18-Virtual-Long Multiphase Flyer

Solids are frequently present in multiphase flow lines. These solids may passively flow along and cause few problems, or they may cause significant problems including erosion and flow blockage. These solids range in character from tough to quite fragile, and include sand, hydrates, paraffins, asphaltenes, and welding slag.

In the study of multiphase transport of fragile solids, topics of interest include solids particle nucleation, agglomeration, deposition, formation inhibition, transport, and blockage formation and remediation. In such studies, it is important to use a facility that simulates field flow lines, and that does not degrade the solids artificially. To avoid artificial degradation (such as the shearing and crushing caused by a pump), the usual proposed solution is a long test loop. The required length of the test loop is a function of the range of conditions and the topics of interest. Typically, before the study is successfully completed, the required length is not known. Of course, a test loop of very great length (many miles) may be built to reduce the risk of building too short a loop; however, generally, such a loop is very expensive.

In order to study multiphase transport of fragile solids at an acceptable cost, a new test loop concept -- a virtual-long multiphase loop -- has been developed. A virtual-long multiphase loop does not force the liquids and solids through a pump and, thus, is able to simulate a longer flow line by repeatedly recirculating fluids and solids around the loop without shearing, crushing, or otherwise degrading the solids. A virtual-long multiphase loop also allows the gas and liquid rates to be varied independently. While a loop of this type cannot address all of the phenomena of a long flow line, such a loop allows study of many key solids transport phenomena.

A rendering and a photograph of a virtual-long multiphase loop are shown in the attached figure. In the rendering, the right portion of the loop (shown with an enclosure for active temperature control) is the "test section" in which specific fluids and solids flow rates are provided. The energy to continuously flow through the test section is provided by a gas compressor. With each pass around the loop, most of the gas is separated from the multiphase stream in the minimal separator in the upper left corner of the rendering. The separated gas is compressed and cooled. The rest of the test multiphase stream (solids, liquids, and gas) quickly passes through the separator, a downcomer, and a riser. In the riser, the compressed gas is commingled with the rest of the multiphase stream. This produces a higher pressure at the top of the riser than at the top of the downcomer, and provides the drive to transport the solids and fluids through the test section and around the loop.

A 3-inch diameter proof-of-concept loop, rated for 1,440 psig, has been constructed. The configuration of the test section may be modified to accommodate studies of various phenomena. In the current configuration, the actively chilled test section consists of the following segments:

In this configuration, the test loop is capable of producing all multiphase flow patterns normally found in oil/gas pipelines. The loop is instrumented with pressure and temperature sensors, distributed throughout the loop, which are connected to a data acquisition system. The loop is also instrumented with a means of detecting the onset of hydrate formation and detecting and measuring hydrate deposition on the test section wall. The loop -- shown in the photograph on the right -- is currently being used to study phenomena under steady-state flow conditions, as well as start-up and shutdown environments. Of particular interest are solid particle nucleation, agglomeration, deposition, inhibition, transport, and blockage formation and remediation.

hydrat.jpg (23613 bytes)

The pictured loop is for the study of solids transport phenomena in multiphase flow. Due to the fragile nature of these solids, such studies are conducted ideally in multi-mile flow lines. In this loop, gas compression is used to provide the multiphase transport energy. The solids and liquids continuously flow around the loop without degradation, allowing simulation of a long loop from a solids and liquids perspective. Initially, this loop is being used for the study of hydrate formation, agglomeration, deposition, inhibition, and transport in multiphase flow lines. (Patent issued).

This flyer was published in April 1989. For more information about the SwRI Virtual-Long Multiphase Loop, contact Flavia Viana, Phone (210) 522-6712, or J. Chris Buckingham, Phone (210) 522-3307, Fax (210) 681-9661, Mechanical Engineering Division, Southwest Research Institute, P.O. Drawer 28510, San Antonio, Texas 78228-0510.