Through careful analysis, Wärtsilä’s Fuel Laboratory Services (FLS) team in Vaasa, Finland, can adapt engines to run more efficiently on…
The FLS team is part of Wartsila’s energy solutions division, which focuses on flexible and more environmentally advanced solutions, according to Tommi Rintamäki, who heads up the team as General Manager.
“Sustainability and intermittency need to be addressed in today’s power systems. We offer plants that are highly energy efficient and can load or unload in a rapid manner, which is a key enabler in matching flexible flows. And then there’s the fuel flexibility,” he said, stressing that the lab’s role is not only to enhance value for the customer, but above all to be an enabler in the transition to a sustainable and modern power system.
In practice, this means Wartsila is looking at offering back-up power and load peaking solutions in parallel with solar or wind capacity, to ensure reliable power supply. “Wartsila is able to offer solar energy hybrids, and storage solutions. Our EPC [engineering, procurement and construction] experience over 10-20 years gives us the flexibility to combine renewables with smart backup and peaking sets, while most OEMs [original equipment manufacturers] rely on contractors,” said Mr Rintamäki. His team’s role is then to make sure the backup engines run as efficiently as possible on whatever fuel is cheapest and cleanest.
Gas is almost always preferable to liquid fuels for backup and peaking, according to Kristian Blomqvist: “Emissions regulations mean gas is better than liquids, with NOx, SOx, and particulates all less than 5% of liquid fuels. Gas prices are also more stable and affordable than liquid fuels. And on the efficiency side, gas is better, converting more of its energy to power,” he said. The team noted that new modular LNG plants, such as Wartsila’s Tornio Manga plant in northern Finland, were extending the reach of gas and displacing dirtier fossil fuels.
Enhancing fuel flexibility
The main objective to the Fuel Laboratory Service’s (FLS) is to enable the use of the widest possible range of liquid fuels or gases in the company’s engines. This broader fuel portfolio should leave it well positioned to capture new markets, as well as allow the upgrading of existing installations to operate on cheaper or lower carbon fuels.
“In our engines we want to be able to burn any gas or liquid that has a decent calorific value. Real flexibility means the ability to choose the cheapest or most appropriate fuel at any time over the life of the plant, which could easily be more than 20 years – It represents a hedge for the future in business terms,” Mr Rintamäki explained.
To achieve its aims, the lab provides a variety of services, including chemical analysis of liquids down to atomic level, and, most importantly, combustion research – “which differentiates us from commercial labs”, he said, stressing the team has developed its dervices over 10 years, and now has have the right techniques to refocus on the customer. “End customer value is the main point, and to further increase fuel flexibility.”
“If from using locally sourced fuels, an engine’s operating parameter is on the high side, a customer will ask us what to do – we can test the fuel in the lab and use the result to adapt the engine onsite,” he said. The trend is away from liquid fossil fuels and towards gas and biofields, especially in the east, including those produced from jatropha and palm oil – “all of which we have tested in our lab”.
The team’s most important piece of equipment, the Rapid Compression Machine (RCM), tests fuel for its knocking limit, according to Per Löfholm: “Knocking means all the gas is detonating at once. It’s the main limiting factor for a fuel’s performance. So, if you have a specification for a gas, we can quickly recreate it in the lab’ and test it using our gas chromatograph to see if we have the right mixture.” The sample is then combusted in the RCM to see if it can be used in a Wartsila engine and at what output level.
“Knocking needs to be avoided, otherwise the engine dies pretty soon.” Rintamäki said. Adding on to this, Mr Löfholm explained said knocking was largely dependent on the methane number, which is the ratio of carbon to hydrogen in the mixture. A low methane number means longer hydrocarbon molecules, which increases the risk of knocking.
From the chart it can be seen that LNG methane numbers can vary from 50 to 100 – requiring a different set up of the same engine, depending on the type of LNG. Wartsila’s DF [duel fuel] engine requires a methane number above 70 to work without adjustment.
Testing in the Lab’ can be done with a couple of litres of fuel in a day or two rather than the six months and many gallons of fuel required to test a real engine. As the sample gas is combusted in the RCM, a high-speed camera, operating at 100,000 frames per second, helps analyse the explosions closely.
“We start with low engine power and then we gradually increase, which produces a ‘knocking curve’. By doing this we find the knocking limit or threshold point at which we can run the fuel without knocking. Then we have a correlation with the real machine through reference curves,” Mr Löfholm said.
As the number and variety of fuel samples (currently around 1500) increases, the lab is building up a library of data. The more samples tested, the more accurate this library becomes, and eventually it could be used for predictive analysis – where information on the fuel’s composition alone will be enough for the team to assess the fuel, without the need for testing. The team already has a pretty good idea what results are likely to be once they have the composition.
Another key piece of equipment is the Combustion Research Unit, which is typically used for biofuels. This helps with assessing energy content and ignition speed, which can also be done quickly. However, Olai Lagus noted that other tests take longer, including acidity tests, metal content and so on. “Once all the tests have been done we can get back to our customer with the results – which may mean altering the way the engine is operated,” he said.
Online Gas Analyser
The team has also developed an online system that can analyse the quality of gas flowing into a power station in real time. The first plant to be monitored using the system is the Dorflund plant in Denmark, where Wartsila is attempting to iron out problems resulting from unpredictable gas quality variations. The plant uses gas from three sources – German gas, North Sea gas and biogas – which vary without notice, leaving it difficult to adjust performance quickly in response.
“With a mixture of fuels going into the system, constant monitoring is required, so we have developed this online near-real time quality content monitor. It uses near IR [infra-red] optics, and because different molecules absorb different wavelengths of light, we can assess the composition from the spectrum of light produced,” Mr Rintamäki said. The multiple gas sources mean the plant has a real problem with knocking, which he is trying to sort out. “We are trying to optimize the operation and performance, and cut NOx emissions too.”
Once the real-time monitoring identifies low methane numbers, the team has a two-stage approach to remedy the situation – firstly they can change engine parameters such as ignition timing to maintain the same load level, which often means burning a little more gas to get the same output. The next stage involves de-rating the engine, or reducing its operating level – to say 85% - just to keep the engine running.
Without the monitoring, the engine is likely to be damaged by the knocking, and once higher quality gas arrives, the rating can go back to 100%. “It’s difficult to quantify how much longer engines will last,” Mr Löfholm said, “but the real-time monitoring and fuel testing decreases maintenance, improves performance, and is also a civilized way to control emissions.”