(131c) Optimized Reflux Application in the Technology Selection of a LPG Production Facility

LPG (Liquefied Petroleum Gas) recovery processes separate the light and heavy hydrocarbon components through the use of cooling and distillation towers. Many high-recovery processes feature the use of a reflux stream which cools the distillation overhead gas, resulting in capturing a higher quantity of heavy hydrocarbon components from the natural gas. By targeting specific component levels of ethane and propane in the sales gas, the reflux stream(s) can be used to define the upper limit of an LPG product recovery scheme through maximizing the integration of the plant's energy exchange. However, depending on recovery range targets, a reflux system may have an undesired effect of recycling too much light components, resulting in increased compressor duties and over-sizing of the column and reboiler.

Since there are multiple configurations or process schemes featuring different equipment, arrangements, and flow sequences which can all arrive at the same objective of recovering the LPG components, evaluating one scheme with another requires a systematic study into its operating and capital cost, defining the production revenue of each process scheme, as well as analyzing less quantitative aspects such as its reliability, complexity, and impact to other units.

This Case study presents the methodology and review of selected ?open art? process schemes for a LPG recovery plant project based on the analytical review of the reflux vs. non-reflux recovery processes. Among the key challenges in the design were to define a suitable target recovery level and to select the optimum processes that would be economically attractive during the 2009 tough investment climate. The process schemes selection focused on LPG recovery levels between 45% and 80%, determined based on economic cases. These boundaries were later expanded to explore the economics of lower recoveries which would avoid modifications to the gas plant's existing dehydration system and maintaining sales gas product targets. The economics of higher recoveries achieved through the use of licensed high-efficiency designs were also analyzed. Finally the selected designs must be flexible enough to allow swings in the extent of LPG production based on target market demands without causing disruption to the existing gas plant. In this aspect, the review of reflux streams' function to maximize product recovery of the selected process schemes became one of the determining factors in the final gas plant design.