Before I joined Martin & Ottaway, I was heavily involved in the fuel cell industry, connecting Bloom Energy’s fuel cells ranging from 210 kW to 3 MW to buildings. Bloom Energy focuses on stationary natural gas powered fuel cells.
The maritime industry is always looking for new ways to meet the International Maritime Organization’s (IMO) growing emission standards. Fuel cells can meet these demands on various levels.
The Maritime Executive published an article about liquid natural gas (LNG) fuel cells as possible prime movers on ships. The article notes that they work well on yachts and auxiliary equipment. The problem currently for the LNG fuel cell to be used as a prime mover is the power to weight ratio. A typical natural gas fuel cell has a power to weight ratio under 0.01 kW/lb. A typical marine LNG internal combustion engine has a power to weight ratio of 0.033 kW/lb. LNG fuel cells are simply too heavy to be a competitor of LNG internal combustion engines. However, this number is based on a fuel cell to an internal combustion engine weight comparison and does not include all the required auxiliary systems. An internal combustion engine needs a lube oil day tank, lube oil storage tank, heat exchangers, reduction gear and gear box. Depending on the ship’s propulsion system, the weight of a boiler and generator(s) also has to be included. The only similarity of auxiliary equipment between LNG fuel cells and LNG internal combustion engines is the fuel storage tank. In recent years there has been a switch from diesel direct drive propulsion to diesel electric propulsion. Today, one can choose to have LNG direct drive or LNG electric propulsion. In fuel cells there would only be fuel cell electric propulsion since fuel cells only produce electricity and do not produce rotational energy directly. Since fuel cells do not need prime movers, large exhausts and generators, even at today’s power to weight ratios, fuel cells could still come close as prime power generators aboard ships.
Today, there are seven types of fuel cells. Each one has their own advantages and disadvantages. I will focus on Solid Oxide Fuel Cells (SOFCs) because they can run on a variety of fuels, and are commercially readily available.
An LNG solid oxide fuel cell is made up of two major parts: the fuel cell and fuel reformer. The fuel cell can only run on hydrogen today and therefore the reformer exists to convert the natural gas to hydrogen and emits CO2 as a byproduct.
The fuel cell is made up of three parts: a cathode, an electrolyte and an anode. As air enters the cathode, the electrolyte extracts oxygen ions from the air. Hydrogen enters the anode, attracting the oxygen ions from the electrolyte, causing a chemical reaction to occur. The product of the reaction is water, heat, and electricity.
The fuel reformer is made up of two parts: a reformer and a shift converter. Natural gas is comprised mostly of methane (CH4). As the fuel enters the reformer, steam from the fuel cell reacts with the fuel to make carbon monoxide and hydrogen. The carbon monoxide and hydrogen flow to the shift converter reacting with steam for a second time. The reaction produces more hydrogen and carbon dioxide. The newly formed hydrogen fuel goes into the anode of the fuel cell to mix with the oxygen ions making water, heat and electricity. The carbon dioxide is vented to the atmosphere.
LNG fuel cells could be used on LNG fueled ships. LNG SOFCs have a sixty percent efficiency when they are only used for electrical purposes. When the fuel cell is used in a combined heat and power capacity, the efficiency becomes 85%. When a natural gas internal combustion engine is used in a combined heat and power capacity, the efficiency ranges from 76% to 82%. The two systems emit similar amounts of CO2. Nevertheless, companies are researching carbon capturing technology for fuel cells.
Most of the fuel cell market is natural gas because it has the most developed infrastructure. Natural gas is also a cheap and abundant fuel source. As of this article’s date, natural gas is the best “bang” for your buck option for fuel cells. Natural gas fuel cell suppliers, such as Bloom and Doosan, provide a range of capacities for the consumer.
Although fuel cells are still in their prototype stages for ships (they are used in submarines for entirely different reasons), there is an opportunity for the use of fuel cells in ports. As IMO and countries put more restrictions on ship emissions, ships will have to use shore power while in port and terminals, straining electrical grids. To avoid straining the electrical grid as well as saving on port fees, shipping companies could invest in microgrids. A microgrid can be looked as a private infrastructure benefitting the environment. Usually, microgrids are made up of various alternative energy sources working as one system. Microgrids could be made up of battery storage units, solar panels (if space was not an issue), and natural gas (either LNG or CNG) fuel cells to power ships while in port.
If a fuel cell users wanted to completely avoid fossil fuels and greenhouse gases, fuel cells could be powered by renewable hydrogen. As the infrastructure of renewable hydrogen becomes more developed, it would also drive down building and operational costs of fuel cells since the fuel cells would be much simpler in construction and would not need reformers.
Solid oxide fuel cells do look promising, but they do have their draw backs. Due to their high operating temperatures, it does not need a precious metal catalyst but uses other sustainable materials that do wear out. Once new materials are discovered that can provide greater durability or lowered operating temperatures, while still matching the high efficiency, a SOFCs’ building and operation cost will be much reduced.
Fuel sources that are starting to be explored, besides hydrogen, that do not emit greenhouse gases are algae and ammonia. Algae used as fuel for a fuel cell is in its infant stages but it is showing promise based on a University of Cambridge project. (Actually algae do produce greenhouse gases, but, because they are a bio fuel, which removes greenhouse gases while they are grown, they are considered to be greenhouse gas neutral.)
Kyle wrote a blog about ammonia as an alternative fuel source. Ammonia would be a good candidate for a fuel cell fuel since the byproduct is nitrogen. The obstacle for an ammonia fuel cell is the heat required to separate the ammonia compound to create hydrogen. As ammonia synthesis is further explored and renewable ammonia infrastructures are built up, ammonia could be an interesting contender for a fuel cell fuel. As for now, ammonia is an excellent storage medium for hydrogen.
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