(655c) Crude Unit Expansion Study for Attock Refinery Ltd

Attock Refinery Ltd. processes domestic crude and supplies local Pakistani markets with petroleum products. The refinery, which is located near the capital city of Islamabad, has been in operation for 80 years and is a simple hydroskimming operation with no cracking operations. Its capacity is 37,500 barrels per day (BPD), and of the three crude units currently in operation, the largest unit has a capacity of 20,000 BPD. This unit, which has been in operation since 1979, was originally designed by global EPC contractor CB&I.

In 2005, CB&I was asked by ARL to review and revise a study it had conducted years earlier on increasing the throughput of this unit from 20,000 BPD to 32,400 BPD. The expansion study, which CB&I had developed in 1989, called for the installation of a preflash tower located upstream of the existing crude tower in order to achieve the desired capacity increase.

While the initial study was tabled, ARL has since initiated efforts to process low gravity crudes ? with gravities ranging from 33.4 to 44.2 degrees API and sulfur contents ranging from .05 to .51 weight percent ? that will yield products such as LPG, light and heavy naphthas, kerosene, high speed diesel, cutback asphalt, and fuel oil. This has resulted in the largest crude unit needing to have the increased capacity to handle the additional product streams.

This paper will provide a detailed examination of CB&I's expansion review for ARL. It will offer details on such areas as:

? The Hysys® simulation software CB&I utilized to study the three crude oil assays provided by ARL.

? The product specifications and crude oil characterizations developed to estimate product properties.

? The process alternatives considered with regard to the preflash tower design, specifically the trade-off between hexane recovery in the isomerization feed versus the preflash tower size and the reboiler duty.

? The STX® and HTRI® simulation software used for the exchanger preheat design, as well as the heat recovery economics and the special constraints unique to the project.

The paper will also look at some of the challenges associated with the design of the preflash tower. Some of the issues that were addressed included:

? Designing the preflash section of the crude unit to be infrequently shut down and bypassed, allowing the operation of the current configuration. This flexibility was required due to the variable local fuel oil market and the refinery's need to drastically reduce crude throughput at times.

? Implementing several special design features in order to utilize the existing equipment to the maximum extent possible. Given the large increase in desired unit capacity, some of these key features included: a new crude preheat train parallel to the existing train to allow the use of existing exchangers; the installation of supplemental pumps, water-cooled trim condensers, and product coolers; multiple service swing exchangers that allow for flexibility in product end-points/yields; and a provision in the design to allow single exchanger trains to be isolated for maintenance with the unit operational at a reduced rate.

Some of the supplementary materials that will be included in the paper are sketches of the crude unit highlighting the new preflash tower and its product streams, graphs showing the match between the crude assay values and the modeling results, and a sketch demonstrating how an accelerated convergence was realized during the study.