A number of organizations have been looking at ways to reduce energy use and emissions offshore. Sintef has been working on a waste heat recovery project, focusing on gas compressors, with research involving operators and equipment vendors.
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Sintef’s Marit Mazzetti. Photos from OE Staff. |
Sintef’s Marit Mazzetti says the Norwegian Continental Shelf has a total 189 gas compressors. Of those, 59 have waste heat recovery units, for processing, and only three have combined cycle units, which also produce power.
Sintef has developed a technology for gas compressors called the compact bottoming cycle, a way to produce power from surplus heat, by heating a working fluid or gas, which expands into a turbine.
By adding a bottoming cycle you can increase power from 32-42MW, Mazzetti says, increasing overall plant efficiency from 38.6-50-%, making it as efficient as onshore “and adds to the discussion about if power from shore is efficient or not.”
This technology means the number of turbines on a platform can be reduced, reducing weight. Most platforms have four turbines, Mazzetti says. We would remove one and add a bottoming cycle, producing another 10MW and reducing fuel consumption by 22% and CO2 by 62,000-ton/yr, or 22%.
A pilot plant has been created onshore, which will require some adaption to be used offshore. If installed at the start of a platform’s life, such a system could save US$17 million, she says.
As a case study, Sintef looked at a Petrobras FPSO, which already had steam onboard for processing. Adding a steam bottoming cycle meant one of the turbines on the FPSO could be removed. An up to 25% fuel saving could be made in this case, she says.
“For the industry it will be important to reduce CO2 emissions in the future. Drilling was stopped in Alaska in 2012 because of high CO2 emissions and regulations are coming in. The shipping industry is implementing rules and restrictions on CO2 emissions on ships. It has come for shipping, it is reasonable to assume it will come to offshore,” she says.
Bottoming cycle deployment would be best suited to a platform designed for four turbines, with one to be replaced, and on greenfield projects, Mazzetti says.
Another company, California-based Energy Recovery, is looking to recover wasted energy from processes involving pressure. Some 15,000 of its systems are in use worldwide, largely in the water processing industry, but also by the navy, cruise liners, and on barges.
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Brage Johansen, CEO, Zaptec. |
The concept, applied to an amine-based gas sweetening process, would involve recovering energy from the letdown valves, allowing the used amine to escape. The recovered energy can then be used to repressurize the amine, once cleaned, get it back into the treatment cylinders. This means high pressure booster pumps can be much smaller. If repressurization is not required, the pressure from the letdown valve can be used to generate electricity.
Meanwhile, Norwegian firm Zaptec has spent 10 years developing miniature power electronics, originally for the oil and gas industry for downhole applications. Slow uptake in the oil and gas industry meant the firm looked to other industries and the firm now has funding from the European Space Agency to work on systems to be deployed on Mars for plasma channel drilling. Zaptec’s miniaturized units can transform 5kVWto 11kW says Zaptec’s CEO Brage Johansen, who presented the technology at ONS.
A system built to charge a Tesla electric motor car developed by Zaptec, for use in Norway, where the grid is different to other countries and means transformers are required to charge cars. Zaptec’s transformer provides 11kW, from the standard 3kW usually supplied to home garages, in a unit that is one-tenth the size and uses one-hundredth the amount of copper and iron compared to traditional transformers, Johansen says.
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