Bi-phase RST enters extended field test

Oct. 1, 2002
A bi-phase separator, expected to drop to 33% the original weight and footprint of typical oil-gas-water separators on platforms, is being installed for further testing at Shell's Mars TLP at Mississippi Canyon block 807 in 2,940 ft of water.

Jennifer Pallanich Hull
Gulf of Mexico Editor

A bi-phase separator, expected to drop to 33% the original weight and footprint of typical oil-gas-water separators on platforms, is being installed for further testing at Shell's Mars TLP at Miss-issippi Canyon block 807 in 2,940 ft of water. The manufacturer, Multiphase Power and Processing Technologies, views the Mars installation as a major step and sees its bi-phase rotary separator turbines (RSTs) as being added to existing Gulf of Mexico platforms as retrofits.

"We recognize that we're introducing something that has tremendous potential," said Eric H. Namtvedt, president of Multiphase Power and Processing Technologies LLC, a Dresser-Rand/Aker Kværner joint operating company.

Multiphase's two-phase gas/liquid rotary separator turbine.
Click here to enlarge image

Yet, potential clients may weigh the savings in weight and footprint versus the risk of using new technology, he said.

For the Shell Mars TLP, the capacity will remain the same, but with the unit at around one-third the footprint of the original unit, and weighing less than 22 tons. This particular bi-phase RST is 7 ft x 11 ft x 8 ft. Capacity will be 32,000 b/d and 64 MMcf/d, rated ANSI 900 for high-pressure wellstreams up to 2,200 psi.

Shell E&P Co. is the asset operator that will install the unit on the Mars TLP in October. The externally-powered bi-phase RST will undergo a six-month program to expose the unit to varying well conditions.

The installation on Mars takes the multiphase technology forward a major step, he said.

"It's an absolute necessity on the road to qualifying the technology," Namtvedt said of the endurance test slated for the Mars TLP.

The Mars test is the second offshore application for Multiphase Technologies' bi-phase technology.

A self-powered unit was tested on Shell's Ram-Powell TLP in 3,214 ft water depth from May 2000 to February 2001. The 20 ft x 8 ft x 10 ft, 21-ton unit placed on the Viosca Knoll block 956 TLP has a capacity of 20,000 b/d and 30 MMcf/d and was rated to 600 ANSI. It was tested for separation, mechanical reliability, slug handling, and chemical reduction.

The Ram-Powell was host to the first self-contained, monitored, and controlled RST skid offshore, Multi-phase Technologies said.

The smaller size and weight of the bi-phase RSTs decreases demands associated with deployment, support, and intervention, the company said. The unit is designed to be motion insensitive with zero emissions while reducing chemical consumption, according to the company. Multiphase Technologies' bi-phase RST unit can be used for oil- and gas-dominated systems, and the company also has a tri-phase RST that is geared for use in oil-dominated systems. The inline rotary scrubber is aimed at gas-dominated systems. The company targets one- or two-step processing leaving less than 29 ppm oil in water, 0.5% oil-in-water, and 99.99% gas separation.

Multiphase Technologies manufactured and delivered two full-scale bi-phase units, as well as the pilot tri-phase RST unit currently undergoing tests at Marathon's Ewing Bank block 873 platform in the GoM.

Inside the unit

The RST contains Laval nozzles, designed to produce a uniform jet of gas and liquid with minimal slip between the liquid and gas phases. The jets impact the rotating drum, forming a chamber to allow the gas to form a vortex and spin the liquid out of the gas stream. This provides two-phase separation of the inlet stream. The liquid that collects on the drum surface drives the drum around the shaft axis. The gas stream also drives the drum through a set of impulse blades (in the case of bi-phase well stream power recovery), and the resulting energy, or shaft power, can drive additional equipment.

The liquid collected on the drum creates a cushion protecting it from erosion by solids that could enter the system with the wellstream fluids. The liquid flows to the middle of the drum surface and through slots in the hub to collect on the backside of the rotor hub. A reaction jet nozzle removes the liquid from the surface and converts the kinetic energy in the liquid to potential energy.

Once the fluid passes through the turbine, the separated gas and liquid streams depart the casing via distinct outlet nozzles.

Creating the technology

Dresser-Rand and Aker Kværner formed the now Houston-based joint operating company in October 1998 to develop a complete first- and second-stage separation, Namtvedt said. The goal was to take previously proven bi-phase technology and develop it to the next-generation separation for oil and gas.

"The bi-phase unit is an important building block in achieving that goal," he said.

The company has come up with several configurations of the gas/liquid separation that are now in the final stages of product commercialization, he said.

The ultimate goal, he said, is to have RST for complete topside processing capabilities.

Shell – together with BP, ChevronTexaco, and Marathon – in a joint industry project with Multiphase Technologies have cooperated in the development and testing of the RSTs since 1998, Namtvedt said, and the most recent tests and installation at the Shell Mars TLP are the fruition of longstanding goal for multiphase rotary separation turbines.

"This is the ultimate test for the technology to get the installation," he said.