BW Gemini

Retrofit highlights use of LPG as a marine fuel

The world’s first LPG-fuelled vessel successfully set sail in October 2020. Powered with Wärtsilä’s customised and reliable Fuel Supply System, the vessel represents a major breakthrough in the search for new ways to reduce marine emissions. 

The world’s first LPG-fuelled vessel successfully set sail in October 2020. Powered with Wärtsilä’s customised and reliable Fuel Supply System, the vessel represents a major breakthrough in the search for new ways to reduce marine emissions. 

BW LPG, the world’s largest owner and operator of very large liquified petroleum gas (LPG) carriers, has reached a major milestone in the retrofit of a number of its very large gas carrier (VLGC) to run on LPG instead of Heavy Fuel Oil (HFO). 

About 20 months ago, BW LPG signed a contract with Wärtsilä to install LPG Fuel Supply Systems (LFSS) on four of its vessels. As part of the contract, Wärtsilä was also asked to manage the integration of the new system into the vessels. This meant making necessary ship design modifications, integrating the LFSS control system with the ships’ integrated automation system (IAS), and acting as a coordinator between the yard, the engine manufacturer, and the owner.

Now, after the successful completion of full-scale testing and installation of the systems, the first BW vessel has successfully completed sea and gas trials, finished a historic transpacific voyage from China to Enterprise Port in Houston, Texas, on full LPG propulsion, and took on a record load of 49,000 MT of LPG as cargo on a single keel. 

Better for efficiency and the environment

Serge Schwalenstocker, Project Manager, BW LPG, says the decision to make the switch from running vessels on Heavy Fuel Oil to LPG made sense from the economic, operational, and especially environmental perspective. 

"Compared with Heavy Fuel Oil (HFO), LPG emits up to 97% less sulphur (SOx), 20% less nitrogen oxide (NOx), 90% less particulate matter (PM) and 20% fewer carbon emissions,” Schwalenstocker says.

"Based on current fuel price levels where LPG is cheaper compared to compliant fuel alternatives, we are using cleaner and cheaper fuel to power our vessel,” he adds.

Kaj Portin, General Manager, Research & Technology Programs at Wärtsilä, says LPG has other benefits as well.

“LPG is portable and easy to handle; it can be stored in pressurized tanks, is easily accessible across all terminals in the world, and is more environmentally friendly than other fossil fuels,” Portin says. 

“If you look at an engine running on LPG, it will have lower CO2 emissions compared to other fossil fuels as it has short molecules — mostly propane and butane. It also has no methane slip and is great for controlling greenhouse gas emissions, too. Only LNG, methane and ethane will be as good with CO2 slip,” he adds.

Meeting challenges

In February, Wärtsilä completed full-scale testing of its LFSS with a full sized 2-stroke marine engine fuelled by LPG. The performance of the system exceeded expectations, and BW LPG exercised its option to extend the project and increased the total number of ships for retrofitting to twelve.  

“Retrofitting twelve of our vessels with pioneering LPG propulsion technology is a significant upfront commitment, but the returns are positive in both financial and environmental terms,” says Schwalenstocker. “It is the result of our company’s focus to invest resources and expertise to pioneer technology that can be used to push our industry towards decarbonization without the need for dedicated newbuilding orders. While building new ships can provide the benefits of operating with the new fuel, this comes at a heavy cost. Counting total emissions, a new ship represents about 70,000 tons of carbon dioxide in the materials and building process. Compared to 2,000 tons of carbon dioxide for retrofitting, the sustainability outcome is much better from retrofitting than from building new vessels.”

Developing the pioneering technology required to retrofit the vessels was not easy. Wärtsilä needed to install two LPG tanks of 900 m3 volume each to replace the Heavy Fuel Oil. The LPG from these new tanks also had to be pressurized and conditioned to make it ready to send to the engine. Once sent and used as fuel, the engine returns liquid. The returning liquid too, needs to be conditioned and handled in varying volumes. Wärtsilä had to ensure that this process was carried out smoothly while integrating and interfacing with the existing systems on the vessel. 

Peter Zürcher, Project Manager, Wärtsilä, outlines the complexity of the task. 

“These are massive tanks. What we are doing is supplying storage volumes and doing process systems. So, we have to set up interfaces ‘to the engine’ to meet their requirement for pressure, temperature and flow. Simultaneously, we also have to ensure the reverse flow ‘from the engine’ is managed in a similar manner. This complicated system has to work seamlessly when the ship leaves the yard,” Zürcher says.  

A New Horizon 

BW LPG expects the next vessels, to be completed within Q3 2021. All these vessels will be fitted with Wärtsilä’s new deck tanks and LFSS on the main deck. In the engine room, the engine supplier will convert the main conventional fuel engine to an LPG dual-fuel engine. This process is expected to take about two months for each vessel, including testing. 

“This is a new system, and this is the first time it will happen on board a vessel. It is not a tried and tested well-defined system. It has to be developed and invented,” says Kjell Ove Ulstein, Director, Sales and Marketing, Wärtsilä. “As system integrators and technology providers, we have to ensure that our solution meets the multiple objectives of our customer, exceeds their expectations of efficiency, and is relevant in the long term.”

Sustainability at the Forefront 

The challenge is that much of what will happen in the long term will be driven by sustainability. Emissions norms are getting tighter, and the marine industry has a long way to go in reducing its environmental footprint. The International Maritime Organization (IMO) has mandated that the shipping industry bring down CO2 emissions by 50% by 2050. Will adopting LPG, a fossil fuel, help meet those goals? 

Mathias Jansson, General Manager Fuel Gas Supply Systems at Wärtsilä, says it is a good interim step.

“For those using HFO, LPG is a first step towards more sustainability and fuel-flexibility in the longer term,” Jansson says. 

Wärtsilä is not alone in its pioneering work on the use of LPG as a marine fuel. There is broad interest in the fuel. The classification agency DNV GL is reported to have developed new class rules and a class notation for the use of gas-fuelled LPG ships. According to reports, a joint study by DNV GL and MAN found “LPG is at least as attractive an energy source as LNG, with shorter payback periods, lower investment costs and lower sensitivity to fuel price scenarios.”

So far, LPG as a marine fuel has only been tried on LPG carriers. But experts believe that with costs declining and the availability and accessibility of LPG rising, it is only a matter of time before many more vessels adopt it. 

Written by
Payal Bhattar
Associate Editor at Spoon Agency