Proven success of dual-fuel technology
Wärtsilä article, 20 September 2011
Producer: Mirja-Maija Santala, Wärtsilä Corporation
Wärtsilä has been a pioneer in the development of dual-fuel engine technology and is the acknowledged market leader in this field. The company’s dual-fuel engines have now exceeded 3 million running hours in commercial applications, a milestone that is significant in establishing their viability for the future.
Although engines capable of burning both a liquid and a gaseous fuel were invented before the Second World War, their practical use is far more recent. Wärtsilä began development work with dual-fuel gas engines in 1987, the first concept being the gas-diesel (GD) engine with high-pressure gas injection. This was followed by the second generation of gas engines in the early 1990s, when the company introduced spark-ignited (SG) pure gas engines, utilizing low pressure gas. The real breakthrough, however, came with the third generation of gas engines, when the dual-fuel (DF) engine was introduced by Wärtsilä in 1995. The result has been the ability to combine fuel flexibility with environmental performance and fuel efficiency. Today, the total number of Wärtsilä DF engines delivered to both marine and land-based applications is 470.
The subsequent years have seen this technology blossom to the point that today, it represents a realistic means of meeting both the environmental and economic challenges that confront the global marine and power plant markets. The fact that Wärtsilä DF engines have been successfully and reliably operating for more than three million hours is testimony to the viability of this concept
Dual-fuel technology meets economic and environmental targets
The essential concept of dual-fuel technology is to provide a means of utilizing natural gas as fuel, while retaining the option and ability to switch to liquid fuels if and when needed. This switch between fuel types can be made automatically, and without loss of operating power. By applying modern electronic combustion control, Wärtsilä has paved the way to improved performance and greater reliability for gas engines. As with many successful innovations, various strands of different technologies have been combined to produce a new and viable solution.
The outcome of all this dual-fuel development work is unprecedented flexibility, both in fuel choice and operational performance. Since natural gas has low levels of harmful emissions, and is relatively low in price, such flexibility is increasingly seen as being the key to compliance with environmental legislation and to controlling escalating operational costs. Flexibility allows the most cost-effective and most readily available fuel to be used where possible, and gas to be used when feasible and where environmental regulations restrict the use of conventional liquid fuels.
Exceptional environmental performance
Wärtsilä’s dual-fuel engines, when running in gas mode, are capable of meeting the most stringent of environmental regulations. Emissions of nitrogen oxides (NOx) are reduced by some 85 percent compared to liquid fuel operation. This is because in gas mode the Wärtsilä DF engines operate on the lean-burn principle, which implies that the mixture of air and gas in the cylinder contains more air than is needed for complete combustion. Since lean combustion reduces peak temperatures, the formation of NOx is greatly reduced. Furthermore, sulphur oxide (SOx) emissions are completely eliminated as gas contains no sulphur, and since natural gas contains less carbon per unit of energy than liquid fuels, emissions of CO2 are also lowered. Natural gas has no residuals, and thus the production of particulates is practically non-existent.
Another factor in the environmental sustainability of Wärtsilä’s DF engine technology is their high level of performance efficiency. This directly impacts fuel consumption, which in turn leads to lower levels of exhaust emissions.
LNG - the marine fuel of the future
Dual-fuel capability is at the spearhead of Wärtsilä’s engine technology. It is seen as opening the path towards a more sustainable future for the marine industry, and a natural complement to the work of the International Maritime Organisation (IMO) in reducing the sector’s environmental footprint.
Of the three million running hours thus far recorded by Wärtsilä DF engines, half have been in marine applications. The trend towards the use of liquefied natural gas (LNG) as a marine fuel is already very apparent, and the development of reliable and highly efficient dual-fuel engines is clearly the enabler. Since carbon-based greenhouse gas emissions can be reduced by at least 15 percent, and because sulphur and nitrogen oxide emissions are practically entirely eliminated when running on gas, ship owners and operators around the world are more and more looking towards LNG as being the marine fuel of the future.
Not that there aren’t obstacles to be overcome. For example, a typically mentioned constraint to further development is the limited LNG bunkering infrastructure. Another is the need for onboard LNG storage and supply systems. However, the former obstacle is in the process of development, and a recent co-operative agreement between Wärtsilä and Shell Oil will speed the process. In any case, the problem can already be solved through the use of trucks and small-scale storage facilities. The latter obstacle has already been overcome with the introduction of Wärtsilä’s LNGPac innovation. The LNGPac system includes the insulated LNG storage tanks for the vessel, the shore-to-ship bunkering connections, the pressure control valves and the overall control system. An integrated solution that includes the LNG storage system can already today be offered.
Increased acceptance by shipping companies
The vessels currently being powered by dual-fuel engines are mostly offshore vessels, LNG carriers and passenger ferries. Wärtsilä is convinced that within the coming ten years the number of dual-fuel powered vessels will have grown to more than a thousand. The expansion of Environmental Control Areas (ECAs) and operating cost economics will certainly drive this growth.
So too will technical advancement. For example, Wärtsilä’s dual-fuel engines enabled the LNG carrier market to conduct an industrial technology shift during the mid-2000s. Old and inefficient technologies, such as boiler and steam turbine propulsion, were replaced by highly efficient dual-fuel technology, and today DF engines are the norm for LNG carriers.
The gas-diesel concept was initially developed for the offshore market, where it has been successfully applied in numerous floating production units. Today, the platform supply vessels (PSVs) serving this sector are increasingly being fitted with dual-fuel engines. The ‘Viking Energy’, owned by Eidesvik Shipping and operated by Statoil, was in 2003 the first PSV to be built for gas engine propulsion. Today six such ships are in operation and another six are currently under construction. Wärtsilä is not only supplying the engines, equipment and electric propulsion for these vessels, but is also the world’s leading designer of such ships, having designed ten of these twelve vessels.
With the development in the LNG sector and in the infrastructural changes, there is a huge potential also for converting vessels to LNG propulsion. Wärtsilä has already undertaken several gas conversion projects, particularly dual-fuel conversions. In 2010, Tarbit Shipping, the Swedish shipping concern, contracted Wärtsilä to convert the ’Bit Viking’, a product tanker, to LNG propulsion, and to supply a Wärtsilä LNGPac system. The vessel is operated by Statoil along the Norwegian coast, and the conversion will enable it to qualify for lower NOx taxes under the Norwegian government’s NOx fund scheme.
Another major project is the new Viking Line passenger ferry being built for the Finland-Sweden route. Billed as being the most environmentally friendly big passenger ferry in the world, it will operate on LNG fuel with Wärtsilä dual-fuel engines.
At the heart of Smart Power Generation
When, in 1997, Wärtsilä supplied the UK with the first power plant utilizing dual-fuel engines, it is unlikely that the true potential of gas as fuel for the power generating sector was fully understood. Since that time much has changed. Fuel costs have escalated, environmental legislation has tightened, and the need for operational flexibility has become a priority.
Natural gas reserves appear to be abundant and, in part because of this, the price of gas in many parts of the world is more competitive than oil. Dual-fuel technology allows gas to be used as the primary fuel for generation, but provides the back-up option to switch to oil should the gas supply be interrupted for any reason. Since the switch is automatic without loss of power, operational security, as well as flexibility, is assured.
Another benefit for the power plant business is that Wärtsilä’s dual-fuel technology offers the perfect bridging solution for switching from liquid fuel to natural gas. While the use of natural gas in power generation is rapidly increasing, many locations are currently without a ready gas supply. Dual-fuel technology enables customers in such areas to generate electricity, first with HFO and then to convert later to gas once it becomes available. In addition, Wärtsilä has also converted several existing power plants to run on gas.
With operational flexibility, high efficiency, low emissions and proven long-term reliability all available from the same technology, power plants running on dual-fuel engines are suitable for grid stability and peaking services, stationary and floating baseload, and for a wide variety of industrial self-generation applications. The Wärtsilä dual-fuel engines are available in power range from 0.8–17.5 MW having speed range from 500–1200 rpm.
This technology also enables a transition to a more sustainable and modern energy infrastructure in a world where the energy industry is undergoing rapid evolution. The growth in alternative sources of energy, such as wind, solar and biomass, introduce diversity into the power generation mix. However, maximum integration of variable wind and solar power causes major power system balancing challenges. Tomorrow’s power systems will need to include significantly more dynamic and flexible features that are not available from existing generation capacity mainly based on inelastic steam power plants. Smart Power Generation based on DF engine technology is at the heart of meeting this need. Smart Power Generation has a rapidly adjustable output that is capable of matching the variable demand for electricity, and which is able to compensate for the fluctuating power output of renewable sources. The starting time of the engines from zero to full load is 5 minutes, and stopping from full load takes just 1 minute. This can be repeated an unlimited number of times per day without any adverse impact on maintenance schedule or costs.
The significance of 3 million hours
Despite all the technological advances that have taken place in our lifetime, change can nevertheless still take time to be accepted. This is true of all industry sectors. It is only when the evidence becomes overwhelming that the new way is indeed a better, easier, and/or less costly way, do we become convinced. Three million hours of reliable and efficient power production represents just such proof.
If the joint and inter-related economic and environmental challenges that face both the marine and the power plant industries are to be met, then gas has to emerge as a mainstream fuel. Wärtsilä’s dual-fuel engine technology makes this both possible and realistic.
Trade & Technical Press release: Wärtsilä and Tarbit Shipping sign contract to convert tanker to LNG operation for reduced NOx emissions