Voith Turbo designed a new subsea hydrodynamic variable-speed drive
10 May 2004
Hydrodynamic variable-speed drives:
Voith Turbo is the leading manufacturer of hydrodynamic variable-speed couplings, variable-speed transmission couplings and torque converters worldwide. They are used in power generation, in the oil and gas industry, the chemical industry, as well as for material handling. Voith hydrodynamic drives are in service under the toughest conditions around the world. These drives are installed in facilities ranging from production to transportation or processing. On offshore platforms, natural gas pipelines, crude oil and liquid pipelines, refineries, petrochemical plants and other industrial facilities, in the desert, or in arctic environments - Voith variable-speed drives are running 24 hours a day, 365 days per year.
Owing to their compact and robust design, hydrodynamic variable-speed drives allow energy and cost savings, higher flexibility, longer service life of machinery and motor, lower maintenance, and applications in toughest conditions. Their output capacities range from 100 kW to 50,000 kW and speeds of up to 20,000 rpm.
New development for subsea applications:
The number of onshore and offshore wells worldwide will soon be equal, with a tendency towards more offshore wells. Major activities are underway in the Gulf of Mexico, Brazil, the North Sea and West Africa. In the North Sea, there are numerous small oil fields spread over a large distance, which require pumping, whereas in the Mexican Gulf the pressure of the well is still high enough for transporting the oil to the platforms. In Brazil and West Africa, the pressure is not high enough in deeper water, which also requires pressure boosting, in order to achieve the growing objective of obtaining acceptable recoveries from subsea wells.
Options currently being considered are:
• Wellbore artificial lift (ESP, gas lift, etc.)
• Subsea separation & single-phase pumping
• Multiphase pumping
In order to cut down on additional platform equipment and also costs, the petroleum industry is planning to locate the pumps, i.e. multiphase or centrifugal pumps, on the sea bed, at depths between 600 m and 3000 m. Almost all recent projects require variable-speed drives for subsea pumping applications, because of the fluctuations in well pressure and flow, as well as the different contents of oil, water and gas to be pumped.
For the drive and speed control of the underwater multiphase pumps, Voith designed a new subsea variable-speed drive, which is located between a fixed-speed motor and the pump. The drive is designed to transmit up to 10 MW and is based on the hydrodynamic torque converter principle. The new drive concept offers significant capital cost savings and increased reliability compared to conventional variable-frequency drive systems.
Further advantages are:
• Very high reliability and availability
• Low space requirements
• Low maintenance cost
• Easy to install
• Simple cable connection
• Unloaded start of motor
• Shock and vibration damping
• No overload of drive motor during operation
• No harmonics
Today, two pump principles are on the market, which Voith is targeting for its new variable-speed drive: twin screw pumps and rotodynamic pumps.
