Zelimir Schmidt, James P. Brill & H. Dale Beggs; The University of Tulsa
Gas and liquid are frequently transported simultaneously in the same pipe. Common occurrences include pipelines for gas and oilfields, piping in refineries and process plants, and steam injection and geothermal production systems. When two-phase flow (i.e. gas-oil-water) occurs in a pipeline, the phases separate geometrically in the pipe into various flow patterns. In general, the flow pattern that results depends upon several flow parameters, of which phase velocities and pipe inclination are the most important. When the flow pattern at the exit of a pipe consists of alternating slugs of gas and liquid (i.e. slug or intermittent flow). special operating procedures are frequently required. Processing such slugs can require first passing the gas-liquid mixture through a larger diameter conduit (i.e. slug catchers) to promote segregation or stratification of the phases. Only then can gas liquid separators be operated properly to minimize pressure fluctuations and assure an acceptable low volume fraction of liquid in the gas or gas in the liquid that leaves the separator. The cost of constructing and locating slug catchers can be extremely high, especially when dealing with large diameter pipelines terminating on offshore platforms. A method to eliminate long slugs of liquid economically is of great interest to companies operating the above types of facilities. It has been found that slug flow in a pipeline-riser pipe system can be eliminated or minimized by careful choking that results in little or no change in either flow rate or pressure level and elimination of pressure fluctuations. The careful choking can be accomplished automatically with a unique control system consisting of a combination of electronic and pneumatic devices. Such a system has been tested using kerosene and air on a 2-in. diameter pipeline-riser pipe test facility at Tulsa University). Slug-flow was eliminated automatically in every test conducted. The devices were also installed in a specially designed facility consisting of approximately 60,ft of 1-in. pipe configured with several rises and falls to simulate a hilly terrain pipeline. Slug flow was eliminated here also in every test conducted.