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In the search for more sustainable fuels, biomethane is a very interesting alternative to natural gas, which is steadily gaining ground in today's energy landscape, thanks to its contribution to the energy transition, the decarbonization of energy, and the circular economy. Could this be the new energy of the future we're dealing with?

What is biomethane and how is it produced?

Biomethane, also called renewable gas, is a combustible gas that is produced from biogas that has undergone a treatment known as “upgrading.”

Through this process, which removes certain impurities from the biogas like CO2 for example, the gas is brought to a methane ratio of around 95%. This purity grade allows for it to be incorporated into the gas network, mixed with conventional natural gas, in a way that it can be used to generate electricity and heat as well as to power vehicles.

Difference between biogas and biomethane

The main difference is basically that biomethane is biogas that has gone through a purification process in order to make its composition as similar as possible to that of fossil natural gas. 

Burned waste material

One of the most noteworthy advantages of biogas is it's renewable. Unlike fossil gas, it's a much more eco-friendly resource. 
As such, biogas is produced from the decomposition of organic remains (agricultural or livestock waste, sludge from water treatment plants, etc.) by anaerobic digestion (i.e., without oxygen). Due to the action of certain bacterias, a gas is generated composed mainly of methane (CH4) and carbon dioxide (CO2). In order to produce biomethane, biogas undergoes a purification process. This process mainly eliminates CO2, the major component, but moisture, hydrogen sulfide, ammonia, volatile organic compounds, O2, and N2, amongst others, are also eliminated. In this way, the ratio of methane increases until the gas can be considered biomethane or methane derived from a renewable source.
Although it can be obtained naturally, biogas plants are used for its production, which have the appropriate facilities to process organic waste.
An operator in a plant

The plants can have several different designs, but they share the stages through which the waste goes through:

  • Reception: The waste is received and, in certain cases, could require a prior treatment as in with solid urban waste. Biomass can have different origins, but each plant usually works with a certain type of waste in order to optimize its treatment.
  • Digestion: Over a period of 20 to 30 days, the waste undergoes the decomposition of microorganisms in the absence of light and oxygen through agitation and at a temperature that, depending on the design, is around 30 °C or is greater than 50 °C.
  • Post-treatment: Once the gas has been generated, the digestion sub-products (called digestates) are centrifuged to separate the water. These can be used to make high-quality organic fertilizers.
  • Energy generation: Through cogeneration equipment, biogas can be used to produce electricity or thermal energy that can be self-consumed or even incorporated into the electrical grid. As an alternative, biogas can be purified through the process called “upgrading” to obtain biomethane and inject into the gas network.

Uses and applications of biomethane

As it has a composition and energy power very similar to those of fossil natural gas, biomethane can be used for the same purposes: 

1. Alternative to natural gas: It can be injected into the gas network to replace natural gas (it is mixed with this in any proportion) and distribute it for both residential and industrial consumption. This makes it possible to make the most of existing infrastructure.

2. Generate electricity and heat: Its combustion also serves to generate electricity and heat. In this case, biogas is usually directly used without the need to purify it to biomethane.

3. Power vehicles: In fact, the use of biomethane as an advanced renewable biofuel enables an improvement in air quality as it emits less greenhouse gases, in a way that it becomes a great ally in the energy transition as a renewable fuel. The use of compressed natural gas or CNG is on the rise among, for example, urban bus fleets.

4. Raw material: As a raw material, for example, for the production of renewable hydrogen.

5. Create employment: The production of biomethane leads to futher development of rural areas and increases the creation of jobs related to the agricultural and livestock sectors. It also contributes to the sustainability of the agro-livestock sector as its self-consumption aids in decarbonizing that sector. 

6. Boost the circular economy: As it allows efficient management and harnessing of organic waste, since the digestates obtained are returned to the field as fertilizers.

7. Waste use: Lastly, the using waste to produce local energy contributes to the energy dependency reduction plan in Europe (REPowerEU plan).

The production of hydrogen from biomethane

Renewable or green hydrogen (i.e., free of emissions) is today considered a key player in the decarbonization of certain sectors that are very difficult to electrify, such as heavy industry or long-distance transportation, so it's crucial to find ways to produce it with the lowest possible impact.

Operator at Cartagena plant

In this regard, Repsol has announced the production of renewable hydrogen with biomethane as a raw material. This feat has taken place at the Repsol plant in Cartagena, where 10 tonnes of renewable hydrogen has been produced from 500 MWh of biomethane. It's a truly remarkable first step in replacing the conventional natural gas needed to produce hydrogen at the existing facilities for biomethane from a renewable source. 

The production of renewable hydrogen by this method is another example of Repsol's effort to transform its industrial complexes into multienergy hubs capable of generating decarbonized products. It's part of its circular economy strategy that, since 2018, is committed to using waste as a raw material for its products. As a leader in the production and consumption of hydrogen in Spain, Repsol dedicates a large part of its efforts to promoting large-scale industrial projects such as the Basque Hydrogen Corridor, the Hydrogen Valley of Catalonia, the Hydrogen cluster in Castilla-La Mancha, and the Renewable Hydrogen Hub in Cartagena, while it promotes several technologies to achieve its renewable hydrogen production objectives.  

Operators at industrial complex

It first electrolyzer at the Petronor facilities with a 2.5 MW capacity is expected to come into operation this year.

Moreover, 2024 will see the start up of a 10-MW electrolyzer at the same facilities with the aim of powering the synthetic fuels plant that the company will build in collaboration with Saudi Aramco.

Thanks to initiatives like this one, which promote decarbonization and the circular economy as well as the production of renewable hydrogen, Repsol is at the forefront of the energy transition.