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Towards liquefied natural gas

From the Florentine Apennines to the world

In Pietramala, a small town hidden in the hills between Bologna and Florence, the careful observer will find a plaque with these words: "Here Alessandro Volta in 1778 made the first experiments with burning air". Actually, it was in Pietramala that Volta characterised the inflammable air native to the marshes he had collected in Angera on Lake Maggiore two years earlier. "The 'burning air' was nothing more than what we know today as natural gas that we heat and cook with every day.

After almost two centuries since Volta's first experiments, the drilling ordered by Enrico Mattei near Lodi led Eni to the discovery of the first deep deposit in Western Europe in June 1959.

Methane and natural gas

Gas is still a key element in supporting the energy transition, as is enhancing the security of the energy supply. For these reasons, the gas component will become increasingly dominant in Eni's production mix, accounting for 60% of hydrocarbon production in 2030 and over 90% in 2050, within a context in which overall hydrocarbon production will grow until 2026 to then even out until 2030.

To open up new horizons for the gas market, projects involving the transformation of natural gas into liquid are decisive: LNG. This can be transported all over the world bridging the gap between places of production and places of consumption, and also freeing Italy from a market dictated by the gas pipeline infrastructure. Recent technological developments and targeted investments are giving rise to a real energy revolution based on Liquefied Natural Gas or LNG.

But the earliest documented uses of natural gas as mentioned in the Tiangong Kaiwu encyclopaedia published in 1637 were in the Sichuan province of China more than 3 centuries before our era: people living near swamps had noticed that the gas that permeated naturally from the seabed and bubbled up in the salt water was combustible. So they channelled it to the shore with pipes made from bamboo canes. Here, gas was burned to boil water from the same swamp inside large containers. Pure salt was thus obtained, one of the main riches of the time.

Average molecular composition of natural gas (varies by a few percentage points from reservoir to reservoir)

 

 

Methane is present in natural gas in percentages ranging from 82% in North African gas to over 99% in Italian or Alaskan gas. The rest consists mainly of light hydrocarbons (ethane, propane, butane), carbon dioxide and nitrogen. It has a significantly Higher Heating Value (HHV=55 MJ/kg) compared to oil (about 48 MJ/kg) and also compared to the main fuels obtained from it (HHV petrol = 46 MJ/kg, HHV diesel = 47 MJ/kg). This means that it contains and is able to develop more energy with the same weight than other fossil fuels.

Gas and gas pipelines

The reason why natural gas has in the past been considered a poor fuel however, stems from the fact that at room temperature it is still a gas; it can only be liquefied by bringing it to temperatures lower than -161.4 °C at ambient pressure. As a gas, its density is only half that of air and its heating value drops to around 36 MJ per cubic metre.

Due to its low density, it is not economically viable to transport it as is on board ships or tankers; the size of the tanks relative to the weight of the gas they contain makes the transportation cost excessive compared to that of coal, oil and derivatives, which can be conveniently stored and moved in large quantities on board suitable means of transport. For this reason, the gas is normally moved by means of continuous chains of large pipes along which compression stations are built at suitable intervals, which push the gas forward by periodically re-establishing the appropriate pressure. These are gas pipelines. It is clear that the costs - and the risks of disruption along the network - increase simultaneously with the distance between the place where the gas is extracted from and the place where it will be used.

Precisely due to the high transport costs involved, natural gas was destined for a strictly regional market. Until the early 1990s, the international gas trade was limited to a great degree to the main European, Russian and North American pipeline networks. A modest LNG trade, based on the still underdeveloped compression and regasification techniques, supplied the Organisation for Economic Cooperation and Development (OECD) markets in East Asia, Europe and North America. However, there was little interaction between the different regional markets. The idea of a 'world gas market’ similar to the thriving 'world oil market' was almost inconceivable. But over the years this reality has completely changed. With the development of natural gas-fuelled combined cycle technology (Combined Cycle Gas Turbine, CCGT), gas has become a key fuel for power generation, stimulating worldwide interest in the purchase of methane supplies both for direct consumption in the form of LNG in thermoelectric power plants and, through regasification, for traditional distribution and consumption networks dedicated to natural gas.

This allowed gas-poor regions to become importers and provided an opportunity for the traditional supplier countries in North America and Europe look further afield to meet the world's growing needs. 

Global natural gas production 2021 (by the World Energy Outlook IEA 2022)

The author: Luca Longo

Industrial chemist specialized in theoretical chemistry. He was a researcher for 30 years before moving into science communication at Eni.



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