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It's a gas

2/28/2019 | Words: Lucie Maluck | Pictures: MTU

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Gas is booming worldwide. More and more countries have access to gas and are using it to generate green power efficiently. The trend is towards smaller, distributed, digitally interlinked gas-fired plants that generate power locally where it is needed – as an alternative to large conventional power plants. In addition, natural gas power plants can compensate for grid fluctuations and thus make a significant contribution to grid stabilization. Gas-fired CHP plants also play a key role in what are now known as microgrids. In order to have the right system solution for every customer application, MTU is constantly expanding its gas engine portfolio. 

Until a few years ago, gas was a straightforward business, with huge pipelines necessary for transport. Then, a wildcard came into play. Liquefied natural gas, or LNG for short, can also be transported by sea over great distances to where it is needed, and fed into local pipelines. New LNG terminals are being built across the world to store gas awaiting onward distribution. Added to this is the fact that more and more countries are gaining access to gas because they are developing their own gas fields. Mozambique, Bangladesh, Myanmar and Israel are just some of these. 

MTU expands its gas engine line-up
“We want to offer suitable solutions to all our customers,” explained Andreas Görtz, the man responsible for MTU's distributed powergen systems business. MTU Onsite Energy gas gensets with an output range of 30 to 400 kilowatts of electricity for emergency power applications are being built in Mankato, USA. In Germany, high-speed gas systems for continuous use in the 200 to 2,500 kilowatt range are produced at the company's Augsburg facility. And in Bergen, Norway, Rolls-Royce gas gensets with outputs of 1.4 to 11.6 megawatts are built based on the company's medium-speed engines. But now, the portfolio is really set to grow. “Over the next few years we're looking to expand our power range offering and develop new system solutions,” said Görtz. “We will then be able to offer customers end-to-end gas systems delivering anywhere between 30 kilowatts to 11.6 mega-watts,” he added, with an eye to the future. 

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Gas engines from Rolls-Royce Power Systems – both large and small – are available under the MTU Onsite Energy and Rolls-Royce brands: the small ones are emergency gensets from Mankato in the US with outputs of 30 to 400 kilowatts, the large ones are Rolls-Royce gas gensets with outputs of up to 12 megawatts. Located inbetween are MTU Onsite Energy gas gensets with outputs of 200 to 2,500 kilowatts electric.

One world: one gas system
One engine that is already expanding this portfolio is a new model in the company's line-up of proven Series 4000 gas engines: the L64FNER. F stands for 'fifty hertz', N for 'natural gas', and ER for 'epsilon reduced', i.e. a lower compression ratio. The engine can be used anywhere – at extremes of temperature and air humidity as well as at high altitudes.

With conventional engines, high humidity means moist air is drawn into the combustion chamber, potentially leading to corrosion. To prevent this, MTU engineers have raised the temperature of the cooling water in the mixture cooler so that the fuel-air mixture is warmer and therefore does not condense. In order to be able to test the engine in real-life conditions, MTU has built a test stand at its Augsburg facility to simulate tropical conditions. Engineers can, say, raise the humidity of the intake air in order to be able to adjust the engine to cope with all possible borderline conditions. The first engine models are presently about to go into full production, with development staff now working to get the others ready. 

120-second start-ups: load-balancing power courtesy of gas systems
In parallel, MTU developers are also working on another variant of the Series 4000 gas engine: an engine with faster start-up capabilities. This one can reach its full output of 130 kilowatts per cylinder within 120 seconds, whereas previous MTU gas engines took much longer to get there. This quick-start capability opens up a wider range of applications for the gas engine. Increasing use of renewables – such as solar and wind – in power generation may make it greener, but there are also major fluctuations in the power grids that have to be compensated for. For example: When everyone turns on their lights at 7am and switches on the coffee machine, or when big industrial users get going, suddenly a lot of electricity is needed all at once. The trouble is, at this time of the morning there is often little wind blowing, and not much in the way of sunshine, so renewables are not reliable or stable enough to cover all the demand. This is where gas systems come in. They can be relied upon to be available and supply electricity safely and predictably until sufficient wind or solar power comes on stream. Many European countries have special programs for this 'balancing power' used in grid stabilization, setting out how quickly gas-fired power plants must be able to bring their balancing power online. 

Hitherto, this was a job mainly undertaken by diesel engines, but that is currently changing. “Gas is cheaper and more CO2-neutral than diesel, which is why more and more customers are opting for it,” explained Andreas Görtz. Moreover, in most cases, the governments' national balancing power programs stipulate that balancing power must be generated using distributed gas engines and associated systems. 

Fast start-up of gas engines is also in demand for microgrids. Microgrids team gas engines with renewable energy sources such as wind and solar power plants, adding battery storage systems and an overarching control system. The controller uses parameters specified by the consumer to calculate which power sources are used at which time in order to deliver power either to consumers or to a battery bank such as the MTU 'battery container'.

The dynamics and the resultant dearth of new applications for gas engines initially presented developers with a challenge, since engines had previously been designed for prolonged periods of operation, with start-up time not terribly critical. A new piece of software now ensures, among other things, that the turbocharger can provide the engine with the required fuel-air mixture much more quickly. A special priming pump also supplies the engine with oil at all relevant bearing points within a very short period of time. Together with further improvements in the start-up procedure, the developers have achieved their goal: The engine reaches full power within anywhere up to 120 seconds.

Gas engines for emergency power generation
However, Michael Koliwer, chief engineer for MTU's power generation systems, knows there is still room for improvement. “We still want to be faster,” he said. Indeed, he also has another vision in mind: combined with a rotating mass and the new MTU battery containers, gas engines could then also be used to generate emergency power supplies. 

So is gas about to beat diesel at its own game? “Certainly not,” said Andreas Görtz. The really important thing to him is that MTU, as a solution provider, is able to offer every customer the ideal engine for each application. “And we're well on our way down that road,” he added.

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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