Filtration key to LPG fuel conditioning

Engine and fuel system developers are exploring the next generation of fuel gas supply systems to accommodate LPG and eventually ammonia for two-stroke engines

MAN Energy Solutions has tested an LPG fuel conditioning module (FCM) from Alfa Laval using its first LPG-burning, dual-fuel ME-LGIP engine. Tests with the fuel valve train and a simulated engine load began in the second quarter of 2018, followed by online tests using MAN’s 4T50ME-X prototype engine Copenhagen in early 2019.

“Both sets of test results verify the booster’s ramping functions and its ability to match the output pressure to our engine’s changing load,” said MAN promotion manager, dual-fuel engines René Sejer Laursen. “In fact, almost no influence from the engine load can be seen, which demonstrates the effectiveness of Alfa Laval’s automation and control.”

LPG must be pumped at a higher supply pressure than other low flashpoint fuels (including LNG and methanol) to avoid it changing state and to handle a variety of compositions on the butane-propane spectrum. To deliver LPG at the 53 barg pressure required, the FCM incorporates new pumping technology and high-pressure heat exchange.

The high-pressure skid has a filtration stage comprising two independent chambers, which allows for servicing while in continuous operation – a setup derived from Alfa Laval’s previous booster experience with methanol. As the use of LNG (and ethane) as fuel in high-pressure systems has increased in recent years, it has become clear that much better filtering and cleaning is needed than was originally expected. The same issues apply to LPG, and potentially there will be more demands placed on LPG before it is used as fuel.

The likelihood of solid contaminants in LPG is even higher than in LNG or ethane, which means the demands on fuel line systems will also be greater. Solid particles such as dust and debris in the fuel may cause equipment failure or engine damage if not properly removed. And if a system is not correctly designed with adequate filtering, the result will be repeated starting and stopping that leads to increased venting and loss of LPG. In turn, this will mean increased emissions and a higher workload for the crew to keep systems operating.

"The likelihood of solid contaminants in LPG is even higher than in LNG or ethane, which means the demands on fuel line systems will also be greater"

Alfa Laval has designed the FCM LPG with a duplex filtration system with ‘double block-and-bleed’ (DBB) insulation. This achieves the solid content limits required by specifications without needing to stop the module to perform filter cleaning procedures, which would lead to a loss of productivity.

The filtration layout, based on experience from the low flashpoint fuel supply system for MAN’s B&W ME-LGIM engines, is intended to protect the system components and to clean the LPG prior to its use in the engine. Once the fuel has passed through the FCM LPG, all particles or debris larger than 10 µm will have been removed, allowing for safe and uninterrupted supply of fuel to the engine.

In the event of one of the filters becoming clogged, the operator can switch to a secondary filter and continue LPG operations without turning off the system or switching to a traditional fuel. In a future marine installation, while running on the secondary filter, the operator can perform maintenance on the clogged filter, since it is isolated with DBB segregation. The operator can also maintain the filter safely by draining it of LPG and purging it with nitrogen, allowing solids that may liquify when warmed up to be drained away without opening the filter up for inspection.

The automation and control system matches the LPG flow to fluctuating engine load without unnecessary heat input from the pumping and flashing of light fractions in the LPG.

The unit is also capable of full liquid LPG recovery and partial gas recovery when the engine or fuel valve train is purged. This saves vessel operators from losing their cargo or fuel and minimises the release of hydrocarbons into the atmosphere, in line with international regulations and guidance.

As reported previously, MAN is developing an ammonia-fuelled engine. Mr Laursen said that the Alfa Laval FCM LPG had been evaluated for use with ammonia fuel. The system can be made compatible with only a small investment, he said.

Alfa Laval previously developed a methanol FCM to work with MAN’s ME-LGI engines onboard seven chemical tankers chartered by Methanex subsidiary Waterfront Shipping in 2017.

Dry scrubber technology installed on French ferry

A new scrubber technology that does not use water to remove sulphur from exhaust gases has been installed without drydocking on La Méridionale ropax ferry Piana.

The 42,180-gt ferry, which sails between Marseille and Bastia on the island of Corsica, had one of two exhaust channels fitted with a dry scrubber system from supplier Andritz in April 2019. By eliminating water, the system reduces power consumption (by water pumps, for example) while avoiding regulatory uncertainty concerning wash water discharge.

The stability reserve and funnel profile of Piana made it an ideal trial candidate

The exhaust ducts on the Piana are routed through two casings in its starboard and port funnels. In the first installation phase, three scrubber chambers were connected to the starboard side funnel ducts, which handle part of the exhaust from the vessel’s seven Wärtsilä engines, with a total power output of 42.18MW.

Andritz sales manager for southern Europe, Marco Dierico, explained that Piana was a good candidate for the first dry installation because its two side funnels meant that the retrofit could be performed with no loss of cargo space and no impact on the ship’s appearance from the side. The fixed sailing route will allow the companies to optimise the supply chain for the reagent, sodium bicarbonate. Truck loading is easier for ferries than for most other vessels and big ferries also offer greater stability, which can be a concern when installing heavy scrubber technologies on a higher deck of the ship.

The installation was completed in less than two weeks without drydocking, and the ship’s acceptance and performance tests will take place over June and July this year. Mr Dierico said that Class approval had been smooth as there was no need for additional water outlets or sea chests, no wastewater discharge and no need for water monitoring.

The Andritz SeaSOx dry scrubber doses sodium bicarbonate powder to the exhaust gases and feeds them through bag filters enclosed in chambers that can be assembled in modular arrangements. Each chamber can handle exhaust equivalent to the emissions from a 5MW four-stroke engine. Exhaust from multiple engines can be processed through one filter.

The technology also removes all other gaseous acid components and reduces fine particle emissions (to below PM1). Andritz plans to verify the efficiency of emission reductions through an independent third party.

The residues produced contain sodium sulphate, a non-hazardous substance which can be safely stored in silos on board. Residues will be discharged on land for disposal or recycling. An on-board recycling process by Solvay (which handles logistics chemical supply and residue disposal) will reduce waste by more than 90%.