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Power plant operators the world over are continually striving to improve the reliability of their turbines and engines.
With renewables forcing their way into the energy mix of more and more countries, operational flexibility has also become vital.
Among the expanding areas of renewables is biogas. For some time overshadowed by its biomass counterpart, it is now recognized as a burgeoning sector, especially in Europe where waste-to-energy plants are growing in popularity.
Biogas consists primarily of methane and carbon dioxide. It also may contain small amounts of nitrogen or hydrogen, and contaminants in the gas can include sulphur or siloxanes.
“Biogas can be an important pillar of the European energy policy in terms of safety and decarbonization,” says Dr Jan Stambasky, president of the European Biogas Association.
Data from the Anaerobic Digestion and Bioresources Association in Britain shows that the volume of biomethane injected into the UK grid will more than quadruple by the end of this year.
Since 2011, the number of biomethane upgrading plants has doubled and the biomethane capacity has more than quadrupled in the last year. There are now 10 biomethane-to-grid plants generating almost 1 TWh – up from 0.16 TWh last year.
ADBA’s chief executive Charlotte Morton says: “That this market is finally taking off is great news for climate and energy security. Biomethane is one of the most efficient forms of domestic renewable energy which, at a time when we are expected to import 69 per cent of our gas supply from some of the most volatile parts of the world, could replace over 10 per cent of the UK’s domestic gas needs – equivalent to 40 TWh – while helping to fight climate change.”
One of the biggest global players in the biogas sector is GE and company spokesperson Susanne Reichelt says that “biogas engines account for a significant portion of our distributed power business, which includes aeroderivative gas turbines and reciprocating engines”.
“Though segment conditions vary from year to year, biogas engines have a significant role in the distributed power business. About 3500 Jenbacher biogas systems with a total electrical output of about 2700 MW have been delivered worldwide.”
But biogas has its own unique challenges for engine makers and, in turn, for the lubricant manufacturers that literally oil the wheels of this growing market.
The chemical makeup of biogas presents the key problem. “Biogas contains methane and carbon dioxide but in most cases it also contains traces of other gases, which are similar and are mainly harmful. That makes it complicated for engines and for lubricants,” says Jarmo Vihersalo, Europe, Africa and Middle East industrial marketing advisor for Energy at ExxonMobil Fuels & Lubricants.
He says that while OEMs tailor engine materials and components such as the bearings, cylinder head and crank case to withstand the corrosion caused by this blend of gases, the lubricant must also be modified for biogas use.
“It is very important that we create lubricants that protect engines against the corrosive substances that are in the fuel” – which is an exacting task given the variety of sources from which the biogas can come.
“Biogas can come from animals, from people’s waste, from other types of waste – this means we never know the true content of the gas: they are all a bit different,” says Vihersalo.
“All the chemical additives of the lubricant need to be carefully selected to manage the demands of the different types of fuel.”
So is one type of biogas more challenging than others?
“If we think about waste generated by food manufacturing or what we can call plant waste, it is easier to filter out the pollutants so that, at the end of the day, when they are clean, they are quite close to natural gas.
“But when it comes to landfill gas, we end up in a situation where there are a variety of elements. Landfill gases can include siloxanes or sulphur content, so it is these gases that are more challenging from a lubrication point of view.”
Vihersalo says that a preference for different types of biogas plant varies from country to country. “In the UK there is a lot of landfill gas being used. In Germany, however, biogas plants use fermented biomass which is burned in a combined heat and power plant to produce power using waste heat.”
Josef Pellmeyer, president of the German Biogas Association and operator of a biogas plant in Munich, says that demand for biogas as a renewable source of energy “is growing continually, worldwide”.
“I can testify to this from my own experience: ever more interested visitors from across the globe are coming to view my biogas plant to find out how it works. In 2012 alone we received groups from South Korea, Ethiopia, China, Japan, Brazil and Russia, to name but a few.”
He says these visitors “are primarily interested in generating power using the residual products of food and animal feed production as well as agricultural waste. This is particularly the case in countries where power from renewable sources is poorly remunerated and substrates need to cost little or nothing.”
In bringing a new biogas lubricant to market, Vihersalo explains that ExxonMobil works closely with its OEMs. The manufacturers do not come looking for a new oil and ExxonMobil does not design one without collaboration.
“It’s an ongoing co-operation,” says Vihersalo. “They [the OEMs] cannot design a new engine if there is no lubricant to meet its demands. With OEMs we work closely to find a product that meets their specifications.”
He adds that it takes between three and five years to develop a new lubricant into market, including laboratory and field tests.
He also explains that both the lubricant manufacturer and engine makers have the same aim – to increase the time between oil change intervals.
The longer the interval, the more operating hours are clocked up – in the hundreds for biogas engines at the moment, in contrast to thousands for natural gas engine.
Vihersalo says that “the economic benefits are very clear”: the operator has to buy less lubricant, needs less personnel to carry out the oil change and has their machines available for longer periods.
He stresses that there is also a safety aspect to a lubricant that offers less downtime, whether planned or unscheduled. “We need to minimize the risks when interacting with the machines.”
However he stresses that there is no typical interval for biogas engines: “It varies from engine to engine. The way the engine operates has an effect, as well as the different gases used in the engines. Therefore, we would always recommend using an oil analysis system, such as our Signum Oil Analysis, to help determine correct oil drain intervals.”
Another variant is the make of the engine: “There are quite big differences between biogas engines. It is not only size: it is also a question of how they are designed; how much oil is linked to the combustion area. It’s about tolerances that are in the engine.”
Reichelt of GE says that “in most situations, the customer choice is not between biogas and natural gas, but instead it is a choice to be more efficient and sustainable”.
“We’ve found that most customers usually have a synergistic supply of agricultural, livestock or food waste, and it can be relatively simple to monetize that supply by producing biogas. The choice for the customer is then whether to utilize that gas to generate power and heat, or upgrade the biogas into a bio-methane facility.
“In addition, government support for the generation of renewable energy, along with the elimination of methane and carbon emissions, certainly can help project economics for many customers.”
So what does GE look for in a lubricant for its biogas engines?
“There are several aspects to be considered with lubricant, says Reichelt. “A lubricant for biogas application has to fulfil several different requirements simultaneously.
“To start, a lubricant must have high capability to neutralize acid components from the fuel, and a challenge can be the variations of biogas and the impact of the biogas source. GE’s Jenbacher biogas engines run on biogas from different sources, like landfill, sewage gas, agricultural gas and crop gas. Our lubricant must be able to accommodate these various sources without issue.
“At the same time, customers need products which provide a long drain interval in order to reduce unscheduled engine shutdowns and, as a consequence, rising operating costs.”
Reichelt explains that there “are often trade-offs between the amount of ash content in an oil and successful engine operation – these trade-offs do not always allow oil to be used for extended periods due reduced neutralization capability”.
“If we used oil past its successful life, we risk engine performance due to the oil’s reduced ash content and less beneficial properties. In the future, longer oil life and higher reserve against acid would help us to improve engine performance and reduce costs for the customer.
“In addition, regulated emissions requirements are resulting in OEMs needing to use more and more pre-cleaned biogas. By reducing the troubles with engine performance due to oil, we can better ensure full operating and economic potential for projects.”
Lastly, Reichelt says that “within the biogas engines segment, there is variation for lubricants. Within GE’s Distributed Power business, Jenbacher lean burn engines differ in oil requirements compared to the requirements of our Waukesha rich burn engines”
Vihersalo says that biogas is “an important part” of the rise of renewables for ExxonMobil. Its Outlook for Energy 2014 report forecasts the demand for oil and natural gas to grow by 60 per cent by 2040.
He says: “Gas engines have been and will be an important part of our business. Now if we look at market demand, biogas is an increasing part of gas engine business. We can see in the product development pipeline that we will have new products for biogas engines – we are developing new products with OEMs all the time.”
In terms of geographic regions, he says: “Europe is an important market for ExxonMobil and for biogas, Germany is very important, as well as Italy, France and the UK.”
He says the UK in particular is making interesting developments in landfill biogas plants.
GE’s Reichelt says that “historically, the largest growth regions have been in Europe – Germany in particular. However, there is now a shift underway, with Asia and North America expecting to be larger growth areas in biogas going forward.”
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