Clear Plans, Designs Necessary for Effective Three-Phase Separation
Because their performance is difficult to predict, the installation of three-phase separators can be a tricky process. In order to allay some of the difficulties in this process, an expert said operators must take a more practical and less theoretical approach to the design and construction of these separators, with an honest assessment of their separation needs.
At a presentation, “3-Phase Separation: Identifying and Addressing Issues Before They Happen,” held by the SPE Separations Technology Technical Section, Luis Caires discussed the conditions that may negatively affect the performance of three-phase separators. Caires, director of product development for liquids at Cameron’s Process Systems Technology Center, also suggested ways to mitigate these conditions during the design and operation of these separators.
Caires described the failure of a three-phase separator in straightforward terms, saying that separators fail when they do not perform the tasks with which they were assigned such as allowing liquid carry-over in the gas phase, oil-in-water carry-under, or the passage of slugs downstream. He said liquid-in-gas carry-over may damage compressors downstream and lead to liquid waste and the plugging or overload of pretreatment equipment downstream. Oil-in-water carry-under may lead to the production of oil-coated solids that are difficult to dispose of, and increase the operating costs of produced water treatment plants. Slugs passed downstream may overload separation equipment downstream.
To prevent failure, Caires said operators must be clear about their needs for the separators, design the separators according to those needs, and build the separators according to the design. It is important to operate the separator as intended and not deviate from proper maintenance practices. While in operation, Caires said operators should look for deviations in the separator’s performance from its intended operational envelope and reassess their separator needs if necessary.
Operators generally determine their separation needs through virtual simulations or through the completion of inquiry forms in which they list the minimum, normal, and maximum separation volume scenarios. Caires said this process is not ideal, since it requires companies to make rigid predictions with limited information. He suggested that in determining need, companies engage in a holistic dialogue about what their projects will entail.
“You can have all of the minimum temperatures, viscosities, or whatever on one side (of an inquiry form), the maximum flow rates, and whatever on the other side, but we need to talk about the scenarios you intend to handle, considering your cycle life, to get a better understanding of the overall separation,” he said.
An ideal separator has perfect inlet momentum control and enables instantaneous gas disengagement regardless of the inlet flow regime. However, if the gas is not released instantly, foaming may occur in viscous fluids along with gas carry-under. Caires said the inlet flow regime is critical to guarding against this, since it defines the initial severity of the interdispersion of the phases that will be separated.
“The inlet flow regime matters,” he said. “If you have a dispersed flow, a stratified flow, or a slugging flow, that matters. That affects the way the fluids are entering your separator and defines the initial level of dispersion inside your separator.”
Caires said the main issue in designing separators according to an operator’s need is figuring the optimal utilization of the available separator volume, and that predicting absolute basic sediment and water quality out from the separator can be a challenge. With that in mind, he said it is important to allocate sufficient space for each phase and their interfaces, which may be larger than an ideal size. The design should also incorporate the correct set of internals to address any foreseeable issues.
This webinar is available here.
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