The term Sustainable Shipping has influenced the Maritime Industry to Go Green. As a result, many shipping companies are adopting zero-waste practices to reduce Carbon Dioxide (CO2) and Green House Gas (GHG) emissions for a sustainable future.
The shipping industry is currently responsible for emitting around 3% of CO2 and GHG. To surpass this, the ship management companies and associations are massively investing in refueling infrastructure. As the introduction to Liquefied Natural Gas (LNG) and Compressed Natural Gas (CNG) has directed the industry to operate sustainably in the ocean, the next big step is the usage of Hydrogen as an alternative to fuel ships. Such use of alternative fuel instead of Heavy Fuel Oil or Diesel cuts the GHG and CO2 emission and also prevent any damages to marine environment.
Hydrogen, an inexhaustible energy source that can be found in almost every compound such as water or methane (air). In fact, 6% of global natural gas and 2% of coal currently go to hydrogen production. It however must be separated into pure hydrogen before using it as a fuel cell to power ships. It can be produced using fossil fuels, which is relatively cheaper, or can be even produced without using fossil fuels by a process called electrolysis (split water into hydrogen and oxygen using electricity from renewable energy), which can be pretty expensive and could produce only 0.1% of hydrogen. The positive side is that hydrogen can be really emission-free on a full lifecycle basis.
Depending upon the precise design of the ship- refueling and transportation, including electrolysers, compressors, storage, tanks and pipelines, the shipping industry is majorly investing in LNG powered vessels.
LNG powered vessels: These vessels use LNG instead of other fuel to run the ship. While designing the vessel, it is important to decide where to place LNG fuel tank along with the ventilation ducts, pressure relief masts, gas piping and other processing equipment. Depending upon the cargo grade, LNG is stored at a pressure range from 1 to 4 bar, whereby the equilibrium temperatures are approximately between -160° C to -155° C. It is significant to consider the materials used for LNG system have been certified for cryogenic temperature and also that the system has built-in pressure relief functionality. If an LNG ship is capable of carrying basic LPG cargoes, a liquefaction plant is installed to handle the boil-off LPG cargo vapours. These vessels are fully insulated as it is not cost-effective or ideal to liquefy methane onboard. In the state of -162° C, 1 litre of LNG contains approximately 600 litres of natural gas.
CNG powered vessels: The natural gas must be conditioned in order to use it as CNG to fuel ships. To do so, it requires high pressure containment technology used in a conventional pressure vessel. Even CNG storage and in pipeline systems must be installed onboard to provide a form of concentrated gas storage. CNG still needs separate gas conditioning and process systems to get the production gas segregated and suitable for transportation along with a separate LPG processing and transportation system. As CNG has not yet entered full commercial development, it is reported that CNG offers refrigerated compressed storage system typically operating at 1800 psig at -29 C, or pressure only systems operating at 3000 to 3600 psig at atmospheric temperatures in order to achieve compressed volumetric storage ratios in the order of 250 to 300 times the natural gas density at Standard Temperature and Pressure (STP).
Hydrogen powered vessel: As the hydrogen is still far away from commercialization, a few crafts running on it do exist. It is believed that hydrogen’s best chance of acceptance is in conjunction with fuel cells, many companies are still experimenting different ways to use hydrogen as a fuel.
