Sizing Gas/Liquid Horizontal Separators Handling Nonstable Multiphase Streams
- Chris Carpenter (JPT Technology Editor)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- December 2014
- Document Type
- Journal Paper
- 107 - 109
- 2014. Society of Petroleum Engineers
- 4 in the last 30 days
- 317 since 2007
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This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 169444, "A Method To Size Gas/Liquid Horizontal Separators Handling Nonstable Multiphase Streams," by J.L. Hernandez-Martinez, Pemex, and V. Martinez-Ortiz, Schlumberger, prepared for the 2014 SPE Latin American and Caribbean Petroleum Engineering Conference, Maracaibo, Venezuela, 21-23 May. The paper has not been peer reviewed.
The sizing procedures for all of the process equipment in the oil and gas industry share a common assumption: The stream flow rate measured at the inlet is always constant or stable. This principle works fine for plants where the process conditions are controlled, but it does not apply to primary production facilities where the streams come from multiphase flowlines or wells. The sizing procedure described in the paper allows one to size horizontal gas/liquid separators considering nonstable flow rate at the inlet or fluctuations in the liquid fraction on the same stream.
From a design standpoint, separators are split into three stages (or sections).
Primary Stage. This is a mechanical operation; it uses an inlet diverter so that the momentum of the liquid in the gas causes the largest droplets to impinge on the diverter, forming droplets that are separated by gravity. The gas stream flows to the disengagement section.
Secondary Stage. Liquid drops immersed in the gas stream are separated by gravity. This separation is governed by the settling liquid-drop velocity inside the gas phase. This velocity must be higher than gas-stream velocity to allow the drop to settle to the liquid phase.
Tertiary Stage. This occurs on the mist eliminator. This is a device that allows small-sized droplets to coalesce to larger drops, which fall down by gravity to the liquid phase.
These design stages or sections are shown in Fig. 1. The primary stage is designed on the basis of a simple volumetric balance, following some well-known rules. The most important parameter to consider in designing the secondary stage is the settling drop velocity inside the gas stream. This velocity can be calculated by performing a balance around each liquid droplet. This balance takes into account two factors, gravity and the drag forces applied by the gas stream. Liquid droplets settle at a constant velocity known as terminal velocity (for its calculation, as well as a discussion of the theoretical model used, please see the complete paper).
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