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

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).

Kinetics of Gas Evolution from Supersaturated Oils at Elevated Pressures and Temperatures

“…A proper design of a gas−liquid separator is of great importance because the costs associated with repairing downstream equipment along with the production downtime in the event of a poorly functioning separator can often far exceed the cost of the initial separator. 4 The design of gas−liquid separators can be improved by understanding the gas evolution rates from liquids. This understanding also helps in modeling the gas evolution process.…”

A Predictive Methodology to Determine the Rate of Gas Evolution in Hydrocarbon Systems at Elevated Pressures

“…The initial pressure was 3.45 MPa, a temperature of 298.15 K, and at various shear rates (100−500 rpm). (6) where ε is the energy dissipation (m 2 /s 3 ), N p is the power number, ω is the impeller's revolution per second (rps), d i is the impeller diameter (m), and V is the volume of the liquid (m 3 ). The power number was determined using the correlation for a flat six-blade Rushton turbine in an unbaffled vessel 35 using the geometry of the impeller, the geometry of the vessel, liquid level, and physical properties of the liquid (density and viscosity).…”

“…The costs associated with repairing downstream equipment in the event of a poorperforming separator can often far exceed the initial cost of the separator. 6 The American Petroleum Institute's design criterion for gas−liquid separators, known as API 12J, recommends different liquid retention times based on the oil's specific gravity to achieve the separation of dissolved gases. 7 The rate of mass transfer of solution gas from the liquid phase into the gas phase is assumed to be instantaneous in most cases.…”

Revisión del proceso de separación de fases del gas natural a alta presión en la industria Oil&Gas

“…y Bymaster et al (2011), desarrollaron nuevos estudios junto con la empresa FMC Technologies acerca del desempeño de separadores gravitacionales y centrífugos de gas natural a presiones que van desde 1500 psig (10.3 MPa) hasta 2600 psig (18 MPa), encontrando principalmente perfiles de eficiencia de separación en función de la cantidad del líquido a la entrada para diferentes configuraciones y condiciones de operación. De acuerdo con los resultados experimentales, se observa que existe una preocupación por los riesgos asociados a la separación de fases a alta presión, tanto en equipos gravitacionales como centrífugos; entre los riesgos se destacan las pequeñas distribuciones de tamaño de gota, el aumento del porcentaje de arrastre y/o inestabilidad de la película de líquido y el hecho de que una disminución en la diferencia de densidades de las fases hace que la separación se dificulte.…”