A highly efficient pump drive for the first underwater compressor system worldwide

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We are surrounded by gas. From water bottles to the insulation in our homes, natural gas is a key ingredient in virtually every product we use on a daily basis. According to the latest report issued by the International Gas Union (IGU) in 2019, the global demand in gas has been rising by 35 percent of the past decade alone. The reasons for this trend are manifold, but the IGU determines three main factors. First, the cost competitiveness of gas in contrast to other energy sources. Secondly, greater security of supply with regard to infrastructure, delivery, and flexible use. Thirdly, gas represents a sustainable form of energy that can mitigate climate change and lower localized pollution. It has 50 percent less CO2 emissions compared to coal, for example.

11 billion cubic meters of gas

In order to meet this growing demand and use the eco-friendly potential, gas will have to be extracted using a sustainable process. One of the largest systems is the Åsgard oil and gas field on the Haltenbanken, 200 kilometers off the coast of Norway. It contains 52 wells combined in 16 gas fields and connected by 300 kilometers of oil pipelines. As of December 2018, the field has estimated resources of 9.9 million standard cubic meters of oil equivalent of oil and 51.1 million standard cubic meters of oil equivalent of gas.

The system used comprises three essential areas: Åsgard A, B, and C. Åsgard A is a floating oil production vessel that has been anchored there permanently since extraction began in 1999. Åsgard B is a floating, semi-submersible gas and condensate processing platform for processing and stabilizing of gas and condensate. This platform is supplemented by the condensate storage facility Åsgard C and the 707 kilometer-long Åsgard gas pipeline to the Karsto processing complex to the north of Stavanger, Norway.

The first of its kind worldwide

Due to a failure in a part of the system – which was not supplied by Andritz – the motor was sent in for repairs in 2017. An extensive study was conducted in the course of these repairs. The results also led to the design of a new plate cross-section for the rotor plates. In view of this situation, the motor to be repaired was also completely overhauled and fitted with a new winding and a new rotor.

Aker Solutions ASA has been supporting the Åsgard gas field with various gas field products, systems, and services since 2010. In the course of time, the pressure in the storage facility in gas-producing fields drops. Compressors are needed to sustain the output. Aker delivered the first-ever underwater compressor system worldwide to Åsgard in order to increase the output to 306 million barrels. These are normally installed on platforms above sea level. However, Åsgard is based on an underwater system. By using compressors on the sea bed, the recovery rates are improved and the investment and operating costs are reduced. In addition, underwater compression leaves a smaller ecological footprint and is more reliable than a platform. The Åsgard system consists of modules for two identical sets of compressors, pumps, scrubbers, and coolers. The motors needed to drive the pumps come from Andritz.

A small, but essential component

International technology group Andritz has occupied the top spot in the development and manufacturing of custom-tailored pump solutions for over 165 years. In 2010, Ritz Pumpenfabrik GmbH in Schwäbisch-Gmünd, Germany, became Andritz Ritz GmbH and a part of the Andritz Group, as did the production of submersible motors.

Due to the renewable winding, Andritz submersible motors are ideal for driving deep well pumps, bottom intake pumps, suction pumps, seawater pumps, and underwater machinery. These are water-filled and water-cooled, three-phase asynchronous motors with squirrel cages and a mechanical seal.

Due to the renewable winding, Andritz submersible motors are ideal for driving deep well pumps, bottom intake pumps, suction pumps, seawater pumps, and underwater machinery. Depending on the area of application, they can be made of cast iron, bronze, or different kind of stainless steel and installed either vertically or horizontally. These are water-filled and water-cooled, three-phase asynchronous motors with squirrel cages and a mechanical seal. They are fitted with special cooling technology – MCT. In designs with interior permanent magnet motor technology, or IPM for short, these maintenance-free motors achieve impressive outputs, efficiencies and, as a result, cost savings.

The effective and measurable motor cooling system keeps the interior temperature as low as possible. Drinking water is used as a cooling liquid, which is why the motors can operate in media of up to 75 degrees Celsius. An impeller with optimized suction and delivery is mounted at the lower shaft end of the rotor. One of its two main tasks is cooling and lubricating the nearby thrust bearing. By doing so, the impeller ensures there is a constant flow of cooling liquid in the right direction. This liquid moves through the inside of the motor from the bottom to the top. The specially developed cooling channels define the exact path over all heat sources to discharge the heat effectively and systematically. At the top end of the motor, the heat from the liquid is then discharged through the outer wall of the motor. Here, it is transferred through the surface of the motor to the medium to be pumped.

The Andritz submersible motors are just a tiny part of the underwater compressor system, but they are also an extremely important part. The entire underwater station cannot operate without these motors to drive the pumps. Since first being installed in 2016, these submersible motors have been operating without any faults. All in all, Andritz Ritz delivered three two-pole submersible motors with an output of 736 kilowatts. The motor forms the condensate unit together with the pump and conveys those liquids that are removed by the separator upstream of the gas compressors.

Due to a failure in a part of the system – which was not supplied by Andritz – the motor was sent in for repairs in 2017. An extensive study was conducted in the course of these repairs. Thermal distribution in the cooling flow and also the hot spots were analyzed in more detail. The results also led to the design of a new plate cross-section for the rotor plates. In view of this situation, the motor to be repaired was also completely overhauled and fitted with a new winding and a new rotor. This study and the implementation of its findings not only benefit the current customer and future customers in this case, but also strengthen confidence in the Andritz submersible motor technology.

Andritz Group

International technology group Andritz offers a broad portfolio of innovative plants, equipment, systems and services for the pulp and paper industry, the hydropower sector, the metals processing and forming industry, pumps, solid/liquid separation in the municipal and industrial sectors, as well as animal feed and biomass pelleting. The global product and service portfolio is rounded off with plants for power generation, recycling, the production of nonwovens and panelboard, as well as automation and digital solutions offered under the brand name of Metris. The publicly listed group today has around 28,400 employees and more than 280 locations in over 40 countries.

www.andritz.com/pumps

pumps@andritz.com

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