Compiled by Elias Panteleakos, Naval Mechanical Engineer, LNG Carrier industry and Alekos Zachiotis, Mechanical Engineer, UK Atomic Energy Authority
It is a gas mixture of hydrocarbons, mostly methane, in concentrations higher than 80%, with traces of inorganic compounds (carbon dioxide, nitrogen, water etc.). Just like oil, natural gas is mined from natural cavities in the subsoil both in dry land and in the sea bed. Unlike oil, though, which consists of heavier hydrocarbons and is usually found in liquid form, natural gas consists of lighter hydrocarbons and therefore remains in gas form in the subsoil 1.
Just like with all hydrocarbon mixtures, natural gas produces carbon dioxide CO2 when it’s burned. Still the CO2 emissions per final energy quantity (MWe electric or MWt thermal) are lower when we burn natural gas than what we get when we burn solid carbon to produce electricity or oil for heating. 2 Also, when natural gas is burned there aren’t any emissions of sulphur compounds or soot, the way there are in the case of coal and oil.
Still, methane, which is natural gas’s main ingredient, is a greenhouse gas and in fact it’s a lot more powerful than carbon dioxide (by 96 times in a 20 year period and by 32 times in a 100 year period). 3 Therefore, the use of natural gas produces a significant amount of greenhouse gases both when natural gas is consumed (burned) but also when it’s mined, processed and transported. In total, methane emissions from hydrocarbons’ mining and transportation make up 18% of the total greenhouse gas emissions for energy production. 4
Up until two decades after World War 2, the main use of natural gas was as fuel and an ingredient for fertilisers. Nowadays, natural gas is broadly used as fuel for electricity production, industry and heating for buildings, while its use in the transportation sector is still rather limited.
The discovery of hydrocarbons’ reserves in the North Sea in the ‘60s and the ‘70s, turned Norway, the Netherlands and the UK into major oil and gas producers and contributed to the rapid increase in the use of natural gas in Europe. In just two decades (1965-1985), natural gas consumption in what today is the EU increased by more than 500%. 5
During this period, the use of natural gas as a fuel for electricity production was relatively small. The gradual phasing-off from nuclear power (the nuclear accident in Fukushima in 2011 accelerated this process), as well as the realisation that we need to switch to a low emissions economy, rekindled interest in natural gas at the beginning of the 21st century. Natural gas was chosen as the “transition fuel”, aiming to gradually abandon the use of solid carbon, while the renewable energy sources’ (from now on RES) contribution to the energy mix would increase. At the same time, electricity plants using natural gas were a popular choice for private corporations (in addition to RES) who wanted to enter the energy market, thanks to their relatively low cost, short construction period and their optimised output and flexibility.
Natural gas’s contribution to the electricity production mix in the EU used to be 7% at the beginning of the ‘90s and increased to over 20% by the end of ‘00s. After a decrease during the economic crisis, consumption reached the same levels by the end of the past decade. Meanwhile, at the same time, natural gas’s share in domestic heating in Europe remained more or less stable at the relatively high percentage rate of 40%. 6 In total, one quarter of the final energy consumption in the EU for 2020 came from natural gas.
In Greece, the first transnational agreement concerning natural gas supply was signed with the Soviet Union in 1987 and the first pipeline at the Greek-Bulgarian border was completed in 1996. From just 0.2% of the final energy consumption in 1995, natural gas will reach 21% in 2020. When it comes to electricity production, natural gas’s contribution will increase from approximately 10% in 2000 (6TWh) to 35% in 2021 (19TWh). This percentage is expected to increase, given Greece’s commitment to shut down DEI’s (note: Hellenic Public Power Corporation HPPC) lignite plants by 2028, as well as the scheduled addition of four (private) natural gas plants by 2024.
Natural gas reaches consumers through transport and distribution networks that consist of pipes of different diameters and working pressure (high/ low), measuring devices and control systems. Other than the road network, pipelines are the most common option for transporting natural gas across countries covering large distances, though liquified natural gas (LNG) transport is becoming increasingly popular in the past few years and is expected to surpass pipelines in terms of the total transported quantity in the years to come.
In order to be transported, gas is compressed at high pressures and then it’s channelised in large diameter pipes that are often placed underground (or even underwater). Along the pipeline’s course, there are intermittent compressor stations, in order to compensate for any pressure losses. At the connection points of a transnational pipeline with a national network of pipelines, there are metering stations, where it is possible to determine with high accuracy the quantity and the consistency of the natural gas that is being channelised in the national network. The natural gas’s consistency determines the energy content (in MWh) of a given gas quantity.
Approximately ¾ of the natural gas that is imported in the EU, comes from Russia, Norway, North Africa and, more recently, Azerbaijan. The rest of the EU’s needs in natural gas are covered by liquified natural gas imports. Russian natural gas has always been transported to the EU via the Ukraine transit pipeline network. In the past decade, the quantity transported via the Ukraine transit has decreased significantly, in favour of other pipelines such as Nord Stream (Russia-Germany), Yamal (Russia-Baltic countries-Poland) and to an extent Turksteam (Russia-Turkey-Greece).
Greece has four natural gas entry points three of which are via pipelines (Sidirokastro, Kipi and Nea Mesimvria) and one concerns LNG (Agia Triada, Revithousa). There are plans to add another entry point in Komotini at the Greek-Bulgarian border in order to connect to the IGB pipeline, as well as two floating LNG terminals in Alexandroupoli. There are also discussions regarding the possibility of an additional floating terminal in Revithousa.
Gas pipelines are the predominant transport method in dry land and underwater for relatively small distances and depths (eg. the Mediterranean, North Sea etc). For larger distances of whole oceans for instance, pipelines are not cost effective and technically they’re almost impossible. Plus, pipelines are usually projects that have various geopolitical dimensions and also need quite a lot of time in order to be constructed and become completely functional.
As an alternative, gas can be transported in liquid form (Liquified Natural Gas – LNG) in tankers (LNG carriers). When it’s liquified, gas shrinks about 600 times in volume, and therefore more fuel can be stored in a given space. In order for natural gas to become liquid, it first needs to be quenched at -162oC and then it gets loaded in the ships’ specially customised tanks, where it is maintained at this temperature using special insulation and pressure levels that are slightly higher than atmospheric pressure. The (small) LNG quantity that regasifies during the transport, is used as fuel for the boats’ propulsion.
In the past decades, there has been significant progress in LNG carriers’ technology, thanks to the use of dual fuel piston engines that offer higher efficiency levels and also thanks to the tanks’ insulation quality. A modern LNG carrier is 300 metres (984 feet) long and can transport up to 190.000 cubic metres of LNG (so 115 million cubic metres of gas), by consuming approximately 1-2% of that quantity along the way, on a transatlantic trip USA-Europe. In Greece, approximately 5.5 billion cubic metres of natural gas were consumed in 2020. If they were all in LNG form, we’d need approximately 50 LNG Carriers to transport them.
During the unloading process, the LNG Terminal receives the liquified natural gas through cryogenic tubes. The LNG is then stored in cylindrical tanks and is fuelled into the network via the regasification unit. LNG terminals are often used as gas storage in order to ensure the national system’s sufficiency.
LNG Terminals can either be on dry land or they can be floating. In that case, they’re called FSRU (Floating Storage Regasification Unit) and they’re either floating facilities or LNG Carriers equipped with a regasification system. The main advantages of an FSRU compared to a mainland facility are the lower construction cost ($200-300 million), the shorter construction timeframes (2-3 years) and the ability to be moved, if necessary. 7
Shale gas is natural gas that is found “trapped” in fine-grained, clastic sedimentary rocks called shales. Shales have very low permeability and in order to mine gas from them, the rocks need to be “stimulated” by drilling pores into their surface, so that the gas that is trapped inside can escape. This process is called hydraulic fracturing or fracking for short, and includes the channelling of large quantities of water, under pressure, in a vertical or horizontal tube. The high-pressure water applies force at the shale’s surface, thus drilling pores from which gas can escape, while special chemicals help the pores to remain open. The natural gas that “escapes” is channelled to the collection tubes and transferred to the surface. 8
This specific method is one of the “non-conventional” mining methods and even though it’s been known for several decades, it hasn’t been used as much because it’s more costly and technically demanding. The shale gas “revolution” in the USA started in the 2010s (during Obama’s tenure) and was based on the wide dissemination of the horizontal mining method that rendered the large reserves of the country’s shale gas available for exploitation. From 2010 until 2020, the total gas production almost quadrupled, while it is expected to increase by 30% by 2035 and by 50% by 2050 (reference year: 2020). The USA produced 9136 TWh of natural gas in 2020, more than any other country in the world. More than Russia’s 6385 TWh, Iran’s 2508 TWh, Qatar’s 1713 TWh and Norway’s 1115 TWh.
Fracking is problematic for the environment for a number of reasons. First of all, it requires great quantities of water and also it increases the possibility of uncontrolled gas leaks in the atmosphere (methane is a powerful greenhouse gas), as well as hydrocarbons’ and other harmful chemical substances’ leaks in the water table, where they can poison drinking water in great volumes. At the same time, it produces a great volume of toxic waste, which after being collected on the surface, often ends up back in the water table, thus adding to fracking’s environmental harmful consequences.