Fuel cellsAuthor Tobias Eriksson
The marine industry is well-known to be a significant source of harmful local (NOx, SOx and particulates) and global (mainly CO2 and CH4) emissions. The high emissions are a result of the traditional low grade “bunker fuels” used, which mainly consist of residuals and low-grade distillates. In recent years, however, public pressure regarding air pollution and climate change has caused governments and authorities to take action to reduce them. As a result, stricter regulations encourage the ship industry to find new clean fuels and/or energy efficient solutions to meet the progressing limits on pollutant emissions.
Making the transition to an alternative fuel in shipping is a major undertaking, but likely required if the set emission reduction goals shall be achieved. As the marine industry is finding itself under pressure on mitigating harmful emissions, it is no longer a question if, but rather when a transition to alternative cleaner fuels will take off. When it realizes, it can offer a good fundament for introducing new alternative technologies for power production onboard. One interesting and potential technology that could play a key role to mitigate harmful local emissions from ships are fuel cells. Fuel cells have, similar to hydrogen experienced a hype cycle before, but thus far the commercialization and widespread interest in marine use has remained low. This, however, could change if new fuels in shipping are to be introduced.
Fuel cells are electrochemical conversion devices that convert the chemical energy of a fuel directly into electrical energy. The process of converting chemical reactions directly into electrical energy offers some unique advantages compared to an internal combustion engine, where conversion of chemical energy goes through thermal and mechanical work before converting into electrical energy. Since there is no combustion involved, fuel cells can produce power with less formation of pollutants. Furthermore, due to the lack of internal moving parts in fuel cells, means they generate very little noise and vibrations during operation. Fuel cells could therefore be an effective solution to also reduce the destructive low-frequency underwater noise radiated from ships machinery, which is known to have both short- and long-term negative consequences on marine life.
A basic fuel cell mainly consists of three active components: two electrodes, i.e. an anode and a cathode, and an electrolyte sandwiched between them. To produce electricity, fuel is fed continuously to the anode, and an oxidizing agent, typically air, is fed to the cathode. The electrochemical reactions take place at the electrodes, producing an electric DC current through the electrolyte. The working principle of a fuel cell resembles a battery. But unlike a battery, which consumes its reactants and oxidant and must be recharged when depleted, a fuel cell will continue to produce electricity as long as fuel and oxygen is supplied to the cell.
Fuel cells can be classified into different categories, but the most common classification is based on what electrolyte is used and includes five major groups:
- Alkaline fuel cell – AFC
- Phosphoric acid fuel cell – PAFC
- Proton exchange membrane fuel cell –PEMFC
- Molten carbonate fuel cell – MCFC
- Solid oxide fuel cell – SOFC
Regardless of which electrolyte is used, a fuel cell system consist of more components than the fuel cell stack itself. The additional auxiliary components required to generate the electrical power from the stack are often referred to as the balance of plant. The stack and balance of plant together form what is generally referred to as a fuel cell unit, or a fuel cell system.
Forget the typical ship machinery compartment layout. Fuel cells modular design give them some unique features that could revolutionize the conventional shipbuilding. Unlike a combustion engine, fuel cell efficiency and load factor is not dependent on system size, which means the performance of a single cell is not different from a large stack. The excellent modularity means that the range of application from less than 1W power outputs up to multi-MW power generation systems is possible. This neat feature means the power production from fuel cells can be distributed over the ship as smaller units, e.g. one fuel cell module per main fire zone. The advantage of a de-centralized powerplant solution is reduced electricity transport losses and improved redundancy.
Hydrogen would be the ideal choice for fuel cell operation, but the characteristics of hydrogen arguably makes it a challenging fuel for marine use. In general, fuel cells can only utilize fuels that are hydrogen-rich and in gaseous phase. This essentially means that none of the current used bunker fuels (i.e. HFO and MGO) are compatible with fuel cells. Fuel requirements also vary depending on the fuel cell technology but typically, the lower the operating temperature of the fuel cell is, the more stringent are the fuel requirements. The chosen fuel will ultimately decide which fuel cell technology may be suitable to use. With so many different types of ships on the water, however,” no one-solution-fits-all” exist. For instance could the hydrogen-fuelled, low temperature fuel cells such as the PEM-based fuel cells be suitable candidates for ships with short autonomy requirements, e.g. small ferries and river boats. Whereas for deep-sea shipping and ships with high power demand (e.g. cruise ships) on the other hand require significant volumes of fuel onboard, which quite quickly rules out hydrogen as a suitable fuel. For such applications the high temperature fuel cells like the solid oxide or molten carbonate fuel cells could be more viable options, as they are more flexible in fuel choices and could utilize fuels already relevant for shipping, e.g. LNG, methanol, truck diesel, and also ammonia has been proven feasible options. The higher operating temperature of the SOFC and MCFC also means high-quality waste heat can be recovered, which further improves the overall plant efficiency.
Fuel cells are still a novel technology, which also is reflected in their price. They are expensive, and not just slightly, but an order of magnitude too expensive to be competitive. To promote fuel cell development, cost reduction, and market deployment, fuel cells are still dependent on state and federal tax incentive programs to help offset their current high system cost. The two major reasons why fuel cells are so expensive are also closely interlinked: low production volumes and expensive constituent materials (such as platinum in some fuel cells). Without widespread adoption of the technology, prices will remain high. The high cost is also closely related to the relative short lifetime of the current fuel cells stacks, which varies from 2000 up to 40 000 h depending on the technology and application. In marine applications, where the powerplant basically is close to year-round in operation means stack replacements would have to be carried out quite frequently with current expected lifetimes. In several lifecycle analysis, however, fuel cells have proven to be cost-competitive, if the key issues related to the initial high investment costs and expensive periodic stack replacements could be addressed.
Adapting fuel cells to marine applications is technically challenging, but by no means unfeasible. Earlier demonstration projects have proven that majority of the fuel cell technologies are suitable for marine use. The biggest chicken-and-egg problem the fuel cells are facing, however, is the lack of fuel cell compatible fuels in the marine industry. Fuel cell suppliers may therefore not see the marine market large enough to be a strategic and profitable investment, and the interest of developing fuel cells specifically for marine use has not been prioritized. Additionally, there’s the common dilemma for any new and unproven technology that “no one wants to be the first customer, and no one wants to be the second or third either”. To overcome these issues, a deep understanding of the market and a striking idea is needed. At Elomatic, we can help with both, let’s collect the pieces of the chicken-and-egg puzzle together!
Biogas – renewable energy at its bestKirjoittanut By Anne Kujanpää
The popularity of biogas as a form of renewable energy has increased at a great pace in Finland during the last decade. Pioneering small-scale innovations have over time grown into industrial operations and the demand...Read more » Lue lisää »