Title : Debottlenecking of CDU-1 by pre-flash tower off-gas integration for enhanced throughput and energy efficiency
Abstract:
HPCL Mumbai Refinery has two Crude/Vacuum Distillation Units (CDUs/VDUs) designed to handle high sulfur lube bearing crude and low sulfur crude separately. As part of the Mumbai Refinery Expansion Project (MREP), CDU-1's capacity increased from 4.5 MMTPA to 6 MMTPA for processing Arab Light Crude (ARL- API 33.4) and Kuwait Crude (KW - API 30.5). Crude distillation units are energy-intensive processes. In HPCL-Mumbai Refinery, CDU/VDU has the highest energy consumption compared to other units. Operating the unit under energy-optimized conditions is always beneficial. Effectively utilizing available unit facilities and optimizing the operating conditions of CDU/VDU are crucial for achieving maximum distillate yield, reducing heat duties on furnaces, and overcoming unit constraints for throughput maximization.
The revamped CDU -1 is designed to process Kuwait (KW) and Arab Light (ARL) crudes. However, economic considerations led to the processing of various other crude types like Basra Medium (BM), URAL, DAS, and Murban. While handling crudes with API ranging from 29 to 40, the refinery (MR) encountered challenges in maximizing throughputs to meet stream specifications.
The CDU 1 at HPCL Mumbai Refinery plays a critical role in maximizing distillate recovery while operating under energy-efficient conditions. During the processing of light crude oils, operational constraints such as high vapor load on the main fractionator, elevated column differential pressure, and limitations in throughput were observed. These challenges restricted the unit’s ability to operate at higher capacities and required additional fuel gas (FG) makeup to maintain column pressure.
To overcome these challenges, an innovative process integration scheme was developed and implemented utilizing existing infrastructure without major capital investment. In this scheme, Pre-Flash Tower (PFT) off-gases were routed to the CDU-1 overhead drum through an available 6-inch spare nozzle on the PFT naphtha drum. This modification effectively reduced PFT overhead pressure, thereby enhancing naphtha recovery from the PFT. The increased prefractionation of lighter components significantly reduced vapor traffic and hydraulic load on the main atmospheric fractionator.
Implementation of the scheme resulted in a substantial reduction in column differential pressure, enabling an increase in CDU-1 throughput by approximately 25–30 m³/hr while maintaining product quality specifications. Furthermore, the integration eliminated the requirement for external fuel gas makeup to maintain CDU overhead pressure, resulting in fuel gas savings of approximately 400 SRFT. The modification also contributed to improved energy efficiency, enhanced distillate recovery, and stable unit operation under varying crude processing conditions.
This highlights how innovative utilization of existing refinery assets, combined with process optimization and operational flexibility, can successfully debottleneck CDU operations, improve refinery margins, and enhance energy performance without significant capital expenditure. The study demonstrates a practical and replicable approach for refineries handling diverse crude slates under constrained operating conditions.
