The answer is hydrogen, but in what form?

Fuel for the future

Paul Turner, Managing Director of CMB Revolve Technologies – CMB.TECH, gives a shipowner’s assessment of the low- and zero-carbon fuel options

At CMB, a diversified shipping and logistics group, based in Antwerp, we are already purchasing verified carbon credits to offset our carbon use, starting in 2020, but our vision is to become a truly zero-carbon organisation. CMB’s UK-located Technologies division faces the challenge of developing and encouraging the technology required to ensure we can achieve this goal. As a shipping business we have reviewed the carbon-free options available: battery systems, liquid or compressed natural gas (LNG/CNG), bio-fuels, synthetic fuels, ammonia and hydrogen.

Battery systems

Batteries have been mooted by some as a potential solution. However, the power required to move vessels, even relatively small ones, is considerable, and the size of the battery and the recharge time needed means that battery propulsion will be constrained to relatively short, low-speed voyages with long turnaround times, such as island-based RORO ferries of the type already operating in Norway.

LNG/CNG

We have a number of LNG-ready vessels; however, LNG is a carbon-based fuel. Although it has a lower carbon to hydrogen ratio than diesel, it reduces the greenhouse gas footprint by only a small amount, which has been demonstrated to be largely offset by ‘methane slip’ emissions and leakage. Even so, LNG offers an excellent short-term win from an air quality perspective, having lower NOx and soot emissions; but its greenhouse gas contribution ranges from modest to significantly worse than diesel. We do not see LNG as a long-term solution to the global warming issue.

Biofuels

Biofuels are interesting, low carbon and sustainable; but feedstock and land use concerns mean that they cannot become the major contender in the marine fuels market, even with their ‘drop-in’ merit (they can be used without any modification of the engines they power). Biofuels will be valuable, especially in the aviation industry, where no other technology is currently practicable, but they are not the solution in shipping.

Synthetic fuel

Like biofuels, synthetic fuels are drop-in fuels, with a technology that is understood. However, synthetic fuel requires two key elements in its creation: hydrogen and carbon. Hydrogen is the key element carried by the carbon in a hydrocarbon fuel such as methanol or a synthetic diesel, and it is relatively easy to produce, as it can be separated from water. But the carbon needs to be captured from carbon dioxide in the atmosphere, where its relatively low concentration makes it difficult to extract at the scale required. With the high energy requirements at all stages of manufacture, shouldn’t we just pause and use the hydrogen produced in the first stage?

Ammonia

Ammonia is a carrier of hydrogen, like the synthetic fuels, but it is not as simple to use. It will not burn on its own; it needs diesel or another catalyst fuel. In addition, like methanol, ammonia gives rise to environmental and safety concerns and it needs to be handled with care; but it does solve the hydrogen storage issue. It also uses air-extracted nitrogen, which is very much easier than carbon dioxide to produce at volume.

Hydrogen

Hydrogen is the central element of all fuels; hence the answer is clearly hydrogen. This element is the most abundant element on our planet, and one that we can never destroy. When we use hydrogen we merely change the way it is stored. If we burn hydrogen with oxygen we get water, H2O, which can then be converted back to hydrogen by electrolysis. Energy is lost in every change of state, so there is no magic option here, and we will need an electrical input source for hydrogen production. Hydrogen’s main and probably only drawback is its storage: it needs a lot of space compared to any other fuel, and space can be precious.

As the three most promising fuel options stem from hydrogen, it is hydrogen that we need to produce as the feedstock. So hydrogen is the answer. How do we use it?

The hydrogen pathway

It is important to CMB to ensure that we develop the technologies in a phased approach, and that the right technology is used in the right place.

We started the zero emissions journey by developing hydrogen dual fuel engines: a diesel engine operated on hydrogen whenever it is available, reverting to diesel mode when the hydrogen supply is scarce. The technology was applied first to a range of road vehicles ranging from small vans to large 60-tonne road trains. Once the technology matured we applied it to our first marine vessel, the Hydroville (www.hydroville.be). The challenge for the Hydroville was not the engine, but the storage of the hydrogen. And again, developing the storage capacity to ensure that the vessel could operate for a full working day without bunkering was relatively easy. The real challenge was convincing a sceptical industry of hydrogen’s merits, including its inherent safety properties, despite concerns in this respect.

Hydroville, Hydrobingo, Hydrotug

A visualisation of CMB’s Hydrocat crew-transfer vessel.
A visualisation of CMB’s Hydrocat crew-transfer vessel. Photo: CMB.TECH

The Hydroville allowed us to challenge the industry and set new benchmarks for hydrogen. The industry challenged us back, and through this process we gained a greater understanding of how we can use the inherent properties of the gas to make it one of the safest fuels that can be used at sea. In respect of safety, the three things to focus on with hydrogen are: ventilation, ventilation and ventilation. The gas’s natural buoyancy does the rest.

From the Hydroville, we are now developing the Hydrocat, the HydroBingo (a passenger ferry for Japan) and the Hydrotug. These projects scale the concept up through different engine sizes, culminating in engines capable of producing 2.7MW.

These vessels deploy hydrogen gas systems with storage pressures of 350 bar (700 bar, an available standard from the automotive sector, is currently price-prohibitive in ships). The vessels also require diesel, though, so they are not zero-carbon. The carbon reduction is based on the hydrogen to diesel ratio, which can range from 50 to 80 per cent, depending on the application. This solution is excellent while we build a consumption demand that allows the refuelling and bunkering infrastructure to develop.

We are already working on the next generation of engines, which will operate solely on hydrogen, but these can only be deployed once the infrastructure is mature. A step-by-step approach is required. Again, these developments are being led by land-based applications: primarily mobile power generation, with which we can develop the technology before putting it out to sea. Our initial work has shown that pure hydrogen engines can be run at almost any size, without any engine-out emissions. Using the inherent properties of hydrogen, we can develop engines that have no NOx or carbon-based emissions, completely avoiding the need for selective catalytic reduction or diesel particulate filter technologies.

Deep sea shipping

However, even with these two great steps forward in hydrogen propulsion, storage is still the factor that limits its use. Short sea and inland waterways are ideal contexts for gaseous hydrogen, the easiest and safest form of hydrogen propulsion. Deep sea shipping, however, will need something else – still hydrogen-based but with a different carrier. The leading candidate is ammonia – yes, it has its challenges, but it can be made at a realistic cost and, as a shipping industry, we know how to handle it. The next candidate, close behind, is cryogenic hydrogen.

Let’s look at ammonia first. Ammonia needs to be kept below –10°C to ensure it stays liquid. No problem; we do this already with LNG, and appropriate safety systems have already been developed by the chemical fleets. But ammonia needs another source of energy to create combustion, and, as with the hydrogen solutions for the short sea shipping, we can use diesel as the catalyst. We can also further develop the systems to allow cracking of the ammonia back to hydrogen, to generate sufficient hydrogen to form the catalyst fuel. Thus, pure ammonia engines are also possible.

Liquid hydrogen is also a possibility. It has been tried before in road applications but the boil-off led to it being abandoned. Ship engines, however, almost never stop, and we can manage the boil-off to provide the gas needed for combustion. Again, dual fuel or mono fuel hydrogen engines are relatively easy to develop from today’s two-stroke engines. The extreme cryogenic nature of liquid hydrogen does, however, pose design, storage, bunkering and safety challenges, which may limit its applications.

We have the technology to take us through the transition steps to zero carbon; and, given the will, the UK can and must move to zero emission shipping as soon as possible. To hit that IMO 2050 target, a large portion of our fleet needs to reduce carbon emissions by 50 per cent by 2030, and all new vessels at zero carbon by 2040. We as an industry have the technology. So let’s not wait – hydrogen is the answer!

Paul Turner, a development engineer with over 35 years’ experience in the automotive sector before he began to work in shipping, is a leader in the development of hydrogen as a low-carbon fuel, both in fuel cells and in hydrogen combustion.