Title : Successful maximization of the feed rate of a diesel & VGO integrated unit from its original design operating capacity of 326 m3/hr to 400 m3/hr with the help of operational changes & innovations
Abstract:
This paper demonstrates the maximization of the feed rate of a Distillate Union fining process-based unit from 326 m3/hr to 400 m3/hr ( 122% of the design feed rate) without using any additional capex in terms of new equipment or new process. The study focuses on the integrated Unionfining unit, which includes Diesel and VGO sections operated as a single unit. The unit operates in two modes: Co-processing and Diesel only. In Co-processing mode, it processes both VGO and Diesel, while in Diesel only mode, it processes diesel range feedstock. The reaction section consists of a VGO hydro treating section integrated with a Diesel hydro treating section in a high pressure loop. VGO reactor effluent provides heat for the DHT reactor feed, and a hot separator provides a clean, hydrogen-rich stream for DHT inlet gas. Diesel from Diesel Unionfining meets a sulfur specification of less than 10 ppm, while VGO is expected to meet less than 500 ppm. The unit processes feed mainly from FR/FRE CDU’s and light cycle oil (LCGO) streams from FCCU/New FCCU. The original plant capacity was 2.2 million tons per year with 8000 hours operating per year, revamped to an integrated unit without any change in capacity. The VGO section processes 176 m3/hr of feed and the diesel section 150 m3/hr in Diesel only mode. The paper highlights constraints addressed to achieve the increased feed rate without compromising sustainability. It discusses strategies to optimize performance, improve efficiency, and ensure long-term operability. The results demonstrate the feasibility of scaling up the feed rate while maintaining operational integrity.
The maximization faced challenges, including high frequency of auto backwash filters and pre-filters' plugging. Strategies were developed to mitigate these issues. High auto backwash frequency spiked diesel product sulfur, leading to off-spec conditions. This was resolved by maximizing hot feed from upstream units, increasing preheat temperatures in both DHT trains and reducing fuel gas consumption in the furnace. Operational challenges included flaring from the fractionator and flooding in the VGO Stripper. Strategies were developed to minimize flaring and prevent flooding. Fractionator overhead temperature was reduced from 153 Deg C to 130 Deg C, and stripping steam was reduced to prevent flooding in the VGO stripper.
Diesel product density and viscosity were adjusted by increasing XVGO and reducing DHT operating pressure from 86 to 63 kg/cm2g, leading to reduced hydrogen consumption and preventing quality giveaway. Increased LCGO addressed low diesel viscosity issues. Recycle gas flow to REAC was maintained to keep velocity above 3m/s. With the increased feed to 400 m3/hr, a new strategy was adopted to manage flow through REAC based on feed rate. In summary, the paper details strategies developed to overcome challenges and optimize performance while maintaining mechanical integrity and sustainability.
