Oil & Gas

Silent power

Posted on 30 November 2012 by Katrin Beck, Images by Oyvind Hagen/ Statoil

Five emergency gensets safeguard the power supply to a natural gas processing plant in Norway.
Kårstø is one of the largest natural gas processing plants in the world. So that all systems can be safely shut down in the event of a power failure, it has five mergency backup gensets.

Safely into the future


The new emergency power supply system from MTU will provide energy for the most important electrical equipment in the event of a mains grid failure. The output of the backup gensets previously installed had become inadequate. So Statoil replaced the aging units with new ones. In the summer of 2011, they were commissioned by MTU engineers after successfully completing a series of test runs. “We had already formed a favorable impression of MTU from a previous project. The price/performance ratio is fair, the quality of the products is very good, and the amount of experience that they have with emergency power systems is very large,” said Asbjørn Søndenå in explanation of Statoil’s choice. “Apart from that, MTU was the only bidder that met our specific demands in respect of sound insulation.” And those specifications were wide-ranging.

Noise level below 104 decibels


The gensets had to operate extremely quietly. The health and safety regulations at Statoil require that the noise of the generators must not be louder than 104 decibels (dB(A)) at a distance of one meter. That is roughly equivalent to the volume of sound you would experience on the ground from a jet airliner flying overhead at an altitude of 300 meters. To make things more diffcult, that sound limit had to be satisfied without substantially increasing the cost of the installation. And that was a major challenge because the most obvious solution – building a soundproof enclosure around the generators – was out of the question. It would have made access to the engines for servicing more diffcult. So MTU engineers came up with an alternative solution. They reduced the air induction noise of the turbocharger by means of special supplementary silencers. In addition, a soundproofed generator housing muffes the air intake and outlet noise. The result is that the noise from the generators is only between 100.7 and 102.6 decibels at a distance of one meter.

The emergency power system


If there is a mains power failure, the system supplies all essential emergency equipment with electricity. That includes fire-extinguishing systems, emergency lighting, battery chargers for uninterruptible power supplies, and HVAC systems that maintain positive air pressure in buildings in potentially explosive atmosphere zones. But auxiliary equipment such as lubrication pumps, cooling systems for compressors, and motorized valves also has to be kept working if the grid goes down.

The generators are driven by 16-cylinder MTU Series 4000 engines. Thanks to modifications to the engines and generators, the noise pressure level close to the units never exceeds the specified limit of 104 dB.

A new generator house built by Statoil according to MTU specifications is the new home for the MTU gensets. Inside it are the five MTU Type 16V 4000 G63 generator engines. Four of them are enough to supply the energy required to run the entire facility in emergency mode after a power outage so that critical systems can be safely shut down. The fifth unit serves as a reserve system. Each of the gensets has a connected load capacity of 2,338kVA and an electrical output of 1,870kW at a frequency of 50Hz and a voltage of 69V. In total, therefore, the four gensets deliver an electrical output of just under 8 MW – enough energy to cover the power requirements of a small European town.

MTU supplied the gensets complete with baseframes and resilient mountings and all necessary system components such as switchgear, fuel tanks and ventilation systems. Five flatbed radiators with very low noise levels mounted on the roof of the generator house were also supplied by MTU. Exhaust silencers make sure that as little noise as possible escapes through the exhaust system – which guarantees that the noise levels outside the building are extremely low as well.

Ten seconds to load take-up


The fuel for the gensets is stored in two special tanks supplied by MTU. If the mains power fails, they contain enough fuel to keep four gensets running at full power for up to 17 hours. MTU also supplied the control systems that monitor the emergency power systems and electricity infeed. They issue the start-up command for the emergency backup gensets if there is a grid outage – and they react very quickly. The Norwegian operators demanded that the gensets had to be able to reach their rated output within 15 to 20 seconds. So they are up and running within ten seconds and operating at full power inside a further ten seconds – doing their job quietly and reliably so that the gas never stops flowing from the middle of nowhere in Norway.

The content of the stories reflects the status as of the respective date of publication. They are not updated. Further developments are therefore not taken into account.

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Jörg Habermaas
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