The idea of using ammonia as a fuel source can hardly be said to be new. One of the first ammonia-powered cars was built in 1935, while during the Second World War buses in Belgium were run on a combination ammonia and coal gas. In the 1960’s it fuelled the North America X-15 rocket-powered aircraft developed by NASA and in 1967 set the air speed record (4,520mph, or Mach 6.72) which still stands to this day.
But its potential as a marine fuel has been almost completely ignored, for the simple reason of economics. Historically, ammonia (NH3) production has been contingent on the availability of hydrogen, which is then combined with nitrogen sourced from the air, which on an industrialised scale is achieved using the Haber-Bosch process. Given this is itself energy intensive and yields a product with a lower heating value halve that of HFO in terms of mass and a third in volume, it’s understandable why this was not considered a preferable option. Moreover, while ammonia combustion itself is carbon free, given that most hydrogen is derived from the cracking of natural gas (or to a lesser extent biomass), it does nothing to mitigate CO2 emissions with conventional production of hydrogen.
But the drive for greener shipping, further galvanised by the commitment announced at IMO’s MEPC 72 that shipping will cut GHG emissions by at least 50% by 2050, means shipowners will soon have little alternative but to start exploring other options. There was encouragement also with the publication at the end of last year of a report by Lloyd’s Register and University Maritime Advisory Services (UMAS), Zero Emissions Vessels 2030, which tested a variety of technology options and concluded that an ammonia-powered internal combustion engine came second only to biofuels in terms of relative profitability (still well behind HFO, naturally) across a range of operating scenarios.
It means, believe Netherlands C-Job Naval Architects, that as a sustainable fuel ammonia is very much back on the radar. C-Job identified Hydrogen Based Renewables as the best solution and sees ammonia (NH3) as one of the high potentials in the role of renewable fuel for the maritime industry. In 2017, C-Job revealed it had started work on a project to explore ammonia’s propulsion potential, both as a fuel for combustion engines and as a power source for fuel cells.
“At the moment we’re at the preliminary concept design stage where we want to explore the possibilities regarding technical feasibility,” explains Niels de Vries, a Naval Architect with C-Job. “We’ve identified several options but also want to understand the environmental benefits and create a breakeven point for when the moment comes when either client or the shipowner is either willing to pay more for clean transport or when CO2 and other emissions are taxed.”
In January 2018, C-Job announced it was joining forces with Netherlands-based chemicals firm Proton Ventures and Enviu, a company which specialises in environmental startups, in a consortium that will explore the technical options and cost effectiveness of an ammonia tanker fuelled by its own cargo. The project is expected to last two years and involve a range of theoretical research, laboratory testing and evaluation of a pilot project. De Vries notes that while Enviu’s main interest is hydrogen, they see ammonia as having high potential as a ‘carrier’.
Usage of surplus renewable energy
De Vries’ interest in ammonia’s potential began several years ago while attending a course at Delft University of Technology. Prof. F.M. Mulder, a specialist in renewable energy, suggested ammonia could be used as an electrochemical storage medium for periodic surplus energy generated by wind and solar power. While peak power production comes during the summer and could be stored to be used for the winter months, de Vries suggests that ammonia could also be ideal for chemically transporting renewable energy between different regions, for example between Australia (which has an abundance of empty space suitable for solar and wind power generation) and Japan.
Using renewable energy negotiates the previous drawback of the associated CO2 production involved in creating ammonia. Rather, the surplus electricity is used for the electrolysis of water and nitrogen production and thereafter to convert it into ammonia.
In some respects it’s a throwback to the 1950’s and ‘60’s, when the first ammonia plants were built in the US and Norway alongside hydroelectric plants. But the idea of sustainable ammonia production is gaining traction around the world. Technology giant Siemens last year participated in the Green Ammonia demonstrator project in Oxford, which aimed to prove the feasibility of producing ammonia from wind power and then turning it back into energy again. Elsewhere, the Japanese government is advancing its SIP ‘Energy Carriers’ program, which envisages ammonia as one of three methods for delivering hydrogen (the others being liquid hydrogen and organic hydrides). The US Department of Energy is similarly invested with its ARPA-E REFUEL project into the potential of utilising energy dense liquids.
That ammonia storage and transportation risks are already firmly understood from its use in the fertiliser industry alleviates some of the safety concerns. But while ammonia has a very different hazard profile, in terms of its storage and management, from that of crude oil or natural gas, its risk level is approximately the same. Moreover, by comparison with pure hydrogen, whether in its compressed or liquid state, ammonia is not only less volatile but offers significantly higher volumetric energy density and can be stored in its liquid state at a far more cost-effective -34°C.
That said, the lower fuel density, around a third that of HFO, would pose certain design challenges for ammonia to become viable as a fuel for longer voyages. But De Vries draws the comparison with where LNG was a decade ago, and indeed some of the technology developed for LNG containment could be adapted for ammonia.“LNG made the first step in requiring more space for fuel and ammonia adds to that. Liquid ammonia can be stored either at 1 bar -34°C in for example a membrane tank or under pressure in a cylindrical tank at 10 bar 20°C, which will take more space than a square box.”
Bunkering infrastructure would also represent a challenge to be overcome. He notes: “We have a several ports with ammonia available which could supply the first vessels powered by ammonia, preventing something of a chicken and egg story. Of course, it would have to be expanded to supply a substantial part of the commercial fleet. The significant advantage over other technologies (such as hydrogen) is that ammonia already has quite some infrastructure available as it is being used in vast quantities around the world for the fertiliser industry.”
Another challenge is that ammonia is less combustible than fossil fuels, meaning that the compression ratio for engines needs to be significantly higher and by extension require efficiency improvements. It is also highly corrosive and, from a mechanical standpoint, will burn through any component using copper, zinc or an alloy thereof. However, De Vries says safe ammonia combustion is feasible as shown by the many prototypes and other examples in transportation in the past and also in today’s time by several research institutes like CSIRO in Australia. C-Job is working with a third party which has developed an improved combustion technology both suitable for conventional fuels and ammonia. This is currently being further explored with engine manufacturers. This could open up the intermediate option of ammonia being used as a dual-fuel and also pure ammonia combustion, particularly in the case of ammonia carriers.
Ammonia fuel cells in the coming decade
One of the options being explored by the consortium is the viability of ammonia fuel cells. De Vries says: “Currently one of the most developed fuel cell technologies is the proton exchange membrane fuel cell (PEMFC). The PEMFC only runs on pure hydrogen, so the ammonia would need to be fully cracked to be utilised, which is costs about 22% and therefore not the most attractive way to use ammonia. But PEMFC has a high power density, offers decent efficiency and are quite affordable at around EUR 1,000 per kW. The solid oxygen fuel cell (SOFC) is somewhat behind the PEMFC in terms of power density and cost with around EUR10,000-15,000 per kW but is also going trough a lot of development to become more competitive.
“SOFC has the main advantage that it is able to cope with varies kinds of fuels and in general has a higher efficiency than the PEMFC. The SOFC works at a higher temperature, which could be beneficial for other purposes [i.e. heat storage]. It cracks the ammonia inside the fuel cell, which is attractive in terms of efficiency. We foresee significant improvements in the coming decade within the fuel cell industry which will make fuel cells more attractive to compete with combustion engines. Using ammonia with either a PEMFC or SOFC does not produce NOx emissions which is a big advantage over a combustion engine. Conventional diesel electric vessels would be the first to use fuel cells for power generation considering that fuel cells provide electrical energy. For diesel direct vessels the fuel cell will have to overcome the losses in the electrical system to be compete with combustion engines.”
Initial discussions have now taken place with classification society Bureau Veritas who have offered their assistance with the risk analysis during the early design stages and re-evaluation when the final design concept is decided upon. De Vries is optimistic that this design stage of the project will be completed later this year.
Ultimately of course the harder challenge will be convincing shipowners, but there are encouraging signs of interest. “Companies acknowledge that exhaust gas treatment and LNG are just intermediate steps towards a sustainable future. Of course, they’re reluctant to make major investments in the application of renewable fuels at the moment. This is mainly because they can still cheaply burn HFO and operate in a highly competitive market, but over the next 10 years we will see more constructive arguments looking into the applications of what we are learning now.