha hydrotreating unit (NHT), where they were hydrotreated to yield ISOM feed. Bottom cut from Splitter I was fed to Splitter II. Mid-cut from Splitter I, top cut from Splitter II, and mid-cut from the ISOM naphtha splitter were routed to the naphtha product pool. Bottom cuts (95- 135ºC) from Splitter II and the ISOM naphtha splitter were routed to the NHT, where they were hydrotreated to yield CCR feed. The RFU pre-reconfiguration is shown in Figure 1 . With the objective of improving the performance of these splitters, BPCL’s Corporate R&D Centre performed detailed analysis of naphtha operations at MR. Based on analysis of feed and products data, it was found that: • Existing configuration was outdated and required upgra - dation as per changes in the refinery configuration • Separation efficiency was low and overall energy con - sumption was high

Details of naphtha splitters (pre-reconfiguration)

Sl. No.

Equipment description

Outer diameter, m

Height, m

Internals

1 2 3

RFU Splitter I RFU Splitter II

3.0 3.4 2.6

21.75 21.75 43.90

3 beds (total 48 layers) of structured packings 3 beds (total of 51 layers) of structured packing 60 Nos. of valve trays with tray spacing of 610 mm

ISOM naphtha splitter

Table 1

PTQ Q1 2023