High Pressure Gas-Liquid Separation: An Experimental Study on Separator Performance of Natural Gas Streams at Elevated Pressures

Abstract

Abstract In an effort to understand separation phenomena, improve separation technologies, and mitigate the uncertainty and risk associated with separator design and operation at elevated pressures, high-pressure separation tests have been conducted at 1,500 psig and 2,600 psig over a wide range of gas flow rates and inlet liquid concentrations. The tests were performed at the Southwest Research Institute® Multiphase Flow Facility using hydrocarbons ? natural gas and a liquid hydrocarbon model fluid (ExxsolTM D110, with components C12-C17). The experimental test section used during this study was equipped with compact, high-capacity separation technologies that accomplish high liquid removal efficiencies while minimizing footprint. The unit consisted of a CDS Separation Systems inline cyclonic separator for bulk liquid-phase removal and a downstream vertical separator equipped with compact internals (i.e., a vane-type inlet device, drainable mesh pad coalescer, and demisting cyclones). The design of the test skid provided significant flexibility to evaluate the performance of the separation devices alone or in combination. In this paper, the high-pressure separation testing approach, performance trends, and impact of the results are presented and discussed. Introduction Efficient gas-liquid separation is essential to the reliability and successful operation of many processes within the oil, gas, and chemicals industries. Poorly designed or inefficient separators can lead to numerous process-related issues. In gas processing, separators are used upstream of rotating equipment (e.g., expanders, compressors, turbines), contactors (e.g., glycol and amine), mol-sieve dehydrators, fuel systems and the like, and are therefore critical to preventing mechanical damage, foaming, fouling, or hydrate formation in downstream equipment. In addition, separators are important to meeting product requirements (e.g., hydrocarbon dew point) or satisfying air emissions and other environmental regulations. The importance of a properly designed separator is quickly realized as costs associated with the repair or replacement of equipment and/or gas treating solvents often far exceed the initial cost of the separator. Gas-liquid separators are designed to handle a mixed-phase inlet stream and use the density difference between the phases to drive phase separation (e.g., remove entrained liquid droplets from a gas-continuous stream). Gravity-based separators often employ more conventional demisting devices (i.e., wire mesh pads or vane packs), and therefore rely on gravity and impingement as the primary separation mechanisms. Unfortunately, conventional gravity separators, and the aforementioned internals employed within, are not always feasible. This is most evident when de-bottlenecking existing facilities (to increase throughput and/or prolong the life of the field) and in the development of resources in challenging environments (e.g., deepwater, arctic regions, or other remote fields) where vessel diameter, wall thickness, weight, or available footprint may be restricted. In such cases, more compact separator internals that use centrifugal forces to drive phase separation can be employed, such as inlet cyclones (bulk phase separation) and demisting cyclones (fine droplet removal). More recently, the demand for compact, efficient gas-liquid separation in such services has launched the development of inline cyclonic devices that employ the same separation mechanism (i.e., centrifugal forces) to achieve bulk phase separation [Fantoft et al., 2010]. Inline cyclonic separators can potentially replace larger, more conventional separators or be paired upstream of a separator to de-bottleneck existing facilities or reduce the footprint in grass-root designs (by reducing the diameter and overall height of the downstream vessel).