Processing of Bakken crude at the Irving Oil Refinery

Abstract

Over the last decade, changes in the crude market have shown that lighter North American Crudes, such as Bakken, have become discounted relative to heavier overseas crudes. While there is a substantial economic benefit in processing lighter crudes, many refineries were designed to process heavier crudes from the North Sea area. Irving wishes to improve their capacity for light crude processing in Crude Unit # 4 (CDU#4), but is currently limited by their atmospheric tower overhead condenser and compressor. The objective of this study is to determine the most economical and efficient way of unloading these key pieces of equipment, while maximizing the refinery's ability to process Bakken with minimal effects to downstream units. Based on a high level screening, the preferred solution to this problem is the installation of a pre-fractionation tower. Simulating the process in a complex HYSYS model made it possible to match existing operating conditions and determine the effects of increasing Bakken flows while keeping a constant flow rate of 160 MBPD (0.294 m3/s) to the crude unit. The results of these tests have shown that optimizing the Bakken flow rate is the most important control parameter, and the optimum case was found to be at 52% of the total crude charge. This was achieved by optimizing the tower location in the preheat train, the stripping rate, the feed tray location, the feed temperature, and the tower pressure. The optimal location for this tower follows the desalters and pre-flash drum, but comes .before the crude furnace in the preheat train. By processing only a portion of the total crude in the Pre-Fractionation tower it is possible to reduce the size requirements of any additional equipment, subsequently reducing the amount of capital investment required. Additionally, operating the pre-fractionation tower at approximately 30 psia (206.8 kPa) reduces the duty requirements in the tower and lowers the operating temperature to 450°F (232 °C). A payback period of 1.1 years was determined from the cumulative discounted cash flow, as well as an ROI of 110% and an IRR of 81%. A savings of up to $55 million per year is predicted by allowing the refinery to process more of this cost-effective crude.