In the search for low emissions technologies the European Maritime Safety Agency (EMSA) now has assessed the use of fuel cells in shipping. Technological maturity has to develop further, but revisions of regulation are already underway – a promising signal
As part of EMSA’s role in supporting EU Member States and the European Commission to find solutions for sustainable shipping[ds_preview], the agency looked at technology, regulations and safety of different types of fuel cell systems together with classification society DNV GL. A main motivation was EMSA’s view that fuel cells in particular have been receiving increased interest as an alternative power supply for ships (see also page 42).
A fuel cell power pack consists of a fuel and gas processing system and a stack of fuel cells that convert the chemical energy of the fuel to electric power through electrochemical reactions. The process can be described similar to that of a battery, with electro-chemical reactions at the interface between the anode or cathode and the electrolyte membrane, but with continuous fuel and air supplies. Different fuel cell types are available, and can be characterized by the materials used in the membrane.
For the study the technologies were ranked against parameters: relative cost, power levels, lifetime, tolerance for cycling, flexibility towards type of fuel, technological maturity, physical size, sensitivity for fuel impurities, emissions, safety and efficiency. The three technologies ranked to be the most promising for marine use is the solid oxide fuel cell (SOFC), the proton exchange membrane fuel cell (PEMFC) and the high temperature PEMFC.
According to the findings the PEM fuel cell is a mature technology, successfully used both in marine applications. The relative maturity also leads to a relatively low cost. The operation requires pure hydrogen, and the operating temperature is low. The main safety aspects are thus related to the use and storage of hydrogen on a vessel. Energy conversion with a PEM fuel cell, from hydrogen to electricity, results in water as the only emission and low quality heat, with the low temperature providing high tolerance for cycling operation. The efficiency is moderate, 50-60%. The modules currently have a size of up to 120 kW, and the physical size is small, which is positive for applications in transport, remarkably for marine use. The major drawback of the PEMFC technology is its sensitivity to impurities in the hydrogen, complex water management and a moderate lifetime.
The HT-PEMFC is less mature than low temperature PEM, addressing however some of the problems of the PEM. The higher temperature reduces the sensitivity towards impurities and simplifies the water management since water is only present in gaseous phase. The efficiency is the same as for traditional PEMFCs, possibly higher due to less parasitic losses, and the higher temperature leads to more excess heat that can be used for ship internal heating purposes. The higher operating temperature allows eliminating a clean-up reactor after the reformer, which improves efficiency and saves costs. Owing to the tolerance for fuel impurities, simpler, lighter and cheaper reformers can be used to produce hydrogen from a range of energy-carriers such as LNG, methanol, ethanol or oil based fuels.
The SOFC is a highly efficient, moderately sized fuel cell. With heat recovery the total fuel efficiency can reach about 85% to date. The fuel cell is flexible towards different fuels, with the reforming from hydrocarbons to hydrogen taking place internally in the cell. The high temperature can be considered a safety concern and when using hydrocarbon fuels, there will be emissions of CO2 and NOx. A promising development for the SOFC technology are hybrid systems combining SOFC, heat recovery and batteries.
Maritime applications of fuel cell systems must satisfy requirements for on-board energy generation systems and fuel-specific requirements regarding the arrangement and design of the fuel handling components, piping, materials and storage. The International Code of Safety for Ships using Gases or other Low-Flash-Point Fuels (IGF Code) provides requirements for ships using such fuels. Presently, it only contains detail requirements for natural gas as fuel, and only for use in internal combustion engines, boilers and gas turbines. A phase 2 development of the IGF Code initiated by IMO and its CCC sub-committee is currently allowing the further development of technical provisions for ethyl/methyl alcohols as fuel and fuel cells. The ship side of the bunkering operation is covered by the IGF-Code, but not the shore part. Therefore, other standards for safe bunkering of the relevant fuels are needed to support the implementation of bunkering technology for maritime use.
There are several industry projects underway to test the feasibility of the technology in vessel operation. The HT-PEM technology was demonstrated aboard Viking Line’s cruise ferry »Mariella« in Pa-X-ell project with three stacks of 30 kW, and in the project »Vågen«, Norway, including a 12 kW HT-PEM for small port commuter ferry. Pa-X-ell is part of the lighthouse project »e4ships« aiming to reduce emissions on cruise ships, yachts and RoPax-ferries through the integration of a fuel cell-based decentralized energy grid. The main partners are Meyer Erft, Fr. Lürssen, FSG, DNV GL, DLR and SerEnergy. Moreover, cruise line operator Royal Caribbean Cruises and Meyer Turku shipyard will develop the next generation of LNG powered cruise ships with a number of innovations such as an application of fuel cells for power generation.
