New Choke-Valve Design Improves Separator Efficiency

Abstract

Technology Update The efficiency of the gas/liquid separation process can have a significant impact on the economics of planned and potential oil and gas developments, as well as on the profitability of existing production operations. A new type of choke valve that improves the efficiency of downstream gas/liquid separators by enhancing the coalescence of dispersed liquids in a fluid stream has been developed recently by Twister. The initial field test of the technology, known as the SWIRL valve, was performed at a JT-LTS production unit operated by NAM in the Netherlands. The test demonstrated that the replacement of a conventional JT valve with the coalescing choke valve resulted in a significant improvement in the dewpointing performance of the gas-processing facility. This retrofit also allowed the maximum plant operating flow rate to be increased from 650 000 to 735 000 m3/d, while still meeting export gas specifications. It was additionally found that by using the coalescing valve, the temperature in the cold separator (SMSM type) could be increased by 4–5°C while still meeting specification, allowing a reduction of approximately 3 bars in the plant feed pressure. Furthermore, it was demonstrated during the field test that the glycol losses normally experienced were significantly reduced. This article presents the initial field-test results and an overview of the subsequent development and deployment of the coalescing-valve technology. Technology Description Pressure throttling in a conventional choke valve is achieved by dissipation of the kinetic energy present in the gas flow through randomly distributed eddies. The new coalescing valve, which was developed with the aid of proprietary computational fluid-dynamics models, uses the excess free pressure in a fluid stream to establish a coherent vortex motion. The total pressure inside the vortex core is gradually reduced along the axis of the flow path. By reducing the total pressure in a vortex flow, the flow shear rates are lower, compared with conventional chokes, thereby avoiding excessive breakup of liquid drops. However, and more importantly, these micron-size droplets are concentrated around the perimeter of the flow path, thus enhancing the coalescence to larger, more easily separable droplets.