Biogas potential check
The biogas upgrading processes
High-pressure water scrubbing (HPWS)
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Within high-pressure water scrubbing, compressed biogas is upgraded to methane gas quality using only water with absolutely no chemicals. The methane content (methane purity) is at least 97 %.
Upgrading by means of HPWS does not require any specific raw gas quality. Fluctuations in quality have virtually no effect on the operating costs and economic viability of the upgrading plant.
The methane-containing waste gas generated through this process has to be post-treated before being released – free from methane – into the atmosphere.
Advantages of high-pressure water scrubbing
- Reliable process, proven in practice
- No use of chemicals
- No waste disposal costs
- No process heat required for regeneration
- High-pressure water scrubbing (exemplary illustration)
Amine scrubbing
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Amine scrubbing is an absorption process using a chemical rather than a physical ”washing agent”. The biogas is dried and desulphurized prior to the separation of the CO2. The absorber – an aqueous monoethanolamine (MEA) or diethanolamine (DEA) mixture – enables the reversible absorption of carbon dioxide.
Chemical washing agents usually have the highest loading capacity and selectivity in respect of CO2.
Advantages of amine scrubbing
- High CO2 loading capacity
- Unpressurized process
- Very high methane purity
- Low methane loss
- No thermal post-treatment of the waste gas necessary
- Amine scrubbing process (exemplary illustration)
Pressure swing adsorption (PSA)
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The pressure swing adsorption process primarily uses kinetic effects to separate undesirable gases out of the raw gas. Activated carbons and hydrocarbon molecular sieves generally act as adsorbers.
The biogas is first compressed, then cooled and desulphurized. During this process, the gas is usually dehumidified to such an extent that separate gas drying is no longer necessary. The CO2 adsorption is then achieved through the use of different pressure levels in various tanks.
The continuous operation requires several adsorber units. Depending on the desired methane content of the biomethane four to nine tanks (adsorbers) are operated.
The methane-containing waste gas generated through this process has to be post-treated before being released – free from methane – into the atmosphere.
Advantages of PSA
- Reliable process, proven in practice
- No use of chemicals
- No occurrence of waste water
- No process heat required for regeneration
- Generally no downstream gas drying necessary
- Pressure swing adsorption (exemplary illustration)
Organic and physical scrubbing
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Like high pressure water scrubbing (HPWS), organic and physical scrubbing processes, such as Genosorb or Selexol, are physical absorption processes using a non-toxic, non-corrosive physical solvent.
While pure water is cheap and abundantly available, gas scrubbing via an organic or physical washing agent has the advantage that relatively more CO2 is absorbed by the same volume of liquid (higher loading capacity). Therefore, the plant can be smaller in size.
The methane-containing waste gas generated through this process has to be post-treated before being released – free from methane – into the atmosphere.
Advantages of organic and physical scrubbing
- Regeneration of washing agents using low-temperature waste heat
- Low washing agent losses
- Good CO2 loading capacity
- Low expenditure for downstream gas drying
- Scrubbing with physical solvents (exemplary illustration)
