Bio LNG is driving the energy revolution

LNG (liquefied natural gas) is now a sought-after resource. It does not take up much space to store and can be transported by ship, lorry or train to almost any location. Bio LNG, i.e. liquefied biomethane, has two additional advantages. It can be generated in a decentralised way – in principle, anywhere where biogas (fermentation gas) systems can be operated. The greatest advantage over methane and LNG from fossil fuels is that biomethane, and therefore bio LNG, are renewable, climate-neutral energy sources. They are generated from renewable sources – which we can expect even when the natural gas reserves are exhausted at some point.

Biomethane is generated through purification of biogas. This, along with carbon dioxide is in turn produced from biomass fermentation. Often fodder remnants, slurry, manure, organic waste from industry, trade and various energy crops are used as fermentation substrate. Here, the methane content varies considerably depending on the type of biomass – between 50 and 75 per cent. What's more, biogas contains water, hydrogen sulphide, oxygen and other contaminants. Before it can be liquefied and used, for example, as fuel in CHP plants or fed into the natural gas grid in gaseous form, the biogas must be cleaned and conditioned. Afterwards, it has a significantly higher methane content of 80 per cent (known as L-gas) up to 98 per cent (H-gas).

In liquefied form, i.e. as bio LNG (liquefied natural gas), biomethane is attributed great potential in ship approval and heavy goods transport since it has low emissions and high energy density. In contrast to diesel, almost no sulphur or nitrous gases and hardly any particulates are released when burned. Compared with the use of fossil LNG, use of bio LNG also saves more than 80 per cent of CO₂ equivalents.

In many countries, demand for LNG could be met fully with bio LNG in road freight transport and ship approval by 2030. In this way, the German Energy Agency DENA assumes that in Germany, demand for LNG from this sector could increased from 35 to 117 PJ by 2030. The biogas potential that could be exploited by then is up to almost 697 PJ. In this way, bio LNG can make a considerable contribution to reducing greenhouse gas emissions in the transport sector. For commercial vehicles over 18 t used primarily for long-distance freight, bio LNG is currently the only suitable mass solution for reducing emissions in a sustainable way. Friedrich Lesche, Manager Public Affairs at commercial vehicle manufacturer Iveco, is even convinced that this is not just creating a bridge technology, but also that bio LNG can be used in the long term for decarbonisation. Bio LNG can also be used for buses, which is already the case in Oslo, for example. The biowaste produced in the city is fermented there.

In the face of high expected demand, liquefaction plants for biomethane are currently appearing in many places. As with natural gas liquefaction, the cleaned biomethane is cooled to a temperature of -162 °C. In liquid form, it takes up a sixth-hundredth of the volume of gaseous methane under normal pressure. In principle, there are two concepts for bio LNG production:

1. The biomethane is liquefied in a decentralised manner at the biogas production location.
2. Biomethane is then fed into the natural gas grid and – after mass-balance removal – is liquefied centrally in large plants or in a decentralised at the place of consumption.

The first concept is particularly suitable when there is no access to the gas grid at the biogas production location. It avoids costs of supplying into the gas grid. If the bio LNG can be used for fuelling agricultural machinery or lorries, for example, transport is also not required. This results in a particularly successful ecological balance.

If liquefaction is decoupled from biogas production, large-scale liquefaction plants can be used as they are already being used for liquefaction of natural gas from fossil fuels. This technology has been tested and matured for decades. It can also be used at very large central biogas plants, such as the one currently being built in the district of Cloppenburg between Friesoythe and Saterland in Germany. In Denmark, several similar large plants are already in operation, such as in Korskro. It is also predicted that biogas production in the USA, China and India will grow significantly by 2030. Liquefaction plants will not be built everywhere – but the potential to do so exists.

Germany's largest bio LNG plant is currently taking shape in the Shell Energy and Chemicals Park Rheinland in Godorf, near Cologne. From the latter half of 2023, up to 100,000 tons per year of CO₂-neutral LNG mixtures of biomethane and natural gas are set to be produced, a quantity that meets the demand for 4000 to 5000 LNG lorries. Likewise in Sweden, a plant with capacity of 220 GWh, built by Scandinavian Biogas AB, is set to be commissioned in 2023. There are similar plans in Norway, where the Finnish technology company Wärtsilä is building a plant with a capacity of 25 tons per day. Contract liquefiers such as BioEnergie/Envitec are also taking over the liquefaction of biogas centrally from producers who do not want to invest in a liquefaction plant themselves.

Small plants for bio LNG production (mini or micro liquefaction plants) will be created in next few years too. Placed directly at medium-scale biogas plants, they can help meet demand for bio LNG. However, in the case of biomethane supply to the natural gas grid, small liquefaction plants may be of interest. For example, if the (bio) methane is only removed from the gas grid on a mass-balance basis and liquefied when bio LNG is required – such as for fuelling seagoing vessels. This saves on use of cryotanks, in which bio LNG would otherwise have to be stored.

Role models for many agricultural operations have initial integrated systems, such as in Darchau in Lüneburg, Germany. It was commissioned in August 2022. Slurry and manure are converted to bio LNG here. According to the operator, Ruhe Biogas Service, the 500-kilowatt plant can replace up to 1.3 million litres of diesel. The Ruhe Group, together with the Italian plant manufacturer Ecospray Technologies, realises projects under the "Green Line Liquid" brand, where carbon dioxide as well as biomethane is liquefied. A decentralised, standardised module is used, which also includes biogas pre-treatment and conditioning, plus storage tanks for the products and an unloading system. It is suitable for biogas plants from a size of 500 kWel (equivalent electrical power).

Safety is the top priority for both large and small liquefaction plants, since both the initial substance biogas and methane are highly flammable. As a result, measures must be taken to prevent explosions during production, conditioning and liquefaction. In the case of biogas – i.e. a mixture of methane, nitrogen, carbon dioxide, oxygen and other substances – an explosive atmosphere occurs when biogas content in the air is approximately 5.0 vol% (LEL, lower explosive limit) to 16.5 vol% (UEL, upper explosive limit) or, according to other information, 22.0 vol%. This depends heavily on the actual composition of the gas. The ignition temperature is around 700 °C. For methane, these values are more defined. Explosive methane–air mixtures are between 4.4 vol% and 17.0 vol%; the ignition temperature is 595 °C. As liquid methane, so bio LNG too, is always just at the boiling point (-161.5 °C), i.e. small amounts of gaseous methane are continuously produced, these values also apply to bio LNG. According to the ATEX and IECEx directives, methane and (bio) LNG are in explosion group IIA and temperature class T1(> 450 °C ignition temperature).