ABSTRACT

As larger quantities of natural gas became more and more available off-shore on the various continental shelves of the world and with proven on-shore gas reserves steadily declining, more and more natural gas transmission companies ventured off-shore to obtain these supplies for their market areas. In what was largely a "sellers" market for the producers, gas purchase contracts became, in effect, transportation agreements whereby the liquifiable hydrocarbons were transported ashore in two-phase flow pipelines requiring large off-shore or near-an-shore compressor stations to meet system through-put requirements. The handling of slugged liquid hydrocarbons in two-phase flow pipelines at high volumetric rates presents problems at large compressor stations not normally associated with small field compressors in on-shore two-phase flow gathering systems where the magnitude of quantities and associated parameters allow for conventional liquid handling facilities to be used. These problems are exacerbated when the installation is sited off-shore where the limitations of platform space, structural support, accessibility, mobility, OCS regulations and all attendant costs thereto must be considered. These considerations have required a rethinking not only of the methodology of handling of the liquids off-shore, but the feasibility of even situating large compressors off-shore on platform. The paper reviews the current art-state for handling large volumes of slugged liquid hydrocarbons and describes a new and innovative concept of on-stream handling of slugged liquid hydrocarbons which may occur at the inlets to large compressor stations or process plants operating in two-phase flow systems. Operating criteria and design considerations for such a concept are also discussed. A prototype land-based installation is described which incorporates features of this concept for liquid handling which, though developed for possible utilization off-shore, has exhibited certain advantages for on-shore application.

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