Green hydrogen is an essential part of the solution to decarbonise industries like the maritime industry that are difficult, expensive or resistant to change. But despite its potential it holds some drawbacks in its pure form.
Of the range of hydrogen-carrying alternative fuels for the maritime industry, ammonia’s characteristics strike a good balance between production cost, volumetric energy density, storage conditions, available infrastructure and launching customers. Over the last two years THRUST has studied ammonia’s potential for use as a maritime fuel, together with Proton Ventures and C-Job Naval Architects. This research focused on three topics:
- Examining ammonia’s capabilities in comparison with other alternative fuels that can be produced with zero harmful emissions;
- Developing maritime systems that release zero harmful emissions; and
- Understanding the current and the future commercial viability of the fuel and its associated technologies.
The results show excellent opportunities for ammonia to propel the maritime sector towards a zero-emission future.
In particular, the consortium investigated the technical, economic and safety needs for sea going vessels when powered by an ammonia-fuelled propulsion system. Given that alternative fuels have a lower energy density than diesel fuels, vessels need to be able to carry greater quantities of fuel. As a result the integration of fuel storage solutions has been an important aspect of the project. Other significant areas of study include fuel efficiency and the safety considerations of using ammonia as a marine fuel.
Finally, the high cost and long lifetime of ships (around 25 years) makes retroactive integration into existing vessels an important consideration. We therefore looked for solutions for both existing internal combustion engines as well as new (fuel cell) technologies.
As a result of our research, we’ve concluded seven arguments that make a serious case for ammonia as a future fuel for the world’s largest vessels.
1. As a fuel ammonia does not contribute to global warming
Ammonia contains no carbon and can be produced sustainably from renewable sources. It consists of nitrogen (N2) and hydrogen (H2), two non-harmful elements naturally present in our earth’s atmosphere. Ammonia can be produced entirely from renewable energy whereas hydrogen is produced through water electrolysis and nitrogen is captured from the air; both proven technologies.
During our experiments applying ammonia in fuel cells we provided evidence that, under the right conditions, no other harmful gases are produced as by-products (such as NOx) in fuel cells and near zero in combustion engines.
2. With ammonia ships can go the distance
We have performed extensive research on several promising alternative fuels, including methanol, ethanol, liquid natural gas, and hydrogen. When comparing ammonia to these other fuel options, ammonia can be considered a well-balanced solution. Compared to pure hydrogen, ammonia has a significantly higher volumetric energy density and is significantly more practical to store when taking into account pressure and temperature. Ammonia is in the same ball-park as methanol and LNG, making it a suitable fuel in terms of volume requirements for ocean going vessels, while pure hydrogen’s low volumetric density has serious drawbacks.
3. Ammonia can offer a price competitive alternative to fossil fuels
Comparing the current costs for the production and use of (green) ammonia and low sulphur 0.5% HFO (Heavy Fuel Oil) today, the ammonia powered option is clearly more expensive. However, when considering near-future scenarios such as the expected decrease in the price of green ammonia based on lower electricity prices, the costs begin to close in on HFO prices rather quickly. When expected emission regulations like carbon taxation are added into the equation ammonia becomes price competitive. When comparing ammonia to other (non-fossil) alternative fuels it can be noted that its production requires less energy than carbon carriers like methanol, ethanol and LNG. The only alternative that can be produced with less energy is hydrogen, but storage of hydrogen requires far more energy – requiring either cooling to -253 degrees Celsius continuously, or high pressure compression (350 to 700 bar). Ammonia only requires cooling to -34 degrees Celsius (liquid) or compression to around 10 bar at room temperature.
| Fuel type | Energy density LHV [MJ/kg] | Volumetric energy density [GJ/m3] | Renewable synthetic production cost [MJ/MJ] | Storage pressure [bar] | Storage temperature [°C] |
| Marine Gas Oil (reference) | 42.7 | 36.6 | Not applicable | 1 | 20 |
| Liquid Methane | 50.0 | 23.4 | 2.3 | 1 | -162 |
| Ethanol | 26.7 | 21.1 | 3.6 | 1 | 20 |
| Methanol | 19.9 | 15.8 | 2.6 | 1 | 20 |
| Liquid Ammonia | 18.6 | 12.7 | 1.8 | 1 or 10 | -34 or 20 |
| Liquid Hydrogen | 120.0 | 8.5 | 1.8 | 1 | -253 |
| Compressed Hydrogen | 120.0 | 4.7 | 1.7 | 700 | 20 |
Comparison of renewable fuel options
4. The infrastructure for (renewable) production, transportation and handling of ammonia is already there
Ammonia is a crucial chemical for the fertilizer industry and large quantities are produced every day around the world. Currently, this is mainly sourced from natural gas but due to the increasing prevalence of renewables in the global electricity sector, large scale sustainable ammonia production sites are expected to become feasible soon. Additionally, ammonia is already one of the most frequently transported chemicals worldwide and there are several vessels that have the infrastructure onboard to carry and handle ammonia across oceans, which means infrastructure for handling ammonia is already in place at all of the larger ports.
5. Procedures for the safe handling of ammonia have been in place for decades
Ammonia is a flammable gas, but has a relatively low flammability risk in comparison to hydrogen and other fossil fuels, making it less explosive. The toxicity levels of ammonia, however, are far more severe than flammability levels making this the main element to focus on when it comes to safety and risks. Ammonia is a gas at atmospheric conditions and highly toxic.[1]Ammonia can cause severe skin burns and eye damage and is lethal if inhaled. Furthermore, when dissolved in water ammonia is a serious threat to aquatic organisms, lethal at high concentrations. Therefore, strict detection systems must always be present when handling and storing ammonia. In addition, means to cope with leakages are required to reduce the concentration, an example being ventilation for enclosed spaces. Though these are serious considerations for ammonia as a fuel, it has been applied in other industries for many decades already. This means all the required protocols for the safe handling of ammonia already exist. It will rather be a matter of transferring these protocols towards maritime applications in order to safeguard the same safety levels. Particularly relevant for ship designs are the procedures to vent ammonia in case of any malfunction to avoid ammonia leaking into the ocean.
Safety precautions and risk handling measures should be installed, maintained and monitored frequently and with critical attention to effectively apply ammonia as a safe marine fuel.
6. Fuel cell technology will make ammonia 100% zero emission
In collaboration with the University of Perugia we developed experiments for the application of ammonia in Solid Oxide Fuel Cells (SOFC). The performance of SOFC operating with ammonia and one with hydrogen was assessed at 750°C. The results indicate that the degradation rate of ammonia is equivalent to hydrogen under stable conditions during the 100 hours of testing. Moreover, analysis shows that there was no nitrification of the anode, which practically means no NOx formation.[2]This study showed for the first time that at operative temperature there is no risk of anode degradation when applying ammonia. In addition, the off-gas analysis showed no presence of ammonia, indicating that a complete decomposition of ammonia occurred inside the cell. With these tests we have reached a system efficiency of 57.5% at a power density of 0.39 W/cm2. This is clearly higher compared to diesel electric configurations (40-45%), using internal combustion engines with a generator. However, compared to diesel direct configurations it scores comparable as the losses in the electrical system need to be included.
7. Ammonia is an excellent transition fuel
Another important advantage of ammonia is that it can be applied relatively easily in a duel-fuel combination into existing on-board internal combustion engines, significantly reducing harmful emission whilst generating the same amounts of energy with the same efficiency as fossil fuels. In its pure form ammonia combustion does have several challenges such as a high auto-ignition temperature and narrow flammability limits. To improve the overall combustion properties of ammonia, its application in mixtures makes sense. The ideal zero-emission mixture would be ammonia with a small percentage of hydrogen to improve combustion, where hydrogen is cracked (extracted) from ammonia. This is currently a relatively complicated set-up, because it means implementing two new fuels into the operations of existing vessels. In the short term, blending ammonia with diesel makes more business sense as it requires only limited modifications to existing engines, with particular attention to the manufacturing materials, because ammonia is corrosive for zinc, copper and other alloys. The National Maritime Research Institute of Japan has done extensive research in this field, with very promising results at a representative scale.[3]
However despite being much cleaner than fossil fuels this solution will never be 100% harmful emission free as it will require NOxremoving. Therefore, we believe this solution should merely be seen as a first step to accelerate the introduction of ammonia as a fuel in the maritime industry before making the next step towards truly 100% zero emission shipping via the use of fuel cells.
The ammonia roadmap
In the medium to long term and when SOFC technology is developed with related price level drops, the operational business case for green ammonia in combination with SOFC will become an increasingly attractive one and a great solution truly free from harmful emissions. An example of what the overall transition pathway may resemble like is visualized in the graph below.
In phase I, ammonia will be used in combination with diesel in an ICE, resulting in a significant reduction in harmful emissions. This allows the operator to select the amount of ammonia himself offering flexibility to cope with the ever changing economic viability and complying with harmful emission reduction regulations. Furthermore, this will allow for a backup solution and the capability to switch back to 100% diesel in case operations fail while implementing this solution. This way continued operations can be guaranteed. In phase II, diesel can be replaced with hydrogen, leading up to the SOFC replacing the ICE in Phase III, eliminating NOxemissions altogether and leading to a truly zero emission solution.
To demonstrate the feasibility of ammonia in existing vessels, THRUST is currently building a consortium with partners who wish to join us at the forefront of the future zero emission shipping industry.
If you are interested in further details: read our summarised report and white paper, or contact us directly. For additional technical information the research of TU Delft and C-Job Naval Architects is also here.
[1]Based on Acute Exposure Guideline Levels (AEGL), exposure for 10 min to 2,700 ppm can be lethal, and pure ammonia usually includes 20-150 ppm. AEGL is the international standard to express the hazardous of fuels
[2]The anode is made from Nickel (Ni) and the tests showed that Nitrogen concentration is negligible in correspondence of nickel particle. This indicates than nitrogen present is not related to nickel nitrification, which means zero NOx.
[3]www.ammoniaenergy.org/articles/maritime-ammonia-engines-in-japan-ammonia-shipbuilding-in-south-korea/
* Renders in this document are courtesy of C-Job Naval Architects
