Hydrate Formation in Chevron Mabee Unit for NGL Recovery and CO_2 Purification for EOR

摘要

In the early 1990’s, Chevron installed a new process to recover natural gas liquids (NGLs) from recycledrnCO_2 in their Rangely Weber Sand Unit. The facility was designed based on a patent issued in June ofrn1988 (U.S. Patent # 4,753,666). The process, as claimed in the patent, used a refluxed distillation towerrnto produce an overhead stream virtually free of n-butane and heavier components and a bottomsrnstream containing the majority of the heavier components. Based on the success of the Rangley plant’srnoperation, a similar facility was designed and fabricated by Dickson Process Systems and installed inrnChevron’s Mabee field near Midland, Texas.rnWhen the Mabee plant faced some unique challenges in the NGL Recovery unit, Chevron contactedrnDickson Process Systems, Bryan Research & Engineering (BR&E), and Sulzer Chemtech USA to helprntroubleshoot the process to operate as designed. The Mabee NGL Recovery unit is a distillation columnrnwith a partial condenser and a reboiler. The condenser, operating between 4-15 oF, experienced whatrnwere described as “reflux events”, where liquid level would rapidly buildup in the reflux accumulator.rnWhile troubleshooting, it was found that hydrates formed in the top section of the column, restrictingrnthe liquid from continuing down to the next tray. The resulting buildup of liquid not only preventedrnreflux from entering the column, but also flooded the trays and quickly overwhelmed the top section ofrnthe column. This paper describes the process used to identify and address the formation of hydrates inrnthe top section of the distillation column and the use of process simulation modelling combined withrnplant data to improve plant operability.