Natural gas a transport fuel
Natural gas can be supplied from large fossil fuel reserves, from biomass and waste as biomethane, where production should come from sustainable sources, and in future also from "methanisation" of hydrogen generated from renewable electricity. All these fuels can be injected into the natural gas grid for supply from a single network. Natural gas offers a long-term perspective in terms of security of supply to transport and a large potential to contribute to the diversification of transport fuels. It also offers significant environmental benefits, in particular when blended with biomethane and provided that fugitive emissions are minimised. Natural gas also presents an advantage in lower emissions.
Gas as a vehicle fuel is available as compressed natural gas (CNG) and liquefied natural gas (LNG). It can be used for cars, vans, buses and trucks, with many different models on the market today from established manufactures. LNG is also becoming the fuel of choice for the shipping industry due to its low sulphur emissions.
Natural gas also offers important synergies with biomethane from waste and biomass or synthetic gas produced using wind and solar energy. When using renewable gas, a carbon-neutral mobility is achieved without any impact on the infrastructure and vehicle technology.
Compressed Natural Gas (CNG)
CNG is the most widely used technique to store natural gas in vehicles. Natural gas provides for CNG to be subsequently distributed to filling stations via the current gas network from where it can be easily compressed and transferred to natural gas vehicles and used as fuel. Natural gas is compressed up to at least 200 bars at the station and stored in high pressure storage system at filling stations where it will be used to fill NGVs through dedicated filling nozzles. A 100-litre gas tank at 200 bars contains approximately 16 kg of CNG, and has the same energy content of 22-23 litres of diesel fuel.
CNG is commonly used by passenger cars, vans, buses and trucks, particularly in urban areas where distances between refuelling points are relatively short. Many city buses, for example, are fuelled by CNG: benefitting from close to zero pollutants of particulate matter and NOx, the use of CNG substantially reduces air pollution and contributes significantly to a healthier urban environment. CNG is increasingly offered as bio-CNG: adding varying percentages of biomethane to the gas mix increases the potential for CO2 reduction.
Liquefied Natural Gas (LNG)
LNG is natural gas converted to liquid by cooling it to -163 degrees Celsius. It is stored in vacuum-insulated containers that keep the gas liquid. LNG achieves a higher reduction in volume than with CNG, meaning that a larger amount can be transported over a longer distance. LNG used in vehicles offers the possibility to cover longer distances, making it an ideal fuel for trucks and buses. Compared to CNG the energy content of the unit of volume is three time higher: 1 liter Diesel fuel corresponds to 4,7 liter CNG at 200 bar and to 1,6 liter LNG. LNG can also be produced from renewable sources, blended with natural gas and used as bio-LNG.
Renewable gas is natural gas produced from any renewable source, and includes biomethane, synthetic gas and hydrogen. It can be produced through different pathways. For example, through anaerobic digestion (biological processes in which microorganisms break down biodegradable material) bio-waste is converted into biogas and upgraded to biomethane. Gasification is a process that converts organic waste with high carbon content into carbon monoxide, hydrogen and carbon dioxide, then combined to produce synthetic methane. Power-to-Gas is a process in which excess renewable electricity is converted to hydrogen and upgraded via methanation to methane. All renewable gas can be blended with natural gas and used as fuel for NGVs as CNG or LNG.