Green gas production: biomethane for cleaner energy

The Renewable Energy Directive RED 2009/28/EC on the promotion of the use of energy from renewable sources indicates that 20% of the energy needs has to be obtained from renewable sources and 10% of the energy needs in transport (transport fuels) has to be obtained from renewable sources by 2020. Biogas and biomethane play an important role in achieving these targets by 2020. The biomethane or green gas production will increase in the future since 10% of the energy needs in transport has to come from renewable sources.

Terpene removal during the biomethane production in AD plants

Raw biogas coming from anaerobic digesters may contain following trace components depending on the feed material used:

• Hydrogen sulphide
• Particles
• Droplets (condensates, aerosols...)
• Siloxanes
• Thiols and terpenes
• Longer alkanes, cycloalkanes and aromatic compounds
• Volatile fatty acids and alcohols

These trace components may have a possible adverse effect on the technical installation and need to be removed during the biomethane production process. Activated carbon is widely used for the removal of, and terpenes from biogas. Terpenes in biogas usually come from the fermentation of biological waste such as fruits, vegetables and vegetation or essential oils from cosmetics.

Isoprene   Terpenes are a group of organic molecules derived from isoprene that are present in fruits, vegetables and vegetation. Terpenes are derived biosynthetically from units of isoprene and the basic molecular formula is (C5H8)_n. These terpenes cause the specific odour: limonene in citrus fruit, pinene in pine tree. Terpenes are removed from the biogas because they can corrode gaskets and piping systems. In addition to that, they can mask the odour component Tetrahydrothiophene (THT) that is added to natural gas for leakage detection.

DESOTEC: Terpenes removal through activated carbon technology

DESOTEC’s activated carbon type AIRPEL^® is used in combination with mobile activated carbon filters type AIRCON^® for the removal of terpenes during the production of biomethane. Some cases:

Case 1: Digestion of municipal waste: 80.000 tpa

 Two mobile activated carbon filters type AIRCON® HC for biomethane production Flow: 1,500 m³/h biogas Type of terpenes in the biogas ●      3-Carene           1.3ppm ●      Limonene          17ppm ●      p-Cymene         200ppm ●      α-Pinene            5ppm Our Solution 2 x AIRCON^® HC AIRPEL^® Result Outlet:     Total terpenes         <0.1ppm

Case 2: Digestion of vegetable, fruit and garden waste: 50,000 tpa

Mobile adsorption filters at an AD plant Flow: 250 to 700 Nm³/h biogas Type of terpenes in the biogas ●      3-Carene           250mg/Nm³ ●      Limonene          650mg/Nm³ ●      Tetramethylbenzene               1,300mg/Nm³ ●      α-Pinene            350mg/Nm³ ●      .... Our Solution AIRCON^® HC AIRPEL^® Result Outlet:     Total terpenes         <0.1ppm

Case 3: Digestion of slaughter waste (fat), sludge and kitchen waste: 165,000 tpa

Fixed bed filter: Emptying by vacuum-truck and filling by crane Flow: 1,000 m³/h biogas max High concentration of limonene/terpene Solution Fixed filter: 10 m³ AIRPEL^® Don’t hesitate to contact us if you need more information about upgrading biogas using activated carbon adsorption including mobile adsorption filters. We’re at you service!

At DESOTEC’s facilities, all used carbon is analysed so the right measures can be taken for handling and removing the saturated carbon out of the mobile filters. All molecules that were adsorbed on the activated carbon at the customers’ site, are desorbed inside DESOTEC’s reactivation furnaces. These contaminants are then fully destroyed, in accordance with National and European legislation, by an incineration and neutralisation setup. The entire installation and it's emissions are under continuous on-line monitoring, which guarantees that only harmless water vapour is seen exiting the chimney.