What is it?

The biomethane is a gas with the same chemical-physical properties of the Natural Gas (NG). Both are CH4 rich gases (up to 99.0%). Differently from the NG which is recovered from non renewable fossil sources, the biomethane is recovered from the biogas which is produced from several renewable sources like agricultural products, zootechnical and agricultural wastes, FORSU and algae.


The Biogas has a content of CH4 in the range of 40-80% with the balance of CO2. By the GM upgrading process the CO2 is selectively removed from the Biogas producing the biomethane which can be utilized as a substitute of the NG.

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Why choose GM

GM technology allows a total selective recovery of the methane and CO2 contained in the biogas feed. The GM upgrading units are very flexible to treat biogas produced by difference sources. The ultimate goal is achieved by working closely with the client.
GM has a strong organization and structure to follow the client from the feasibility study to the plant management.
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How does it work?

The pretreated Biogas is compressed to about 8 bar (g) before entering a column for the selective absorption of CO2 by backwashing with an aqueous solution of Br Carbonate
Potassium (K2 CO3). The Biogas, purified from CO2, comes out as Biomethane from the head of the absorber at a pressure of about 8 bar (g). The residual CO2 present in the Biomethane does not exceed 2% by volume, but it is possible to reach values of 0.5% if convenient. In fact, the non-condensable substances present in the Biogas


(quali ad es O2, N2,H2), rimangono prevalentemente nel Biometano. Il Biometano, dopo raffreddamento, essiccamento ed odorizzazione, può essere immesso nella rete del Gas Naturale (NG), la quale prescrive le quantità massime di incondensabili ed il rispetto ed eventuale correzione dell’indice di Wobbe. Quindi poter disporre di Biometano di grande purezza come garantito da GM, che fornisce Biometano con un contenuto in CH4 , al netto degli incondensabili, che può arrivare al 99.5%, ha un grande beneficio sul costo


correction of the Wobbe index. Biomethane, alternatively, can be further compressed and used as a biofuel.
The solution that has absorbed the CO2 leaves the bottom of the absorber and enters a regeneration column at atmospheric pressure where the CO2 is partly released thanks to the pressure jump and partly by stripping with steam produced by the same solution by means of an external heat source.

0,15 - 0,2 kWh/Nm3 of biogas
0,10 - 0,15 kWh/Nm3 of biogas
CO2 in the biomethane
0,5 - 1%
0,06% (no post-treatement required)

Process scheme

  1. Biogas
    • Pressure: any
    • CO2: 20 - 60 %
    • CH4: 80 - 40 %
    • Other gases: as per grid injection
  2. Dried biomethane
    • Pressure: 8 bar(g)
    • CO2: 0,5 - 1 %
    • CH4: balance
    • Other gases: as per grid injection
    • Dew point: -5°C@ 70bar(g)
  3. Off-Gas
    • Pressure: 0 bar(g)
    • CO2: 99,94%
    • CH4: 0,06%
    • H2S: as per grid injection


GM has selected a simple and safe CO2 removal process wide referenced in the world in several different applications. Simple because is utilizing well know and reliable equipments successfully proven in the industry since many years. Safe because free from utilisation of hazardous products and componentsThe up to date technologies and know-how are applied during the activities of designing, construction and operation of the unit.


The maintenance cost is reduced at the minimum thanks to the selection of top quality equipments and to the adoption of first class engineering standard. The operating cost is at the lowest range compared to the competitors technologies available on the market.


The efficiency, in term of amount of CH4 recovered from the Biogas, is extremely high overcoming the 99.90%. The final purity of the biomethane from the upgrading unit is very high and, depending on the characteristics of the biogas, a CH4 content of 98.0-99.0 is easily achieved.

Recovered CO2

By implementing the optional CO2 recovery unit supplied by GM, the totally of the CO2 removed from the biogas is available at high purity for food industry like dry ice production, soft drinks and breweries or other industrial application like cryogenics uses and greenhouse or algae growing.
Comparing technologies
“Some say that the optimal biogas upgrade technology has yet to be discovered....”
We disagree.

The solutions of Amines or K2CO3 utilised in Chemical Absorption are the most efficient and generate the purest Biomethane with high heating values.

Due to the low solubility of methane in the absorption solutions, the processes do not require any post- treatment of the Off-gas, as the loss of Biomethane in the process is negligible.

K2CO3 solution additionally is more stable (no degradation of the solution during the process) than an Amines solution and not dangerous to manipulate. K2CO3 also requires less regeneration heat and allows for a simpler more compact plant layout.

Physical absorption uses either Pressurized Water Scrubbing (PWS) or organic solvents.

Water scrubbing when compared to chemical scrubbing absorbs less CO2 and requires larger columns with greater liquid circulation.

The Methane recovery is also lower, as Methane partially dissolves in water, therefore the Off-gas requires post- treatment by thermal or catalytic oxidation before it can be released into the atmosphere.

Membrane separation exploits the different molecular size of each component of Biogas to separate each other by a semi- permeable membrane.

As the separation of the CO2 from the raw Biogas is only partial through each pass, the scrubbing process requires several stages of membranes to achieve an acceptable separation, increasing investment and operating costs.

Membranes are very sensitive to impurities contained in the raw Biogas and periodical or emergency replacements are required during the normal operation.

In Pressure Swing Adsorption (PSA) CO2 is adsorbed in vessels filled with a molecular sieve made-up of activated carbon or zeolites.

The adsorption takes place at an elevated pressure while thesaturated vessels are regeneratedby cyclical depressurization.

The Off-gas however requires a post-treatment to oxidize the significant residual methanecontent prior to it being releasedto the atmosphere.
The high CO2 absorption rate and minimal Methane loss of an Amines chemical scrub solution.

The environmentally friendly features of a PWS.

The limited unit footprint of a Membrane Separation process.

No Off-gas post-treatment.

The base configuration of the GM upgrading unit can be expanded by adding optional units according
to the clients or to the market requirements.

Removal of contaminants from the biogas

The biogas from the anaerobic digestion can be contamined by differents impurities like hydrogen sulfhide (H2S), ammonia (NH3) and siloxanes (R2SiO)n, depending on the quality of the feed to the digesters and on the applied digestion technology.GM can offer suitable technologies for the removal of the contaminants in order to meet the following targets:ul>
  • Reliable operation of the GM upgrading unit;
  • iBiomethane specification according to the required standards;
  • Food grade for the recovered CO2 (if required);
  • Gases emission according to the local regulations;
  • Drying of the

    The biomethane from the GM upgrading unit is saturated by water at about 10°C.GM can offer a suitable drying unit to achieve the biomethane dew point required by the final users standards.

    Heat recovery 

    As the hot off-gas (CO2 + H2O) from the CO2 stripping column shall be to some extent cooled, the available heat can be advantageously recovered for other services like an integration to the heating for the anaerobic digestion or to the building heating system.GM can offer a package heat recovery unit customized according to the clients requirements.

    Recovery of the CO2

    The high purity CO2 from the stripping column of the GM upgrading unit, instead to be vented as normally is done with the upgrading competitors processes, can be liquified and sold in the market at food grade quality.
    GM can offer a package CO2 recovery unit customized according to the clients requirements.
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