The requirements for power are so high that many platforms use legacy aero-derivative gas turbines
Offshore oil and gas platforms pose an interesting conundrum; they need immense amounts of power while having no direct access to a power source. Electricity is required for the platform itself as well as for pump and capacity of the operations
The requirements for power are so high that many platforms, run by the likes of BP, Shell, Exxon Mobil and Chevron, use legacy aero-derivative gas turbines. These are engines that were original designed for aeroplanes by companies such as Rolls-Royce.
These turbines are bolted into the floor of a platform and turned into a generator for electricity and/or used as a compressor to push gas and oil down pipelines and onto the mainland.
Many of these platforms were built in the 1970s, using engines that were designed in the 1950s. The engines are therefore aging and have begun causing problems for the operators. James Davies, head of gas turbine services at Sulzer, explains how the company is currently working with several North Sea oil and gas operators to help repair and maintain these engines: “Over the last ten years or so these turbines have begun failing or suffering from life fatigue,” he says. “At almost 50 years old some are being decommissioned, others are being maintained by companies like ours.”
He adds: “Although there is always redundancy, with several turbines on the one platform, occasionally all will go down leading to a total emergency situation. Non-essential staff need to be airlifted to safety and the operator will inevitably suffer considerable financial losses. Our business ensures this doesn’t happen. We meet the operator’s requirements in real time, helping them to prevent such a situation. We guarantee reliability and this means making a turbine work when you need it to work.”
IN THE BUSINESS OF REPAIR
Sulzer’s business involves looking at these aged assets. The turbines are typically housed ‘deep in the bowels of the platform’ and covered in pipe work and infrastructure. The engine is surrounded by pipes that feed the control systems and all the wires that manage and monitor the engine. “You would have to cut a house-sized hole in the platform to replace it,” James says. “This means taking out an old gas turbine and replacing it with a newer, cleaner burning version isn’t an option. You’re pretty much stuck with that power-generating unit for the life of the platform.” This means that Sulzer is in the business of repair.
The company begins its assessment of any particular turbine by using a borescope – a tube with a camera and a light – with which the engineering team can view all the critical components while the turbine is still on the platform and provide a rough assessment regarding which parts are worn or damaged. Following this, the team will remove the engine itself (minus the surrounding infrastructure) and take it to the Sulzer factory for a bulk and detailed strip to assess the thousands of individual components.
Sulzer then reports back to the customer on the state of the parts, whether they are repairable or replaceable, and the likely cost.
The company repairs blades and vanes and replaces seals and gaskets and anything else that requires attention, then rebuilds and function tests the turbine to make sure it’s operating as it should before sending it back offshore. Many of these turbines – such as the one based on the well-known ‘Avon’ engine built by Rolls Royce – are no longer being made. Production of that particular engine stopped in 2014. “When this happens the supply chain and associated parts begin to dry up,” James explains.
This means a big part of Sulzer’s job is to source and maintain a critical inventory of the many thousands of parts that make up these original engines, and these are gleaned from all over the world. Once found, the team perform a laboratory analysis on each part to ensure there is still life left in it. “We assess these pieces, then repair, coat, and refurbish them ready for reuse. We’re doing that on a constant basis,” James says.
Such aero-derivative engines are also used on gas pipelines. The national gas infrastructure is powered by them with an engine and a pumping station located along every 50-60 miles of gas pipes. In addition, engines are used for ‘black start’ operations in nuclear power stations – there is currently an old Concorde derivative engine in several operational stations for example.
If power generated by nuclear energy disappears, caused by a cut or a trip or something similar, the engine starts up immediately (a black start emergency generation station) helping to keep operations safe.
EFFICIENCY AND THE CIRCULAR ECONOMY
In addition, retrofit upgrades of the sort conducted by Sulzer can cut emissions significantly, since the old gas turbines can be modified and better maintained to produce fewer emissions. James elaborates: “If the parts that inject fuel are clogged, cracked or uneven, you’ll get an uneven burn, this means unburnt fuel is released and just vaporises in the atmosphere. Good maintenance of the turbine and the systems surrounding it will help to reduce fuel usage and increase efficiency.
The parts that go into these turbines often hail from various corners of the globe, potentially increasing an operator’s global carbon footprint if made from scratch. For example, a central shaft is made from alloys that would begin life in Australia as an iron ore, then shipped to Switzerland to be melted in a foundry (using huge amounts of electricity); the shaft would then be machined somewhere else. By the time it is installed into the turbine, the piece has travelled around the world a couple of times. “Using old parts is just far more energy efficient,” James concludes.
For more information visit: www.sulzer.com
